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Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now. StarTalk, Cosmic Queries Edition. Neil deGrasse Tyson here, your personal astrophysicist. And as is not always, but most of the time, Chuck Nice.

Hey. Co-host.

Good to be here, man.

We just fist bumped in front of our guests.

Yes, we did. How about me? Here we go, now we'll do a three-way fist bump. Three-way, three-way. Commuted to property of fist bumps.

Brian Green is our guest.

That's

right. We're doing Cosmic Queries Until the End of Time. I didn't just pull that out of an orifice.

I was gonna say.

It is actually the subtitle of the book.

And that's actually

the title.

That's the title.

That's the title.

No, the subtitle, what's the subtitle? Mind, Matter, and Our Search for Meaning in an Evolving Universe.

Nice.

That kind of means everything, right?

That is, But doesn't the universe automatically elicit questions of what is my purpose, my meaning, why?

That's why we have him here to talk about this for the show.

Oh, cool. I thought we were doing a cooking show.

So we solicited questions About this book. I don't know, people read your book already? Wow.

Is that possible?

It's conceivable.

I'm looking at the questions. I just know he's

got a fan base out there.

He does. And there is several of the questions of people who have already, they say, in your book. Okay, so, right. Look, look at this 1 right here. Your book, until the end of time, brings me to the conclusion.

Wow, look

at that. So there you go, man.

All right, so this is the Venn diagram that overlaps his fan base with our viewers.

There you go.

Because we solicited it from our viewers.

For your base, yeah, great.

There you go.

To our people, your people.

I love that.

All

right, so Chuck, you got the questions. Yes. Just to remind everybody how this works, it's Cosmic Queries, and these are solicited from our fan base.

That's right.

I have not seen them, certainly our guest hasn't. That's right. Chuck, you might have seen them.

I've read them before.

And Brian Green and I have very strong scientific overlap, but we're gonna get his view on this, and I'll just sit back and listen, and if he's full of shit,

I'll tell you. No you won't. No you won't. Thank you. Wow.

I will not sit back and look.

I've never heard that before.

And that, yeah. That was funny.

Plus I should have said it differently.

No, you won't. Brian Green

knows almost all the astrophysics I know. And I only know some of the physics he knows.

Nice. So he can

take my physics to new places.

That's very gracious. I don't know if it's true,

but it's

very gracious.

Thank you.

And he's a good mathematician too. All right.

Yeah. I mean, I'm going to say yes to that Because he's an astrophysicist and a physicist.

Math is a language of the universe in which he is fluent. Very cool. I'm delighted to have an old-time friend and colleague. All right. Let's do this.

Let's do this and as usual, we always start with a Patreon question. A question from our Patreon patron.

Oh, wait, wait, wait, excuse me.

Go ahead.

Brian Green is professor of physics at Columbia University.

Wow.

And also joint appointed in the Department of Mathematics.

That's great.

Wow. And He and his spouse co-founded the World Science Festival here in New York City every year, where science and art and music come together to celebrate science.

Wow. That's right.

He does this.

That is incredible. It's not

just some person who's sitting between us right now. Right. This is Brian Green.

I mean, he is still that. He's still that. I didn't want to undo the fact that he's a person sitting between us. Let's not demote him from personhood.

And I think this is his fourth book.

Yes,

right. Okay, and his first book that anyone knows about was a mega bestseller, which was?

The Elegant Universe.

The Elegant Universe. And he's 1 of our leading string theorists, and this was a way to share not only the frontier of his research with all the rest of us, give us a sense of hope that maybe 1 day we'll understand everything. Cool. Or not. Or not.

So that was a mega bestseller. And we shared publishers back then. We had the same publisher.

Oh, Norton?

W.W. Norton. Then he got so famous, he found another publisher. Yeah, yeah, yeah, yeah. And then he published another book after that, and it didn't do as well as the first book.

Okay? I just want to just hang some publisher.

You're just giving your publisher some cred right now.

Dirty laundry out here.

There you go. Okay.

Brian Greene, Alfred Knopf, publisher.

Let's do this. All right, here we go. As I said, we always start with a Patreon patron because they give us money. And this is Michael Tobias. He says, hello, Neil and Brian.

I often wonder how far we will journey through space within our lifetime will we be able to achieve interstellar travel or will the human race go extinct before we have the opportunity and technology now he started off with our lifetime but I think he means the lifetime of the species of human beings, because our lifetime, the answer is no, and I am not an astrophysicist at all.

Okay, we're done with that.

No, within the lifetime of the human species. First of all, what is the lifetime of a human species? What would that be? A few million years. A few million?

Well, that's a guess, right? If you look at the historical

trend. If you

look at the life expectancy of mammal species, 1 in 3000000 years, somewhere around there.

Yeah, but we're so much special, right? I mean, we have this thing on top of our head that able to figure things out. So either that is going to be our own destruction because we can build things that can kill ourselves or we'll be able to figure out a way of living beyond the traditional lifetime of many species. So unclear. But if you take...

But let me

answer that question. Yeah. There's what's possible in the laws of physics and there's what's within reach with our engineering. Absolutely. So give me your read on that.

Well, the laws of physics constrain any speed of any spacecraft traveling through space to be less than the speed of light. So if you're not going to play games with imagining that we can actually warp the fabric of space and

have warp drives. It's not playing games, that's real.

Yeah, well, you know, it's unclear that

we'll be able to achieve that.

It's real in every movie I've ever seen.

I agree, I agree. But taking the speed of a craft to be less than the speed of light, then I mean achieving great space travel is challenging, right? Now, the weird thing is, because time slows down when you have a spacecraft or a clock of any sort that's in motion, you could have a spacecraft going out near the speed of light, and we on Earth would watch its clock, and its clock would be ticking off time so slowly that to the person on the ship, they would be able to go much further than we would think they would be able to if we didn't take that into account. Right. So, you know, we could send, you know, some intrepid voyager out into space and they could go-

And near the speed of light.

Near the

speed of light, and they could go arbitrarily far in their lifetime.

In their lifetime.

Yes, so-

Then they come back home and everyone would have forgotten about them because hundreds of thousands of years would have passed.

Or millions or billions of years. You're absolutely right.

Right. Right. Wow. So that's not what people are imagining when they're thinking of space travel.

No. Yeah. I mean, so...

But it really matters, you know, if we were to take, you know, a group of our species and send them out into space, it really would be within their lifetime that they'd be able to, according to the laws of physics, go arbitrarily far. And so it's kind of, now you're right, the people back on Earth, they perhaps would be long extinct.

Wow, imagine you come back and your species isn't even around.

Right, yep.

And the roaches took over and the rats. Right. And they say, wait a minute, we're, you come back and there's a museum that the rats have and they're the skeletons of humans there.

That long ago, it's terrorized the...

Or they could even have an homage, an exhibit to the spacecraft that left a hundred thousand or a million years ago and you can sort of see the origin of your own trip.

Man. That's kind of cool though. I mean, you could actually, so. Okay, so you can,

but no 1 else can really participate in that.

Unless they're part of the literal journey.

Right, right, right.

Good answer. So now what about this in terms of when you say you put these people on a ship, all right? So you take a colony of people, you put them on a ship, and now they go and they're looking for some place to live. And now you're just seeding the universe, you know? Or at least another part of our galaxy, because you can't really say the universe,

you know.

Milky way.

The Milky Way, you know, because we're not gonna, how long would it take us to get out of the Milky Way?

Well, millions of years to the nearest galaxy.

Oh, there you go. So, but with that. Sorry, sorry.

Well, it's hundreds of thousands, you

know, a

hundred thousand light years across. Wait, wait, just get the numbers right. So our galaxy is about a hundred thousand light years across.

Light years across.

So if we watch you travel at the speed of light, it'll take us a hundred thousand years to observe that, but you could live an arbitrarily short amount of time, depending how fast

you go.

So that being said, you in principle could go to the Andromeda galaxy, 2000000 light years away. We are long dead here, maybe, and unless we're smart as Brian wants to believe we are. And so, yeah, so you could go and you could actually practice you want to you want to pass by stars not Devoid of empty intergalactic space

actually right right yeah, you want to go someplace where there's where there is something

But Brian's point that I'm take to heart is when I think of these ships I think that they're generational ships and they have to be really fertile people, make babies, babies grow up. But what's odd is you will be giving birth to children who will never have known Earth.

Yeah.

And that's kind of diabolical to me because they would not have had free choice to have taken that trip.

Do you

have any moral sense?

Well, you know, I don't think any of us have free choice or free will. So if you want to get into that part

of the conversation.

That's another thing.

Wow. You know, we can go there. Okay, let's just pull out 2 of those worms from that can. Wow, holy moly. All right, we'll get back to that.

Look it, we got, I can't, I can't.

Yeah, that's a big 1 right there. I don't

have a certain bandwidth.

Okay. All right, so let me ask you, and maybe- No,

I was just, I'm glad to be reminded that you can send a colony of people- Right. And they can get anywhere they want in their lifetime, provided they travel fast enough.

So now let me ask you this. Let's say they wanna, they're gonna go someplace even further, right? We're talking about true interstellar travel, right? Intergalactic. Intergalactic.

Because they're going to another galaxy, all right? And then they're coming back, okay? And they have kids and kids. What would that do? And maybe this is outside of your purview, I don't know what would that do to us as a species What would they be that much different from not having any of the effects of being on this spinning Rock going around this little teeny star that we live in right now

That's beyond my purview No,

I would say that it is possible to speciate. 1 of the ways you split a species is you strand a variety of yourself in a place and then there's no more communication. That's why every freaking animal looks so different in Australia. Okay?

But you still need sufficient time during their isolated periods. And in this case, it could only be even a handful of generations, right?

Right. But there still would

be generations, as you said, who would never have experienced life on planet Earth.

But you also need pressure to select against some features and promote others. So that those features then become something else that are not recognizable to where you came from.

Okay, I got you.

So you need that. And if that ship is exactly the environment that Earth has always been and

always will be. If you create 1G and you do all this stuff, you're not really creating a circumstance where there's a pressure to... A pressure.

But if you create a reality show where it's Survivor on the ship, and then you have artificial pressures, yeah, you could drive the species into some different place.

That's kind

of wild.

I think we just came up with...

So it wouldn't be natural selection, it would be artificial selection.

Yeah, that's right.

You just inject them from the ship and they...

All right, we're going to space you. All right, Let's do the next question. All right, here we go. This is Cheyenne Leo, who is also from Patreon. Cheyenne Leo, that's a nice name.

Hello, Mr. Green. I hail from Canada and I love your books. I've been wondering lately, what is time made of? I might be a little out there, but I was thinking that it must be made of something because presumably it was created in the Big Bang and it interacts with things like light and gravity.

Light takes time to get there, gravity slows it down in extreme circumstances, etc. Etc. So, if it can interact with other forces, shouldn't it be made of something? I love

that question.

It's a great question.

Yeah, when is something more than just an idea? When does it become a thing?

Well, this is an idea that is starting to become a thing right now. So it's certainly the case that the intuition of the question is right on target. When we look at ordinary material objects in the real world, they are made of stuff. They're made of molecules, made of atoms, made of subatomic particles. Could that idea be relevant for space and time themselves?

And people have thought about this for a long time, but recently there have been developments in a variety of fields, string theory being 1 of them, where we're starting to catch a glimpse of what the ingredients of space and time might actually be. And in fact, there's work that's being done that

shows that…

You're not talking about a time particle.

Not really a time particle per se, but it's easier to talk about this in space, even though space and time are really the same thing. But we have some evidence that space itself may be stitched by the threads of quantum entanglement. So this idea of quantum entanglement that links together distant objects in a way that makes it appear as though they're right next to each other in terms of their physical properties. It may be that the threads of quantum entanglement are the stitches in the fabric of space-time itself.

Is this where you get to the idea that in the distant future, where dark energy accelerates us ever greater, that it might accelerate us faster than quantum phenomenon can keep up, creating a tear in the fabric of space-time?

Yeah, and in fact, you don't even need to know about the ingredients in the fabric of space in

order to come to that conclusion. You didn't even

pause when I said that. That means it could really happen.

Yeah, So the idea that the dark energy might get stronger over time. So right now we all know that there is dark energy pushing the distant galaxies away.

We all

know. We've spoken about this before. We actually have.

We actually have. We actually have spoken about this before.

Exactly, exactly. Right, so, but it's possible that that dark energy gains strength over time, which means that it would not only drive the distant galaxies away ever more quickly, but it would start to drive even planets away from their stars.

And it

would even drive electrons away from the nucleus of atoms, which would rip matter apart. And yes, you're right, depending on the very nature of space-time, it could be that this dark energy growing over time might sunder space itself, might rip the fabric of space apart.

And then what's- That's amazing, you're talking about the actual tearing of the universe itself. Yeah. I

don't even wanna think about that.

Now I should point out that since you brought up the tearing of the fabric of space, a paper that I wrote with a couple of colleagues years ago was the first mathematical demonstration within string theory that the fabric of space can rip apart in a manner that would not yield a catastrophe. The fabric of space would repair itself and it would just be a new behavior within the repertoire of things that space can accomplish that Einstein would never have thought of. But Einstein didn't think about quantum mechanics and the general theory of relativity. And when you unite them, as string theory does, You get new things that space and time can do. And 1 of them may be tearing apart.

And it repairs itself.

And it

repairs itself. So it may not be as catastrophic as you think. And ointment

for that,

ointment. We have a salve. Put some mice on it.

But actually, it's not so much a sad. The strings and string theory can surround the tear and form more of a band-aid. So it's more that the strings form a band-aid that protects us from the rip in the fabric of space. And there's math behind this. It's not like

a crazy idea. I was

gonna say,

because that is- You look

very skeptical at this.

I did too because that sounds

eerily like- Just because it's math, don't hide behind this.

No, I'm not hiding, I'm just trying to

let you know. Math can talk about some crazy stuff that had nothing to do with reality, and you know it. Don't tell

me there's math behind it.

Of course. So therefore-

this emerges right from the most natural interpretation of the equations of strength. So I'm not standing on my head to make this happen.

Okay. No, that's

an important point.

It is. Because there's a lot of stuff that we think about where you have to go out in left field to try to get the explanation. But if this flows out of your stuff naturally, it's a beautiful thing.

Very cool. Can I

tell you what else happens?

Oh, please.

Black holes shrink down to a very small size, very small mass, and they transmute into elementary particles. So, black holes that you normally think as being kind of this big thing out in the cosmos, different from the fundamental constituents of matter. When space rips, the process that repairs it involves black holes turning into particles.

So, you know, he just made that up. Yeah. No, no, no. You had me until the universe

repairs itself.

I don't make that up. No, no, no.

No, No, black holes are the doctors and the nurses. No, I'm sorry. No, you're full

of shit now. Oh, man. Oh, okay. We gotta wrap this segment. We gotta wrap this segment.

I know,

I'm sorry. We're taking too long to answer

this question. No, no, we're not. This is great stuff.

Okay. When we come back.

Oh, I wish we were here every day, Brian. Oh, that

was amazing. More Cosmic Queries until the end of time. Questions from the heart of the cosmos when we return.

Hi, I'm Chris Cohen from Hallwarth, New Jersey, and I support StarTalk on Patreon. Please enjoy this episode of StarTalk Radio with your and my favorite personal astrophysicist, favorite personal astrophysicist Neil DeGrasse

Tyson. We've got Brian Green here. Yes. The 1, the only, longtime friend, colleague, love this man to death. He's been a friend of StarTalk

From the beginning.

From the beginning. Absolutely. This is not his first rodeo with us here. So Brian, congratulations on your fourth book.

Thank you.

And got a great write-up in the New York Times. Very enthusiastic write-up. And even when he was criticizing it, he was praising it.

Yeah, right.

It's like, oh, it got complicated, but it needed that. And I kind of liked it. And it got me into it. You know, it was like 1 of those kinds

of things. So who actually reviews your books? I'm serious. Like you 2 guys, you write these books. Who is it that sits down and says, okay, let me go through here and see.

This is mom.

Brian's mother. That's so funny. Intimate employee for the New York Times. Son, I have to tell you, I don't know about this whole thing about black holes and particles. So no, really, who is it?

I mean, I would say there's not a lot of people that can do that.

There's science editors. That's their job. If they can't handle it, then they don't review it.

There are

plenty of newspapers that don't review science books.

Oh, actually, the number of reviews of science books is going down because newspapers are really winnowing the staff

so people can do it. They're cutting their staff so they can't afford it. Wow.

So this just to give him credit because he's in the club, Dennis Overby, long time science writer and editor.

1 of the best, really.

For the New

York Times. And he leans cosmological, although when we demoted Pluto here, he wanted to dip into that. When I said, this is not your beat, this is too nearby for you. But I think he wanted some Pluto street cred.

Right.

So he did a little Pluto article on our demotion.

And was he for or against your postulate? He was antagonistic. Oh, okay. Yeah. I got you.

But anyhow, he's a long time editor and he has a book of his own.

Oh, yeah.

So the

real meta question is

who reviews the book? So did you

2 actually review his book?

I think he wrote a book, The Lonely Hearts of the

Cosmos, which

was about 2 astronomers trying to find the scale of the universe. Was that the book I'm remembering?

I don't remember the details.

Okay,

but it was biographical. Okay. Astronomers who had access to big telescopes. Alright. And you're there at night looking up at the night sky with the telescope and nobody else, lonely hearts of the cosmos.

Okay, that sounds about right. Okay, no, I'm joking. All right, here we go. Let's get back to our questions. This is CS201.

Hold it lowered so people can see

your beautiful face.

Sorry, here we go. CS211, I forgot We're on camera too. Hey, do you think the laws of physics are finite and knowable? Can we ever fully understand the universe in its entirety? If so, what forces might we be able to manipulate that are beyond us now?

Ooh. That's a very, very cool question.

No, it's a deep question because look, you look around the world and there are intelligent beings walking around, dogs, right? And they don't, we think, understand the general theory of relativity or quantum mechanics. So these are intelligent brains. Although when I say that, I always think the dogs are about there barking and

say, ah, he thinks you don't

understand general relativity. But seeing if that's really the case, then why do we think that the human brain would be able to understand it all? We may have limitations on the deep truths that we're able to grasp. Now having said that, there's no evidence that there's any limit to what we can figure out. We haven't hit the wall, right?

We did develop quantum mechanics, we did develop relativity, you know.

Wait, wait,

wait, wait, wait.

You and your compatriots have been at this string theory thing for 30 years.

Yeah, here we go. Here we go.

Maybe that's the wall. It could be. Maybe you guys aren't smart enough. You found the wall.

But here's what I would say to that.

Let me hold up a mirror to you

here, okay?

Who's the 1 who's at the edge of the wall?

See, but that would only be the case if we were sitting here saying we can't make any progress in understanding the mathematics of string theory. We're making incredible progress, but the thing is, in the part that you're responding to, which is completely justified, we haven't been able to make contact with observation or experiment. But that's not all that surprising when you're dealing with a theory whose energy scale is like 10 to the 15, 10 to the 16 times greater than that of the Large Hadron Collider, the most powerful machine in Geneva, Switzerland. So I agree that we have hit roadblocks, but it's not us theorists, it's the experimenters.

There you go. And if I might chime in here, let me just add...

That's the dog saying, we have a solution, but You just...

There's your answer, guys. You're neutering us and

you're taking us to...

And you're feeding me Alpo. Yeah. I don't know. Okay, cool, man. Oh, that's a great answer.

Wait, wait, so... That's a great answer.

Wait, wait, so let me...

Go ahead.

Let me give a nuance to that question and hand it back to him. All right. Okay, do you believe there may be missing laws of physics that'll help us get further, or that kind of all the laws of physics are there, we just need to be more creative with what we've got?

Yeah, I think it would be hubris.

That's

a little bit of that.

Yeah, it is, it is.

It's a different tact. Yeah, to think that we really have it right now would be sort of the classic act of hubris, right? I mean, every time we thought we figured it all out, there was a new law, there was a new particle, there was something else to find. So I would imagine at sufficiently high energy scales, we're gonna find new stuff, new particles.

Energy scales would be beyond where anyone has gone before.

Yeah, so right now.

Bold, too boldly go.

Yeah, so let's say we've basically gone on the order of 10, 000 times the mass of a proton, roughly speaking. Energy. Energy, energy scale. And we haven't found anything new yet. But I would imagine that between that scale and the so-called Planck scale, which is where the fundamental laws of quantum mechanics and gravity come together, that's 10 to the 19 times the mass of a proton.

So that's 19 orders of magnitude bigger than a proton, and we've only gone up to sort of 4 orders of magnitude bigger than a proton. So in that range, I suspect there's going to be something new to be found.

Okay. Because they, because just in all fairness to those who've come before us, they would be working in a tabletop, right? And there'd be some phenomenon they don't understand, and then they'd experiment with it, and then they'd isolate it, and name it, and characterize it, and mathematize it. And so, our basic known 4 forces of nature come out of that kind of experiment. Exactly.

Kind of tabletop plus simple particle accelerators, right? And astronomical observations. And observations. So, what you're saying is, that's a regime that manifested some aspects of nature that we have figured out in a tidy way. But there could be bigger questions we don't even get to yet, because we haven't tested the regime, and that regime is not on our table

top. Exactly.

Okay. That means the future of physics is big money, big accelerators.

That is 1 way.

The lone candle burning.

It's that, but I also like to think that if we're sufficiently clever, we might find indirect ways of probing realms that you'd think would require that big machine. But maybe we can be smarter about it.

Okay. On Star Trek, it's just all computer simulations. So.

By the way, just as a signal to my people, being clever, it was how are you gonna put a big telescope in orbit? Well, you can't make a rocket that wide. No, so you.

Build it, let's build it.

Well, you can build it in space, or you can get a mirror that unfurls, right?

All of

a sudden, the engineers say, hey, I got this. Let me be clever and figure it out. So we've actually overcome many challenges that previously were considered intractable just by clever people. Yeah, exactly. I'm echoing your point.

Yeah, yeah, exactly right.

That is super cool, super cool, super cool. All right, here we go. This is Janesh from Instagram. It says, finding slash creating your own meaning is fine, but objectively, What do you think, Brian, is the actual meaning of this creation? Yeah.

Ooh.

Yeah, that's

a big part of where you try to go in this book.

Yeah, and the answer that I give to that question, where I had to develop completely and more fully, I should say, not completely in the book, is that there is no ultimate meaning floating out there in the void, right? Throughout these-

I gotta go through all these pages to find out that there's

no meaning? Well, I'm gonna give you the- I

gotta read this for you to tell me There's no meaning?

Cliff notes, cliff notes right here. So the cliff notes are that we are the product of the mindless, purposeless laws of physics. We are all just bags of particles governed by those ironclad mathematical, that's it. And what we have the capacity to do, which is remarkable, is impose order, impose coherence, impose purpose and meaning on the external world and the internal conscious experience. And so it's not as though there are 2 things, the real answer that's floating out there in the void awaiting our discovery and sort of the internal 1 that we manufacture, it is only the internal 1 that we manufacture because there is nothing else.

How do you know this?

I don't know this beyond my experience in a lifetime of working with the laws of nature, the particles of nature and trying to give explanations for the things that we observe in the external world. So the particles are your gods? Well, you know, there is a place for religion.

You need to answer that question way faster

than that.

No, no, no. You don't want to go there. Let me think about it. My altar

has some neutrinos on it, but...

No, no, but honestly, seriously, I do think there's a role for religion that some of our colleagues step on and dismiss out of hand entirely.

And what would that be?

Well, it's not to understand the external world. No 1 can use any religious doctrine to calculate the electron's magnetic moment to 9 decimal places which is what we can do routinely with quantum field theory. But if you think about religion and the spiritual journey as something that doesn't illuminate the external world, but rather the internal world of conscious experience. Which many people go

to it for meaning in life.

Yes, exactly, then there is a role for it. And you don't judge it by whether it can explain the external world, that's not what it's meant to do. You judge it by whether it is a satisfying way of trying to understand your place in the universe.

90% of religious people would say that, the other 10% who are fundamentalists. Yeah, of

course, go different directions.

Get their science out of the Bible.

I agree, and that's problematic.

Enlightened religious people are where you're coming from. I agree.

That's very good. That was a little journey. I liked it,

man. I still think he's got an altar in his home. A neutrino

altar. I'm pretty sure.

He sacrifices to the particle gods.

I'm pretty sure. I'm pretty sure about that.

All right, okay, let's move on to Lee Bird, okay? So Lee Bird from Facebook says, hello, Dr. Tyson and Dr. Green. My wife has asked, where, where does our universe end?

Not how, but where does our universe end? And I would like to say, are there more than 1 ending? Is there an ending and then more endings? Are there levels of endings? That's a time

ending rather than a place ending.

Well, that's what I'm saying.

But is this a place ending? That's what I'm hearing.

No, that's a place.

You think it's a time ending?

Where? Where? Where's a place?

So there's a place ending.

Yeah. Where's the sign that says...

It says stop.

Stop here.

Can't go any further. Bridge is out. And look, the quick answer is we don't know, but the possibilities are space could go on infinitely far, in which case there never would be an end. That's a strange idea to us beings that live in a finite environment, but nevertheless the math allows that as a real possibility. Or space could be curved, which means you could go out in that direction and ultimately circle back and return to your starting point.

So there again wouldn't be an end, but nevertheless the space would be finite in its extent. So these are sort of 2 big

possibilities people think about. So you could travel an infinitely finite space.

Yeah, infinite, yeah.

You could go infinitely far, but it would be a finite extent.

You're talking

about infinite, right?

Like the surface of the earth.

Yeah, like the surface of the earth. Exactly.

Wow. So the answer is you don't know.

Neither do you.

You didn't ask me.

You're asserting I

don't know. You didn't

ask me. I can tell you this.

Yes.

We look out to the edge of the observable universe and we see light that has been traveling for 13.8 billion years. That gives us evidence of the Big Bang for that part of the universe experiencing it at the time it emitted that light. That horizon continues to push out. Right. As long as we keep seeing evidence of the Big Bang, we are still moving into a universe that's our whole.

Imagine the day where that horizon washes over the last bit of matter that experienced the Big Bang. Then the information coming to us about the Big Bang ceases. And all of what we know of cosmology would have no data set at that point. And at that point, you're basically, the moving horizon which gets 1 light year away from us per year, at that speed, would have overtaken the last matter of the universe and that would be the edge of the universe. Do you agree with that?

Well, there's a version of that that I think I can agree with more precisely, which is...

I meant no, but he's

a guest on my show. He's a guest, he's gotta be polite.

By the way,

I am taking notes. I gotta learn to talk to my wife like this. I have got to learn how to talk to her like this. Would you agree? Well, there's a verbal 1 that I would agree with more precisely, dear.

Everything but the dear. He didn't say dear. Can I get a dear out of that, please? Throw the brother a dear, at least.

So even right now, with the accelerated expansion of space, We can do calculations that show us quite clearly that the distant galaxies that we have used to figure out this space is expanding They are going to disappear over the cosmological horizon. We will not be able to see them in roughly 100 billion or a trillion years. So the evidence that we've used to even figure out that space is expanding.

It's going away. It's

going away.

What you're saying is the matter that is giving us this information will overtake the moving horizon. And then it's a moot point.

Yeah, It'll basically drop over a cliff at the edge of space, which is the horizon, because it's moving away so quickly.

Yeah, outrunning your headlights. Yeah. Ooh. That's what you're doing. Yeah.

That's cool, man. All right.

Okay, we gotta take

a break. Oh, Really?

I know.

This is so good.

I know.

I forgot we were doing a show.

I know, right? Of course, I still get my deer out of that. Deer. Deer.

That's a different marriage. That's a real 1. That's a real marriage.

All right, StarTalk, Cosmic Queries, Brian Green, Chuck Nice. We'll be right back. Start call, we're back. Cosmic Queries, Until the End of Time. Search for meaning in the universe and Brian Green goes there.

He does. In how many pages, Brian?

Oh, it's only 300. A lot of end notes. That's why it looks so thick.

Oh, there you go. That's a nice picture of you.

Thank you.

Yeah, nice picture. Oh, wow. And it's recent and handsome. 5 minutes ago. Not like a Tinder picture.

Like, wait a minute, this dude is

23. So Chuck, give us the questions. All right. That's our

last thing. Let's see how many we can squeeze in. Real quick, real quick, we'll get a quick, let me just ask a quick question for myself. All right, we're able, this is hypothetical because we're not able to, but we're able to get beyond this horizon that you were talking about. We're able to observe that there, whatever, right?

But now we are outside of the universe that was created at the Big Bang. What is time in that place?

Well, it could be the same as time here. So that cosmological horizon is, as Neal was pointing out, just the distance that we can possibly see because light has had the time to travel from it to us since the Big Bang. But it could be that time applies throughout this realm of space,

And

it could be that it looks out there much like it looks in here It's not as though you pass through it and you've been in some entirely new domain However, it's possible that it could be different since we've never been there the math suggests that it will be the same But were it different that would be shocking and wonderful.

Wait, wait, but Brian, let me take issue with that.

Yeah, please. Dear. Yeah. Yes. Yes.

Yes.

The horizon is not a real place.

Yeah.

It's just the property of where we are

and the

speed of light. Yes. So when I'm a-

So that's what I meant,

but yeah.

Well, when I'm a ship at sea, and I go to my horizon, whatever 10 miles away, now I have a new horizon,

and I'm still at sea.

Exactly.

So why are you telling me something different is

gonna happen?

No, that's my point. I believe that that will be the

case in the universe. But it's also conceivable.

That is not what he said.

No, no, but it's conceivable. You would agree that when you take your ship, it's possible that when you reach your current horizon, it could be that things are completely different. It could be the dragons are there. It could be the gates of hell.

There'd be

dragons. You've never been there.

Or you'd have to presume that at exactly that distance, and you were in the middle of where all those dragons were. And that's

kind of-

It's a

very special space. That's a very special space. I can't- That was the point. So if I said

it- I can't go wrong with that.

Yeah, so if I didn't say it clearly, I suspect, and the math strongly argues, that it will be the same out there. But it's conceivable that it would be different.

But I get, what I really get out of that, and maybe it just helped me out here, what you're saying then is what we are seeing is a reference, That's what we're seeing. We're not really seeing an edge, we're not seeing, we're seeing a reference is what we're seeing.

Any more than a ship at sea, that's not the edge of the earth. You can think it's the edge of the earth, and it might be the edge of the earth, it probably isn't.

However. Uh-oh. Uh-oh. Uh-oh, Getting

too much time to think.

Oh my God. I should point out.

I should point out.

Here we go.

I should point out that in a universe where the spatial expansion is accelerating, that cosmological horizon would actually have a temperature. You're right. It's not a real location in space, but from that spot we would have heat emerging that would give a background temperature that at the moment would be about 10 to the minus 30 Kelvin. So it actually has a physical presence even though it is in some sense just a reference.

It's a thing to measure. Oh, I love that. A thing to measure.

That is

awesome. I love things to measure.

Moreover, can I point out, just since we're going on this tangent, that temperature that comes from that distant cosmological horizon may imperil the future of thought itself? Uh-oh. So 1 of the things I describe in the book is that in the far future, any kind of- That's where the

book ends, the thought ends.

Yeah, it is.

I don't

get my

limits. It's close, at the end of thought. It ends like this, I'm cold.

Never hears the idea.

Go ahead.

So any cogitating being through the act of thought has to release heat, right? Second law of thermodynamics. And if it's the case that that cogitating being can't release its heat, it will burn up. And because of the heat emitted by the distant cosmological horizon, in the far future, a cogitating being will not be able to release that heat, and if it thinks 1 more thought- But

that's not very much heat.

I know, but in the far future- That's all you got. That's all you got.

Oh, that's all you got. Yeah. So you're saying, oh, this is scary. Don't tell me this. Yeah.

Oh, now I'm sad.

Yeah. Now

you're gonna read the book.

No, okay, no. Now, let me repeat what I think you said. That every act of thinking is a thermodynamic electrochemical process, as far as we know. Yeah. So that creates heat that needs to dissipate so that you can have your next thought.

If the bath, the thermal bath in which you were immersed has a greater temperature than the temperature of your thoughts, then your thoughts will back up and overheat and you can't sustain that.

Yeah, that's the basic idea.

Like an overloading phaser. Yeah. Yes! Yeah, yeah. Very good.

But now it's the brain of the thinking being.

But now it's the brain that's actually doing that.

So it tries to

think and

it explodes. It forgot all about the overweight and it self-destructs. Self-destructs. Wow! All right, let's get back to this.

Okay, we're short on time. Okay, all right.

All right, what

do you got? Here we go. This is Juan91 on Instagram, Juan91. He says, hi, Neil and Brian.

Is that 911? It's just. It is 911. It is?

It is. Okay. That is great.

You were absolutely right,

it's 911. And he goes, hi, Neil and Brian, and maybe Chuck. My question is the following. Hypothetically, if we were living in a universe where we can increase or lower the entropy. Would it be possible to travel in time?

Greetings from Montreal, I really love the podcast and it makes my commute all the way.

So let me reshape that so more people can be part of that. So as you know, and as you've written, the increase of entropy is 1 of the arrows of time. So if we somehow had control over entropy in the universe to reverse it, will that imbue us with powers over the arrow of time?

I don't think so. So you're right, we often do think about entropy and its relentless increase as an arrow of time, but if it were to reverse itself, time would still carry on in the direction that it was always traveling. We would just see some weird things happening in the environment around us. We might see, for instance, eggs unbreak or candles unburn, but it wouldn't be time going backward, it'd be those physical processes going backwards.

Okay,

so. Now, if everything went backwards, that would be something else, but that's not what the question is. It's just we're able to reduce entropy in some way.

Okay, so if we're able to reduce entropy of the universe, because we know we can do it locally, that's what life is. Yeah. Life is organized matter, so it has lower entropy than it would otherwise have if life did not form, we're using energy from the Sun basically to do this. So if we somehow did have power over entropy of the entire universe, do you think that would have any consequences at all?

Well yeah, I mean it would radically change our predictions for what will happen in the far future you know

yeah yeah things that our understanding of nature is so intermixed intertwined with an increase in entropy yeah that if entropy Systemically decreased we have to rethink what with what would cause and what was effect?

That's right, and we'd have to rethink where we are headed in the far future.

Yeah. Yeah. Okay, that's really cool Okay. All right. Let's do this 1

and I have to rewrite 1 of the chapters of my book

team Forsyth Team Forsyth Observatory on Instagram would like to know, hello Neil, Brian, and Chuck, what do you all believe would be the world's religions response when we are contacted from another civilization outside of our own existence. Give it

to me, where you at?

There you go.

Yeah, I don't think it will make all that much of a difference. I think the nature of reality for us scientists would change completely because now we'd have a second instantiation of life out there in the universe, which would be a radical moment. But I think for the world's religions.

No, I

just like

the intelligent life.

Oh, intelligent, even better, yeah. But for the world's religions, I don't think that there'd be much of a difference because they have a certain perspective on where we've come from and why we're here and what we're doing and I don't think that the existence of additional intelligent life would really change things in any substantial way.

Oh, okay. Let me just put, let me do this for both of you. Here's the deal. That same thing, but now, here's the deal. Those beings tell us, we put you here.

Now, what do the religions do?

Well, so there's already religion about that.

What they

call the Ray aliens What? Just saying I'm just it's

true. Yes Is this really

the Ray aliens? So so this religion is a religion where God is not God as imagined in the Hebrew Bible, but God is an intelligent race of aliens that created us. Really? And so there's strong overlap with a God, because if a God created us, and they're the external thing.

Well, there's a creator.

A creator, right. So there's a whole religion that's already there, is my point.

So they would just be like, told ya. Exactly.

But to your point, there are some religions or some branches of religions where it is very important to them that the universe was created for us and for no other life. They would have an issue with this. But most religions have gotten past that. And religions are more than just belief systems, they're also institutions. And institutions generally have their own survival as a fundamental part of what they do and why they do it.

And moreover, There

are so many religions already practiced on planet Earth and each 1 needs to deal with the existence of the others. The other religions. The other religions. And they're able to do that by virtue of saying ours is the real 1 and theirs is not.

So I

think we'd have that same kind of response if aliens came down. But to your point about Ray-aliens, if that's the name of it, there's also the simulation hypothesis, right? If we are all just a simulation of future supercomputer, then again, there's a god-like being, the kid in the garage who's fired up the supercomputer, and again, you don't have anything supernatural, and yet we would be the outcome of a creator's desires, wishes, whims because that kid fired up that simulation.

Hmm, okay.

So he has another altar and it's a kid.

The kid god as well.

That's not his altar. Right, gotcha. All right, let's see if we can get another 1 in. This is Ascot. I think

we can. Ascot.

He says, from Twitter, since the beginning of our civilization, the human mind and consciousness have evolved so much. Can the human brain figure out the human consciousness? In what ways can we confidently predict that we will acquire the ability to comprehend the majesty of the cosmos?

So do you get into consciousness?

I do, yeah, there's

a whole focus on it. So we gotta go quick, what's your take on it?

My take is that consciousness is an exquisite physical process, but nothing more than a physical process. It is simply particles coursing through a gloppy gray structure inside our heads, again, fully determined by physical law.

Do you think it was emergent?

And is the organism, yes, it certainly emerged by virtue of the organization of this structure inside of our heads. I don't think there's anything else beyond the particles and the laws of physics required for consciousness to exist. I mean, do you?

No, no, I'm not convinced by so much of what's written about consciousness. I mean, the fact that there's so many books on consciousness and everybody's talking about it, it means no 1 knows anything about it. The evidence you don't know anything is people keep writing about it, right? How many people are still writing about Einstein's general relativity? The book is on the shelf.

Of course,

yeah, yeah. Right?

Yeah, so it is, but I agree. I think everyone would agree, it is a grand mystery. You know, where does consciousness come from? And many take the approach that we know historically, people use with life. People thought vitalism.

It couldn't just be particles in the laws of physics. You gotta inject something else, a life force. Nobody talks that way any longer, right? And now- Some Christians

will talk about a soul.

Right, but few scientists think that way any longer. Similarly, there are some scientists who think you have to inject something into the particles and the forces to get conscious self-awareness. I think

100

or 1, 000 or whatever number of years from now, people will look back and smile at how quaint that idea was, but there's nothing more than particles and physical laws.

What was the question about consciousness though?

Will we be able to understand consciousness and then using that, be able to understand or comprehend the majesty of the cosmos?

So let me reshape that. So is there a level of consciousness that awaits us that will enable us to appreciate the cosmos even deeper than we already

do. Yeah, I certainly hope so.

I mean, what a level of awareness that is.

Yeah, you

know, I think as we learn more about reality, we reshape our sense of who we are and what the grand mysteries of existence are. And I think that's a beautiful journey that we've been on for thousands of years and it will carry onward.

Ooh. Cool.

Those are some final thoughts.

Those are very good final thoughts.

Yeah. Brian,

you don't come by often enough. Invite me, I'll be here. I'll be here. I'll be here. Dear.

We have to write him, Dear. We have to

invite him more often than the rate at which he writes books. That's the problem. There you go. All right, Brian, always good to have you.

Thank you, sir.

Chuck. It's a pleasure. My boy.

My man. All right, this has been Cosmic Queries. I'll just have to say it, the Brian Greene edition. Yeah. Yeah.

All right, Neil deGrasse Tyson here, your personal astrophysicist, as always bidding

You