Astrophysicist Explains Gravity in 5 Levels of Difficulty | WIRED

hi I'm Jan 11 I'm an astrophysicist and I've been asked to explain gravity in five levels of increasing complexity gravity seems so familiar and so everyday and yet it's this incredibly esoteric abstract subject that has shaped the way we view the universe on the largest scales has given us the strangest phenomena in the universe like black holes that has changed the way we look at the entirety of physics it's really been a revolution because of gravity are you interested in science yes yes you are yes do you know what gravity is it's something that so right now there was no gravity but since there's gravity we're sitting right down on these chairs that's pretty good so gravity wants to attract us to the earth and the earth to us but the earth is so much bigger that even though we're actually pulling the earth a little bit to us you don't notice it so much you know the moon pulls on the earth a little bit just like with the ocean tides exactly the moon is such a big body compared to anything else very nearby then it has the larger effect pulling the water of the earth but more than the moon think about the Sun pulling on the earth we orbit the whole Sun just the way the earth pulls on the moon and causes the moon to orbit us all of those things are electing on you and me right now gravity was too strong will we be able to get up that's such a good question no we actually couldn't the moon gravity is weaker can almost float between footsteps if you look at the astronauts on the moon on the earth it's harder because it's bigger if you go to a bigger heavier planet it gets harder and harder but there are stars that have died that are so dense that there's no way we could lift our arms no way we could step or walk but the gravity is just way too strong do you know how tall you are I mean the force in the force maybe for three people think that while you're sleeping your body has a chance to stretch out and grab crunching you together but when you're standing and walking or sitting that gravity contracts your spine ever so slightly so that in the morning you might be a little bit taller than in the evening see if it works for you yes they say that astronauts in space definitely their spinal long gates there were two twin astronauts one who stayed here on earth and the other who went to the International Space Station it was there for a long time and when he came back he was actually taller than his twin brother yeah and that was because gravity wasn't compressing him all the time and he was floating freely in the International Space Station and his spine just kind of elongated after a while here on earth though he'll readjust they'll go back to the same size have you ever heard of how cavity was discovered Isaac Newton would ponder how does the earth cause things to 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 understood this law this mathematical law for how that works I don't actually think it's a true story but it's a good story so Isaac Newton who realized that even if you're heavier you will fall at the same rate as something much lighter that that's the same once you hit the ground if you're heavier you'll hit the ground with much greater force but you will hit the ground at the same time so if we both drop down from the plane we would both wind at the same time but you would land heavier yep so like a penny from the Empire State Building will fall at the same rate as a bowling ball yeah amazing want to try it oh yeah a light object see how light that is that's very late and a heavy object they look the same but this is much heavier right okay so try it just try holding your arms out and a little higher maybe give him a chance to drop and then drop them did they fall at the same time did he hit at the same time so Isaac Newton he was also the one who realized that that's the same force that keeps the moon in orbit around the Earth on the earth in orbit around the Sun and that's a huge leap here he is looking at just things around him and then looks at the Stars and has this really big realization that that's actually the same force so what have you learned today talking about gravity I've learned that the person that learned about the Apple Newton um he was learning about gravity just about what he saw on this planet I also learned that if you drop one light thing one heavy thing at the same height at the same time they're both gonna drop at the same time but one's gonna drop a little heavier than the other that's beautiful I'm impressed so Rio you're in high school yeah I'm a junior and are you studying any Sciences in high school I'm taking physics and do you think of yourself as curious about science well they're like some things that interest me and how is that for me is what it like depends what interests you well like I'm a gymnast selling in physics they talk about like force and stuff and then I think of like how I use physics and like my own life what's your impression of what gravity is I think that if there's like no gravity I really like float everywhere it like pulls things down and without it like everything would just be like chaos so you're saying gravity pulls things down yet we've launched things into space have you ever wondered how we do that that's it like a slingshot like if you put something back enough it'll to go in the opposite direction well that's true we do use slingshot technology once things are out in the solar system so for instance we use Jupiter and other planets so that when some of the spacecraft gets close it'll slingshot around and it'll cause it to like speed up but mostly 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 to the International Space Station the trick is to get something moving fast enough that it escapes the gravitational pull of the earth have you heard the expression what goes up must come down it's actually not true if you throw it fast enough you can actually get something that doesn't come back down again and that's basically how rocket launches work you have to get the rocket for the earth to go more than 11 kilometers a second think of how fast it is just one breath and it's gone 11 kilometers if you get it to go that fast it's not gonna come back down again so you know the International Space Station where which is orbiting the Earth that's going around the earth at like 17,000 miles an hour it has no engines anymore the engines are turned off so it's just they're falling forever so once it's out there it's not coming back down as long as it's cruising like that and like does the gravity part and it is just like in a weird way that is gravity pulling it so have you ever um had a yo-yo where you swing it around like this the string is pulling it in at all times but you've also given it this angular momentum and as long as you give it the angular momentum pulling it in actually keeps it in orbit and so the earth is pulling it in at all times so that's why it doesn't just travel off in a straight line it keeps coming back around so it's funny people think that the International Space Station is so far away that they're not feeling gravity and that's not the case at all they're absolutely feeling gravity they're just cruising so fast that even though they're being pulled in they never get pulled to the surface it's like that the roller coaster is really yeah you go in and it spins super fast and you can't feel it spinning fast yeah you feel pinned to that it's exactly like that there's something called the equivalence principle where people realized and specially Einstein that if you were in outer space in a rocket ship and it was dark and painted and it was accelerating at exactly the right rate you actually wouldn't know if you were sitting on the floor of a building around the Earth or if you want a rocket ship that was accelerating it's crazy you ever had that experience where you're sitting in a train and the other one moves and for a second you're not sure if you're the one moving yeah cuz I don't train go to school I never feel like I'm moving when I'm in the chain and I'm like wait what that's because in some sense you're really not imagine you're in this chain and it's going near the speed of light relative to the platform but it's so smooth then you should be in a situation in which there's no meaning to your absolute motion there's no absolute motion so that if you throw a ball up you might think from the outside of the platform be confused that when gravity pulls that back down it's going to hit you or something but it'll land in your palm as surely as if you were in your living room it's not kind of easy so imagine you are an astronaut you are floating in empty space so you can't see anything there's no stars there's no earth you can ask yourself am i moving just really no way for you to tell so you would probably conclude well I'm not having so then your friend marina comes cruising past you and maybe she's going thousands of kilometers a second and you say marina you're cruising it like thousands of kilometres a second you're going so fast but she had just done the same experiment she was just floating in space thinking you know am i moving there's no way to know which one of you is moving and there's no meaning to the absolute motion the only thing that's true is that you're in relative motion that's true you both agree you were in relative motion and that's clear but neither of you can say it's actually you who's moving and I'm 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's 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 to be 300,000 kilometers per second but here comes marina and she's racing at the light pulse as far as you can tell two cars driving towards each other seem like they're going faster towards each other than somebody who's standing still relative to one of the cars right so you would say Oh marinas gonna measure a difference be like but she comes back and she's it's no 300,000 kilometers per second because from her perspective she's standing still and the laws of physics had better be the same for her the speed of light is a fact of nature that says true as the strength of gravity and the two of you are in this quandary because of one of you is the preferred person who correctly measures the speed of light that ruins everything about the idea of the relativity of motion which one of you should it be so Einstein decides they must both measure the same speed of light how could that possibly possibly 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 he goes from the constancy of the speed of light and a respect for this idea of relativity to the idea that space and time must not be the same for you and for marina and that's how he gets the idea of the relativity of space and time you're the best expression it's pretty wild but that is a starting point actually of the whole theory of relativity that starting point leads to this complete revolution in physics where we suddenly have a Big Bang in black holes and space-time just from that one simple starting point so is your impression of gravity different than when we started the conversation yeah cuz like I knew that like when I was on the train I didn't feel like I was moving but I didn't know like why and that it was a thing and I wasn't crazy yeah and it's really deep principle and what about the theory of gravity I don't know like usually when I just heard gravity it's like for my coaches but I didn't know like it was like all these things mm-hmm it's like a big paradigm so you're in college yeah what are you studying in college I'm a physics major so from your perspective how would you describe gravity I'm taught that it's a force it's described by inverse law but I also know that the field and there's a recent discovery with like gravitational waves although I don't like the specific details of that about that so when you say it's an inverse square law yeah that means that the closer you are yeah the more strongly you feel the gravitational pull yeah that makes sense yes very few things that are stronger when you're further apart yeah so you can also think of a gravitational field something that permeates all of space the earth three stories below us it's not as though it's pulling at us from a distance right we're actually interacting with the field at this point and there's a real interaction right here at this point and that's nice because people were worried that if things acted at a distance yeah that the way the old fashioned inverse-square force law describes it that it was as spooky as like mind-bending a spoon that it was like telekinesis you know if you don't touch something how do you affect it and so the first step was to start to think of gravity as a field that permeates all of space and it's weaker very far from the earth and it's stronger very close to the earth so one way to think of this field is as a field that's really describing a curved space-time that is everywhere forget the difficulty of the math just the intuition comes from two kind 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 in our feet or standing in an elevator cab and Einstein would have said what does it chair you have to do with it or the floor or the elevator those aren't gravitational objects and so he wanted to eliminate them and one way to do the thought experiment is to imagine standing in an elevator that you can't see out of a black box and imagine the cable is cut and you and the elevator begin to fall so I'm free fall you're in total free fall now because things fall at the same rate yeah including the elevator and you yeah you can actually float in the elevator if you just float it in the elevator the two of you would drop and you might not even know it you're falling you can 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 really doing when you're experiencing gravity isn't being heavy in your chair it's falling weightlessly in the gravitational field and that was the first step to think of gravity as weightlessness and falling I know like as your gravity experienced you're done with planes Emily yeah exactly yeah you can make somebody look like they're in the International Space Station by flying up in a plane and then just free-falling the plane just drops out of the air and while it's falling they will float weightlessly and there's been a lot of experiments about it but you don't want it to end unhappily so the play has to scoop back up yeah and then you see them become pinned to the floor of the ball okay because then the plane is interrupting their fall so that's the first thought and then the next is what is the shape that's 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 it would chase the path well if I threw it straight I would think it would go it's straight yeah it would just go straight but if you did that on the earth what would happen it would just go down yeah but it would call it with tracing curved oh yeah Jason Hart yeah and the faster you throw it you look kind of longer the arc so the second step to thinking about curved spacetime is to say that when things fall freely around a body like the earth they trace curved paths as those space-time itself space itself was curved and so so that's the intuition that's how Einstein gets from thinking that space-time is curved from the idea that well there's just field that permeates all of space and what it's really describing is the curves that things fall along and from there it's a very long path to finding the mathematics and the right description that's really hard but that intuition is so elegant and so beautiful and just comes from these two simple thought experiments that's amazing isn't it kind of a so you described learning in a class about light the theory of special relativity or Einstein is really adhering to the constancy of the speed of light and questioning the absolute nature of space and time and it seems like that has nothing to do with gravity but he later begins to think about the incompatibility of gravity with his theory of relativity so suppose the Sun were to disappear tomorrow from like evil genius comes and just figures out a way to evaporate the Sun in Newton's understanding of gravity we would instantaneously know about it all the way over here at the earth and that's incompatible with the concept that nothing can travel faster than the speed of light no information not even information about the Sun could possibly travel faster than the speed of light so we shouldn't know about what happened to the Sun for a full eight minutes which is the time it would take light to travel to us and so he begins to question why gravity is so incompatible with relativity but he already knows he's thinking about space and time in relativity so then he gets to his general theory of relativity where he realizes if I eliminate everything but just the gravitational field of let's say the earth and I look at how things fall and I see that they follow curves well then he realizes that space and time don't just contract or dilate that they can really warp that they can bend him that they can curve and then he finds a way to make gravity compatible with relativity by saying if the Sun were to disappear tomorrow the curves that the Sun imprinted in space-time would actually be into ripple and those are the gravitational waves and they would change and they would flatten out because the Sun was no longer there yeah that would take the light travel time to get to us to tell us that the Sun was gone uh-huh and then we would stop orbiting and just travel along a straight line Wow Wow so what do you think you walk away with what do you think you learned well more about the intuitions behind the concept because we already just do with the problems but sometimes you get lost in a math but like speaking like this it's really helps build my intuition yeah it just it does for me too so thank you [Music] so you're getting your PhD in physics that's right theoretical high-energy physics basically the physics of really really small fundamental things so what would that have to do with gravity or astrophysics well what I'm looking at is states of matter that might exist inside neutron stars so when a star dies if the star is massive enough there's a huge explosion called a supernova and the stuff that's left behind that doesn't get blown away collapses into a tiny compact blob called a neutron star so what I love about neutron stars personally is that they're kind of City sized that's right about the size of a city so you're imagining something more than the mass of the Sun yep or about the mass of a Sun condensed to the size of a city it's dense enough that one teaspoonful would weigh about a billion tons here on earth no that makes the gravitational field incredibly strong that's right around the neutron star so what would happen if we were on a neutron star because we would immediately be crushed into the ground I think our bodies would be shred into their subatomic particles so what's the connection between neutron stars and black holes so as I understand it a black hole sort of like a neutron stars big brother it's more intense if you have so much matter when a star is collapsing that it can't hold itself up it collapses to a black hole and those are so dense that space-time breaks down in some way or another black holes are so amazing that where the neutron star stops and there's something actually there right there's a material there if it's very heavy it becomes a black hole so it keeps falling once the event horizon of the black hole forms which is the shadow the curve that's so strong that not even light can escape the material keeps falling and like you said maybe space-time breaks down right at the center there but whatever happens the star is gone that black hole is empty so in a weird way black holes are a place and not a thing so is there a sensible way to talk about what's inside a black hole or is that should you think of it as there is no space-time there isn't a sensible way to talk about it yet and that probably means that's where Einstein's theory of gravity as a curved space-time is beginning to break down and we need to take the extra step of go took some kind of quantum theory of gravity and we don't have that yet so even though the black hole isn't completely understood we do know that they form astronomically that in the universe things like neutron stars form and things like black holes form the consequences are very much speaking to this curved space-time so for instance of two black holes orbit each other they're like mallets on a drum and they actually cause space-time to ring and it's very much part of gravitation the ringing of space-time itself we call gravitational waves and that's what's what's something Einstein thought about right away in 1915 1916 he was thinking about that those waves are very exciting for me too because neutron stars orbiting each other also give off gravitational waves and we might be able to get some data about neutron star material from that kind of signal yes the ring space-time also like a drum and you can record the sound of that ringing after a billion years when it's 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 matter which you study it becomes this firework of different explosions it's really quite spectacular that's right in fact when we recorded that for the first time with gravitational waves we then pointed telescopes at it and were able to see it optically as well and that gave scientists a lot of data yeah it was um to my knowledge the most widely studied astronomical event in the history of humanity Wow so where the gravitational waves were recorded and they realized oh this sounds like you can reconstruct the shape and size of the mallets of the drum from the sound these sounds like neutron stars colliding not black holes and so like you said there was a trigger for satellites and experiments all over the world to point roughly in the direction that the sound was coming from so from your point of view I mean they're like two superconducting giant magnets colliding an experiment you could never do on earth that's just of the most tremendous scales and peculiarities of matter absolutely I've heard statistics like many earth masses worth of gold or created forged in the yeah a neutron star collision that that we used to think that most elements in the universe were created in supernovae which is when stars explode because there's so much violent activity at the center that you need that kind of energy to create new elements the way you do in a bomb it's basically nuclear fusion sure but we now think that that kind of fusion happens when two neutron stars collide if you think about it you have two massive blobs of neutrons when you smoosh them together you've got 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 of the heavy elements after some number are created in neutron star collisions so you are already a PhD student you know a lot about gravity but what do you think you've taken away from this conversation well I've definitely taken away that the way that we think about gravity today is very different from how Newton thought about it and that even though we have a very good understanding there's lots of things that we don't fully understand there's still a lot of questions to be answered which i think is really exciting see you're a scientist isn't the best part being able to ask the questions oh yeah so we've been talking about gravity from Newton and celestial bodies the earth the moon pulling on each other in the conventional sense of gravity being an attractive force to the earth creating curves in space-time then we moved on to just diffuse seeds of energy and space-time as the real universe and gravitation is really just talking about space-time in general and here we are and you're really hardcore in theoretical physics where would you take the exposition of gravity from that point well one thing is quantum mechanics quantum mechanics it's the most accessible theory in the history of science it explains the most different phenomena the most precisely yet many people would still say we don't understand even the basics of it so when we think about quantum mechanics we think about particles and their quantum charges and in the Fineman way the way that Fineman taught us you know come in and they exchange a forest carrier and then they come out again so that's how we think of an electron and light scattering for instance or something like that and the language that Einstein gave us is so different it's completely geometric it's all of this space-time and it's also unnecessary yeah for me the the beauty of the theory of gravity is is the way Einstein formulated it as a theory of geometry of curved space and time I think like you that's one of the things that really pulled me into it 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 is really space time in the sense that it's a description that works really well so there has to be something right about it I mean if we're gonna talk about what's really really underlying that yeah and we're gonna 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 its together yeah any two states any two possible states of the world you can just literally put a plus sign between them and that's a that's a sensible state that's a good state make sense so do you think there's some sense in which we shouldn't be thinking about individual universes individual space-time so we should be thinking about superposition subspace please yeah think so I think if you were to go far enough back in the history of the universe back to when it was very very dense very small and when quantum mechanics was certainly important then it must have been like that I mean if we believe that 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 over there let's say and not over there so how did that happen why is there galaxies they are not there in the standard theory as you know that was a quantum event a random event yeah and it doesn't mean that it happened they're not there because you flipped a coin it actually happened in both places there's got to be a wavefunction where in one branch of the wave function is galaxies they're not there and any other branch it's the opposite so when we're talking about the multiverse or the Big Bang we are really talking about gravity ultimately and we're talking about how a theory of gravitation which we now think of as a theory of space-time has a quantum explanation has a quantum paradigm imposed on it that will help us understand these things and we don't have that yet one of the things that I think is so amazing is that the terrains in which we're going to understand quantum gravity are very few right it's the Big Bang because that's where we know that quantum and gravity both were called into action and there's black holes one of the most interesting discoveries of course Hawking's discovery kick-started a kind of crisis right in thinking about why quantum mechanics and gravity were so knocking heads it was one of the most beautiful examples sure yeah it's it is a beautiful beautiful idea so first of all to be totally clear that we've never observed Hawking radiation which is what he predicted directly I don't think very many people doubt that it's there but yeah how can you discover it mathematically that's when you have a black hole it's got an event horizon it's got a surface which is a point of no return if you fall through that surface no matter what you have no matter how powerful of a rocket you got even if you beam a flashlight back behind you in the direction you fall from nothing escapes not even like it all gets sucked in and spaghettified and destroyed at the singularity or something something happens it doesn't get out but in quantum mechanics you can't really pin down the location of something for cisely if you try to pin down an electron and a tiny circuit and a microchip sometimes you discover that it's not actually there and then your computer crashes this is the Heisenberg uncertainty principle in reality you can't precisely say where the electron is and you can't precisely say how quickly it's moving exactly yeah so when you get the blue screen of death that might be because of quantum physics you know you try to pin something down near a black hole well it's a surface it's got a particular radius for a round black hole and you want to say something is inside or outside well you can't absolutely say that quantum mechanics and this kind of uncertainty produces a radiation which you can think of as pulling some of the energy out of the black hole the black hole was formed out of some mass and there's an energy in that you can think of pulling some energy out of that and sending it off to infinity in the form of particles being emitted yeah and what Hawking found is that it's a thermal spectrum it looks like a hot or not so hot for a large black well but like an oven the kind of radiation that comes out of it cast iron this idea that the darkest phenomena in the universe actually is forced to radiate quantum particles it's pretty wild I think everyone understood that the that it was a correct calculation but I don't think a lot of people understood the implications that it meant something really terrible was happening because this black hole which could have been made of who knows what is disappearing into these quantum particles which in some sense have nothing to do with the material who went in so do you think that's a big crisis the black hole evaporates the information is lost it's a crisis because of some of the details of it but I would say the way you just described it I mean if I build a big bonfire or an incinerator and I throw an encyclopedia into it good luck reconstructing what was in that inside information is lost for all practical purposes practical fair yes so this is a huge crisis because either quantum mechanics is wrong and as you described it's the most accurately 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 anytime you have a state of the world and another state of the world you can you can literally add them together and get a third possible status raises that sounds and 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 an event resident or not oh this isn't because we could always take a state that had an event horizon and a state that doesn't or has the event horizon in a slightly different position maybe and add them together so the existence or position of an event horizon can't possibly be you know determined as a fact anymore than the position of electron is determined so I think that's the loophole that's a nice way of looking at it so that you're not actually violating classical relativity once you're in a regime where the wavefunction has really peaked around a very well-defined stage that's right I'm whatever one of the most exciting developments in 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's got sort of 3d information built into it right and this in a fundamental way really has that freedom for a higher dimensional information built into it yeah it's exactly the same as this theory of gravity in more dimensions yeah so one of the things I like to think of it with holography is that I can pack a certain amount of information about Cole I mean you can literally think of as like storing things into it let's say I have information and some volume and I'm under the illusion that I could just keep packing information in that volume as much as the volume will contain eventually I'll make a black hole and I'll find out what the maximum amount of information I can pack into anything in the entire universe is what I can pack on the area right and since areas projecting the illusion maybe a volume maybe the whole world is just a hologram it's not a principle that only applies to black holes it's saying that if this theory of quantum gravity is correct then this whole three dimensionality is an utter illusion and really the universe is two-dimensional and as practice speaking you mentioned before in a conversation that it's really interesting the Heisenberg uncertainty principle is a practical limit now and microchips yeah and if we make microchips much much smaller than they already are even as they already are it causes errors because you don't know that bad Johnson if holography if this limit on how much information you can ever pack if that ever became a limit as far as we know that's an absolute limit right we started off with with clay tablets not so much information yeah okay yeah but then we had written stuff it's getting better and psychic videos with thin paper that's even better CDs dancer interns renovation eventually make a black hole at some point you try to fill up your encyclopedia with knowledge and the most knowledge you ever have would only be a two-dimensional on a two-dimensional surface right and as big as the universe and then you're done yeah so you know it's not likely that we're gonna hit that limit any time soon do you think it's possible that gravity is really ultimately just quantum mechanics and doesn't exist at all in the fundamental ways that we've been talking about so far like the Newtonian way and the space-time way that those are just these kind of macroscopic illusions and sometimes I talk about in terms of temperature temperature it's not a thing there's no single thing called temperature right it's a macroscopic illusion that comes from the collective behavior really quantum behavior of random motions of atoms and is it possible at the whole of gravity is like some kind of emergent illusion from what's really quantum phenomena underlying it well if we buy the idea of holography then absolutely that's for sure that's what that's what it's telling us although which side is the illusion and which that is the reality right they're the same I mean temperatures still great to talk about 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 closer and closer and closer we realize there's not a thing in the world that has a quantum value temperature yeah isolated and so maybe there is no such thing as gravity isolated from quantum mechanics right so I guess with the holographic description we've got two sides which are which are actually secretly the same on one side there's definitely not gravity on the other side well it's a quantum theory of gravity whatever that means but the point is you can get it out it's equivalent to this neighborhood definite so that's like just saying there's the the idea of a dual description is just saying there's a perfect dictionary between these two descriptions and so to believe or which ones real is silly it's like saying as French wheeler is English we all right yeah oh I like to give is if you take some extra dimensions and you compactify them let's say just one all that is it's exactly equivalent to whatever particles you had whatever fields you had in your original theory before you rather you just add an infinite Tower of new particles with certain properties that are all easy to calculate for me it's a question of which one which description is most useful I mean if you want to say gravities and it's all quantum that's great but then you fall down the stairs and bang your head like this description that works pretty well you don't go to the doctor about certain defensible cost plus you raise a fluctuation so there's so many open questions the fact that there are all these fundamental issues that we really don't understand but on the other hand there's all of these moving parts that fit together so neatly there's definitely something that's working here but ultimately what is going to emerge from that what structures lying under it 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 that it's an opportunity that's exciting it's great thanks so much for coming thank you good to have you here thank you very much John it was my pleasure I [Music] hope you learned something about gravity you hadn't thought of before and I hope even more that it provoked some questions so thank you for watching [Music]

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Keywords: 5 levels, astrophysicist, astrophysics, gravity, gravity explained, how gravity works, 5 levels gravity, gravity 5 levels, 5 levels of gravity, gravity explanation, elif, elif gravity, explanation gravity, astrophysics wired, wired gravity, wired 5 levels, janna levin, janna levin gravity, science, gravity explained to kids, science explained, science explained to kids, 5 levels of difficulty gravity, how gravity functions, why do we have gravity, wired

Id: QcUey-DVYjk

Length: 36min 31sec (2191 seconds)

Published: Fri Dec 20 2019

Reddit Comments

[u/chuckdooley]

That was really interesting, thanks for posting.

Discussions around Space/The universe fascinates me, but I often times lose track of the conversation because I have trouble comprehending the ideas that are being discussed

[u/BurnerAccount-03]

Her look when expert says “quantum mechanics” @25:28