Speaker 1: My welcome to Stuff to Blow Your Mind, the production
Speaker 1: of My Heart Radio. Hey you welcome to Stuff to
Speaker 1: Blow Your Mind. My name is Robert Lamb and I'm
Speaker 1: Joe McCormick. And for today's episode, we're going to be
Speaker 1: chatting with Daniel Whitson, who is a particle physicist and
Speaker 1: science communicator and one of the hosts of the podcast
Speaker 1: Daniel and Jorge Explain the Universe. This is Daniel's third
Speaker 1: time hopping on the show with us. The previous episodes
Speaker 1: were in September of twenty nineteen and April of And
Speaker 1: for this episode, we're gonna be talking about a book.
Speaker 1: Daniel and his co host and co author Jorge cham
Speaker 1: have a new book called Frequently Asked Questions about the Universe.
Speaker 1: So it was a real pleasure to have Daniel on
Speaker 1: the show for the hat trick, and I guess without
Speaker 1: any further delay, we will go right into the interview. Daniel,
Speaker 1: welcome back to the show. We're so glad you're here.
Speaker 1: Thanks very much for having me back. Always fun to
Speaker 1: talk to you guys about things that blew my mind. Awesome,
Speaker 1: So um, the podcast Daniel and Jorge Explain the Universe
Speaker 1: still going strong um. How how far are you into
Speaker 1: explaining the universe in its entirely? We have explained zero
Speaker 1: point zero zero zero zero zero zero zero zero one
Speaker 1: percent of the universe so far. Nice. I actually I
Speaker 1: was looking at your recent episodes and I saw did
Speaker 1: you recently do one that was an interview with Sean
Speaker 1: Carroll about the uh, the many worlds interpretation of quantum mechanics.
Speaker 1: I know, I know he favors that, right. Yeah, we
Speaker 1: actually have a series where I interview an expert on
Speaker 1: each of the interpretations of quantum mechanics. We did one
Speaker 1: on Copenhagen interpretation with annam Becker, We did one on
Speaker 1: the relational interpretation of quantum mechanics with Carlo Rovelli, and
Speaker 1: then we talked to Sean about many Worlds interpretation. And
Speaker 1: just a couple of weeks ago we did one about
Speaker 1: the pilot wave theory of quantum mechanics, which totally blew
Speaker 1: my mind. Really much overlooked and unnecessarily maligned interpretation of
Speaker 1: quantum mechanics, in my opinion, malign, like people are being
Speaker 1: mean to it. Well, there's this famous proof by John
Speaker 1: von Neuman like seventy years ago demonstrating that it was
Speaker 1: essentially impossible, and because von Neuman is such a giant
Speaker 1: of the field, everybody thought, well, that's that. Turns out
Speaker 1: he was wrong, though, and and it took people years
Speaker 1: to figure it out. It was Bell actually who figured
Speaker 1: out that Noeman was wrong, and that it's possible to
Speaker 1: have a theory of quantum mechanics with hidden variables that's deterministic,
Speaker 1: that's not random at all um. But still to this day,
Speaker 1: nobody really takes pilot wave theory seriously, to Bell's great restoration.
Speaker 1: And I think it's because Neuman sort of threw shade
Speaker 1: on it decades ago and it never really recovered. I
Speaker 1: guess that's always dangerous when there's like a famously smart
Speaker 1: person who has an opinion absolutely and I find that
Speaker 1: physics Nobel Prize winners are especially guilty of this imagining
Speaker 1: that they are experts in every corner of everything and
Speaker 1: opining on economics or you know, social politics or whatever.
Speaker 1: If you have Nobel Prize winner in front of your name,
Speaker 1: you're an expert. Uh So, today we wanted to talk
Speaker 1: about a couple of chapters that are in a book
Speaker 1: of yours. Did that come out earlier this year? Tell
Speaker 1: us a bit about the book. Yeah, so the book
Speaker 1: is called Frequently Asked Questions about the Universe that I
Speaker 1: wrote together with my co host on the podcast and
Speaker 1: longtime collaborator Or Cham who's also famous for being the
Speaker 1: genius behind PhD comics. And the book comes from noticing
Speaker 1: that people who write into our podcast often ask similar
Speaker 1: types of questions. There are a few things that seems
Speaker 1: like everybody just wants to know about or understand or
Speaker 1: the things that people grapple with. You know, I'm a
Speaker 1: professional particle physicist in my day job, um, and so
Speaker 1: I like asking questions about, you know, the deep nature
Speaker 1: of the universe, usend, how our space and time really related.
Speaker 1: But you don't have to be a professor of physics
Speaker 1: to find these things interesting. And we feel like, in
Speaker 1: a sense, you know, curiosity is democratic. Everybody wonders about
Speaker 1: these things. So we wanted to try to attack some
Speaker 1: of these really big questions that everybody wonders about in
Speaker 1: an approachable way, in a way that doesn't require you
Speaker 1: to really have any knowledge of modern physics at all. Yeah.
Speaker 1: I've really been enjoying the chapter as I was reading.
Speaker 1: One thing I like that you do in this book
Speaker 1: is um is that you know, it's not like a
Speaker 1: continuous narrative that has to you have to have read
Speaker 1: everything that came before in order to understand. Like, the
Speaker 1: chapters can be consumed pretty much on their own, right. Yeah,
Speaker 1: we figured, you know, each chapter should be like one
Speaker 1: long bathroom break. So I mean, I'm not telling you
Speaker 1: where to read it, but if you're looking for reading
Speaker 1: while you're busy sitting down doing something else, each chapter
Speaker 1: you know, should entertain you while you're doing your business.
Speaker 1: Just you know, don't get so distracted that you forget
Speaker 1: to flush right now. Obviously this edition would lack the
Speaker 1: wonderful illustrations that are in the print and the Kendall version.
Speaker 1: But um, but you guys put together an audio version
Speaker 1: as well, right, yes we did. We got to record
Speaker 1: the audio version of the book, which is out now also,
Speaker 1: and the chapters are read by me and by Jorge alternating,
Speaker 1: which is a lot of fun just sort of hear
Speaker 1: your words come to life. But yes, the audiobook does
Speaker 1: miss some other the real genius of Jorge's drawings. Um.
Speaker 1: Jorge and I started working together on science communication more
Speaker 1: than ten years ago when I reached out to him
Speaker 1: because I thought that cartoons would be a really great
Speaker 1: medium for communicating science because they don't take themselves seriously,
Speaker 1: you know, they're a cartoon is different from like a
Speaker 1: figure into science paper, you know, which is very official
Speaker 1: and formal. A cartoon like makes fun of itself and
Speaker 1: is easy to you know, hang out with and accessible.
Speaker 1: And Jorge was great at that kind of stuff. So
Speaker 1: he and I started working together on explaining science using
Speaker 1: cartoon is a long time ago. Um, And one thing
Speaker 1: I really value about his cartoons is not just that
Speaker 1: they are good visual explainers. He has a real visual
Speaker 1: skill for explaining something simply on the page, but also
Speaker 1: that there's sort of a second voice there you can hear,
Speaker 1: like in the text is the voice of me as
Speaker 1: a physicist, and then the cartoons you can hear sort
Speaker 1: of his response to some of the crazy ideas UM.
Speaker 1: And that sort of mirrors the way the podcast works.
Speaker 1: On the podcast, I'm talking about physics and Jorges you
Speaker 1: know something like that doesn't make any sense, or how
Speaker 1: could that possibly be? Or what you got to explain
Speaker 1: that again? Because so it sort of tries to capture
Speaker 1: those two voices. Yeah, I really liked that the the
Speaker 1: illustrations almost seem kind of riffing on the written contents
Speaker 1: of the book. Well, so, the parts of the book
Speaker 1: that we wanted to focus on today, I think we're
Speaker 1: mostly centered around the idea of time and so maybe
Speaker 1: maybe a good place to start is you have a
Speaker 1: chapter in the book where you talk about time travel
Speaker 1: and you make some arguments about which types of time
Speaker 1: travel are plausible from a physics perspective and which are not.
Speaker 1: So maybe that would be a good place to start
Speaker 1: to give us the way of the land, like what
Speaker 1: types of time travel are the least consistent with the
Speaker 1: known laws of physics and which are the most consistent. Yeah. Sure,
Speaker 1: So for those of your listeners who are busy building
Speaker 1: their time travel devices, of this useful advice. Well, you know,
Speaker 1: the kind of time travel that's most inconsistent with the
Speaker 1: law of physics is the kind that most people want
Speaker 1: to do, you know, which is I want to go
Speaker 1: back in time and change something. I want to not
Speaker 1: spill my coffee on my lap, or I wanted to
Speaker 1: go you know, not um make a mistake, or I
Speaker 1: want to go ask that person out in high school,
Speaker 1: which I was too timid to do. And now I
Speaker 1: realized I should have that kind of thing. It's not
Speaker 1: just that it's ruled out by the laws of physics.
Speaker 1: In my view, it's not even sort of internally self
Speaker 1: consistent what it means um, you know, and and a
Speaker 1: lot of people think about time travel is like I
Speaker 1: want to go back in time, as if time was
Speaker 1: a place, like if it's a somewhere you can go.
Speaker 1: It's just sort of like along a different direction or something.
Speaker 1: And it's tempting to think about it that way because
Speaker 1: we we hear a lot about modern physics telling us
Speaker 1: that space and time are related and time is like
Speaker 1: a fourth dimension of space, and so it makes you
Speaker 1: want to think about time as a direction in which
Speaker 1: you can move and maybe you could just rewind it somehow, right,
Speaker 1: But the problem is that time. You know, first of all,
Speaker 1: we don't understand time like at all, and we can
Speaker 1: dig into that in a minute if you like. Um.
Speaker 1: But the problem is that time sort of reflects how
Speaker 1: the universe changes. And so you know, I think about
Speaker 1: time is like you have a timeline. That timeline is
Speaker 1: the universe changing, Like you have the universe at one moment,
Speaker 1: and you have the universe at another moment. The next
Speaker 1: moment comes later in time, and things can't change without time.
Speaker 1: Time is that change. So the self consistency problem is
Speaker 1: that going back in time to change it changes the
Speaker 1: timeline itself. So like, how does the timeline change If
Speaker 1: the timeline is the change, how does the timeline itself change?
Speaker 1: It would need like its own time, Like the timeline
Speaker 1: is now moving through time because it was a time
Speaker 1: before you changed in a time after you changed it.
Speaker 1: So it needs like a second dimension of time. I mean,
Speaker 1: it just sort of all becomes very complicated and falls
Speaker 1: apart as soon as you start thinking about it carefully.
Speaker 1: So going back and changing something in the past really
Speaker 1: just makes no sense from a physics point of view. Yeah,
Speaker 1: I love this because I have long kind of been
Speaker 1: skeptical about the idea of time travel into the past.
Speaker 1: And one of the reasons I had doubts about this
Speaker 1: is that wouldn't we expect to have already encountered lots
Speaker 1: of time travelers at some point in history? And there's
Speaker 1: no unambiguous evidence of that. I mean, obviously some people,
Speaker 1: you know, they're weird little things people think or time travel,
Speaker 1: but nothing that looks really clear. So It kind of
Speaker 1: makes me think that if if time travel into the
Speaker 1: past ever happens in the future, it will be of
Speaker 1: a very limited nature. Yeah, I love that as an
Speaker 1: experimental proof, you know, like, if time travel exists any
Speaker 1: time in the future, then you would expect to see it. Now.
Speaker 1: I love that. It's just such a powerful argument. It
Speaker 1: sort of reminds me of Stephen Hawking's famous invitation to
Speaker 1: time travelers where he threw a party and then he
Speaker 1: posted the invitation later after the party. The idea of
Speaker 1: being the time travelers, you know, they should be able
Speaker 1: to get there anyway, And of course nobody showed up
Speaker 1: to his party. Well we know he might have dispensed
Speaker 1: with them, or maybe he is a time traveler. Oh
Speaker 1: that's a good premise for a sci fi movie like
Speaker 1: The Time Traveler Hunters, trying to eliminate all evidence of
Speaker 1: the time travelers. Well that that kind of plays into um,
Speaker 1: you know, someone, what you're talking about about it being
Speaker 1: if it if it does exist in the future, then
Speaker 1: it must be limited in scope. And I guess you
Speaker 1: could look at it a couple of different We could
Speaker 1: basically just scify the hell out of it in multiple directions.
Speaker 1: But you know, you could say, like, well, maybe travel
Speaker 1: into the past. It has a range, and we haven't
Speaker 1: reached the point to where time machines of the future
Speaker 1: can reach us. Or it's just so tightly policed that
Speaker 1: nobody can make it back. You know, we have time
Speaker 1: cops or or something that are that are keeping people
Speaker 1: from making too much of a show of the whole thing.
Speaker 1: There's so many of those science fiction depictions of like
Speaker 1: a big time bureaucracy, you know that's managing the time flow,
Speaker 1: like you saw that in Loki and in Umbrella Academy
Speaker 1: and and It and in um that book recently, this
Speaker 1: is how you win the time war. And those can
Speaker 1: be a lot of fun, but also I feel like
Speaker 1: they're they just make no sense at all. You know,
Speaker 1: how do you have this weird administration that's separated from
Speaker 1: time and also weirdly frozen in like nineties bureaucracy. It's
Speaker 1: you know, it's fun, but not not if you think
Speaker 1: about it really at all. What also reminds me a
Speaker 1: lot of something I was actually chatting with you about
Speaker 1: a couple of weeks ago, when I interviewed you for
Speaker 1: a short freelance piece for How Stuff works dot com
Speaker 1: about UM about the zoo hypothesis. Uh you you spoke
Speaker 1: about about that for the interview, and uh you mentioned
Speaker 1: that one of the strong arguments against it is that
Speaker 1: if there is actually this, um, this conspiracy of of
Speaker 1: aliens to avoid contact with humans and and and keep
Speaker 1: us in the dark about the uh you know, the
Speaker 1: galactic civilizations just outside of our view, UM, the main
Speaker 1: argument against it is that governments as we know them,
Speaker 1: by the only model that we know the the the
Speaker 1: human model, are not really good at keeping secrets. They're
Speaker 1: not good at advanaging secrets. And it seems like you
Speaker 1: could also apply that to the idea of intelligent beings
Speaker 1: or humans and the future managing the timeline and so forth. Exactly,
Speaker 1: you know, some version of Elon Musk and the future
Speaker 1: is get his hands on it, and he's gonna launch
Speaker 1: a bunch of crazy, you know, missions, and somebody's gonna
Speaker 1: mess something up. So it's hard to imagine that people
Speaker 1: in the future having time travel and somehow keeping a
Speaker 1: secretor slipping into the past unnoticed and nobody ever, you know,
Speaker 1: breaking the protocol or something. It's it just becomes totally
Speaker 1: implausible the more you think about it. Picking up off that.
Speaker 1: I mean, this is another one of the weird things
Speaker 1: about time is it seems like time is actually one
Speaker 1: of the arguments against the idea of a coherent galactic civilization,
Speaker 1: if this makes any sense, because like you think, a
Speaker 1: civilization in order to organize itself, has to have some
Speaker 1: pretty close to synchronous uh, you know, thing going on,
Speaker 1: Like things have to be happening pretty close to around
Speaker 1: the same time for them. But does it even make
Speaker 1: sense for I don't know, one planet in a galactic
Speaker 1: civilization to be part of a civilization with one on
Speaker 1: the other side of the galaxy. I mean, is there
Speaker 1: you know, can they say, uh, is there such a thing?
Speaker 1: Is what's happening right now on a planet on the
Speaker 1: other side of the galaxy? Yeah. You make a great point,
Speaker 1: because there's a speed limit to information moving through the universe,
Speaker 1: which puts an effective limit on like how well you
Speaker 1: can coordinate and organize things. Actually, think about this in
Speaker 1: cosmology all the time, because there's a like the largest
Speaker 1: thing that can exist in the universe just from very
Speaker 1: simple arguments like the age of the universe and the
Speaker 1: speed of light. You can't have an object that's like
Speaker 1: ten thousand billion light years wide, that's like coordinated, that
Speaker 1: has like a structure that's like gravitationally bound on itself,
Speaker 1: because there hasn't been time for like a photon to
Speaker 1: even cross over the entire size of that object. So
Speaker 1: there's like a limit to how big the universe can
Speaker 1: even build like a thing, not to mention like the
Speaker 1: close coordination required to like organize a galactic empire. And
Speaker 1: so yeah, absolutely, um, I think that the sheer size
Speaker 1: of space definitely limits our ability to exploit it unless
Speaker 1: it breaks down into you know, lots of different unorganized entities,
Speaker 1: Like maybe we send humans in an arc off to
Speaker 1: another star and they start their own human colony and
Speaker 1: we're not in touch and a part of them, you know,
Speaker 1: political nation state. But at least we're humans here and
Speaker 1: there are humans there. Yeah, I think that's a great
Speaker 1: way to conceptualize it. So, I guess coming back to
Speaker 1: time travel for a minute, I wanted to talk about
Speaker 1: some of the specifics you offer about physically plausible ways
Speaker 1: of traveling into the past. Uh. So you mentioned a
Speaker 1: couple of things. You mentioned the idea of wormholes, and
Speaker 1: then you also mentioned one that might be less familiar
Speaker 1: to people. The idea of an infinitely long cylinder of
Speaker 1: spinning dust, which could potentially, at least maybe depending on
Speaker 1: something about whether something about relativity is true or not,
Speaker 1: could potentially allow time travel into the past through something
Speaker 1: called time loops. Could could you explain how this would work? Like,
Speaker 1: what would this experience be like for the time traveler? Yeah, well,
Speaker 1: the short answer is, we just don't know. Uh, this
Speaker 1: is a realm where we are like on the cutting edge. Theoretically,
Speaker 1: people are looking at the rules of how space and
Speaker 1: time bend and twist because you know, general relativity, our
Speaker 1: theory for space and time itself essentially tells us that
Speaker 1: space and time bend in response to mass and then
Speaker 1: tell masses how to move. So, for example, you have
Speaker 1: an empty universe and you put a star in it,
Speaker 1: it bends the space around the star, and then the
Speaker 1: bending of that space tells things how to move, and
Speaker 1: not just through space but also through time. So you
Speaker 1: go near a black hole, for example, time is slowed down.
Speaker 1: So there's definitely some deep connection there between space and
Speaker 1: time and what people have done is trying to explore
Speaker 1: extreme scenarios about what happens if you do this, what
Speaker 1: happens if you do that? Is this allowed? Is that allowed?
Speaker 1: And so it's sort of like exploring the universe, but
Speaker 1: just inside our own heads. We can't necessarily yet go
Speaker 1: out there and build these things in space and say,
Speaker 1: let's see what happens experimentally, but we can do similar
Speaker 1: like fought experiments, where we say, what would happen if
Speaker 1: you did this, and let's just let's assume the equations
Speaker 1: are correct and see what happens. And so there's a
Speaker 1: couple of fund scenarios there. One, as you said, is wormholes.
Speaker 1: These aren't really crazy because they are like connections between
Speaker 1: different points in space. And when you think of space,
Speaker 1: you probably think of like just sheer emptiness, you know,
Speaker 1: the back drop the stage on which the universe happens.
Speaker 1: But now we know that space is more complex. It
Speaker 1: can bend and it can twist, and that might be
Speaker 1: something that you can put in your head. You can
Speaker 1: imagine like space bending around the sun. But because space
Speaker 1: is like a thing with an arrangement, it could also
Speaker 1: do other really weird things, like be connected non trivially,
Speaker 1: so you have like a chunk of space over here.
Speaker 1: It can be directly connected to a chunk of space
Speaker 1: over there. What does that mean. Well, you're used to
Speaker 1: the space around you being connected to the space right
Speaker 1: next to it. That's what it means to be right
Speaker 1: next to it. Right, you take a step to the left,
Speaker 1: you move to the next sort of piece of space.
Speaker 1: Think of it sort of like pixels on a screen. Right, Well,
Speaker 1: a wormhole is a connection between two points in space
Speaker 1: that are otherwise really distant. And so you take a
Speaker 1: step from a from one pixel and now you're in
Speaker 1: a pixel on the other side of the screen. And
Speaker 1: so that seems weird and impossible, but remember space can
Speaker 1: have all sorts of strange connections, and according to the
Speaker 1: equations of general relativity, the ones that define how space
Speaker 1: is organized, that is allowed. It is possible. And so
Speaker 1: a couple of folks at cal Tech we're thinking about, well,
Speaker 1: you know what about time? Is it possible for one
Speaker 1: end of the wormhole to be in one place and
Speaker 1: the other end to be in another time? Because, as
Speaker 1: you were mentioning earlier, like the notion of simultaneity, like
Speaker 1: when is now depends really on where you are. Also,
Speaker 1: so they have this idea to take one end of
Speaker 1: the wormhole and you accelerate it near the speed of light.
Speaker 1: That effectively it can be sort of back in time.
Speaker 1: And this all works theoretically, but it also sort of
Speaker 1: contradicts other things we know, like if you go through
Speaker 1: this wormhole and you come out in the past, you know,
Speaker 1: doesn't that break things like causality? And you come out
Speaker 1: in the past and kill yourself before you um do
Speaker 1: the experiment, Then you don't do the experiment, you don't
Speaker 1: come out in the past. So it appears to create paradoxes,
Speaker 1: and nobody knows like how to resolve that. Does that
Speaker 1: mean that these things are impossible? Does that mean if
Speaker 1: you did that, the universe would like disappear in a
Speaker 1: puff of logic. Nobody really knows what would happen. So
Speaker 1: that's a bit of a contradiction in the theory itself
Speaker 1: that it predicts something which seems to be disallowed by
Speaker 1: other parts of the theory. And it's a similar idea
Speaker 1: for these closed timelike curves. People said, if you create
Speaker 1: these infinitely long the cylinders of spinning dust, which doesn't
Speaker 1: sound easy to do, then it bends time in this
Speaker 1: way that the time then as you move forward in
Speaker 1: time you're actually moving sort of like sideways through space
Speaker 1: time in a way that's similar to the experience of
Speaker 1: going into a black hole. Outside a black hole, time
Speaker 1: always moves forwards. Inside a black hole, space has bent
Speaker 1: so much that space only moves towards the center of
Speaker 1: the black hole. It's like one direction to space. So
Speaker 1: if you imagine space being distorted, not quite as much
Speaker 1: as a black hole, but sort of in a similar
Speaker 1: direction that it sort of bends space sideways, then you
Speaker 1: can create these paths where something can move in a
Speaker 1: loop through time. Um, but you would be trapped on
Speaker 1: that loop, so you wouldn't be able to like change anything.
Speaker 1: It's like a fixed loop, sort of like Harry Potter
Speaker 1: style loop through time, where every time you go through
Speaker 1: it's exactly the same thing happening. And these are really
Speaker 1: fun because nobody knows like if these are actually possible
Speaker 1: and what would happen if you actually went through them.
Speaker 1: So so we don't really know, for instance, like what
Speaker 1: conceivable reason there would be for a civilization to conceivably
Speaker 1: construct one of these, yeah, because we don't know practically
Speaker 1: what you could achieve. And also, an infinite cylinder of
Speaker 1: spitting dust sounds like an expensive project. You know, the
Speaker 1: word infinite seems to raise some doubts. And when it
Speaker 1: comes to wormholes, people know how to calculate whether a
Speaker 1: wormhole is allowed by the theory of general relativity. Nobody
Speaker 1: knows how to build a wormhole. You know. It's sort
Speaker 1: of like saying, Okay, it's possible to have an apple pie,
Speaker 1: but but we we don't have a recipe for making one. Right.
Speaker 1: It's a different thing to say, like I know how
Speaker 1: to put it together than to say it's technically allowed
Speaker 1: to exist in the universe. You know. It's like if
Speaker 1: you say, well, the sun is allowed by the laws
Speaker 1: of physics, but I don't know how to make it
Speaker 1: happen if I just start from a cloud of gas,
Speaker 1: for example, And so that's a big le. Nobody really
Speaker 1: knows how to build a wormhole or even keep one open. Um,
Speaker 1: if you did manage to build one, Are there any
Speaker 1: reasons to suspect that wormholes exist naturally? Oh, great question,
Speaker 1: Not yet, No, um. Some people wonder if there are
Speaker 1: wormholes that connect the super massive black holes at the
Speaker 1: hearts of all of our galaxies, But there's not like
Speaker 1: any evidence out there anything that can't be explained without wormholes,
Speaker 1: that you would need wormholes to explain. Um, that would
Speaker 1: be super cool, though no, Um, I'm not aware of
Speaker 1: any evidence like that. Well, Daniel, you also have a
Speaker 1: chapter in the book that I really liked on the
Speaker 1: question of will time ever stop? And I think this
Speaker 1: is one of those great questions because it's a yes
Speaker 1: or no question, and like many big questions in physical cosmology,
Speaker 1: it's a binary. But no matter which answer it is,
Speaker 1: it's mind boggling, like it is impossible to imagine time
Speaker 1: either stopping or going on forever. Uh So, so what
Speaker 1: are your thoughts here about whether time will ever stop?
Speaker 1: I go, you're feeling there, And I also think it's
Speaker 1: really fascinating to go back through history and read about
Speaker 1: which concept felt more natural to people. Initially, it felt
Speaker 1: to people like time should go on forever. Obviously, that
Speaker 1: was like a hundred fifty years ago, before we knew
Speaker 1: that the universe was expanding. People looked out in the
Speaker 1: stars and they looked like they were just sort of
Speaker 1: hanging out, and they thought, maybe the universe is just
Speaker 1: sort of there, and so obviously it's been there forever, right,
Speaker 1: And that was like this you know, de facto assumption
Speaker 1: in science until Hubble discovered that the universe is expanding,
Speaker 1: and that gave the universe sort of like a direction.
Speaker 1: It's like things are changing, and as you look back
Speaker 1: in time, that suggests, you know, something a moment when
Speaker 1: the universe was like crazy infinitely dense. So it suggested
Speaker 1: a beginning. And that must have been an incredible sort
Speaker 1: of mind bending mental gymnastics to execute to go from thinking, oh,
Speaker 1: it makes sense for the universe to be infinite in time,
Speaker 1: to go into like, oh, the universe had a beginning
Speaker 1: and now let's trying to figure out what that beginning was. Um.
Speaker 1: So I think that's really interesting. And you know, I
Speaker 1: think the thing that's really cool about this question is
Speaker 1: not just that it's tangible because it makes you wonder
Speaker 1: like am I going to go on forever as the
Speaker 1: universe always going to be here? But because it really
Speaker 1: gets at the heart of a the deepest problem in
Speaker 1: physics right now, like the fundamental conflict we have between
Speaker 1: two ideas in physics, which are quantum mechanics and general relativity.
Speaker 1: You know, we have a quantum mechanical description of how
Speaker 1: like particles bounce off each other and we you know,
Speaker 1: have a lot of questions about how that works. But
Speaker 1: we have a pretty good theory for you know, understanding
Speaker 1: quantum particles, and we've been talking about general relativity, you know,
Speaker 1: how space bends and how it affects time and what
Speaker 1: happens in black holes and all that stuff also very successful.
Speaker 1: The problem is that these two theories nobody knows how
Speaker 1: to bring them together end critically. They have very different
Speaker 1: stories to tell about what time is. They treat time
Speaker 1: totally differently, with huge consequences for the answer to this question,
Speaker 1: will time ever stop? And so to me, this is
Speaker 1: a fun question because it puts its finger on right
Speaker 1: on that conflict. Yes, so there is. There's a concept
Speaker 1: that you introduce in this chapter about uh sort of
Speaker 1: time as we experience it being a sort of special
Speaker 1: case or special circumstance of a hypothetical substance you refer
Speaker 1: to as meta time. Can you explain something like what
Speaker 1: are you getting at here? Well, one of the basic
Speaker 1: questions is is time fundamental or is it emergent? You know,
Speaker 1: a deep question in modern physics is like what are
Speaker 1: the essential ingredients to the universe? What did it start with?
Speaker 1: And then what sort of arises out of that, out
Speaker 1: of the complexity of the possible interactions. You know, for example,
Speaker 1: if you're playing with legos, the fund mental ingredients are
Speaker 1: the basic pieces, and from that you can make complicated
Speaker 1: things dinosaurs or pirates or spaceships or whatever. But those
Speaker 1: spaceships they're emergent, you know, they're not necessary. They don't
Speaker 1: have to exist. You can take it apart and just
Speaker 1: have the legos. In the same way in our universe
Speaker 1: there are complicated things like ice cream and hurricanes, but
Speaker 1: those don't have to exist in the universe, right, You
Speaker 1: can imagine a universe without hurricanes or without ice cream,
Speaker 1: as sad as that is. So then the question is
Speaker 1: what are the basic elements of the universe. And for
Speaker 1: a long time, you know, people like Newton thought that, well,
Speaker 1: obviously space and time are fundamentals of the universe. They're
Speaker 1: just like you gotta have that, right, And now people
Speaker 1: are wondering, like, well, is that really true? Is it
Speaker 1: possible to have a universe without space or without time?
Speaker 1: You know, we gotta when you're really digging deep into
Speaker 1: the nature of the universe, you gotta push hard on
Speaker 1: the fundamental assumptions. So There are a lot of ideas
Speaker 1: now about how space could be emergent, you know, how
Speaker 1: it could be that the universe that self, that space
Speaker 1: is not a natural thing, that like ice cream, you
Speaker 1: could have a time in the universe where there wasn't
Speaker 1: any space. That space is like just briefly, the stitching
Speaker 1: together of these um separated pixels of space using quantum
Speaker 1: entanglement to sort of weave together this idea of space,
Speaker 1: these relations between different locations that we experience, and we
Speaker 1: could talk about that for an hour um. But even
Speaker 1: moving beyond that, now folks are wondering, like, is time
Speaker 1: also emergent? Is it possible that time is not a
Speaker 1: fundamental property of the universe but it just sort of
Speaker 1: something that exists now. And it's really hard to even
Speaker 1: think or talk about it because, like I just said,
Speaker 1: it exists now I'm using time to talk about when
Speaker 1: time is. It's very complicated and confusing. But there are
Speaker 1: some theories that tell us that time might be not
Speaker 1: an illusion, right, not in the sense that it doesn't exist,
Speaker 1: but it might not be fundamental, that it might rise
Speaker 1: from complex interactions of smaller, more fundamental elements of the universe,
Speaker 1: and so that's this idea of meta time. You have
Speaker 1: to imagine some like deeper laws of physics that control
Speaker 1: those fundamental bits that I'm being vague about because we
Speaker 1: have no idea what they would be or what they are,
Speaker 1: what the rules are. And And if this seems sort
Speaker 1: of like frustrating, it's because we're at the very beginning
Speaker 1: of even talking about the answers, because we're just formulating
Speaker 1: the questions. You know, sometimes it takes like a hundred
Speaker 1: years to figure out Okay, the important question to ask
Speaker 1: is is there always time in the universe? What does
Speaker 1: that mean? And how do you even think about a
Speaker 1: universe without time? Then you can start to make progress
Speaker 1: on the crazy ideas that might explain it. Uh. This
Speaker 1: may be kind of a tangent, but this actually makes
Speaker 1: me wonder about a question that's come up on the
Speaker 1: show before. Do you have a view on what the
Speaker 1: present is, on whether something special is actually happening in
Speaker 1: the present? Uh? Like, does only the present exists or
Speaker 1: does all of time exist? It's a really great question.
Speaker 1: We don't understand that at all. I don't understand it.
Speaker 1: I don't even know if it's a question of science
Speaker 1: or if it's a question of philosophy because it goes
Speaker 1: into the nature of consciousness. You know, does the whole
Speaker 1: timeline exists and we only experience part of it? Or
Speaker 1: you know, does the only this moment exist um? Physics
Speaker 1: doesn't have a great way to even define what the
Speaker 1: present is um, and so it's it's pretty hard to
Speaker 1: put your finger on it um. And I love that
Speaker 1: because these are questions that like, we don't even really
Speaker 1: know how to attack these questions. And what that suggests
Speaker 1: is that there's something wrong in the way we're organizing
Speaker 1: our thinking. You know. It's like if you're asking a
Speaker 1: question and you're just using the wrong language, we're using
Speaker 1: the wrong notation, then your question seems really complicated and confusing.
Speaker 1: And if you learn a new perspective and then suddenly
Speaker 1: would make sense. You know, I'm reminded of that Far
Speaker 1: Side cartoon where the scientists are trying to understand dolphins
Speaker 1: and they're writing down phonetically with the dolphins are saying,
Speaker 1: and they're saying things like, you know, obla Espanol, and
Speaker 1: you know, the scientists don't speak Spanish, so though to
Speaker 1: them it's just nonsense. My boys, if they knew the language,
Speaker 1: it would all click together. And I feel like that's
Speaker 1: the problem we have sometimes that was just not speaking
Speaker 1: the right language at the universe yet, and that's why
Speaker 1: some of these questions are awkward and really hard to
Speaker 1: grapple with. I thought you were gonna say today's physicists
Speaker 1: are only equipped with cow tools only for spherical cows, exactly,
Speaker 1: you know, all of this um Also, it reminds me
Speaker 1: a bit of the Copernican principle to UM. But but
Speaker 1: going beyond just the idea of like, you know, there
Speaker 1: being some uh I we should not not see that
Speaker 1: there's something privileged about about our planet or about humans.
Speaker 1: But but could you could you even apply that based
Speaker 1: on what you're saying to to the present moment, to
Speaker 1: this time that in which from which we are viewing
Speaker 1: the universe. Yeah. Probably. I think that's why a lot
Speaker 1: of progress could be made if we ever did get
Speaker 1: to talk to alien scientists, because I think we would
Speaker 1: learn a lot about um, you know, the biases that
Speaker 1: creep into our questions and our reference frame for answering
Speaker 1: those questions because of our human experience, and alien intelligence
Speaker 1: that might have a very different relationship with a concept
Speaker 1: of time might have a very different treatment of it
Speaker 1: mathematically and physically, and might make a lot more sense,
Speaker 1: you know. Um, The problem with alien intelligence, of course
Speaker 1: is you know, finding them, talking to them, decoding their language,
Speaker 1: and then if they are so fundamentally different that they've
Speaker 1: made that they avoid human biases, they might be impossible
Speaker 1: to ever understand. And so while it's tantalizing to imagine
Speaker 1: that like aliens are out there with the answers the
Speaker 1: deep questions about the universe, it might also be that,
Speaker 1: uh that we could never understand what they have to say.
Speaker 1: I have long thought we should outsource all of our
Speaker 1: physics research to like a seven in dimensional octopus. Um,
Speaker 1: if you know one, I'd like to meet it because
Speaker 1: I got questions, thank uh so. But to come back
Speaker 1: to the idea of will time ever stop? You talk
Speaker 1: about a couple of possibilities for what that would look like.
Speaker 1: Say that you know the far future of our own
Speaker 1: universe at least at least what we can reason from
Speaker 1: what we know today, and and a couple of these
Speaker 1: options are are the Big Crunch and the heat death
Speaker 1: of the universe. Do you do you want to talk
Speaker 1: about what those would mean as as best we can
Speaker 1: guess for time itself. Yes, So remember that there are
Speaker 1: two paths to go down if you're asking questions about
Speaker 1: the deep future of the universe, and one is quantum
Speaker 1: mechanical and the other one is general relativity. And quantum
Speaker 1: mechanics is pretty straightforward about this. It says that, look,
Speaker 1: time always existed and time will always exist. And there's
Speaker 1: a pretty simple argument there because according to quantumy annex,
Speaker 1: quantum information can't be destroyed, like when something happens um,
Speaker 1: you know, the information about what used to happen is
Speaker 1: encoded into the future, and so it suggests the time
Speaker 1: has always existed. There's no mechanism in quantum mechanics for
Speaker 1: time to start. It should always have existed, and you
Speaker 1: flip it around the other direction, it should always exist.
Speaker 1: So there should always be a universe and clocks should
Speaker 1: always tick forwards according to quantum mechanics. But that assumes
Speaker 1: you know that space is flat and simple, and general relativity,
Speaker 1: the other pillar of modern physics, tells us that space
Speaker 1: is not simple. It's not flat, it's complicated. It's expanding,
Speaker 1: and you know, the mechanism by which space is expanding
Speaker 1: is not something that we understand hub Will discovered a
Speaker 1: hundreds something years ago that the universe is expanding and
Speaker 1: things are moving away from us, And then twenty something
Speaker 1: years ago we discovered even more mind boggling lye that
Speaker 1: that expansion is accelerating. Right, It's not like stuff is
Speaker 1: moving through space and gradually slowing down and maybe eventually
Speaker 1: gonna stop and turn around and come back um and collapse,
Speaker 1: but that it's speeding up, which means that there's some massive,
Speaker 1: incredibly powerful force in the universe that's literally tearing it apart.
Speaker 1: Because we don't know the mechanism for it, though, we
Speaker 1: can't predict what it's gonna do, Like it turned on
Speaker 1: about five billion years ago, started tearing the universe apart.
Speaker 1: Will it do that forever? If so, you end up
Speaker 1: with like a universe where everything is super far apart.
Speaker 1: It's just like a bunch of black holes from collapsed galaxies,
Speaker 1: separated by you know, unthinkably vast distances, even compared to
Speaker 1: the distances we see between our galaxy and other galaxies today.
Speaker 1: You know, these galaxies would be so far apart that
Speaker 1: they could never even see each other. You know, light
Speaker 1: would never reach one from the other. On the other hand.
Speaker 1: Dark energy could change its direction, it could stop, it
Speaker 1: could turn around, it could cause the universe to collapse
Speaker 1: back down into an incredible moment of singularity at the
Speaker 1: end of the universe UM, and then we can ask
Speaker 1: questions like, well, what happens then, you know, does the
Speaker 1: universe stop when you reach another singularity, another moment of
Speaker 1: incredible density. We just don't know because general relativity describes
Speaker 1: that process. But when you actually get to the singularity,
Speaker 1: people think of singularities is like a feature of general relativity.
Speaker 1: Really they're like a failure of general relativity. It can't
Speaker 1: predict anything that happens there, doesn't know what to do.
Speaker 1: It's like, well that's the direction you're going, but once
Speaker 1: you get there, I can't tell you what's going to
Speaker 1: happen next. So if that happens, we just really don't
Speaker 1: know what the fate of the universe would be in
Speaker 1: that scenario. But you know, it wouldn't be pleasant for
Speaker 1: humans or for seventeen seventeen dimensional octopi. But I guess
Speaker 1: with with the other option, with like you know, the
Speaker 1: heat death of the universe, everything just expanding and cooling
Speaker 1: and reaching some kind of equilibrium where UM where there's
Speaker 1: no there's no imbalance to distribute any further. Now, I
Speaker 1: think in the book you raised the idea that this
Speaker 1: could in a way represent a threat to to our
Speaker 1: concept of time, because time would maybe in itself, time
Speaker 1: has something to do with entropy, and this would be
Speaker 1: a state of maximum entropy. Yeah, we see the universe
Speaker 1: proceeding through time and we see entropy increasing. And entropy
Speaker 1: is a really tricky topic. You hear people talk about
Speaker 1: it a lot, but it's really hard to sort of
Speaker 1: grapple with intellectually, and people try to think about it
Speaker 1: in terms of like amount of disorder in the universe,
Speaker 1: but that can be pretty misleading technically. It's really relates
Speaker 1: to the number of different ways you can arrange the
Speaker 1: microscopic nature of the universe to be consistent with the
Speaker 1: macroscopic nature that you observe. That's a little bit more subtle,
Speaker 1: but it's actually a more accurate guide to what entropy is.
Speaker 1: And what we notice is that entropy seems to be
Speaker 1: increasing through the universe, Like there's something we've observed, and
Speaker 1: a lot of places in physics seem to be sort
Speaker 1: of like and bivalent about time. The laws will run
Speaker 1: the same forward or backwards. It doesn't really matter, if
Speaker 1: you know, without friction or air resistance. For example, you
Speaker 1: can throw a ball up in the air and it
Speaker 1: lands back in your hands. If you played a movie
Speaker 1: of that backwards, it would look exactly the same again
Speaker 1: without air resistance, because that increases entropy. Um. But entropy
Speaker 1: is the one place where in the laws of physics
Speaker 1: there seems to be a preference for things moving forwards.
Speaker 1: So it's often claimed that entropy might be the reason
Speaker 1: time moves forwards. And I think that's a bit of
Speaker 1: a step too far. You know, we see that entropy
Speaker 1: increases as time moves forward, so there's a connection between them.
Speaker 1: That doesn't mean necessarily the time has to move forward.
Speaker 1: I mean, if time moved backwards, it just means that
Speaker 1: maybe entropy would decrease, right it um creates this connection
Speaker 1: between entropy and time, It doesn't necessarily imply a direction.
Speaker 1: But some people wonder what would happen when you reach
Speaker 1: a state of maximum entropy, and maximum entropy would be
Speaker 1: as you say, a everything progresses forward and the universe
Speaker 1: so spreads out and it becomes maximumly even there's no
Speaker 1: like hot spots and cold spots because that allows you
Speaker 1: to rearrange the microscopic state as many ways as possible,
Speaker 1: so the most freedom to rearrange the microscopic state and
Speaker 1: so the most entropy. And in that state, it's called
Speaker 1: the heat death of the universe because you have no
Speaker 1: hot spots and no cold spots, so no way for
Speaker 1: like energy to flow. Nobody like do anything. The way
Speaker 1: that you operate as a human being is through energy flows,
Speaker 1: and the way that computation happens is through energy transfers,
Speaker 1: and so you can't really do anything if there's no
Speaker 1: energy ingredients. So that's why it's referred to as the
Speaker 1: heat death of the universe. And people who think that
Speaker 1: time is deeply connected to entropy, wonder if one entropy
Speaker 1: reaches its maximum point, if time then somehow stops, or
Speaker 1: maybe time stops and then turns around and entropy starts
Speaker 1: to decrease like a bounce in time. And nobody knows
Speaker 1: the answer to these questions when he's gonna be around
Speaker 1: to know the answer to the questions, even if you're
Speaker 1: optimistic about the length of human civilization. But they're really
Speaker 1: fun to think about because they make you think about
Speaker 1: what time is and you know, and how it relates
Speaker 1: to the whole universe. Well, though, on the question of
Speaker 1: nobody being around this, this may also be a tangent.
Speaker 1: But this makes me wonder do you have opinions on
Speaker 1: the alleged Boltzman brain problem. I know we talked about
Speaker 1: this on an episode a few years back, and um
Speaker 1: so maybe kind of fuzzy on the details, but if
Speaker 1: I recall, it has been used to argue against some
Speaker 1: types of future eternity ees. But basically the the argument
Speaker 1: is if the universe were to go on existing literally forever,
Speaker 1: with certain types of properties in play, eventually people whose
Speaker 1: brains randomly formed from fluctuations in space would outnumber people
Speaker 1: who exist through biological evolution on Rocky Planet, and thus
Speaker 1: we would expect to be those brains instead of these
Speaker 1: biological brains. Is that roughly right? Yeah. Essentially, it's arguing
Speaker 1: that if the universe reaches heat death and then goes
Speaker 1: on forever, that most of the time in the universe
Speaker 1: is during heat death, right, that really basically randomly sampled
Speaker 1: moment in the universe should be when the universe is
Speaker 1: spread out and boring and gray. So then Boltsman said, well,
Speaker 1: what if you just had a quantum fluctuation while he
Speaker 1: was before quantum mechanics. But what if you had a
Speaker 1: random fluctuation, Because you know, the law of entropy is statistical,
Speaker 1: it's not exact, allows for fluctuations. And so he said, well,
Speaker 1: what's the chances of the whole universe then being like
Speaker 1: a fluctuation in some vast or heat dead universe that
Speaker 1: already has existed for unknown millions of years. So he
Speaker 1: was trying to fluctuate an entire universe out of basically nothing.
Speaker 1: And so as a counterpoint, people are like, well, you know,
Speaker 1: there are smaller but more ridiculous things that you could
Speaker 1: fluctuate out of the universe, like a galaxy or even
Speaker 1: just like one brain. And so at the point was
Speaker 1: made actually to criticize those kinds of cosmological models, because
Speaker 1: if your cosmological model seems less likely than you know,
Speaker 1: brains forming spontaneously in space and thinking that they're people,
Speaker 1: then it seems pretty unlikely. Um, And so I don't
Speaker 1: think anybody really takes it seriously. Is like a theory
Speaker 1: of the universe. It's sort of just more like a
Speaker 1: mental exercise to wonder, like, how likely is your theory
Speaker 1: of the universe. Um, you know, is it less likely
Speaker 1: than this absurd scenario. So there's another thing you bring
Speaker 1: up in your chapter. Will time ever stopped? Is an
Speaker 1: idea I was instantly captivated by, which is you point
Speaker 1: out that technically, um, time could be stopping and restarting
Speaker 1: all the time, frequently without us ever realizing it, because
Speaker 1: how would we know, right, Like, our consciousness or experience
Speaker 1: of the world is through time, So if time were
Speaker 1: to stop, uh and then restart, that might just be
Speaker 1: invisible to us. So you know, maybe they're just uh,
Speaker 1: these huge gaps in our life. Though. That makes me
Speaker 1: wonder if time we're stopping, would it be possible to
Speaker 1: measure how long it stopped for? Oh, that's really interesting.
Speaker 1: You know, this sort of presupposes some sort of like
Speaker 1: meta time, some you know, other rules of the universe
Speaker 1: that's controlling our time. And because time itself controls how
Speaker 1: our universe changes, then strictly speaking, if time does pause,
Speaker 1: you know, according to this meta time, and then pick
Speaker 1: up again, nothing should change because that would require our
Speaker 1: time to tick forward. Like, no particles can move, no galaxies,
Speaker 1: no space can be created, you know, no expansion can happen.
Speaker 1: Without time our time ticking forward. That means that there's
Speaker 1: nothing in our universe that should change if time doesn't
Speaker 1: take forward, which means that there should be no way
Speaker 1: to tell. So it could be like a near infinite
Speaker 1: amount of time between every tick of our universe could
Speaker 1: be passing in sort of like the meta universe. I
Speaker 1: think the easiest way to imagine this is in the
Speaker 1: simulation hypothesis, the idea that the universe is like a
Speaker 1: computer program running on some mega computer, and you know,
Speaker 1: if the aliens or super beings running that simulation paused
Speaker 1: the simulation to go to the bathroom and come back,
Speaker 1: then we don't know that they've paused it. Right. It's
Speaker 1: just like the characters in your video game. They're not like,
Speaker 1: hey buddy, that was a long number two. You know
Speaker 1: what you're doing? Everything okay when you come back, They
Speaker 1: have no idea, and to them, you know, the experience
Speaker 1: is completely smooth. So I think, no, there's no way
Speaker 1: to know how long time has been paused for if
Speaker 1: it does get paused. I always wondered with that hypothesis,
Speaker 1: would we notice if the resolution on our simulation was downgraded?
Speaker 1: You mean, if they lost their funding and had to
Speaker 1: had to go to a more course resolution decreased render distance. Yeah,
Speaker 1: I don't know. Sometimes it does feel like the resolution
Speaker 1: decreases or increases, and depending on what's going on, I'm
Speaker 1: gonna blame my failing memory for that, Like you know
Speaker 1: what the aliens have just been like cleaning up the cash,
Speaker 1: and that's why I can't remember, you know, what happened
Speaker 1: last week or when I agreed to clean to the
Speaker 1: garage or whatever. Um. But there are always that we
Speaker 1: do think we might be able to probe the resolution
Speaker 1: of the simulation of the universe under the assumption that
Speaker 1: we live in that crazy scenario, because these simulations the
Speaker 1: way we do them, at least as we tend to
Speaker 1: like divide the universe into huge cubes and stimulate each
Speaker 1: cube separately, assuming that like the interactions between cubes are
Speaker 1: pretty small, which works pretty well, you know, if you're
Speaker 1: in if you're stimulating like a single galaxy at the time,
Speaker 1: because mostly you're dominated by what's going on inside the
Speaker 1: galaxy and now stuff from other galaxies. But we have
Speaker 1: these particles, these crazy high energy particles that whizz through
Speaker 1: space at velocities nobody's ever seen before or energies nobody's
Speaker 1: ever seen before, much much higher energy than anything like
Speaker 1: created by our particle accelerators. And they might be like
Speaker 1: tripping up that simulation because they skipped through several of
Speaker 1: these simulation pixels faster than anything you should expect. And
Speaker 1: you know, there are some things about those particles we
Speaker 1: see out there in space that we don't understand, and
Speaker 1: so that opens the door to like maybe you could
Speaker 1: explain those particles as being like a glitch in the simulation. Now,
Speaker 1: speaking of simulations and going back to time travel, does
Speaker 1: anyone out there like make any kind of an argument
Speaker 1: for time travel into the past by saying, well, if
Speaker 1: we are living within a simulation, then time travel into
Speaker 1: the past and the ability to change the past would
Speaker 1: be possible within the confines of that simulation. Yeah. You know,
Speaker 1: if you're living in a simulation, then the rules are
Speaker 1: essentially arbitrary, and then yeah, you could wind time backwards.
Speaker 1: I think this goes to the heart of, like I
Speaker 1: think a basic confusion about time travel because people imagine,
Speaker 1: like you get in a time machine and you and
Speaker 1: the time machine does something to you, and then you
Speaker 1: end up back in the past. I don't really see
Speaker 1: how that could possibly work. What you really want in
Speaker 1: time travel is for the whole universe to travel back
Speaker 1: in the past and for you to not. So you
Speaker 1: gotta like get in the time machine, and it's got
Speaker 1: to like rewind the clocks of the rest of the universe, right.
Speaker 1: You don't want to be like, Okay, it's still today,
Speaker 1: but now I'm ten years younger. I mean maybe some
Speaker 1: people want that. That's a whole different thing to look for.
Speaker 1: If you want to like unspill your coffee, but you
Speaker 1: still want like the ideas, you want to remember having
Speaker 1: spilled it on yourself, so you cannot just repeat it.
Speaker 1: Then you need to rewind the whole rest of the
Speaker 1: universe somehow. It seems like a much bigger job that. Yeah,
Speaker 1: that's a great point. Yeah, that so the time machine
Speaker 1: would have to change the universe, not you. Yeah, I
Speaker 1: never thought of it that way. Yeah. And a lot
Speaker 1: of our listeners right in when we talk about time
Speaker 1: travel and raise a similar point and a criticism of
Speaker 1: science fiction levels, which is that you know, if you
Speaker 1: do go back in time somehow, how do you know
Speaker 1: where you're going to be? You know, because the Earth
Speaker 1: and the sun and the milky way they're all moving, Um,
Speaker 1: so how do you know where you're going to end up?
Speaker 1: And it's a fun question. Um though, I think if
Speaker 1: you're gonna pose it like, okay, you can travel through time,
Speaker 1: then ostensibly probably you can travel travel through space time,
Speaker 1: so you can appear wherever you want. But the problem
Speaker 1: is like, actually, I'm not even really necessarily well defined,
Speaker 1: because what does it mean to be here at a
Speaker 1: point in space, or there at a point in space,
Speaker 1: or now this point in space? Now where is that
Speaker 1: point in the future because there is no like marker
Speaker 1: to space. Space is all relative. It's not absolutely you
Speaker 1: can't like grasp this point of space and give it
Speaker 1: a name and say where does this bit go? There's
Speaker 1: only stuff moving through space relative to each other. So
Speaker 1: it turns out that's not even really well defined. Like
Speaker 1: where was the Earth, you know, a million years ago
Speaker 1: in our space? Doesn't actually have a meaning? That is
Speaker 1: when I had thought of before that always seemed an
Speaker 1: insurmountable problem. But this actually reminds me of another thing
Speaker 1: I wanted to talk about briefly, which is relating time
Speaker 1: to the history of the universe and the Big Bang,
Speaker 1: a thing people often ask and I know, there are
Speaker 1: theories to address this is is what happened before the
Speaker 1: Big Bang. But if you have an understanding that, you know,
Speaker 1: you have a singularity at the origin of the Big Bang,
Speaker 1: that was the beginning of time itself as we know it.
Speaker 1: What are physicists talking about exactly when they try to
Speaker 1: envision causes leading to the first instant of the Big Bang?
Speaker 1: Mostly they're trying to avoid that singularity because that singularity
Speaker 1: is a problem. You know, we don't see things like
Speaker 1: singularities in the universe. We don't see infinities, we don't
Speaker 1: see things with infinite density, we don't see things of
Speaker 1: infinite size. I mean, maybe the universe is itself infinite.
Speaker 1: There's nothing that's like infinitely smooth or perfectly circular. These
Speaker 1: are sort of abstractions in our mind. And so most
Speaker 1: physicists who are working on the very early universe are
Speaker 1: trying to avoid that singularity because, as I said earlier,
Speaker 1: general relativity breaks down. That's what it means like, if
Speaker 1: your theory predicts something infinite, it doesn't know how to
Speaker 1: do any calculations beyond that. So instead of having like
Speaker 1: a moment of singularity, which is sort of like the
Speaker 1: naive general relativistic prediction of increasing density. Instead, they're going
Speaker 1: back and saying, well, maybe the Big Bang was just
Speaker 1: like a rapid expansion of space from a previously dense
Speaker 1: kind of universe that we don't understand at all. So
Speaker 1: the basic sketches like you have some kind of weird state.
Speaker 1: The universe is filled with like inflotons, some particle we
Speaker 1: don't know if it existed, but maybe it did. And
Speaker 1: then those inflotons they are causing the rapid expansion of
Speaker 1: space and decay then into normal matter. So that's so
Speaker 1: now the Big Bang is that moment when the in
Speaker 1: photons are expanding and then decay into like our universe.
Speaker 1: That's how our universe is sort of created out of
Speaker 1: these in photons, and that avoids this moment of singularity.
Speaker 1: It's never like a moment when the universe is infinitely dense.
Speaker 1: But you know, again, this is very speculative stuff. We
Speaker 1: think inflation happened, this crazy expansion in the very beginning
Speaker 1: um and this is like a way to avoid having
Speaker 1: to put before that this dot, this singularity that breaks
Speaker 1: all of the mathematics, instead of replacing it with like
Speaker 1: some other weird kind of substance. We don't even really
Speaker 1: know what it's like or what it's about. Um, we're
Speaker 1: just really beginning to know how to ask questions about it.
Speaker 1: And you know, that suggests a really interesting question, which
Speaker 1: is like, if there is something before the Big Bang,
Speaker 1: what was it? And was there something before that? It
Speaker 1: seems like, in one hand, super frustrating because you're just
Speaker 1: kicking the can down the road, Like, alright, so the
Speaker 1: early universe was this expansion, and before that came something
Speaker 1: which caused the expansion, and before that came something which
Speaker 1: caused that, which caused the expansion. But is there in
Speaker 1: the end something original which caused it. We don't know.
Speaker 1: And there's two possibilities. One is that we just keep
Speaker 1: digging forever and dig further and further and further and
Speaker 1: further back and never get to anything which seems like
Speaker 1: could have caused itself. Or it could be that we
Speaker 1: get to some state where we're like, this makes sense
Speaker 1: to have to be a beginning. It's like it's sort
Speaker 1: of the only way things could have happened to me.
Speaker 1: It's it's hard to grapple with these ideas, so it's
Speaker 1: easier to think about it sort of in a parallel way,
Speaker 1: which is like, what is the smallest thing in the universe.
Speaker 1: We don't know if as we tear apart, particles will
Speaker 1: keep finding things that are smaller and smaller and smaller
Speaker 1: and smaller, or if eventually we'll get to one where, like,
Speaker 1: you know, what, this one it makes sense to be
Speaker 1: a fundamental ingredient to the universe. We can just start
Speaker 1: from here and build up. You know, maybe it's like
Speaker 1: the smallest fundamental thing. It's at the plank length or something.
Speaker 1: We don't know if we'll ever get there, or if
Speaker 1: it will be self evident, or if there will be
Speaker 1: always people who say, like, I don't know, I want
Speaker 1: to dig deeper. In the same way, it might be
Speaker 1: that we're doomed to keep digging deeper and deeper back
Speaker 1: into the history of the universe, never finding out if
Speaker 1: there was an original cause. All right, so I think
Speaker 1: we're probably getting close to the end of our time.
Speaker 1: But I got to come back to time travel before
Speaker 1: we do, because I'm wondering, what what do you think
Speaker 1: You mentioned Stephen Hawking's party where the the invitations were
Speaker 1: sent out after it happened, But what what is your
Speaker 1: personal favorite way to hunt for a time traveler. What
Speaker 1: would you do if you wanted to find evidence of
Speaker 1: people from the future. Wow, I know I have never
Speaker 1: given that any thought about evidence for people from the future. UM.
Speaker 1: I try to think about what people would want to do,
Speaker 1: Like if I were a time traveler, why would I
Speaker 1: come to one? Uh? You know the obvious answers are
Speaker 1: like change history. Uh, in which case, you know, I
Speaker 1: guess you can blame those time travelers for you know,
Speaker 1: the reason things have gone the way they are. Maybe
Speaker 1: there because time travelers have come back and tweaked election
Speaker 1: results or you know, or something like that. Um. So
Speaker 1: I guess the best way to find time travelers with
Speaker 1: then to be present at critical hinge moments in history
Speaker 1: and look around for suspicious behavior. I suppose I don't
Speaker 1: really know. That's a great question. Yeah. I was thinking
Speaker 1: about all this in terms of of ancient aliens as well,
Speaker 1: because both you have you have people of course who
Speaker 1: obsess about the idea of of aliens having visited during
Speaker 1: ancient times and so forth, and and you also have,
Speaker 1: I guess a more recent phenomenon of people looking back
Speaker 1: at old pictures and paintings and you know, playing this
Speaker 1: game of basically misinterpreting um things and paintings and photos
Speaker 1: of like looking back in an old picture and saying, oh, well,
Speaker 1: that person, their their style of dress does not look
Speaker 1: archaic enough. They must be traveler. Yeah. Or this painting
Speaker 1: she's holding something that looks like an iPhone. Obviously this
Speaker 1: is a Renaissance painting of a time travel No. I
Speaker 1: think that just says a lot about us, you know,
Speaker 1: and who we are, you know, the same way that
Speaker 1: like photos of UFO, those seemed to be constantly greeny.
Speaker 1: As you know, imaging technology improves, it's always on the
Speaker 1: edge of the our ability to capture it. So I
Speaker 1: think it says something about our desire to discover weird
Speaker 1: things and reveal the truth, which I'm totally sympathetic to.
Speaker 1: I also want to peel back a layer of the
Speaker 1: universe and wake up to its true nature. I remember
Speaker 1: Carl Sagan, and I forget which which book this was,
Speaker 1: but it was in one of the books where he
Speaker 1: talks a little bit about the idea of ancient aliens,
Speaker 1: and I remember him him basically outlining the sort of
Speaker 1: ancient account, the sort of myth that one might look
Speaker 1: to as as the sort of ancient astronaut account that
Speaker 1: could exist. I have such things were possible, And I
Speaker 1: wonder if anyone has ever taken a similar approach to
Speaker 1: the concept of time travel, like like basically like boiling
Speaker 1: it down, saying, Okay, if there is actually evidence, say
Speaker 1: in you know, the historical record, all of people having
Speaker 1: traveled back in time, you know, well, what ex exactly
Speaker 1: what would be looking for? What exactly what they would
Speaker 1: they have been doing? Um and uh and and how
Speaker 1: would and I guess it would come down to, like
Speaker 1: you'd have to imagine, like how truthful are they going
Speaker 1: to be? Are they just gonna lie about themselves being
Speaker 1: time travels, Because that's then you can basically point to
Speaker 1: any pivotal individual or any person in a pivotal period
Speaker 1: of time, right, yeah, And would they even be humans? Right?
Speaker 1: Like we fantasized about going back to see the dinosaurs.
Speaker 1: So if now we're putting ourselves back in the past
Speaker 1: and imagining time travelers, we might have to imagine some
Speaker 1: like post human apocalyptic, newly intelligent species of you know,
Speaker 1: who knows what, penguins or or something coming back in
Speaker 1: time to investigate humans, you know, to understand what happened
Speaker 1: before the apocalypse or whatever. Um, but I thot machines machine.
Speaker 1: Most of the most of our space exploration is uncrewed probes.
Speaker 1: Now you would have to imagine that the same would
Speaker 1: hold true for time. Yeah, it's probably true, or you know,
Speaker 1: after the mission needs have killed us all and they
Speaker 1: just have myths about those weird meat creatures that used
Speaker 1: to uh roam the earth or something. Um. That's fun,
Speaker 1: but it's fundamentally is limited by our imagination. It's the
Speaker 1: same problem with trying to look for aliens. We look
Speaker 1: for aliens in the way we expect to see them,
Speaker 1: although we're pretty sure that if aliens exist, they're not
Speaker 1: anything that we expected. So we need to like push
Speaker 1: really hard on all the boundaries of our imagination to
Speaker 1: make sure we're looking for aliens as broadly as possible
Speaker 1: so we don't miss them. We don't just like come by,
Speaker 1: we're like, oh, that's not aliens. So it's the same
Speaker 1: problem with imagining future time travelers, like who these these
Speaker 1: people or things or entities are are well beyond I
Speaker 1: think even our most creative science fiction UM writers. Well, so,
Speaker 1: like you said, like what's interesting, what would be interesting
Speaker 1: about to someone from the future, and we instantly think, too, oh, well,
Speaker 1: the you know, the coronavirus or something going on in
Speaker 1: you know, geopolitics, or even in the environment. But it
Speaker 1: could be something entirely different. It could be you know,
Speaker 1: the very beginning of something um that doesn't matter at
Speaker 1: all today, right, but but matters, say in exactly which
Speaker 1: we could never possibly imagine. I mean, think about people
Speaker 1: a thousand years ago trying to anticipate was important to
Speaker 1: us today. We couldn't even do that from twenty years ago,
Speaker 1: not to mention a thousand Okay, last question, Daniel, what's
Speaker 1: your favorite time travel movie? Oh? My favorite time travel
Speaker 1: movie has to be Primer, So I think that most
Speaker 1: clearly sets out rules, rules that make sense, and then
Speaker 1: follows those really carefully with lots of fascinating and unexpected results.
Speaker 1: Good answer, good answer, Yeah, that's a good one. I
Speaker 1: often gravitate towards the ones that have really goofy time
Speaker 1: travel rules. But they but if they still stick to
Speaker 1: those rules, then I tend to forgive them. They're always
Speaker 1: boundary cases, though they're always cased to were like, I'm
Speaker 1: not sure what would happen in this scenario or that scenario.
Speaker 1: So I like Prime Room because it has really clear
Speaker 1: Chris Brules and those it has cost. You can't just
Speaker 1: like pop back in time. You have to like spend
Speaker 1: time going backwards um, which has really interesting consequences. So
Speaker 1: I found it to be really creative totally. All right, well,
Speaker 1: thanks so much for joining us today, Daniel. This has
Speaker 1: been a lot of fun. Thank you very much. Always
Speaker 1: a pleasure to talk to you guys. All right, well,
Speaker 1: thanks well once more to Daniel Watson for jumping on
Speaker 1: the old podcast machine and letting us uh pokemon prod
Speaker 1: um with various questions about time travel and wormholes and
Speaker 1: what have you. Yeah, if you want to learn more,
Speaker 1: so if you're not subscribed to Daniel and Jorge Explain
Speaker 1: the Universe, you can find that wherever you get your podcast,
Speaker 1: but you can also go to www dot Daniel and
Speaker 1: Jorge dot com. And you can also find the website
Speaker 1: for their new book. Again. The book is called Frequently
Speaker 1: Asked Questions about the Universe, and the website for that
Speaker 1: is www dot you Diverse f a Q dot com.
Speaker 1: And if you'd like to check out other episodes of
Speaker 1: Stuff to Blow your Mind, well you can find our
Speaker 1: show wherever you get your podcasts. Just look for the
Speaker 1: Stuff to Blow Your Mind podcast feed. We run multiple
Speaker 1: episodes per week, with core episodes dealing with science and
Speaker 1: culture on Tuesdays and Thursdays. On Monday's we do listener mail,
Speaker 1: on Wednesday's we do a short form artifact titled the Artifact,
Speaker 1: and on Friday's we do something called Weird House Cinema,
Speaker 1: which is our time to set aside most serious matters
Speaker 1: and just discuss a strange film. So, of course, thanks
Speaker 1: again to Daniel for joining us today, and as always
Speaker 1: a big thank you to our excellent audio producer Seth
Speaker 1: Nicholas Johnson. If you would like to get in touch
Speaker 1: with us with feedback on this episode or any other,
Speaker 1: to suggest a topic for the future, or just to
Speaker 1: say hi, you can email us at contact at stuff
Speaker 1: to Blow your Mind dot com. Stuff to All Your
Speaker 1: Mind is production of I Heart Radio. For more podcasts
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