Spiros asks me to forget what I know about physics and imagine we are in ancient Greece. I’m holding a rock. If I let go, why does it fall? Can I make it stop? Can I make it fall up? Those simple questions lead into his thought experiment about gravity and our movement through time — without starting with calculus or Einstein.
We follow that thread through anesthesia, memory, entropy, and the difference between what is possible and what is likely. I bring in self-driving cars, aikido, a rock-climbing close call, and salsa dancing to explore how we build a picture of the world beyond our own point of view.
Transcript
Spiros: Before you even say anything, stop. Because you know too much. And you will have more trouble answering the simplest questions. Try to put yourself in a position of someone from 3,000 years ago. I'm not joking. Maybe ancient Greece.
Pablos: 3,000 years ago, you might think gravity was something pushing you down.
Spiros: We know what people thought. The smartest person of ancient Greece, Aristotle, he had no idea. He was just like, oh, let me take a crack at this. Depending on the essence of the thing, if it is made of matter or earth, it's attracted to something that is similar to it, so it wants to go towards the earth. If it is fire, it wants to go towards the sky. He made shit up basically. It was almost like it was fantasy. But let's just do this: the Socratic method.
This is important, because this is hard, but I think it's possible to do. If at any point I fake it and I bring in a concept that is modern or something you wouldn't know how to answer… Let's do it.
Pablos: Does anybody besides Caltech do the Socratic method, by the way?
Spiros: I don't think even at Caltech we do the Socratic method. I think shifting your point of view can allow you to see questions that were the right questions. First thing here: I will give you my phone.
The answer we are looking for is to the question of why do things fall. Sounds very simple, but it's the equivalent to quantum gravity that we're trying to get to. We're way too early in civilization, so we don't know any of the intervening stuff. Think of the phone you're holding on right now as a rock. You just have a rock in your hand.
Grab a rock, hold it, and let's try to figure out what happens if you let go. What happens if you let go? It falls. What if I were to ask you to make it stop from falling for half a second?
Pablos: I would just hold on longer.
Spiros: You let it go, but I want you to just think so hard so it doesn't fall. The moment you let go it just hovers there. Can you do it? No, it doesn't. It's science, right? You could have asked any human being.
Pablos: Tape it to a bird.
Spiros: Over there, maybe. If you just let go and don't have some other fancy magic going on, it just goes immediately. You can't even let it stop for a nanosecond.
What if I were to ask you now to grab it again? We know it's gonna go — you can't stop it from moving. How about you have it fall up?
Pablos: I could throw it up.
Spiros: But if you just let go, it goes one way. We've established two things, my ancient friend. When you let something go, it moves — you can't stop it. Even for a second it'll just go, unless something else hits the ground or whatever. And the second thing is that it goes in one direction.
Because you're one of the smartest people on earth, I will take a shortcut right now. Can you think of any dimension where you cannot stop from moving in it and you cannot go back even a little bit?
Pablos: I can't stop it from going.
Spiros: You can't stop moving in it. In space, for example, we haven't moved, and we can clearly go back and forth in two out of the three dimensions of space. Can you think a dimension where no human being has ever be able to just stop moving in it or go back?
Pablos: I don't know that I understand the question, but I think the planet is hurtling through space. I can't control that.
Spiros: The planet is moving in what dimension?
Pablos: I guess one 2D orbit around the sun, so I can't go out of orbit.
Spiros: Could you imagine somebody pushing it out of orbit, or something crashing and pushing it back? Lots of ways. We don't even know there's planets back then, but imagine you have something you're pushing around.
As we move through space, two out of three dimensions had some trouble jumping and going the other way, but I can just move back and forth or I just stop. Nothing is pulling me. It's like a force.
Pablos: Force pulling me somehow.
Spiros: It doesn't seem to be part of space. We have more control over how we move in space.
Pablos: By space, do you mean?
Spiros: Just space, like literally moving through space — moving on the ground. Can you think of any other dimension where it's different, and we have no control over how we move and when we move?
Pablos: It's a little different in water, it's a little different for birds. But I don't know anywhere for a human to go where that experience is different.
Spiros: Maybe outside of space. Can you think of another dimension?
Something that moves, has its own units, like you can go this far or a little bit further.
But you cannot go back for some reason, and you cannot stop from moving. You're moving whether you like it or not in that dimension.
Pablos: I'm thinking of vision and sound and maybe dreams or something, but I'm probably not understanding the question.
Spiros: It's perfectly fine. I would ask you then to look up at the sun as it moves.
Pablos: The sun causing me to move in relation to the sun, or the sun's moving in relation to me, but I might not distinguish between the sun and clouds for that matter.
Spiros: Do things sometimes repeat every day? Do you see things going in weird ways, backwards?
Pablos: Why are the clouds going this way or that way? Why are waves coming at me? Why is the sun and the moon passing or whatever it is they're doing? If you don't know, you don't know.
Spiros: We were supposed to meet the ancient Greek agora, and I was like, we need to meet when the sun is at that height.
Pablos: Even more than people now, I'd have a pretty good intuitive sense of when and where the sun is. That pattern becomes pretty ingrained.
I have a watch, so I don't need to look at the sun. But if you were living by it and you knew people were going to meet people based on where the sun is, you'd start keeping track of it.
Spiros: Keeping track of what? What is that?
Pablos: Pattern — just the repetition.
Spiros: Time. The answer is time. The one dimension that we, even back then, knew is the one where we cannot stop moving in it and we cannot go back even a second. No human being has ever been able to just freeze time or go back. First of all, why is that the case? And second of all, there is an insane coincidence here: the dimension of time has exactly these two very special parts to it that seem exactly like what happens when you let something go — you cannot stop it from moving, and you cannot have it move backwards, can't change the direction.
Even though it's happening in space, it looks like that. It's not something that happens in space. We can stop from moving or just float in the water. You just float in outer space, which is petrifying — you cannot go anywhere, you're just stuck there. There is something interesting here.
Pablos: But the interesting thing is that gravity and time share these properties.
Spiros: Exactly the same — things fall in just their same way as we fall towards the future.
Pablos: I'll take that for now.
Spiros: Let's try to figure out in ancient times: why the hell can't we stop time? We can stop from moving in space, but why can't we stop time? What would happen if you stop time? We're in the platonic dialogue situation, we have some wine and we're trying to understand what the hell is time.
I would venture to say time just keeps track of change. With the clock or whatever is happening, it's just a way we have to keep track of something changing. Why does this make sense? Because if nothing is changing, you get this weird feeling like time has frozen. You have an internal clock that you're still like, I'm breathing, but otherwise you get freaked out. You have something moving, but it's the same thing and it's not changing, it feels like it's frozen in time as well.
Time has something to do with keeping track of change. But it's not just external change. Internally, we're capturing change that is happening.
What happens if your ability to perceive change freezes?
Time stops, it means you cannot perceive change anymore. What would that feel like? I know that back then they didn't understand about consciousness and all that stuff, but maybe enough that you're like, maybe your brain is responsible for keeping track of what's happening outside of you. But what would happen if your ability to have memories or create the concept like, oh, something changed, something happened — what if that went out the window? Would you even know that you exist?
Pablos: I don't know.
Spiros: We're going on a detour, by the way, where this is harder. This is from thousands of years ago.
Pablos: I think it's a very difficult thing to imagine. If I can't observe or feel any change, then everything just seems frozen to me.
Spiros: Would you even know that you exist? There is an answer to this. I don't know if you've ever had a surgery where you had to go under general anesthesia. What happens every time they ask you to count down? They lie to you. They should start from three, because you're down by seven or six, you're out.
But do you dream or something else happens? Because when you go out, it's not like you're in a dreamlike state where no time passes in different weird ways — it expands, dilates, or contracts. No, it's just gone. You go and you're out and you don't even know you exist. Everybody else is still around doing whatever they're doing on you, but then you lose your ability to keep track of changes.
We're gonna add our own frame in there for the next two, three hours and then come back. I had surgery a year ago and it was something new from the previous ones. I was like, wait, something terrifying just happened. I was conscious and lucid — no, not during the procedure, which is great — but afterwards, after everything was done, everything was fine. I was having conversation and the nurses were asking me and I was apparently very charming and all that stuff, and I have no memory of any of this.
Even when I was awake and after the anesthetic, there was an in-between moment. I was conscious but not remembering being conscious. I was like out of order, the zombie kind of thing. It was just so weird.
I think for me it kind of answers the question of what's so special about time that we can't stop it. It's the equivalent to erasing your point of view, disconnecting it from the entanglement that it has to the outside, what we call space. And when that happens because it's overridden or because you die — let's just answer what happens when you die now — then you exist for a bit but you don't even know you exist, and then you cease to even have capability of coming back online. That's the only difference: somebody brings you back online, you're like, oh, what just happened? It's kind of creepy.
That's, I think, why you can't stop time. Why you cannot go backwards is simpler from our point of view: entropy. But understanding entropy, it's pretty interesting because it's just a difference between a point of view that is microscopic versus macroscopic.
We think that the world exists only from our point of view, and that's wrong because it exists from an infinite number of points of view, each of which will give you self-consistent answers, even though they may be inconsistent with your point of view.
Pablos: For me, entropy seems easier to understand in humans than anything else, because humans, for what you just described, all have their own point of view. You cannot really predict how they're going to act.
Spiros: Even when you're looking at the same thing or experiencing, right?
Pablos: —do all the same dumb shit as each other. But if you had to predict on any given one of them what they were going to do, you could get it wrong.
Spiros: The averaging, the coarse graining. Yes, you can predict the masses, but not the individuals. And that's why time flows with a particular arrow, only forward. Why? Because the arrow tells you it is much more likely for you, even though every possible configuration, every possible universe in the omniverse is available to you. But it's not about what is possible. It is about what is plausible. And in fact, what is the most highly likely for you to do?
You could walk through a wall, any wall, but it has to be that you coordinate the electrons, the protons, every charged particle of your body to go through this electromagnetic field, one after the other, which is the equivalent of flipping a coin one trillion trillion times and getting it head every time. It's possible, of course. It's just not likely unless you change your point of view. You change the underlying amplitudes, the probabilities, and it becomes something you can do on demand.
It's the macro to micro — the fact that we are low-dimensional observers of an infinite-dimensional structure. It's not even a universe, it's a structure. It's almost like a database.
Pablos: No, I like that.
Spiros: That's the issue. It's something that is known as concentration of measure. It comes from high-dimensional geometry.
You probably know as a computer scientist and a hacker that a sphere in two dimensions is a circle. A sphere in three dimensions is the usual thing. But a sphere in 10 dimensions looks nothing like a sphere. It looks like a hyper-ribbon on a pancake, where most of the volume, the mass of it, is just very thin line around the equator — any one of the equators — which is insane. It is so counterintuitive, and that's where order comes from the infinite possibilities. When you have a low-dimensional subspace, you can only ask 10-dimensional questions of a 30-dimensional structure. You don't get 10 divided by 30.
You get exponential in negative 30 over 10. You start getting way less.
Pablos: It's equivalent to any one person having an idea of what's going on in geopolitics. You're one guy, you went to Starbucks this morning and you think you know how international trade is going to play out.
Spiros: If only they listen. Or in a lower-stakes situation, you're like, no man, I could have coached the soccer team so much better. What are they doing? Idiots.
Pablos: Everyone's a spectator.
Spiros: This is a great example because the players, even though they can leave any one of us in the dust, they only see a local field of view, but we get to see from the outside the camera all the things.
Pablos: We actually know more than they do.
Spiros: So much more difficult for them. If they had access to that, it'd be amazing plays all the time.
Pablos: If you think about what's a self-driving Tesla doing: it's got some cameras. You got two cameras looking forward, and from that it's trying to create a 3D model of everything it sees. Once you have the 3D model, then you could go get a camera angle outside of what those two cameras actually see. We could render that scene from above, like bird's-eye view, and that is very possible and practical for computers to do now.
We do it all the time for robotics and for self-driving cars. The thing is not 100% accurate — it can't see occlusions. As Tesla is driving up and there's a semi truck in front of it, it can see the back of the semi truck.
That's just a big rectangle. A couple of wheels. But because it's seen lots of other semi trucks in the past, it can infer that there's probably a whole truck in front of that triangle. And even though it can't see it, it could render a highly probabilistic semi truck in front of you.
I've heard accounts from humans who've had that experience, rarely, but a kind of out-of-body experience. I used to train in aikido, which is this Japanese martial art. It's a pretty fixed environment. You're training in a room on a mat with a bunch of people, and you're training in all these spiral motions with people attacking you and you throw them around.
You're in a 2D plane mostly, because they're all on their feet coming at you. A lot of these techniques take you taking this energy that's on a 2D plane, turning it into a spiral. A lot of times there's a little bit of a third axis because you're going to throw them over your shoulder and they land flat on the ground.
We practice taking attacks from every direction, practice with our eyes closed. It's very difficult for most people to defend against an attack. If someone's gonna beat you over the head with a bat, it's really hard to feel that coming with your eyes closed and react in time. But for the attacks where you get grabbed, just that little bit of information — if you grab my arm, I can infer where the rest of you is and where I can move.
They describe feeling like they could see the room from above. They can see all these attacks. And in aikido you train with multiple attackers, so they're coming from all directions. That's not something I've experienced in aikido. I have experienced a thing like that rock climbing.
I used to rock climb in Alaska when I was a kid, and we were way out in the valley somewhere climbing something that nobody's ever climbed before, which now is hard to imagine because rock climbing is a very popular thing, but in those days it wasn't, so we were always climbing things no one had ever climbed before.
I'm belaying, which means I'm on the ground managing the rope. We're top roped, meaning the rope goes up from me to the top of the face of the climb and my friend is climbing up towards the anchor. And he pulls off a rock the size of a refrigerator. It just comes loose.
Fortunately the anchor is above him, so that he doesn't come down on top of him. He basically shoves it down between his legs, but I'm on the ground, so you got a refrigerator and you got a bunch of toasters all flying at you once. They're all coming down at me. Another friend of mine who is with us, she's sitting off to the side, and I was able to track every moving object.
I could track the refrigerator, all the toasters, all the little salt and pepper shakers, a lot of junk, and project where it was going to land so I could just move a little bit so nothing landed on me. I could see that where she was she was going to get missed, and it all plays out in three seconds, of course, and it's over. But I think your brain just doesn't need to do that most of the time.
Spiros: It doesn't need the superpower to be on all the time.
Pablos: I guess what I'm saying is this just goes back to what you're describing. I have one perspective, but I'm able to maybe empathize — is the word you're using. I have a semantic problem with the word, but never mind that for now. I'm able to empathize with the position of it, with the rocks.
Spiros: Occupy that different point of view.
Pablos: I eventually defected from aikido to salsa dancing. You're in a big room, 2D plane, everybody's dancing at 180 miles an hour, it's packed full of people. You're dancing with a partner. Usually got a girl, and typically the guy is leading the girl. The girl is doing all these blinding spinning motions and she can't see anything. She doesn't look at anything except for me. I look at everything except for her. She's attached to me because I'm holding her hand, or we have just a very small physical attachment, but that's enough for my body to infer everywhere she is. I make space for her and I track every moving object.
I'm seeing every other dancer that's coming and going, which one's going to hit her, and I'm putting her in a space that is currently occupied, but I know that in the timing that space will be opened up for her by the time she gets there.
This all happens very naturally to salsa dancers, but they don't even realize that's what's happening. For me, I love it. I love that feeling of when I can track all the other dancers. They're doing all kinds of stuff that seems random, but I sense the motion and I'm putting my partner in a safe spot all the time. I'm making space for her.
Spiros: What is interesting about this is that this is just level one of superpowers. Level two is when you realize that every other lead has to do the same thing and then you have to coordinate in resonance, so that, oh, I need to move because you're going to be in that space, but then you have to move. That's what an animal is. Are we a murmuration? It's an emergent thing, right? Maybe.
Pablos: It is.
Links
- Spiros Michalakis at Caltech
- Gravity: from weightlessness to curvature — Einstein Online