The Big Bang might not be the start of the universe | Phil Halper

0:00 Now, of course, these are speculative ideas.

0:01 Nobody wants to say this is what happened.

0:04 But what I think they do is give us caution.

0:08 They say maybe scientists were premature to say

0:11 the big bang was actually the beginning of time.

0:14 Maybe it wasn't the beginning of time after all.

0:16 Maybe the universe has always existed.

0:24 Phil Halper, welcome to How the Light Gets In.

0:27 Thanks.

0:27 Thanks for having me on.

0:28 It's great to be here.

0:29 So you are a fellow of the Royal Astronomical Society,

0:32 host of the YouTube series Before the Big Bang,

0:35 and the co-author of the recent book Battle of the Big Bang.

0:40 So we have a lot of evidence that's pointing towards, you know,

0:43 a hot dense early stages of the universe with the red

0:47 shift of distant galaxies and the cosmic background radiation.

0:51 But there's a growing consensus that this might not be the exact origin,

0:56 the absolute origin of our universe.

0:58 Why is that?

1:00 So what the big bang theory tells us as you rightly

1:03 said was that the universe was in a very hot dense state.

1:07 We see the universe expanding.

1:09 So if you wind that back it's contracting.

1:12 So it must be getting denser.

1:13 It must be getting hotter.

1:15 Now what was believed was that this would actually if you followed it

1:18 back to about 13.8 billion years this would mark a singularity in spaceime.

1:24 So this is where the space-time curvature, the density, the pressure,

1:28 the temperature could become infinite

1:30 and it's certainly where clocks stop ticking.

1:33 So that is the beginning of time.

1:36 What's happened in the last few decades is that people have

1:39 started to challenge the theorems that suggest this is what happened.

1:44 And in fact uh Roger Penrose who's one of the creators of these theorems

1:48 um suggested that you know it was it was mentioned to him

1:51 when he when he when he proved it um that this didn't really

1:54 mark the beginning of the universe rather

1:56 it marked the end of general relativity.

1:58 This is our theory uh of gravity if you like it's a theory of very big things.

2:04 So, of course, if you want to model the universe,

2:06 you're going to use a theory of very big things.

2:09 But if you're going back in time,

2:10 eventually the observable universe gets smaller and smaller,

2:13 and now you're going to need a theory of very small things, quantum mechanics.

2:17 So, people have said, well, you know what,

2:19 these singularity theorems, they were proven by Penro and Hawking.

2:23 Um, they really are incomplete.

2:25 Um in fact they have a number of assumptions but probably the one people focus

2:29 on the most is that it doesn't

2:31 include a quantum description doesn't include quantum mechanics.

2:35 So therefore we need a theory

2:37 that will combine general relativity and quantum mechanics.

2:41 Now we don't have an agreed upon theory

2:43 but there are candidates string theory loop quantum

2:47 gravity causal set theory ha lift shift gravity

2:51 there's there's a few candidate ideas out there.

2:53 Some people call them theories, some people don't like that term.

2:56 It doesn't really matter what you call them.

2:58 But what has happened is that people have started to apply them to the big bang.

3:03 And what they've noticed is that the big

3:05 bang was not the beginning in these theories.

3:08 So now, of course, these are speculative ideas.

3:10 Nobody wants to say this is what happened.

3:13 But what I think they do is give us caution and say maybe

3:18 scientists were premature to say the big

3:20 bang was actually the beginning of time.

3:22 Maybe it wasn't the beginning of time after all.

3:25 Maybe the universe has always existed.

3:27 So that's one assumption of the Penrose Hawking theorem that was supposedly

3:31 proved the beginning of time at the big bang that's being challenged.

3:34 Although you know there are others as well.

3:35 I mean we I think we mentioned four assumptions

3:37 in the book and every one of them is being challenged.

3:42 This is true.

3:43 It's very open for discussion right now.

3:46 But for you, what do you think are

3:47 the kind of the technologies and the avenues that are

3:49 going to be the richest for helping us explore

3:52 all all of these different theories that are coming out?

3:55 Yeah.

3:55 So, of course, these are very speculative ideas that are being

3:58 played with in the early universe or the very early universe.

4:02 So, question is, is this fantasy?

4:04 You know, some scientists think so.

4:05 Sometimes think this isn't even worth bothering with.

4:08 But actually I think there are um signals that we could look

4:12 for that could help differentiate uh different models of the early universe.

4:17 And the one that excites me the most is gravitational waves.

4:21 So these are ripples in the fabric of space and time.

4:24 Think of throwing a a rock uh on a pond and you see these ripples.

4:28 Well, these are ripples in spaceime and we've seen them only for the first time.

4:33 Well, I think the first detection was or direct attention was in 2016.

4:37 Um they built these giant lasers 4 kilometers long.

4:41 Um there's one in uh Washington and one in Livingston.

4:45 Um in Louisiana, that's the other one.

4:48 and um they managed to detect gravitational waves but they are not

4:53 from the big bang they are from uh usually most of them

4:56 are black holes colliding so when these black holes collide they

5:00 shake the fabric of spaceime and we actually feel that of course

5:05 I say we feel it obviously you and I don't feel it

5:07 because it's so incredibly feeble it's

5:10 absolutely incredible engineering what these scientists

5:14 and engineers have done to be able to detect these gravitational

5:17 ways because they are so faint when they pass through the earth.

5:20 Um but they are detectable and they have been detected.

5:23 Um now the reason why these are so

5:25 exciting is because they they could actually travel through

5:30 the fog of the early universe because the early

5:33 universe is something very much like the sun.

5:36 It was a plasma.

5:38 And if you ever look at the sun, don't do it with your naked eyes,

5:40 but actually I have a solar telescope at home and I

5:43 take pictures of the sun and you can look at the surface,

5:46 but you can't look at the interior, right?

5:49 Because it's opaque.

5:50 The sun is opaque.

5:51 So, you can't look at the interior.

5:53 But actually, what scientists do to study the interior

5:55 of the sun and actually of the earth is to do seismology.

5:58 Um, so essentially what we're trying to do is something like seismology.

6:02 um scientists want to look for these ripples in the fabric

6:06 of space on these gravitational waves coming from the big bang.

6:11 So, and in fact, some of the um speculative models predict

6:14 that we should find these ripples and some say we shouldn't.

6:18 So, this is a good test to see which one of these models

6:20 is right and and other models might predict different properties of these waves.

6:24 So, actually it's not just a question of finding them or not finding them,

6:27 but you know, measuring their specific properties.

6:30 So, and there are two ways that you there's the main ways to do this.

6:34 One is to look at patterns in the light of the cosmic microwave background.

6:39 Uh, and there there are certain patterns known

6:41 as beam modes that would be um a signature.

6:44 They would these would imprint on the light

6:47 that comes from the cosmic microwave background.

6:48 But remember that light was emitted 380,000 years after the big bang.

6:54 So, this is sort of imprinting on it.

6:56 Um, however, you know, if you if you could do direct detection,

7:00 these lasers that they have on the ground,

7:03 um, with this instrument called LIGO, um, if you could put that in space,

7:08 maybe a very grand version of this, then maybe you

7:11 could do a direct detection of the Big Bang ripples

7:14 and that may help you distinguish between which model

7:17 of the Big Bang is right and which model is wrong.

7:20 So, that's the one that I would probably um, say is the most exciting.

7:24 Interesting.

7:25 Um, I just want to go back to you mentioned black holes there and one

7:28 of the theories that you explore in the book is the idea that our universe was

7:31 born from a black hole and the theorized singularity at the center of a black

7:36 hole is the flip side of the coin from the alleged singularity in the big bang.

7:41 Do you give much weight to this theory?

7:43 Do you think it's possibly one of the avenues that would give you know

7:47 it's certainly a possib it's certainly a possibility.

7:50 Um, and of course it's very seductive, isn't it?

7:52 because well there's a singularity in the black hole and there's a singularity

7:57 at the big bang at least in general relativity with various other assumptions.

8:02 If you take those assumptions they both have

8:04 a singularity with these these could be a clue maybe

8:08 maybe these two things are connected and people have

8:11 explored that connection and there are various proposals for it.

8:15 In fact, the idea that a universe could be born from a black

8:18 hole um goes all the way back to I think the 1960s.

8:22 Um but more recently it has has been proposed in a number of models.

8:27 So for example um one actually doesn't use quantum gravity.

8:33 Um so that's you know this combining

8:35 of relativity and quantum mechanics and the hope

8:39 is you know that will give us an understanding of the big bang and black holes.

8:42 But there's another feature that some scientists suggest we've overlooked.

8:46 So um we know in relativity that spacetime can curve

8:51 but um some people have suggested it could also twist.

8:55 Now in general relativity you set this twisting it's called the torsion

8:59 to zero because it's easier and we

9:00 don't really see any evidence of this twisting

9:02 but there are very high high densities

9:05 um maybe this twisting will become relevant

9:10 and some people have suggested that this twisting

9:12 would actually sort of stiffen the spaceime

9:14 means it couldn't be compressed and maybe it would then bounce bounce back out.

9:18 Now the matter couldn't bounce out into uh past the event

9:21 horizon of the black hole has to go somewhere else.

9:23 So it makes a new universe.

9:25 Um so that's one idea.

9:26 It comes from this twisting of space called torsion.

9:30 Another is to say yeah no no come on we need to go to quantum gravity

9:34 and uh again proposals in quantum gravity have

9:37 suggested that a black hole could could bounce out.

9:40 So the matter would bounce out.

9:43 So um one idea that's uh I think theorists are

9:46 reasonably confident that it does bounce out is l quantum gravity.

9:50 So that's a sort of alternative to string theory and but there

9:54 they have some different ideas about how it bounces out.

9:58 So they're not quite sure how the matter bounces out.

10:01 So one idea is that it bounces out into our universe.

10:04 And in fact what would happen is the matter bounces out very very quickly.

10:08 So in in you go out you go very quickly.

10:10 And you might think hang on but we don't see lots of matter coming out.

10:14 Well, very quickly from the perspective of the infalling observer,

10:17 but in relativity, you know, they have this thing called time dilation,

10:21 which is, you know, the time could be stretched.

10:24 So, what happens is the infalling observer um sees the journey being very quick,

10:29 but if you're outside, it could take gazillions of years.

10:33 Um, so that's one idea that would not help uh the the black hole genesis model.

10:39 But another idea is that actually bounces out and forms it

10:43 tunnels to a new region of spaceime and and so if that's

10:47 right then you will get this what we call black hole genesis

10:50 models and there's a third proposal actually by my co-author Nayesh which

10:54 is that actually what happened was there was a higher dimensional black

10:59 hole um and that collapsed and formed our universe and the interesting

11:04 thing about that is that the um properties that would come

11:07 out of that universe seem to fit very nicely with our universe.

11:11 And so this could actually be

11:12 an alternative to what's called inflationary cosmology,

11:15 which we haven't talked about, but that's probably the most popular um

11:19 hypothesis for what happened before the Big Bang.

11:22 And I I say that um with with underlining that phrase before the Big Bang,

11:26 because a lot of textbooks will tell

11:28 you that inflation happened after the Big Bang.

11:30 But we argue in the book, no, no, it happened before the Big Bangs.

11:34 There's also this kind of element of the theory about the the big

11:38 bangs being the origin of our um the black holes being the origin

11:40 of our universe which it kind of rhymes with some of the other theories

11:44 in the book that you explore like Roger Penrose's CCC and the big bounce.

11:48 All of which have this they kind of lean towards

11:51 the idea that our universe doesn't necessarily have a hard beginning

11:54 and you kind of just mentioned it there with the difficulties

11:57 of using the word even before when referring to it.

12:00 Do you think that when we if we ever do get

12:03 a theory um to fully understand the secrets of the universe,

12:07 it's going to be about a universe that is eternal or will it have a beginning?

12:12 What do you think is more likely?

12:13 I think well I think that's still an open question and I I think it's when

12:16 you have open questions like that the best

12:17 thing to do is to be agnostic about it.

12:19 Don't pick a side before the evidence is in.

12:22 Now people think the evidence is in that we've proven

12:24 that the universe had a beginning with these sort of Penrose Hawking theorems.

12:27 There are some other theorems that people have have

12:29 suggested uh but I think we don't know yet.

12:32 So we we want is a quantum theory of gravity

12:35 and may maybe we could do early universe cosmology without quantum gravity.

12:38 Roger Penrose's conformal cyclic cosmology doesn't actually use quantum gravity.

12:43 Um so either way though we need better theories

12:47 and so we will see what they say and it it

12:49 might be that we can never know whether the universe

12:52 had a beginning or whether it's eternal into the past.

12:55 I think what scientists are trying to do

12:57 is to push the envelope of our knowledge.

12:59 So we shouldn't say that the big bang is the beginning

13:01 of time rather it's the edge of our knowledge and we

13:04 want to push beyond that and maybe we can go

13:07 from just after the big bang to just before the big bang.

13:10 Um but trying to answer the ultimate

13:11 question is did the universe have a beginning?

13:14 Well, maybe maybe someone will come up with a way.

13:16 There's no observational test that can tell us the universe had a beginning.

13:19 And I have heard, you know, popular scientists uh come communicators say, "Oh,

13:24 we can test whether the universe had a beginning." I don't think that we can.

13:27 All we all we can do is test a model that maybe goes back before the big bang.

13:33 There could be.

13:33 I mean, there could be a model which is

13:35 infinite by definition and then if you tested that model,

13:39 you know, that would give you pretty high credence

13:40 that it that it was eternal into the past.

13:43 So I guess that's a possibility.

13:45 Um but you know these singularities they don't give us

13:48 predictions for what would happen if there actually was a singularity.

13:51 So um so I can't see a way to test those.

13:55 Um but of course at the level of theory we could

13:58 explore more and maybe that will at least up our credence.

14:01 So the universe could be infinite in time.

14:04 It might it could have a finite beginning.

14:06 I think the jury is still out.

14:09 So I wonder as you know as you're explaining it's very

14:12 difficult to get to any kind of hard answers but what

14:16 we've seen throughout your book is that there are lessons

14:19 to be learned from other disciplines

14:21 with Lee Mullen applying Darwinian evolution

14:25 uh to the idea of black holes

14:26 and universes and then Roger Penrose himself taking

14:31 inspiration from the artwork of MCSE.

14:33 How much of a role do you think these other

14:35 disciplines have to play in the search for answers?

14:37 Yeah, I mean I think you want to take

14:39 a holistic view and and learn from other disciplines

14:41 for sure and Lee Smolan is a fantastic example

14:44 of that because what motivated Smolin was this idea of fine-tuning.

14:49 So this is the suggestion that the concepts of nature have very precise values

14:56 conducive to life and if they were even slightly different life would not exist.

15:01 And Simon was certainly inspired by biology

15:04 to to look for an answer to this paradox.

15:06 if if you want to call it a paradox.

15:08 I'm not sure that's the right word.

15:09 Uh certainly it's a problem.

15:11 Um so his suggestion was well hang on we've seen this problem before because

15:17 if you just arranged genetic material randomly

15:21 you're not going to get a living organism.

15:23 So what's the explanation?

15:26 Well the explanation is that there's Darwinian evolution.

15:29 Darwinian evolution can select for something that can reproduce and that will

15:34 give you an appearance of design but without any designer.

15:38 So Simon was very inspired by um evolutionary biologists like

15:42 Richard Dawkins and Lim Margolus and of course Darwin himself.

15:46 Um so what he did was to say well hang on maybe universes can reproduce

15:52 and this takes us back to what we

15:54 said about black holes giving birth to new universes.

15:57 But here you have to have a little twist on the idea.

15:59 And the twist is that when the new universes are born,

16:02 they will inherit the constants of nature from their parents,

16:07 but with a small variation.

16:08 Just like when you're born,

16:10 you have the genes of your parents, but with some mutations.

16:13 It's never a perfect copy.

16:15 So if you have a small mutation, then what you what nature will do is

16:19 select those universes that will have more children.

16:23 And which universes would would those be?

16:25 Well, it'll be the ones with more black holes.

16:27 How do black holes form?

16:28 Well, we know for sure they form from stellar collapse.

16:31 I mean, they there could be other ways for black holes to form,

16:33 but they certainly form from stellar collapse.

16:35 So, what's being selected for is black holes,

16:37 but the consequence is that you have stars and that's basically

16:42 the finetuning argument because they're not

16:44 it's not really fine tuning for life.

16:45 It's fine tuning for complexity and for stars.

16:47 Once you have stars, then okay, life comes comes afterwards.

16:50 So this is a very neat solution and it did draw from inspiration

16:55 from biology and as you rightly point

16:56 out Penrose drew his inspiration from from Cher

17:01 has these wonderful pictures something called circle limit 4 which shows a sort

17:05 of squashing down of infinity and that's

17:09 exactly what happens in his conformal cyclic cosmology.

17:12 you have this sort of infinite future but there

17:14 are ways in geometry to sort of squash it down

17:17 so it becomes finite and um then you could

17:20 ask okay and what's beyond that and in his view

17:22 it's another universe so definitely um you'd be surprised

17:26 where inspiration comes from and uh it it's it's

17:30 enriching I think um to look at other fields

17:33 of study and find that it's relevant in your field

17:37 well thinking of this um further down the line of um

17:40 different fields of inquiry Um throughout the whole history of cosmology,

17:44 there's been this fraught relationship with religion.

17:48 What relationship do you think religion

17:50 and cosmology should have in the modern day?

17:52 What role does religion have to play?

17:54 Is is it contrary?

17:55 Can they work together?

17:57 So I think religion is a very broad term.

17:59 So it's hard to give a specific answer because it's

18:01 going to depend on the religion and the degree of religiosity.

18:06 So, um, some forms of religion, I would say,

18:09 are in serious conflict with, uh, our scientific narratives.

18:14 Um, so those that take their biblical

18:16 texts or other religious creation stories literally, um, that that's a tension.

18:21 That's a conflict.

18:22 Okay.

18:23 Um, however, um, not everyone takes their creation stories literally.

18:28 Some see them as metaphors and there, you know,

18:30 there's going to be less and less of a conflict.

18:32 And some people may be inspired by their faith.

18:35 uh maybe they see elegance in the beauty of nature or things like that.

18:38 Um and there you know maybe that's that that could be

18:41 helpful anything that inspires someone um to to work in science.

18:46 Uh I think Lmetro is an example of that.

18:48 Um you know all power to them.

18:51 Um so it very much depends on the on the type of religious belief.

18:55 Of course one other aspect um that uh I'm not a fan

18:59 of is using um discoveries in cosmology to try and sort of prove God.

19:04 So this is what's called natural theology.

19:06 Now there's not nothing wrong with the program

19:08 in principle um in principle fine.

19:11 You know if there if there is evidence in science

19:14 that points to God great you you should use that.

19:17 Um unfortunately I don't think the evidence has been proposed

19:19 and there are various arguments uh for God from cosmology.

19:23 I don't think those are successful arguments.

19:26 Um so I would steer clear of those and in fact some of the critics

19:29 of those arguments are themselves uh religious

19:32 and they're physicists or philosophers of physics.

19:35 Um so I I would I would follow

19:38 them in their advice saying don't use these arguments.

19:41 So here are you alluding to the calam argument?

19:44 So there's the calam cosmological argument and there's the finetuning argument.

19:46 I don't know if you want to unpack those.

19:49 Let's let's do it.

19:50 Okay.

19:50 So the kalam cosmological argument uh basically goes like this.

19:54 Everything that begins to exist has a cause.

19:57 The universe began to exist.

19:59 Therefore, the universe has a cause.

20:01 And then there's a sort of second stage of the argument where

20:03 where they they try and argue the cause must be must be God.

20:06 Now, what establishes that the universe began to exist?

20:10 Well, supposedly the big bang.

20:12 And and indeed, this is an old argument for God.

20:15 I mean, it's it's it goes back at least to the Middle Ages.

20:18 In fact, it probably goes back even older to to John Foponus.

20:22 Um and it got revived by uh

20:26 an American uh Christian philosopher called William Lane Craig.

20:29 Um he noticed in the 70s that hey scientists are telling us the universe had

20:33 a beginning and this sort of argument for God says the universe had a beginning.

20:36 I mean they obviously they didn't

20:37 use cosmology that they had philosophical arguments

20:40 that they thought were successful um to prove

20:42 a beginning without any sort of science.

20:45 Um, by the way, I don't think those philosophical arguments work

20:48 either for to we can go into that if you want,

20:50 but the point is at that time in 1979,

20:54 it was a consensus that the big bang was the beginning to the universe.

20:57 So, I can see what motivated Craig to deploy it.

21:00 But of course, I think Lmetra,

21:02 who is like the father of the big bang and not only a brilliant cosmologist,

21:06 but also a Catholic priest,

21:07 I think he would have hated this argument because he was in the camp,

21:10 let's keep our science and our religions separate.

21:12 But of course it's very tempting uh to untangle them and that's what Craig did.

21:17 Uh and I think Lmetra would have been worried that you

21:19 know look in fact I think Lmetra did say that be very

21:23 careful here because this is a very provisional idea and we can't

21:26 rule out that there could have been a pre big bang phrase.

21:30 I mean you wouldn't have used the phrase big bang

21:31 but there could have been a pre- big bang phase.

21:33 I think he said prior era of construction or something like that.

21:37 Um so and indeed what's happened now is actually cosmologists are I think more

21:43 sympathetic to the view there was a pre- big bang phase and in fact

21:46 before we talked about this inflationary cosmology

21:48 and that is pretty mainstream the way

21:51 it's often taught is that you have the big bang and then inflation

21:54 but as I said uh I think there's very good reasons that we explore

21:56 in the book to say no no it was inflation then the big bang

21:59 so in this sense then even

22:00 in this mainstream inflationary cosmology you have a pre-

22:04 big bang state and then if we go to these these quantum gravity ideas,

22:08 they're also sort of implying we have a pre- Big Bang state.

22:11 So, um, so I think it's false to say

22:14 that the Big Bang has established the universe had a beginning.

22:17 I also think we don't really know that causality is sort of fundamental.

22:21 So, even if the universe did have a beginning, and it might have,

22:24 we do not argue in the book that the big

22:26 bang that the universe couldn't have a beginning.

22:29 I mean, might have, we just don't know.

22:31 But if Okay, let's go with the assumption that it did have a beginning.

22:34 Well, uh, it's not clear then that it would need a cause.

22:36 I mean, after all, causes happen before their effects.

22:40 So, if there was a beginning to the universe, there was a beginning of time.

22:43 And, and how could you have a cause, you know, if there's a beginning of time?

22:47 You'd have to have some very weird notion of causality.

22:50 Certainly not a standard notion of causality.

22:52 And the whole point is you're kind of trying to use standard notions,

22:55 the things that we're familiar with.

22:56 And so, if you give up this this notion of sort of standard causality,

23:00 why not just give up causality at all?

23:02 You know, and and in indeed many people say that if we go um

23:06 to a quantum picture of the universe and causality

23:08 disappears and there are other philosophers that say,

23:12 you know, um maybe causality is emergent.

23:15 Maybe it's not even part of our physics anymore that really physics is

23:19 just described by differential equations and you

23:22 don't even need the term causality.

23:23 So that's called the eliminative school of causality.

23:26 So I think both of these premises are are

23:28 extremely dubious quite frankly but that's just my view.

23:33 Um so as you're mentioning here there's this kind of strange era of our universe

23:38 in the you know kind of pre big bang where our traditional laws of physics

23:43 seem to break down and some theorize that you know the fourth dimension of time

23:48 becomes a physical dimension and maybe even there's a a varying speed of light.

23:53 That's another idea.

23:54 Yeah.

23:54 And in one of the chapters in your book, you tie this in or you explore the idea

23:59 of how this fits in with the universe creating itself.

24:03 How do these two all these different pieces come together?

24:06 Okay.

24:06 Well, let's let's be careful cuz some of these ideas are sort of separate.

24:09 So the variable speed of light idea is

24:13 that again this is a competitor to inflation.

24:15 So we keep mentioning inflation.

24:16 I should probably explain what inflation is.

24:18 So inflation is this idea that the universe expanded exponentially.

24:23 So it would double in size something like every 10^ theus 37 seconds.

24:28 So if you don't know your scientific notation that's what is that 10

24:32 trillionth of a trillionth of a trillionth of a second I think.

24:34 It's this incredibly rapid period of expansion

24:37 and it's sought to solve some of the problems

24:40 of the big bang because people don't know well not everyone knows that big

24:44 bang actually has several really difficult problems

24:46 with it and if you if you add this period of inflation you can actually solve

24:50 these problems but inflation has its own problems.

24:53 So some people think okay the best thing to do then is to improve

24:57 our inflationary models see if we can

24:59 fix those problems within the inflationary framework.

25:02 Other people say no no no let's drop inflation let's have a different idea.

25:06 So here if you have the speed of light much much

25:09 faster in the early universe rather than the expansion rate uh

25:13 being really high uh then it turns out that you can

25:16 solve some of these problems that inflation is thought to solve.

25:18 So VSSL or various speed of light theory is an alternative to inflation.

25:22 Now the other idea that you mentioned was that um time could turn into space.

25:28 So yes, we have three space dimensions up, down, left,

25:32 right, forward and backwards and we have a time dimension.

25:36 So that makes a fourdimensional space time.

25:38 But uh Steven Hawking and his colleague Jim Hartwell

25:41 suggested actually when we go back to the big bang,

25:43 we could have a picture where actually time turns into space.

25:46 So we have four space dimensions and no time dimension.

25:50 And and there are technical reasons why they thought this would be the case.

25:53 And uh lo and behold, it seems to remove the singularity.

25:57 So, so in fact, Hawking was the one that proved the singularity

26:00 and then um he suggested oh actually we can get rid of it.

26:04 Um so that's another idea.

26:06 Now the the self-creating universe is with a time loop.

26:12 That's that's another idea again.

26:14 Um so here it takes advantage of the fact

26:17 that there are solutions to Einstein's equations

26:21 that would allow uh space to curve so much

26:24 that it sort of curves back into a loop

26:27 and so now you would actually be able to travel

26:29 backwards in time if you could go on this loop.

26:32 So it might be something like the movie Groundhold Day um

26:34 if you were if you were on one of these loops.

26:37 So these are called closed timelike curves

26:39 and there are two models that we talk about

26:41 in the book that exploit closed time like curves.

26:44 So one is is in the inflationary tradition.

26:48 Um so this was proposed by Richard got and Leian Lee and in fact

26:52 um I should mention that inflation is thought to actually produce a multiverse.

26:57 So in inflationary cosmology you sort of think of bubbles in a in a in a pot

27:01 of water and our universe is like one of those bubbles.

27:04 But the pot of water, you know,

27:05 when you boil a pot of water, the the amount of water goes down.

27:09 But inflationary cosmology actually would never go down.

27:11 So you can make infinite number of bubbles

27:13 and there'll be infinite number of universes.

27:15 Um so what Got and Lee wanted to do

27:17 was to sort of trace the evolution of this multiverse.

27:21 And then what they what they suggested was

27:23 if you went far enough backwards in time,

27:26 the the bubbling wouldn't go back forever.

27:27 It might go forever into the future,

27:29 but it wouldn't go forever back into the past.

27:31 In fact, what you would encounter is this closed timelike curve.

27:35 So the universe then creates itself.

27:38 The other version of this um is what's called periodic time cosmology.

27:42 And that was actually proposed by my co-author

27:43 Nia Shorty and his student Beth G.

27:46 And what they did was they sort of combined

27:49 the sort of Richard Got's idea with Roger Penrose's idea.

27:53 So what Roger Penrose is his cyclic model.

27:55 What it what it suggests is that if you go far enough into the future,

27:59 you'll actually lose the mass of the universe and without mass you

28:03 can't build any rulers or clocks and without rulers or clocks there's no

28:07 sense of scale to the universe so the universe in some sense sort

28:10 of comes back around now Penrose had it as a sort of cyclic

28:14 scheme sort of progressing in time but what what um Nish and Beth

28:19 G suggested was well maybe the whole universe could be a closed

28:23 timelike curve and um and how would you join the expanded universe

28:29 to the dense universe verse where you use Penrose's trick of this conformal

28:33 rescaling and then you will get a loop and what what's really

28:36 beautiful about this idea is that you have this property in the cosmic

28:40 microwave background the old dislike that we can see and that is

28:43 it's scale invariant um so scales you know they don't matter so much

28:48 should we say it's not perfectly scale invariant but if you have

28:51 this conformal rescaling then the argument

28:53 is actually you get the scale variance

28:55 out of it um so it sort of comes for free as it

28:58 were and that's then you I think a motivation to take this seriously.

29:03 Um, but of course we should remember these are speculative

29:06 ideas and it's one of many that that we talk about.

29:09 But I it's kind of one of the most fun ideas you because

29:12 just thinking the title of Got's paper was can the universe create itself?

29:17 Just the title is so provocative.

29:19 Uh, how can you not be fascinated by that?

29:22 Well, just to wrap up,

29:24 so all of these different explanations, they're fantastical.

29:27 They're often hard to wrap your head around.

29:29 something counterintuitive and yet they all have experts

29:31 in the field who back them to the hill.

29:35 On the other hand, are there any theories that you've come

29:37 across which you think not a chance at all that it's true,

29:40 but nonetheless you find interesting or thoughtprovoking?

29:44 I don't know about not a chance that it's true.

29:47 I mean, I guess anything might have some chance it's true,

29:49 even if some very speculative idea.

29:53 I mean, uh, I'm not sympathetic to, uh, the idea that we live in a simulation.

29:58 And I don't think we actually mentioned the simulation hypothesis in the book.

30:02 Um, because I just don't see where it gets you.

30:06 Um, and who knows whether universal could be simulated,

30:10 but of course, you can't help but wonder about it, right?

30:13 I don't think there's much physics to be done with it.

30:15 I think I think that's maybe why we didn't really include it.

30:17 However, there is a sort of variation on that theme.

30:21 U there's something called the Far Guth Gumman mechanism and it's

30:24 been suggested that maybe you could make a universe in a lab.

30:29 Um now I just can't imagine that a civilization would

30:32 ever get that advanced to make a universe in a lab.

30:35 Uh but they suggested that you know in principle maybe it could be done.

30:40 Uh they have to assume a few things.

30:41 So it's certainly not for sure that it could be done.

30:44 But I find that quite fascinating because, you know,

30:47 then there would in a sense be a god,

30:50 but they wouldn't be a god like you might think of.

30:52 There's no reason to think they'd be a perfect being.

30:54 Uh they wouldn't.

30:55 In fact, what's super interesting about this, they

30:57 actually can't communicate with their creation in this scheme.

31:00 That the universe would be completely separated from from your space.

31:05 It would appear to you as a black

31:06 hole and you couldn't communicate it with at all.

31:08 I think it would evaporate as well.

31:10 So, it would be lost to you.

31:11 So the god could not communicate with their creation

31:14 and there'd be no reason to think they're a perfect being.

31:16 In fact Alan Guth who is a brilliant scientist and a lovely guy.

31:22 Um he did win an award for having the messiest office in Boston.

31:26 So not a perfectly um but nevertheless that's a fun idea to to play with.

31:31 I think Phil Halper thank you very much for coming to How the Light Gets In.

31:35 Thank you so much.

31:35 It's been a pleasure.