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Speaker 1: Hey everyone, Daniel here.

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Speaker 2: My kids were into fantasy novels a few years ago,

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Speaker 2: and I remember one of them asking me if I've

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Speaker 2: ever seen.

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Speaker 1: Magic in real life. I knew what they had in mind.

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Speaker 2: Sorcerers and spells, someone turning rocks into frogs or whatever,

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Speaker 2: and so of course my first answer was no. My

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Speaker 2: second thought, since that felt kind of boring and deflating,

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Speaker 2: was to try to help them realize how amazing and

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Speaker 2: wonderful and almost magical our world is. They don't need

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Speaker 2: official magic to appreciate the awesome power of the sun,

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Speaker 2: or the incredible feats of technology inside their phones, or

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Speaker 2: the amazing biomechanics inside their bodies. It's an extraordinary universe

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Speaker 2: out there, and we love to understand it. But that

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Speaker 2: doesn't feel like magic. The scientific view of the world

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Speaker 2: is appreciation through explanation. The thing that makes something magic

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Speaker 2: is that it's not understood. And though it feels rare

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Speaker 2: today to see something truly baffling with your own eyes,

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Speaker 2: it used to be a very common experience. What did

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Speaker 2: prehistoric people, biologically equivalent to us, and with just as

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Speaker 2: much brain power, What did they think when they saw

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Speaker 2: lightning or an eclipse or got sick. To them, it

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Speaker 2: might as well have been magic, because none of it

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Speaker 2: was understood. I think that's kind of what my kids

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Speaker 2: were asking about, and it made me realize that actually,

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Speaker 2: there's still a lot of magic in our lives, because

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Speaker 2: there's plenty of the universe that remains unexplained, Not little

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Speaker 2: details of scientific trivia, but things as basic and as

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Speaker 2: every day as lightning and disease, things so fundamental to

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Speaker 2: our existence that we sometimes don't even realize how magical

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Speaker 2: they are. So here's a magic trick for you. Turn

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Speaker 2: the future into the present, turn the present into the past.

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Speaker 2: The universe is doing that all the time, unintended, and

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Speaker 2: yet we don't really understand it or how it works.

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Speaker 2: And it does it without any apparent lag or delay.

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Speaker 2: So on today's episode, we'll dig deep into the nature

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Speaker 2: of time and explore what physics can tell us about

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Speaker 2: what it is, why we have it, and why it works.

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Speaker 2: Today in the pod, we're asking what is time?

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Speaker 1: Hi? I'm Daniel Whitson.

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Speaker 2: I'm a particle physicist and a professor at UC Irvine,

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Speaker 2: which means my.

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Speaker 1: Time is not my own.

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Speaker 3: Hi.

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Speaker 4: I'm Kelly Wiener Smith and ever since having kids I

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Speaker 4: never feel like I have enough time, but the time

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Speaker 4: has been higher quality. And welcome to Daniel and Kelly's

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Speaker 4: extraordinary universe where you'll have the time of your life.

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Speaker 4: That was really corny. I should lose my job, but

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Speaker 4: I'm going with it. I'm leaning in. So Daniel, speaking

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Speaker 4: of corny, here is my question for you today. So

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Speaker 4: last episode we talked about space, and this episode we're

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Speaker 4: talking about time. So space time and space time are

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Speaker 4: topics that sci fi deals with a lot. So what

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Speaker 4: is the worst, most inaccurate representation of those concepts in

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Speaker 4: any movie or TV show that you have experienced?

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Speaker 1: Wow?

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Speaker 2: How much time do you have? We should go a

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Speaker 2: whole lot last episode just on that.

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Speaker 1: Oh my gosh.

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Speaker 2: I think one of my least favorite trips in science

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Speaker 2: fiction is subspace or hyperspace that you've like dropped into

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Speaker 2: some other kind of space where you can move faster

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Speaker 2: than light or something. And I'm always wondering, like, you know,

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Speaker 2: if space has multiple dimensions, you're still in that other

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Speaker 2: space and you're in this space. What does this even mean?

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Speaker 2: Where are we? What is the physics of this space?

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Speaker 2: To me, it feels like you're just escaping rules and

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Speaker 2: there's always gotta be rules, even in subspace or hyperspace.

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Speaker 2: So yeah, it's pretty hard to watch science fiction as

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Speaker 2: a physicist.

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Speaker 4: So it actually like detracts from your enjoyment of it.

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Speaker 1: Oh, absolutely it does.

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Speaker 2: Yeah, And you know, I don't mind if the rules

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Speaker 2: on the screen are different from the rules in our universe.

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Speaker 1: That's awesome, that's cool, that's.

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Speaker 2: What I want. But I want them to follow them.

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Speaker 2: I want them to always be rules, because you know,

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Speaker 2: without rules, there's no story, anything can happen, there's no stakes.

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Speaker 2: It's not worth watching.

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Speaker 4: So I know this movie was loved by many, but

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Speaker 4: I kind of felt that way about like from dust

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Speaker 4: till Dawn, like everything seemed normal and then vampires and

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Speaker 4: you're like, what, this is not okay with me. Tarantino

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Speaker 4: has more fans than I ever will have, so good

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Speaker 4: for him.

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Speaker 2: Maybe we should add vampires to this podcast.

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Speaker 4: Oh sure, why not? I loved Anne Rice books when

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Speaker 4: I was a kid. I don't know what that says

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Speaker 4: about me.

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Speaker 2: I worked with somebody in educational television who used to

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Speaker 2: work in publishing, and she told me the day she

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Speaker 2: had to leave publishing was the day she pitched a

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Speaker 2: really great book. And the executive told her this is wonderful,

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Speaker 2: but can you add sexy vampires to it? No, she

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Speaker 2: was like, h we're done, yes.

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Speaker 4: Up the end. Oh my goodness. Yeah, that's a good

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Speaker 4: time to throw in your head.

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Speaker 2: All right, But today on the podcast, we are not

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Speaker 2: talking about sexy vampires or travel through subspace. We're talking

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Speaker 2: about one of the slipperiest questions in all of physics,

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Speaker 2: the kind of question that's hard to answer and hard

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Speaker 2: to ask and hard to think about, which means it's

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Speaker 2: one of the most important questions. It's a question you

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Speaker 2: shouldn't shy away from. It's the kind of question you

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Speaker 2: should dig into, you should confront, you should really try

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Speaker 2: to tackle with everything that you have.

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Speaker 4: And that's what we're gonna do today. We're gonna have

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Speaker 4: another brain bending but absolutely critical discussion about something that

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Speaker 4: feels like it makes sense but then doesn't when you

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Speaker 4: dig a little deeper.

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Speaker 2: And i'd encourage you to remember that in the history

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Speaker 2: of physics and the history of science, there's been lots

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Speaker 2: of times when a topic has gone from like weird

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Speaker 2: and fuzzy and hard to grapple with to totally understood

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Speaker 2: and like mathematically formulated and that's just the process of science.

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Speaker 2: But the beginning steps, the first bites of the apple

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Speaker 2: are hard, you know. When people were thinking about like

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Speaker 2: what is everything made out of? Or like where did

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Speaker 2: the earth come from? Or where are those shiny dots

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Speaker 2: in the sky. Those were fuzzy questions, and people had

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Speaker 2: pretty silly ideas and went down the wrong path lots

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Speaker 2: of times. But hey, we got there, and we only

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Speaker 2: got there because people took those first bites of the apple.

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Speaker 2: People tried when it was still hard. So that's why

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Speaker 2: we're asking these weird, fuzzy questions about something so basic

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Speaker 2: as time.

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Speaker 4: It's exciting. I remember when I was in undergrad and

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Speaker 4: I was learning, you know, so much in my classes,

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Speaker 4: but I started to think about grad school, which wasn't

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Speaker 4: on my radar until I took like thiss ecology class

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Speaker 4: that I loved, And I remember thinking, like a but

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Speaker 4: we figured out so much already, Like what is there

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Speaker 4: left to learn because it's all new when you're an undergrad,

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Speaker 4: and it's like, no, there's so much left to learn

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Speaker 4: and some of it is still fundamental, and I don't know,

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Speaker 4: it's just exciting to know that there's still so much.

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Speaker 2: To contribute, absolutely, and some of the things we have

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Speaker 2: left to learn are things that we don't think about

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Speaker 2: because they are just at the base level of our understanding.

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Speaker 2: They're like the assumed context. And later, in one hundred

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Speaker 2: years or a thousand years, when we understand these things better,

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Speaker 2: people are going to look back and be like, Wow,

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Speaker 2: what was it like to be human back then when

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Speaker 2: they thought time worked this way? And now we know

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Speaker 2: what actually is this completely other thing? And ha ha ha,

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Speaker 2: how silly were they?

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Speaker 1: Right?

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Speaker 2: Yeah, it shapes our very existence and the way we

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Speaker 2: think about our lives, and so it's definitely worth digging into.

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Speaker 2: And if we don't do this work today, then they're

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Speaker 2: not going to figure it out in a thousand years.

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Speaker 4: All right, Well, I am hoping that by the end

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Speaker 4: of today's episode I have a science based excuse for

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Speaker 4: why I'm late all the time that has something to

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Speaker 4: do with the confusing nature of time. So first, let's

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Speaker 4: hear what our listeners had to say about what time

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Speaker 4: really is.

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Speaker 2: That's right, I went out there into the internet and

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Speaker 2: asked a bunch of folks this hard question, what is time?

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Speaker 2: If you would like to answer questions like this for

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Speaker 2: the podcast. Please don't be shy. Right to us two

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Speaker 2: questions at the day, and Kelly dot Org will hook

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Speaker 2: you up and you can hear your voice on the podcast.

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Speaker 2: In the meantime, here are fuzzy thoughts about a fuzzy

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Speaker 2: question about time.

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Speaker 5: Time is represented as its own dimension, like a column

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Speaker 5: in an array. But I just think of it as

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Speaker 5: one thing happening after the other.

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Speaker 1: Time is a human experience. Time, I think is a

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Speaker 1: measure of change.

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Speaker 6: Time is change made measurable by quantification of entropy and

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Speaker 6: by using some caesium oscillations.

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Speaker 4: Time is an artificial.

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Speaker 2: Construct humans have created to try and help explain.

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Speaker 1: The universe.

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Speaker 5: Is the second law of thermodynamics.

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Speaker 1: Our perception of change.

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Speaker 4: Time is a one way trip into the future.

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Speaker 3: The human constructor rived from the sound cycles. I think

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Speaker 3: that time is an abstraction. It's our capability to perceive

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Speaker 3: changes occurring, to make connections between events and their consequences.

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Speaker 3: But I don't believe that time is some sort of

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Speaker 3: substance with an arrow of direction that can be flipped entropy.

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Speaker 1: I guess the fourth dimension in Albert Einstein's theory.

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Speaker 4: Oh wow, I would say it's how we experience events.

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Speaker 1: Happening one after the other in a sequence.

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Speaker 5: I'd have to say that it's the result of quantum processes, decisions,

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Speaker 5: random interactions that occur between inside fields. It's kind of

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Speaker 5: a direction of events in succession.

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Speaker 4: So before we got to the listener questions, you said,

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Speaker 4: these are fuzzy thoughts about a fuzzy question about time.

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Speaker 4: And I gotta say, I was really impressed by how

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Speaker 4: deep some of the these answers were and how seemingly

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Speaker 4: thought out they were. And I guess how many like

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Speaker 4: polysyllabic words they used in these explanations. That made me

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Speaker 4: think you are kind of aware of the underpinnings of

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Speaker 4: this question. And so yeah, I was impressed with the answers.

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Speaker 2: And there's also an extraordinary breadth here. I mean, there

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Speaker 2: are folks who are philosophizing about it it's an artificial construct,

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Speaker 2: and then folks are just trying to describe it. You know,

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Speaker 2: it's a one way trip into the future. People talk

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Speaker 2: about how we measure it. It's really interesting how many

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Speaker 2: different responses there are to this question. They tell you,

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Speaker 2: like how many facets there are to it, and how

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Speaker 2: hard it is to answer a basic question because we

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Speaker 2: don't all necessarily even agree on, like what form the

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Speaker 2: answer is. Like if you ask me what's one plus two?

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Speaker 2: We all know the answer should be a number, right,

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Speaker 2: and maybe we get it right or we can get

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Speaker 2: it wrong. But the answer to the question like what

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Speaker 2: is time? What does that answer look like?

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Speaker 1: You know?

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Speaker 2: Is it just a description of our experience? Is it

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Speaker 2: a mathematical structure that tells us how time works? Is

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Speaker 2: it a philosophical delve into like why it exists and

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Speaker 2: why the universe needs it, or maybe why it doesn't

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Speaker 2: need it, where it actually comes from, why we have it,

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Speaker 2: and how it began. There's such a breadth of things

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Speaker 2: to explore there.

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Speaker 4: Yeah, And I feel like we had pretty much the

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Speaker 4: same conversation when we were talking about space in the

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Speaker 4: prior episode that, like, you can just come at it

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Speaker 4: from so many different angles. There's so many absolutely fundamental

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Speaker 4: things where it's even hard to figure out what kind

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Speaker 4: of question we should be asking.

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Speaker 2: That's right, And since this isn't a philosophy podcast or

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Speaker 2: an engineering podcast, we're going to sort of take the

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Speaker 2: middle road. We're not going to describe the details of

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Speaker 2: how caesium atoms measure time or delve into like the

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Speaker 2: philosophical underpinnings of a theory versus b theory. In philosophical

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Speaker 2: questions of time, we're going to talk about the physics

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Speaker 2: of time and what physics tells us about time, because

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Speaker 2: obviously time is really important to physics, and it is

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Speaker 2: deeply woven into how we have made sense of the

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Speaker 2: world so far. And so what we can do is

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Speaker 2: turn that around and say, all right, time is part

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Speaker 2: of our understanding of how the world works. What does

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Speaker 2: that tell us about what time is? And as usual,

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Speaker 2: the answer is going to be a bunch of incoherent,

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Speaker 2: inconsistent ideas that don't really come together because we don't

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Speaker 2: understand it. And so we'll do our best to try

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Speaker 2: to weave that all together into an excuse for Kelly

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Speaker 2: for why she's always late.

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Speaker 4: Yes, anyone who's thinking about working with me in the future,

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Speaker 4: I'm actually usually five minutes early that I'm worried about

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Speaker 4: my reputation here. But so for our space episode, the

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Speaker 4: answer depended on whether you are in a quantum mechanics

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Speaker 4: or a general relativity framework. Is that where we're going

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Speaker 4: to get again, there's not just one answer. It depends

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Speaker 4: who you talk to.

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Speaker 1: Yes, exactly.

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Speaker 2: There's a fascinating evolution of our understanding of time with

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Speaker 2: respect to space and gravity, and that's super interesting and counterintuitive.

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Speaker 2: It's also completely at odds with our understanding of time

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Speaker 2: in a quantum mechanical universe. So, yeah, we're going to

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Speaker 2: have a couple of threads here, we're going to show

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Speaker 2: how they don't tie together. And then on top of that,

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Speaker 2: there's statistical mechanics and particles iss which also have different

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Speaker 2: views on time, and so we hope that one day

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Speaker 2: somebody's being able to pull us all together into one answer.

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Speaker 2: What we have right now are a bunch of threads,

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Speaker 2: none of which are completely satisfactory. And you know, the

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Speaker 2: thing that we're trying to describe in the end is

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Speaker 2: something pretty intuitive, right, it's our daily experience. It's this

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Speaker 2: kind of magic where like we have the present, like

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Speaker 2: right now I'm experiencing something and five seconds ago you

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Speaker 2: were saying something and I was laughing about it, and

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Speaker 2: there's a difference between that. There's like what I'm doing

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Speaker 2: right now and what I was doing and what I

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Speaker 2: will be doing. And we know that there's a difference there.

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Speaker 2: Right when we experience, when we remember when we anticipate,

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Speaker 2: and that's just like our intuitive understanding of what time is.

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Speaker 2: I think that's what we're trying to grapple with.

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Speaker 4: I feel like, even in our day to day life, though,

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Speaker 4: time can sometimes feel weird. And this is the biologist

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Speaker 4: in me. You know, my daughter is not very coordinated.

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Speaker 4: And once we were playing a game on a wooden

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Speaker 4: floor where we were kicking a ball around, and she

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Speaker 4: kicked it and one foot went up and landed on

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Speaker 4: the ball, and she stood on top and she started

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Speaker 4: falling forward and she didn't put her arms out to

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Speaker 4: catch her. No, because she's my daughter. And I swear

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Speaker 4: the world slowed down as her teeth hit the wood floor.

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Speaker 4: Oh my gosh, something as easy as time. I feel

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Speaker 4: like I've had jobs where I had like two weeks

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Speaker 4: left and it felt like time had fundamentally changed. But anyway,

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Speaker 4: this is the biologist's perspective and how brains work, I suppose.

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Speaker 4: I guess we're not getting into that today.

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Speaker 2: That is a really important angle. And if you've read

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Speaker 2: folks like Daniel Dennett, he suggests that there is no

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Speaker 2: present moment of consciousness, that the only experience we have

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Speaker 2: is actually remembering the immediate past, that your brain assembles

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Speaker 2: the present as an illusion. You never experience it, you

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Speaker 2: just remember it. It's a weird concept. It makes a

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Speaker 2: lot of sense when you're reading the book, and then

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Speaker 2: later you're like, what, how does that possible? Like with

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Speaker 2: a lot of philosophy. So, yeah, that's not something we're

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Speaker 2: going to dive into today, but we will ask questions like,

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Speaker 2: how does time work?

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Speaker 1: What is it?

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Speaker 2: Can we travel through time? Did time have a beginning?

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Speaker 2: What does that even mean? Why does time seem to

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Speaker 2: only go forward?

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Speaker 1: Words, all this kind of stuff.

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Speaker 4: All right, So we could have a whole podcast called

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Speaker 4: Daniel and Kelly's Extraordinary Conversations about Time. We could take

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Speaker 4: biology philosophy anyway. But today we're just doing physics, all right.

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Speaker 4: So when we were talking about space, we went through

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Speaker 4: sort of like the history of ideas about space? Where

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Speaker 4: should our history of ideas about time start?

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Speaker 1: This time?

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Speaker 2: So, like so many things in physics, we got to

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Speaker 2: start with Newton. I mean, people talk about time before Newton,

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Speaker 2: but really Newton was the first person to systematize it

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Speaker 2: and to incorporate it into his physics. And you know,

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Speaker 2: he figured out gravity and the loss of motion and

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Speaker 2: all this stuff so much depends on time. And for Newton,

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Speaker 2: time was absolute. He imagined like a single clock for

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Speaker 2: the whole universe. And the way Newton thinks about time

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Speaker 2: is sort of like the way a movie works. You know,

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Speaker 2: you imagine a movie is like some continuous motion, but

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Speaker 2: really it's a bunch of snapshots.

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Speaker 1: Right.

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Speaker 2: If you slowed down a movie, you'd see it's a

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Speaker 2: bunch of still frames and those are tied together in

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Speaker 2: a sequence. Right, So you're watching like a whole movie

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Speaker 2: of your daughter falling into the floor. You see her

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Speaker 2: standing on the ball. The next frame she's falling a

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Speaker 2: little closer to the floor, and the next frame, the

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Speaker 2: next frame. Finally there is a frame where like the

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Speaker 2: teeth make contact with the wooden floor.

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Speaker 4: Right, yeah, yeah, why did I bring this up? I'm

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Speaker 4: gonna have to relive it so many times?

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Speaker 2: And it's a series of moments, right, still moments, and

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Speaker 2: time is what ties those still moments together. In Newton's universe,

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Speaker 2: time is what connects those as well, Like the laws

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Speaker 2: of physics tell us if the universe was at this

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Speaker 2: state in this organization, if your daughter's face was this

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Speaker 2: far above the floor, then when is her face going

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Speaker 2: to impact the floor. The physics predicts the future from

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Speaker 2: the past. It connects all of these into a causal chain,

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Speaker 2: and the whole universe ticks forward together like tic tick.

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Speaker 2: You imagine the whole universe as a still frame, and

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Speaker 2: then you tick it forward, and everything in the universe

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Speaker 2: has taken one time step.

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Speaker 4: So intuitively this makes sense to me who was the

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Speaker 4: first person to make it? Confusing but more accurate, Confusing

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Speaker 4: but probably more accurate.

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Speaker 2: Let's not confuse people just yet. Let's marinate in how

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Speaker 2: much sense it makes, just for what longer, because it

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Speaker 2: is kind of wonderful, right imagining that far away in Andromeda,

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Speaker 2: you know, the aliens are also rescuing their daughters from

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Speaker 2: wooden floors or whatever. That the whole universe is following

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Speaker 2: some laws of physics, and if you knew the state

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Speaker 2: of the universe, you could predict its future, right. It's

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Speaker 2: an incredible thing about physics. I remember learning it in

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Speaker 2: high school and being like, oh my gosh, physics is

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Speaker 2: the power to predict the future. You know, if I

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Speaker 2: tell you the angle of my cannonball, I know whether

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Speaker 2: it's going to go over that castle wall or not.

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Speaker 2: Because it's described by the laws of physics. The past

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Speaker 2: predicts the future. That's wonderful. It also tells you what

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Speaker 2: can't happen right. It tells you that like your ball

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Speaker 2: can't be here and then suddenly appear.

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Speaker 1: On the other side of the wall.

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Speaker 2: Or for example, you can't shoot a laser at those

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Speaker 2: Aliens and Andromeda and fry them today because light takes

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Speaker 2: time to get to Andromeda. It's like this sphere of

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Speaker 2: influence you have over the universe. You can't affect things

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Speaker 2: outside that sphere because light only travels at a certain

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Speaker 2: speed and nothing can go faster than that. And so

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Speaker 2: time is intimately connected with how the universe moves forward.

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Speaker 2: And this is a beautiful vision to imagine we're all

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Speaker 2: linked together in time. But Einstein was the first one

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Speaker 2: to make this confusing because he realized that we don't

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Speaker 2: actually have a single clock for everybody in the universe.

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Speaker 2: His theory of special relativity messes that up.

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Speaker 4: So for a second there you had me feeling like

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Speaker 4: maybe I shouldn't have studied animal behavior, where everything is

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Speaker 4: confusing and hard to predict, and you don't know if

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Speaker 4: the person's going to catch the ball you were talking

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Speaker 4: about But now you've made me feel like no, I

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Speaker 4: made the right choice because physics is confusing too. Is

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Speaker 4: it confusing in a predictable way or is it just yeah,

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Speaker 4: what did Einstein say?

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Speaker 2: So we're not doing quantu mechanics. Yeah, the universe isn't random.

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Speaker 2: We're still dealing with the deterministic, predictable universe where the

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Speaker 2: past perfectly predicts the future. It's just that it predict

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Speaker 2: it differently than what Newton thought. The reason that time

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Speaker 2: is all messed up is because of this amazing experimental

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Speaker 2: fact that Einstein relied on about the speed of light.

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Speaker 4: We are taking a break, and when we get back,

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Speaker 4: we'll hear about how Einstein ruined Newton's beautiful idea of time.

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Speaker 4: So we're back. One of the most exciting things to

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Speaker 4: me about physics is how you have these predictions that

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Speaker 4: are sort of counterintuitive but then actually help you really

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Speaker 4: understand complex things and create new technologies and stuff like that. So,

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Speaker 4: all right, you're about to tell us how Einstein came

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Speaker 4: up with this complicated, counterintuitive idea, but it's correct and

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Speaker 4: we use it all the time.

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Speaker 2: Yeah, So Einstein's special relativity really messes up our concept

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Speaker 2: of time. Newton's idea that everybody in the universe, can

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Speaker 2: you share the same clock, that you can imagine like

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Speaker 2: a still frame for the whole universe, and then take

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Speaker 2: that forward to the next still frame for the whole universe,

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Speaker 2: and that like physicist and Andromeda and physicists in the

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Speaker 2: Milky Way can agree on how that all works. And

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Speaker 2: this all comes out of a pesky little fact which

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Speaker 2: initially doesn't sound all connected to time and watches and clocks,

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Speaker 2: but it intimately is. And that's about how light works.

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Speaker 2: In the late eighteen hundreds that people did experiments and

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Speaker 2: discovered that light travels at the same speed for all observers.

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Speaker 2: So like if you're holding a flashlight and you turn

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Speaker 2: it on, you measure the speed of the photons will

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Speaker 2: come out to be the speed of light. Now, if

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Speaker 2: you're in a car and you're going sixty miles an

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Speaker 2: hour and you turn the flashlight on, you measure those

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Speaker 2: photons to be moving at the speed of light. Somebody

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Speaker 2: on the ground who isn't in the car, they don't

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Speaker 2: measure the photons to be moving at the speed of

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Speaker 2: light plus sixty miles an hour. They still measure it

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Speaker 2: to be moving at the speed of light anywhere, anybody, everywhere.

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Speaker 2: Everybody always measures the speed of light to be the same,

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Speaker 2: no matter how fast they're going.

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Speaker 4: If you were in a car going sixty miles an

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Speaker 4: hour and you took a ball and you threw it

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Speaker 4: out your window, would you get a different answer or

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Speaker 4: is it the same as the speed of light?

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Speaker 1: Exactly.

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Speaker 2: Balls work very differently than light does. If you're in

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Speaker 2: the car and you throw the ball at sixty miles

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Speaker 2: an hour, you measure it moving relative to you at sixty.

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Speaker 1: Miles an hour.

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Speaker 2: But if I'm on the ground and the car is

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Speaker 2: moving at sixty miles an hour, I'm going to measure

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Speaker 2: the ball to be going sixty plus sixty at one

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Speaker 2: hundred and twenty miles per hour. That's also true of

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Speaker 2: simpler things like sound. If you're in the car and

440
00:21:39,960 --> 00:21:42,879
Speaker 2: you shout your daughter's name, like hey, watch out, you know,

441
00:21:43,000 --> 00:21:45,960
Speaker 2: then that sound moves away from you at the speed

442
00:21:46,000 --> 00:21:49,400
Speaker 2: of sound relative to the air. So I'm on the ground,

443
00:21:49,480 --> 00:21:52,160
Speaker 2: I see that shout moving at the speed of sound

444
00:21:52,200 --> 00:21:54,760
Speaker 2: relative to the air. If you're in the car, you

445
00:21:54,800 --> 00:21:57,080
Speaker 2: could even catch up to that shout. The speed of

446
00:21:57,080 --> 00:21:59,680
Speaker 2: that shout for you depends on how fast you're moving

447
00:21:59,680 --> 00:22:02,040
Speaker 2: through the air. You could even catch up to that

448
00:22:02,160 --> 00:22:04,560
Speaker 2: shout right, because the speed of sound is not that fast.

449
00:22:05,200 --> 00:22:07,760
Speaker 2: You could have no speed with respect to your shout.

450
00:22:07,840 --> 00:22:09,800
Speaker 2: Like if you're traveling at the speed of sound at

451
00:22:09,800 --> 00:22:12,800
Speaker 2: mock one and you shout, your shout just stays there

452
00:22:12,840 --> 00:22:16,600
Speaker 2: with you. Whereas photons, they're always moving at the speed

453
00:22:16,600 --> 00:22:20,160
Speaker 2: of light relative to you. So light is very different

454
00:22:20,200 --> 00:22:22,399
Speaker 2: from baseballs and from sound and all this stuff. And

455
00:22:22,440 --> 00:22:25,199
Speaker 2: this says really important consequences for what time is and

456
00:22:25,240 --> 00:22:26,080
Speaker 2: how we measure it.

457
00:22:26,240 --> 00:22:26,520
Speaker 4: Why.

458
00:22:27,040 --> 00:22:29,359
Speaker 2: Yeah, great question, And to answer it, let me give

459
00:22:29,359 --> 00:22:32,840
Speaker 2: you an example. This is Einstein's classic example for why

460
00:22:32,960 --> 00:22:35,000
Speaker 2: the speed of light misses up time. And Einstein isn't

461
00:22:35,000 --> 00:22:37,719
Speaker 2: thinking about big clocks in the sky. He's just thinking about, like,

462
00:22:38,240 --> 00:22:41,240
Speaker 2: when does stuff happen at the same time. So imagine

463
00:22:41,240 --> 00:22:43,000
Speaker 2: instead of in a car, you're standing in a train

464
00:22:43,520 --> 00:22:45,560
Speaker 2: and you have a flashlight, and you shine a flashlight

465
00:22:45,600 --> 00:22:47,720
Speaker 2: forwards and backwards, or you turn on a light bulb

466
00:22:47,760 --> 00:22:51,000
Speaker 2: so it shines in both directions. When is the light

467
00:22:51,040 --> 00:22:52,399
Speaker 2: going to hit the front of the train and the

468
00:22:52,440 --> 00:22:55,280
Speaker 2: back of the train. Well, you're in the train, You're

469
00:22:55,280 --> 00:22:56,720
Speaker 2: in the middle of the car. It's going to hit

470
00:22:56,760 --> 00:22:58,560
Speaker 2: the front and the back at the same time, right,

471
00:22:58,760 --> 00:23:01,919
Speaker 2: No big deal. Okay, that's cool, But what about somebody

472
00:23:01,920 --> 00:23:04,119
Speaker 2: on the ground. You know what, if you're in the train,

473
00:23:04,240 --> 00:23:06,159
Speaker 2: you turn on your flashlight, you see the light hit

474
00:23:06,200 --> 00:23:07,359
Speaker 2: the front of the train at the back of the

475
00:23:07,400 --> 00:23:09,560
Speaker 2: train at the same time. I'm on the ground. I'm

476
00:23:09,600 --> 00:23:11,600
Speaker 2: not in your train with you. To me, the train

477
00:23:11,680 --> 00:23:13,600
Speaker 2: is moving past me at one hundred miles per hour

478
00:23:13,720 --> 00:23:14,119
Speaker 2: or something.

479
00:23:14,760 --> 00:23:15,600
Speaker 1: What do I see?

480
00:23:16,000 --> 00:23:17,720
Speaker 2: I see the light moving forward at the speed of

481
00:23:17,760 --> 00:23:19,840
Speaker 2: light and backwards at the speed of light. But the

482
00:23:19,880 --> 00:23:22,480
Speaker 2: back of the train is moving towards the light bulb

483
00:23:22,600 --> 00:23:24,600
Speaker 2: and the front of the train is moving away from it.

484
00:23:24,960 --> 00:23:27,679
Speaker 2: So from my perspective, the light hits the back of

485
00:23:27,720 --> 00:23:29,639
Speaker 2: the train before it hits the front of the train,

486
00:23:29,880 --> 00:23:32,200
Speaker 2: because the back of the train is rushing to meet

487
00:23:32,400 --> 00:23:34,760
Speaker 2: the light. So you see these things happening at the

488
00:23:34,800 --> 00:23:37,640
Speaker 2: same time. The front and the back are simultaneous for you,

489
00:23:37,680 --> 00:23:41,720
Speaker 2: but they're not simultaneous for me. And that's only because

490
00:23:42,280 --> 00:23:45,520
Speaker 2: light travels at the same speed for me and for you.

491
00:23:45,960 --> 00:23:49,440
Speaker 2: We did this example in sound or with baseballs, then

492
00:23:49,480 --> 00:23:52,240
Speaker 2: we would agree about whether they're simultaneous or not. But

493
00:23:52,320 --> 00:23:55,200
Speaker 2: because light always travels at the same speed for everybody,

494
00:23:55,400 --> 00:23:58,119
Speaker 2: we don't agree about whether the events are at the

495
00:23:58,160 --> 00:23:58,760
Speaker 2: same time.

496
00:23:59,160 --> 00:24:01,359
Speaker 4: Okay, so the first this person turns on their flashlights

497
00:24:01,359 --> 00:24:04,040
Speaker 4: and the answer is three seconds for forward and for back,

498
00:24:04,160 --> 00:24:07,040
Speaker 4: and for somebody else the answer is four seconds for

499
00:24:07,040 --> 00:24:08,600
Speaker 4: forward and two seconds for back.

500
00:24:09,200 --> 00:24:10,120
Speaker 1: Yeah, exactly right.

501
00:24:10,160 --> 00:24:12,239
Speaker 2: And if we did the same experiment with sound, right,

502
00:24:12,280 --> 00:24:13,840
Speaker 2: if you stood in the center of the car and

503
00:24:13,880 --> 00:24:16,800
Speaker 2: you shouted instead of turning on a light, then the

504
00:24:16,840 --> 00:24:18,520
Speaker 2: shout would reach the front and the back of the

505
00:24:18,560 --> 00:24:19,480
Speaker 2: train at the same time.

506
00:24:19,480 --> 00:24:21,320
Speaker 1: For you, you're on the train, and.

507
00:24:21,280 --> 00:24:24,040
Speaker 2: What would happen for me? For me, sound doesn't have

508
00:24:24,119 --> 00:24:26,359
Speaker 2: to move at the same speed no matter what. So

509
00:24:26,520 --> 00:24:29,200
Speaker 2: I would see the sound moving forward faster than I

510
00:24:29,240 --> 00:24:31,600
Speaker 2: would see it moving backwards, because it's moving with the

511
00:24:31,720 --> 00:24:35,240
Speaker 2: air inside the train. Right, sound doesn't have to move

512
00:24:35,240 --> 00:24:37,680
Speaker 2: at the same speed for me, it doesn't have to

513
00:24:37,720 --> 00:24:41,360
Speaker 2: follow Einstein's weird special rule, so I see it also

514
00:24:41,400 --> 00:24:44,440
Speaker 2: as simultaneous. I see the front of the train racing away,

515
00:24:44,520 --> 00:24:46,880
Speaker 2: but the sound is moving faster forward. And I see

516
00:24:46,920 --> 00:24:49,439
Speaker 2: the back of the train rushing towards you, but the

517
00:24:49,480 --> 00:24:52,280
Speaker 2: sound is moving slower in that direction, and so it

518
00:24:52,320 --> 00:24:54,639
Speaker 2: all works out. It's all simultaneous for me and for

519
00:24:54,760 --> 00:24:57,480
Speaker 2: you for sound. But because light breaks that, it says,

520
00:24:57,840 --> 00:25:00,159
Speaker 2: I don't care how fast I'm going. Daniel's can to

521
00:25:00,160 --> 00:25:02,160
Speaker 2: see me go in at the speed of light forward

522
00:25:02,240 --> 00:25:05,560
Speaker 2: and backwards, And so Daniel doesn't see it simultaneous, and

523
00:25:05,640 --> 00:25:06,320
Speaker 2: Kelly does.

524
00:25:06,560 --> 00:25:07,879
Speaker 4: And this is something we got to a little bit

525
00:25:07,880 --> 00:25:11,120
Speaker 4: in the last episode. It sounds like you can't really

526
00:25:11,160 --> 00:25:14,919
Speaker 4: separate space and time. You need to understand them both.

527
00:25:15,920 --> 00:25:20,240
Speaker 4: So we have two complicated concepts to try to define together.

528
00:25:20,080 --> 00:25:23,040
Speaker 2: Exactly, and you put your finger on it. Whereas Newton said, look,

529
00:25:23,040 --> 00:25:26,400
Speaker 2: there's one clock for the whole universe, Einstein says there's

530
00:25:26,440 --> 00:25:30,560
Speaker 2: one clock at every point in space. Every location in

531
00:25:30,600 --> 00:25:34,400
Speaker 2: space has a different clock, right, And so I see

532
00:25:34,400 --> 00:25:36,720
Speaker 2: one clock running fast, you see another clock running slow.

533
00:25:36,760 --> 00:25:39,040
Speaker 2: It's not just that there's a different clock at every space.

534
00:25:39,359 --> 00:25:42,639
Speaker 2: How you see those clocks running also depends on your velocity,

535
00:25:43,200 --> 00:25:46,200
Speaker 2: So there's no sense of universal time. There's not one

536
00:25:46,280 --> 00:25:48,880
Speaker 2: time for the whole universe. This image we had where

537
00:25:48,880 --> 00:25:51,520
Speaker 2: like the whole universe is frozen and then it ticks forward.

538
00:25:51,560 --> 00:25:53,359
Speaker 2: According to physics, Like, if you're going to run a

539
00:25:53,359 --> 00:25:56,200
Speaker 2: simulation of the universe, that's the way you might do it.

540
00:25:56,400 --> 00:25:59,280
Speaker 2: That's broken. Now you can't have a single clock for

541
00:25:59,320 --> 00:26:01,119
Speaker 2: the whole universe. We have to have a different clock

542
00:26:01,160 --> 00:26:04,320
Speaker 2: at every location, and a different clock for people moving

543
00:26:04,320 --> 00:26:08,600
Speaker 2: at different speeds. It really breaks Newton's idea that time

544
00:26:08,680 --> 00:26:09,399
Speaker 2: is universal.

545
00:26:09,760 --> 00:26:13,760
Speaker 4: Okay, but so on our planet we have people who

546
00:26:14,000 --> 00:26:17,560
Speaker 4: travel in super fast jets, but we're all able to

547
00:26:17,600 --> 00:26:21,080
Speaker 4: stay on the same clock without feeling confused. Are we

548
00:26:21,200 --> 00:26:23,840
Speaker 4: just not going fast enough for this to be a problem?

549
00:26:24,160 --> 00:26:28,159
Speaker 4: You know, the Andromeda Galaxy version of Daniel and Kelly's

550
00:26:28,160 --> 00:26:32,760
Speaker 4: Extraordinary Universe. Could we schedule a time to interview them

551
00:26:33,640 --> 00:26:36,080
Speaker 4: or no? Because we would never be able to figure

552
00:26:36,080 --> 00:26:37,359
Speaker 4: out what time we meant.

553
00:26:38,320 --> 00:26:40,040
Speaker 2: Well, first of all, it would take them millions of

554
00:26:40,160 --> 00:26:42,399
Speaker 2: years to answer our email, right because and drama is

555
00:26:42,400 --> 00:26:46,520
Speaker 2: still millions of years. So stay tuned, everybody. Let's hope

556
00:26:46,520 --> 00:26:49,280
Speaker 2: this podcast lasts that long. That would be awesome. It

557
00:26:49,359 --> 00:26:52,840
Speaker 2: also be a slow conversation the reason all.

558
00:26:52,840 --> 00:26:55,040
Speaker 4: Right, so not fast paced storytelling.

559
00:26:55,640 --> 00:26:57,439
Speaker 2: But you make a really good point, which is that

560
00:26:57,520 --> 00:27:00,520
Speaker 2: we don't notice these effects our clocks. To get out

561
00:27:00,520 --> 00:27:03,159
Speaker 2: of sync because somebody got on a train or an airplane.

562
00:27:03,600 --> 00:27:06,119
Speaker 2: And that's because these effects depend on the velocity and

563
00:27:06,160 --> 00:27:09,560
Speaker 2: they're mostly ignorable unless you get up to like seventy

564
00:27:09,640 --> 00:27:12,720
Speaker 2: eighty ninety percent of the speed of light. It turns

565
00:27:12,760 --> 00:27:15,199
Speaker 2: out that this is the way time actually works. This

566
00:27:15,240 --> 00:27:18,320
Speaker 2: is the fundamental nature of time. But if you're going slow,

567
00:27:18,359 --> 00:27:20,600
Speaker 2: those effects are very small, and you can basically just

568
00:27:20,680 --> 00:27:24,120
Speaker 2: assume that time is the same for everybody. So Newton's

569
00:27:24,160 --> 00:27:27,520
Speaker 2: idea works except when you're going really really fast. And

570
00:27:27,600 --> 00:27:31,720
Speaker 2: because nobody's really ever going that fast, Newton didn't notice,

571
00:27:31,720 --> 00:27:34,639
Speaker 2: and nobody noticed for a long long time that this

572
00:27:34,840 --> 00:27:37,919
Speaker 2: was the true effect of time. So time is almost universal,

573
00:27:38,000 --> 00:27:40,200
Speaker 2: but moving really really fast breaks it.

574
00:27:41,000 --> 00:27:44,439
Speaker 4: So clearly, the most important question that we're going to

575
00:27:44,480 --> 00:27:48,760
Speaker 4: tackle today is it possible to travel back in time?

576
00:27:50,560 --> 00:27:53,640
Speaker 4: And have we learned anything yet that helps us think

577
00:27:53,680 --> 00:27:54,440
Speaker 4: about that question.

578
00:27:54,800 --> 00:27:57,000
Speaker 2: Yeah, this might give you the impression like, wow, time

579
00:27:57,080 --> 00:28:00,640
Speaker 2: is sort of controllable. I can control whether I see

580
00:28:00,680 --> 00:28:02,239
Speaker 2: things happening at the same time or not. I can

581
00:28:02,320 --> 00:28:05,360
Speaker 2: even like reorder things. You know, if you're moving at

582
00:28:05,359 --> 00:28:07,880
Speaker 2: one speed, you can see the light hit the front

583
00:28:07,880 --> 00:28:10,080
Speaker 2: of the train first, and then the back of the train. Second,

584
00:28:10,080 --> 00:28:12,199
Speaker 2: if you're moving at another speed, you can see the

585
00:28:12,240 --> 00:28:15,160
Speaker 2: opposite order of events. Right, the light hits the back

586
00:28:15,200 --> 00:28:17,120
Speaker 2: of the train first and then the front of the train,

587
00:28:17,600 --> 00:28:19,480
Speaker 2: And that sort of boggles the mind. It makes you

588
00:28:19,520 --> 00:28:22,560
Speaker 2: feel like I have control over the order of events

589
00:28:22,600 --> 00:28:25,560
Speaker 2: in the universe. Newton was like A, then B, then C,

590
00:28:25,760 --> 00:28:28,280
Speaker 2: then D in Einstein's like, no, if you're going fast enough,

591
00:28:28,359 --> 00:28:30,919
Speaker 2: then you can have D before C. And you're like, what,

592
00:28:31,160 --> 00:28:33,399
Speaker 2: that's crazy. And at least the questions like you just asked,

593
00:28:33,400 --> 00:28:36,280
Speaker 2: like can we control the flow of time? And can

594
00:28:36,320 --> 00:28:39,320
Speaker 2: we even make it go backwards? And so there are

595
00:28:39,400 --> 00:28:43,360
Speaker 2: limitations to what Einstein lets you do. Einstein says, yes,

596
00:28:43,440 --> 00:28:46,480
Speaker 2: the order events depends on your speed. But there's a

597
00:28:46,520 --> 00:28:49,240
Speaker 2: limitation to how fast you can go in the universe, right,

598
00:28:49,400 --> 00:28:51,000
Speaker 2: And you can only go the speed of light, and

599
00:28:51,000 --> 00:28:54,120
Speaker 2: that limits how much you can reorder events.

600
00:28:54,520 --> 00:28:56,280
Speaker 4: So, if I could move at the speed of light,

601
00:28:56,840 --> 00:29:00,280
Speaker 4: could I have caught Ada before she fell? Less of

602
00:29:00,280 --> 00:29:03,400
Speaker 4: a time question and more of a Kellius Sluss like question.

603
00:29:06,440 --> 00:29:09,200
Speaker 2: No, that's a great question. If you could go faster

604
00:29:09,360 --> 00:29:11,640
Speaker 2: than the speed of light, you would have all sorts

605
00:29:11,680 --> 00:29:14,640
Speaker 2: of causal contradictions. If you go faster than the speed

606
00:29:14,640 --> 00:29:17,000
Speaker 2: of light, then for example, you could see the light

607
00:29:17,080 --> 00:29:19,560
Speaker 2: hit the end of the train before it even leaves

608
00:29:19,600 --> 00:29:22,880
Speaker 2: the light bulb. Right, there's a limitation there. Light will

609
00:29:22,920 --> 00:29:25,120
Speaker 2: let you reorder those events, but not in a way

610
00:29:25,160 --> 00:29:28,880
Speaker 2: that breaks causality, So you can't make something happen first

611
00:29:28,960 --> 00:29:31,840
Speaker 2: which is causally connected to something else in the future.

612
00:29:32,040 --> 00:29:35,440
Speaker 4: That almost sounds like there's a little bit of time

613
00:29:35,480 --> 00:29:38,920
Speaker 4: travel possible, but within some bounds of causality.

614
00:29:39,000 --> 00:29:42,719
Speaker 2: But if I misunderstanding now, you can rearrange the order

615
00:29:42,720 --> 00:29:44,520
Speaker 2: of events in the universe. You can make one thing

616
00:29:44,560 --> 00:29:47,320
Speaker 2: happen before another thing, and somebody else can disagree, which

617
00:29:47,320 --> 00:29:48,040
Speaker 2: is kind of crazy.

618
00:29:48,080 --> 00:29:48,240
Speaker 6: You know.

619
00:29:48,280 --> 00:29:50,640
Speaker 2: You can imagine like two people running a race and

620
00:29:50,640 --> 00:29:54,000
Speaker 2: people having different opinions about like who wins the race,

621
00:29:54,320 --> 00:29:56,400
Speaker 2: and you feel like, no, somebody is faster. Well the

622
00:29:56,440 --> 00:29:59,440
Speaker 2: answer is there isn't really anybody faster. But yes, there

623
00:29:59,480 --> 00:30:02,680
Speaker 2: are limited like you can't make the runners reach the

624
00:30:02,680 --> 00:30:05,960
Speaker 2: finish line before they leave the starting line. And it

625
00:30:06,000 --> 00:30:08,200
Speaker 2: might sound like, hey, I'm just adding an exception to

626
00:30:08,280 --> 00:30:10,880
Speaker 2: fix physics so that it makes sense, but this really

627
00:30:10,920 --> 00:30:13,959
Speaker 2: is systematized, like the things that you can reorder are

628
00:30:13,960 --> 00:30:16,480
Speaker 2: things that are like outside of your sphere of influence.

629
00:30:16,800 --> 00:30:18,680
Speaker 2: We talked earlier about how like, if you shoot a

630
00:30:18,760 --> 00:30:21,240
Speaker 2: light rate at Andromeda, you can't hit the alien version

631
00:30:21,240 --> 00:30:23,920
Speaker 2: of Daniel and Kelly and Anddrameda right now. You can't

632
00:30:23,960 --> 00:30:26,400
Speaker 2: hit them for millions of years because it takes light

633
00:30:26,640 --> 00:30:29,160
Speaker 2: to get there. So this is like sphere of influence.

634
00:30:29,200 --> 00:30:32,280
Speaker 2: You have control over. Anything you have control over, you

635
00:30:32,320 --> 00:30:36,360
Speaker 2: can't reorder, right because that would break causality. Anything outside

636
00:30:36,400 --> 00:30:39,280
Speaker 2: your light cone you can reorder, so you can move

637
00:30:39,320 --> 00:30:42,640
Speaker 2: stuff around that you don't have influence over because it's

638
00:30:42,640 --> 00:30:44,000
Speaker 2: not constantly connected to you.

639
00:30:44,560 --> 00:30:46,400
Speaker 4: All right, So what's the coolest thing you could do

640
00:30:46,760 --> 00:30:49,960
Speaker 4: with that power? What is our superhero movie going to

641
00:30:50,000 --> 00:30:51,640
Speaker 4: be about?

642
00:30:52,000 --> 00:30:52,200
Speaker 1: Oh?

643
00:30:52,240 --> 00:30:54,280
Speaker 2: Man, I think the coolest thing you can do is

644
00:30:54,360 --> 00:30:57,680
Speaker 2: be younger than your twin. You know, you can actually

645
00:30:57,680 --> 00:31:00,840
Speaker 2: like fly in a spaceship at a high speed, turn around,

646
00:31:00,920 --> 00:31:02,800
Speaker 2: come back and find that a lot of time has

647
00:31:02,840 --> 00:31:05,440
Speaker 2: passed on Earth and you're still young. And that's pretty cool.

648
00:31:05,480 --> 00:31:10,040
Speaker 2: That seems so toxy. That's basically time travel into the future, right,

649
00:31:10,440 --> 00:31:12,280
Speaker 2: and that you could actually do and they've done that.

650
00:31:12,320 --> 00:31:14,760
Speaker 2: You know, there are twin astronauts, and one of them

651
00:31:14,800 --> 00:31:15,520
Speaker 2: was in space.

652
00:31:15,280 --> 00:31:15,880
Speaker 1: For a long time.

653
00:31:15,920 --> 00:31:18,240
Speaker 2: It moved at a pretty high speed, and now his

654
00:31:18,280 --> 00:31:19,720
Speaker 2: twin is like three minutes.

655
00:31:19,480 --> 00:31:23,000
Speaker 4: Older, got it, And that doesn't break causality even though

656
00:31:23,000 --> 00:31:26,280
Speaker 4: they were born at the same time, because they both existed.

657
00:31:25,960 --> 00:31:28,960
Speaker 2: And because they were separated in space, okay, right, and

658
00:31:29,040 --> 00:31:31,040
Speaker 2: so their time was flowing different and they were far

659
00:31:31,080 --> 00:31:33,320
Speaker 2: apart from each other, so they couldn't break causality. They

660
00:31:33,360 --> 00:31:35,080
Speaker 2: couldn't do things that influenced each other.

661
00:31:35,520 --> 00:31:36,240
Speaker 1: Yeah, exactly.

662
00:31:36,600 --> 00:31:38,600
Speaker 2: You can't have time to flow differently if you're in

663
00:31:38,640 --> 00:31:41,320
Speaker 2: the same place. So if those twins like never separated,

664
00:31:41,560 --> 00:31:43,560
Speaker 2: then their clocks would be inextricably linked.

665
00:31:43,600 --> 00:31:45,880
Speaker 4: All right, Okay, all right, I think we could probably

666
00:31:45,920 --> 00:31:50,640
Speaker 4: pitch that to Hollywood. So this is the general relativity

667
00:31:50,920 --> 00:31:53,920
Speaker 4: understanding of things, right, because we're talking about Einstein.

668
00:31:54,360 --> 00:31:57,840
Speaker 2: This is the special relativity. Einstein at two theories of relativity.

669
00:31:57,880 --> 00:32:00,240
Speaker 2: One is special relativity has to do with the speed

670
00:32:00,320 --> 00:32:02,280
Speaker 2: of light and clocks and all that kind of stuff

671
00:32:02,280 --> 00:32:04,640
Speaker 2: that we've been talking about. But that's assuming that space

672
00:32:04,720 --> 00:32:07,960
Speaker 2: is smooth and flat. There's no like weird curvature to it.

673
00:32:08,040 --> 00:32:11,240
Speaker 2: There's no mass in the universe. Things get even weirder

674
00:32:11,280 --> 00:32:15,120
Speaker 2: when Einstein allows us to add mass to the universe.

675
00:32:15,320 --> 00:32:17,960
Speaker 4: And we talked last time about how space can bend.

676
00:32:18,720 --> 00:32:22,600
Speaker 4: So if you're going around to space bends, how does

677
00:32:22,640 --> 00:32:23,560
Speaker 4: that change time?

678
00:32:25,040 --> 00:32:28,120
Speaker 2: So you're right earlier that we're connecting time and space

679
00:32:28,160 --> 00:32:29,080
Speaker 2: in an important way.

680
00:32:29,560 --> 00:32:29,720
Speaker 1: Right.

681
00:32:29,760 --> 00:32:32,240
Speaker 2: The way that time flows depends on where you are

682
00:32:32,280 --> 00:32:34,840
Speaker 2: in space, and we link them together like space time.

683
00:32:34,880 --> 00:32:38,120
Speaker 2: We have this four dimensional construct and that's really important

684
00:32:38,160 --> 00:32:41,320
Speaker 2: in general relativity, and sometimes it makes people think, well,

685
00:32:41,520 --> 00:32:44,400
Speaker 2: time is part of space time, so maybe time is

686
00:32:44,480 --> 00:32:47,600
Speaker 2: like a dimension the way space is, right, and that's

687
00:32:47,720 --> 00:32:49,880
Speaker 2: very tempting because when you look at general relativity, you

688
00:32:49,920 --> 00:32:52,480
Speaker 2: see that Einstein just treats time as like the fourth

689
00:32:52,480 --> 00:32:55,080
Speaker 2: dimension of space. But we also know that time is

690
00:32:55,120 --> 00:32:58,280
Speaker 2: different from the fourth dimension. It's not just like xyzt

691
00:32:58,920 --> 00:33:01,600
Speaker 2: another fourth dimension operates the same way as you were

692
00:33:01,640 --> 00:33:04,320
Speaker 2: saying earlier, like you can't go backwards in time, you

693
00:33:04,360 --> 00:33:08,320
Speaker 2: can't revisit the same location in time, and general relativity

694
00:33:08,360 --> 00:33:12,200
Speaker 2: respects this. There are a spacelike and timelike coordinates, and

695
00:33:12,280 --> 00:33:15,120
Speaker 2: it tells us that time ticks very differently, but there

696
00:33:15,120 --> 00:33:17,880
Speaker 2: are a lot of similarities for example, time is also

697
00:33:17,960 --> 00:33:21,320
Speaker 2: affected by mass. Like you were saying you put mass

698
00:33:21,320 --> 00:33:24,400
Speaker 2: in space, space bends and as we were saying last time,

699
00:33:24,440 --> 00:33:29,479
Speaker 2: like photons curve around masses, Well, mass also bends time.

700
00:33:29,680 --> 00:33:32,920
Speaker 2: It's not just space that gets bent, but time gets bent.

701
00:33:33,440 --> 00:33:34,480
Speaker 1: Like, well, what does that mean.

702
00:33:34,760 --> 00:33:36,760
Speaker 2: It's like a set of words that I don't know

703
00:33:36,800 --> 00:33:39,960
Speaker 2: how to process right practically, what it means is that

704
00:33:40,080 --> 00:33:43,680
Speaker 2: clocks tick slower near masses. So if you're near a

705
00:33:43,680 --> 00:33:46,920
Speaker 2: black hole, for example, your clock will tick slower than

706
00:33:46,920 --> 00:33:49,080
Speaker 2: someone who's further from a black hole.

707
00:33:49,480 --> 00:33:51,080
Speaker 4: All right, well, I think the one thing my brain

708
00:33:51,120 --> 00:33:53,640
Speaker 4: is having trouble with is like I'm picturing a clock

709
00:33:53,680 --> 00:33:56,160
Speaker 4: from my childhood with the two hands, and I'm like,

710
00:33:56,240 --> 00:33:58,520
Speaker 4: is it moving slower because the arms are getting pulled

711
00:33:58,520 --> 00:34:00,040
Speaker 4: on it in a different way. But that's not the

712
00:34:00,160 --> 00:34:01,040
Speaker 4: right way to think about it.

713
00:34:01,240 --> 00:34:03,960
Speaker 2: Yeah, it would work with any clock exactly, because the

714
00:34:04,040 --> 00:34:07,080
Speaker 2: laws of physics themselves slow down, and it depends here

715
00:34:07,120 --> 00:34:09,720
Speaker 2: on the observer, Like if you're looking at that clock,

716
00:34:09,800 --> 00:34:12,920
Speaker 2: you always experience time at the same rate, Like for you,

717
00:34:13,040 --> 00:34:15,560
Speaker 2: it's one second per second, no matter what. But say

718
00:34:15,600 --> 00:34:18,359
Speaker 2: you're orbiting near a black hole and I'm further away

719
00:34:18,360 --> 00:34:19,839
Speaker 2: from the black hole, and I'm looking at you through

720
00:34:19,840 --> 00:34:23,160
Speaker 2: a telescope. I'm comparing my clock to your clock. I'm

721
00:34:23,200 --> 00:34:26,080
Speaker 2: going to see your clock ticking slower than mine. Every

722
00:34:26,080 --> 00:34:28,799
Speaker 2: time your clock ticks one second, my clock is going

723
00:34:28,880 --> 00:34:32,280
Speaker 2: to tick two. The amazing thing is in general relativity,

724
00:34:32,520 --> 00:34:33,960
Speaker 2: you and I will agree on this. If you have

725
00:34:34,000 --> 00:34:37,439
Speaker 2: a telescope and you're looking back at me, then you're

726
00:34:37,480 --> 00:34:39,960
Speaker 2: going to say, oh, every time my clock ticks, Daniel's

727
00:34:40,000 --> 00:34:42,879
Speaker 2: clock ticks twice. Right, So you and I agree that

728
00:34:42,920 --> 00:34:45,160
Speaker 2: my clock is ticking faster than yours. The time is

729
00:34:45,200 --> 00:34:48,040
Speaker 2: going slower for you, which means that the way to

730
00:34:48,080 --> 00:34:50,080
Speaker 2: get into the future is like orbit a black hole

731
00:34:50,360 --> 00:34:53,120
Speaker 2: and you'll see the future of the universe. Like all

732
00:34:53,160 --> 00:34:56,640
Speaker 2: the clocks in the universe will fast forward. So you're curious,

733
00:34:56,719 --> 00:34:59,040
Speaker 2: like what's going to happen in a billion years or

734
00:34:59,080 --> 00:35:01,880
Speaker 2: a trillion years the universe? Boom, Just go orbit a

735
00:35:01,880 --> 00:35:04,520
Speaker 2: black hole and you will be fast forwarded to the

736
00:35:04,560 --> 00:35:05,560
Speaker 2: future of the universe.

737
00:35:05,840 --> 00:35:08,400
Speaker 4: All right, we made it to my goal. Then okay, oh,

738
00:35:08,480 --> 00:35:10,400
Speaker 4: I'm so sorry. You think I'm late. Your a clock

739
00:35:10,480 --> 00:35:12,920
Speaker 4: must be taking faster than mine. I got here at

740
00:35:12,920 --> 00:35:13,600
Speaker 4: the right time.

741
00:35:13,440 --> 00:35:16,120
Speaker 2: For me, and this is something we actually can measure.

742
00:35:16,360 --> 00:35:18,359
Speaker 2: You know, we haven't visited a black hole, of course,

743
00:35:18,400 --> 00:35:21,080
Speaker 2: so we don't see really dramatic effects of this, but

744
00:35:21,520 --> 00:35:23,239
Speaker 2: we can tell that this is happening. People done these

745
00:35:23,280 --> 00:35:27,120
Speaker 2: amazing experiments with have super precise clocks, like one on

746
00:35:27,160 --> 00:35:29,400
Speaker 2: the ground and one just like a couple of meters

747
00:35:29,440 --> 00:35:33,160
Speaker 2: above the ground. And because the second clock is further

748
00:35:33,400 --> 00:35:37,360
Speaker 2: from the Earth, it's experiencing less curvature of space and

749
00:35:37,400 --> 00:35:40,799
Speaker 2: so it's not slowed down as much. And satellites in

750
00:35:40,880 --> 00:35:43,759
Speaker 2: space also have super accurate clocks, and we can tell

751
00:35:43,800 --> 00:35:45,799
Speaker 2: that those are going faster than the ones on the

752
00:35:45,840 --> 00:35:48,799
Speaker 2: surface of the Earth. And in fact, our GPS is

753
00:35:48,840 --> 00:35:50,960
Speaker 2: so precise that it has to take this into account,

754
00:35:51,160 --> 00:35:53,520
Speaker 2: the fact that time clicks slower in space.

755
00:35:53,640 --> 00:35:54,520
Speaker 1: I bet you didn't know that.

756
00:35:54,880 --> 00:35:56,560
Speaker 4: I did know that. I learned that when I was

757
00:35:56,600 --> 00:35:58,200
Speaker 4: an adult, and that was the first moment where I

758
00:35:58,200 --> 00:36:02,879
Speaker 4: thought to myself, all right, these like esoteric conversations about

759
00:36:02,920 --> 00:36:05,359
Speaker 4: space and time are important because there are practical things

760
00:36:05,360 --> 00:36:07,520
Speaker 4: that have to change because of these things. It's not

761
00:36:07,600 --> 00:36:11,319
Speaker 4: just like I smoked too many banana peels. It's like, no, no,

762
00:36:11,360 --> 00:36:12,560
Speaker 4: this stuff is really happening.

763
00:36:12,800 --> 00:36:14,760
Speaker 2: I always felt like maybe that was a good excuse

764
00:36:14,760 --> 00:36:17,279
Speaker 2: for why space projects are so delayed, Like, hey man,

765
00:36:17,320 --> 00:36:20,799
Speaker 2: everybody knows time ticks slower in space, right, So that's

766
00:36:20,840 --> 00:36:23,400
Speaker 2: why this NASA mission is five billion over budget and

767
00:36:23,400 --> 00:36:23,839
Speaker 2: ten years.

768
00:36:24,080 --> 00:36:27,280
Speaker 4: Oh I don't think that's going to fly with Congress.

769
00:36:28,120 --> 00:36:30,719
Speaker 4: All right, let's take a little break, and when we

770
00:36:30,760 --> 00:36:33,760
Speaker 4: come back, we're going to tackle the big question about

771
00:36:34,080 --> 00:36:53,440
Speaker 4: is there even a beginning to time? All right? So Daniel,

772
00:36:54,040 --> 00:36:57,080
Speaker 4: time is different depending on like where you are, how

773
00:36:57,120 --> 00:37:01,759
Speaker 4: fast you're going, is the space around you. What does

774
00:37:01,800 --> 00:37:04,320
Speaker 4: all of this tell us, if anything, about whether or

775
00:37:04,400 --> 00:37:08,279
Speaker 4: not there was a point where time began, or has

776
00:37:08,320 --> 00:37:10,760
Speaker 4: the universe been around for like infinite time.

777
00:37:11,040 --> 00:37:12,839
Speaker 2: Yeah, again, we can rely on the fact that time

778
00:37:12,880 --> 00:37:15,839
Speaker 2: and space are connected to get some insight into this,

779
00:37:16,400 --> 00:37:18,719
Speaker 2: because one thing we learned about one hundred years ago

780
00:37:19,239 --> 00:37:22,560
Speaker 2: is that the universe is expanding, right, It's not just statics,

781
00:37:22,600 --> 00:37:26,120
Speaker 2: not just galaxies hanging there in space. It's expanding. And

782
00:37:26,160 --> 00:37:28,360
Speaker 2: that means we can run the clock backwards and say, oh,

783
00:37:28,440 --> 00:37:29,720
Speaker 2: the universe used to be denser.

784
00:37:29,960 --> 00:37:30,799
Speaker 1: We keep running the.

785
00:37:30,760 --> 00:37:33,480
Speaker 2: Clock backwards and backwards and backwards, the universe gets to

786
00:37:33,560 --> 00:37:36,960
Speaker 2: some like crazy high densities, like filled with plasma, and

787
00:37:37,000 --> 00:37:39,400
Speaker 2: you keep pushing it further and further back in time,

788
00:37:39,880 --> 00:37:42,080
Speaker 2: and you get to some moment when the universe is

789
00:37:42,160 --> 00:37:44,560
Speaker 2: so dense, so jam full of stuff that our theories

790
00:37:44,560 --> 00:37:47,719
Speaker 2: don't work anymore. Like quantum physics and gravity and all

791
00:37:47,760 --> 00:37:50,440
Speaker 2: that stuff. We don't understand how to do those calculations.

792
00:37:50,840 --> 00:37:52,640
Speaker 2: But if you ignore the quantum physics and you just

793
00:37:52,680 --> 00:37:55,080
Speaker 2: said I'm just going to keep pushing and keep squeezing

794
00:37:55,120 --> 00:37:57,840
Speaker 2: things down, that eventually what you get to is general

795
00:37:57,840 --> 00:38:01,759
Speaker 2: relativity predicting a singular. This is not the Big Bang

796
00:38:01,760 --> 00:38:03,080
Speaker 2: that a lot of people have in their minds. The

797
00:38:03,080 --> 00:38:06,480
Speaker 2: big Bang is from that moment we can't understand when

798
00:38:06,520 --> 00:38:09,440
Speaker 2: things are super dense and unique quantum gravity. It's that

799
00:38:09,520 --> 00:38:12,799
Speaker 2: expansion forward before that we don't know what happens. But

800
00:38:13,120 --> 00:38:15,920
Speaker 2: we can just say, oh, let's assume general relativity is correct,

801
00:38:15,920 --> 00:38:18,120
Speaker 2: even though we know that probably isn't at this moment,

802
00:38:18,560 --> 00:38:22,160
Speaker 2: and you can extrapolate back to this moment of incredible density,

803
00:38:22,200 --> 00:38:27,319
Speaker 2: this early universe singularity. So general relativity tells us that

804
00:38:27,360 --> 00:38:30,280
Speaker 2: there was a moment when the whole universe was a singularity,

805
00:38:30,560 --> 00:38:33,200
Speaker 2: and that that was the birth of space and time.

806
00:38:34,400 --> 00:38:38,880
Speaker 4: All right, That feels like a very satisfying answer. So

807
00:38:39,000 --> 00:38:42,600
Speaker 4: of course it's got to get a little bit more complicated,

808
00:38:42,640 --> 00:38:45,040
Speaker 4: which is a okay, all right, so we've got this set.

809
00:38:45,080 --> 00:38:48,680
Speaker 4: One answer from general relativity is there's a point when

810
00:38:48,680 --> 00:38:51,799
Speaker 4: time starts. That is like kind of confusing. If time

811
00:38:51,880 --> 00:38:56,640
Speaker 4: had a moment where it started, what was before that?

812
00:38:56,800 --> 00:38:58,760
Speaker 4: But I guess the point is there was nothing before

813
00:38:58,800 --> 00:38:59,919
Speaker 4: we Yeah what does that mean?

814
00:39:00,280 --> 00:39:02,880
Speaker 2: Yeah, it's really confusing, and even for people who like

815
00:39:02,920 --> 00:39:06,680
Speaker 2: understand general relativity, it's very confusing and for the general public,

816
00:39:06,760 --> 00:39:09,279
Speaker 2: like there's a lot of also mis explained ideas out there.

817
00:39:09,360 --> 00:39:12,000
Speaker 2: You know, people think about the beginning of the universe

818
00:39:12,080 --> 00:39:14,799
Speaker 2: as the singularity is a point in space. Really it's

819
00:39:14,800 --> 00:39:17,839
Speaker 2: a singularity in time. You know, it's this moment when

820
00:39:17,880 --> 00:39:22,040
Speaker 2: everything was incredibly dense and filling the universe. But nobody

821
00:39:22,120 --> 00:39:25,400
Speaker 2: really knows what it means for time to begin there

822
00:39:25,480 --> 00:39:28,719
Speaker 2: because beginning even means like now you're ordering events and

823
00:39:28,760 --> 00:39:30,880
Speaker 2: there's a before and after, and how do you have

824
00:39:30,920 --> 00:39:33,080
Speaker 2: a moment before time begins?

825
00:39:33,200 --> 00:39:33,399
Speaker 1: Right?

826
00:39:33,560 --> 00:39:37,240
Speaker 2: Like, without time, nothing can change. So if the universe

827
00:39:37,280 --> 00:39:40,000
Speaker 2: was in some state before time begin how did it

828
00:39:40,120 --> 00:39:42,880
Speaker 2: go from that state to a different state that requires

829
00:39:43,000 --> 00:39:47,080
Speaker 2: change right, which seems to require time. Nobody understands it.

830
00:39:47,360 --> 00:39:49,600
Speaker 2: And fundamentally the problem is, we know this is not

831
00:39:49,640 --> 00:39:53,320
Speaker 2: the true story of the universe. This requires an extrapolation

832
00:39:53,400 --> 00:39:56,880
Speaker 2: of general relativity beyond where we know it's true. You know,

833
00:39:56,920 --> 00:39:59,120
Speaker 2: we think back into the early universe when things get

834
00:39:59,160 --> 00:40:01,600
Speaker 2: denser and denser in death answer, and at some point

835
00:40:01,840 --> 00:40:05,840
Speaker 2: we can't ignore quantum mechanics anymore. General relativity doesn't align

836
00:40:05,880 --> 00:40:08,439
Speaker 2: with our quantum mechanical understanding of the universe, and we're

837
00:40:08,480 --> 00:40:11,440
Speaker 2: just ignoring it, and we're extrapolating something beyond where we

838
00:40:11,480 --> 00:40:14,280
Speaker 2: know it's reasonable. Like if you took your daughter's growth

839
00:40:14,360 --> 00:40:16,799
Speaker 2: chart that you probably mark on the wall, and you say, oh, look,

840
00:40:16,840 --> 00:40:19,000
Speaker 2: she's growing six inches a year. And I asked you,

841
00:40:19,200 --> 00:40:21,200
Speaker 2: how tall is she going to be when she's eighty Kelly,

842
00:40:21,440 --> 00:40:23,279
Speaker 2: And you said, oh, she grows six inches a year,

843
00:40:23,360 --> 00:40:26,440
Speaker 2: so she's going to be forty feet high. Like that's nonsense.

844
00:40:26,560 --> 00:40:28,919
Speaker 2: You and I both know that's nonsense. Doesn't make sense

845
00:40:28,960 --> 00:40:31,520
Speaker 2: to dig into the philosophical implications of it. It's the

846
00:40:31,560 --> 00:40:35,120
Speaker 2: same thing with the early universe. We know general relativity

847
00:40:35,160 --> 00:40:37,840
Speaker 2: is wrong about what happened to the very early universe,

848
00:40:38,239 --> 00:40:39,719
Speaker 2: and so to ask, like, what does it mean for

849
00:40:39,800 --> 00:40:42,040
Speaker 2: time to begin? Is like asking what does it mean

850
00:40:42,040 --> 00:40:43,919
Speaker 2: to be forty feet tall when you're eighty years old?

851
00:40:44,360 --> 00:40:47,520
Speaker 4: Was this a bit of a like false setup because

852
00:40:47,719 --> 00:40:50,799
Speaker 4: general relativity wasn't meant to be extrapolated back that far.

853
00:40:51,640 --> 00:40:54,200
Speaker 4: And so if you asked a physicist, what does general

854
00:40:54,200 --> 00:40:56,440
Speaker 4: relativity tell us about the start of time? You'd be like, no,

855
00:40:56,560 --> 00:40:57,439
Speaker 4: not a relevant question.

856
00:40:59,280 --> 00:41:02,440
Speaker 2: I'd say, can't answer that question. We don't know the answer.

857
00:41:02,760 --> 00:41:06,520
Speaker 2: And we hope eventually to integrate general relativity with quantum mechanics,

858
00:41:06,560 --> 00:41:09,400
Speaker 2: which has a very different concept of time, and figure

859
00:41:09,440 --> 00:41:11,960
Speaker 2: it all out. But you can't use generativity by itself

860
00:41:11,960 --> 00:41:14,399
Speaker 2: to answer this question. There just isn't an answer, even

861
00:41:14,440 --> 00:41:16,719
Speaker 2: though it sounds sexy, and people talk about like the

862
00:41:16,719 --> 00:41:18,640
Speaker 2: beginning of time is like the north pole. With this,

863
00:41:18,960 --> 00:41:21,719
Speaker 2: you can't go further north. I think that's a distraction

864
00:41:21,800 --> 00:41:24,200
Speaker 2: from the fact that we really don't know what happened

865
00:41:24,200 --> 00:41:26,279
Speaker 2: in the early universe. And the reason is that we

866
00:41:26,400 --> 00:41:29,080
Speaker 2: know there were quantum mechanical effects, and that again, quantum

867
00:41:29,080 --> 00:41:31,160
Speaker 2: mechanics has a very different conception of time.

868
00:41:31,400 --> 00:41:34,120
Speaker 4: Okay, so let's start talking about quantum mechanics. Then it

869
00:41:34,320 --> 00:41:36,279
Speaker 4: just to jump to the chase. Is this going to

870
00:41:36,280 --> 00:41:38,480
Speaker 4: give us an answer that we feel pretty good about

871
00:41:38,560 --> 00:41:39,920
Speaker 4: when we get to the end here, or is this

872
00:41:39,960 --> 00:41:42,000
Speaker 4: another quantum mechanics breaks down at that point.

873
00:41:42,200 --> 00:41:44,120
Speaker 2: No, I think you basically cooked all the physics when

874
00:41:44,160 --> 00:41:46,560
Speaker 2: you said, hey, this feels like a false setup. Most

875
00:41:46,560 --> 00:41:48,560
Speaker 2: of physics is like, hey, let's understand the universe.

876
00:41:48,600 --> 00:41:48,799
Speaker 1: Say.

877
00:41:48,840 --> 00:41:51,919
Speaker 2: The answer is, we don't understand the universe. Sorry, guys,

878
00:41:53,120 --> 00:41:55,759
Speaker 2: but maybe along the way we'll learn something. Okay, So

879
00:41:55,880 --> 00:41:59,560
Speaker 2: quantum mechanics has a very different view of what time is. Right,

880
00:42:00,120 --> 00:42:02,719
Speaker 2: put everything we've just been talking about aside. Imagine you

881
00:42:02,760 --> 00:42:05,720
Speaker 2: had a completely different set of physics, group of people

882
00:42:05,719 --> 00:42:07,680
Speaker 2: you locked in a completely separate room, came up with

883
00:42:07,719 --> 00:42:10,400
Speaker 2: a very different idea about how the universe worked and

884
00:42:10,440 --> 00:42:13,400
Speaker 2: what time is. And that's basically what quantum mechanics is.

885
00:42:13,440 --> 00:42:16,440
Speaker 2: It's like a completely separate thread. It doesn't integrate nicely

886
00:42:16,719 --> 00:42:18,960
Speaker 2: with anything we've been talking about, but we also know

887
00:42:19,040 --> 00:42:23,200
Speaker 2: it's pretty accurate and in quantum mechanics, time is like

888
00:42:23,239 --> 00:42:26,359
Speaker 2: a parameter. Quantum mechanics says there's space, and on top

889
00:42:26,400 --> 00:42:29,680
Speaker 2: of that there are these weird quantum fields, and time

890
00:42:29,800 --> 00:42:31,920
Speaker 2: is like a knob that you can turn and you

891
00:42:31,960 --> 00:42:35,280
Speaker 2: can see things change, and we have equations that describe

892
00:42:35,280 --> 00:42:38,360
Speaker 2: how things change. But for quantum mechanics, there's no connection

893
00:42:38,400 --> 00:42:41,279
Speaker 2: between space and time, like space is where you put

894
00:42:41,280 --> 00:42:43,480
Speaker 2: the things, and time is this parameter that tells you

895
00:42:43,760 --> 00:42:48,239
Speaker 2: how things change. So whereas in relativity and Einstein tells

896
00:42:48,280 --> 00:42:50,879
Speaker 2: the space and time are deeply connected and even interwoven

897
00:42:50,960 --> 00:42:54,279
Speaker 2: because clocks move differently at different points, quantum mechanics is

898
00:42:54,280 --> 00:42:57,040
Speaker 2: like nab or whatever. Let's just have space bio thing

899
00:42:57,120 --> 00:42:58,319
Speaker 2: and time be its own thing.

900
00:42:58,560 --> 00:43:02,120
Speaker 4: So because you can separate them, does quantum mechanics have

901
00:43:02,160 --> 00:43:05,760
Speaker 4: a different answer to the time travel question.

902
00:43:06,440 --> 00:43:08,400
Speaker 2: It doesn't have a different answer to the time travel

903
00:43:08,480 --> 00:43:12,160
Speaker 2: question because there's still a sense of causality in quantum mechanics.

904
00:43:12,560 --> 00:43:15,200
Speaker 2: People seeing like, oh, quantum mechanics is random and therefore

905
00:43:15,200 --> 00:43:17,840
Speaker 2: the universe is nonsense. That's a bit too far right.

906
00:43:18,200 --> 00:43:21,480
Speaker 2: Quantum mechanics says that the universe isn't deterministic. It's not

907
00:43:21,520 --> 00:43:25,800
Speaker 2: that the present completely determines the future, but the presence

908
00:43:25,840 --> 00:43:28,560
Speaker 2: still determines what's possible in the future. You know, it

909
00:43:28,640 --> 00:43:31,120
Speaker 2: gives you a set of probabilities for what could happen

910
00:43:31,160 --> 00:43:34,480
Speaker 2: in the future. So while the future isn't completely determined

911
00:43:34,480 --> 00:43:38,000
Speaker 2: in quantum mechanics, it's still controlled by the past, and

912
00:43:38,040 --> 00:43:41,120
Speaker 2: that means causality is still important and you can't go

913
00:43:41,200 --> 00:43:43,680
Speaker 2: back in time and kill your grandfather. But it also

914
00:43:43,760 --> 00:43:46,439
Speaker 2: tells us something else about the past, because in quantum

915
00:43:46,480 --> 00:43:50,960
Speaker 2: mechanics is a really important principle that information is never destroyed,

916
00:43:51,480 --> 00:43:54,680
Speaker 2: which means that the present determines what's possible in the future.

917
00:43:54,800 --> 00:43:57,120
Speaker 2: Right That means that you can look at the future

918
00:43:57,239 --> 00:43:59,040
Speaker 2: or any moment in the present, and you can tell

919
00:43:59,040 --> 00:44:03,440
Speaker 2: what happened in the past, because every moment is uniquely determined.

920
00:44:03,840 --> 00:44:06,360
Speaker 2: So this present, the moment we're having in the universe

921
00:44:06,440 --> 00:44:10,400
Speaker 2: right now, encodes the entire history of the universe in

922
00:44:10,440 --> 00:44:13,280
Speaker 2: it because there's only one way to get to this present.

923
00:44:13,320 --> 00:44:16,640
Speaker 2: There's one unique past that leads to this present. So

924
00:44:16,719 --> 00:44:18,640
Speaker 2: if you look at all the details of this present,

925
00:44:18,680 --> 00:44:20,720
Speaker 2: you could tell how we got here.

926
00:44:21,239 --> 00:44:25,160
Speaker 4: But that doesn't necessarily mean you personally can figure it out.

927
00:44:25,200 --> 00:44:27,400
Speaker 4: Like if there's a ball in the middle of the room,

928
00:44:27,960 --> 00:44:30,520
Speaker 4: you don't know if it rolled from the door to

929
00:44:30,560 --> 00:44:32,040
Speaker 4: the middle of the room or from the opposite wall

930
00:44:32,080 --> 00:44:34,239
Speaker 4: to the middle of the room. It's just there's only

931
00:44:34,320 --> 00:44:36,240
Speaker 4: one way it could have happened, but you don't necessarily

932
00:44:36,239 --> 00:44:36,960
Speaker 4: know which one it is.

933
00:44:37,440 --> 00:44:40,120
Speaker 2: Yeah, in principle you could figure it out, but you

934
00:44:40,239 --> 00:44:43,279
Speaker 2: need an extraordinary amount of information and infinite computing time.

935
00:44:43,480 --> 00:44:46,200
Speaker 2: There's actually a pretty cool TV show called Devs that

936
00:44:46,320 --> 00:44:49,120
Speaker 2: use this principle and they try to reconstruct like historical

937
00:44:49,160 --> 00:44:52,799
Speaker 2: events to like view the crucifixion of Jesus from the

938
00:44:52,840 --> 00:44:56,279
Speaker 2: air molecules outside, because in principle they're encoding everything that's

939
00:44:56,280 --> 00:44:58,560
Speaker 2: ever happened, which is kind of cool, you know, but

940
00:44:58,960 --> 00:45:04,040
Speaker 2: totally impractical. It's basically impossible. But what it means philosophically

941
00:45:04,960 --> 00:45:08,680
Speaker 2: is that the universe can't destroy information. Information is constant,

942
00:45:09,160 --> 00:45:11,360
Speaker 2: and that means that there has to be an infinite past.

943
00:45:11,400 --> 00:45:14,200
Speaker 2: It means that time can't have a beginning because this

944
00:45:14,280 --> 00:45:17,600
Speaker 2: information has to be propagated forward moment by moment by

945
00:45:17,640 --> 00:45:21,719
Speaker 2: moment by moment. Is time is a continuous parameter, and

946
00:45:21,800 --> 00:45:24,160
Speaker 2: so in quantum mechanics, it makes most sense for the

947
00:45:24,239 --> 00:45:28,120
Speaker 2: universe to have always existed and to always exist because

948
00:45:28,160 --> 00:45:31,920
Speaker 2: this is this continuous flow of information. It can't be destroyed.

949
00:45:32,120 --> 00:45:35,280
Speaker 2: It can't just come from nowhere. It's created by the past.

950
00:45:35,480 --> 00:45:37,560
Speaker 2: And so you can take the present moment and you

951
00:45:37,560 --> 00:45:40,440
Speaker 2: can evolve it backwards using the equations of quantum mechanics

952
00:45:40,600 --> 00:45:43,560
Speaker 2: to any moment in the past, right, And so there

953
00:45:43,600 --> 00:45:45,920
Speaker 2: has to be those moments in the past. That's very

954
00:45:46,000 --> 00:45:48,440
Speaker 2: much in contrast to what general relativity says that you

955
00:45:48,480 --> 00:45:50,840
Speaker 2: can have this like singularity in time where space and

956
00:45:50,880 --> 00:45:55,239
Speaker 2: time begin. Both of these are probably wrong, right, there's

957
00:45:55,280 --> 00:45:58,640
Speaker 2: some future theory of quantum gravity where somebody is like,

958
00:45:58,880 --> 00:46:01,120
Speaker 2: figured this out and will in this together and made

959
00:46:01,200 --> 00:46:04,680
Speaker 2: sense of this, and both of these ideas quantum mechanics

960
00:46:04,680 --> 00:46:07,680
Speaker 2: and general relativity will later see the way we look

961
00:46:07,680 --> 00:46:09,719
Speaker 2: at Newton's idea of gravity, we're like, well, you know

962
00:46:10,120 --> 00:46:13,200
Speaker 2: that mostly works under certain circumstances, but it's not the

963
00:46:13,200 --> 00:46:17,279
Speaker 2: way things fundamentally operate. It's not the true story of

964
00:46:17,320 --> 00:46:19,840
Speaker 2: the universe. It's just it works if you don't have

965
00:46:19,880 --> 00:46:20,360
Speaker 2: the full.

966
00:46:20,200 --> 00:46:25,840
Speaker 4: Picture quantum mechanics or general relativity. Does one of them

967
00:46:26,280 --> 00:46:29,399
Speaker 4: give us a practical understanding of time that we can

968
00:46:29,440 --> 00:46:32,839
Speaker 4: do things with better than the other, Or is that

969
00:46:32,920 --> 00:46:35,200
Speaker 4: not a reasonable question, because it depends on the scale,

970
00:46:35,280 --> 00:46:37,840
Speaker 4: and they both tell us practical things depending on what

971
00:46:37,920 --> 00:46:39,160
Speaker 4: scale we're asking the questions.

972
00:46:39,520 --> 00:46:41,799
Speaker 2: Yeah, that's exactly right. They both tell us practical things

973
00:46:41,840 --> 00:46:43,840
Speaker 2: depending on the scale. You want to talk about particles,

974
00:46:44,040 --> 00:46:47,320
Speaker 2: you just ignore general relativity, and you can make amazingly

975
00:46:47,440 --> 00:46:51,080
Speaker 2: accurate predictions for what electrons are going to do milliseconds

976
00:46:51,080 --> 00:46:53,719
Speaker 2: apter u zap them with a laser. You want to

977
00:46:53,760 --> 00:46:56,080
Speaker 2: talk about asteroids and whether they're going to hit the Earth,

978
00:46:56,160 --> 00:46:58,640
Speaker 2: you ignore quantum mechanics, and you can make very accurate

979
00:46:58,640 --> 00:47:00,960
Speaker 2: predictions for when and that rock is going to swing

980
00:47:01,000 --> 00:47:03,160
Speaker 2: around the Sun and hit the Earth or miss the Earth,

981
00:47:03,200 --> 00:47:05,520
Speaker 2: and how much you have to deflect it. So, yeah,

982
00:47:05,520 --> 00:47:07,360
Speaker 2: it depends on the question you're asking. And that's the

983
00:47:07,360 --> 00:47:10,160
Speaker 2: frustrating thing is that these two things hardly ever talk

984
00:47:10,200 --> 00:47:12,840
Speaker 2: to each other. They disagree vehemently about the way the

985
00:47:12,920 --> 00:47:16,319
Speaker 2: universe works, but usually one is irrelevant, and so we

986
00:47:16,440 --> 00:47:18,759
Speaker 2: never get to see which one is right which one

987
00:47:18,800 --> 00:47:21,560
Speaker 2: is wrong, because they basically always one of them taps

988
00:47:21,560 --> 00:47:22,839
Speaker 2: out and the other one steps in.

989
00:47:22,960 --> 00:47:26,680
Speaker 4: Okay, they're like the best wrestling team ever. So if

990
00:47:26,680 --> 00:47:32,759
Speaker 4: I'm understanding things correctly, both of the theories say that like,

991
00:47:32,840 --> 00:47:37,360
Speaker 4: for the most part, time is moving forward, and you

992
00:47:37,360 --> 00:47:40,040
Speaker 4: can move a little bit faster and tinker with some things,

993
00:47:40,080 --> 00:47:43,680
Speaker 4: but you can't break causality, and so they both are

994
00:47:43,760 --> 00:47:45,399
Speaker 4: like no time is like a forward thing.

995
00:47:46,239 --> 00:47:48,840
Speaker 2: It's interesting because both theories have time in them and

996
00:47:48,840 --> 00:47:52,040
Speaker 2: they're very different conceptions of time. But the reason why

997
00:47:52,080 --> 00:47:55,920
Speaker 2: time moves forward is actually still kind of a deep mystery.

998
00:47:56,480 --> 00:47:58,720
Speaker 2: Like if you look at the quantum mechanics view of things,

999
00:47:59,320 --> 00:48:02,000
Speaker 2: a lot of the r quantum mechanics work the same way.

1000
00:48:01,800 --> 00:48:02,800
Speaker 1: Forwards and backwards.

1001
00:48:03,160 --> 00:48:05,839
Speaker 2: Like we have this Shortener equation that tells you, if

1002
00:48:05,880 --> 00:48:08,280
Speaker 2: you have the present, what's going to happen in the future.

1003
00:48:08,480 --> 00:48:09,680
Speaker 1: It also works backwards.

1004
00:48:09,760 --> 00:48:11,720
Speaker 2: That's why it's symmetric, Right, you can take the present

1005
00:48:11,719 --> 00:48:14,040
Speaker 2: and say, oh, what had to happen in the past

1006
00:48:14,080 --> 00:48:16,560
Speaker 2: in order to get here in the present. So the

1007
00:48:16,600 --> 00:48:19,440
Speaker 2: equations work the same way forwards and backwards. And in

1008
00:48:19,480 --> 00:48:22,640
Speaker 2: most situations, if you just like watched a video of

1009
00:48:22,719 --> 00:48:26,279
Speaker 2: particles interacting, you couldn't tell whether somebody was playing the

1010
00:48:26,280 --> 00:48:29,520
Speaker 2: tape forwards or playing the tape backwards just by looking

1011
00:48:29,600 --> 00:48:32,200
Speaker 2: at what happened, because the same rules apply the rules

1012
00:48:32,239 --> 00:48:33,840
Speaker 2: are symmetric in most cases.

1013
00:48:34,360 --> 00:48:35,000
Speaker 1: It's like if.

1014
00:48:34,840 --> 00:48:37,600
Speaker 2: Somebody's bouncing a ball and there's no air resistance and

1015
00:48:37,640 --> 00:48:40,359
Speaker 2: no friction, whatever ball is going to go down, hit

1016
00:48:40,360 --> 00:48:42,759
Speaker 2: the floor, come back up to your hand. You play

1017
00:48:42,800 --> 00:48:45,880
Speaker 2: that video backwards, it looks the same, right, And so

1018
00:48:46,200 --> 00:48:48,080
Speaker 2: if I play that video, you can't tell whether I

1019
00:48:48,120 --> 00:48:50,800
Speaker 2: flipped it or not. That's sort of a big puzzle

1020
00:48:50,840 --> 00:48:53,239
Speaker 2: about physics is that it works the same way forwards

1021
00:48:53,280 --> 00:48:55,719
Speaker 2: and backwards. So like, why is time go forwards or

1022
00:48:55,920 --> 00:48:58,680
Speaker 2: in one direction that we call forwards? Why isn't it

1023
00:48:58,760 --> 00:48:59,760
Speaker 2: going the other direction?

1024
00:49:00,480 --> 00:49:04,239
Speaker 4: So is answer to to my question I could tell

1025
00:49:04,320 --> 00:49:07,840
Speaker 4: someone like I'm sorry, I'm more in the quantum mechanics universe,

1026
00:49:07,880 --> 00:49:10,600
Speaker 4: where time sometimes moves backwards and it's the same and

1027
00:49:10,640 --> 00:49:12,120
Speaker 4: you're just confused time on time.

1028
00:49:12,160 --> 00:49:15,399
Speaker 2: It's okay, yeah, we made this appointment back in time.

1029
00:49:15,480 --> 00:49:19,880
Speaker 2: Actually you went to this time. That's right, exactly. No,

1030
00:49:19,960 --> 00:49:22,720
Speaker 2: it's a big puzzle in physics about why time moves forward,

1031
00:49:23,080 --> 00:49:25,080
Speaker 2: and so you can always tell your friend like even

1032
00:49:25,120 --> 00:49:28,360
Speaker 2: physicists don't understand how time works, so don't worry about.

1033
00:49:28,160 --> 00:49:28,760
Speaker 1: It so much.

1034
00:49:29,040 --> 00:49:31,360
Speaker 2: But there's a lot of talk in popular science about

1035
00:49:31,520 --> 00:49:34,880
Speaker 2: how the direction that time moves being explained by the

1036
00:49:34,920 --> 00:49:38,080
Speaker 2: second law of thermodynamics. We can outline that argument, but

1037
00:49:38,120 --> 00:49:39,960
Speaker 2: I don't think it works as powerfully as a lot

1038
00:49:40,000 --> 00:49:43,600
Speaker 2: of people think it does. The argument basically is like, yeah,

1039
00:49:43,640 --> 00:49:46,359
Speaker 2: at the particle level, everything seems symmetric, but then when

1040
00:49:46,360 --> 00:49:49,960
Speaker 2: you zoom out and you're like watching stuff happens, there's

1041
00:49:50,000 --> 00:49:53,160
Speaker 2: this thing we can calculate called entropy, which is kind

1042
00:49:53,200 --> 00:49:55,640
Speaker 2: of like a measure of the disorganization of the universe,

1043
00:49:55,640 --> 00:49:58,560
Speaker 2: the messiness of it. And as time goes on, this

1044
00:49:58,760 --> 00:50:02,160
Speaker 2: entropy increases. You know, so for example, you run a refrigerator.

1045
00:50:02,160 --> 00:50:05,280
Speaker 2: You're cooling the inside of the refrigerator. That decreases the entropy,

1046
00:50:05,640 --> 00:50:07,480
Speaker 2: but you got to also run the compressor to run

1047
00:50:07,520 --> 00:50:10,239
Speaker 2: the refrigerator. That creates heat on the outside, and it

1048
00:50:10,320 --> 00:50:13,720
Speaker 2: more than compensates. And so anytime you try to decrease entropy,

1049
00:50:13,719 --> 00:50:16,120
Speaker 2: you make things like more ordered. You're in the end

1050
00:50:16,320 --> 00:50:19,200
Speaker 2: increasing entropy, And if you look at the universe, this

1051
00:50:19,400 --> 00:50:21,919
Speaker 2: just keeps going. And so the argument is like, oh,

1052
00:50:22,400 --> 00:50:26,080
Speaker 2: maybe time is entropy increasing. This is the one part

1053
00:50:26,080 --> 00:50:29,359
Speaker 2: of physics that seems to prefer one direction to the other.

1054
00:50:29,640 --> 00:50:30,680
Speaker 1: That's the typical.

1055
00:50:30,440 --> 00:50:31,960
Speaker 4: Argument, and do you buy it.

1056
00:50:32,640 --> 00:50:34,880
Speaker 2: I don't really buy it for a couple of reasons.

1057
00:50:35,480 --> 00:50:38,600
Speaker 2: Number one is that the premise is wrong. You know,

1058
00:50:38,640 --> 00:50:41,560
Speaker 2: the argument that like, at the particle physics level, everything

1059
00:50:41,600 --> 00:50:45,280
Speaker 2: is perfectly symmetric isn't actually true. There are some particle

1060
00:50:45,280 --> 00:50:49,719
Speaker 2: physics processes that operate differently in time forwards and backwards.

1061
00:50:50,160 --> 00:50:52,759
Speaker 2: This has to do with violation of some fundamental symmetries

1062
00:50:53,080 --> 00:50:55,640
Speaker 2: amid a video actually with veritassium a few years ago.

1063
00:50:55,680 --> 00:50:56,279
Speaker 1: You can look it up.

1064
00:50:56,320 --> 00:50:59,799
Speaker 2: It's called this particle breaks time for some details about that.

1065
00:50:59,840 --> 00:51:02,080
Speaker 2: So so even at the particle physics level, it's not

1066
00:51:02,120 --> 00:51:04,840
Speaker 2: one hundred percent true the time is the same forwards

1067
00:51:04,880 --> 00:51:09,160
Speaker 2: and backwards. But my real complaint about this argument is that, yeah,

1068
00:51:09,160 --> 00:51:12,960
Speaker 2: it shows us that there's a connection between entropy and time.

1069
00:51:13,160 --> 00:51:15,880
Speaker 2: Entropy seems to go up as time goes forward. But

1070
00:51:15,920 --> 00:51:17,960
Speaker 2: to me, that doesn't tell you why time goes forward.

1071
00:51:18,280 --> 00:51:20,200
Speaker 2: Just says, look, if time is going to go forward,

1072
00:51:20,239 --> 00:51:22,239
Speaker 2: then entropy is going to go up. If time is

1073
00:51:22,280 --> 00:51:24,440
Speaker 2: going backwards, then entropy would be decreasing.

1074
00:51:24,560 --> 00:51:24,719
Speaker 1: Right.

1075
00:51:24,760 --> 00:51:26,879
Speaker 2: It doesn't tell you why time has to go one way,

1076
00:51:27,040 --> 00:51:30,000
Speaker 2: just says these two things are connected. That's not enough

1077
00:51:30,440 --> 00:51:33,960
Speaker 2: to drive the arow of time forward. It just says, yeah,

1078
00:51:34,000 --> 00:51:36,040
Speaker 2: the universe would be different if it went backwards.

1079
00:51:36,160 --> 00:51:38,239
Speaker 4: Are these the kind of things that physicists discuss at

1080
00:51:38,239 --> 00:51:40,120
Speaker 4: the bars late into the night at your conferences.

1081
00:51:42,440 --> 00:51:45,000
Speaker 2: I think most physicists honestly would run screaming from these

1082
00:51:45,080 --> 00:51:47,759
Speaker 2: kind of conversations. But you know, there's some category of

1083
00:51:47,760 --> 00:51:52,120
Speaker 2: physicists who like the philosophical implications of these things. For me,

1084
00:51:52,360 --> 00:51:55,359
Speaker 2: I'm into these questions in physics not just because hey,

1085
00:51:55,440 --> 00:51:57,759
Speaker 2: I want to build a faster iPhone and I want

1086
00:51:57,760 --> 00:51:59,600
Speaker 2: to be a master of the universe, but because they

1087
00:51:59,640 --> 00:52:02,680
Speaker 2: brush up against these deep questions about like what is

1088
00:52:02,719 --> 00:52:04,279
Speaker 2: the universe and how does it work?

1089
00:52:04,280 --> 00:52:05,680
Speaker 1: And is the whole thing an illusion?

1090
00:52:06,200 --> 00:52:07,800
Speaker 2: And in the one hundred years and we're going to

1091
00:52:07,840 --> 00:52:10,200
Speaker 2: pull back the veil and discover the things work fundamentally

1092
00:52:10,200 --> 00:52:12,759
Speaker 2: differently from the way we experienced, or are we going

1093
00:52:12,840 --> 00:52:14,520
Speaker 2: to meet aliens and they're gonna be like, ha ha ha.

1094
00:52:14,719 --> 00:52:16,920
Speaker 2: You guys still think that that's hilarious, how cute?

1095
00:52:17,440 --> 00:52:17,680
Speaker 1: You know?

1096
00:52:17,880 --> 00:52:19,920
Speaker 2: This is what I want And so to me, these

1097
00:52:19,960 --> 00:52:22,680
Speaker 2: philosophical questions the other reason I got into physics, and

1098
00:52:22,719 --> 00:52:25,240
Speaker 2: anytime the physics bumps up against those I get excited

1099
00:52:25,480 --> 00:52:27,560
Speaker 2: while everybody else runs screaming. But you know, I'm not

1100
00:52:27,600 --> 00:52:29,600
Speaker 2: alone in this. You know, folks like Sean Carroll and

1101
00:52:29,600 --> 00:52:31,680
Speaker 2: Carlo Ravelli and a bunch of folks that are interested

1102
00:52:31,719 --> 00:52:34,600
Speaker 2: and have done a really important work on what all

1103
00:52:34,640 --> 00:52:37,360
Speaker 2: these concepts and physics mean for time and the direction

1104
00:52:37,440 --> 00:52:40,360
Speaker 2: it flows and could we actually build a time machine?

1105
00:52:40,440 --> 00:52:43,840
Speaker 4: And so the physicists who aren't interested in these questions,

1106
00:52:44,480 --> 00:52:47,000
Speaker 4: what is their reason for not being interested? Or is

1107
00:52:47,040 --> 00:52:48,840
Speaker 4: that not fair? You're not in their heads, you don't know.

1108
00:52:49,360 --> 00:52:52,000
Speaker 2: No, that's a really fine question, you know. I feel

1109
00:52:52,000 --> 00:52:54,160
Speaker 2: like one of the wonderful things about science is that

1110
00:52:54,160 --> 00:52:57,239
Speaker 2: there's so many opportunities to get excited, and it's just

1111
00:52:57,360 --> 00:52:58,440
Speaker 2: very personal, you know.

1112
00:52:58,600 --> 00:53:00,719
Speaker 1: Like even within article.

1113
00:53:00,400 --> 00:53:03,960
Speaker 2: Physics, there are folks who like to build the detectors

1114
00:53:04,160 --> 00:53:06,360
Speaker 2: and they think it's really fun to get greasy and

1115
00:53:06,400 --> 00:53:08,960
Speaker 2: climb around on those things and like figure out how

1116
00:53:08,960 --> 00:53:11,080
Speaker 2: to line everything up and use a laser beam to

1117
00:53:11,120 --> 00:53:13,279
Speaker 2: calibrate everything. And there are other folks who like to

1118
00:53:13,280 --> 00:53:15,319
Speaker 2: write computer programs to analyze the data, and to them,

1119
00:53:15,360 --> 00:53:18,239
Speaker 2: that's the jam. And everybody finds a different thing to

1120
00:53:18,280 --> 00:53:21,640
Speaker 2: be excited about, which means that like science takes all kinds,

1121
00:53:21,760 --> 00:53:24,319
Speaker 2: you know, and everybody thinks that their bit is the

1122
00:53:24,360 --> 00:53:27,600
Speaker 2: most important, the most exciting bit, and everybody else is

1123
00:53:27,680 --> 00:53:30,120
Speaker 2: just like you know, box checking and stamp collecting. And

1124
00:53:30,120 --> 00:53:32,160
Speaker 2: that's fine because that means everybody gets to do the

1125
00:53:32,200 --> 00:53:35,279
Speaker 2: fun part, you know, and the most important part. The

1126
00:53:35,320 --> 00:53:38,120
Speaker 2: truth is, every part of it is important. The engineering,

1127
00:53:38,280 --> 00:53:42,080
Speaker 2: the physics, the philosophy, the biology. It's all important stuff.

1128
00:53:42,080 --> 00:53:45,040
Speaker 2: Everybody's contributing, and I just think it's great that everybody

1129
00:53:45,040 --> 00:53:47,120
Speaker 2: finds their own bit to be the best bit.

1130
00:53:47,600 --> 00:53:49,640
Speaker 4: As a biologist, you don't have to convince me that

1131
00:53:49,640 --> 00:53:56,360
Speaker 4: diversity is important. Intellectual diversity is important too, exactly.

1132
00:53:56,880 --> 00:53:59,400
Speaker 2: And so you know, the big picture to physics answer

1133
00:53:59,440 --> 00:54:03,239
Speaker 2: about what time is? Boy, we have a few ideas,

1134
00:54:03,280 --> 00:54:05,759
Speaker 2: and some of them seem to work pretty well, and

1135
00:54:05,880 --> 00:54:08,880
Speaker 2: let us do all sorts of things like design interconnected

1136
00:54:08,960 --> 00:54:13,880
Speaker 2: global position systems that work within centimeters and shoot laser

1137
00:54:13,920 --> 00:54:17,600
Speaker 2: beams across fast distances, all sorts of stuff, but we

1138
00:54:17,640 --> 00:54:20,240
Speaker 2: don't really understand what time is. We know that it flows,

1139
00:54:20,280 --> 00:54:23,279
Speaker 2: we know it's connected to space, we don't understand that

1140
00:54:23,400 --> 00:54:25,759
Speaker 2: in detail. We have a lot to learn about what

1141
00:54:25,800 --> 00:54:26,319
Speaker 2: time is.

1142
00:54:26,560 --> 00:54:29,000
Speaker 4: So for the kids who are sitting in a room

1143
00:54:29,040 --> 00:54:31,480
Speaker 4: their parents are listening to a podcast about what is time,

1144
00:54:32,320 --> 00:54:34,719
Speaker 4: you could answer this question and you could change the

1145
00:54:34,760 --> 00:54:37,000
Speaker 4: world if you could figure out what space or time are.

1146
00:54:37,960 --> 00:54:39,480
Speaker 4: There's got to be a Nobel prize in there.

1147
00:54:39,800 --> 00:54:43,040
Speaker 2: Oh yeah, there's lots of Nobel prizes for even the

1148
00:54:43,040 --> 00:54:46,560
Speaker 2: mini steps along the way. Absolutely, kids, there's so much

1149
00:54:46,680 --> 00:54:49,719
Speaker 2: left to discover about the universe, to unravel, to figure out.

1150
00:54:50,040 --> 00:54:52,680
Speaker 2: We are at the very beginning of understanding the way

1151
00:54:52,680 --> 00:54:53,600
Speaker 2: the universe works.

1152
00:54:53,920 --> 00:54:54,600
Speaker 1: We've just sort of.

1153
00:54:54,520 --> 00:54:56,600
Speaker 2: Like set the stage for the next generation to come

1154
00:54:56,640 --> 00:54:58,120
Speaker 2: in and figure it all out.

1155
00:54:58,480 --> 00:54:58,960
Speaker 1: That's you.

1156
00:54:59,200 --> 00:55:01,400
Speaker 4: We've done some cool stuff, but there's more to do.

1157
00:55:03,080 --> 00:55:03,400
Speaker 1: All right.

1158
00:55:03,440 --> 00:55:05,680
Speaker 2: Thanks everyone for taking the time to go on this

1159
00:55:05,800 --> 00:55:08,280
Speaker 2: journey to some of the deep questions about the nature

1160
00:55:08,360 --> 00:55:10,719
Speaker 2: of the universe on this podcast. You know, we think

1161
00:55:10,760 --> 00:55:13,960
Speaker 2: the universe is extraordinary and we love to share our

1162
00:55:14,080 --> 00:55:16,600
Speaker 2: joy of it with you. If you have questions about

1163
00:55:16,600 --> 00:55:18,759
Speaker 2: what you heard today, please don't be shy. I would

1164
00:55:18,840 --> 00:55:21,680
Speaker 2: love to answer them. Everybody gets an email back. Just

1165
00:55:21,719 --> 00:55:25,360
Speaker 2: write to us to questions at Daniel and Kelly dot org.

1166
00:55:25,600 --> 00:55:27,200
Speaker 4: And if there's a topic you want to hear about

1167
00:55:27,320 --> 00:55:27,719
Speaker 4: let us know.

1168
00:55:28,320 --> 00:55:29,960
Speaker 1: Please do. We love to hear from you.

1169
00:55:36,640 --> 00:55:40,480
Speaker 4: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We

1170
00:55:40,520 --> 00:55:42,920
Speaker 4: would love to hear from you, We really would.

1171
00:55:43,080 --> 00:55:45,839
Speaker 2: We want to know what questions you have about this

1172
00:55:46,040 --> 00:55:47,720
Speaker 2: Extraordinary Universe.

1173
00:55:47,840 --> 00:55:50,800
Speaker 4: We want to know your thoughts on recent shows, suggestions

1174
00:55:50,800 --> 00:55:53,799
Speaker 4: for future shows. If you contact us, we will get

1175
00:55:53,840 --> 00:55:54,279
Speaker 4: back to you.

1176
00:55:54,480 --> 00:55:57,960
Speaker 2: We really mean it. We answer every message. Email us

1177
00:55:58,000 --> 00:55:59,799
Speaker 2: at Questions at Daniel and.

1178
00:55:59,760 --> 00:56:02,520
Speaker 4: Kelly, or you can find us on social media. We

1179
00:56:02,560 --> 00:56:06,440
Speaker 4: have accounts on x, Instagram, Blue Sky and on all

1180
00:56:06,480 --> 00:56:08,799
Speaker 4: of those platforms. You can find us at D and

1181
00:56:09,200 --> 00:56:10,200
Speaker 4: K Universe.

1182
00:56:10,360 --> 00:56:11,879
Speaker 1: Don't be shy, write to us