Gravity and the universe | Sabine Hossenfelder, Erik Verlinde, Priyamvada Natarajan [FULL DEBATE]

I'm of two minds about this on the one hand they do have some really appealing properties where you can explain certain types of correlations that we observe like as a matter of fact we can explain them very easily but on the theoretical side they don't seem to work [Music] properly thank you very much we all know the story of Newton framing his theory of gravity as a result of watching an apple fall from a tree but 350 years on we still don't understand this seemingly simple Force so current theories cannot apply both at the small scale of atomic particles and at the giant scale of galaxies or on the scale of quantum mechanics and on the scale of general relativity without a solution the mystery of gravity threatens to undermine any overall account of the universe now is the fault for this with Einstein's theory of general relativity or with our understanding of quantum mechanics do we need an entirely different account of gravity or perhaps remove Gravity from our explanations altogether or should we just accept that a single holistic account of the universe is not possible and see our theories as limited to a given frame and reference so I'm delighted to be on stage here as the philosopher of science with three of the world's top physicist we have a fantastic panel for you Saina hosen felter is a physicist who specializes in the foundations of physics uh she is the host of the YouTube channel sence without the Goble deg which I believe just reached one million subscribers uh priia Nat uh is a professor of astronomy and physics at Yale University whose research is on the Dark Universe She is the author of The pioneering work mapping the heavens the radical scientific Cosmos Eric verinda to my left is a theoretical physicist and string theorist he is famous for the verinda formula and winner of the Spinosa prize Eric is developing his own radical theory of gravitation so welcome to the panelist and to all of you for being present so we begin by the simple question can we solve the mysteries of gravity and if so how so for this I invite uh Sabina to begin thank you and thanks everyone for being here uh it's always good to be in London so since I'm the first to get to say something I want to say a little more about the problem that we're talking about in the first place so we have we know of four different fundamental forces in physics that's the electromagnetic force that most of you have probably heard of then we have the strong and weak nuclear force and we have gravity and the problem is that three of those forces the electromagnetic IC and the two nuclear forces have Quantum properties so we have some particles like electrons and quar and clu and stuff like this and we know that they do funny things like they obey the uncertainty principle they can be in two places at the same time that kind of weird stuff and then there's gravity which is described by Einstein's theory of general relativity and that theory doesn't know anything about Quantum properties and this brings up the question if I have a particle like an electron that can be in two places at the same time and it has a mass and that mass generates a gravitational Pole where does the gravitational pole go you'd expect that to also go to two places at the same time but Einstein's theory can't make that work because it doesn't know anything about Quantum properties so this leaves us in this weird position where we just don't know what the gravitational pull of an electron is so it's a it's a really simple question like what's going on with the gravitational field of this electron and we don't know and um if you ask like more technically uh what's the matter it's just that those two theories the quantum field theories that we used to describe particles uh like the electron and a couple of other particles um Einstein's the of general relativity they're just mathematic particularly incompatible if we just put them together it doesn't work but nature knows how it works so there's got to be a solution to this uh and we don't know what it is there have been many people have tried to solve this problem what we need is a theory of quantum gravity so a theory that gives properties to gravity at least that's the way that it's normally put but more generally we need some way to resolve this discrepancy between between the two theories and the probably best known approach to this is string theory that most of you would have heard of there are other ideas like uh luk quantum gravity and then there are less wellknown ones like maybe as ASM totically save uh gravity and stuff like this but so far we don't know if any of those is correct uh or how we can even test them and yes I think it's a really big problem now when it comes to my personal opinion on what to do as I just said like people have worked on this problem for a long time it's been known since the 1930s or something so it's definitely not a new thing and there are lots of smart people have spent their whole life trying to fix something that they think is wrong with gravity and I have a lot of respect for all those people and if they couldn't make it work I'm pretty sure I can't make it work either so this is why I think it's a better strategy to try try and figure out if not there's something wrong with the quantum side of things that the problems may be caused by us not understanding what quantization means in the first place excellent uh Eric yes uh can we understand the mysteries of gravity I do think that Newton and already Einstein know a lot I mean they describe a lot about gravity that well they solved partly the mystery of gravity but we are now a century further and we need have to think about how to combine this theory that Einstein wrote down general relativity with what we know about the microscopic world the quantum mechanics and indeed we are learning that uh we may have to rethink uh gravity again and try to understand uh where it comes from but basically what are the foundations of what what gravity is and the way we have been approaching this and and just not just me but but many scientists in the world is by thinking about places in our universe where anded things make down from from relativity so these are places like near black holes black holes turned out to have what are called Horizons uh Beyond which light cannot escape and and step Hawking I think everyone knows him of course is famous for discovering that when you combine General activity with quantum mechanics that there are special things happening near Horizons and when we take his results and his his scientific breakthroughs basically seriously they tell us that we should indeed rethink gravity maybe think about how to understand it from a more microscopic uh perspective So my answer to the question is should we change general relativity or quantum mechanics I would say that that uh the way I approach this and actually many of my colleagues is that we take quantum mechanics as a working Theory and then try to understand how the microscopic descript destion of space and time which sort of directly related to what what gravity is U how how that leads to the gravitational force so we like to understand the origin of gravity at a more deeper level so I would say the problem of quantum gravity is not how do we apply quantum mechanics to gravity but how do we understand where gravity comes from from a quantum theory that's that's underlying it so I will I will be saying more about this uh later but my answer indeed is well we can understand better what gravity is I think we have already very good description but we can make a Next Step by thinking more about uh well the connection with quantum mechanics okay excellent so priia can we solve the mysteries of gravity and if so how yeah I think that we can solve the mysteries of um uh gravity and I think that um I agree with both Saina and Eric that um you know what we are aspiring to is sort of a synthetic description of gravity that combines a microscopic view with the macroscopic view Einstein's theory of general relativity has been incredibly successful so far in the settings that we've been able to test it right so in my opinion the new Theory and we know Einstein's theory is incomplete we know that already the question is how do we complete it and what will show us the way and data will show us the way right I think um more accurate data sets Precision measurements in the cosmos that actually tests the limits of uh Einstein's theory are the way forward I think because I believe if you look at the history of science look at the history of ideas in um in um theories of gravity it's really data that leads way that opens up that you see a gap in a current description and there are multiple data sets multiple independent lines of evidence that show you that there is a gap this uh there is there are data that are not explained within the current framework and that kind of leads you and shows you the way and you know if you look at Newton's Theory versus gr for example although Einstein didn't set out to solve the problem you know when the uh orbit of Uranus could not really be explained fully with you know Newtonian description um there was a lot of panic right and they thought oh my God this sacred Theory do we have to give it up already it turns out that the solution was within Newtonian gravity itself right that there was a perturber there was Neptune the location of Neptune was predicted and it was found so um similarly U and so the theory just had to be modified you didn't have to overthrow the theory meanwhile when mercuries the peran procession of mercury could not be explained uh there was no adjustment you know you couldn't there were suggestions that maybe there was another planet maybe there was Vulcan that was in between the Sun and Mercury but that's not a that was not a that didn't work as a solution right so something else was needed you couldn't tweak Newtonian gravity to explain that and you needed Einstein theory of uh general relativity to actually describe uh and account for the observations so we were able to do this because we were able to get more precise uh observations more accurate data over longer times so I really believe that data will lead the way and that we already know that Einstein's theory is incomplete and we do expect a Reconciliation between the microscopic and the microscopic okay so we have uh three Divergent positions on the same problem uh let's try to dig into a little bit more of the core of the debate so we move on now to the First theme which has already been outlined from the start does default lie in our theory of with the theory of gravity lie with Einstein's theory of relativity or with the current interpretations of quantum mechanics and I'd like to invite Sabina to elaborate on this question and your own view first okay so um I don't think the issue is with the interpretation of quantum mechanics I actually think we do need a better Theory than quantum mechanics and the reason I think this is that um I mean maybe let me say I I agree with Priya that uh data has to lead the way because this is science right so uh we need to observe something and then try to explain it and I think the same is true for quantum gravity eventually we'll need some kind of some kind of observation that we'll have to explain but the question is where do we look and for this you need some kind of theoretical approach that says that's what we need to look for this is what we need to test so um just because data eventually will be the decisive Factor doesn't mean we can just get rid of theorists right okay um so and and the we definitely don't want to be out of business theorists right I mean our jobs will be in Chardy if we had throw Theory out right right so we need both basically um Theory and observation um now the issue with quantum theory is that uh this quantization of gravity isn't the only problem we also have What's called the measurement problem of quantum mechanics which is pretty much as old as uh quantum mechanics itself so it's even older than the problem of quantum gravity and the issue with uh the measurement is that we just don't know how it works so if we use quantum mechanics we make a measurement we just say and now a measurement happens that's like and our Miracle happens and everything changes and here's our measurement result and so we we know how to apply this theory in the laboratory because we know a measurement when we see one but we can't explain what it is and I think that this problem is going to become more and more important now that we're building quantum computers and all kinds of you know Quantum measurement devices Quantum sensing and and and all that kind of thing so this is where I think the data is going to come from they'll stumble over it sooner or later whether they want to or not not your own work on quantum gravity would you give the audience a very brief explanation on how to understand or conceptualize quantum gravity in this context for the debate yeah well okay so you know um when when you when we talked about the introduction that you would give I had him strike out the word theoretical in front of uh physicist because I don't really understand myself as a theoretical physicist I work on phenomenal ology and this is what I've worked on when it comes to quantum gravity I've worked on the phenomenology the reason I don't call myself a phenomenologist is that no one knows what it means so so what it means is that we're trying to make a connection between theoretical approaches and how you can make an an experiment and that in quantum gravity I've tried to figure out what we can do to test it so physicists like to tell a long story about how we can't test quantum gravity ever and if that was true I would have said well then it's not signs why even think about it but I don't think it's true and the major reason I don't think it's true is that we don't necessarily need strong gravity to test quantum gravity which is what a lot of people seem to think like we need a black hole or we need to look at the origin of the universe or something like this what we actually need is we need some kind of quantum object that's massive enough so that we can measure the gravitational field because think about what I told you in the beginning we don't know what the gravitational field is of an electron why not take something more massive where because normally more massive things they don't have Quantum properties so we can't measure this effect but this is another thing where there's a lot of progress in the technological development they're bringing more and more massive objects into Quantum States and at some point we'll just be able to measure it priia do you agree that it's a quantum mechanics that needs to catch up with theory of gravity that's more established well I mean I'm actually agnostic about who needs to catch up with home I think the question is they're not reconcilable at the moment they're not inte you know you can't integrate them at the moment you know I I prefer a slightly safer approach which is why don't we see how far we can push the general theory of relativity and see where it breaks because I really believe that the gaps and where the theory breaks really points out as Sabina said right the the quantum gravity the quantum nature of macroscopic objects lots of thorny problems there so this is in many ways a slightly easier route I would take which is and I really believe that um very soon we'll be able to push much further than we already have uh in terms of tests of general relativity especially in the strong region so when you're testing general relativity the event Horizons uh telescope for example you know this is the telescope that produced The Donut shaped image of this uh black hole in the center of a nearby Galaxy so that allowed us to test the predictions of uh general relativity at a few percent level and we can push down and I firmly believe that because I think that the theory is incomplete it is going to break and I think we are similarly at U you know technologically in terms of instrumentation computation modeling and understanding we're at a place where we can get more accurate measurements and we can test the theory to Greater precision and I believe that it will break and that that break will show us what the next step really should be so my Approach would be sort of Contra to Sabinas to say that maybe we already know gr is incomplete so let's kind of push it with the data because we know we can articulate the experiments it's sort of the as I said it's it's a more sort of cautious way out um and perhaps an easy way out because we know how to set up these experiments we know the limits of our experiments and therefore if we can push harder and make more precise observations and test the theory to to the sub perent level maybe that's where we'll see where we need to go next okay so Eric what do you make of these approaches that are data will lead the way and and so on they they are important uh but I I think that well from my perspective I come from the theory side I do call myself a theoretical physicist and I like to also like take Theory as a leading uh guide to which of the two should be changed and there I mentioned the the important work of Steven Hawking and his collaborators uh which is actually about a point where generativity may break down namely near the horizons of black holes and even in in our universe we have a a horizon where things may break down and there you notice that that the loss of gravity actually becomes to look like what we call are the laws of thermodynamics those are laws that apply to gases and and molecules that are forming a gas and they only describe everything in terms of temperature in the case of Hawking this is the Hawking temperature but also Notions like entropy and maybe pressure but those are are things that we understand from a microscopic level because of the molecules that make up the gas they are basically statistical properties of all the mo motions of the molecules now turns out that the gravitational equations look exactly like that and this is also what we're trying to look for is name a an explanation of what the LW of gravity look like as Newton and Einstein wrote down but then explained from the microscopic set of molecule say of space and time and we we are making progress there because we have been able to think about black holes really as quantum mechanical objects where we can basically derive uh the gravitational loss just like we can derive these these uh law of thermodynamics and so from the theory side it's it's I would say almost obvious that that the thing that has to change is the the the description of gravity in terms of general relativity and that we have to get a deeper understanding of that but eventually of course we have to take the theory and see what it implies also for observations and this is where I think it's exciting that there are these new observations of well the Event Horizon telescope but also gravitational waves what happens near black holes but also in the cosmos when we look further out and more into the past there are questions we don't fully understand like what is well things like dark energy or things that make the universe expand faster there are all kinds of questions Associated to that that uh well we we have to then answer using a new perspective on this quantum gravity Theory and so the way I think about quantum gravity is that we combine quantum mechanics we start from quantum mechanics and we leave it as it is and then explain what what the laws of gravity are and how we can then derive general relativity from this more microscopic Theory okay so Eric represents a different approach and let's now move uh a little bit further into the next theme which will'll elaborate a bit more on this so the the question here really is whether we need an entirely different account of gravity or perhaps do we need to remove Gravity from our explanations altogether which something Eric has previously suggested uh Pria what is your take on this question well I mean I think we um it's hard to it's hard for me to see how we could remove gravity entirely from our frame of descriptions of the physical Universe especially given that um we really do understand that over the largest Cosmic scales gravity is what appears to be ordering the universe right so I think throwing out gravity completely completely I think it's not an option I think the option is to find uh perhaps you know a more refined description of what gravity is um and um I concur with Eric that the the theory will direct us to what the best experimental setups are whether um but I I but I think that you know again you know we need to push general relativity we need to think up of new Realms we know that the strong gravity regime is where we are likely to see departures from general relativity and I think we need more innovative ideas of other regimes where you could actually test so I I believe that an alternate new description is in order because I think when we look at the current General relativistic description of the universe and its constituents there are many open questions questions and there is a standard theory that seems to work reasonably well across a wide range of scales and I'm referring to all these dark entities right dark matter um you know Dark Energy uh and sort of the entire Cosmic inventory but there are cracks that are starting to appear from data very interesting and important cracks that are starting to appear that sort of show that maybe this Frame that maybe we are missing something in this Frame and as I said it's too early to tell whether some tweak in the current theory can accommodate these cracks that we're seeing or we need something really brand new I mean I like to believe that um we of course need to be always open to something brand new but I think the number of cracks that are starting so there are many of these what are called crises in cosmology that are starting to show up so there's a you know problem with the measurements of the Cobble constant in the near Universe far universe so sort of reconciling distant scales is becoming an issue and I think it points to the fact that we can't dispense with gravity but we probably need a new kind of explanation indeed and there are uh many cracks that are appearing nowadays and that is reframing a bit of the debate in cosmology uh which makes it pertinent this kind of question about where gravity fits into the into the picture uh Sabina do you uh agree that there is that you what do you make of this idea that we could come up with the description that would remove gravity altogether or um would you think there's an entirely different account of gravity that's possible well I would first like to try to clarify uh the trend that this discussion has taken because we started out talking about quantum gravity and now you say well we should push the boundaries of general relativity looking astrophysics black holes uh and so on and so forth and it's true of course that we do have problems with general relativity looking out in the cosmos because we don't really understand what's going on with with galaxies why do they rotate so fast what's going on with Galaxy clusters uh why does the universe why does the expansion of the universe accelerate this is why we've introduced those things called Dark Matter and dark energy but those are different problems than the ones that we started out with like the ones with the quantization of gravity and they might be related or they might not be related so um I see the problem that you might you know you might test the boundaries of general relativity looking at uh black Hool uh whatever but the solution to those problems might not require actually fixing the problem of the quantization of gravity it might just be that we have to modify gravity um or this is a more complicated dark meta model uh that kind of thing now when it comes to throwing out gravity I think that question is somewhat of a red herring because we we know that gen relativity is a great Theory certainly we're not going to throw it out that would be Madness but what might happen is that we might find an underlying Theory from which it can be derived for example String Theory uh is one of those candidates but it might be something else and then we would say well gravity is emergent from something else um and it must it doesn't have to be String Theory could be some other atoms of SpaceTime or things like that Eric is uh yeah gravity or red herring no I understand so gravity is something that we experience so we need to have an explanation MH well we first can accept that's there and then we can describe it but an explanation might also be that you start from a theory where you don't assume Gravity from the beginning and then you start looking at what happens when when we start describing physical objects and what space in time R and then we discover that gravity is a natural consequence of that theory and sort of just like what I mentioned for for the laws of thermodynamics of gases and so on if I look at an individual molecule uh temperature doesn't mean anything it's the molecules together that give us the impression of a temperature because they they together move and then while having a large number of molecules these laws become make sense so this is what we also call imers the ter term was already mentioned namely that you start from a microscopic Theory and then describe what happens when you combine well go to larger distances for instance and then gravity can appear so I think that microscopically the world doesn't care about gravity but of course we need to explain what it is so it's not like we can ignore that there is gravity it is there and we need to have a theory for it and general relativity works very well so you might say well we have to understand where General relativity comes from but I also believe that that there may be circumstances that the theory that we may derive from the microscopic perspective may be different from General and those circumstances can be also in galaxies or or in the cosmos and then well you mentioned Mercury as a problem and that new Neptune was sort of in other cases solution maybe dark matter is a similar uh discrepancy that we try to sort of solve by adding things and I think that indeed uh we have to take those measurements and this observations seriously as also maybe indic Cas that there may be something wrong with the theory of gravity and not just that there may be some particles that we haven't found absolutely that is really what I was alluding to that the more uh accurate High Precision measurements may actually show you that a gap in the theory in the theoretical description not just a fix like Neptune where you add in another degree of freedom and you're able to explain within the current framework itself yes so from a philosophical and theoretical point of view you could say this this would make seem to make sense as an approach to widen the frame so as to make the problem appear in A different light but uh Sabina from a physics point of view um do you find this approach uh useful to pursue or are the problems with this way of reframing the problem to get eliminate gravity well she was just talking about modifying gravity not eliminating gravity yeah I think we shouldn't left anything untried basically and personally I think there's been too much time and effort spent on trying to come up with all kinds of different dark meta particles you know there are gazillions of those models and they all make more or less the same predictions and then you can adjust them to slightly fit this type of galaxy a little bit better or that kind and it didn't really go anywhere because the model is just too it's too flexible and there are very obvious correlations in in the data as you certainly know like for example the bionic Tully Fisher relation that kind of stuff which dark mattera just can't explain and there are other modifications of gravity that explain those things but then they have different problems so it becomes really complicated and I generally think it's not good to um put all bets on one thing so um I I'm really supportive of spending some time on modified gravity and that different approaches to that kind of thing spending some time on the idea of trying to replace gravity or explain it as something emergent or induced gravity this a similar but related idea or maybe just saying maybe the for is with uh the quantum side of things which is what what I uh personally work on okay so there we have three different approaches to this that you're outlining is the modified gravity as one way to go there's this emergent picture of trying to reframe the idea of gravity to begin with and then you have quantum gravity so to the three Deb uh Debaters here if you had to place your bets priia on either of these you say you're agnostic but if you had to put some if I gave you some chips now you had to put them down on the so what are the what's the third option so I think modifying gravity just with a view to adding um additional degrees of freedom but stay within the same framework where other cracks are opening up is clearly not that's not where I would put my bet but not little tweaks to the theory but push it so that the cracks to try to make sense of all these crises so the modifying gravity so far has been really focused on the Dark Matter problem so new and I think it's the been point out new zoos of particles right alternative particles I think that is and that's an approach that has been tried a lot of energy has been spent and I think it's it's it's been useful it's taught us more but that's not where I would put my bet on the kind of uh pushing the theory that I'm talking about is actually trying to see these crises you know going Beyond just having a different kind of dark matter particle I think that's where things are pushing us fundamentally look at the nature of dark energy and what we think dark energy is for example and then fundamentally looking at whether these conceptual ideas of dark matter and dark energy can somehow be mean could they be two manifestations of the same thing I mean you know I think those kinds of ideas are totally worth exploring and I think they should be and not as much attention is being paid to them we've been uh spending too much uh so I would not bet on the modifying gravity and I said with the quantum um with the quantum theory of gravity I think that there's just like vast bits of things that we don't understand so as a pragmatist I would stick to sort of my view of uh really pushing the theory of general relativity with the view of finding a replacement theory for it and I firmly believe that we will see new directions but Sabina this approach to modifi gravity which has been uh which has come to the four a lot in the last 5 to 10 years it's really um gained a lot of uh interest and a lot of research uh in the field I know you have also engaged a lot with that field do you see it as priia suggesting here more that it's limited kind of tinkering with the existing model or do you think that there's a real promise and a kind of a breakthrough with understanding modified gravity well as you say I've actually worked on modified gravity for a couple of years and uh I used to think it's really promising it's going to solve all the all these problems and I don't work on it anymore because it turned out it doesn't work quite as well as I thought it would it's like from a theoretical side it's really really difficult to make those theories work and you know I'm of two minds about this on the one hand they do have some really appealing properties where you can explain certain types of correlations that we observe like as a matter of fact we can explain them very easily but on the theoretical side they don't seem to work properly so and this I I think I I'm afraid I actually agree with you it just makes me feel like we're missing something really big like there's something fundamentally wrong with this type of theory because they don't work with the the mathematics doesn't work the way that we expect it to work especially light deflection I think one of the big you know I was open-minded like um so mean I dabbled a little less uh because you know I'm invested in light detection uh gravitational lensing those theories are unable to provide a description and we see these lenses we see these arcs Hubble Space Telescope has shown us these arcs right so well there are there are models which can explain that kind of thing but then they have other problems so it's like you're pushing around the bump under the carpet you know it always comes up somewhere so Eric where would you place your chips well someone said I mean don't modify gravity but try to understand it and I think that's my Approach is I want to understand gravity and then find answers and maybe I should mention it here more more clearly there has been a lot of progress made in our field in understanding gravity that comes from strength Theory we have a theory that explains Gravity microscopically the only drawback is that it's not yet in a universe that looks like our own it's namely one where there's no dark energy that makes things a lot simpler so the step that we need to make as the is eventually is to develop this theory that we understand very well but in a context where there is dark energy and there I feel that we can indeed understand gravity to the level where we can do computations and make descriptions that clarify these these observation not by modifying it but by really understanding what gravity is to make clear so I think it's it's starting from quantum mechanics and then deriving gravity again and maybe I should mention that I mean Newton had a theory of gravity Einstein didn't modify exactly the equation of Newton he had a much better much deeper understanding so the the because he he combined it with space and time and everything a curvature of space and time a totally New Perspective and I think our next theory of gravity will again not be a modification of the the laws of Newton or or the Einstein equations no it will be a total totally New Perspective that will be given on what gravity is what do you see as the problem with this approach uh Saina do you see a problem with it or um what Eric is outlining no um for me the question comes down to like strategically what's the kind of experiment that we should look at to test those kinds of ideas and as I was trying to say earlier I think if you look at astrophysics cosmology all those kind of big scale questions it becomes basically impossible to tear apart the problems with dark meta Dark Energy uh modified gravity quantum gravity and then let's not forget there might be other problems like with uh the kind of model that we use in general relativity they might just be too simple or there might be issues with the numerical simulations you know they you know just on the numerical side or because we're neglecting some kind of feedback or subgrid parameters and all kinds of things so this is why I'm thinking it would be strategically much better if we looked at something clean like this kind of tabletop experiment where we're trying to put those masses into some kind of uh super positions and I understand that Priya disagrees because she things I think that's much more complex actually coming up with those experiments because quantum mechanics is so complicated um well these are uh I mean very different kinds of approaches let's uh let's uh move to the last theme and try to put this in a bigger frame again um a little bit uh also really more philosophically should we just accept that a single holistic account of the universe is not possible should we see our theories as inevitably just limited to a given time in a given reference and accept them as working within that range only Eric would you like to begin now I do think that we can make it next step in understanding gravity whether it's the final understanding I don't think that as humans we can understand everything about the universe that's one thing the other thing that I find quite important is that we also have to realize that we are here at Planet Earth looking at the universe out there and that we are doing observations and we have to explain those things in a framework that we invent like space and time and so on but we are doing it from a certain perspective so I do think that we should be aware of the fact that we may have an incomplete description of everything and suddenly the edges of the universe may be sort of Beyond where we can observe so I think that in our current theories we have um not enough taken into account that we are making our observations from a certain perspective and maybe our description of what we call the universe should also be more well from our own uh reference frame and because you used that word in your question and I mean I do think that we have to take into account that there's a certain Observer dependence of how we interpret what we are uh looking mhm but Priya is it possible to have a single holistic account or are we just limited the way we are I I I think we could aspire to it yeah um and I think I concur with Eric on this point that from a sense of sort of cosmic humility right there's no reason why the brain size of a gelatinous thing the size of a c vope should be able to comprehend everything in the universe including itself so I believe that there are limits but I think it is worth uh aspiring to and we may yet get to a fundamentally different description that feels more complete than what we have right now which we know is incomplete Sabina would you agree well I certainly agree that we should aspire to you know Finding an overarching holistic account of everything uh but I'm not sure we need one so when when it comes to this particular question like can we just make do with what we have like with um gr and and quantum theory I think the answer is clearly no because as I said in the beginning they're just questions that we can't answer and sooner or later we we're going to have a situation in a laboratory where the theorists can just say well we don't know we don't have the theory so we need this Theory so we need a theory of quantum gravity now do we do we need a unified theory of everything that kind of stuff which string theory is aspiring to I'm not sure about this you know I guess it would be nice but it's not really necessary so if I had an apple in my hand or you imagine this is an apple I would do like this this is how we started we all know uh gravity is an experiential Force like we all feel it but we don't know entirely what it is now we have three of the brightest Minds working on on this problem on uh here on stage and I'd like to just ask you a simple question when you are it could be a question from either of you anyone asking you priia what is gravity oh gosh uh H uh I think it's very hard for me as you probably all guessed I'm trapped within einsteinian theory of general relativity so um um I would probably uh defer to that kind of you know it's a profound Confluence of space and time that illuminates the nature of a very fundamental force that orders the visible and invisible Universe Confluence of space and time that orders our universe and as I said I'm pretty trapped by Einstein still right so I think um I haven't broken out of the box although I'm open to and I want to break out of the box okay Eric what is gravity well just to introduce this I mean the the way we try to understand gravity now is by thinking about more microscopically what space and time is made of and then we use words like information especially also the the quantum information you have to think about things like what you have on your computer like data and so on but SpaceTime is also filled with that information and gravity I have has actually written down somewhere uh is then a consequence of moving information around so it's the cost mhm of moving information okay so and that would be a microscopic explanation of where it comes from so gravity is consequence of moving information view microscopically that's right okay interesting Sabina what is gravity so I I have to be on another panel later today where I'm supposed to answer the question what's a particle uh which is why I've actually thought about this question I came to the answer that I don't think this is a question for science I would say what we do in Sciences we describe observations so I can tell you what we use to describe the effect that we call gravity we describe it with a curved differential manifold uh of Dimension four that has lorenzian signature and to me that's a satisfactory answer that that's that's what I would say it is uh I'm just afraid that most people wouldn't understand what it means so does that mean uh we don't need to know what it is as a physicist right we just have to explain what we observe we accept it as a given it is something we work with to try to calculate or yeah so from a pragmatic perspective we just need mathema we are both saying something like we have an operational definition that we think works and we're happy with it well it works more or less yeah yes more or less yes okay three different uh takes on gravity so gravity is kind of special and I think with that we have to let this debate fall to the ground I really want to thank the amazing speakers Kaa Eric and Sabina the podcast talks debates courses and articles visit the Institute of Art and ideas click the link on 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Channel: The Institute of Art and Ideas

Views: 246,237

Keywords: learning, education, debate, lecture, IAItv, institute of art and ideas, IAI, philosophy, quantum mechanics, theory of gravity, general relativity, einsteins theory of general relativity, what is the problem with our current theory of gravity?, why is our theory of gravity wrong?, science debate, quantum physics, science communication, sabine hossenfelder, erik verlinde, priya natarajan, priyamvada natarajan, einstein, quantum field theory, string theory, quantum gravity

Id: 1j0Xh9XM34M

Length: 46min 25sec (2785 seconds)

Published: Sat Jan 20 2024