Biggest Mysteries in Physics: Antimatter, Dark Energy & ToE - Don Lincoln | Lex Fridman Podcast #497

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.