Metaphysics and modern AI: What is space and time?

We explore how space and time form a single fabric, testing our daily beliefs through questions about free-fall, black holes, speed, and momentum to reveal what models get right and where they break. 

To help us, we’re excited to have our friend David Theriault, a science and sci-fi afficionado; and our resident astrophysicist, Rachel Losacco, to talk about practical exploration in space and time. They'll even unpack a few concerns they have about how space and time were depicted in the movie Interstellar (2014).

Highlights:

• Introduction: Why fundamentals beat shortcuts in science and AI
• Time as experience versus physical parameter
• Plato’s ideals versus Aristotle’s change as framing tools
• Free-fall, G-forces, and what we actually feel
• Gravity wells, curvature, and moving through space-time
• Black holes, tidal forces, and spaghettification
• Momentum and speed: Laser probe, photon momentum, and braking limits
• Doppler shifts, time dilation, and length contraction
• Why light’s speed stays constant across frames
• Modeling causality and preparing for the next paradigm

This episode about space and time is the second in our series about metaphysics and modern AI. Each topic in the series is leading to the fundamental question, "Should AI try to think?" 

Step away from your keyboard and enjoy this journey with us.

Previous episodes:

• Introduction: Metaphysics and modern AI
• What is reality?

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Chapters

• 0:00 Framing space and time
• 3:20 Why fundamentals matter In AI
• 10:56 Time as a human and physical concept
• 14:50 Plato, Aristotle, and change
• 19:55 Practical problems in space-time
• 23:40 G-forces versus free-fall intuition
• 28:55 Gravity control and sci‑fi acceleration
• 33:40 Newton to Einstein: Curved space-time
• 37:15 Black holes and spaghettification

Transcript

SPEAKER_04: 0:02

The AI Fundamentalists. A podcast about the fundamentals of safe and resilient modeling systems behind the AI that impacts our lives and our businesses. Here are your hosts, Andrew Clark and Sid Mongolik. Welcome to the AI Fundamentalists. Today we'll be talking about space and time. This is the second full episode of our mini-series on metaphysics. In the last episode, we discussed the concepts of reality and objects. Today, we will focus on space, time, and how these two concepts relate to each other.

SPEAKER_01: 0:40

And I think this is going to be a pretty fun episode. There'll be some nice surprises for you here at the end, but we just want to tee up a little bit of the nature of this discussion. So we last talked about reality, which is in some sense the metaphysics about existence and the metaphysics about objects, which exist in space. And as we mentioned, in order for us to identify objects from each other, we're necessarily going to look at where they exist in space. But space doesn't exist on its own. Space also exists in time. We almost can't imagine what it would mean for something to change from one thing into another without some amount of time passing between those two points.

SPEAKER_03: 1:21

Well, purposely want this to be a little bit of a lighter episode. I know the last one was a little bit heavier on uh on the nature of reality and things. So I think this is nice, like kind of a bridge episode, and also a little bit of almost practical metaphysics, if you will, of metaphysics is asking these types of questions to under to like almost for the sake of questions sometimes and trying to like think outside the box. And as we've talked about some of the value of this type of discussion. And then I think as we get into the the next episode when we're picking up causality and then and then ending with with our definitions of thinking is going to be a lot lavier and more technical. So try and get this a little bit of a lighter practical metaphysics discussion of um we're definitely in this age of AI and things we've very much the the how do we do things faster and just productivity and like trying to skip steps. And as we've talked about a lot on this podcast, and in the nature of the name, even the AI fundamentalists of you look at the best of any field, you name the field. They're not the people that do the fanciest things the fastest and skip the steps, they're the people that master the fundamentals the best. And I think that's um the big thing we have to guard against as a society is actually creating new knowledge and not spending trillions to just replicate existing knowledge. Um, but really, how do we think outside the box, think creatively, and master the disciplines? And some and sometimes that's harnessing childlike curiosity for like thinking outside the box and asking questions that nobody else is asking. So I I think this discussion that we're gonna get into is gonna be a really a great example of that. And um kind of a uh I find it like kind of a fresh take on on some some things and uh just a good refresher in um some of the the down news that's going on these days and just different ways to to think about the problem. And then um I really want to get your thoughts on on that, Sid, and then I think we can also talk a little bit of framing around some uh some time and kind of like time is a very interesting concept in metaphysics and some some interesting stuff we can get into there.

SPEAKER_01: 3:13

Of course. I mean let's I mean let's quickly do a little piece on time here, right? So time is understood by us as humans, living through the world as like moving through one second per second, right? We can't really imagine what it means for time to go faster than that, we can't really imagine what means for time to go slower than that. Maybe we have some perceptions of time moving faster if we're driving a car, but the the time is still moving exactly how it's moving. Um, but as we'll dig into a little bit later today, time is not so different from space. In fact, they may even be the same thing. And this can create some really weird consequences where time is experienced and exists in ways that are not how we would normally perceive them.

SPEAKER_03: 3:57

Tully agree. And just a little bit of framing from like our last conversation, we talked about like Aristotle and Plato approaches, um, is really different philosophical ways of looking at it. Of Plato, one of his thing points was like you wouldn't know if a year was skipped, and kind of like that reference of how you're looking at at time. Um it's they kind of and and Aristotle is kind of like you start with the change, kind of like that delta or like the I mean the derivative, if you will, of like looking at how how change is. So like Plato, as we talked about, like the ideal and things like that, he has a different way of what's like that the framing, and we kind of discussed in the last episode there's really those two boxes, if you will, of how to how to view metaphysics and and some of these different areas where Plato is it's it's it's kind of relative. Like we wouldn't know like if if a year skipped because we're all in the same, you know, uh situation. We don't next as you know that, and then Aristotle is more about the change. So I think those are some just different, um sort of want to get your thoughts on that, but like some different perspectives of when we're looking at the more practical space-time and things like that, of like some of this way before we got as technical into those areas, back in I don't know how many uh BC, uh I I don't have it at the top of hand right here, but like Aristotle and Plato, like a long time ago, just like the basic building blocks of how we started thinking about this, which as it expanded as as knowledge progressed.

SPEAKER_01: 5:11

Yeah, yeah, absolutely. And I and I guess to to answer your question, I guess that you know, unlike the last episode, I think we're gonna look at this a little bit more practically today. I think that the the hope is that, you know, with this discussion about to queue up here, we will see through practical examples and practical problems working with space-time from a physics perspective, how we could track these problems and how we can potentially solve them and resolve them and get some deeper understanding uh by just solving some problems. And to the end, the discussion you're going to hear today is between two special guests, our friend David Thereo, a science and sci-fi aficionado, and our resident astrophysicist, Rachel Lasako. Glad to have you on, David, and we're glad to have you back, Rachel. David has some very challenging questions for you today.

SPEAKER_02: 6:01

I do. Thank you so much for having me. I'm super happy to be here. There have been lots of times when I uh listening to a podcast or reading an article and thinking about um these crazy types of science questions. And a lot of times I'll get great answers, but there'll always be one thing that I'm thinking of that they don't get to. So it's wonderful to have somebody to actually talk with uh live and get these uh answers to all these nagging questions that I've had.

SPEAKER_00: 6:34

Awesome. I'm also glad to be back. Um, I've also had nagging questions like this since I was pretty young, and I decided to keep studying, get some degrees in astrophysics to try and answer them. And the surprising thing is that not all the answers are out there, but I'll try my best to answer your questions today.

SPEAKER_01: 6:55

And with that, let's begin. Let's start our discussion off. Uh, David, take it away. Wonderful.

SPEAKER_02: 7:01

All right. So for this question, um, I'm thinking about pilots will uh undergo a lot of g force when they're doing maneuvers. Um, a g force is uh representation of feeling the Earth's gravity. Uh, you could probably define it better than me. Um but uh I know they can say we stand up to maybe 10 G's, they'll say, uh before passing out for a short period of time. Um and when they pass out, uh, this would be because the force is pressing them down, pressing them into something, and that can prevent the blood in their body from moving around, not reaching their head, uh, not reaching their brain, and then they pass out. Does that sound right so far? Yes.

SPEAKER_00: 7:49

Uh yeah, I'm familiar with uh this concept of either testing it down on Earth or when a rocket launches and they're going up into space, there's a lot of G force or the feeling that suddenly there's much more gravity than you're used to on the surface of the Earth acting on your body.

SPEAKER_02: 8:09

Right. And so where I got really interested was starting to think about this um outside of the earth, because when we think about how we experience gravity, it's always with us being pushed onto something or feeling this opposing force. So we feel pulled to the ground, over on a roller coaster, we feel pushed into our seat or pulled out of our seat, depending if the roller coaster is going up or down. Um and from that we can kind of get this sensation of there's only so much we can take, right? Until you're going to be squished in the seat or ripped out of your seat. But in space, it's different because the way that gravity from say another um orbital body or the earth itself would affect something is that it's going to affect everything around you, including you at the same time in the same way, I think. So my question is if we have some astronauts in space in a spaceship, and say suddenly the mass of the earth were to change for some reason. So now it's a hundred times bigger, that's gonna have a big gravitational effect uh on the astronauts and the ship, and it should make them start to accelerate, I think, towards this new earth uh rapidly. However, since it's affecting the ship and the astronauts all at the same time, if they didn't have instruments or a window and they were just there, would they even be aware that this event is happening? And would it affect them in any way in terms of we talked about the g forces the pilots experiencing? Now uh with the Earth being so much bigger, a hundred times bigger, uh they would be experiencing this g force, which we know would make the pilots ass out on the Earth scenario. Are we expecting the astronauts to have any ill effect from this?

SPEAKER_00: 10:22

Right. So when you're in a rocket blasting off from Earth or you're in a roller coaster, you have a seat up against you, and that is pushing you or pulling you around the roller coaster, blasting you off of Earth. Uh, and that's a change in where you were before in your inertia. That is the G-force that you're feeling. When you're on that roller coaster and it's bringing you up or pulling you down, you're changing uh separate from the roller coaster. If you and the roller coaster are just suddenly falling together, you actually don't feel the roller coaster pushing against you. And so you could be going 10, 20, 50, 100 Gs, let's say, but if you're moving with that roller coaster, you don't feel it, and you're probably not going to pass out. So these astronauts in their ship suddenly over an extremely massive Earth will fall together. Nothing is pushing against the astronauts, and so my understanding is that they won't pass out the same way that they might have during training. However, they probably will pass out when they land. Uh, you have to go quite a bit faster in order to maintain orbit around this new massive Earth. And if you don't, you'll start to fall out of orbit towards the Earth.

SPEAKER_02: 11:49

I just think the implications are really neat. So if you want to say how long would it take to say reach 20% the speed of light, have to do some napkin math. But I mean, if you're going at like one G, that would take a really long time still. But if you're have the ability to control gravity in a way where now you can accelerate at 100 G's, then that's going to take a lot less time. So the implications for space travel are really huge. I think that from a sci-fi standpoint, if initially when I thought of, oh, you could control gravity, it would just mean that you've got like a ship that can kind of hover. And like, yeah, that's neat, but it's really much more uh powerful in terms of this acceleration that's unbound or the ability to just uh a ship could just make a lateral movement, you know, without slowing down because everything moves at the same at the same weight at the same time.

SPEAKER_00: 12:47

Right. I think I understand. So the idea is using gravity, uh manipulating it in a way to propel yourself in kind of the opposite way that gravity pulls you towards the center of an object.

SPEAKER_02: 13:03

Yeah, it's sort of like if you have um, you know, you have a carrot dang on a stick and it's pulling a donkey. If you were um at this carrot that and the carrot is this giant gravity well kind of thing that's just then pulling you, um then you're just getting pulled really fast and uh much faster than you otherwise could.

SPEAKER_00: 13:25

Yeah, for sure. I think one way to think about this is now switching gears from an idea of gravity that we have from Isaac Newton, where massive objects have gravity and pull towards the center. And that's kind of the end of it. You can have orbits uh and you can watch an apple fall. Uh, but Einstein brought about a new way of thinking about gravity, which is considering space-time. You can think of space-time kind of like a fabric, and everything that has mass or energy will make a dent in this fabric, and objects will move according to the bends and curves and dents in the fabric. So if you have something that could distort space-time in front of your spaceship, like this carrot, uh, you will fall into the gravity well, into this divot in space-time, and it will actively move ahead because it's attached to your falling spaceship and propel you forward. I don't know if propel's the right word, but drag you forward perhaps, as there's this bend that moves along the fabric of space-time.

SPEAKER_02: 14:51

And so another way I suppose to test this, which would probably not be anything that what anybody would want to volunteer for, but if you did have a space a ship going into a black hole, what would happen?

SPEAKER_00: 15:07

A lot of pretty horrible things would happen. Uh black holes are not something you want to mess around with. Um, black holes in this idea of Einstein's space-time are kind of just straight holes, these huge, endless wells that dip so suddenly into the fabric of space-time. And you have to go faster and faster to keep an orbit around it as you get closer and closer to the center. At some point, you have to go the speed of light in order to just orbit and not completely fall in. And past that point, you're falling in no matter what. Even light cannot escape, and that is called the event horizon. If you were to fall feet first into a black hole, you might experience something that's called spaghettification. It sounds really fun, but it's really not. The gravitational pull on your feet, if you're falling in feet first, is suddenly more heavy than any other part of your body. And so your toes get dragged in much, much faster. And then your knees get dragged in much faster, and then your hips and your chest, and then your head. And so you're experiencing and watching your toes just get ripped up, slurped in like spaghetti, atom by atom, into the center of the black hole. And it's because black holes are such an extreme gravitational thing that there's so much more gravity, even just a couple of feet in towards the center. Not a fun time.

SPEAKER_02: 17:02

No, definitely not. I was thinking that you might solve part of that problem. I mean, not really solve, but if the black hole instead of collapsing to a single point, was somehow a massive object that was the width of your feet, so that would be pulling you more uniformly, not to a single point, it might help. But it sounds like that still wouldn't matter because the distance is going to be very important as well.

SPEAKER_00: 17:35

Or maybe maybe imagining the black hole just being the size of your feet. Uh, unfortunately, also not going to be a very pleasant time. Your feet would start to swirl around the black hole as it eats it up. And, you know, just your feet maybe becoming more like lasagna than spaghetti. Plenty of pasta shapes to choose from, all of them not something you want to turn into.

SPEAKER_02: 18:06

So avoid the black hole. All right. Next question. So there's a thought experiment where with space exploration, there's a limitation to distances and speeds that we can go, particularly when we are using methods such as rockets which carry fuel, and uh because of the mass of the fuel, you need more fuel and more rockets to move that mass, so you get these diminishing returns, and it becomes very difficult to go longer distances. There was a thought experiment where the idea is what if instead of having propulsion on the payload, we instead could push it with a laser. Uh now, if we're using a laser and we don't want to melt or destroy this thing, then the payload will have to be very small. Um, but in this thought experiment, we can have a very small payload that just essentially has a very minimal sensor. And if we do this, the idea would be we can accelerate uh this probe to incredible speeds, um perhaps 15-20% speed of light. And that would mean that we could actually reach another star system in 20 to 30 years, which is I think quite reasonable. So this all sounds really great. My question is if the probe is traveling that fast, um one, do we have any way to really slow it down because we can't buy the brakes from Earth? And two, if not, then are we going to be able to get good readings from an instrument um at these speeds? Because, you know, despite improvements to say cameras, if I take a picture of my phone from a moving car, it tends to be blurry, and that's only a few miles per hour, let alone 20% of the speed of light.

SPEAKER_00: 20:28

Yeah, this is a really interesting thought experiment. So the laser is propelling the probe because the photons from the laser have momentum. They're all targeted in a very highly concentrated beam. And so those photons can be shot directly at something like a sail or something to catch the photons and transfer that momentum. With the transfer momentum, the probe attached to maybe this parachute or sail can suddenly go very fast speeds without any fuel, just with catching these photons from this laser. There's no laser at the next closest star system that we know of. Instead, there are three stars at um Proxima Centauri and Alpha Centauri, uh, which has two stars. Those three stars let off photons as well, so the parachute or sail might be able to catch some to try and slow it down. But they're scattered in all different directions, and the sail would only be catching photons going in its direction, so slowing down might not be very feasible, especially because these stars are only about as bright as the sun or dimmer, and you might need something much, much brighter, giving off many more photons at higher energy to try and slow down the probe. The instruments on the probe would be able to look at any light out in space during its trip up until it gets very, very close to the star system. Before that point, the star system will look a little bit bluer as it heads towards it at these incredibly fast speeds, because the light coming from it ends up getting blue shifted. This happens when anything traveling towards you very quickly, or when you're traveling something toward when you're traveling towards something very quickly, the waves of the photon are squished. Kind of like sound waves are squished when a siren is coming towards you. The pitch goes up when a siren comes towards you, and the pitch goes down as it goes away from you. Similarly, the waves of a photon, which is its wavelength, will go up, shifting it towards blue when it's coming towards you, and it will shift down, looking redder when it goes away from you. So the probe looking back at Earth will see a very red Earth as it zooms away. Us on Earth will see a very red probe as it leaves us, and the probe will see the stars suddenly looking very, very blue as it travels towards them. Another really weird thing that happens when you're traveling close to the speed of light is that time doesn't take as long. So on Earth we'll be waiting 20 or 30 years for that probe to reach the star system, but the probe will only age maybe 15 years. You put a clock on that probe and it's not going to reach 20 years. It's going to take much less time. The distance it also travels is much less. If you put an instrument on that measures how far it's gone from Earth to the next star system, it will measure much shorter distances. And this is all weird phenomenon that happen when you travel close to the speed of light.

SPEAKER_02: 24:09

So when the probe is traveling from its perspective, a shorter distance and a shorter time, does that distance over time equate to the same speed that we think of it as achieving?

SPEAKER_00: 24:24

No. Which is really weird. The most important thing that has to happen is both people on Earth and the probe see light traveling at the speed of light. And so this is why we have time dilation and this shrinkage of distance. Time and distance have to change when you're at these higher speeds in order for light to stay the same speed. So a flashlight on the probe shined outward in the same direction the probe's going will leave the probe at the speed of light, not 80% the speed of light if it's going 20% by itself. Light shined from Earth will reach the probe at the speed of light, according to both people on Earth and people and the probe measurements. Light traveling the speed of light will always go the speed of light, no matter how fast you're going. And that's why distances shrink and time shortens, is to just make that math work out.

SPEAKER_02: 25:41

That is wild.

SPEAKER_00: 25:43

It is. And it's hard to prove it. There have been some experiments, I can't recall them off the top of my head, but a lot of this comes directly from theory, pencil on paper, on specifically Einstein's pencil and Einstein's paper. He was able to figure this out with thought experiments like what we're doing today, talking it through, and reasoning that the speed of light has to go be the same everywhere in order for causality to make sense.

SPEAKER_01: 26:16

Which Rachel's absolutely teasing our future episode on causality, but we'll get there when we get there.

SPEAKER_04: 26:21

I was gonna say.

SPEAKER_00: 30:00

Over the course of maybe several weeks or months before hearing the rest of the message. And it would have taken at least a couple years to hear the whole message the first time before she maybe sends it out again. That's how time dilation works, and that the information coming from the planet can't suddenly be several years of information that haven't been sent out. So they would have known that the gravity was really intense on the planet, causing time dilation and distorting the message.

SPEAKER_02: 30:33

I think it seems obvious the difference in a voice message. I'm trying to think of how that works with a digital message of it just giving some status of yeah, this is you know the temperature of the planet.

SPEAKER_00: 30:52

Yeah, my guess would be that the signal might have blacked out because it just wasn't receiving enough energy consistently. Or if it was something like Morse code, you just hear a very long beep that goes on for like a year. And maybe that's just a short beep in Morse code. And so however it comes out, the signal is going to be severely distorted or completely cut off. I think it's unrealistic that they would arrive at Miller's Planet thinking that everything's hunky-dory and that Miller's there doing fine, that she sent out years of messages saying everything's okay.

SPEAKER_02: 31:35

Yeah, I think because I like the movie, I'm going to play a little bit of Devil's Advocate to see if I can think of a way for it to make sense from their perspective. So perhaps it was Morse code, and nobody was paying attention, and the computer is just interpreting it and saying, yep, that's what it is. You know, nobody was looking at the log file to see that it took 10 times as long to process.

SPEAKER_00: 32:08

I believe in the movie, NASA is completely stripped of funding. There's only like three guys left, and they're in a cornfield or something. It's been a while since I've seen the movie, but maybe that's why they didn't realize there was some time dilation.

SPEAKER_02: 32:22

That's right. They cut their funding. That's what happens.

SPEAKER_00: 32:28

I also thought of another way, potentially, to have solved the issue that the remaining crewmen on the endurance had experienced. So he's sitting up in the endurance for several years waiting for his crew to come back. If he had realized that there was some time dilation issues going on, where being on the surface suddenly slows down time compared if you're outside of the surface in orbit, he could have moved the rocket to be the same distance away from the black hole as the planet. Because it's not that the planet has so much gravity that suddenly there's time dilation due to this relativistic effect. It's the black hole. The planet being closer to the black hole slows down time. And so if he simply orbited the black hole, got a little bit closer to it, he would also catch up to the way that time was moving on the surface. He probably would have also only experienced an hour waiting for his crewmen to get back if he was the same distance from the black hole.

SPEAKER_02: 33:44

That's a good solution. My last comment on the movie is that I think it was way too clean when they went back up to the ship, and the one guy was by himself for 20 or so years. I think there probably would have been writing on every single panel, and there would have been pillows stuffed in spacesuits, and he's pretending they're people talking to him and all kinds of things. He really held it together and stayed very professional in the absence of human contact.

SPEAKER_00: 34:13

Also sounds like we shouldn't leave you alone for too long.

SPEAKER_02: 34:18

Yes, that is true. I will start uh making friends.

SPEAKER_04: 34:22

That's similar to cast, y'all sound similar to Castaway.

unknown: 34:25

That's right.

SPEAKER_04: 34:27

In regard to space-time and like throughout the discussion, Rachel or David, let's start with Rachel. What's like one thing to distill out of this conversation with regard to metaphysics, AI, or any point you'd want to draw on all of this?

SPEAKER_00: 34:44

Yeah, I think the biggest takeaway I've had from learning about general relativity and this new way of looking at gravity as a bend in space-time is that our ideas of how the physical world works and the models we want to use to explain it can change. Einstein was not that long ago. And the next big revolution in our understanding of the universe can easily come again, maybe not from just one person, but through the scientific method and community striving to not feel settled in just Einstein's work, the way that we were for several hundred years with Newton's work. So the next big revelation can come, and I'm really excited for it whenever it does. Uh, and I think that you can learn this now, it is helpful, but it might get replaced. And that's a really exciting thing to look forward to.

SPEAKER_04: 35:53

Very cool. David, what about you?

SPEAKER_02: 35:58

You know, there's so much information out there. I think sometimes it can be intimidating to ask questions or think that the answer isn't already there, but there's so much that we don't know, and the only way that we learn is by asking. And even if somebody, you know, even if it already has been discovered, we only carry on our knowledge through sharing it with others. And I think it's just so important to always be asking why, learning about ourselves, learning about our environments. Um, I love having these types of conversations.

SPEAKER_01: 36:36

This this has been an awesome discussion on the uh relationship between space and time. I think time dilation really, really clearly shows us that there's a very intricate connection between these two things that we kind of take for granted, right? You know, does time move one second per second? Is space exactly what we see in the in like our apparent world? Uh and so I think this ties up really nicely with our conversation on metaphysics, showing that you know, the reality of the world and the way that we model the world isn't necessarily describable as how we see it with our eyes, that you really need to think more critically and more mathematically about these things. Our next episode is dealing more with time, where we're gonna be talking about that causality piece, right? How do we know that A causes B? What is A, what is B, and what is this medium in between them that causes the effects in our in our lives and our world to happen? And are they real? Uh so it'd be another deeper question, but also just as important. I think that you know we we deal with we deal with this assumption that things cause other things, and so we should understand what that means.

SPEAKER_04: 37:39

Awesome. Well, we thank everybody for your time and for our listeners. We hope you're enjoying this series and looking forward to the next episode. Thank you, and until next time.