Biggest Mysteries in Physics: Antimatter, Dark Energy & ToE - Don Lincoln | Lex Fridman Podcast #497
Lex Fridman
0:00 The following is a conversation with Don Lincoln,
0:03 a particle physicist at Fermilab,
0:05 who has spent decades working at the frontier of high energy physics.
0:10 This was a mind-blowing and inspiring conversation.
0:14 Don turned out to be one of my favorite people to talk to about physics.
0:18 Truly a unique mind with that Richard Feynman ability
0:22 of taking very complicated ideas and explaining them simply,
0:27 without losing any of the essential,
0:29 brilliant insights at the core of those ideas.
0:33 This is a Lex Fridman podcast.
0:35 To support it, please check out our sponsors in the description
0:38 where you can also find ways to contact me,
0:41 ask questions, give feedback, and so on.
0:45 And now, dear friends, here's Don Lincoln.
0:49 In describing the search for a theory of everything in physics,
0:54 you describe the history of physics can be
0:57 told effectively as a kind of history of unifications.
1:01 There's this centuries-long quest to show that these distinct phenomena are
1:07 actually linked by some unified underlying principles even starting with Newton,
1:14 that you can think of the effort of physics as one is trying to unify-...
1:20 the laws of nature.
1:21 So I was wondering if we could talk through the history of unification-...
1:25 that lens of physics.
1:28 There are, of course, lots of different ways to do physics,
1:31 but the way that I would say that particle physicists,
1:34 cosmologists do is they are trying to really find
1:39 basically the underlying principles that govern the laws of nature.
1:44 If we go back, say, to the, I don't know, 1650s or so,
1:49 you're the most brilliant person around, and you've noticed two things.
1:53 One you've noticed is that when you trip, you fall.
1:56 That is the nature of gravity that we all experience day to day.
2:00 But then there's sort of astronomy,
2:02 where you look out at the heavens and you see the stars march across the sky.
2:07 You see the planets move through the stars.
2:11 And there, that seems to have absolutely nothing to do with what
2:15 happens when you drop your sandwich and the dog grabs it from you.
2:21 So-...
2:21 the brilliant thing was when Newton looked at that and he thought about,
2:26 maybe the moon is falling, but it's missing the Earth.
2:29 So what we had is that in maybe 1650,
2:32 you had what we might call the laws of celestial gravity,
2:36 the gravity that governs the heavens, and terrestrial gravity,
2:40 the gravity that is here on Earth.
2:42 Now, we don't think of it that way anymore.
2:45 We think of it as just gravity.
2:47 But at that time, that wasn't at all obvious.
2:49 And in fact, if you look in the books,
2:52 Newton's theory is Newton's law of universal gravity.
2:55 The universal is there,
2:56 and the reason is because he realized these two things that seemed
3:00 to have nothing to do with one another were indeed one and the same.
3:04 I mean, this is absolutely brilliant.
3:05 I mean, Newton is arguably one of the most
3:09 brilliant humans of which I'm ever aware.
3:12 But at any rate, it is the first sort of easily to describe unification
3:17 of physics that you can state in a way that sort of makes sense to modern-...
3:23 Humans.
3:23 I mean, you can go back farther
3:25 than that, where people are talking about chemistry, the nature of atoms.
3:28 You go back to Democritus, who was wrong about very many things,
3:31 but the idea that there was a smallest particulate form of matter is right.
3:35 So it's kind of funny.
3:36 You talk— You read the chemistry books,
3:38 and they say that the idea of atoms goes back to Democritus, and, you know, he,
3:43 his idea was that, like, there was a smallest atom of oil,
3:46 which was smooth, and it was smooth, of course, because, well, oil is smooth.
3:50 There was a smallest atom of vinegar because
3:52 vinegar is tart and it pricks your tongue-...
3:55 so therefore, atoms were little sharp, pointy things.
3:58 Um, and so he was wrong about a lot,
4:00 but he was right about the idea that there was a small particle,
4:06 and we now know a very— we have a very different concept than he did.
4:11 So you can go back farther than that.
4:13 But getting the unification, there are more examples.
4:16 For instance, if you go back to, say,
4:19 1830 or so, scientists were trying to understand electricity, for instance.
4:26 And there was a lot going on.
4:27 People really understood things.
4:28 But at the time, you would have two phenomena that are familiar to us now.
4:34 One is a magnet, which, you know, at the time,
4:37 mostly magnets were simply little pieces of iron
4:40 that had been magnetized and they could stick to steel.
4:44 And then you had electricity,
4:45 which was at the time they were generating little sparks
4:48 that they could play and, and have fun with, or more broadly,
4:52 a lightning bolt blazing across the sky.
4:55 And so when you think about this, that lightning
4:58 bolt and that little magnet seem to be really unrelated.
5:02 Um, but over the 1800s,
5:04 a number of scientists were exploring little aspects of it.
5:09 What happens when you run electricity through a wire?
5:12 It seems to make a magnetic field.
5:15 You know, they, they— There was a whole bunch
5:16 of experiments and there were a lot of names.
5:18 But in about the 1860s or so,
5:21 James Clerk Maxwell took all of those ideas that had been percolating
5:25 around for the previous 50 years and wrote his laws of electromagnetism,
5:30 and they're really fascinating.
5:31 If you look at the laws of electromagnetism,
5:34 they are— they're differential equations or inter- integral equations.
5:38 But basically, what they say is on one side,
5:42 you have a bunch of terms that have electricity in them,
5:46 and then you have equals on the other side, a magnetism thing.
5:50 So forgetting all of the mathematical symbols,
5:53 you have electricity side equals a magnetism side.
5:56 Electricity equals magnetism.
5:58 And that is a staggering concept, the fact that these two things,
6:03 a lightning bolt and the magnet that holds your kids' art to the refrigerator,
6:06 are one and the same.
6:08 And this was another case where
6:10 electricity and magnetism became unified into electromagnetism.
6:14 So now we have two examples: one, gravity being unified,
6:18 terrestrial and celestial gravity, and then electricity and magnetism.
6:22 So I'll tell you about some more in a moment,
6:24 but one thing that's kind of important because the goal is,
6:28 of course, to unify everything.
6:30 That if I could do what I want to do,
6:32 I would have some unified theory that would
6:34 explain all the behavior of all energy,
6:36 matter, space, and time, which is a grand goal.
6:40 And we should say that maybe one of the goals of science more broadly,
6:44 outside of physics even, is to construct models that can generalize the world.
6:52 So if you look at Darwinian evolution-...
6:55 that was a very beautiful theory
6:59 that captures another layer of reality of, like,
7:03 how this particular thing that we see here on Earth happens.
7:07 Right.
7:08 So when we talk about theory of everything in physics,
7:10 that's capturing a different layer of abstraction
7:13 about the functioning of the universe.
7:16 Right.
7:16 The whole Darwinian evolution,
7:18 the fact that our genetics has significant overlap
7:21 with the genetics of a banana is pretty staggering, is astonishing-...
7:26 that that works.
7:28 So that is amazing.
7:29 But for at least the class of scientists that I am,
7:34 what we think of is, well, sure, biology is interesting and all,
7:39 but when you get right down to it, it's,
7:42 it's caused— whatever happens in biology is caused by the movement of molecules.
7:46 And then you say, "Well, that's great and all, but molecules,
7:50 they do what they do because they're made of atoms." And then the next step is,
7:54 well, you know, atoms, that's great,
7:56 but atoms work the way they do because of the nucleus and the electrons,
7:59 and then the nucleus is protons and neutrons.
8:01 And so there are those of us, myself included, who want to dig down to the very,
8:07 very bottom and find out what is the smallest building block of nature
8:12 from which all of these other far
8:14 more complex and interesting and abstract things are.
8:18 But what is at the very, very bottom?
8:20 And also, that's great, but if you know what the smallest building blocks are,
8:25 that doesn't tell you the story.
8:27 It's like having a whole bunch of LEGOs,
8:29 but not knowing how to put them together.
8:31 You also need to know how they interact,
8:33 how they work, and so that's why we study forces.
8:36 So there are the various subatomic forces
8:38 of which we're familiar and for instance,
8:41 electricity and magnetism are components of electromagnetism,
8:45 which then governs the behavior of things like— This is amazing.
8:51 Electromagnetism explains, of course, electricity, magnetism,
8:54 but it explains how light works.
8:56 It explains how much of chemistry works.
9:00 So electromagnetism, 1860 or '70 the wonderful thing about that is if you
9:06 take Maxwell's equations and you apply a little bit of calculus,
9:09 it's very easy to see that the laws of electricity
9:12 and the laws of magnetism combined together make what's called a wave equation,
9:18 which that shows that these electric and magnetic fields oscillate.
9:23 They vary, and if you have something that's varied,
9:27 that's a wave, and the wave then moves.
9:29 And if you do the math,
9:31 you find out that the speed at which these waves move is the speed of light.
9:35 And so people said, "Wow,
9:38 the speed of light comes out of those equations." And that had to be,
9:42 I think, very persuasive.
9:44 And of course, electromagnetism also plays a really
9:48 significant role in chemistry because after all,
9:52 atoms are held together by electromagnetic forces.
9:54 There's more to how atoms work.
9:57 There is all the quantum mechanics stuff.
9:59 But if you did not have electromagnetism,
10:01 or if electromagnetism was very different, then atoms would be very different.
10:05 So it plays a very big role in holding us together.
10:09 So it's a staggering advance in science to have a good behavior on that.
10:16 And of course, being able to, to tame
10:21 electromagnetism is why people can hear you when you
10:25 do your podcast because through the miracles
10:27 of the internet just— or just electricity running the computers.
10:30 I mean, this is a case if I can get on a small soapbox,
10:36 where people back then said, "Well,
10:37 why are you messing around with magnets and sparks?" And who cares?
10:42 Well, that very fundamental digging into the laws of nature has spinoffs,
10:50 and it has spinoffs— One of the big
10:52 spinoffs is our entire technological society.
10:54 Without being able to govern electricity,
10:57 we'd still be farmers and shoemakers in cities.
11:00 We certainly would not have everything that we do, so off my soapbox.
11:05 But it's really a lovely thing to show how this digging into deep, fundamental,
11:12 not understood, mysterious things can,
11:15 a hundred or two hundred years later, transform the world.
11:19 And the type of science I do now, people often ask,
11:23 "Well, what good is knowing about how the inside of atoms work,
11:26 how the inside of quarks work?" And I don't know
11:29 the answer to that but just being a little more pragmatic,
11:33 if I go back, say, a hundred years, where people were trying to understand how
11:38 the protons and neutrons inside atoms held together,
11:42 how they split, how they, how you could combine them and so forth,
11:47 this has led to nuclear power.
11:49 Now, whatever you think about nuclear power,
11:52 and some people like it and some people don't, but it is powerful.
11:55 It will generate energy for humanity,
11:57 and it may be that is the path that we take
12:02 as we move away from digging fossil fuels out of the ground.
12:07 Humanity is going to need power no matter what.
12:10 Nobody is going to go back to the way things were in the 1700s.
12:14 And one enormous source of energy that is there for us to take
12:20 if we so choose is the modification of the nucleus of atoms.
12:24 Seemed to have absolutely nothing to do with anything,
12:26 and yet it provides humanity with an opportunity,
12:30 which of course requires that we think carefully of how we do that and if
12:34 we want to, but it gives us something that we didn't have before.
12:38 Yeah, it's very clear that nuclear fusion and nuclear fission will
12:42 unlock huge amount of energy that's required for a civilization to flourish,
12:47 but that's almost like near term.
12:52 Longer term, you can think about things
12:55 like we'll talk about dark energy crisis- antimatter.
12:59 Maybe if you figure out some of the mysteries around antimatter,
13:06 that too would lead to energy sources, how to produce energy.
13:10 That too might lead to counterintuitive propulsion systems-...
13:16 for us humans to travel through the universe.
13:18 Now, right now it seems far-fetched,
13:20 too expensive, too complicated, too difficult,
13:23 but breakthroughs in fundamental theoretical physics might
13:28 lead us to unlock some incredible energy sources,
13:31 incredible technologies that will allow humans to explore the universe.
13:36 And of course, we should also mention that as always with technology,
13:40 it's a double-edged sword.
13:41 It will most likely lead to the development of more dangerous weapons or-...
13:47 other sources of harm.
13:48 And then we as a civilization kinda have to walk that line and hope
13:54 we figure out how to do more good than bad with the technologies we build.
14:00 Right.
14:00 But we have to really remember, while people worry about nuclear weapons,
14:04 which are admittedly very dangerous, and even nuclear power,
14:08 which has waste that has to be dealt with, what science is doing is working out,
14:16 finding power that nature has presented to us.
14:20 This is not new.
14:22 Fire is like that too.
14:24 Fire can burn down your house or it can cook your steak.
14:27 Power is like that, and that's just
14:30 something that we have to understand as humanity,
14:32 and that's why this needs to be a— you know, when we talk about science,
14:35 it has to be a broad conversation by all of society
14:39 because what scientists can do is figure out how the world works.
14:44 Society has to figure out how we wish to apply that or not apply that.
14:49 Also, solving the mysteries and the puzzles
14:53 of the universe in itself is effing awesome.
14:56 It is.
14:57 It is.
14:58 So that means that's the thing that makes us
15:00 human in part is looking at a thing and saying,
15:04 "How does this work?" And then together a bunch of apes get together,
15:08 like poke the thing, kinda shake the thing.
15:11 And then over time you have rockets going all into space.
15:15 You build roads and bridges.
15:17 You build the internet.
15:18 Anyway, so we talked about Newton, we talked about Maxwell.
15:22 That takes us into 20th century in terms of unification.
15:25 There's a guy named Einstein-...
15:28 on whom you wrote a book, who did-...
15:30 quite a lot of progress on the effort of unification.
15:34 Sure.
15:34 So Einstein, he's a pretty amazing guy.
15:37 In 1905, he had his miracle year where he wrote multiple papers.
15:41 The one that most people know about is special relativity,
15:45 where he showed something that makes no sense
15:50 to anybody who's not really dug into it very hard,
15:54 and that is that two people experience time differently.
15:59 Time, you know, is a fascinating thing.
16:02 We don't really understand what time is, which is weird.
16:04 You'd think that that'd be something we'd understand very well,
16:06 but we really don't.
16:08 We know a lot about it, but really understanding it, not so much.
16:13 But Newton thought that time was just universal for everyone,
16:17 so my time, your time, some person's time on Mars or on Alpha Centauri,
16:23 everybody experienced time the same.
16:25 What Einstein showed was that that wasn't the case,
16:28 that different people moving at different speeds
16:31 with respect to one another experience time differently,
16:34 which is absolutely a mind-blowing concept.
16:38 Now, most people think that Einstein then said, well, he invented spacetime,
16:42 that, that space and time are the same thing, and he was behind that.
16:47 But that actual insight came from one of his teachers,
16:50 a guy by the name of Minkowski, who looked at Einstein's equations.
16:55 Minkowski was a little bit more mathematically inclined than Einstein,
16:59 and he saw that if you look at the equations,
17:02 you have basically one person's space and time
17:06 equals some numbers times this person's space and time.
17:10 And so that's kind of a staggering thing.
17:14 So that is where Einstein and Minkowski really did this unbelievable
17:21 concept that space and time are actually pretty much the same thing.
17:26 That runs afoul of our understanding of how
17:29 the world works because time just moves, it's continuous.
17:33 We know what it is at a visceral level and an experiential level.
17:39 We might not understand it at a formal level, but we know what time is.
17:43 It's what keeps, makes today today and not yesterday or tomorrow.
17:46 Space is a little different.
17:48 You can walk somewhere, you can walk back, you can move around.
17:51 You have more freedom to move in space than you have to move in time.
17:54 You can always move forward in time.
17:56 It's just moving backwards that turns out to be a little more difficult.
17:59 But yeah, Einstein's understanding that that is the case,
18:04 it caused everybody to think about the world very,
18:08 very differently, and that was in 1908 when
18:11 Minkowski really laid it out in a strict spacetime.
18:15 And that also led to the work on special relativity,
18:19 led to the speed limit, the speed of light.
18:22 Well, it was a premise.
18:23 He had two premises.
18:24 One was that the laws of nature are the same for everybody,
18:27 so if you're moving at some speed, or if I'm moving at some speed,
18:31 I can say I'm not moving and saying you're moving at some speed.
18:35 That's not controversial.
18:36 That is what we call Galilean relativity.
18:39 It's from hundreds of years ago.
18:42 But what Einstein said that was controversial was that everybody
18:46 measures that the speed of light is the same.
18:51 Irrespective of how we're moving with respect to each other,
18:54 you'll measure the speed of light to be a number,
18:56 I'll measure the speed of light to a number, and that's very,
18:59 very different from what Newton would've said or Galileo or any of the old guys.
19:03 And it was taking those two things together
19:06 that caused all of the weirdnesses of special relativity.
19:10 Now, you could then very easily say, well,
19:13 that second premise that everybody measures the speed
19:16 of light to the same is just dumb, and that, you know, you could test that.
19:23 So that's where testing relativity comes in.
19:26 And Einstein's equations, which include those two assumptions,
19:31 it predicts the behavior of everything perfectly well.
19:34 Now we've actually measured, done experiments where we can say that the speed
19:39 of light is the same for everybody.
19:41 That's not how that's been in the beginning.
19:44 It was really that assumption leads to predictions.
19:48 The predictions are true, so the assumption is true.
19:51 Now, there is a— for those people, for your viewers who wanna say, "Well,
19:55 how do you measure that the speed of light is the same for everyone?"
19:58 The particle physicists do this, and the way you do this is the following:
20:04 There are some subatomic particles that when they decay, they emit light.
20:08 That's their decay product.
20:10 And so you collide two things together
20:13 so you know when the particle was created,
20:17 then you have surrounded your collision point by a detector,
20:22 and you measure how long it takes for light to get to your detector,
20:28 and by God, it's the speed of light, which it should be.
20:32 However, sometimes in these collisions,
20:34 some of these subatomic particles you make are coming out at very high speed.
20:39 They might be coming out at ninety-five or ninety-seven
20:41 or very large fraction of the speed of light, and then they decay into photons.
20:47 And so you measure how long it takes for the photon to get to your detector,
20:54 and it says it's— light travels at the speed of light.
20:58 Now, if it were that if Einstein's conjecture was incorrect,
21:02 you'd have a particle coming out at near the speed of light,
21:04 it would be decaying into a particle traveling at the speed of light,
21:08 then that particle should have traveled at, say,
21:09 two times the speed of light or something like that, so it should
21:12 have taken half as much time to get to the detector, but it doesn't.
21:16 So this is a hard, serious measurement that shows that something, you know,
21:22 we can measure the speed at which
21:24 light comes out of this stationary created particle,
21:27 and it's the speed of light.
21:30 Then we can measure what the speed is
21:31 of it coming out of something that's moving, and it's still the speed of light.
21:35 So that is an actual measurement,
21:37 but that is not something that was possible in Einstein's day-...
21:40 but it is now.
21:42 Just to take a small tangent,
21:44 how weird is it in the full ranking of weirdness that is physics,
21:48 how weird is it that there's that speed limit of the speed of light?
21:53 Well, I have to tell you,
21:54 when I first encountered this, it's pretty freaking weird.
21:56 It peaks the weird meter.
21:59 But as you become more familiar with it,
22:03 as you become more comfortable with the idea,
22:06 the thing to remember is the speed of light,
22:11 it's the speed of light through spacetime.
22:16 Once you embrace that, that makes a whole ton of sense.
22:18 It all of a sudden makes everything fall much more into place.
22:23 I think that there is an ultimate speed isn't that shocking.
22:27 It just simply says that it's a property of space in the same way that there is,
22:33 you know, space can transmit a certain strength electric field.
22:37 It can transmit— it can support certain things.
22:41 Whatever space is, and we don't know what space is, but whatever it is,
22:45 it has the capability of transmitting these things
22:48 at that one speed through space or time,
22:52 and everything else comes from our insisting
22:54 that we keep space and time different.
22:57 That's how I view it, and at least for me,
23:01 that once I accepted that, it all became very comfortable.
23:07 So the nature of my question actually here-...
23:09 that will apply over and over is trying to empathize,
23:12 trying to put ourselves in the shoes
23:14 of the people before space and time are unified-...
23:18 into space time and really experience and think
23:21 through how difficult of a leap is that.
23:24 Huge.
23:25 The reason I sort of say that is we
23:29 are now in the modern day in the twenty-first century,
23:32 and of course, we're gonna have to make leaps like that in our future.
23:36 So what are the unifications we're not seeing in front of our eyes?
23:40 So for example, there's so many examples through your work,
23:43 through your lectures of Paul Dirac taking antimatter seriously.
23:51 Looking at what the math shows and saying,
23:54 "I really think this thing exists." I mean, it just sounds insane.
23:59 It does.
24:00 And so I think this is a good warm-up.
24:03 The space-time unification-...
24:05 is a good warm-up as we march through the twentieth
24:07 century 'cause it gets in my view at least,
24:10 weirder and weirder, even with Einstein himself.
24:13 Well, let me give you an even more basic example, sodium and chloride.
24:19 Sodium is an explosive metal.
24:20 You put it in water and it's kind of neat.
24:23 You put it in water, and it just,
24:25 it doesn't quite explode, but it gets hot, and it pops around.
24:28 Chlorine, it's a gas.
24:29 It's going to kill you.
24:31 So these two things are deadly.
24:33 They're awful.
24:34 And yet when you mix them, you put it on your food at night.
24:39 It's salt, right?
24:40 And so this is a case where, where this whole,
24:44 A, unification and B, this deeper understanding, in this case of chemistry,
24:49 of how—Two things that are dangerous can be
24:53 brought together and turned into something not only innocuous,
24:56 but necessary for human life.
24:58 And so this is not unusual, what you're describing.
25:02 I mean, when you think about it,
25:04 forget about everything else, just the fact that, you know,
25:07 we tell little kids, little kids, that the world is made of atoms.
25:11 Now, that's crazy.
25:12 Most people have never seen atoms, and yet nobody really doubts it anymore.
25:17 And I think it's just a case of familiarity,
25:20 and then the culture slowly accepts it,
25:23 and it's then, it's real even without the evidence.
25:26 In fact, one of the courses you described there,
25:28 How We Know What We Know, I think that's a valid question.
25:31 How do we know there are atoms?
25:33 And, and of course, there are ways we do.
25:35 And by the way, on that front, I would love to go through how we know
25:40 the building blocks in the universe as we march towards quarks.
25:43 That, in the course that you mentioned,
25:45 is one of the most fascinating things of this philosophy
25:48 of atoms being around for a very long time.
25:52 Then you concretize and you actually can prove
25:55 or have strong observations that indicate that there is atoms,
26:00 and then there is a nucleus, there is electrons,
26:03 there is photons, there is quarks and I mean, it gets weirder and weirder,
26:07 and now we're facing the mystery is
26:09 there's building blocks even smaller than that.
26:12 But anyway, Einstein, turns out, didn't just do special relativity.
26:17 By the way, I really think he deserves three Nobel Prizes.
26:20 He got it for photoelectric effect.
26:22 The fact that he didn't get it
26:24 for general relativity is a crime against humanity.
26:27 I don't understand.
26:28 Obviously should have gotten it
26:30 for general relativity and, and special relativity.
26:33 I mean, I think special relativity is separate
26:35 for general relativity in as far as Nobel Prizes go.
26:39 So general relativity is another unification.
26:42 Yes, that's right.
26:43 What Einstein realized was that if you were in a rocket ship
26:47 and the rocket ship was a very quiet rocket ship and it was accelerating,
26:52 it would feel like you were experiencing gravity.
26:54 And so as you say, it's one of his happiest moments
26:57 when he realized that acceleration and gravity feel very much the same.
27:03 What I'm impressed by is that idea, which is already a pretty neat idea,
27:09 somehow led him to take his space-time idea,
27:13 take this acceleration gravity idea,
27:17 and realize that he could describe gravity as the bending of space-time.
27:23 Space-time being constant like east, west,
27:26 north, south, that's already hard enough.
27:29 But now he's saying, "Well, you know, take your, your map and crinkle it
27:33 and bend it," and so forth, and that's gravity.
27:36 That is a staggering, mind-blowing idea.
27:40 I guess, I wonder if you can comment on what do
27:43 you think is the idea generation process that leads to that.
27:47 So probably an Einstein case has to start
27:51 with what if gravity is itself space-time geometry?
27:55 You, you have to have a thought like that, right?
27:59 Yes, I think so.
28:01 There's a lot about science.
28:02 There's, of course, knowing what went before.
28:05 There is knowing the mathematics that allows you
28:08 to figure out the implications of your theory.
28:11 There is the discipline to argue with yourself
28:14 and other people because most ideas are wrong.
28:17 But then there's what you just described, that intuitive spark,
28:21 and that is something that is very, very difficult to, to create.
28:26 There's a reason that we venerate these people,
28:29 is because it is an unusual feature,
28:32 and most people only have that aha moment once in their lifetime,
28:38 if they have it at all.
28:40 And then there's a tricky business because I'm sure you do,
28:44 and I get a lot of letters from, from creative thinkers who
28:48 don't have all of the history and the mathematical discipline and the self,
28:54 you know, self-critique that's necessary.
28:56 And so they come up with these ideas,
28:59 and often it's easy to see where they just don't play out.
29:04 So in order to be that person who changes the way we see the world,
29:10 ideas themselves are not enough.
29:12 These creative ideas, that's not enough.
29:14 You need it with the discipline and the critique,
29:18 and it's that amalgam of those things that you know,
29:23 make you a genius that history remembers.
29:26 But it's hard to know.
29:28 In a field of people you might be tempted to call crazy,
29:32 there could be geniuses there, and it's hard to know which is which.
29:36 We should mention that Einstein himself couldn't
29:41 see the genius in quantum mechanics initially,
29:44 couldn't see the correctness, I should say.
29:47 So he could see the insanity of gravity bending space-time,
29:53 but quantum mechanics was too weird for Einstein.
29:58 In all fairness, it's weird for me too.
30:00 But...
30:01 but the thing is, even while that is true,
30:04 and Einstein maybe spent the last few years of his life trying
30:08 to blend electricity and magnetism and gravity in a, a single thing,
30:13 and he was unsuccessful, but he still was a very, very valuable critic—...
30:20 of quantum mechanics.
30:21 It's not that he didn't understand it, because he did understand it.
30:24 He thought about the implications and all this quantum entanglement business,
30:27 you know, not all of it.
30:29 But he was responsible for saying, "Well,
30:32 if you're right, then this." And of course, then people went out and found out
30:37 that, that Einstein's implication of quantum mechanics was real,
30:40 and so they could say, "See?
30:42 Quantum mechanics is real." So, you know, he was thinking deeply about it,
30:47 and he was doing exactly that thing I said.
30:50 There's that spark idea, but there's that critique idea.
30:53 And if you're able to critique an idea, you might kill it.
30:58 And that is—it's always depressing when I
31:01 have this brilliant idea and it gets killed,
31:03 but it's better to be killed than to keep it around and waste time on it.
31:09 And so he was, in that case, not generating the aha,
31:14 what he was saying is, "All right, let's take your aha.
31:18 Let's see it's right.
31:19 What does it mean?
31:21 It means this." That allows people to go test it,
31:25 and so he was contributing very crucially
31:29 to that other part of scientific advancement,
31:32 which is not just the aha moment, but the beat it to death, test it-...
31:37 critique it, and make sure it's real.
31:40 And it's only after all of that has
31:42 been done that you really assure you're right.
31:45 And that's why science is such a powerful tool.
31:49 It is that, that combative,
31:51 just downright kinda jerky critique that most people don't like.
31:55 They don't like people saying, "Uh, your ideas, you know,
31:58 might be wrong." But that is— it is crucial.
32:01 It is a crucial part of the scientific process.
32:05 Plus, there's that quote on the other side of it that I've heard you mention,
32:09 which is you know, "I believe your idea is crazy,
32:13 but is it crazy enough?" Was that Niels Bohr?
32:17 I love that one.
32:17 Yes, yes, we all agree that your idea is crazy, but is it crazy enough?
32:21 And there is some degree of taking those leaps of crazy,
32:25 but it has to be backed with rigor.
32:27 Right.
32:28 And the unifications continue that as we
32:31 take steps towards the Standard Model-...
32:34 which is such an incredible part of physics in the 20th century.
32:37 So can you describe that unification?
32:39 So, you know, we're sort of jumping forward here now to the 1930s or thereabout.
32:44 And at, by that time, people had realized that there are four distinct
32:50 forces that do not seem to be connected.
32:55 One is gravity, two is electromagnetism,
32:58 and those are things people are relatively familiar with.
33:01 But there are two other forces that only
33:04 have any real importance inside the nucleus of atoms,
33:07 which is why most people have no experience with them.
33:10 One is the strong nuclear force, which holds the nucleus of the atoms together,
33:15 and the other one is what we call the weak nuclear force,
33:18 which is responsible for some types of radioactivity.
33:21 And since most people don't play around with nuclei,
33:25 and most people don't play around with radioactivity,
33:27 they don't know what that is.
33:29 But by the '30s, scientists had done enough experiments,
33:35 done enough theorizing to say that there were these four forces,
33:40 and that was already a triumph.
33:42 I mean, we, in our goal for a theory of everything,
33:45 we'd like to think that there is one force,
33:47 which is what we're talking about, the unification.
33:49 Maybe these four forces are just different
33:52 ways of looking at a single underlying force.
33:54 But in the '30s, that's where we were.
33:58 There were the four forces.
33:59 So we move ahead, and in the late '50s and early '60s,
34:07 some people were thinking that maybe the weak
34:12 nuclear force and electromagnetism actually were the same.
34:18 So they were working on trying to bring
34:21 together these two forces to show that they're connected.
34:25 And it came true.
34:26 They were able to show that electricity and magnetism were actually two
34:32 different facets of a single force that we now call the electroweak force.
34:37 Now, the story that you're told in articles about this, about what people
34:43 have called the Higgs boson or the God particle, the story is very,
34:48 very simplified because in 1964,
34:53 there were three groups with six individuals who came up
35:00 with important papers talking about what's called the Higgs field.
35:03 And I'll get back, get to what that is in a minute,
35:05 but the Higgs field is important.
35:06 But it wasn't until 1967, so three years later,
35:10 that Steven Weinberg and some others
35:14 actually unified electromagnetism and the weak force.
35:18 Sheldon Glashow, Abdus Salam,
35:20 and Steven Weinberg successfully unified electromagnetism and the weak
35:25 nuclear force that showing that at high energies-- Right-...
35:31 these two forces were merged into a single electroweak force.
35:35 Right, and that was in '67, all right?
35:37 Everybody talks about this thing happening in '64, but it really wasn't.
35:41 It happened over quite a few years actually.
35:44 But all right, so now let's— what you said is true.
35:49 So Weinberg, Glashow, and Salam showed that electromagnetism and the weak
35:54 force at high energies were the same.
35:57 There was a problem, however,
35:59 and the problem is that electromagnetism has an infinite range,
36:05 And we know that because we can see stars that are millions of light-years away.
36:09 I mean, that shows you that the range of that force is essentially infinite.
36:15 The weak force, however basically becomes nonexistent on distances
36:21 much smaller than the size of a proton.
36:25 So that, you know, to say, "Oh, they're the same," and yet one can reach across
36:29 the universe and one can't reach out of an atom, well, that's just dumb.
36:33 I mean, the obvious thought here is, well,
36:37 we just proved that that whole idea is stupid, so throw it away.
36:42 Ridiculous.
36:43 And that is where these ideas from 1964 came in and saved the day.
36:48 So how can it be true that the electroweak force
36:55 is real and electromagnetism and the weak force act so differently?
37:02 The way that could happen is if these forces were transmitted
37:09 by a particle moving from one subatomic particle to the other.
37:16 In the case of electromagnetism, it's the photon.
37:19 In the case of the weak force, we call them now the W and Z particles.
37:25 So the idea is that Higgs and his colleagues came up with is saying,
37:30 "All right, electroweak force is real.
37:35 The way we make it so that there is now an electromagnetic force
37:40 and a weak force is the force-carrying particle of electromagnetism has no mass.
37:47 The force-carrying particle of the weak force has
37:52 a mass." And so what was done is a field
37:59 was postulated that there was this additional field
38:03 that was kind of distinct from this electroweak field,
38:08 and we call it the Higgs field.
38:10 And the Higgs field permeates all of space.
38:14 And here's the kicker, some particles interact with the field,
38:18 and some particles don't interact with the field.
38:21 The ones that interact with the field get mass,
38:24 and the ones that don't interact with the field don't have mass.
38:28 And so that's the idea,
38:30 is that the Higgs field gives the weak force particles mass.
38:35 However, the photon laughs at the Higgs field,
38:38 doesn't see it, and it has no mass.
38:41 And I should say here, going to Perplexity, the big-picture view,
38:44 the Higgs field is the quantum field that fills
38:47 all of space and gives many elementary particles,
38:49 just as you're saying, their mass through their interaction with it.
38:54 The Higgs boson is the particle associated
38:56 with ripples or excitations of this field.
39:01 In modern particle physics,
39:02 every type of particle corresponds to a field that exists everywhere.
39:05 The Higgs field is one such scalar field, meaning at each point in space,
39:11 it has a single numerical value rather than a direction.
39:15 The Higgs field differs from most other fields because even in empty space,
39:21 empty in quotes, by the way, empty space, its average value is not zero.
39:26 This non-zero vacuum value is what enables it to endow particles with mass.
39:32 Right.
39:32 So let's talk about something a little more familiar just to try and hang some,
39:36 some intuition on those words.
39:38 Mm-hmm.
39:39 Awesome.
39:39 All right, so right in front of us, there is a gravitational field.
39:42 Now-...
39:43 you can't see it, but right there.
39:44 Right there.
39:45 Check it out.
39:46 Yep.
39:47 If I were to take something, a pen or whatever,
39:49 and put it there, it feels a force, and it falls.
39:53 Very insightful, I know.
39:55 So we have the gravity field, and we have the pen that has a mass,
40:00 and the mass and the gravity field interact, and it drops.
40:04 Now-...
40:05 if we had another-- I have a-- Oh, yes-...
40:09 object for you.
40:09 All right, so like-- Demonstration purposes.
40:10 This is great.
40:11 Performance art.
40:12 Here we go.
40:13 This is great.
40:13 This thing has mass, and we drop it.
40:16 How remarkable.
40:17 It falls.
40:18 But when we step back and think about what really happens,
40:21 it's the mass of this thing and the interaction
40:25 with this invisible field we see here.
40:28 That's what gives this weight.
40:30 Now, I have this particle here that you can't see, but it's there.
40:33 It has no mass.
40:36 And I leave it there.
40:37 Well, since it has no mass, it doesn't feel gravity.
40:41 It's still floating there.
40:42 And that is really all the Higgs field is.
40:47 Some particles have effectively what you could call
40:49 the Higgs charge that interacts and sees the field, and other particles don't.
40:54 And and that is really what you read just basically means.
40:59 Now, it's kinda neat because in the ordinary day,
41:03 there is a Higgs field right there, and the Higgs field is not zero,
41:07 just like gravity is not zero, and things will get mass.
41:10 But at super high energies, the Higgs field,
41:13 the strength of the Higgs field goes to zero.
41:15 So whether things have mass or whether they have a Higgs charge or not,
41:19 they have no or they have the Higgs charge,
41:21 Higgs field zero, they don't interact.
41:24 It has no mass.
41:25 So that's kind of what, uh, Weinberg and Salam and Glashow said,
41:29 is at very high energies, the Higgs field is zero.
41:34 Since the Higgs field is zero,
41:36 the weak force particles don't feel mass, and therefore,
41:39 they can travel at the speed of light,
41:41 just like the photon does, and everything's happy.
41:45 It is when the universe cooled down.
41:47 After the Big Bang, it was very hot, very high energy.
41:51 Nothing had mass.
41:53 The universe cooled, and at a certain temperature,
41:56 what happened is the Higgs field turned on.
41:58 And at the moment it turned on, it gave mass to the weak force particles,
42:03 did not give mass to the photon.
42:05 So that's what we call electroweak symmetry breaking, so it's a mouthful.
42:09 But all it says is there was a moment in time early in the history
42:13 of the universe at 10 to the minus 12 seconds after the Big Bang,
42:17 the Higgs field turned on and particles got mass.
42:21 So that's the whole idea.
42:24 So this is another really neat thing.
42:27 So the electroweak symmetry theory doesn't need Higgs because
42:31 that only really applies at very, very high energies.
42:36 But in order to make it work at low energies, you need to fix the theory,
42:41 and you need to fix the theory by effectively putting a Band-Aid on the theory.
42:46 Higgs theory is just a Band-Aid on top of electroweak symmetry theory,
42:51 and that is the Band-Aid that fixes it
42:54 because it gives mass to particles at low energy.
42:57 But how does then the Higgs— this Band-Aid,
43:00 the field and the Higgs boson come into play on the experimental front,
43:05 on the evidence-- Okay.
43:08 discovery front?
43:08 Right.
43:08 So what is this Higgs boson thing then?
43:10 Okay, excellent.
43:11 So we have never seen the Higgs field.
43:13 Higgs field is a hypothetical theoretical thing.
43:17 But that is true of most of our fields.
43:21 We've never seen the electromagnetic field.
43:22 We've never seen the gravity field.
43:24 We've seen the effect of the field.
43:26 And so all of these theories are now what we call quantum field theories,
43:30 and that— the whole idea of quantum fields,
43:34 if you have a quantum field, but that field can vibrate like a drumhead.
43:40 And so it doesn't vibrate just exactly like a drumhead, but it vibrates locally.
43:44 So you can have specific localized vibrations,
43:48 and those specific localized vibrations are the particles.
43:51 In the electromagnetic field, the vibration is the photon.
43:54 In the Higgs field, the vibration is the Higgs boson.
43:59 And so what we can do is not see the field,
44:03 but we can actually excite the field,
44:06 make it vibrate, and detect the vibrations.
44:10 So the Higgs boson idea was predicted in sixty-four.
44:14 It became useful in sixty-seven, and then scientists started looking for it.
44:20 So in the early 2000s,
44:23 people were starting to think that we had built particle accelerators powerful
44:29 enough to actually to be able to create these vibrations and detect them.
44:35 So the accelerator that was working at the time was
44:39 a large particle accelerator outside Chicago at Fermilab called the Tevatron.
44:44 And we were colliding protons and antimatter protons
44:46 at near the speed of light at very high energy,
44:50 and that was the accelerator at which
44:52 the top quark was discovered in ninety-five.
44:55 But we had upgraded our apparatus.
44:57 We had ten times the number of collisions per second.
45:00 We had slightly more energy,
45:02 and we were banging the protons and the antimatter protons together,
45:06 hoping that we would actually find the Higgs boson.
45:09 Can you actually back up a little bit and look at the bigger picture?
45:13 So Fermilab has this legendary accelerator that there's also
45:17 a personal story with you connected to it because,
45:19 I mean, there's a million questions I wanna ask you,
45:22 and we'll ask you about some aspects of that.
45:25 So this idea of an accelerator, the design and the physics of an accelerator,
45:30 how is that productive for understanding
45:33 and discovering different aspects of particle physics?
45:37 Well, I'm so glad you asked I mean, this is fascinating.
45:41 All right.
45:42 Everybody has heard Einstein's equation E equals MC squared.
45:46 Nobody knows what it means.
45:47 Maybe they heard that energy equals mass and mass equals energy.
45:49 I don't know.
45:50 You know.
45:51 But they've heard the equation, the most famous equation in all of science.
45:56 But buried inside that equation is a really thoroughly fascinating concept,
46:03 that energy and matter are equivalent, and you can,
46:08 in fact, convert movement energy into mass.
46:12 And so this is something that we've known for a long time.
46:17 This was predicted back in basically 1928,
46:21 so a long time ago, actually almost a hundred years ago.
46:25 And it is not in the slightest bit controversial.
46:28 We can do this all the time.
46:30 So the simplest thing is to take two particles that have no structure, so,
46:37 you know, the closest thing you can have
46:40 to BBs that are just true mathematical BBs.
46:43 If you smash those two things together,
46:46 it's coming in with a huge amount of energy from one direction,
46:49 a huge amount of energy from the other direction.
46:52 The directions cancel, so the net momentum,
46:54 the net energy of this has no motion.
46:56 So you have these two things coming in with a, you know,
47:00 exactly balanced energy, and if they collide, they could stop.
47:04 Well, that energy has to go somewhere,
47:07 and that energy can literally create mass, create particles.
47:12 Now, there are special rules about what happens.
47:14 If you have two things coming together and it creates a particle,
47:17 it has to create an antimatter particle to balance it.
47:20 That's just kind of the rules of the laws of nature.
47:23 Why is that the case?
47:24 Well, we have some ideas, but in many respects,
47:27 the answer is because those are the laws of the universe,
47:30 and that's the things that we try to understand.
47:33 But this is absolutely true.
47:35 So what, what particle accelerators do,
47:39 among other things, is simply transform energy into particles.
47:45 And so basically, any particle that doesn't exist in nature,
47:51 we can make in this way.
47:53 You can make the antimatter electron by taking two particles,
47:58 smashing them together.
47:59 The energy sits there,
48:00 and it will make an electron and an antimatter electron, and it just does.
48:04 And we know that.
48:06 The antimatter electron was discovered in 1932.
48:10 This is all pretty easy.
48:12 The antimatter proton was discovered in 1955 at the Berkeley Bevatron.
48:18 And so this is just what you do.
48:20 You can convert energy into a matter-antimatter particle.
48:24 Now, the converse goes true, and that's something we might talk about.
48:27 You can take matter and antimatter and bring it together, and it'll make energy.
48:32 It's the the process can go both ways.
48:36 Energy can make matter and antimatter.
48:38 Matter and antimatter can make energy, and this is just true.
48:42 We do it all the time.
48:43 There's no question that this is the case.
48:45 And we should also mention that this is the reason
48:48 why Fermilab had a nice stash of antimatter particles.
48:52 So as a side effect, you can also collect antimatter in this kind of way.
48:57 You can produce antimatter,
48:58 but it's at an extremely costly-- Oh, very, very costly.
49:02 In order at, at the Fermilab machine, we would have to smash 100,000 protons
49:08 into something to make one antimatter proton.
49:11 So I mean, it took some work.
49:15 Is there some extremely precise recipe of being able to produce
49:20 particular kinds of particles and all this kind of stuff?
49:23 When you smash two things together, together,
49:26 is there like how can you control accurately
49:29 which kind of particles you're trying to produce?
49:32 If you wanna make antimatter electrons, you smash together energy at a certain—
49:38 It's just easier with electrons because the electrons,
49:41 to the best of our knowledge, have nothing inside them, so they're simple.
49:45 They have a certain mass, and that's that.
49:48 So if you smash particles together with the right energy,
49:51 you can make them very, very easily because you can— It's like a old style radio
49:55 back in the day where you had to dial it in.
49:57 You could get right on the station, and you could hear the, the signal,
50:00 and if you were off a little, it didn't work.
50:03 The problem for things like protons
50:05 and so forth is they're not point-like particles.
50:07 They're kind of like garbage cans full of stuff,
50:09 and so it's very difficult to make antimatter protons.
50:13 Now, you can get more of them by increasing
50:18 the energy at which you collide two particles together.
50:22 If you're at below a certain energy,
50:25 the— and say you collide two protons together at kind of low energy,
50:29 you just don't have enough energy to make an antiproton.
50:33 And so it doesn't happen.
50:34 You get to a certain energy, and you can just barely make them.
50:38 The more energy you collide them together, the more you make.
50:42 So that is just sort of how it works.
50:44 More is better.
50:45 And then with CERN, if you compare maybe CERN and Fermilab,
50:49 going to Perplexity here, CERN's accelerator, the Large Hadron Collider, LHC,
50:55 is the world's highest energy proton collider,
50:58 while Fermilab's current and planned accelerators focus
51:01 on intense proton beams for neutrino physics-- Correct-...
51:06 rather than pushing the absolute energy frontier.
51:08 Absolute energy frontier meaning highest
51:11 possible energy smashing of protons together.
51:16 Correct.
51:17 So one, we were talking about, like, accumulating antimatter.
51:21 All right?
51:22 And so there, that is typically making antiprotons,
51:26 as opposed to making all particles in general.
51:29 So let's focus on the antiproton side to begin with.
51:32 All right?
51:34 So Fermilab doesn't make antiprotons anymore.
51:35 We stopped making them in 2011,
51:38 and it's because we shut our big accelerator down
51:41 to concentrate on a different facet of particle physics.
51:46 However, at the time, we would smash protons with an energy of 120 GeV,
51:55 and in that, we would make antiprotons.
51:57 So that's a ton of energy.
52:00 It's true that the CERN accelerator, the big accelerator,
52:04 is now much higher energy than the Fermilab accelerator was.
52:08 No problem.
52:08 But that's not how they make antiprotons.
52:12 The— A-all of these big beam big laboratories, it's not one accelerator.
52:18 At Fermilab, there were five distinct accelerators,
52:20 and it was basically like shifting an old standard car,
52:23 'cause you couldn't just go zero to super speed in one accelerator.
52:27 You had to go from one to another, getting higher and higher.
52:31 Well, at CERN, they use one of the, basically their second
52:35 gear in their very big accelerator complex to make antimatter protons,
52:40 and their accelerator is only 26 GeV compared to the 120 GeV at Fermilab.
52:47 Fermilab's not operating, but when it was operating,
52:50 it operated at an energy about four times higher than what CERN is doing now.
52:55 And why is that?
52:56 Well, it's because what CERN needs to do is
52:59 to not make as many antiprotons as Fermilab did.
53:03 They are doing a very different current experimental program.
53:06 They're doing a fascinating experimental program,
53:08 including trying to figure out does antigravity fall up or down,
53:12 which is kinda neat.
53:13 And we sort of know the answer to that.
53:15 That's separate.
53:16 But anyways, so getting back to the antiproton business-...
53:21 while Fermilab doesn't do it now, it was top dog.
53:23 It's not anymore.
53:24 The only really big antiproton accelerator
53:27 creator is a small accelerator at CERN.
53:31 Okay, so that's the antiproton thing,
53:33 and if we get back to antimatter, we can talk about that-...
53:35 'cause that is way cool.
53:37 Yeah, super cool.
53:37 But now the other side of your thing
53:39 about making high-energy unknown particles, bigger is better.
53:44 And it is true that the LHC is a very high-energy machine.
53:48 It is about seven times more powerful in terms of energy per collision.
53:53 It is also about 100 times more collisions per second than the Fermilab machine.
53:59 So it is true that the LHC can make bigger,
54:04 heavier particles that the old Fermilab, the Tevatron, ever could.
54:11 And that is true.
54:12 So if you wanna look at high-energy stuff, yeah,
54:14 you go to CERN now, which is why many of my colleagues, including myself,
54:19 once we had measured all of the sort of frontier
54:23 measurements we thought we could make with the Fermilab accelerator,
54:28 we saw this bigger, more powerful machine with seven
54:31 times the energy and 100 times more collisions per second.
54:34 We said, "Heck yeah, let's go work on that." And to give you a sense of scale,
54:39 the top quark, which is the heaviest particle ever discovered,
54:42 discovered at Fermilab in 1995, there were two discovery papers,
54:46 and the one on which I was a co-author,
54:48 we had worked for a good chunk of between
54:52 six months and a year of collecting collisions,
54:55 and there were a lot of collisions, and our paper had 38 top quark candidates.
55:02 38.
55:03 And we knew that half of them were crap because when
55:06 you make a detector like that, there's what you call background,
55:09 so you have the background and the good stuff, and we know it was about 50/50.
55:13 So we had maybe 19 top quarks after working
55:16 for between six months and a year of collecting data.
55:20 But now, at the LHC, we make a top quark every second.
55:26 And that's what higher energy and more collisions per second will do for you.
55:31 That extra energy, you're above threshold, you make a ton of them,
55:35 and when you compare the 1995
55:37 Fermilab accelerator to the current CERN accelerator,
55:41 it's probably 1,000 times of collisions per second.
55:44 So it went from painstaking, pulling teeth,
55:48 to, yeah, now top quarks are a background.
55:50 We try to get rid of them.
55:51 There's just too many of them.
55:53 They get in the way of searching for the stuff we really wanna search.
55:56 They are, like, so 30 years ago.
55:59 By the way, is there something to be said
56:01 about the kind of sort of signal processing here,
56:03 how you remove the noise, how you remove the background,
56:07 how you determine which particle is which?
56:09 There's probably some, like, incredible nuance there,
56:12 even outside of the scope of this conversation.
56:15 So let me just throw some numbers out, all right?
56:17 So at the CERN accelerator, when it's operating,
56:20 the collisions occur at a prodigious rate.
56:23 We get about a billion, with a B, collisions per second.
56:28 Now, each one of those- Wow.
56:29 Yeah, yeah, that's what I said.
56:31 Wow.
56:31 Now, it turns out some of them are happening at the same time, so there's about,
56:35 of order 40 million moments in time per second where you would take a shot,
56:41 and inside that moment, there might be 20 collisions.
56:46 So that's why we get to the billion.
56:48 Yeah, but can you individually pinpoint the collisions?
56:51 Sort of, to a degree.
56:53 So the beams are, you know...
56:56 When people think of beams, they think of, like,
56:58 laser beams, but that's not really what particle beams look like.
57:01 Particle beams look like little tiny sticks of spaghetti,
57:05 except they're much thinner.
57:06 They're not as fat as a stick of spaghetti, and they're at the LHC,
57:11 different accelerators are different, they're about this long.
57:14 And so you have one of them going one way full
57:17 of protons— ...and another one going the other way full of protons,
57:20 and they pass through each other.
57:22 And as they— ...pass through each other,
57:23 you should think of this as like a swarm of bees.
57:26 Yep.
57:26 And this is like a swarm of bees,
57:28 and mostly the bees pass through each other and don't do anything.
57:31 But every so often, some of the bees hit
57:33 nose on and stripes and wings and everything everywhere.
57:38 That's awesome.
57:39 That's awesome.
57:39 And so as they collide through each other, you know,
57:42 one collision's here, and one's here, and one's here.
57:44 And you can't tell too much side to side because the beams are really small.
57:49 They're sort of the thickness of a human hair.
57:51 But you can see along the direction.
57:53 And they're, you know, this is about the right size.
57:56 And so we have detectors around them, and we can actually see,
58:00 oh, particles came from here, and particles came from here.
58:04 And that's amazing.
58:05 All right.
58:05 So at any one crossing, there's maybe 20 collisions.
58:10 Now, most collisions are absolutely boring.
58:13 They're boring because they are— they exemplify physics
58:18 that we know a great deal about already.
58:21 We've tested it for decades.
58:22 We know all about it.
58:24 We don't care.
58:24 I mean, it's kind of blasé that we can say, "Oh, yeah, yeah,
58:28 we're making a billion subatomic particles every
58:31 second," but who cares because, you know?
58:32 But that's just the way of, you know, frontier scientists.
58:36 So what you need is you need to pick out the cool ones,
58:40 the weird ones, the ones that nobody's seen before.
58:43 And so what happens is, these things, these beams collide,
58:50 and we surround the collision point with an enormous detector.
58:54 There are two absolutely ginormous detectors at the LHC, one of them called CMS,
59:00 which is the one I'm on, and the other one is called
59:04 ATLAS— ...which is the other one and we don't speak of— no,
59:07 they're both really amazing.
59:09 Okay.
59:09 It's good to know that there's friendly competition even inside CERN.
59:13 Yes, yes.
59:13 That's awesome.
59:14 I mean, the fact is they are both amazing, absolutely amazing detectors.
59:17 Right.
59:18 But CMS is just a little cooler than ATLAS.
59:19 Oh, yeah, yeah.
59:20 I mean, you know, in particle physics,
59:22 we really absolutely want our competitors to do extremely well,
59:27 just not quite as well as we do.
59:30 Got it.
59:30 Yeah, yeah.
59:30 All right.
59:30 So-- So these two giant detectors.
59:32 Right.
59:33 So, but one of them, our detector, the CMS detector, it's the small one.
59:37 It is 70 feet long, 50 feet high, 50 feet wide.
59:40 It's five stories tall.
59:42 It weighs 14,000 tons.
59:44 Mm-hmm.
59:44 Small one, yep.
59:45 Small.
59:46 ATLAS experiment is 150 feet long, 80 feet across.
59:49 It weighs only 7,000 tons.
59:51 Just piece of cake.
59:52 You could take the ATLAS detector,
59:53 and you could put four of them on a soccer or a football field,
59:56 and it would fill the field up with just enough room on the sidelines
1:00:00 for the cheerleaders and the water boy and the coaches and stuff.
1:00:03 That's how big they are.
1:00:04 Nice.
1:00:05 So these are absolutely ginormous detectors, and basically they're cameras,
1:00:08 and what they can do is they can take pictures 40 million times per second.
1:00:13 Now, all the data comes streaming off that detector, and we can't record it all.
1:00:17 It would just fill up all of our tapes,
1:00:19 and it would be full of all these boring things we don't care about.
1:00:22 So what we do is as the beams pass through one another,
1:00:26 we teach our detectors to say,
1:00:29 "We only want one where there are certain configurations that might
1:00:33 be interesting," like there's gobs of energy in the detector,
1:00:37 or there's a gob of energy on one side and nothing on the other side,
1:00:41 or there's four gobs of energy or whatever.
1:00:44 These are called triggers.
1:00:45 And so these— what we have is fast electronics
1:00:48 that take the 40 million possible pictures per second,
1:00:52 and it says, "You know, about 100,000 of those are really cool.
1:00:58 We should think about them." And then it passes not all of the 40 million,
1:01:03 but those 100,000 to the next level,
1:01:06 which are commercial processors that have, Basically our final analysis code,
1:01:13 but optimized to run very, very quickly.
1:01:16 And what they do is they do a really quick and dirty analysis to say,
1:01:21 to further refine what's good and what's not.
1:01:25 And that, that computer farm then accepts about 1,000 collisions per second,
1:01:31 and we record those for further analysis.
1:01:34 So that's what's really happening.
1:01:35 Of the 50 million possible collisions per second,
1:01:38 the fast electronics and then the computers pick the thousand.
1:01:42 And then we pass those through analysis
1:01:44 software and hand them to the graduate students, and they pick through them,
1:01:47 looking and finding the handful that are the next Nobel Prize.
1:01:51 So that's how that works, and that, that is truly astonishing.
1:01:55 I'm— hats off to the accelerator builders,
1:01:58 the detector builders, the people who make the software work,
1:02:01 the people who make the not gigabytes, not terabytes,
1:02:05 but petabytes of data flow around the world seamlessly.
1:02:09 It's really amazing.
1:02:10 I'm very grateful.
1:02:12 So take me to July 4th, 2012, the discovery of Higgs boson.
1:02:19 So this is really fun because the people searching for the Higgs,
1:02:24 it's a community, and the entire community knew that the LHC was coming online.
1:02:31 So even though many of us had been working on the Fermilab accelerators,
1:02:36 a lot of us were transitioning to the CERN accelerator.
1:02:41 So we were in the very funny
1:02:43 business of wearing our Fermilab detector people hats,
1:02:47 trying desperately to find the Higgs boson
1:02:50 at Fermilab-- Mm-hmm while simultaneously wearing our CERN hats,
1:02:55 knowing that CERN was going to be able to find it if existed.
1:02:58 And so, you know, we were a little neurotic, kind of wanted, you know,
1:03:02 our, our old stuff to work and, and there
1:03:05 was an awful lot of people on both experiments.
1:03:08 Did you have a sense that one of the two places would be able to find the Higgs?
1:03:13 First, did you think the Higgs boson existed, and second,
1:03:17 did you think that these accelerators have the chance to find them?
1:03:22 So I was cognizant of the fact that the Higgs boson might not exist,
1:03:26 but there was a lot of evidence pointing in the direction that it might be.
1:03:31 I knew that both experiments, the Fermilab accelerator and the CERN accelerator,
1:03:37 would either find or rule out the Higgs if it existed.
1:03:42 Rule out?
1:03:43 Well, that's a possibility.
1:03:44 I mean-...
1:03:45 maybe the Higgs theory was wrong.
1:03:46 Right?
1:03:46 Until you, till you know it's there, it might be wrong.
1:03:49 It's like dark matter.
1:03:49 People talk about dark matter, it might not be real.
1:03:52 I mean, I— it probably is, but it might not be.
1:03:55 So you knew at these energy levels,
1:03:56 you would be— you should be able to find-- Yes-...
1:03:59 the Higgs boson.
1:03:59 Yes.
1:03:59 So that's the nice thing about this kind of physics,
1:04:03 because there was a theory, that theory made predictions.
1:04:07 Now, there were parameters in the theory we didn't know.
1:04:10 If the mass was this, we'd get this thing.
1:04:12 If the mass was this, we'd get this thing.
1:04:14 But we could do the the calculation for every conceivable Higgs mass,
1:04:19 and so then we could search.
1:04:21 Look, well, let's say the Higgs mass is 100 in some units.
1:04:25 Did we see it there?
1:04:26 No.
1:04:27 Then it's not 100.
1:04:29 Well, let's look at 103.
1:04:30 Is it there?
1:04:32 No.
1:04:32 So we could do that.
1:04:34 Both accelerators could either find it or definitively rule
1:04:38 out the predictions of simple Higgs theory, 100% guaranteed.
1:04:45 However, the CERN accelerator had 10 times the collisions
1:04:50 per second and three and a half times the energy.
1:04:55 So remember when I said it— with the top quarks,
1:04:57 it was, like, six months for 19 versus one a second?
1:05:01 There's no question.
1:05:02 The writing is on the wall.
1:05:04 The Hi- the, the LHC was gonna have an easier time of it-...
1:05:08 if it was real.
1:05:09 However, so but, you know, I'm a Fermilab scientist,
1:05:12 and we wanted Fermilab, you know, come on, we want Fermilab-...
1:05:15 to win.
1:05:15 Of course.
1:05:16 Not, you know.
1:05:16 So we were busting our butt, and we had done what I said.
1:05:20 We had ruled out this region.
1:05:22 We had certain mass ranges.
1:05:24 We knew it wasn't there.
1:05:26 And we finally said, if there was a Higgs boson, if it existed,
1:05:30 which we didn't know at the time, its mass was somewhere between,
1:05:34 if I recall, between, like, 120 and 145.
1:05:37 All right?
1:05:38 We'd ruled out all the other stuff.
1:05:41 And so wearing our CERN hat, we said, "Okay,
1:05:45 we're gonna find that." But we were really, really, really trying to do it.
1:05:49 Now, if we had had another two years
1:05:51 or maybe three years of running the Fermi accelerator,
1:05:57 Fermilab would have discovered or ruled out, or in this case,
1:06:00 it turned out, discovered the Higgs boson, 'cause it's a real thing.
1:06:03 We would have found it without a question.
1:06:05 But we didn't have enough data in July of 2012.
1:06:10 We needed a couple more years.
1:06:14 Unfortunately, in 2008, or fortunately, the LHC had turned on.
1:06:18 It broke.
1:06:19 They had to fix it.
1:06:20 Turned on again in 2010.
1:06:21 It ran poorly in 2011.
1:06:24 In 2012, they pushed up their sleeves and said,
1:06:27 "Let's do this," and it turned on.
1:06:30 And so, you know, there was this— the Fermilab knew if it didn't have it now,
1:06:36 it wasn't— it was too late.
1:06:40 Anyways, come 2012 rolls around, and like two days before,
1:06:46 The announcement at CERN was July 4th,
1:06:48 so two days before that, Fermilab made a measurement and said,
1:06:52 "We can rule out certain regions, but certain regions we can't rule out.
1:06:58 But what we know, and this is important, if the Higgs boson exists,
1:07:03 it must be in this region for which we are not capable yet
1:07:07 of ruling out." So that's where we were two days before the LHC said,
1:07:15 "We got it." That was July 4th, 2012.
1:07:20 So detecting the Higgs boson confirmed the existence of the Higgs field,
1:07:25 the mechanism through which fundamental particles like electrons
1:07:28 and quarks acquire mass in the standard model.
1:07:31 Correct.
1:07:32 Although, let's be very specific of what we did then.
1:07:37 We found a particle consistent with the existence of the Higgs boson.
1:07:43 There were alternative theories at the time that predicted not one,
1:07:47 but multiple Higgs bosons.
1:07:48 So there's a theory called supersymmetry,
1:07:51 which said that there was not one, but five Higgs bosons.
1:07:55 The standard original 1964 Higgs theory says there was one.
1:07:59 And so all we really knew at the time was we found a theory.
1:08:03 We did not necessarily confirm that Higgs was right.
1:08:06 We found data that said that it looked like Higgs was right,
1:08:10 but until we ran for longer,
1:08:13 we were unable to rule out other alternative theories.
1:08:17 So that's the deal.
1:08:19 Now, in the fullness of time, it is after all what, 14 years now later,
1:08:25 we have been able to basically rule out some of those other things,
1:08:29 and by now we have validated things.
1:08:31 We found the mass of the particle.
1:08:33 We know the spin of the Higgs boson.
1:08:36 It has a spin of zero.
1:08:38 We have discovered the Higgs boson decays.
1:08:41 It preferentially decays into the heaviest
1:08:45 particles it can through energy conservation.
1:08:49 Can't decay into top quarks, it's too light to decay into top quarks,
1:08:52 but it can decay into bottom quarks.
1:08:54 It can decay into W and Z particles, can decay into a weird way into photons.
1:09:00 And we have looked for all
1:09:03 of the hypothesized decays of the original Higgs theory-...
1:09:08 and we have validated that it decays
1:09:10 in those ways at the rates that theory predicted.
1:09:14 And so now in the fullness of time,
1:09:17 I'm pretty comfortable saying Peter Higgs and Robert
1:09:20 Brout and François Englert and his colleagues, they were right back in the '60s.
1:09:24 But we weren't sure on July 4th.
1:09:27 All we knew was we found a particle consistent.
1:09:30 But the thing is, with these discoveries, they're often just barely discoveries.
1:09:34 It takes a while to go and do the more complex,
1:09:38 detailed measurements and that's what we've done.
1:09:41 So at the time, I remember it being called referred to as the God particle.
1:09:46 Uh, you also had a minor in theology, so throwing that all together,
1:09:54 so calling it the God particle is speaking to the importance,
1:09:58 the potential importance of discovering this particle.
1:10:01 Do you think that is in some degree justified?
1:10:03 Like, if we look at the big impact of it on the history of physics,
1:10:07 how important was it to find and show that the Higgs field is real?
1:10:14 Well, I don't think it is as important as, for instance,
1:10:17 some of Einstein's stuff.
1:10:18 I mean, it was— it's an important prediction.
1:10:20 Like, the prediction of quarks was
1:10:23 very important and interesting in validating this.
1:10:26 The Higgs was kinda like validating that quarks existed.
1:10:30 It's an important stepping stone, and I,
1:10:34 I do not wish to denigrate it in any way, but there's ones that changed the way
1:10:39 we thought about the world, like Einstein did.
1:10:41 It wasn't that sort of thing.
1:10:43 And there is a funny story.
1:10:44 So the reason they call it the God particle is this book by Leon Lederman,
1:10:49 and if you read his book, he he says,
1:10:53 "Well, you know, we call it the God particle,
1:10:56 but we should call it the goddamn particle because it's been causing
1:11:00 us so much trouble trying to find it." And Leon ran Fermilab,
1:11:04 so— and he wrote a foreword for one of my books and, you know, I talked to him.
1:11:08 He's a— he was a really funny guy.
1:11:10 And the real truth was the book was called "The God
1:11:13 Particle" because his publisher thought it would sell more copies.
1:11:18 But, you know, then that got into the mindset of the reporters and so forth,
1:11:21 and we called it the God particle.
1:11:23 Leon never really thought of it as anything
1:11:26 to do with the religious or even— I mean,
1:11:27 the, he was an incredible jokester, the goddamn particle.
1:11:30 It is a really important part of our model of the universe.
1:11:33 It is.
1:11:34 That there's this field that it gives mass
1:11:36 to some particles and not others, that's-- Right.
1:11:38 It— I— it's a huge thing, but it was part of the Standard Model.
1:11:42 The Standard Model had known forces, it had known particles, it had all that.
1:11:47 The, the Higgs boson, the one thing that is true is it
1:11:51 was the last unvalidated piece of the Standard Model.
1:11:55 The Standard Model does not answer all questions,
1:11:58 which is why we have unanswered questions in physics,
1:12:02 but it was a punctuation point,
1:12:04 end of about 50 years of discovery and searching,
1:12:07 where we finally were able to say the Standard Model,
1:12:11 while, while incomplete, it's mostly right as far as it goes.
1:12:17 Quick 10-second thank you to our sponsors.
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1:12:24 And now, dear friends, back to my conversation with Don Lincoln.
1:12:31 We did a whirlwind tour of the history of physics and took
1:12:37 a little tangent on this incredible discovery of the Higgs boson.
1:12:42 But we didn't go all the way yet.
1:12:44 There's this dream of the grand unified theory, the GUT,
1:12:49 that is a step towards the TOE, theory of everything.
1:12:52 So can we talk about the GUT first?
1:12:54 So what, what's, what's entailed in the GUT?
1:12:58 So the GUT is short for grand unified theory.
1:13:01 We talked about that there were four known subatomic forces,
1:13:05 the electromagnetic force, gravity, the strong force, and the weak force.
1:13:10 And electroweak symmetry unification merged the weak
1:13:14 force and electromagnetism into the electroweak force.
1:13:17 So what GUT hopes to do is to merge the electroweak
1:13:22 force and the strong force into one grand unified force.
1:13:26 Now, that leaves gravity outside because
1:13:29 gravity is seemingly fundamentally significantly different.
1:13:32 Then subsequently, it is hoped that a higher energy,
1:13:35 we will be able to blend the theory
1:13:38 of everything together with all of the known subatomic forces,
1:13:41 the strong, weak, and electromagnetic forces, and then gravity.
1:13:45 But so, as you say, GUT is sort of a, a, a way station along the way.
1:13:50 That's the goal, and at this point,
1:13:53 I would have to say that I do not see a fast progress in the immediate future.
1:14:00 I think we're a ways away from that at this point.
1:14:03 You mean on the gravity front?
1:14:04 Maybe we'll come up with something really cool.
1:14:06 We certainly had some ideas back in the early '80s that we tested,
1:14:10 and they didn't pan out.
1:14:12 Uh, speaking of which, string theory is the thing you're referring to.
1:14:16 Uh, so string theory posits that particles are tiny vibrating strings,
1:14:22 and by tiny we mean extremely tiny at the scale of a Planck length.
1:14:27 Then there's other leading candidates like loop quantum gravity.
1:14:32 Maybe there's some alternate theories in the works.
1:14:35 So can you link on that a little bit more?
1:14:40 Do you think a theory of everything exists?
1:14:42 So I hold personally that there are rules that govern matter and energy,
1:14:47 space, time, and they probably are rules that I don't know.
1:14:50 There are probably phenomena I'm not aware of.
1:14:53 But I do believe that something, there are, is a rule that governs reality.
1:15:00 And so in that sense, once we understand the rules that govern reality,
1:15:05 the fundamental rules, that would be a theory of everything.
1:15:08 You know, there are things that are unknowable,
1:15:10 like for instance, inside black holes, we don't know what's inside there,
1:15:13 but that doesn't mean that there's not something inside there.
1:15:16 So there's a distinction between what we can know and truth.
1:15:20 So I do believe that there are the rules,
1:15:25 and I do believe that with sufficient time,
1:15:28 technology, effort, we will be able to figure this all out.
1:15:31 Now, this isn't a thing in my lifetime.
1:15:34 It's not a thing in my grandchildren's
1:15:36 lifetime or even their grandchildren's lifetime.
1:15:38 Whoa, whoa, whoa.
1:15:39 That's a pretty strong statement, right?
1:15:40 That's a pretty strong statement saying we're,
1:15:44 we're fifty to a hundred years out from finding a theory of everything.
1:15:49 It took two hundred years to go
1:15:51 from unifying gravity to unifying electromagnetism.
1:15:53 It took a hundred years to go
1:15:55 from unifying electromagnetism to unifying the electroweak force.
1:15:59 Now, you could say, well, gee,
1:16:01 that's went from two hundred to a hundred, so it's getting faster.
1:16:04 But it's also getting harder because the unification
1:16:07 scale is of order ten to the fifteen, which we can do the math.
1:16:14 That's a quadrillion times higher than
1:16:16 the highest energy accelerator we can build today.
1:16:19 And it was one thing to, you know, we are reaching diminishing returns.
1:16:24 We get something like a factor of seven
1:16:27 increase in particle accelerator energy every twenty years.
1:16:31 And so we have to get to a quadrillion times.
1:16:36 Now, you know, if you really did believe, A factor of seven every twenty years,
1:16:42 then that's— we're talking like five hundred years.
1:16:44 But you know, this is like Moore's Law, that it doesn't continue forever.
1:16:48 We're not going to every seven year— I mean,
1:16:50 every twenty years get another factor of seven.
1:16:52 So yes, I think it's a very long time.
1:16:54 That's my prediction.
1:16:55 You know, some people are far more optimistic, and we can talk about that.
1:17:01 We should also, I should mention that I
1:17:03 guess your intuition behind that is not just
1:17:07 the part where you come up with a theory
1:17:09 that's beautiful and seems to be internally consistent,
1:17:12 but you have to have a theory that's making falsifiable, testable predictions.
1:17:19 Correct.
1:17:20 And you have to have a feasible engineering construction,
1:17:26 a methodology for creating an experiment that tests that prediction.
1:17:30 So I think a lot of your, this is fifty, a hundred, two hundred years from now,
1:17:36 intuition is maybe about the second part of that, which is like,
1:17:39 you need to have an experiment.
1:17:42 Yes.
1:17:42 Yes.
1:17:42 But you know, let's say, I mean, you alluded to super strings.
1:17:47 I haven't answered that question.
1:17:48 I'll table that for a moment.
1:17:50 Super strings is a fascinating idea.
1:17:52 I don't believe it but I love it.
1:17:55 I hope it's true.
1:17:56 And there's a real, you know, aphorism,
1:17:58 and it says you should absolutely never believe what you think.
1:18:01 So even if you think super strings is true,
1:18:04 you shouldn't believe it because it hasn't been tested.
1:18:06 Now, let's say super string is correct.
1:18:11 I mean, hypothesis, it's correct, hundred percent correct.
1:18:13 I don't know it's correct, so I don't care.
1:18:16 I mean, you know, it could be correct, but I don't,
1:18:20 you know, until it's validated, it's just a wild-ass guess, you know?
1:18:23 So I, we have to have a way of validating it.
1:18:27 So yes, the empirical side of it is important.
1:18:31 I mean, you could wake up tomorrow
1:18:33 and have the theory that is the perfect theory,
1:18:35 but if I can't prove it, I don't care.
1:18:39 If we were to think,
1:18:40 this is going back to The Great Courses on the evidence for modern physics-...
1:18:45 we're talking about energy levels and tiny particles to the degree where
1:18:52 the kind of prediction we would be making is not accelerator-type predictions.
1:18:57 So it's probably going to be impossible to build
1:19:02 an accelerator that detects something like a string.
1:19:05 So you have to make predictions about macro scale behaviors.
1:19:13 That's another alternative.
1:19:15 It's a different kind of prediction.
1:19:18 Do we even have intuitions about what kind of predictions they would be?
1:19:21 So one, one of course,
1:19:23 one of the lines of intuitions has to do with black holes or in the singularity.
1:19:27 The physics of black holes combine certain
1:19:30 elements of general relativity and quantum mechanics.
1:19:33 So there-...
1:19:35 you could see some kind of predictions you could make,
1:19:38 But you can't really mess with a black hole.
1:19:40 It's not like you can create a black hole in the lab.
1:19:43 And the energies that we're talking about,
1:19:45 the sizes we're talking about are inside a black hole,
1:19:48 which you can intrinsically never see.
1:19:51 So, you know, you can only see the outside of a black hole,
1:19:53 not the inside of a black hole.
1:19:55 So what you said, you did say something that was
1:19:58 incredibly important and incredibly correct and probably won't happen,
1:20:01 but that's still good, okay?
1:20:03 So we have two choices.
1:20:05 When you talk about superstrings,
1:20:07 either superstrings are correct and they're making
1:20:10 predictions up at the Planck energy scale, at which point we have to somehow
1:20:14 build facilities that can generate Planck energies.
1:20:17 That's possibility one.
1:20:19 Possibility two is this theory,
1:20:22 which is currently only applicable at Planck energy scales,
1:20:27 someone figures out a way to take those equations
1:20:33 and solve them in a way that, say, predicts the mass of the electron.
1:20:37 Mm-hmm.
1:20:38 Right?
1:20:38 And that is a tricky business.
1:20:41 I am not a string theorist, so I can't tell you that that's likely,
1:20:45 but I can tell you that they've been working
1:20:47 on it since the '80s and they haven't gotten very far.
1:20:51 Furthermore, if I I think it's fair to characterize
1:20:55 that string theory is still a vague idea, and that's unfair,
1:20:59 but let me tell you why I say
1:21:02 that because what they have are approximate solutions to approximate
1:21:07 equations and that is already saying that we're
1:21:13 a ways away from really getting a handle on that.
1:21:17 So yes, there could be some bright young lad or lass out there,
1:21:21 someone listening to this podcast right now who figures
1:21:24 out a way to take superstring theory and solve them
1:21:27 in tractable ways that makes predictions from the scale
1:21:30 at which they currently apply down to measurable scale today.
1:21:34 And if that happens, well, then I might retract my question or my concept.
1:21:39 There's a reason why I think that probably isn't true.
1:21:44 That's probably not valid.
1:21:46 So let me— I, I love this, all right?
1:21:49 So let's back up.
1:21:50 I'm going to pitch.
1:21:51 I wrote this book for Oxford, Einstein's Unfinished Dream,
1:21:54 and Einstein's unfinished dream was to come up with a theory of everything.
1:21:57 It was unfinished because, well, it's unfinished.
1:22:00 And so the, the second part,
1:22:02 the tagline of that book is Practical Progress Towards a Theory of Everything,
1:22:06 with the emphasis on practical because when
1:22:09 you read books about theories of everything,
1:22:12 when you see podcasts, when you listen to YouTube videos or whatever,
1:22:16 they are often written by theorists.
1:22:19 Mm.
1:22:20 And theorists are— they're big idea people.
1:22:23 They're very, very smart,
1:22:25 but there's a pragmatism that is often missing in the sense that they say,
1:22:31 "Well, superstrings, look, you know,
1:22:33 have these little vibrating things, and wouldn't it be cool?" And, you know,
1:22:36 but you gotta get to the do you know it?
1:22:39 So let's pretend superstring theory or something like it is correct.
1:22:43 The energy scale at which that should occur is of order,
1:22:50 um, 10 to the 15 times higher, 10 to the 19 GeV.
1:22:54 We can currently do things at 10 to the fourth GeV, give or take.
1:22:58 So that is 10 to the 15.
1:23:00 That's a quadrillion times higher energy.
1:23:03 So what we are doing now is we are
1:23:05 looking at the world with our very best measurements,
1:23:08 and we are trying to project out a quadrillion
1:23:11 times higher and figure out a theory that explains everything.
1:23:17 Now, I have this— I have a couple of analogies, but I like this.
1:23:20 Suppose that you were some, you know,
1:23:23 Joe Australopithecus 2 million years ago or something in Africa,
1:23:27 wandering around somewhere in Kenya.
1:23:29 Mm-hmm.
1:23:29 Right?
1:23:30 You're about a meter in size, so you can walk a meter.
1:23:34 Meter scale is like your scale.
1:23:35 Mm-hmm.
1:23:36 You can walk 10 meters in every direction.
1:23:38 That's 30 feet, no problem.
1:23:39 You can work 100 meters, 300 feet.
1:23:41 You can work 1,000 meters.
1:23:42 That's half a mile.
1:23:44 You can work 10,000 meters.
1:23:46 That's 60 miles.
1:23:48 100,000 meters is 10 to the fifth and that's unlikely.
1:23:52 But the distance that we need to go from what we can see to the Planck scale,
1:23:57 it's not 10 to the fifth, it's 10 to the 15th.
1:24:00 So that means, in my analogy, think about this guy who's walking around Africa.
1:24:05 Now, if he walks, you know, 100 feet or something,
1:24:08 it looks a lot like what it is now.
1:24:10 He can make a prediction about what he sees,
1:24:12 and when he goes to that new place, it's probably going to be okay.
1:24:15 But if he starts walking 500 miles east, well, he,
1:24:20 walking around the center of Africa,
1:24:22 has no concept of, for instance, the Indian Ocean.
1:24:25 He would never predict sperm whales or kraken.
1:24:28 He would never predict what it's like the bottom of the ocean is going north.
1:24:33 He's in Africa.
1:24:34 He would never, ever have a clue about the Alps or Antarctica.
1:24:39 Going even smaller distances, going a mile up,
1:24:43 things wouldn't be very different.
1:24:44 But if he goes 10 miles up, he wouldn't breathe and he'd freeze.
1:24:47 If he goes 100 miles up, he would die.
1:24:49 If he goes two miles down, he would roast.
1:24:53 The point being is we are like that Australopithecus.
1:24:59 We have a realm that we can study, and we can even predict to some validity
1:25:05 what would happen if we go some distance away.
1:25:08 But the farther away we go, the less and less our local prediction really
1:25:15 represents the reality of those more distant times.
1:25:18 And so basically, his theory about the world would be totally bogus.
1:25:24 So even if he had the best theory,
1:25:26 his theory would not have anticipated the Alps.
1:25:29 It would not have anticipated penguins.
1:25:33 Right?
1:25:33 Flamingos, not there.
1:25:35 You know?
1:25:36 And that is just the case.
1:25:38 So now that's what we're doing.
1:25:40 We are taking something and we have reason to understand what
1:25:44 we know and we can predict a factor of 10 or 100.
1:25:47 But I think it is the absolute, the pinnacle of arrogance to think that what
1:25:53 we can do given the understanding that we have
1:25:56 from what we've measured now and predict it out
1:25:59 a quadrillion times higher than we can see now.
1:26:02 So my opinion, and this is partly because I'm an experimentalist,
1:26:07 the correct way to make progress,
1:26:09 practical progress towards a theory of everything is to look around
1:26:12 at the things that we don't have answers to right now.
1:26:17 For instance, are there some things smaller than quarks?
1:26:20 I don't know.
1:26:21 Is dark matter real?
1:26:23 I don't know.
1:26:24 If it's real, what is it?
1:26:27 I don't know.
1:26:28 Is dark energy real?
1:26:29 Yes, probably, but I don't know.
1:26:31 What is the nature of space and time?
1:26:34 I don't know.
1:26:35 But these are questions we can explore, and I would expect,
1:26:38 and this is my prediction, that, all right,
1:26:40 we're gonna figure things out at a factor of 10
1:26:43 or 100 times better than we can do now,
1:26:44 and we might be able to do that in my kid's lifetime or something like that.
1:26:48 But in order for us to predict a quadrillion times higher,
1:26:53 I'm pretty sure superstring theory is wrong.
1:26:55 Not because people aren't smart, but because something new is going to happen.
1:27:00 I mean, if you were talking about chemistry,
1:27:02 you would have never predicted nuclear physics,
1:27:05 and that's a small increase in energy, right?
1:27:08 The idea that there's something in the nucleus
1:27:10 of atoms that causes the sun to burn,
1:27:12 there's a reason why people didn't believe,
1:27:15 you know, they calculated how old the sun should be,
1:27:18 and it should only be 10 million years old because otherwise it would burn out.
1:27:22 Well, that's clearly wrong, and it's wrong because of nuclear physics.
1:27:25 That is why I feel fairly confident to say, while someone could think, well,
1:27:32 superstring might be right or something,
1:27:33 and maybe it's right, and I hope it's right.
1:27:35 It would be awesome if it's right.
1:27:37 But what are the odds when you're making something with that tiny lever arm,
1:27:42 predicting it out a quadrillion away and say, "Oh,
1:27:45 yeah, we got it right." What are the odds?
1:27:47 And my answer is, you gotta be kidding me.
1:27:50 Now, I could be wrong, and I admit that I could be wrong,
1:27:54 but that's why I think the real issue is not the brilliance of humanity.
1:27:58 It's the stuff we haven't found.
1:28:01 We don't know— I mean, the simple one, I,
1:28:04 and I'm saying it simple, and it's not, but what is dark matter?
1:28:09 We don't have a bleeping clue.
1:28:10 Not a clue.
1:28:11 We know a lot of what it isn't, but we don't know what it is.
1:28:16 And so, you know, talk about superstrings.
1:28:17 All right, well, maybe dark matter fits in superstrings,
1:28:20 or maybe dark matter is governed by a physics
1:28:23 that is completely diametrically opposed to the superstring concept.
1:28:27 And allow me a bit of a thought experiment here, a brief thought.
1:28:31 My intuition says that when you propose a theory of everything,
1:28:35 the kind of prediction you want to make involves
1:28:39 a kind of leap of conceptual understanding that Einstein did.
1:28:43 So, for example, you want to come up with something
1:28:47 like spacetime and then gravity—- Sure- ...bends space, spacetime.
1:28:53 So it's not merely that you have this beautiful mathematical framework,
1:28:57 but that framework allows you to rethink how you see
1:29:04 reality enough to make a prediction that's about the macro world.
1:29:11 I mean, to come up with something like spacetime, you know,
1:29:14 there's one idea, for instance, to say that space and time aren't real.
1:29:18 They, they emerge from entropy.
1:29:21 Yeah, that's a way of, a new way of thinking,
1:29:23 and maybe there's some validity, and I want people to think about it.
1:29:26 But in the end, it's just an idea, and that's the real key thing.
1:29:31 And, and as you say, it has to tie to a macro world.
1:29:35 You have to validate.
1:29:36 If you don't validate, it's a crazy idea.
1:29:39 Theorists are incredibly creative, smart,
1:29:43 wonderfully interesting people, but I don't care.
1:29:47 I want a measurement that validates the idea because there are so many— I mean,
1:29:53 if you read the, the journals,
1:29:54 there are so many theoretical papers with all these nifty ideas that die.
1:29:59 You know one that was recently I liked and, and might
1:30:02 still be true was that dark matter that, you know,
1:30:07 our simple model of dark matter is
1:30:09 that there's a subatomic particle out there that's heavy,
1:30:12 and it's floating around, and it's causing gravity.
1:30:14 But someone said, "Well, you know,
1:30:15 maybe there's complex dark matter," which means there's a whole dark sector,
1:30:18 so there are dark atoms, and they interact with one another.
1:30:21 And that is a nifty idea, and I love it.
1:30:25 And that was all the rage for a while,
1:30:27 and we looked at it, and it may still be true,
1:30:30 but the simple ideas have been mostly invalidated
1:30:33 because we've tested it and it doesn't work.
1:30:35 Same thing, there was a talk about large extra dimensions.
1:30:38 The reason that gravity is so much weaker than the other forces was,
1:30:42 well, maybe gravity can sneak into more dimensions than the other forces.
1:30:47 It leaks into those dimensions.
1:30:49 That was a cool idea.
1:30:50 I mean but that's the point is you have these lovely,
1:30:52 cool, interesting ideas that constantly die.
1:30:57 And so, you know, I would love for a new nifty idea to be the idea,
1:31:03 but I don't know how to pick it out of the hurricane of wrong ideas.
1:31:09 I mean, that's the real beauty of science.
1:31:11 It really is— I mean, the theories kind of get some of the glory sometimes,
1:31:16 but the real beauty emerges from the experiment
1:31:19 and the demonstration that the theory is correct.
1:31:22 And there are two directions.
1:31:23 You're talking a top- down.
1:31:24 Someone comes up with this big idea that's testable.
1:31:26 But you also have the other way that science advances,
1:31:30 and it's not with a theory that is then tested.
1:31:34 It's with the, "Huh, that's weird." For instance,
1:31:39 either in, in the 1930s with Fritz Zwicky or in the 1970s with Vera Rubin,
1:31:45 she did a simple thing.
1:31:46 She said, "How fast are galaxies rotating?"
1:31:48 'Cause it's an easy thing to calculate.
1:31:50 You could literally calculate that with high school physics.
1:31:53 And you get an answer, and then you measure it, and it's wrong.
1:31:57 And so I'll— That's the, wow, huh, I don't know what that is.
1:32:01 And that led to the hypothesis of dark matter.
1:32:03 Now, dark matter is not a theory of everything, but it's a clue.
1:32:07 It's a powerful clue.
1:32:08 We should pull, tug at that thread.
1:32:10 Maybe our entire theoretical edifice unravels, or maybe it doesn't.
1:32:14 Maybe it's just a snag, and we can fix what we have now.
1:32:17 I'm not sure.
1:32:18 So that's another option is to simply look at many measurements that are very
1:32:24 precise and find ones where the outcome
1:32:27 and the prediction with established theory disagree,
1:32:30 and that is a clue- Before we leave the topic,
1:32:35 we gotta talk about string theory.
1:32:37 In your view, is it basically dead?
1:32:40 As I understand one of the primary flaws of string theory,
1:32:44 outside of the testable experiments that we're talking about,
1:32:49 is because it relies on these unobserved extra dimensions,
1:32:54 there was a hope that it uniquely could explain our universe,
1:32:58 but it turns out this, quote, "landscape," there's an enormous so-called
1:33:03 landscape of possibilities it leads to.
1:33:06 And so it renders the theory basically unpredictive,
1:33:09 'cause it can describe all kinds of universes-- Sure-...
1:33:14 and therefore you can just select, tune it to describe ours.
1:33:19 I agree to a degree.
1:33:21 But I bring it back to my prior objection.
1:33:26 It is absolutely true that super string theory at, in its current manifestation,
1:33:34 aside from the extra dimensions, which are some level small potatoes,
1:33:38 it allows for an extremely large number of possible universes.
1:33:46 But if we were able to take those predictions
1:33:53 and somehow connect it to a physical measurement,
1:33:57 then what we would do is we'd lop off those alternatives.
1:34:00 We'd throw them away as saying, "Well,
1:34:03 you know, those are like an equation, you know,
1:34:07 X plus five." I can put in any number I want in there, it doesn't matter.
1:34:10 But if X plus five equals nine,
1:34:12 then I've ruled out a whole bunch of— numbers except four.
1:34:16 And so this is a case of string theory does allow for many predictions,
1:34:22 but if we could rule them out by connection to a measurement,
1:34:26 then it would no longer do it.
1:34:28 We would modify string theory,
1:34:29 and we would retain the vibrating string concept, which I really, really like.
1:34:34 I mean, I really like it.
1:34:36 But until we can validate this, it's, it's, I, I, we can't.
1:34:42 So now you ask, is it dead or not?
1:34:46 In my opinion, it is very difficult to kill such a theory.
1:34:49 I mean, really, truly kill it,
1:34:50 'cause kill it means make a prediction and it fails.
1:34:54 But what can happen and what is happening is
1:34:56 people have been working on it since the '70s.
1:35:00 So we're talking of order 50 years,
1:35:02 people have been working on it, and it has not solved the problem.
1:35:07 And so I think what's happening is people are looking at that and saying,
1:35:14 "Do I wanna spend my life working in this direction with the very
1:35:18 likely possibility that 30 years from now we'll be not much
1:35:22 farther along than we are now?" It's a lot like back
1:35:25 in the 1940s when people started
1:35:27 thinking about the meaning of quantum mechanics.
1:35:31 And I wanted to do that when I was a kid in the '70s.
1:35:35 But then when I went to grad school, I realized that people, very smart people,
1:35:39 people smarter than me, had been working on that for most
1:35:42 of their lives and made no definitive progress.
1:35:44 And so you have to decide, as a scientist who wants to answer questions,
1:35:49 do I really wanna take on a question that is
1:35:52 so hard that it will not be answered in my lifetime?
1:35:54 And I think that's what's happening with a lot of superstring theories.
1:35:58 People are saying, "It's really neat.
1:35:59 It might be right, but I don't wanna devote my life to something that I
1:36:04 might not see progress forward in my lifetime."-
1:36:09 What do you think about the alternate theories?
1:36:11 Do you think there's anything interesting in those?
1:36:14 You know, many of those theories are espoused by passionate people.
1:36:18 They have fans.
1:36:20 People love them, but they don't do what science needs to do,
1:36:24 which is make predictions.
1:36:25 Now, loop quantum gravity is a little different.
1:36:28 That one is better developed, and that one is not a theory of everything,
1:36:32 so we should make that clear.
1:36:34 Loop quantum gravity is not a theory of everything.
1:36:37 It is simply a theory of quantum gravity, period.
1:36:40 It does not aspire to include all of the known forces.
1:36:44 It simply tries to take gravity, which is currently intrinsically,
1:36:50 it treats space as smooth and continuous.
1:36:53 For those of your viewers who are mathematically inclined,
1:36:57 in Einstein's theory of general relativity, gravity is infinitely divisible.
1:37:03 There is no smallest bit, and so essentially the laws of calculus apply.
1:37:11 However, it is possible that at a small enough scale,
1:37:15 space is no longer divisible in the same way that you can,
1:37:20 you know, take a cup of water out of a swimming
1:37:22 pool and then a quarter a cup and so forth.
1:37:25 But eventually, once you've taken out a single molecule of water,
1:37:28 you can no longer take out a smaller thing.
1:37:30 So loop quantum gravity attempts to quantize gravity, so that's what it does.
1:37:37 And so this is unlike string theory,
1:37:40 which attempts to bring gravity in with the other forces.
1:37:44 And in fact, the reason, the fundamental,
1:37:46 the one reason why string theory became so interesting to the theoretical
1:37:54 community is string theory was not being developed as a theory of everything.
1:38:01 It was being developed as a theory of the strong force,
1:38:05 and it was in competition with QCD,
1:38:07 which is the currently accepted theory of the strong force.
1:38:11 And it turned out the two groups,
1:38:13 the string theory groups and the QCD groups competed for a while,
1:38:18 and string theory basically failed the race,
1:38:22 and people paid attention to quantum chromodynamics, QCD.
1:38:27 But then somebody noticed in string theory that one
1:38:29 of the things it predicted was a zero mass spin-2 particle.
1:38:34 And you can prove that any zero mass spin-2 particle is the graviton.
1:38:40 And so if you see a theory that has a zero mass spin-2 particle,
1:38:46 you now have a candidate for dragging gravity in, and then, oh my gosh,
1:38:50 people got terribly excited because now this theory,
1:38:53 which was working in the direction of the other quantum forces,
1:38:56 brought in gravity, and now it was a candidate theory for everything.
1:39:01 But but that's not what loop quantum gravity is.
1:39:04 Loop quantum gravity is simply trying to understand the nature of space itself,
1:39:08 which is already a fantastic thing.
1:39:11 And, you know, I talk to Rovelli every so often.
1:39:13 I write about his theory and I point out some of the issues with the theory,
1:39:19 but I'm usually about, like,
1:39:20 two months behind as he and his colleagues are developing and so forth.
1:39:24 'Cause one of the things is originally loop quantum gravity
1:39:29 predicted that the speed of light would not be universal.
1:39:32 The speed of light would depend on the frequency of the light.
1:39:36 So high frequency would travel at one speed,
1:39:39 and low frequency would travel at a different speed,
1:39:41 and it had to do with the wavelength of light
1:39:44 basically interacting with the structure of space if, you know.
1:39:48 And so that was an issue with loop quantum gravity.
1:39:51 And so if you look at gamma ray bursters, which are, you know,
1:39:55 super explosions of astronomical events that are
1:39:57 a billion light years away or more, and they spit out light in all wavelengths,
1:40:02 and if that loop quantum gravity prediction were correct,
1:40:06 when you saw a, One of these gamma ray bursters,
1:40:10 you would see the wavelength of one light appearing on Earth
1:40:14 at a different time than another wavelength because of the different speeds,
1:40:17 and that wasn't the case.
1:40:18 They appear at the same time.
1:40:20 And so I went on to say, "Well, this pretty much killed loop quantum gravity,"
1:40:26 only to get a prickly note from Mr.
1:40:29 or Dr.
1:40:29 Rovelli saying, "You know, we've disproved that.
1:40:32 We've changed the theory.
1:40:33 That's no longer true, and now that, that prediction,
1:40:36 that old prediction of loop quantum gravity
1:40:38 is no longer valid." And so that observation
1:40:42 of the uniformity of the speed of light
1:40:47 no longer kills the new loop quantum gravity.
1:40:49 It would've killed the old one, but it didn't kill the new one.
1:40:52 By the way, that example of different speeds of light based on wavelength,
1:40:57 that's a beautiful thing that a theory— That's a testable thing.
1:41:02 It is.
1:41:03 Right?
1:41:03 So, like, those kinds of things,
1:41:05 and if it in fact did explain a phenomena of that sort,
1:41:08 that's a good sign for the theory, right?
1:41:10 If it correctly predicted.
1:41:12 There was another brilliant observation recently.
1:41:14 Love it.
1:41:16 The observation of gravity waves.
1:41:20 And it was from two neutron stars orbiting and coalescing.
1:41:25 And so they made gravitational waves, fantastic,
1:41:29 but they also, because they were not black holes,
1:41:32 they were neutron stars, they hit and exploded,
1:41:35 gave off a tremendous bright flash of light.
1:41:39 And so astronomers saw the flash.
1:41:42 Gravitational wave astronomers saw the ripples of space-time.
1:41:47 It was 140 million light years away,
1:41:50 which means light would've traveled 140 million years to get here,
1:41:54 and the two incidents, light and gravity,
1:41:57 both arrived within 1.7 seconds of one another.
1:42:01 And that tells you that gravity travels at the speed of light.
1:42:05 That was a brilliant, fantastic measurement.
1:42:07 Now, we thought gravity traveled at the speed of light,
1:42:10 but now we have a measurement, we proved it, and damn it, I am impressed.
1:42:15 Our universe is so fascinating.
1:42:17 Speaking of which, since we brought up antimatter, we'll have to talk about it.
1:42:22 You've talked about it in several of your lectures from different angles,
1:42:26 including the dark energy crisis and including empty space and vacuum and so on.
1:42:32 So let's look at the empty space angle.
1:42:35 So you know, it turns out that empty space is not empty.
1:42:40 It's true.
1:42:40 Which is kind of bizarre.
1:42:42 Can you speak about what do we know about what makes up empty space?
1:42:47 That's a hard question because we don't know what space is.
1:42:51 But let's start out—...
1:42:52 let's just start out with something simple.
1:42:55 We'll assume that space is not quantized, okay?
1:43:00 Now, it probably is, I don't know, but, you know, we gotta start with somewhere.
1:43:03 So let's start out with sort of the space of calculus,
1:43:06 the space that you can divide forever.
1:43:08 The modern version of quantum mechanics is called quantum field theory,
1:43:14 and it postulates that, A, space exists.
1:43:18 Then it postulates that within space there
1:43:22 exist fields for every known subatomic particle.
1:43:26 So there is a photon field, there's an electron field,
1:43:29 there's an up quark field, there's a down quark field.
1:43:32 There's all the fields.
1:43:35 And those fields can vibrate,
1:43:38 and when they vibrate, those are the subatomic particles.
1:43:42 So an electron field vibrating in a characteristic way is an electron.
1:43:48 Now, it's also possible for the electron
1:43:51 field to vibrate not in the characteristic way,
1:43:54 but in a way that's still vibrating, but it's not an exact electron.
1:43:59 So this is what we call virtual particles.
1:44:03 Now, virtual particles, there are lots of ways to talk about them,
1:44:07 and the way I'm talking about now is the most correct
1:44:11 and the most sophisticated way that we can talk about them.
1:44:17 I will talk about them briefly in a simpler way to help.
1:44:21 But right now, that's the important thing, is that there are these fields.
1:44:25 Specific vibrations are the known particles.
1:44:28 Vibrations that are a little different are, these virtual particles.
1:44:33 They're particles that don't truly exist.
1:44:36 And so that is what we think space is.
1:44:41 There is all of these these, these fields.
1:44:45 They're all vibrating a little.
1:44:47 If you insert the right amount of energy, you can get it to vibrate
1:44:51 in the characteristic way and make that subatomic particle.
1:44:54 But even when you don't—there is the particles,
1:44:58 I mean the fields are there and they are vibrating.
1:45:01 So those vibrating vibrations are what we called virtual particles.
1:45:04 Now, your viewers may have heard of virtual particles in other ways,
1:45:08 in which case it says that space is just empty,
1:45:11 and what happens is matter and antimatter
1:45:14 particles briefly appear for a very short period
1:45:17 of time before they coalesce back again
1:45:20 and disappear and, re-emerge back into the field.
1:45:24 And so that— these are both correct.
1:45:27 So what happens is, is that's what quantum field theory says,
1:45:30 is it says that these ripples are
1:45:32 appearing or these particles are appearing and disappearing.
1:45:35 And so that just sounds nuts.
1:45:39 You look at empty space, you're not seeing anything happening.
1:45:42 But they're happening fast enough that they can't be seen,
1:45:45 but they do have consequences.
1:45:47 And there are two experimental measurements that I can think
1:45:52 of that validate that this thing that sounds crazy is really happening,
1:45:56 and one is called the Casimir effect.
1:45:59 So in the Casimir effect, you take two metal plates,
1:46:04 the parallel plates, and you put them near one another, very, very close.
1:46:08 Now, if this is the case,
1:46:11 if these virtual particles exist, then in between the plates,
1:46:15 these particles appearing and disappearing, and outside the plates,
1:46:19 the particles are appearing and disappearing.
1:46:21 However, because these plates are close to one another,
1:46:26 this puts a constraint on the wavelength of the particles
1:46:29 that can occur between the two plates because they,
1:46:33 the particles cannot extend outside the plates.
1:46:37 So the short wavelength particles can exist inside the— between the plates,
1:46:42 but the longer ones cannot.
1:46:44 However, outside the plates, there is no constraint,
1:46:47 so short wavelength and long wavelength particles can exist there.
1:46:52 And the net effect is there are
1:46:54 more virtual particles outside and less particles inside,
1:46:57 and therefore you have a net pressure
1:47:00 which would then push those two plates together.
1:47:03 That is a prediction we've been talking about, and guess what?
1:47:06 It happens.
1:47:07 Those plates push together.
1:47:09 So that is a validation for the existence of these particles in empty space.
1:47:14 Now, there is another measurement,
1:47:16 and this changes the magnetic properties of particles like the electron,
1:47:20 the muon and, and so forth.
1:47:23 And so this was discovered in 1948.
1:47:27 So if you take old school standard quantum
1:47:31 mechanics you know the spin of an electron,
1:47:34 you know its charge, you can calculate its magnetic moment,
1:47:37 and it comes out to a number.
1:47:39 If you do the measurement,
1:47:42 what you find is the measurement disagrees with the quantum mechanics,
1:47:47 the nineteen thirties quantum mechanical prediction by point one percent,
1:47:51 and that was measured in nineteen forty-eight.
1:47:54 And people went, "Huh".
1:47:56 So this happened at Shelter Island Conference in New York.
1:48:01 And on the way home, someone who saw the, this measurement thought about it,
1:48:07 and they invented what we now call quantum electrodynamics.
1:48:11 So old quantum mechanics quantizes matter.
1:48:14 The second quantization quantizes both matter and the fields,
1:48:19 in this case, quantized the electric fields.
1:48:24 And so in this quantized field, it predicts that surrounding a bare,
1:48:31 say, electron, which is spinning and has a, has a charge,
1:48:36 there is this, this bath of particles,
1:48:39 virtual particles appearing and disappearing all around it.
1:48:42 And the ensemble of all of those particles appearing and disappearing will
1:48:47 alter the magnetic properties that you can measure for the subatomic particle,
1:48:52 and it changes it by point one percent.
1:48:55 And we have measured this, and we have not measured this imprecisely.
1:48:59 We have measured the magnetic properties of both
1:49:04 the electron and the muon to twelve, count them, twelve significant figures.
1:49:11 And the theory and the data agree number for number for ten places.
1:49:16 And then once you get out to the very end where
1:49:20 both the theory and the data have some imprecision, they then disagree.
1:49:24 And so maybe there's some interesting stuff going on there.
1:49:28 But ten figures, it's just staggering.
1:49:32 So virtual particles refer to matter and antimatter particles coming to life.
1:49:37 Correct.
1:49:38 Can we just talk about the antimatter part of that?
1:49:41 So starting with Paul Dirac,
1:49:42 one of the most legendary examples of math leading to physics.
1:49:47 So the math suggesting that something like antimatter should exist,
1:49:53 and Paul Dirac taking it seriously
1:49:55 and then eventually showing that it does exist.
1:49:58 So what evidence do we have for antimatter?
1:50:02 So antimatter was predicted in nineteen twenty-eight.
1:50:05 Paul Dirac was trying to merge quantum mechanics
1:50:08 and relativity because the original Schrödinger equation did not,
1:50:11 was not relativistic.
1:50:12 And in doing so, he basically, the equations were complex,
1:50:16 but in the end it came down to something like equation squared equals one.
1:50:21 You take the square root of both sides,
1:50:23 you get equation equals plus one or minus one.
1:50:26 Plus one was the electron, minus one was something.
1:50:29 He didn't know what it was.
1:50:31 There was some conversation for a while,
1:50:33 thought maybe it might be the proton, but that didn't seem to work out.
1:50:36 And so he insisted that his equations
1:50:38 were right and that there was an antimatter, he didn't call it an antimatter,
1:50:44 but a positively charged sibling of the electron,
1:50:48 what we now call the positron, the antimatter electron.
1:50:51 So it was predicted.
1:50:52 It was discovered in nineteen thirty-two
1:50:55 by Carl Anderson and his student Seth Neddermeyer.
1:50:59 They saw an antimatter electron.
1:51:02 And that was pretty cool.
1:51:05 So that right there, they knew it was real.
1:51:08 Antimatter was predicted, it was observed, that's that.
1:51:11 In nineteen fifty- six, the antimatter proton was created,
1:51:14 and that required a large particle accelerator,
1:51:18 high enough energy to make it, and that was done at Berkeley.
1:51:22 And a year later, the antimatter neutron was discovered.
1:51:25 So at this point, and now jumping ahead to now, we can make,
1:51:31 using energy by smashing particles together,
1:51:35 we can make antimatter protons, we can make antimatter electrons.
1:51:39 We have gone so far to make antimatter helium nuclei.
1:51:44 So we have made two antiprotons and two antineutrons,
1:51:50 combined them together to make an antimatter helium nuclei.
1:51:54 This has been done, been observed, no question.
1:51:57 At CERN, they have gone so far as to make antimatter hydrogen.
1:52:01 They take a beam off one of their lower energy accelerators.
1:52:06 They make antimatter protons.
1:52:09 They collect them, they slow them down, they cool them to almost absolute zero.
1:52:13 They take Sodium-22, which makes antimatter electrons.
1:52:18 They slow them down, they bring them together, they coalesce them,
1:52:22 and they make literal antimatter hydrogen atoms
1:52:26 with an antimatter proton surrounded by an antimatter electron.
1:52:31 And they have done incredible measurements.
1:52:34 They have agitated the atoms and caused it to emit light.
1:52:38 They have looked at the light that comes out of antimatter atoms.
1:52:42 And the question is, is does the light coming out of antimatter hydrogen
1:52:46 atoms have exactly the same spectral characteristics as ordinary hydrogen,
1:52:50 which we predict that it does?
1:52:53 And the answer is it does.
1:52:55 So the tests have been staggering.
1:52:58 We now know a great deal about antimatter hydrogen.
1:53:01 Recently, recently like 2023, I believe it was,
1:53:04 one of the experiments called ALPHA at CERN made antimatter hydrogen,
1:53:09 put it in a bottle and released it and watched which way it would go.
1:53:17 Did it fall up or did it fall down?
1:53:20 Because while it kind of makes sense maybe to think that maybe
1:53:25 antimatter falls up in the same way that we have Coulomb's law,
1:53:28 you've got electric charges, and they might attract or repel.
1:53:32 However, there was lots of ample theoretical reasons
1:53:36 to believe that antimatter also would fall down.
1:53:39 So they did this fantastic measurement, and they first they put in hydrogen,
1:53:44 and they calculated that some— if they did this, something like eighty
1:53:48 percent of the hydrogen atoms would fall through the bottom of the bottle,
1:53:53 and twenty percent would go through the top just because gravity
1:53:57 is very weak and the atoms will escape wherever they do,
1:54:01 but there will be a bias pulling hydrogen atoms down.
1:54:03 So they did exactly the same thing, and what did they find?
1:54:08 They find that antimatter falls down.
1:54:11 Now, they do not have a good enough measurement at this time to say
1:54:16 that the gravity that antimatter experiences
1:54:19 is one hundred percent that of matter.
1:54:23 What they have measured is that antimatter fell down
1:54:28 with a seventy-five percent the strength of regular matter,
1:54:33 but there were big uncertainties.
1:54:35 There was plus or minus .13 three due to the experiment,
1:54:40 which was good but imperfect,
1:54:42 and plus or minus .16 due to their theoretical model.
1:54:47 So it's like point seven five plus or minus something like point two nine.
1:54:53 And that means there's a good chance it's between point five and one-...
1:54:57 which means it's consistent with one.
1:55:00 So they are improving their measurements.
1:55:03 Well, if I can, I would love to take a bit of a tangent
1:55:06 on that topic 'cause I went down a rabbit
1:55:08 hole watching some of your videos on antimatter.
1:55:11 And I mean, Fermilab was the hub
1:55:15 for the production of antimatter for quite a while.
1:55:17 It was.
1:55:18 I saw that NASA said that the global estimate for the current
1:55:22 rate of production of antimatter is one nanogram per year.
1:55:27 Can you speak to how hard was it to make antimatter?
1:55:30 And also, you did mention in a video that, you know,
1:55:33 if matter and antimatter meet, they produce a lot of energy.
1:55:38 I think twenty grams of antimatter is equivalent
1:55:42 to a one-megaton nuclear warhead in terms of explosive energy.
1:55:47 Yeah, so all of those questions together.
1:55:49 So how hard is it to produce antimatter?
1:55:52 It's freaking hard.
1:55:53 Okay.
1:55:53 All right.
1:55:54 So here's the deal.
1:55:56 So at the time until two thousand and eleven,
1:55:59 Fermilab was the most powerful antiproton production facility on the planet.
1:56:05 Every two point three seconds,
1:56:08 we would smash ten to the thirteen protons into a target,
1:56:13 and we would get out ten to the eighth antiprotons.
1:56:17 So basically, in order to get a single antiproton,
1:56:20 we needed to smash a hundred thousand protons into material.
1:56:26 So every two point three seconds,
1:56:28 we would get of order ten to the eighth antiprotons.
1:56:32 And what we would do is we would collect
1:56:35 them over the course of twelve hours or so, and we would get, in the end,
1:56:40 we would have to collect them and cool them down and so forth,
1:56:44 of order ten to the twelfth antiprotons every twelve to twenty-four hours.
1:56:48 So ten to the twelfth sounds like a lot.
1:56:51 It really does.
1:56:52 That is a trillion.
1:56:54 But you need to remember that a gram
1:56:57 of antimatter is ten to the twenty-three antiprotons.
1:57:00 So that means over the course of a day,
1:57:04 we were able to create something like one hundred billionth of a gram.
1:57:11 And so if we did that for a year, then that would be about a nanogram.
1:57:17 So about a nanogram a year, give or take.
1:57:20 That's a reasonable estimate.
1:57:22 So a nanogram, one billionth of a gram,
1:57:26 so that means at that rate, with that facility,
1:57:29 it would take a billion years running with very
1:57:32 little downtime to make a single gram of antimatter.
1:57:36 If you combine one gram of antimatter and one gram of matter together,
1:57:43 the energy release is equivalent
1:57:45 to the combined Hiroshima and Nagasaki explosions.
1:57:48 So that tells you if you wanted a megaton, you need about 25 times more.
1:57:55 So you would have to run for 25
1:57:57 billion years to get a megaton of explosive power.
1:58:01 Let me lay it all out, because I think it's pretty interesting actually.
1:58:04 This is a NASA estimate of how much it costs to produce antimatter.
1:58:09 So looking at all the costs of the accelerator, all,
1:58:14 everything combined together, to do enough for a one-megaton antimatter bomb,
1:58:19 if such a thing would be even possible,
1:58:21 on the order of 25 grams, like we mentioned-...
1:58:24 will cost about, based on the NASA estimate, uh, $1.5 quadrillion.
1:58:29 By the way NASA wasn't talking about a bomb.
1:58:33 It's just me adding- NASA was talking about the estimate,
1:58:36 the cost of 62 to 63 trillion dollars per gram of antihydrogen,
1:58:43 actually is what they're referring to.
1:58:46 So compared— I was looking at estimates, the current best estimate is how much
1:58:50 it takes to produce a one-megaton nuclear warhead.
1:58:55 Everything combined is about 10 to 50 million dollars in the United States.
1:58:59 So you're talking about difference in terms of a weapon with equal power,
1:59:04 50 million dollars versus $1.5 quadrillion.
1:59:07 To me, what's interesting, weapons is just one indication of this.
1:59:13 One other possibility,
1:59:14 and NASA also writes about this, is the use of antimatter in propulsion systems.
1:59:20 Uh, just like you can use nuclear fission
1:59:23 and maybe even nuclear fusion down the line.
1:59:26 In propulsion systems,
1:59:29 I saw that one gram can help get us to Alpha Centauri star system
1:59:33 if we can get to 0.2 times the speed of light in 20 years.
1:59:40 Meaning it would take us 20 years to get to Alpha Centauri.
1:59:43 Is any of this a possible future,
1:59:46 the use of antimatter for generation of energy?
1:59:48 Because we should mention that it's extremely compact.
1:59:51 It has the obvious downsides that it's extremely costly to produce.
1:59:55 We don't know how to do that kind of scale.
1:59:58 The upside is it's compact.
2:00:01 It's very powerful.
2:00:02 So the short answer is it is not a physics problem, it's an engineering problem.
2:00:06 So I have people for that.
2:00:09 Well, yeah.
2:00:10 But no, no.
2:00:12 The truth is that antimatter, if you are able to assemble it and store it,
2:00:19 sure, it would be able to take that antimatter, heat up matter,
2:00:23 and shoot it out the back of a rocket, and it would, you know,
2:00:28 do what rockets do, and it would make us go quick, and that would be fine.
2:00:32 And we should mention the thing that you just mentioned is correct.
2:00:34 One of the hugest challenges is the containment-- Oh, 100%, yeah-...
2:00:39 because antimatter, when it comes in contact with matter-...
2:00:42 Is a problem.
2:00:44 Right.
2:00:44 So if you were unable to contain your trip
2:00:48 to Alpha Centauri for even a millionth of a second,
2:00:51 boom, that would not be good.
2:00:54 It reminds me of the the Star Trek where Scotty's saying,
2:00:58 "Captain, you know, the antimatter pods are about— look,
2:01:01 we're losing containment.
2:01:02 It's gonna blow." And that's exactly what would happen.
2:01:06 So the short answer is yes, antimatter as, in principle,
2:01:10 we could make and use as a, a source of energy.
2:01:16 But there are probably far less expensive sources of energy.
2:01:21 you know, it depends on what you need to do.
2:01:24 The Voyager probes are still chugging along with plutonium.
2:01:26 Now, they're running out of energy at this point, but we could,
2:01:29 you know, presumably do a somewhat better job if we needed to.
2:01:33 So I like the idea of antimatter, you know,
2:01:36 but the reality is the danger, not the obvious danger of weapons,
2:01:40 but the danger of if you wanted to be in a ship run by antimatter,
2:01:45 if it ever got loose, well, you would never know it.
2:01:50 That would be that.
2:01:51 The reason I find this kind of inspiring is antimatter is
2:01:56 in the space of physics that has a lot of mysteries.
2:02:00 There's a lot of exploration to be done.
2:02:02 And so this kind of connection to energy means that if
2:02:07 we have a bunch of breakthroughs on the antimatter side,
2:02:11 that might lead to a better propulsion system, better energy generation systems.
2:02:16 In principle.
2:02:17 There's some combination of engineering here,
2:02:19 but there's some combination of understanding the fundamental physics.
2:02:23 I mean, we know how to do this.
2:02:25 You know, we know you take energy, you make antimatter.
2:02:30 You have to contain it.
2:02:31 You have to store it.
2:02:31 You have to do all the hard things.
2:02:34 But I, I would be shocked if there was some, like, new addition to the-...
2:02:39 theory that made antimatter production easier.
2:02:42 Interesting.
2:02:42 So we know how to produce antimatter with accelerators.
2:02:46 You're saying there's not breakthroughs in physics that could
2:02:51 lead to different mechanisms for the generation of antimatter.
2:02:54 You have to concentrate energy.
2:02:56 That's it.
2:02:56 If there's another way to concentrate energy, that would work too.
2:03:00 And our best knowledge of how to concentrate energy is the accelerator.
2:03:04 And remember, we're talking concentrating it into volumes the size of a proton.
2:03:09 I mean, if you concentrate it to the size of your thumb,
2:03:12 well, then, you know, it's really the density that matters, the local density.
2:03:16 And so when you smash two protons together, all of that's occurring in a tiny,
2:03:21 tiny volume, so it's the local density of energy that matters.
2:03:24 If you had a lot of energy in a thimble or something-...
2:03:29 It's probably not dense enough.
2:03:31 You know-...
2:03:32 it really has to be in close proximity for that to happen,
2:03:35 and then when it does, it's okay.
2:03:39 So if there's another way, we know how to do it,
2:03:43 to make that density thing with accelerators.
2:03:45 If someone has a bright idea on how to make highly dense energy,
2:03:52 then yeah making antimatter is a piece of cake.
2:03:55 But that's the crux-...
2:03:57 concentrated energy.
2:03:59 Yeah, and how to do so in a cost-efficient manner, not trillions of dollars.
2:04:05 Well, yeah.
2:04:06 So one of the big mysteries with antimatter is the bigger why.
2:04:11 Where is the antimatter that should kind of be there
2:04:15 if the whole idea is that anytime you generate matter,
2:04:18 you generate the same amount of antimatter,
2:04:20 and yet when we look out into the observable universe,
2:04:23 it seems like there's not antimatter for the most part there.
2:04:27 Correct.
2:04:27 So what do we understand about this mystery?
2:04:29 What are the possible explanations as to why?
2:04:33 So there's this thing called baryogenesis and, as you say,
2:04:37 so reiterating a little bit what you just said these are both Einstein things.
2:04:43 Einstein says that when you take energy,
2:04:45 you make matter and antimatter in equal quantities,
2:04:47 and Einstein says after the Big Bang, there was a lot of energy in the universe,
2:04:52 which should have made matter and antimatter.
2:04:54 We only see matter.
2:04:55 Where'd the antimatter go?
2:04:56 And the answer is, we don't know.
2:04:59 However, there are some ideas,
2:05:01 and there's a lot of thinking on it, and in fact, for me,
2:05:05 it's doing an experiment right now with neutrinos,
2:05:08 trying to better understand what it was that made
2:05:15 the matter and antimatter not be the same.
2:05:18 Now, we do have a measurement of how much different it should be,
2:05:23 and it's kind of neat.
2:05:24 We can do this by counting the number of protons in the universe,
2:05:29 just looking at galaxies and so forth,
2:05:31 and then we can look at the cosmic microwave background,
2:05:34 which is sort of the aftermath of the Big Bang,
2:05:37 and we can count the number of photons from the cosmic microwave background.
2:05:41 And with a little bit of math,
2:05:44 what we can do is we can then say that somehow in the early universe,
2:05:52 something made a very,
2:05:54 very tiny asymmetry, so that for every billion, billion with a B,
2:06:01 antimatter particles that existed in the universe,
2:06:04 there were a billion and one matter particles.
2:06:09 The billions canceled, annihilated, destroyed each other,
2:06:12 and that extra one that's left over is us.
2:06:17 And so what physics mechanism made
2:06:21 that ever so slight asymmetry is not understood.
2:06:27 There are some thoughts.
2:06:29 One thought is that, well, it's just how it was.
2:06:34 When the universe was formed, there was an asymmetry.
2:06:36 It was not made by matter and antimatter.
2:06:41 Another possibility is there are various numbers
2:06:44 of theories all under the word baryogenesis, baryo coming from word baryon,
2:06:50 which basically means protons, and genesis meaning the creation of, and we'd say
2:06:55 that simply because the protons are the heaviest particles.
2:06:58 And so baryogenesis is just the creation of matter.
2:07:02 And there are just a number of theories
2:07:05 in quantum mechanics that say that matter and antimatter can,
2:07:09 can oscillate back and forth into one another,
2:07:12 and there is a slight, slight asymmetry in how that happens.
2:07:17 And we know that this is true to a degree.
2:07:21 We've measured it in the 1960s with a different form of matter.
2:07:26 I mean you know, not protons,
2:07:28 but a, a type of ephemeral matter that only exists in particle accelerators.
2:07:33 And so we know that there is a slight difference between matter and antimatter,
2:07:38 but it's not enough.
2:07:39 It doesn't explain that.
2:07:40 We're not sure.
2:07:41 So at Fermilab, we have this idea which kind of turns things on its head,
2:07:46 and it's not baryogenesis, it's leptogenesis.
2:07:48 So leptons are the electrons.
2:07:52 And because Fermilab is currently
2:07:55 the world's most powerful neutrino accelerator,
2:08:01 and neutrinos are leptons, there is this idea.
2:08:04 Now, leptogenesis is incredibly complicated,
2:08:06 but the idea is that it is possible.
2:08:11 We know that neutrinos actually change their identity.
2:08:14 There are three different types of neutrinos like I don't know,
2:08:18 cats and jaguars and tigers, and if you have a beam of just cats,
2:08:22 if you go along a little while,
2:08:24 you find there's cats and jaguars and then tigers,
2:08:26 and then they'll be back to all cats again.
2:08:28 And so this oscillation thing is called neutrino oscillation.
2:08:31 We've known it's been true since 1998,
2:08:33 and what we are studying is we're going to make
2:08:38 a beam of neutrinos and another beam of antimatter neutrinos,
2:08:42 and we're going to study the oscillation behavior of the two of them.
2:08:46 And it is possible, it is unlikely, but it is possible that the two
2:08:51 of them will oscillate at slightly different rates.
2:08:55 And if the neutrinos oscillate at slightly different rates,
2:09:00 then that, along with several other highly improbable things,
2:09:04 can tie together and might explain why there is more matter in the universe.
2:09:11 So if I was gonna bet the farm, I'll bet that they oscillate at the same rate,
2:09:15 but I don't know, and you don't know till you do the measurements,
2:09:18 so that's what we're doing.
2:09:19 There are some other experiments trying to measure it right now,
2:09:23 so there's a big race between the Fermilab group and another group
2:09:27 in Japan to see who gets there first and, and make this measurement,
2:09:31 and we will find out.
2:09:32 If it turns out, though, that there is a difference
2:09:35 in this oscillation rate between matter and antimatter,
2:09:37 it will be a huge clue in this very, very difficult puzzle.
2:09:43 I wish I could tell you I knew what the answer is, but literally nobody knows.
2:09:47 I mean, and that's the thing of being
2:09:50 a research scientist like me is if you're not confused-...
2:09:53 you're not doing your job.
2:09:55 So there is this desperate or not desperate,
2:09:58 exciting search for this tiny asymmetry.
2:10:01 Yes.
2:10:02 It's so, so crazy to think that everything we
2:10:05 see around us is a result of this tiny asymmetry,
2:10:10 that there was this gigantic annihilation
2:10:12 of matter and antimatter in the early-- Yes-...
2:10:15 universe, and this is just some little accident.
2:10:19 But yeah.
2:10:20 Yeah, that's crazy.
2:10:21 It's a happy accident.
2:10:23 That is—I mean, it's totally crazy.
2:10:25 This is one of the areas of physics where there's a lot of mystery.
2:10:31 Okay.
2:10:32 So can we pull at that thread a little further?
2:10:36 Let's talk about our intuition of what is dark energy
2:10:39 as it connects to empty space and everything we've been talking about.
2:10:43 What's the cleanest definition of dark energy?
2:10:47 So dark energy is either energy of space or energy in space.
2:10:54 The most common statement is the energy of space,
2:10:59 and it is essentially a repulsive form of gravity.
2:11:05 And we believe this is real,
2:11:07 and the reason we believe this is real is from observation.
2:11:11 This is one of those things where we talked
2:11:13 about a while ago where I said that, you know,
2:11:15 you can think about things up this theoretical
2:11:18 stuff and try to come up with a measurement,
2:11:20 or you can make measurements and see where they
2:11:23 disagree with predictions and lead that in a direction.
2:11:27 So back in the late 1990s,
2:11:29 some astronomers were looking at the expansion rate of the universe.
2:11:32 So the Big Bang occurred, the universe is expanding,
2:11:36 the universe is full of matter, matter attracts,
2:11:39 so the gravity due to the matter
2:11:42 of the universe should slow the expansion of the universe.
2:11:45 And the only question was how much?
2:11:48 There were three possibilities.
2:11:49 The possibilities were there was so much gravitational
2:11:52 force that the expansion of the universe would slow,
2:11:56 stop, and be pulled back together in a big crunch.
2:12:00 Number two was that the universe would continue expanding,
2:12:04 slowing down, but never really stopping.
2:12:08 And then the third possibility was the exact critical case,
2:12:11 where expansion would slow forever and approach zero only at infinity,
2:12:15 never quite stopping or reversing.
2:12:17 So those were the possibilities, door number one, two, or three.
2:12:21 So they did the measurement, and what did they found?
2:12:23 It was door number four.
2:12:25 The universe was not only expanding, but the expansion was speeding up,
2:12:29 and the only way that could happen,
2:12:31 given that gravity slows it down, is there was a repulsive force,
2:12:35 and the name we give to that repulsive force is dark energy.
2:12:40 This is something that Einstein postulated early
2:12:44 on in his development of, of general relativity, but then because at the time,
2:12:52 he knew that his theory predicted that the universe would
2:12:55 collapse but he believed the universe was eternal and not unchanging,
2:12:59 and so he needed something to counterbalance the that collapse,
2:13:04 and so he invented dark energy.
2:13:06 He didn't call it that.
2:13:08 Called it the cosmological constant.
2:13:09 But then a few years later,
2:13:12 Edwin Hubble discovered that the universe was indeed expanding,
2:13:16 and so since the universe was no longer static,
2:13:19 Einstein said, "No need for cosmological constant," took it back out.
2:13:23 Thought it was a dumb idea that he put it in, and was embarrassed.
2:13:27 However, in 1998 it became clear that his original idea that there
2:13:31 should be some sort of repulsive form of gravity was real,
2:13:35 and it's put back in the theory.
2:13:38 And so that's what it is.
2:13:39 We are pretty confident at this point
2:13:41 that the expansion of the universe is speeding up,
2:13:44 and the thing driving it is dark energy.
2:13:47 Now, what is dark energy?
2:13:49 I don't know.
2:13:50 As I said, the most common thought is that it is the energy of space itself,
2:13:58 but it is at least conceivable that there
2:14:01 is a field in space where space exists-...
2:14:05 and that field is pushing space apart.
2:14:08 That's another conceivability that I'm not sure
2:14:11 that we have the instrumentation to distinguish,
2:14:14 but that's not what normally people think.
2:14:16 People think it is literally a property of space.
2:14:20 But there is the what, what you call the worst prediction in physics,
2:14:25 which is a nice-- Oh, yeah.
2:14:27 That's another one-...
2:14:28 a nice little insight about the complicated nature of dark energy.
2:14:33 So the observations, as you describe, say that empty space has a tiny energy
2:14:38 density that, to accelerates expansion of the universe.
2:14:42 But quantum field theory's prediction for what vacuum energy
2:14:47 should be when coupled with gravity is much larger.
2:14:52 Uh, so this is what makes for the quote,
2:14:54 you have a video on this worst prediction in physics.
2:14:58 Yes.
2:14:59 Can you, can you explain this crisis?
2:15:00 Well, the— there's a measurement,
2:15:02 and you can measure how fast the universe is expanding,
2:15:04 and from that you get a measurement of dark energy.
2:15:08 However, if you then say, well,
2:15:11 suppose the dark energy is due to fields in space.
2:15:16 So that's quantum field theory.
2:15:17 Hey, I know a lot about quantum field theory.
2:15:20 And so we can take the quantum field theory,
2:15:23 and we can calculate what the density of energy is due to quantum field theory.
2:15:30 And basically what you do is you take
2:15:33 within a volume the all of the wavelengths,
2:15:37 the longer wavelengths, the shorter wavelengths,
2:15:39 the shorter wave— shorter and shorter, and you can add them all up.
2:15:42 And each wavelength adds a certain amount of energy,
2:15:46 and if you add that all up, then you get a number,
2:15:52 and that number is the rather embarrassing 10 to the 120 power times,
2:16:00 that's a one with 120 zeros after it,
2:16:04 bigger than the measurement of dark energy.
2:16:08 So you go, "Yuck, that is not fun
2:16:12 at all." And that is because the equation comes
2:16:17 to the highest energy or the smallest wavelength
2:16:21 particle that you can imagine to the fourth power,
2:16:24 since anything to the fourth power is a big deal.
2:16:28 So that's where you get that awful number.
2:16:31 Now, if it turns out that there is some new physics that's just
2:16:35 about at the energy scale we
2:16:37 can measure using our biggest particle accelerators,
2:16:40 remember I told you that that was a factor, the maximum energy scale,
2:16:45 Planck scale, is 10 to the 15 times bigger than what we can measure now.
2:16:50 So let's say that we don't have to calculate
2:16:53 up to the Planck scale because something happens,
2:16:56 something changes at the energy that we know right now.
2:17:00 Well, then that means we don't have to integrate to Planck scale,
2:17:03 we integrate to 10 to the 15th less of the Planck scale,
2:17:07 and this thing is to the fourth power,
2:17:09 so 10 to the 15th to the fourth power is 60.
2:17:12 So now, even if we say, you know, Don, he's brilliant,
2:17:16 he's gonna find something at the LHC
2:17:18 tomorrow that's gonna solve all this problem,
2:17:20 now we've solved it, it's much better.
2:17:22 It's only different by 10 to the 60th power, which is still pretty bleeding big.
2:17:28 So the short answer is there is
2:17:31 very clearly something going on, something wrong,
2:17:34 very badly wrong in the quantum field theory.
2:17:38 You know, we have to have,
2:17:40 maybe there's another field that balances out the energy, that cancels it down.
2:17:44 And even that, you know, that's not so outrageous.
2:17:48 You know, you could imagine that there's another, you know,
2:17:52 like we have matter and antimatter, they balance pretty well.
2:17:55 Okay, maybe there's something going on, you
2:17:57 could cancel that out, that'd be perfect.
2:17:59 But canceling something to zero is easy 'cause,
2:18:03 you know, plus one and minus one, zero.
2:18:05 Plus two, minus two, zero.
2:18:07 But we still have dark energy.
2:18:09 Dark energy is a little bit, so if it cancels,
2:18:11 it doesn't cancel exactly 'cause it left over that little bit of dark energy.
2:18:16 So that is its own curiosity.
2:18:19 Perfect cancellation, pretty easy.
2:18:21 Theorists do that, you know, eight times before breakfast.
2:18:25 Imperfect cancellation, much harder.
2:18:28 Just to elaborate that a little bit, what do you think solving,
2:18:30 in quotes, solving dark energy would look like?
2:18:33 Well, what you would do is you would hypothesize that there existed
2:18:36 some other field that had the reverse effect of existing quantum fields.
2:18:44 But not to zero.
2:18:45 But not to zero.
2:18:46 So if you had it to go to zero, you know sure,
2:18:49 maybe there's a field that, that exists
2:18:51 at really high energies that we haven't seen yet.
2:18:54 I don't know, but it canceled things out, and we're cool.
2:18:58 How would we then demonstrate the existence of that field?
2:19:01 Uh, well, that would depend on the, the prediction.
2:19:03 How do you even come up with a new field?
2:19:05 Like all theorists do.
2:19:06 Well, let's add something to my equation and see what happens.
2:19:10 I mean, and that's okay.
2:19:11 I mean, I—...
2:19:12 I'm being glib about that, but that is precisely what you do.
2:19:15 You say, what change?
2:19:16 We, we have this thing that works quite beautifully except it fails here.
2:19:21 What is the addition that we need to make that changes very
2:19:26 little in the realm that we measured and yet fixes this hard thing?
2:19:31 And so you literally just go, da, da, da, okay, what do I need?
2:19:35 Plus six or something.
2:19:37 And as long as it makes no changes where
2:19:41 it would hurt our measurements and fixes the big thing,
2:19:44 then that is at least a candidate theory.
2:19:46 Now, that doesn't mean it's right, but it at least gives you an understanding
2:19:53 of what the right answer should look like.
2:19:58 And so that's the first step,
2:20:00 is what should the real answer look like or what is a possible real answer?
2:20:04 And then once you kind of know that, then other people can look and say, "Well,
2:20:09 let me think about a theory that kind of has the required properties
2:20:15 to do what we need it to do." So it's a multi-step process,
2:20:18 but the first step is how do we tame this problem
2:20:23 without coming up with really terrible predictions that we've already ruled out?
2:20:31 And so that's what you do.
2:20:33 And, you know, that is literally a sensible, viable,
2:20:37 theoretical thing, you know, 'cause you have to explore cool ideas.
2:20:42 I mean, one of the reasons dark energy is super interesting is it kind of gives
2:20:47 us a mechanism by which we can talk about the deep future of the universe.
2:20:51 I mean, it's making— We have observations about the expansion of the universe,
2:20:57 but it's also giving us the mechanism of that, right?
2:21:01 Sure.
2:21:01 So we can talk about, Any weirdness,
2:21:04 any good model we have that, that captures some of the weirdness
2:21:08 of dark energy might give us insights about how this thing ends,
2:21:12 how the universe-- Sure, sure-...
2:21:14 about the deep future of the universe, right?
2:21:16 Absolutely.
2:21:16 As it stands right now, if dark energy is real,
2:21:19 and who knows, you know, if it's real exactly as we've measured it,
2:21:23 then as the universe gets bigger and bigger,
2:21:29 dark energy becomes a bigger and bigger component of the-...
2:21:33 energy balance of the universe, and it takes over,
2:21:35 and it drives the continued accelerated expansion of the universe.
2:21:40 And if dark energy gets lower, you know,
2:21:42 for some reason that we don't understand,
2:21:44 maybe it changes over time, gets smaller.
2:21:46 That could change things.
2:21:48 If it gets bigger, it could change things--
2:21:50 That is one of the big open questions,
2:21:51 whether it's constant over time or not-...
2:21:54 Right.
2:21:54 And there has been a recent measurement
2:21:55 that suggests that dark energy is getting smaller.
2:21:58 However, that is a new measurement, not confirmed, blah, blah, blah, blah, blah.
2:22:03 Nobody should believe it, but it's a hint that maybe it's changing,
2:22:07 which is kind of cool in itself because the current
2:22:11 bias until recently is that dark energy is constant.
2:22:15 Now, I wanna be super careful because it's misleading.
2:22:19 People say dark energy is constant.
2:22:22 Dark energy is a density.
2:22:25 Now, that— think about that.
2:22:26 You have a certain density, let's start with that.
2:22:29 Then the universe expands.
2:22:31 So energy is volume times density.
2:22:34 If the universe gets bigger and the density is constant,
2:22:39 that means dark energy is increasing.
2:22:42 It's not just increasing as a fraction and overwhelming ordinary matter,
2:22:46 but ordinary matter, as the universe expands,
2:22:50 its density decreases because it's constant
2:22:52 and the volume gets bigger, the density drops.
2:22:56 Dark energy, until recently, is thought to be constant density.
2:23:02 So that's what's implied when you say constant.
2:23:04 You say constant density,
2:23:05 which means it's actually increasing because space is increasing.
2:23:07 The size of space-- Right-...
2:23:09 is increasing.
2:23:09 Interesting.
2:23:10 And so that's a weirdness, and that then ties into the nature of space.
2:23:15 Why does that tie into the nature of space?
2:23:18 Well, because if dark energy is a field in space,
2:23:21 if you increase the volume, you would think the energy density would drop.
2:23:26 But if space is increasing and space is quantized, and I don't know if it is,
2:23:31 then maybe what's happening is space isn't stretching,
2:23:34 but like little space particles are appearing as the space, you know,
2:23:39 there's like bubbles of space appearing,
2:23:41 and each bubble contains a certain amount of dark energy.
2:23:45 And so therefore, that would give you a sense that dark
2:23:48 energy is a property of space rather than a field in space.
2:23:54 But that's all very hand-wavy guess-worky stuff.
2:23:58 So if you had to bet all your money, is dark energy like a real physical,
2:24:03 what does that even mean, thing that exists versus is this just
2:24:08 an, a renaming of the cosmological constant?
2:24:13 Unfortunately, I think it's both.
2:24:15 I mean, well, I mean— it is, it's describing a reality,
2:24:19 but it's also maybe telling us something about space.
2:24:24 Literally a property of space.
2:24:25 Yeah.
2:24:26 It's, I mean, that's kind of what it looks like.
2:24:28 Given that it seems to be constant density,
2:24:31 that seems to me— Now, this is not something anybody should believe.
2:24:36 Please, nobody believe this.
2:24:37 But it seems to me that this is leaning
2:24:42 towards the idea that, A, it's a property of space,
2:24:48 B, space is quantized, C, as space is expanding,
2:24:52 little quanta of space are appearing, and D,
2:24:56 each one of those quanta has a certain amount of energy associated with it,
2:24:59 and that would kind of explain the constant density.
2:25:03 Now, please, that's not— Anybody should— Nobody accepts that.
2:25:07 This is just nonsense.
2:25:09 But a lot of the stuff that you just said is experimentally,
2:25:13 probably experimentally testable.
2:25:14 You can probably construct-- Well-...
2:25:17 experimentally the bubbles of- Well, finding out the bubbles of space,
2:25:22 but those quanta conceivably are Planck size bubbles.
2:25:25 Yeah, the quanta.
2:25:26 Well, they'd be quanta of space.
2:25:27 I mean, the idea is, you know,
2:25:29 you look at a sand dune and it looks smooth and continuous,
2:25:32 but you can see individual grains of sand, right?
2:25:34 And so what this is saying is as this dune expands,
2:25:39 new grains of sand are appearing, and each one of them is a quantum of space.
2:25:44 So what kind of experiments can we do
2:25:46 in the coming decades or centuries to understand dark energy better?
2:25:51 I mean, people have been talking about quantum entanglement of gravity.
2:25:56 In standard quantum mechanics, a particle can be in two places at the same time.
2:26:00 All right?
2:26:01 So now you have two particles.
2:26:03 So this particle can be in two places at the same time.
2:26:05 This particle can be in two places at the same time,
2:26:07 and you put them near one another.
2:26:09 Well, if they're close to each other, there's a certain gravitational force.
2:26:12 If they're far apart, there are certain...
2:26:14 And if they, one is close and one is far, you have another one.
2:26:17 You can calculate the effects of gravity having
2:26:22 to do with quantum entangled particles being in two places.
2:26:26 And people are talking about doing this and trying
2:26:30 to see if in doing such a measurement,
2:26:34 they might be able to definitively determine whether
2:26:39 gravity is a quantum phenomenon or a continuous phenomenon.
2:26:45 And that is potentially a measurement that could be done
2:26:51 soon-ish because the technologies of inherent in all of this recent
2:26:57 work on quantum mechanics is allowing people to be able
2:27:02 to make instrumentation that might be precise enough to do this measurement.
2:27:08 Now, this will not tell us what quantum gravity is.
2:27:11 It will not tell us anything, but it will tell us that gravity is quantized.
2:27:17 And just knowing that, well, for one thing,
2:27:19 it shuts out a whole realm of continuous gravity,
2:27:23 and the theoretical community will then turn its attention,
2:27:26 forget this stuff, and, and think over here.
2:27:29 Now, that doesn't tell you that space is quantized,
2:27:31 but it tells you that gravity is quantized if it bears out.
2:27:37 So if gravity is quantized,
2:27:38 then people will start thinking more about space being quantized.
2:27:42 I have to ask 'cause you mentioned dark
2:27:44 matter is perhaps even more mysterious than dark energy.
2:27:48 Okay.
2:27:48 Can you, can you build up the intuition why it's more mysterious?
2:27:52 What is dark matter?
2:27:53 Oh gosh, what is dark matter?
2:27:56 A, I don't know.
2:27:57 B, it's terribly fascinating.
2:27:59 All right?
2:27:59 So first thing, and the most important thing 'cause I'm an experimentalist,
2:28:03 by God, the first thing is why do we believe there's dark matter?
2:28:07 And the reason is that astronomical measurements do
2:28:10 not agree with predictions by Newtonian or relativity theory.
2:28:15 Galaxies spin too fast, clusters of galaxies move too quickly,
2:28:21 and the distortion of very distant galaxies
2:28:24 due to the gravitational field of nearer
2:28:26 galaxies disagrees with the prediction from what
2:28:30 we see from the observed matter.
2:28:32 So there are three very distinct reasons
2:28:36 why we are predicting that, something is wrong
2:28:40 in our understanding of either the laws
2:28:44 of physics or the matter budget of the universe.
2:28:48 The easiest one to talk about is the spinning galaxies.
2:28:51 Now, this is— what I'm saying is not unique to spinning galaxies,
2:28:55 just easiest to talk about.
2:28:58 So galaxies are observed to spin more quickly than
2:29:02 they should if we add up the gravity we see.
2:29:06 By all rights, galaxies spinning that fast
2:29:08 should blow themselves apart, and they don't.
2:29:11 So what can be the answer?
2:29:14 Well, you have the force required for a star to orbit to move in a circle,
2:29:19 and you have the force due to gravity,
2:29:21 and they're connected by an equal sign, and the prediction is wrong.
2:29:25 So either the force due to gravity is wrong,
2:29:30 the force needed to move in a circle is wrong, or the equal sign is wrong.
2:29:33 I mean, this is really simple.
2:29:35 One of those things is wrong.
2:29:38 So one possibility is simply that Newton's law of gravity,
2:29:42 mass times the mass over R squared times a constant, that's just wrong.
2:29:47 Another possibility is Newton's F equals ma
2:29:49 that we are taught in introductory physics is wrong.
2:29:53 Both of those are eminently possible.
2:29:55 Over here, maybe we don't understand gravity,
2:29:59 or maybe there's more mass than we can see.
2:30:04 So these, you know, I mean,
2:30:05 it's nice that you can look at this really simply and come up with a list,
2:30:09 you know, a cookbook of things we can test.
2:30:12 And and so we've done that.
2:30:15 We've gone and said, "What are the possibilities?" Well,
2:30:18 the most obvious possibility is that there is more mass than we can see.
2:30:23 There's black holes, there's, hydrogen gas that we can't see, whatever.
2:30:27 There's something out there.
2:30:29 So that was the first thing.
2:30:31 So you go and you look,
2:30:32 and there's no hydrogen gas because we can see that with radio waves.
2:30:35 That's not it.
2:30:36 In the '90s, we went looking for black holes, rogue planets, things like that.
2:30:41 Those exist, but not enough of them.
2:30:43 That's not it.
2:30:44 And so now we're left with there's some sort of matter that we can't see,
2:30:50 or we don't understand gravity, or we don't understand inertia.
2:30:53 Now, I personally, if you asked me this, oh, I don't know, 25 years ago,
2:31:00 I would've said the most likely answer
2:31:04 is that we don't understand inertia or gravity.
2:31:09 You know, I— if 20 years ago,
2:31:10 25 years ago, that's what I would've said, no problem.
2:31:13 However, there have been a couple of observations
2:31:17 that that have caused me to change my thinking,
2:31:21 and I think that dark matter is more likely.
2:31:23 One of them is called the Bullet Cluster.
2:31:26 So the Bullet Cluster, there are two large clusters of galaxies.
2:31:31 In these large clusters of galaxies, well,
2:31:34 any galaxy consists of a couple of components.
2:31:37 There are the galaxies themselves,
2:31:39 there is the hydrogen gas that surrounds the galaxies,
2:31:42 and maybe there is dark matter.
2:31:46 And if dark matter is real or dark matter is not real,
2:31:50 you will get different answers if those two galaxies pass through one another.
2:31:54 The galaxies themselves should pass
2:31:56 through one another basically not interacting,
2:31:57 but the big thing is the gas clouds.
2:32:00 So if there's big clouds of gas, as the galaxies pass through one another,
2:32:04 the clouds should interact,
2:32:05 and the gas clouds should stop in the middle and be really, really hot.
2:32:09 So then you would see, if there were no dark matter,
2:32:12 you would see a cluster of galaxies,
2:32:14 cluster of galaxies, a big gas cloud in the middle,
2:32:18 and because the big gas cloud in the middle
2:32:22 is much more massive than the galaxies themselves,
2:32:25 you would expect to see distortions that we
2:32:28 call dark matter distortions in the middle.
2:32:31 If, however, dark matter is real, the galaxies pass through one another,
2:32:34 the cloud stops, dark matter doesn't interact with the cloud,
2:32:37 so it passes through.
2:32:39 In that case, you would expect to see the distortions where the galaxies are.
2:32:43 And that's what we see.
2:32:45 So that is strong evidence in my mind.
2:32:47 The Bullet Cluster is strong evidence that dark matter is a real thing.
2:32:51 And there is another example which is much more recent,
2:32:53 dark Bullet Cluster was a while ago, called the Dragonfly galaxies.
2:32:56 There's Dragonfly 2 and Dragonfly 4.
2:33:00 These are galaxies that rotate exactly according to Newton's laws.
2:33:08 And so the fact that they rotate exactly according to Newton's laws says
2:33:14 that whatever's causing galaxies to rotate too fast is not a property of matter.
2:33:19 But if you had a galaxy where there was no dark matter,
2:33:23 for whatever reason it got stripped off or something,
2:33:26 this is one of those lovely ironies
2:33:27 that the existence of a galaxy with no dark matter
2:33:31 is very strong evidence that dark matter is
2:33:33 real because you can take the dark matter out.
2:33:36 So the DF2 and DF4 also suggests to me that dark matter is real.
2:33:41 So now, while it remains possible that we need to modify
2:33:47 the laws of inertia or we need to modify the laws of gravity,
2:33:50 those are possible still.
2:33:51 In my opinion, and now this is Don's opinion,
2:33:54 but it's probably the opinion of most of the scientific community,
2:34:00 dark matter is likely a real thing.
2:34:04 Now, that's great.
2:34:04 I've taken you all the way to dark matter.
2:34:06 So now you're gonna ask me, you're gonna say, "Don,
2:34:08 what is dark matter?" I'm gonna go, "I don't know." But I know what it isn't.
2:34:14 Okay?
2:34:14 I know that it is not black holes.
2:34:17 I know that it is not rogue planets.
2:34:20 I know that we've done the measurements.
2:34:22 We've looked across nearly every mass range
2:34:24 for compact objects and ruled them out.
2:34:26 So if dark matter is real, it can't be made of those.
2:34:31 So then you're left with the idea that dark matter is a particle,
2:34:34 and that's what we've thought The name for the dark matter
2:34:36 particle that we've called for a long time is a WIMP,
2:34:39 for a weakly interacting massive particle, and we have spent the last,
2:34:43 God, 30 years looking for them in the various ways.
2:34:47 There are three ways that we might see dark matter, the direct way,
2:34:52 which says that dark matter exists literally everywhere in this room,
2:34:55 in our laboratory, and the dark matter is passing through the Earth like a wind,
2:35:00 and we put up detectors trying to see those.
2:35:02 We have done that, and we've seen nothing.
2:35:06 So we should say we have done that for neutrinos.
2:35:08 We've done that for many different types of dark matter.
2:35:11 We just simply put detectors in labs deep underground,
2:35:16 and we can see neutrinos in them, it's true, but dark matter would have,
2:35:19 especially heavy dark matter, what these WIMPs,
2:35:23 They have a different signature, and we've seen no evidence-- Got it.
2:35:27 of dark matter interaction in these detectors.
2:35:29 So neutrinos are also weakly interacting and also-...
2:35:32 have mass, but-- They are-...
2:35:35 but not enough so WIMPs are-...
2:35:37 heavy on the M.
2:35:39 Right.
2:35:39 Neutrinos are indeed WIMPs of a sort.
2:35:41 Now, we have to be careful what we mean by WIMPs.
2:35:44 They are weakly interacting massive particles, but we can calculate,
2:35:47 and there's just not enough mass in them.
2:35:49 It's not it.
2:35:50 Got it.
2:35:50 Got it.
2:35:51 So we need another form,
2:35:53 and we have seen zero evidence of this wind of dark matter through the Earth.
2:35:59 Another possibility is you look where you think dark
2:36:02 matter might be concentrated at the center of galaxies,
2:36:06 and if dark matter exists and there's antimatter dark matter,
2:36:11 maybe they annihilate and make photons.
2:36:12 And so we look for gamma rays
2:36:14 and various other signatures of annihilating dark matter,
2:36:17 and there are always constantly announcements of, "Oh, we saw it.
2:36:23 Oh, we didn't.
2:36:24 Oh, it..." You know, it's— the problem is that way of looking for dark
2:36:28 matter is hard because there are other ways of making,
2:36:31 for instance, gamma rays like neutron stars and stuff,
2:36:34 and you really need to understand the details of galaxies really,
2:36:38 really well to believe that.
2:36:39 And then the final option is what I do,
2:36:42 where we smash particles together at high or high energy.
2:36:45 We try to make dark matter particles.
2:36:47 If you make dark matter particles,
2:36:49 because they don't interact except via gravity, they escape with your detector.
2:36:53 So what you're seeing, what you hope to see,
2:36:55 is an event where you collide particles, a dark matter particle escapes,
2:37:00 and you don't see it,
2:37:01 but the recoil you see on the other side because momentum is conserved.
2:37:04 So you see a blob of energy on this side, nothing on the other side.
2:37:08 Maybe that's dark matter, and that also happens with neutrinos.
2:37:12 So you need to understand everything about neutrinos and calculate how
2:37:15 many of those you see and then hope you see more,
2:37:17 and then that might be dark matter.
2:37:19 Again, that hasn't worked.
2:37:21 So we've ruled out some dark matter particles,
2:37:24 but the problem is the range of space of possible mass,
2:37:29 if dark matter is of a particulate form,
2:37:33 the range of viable dark matter ranges from something like the mass
2:37:39 of an asteroid to far lighter than an electron and everywhere in between.
2:37:45 And we have looked.
2:37:46 We've ruled out some little spots in that phase space, but that's a big range.
2:37:50 Is it really possible to miss a particle the size of an asteroid?
2:37:54 The astronomical searches were not sensitive to that level
2:37:58 of, of dark matter, but, you know,
2:38:01 then you would expect that there would be some of those in the solar system.
2:38:05 And if they're what we think, like asteroids or something,
2:38:08 then we'd heat them up, and we'd eventually see them.
2:38:11 But if they're really, like, truly dark matter, doesn't interact with matter,
2:38:16 which means they wouldn't absorb energy from the sun, so they'd be really dark.
2:38:20 I don't know.
2:38:21 Maybe they're out there.
2:38:22 But the only way we searched for them was a thing called microlensing.
2:38:28 So if a massive object, you have a distant star,
2:38:33 and a massive object passes between that star and your eye,
2:38:38 that star will momentarily brighten.
2:38:42 And so you just look for these, what they call microlensing events,
2:38:46 and you count them, and you see some.
2:38:48 And we did see some.
2:38:50 You know, black holes pass in front of stars,
2:38:52 and we've seen them, but we just haven't seen enough.
2:38:56 And for very low-mass particles like asteroids, they,
2:39:01 They just wouldn't make enough brightening effect to see.
2:39:05 So there's, like, a minimum sensitivity of brightening
2:39:08 and that about a third the mass of a moon,
2:39:12 our moon, is about the sensitivity that we had.
2:39:15 So, you know, that nobody, I think,
2:39:18 really thought that these low-mass guys were likely.
2:39:21 What they thought was more likely they
2:39:23 were just unseen black holes, which I thought-...
2:39:25 you know, I think is completely reasonable.
2:39:26 And then when that got ruled out,
2:39:29 I thought, okay, modified gravity or or inertia.
2:39:32 Well, now the, you know,
2:39:35 Bullet Cluster in Dragonfly seems to have ruled that out.
2:39:37 So I'm stuck in my head with dark matter seems to be real,
2:39:41 and it— we don't know what it is.
2:39:44 And it makes up a giant percentage of matter in the universe.
2:39:46 It is-- What is it?
2:39:47 five times more prevalent than ordinary matter.
2:39:49 Wow.
2:39:50 This is incredible.
2:39:51 It is incredible.
2:39:52 This is so fascinating.
2:39:53 And that's why it's cool.
2:39:54 So if someone out there is, you know, a young person who wants to get
2:39:58 into this, understanding dark matter is a big deal.
2:40:01 I mean, it's five times more prevalent.
2:40:02 The problem is, is as I told you.
2:40:05 If the mass is ranging from an asteroid to far lighter than an electron,
2:40:09 if you get on an experiment that looks at one little range of mass,
2:40:13 maybe you weren't the lucky guy that measured the right place, you know?
2:40:19 And that's one of the reasons why,
2:40:20 as fascinating as I think it is, I'm not doing dark matter experiments because,
2:40:25 you know, if you make an experiment that searches one mass range,
2:40:29 it'll be blind to another mass range.
2:40:31 So what you need is you need many
2:40:34 groups doing all sorts of radically different experiments,
2:40:37 exploring all sorts of parameter space.
2:40:41 And with all that said, until you see it,
2:40:44 there still is the possibility that maybe
2:40:46 we don't understand gravity or inertia right.
2:40:49 You know, you can't rule that out.
2:40:52 If there is dark matter out there,
2:40:54 you're hoping it's actually somehow detectable.
2:40:56 I mean, I don't know what it is.
2:40:58 I think it's cool.
2:40:58 It's very, very fascinating.
2:40:59 That is one thing I really do hope in my lifetime
2:41:03 is understood 'cause I'd like to know the answer to that.
2:41:07 And that's the thing that you could— there legitimately you
2:41:10 could see a discovery of-- You gotta get lucky though.
2:41:13 I mean, you gotta look in the right place, whatever it is.
2:41:16 Just imagine.
2:41:17 Or you have to come up
2:41:19 with that really cool theoretical idea that everybody's overlooked,
2:41:21 which is another possibility.
2:41:22 And there are people who are really, really religiously hating dark matter,
2:41:28 largely because we've looked so hard for so
2:41:30 many years and the experiments in today's
2:41:33 world are a million times more sensitive than when I was a starting student-...
2:41:38 and they still haven't seen anything.
2:41:40 And that's why people really hate dark matter.
2:41:43 I mean, some of them-...
2:41:44 because they think we should have seen it by now, but-...
2:41:47 you know I don't know.
2:41:49 I mean, I'm a sucker for direct observation.
2:41:51 Not— In-indirect is o-obviously also really great, but direct,
2:41:54 just imagine pointing your telescope in a certain
2:41:57 direction and because of some artifact of cosmology being
2:42:01 able to directly detect a giant amount
2:42:04 of a thing that you could say is dark matter.
2:42:08 Yeah, you would see it orbit, things orbit it.
2:42:10 Yeah.
2:42:10 Or it would-...
2:42:11 eclipse things in front of it or-- Yeah, like in an obvious way.
2:42:15 'Cause some of the stuff you mentioned with DF-2 and DF-4,
2:42:18 those are like brilliant indirect, um,
2:42:23 deductions that there should be something like dark matter.
2:42:27 But some obvious, yeah, blocking, occluding, this kind of thing.
2:42:32 We did that in the '90s with experiments called MACHO, OGLE, and some others.
2:42:37 They looked for a black hole that you just can't see,
2:42:39 you know, a black hole you can't see.
2:42:41 It's perfect.
2:42:42 It's a perfect candidate for dark matter.
2:42:45 And if there's enough of them out there— Now remember, there's five times-...
2:42:49 the number of stars,
2:42:50 which means there's a whole lot of freaking black holes out there.
2:42:53 We should have seen them, and we didn't.
2:42:56 What a grand mystery.
2:42:57 We've covered so many of them.
2:42:59 I could talk to you for a thousand more hours, Don.
2:43:02 Let me, if I can ask you about a little bit more of a, On the personal side.
2:43:09 You have a really inspiring life story.
2:43:13 Your folks didn't go to college.
2:43:15 Can you just tell me about your childhood
2:43:18 and where you found the love for physics and science,
2:43:21 and maybe how you found your journey to become a physicist,
2:43:26 given the, the context of where you came from?
2:43:31 Well you know, I grew up a poor kid in the boondocks.
2:43:37 Great parents, but not ones that could guide me terribly academically,
2:43:41 but very very nurturing.
2:43:44 You know, my mom would laugh that she could stop
2:43:46 helping me math after like sixth or seventh grade, you know.
2:43:49 But they were supportive.
2:43:51 And there were a couple of things that— couple,
2:43:55 three things I think that folded into it.
2:43:58 One is I was a voracious reader as a kid.
2:44:01 I loved science fiction.
2:44:02 I would read a book a day.
2:44:04 It drove my mother nuts 'cause she would try to be nice.
2:44:06 She'd buy me a book, and I'd say, "Thank you," and the next day it'd be done.
2:44:10 You know, it just drove her completely nuts.
2:44:11 But anyways, but science fiction is good for fostering imagination,
2:44:17 and so that's precisely what it did.
2:44:20 In addition, and this is where the more serious science came along,
2:44:26 there were lovely science communicators that were popular in the 1970s,
2:44:34 Isaac Asimov, Carl Sagan, a guy by the name of George Gamow.
2:44:38 They wrote books about science aimed at a layperson.
2:44:40 You know, as a kid, I surely couldn't read a textbook and understand it,
2:44:46 but I could read and, you know, get a hint of what science was.
2:44:52 And on top of that, you know, I was,
2:44:56 as most people who became scientists, irrepressibly curious about everything.
2:45:01 And I had sort of a quasi-philosophical mind.
2:45:06 I mean, I was interested in things that, questions that have
2:45:09 in the past been theological and then philosophical and now are more scientific.
2:45:14 Questions about how did the universe come into existence?
2:45:18 Why is the universe the way it is?
2:45:20 Why are the laws of the universe what we see them to be?
2:45:24 How will the universe— Was it created?
2:45:26 How will it be destroyed?
2:45:27 These are, you know,
2:45:28 big questions that have bothered humanity for, well, thousands of years.
2:45:32 And so, you know, I did.
2:45:35 You, you said I had, you know, philosophy and religion minors in college,
2:45:40 and I did 'cause I was curious about that.
2:45:42 Um, I was hoping that learning
2:45:45 that history might help me understand these questions.
2:45:49 And it was in college where I came to realize that the answers
2:45:52 that I was searching for were not to be found in those directions,
2:45:56 but I still learned about how those questions have been asked in the past.
2:46:01 And so I became a scientist, and the only question was,
2:46:05 was I going to be, A cosmologist/astrophysicist-...
2:46:10 or a particle physicist?
2:46:11 And when I had to make that decision.
2:46:14 It was the mid-'80s, and at the time,
2:46:18 there were a lot fewer cosmology measurements.
2:46:22 There was an awful lot of thinking about the universe and not enough measuring.
2:46:27 Whereas with particle physics, by God, you could do experiments.
2:46:31 And so the— what attracted me was the ability to actually get
2:46:35 an answer and not just mull over what an answer might be.
2:46:40 And so I became a particle physicist.
2:46:42 It was difficult without having, you know,
2:46:47 family mentors or anything like that, but, you know, I managed.
2:46:52 And that actually is why, well,
2:46:55 I'm here and why I have spent a fair bit of my time writing books and so forth,
2:47:01 because I figure that there has to be
2:47:04 some other kid out there in Iowa or Kansas,
2:47:06 Montana, somewhere out in some little town without a lot
2:47:10 of access to the kinds of thing that people,
2:47:15 you know, who have highly educated parents do.
2:47:19 And I'm hoping that, you know, some of them will have read some of the things
2:47:23 I've written and will find their own path forward,
2:47:26 because I found it very rewarding over the years.
2:47:30 And, You know, I've been doing this long enough that I'm sure this is true.
2:47:35 I've had kids come up to me at the lab and say, "Hey,
2:47:38 I'm a summer intern because I saw your video
2:47:40 or read your book," or, you know, whatever.
2:47:42 So I know that at least I've made a small impact.
2:47:46 I mean, I always would like to do more, and, you know,
2:47:49 I appreciate the opportunity that your audience affords me
2:47:55 'cause I think it's important to talk about these things.
2:47:59 These are really cool, fascinating questions.
2:48:01 They are unanswered, and they are just waiting for youngsters
2:48:06 to come and spend some time thinking about them,
2:48:09 'cause one of your viewers might be one of the people
2:48:12 who answer these questions that have stymied very smart people for decades.
2:48:18 And we should also say that you're a legit scientist.
2:48:22 So what— we'll mention Sean Carroll, who's a legit scientist,
2:48:26 legit physicist, but is also a good science communicator.
2:48:30 Anyway, I did wanna mention, I don't know if this is true,
2:48:33 but I kind of heard you talk about
2:48:35 this, that when you first showed up to Fermilab,
2:48:37 you were, like, working crazy hours, working extremely hard-...
2:48:41 eight AM to midnight.
2:48:44 I did.
2:48:44 Uh, first of all, I love that.
2:48:47 Can you speak to what drove you and maybe
2:48:50 the value of hard work in those contexts,
2:48:54 in your early career when you discover a thing you're passionate about?
2:49:00 Well, yeah.
2:49:01 I mean, obviously being smart, you know,
2:49:03 if you're Einstein, then maybe you can slack, I guess.
2:49:06 Although even he didn't do that, but I'm not Einstein.
2:49:09 But the fact is, when I was young, and I was unencumbered, no,
2:49:13 no family, no kids or something,
2:49:16 I couldn't imagine anything I wanted to do more.
2:49:19 I mean, some people, they wanna go out to the club.
2:49:21 They wanna, I don't know, play soccer or something.
2:49:23 But I wanted to make measurements,
2:49:26 and I wanted to understand and, and learn, and that was fantastic.
2:49:30 And so as a graduate student,
2:49:32 and this isn't for everybody, but I worked outrageously.
2:49:35 I would, from Monday through Saturday,
2:49:37 I would be at the lab voluntarily because I wanted
2:49:41 to be from eight AM to midnight, and on Sunday,
2:49:45 I would work from eight until about five,
2:49:47 and that's because from five to midnight,
2:49:49 I had to wash clothes and buy groceries and things like that.
2:49:54 And I loved it, you know.
2:49:56 And I still love it.
2:49:57 I can't do that anymore.
2:49:59 But that's simply because I have other obligations.
2:50:04 But had I been rich, I would've done the same thing.
2:50:09 You know, it's something I truly, truly loved.
2:50:13 And the— I mean, there is absolutely nothing more fascinating
2:50:18 to me than having a hard problem and figuring it out.
2:50:22 And that, you know, that work ethic— Well, there's a couple of things
2:50:26 that separate smart people from no-kidding scientists,
2:50:30 'cause all scientists are smart.
2:50:32 But the thing that separates, that many scientists have is,
2:50:37 A, a drive and a real grit.
2:50:41 The, um— For me and for so many scientists that I know,
2:50:49 trying to measure something and having it not work just kinda ticks me off,
2:50:53 and I am not going to let the universe in my lab or whatever beat me.
2:50:59 And, you know, some people-...
2:51:00 they, you know, if the thing breaks, it's like, "Oh, man,
2:51:03 that didn't work." And a lot of people, "Well, I'm gonna go home.
2:51:07 I'm fed up." Nah, it would just kinda make me mad,
2:51:09 and I'd put more effort into it.
2:51:11 And, you know, not every— I mean, okay, I was crazy.
2:51:14 I worked long hours.
2:51:16 But I think-...
2:51:17 the people who are really good at this will do maybe not that much, you know.
2:51:21 Some people have to have a better life than that.
2:51:24 But a lot, because it's just you can't imagine not knowing the answer.
2:51:29 And that if— When, when you see that as an older guy,
2:51:34 you don't— maybe not to that degree, but when you see that kinda drive,
2:51:36 that, that intensity of trying to get the answers,
2:51:43 you know that person's a winner.
2:51:45 And so if, you know, some student out there, if it doesn't,
2:51:50 you know, bring you joy, as uh, what's her name?
2:51:53 The Japanese girl says, "If it doesn't bring you joy,
2:51:55 then it might not be for you." And then you could
2:51:57 be a person who reads about it and, you know, is involved.
2:52:00 But if you wanna be a real scientist,
2:52:02 it has to be just part of what you are here.
2:52:06 And by the way, it is a hard life, but it is also a very fulfilling one.
2:52:12 So working hard towards the thing you love is a really fulfilling way to be.
2:52:19 I think that's true for an artist or something,
2:52:21 you know, anybody, a musician, you know?
2:52:23 Musician, they just keep practicing because it is who they are.
2:52:28 Mm-hmm.
2:52:28 Well, I'm glad there's people like you at a place I admire,
2:52:32 like Fermilab one of the many places in the United States and the world
2:52:38 that is carrying the beacon of great science and great engineering forward.
2:52:45 Uh, Don, thank you so much for everything you do,
2:52:48 for all the teaching you do, online,
2:52:51 for all the incredible physics work that you do at Fermilab,
2:52:56 and thank you so much for talking today.
2:52:59 Thank you for having me.
2:53:01 Thanks for listening to this conversation with Don Lincoln.
2:53:04 To support this podcast, please check out our sponsors in the description,
2:53:07 where you can also find links to contact me,
2:53:10 ask questions, give feedback, and so on.
2:53:13 And now, let me leave you with some words from Marie Curie,
2:53:16 a two-time Nobel Prize winner,
2:53:19 first in physics, second in chemistry: "Nothing in life is to be feared.
2:53:24 It is only to be understood." Thank you for listening.
2:53:29 I hope to see you next time.