Listener Questions 51

Published Mar 28, 2024, 7:00 AM

Daniel and Jorge answer questions about the speed of light, entanglement and time!

See omnystudio.com/listener for privacy information.

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Hey Daniel, have you been watching the latest Marvel movies and TV shows? Mmm?

I hope you're not going to ask me about the physics of it.

Oh. I wasn't gonna ask you about time travel in Loki, but now you're not well here in your reaction, I think I have to travel back in time now and maybe think of another question.

See that's the problem. If you had done that, we'd never be having this conversation.

Oh well, maybe it depends on which branch of the timeline we're on.

No, my god, there are no branches to timelines. Oh my gosh.

Or maybe I did go back in time and this is a better outcome than the one that I originally pitched to you. This might be the best timeline where that could be.

Then I'm disappointed in the multiverse.

Maybe you just don't know how much worse it could be.

If this is the best it gets, then it must get pretty bad.

Sounds like you maybe need to switch to the DC universe. Hi. I'm Jorge Made, cartoonist and the author of Oliver's Great Big Universe.

Hi.

I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I can mostly read science fiction without being grumpy.

Mostly. What percentage would you say is your grumpiness level when you're reading science fiction?

There is a spot on the wall across the bedroom where the books usually land when I throw them in frustration.

I'll just say that there's a dent there, more like.

A mark, but yeah, there's a physical impression left.

Have you actually thrown a book? Oh many, Yes, No way, Wow, that's a strong reaction.

It's just so disappointing when they set you up for something. They have some interesting ideas, and then they can't even be consistent, or they just write stuff that doesn't make sense. It's just frustrating because it makes me think about what it could have been.

Oh man, But you're not angry at the physics, because I imagine the physics is all made up in science fiction to some degree. You're more frustrated with the storytelling or the logic of the story.

Well, it's all tied together, right, of course, the physics is made up. It's science fiction. After all. They can have fictional science, but it's still science. They got to stick to it. If they're going to tell a story, they got to follow the rules. Otherwise, if there are no rules, it's hardly an interesting story.

Now, after you throw the book, do you go and pick it up and finish it anyways? Or do you leave it there on the pile?

It depends on what's on the top of the two read pile.

I suppose you're not like a complete is like some people, when they start a book, they have to finish it.

Oh no, I don't finish most books.

Oh interesting. Have you ever thrown a podcast at the wall?

No, I've never thrown podcasts at the wall. I've just paused them.

Although it does feel like this podcast is just us throwing things on the wall to see what sticks.

No, this is us trying to explain physics to everybody out there listening.

Well anyways, Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.

Where we do our best not too frustrat hit you into throwing europhone or computer or car across the wall, whatever device you're using to listen to us. We want to take you on a tour of everything that we understand in the universe and everything that we don't. We want to explain to you our vision of how the universe works, from the tiniest little itty bitty bits all the way up to the biggest monster black holes. We think the universe does make sense, can be made sense of, and we want desperately to explain all of it to you.

That's right. The universe we live in is not science fiction. It is science period, science reality, and so we all have questions about how it works while we're here and what happens when you throw a bunch of books at a wall.

Science reality. I like how you just renamed the whole nonfiction genre. It's a better name though.

Yeah, science reality. There you go. Well they have like reality TV, why not have reality science?

Yeah? I don't want to be lumped in with reality TV. Actually, hey, the problem with nonfiction you're defining it by what it isn't instead of what it is. Right.

Oh yeah, yeah, nobody wants to be a non anything.

I don't not want to be that.

You don't want to be a non conformist. Science trail blazing, that's your job, basically. How about reality trail blazing.

Exploring the dense underbrush of reality, hacking our way through the jungles of truth.

Yeah, that could be a nice show like on Netflix, like Big Science, where you put a bunch of physicists in one house with a large particle collider and you see what happens every week they have to vote a physicists off.

Or maybe they have to vote a physicist into the collider.

Oh my goodness. That is both good and horrifying.

Probably good TV.

Yeah, yeah, yeah, it's like squid games exactly, h squid physics game, science game. Science games. Yeah, there you go, particle games.

But science isn't just a game. It's a serious effort to understand the universe, and that's what we try to do in our jobs. We try to do on this podcast, and we also encourage you to do because you can also pick up a machete and help us hack through the jungles of truth to understand the universe just by thinking like a physicist, which means just being curious and not settling for not understanding. There's too many knots there, huh. I should define it in terms of positives demanding sufficient explanations. And when you don't understand something about the universe, we want you to write into us share your question, because probably somebody else out there has the same thought.

I don't know if that was better. I'm a little nonplussed about it.

I'm pretty plussed.

Well, let's plus it. Let's plus it some more.

I might even be multiplied it. But I don't want to divide us over it.

But yeah, science is a game, and it all starts with questions. The whole journey of science starts with looking at the world around us and wondering why is it like that? How does it work? And what would happen if I throw this at the wall.

So you can either throw that thing at the wall, or you can just write to us with your question and we'll do our best to answer it. We answer every question and we get from listeners. Just write to us to questions at Danielandjorge dot com. And some of the questions we think other people might want to hear the answers to, and so we select them to answer on the podcast.

So today on the podcast, we'll be tackling listener questions number fifty one. Oh boy, listener questions in that over middle eight.

That's right, we're rounding up to one hundred.

Now it's fifty plus.

We're going to get senior citizen discounts pretty soon. We start at three pm.

That's right. Yeah, yeah, the discounts. Oh man, Does that mean we have to give shorter answers.

I'm not going to offend our senior listeners by suggesting that they can't comprehend long, complex answers.

No, I'm just saying, you know, your appetite goes down as you age.

Oh, I say, smaller meals.

I don't know what I'm saying.

More top us maybe more top us.

Yeah, there you go, more variety, because let's face it, the time is running out for those of us over fifty.

Unless you live near the vicinity of a black hole, in which case time is slowing down for others but not for you. Yeah, but relatively for you. You see everybody else living really fast.

Well, let's try to get through these questions as fast as we can then.

And the first one is actually about time.

Yeah, yeah, we have some awesome questions here today about the speed of light near a black hole, about quantum entanglement, and also about possible time travel. Pretty awesome questions from people, Daniel, Do these questions make you smile when you get them?

All the questions make me smile. I love that ding when I get a question in the listener inbox and lets me take a break from whatever else I'm doing and think about physics.

But way you were thinking about physics before, So your break from physics is to think about physics.

Mostly I was thinking about spreadsheets and email every job, spreadsheets in email.

And grants and grant proposals, budgets. Oh I see, So then do you actually get to think about physics?

Yeah, exactly.

Yeah, what if your grant students send you a question about physics? Is that the flatter or the former situation. No comment depends on the student. Actually is it an involve a spreadsheet or a budget question?

Depends Maybe their question is, hey, are you funding me next quarter? Or their question is like, how do we do anomally detection in this space of multiple tracks? You know? Depends on and they're asking.

I see and one of those is good and the other one is bad. Is that they're different. They're different different, I see? Are all right? Well, we have some awesome questions here to the answer. Let's just jump right in. Our first question comes from Nathan from Seattle.

Hey, Daniel and Hora. My name is Nathan Ramon from Seattle, Washington, and I have a question for y'all. I was watching ant Man last night, and it occurred to me that they are so small in that movie right, that the speed of light might actually act a little bit differently. They're so small at that point that if the universe is still reacting, like, still has the speed of light at the same rate, which it might not necessarily. They do talk a lot about how they're outside of space and.

Time, but if it has that same speed limit, if you're so much smaller, it would make it feel to me like White was going way way faster. Sorry for my ranblem. Let me know if you need clarification on that. And thanks for all you guys. Do I love your podcast?

All right? Awesome question from Nathan, a Marvel fan. It seems well he didn't say whether he liked those movies. He just as he watched them and he had a small opinion about at Man.

Well. The cool thing is he was watching him and he was thinking about the physics of it, like, does this make sense? How would this work? What would it actually be like to be that small? Would the experience of it be based on the physical principles of the universe?

Have we done an episode on the physics of the Marvel movies? I feel like we talk about them all the time, but have we done like a whole dedicated episode to it.

M Is there any physics of the Marvel movies or is it.

Always it's science fiction?

Daniel's for sure.

But the an Men movies are pretty good. The first one was really good, the second one was maybe not as good, and the therem one was not as good. But overall it's sort of a charming character.

Yeah, and I saw the first one. I enjoyed it, and the visit to the quantum realm. I thought was visually very creative. I thought the way they displayed it was very cool, very different from your standard depictions. So it was a lot of fun. I enjoyed it.

Did I tell you I know the guy who came up with the term the quantum realm?

Oh wow?

Yeah, my friend Spiris mclaucus. He's a physicist and he consulted for Marvel and one day he was giving them a little spiel in the conference room and he's like, things are very different in the quantum realm. And they're like, we like that. That's in the script.

Oh, quantum real Yeah.

He kind of has mixed feelings about what they've done with the term and the whole idea of quantum physics, but it's pretty cool that he had that contribution.

The lesson is be careful what you say around writers.

That's right. Yes, we cannot be trusted with the innermost secrets or emotions or physics. But yeah, Nathan has an interesting question. His question is does the speed of light seem faster if you're smaller? So, if you were small, I guess at the level of ant man, does it mean that you see light move faster for you.

Yeah. I think this is a really interesting question because it makes us think about the speed of light and the impact on physics sort of the big and the small, and the way that I think about the speed of light, and I think the way most physicists do, is that it's like a ratio between space and time. It's like a conversion between meters and seconds. Like meters is a measurement of distance, seconds is the measurement of time. And the fact that the universe has this number, this maximum speed tells you a relationship between space and time. It tells you how to convert a huge distance into a time, and we're often doing that. Like the phrase a light year tells you how far light will go in a year. It sounds kind of like a unit of time, but it's actually distance. You've taken time, you're multiplied by the speed of light, and you've gotten a distance.

It's like a measurement that you get by the distance divided by time. But does it really tie those two concepts together, like at a fundamental you know, physics level, because like you know, you can talk about the speed of whorehet down the track that like my speed is a speed that you can measure and compute, but it doesn't really tell you anything except how out of shape I am.

Yeah. Also, the speed of foretete probably changes as a function of time in the universe. And how much chocolate do you have?

Yeah? How many bananas of eaten?

But the speed of light really does play a deep role in physics, and it really serves that purpose of converting between space and time. You know, we often talk about like space time being a four dimensional object, with the original three dimensions of space and this fourth dimension of time. But there's a subtle thing there we don't often talk about, which is that when we include times fourth dimension, we usually multiply it by the speed of light. So the four dimensions are actually like x, y, z and then ct, not just time because we want to convert it to effectively a distance.

Right, Well, you do have to keep the units consistent. But like for example, if we had a different speed of light in our universe, you know, things would be different. The physics of the universe would be different. But with space itself and would time itself be different.

They would be the same, but their relationship would be different. That's what the speed of light is. It's a ratio a relationship between these two different kinds of measurements. Yeah, fundamentally, it really is telling you how these two things relate.

H all right, Well, to answer Nathan's questions, Let's say I shrink down. Let's say I'm ad Man or the Wasp and I shrink down. Is the speed of lighting? It seemed faster for me? Like, if I measure the speed of light at that scale, isn't going to seem faster? Or like if I shine a flashlight, will somehow the flashlight seem quicker or brighter or something.

Yeah, the speed of light is going to be the same because it's the same ratio between distances and times. Right, So you measure the speed of light using a tiny little experiment or a huge experiment, you're going to get the same answer. But if you think of the speed of light as a ratio between distance and time, what it means is that everything seems faster when you're small. Like basically, shorter distances mean shorter times. Things that are smaller can happen faster than things that are bigger.

So like, for example, if you not just shrink me, but I use shrink the whole earth, then for example, light can go around the Earth many more times per second.

Yeah, exactly. Or if let's say you build a machine like a computer or even a mechanical device to do something, if it's smaller, it can finish faster than if it's huge. The bigger it is, the longer it will take to finish, because there's this maximum speed limit. And that's why, like the speed of light seems really really fast to us here on Earth, is this crazy high number. It's basically irrelevant to our experience. It's because things that are almost instantaneous. But imagine if you are a brain made of like stars, you're like a galaxy sized brain, it would take like one hundred thousand years to even have a thought.

But then your thinking would be slower, so your cognition or your perception of time would be slower. So I think maybe Nathan's question I wonder is whether time will seem to be going faster or maybe it will seem to be the same, right, because like, if I'm the size of a galaxy, my thoughts are going to be super slow. And so even though any effect I'm in the city is going to be super slow because with the distances, my thoughts are going to be slow, and so therefore the experience of being that person is going to be the same as our experience here on Earth.

Yeah. I think there's a few things there to disentangle, but basically you're right. Number one, if you measure the speed of light, you're going to get the same number. It doesn't matter if you're a galaxy brain or an ant brain, right, as long as you do it correctly, you're going to get the same number. Number two, things do seem to happen faster when you're smaller because you're just not as limited by this speed of light. Things have shorter distances to cross in order to accomplish some thinking or some task or whatever. Number Three. Finally, we don't really know what it would be like to experience that what it seemed like time goes faster. We don't understand our experience of time or why we seem to experience it at you know, one second per second. So I don't know what it would be like to be a galaxy brain. They might have the same kind of subjective experience we do.

Yeah, Or like thinking about the shrinking case, like if I shrink down to enman size, now my brain is smaller, Like the distances between my neurons are smaller, and so maybe my thinking will be sort of like hypercharge. Yeah, like I'll have a million of thoughts in the same amount of time that it used to take me to have one thought, and so I'll be sort of super bored looking at the bigger world, but looking at the small world, maybe it'll just seem like the same regular because things are moving faster. But I'm also like having a bazillion more cycles in my brain than I did before.

Yeah, exactly, So we don't know what the experience would be like. This is an interesting wrinkle of evolutionary biology. There also which is wondering, like could humans be smarter? You can imagine being smarter by having like a bigger brain in more neurons, but then it's harder to get that brain through the birth canal. You could also imagine getting smarter by having more neurons by making the neurons smaller. But I was reading a paper that said that if neurons got any smaller, they would be noisier, like more randomness and fuzz so it might not actually add computing power. So he might be at like the sweet spot of like the densest neuronal systems.

Well, the other thing to consider is that neurons work by bioelectricity, right, biochemistry, not necessarily by like transmitting electrons.

Right.

It all depends on sort of reactions and electric fields and like molecules moving in and out of the little cell walls.

Yeah, exactly, if you could actually shrink all that stuff, it would happen faster. Of course, you know, the physics wouldn't work if you shrink all that stuff because all the numbers would change. So the fundamental physics of ant Man is silly because you know, if he's shrunk down to the size of an electron, then how big are his electrons?

Right?

Right, So basically we get into the fuzzy area of like perception and the subjective experience. But generally speaking, I think from a physics point of view, if you were down to the size of ant Man, the light would sort of seem to travel faster, right, Like, it would go one body length in a much shorter amount of time than it would go at our size.

Yeah, your body would be shorter, so light would go across you faster, and I think a lot of things would happen faster I don't know how we can say what it would be like though, to experience it.

I wonder if it would be even that different, Like what's the difference between almost interustaneous and almost almost insantaneous? Maybe the difference is not that great, or maybe he's thinking about it, like when admin goes down to like the quantum size.

Yeah, but as you say, distances are already so small compared to the speed of light, then our experience is very difficult to even tell that it's not instantaneous. It took people a long time to be able to devise experiments to measure the speed of light. That to be very very clever, because it's so blazingly fast compared to the distances in which we live. If you really galaxy brain and then you got shrunk down to ant man, that might be more dramatic.

Yeah, Or I wonder maybe the equivalent conversion is like, let's say you and I are living in our everyday lives here, but suddenly the speed of light goes up by a factor of ten. Let's say it was now three million kilometers per second. Would we even notice a difference.

We wouldn't notice the difference here on Earth, but suddenly, the rest of the universe would effectively be closer to us. You know, we could see things happening faster, We could get places faster. The size of a galaxy would effectively seem smaller.

Well, seem smaller. No, it'll still be the same distance. We would just see it sooner.

Yeah, like our information bubble would be larger. The distance over which things appear to happen instantaneously would be bigger.

Right, we can maybe see further out or or I guess what we see would be more up to date, Yeah.

More recent exactly. The time lag would no longer be noticeable for things that are close to us. Is to look even further out to notice that time lag.

Well, I feel like they're not even noticeable now, Like like I can tell the difference between a billion year old star and a million.

Year old star, astronomers can all.

Right, well, I think that answer is a question, which is that the speed of light would not be different, but maybe your experience of it would be different. All right, Well, thanks for that question, Nathan. Let's get to our other questions. We have one here about quantum entanglement and time travel, so we'll get to those, But first let's take a quick break.

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All right, we're answering listener questions here today, and our next question is about quantum entanglement.

How did Daniel question for you? Assume we know particle A and particle B are entangled, and for simplicity's sake, let's say the states are positive or negative, and there's a fifty to fifty chance. Now, what would happen if two independent observers we can call them A and B for their respective particles, observed these two particles at the exact same time. This question really breaks my brain. The more I think about it, the less I feel like I understand special relativity and the less I feel like I understand quantum mechanics. And adding to their question, is it even possible to make two observations with two observers at the same time. I really appreciate it. Thanks for helping me understand.

All right, Well, that's quite a mindful of a question here, And Daniel, I noticed he asked a question of you, not me, So I think I can just sit this one out because honestly, I don't understand the question. I'm being entangled into whole flurry of words.

You felt like some of the other physics questions were aimed towards you.

Last one, did say Daniel and Jorge, I think I was one of the targets. And sometimes they say hey, guys plural, so it does mean the two of us.

Well, I think he's also counting on you to help me translate my understanding into something.

Ever, no, no, no, I feel snubbed, So I'm not even gonna chime in.

I'm gonna do my best, but I'm pretty sure you're going to have a hard time not interrupting.

What are you trying to say? What are you trying to say?

Job? And you do it beautifully, matn.

Why are you trying to say, Daniel, did I interrupt you?

Yes?

Exactly, all right, So what is the question? I know it's about quantum entanglement, but it didn't quite get the gist of it.

Yeah, So the question is about quantum entanglement and special relativity and how these two things come together. But let's start just with the basic issue of quantum entanglement, which is weird enough, right. Quantum entanglement says what happens if you have two particles that are like the output of a single process. Something makes two particles, and so their fate is connected. Like let's say you have two electrons created, and one has to be spin up and one has to be spinned down because of the way they're made. The universe doesn't care which one is spin up and which one is spin down as long as they point opposite. Now, if you take those two particles and you send them different directions, they're now far apart. Quantum entanglement says that they're still somehow connected, that their fates are joined. And so if you measure one to be spin up, you now know the other one is spinned down. But it's more than just like no knowing that they have to be opposite. Quantum entanglement tells us that they're actually not determined, that neither one is spin up or spin down. They both have that possibility, and that as soon as you measure one, then the fate of the other one is determined. That's a weird bit about quantum entanglement.

Oh wait to jump in now you're going to interrupt. Yeah, So that's the basic of entanglement, right, Like you have two quantum things, like a particle or an atom or some sort of quantum object, and it's fuzzy, you don't know what it actually is inside. But if two of them have some sort of shared history, some sort of shared origin that ties them together, that's what quantum intalgent Guildman is.

That's right, there's some correlation between them that's created locally when they're like both made and sent apart. But then the correlation persists as they get further and further apart. And again, this is not a scenario where one of them actually is spin up and the other one actually is spin down and we just don't know. We've proven through a whole complicated series of experiments suggest John Bell that they actually are undetermined until you measure. So the weird bit and the thing that makes it hard to reconcile with special relativity is that apparently this happens instantaneously. You have these two particles that have a shared fate, but they're both undetermined. Now you send them like five kilometers apart, you measure one of them, you get to spin up instantly. The other one has to be spinned down. It went from I don't know, maybe up or down to has to be down instantaneously across space.

And time, right, which that first glance seems to violate the speed of light, right because something changed in one part of the universe and then it suddenly costs something else to change in another part seemingly instantaneously.

Exactly what you said is important. You said it violates a speed of light, and that's correct. This is something that happens faster than the speed of light. Speed of light says is a limit to how fast things can happen across the universe. This is instantaneous, but doesn't actually break special relativity because you're not sending information faster than the speed of light. Like the quantum state is non local it stretches over space and collapses instantaneously the whole thing at the same time. But you can't actually use that to send information. People are often writing in and saying, well, can't I send information by making a measurement and the other person's going to see that theirs is now collapsed. You can't actually tell when your probabilities have collapsed. All you can do is measure or not measure. When you measure your particle, you don't know if it was already collapsed or if you're collapsing it by measuring it.

Right. Also, when you collapse one of them, it's not like you're sending that information to the other person. Like let's say we entangle to particles. I have one, and when we split up part I have one, you have one. If I open mind, I measure it and I see it that for example, it's up, and I know that yours is down. Like I know something about your particle, But that doesn't mean you know that about your particle. Like to you over there in Irvine, your particle is still this quantum object that could be fifty percent up or down. So like, no information is actually traveled unless I sent you an email which would then be limited by the speed of light exactly, and or my sale signal exactly.

And if I still have my particle in the box you measure yours, I can't tell if you've measured yours, Like mine doesn't look any different if I'm not measuring it. I'm just waiting to measure it. I don't know if you've measured yours or not. I can't tell that you have measured it.

So it's like information about something far away has been revealed to me instantaneously, But that doesn't mean that information actually got transmitted from one place to the other.

Yeah, exactly.

So then what's the actual question here?

So the question is what happens we measure them at the same time. Who collapses the wave function? Mmmm?

So we each have a particle that's been entangled the other and we open it at the same time. Nothing happens, right, Well, this is a really interesting question, Like you'll find that you'll find yours up and I'll find my down, or I'll find mine up and you'll find yours. Now that's all that really happens, isn't it.

Yeah. I love your answer, and you're right from the point of view of like what we experience. You open your box, you measure it up or you measure it down. But I think what he's asking is like, what's happening behind the scenes? You know, what is the wave function doing? Even if we can't observe it and can't measure it and can't ever know what in theory is the explanation for how this happens. And I think it's touching on a deeper question, which is about simultaneity. We talked to the podcast how special relativity tells us that at the same time is a fuzzy concept. Two events could occur at the same time for one person, but not for somebody else if they have a different velocity or different location in space. And so this seems very fuzzy all of a sudden, like two people measure the wave function at the same time, what happens to that wave function? And what happens according to somebody flying by in a spaceship at nearly the speed of light?

So then what's the answer for our question, asker?

So the best answer to the one you just gave, which is this is not a physical problem.

This is only I answered the question even though he didn't ask me. I'm the one who ended up assering.

You answered it in the classical dismissive way, which is like, it doesn't matter. It's just a philosophy question about what's happening to the wave function.

It's not a dismiss it. I mean, I always being pejorative, maybe, but it's.

True though it's an important distinction, like we know what would happen. I measure mine, you measure yours done, it doesn't really matter, right, But the question is what's happening behind the scenes, which is a philosophical question about something we may never be able to know, like what is the wave function really? And there's whole philosophical debates about whether the wave function is just a mathematical tool we use to make these calculations, or if it's a real physical thing in the universe. And so there's long answer is it depends on what you think the wave function is. It depends on your philosophical interpretation of quantum mechanics. And we can walk through a few of those examples.

Like is there a wave function that physically connects my particle to your particle? Or is the wave function just some mathematical tool we used to explain things When things are not far apart. Yeah, and then when you split them, maybe actually you get two ways functions. Or maybe there is no such thing as a physical common wave function.

Or maybe there are many wave functions, or maybe the wave function never collapses. Now in the standard interpretation of quantum mechanics, which I'll say up front is nonsense, the Copenhagen interpretation, which doesn't work and is deeply flawed, but it's still the one most people think about and is most often taught. In that interpretation, the wave function is a thing, and it's real, and before you measure something, it allows for multiple possibilities, like the wave function says you might be up and you might be down. And then when you make a measurement with a classical object where classical object is not defined just something big, then it collapses and it chooses one of these options. And I think it's in that scenario that the question is asking, like number one, what happens if two people make the measurement at the same time, who collapses it? And then what happens to an observer flying by the speed of light? The answer is sort of nonsense. Like number one, if two people make their measurement at the same time. Well, you can't do that in Copenhagen interpretation because you can only make one measurement on a way function at a time. It's just not allowed because making a measurement changes the wave function, and you have to do them in sequence. That's why it's like important whether you're measuring position or momentum first, or momentum and then position, because every measurement change is a wave function. There's no way to even describe making two measurements at the same time.

I see, well, if there is sort of like a physical wave function connecting my particle to your particle, then you do sort of get the sense of that there is a shared now.

But even though it's quantum mechanical, unless you're going to pixelate time, time itself is infinitely divisible. So saying you're making two measurements at the same time would mean you're like exactly matching those two moments.

Meaning like maybe there's no way to know who collapsed it first unless we somehow sink clocks or something beforehand and then we compare clocks afterwards.

But you'd have to sink them exactly perfectly to like an infinite number of digits, which seems impossible, right, And it gets even weirder if you ask, like what happens according to other observers, Like what if I make my measurement and then ten seconds later you make your measurement, And now, in our frame of reference, I was first and you were second, But somebody flying by at the speed of light, they could see your measurement happen first before mine, because the order events is not guaranteed in special relativity depends on the observer.

Interesting, So I think what you're saying is that in the quantum realm, at man would not know what time it is.

I'm saying that this picture of the wave function collapsing and happening instantly across space in time, that picture itself doesn't really work in the Copenhagen interpretation. You know, imagine a more complex situation, for example, like an observer flying by and then changing directions and going the other way. As they change directions, their concept of what happens first what happens second changes, So you could arrange a trajectory where they're seeing me make my measurement first, and then later they see you make your measurement first, because their velocity is changing and In that scenario, the wave function collapses in one way and then uncollapses and recollapses in a different way. So like the whole picture becomes very confusing and it's kind of nonsensical, but it doesn't change anything physical. This is just philosophical, and there are other philosophical approaches to quantum mechanics that don't have these issues that the Copenhagen interpretation has. And Copenhagen is already known to be nonsense because this division between like what is quantum and what is classical is not even defined or described.

Well, it seems like kind of the main problem is that you're basically trying to put together general relativity and quantum mechanics, which, as we've talked about a million times in this podcast, like they don't really play well with each other, right, Like, quantum mechanics is kind of a local effect and general relativity things that happen over maybe big distances or big amounts of time, and it involves curvatures time and space, and so we don't really know how to marry those two.

Well, I'm not sure we're getting into general relativity here. Really, all these questions are about special relativity, and we do know how to marry special relativity and quantum mechanics into a theory. We have relativistic quantum mechanics and we have quantum field theories, and those make predictions about all the measurements, and those all work. The philosophical underpinnings of what happens when you try to bring these two together is more complicated, and there people have a lot of disagreements about what's going on behind the scenes.

Well, I think maybe the basic conclusion is that I answered this question and even though I wasn't asked.

Ten points for you.

All right, Well, let's get to our last question, which is about time travel, and the question people should think about during this break is do we already answer this question or are we going to answer it in the future.

Or have we already answered it in the future?

Yeah, Or have we already asked this question about answering the question in the past?

Have we already made every possible time travel show.

Let's go back in time and make some more, But first, let's take a quick break.

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Guess what, Mango? What's that?

Well, so iHeart is giving us a whole minute to promote our podcast, part time genius.

I know.

That's why I spent my whole week composing a haikup for the occasion. It's about my emotional journey in podcasting over the last seven years, and it's called Earthqua Mega Mengo.

I'm going to cut you off right there.

Why don't we just tell people.

About our show instead? Yeah, that's a better idea.

So every week on Part Time Genius we feed our curiosity by answering the world's most important questions, things like when did America start dialing nine one?

One?

Is William Shatner's best acting work in Esperanto? Also what happened to Esperanto? Plus we cover questions like how Chinese is your Chinese food? How do dollar stores stay in business? And of course is there an illuminati of cheese? There absolutely is, and we are risking our lives by talking about it. But if you love mind blowing facts, incredible history and really bad jokes, make your brains happy and tune into Part Time Genius. Listen to Part Time Genius on the iHeartRadio app or wherever you get your podcasts.

Or right We're answering you listening to questions here today, and our last question of the day is about the past, the present, the future and whether we can move between them. Hey guys, this is Trevor.

I was recently listening to an episode of the podcast in which Daniel mentions that we have never observed anything that was moving backwards in time. My question is, how would we be able to identify whether an object we're observing was moving backwards in time? What characteristics would make backwards motion in time distinguishable to us? Are we sure we would even be able to observe a reverse time object while we are moving forward in time. I love what you guys do, and I sincerely appreciate you taking my question.

Interesting question. I feel like this question relates to the movie Tenet. Have you seen that movie?

I've seen that movie, and I saw that. Christopher Nolan was like, people who try to understand Tenant are not really getting what I was after, Like, it just doesn't make sense.

He's like, why are people throwing my movie at the wall? It's signs fiction people.

It's not supposed to make sense, he says, as he presents and asks you to solve it.

Like what, Yeah, It's all about the experience of the mystery, right.

I'm not being a physicist. I'm just like experiencing the universe. Man, I'm not trying to figure it all together in my head in the way that makes sense.

Yeah. Yeah, maybe your wall would be intact if he took that attitude more. But yeah, in the movie Tenet, they sort of figure out how to make something move backwards in time, Like they can make a bullet move backwards in time, and so even though we're moving forwards in time, the bullet is moving backwards in time. And at some point they make people move backwards in time, right, I don't know.

I went back in time and eras that movie from them.

I think that's the basic question that Trevor has here, which is like, could something move backwards in time? And what we know it's moving backwards in time.

Yeah, it's a really cool question with a lot of interesting subtlety, depending exactly what you mean by move backwards in time, because there's a fundamental question we have about time, which is like why does it flow forward? If you look at the equations of physics, they seem to work just as well forwards and backwards. You know, for most things. If you took a video of them, and then you play the video forwards and you play the video backwards, the laws of physics would work just as well for both scenarios. Like you're playing pool and you hit a ball and they bounce off each other. You could play that whole reaction backwards and the same thing would work according to the laws of momentum and all that kind of stuff.

In like a perfect world, in a perfect bouncy ball that doesn't lose energy each time it bounces, like a bouncing ball moving forwards in time looked exactly like a bouncing ball moving backwards sometimes.

Yeah, and we could start with the individual particles, so we're not thinking about like ten to the twenty nine objects and thermodynamics. Yet for like the individual particles, these rules work just as well forwards and backwards in time.

Meaning like, give you records and particles having some interactions, and you play it backwards. That's also a perfectly feasible thing for the particles to do, or what you observe I'm doing is also perfectly feasible.

Yes, ninety nine point ninety nine percent. There's a little asterisk there about how some particle interactions do prefer one direction in time, but it's a really really tiny effect.

So then what are you saying. Are you're saying like we are technically all moving backwards and forwards in time or there's no meaning to something moving backwards in time?

I think that implies something really interesting about the universe, about causality. It implies that, of course the past determines the future, right things flow, the laws of physics determine things, but also that the future is unique because the future is determined by the past. But you could also flip it the other way around. You could say the future determines the past, right, Like if there's only one possible future for every past, and you can go from the future and predict the past, if they're you know, connected by the laws of physics in the same way, then like what direction is causality anyway? And so that's what we mean when we say, like which direction does time flow? The laws of physics don't care. They're sort of like time independent.

Right, Well, you're sort of getting into the idea of determinism and whether things move in a predictable way, But doesn't quantum mechanics sort of do away with that? Like, you know, I can't really predict the future because what absurdain particle is going to do is sort of random according to quantum physics, And if I have an outcome of a particle, I can't really trace back its history because there was a random process somewhere in the middle.

Yeah, great question, and there's a couple of directions there. Now, if you only have quantum interactions, then what you said is not technically correct because quantum information is preserved and you can go forwards and backwards, like if there's no wave function collapse, then the future is completely predicted by the past, and you can derive the past from the future. You know. Quantum information just flows through time like particles interact with each other. There may be randomness, but if there's no wave function collapse, so you don't force the universe to choose from those probability distributions, then all that information is preserved. So wave function collapse does break that deep rule of quantum mechanics, which is another reason why wave function collapse is kind of nonsense from a philosophical and a physics point of view and not something we understand.

Wait wait, we're having your crossover here with another question. The other question.

Connected man in the quantum realm, there is a larger sense in which we think quantum mechanics does yield a definition of time because the randomness of quantum mechanics does affect like multiple particles. And we talked about an individual particle and what happens to it. Now imagine like ten to the thirty particles. Instead of tracing each of them individually, you're thinking about the population of those particles. What are they more likely to do or less likely to do? And because they're governed by randomness.

Let's stick to maybe one particle. Like the classic example of a of a quantum particle is like, if I shoot an electron at a magnetic electric field, is it going to veer to the right or is it going to veer to the left. Now, in the past, I don't know whether it's going to be veering to the right or to the left. But then I shoot it at the electric field and the particle goes right or left. Now I'm in the future, and the particle went right.

Because you collapse the wave function by insisting on measuring it with a classical object. Let's change your experiment a little bit. Let's say you shoot the electronics the magnetic field, but you don't measure which direction it went with some big classical thing like a detector or an eyeball or a graduate student. You record whether it went left or right into some other quantum object, you know, another particle or photon or something.

But I reject your scenario, Daniel. I reject your scenario, and I want to stick to my scenario in my scenario, there's a future which is the wind right that I couldn't know in the past.

Yeah.

And if I'm in the future and I saw that the particle went right, I can still sort of figure out where the particle came from. So it just sort of seems like there is direction to time. In the past, I couldn't tell the future, but in the future I could tell the past.

Yes, if there's wave function collapse.

Which there was in this scenario.

Which violates a basic principle quantum mechanics loss of information, then yes, the future is different from the past because the collapse makes the future different. If you don't believe in collapse because it's fundamentally nonsense, then your whole premise, then the whole setup is flawed.

But I have to believe in collapse because I live in a collapse world. Like when I'm talking to you, I'm collapsing things. You don't know that man grab my steering wheel. My experience. Maybe there's a multiverse little bit somebody else does something else, but to me, in this multiverse version, there's collapse. It's a real thing. And so is there a direction of time in my universe?

Well, if there's a multiverse. Then the wave function doesn't collapse. It splits into many pieces. They're all part of the same big universe wave function, but they can't interact with each other, and that preserves the flow of information. All those things do happen, they're just sort of like happening on top of each other in a way that they can't interact with each other. It's the quantum multiverse. So there is a scenario in which there is no collapse and quantum information is not changed as time goes on.

Sure, if you're like a mega entity, then you can see all the multiverse at the same time. But to me, to us right now talking to each other, we live in a collapse universe. This is our universe, and we don't even know if there are other universes. So does that mean that time does have a direction? This make it about me Dan, not the watcher who's watching the multiverse from afar.

I think portions of the universe no longer have access to the full information. That doesn't mean that time couldn't flow backwards, right, The same physical process could still go in the other direction.

Well, it could, But to us, to our understanding and our experience of the universe. This is all the information that we have, and you don't know if there's actually other information.

Yeah, we don't know. That's true.

So we have to assume that this is maybe what all there is. This could be all that there is.

We don't have to assume that.

It's not all there is to our experience of the universe. In this universe we live in, there is a direction of time.

If you don't have the full information, you might not have enough information to reconstruct the past.

Yeah, okay, so then is that what do you think Trevor means by things moving backwards in time? Like could there be something moving in the opposite direction of this direction of time?

I don't think that's what Trevor is asking about at all, and he's probably wondering, like, why these guys talking about quantum mechanics I was thinking about? So let's get to time.

Okay, Well, let's get to this ques. The question is can something move backwards in time?

Yeah?

And would we notice you're the one who went into quantum mechanics, I mean, or are we not answering the question with quantum mechanics.

Or are we No, we're not. We're not so okay that was a stepping stone towards the concept of thermodynamics, which builds up from the microscopic picture of quantum mechanics. It says, zoom out from the tiny particles. Experience is not of tiny particles. It's of big things with ten to the twenty nine or ten to the thirty particles. And on that scale something else emerges, and it's called entropy. You have lots of quantum particles interacting. You notice that they tend to spread out over the possibilities, which is another way basically saying entropy increases as time goes on. And that's where our experience of time comes from. What you were alluding to earlier. Like a bouncing ball bouncing up and down, that's a lot of particles interacting. What happens there is that energy tends to spread out, and the ball loses some energy and it bounces lower and lower as time goes on. So that video you could definitely tell if something going forwards or backwards in time.

I see you're saying, let's not think about quantitum physics. Let's start think about a bouncing ball. And so maybe in Trevor's question, something moving backwards in time is maybe like a ball whose entropy to us seems to be decreasing.

Yes, exactly, there's a sort of a subtlety hear, like, take that ball that's bouncing and entropy is increasing. You could also say, well, how do we know that ball is not going backwards in time with decreasing entropy. You're like, well, that's just sort of like definitional. Is it moving forwards in time with its entropy increasing, or is it moving backwards in time with its entropy decreasing. It's basically the same thing. I think what he's asking about. And the original continent that inspired this is that we don't see things moving forwards in time with their entropy decreasing, Like we don't see coffee cups reassembling themselves, we don't see ice freezing on a countertop, all these things that have entropy decreasing, And that's what it would look like. It's to see something moving backwards in time, because it would be moving backwards in time with its entropy increasing, backwards in time, which to us would look like it's moving forwards in time with its entropy decreasing.

So then the answer to the question is that if something was moving backwards in time in our world, which is moving forwards that you're saying, we would be able to notice that it is moving backwards in time because its entropy would be decreasing.

Yeah, and I don't remember it, but that probably happened in tenet. Right, somebody moved backwards in time and drop the coffee cup, and to the people moving forwards in time, it looked really weird because they saw a broken coffee cup jump up off the floor and reassemble itself.

Yeah, no, no, no, that's exactly. That's the trippy thing about the movies that you see things sort of moving in unnatural ways. Yes, which really to our brain is like you're seeing entropy decrease, which we're not used to.

Right, Yeah, exactly, that's what it would look like to see something move backwards in time.

Well, I feel like we answered the question, which is like, you know, it's all about entropy, but entropy is not really kind of like a fundamental thing in the universe, right, Isn't it sort of like something that emerges from the interaction of lots of things, Like at the quantum level, do you still have entropy and does it play a role Like let's say we go back to the idea of looking at an electron, Could you tell if an electron was moving backwards in time?

Yeah, great question. We don't really understand how the air of time emerges. But you're right, it's not something that's fundamental to the universe. It's emergent. But you know, we don't really understand emergence either, like why do laws ever emerge? Why isn't everything just controlled by the tiny little objects and chaos rules? On top of that, we don't understand emergence. We don't understand how time emerges. From quantum mechanics, we don't understand the importance of emerging things. There are some hints there and some clues maybe in particle physics, but fundamentally that's not an understood question. You can't even really ask what is entropy in quantum mechanics because entropy is about differences and how things are arranged in the macroscopic and the microscopic. You have to like define two levels of information even be talking about entropy.

I wonder if then the answer to Trevor's question is, like, you can't do something's moving back to in time unless it's really small, or unless it's only one particle.

No, for the one particle, you can't tell at all. Right, there is no sense of entropy for a similar particle.

That's what I mean. You can't tell. Like a ball, you could tell if it was moving backwards in time, but an individual electron you cannot. Yeah, that's exactly right, that's what you're saying unless the multiverse doesn't exist.

Yeah, that's right.

All right. Well, do you think you need to go back in time and re answer this question?

I think I want to go back in time and not bring up quantum mechanics.

No, but it totally changes the answer, right, Like if you ignore quantum mechanics, and yes, you can tell something to going backwards in time, if you do things about quantum mechanics, then you can.

No.

I'm very glad we got into quant mechanics.

That's just I think you're always glad to get into quantum mechanics. He has a particle physics. I think the problem sometimes is getting you off of quantum mechanics.

Yeah, totally agree.

It's a little interesting reversal here. It's like we went backwards in time. All right. Well, thanks to all of our questions askers today, really interesting questions and If.

You have questions about how the universe works, please don't be shy or write to me two questions at Daniel and Jorge dot com. You can address your questions to me, or to me and Jorge, or to anybody you like. You'll still get an answer from me.

We hope you enjoyed that. Thanks for joining us, See you next time.

For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Instant, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit us dairy dot COM's last sustainability to learn more.

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Daniel and Jorge Explain the Universe

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