Astrophysicist Explains Gravity in 5 Levels of Difficulty | WIRED

Hello, it's January 11th. I'm an

astrophysicist

and I was asked to explain

gravity

in five

levels

of increasing complexity. Gravity seems so familiar and so everyday, and yet it is this incredibly esoteric abstract topic that has shaped the way we see the universe. On the largest scales it has given us the strangest phenomena in the universe, such as black holes, which has changed the way we view physics as a whole. It really has been a revolution because of

gravity

. Are you interested in science? Yeah, yeah, yeah, you know what? Gravity is something that right now there was no gravity, but since there is gravity, we are sitting in these chairs, that's pretty cool, so gravity wants to pull us to the Earth and the Earth to us, but the Earth is much bigger.

Although we are actually pulling the Earth towards us a little bit, you don't notice it as much, you know, the Moon pulls the Earth a little bit, just like with the tides of the ocean, exactly the Moon is such a large body compared to anything . otherwise very close, then it has a greater effect in attracting the earth's water, but more so than the moon, think of the Sun attracting the Earth, we orbit the entire Sun in the same way that the Earth attracts the Moon and makes the Moon orbit us all. Of those things are affecting you and me right now gravity was too strong can we get up?

That is a good question. No, actually we couldn't. The moon's gravity is weaker. It can almost float between the steps if you look at the astronauts. the moon on earth is more difficult because it is bigger if you go to a bigger and heavier planet it becomes more and more difficult but there are stars that have died that are so dense that there is no way we can lift our arms or be able to take a step or walk but the gravity is too strong, do you know how tall you are? When you stand, walk or sit, gravity contracts your spine slightly, so in the morning you might be a little taller than at night, see if that works for you.

Yes, they say astronauts in space definitely had their long spinal gates. two twin astronauts, one who stayed here on earth and the other who went to the International Space Station, he was there for a long time and when he came back he was actually taller than his twin brother, yes, and that was because gravity didn't I was compressing it. all the time and he was free floating on the International Space Station and his spine got a little longer after a while here on Earth, although it will readjust, they will go back to the same size. Have you ever heard about how the cavity was discovered?

Isaac Newton would reflect on how the earth makes things fall. There's a famous story that Isaac Newton was sitting under a tree and the apple fell from the tree and hit him on the head and he had an epiphany and he understood this law, this mathematical law of how that works, I actually don't think it's a true story but it's a good story so Isaac Newton realized that even if you are heavier you will fall at the same rate as something much lighter and that's the same thing once you hit the ground if you are heavier you will hit the ground. ground with much greater force, but you will hit the ground at the same time, so if we both fell from the plane, we would both spin at the same time, but you would land with more weight, yes, like a penny from the Empire State Building will fall at the same rate as a bowling ball, yes, amazing, I want to try it, oh yes, a light object, look how light it is, that's too late and a heavy object look the same, but this one is much heavier, okay? so try it just try to extend your arms and a little bit higher maybe give it a chance to fall and then let them fall if they fell at the same time if it hit at the same time so Isaac Newton was also the one who realized that that's the same force that keeps the Moon in orbit around the Earth in the Earth in orbit around the Sun and that's a big jump here, he's just looking at the things around him and then he looks at the Stars and he realizes that that's actually the same force, so what have you learned today by talking about gravity?

I learned that the person who learned about the Apple Newton was learning about gravity, just because of what he saw on this planet. I also learned that if you drop one light thing, another is heavy. thing at the same height at the same time both will fall at the same time but one will fall a little heavier than the other that's beautiful I'm impressed so Rio you're in high school yes I'm a third year student and what? Are you studying any science in high school? I'm taking physics and do you consider yourself curious about science? Well, there are a few things I'm interested in and what that's like for me.

It depends on what interests you. I'm a gymnast who sells physics, they talk about strength and stuff and then I think about how I use physics and in my own life, what's your impression of what gravity is? I think if there's no gravity, I really like floating everywhere. It kind of pulls things down and without it, everything would be like chaos, so you say that gravity pulls things down, but we have launched things into space, have you ever wondered how we do that? It's like a slingshot, like you put something back. It will be enough to go in the opposite direction, well that's true, we use slingshot technology once things are out in the solar system, so for example we use Jupiter and other planets so that when any of the spaceships get closer, turn around and It will make you like to speed up, but mainly around the Earth, gravity pulls things down, so when we want to send a rocket into space and we want to go to the Moon, some supplies for the International Space Station , the trick is to make something move. fast enough to escape the earth's gravitational pull, have you heard the expression what goes up must come down?

It's not really true, if you launch it fast enough you can get something that doesn't come back down and that's basically how you launch a rocket. The launches work, you have to get the rocket to Earth to go more than 11 kilometers per second, think about how fast it is with just one breath and it has traveled 11 kilometers, if you get it to go that fast it won't come back down, so Meet the International Space Station which is orbiting the Earth, which is orbiting the Earth at about 17,000 miles per hour, it no longer has engines, the engines are off, so they are just falling forever, so once you are there , it won't go down again.

While you're sailing like that and gravity splits and it's like in a strange way it's gravity that pulls you. So have you ever had a yo-yo where you swing it like that, the string is pulling it in? at all times, but you've also given it this angular momentum and whenever you give it angular momentum, by attracting it, it actually keeps it in orbit, so the Earth attracts it at all times, which is why it doesn't just travel in a straight line , it keeps coming back, so it's funny that people think that the International Space Station is so far away that they don't feel gravity and that's not the case at all, they absolutely feel gravity, they're just cruising along. so fast that even though they are being dragged they never come to the surface it's like the roller coaster is really yes you go in and it spins super fast and you can't feel it spinning fast yes you feel trapped in that it's exactly like that there's something called the equivalence principle where people, especially Einstein, realized that if you were in outer space in a rocket and it was dark and painted and it was accelerating at exactly the right rate, you wouldn't actually know if we were sitting on the floor of a building around the Earth or if you want a rocket that was accelerating, it's crazy, have you ever had that experience where you're sitting on a train and the other one is moving and for a second you're not sure if it's you that's moving , yeah, because I don't train, I go to school, I never feel like I'm moving when I'm on the chain and I'm like, wait, what is that, because in a sense, you can't really imagine it. you are on this chain and it is approaching the speed of light relative to the platform, but it is so smooth that you should be in a situation where your absolute movement has no meaning, there is no absolute movement, so if you cast a ball up You may think that from the outside of the platform you will be confused and that when gravity pushes it down it will hit you or something, but it will land in your palm as safely as if you were in your living room.

It's not easy at all, so imagine. you're an astronaut you're floating in empty space so you can't see anything there are no stars there is no earth you may wonder if I'm really moving there's no way for you to know so you'd probably conclude well I'm not going to have it So your friend Marina it passes by you and maybe it's going at thousands of kilometers per second and you say Marina, you're sailing at thousands of kilometers per second, you're going so fast, but she had just done the same experiment, she was just floating. in space thinking you know I'm moving there's no way to know which one of you is moving and there's no meaning to absolute motion the only thing that's true is that you're in relative motion that's true you both agree that you were in relative motion and that is clear, but none of you can say that it is actually you who is moving and I am stationary.

I don't even know what to say to that, so let me tell you where it gets really crazy, so let's say you and Marina are floating in space. and you can't tell who is moving, let's say you both see a flash of light, the flash of light comes from somewhere you don't know where, so you measure the speed of light at 300,000 kilometers per second, but here comes Marina and she is running. in the light pulse, as far as you can see, two cars coming towards each other appear to be going faster towards each other than someone standing still relative to one of the cars, so you'd say Oh, the marinas They will measure a difference. but she comes back and it's not 300,000 kilometers per second because from her perspective she's still and the laws of physics should be the same for her.

The speed of light is a fact of nature that says it is true like the force of gravity and the two of you are in this dilemma because one of you is the preferred person who correctly measures the speed of light, which It ruins everything about the idea of ​​relativity of motion, which one of you should be, so Einstein decides that you both should measure the same thing. speed of light, how could that be the case? And he thinks well, if speed is how far you travel your spatial distance in a certain amount of time, then there must be something wrong with space and time and it goes beyond the constancy of speed. of light and respect for this idea of ​​relativity to the idea that space and time should not be the same for you and for marina and that is how you get the idea of ​​the relativity of space and time you are the best expression, it is Pretty wild but that's actually a starting point of the whole theory of relativity, that starting point leads to this complete revolution in physics where suddenly we have a Big Bang in black holes and spacetime from that simple starting point, this is your impression of gravity. different than when we started the conversation, yes, because I knew that when I was on the train I didn't feel like I was moving, but I didn't know why and that it was a thing and I wasn't crazy, yes. and it is a very profound principle and what about the theory of gravity?

Don't know. Usually when I just hear gravity, it's like for my coaches, but I didn't know it was all this mm-hmm stuff, it's like a big paradigm. so you're in college, yeah, what are you studying in college? I'm a physics student, so from your perspective, how would you describe gravity? I was taught that it is a force that is described by the inverse law, but I also know that the field and there is a recent discovery with similar gravitational waves, although I don't like the specific details about it, so when you say that it is a square law inverse, yes that means the closer you are the stronger you feel the gravitational pull, yes that makes sense. yes, there are very few things that are stronger when you are further away, yes, so you can also think of a gravitational field, something that permeates all of space, the earth, three floors below us, it's not like it's pulling us in from a distance, right? actually interacting with the field at this point and there's a real interaction right here at this point and that's good because people were worried that if things were acting at a distance, yeah, the way the old law of force describes it of the inverse square would be like creepy like bending your mind with a spoon, it was like telekinesis, you know, if you don't touch something, how do you affect it, so the first step was to start thinking about gravity as a field that permeates all of space and is weaker. very far from the Earth and is strongest very close to the Earth, so one way to think of this field is as a field that actually describes a curved spacetime that is everywhere.

Forget about the

difficulty

of mathematics, it's just that intuition comes from twotypes of Simple Observations: one was what Einstein described as the happiest thought of his life, so right now you might feel heavy in your chair and we might feel heavy on the floor at our feet or standing in the booth of an elevator and Einstein would have said what chair? you have to do with that or the floor or the elevator those are not gravitational objects and that is why I wanted to eliminate them and one way to do the thought experiment is to imagine standing in an elevator that cannot be seen from a black box and imagine that the cable is cut and you and the elevator start to fall, so I'm in free fall, you're in total free fall now because things are falling at the same rate, yes, including the elevator, and you, yes, you can float in the elevator if you just you float him in the elevator, both of you. you would fall and maybe you wouldn't even realize you were falling you could take an apple and drop it in front of you and it would float in front of you you would actually experience weightlessness it's called the equivalence principle it was Einstein's happiest thought that what you're actually doing when You experience gravity is not being heavy in your chair, but falling weightless in the gravitational field and that was the first step to thinking of gravity as weightlessness and falling, I know, as if your gravity were experiencing you.

You're done with airplanes Emily, yes, exactly, yes, you can make someone look like they're on the International Space Station by flying in a plane and then just free fall, the plane just falls out of the air and as it falls it will float. weightless and there have been many experiments with this, but you don't want it to end badly, so the play has to be restarted, yes, and then you see that they get stuck on the ground of the ball, okay?, because then the plane stops its fall , so that's the first thought and then the next one is what is the shape that has changed, so if you are floating in empty space, really empty space, yeah, and you had an apple and you threw the apple, what shape Do you think I would follow the path well?

If I threw it straight, I'd think it would go, it's straight, yeah, it would just go straight, but if you did that on land, what would happen? I would just go down, yeah, but I would call it curved layout, oh yeah, Jason Hart, yeah and. the faster you throw it, the longer the arc appears, so the second step in thinking about curved spacetime is to say that when things fall freely around a body like the Earth, they trace curved paths like spacetime. space itself was curved and So that's the intuition that Einstein gets from thinking that spacetime is curved from the idea that well, there's just a field that permeates all of space and what it really describes are the curves through which things fall and from there it is a very long road.

Finding the math and the right description is really hard, but that intuition is so elegant and so beautiful and it just comes from these two simple thought experiments. That's amazing, isn't it? This is how you described learning in a class about light, the theory of light. Special relativity or Einstein really sticks to the constancy of the speed of light and questions the absolute nature of space and time and it seems like that has nothing to do with gravity but then you start thinking about the incompatibility of gravity with his theory of relativity, so suppose the Sun disappeared tomorrow as if the evil genius came and simply found a way to evaporate the Sun in Newton's understanding of gravity, we would know it instantly here on Earth and that is incompatible with the concept that nothing can travel faster than the speed of light no information, not even information about the Sun could travel faster than the speed of light, so we should not know what happened to the Sun for eight minutes complete, which is the time it would take for light to travel to us and then you start to wonder why gravity is so incompatible with relativity, but you already know that you are thinking about space and time in relativity, so you come to your theory general relativity where you realize that if I eliminate everything except just the gravitational field of let's say the earth and look at how things fall and see that they follow the curves well, then you realize that space and time not only They contract or expand, they can really deform, they can bend, they can curve. and then he finds a way to make gravity compatible with relativity by saying that if the Sun disappeared tomorrow, the curves that the Sun printed on spacetime would actually ripple and those are gravitational waves and they would shift and flatten out. . because the Sun was no longer there, yeah, that would take the travel time for light to get to us and tell us that the Sun was gone, huh, and then we would stop orbiting and just travel in a straight line.

Wow Wow, what are you doing? I think you stay with what you think you learned well more about the intuitions behind the concept because we only do it with problems anymore, but sometimes you get lost in the mathematics, but talking like that really helps develop my intuition, yes, that's how it is . It does for me too, so thank you, you're getting your PhD in physics. That's theoretical high energy physics, basically the physics of really small fundamental things, so what would that have to do with gravity or astrophysics? Well, what I'm seeing. They are states of matter that could exist within neutron stars, so when a star dies, if it is massive enough, a large explosion called a supernova occurs and what remains that is not swept away collapses into a small mass. compact called neutron.

So what I love about neutron stars personally is that they're the size of a city, I mean, the size of a city, so you're imagining more than just the mass of the Sun, yeah, or about the mass of A Sun condensed into the size of a city is dense enough that a teaspoon would weigh about a billion tons here on Earth. No, that makes the gravitational field incredibly strong and it's right around the neutron star. So what would happen if we were in a neutron star? Because we would immediately be crushed. on the ground, I think our bodies would fragment into their subatomic particles, so what is the connection between neutron stars and black holes?

As I understand it, a black hole is something like the big brother of a neutron star, it is more intense if you have so much matter when a star is collapsing and can't hold on, it collapses into a black hole and those are so dense that space-time decomposes in one way or another. Black holes are so amazing that where the neutron star stops and there is something really there right, there is a material there, if it is very heavy it becomes a black hole, so it continues to fall once the horizon forms of events of the black hole, which is the shadow, the curve that is so strong that not even light can escape, the material continues to fall and, as you said, maybe space-time breaks down right in the center, but whatever happens let it pass, the star is gone, that black hole is empty, so in a strange way black holes are a place and not a thing, so is there a sensible way to talk about what's inside a black space? hole or is it that, if you think of it as there is no spacetime, there's no sensible way to talk about it yet and that probably means that's where Einstein's theory of gravity as a curved spacetime is starting to fall apart. and We need to go one step further, we take some kind of quantum theory of gravity and we don't have it yet, so although the black hole is not fully understood, we do know that they form astronomically and that there are things like neutrons in the universe. stars form and things like black holes form, the consequences speak volumes about this curved space-time, so for example, two black holes orbiting each other are like mallets on a drum and actually make the space- time sounds and it is very A lot of gravitation, we call the sound of space-time itself gravitational waves and that's what Einstein immediately thought in 1915 1916 I was thinking that those waves are very exciting to me too because the stars Neutrons orbiting each other also emit gravitational waves and we could get some data about the material of neutron stars from that type of signal.

Yes, the space-time ring is also like a drum and you can record the sound of that ring after a billion years when it has traveled through the universe, but then the next thing that happens is those neutron stars collide and Because of this incredibly high energy state of the matter that you study, it turns into these fireworks of different explosions, it's really quite spectacular, that's how it is, in fact, when we first recorded that with gravitational waves. Then we pointed telescopes and we were able to see it optically as well and that gave the scientists a lot of data.

Yes, as far as I know, it was the most studied astronomical event in human history. Wow, so where were gravitational waves recorded? They realized that this sounds like you could reconstruct the shape and size of the drum mallets from the sound. These sounds sound like neutron stars colliding, not black holes, and as you said, there was a trigger for satellites and experiments around the world to target. roughly in the direction where the sound was coming from, so from your point of view, I mean, it's like two giant superconducting magnets colliding, an experiment you could never do on Earth, which is one of the scales and peculiarities of the most tremendous stuff I have ever known.

I've heard statistics like many Earth masses are worth gold or were created forged in the yes, a collision of neutron stars we used to think that most elements in the universe were created in supernovas, which is when stars explode because there is so much activity violent in the center that you need that type of energy to create new elements like you do in a bomb, it is basically nuclear fusion, of course, but now we think that that type of fusion occurs when two neutron stars collide. If you think about it, you have two massive masses of neutrons when you put them together, you have neutrons colliding, it creates the conditions where new elements can be created, that's amazing, it's literally populating the periodic table.

Yes, we now think that most heavy elements after a certain number are created in neutron star collisions, so you are. You're already a PhD student, you know a lot about gravity, but what do you think you've learned from this conversation? Well, I've definitely learned that the way we think about gravity today is very different from how Newton thought about it and that although we understand it very well, there are many things that we don't fully understand, there are still many questions to be answered, which I think it's really exciting. Seeing that you are a scientist is not the best part to be able to ask. the questions oh yeah, so we've been talking about Newton's gravity and the celestial bodies, the earth, the moon, pulling on each other in the conventional sense that gravity is an attractive force for the earth, creating curves in space- time, then we move on to just diffuse seeds of energy and space-time like the real universe and gravitation is really just talking about space-time in general and here we are and you're really hard on theoretical physics, where would you take the exposition of the gravity from that point?

The thing is quantum mechanics, quantum mechanics, it is the most accessible theory in the history of science, it

explains

the most different phenomena with greater precision, but many people would still say that we do not understand even the basic concepts, so when we think in quantum mechanics, we think. about particles and their quantum charges and the way Fineman taught us, you know, they come in and exchange a forest carrier and then come out again, that's how we think of an electron and the scattering of light, for example, or something like that . and the language that Einstein gave us is so different that it is completely geometric it is all this space-time and it is also unnecessary yes, for me the beauty of the theory of gravity is the way in which Einstein formulated it as a theory of geometry of the curved space and time, I think, like you, that's one of the things that really attracted me: is there really space-time or are we just using unnecessary language because it's elegant and we like it and it's beautiful?

Well, I think there really is space-time in it. I feel like it's a description that works very well, so there has to be something right about it. I mean, if we're going to talk about what really underlies that, yeah, and we're going to put quantum mechanics into the mix, then there should be some quantum. mechanical wave function for space 9, you should be able to take two different space times and add them together because one of the crazy things about quantum mechanics, as you know, is that they are together, yes, any two states, two possible states of the world, you can literally put a plus sign between them and that is a sensitive state, that is a goodstate, it makes sense, so do you think there is some sense in which we shouldn't think about individual universes, individual spacetime, then we should think about superposition subspace please?

Yes I think so. I think if you went back far enough in the history of the universe, to when it was very, very dense, very small, and when quantum mechanics was certainly important, then it should have been like that. I mean, if we believe the dominant standard model of cosmology, something had to produce the density perturbations, the things that seeded all the galaxies and stars and us, everything else in the world, so there's a galaxy there, let's say, and not there, so how did that happen? Why are there galaxies? They are not there in the standard theory, as you know, it was a quantum event, a random event, yes, and that does not mean it happened, they are not there because you flipped a coin, it actually happened in both places, there has to be a function of vibe. where on one branch of the wave function there are galaxies, they're not there and on every other branch it's the opposite, so when we talk about the multiverse or the Big Bang, we're actually talking about gravity, ultimately, and we're talking how a theory of gravitation that we now consider a theory of space-time has a quantum explanation and a quantum paradigm has been imposed on it that will help.

We understand these things and we don't have them yet. One of the things that I think is so surprising is that the areas in which we are going to understand quantum gravity are very few, right, it is the Big Bang because that is where we know that Both quantum and gravity were called into action and there are black holes, one of the most interesting discoveries, of course, Hawking's discovery started a kind of crisis when thinking about why quantum mechanics and gravity were so surprising, it was one of the most beautiful examples. Sure, yes, it's a beautiful idea, so first of all, let's make it absolutely clear that we have never observed Hawking radiation, which is what he directly predicted.

I don't think many people doubt that it's there, but yeah, how do you find out? mathematically it's when you have a black hole, it has an event horizon, it has a surface that is a point of no return if you fall through that surface, no matter what you have, no matter how powerful the rocket you have, even if you turn on a flashlight. behind you in the direction you fall, nothing escapes, not even like everything is absorbed, spaghettized and destroyed in the singularity or something happens, it doesn't come out, but in quantum mechanics you can't really pinpoint the location of something precise , if you try to locate an electron and a little circuit and a microchip, sometimes you discover that it's not really there and then your computer crashes.

This is the Heisenberg Uncertainty Principle, you actually can't say precisely where the electron is and you can't say precisely how fast it's moving exactly, yeah, so when the blue screen of death appears, that could be because to quantum physics, you know you try to fix something near a black hole, well, it's a surface for which it has a particular radius. a round black hole and you want to say that something is inside or outside, well, you can't say at all that quantum mechanics and this kind of uncertainty produces radiation that can be considered to extract some of the energy from the black hole.

The hole was formed from a mass and there is an energy that you can think of taking some energy out of that and sending it to infinity in the form of emitted particles, yes, and what Hawking discovered is that it looks like a thermal spectrum. hot or not so hot for a big cesspool but like a furnace the kind of radiation that comes out of it molten iron this idea that the darkest phenomena in the universe are actually forced to radiate quantum particles is pretty far-fetched I think everyone got that which was a correct calculation, but I don't think many people understood the implications that it meant something really terrible was happening because this black hole that could have been made of who knows what is disappearing into these quantum particles that at some point make no sense.

It has nothing to do with the material that came in, so do you think it's a big crisis? The black hole evaporates, the information is lost. It's a crisis because of some of the details, but I would say the way you just described it, I mean. If I build a big bonfire or an incinerator and throw an encyclopedia at it, good luck reconstructing what was in that privileged information is lost for all practical purposes, fair practice, yeah, so this is a big crisis because quantum mechanics is wrong and as you described is the most precisely tested paradigm in the history of physics, how could it be wrong, right? or the event horizon is letting information out and violating one of the most sacred principles of relativity.

One thing about quantum mechanics is that at any moment you have a state of the world. and another state of the world, you can literally add them together and get a third possible state, that sounds like it, so if you're going to have a quantum theory of gravity, then we can't really talk about there being a black hole. or not, a black hole, hmm, right, or a resident event or not, oh, this is not because we could always take a state that had an event horizon and a state that does not have an event horizon or that has the event horizon. events in a slightly different position, perhaps and add them together, so the existence or position of an event horizon cannot be determined as a fact, any more than the position of the electron is determined, so I think that is loophole, that's a good way to look at it so that it doesn't actually violate classical relativity once you're in a regime where the wave function has actually peaked around a very well defined stage, that's right.

One of the most exciting developments of the last 10 or 20 years is called holography and it's called holography. Because a hologram is a two-dimensional surface, it's a three-dimensional image, it has sort of 3D information built into it, and this, fundamentally, really has that freedom for higher dimensional information built into it, yes, it's exactly the same as this. theory of gravity in more dimensions, yes, so one of the things I like to think with holography is that I can package a certain amount of information about Cole. I mean, you can literally think of it as storing things in it, let's say I have information. and some volume and I have the illusion that I could keep packing information into that volume as much as the volume will contain.

Eventually I will make a black hole and find out what is the maximum amount of information I can pack into it. in anything in the entire universe it is what I can pack into the correct area and since the areas that project the illusion maybe a volume maybe the entire world is just a hologram, it is not a principle that only applies to holes blacks, what it says is that if this quantum theory of gravity is correct, then all this three-dimensionality is a complete illusion and really the universe is two-dimensional and, as a practical matter, you mentioned before in a conversation that is really interesting, the uncertainty principle of Heisenberg is a practical limit now and microchips, yes, and if we make microchips much smaller than they already are, even as they already are, it causes errors because you don't know how bad Johnson if holography if this limit on the amount of information that you can pack if that ever became a limit as far as we know, that's an absolute limit, right, we started with clay tablets, not as much information, yeah, okay, yeah, but then we write things down, it's getting better and psychic videos with thin paper, which is even better, CDs, dancer's interns, renovation eventually creates a black hole at some point, you try. fill your encyclopedia with knowledge and the most knowledge you've ever had would be just a two dimensional surface on a two dimensional surface and as big as the universe and then that's it yeah so you know it's not likely that we.

We will reach that limit in the short term. Do you think it's possible that gravity is ultimately just quantum mechanics and doesn't exist at all in the fundamental forms we've been talking about so far, like the Newtonian form and spacetime? Those are just these kinds of macroscopic illusions and sometimes I talk in terms of temperature. Temperature is not a thing, there is not a single thing called temperature. It is a macroscopic illusion that comes from collective behavior, really the quantum behavior of the random movements of atoms. Is it possible that gravity as a whole is like some kind of emergent illusion of what are really underlying quantum phenomena?

Well, if we buy the idea of ​​holography, then absolutely that's for sure, that's what it's telling us, although which side is the illusion and which side. That's the reality, right, they are the same. I mean, it's still good to talk about temperatures, it doesn't mean we shouldn't talk about temperature. I mean, we should absolutely adjust your thermostats and talk about temperature, but if we look at it more and more closely. and closer we realize that there is nothing in the world that has a quantum value of temperature, yes, isolated, so maybe there is no gravity isolated from quantum mechanics, so I guess with the holographic description we have two sides, which are actually secretly the same on one side, there is definitely no gravity on the other side, well, it's a quantum theory of gravity, whatever that means, but the point is that you can take it out , is equivalent to this defined neighborhood, so it's like simply saying that the idea exists. of a dual description is simply saying that there is a perfect dictionary between these two descriptions and then believing or which ones are real is nonsense it's like saying that since the French Wheeler is the English, we're fine, yeah, oh, I like to give if you take some extra dimensions and the compact ones, let's say just one, all of that is exactly equivalent to whatever particles you had, whatever fields you had in your original theory before you just added an infinite tower of new particles with certain properties that are all easy for me to calculate. a question of what is the most useful description, I mean, if you want to say gravities and everything is quantum, that's great, but then you fall down the stairs and hit your head like this description that works pretty well, you don't go to the doctor . on some defensible cost plus you create a fluctuation, which is why there are so many open questions, the fact that there are all these fundamental questions that we don't really understand but on the other hand, there are all these moving parts that fit together so perfectly that there are definitely something that's at work here, but ultimately what's going to emerge from that, what structures lie beneath this, we just don't know, but I think the fact that there are so many fundamental questions that we just don't know the answer to , it's an opportunity that's exciting it's great thank you very much for coming thank you it's good to have you here thank you very much John it was a pleasure I hope you learned something about gravity that you hadn't thought of before and I hope even more that it raised some questions so thank you to look