Carlo Rovelli, "Current Quantum Gravity Theories, Experimental Evidence, Philosophical Implications"

okay thank you very much wonderful being here sorry for the ABS or something all surface but there are some below this present and the audience is really spectacular so it's a whole new to stoke um this morning we have heard Gabriella and still give her two different very different in fact perspective on the problem Quentin relative was a bit gloomy in different in different manners I had listened very carefully to what the two of them have said and I think I would agree and subscribe with virtually all the statements that they have made maybe some opinion and some prejudices are different but I think we agree that we are getting prejudices so that's that's good because we have to link it's more different however I'm going to now present a different perspective third perspective quantum gravity which is not so blue and in fact it's far more optimistic and to some extent is just you know this glass half-full or half-empty you can insist on what is missing on color system what is present so I'm I'm gonna insist on the half-empty quantum gravity but I think that a fool yes because I took the night train for Mercedes I mean oh yeah no yeah well depend if you like more emptiness with I will also insist on things happening quantum gravity in the last five or ten years very dimensions which I think has changed to be true so the picture is not the same feature has been from long time and and and that's largely this experimental evidence that we'll talk about I will you really started saying I'm scared by the world philosophy I'm not which I don't know whether it weights positively or negatively but I will talk about what I think are interesting those optical implications of what we do have of the half-filled and in my style I will start with a little bit a set of provocative points which will have to be clarified and specified and this is gonna be the list of thing I'm gonna talk about the first two will take most time the more philosophical one will be take shorter time so the two a little bit provocative statements the first a fun which I wanna claim that we do have quantum theory of gravity is gravity problem of course is yes we would like to add a pond to see of gravity and but more strongly and I think this is perhaps the main message of my talk I want a system we do have empirical evidence which count of course not as much as we wish no there's a lot of education that we will put in what we do at the end of the talk I will pick up the invitation to talk about philosophical issues and very rapidly I will cover the three topics plus one which I think after all though is probably less disagree that if look looks like a all the people doing quantity maybes made my perspective the people I talk to more but I don't find there is this sense of gloom I don't find a sense of pessimism and I do find a number of convergence on different things I said so we don't have a full theory of gravity of which we agree ELISA story make them verify this so I don't want to see of gravity we have not one but may like this is a difficulty literature these are also the theories of gravity in one way which is obviously too many to be to be miserable but first of all and it's like that it's misleading in a number of reasons first of all the number of people involved in the research is why varies widely from from among this direction which doesn't mean that if we're more we write and if you're less we're wrong but it does mean that the community as a whole is going in some direction not in others second many of these are not really theory of gravity our ideas incomplete sketch that could be useful could work could leave some way but a far from being a quantum theory of gravity also the many they're much less than what it looks like because many are are connected right they DFC ft in the mind of people is strongly connected to string theory good few theories is a variant of loop quantum gravity and so on and so on and so forth there are many connections the linear relation between these some may even be the same theory presented in different in different manners the boundary fluids many as I said can offer useful insight also within other context but in this last point a few of these are quantum field gravities with incompleteness with open questions but definitely a set of equations with which you can do some calculation which suggests some physical phenomena and indicate some some possible measurable thing that may be right or wrong we could test and we'll talk about I'll talk about testing in the second part so this is a sort of completely non-scientific vague attempt to put things in order if you are surprised let's see if you were surprised about the string theory loop quantum gravity collection this is Herman that Linda this summer giving a talk explaining to all of us that quantum gravity come out from string theory Medina is also next token which this happens in foldy I don't know if you mate loop people happy or unhappy if it's doing people and unhappy or happy but this is one of the most respected string theorists around this is Herman is the Princeton brother not made a little brother so back here this is a list of things can I get them Yenta yes first of all there is a big division here between two different hypotheses one hypothesis is that one way of the other you cannot go smaller than a certain scale and this is completely obvious in approaches like to look back to gravity goofy thick as a set but it's also to listens to in theory I was prepared to to give argument for that but Gabriela gave very good arguments exactly that direction this morning so I'm not going into into into that while the other possibility is that there are the quanta gravity is like quantum field theory or like the pontifical we studied at school at the cocoanut well maybe there are infinite number of degrees of freedom all the way down to infinitely small so these are two two different worlds which I think are hard to connect to one another a place to further sketch as I said there are many things which could be enormously interesting and from which we can learn a lot but which are not yet quantum theory of gravity I mean the crucial one alone is here and we know community geometry in a wonder where it could be known serenity of telling us how to put gravity together with the other theories and how to think about geometry in the very small but not necessarily it's a regular point to see of gravity and Allah will correct me if I if I misrepresented it but that's not the main thing I wanted to say that maybe I wanted to say is that this theory have different physics some of them still sort of already introduced this a little bit some of them basically have a physics which is look at low energies gr at higher energy than some quantum effects of some sort others I have clear other physics supersymmetry high dimension strings Lawrence violation violation of quantum mechanics which can be observed and so on so we are talking about different and potus's about how the world is visibles such that there's this other is that it's Lorentz invariance violated when you go to the Planck scale or not it's serious exploring different possibility of bringing together what we know about about the world so you can make a list noise violation something we say yes at the scene or a few degrees of freedom some yes some no eccentric cetera you take your favorite and this is harmful from incomplete it brings me to the second point which is a main point is that we do it empirical evidence we have some empirical evidence which is already here and some empirical evidence which is perhaps coming soon and the novelty is that for many years we have been saying telling one another Oh we'll never know anything about quantum gravity chemically we'll have to wait next millennium 20 the next billion has arrived so where is it well first unless perhaps the most is morally marked the one of the approaches that at some point became extremely popular is each other lifted see me which it's a very simple idea if you if you ride the Lord tomorrow see me you can actually write or see this is great I mean you can write a fantasy of gravity which is so a normalizable behave nicely at the low energy limit it's all it's a policy of gravity um you ladies for say n is equal to four okay yeah and and and so this violation Lauren's violating turns with you you take any words for for what yes what is wrong guys are yeah yeah yeah yeah yeah sure sure sure sure so it's very sorry this suggestions prompted a huge experimental effort that went in a number generation most used to physical to test for violations of Lorentz invariance in bursts that come from very far away we give some a special relation connection to dispersion relation that and other thresholds of the way things interact with it cost me my calculations on support that's the point I mean you can get it normalizable with with n equals 4 and people started searching corrections to this or to this plus the maths I didn't try the mask is generic in fact for various ends forgetting of anomalies ability and empirically and there are number of phenomena that can be made now we don't have just tell it's LHC we have some physics and there's a huge industry there and it's remarkable how strong violations of Lorentz invariants has been bounded experimentally to numbers this is a 13 and I guess 2013 with you two numbers which go to my 10 to the minus 16 depending of so among those people there is a consensus today that Corrections of that sort at the Planck scale are essentially ruled out could be violation rows lines of the different kind it could be some other non soap way but the direct empirical consequences of a few middle vibrates Lorentz invariants the Planck scale in the natural way to give you the Romanovs ability are in clinically under enormous stress you don't prove the theory wrong you put very stress strong stress on the only thing that's the first point a small parenthesis if we bring this Lauren Seaver is the Planck scale with the idea that there is some sort of discreteness Planck scale does this imply that is it possible or is a contradiction to the two is often said that this contradiction between the two and it is constitutionally to classical discreteness there is no contradiction between the two if you have a quantum description a cell just think about angular momentum theory you you have discreteness and and and and your the the symmetry with the two things go together I skip this because it could be a little bit more in in detail but the two are compatible foundations of ionization exactly exactly it is but it does not change the result is what I got what I also when I don't were to continue to this country I'm happy to continue the discussion later but we are attending I've been discussing this program to tea convinced of that so we can could be one of the topics in the discussion this afternoon actually the previous transparency my recollection was that very crude [Music] violations no no no I'm saying I'm saying that the the the leaks the people doing measurements don't care about work these imitations in detail wants there's a open chance which is to measure Lorentz invariants violating effects at high energy and they tried sundeck a variable for always hopeful was popular because we don't know no secret it's hopeless crystal check no that's a point but that was ten years ago but and many calls for look at the numbers that's a point value of CN cn [Music] I know but this is a nothing changing in the last I mean there are conferences the title is a phenomenological quantum gravity and they discussed this kind of things there's Crab Nebula neutrino oscillations it's a number of techniques I don't ever going to into that skip this second supersymmetry this is even more controversial now you want to say try to say things precisely it is a fact that they expected the supersymmetry at let first and HC later is not coming out this is one just I just pick the recent one of the many articles that are coming out no evidence is found for supersymmetry assembly model so I wanted plain that this obviously does not once again does not move out supersymmetry because supersymmetrical be a higher scale and does not disprove in the apparent sense and here in unless the theory that really really really wants supersymmetry of that particular energy but since we're asked to think philosophically I think this brings in a point about philosophy of science which I want to underline we all know prepare Ian falsification is well but prepare offensive condition this is a criterion for limitation to insides and outsides it's not pretty good as a criterion for evaluating theories and that's not what scientists do have done or ever done because according to Papa Theory I have a theory that there are giraffes in the Alps and nobody can falsified right there are in the Alps there are many giraffes but they're very good in hiding it's a it's a part of my theory it's completely unsafe our survival right order giraffes on the backside moon there are special job yeah I can do the normalizing thing and things that I mean I can do things but of course I guess non-perturbative Wenders what you that's not the wait what is another to win which evaluate theories the way we evaluate theory one possible way of thinking about that is that we associate degree of confidence to the theories that can go to very low four five is very low to very high QD is extremely extremely high everything's in between there so 10 is low but not so low and so on and so forth and the only thing is that we are working on also it gives degrees of confidence which is what motivated us to work in one thing or the other I mean string theory is interesting because there's a number of things that increase our confidence in it and we heard from the real a number of reasons for taking it seriously so this increase but in the same manner the things that decrease confidence easily and everything that if he would happened would have increased the confidence level of the theory obviously finding supersymmetry does not prove string theory right but I would say a lot of people in this came through committee we say great is an indication that we're on the right track not finding where it was expected decreases trip then the common level of competence is the city this is what happened defect so um not seeing a giraffe in the office does not cover maybe there are giraffes let's see but for 30 years nobody sees it you have what you started me maybe then don't you accidents right and wherever the supersymmetry is going to be seen so more than 30 years so I think means that there is a moment in which you say this does not disprove anything in the puparia sense but it's a fact that there is more stress on the cartographic solution that require that a third direction of empirical evidence is laboratory experiments Steve have already talking about a number of that just a few comments there is a lot going on in other local systems for black homes and things like that my teeth is that they tell us about the theory but they tell us anything about the world because we have a theoretical model say of Hawking radiation we find a condensed matter system which has the same equations in some machine and of course we find the consequences that are the same consequences of so we test our understanding of the feeling we don't test whether the theory is right or wrong it's not that these things are not in to see we are know mostly interesting but they're not telling us about my hopes they are telling us about the seeming were using there are many other plants are affected in the lab that have been tested and it is good that Steve made a list of them most of them predict most of them testing that were not actually predicted by any country may be severe like no like this interference between quantum interference between the different arms of two to the thermometers or definitely relevant are the kind of experience that tests quantum superposition which could rule out theories like tangles which little not many people a lot of clearance in in in it pero says quantum it breaks the narrative Lords of Ponte mechanics now this can be tested in the lab and then in Vienna in other places people try to do that everybody would bet that part two more wins and Penguins lose and then we're basically a square one with a little bit less credibility in tangos hypothesis but but and this is a four think there are proposed la brutal experiments to test whether the additional field is classical and you know it's a bit I was completely surprised in my talk I essentially have a single reference paper since the paper references and still Catholic but I mean we hadn't talked do we have and where we have talked for several months and he gave a token had the same reference so this is the same as he he described that you take one particular superposition of the part of a superposition and then there is an interference of the two which is built by the fact that this particle is in the gravitational field of this superimposed to the gravitational field of that now you're gonna think of in a moment I mean this it's too weak I'm confused because they actually receive it this one is a potential disease plus in the sense of quantum mechanics the potential so there are three distances there this one the long one into intermediate ones now is not the attraction that matters here it's it's time dilation is the fact that the sense of potential is a little bit difference time goes the different speeds of the face turn the quantum phase tone a different speed so the quantum phase of this turns in one branch of the universe on the rate given by that or the other we reviewed everything together there are the four the combined state is not the Texas anymore because this factor here depending on different distances and if you want evaluate the strength of the effect is very simple because just look at this factor and there's a separation H bar GM and the time they stay there so you take the M of nanoparticles because these are the ones you can superimpose on your computer and as Steve said that you get a second or two so if you just can hold this thing they get entangled and then these people have good ways to test whether they entangle no not because that's a job and so there's a if there are entangled it means that each one of this was on the superposition of two different potentials which means the gives you its quantizing this it's a gravitational field is squattin of the particle quantizer that's given for granted that night so do you know the gravitational time because this one sees not on a single potential but on a superposition of two potentials if gravity is the same as space-time then there is a single space-time there's a single gravitational field there is a single Newtonian potential you cannot have two newtonian potentials I think our streets if you don't have to quantize yeah the convention are the people seem difference did they think this is a quantization sponsor sister the only way to encounter the two is via quantum something we have a theorem that says you cannot entangle two things without the class that's where they take both of the argument I know but you're creating a position of to me yes you can use you can use you can do it in want to feel seaming and then you have at the other you have a photon longitudinal photon that it's it's in a quantum superposition it's not in a in an eigenstate of itself is not a semi-classical configuration well it the intended the good thing is that the the internal thing go works for you not against you in the sense that they cancel the effect so if you see the effect you're pretty sure that we're gonna wait this is there are two different groups that come out the same proposal at the same time I have the two references here what is the nature is nature of the last year and what is the same return alright third and fourth and last an experimental evidence this is also the future and this is the message is also not we have experimental evidence here but there's a community is expecting it to come soon in two directions a reunion is quantum cosmology there's a huge amount of work whether it will work or not we have see and I want to say something about black holes because that's what number of people including Michael Peres involve this cosmology it's very simple I mean you have your quantum theory of gravity that in one way or the other talks about the Big Bang you expect to see effect of the CMB so the hundreds of people they are computing corrections to the stand the CMB prediction of inflation due to early effect a long time and the the plane is that with some assumptions about quantum gravity physics the universe you might predict something which could turn out to be visible soon so far nothing has happened yet but I will mention this because there's a large number of people focusing and working on that okay the multiple expansion of the degree in the sky the CMB distribution expanded in a moment in motoring in the modes of the sphere so it's table then there were the distance of them yes so this is a this is a prediction of the current cosmology and and the data points are spectacularly good early the idea is that the distinguished under cosmology from some quantum gravity cosmology whether is you get to do the low mode where where we have of course of course it is far from of is it gonna work because there's a statistical few points over the error bars and it's really not but this big community working there and now I need to talk about holes I'll spend a little bit more time than that okay doing very good time the point is that this is a this is my Concentra coordinate so this is charge irradiation short shoot time so something that falls doesn't fall in these coordinates here now this still represent in theory of the black hole here near R equals 0 the curvature their villages and before diverging against the plan can value and that's where we expect quantum gravity phenomena in but a number of people have come out of serving that the quantum gravity phenomena that happened for long times when the time is longer even if in original you wouldn't expect directly quantum effects in other words quantify can be small but over a long time they can pile up and do something the quintessential one is standing you take a hydrogen atom sorry a radio Madame you put it there you put the detector here you look at the around the detector there's no region for part two phenomena to happen but after a while it clicks because of alpha particle whatever comes out so if you if you compute the curvature times the time at a distance R short distance are the product of the two as a maximum a little bit outside the short radius and it reached one can value after a time which is M square in plank unit it's very very long for a microscopic black hole but is short compared to open radiation time so a lot of people come up saying look maybe there are quantum gravity phenomena outside the black hole due to that and there is a number of suggestion I want to mention to one by Steve Giddings which is to very soon we'll have the the event horizon telescope which is this bringing radio telescopes online from all around the earth which build a sort of single ragged telescope with the size of years with which we're going to see the black hole we're going to resolve the charge radius okay so this is a simulation of what we're going to see and the black hole the easiest block want to see is the one in the center for ArmA galaxies and you tell you say star we talk about micro seconds of arc of resolution so this thing should see a tennis ball on the moon and the test remarkably correspond to a to a black hole on the center of the galaxy however I will flusha we actually helped by lensing lensing increase increases the the effective angle is huge so we the lot of phenomena which happen around the black hole that can be observed in its calculation and and if if there is something outside the black hole it might have some effect and still Givens has suggested that may disrupt the photo ring and there is something observable there that's one possibility it's stretched but it's the people in observations are going to look into that the thing which we've been working in the contour ellika we're going to talk about new pronto gravity in a moment because they want to talk about that working upon to gravity for his lights also it's a so this is a collapsing shell a black hole and the possibility that su pointing region you can explode the black hole can disrupt and and and explode so this will be the the Carter Penrose diagram here the shell here coming out and the reason this is interesting is that there is an actual solution of ice and equations true solution of ice an equation exactly here here here in the black hole in the white hole here everywhere with with some matter collapsing and bouncing out except in a region and so you can view the region where the isolation violated studying quantum tunneling okay any other mechanics permits everything provided that is short times small and there's a suppression of probability which suppresses it so we've been studying this is an old idea in fact it's all people a lot of people have worked starting from fall of this police in the late seventies and the the pictures ring increasing increasingly clear and and we found external matrix nicely so we can do calculations and this is the point of gravity so once you have a quantum theory you can ask what is the actual amplitude for this transition right for the leaning math tool you can use standard patency we compute my stein on the radio atom on the basis of a single model of the nucleus and how the particle can escape the potential well inside this are the basic equation of loop quantum gravity is the kinematics this is a way I'm not gonna go into that this is a way of computing an amplitude is a well-defined set of equations you can do computation with that and the way you work with these equations which is important for them what I'm going to say in a moment about space and time is that they allow you essentially to do the path interval or the metric intuitively active and boundary so even the gravitational field and the matter fields here and here you compute an amplitude or more precisely given a state or a boundary you can do an LP to dissociate into this state so I go back this is the hilbert space these are the operators that connect that to the gravitational field and to geometry and this is just a way of computing the the transition amplitude okay that's the way the theory the theory works and let me know this I'm talking about the feeling which I'm working and a few hundred people around the world is working the thing is far from being complete there are a lot of things which are unclear where I answer there but this was I added this slide while stevecarroll it was talking this morning he said the requirement is a part in theory disable space so Plato's transition amplitude the classical limits there were theorems indicating that the classical limit is right there's no strong complete proof at all but a strong indication the classic abilities by its cause this thing's depend of the level of witnesses people some mathematicians say that nobody has proven that Newton theory comes from generativity something you want extreme freedom we are certainly not at that level of rigor but the amplitude can be shown to go to the exponential of I the classical general relativity action in some under some conditions there are no ultraviolet divergences this is stronger than assyrians and the reason is pretty clear that's sort of fun there's an emu length and there's an attempt of understanding you are consuming a mix of things I wanted to say not that this is a final thing but the reality notices of that prove the empirical support the theory of quantum gravity but it's a significant rise and swing series as he referred to gravity Gabrielle is computing scattering and fact-finding result with ease so this is a way it works and you see where is facing time well there's no space in time you already have boundaries states which had interpretation of the geometries and so in quantum gravity suppose that serve at CERN and this is a scattering thing you want to give the boundary data which includes the particles the distances and the time so the lambda mistake knows about the geometry boundary geometry which include how much time has passed so time is the integral of square root of G mu nu DX mu DX you along the line is in the gravitational field it's not it's not external so we know the geometry outside we can compute the three geometry intrinsic intrinsic of this region you can use the theory within a truncation for computing this amplitude you work with figure out the students for two years and that's the result and then we try to extract from it the the dependence of the bouncing time from the master section how long it takes this thing for we're working on this yesterday the reason I took the night training because yesterday was a thesis in marseille of poor guy man have skills to do low fool spent years struggling with these equations in fact on this thing of course I I skip all the complication technical but but what does it mean for instance and the many papers study the family knowledge of that if there are primordial black holes this is expiring universe a black hole collapsing say at the end of inflation in the heating phase could explode a certain time Siam Square after and we see the signal of it and knowing the how the mass depend of the time you can compute things and the key thing you can compute is the fact that you see if a black hole if what is it explosion happens farther away from us the black hole has lived less so it must be smaller so there is an effect that counterbalance redshift so instead of the standard shift curves the other flat a village chief curve if we find something like that this is a hint this is a sign what what else can have a flattened image shift curve that these are exploding block all via parting traveling which is that shift the length the wavelength as a function of ya instead of instead of the standard shift which is linear you have a you ever the thing far away you see the it's more an issue of less than she - exactly so this is a testable thing computed with a fantasy of gravity might be wrong and oh man mistakes but the theory says is why is doing physics with things here and in fact this is a you probably know the Square Kilometre Array this big thing telescopes with many little components at their building in Australian South Africa and in their white paper in which they say what you want to they want to do they have a full chapter on contragravity promote the black hole exploding they are looking at that there they consider it as one of the think that it was investing so this close the experimental part the empirical part I want to say that at least four directions in which we are either already refers to war hopefully in the future but really hopefully time to say something and the ones we already have it's Lorentz invariants which are put to the normal stress Lawrence validating theories of course you can still have our normalizable theory with the Lorentz valuation scale is much much beyond the Planck scale but it becomes less you can always cheat your theory right so additions know that nothing can be disproved I argued and that not financed with supersymmetry Adelaide's a net left first and LHC second put some weight against the idea that supersymmetry is right direction and it's because the world even of course it can be a high energy soon will have probably if all goes well a very strong and critical indication that you can put geometry on super positions and if there is some hope not certainly at all that somehow we could see quantum gravity effect in the sky I don't know if you want to go to this transparency because I will make a lot of enemies but allow me to go through it and take it with with with a smile please and not with so I'm open to violent criticism in the lady it is in loop quantum gravity this with the open problems if you go to a conference everybody will discuss these problems Steve Calgary will say look guys do I look on to guarantee you don't have it cleaned official river space is what romantic affirmation is shaking you don't have tapping to matter you don't know how to cover the Exeter Exeter etc many as a pastor have been enormous amount of all this is completely under control this is completely under control this has been worked out okay it's two things good good it's two things it's to suppress it first of all the hill space of the quad of the the state of space is has this graph structure and it's this one which is variable space of lattice QCD okay and it's very easy to put marker to couple fermions with lattice QCD it's just the way blood is gives me people do it and it's very easy to add another I know I know tell this to of that excuse me I'm sorry I mean you ask you to reside in a studio just is not correct correct in fact the phrase I was going to say it is also easy to add the yang-mills things here by adding the before I know because doing that is not love doing that exclusively we need that you actually approximately this face face face and exactly exactly so to start with the this is just a discretization of like lattice QCD so in lattice QCD you have a lattice spacing you're taking two to zero right and then that you recover the Lorentz invariance the rotational invariance by sending the lattice base to zero once you here however the the size of the of the of the lattice is not a parameter that defined the lattice is given by the gravitational fields the sit on the lattice itself so if you want if one would think in terms of path integral we're going to integrate over possibility size in some sense now that you fix the number of vertices let me do first a fixed number of vertices and then we take limit in which the the number of edges become become large let me go one step at a time the difference with QCD or qcb plus gravity is crucial and this can be worked out in detail if you just think about the classical feeling in the classical theory you can write the discretization and in the case of QCD alone you have to take two limits to separate limits and becoming going to infinity and AE going to 0 beta coupling constant illuminizer yes if you take anything very thinly you discretize it you still have to take the limit that you're saying and going to Finity but the other one is not there and it's the first time you see it by doing a calculation yourself is a coup the lattice face it drops up from the from the action the reason being the Americans because so you only have one kind of unit which is which is that one so where is then once you have this structure here where is then the Planck scale well the distance is given by these operators here and these operators here that was the writing here have discrete spectral so it's there in the same sense in which the energy of a lot of momentum is quantized so so when we competitive so all that even end on a fixed end the effective lattice spacing is that it's always bounded down by the other body okay this is what pure data by the vergence is all a fix a graph okay once you go to the limit of large n you have a that's a part that we don't control of course we control s the limit of loss so you have exultation OD by ordering at me which is a temptation in degrees of freedom at each order of which there is a intrinsic at of the Planck scale so at each order you don't have interval at divergences that I have no idea yes yes the depend of what exactly you mean if it's depression I mean Kabir has been long every time in which means it can you computer globalization of the lambda from the Planck scale tool to and ionosphere simple in both mother just mother yeah yeah yeah yeah sure because it's not I have no police I just want if you want what I would say is that the silly walk of insulin if it's not possible by doing that to actually say okay look no I can do that but I can say that this means that you cannot avoid infinity because infinity is out there besides you to give you the freedom to have these photographers which are if you don't have these infinities you are forced to predict they don't have X in it is so how can they do exactly that's the point that's the point oh she's very valuable to say that you don't have the vertices that was the first I mean that was the first slide that's why with the first slide on so sorry either you think that there are two big set of prejudices 2.0 remit each of each of us start with prejudices that's why I let me disagree it was okay which you put equal segments for different directions I can never prove that my prejudice a better than yours the only chance is one prejudice is is is this one one part of this is this one so this is the logic of asymptotic safety which is pushing that's another really existing point to see of gravity which open questions so it's how to groove the Exeter Exeter Exeter thousand denominator variation also works in the same in the same manner so the idea is what do gravity should work on a quarter facility namely derive this if individualization loop that goes all the way to to infinity and this is the way we we describe the relative corrections in a sort of way that does not sit on on ensemble on some length scale the other prejudice is that the world is not like that the ones like on that's a matter is ultimately like convincing matter and some elegant and strange manner but it's like unless the matter so there's a scale there are atoms and molecules and you can do the quantum field seeing of the phonons you can do its own wonderful but this beautiful mathematics of randomization you have actually is an approximation in to this is a confirmation to me of something that sits on a discrete structure down there of some sort now classically you can even not list in structure but you can either receive structure in the sense that the size of things is given by operators with a discrete spectrum and this gives QCD with a cut-off maybe we can open this blowing they'll exactly but it's exactly my question so my question is imprecise fathers fancy at the consulate which is then now today father and then get the desserts which are consistent with what we see that I would completely but I don't see so far yeah yeah I'm sure that each of us in each other theory we don't see things that we would like to see I mean I'm not saying I'm not trying to sell a final theory and saying look you should all agree with that solve the problems they're all good promise by combining matter in the sense that I I have a version of those equations that I put down which ought which is not written here which include matter and which naively give fermions in your new situation it's in a very simple way and it's a this and and and then there's a bunch of paper by Thomas team and saying look now evenly this is like matter cut off for the Planck scale I definitely don't have the calculation that you would like to and even worse I don't have the calculation that Bailey's asking me maybe okay good so you have always fine why don't you compute the normalization of plan that then from is it be it is more looser it's a it's it's I would say is the factor of three but a cosmological constant there are any of the cosmological constant from this rate or the heat of the higgs mass which is the same so we don't disagree on the on the substance we disagree on on what we consider crucial important I'm here here so this was a new controversial part okay now this was a rhetorical thing because now the bill is going to be I want to compare this with what was a list of problem in string theory in the eighties so take a take a paper a paper in the eighties and see what I did this is what everybody hopes to do at the time right compute the parameter of the standard model deriving this finding from the relative ratios here is a set of fundamental equations and I think everybody would agree that's actually this is this he ran for more optimistic than than complaining I think there's much more understanding of non-paternity string theory today and there are spectacularly beautiful thing in with the dualities which I think do teach us something about contract yet same beautiful calculations which have a black hole inside and you do the you can use the duality to compute the coupon functions at infinity and you see how before taking a limit which is not a physical limit because Planck scale the thing is unitary with no information loss and you lose it just in the moment in which to delete so there things and also think you had predictions except that they got wrong no this is a strongly biased perspective I'm sure I understand well yes for those I would say yes for both yeah I would say yes we both I mean of course is our calculation of test or maybe more yes here than I mean this I know okay so how much time do I have zero okay um more philosophical issue nature of physical space this is something I I care not philosophers used to say that there two ways of thinking about space is the Newtonian way image of an entity over which things move and the relational wave in which have just thinks that move and space are in a relation who's next to who now the people very fast so the authority of physics the cart had just matter which are the property of extension is Newton who invented this entity space and space which is there even if you take away matter and time which passes Simmons nothing happened right this is a very Newtonian idea but then things started to evolve because Friday Maxwell added the field to the ontology of fundamental physics Alec Stein realized that is hard to separate these two I start again realize that space-time is just a field so in classical general activity we learn that this gravitational field and particles and that's it reason the space-time separated from the field space-time is a field and in part the mechanics we we see that the he'll have particle-like properties some invited made by photon in some sense and an electron type of their own Dirac field if you bring everything together you have you have just one object is covariant cotton fields from which particles fields space-time emerge in approximation in in various manner so this is a this is a picture of in mind pre general activity your fields over space-time and when you quantize them you see the planted the particles is just the excitations the quantum excitation of the field is are very variable if your space time which is concurrent because this general activity is a field it is made by Fanta and if you want look whatever it is the mathematics of this thing here so continued space-time emerge from the states of the hilbert space exactly the same manner in which continuous electromagnetic field emerged from fox base we know how to do that right we know how to go into Fox space go to the particle basis the n basis and K basis and from that say look I have a continues electromagnetic field well just leave the queried state which is a good approximation of the head and some I can do exactly the same thing yes oh I would say yes for the rate-o-matic field is filter confidence I don't know no I think the way that yes in total confidence there is a lot of work on all the basis of this Hilbert space still in this operator here to be queried state here this coherent state looking like classical geologists on large scale of course not if you go down lower scale having small fluctuations compared to though there's a huge amount of literature on coherent States there and there is a huge amount of literature that connects the transition amplitudes to the classical action or more precisely to the classical handle function which is reaction as a function of the initial and final States I'm not defending the technicalities here I'm defending the the overall picture so if the technicalities work this is a Korean consistent way of thinking of continuous space-time as emerging a classical of fine but you can also fine what I'm saying is that it's a framework there actually is so loose because you are yeah this is possible because of is a huge family of bacteria that you are so I mean this is the main problem it's only is possible to actually realize somewhere in huge landscape that you realize what you want the problem is that you having recently that you are actually targeting if you if you keep placing general question I cannot get to the top and see what you mean this is a look we have transition ampules that in the limit of small each bar of course the property meters for each bar and before the limit n going to infinity becomes exponential of there is an action action action for what for something that you put in by a no-no the habit of function I mean even the initial physiology and the final food geometry for any geometry for any initial finally geometry up to degeneracy complications there is a classical solution between the two when there is a classical solution the two days of items the action time there is no time yeah the transition amplitudes this is very simple and this is my standard way you think about that we use time clocks clocks were had an oscillator the guy who realized that oscillations don't depend on the amateurs Galileo he was in the Pisa Cathedral usually pulls you make sure that the period of the oscillation of the big chandelier few years later doctors use rocks from relatives of the patients so the old major pulses in terms of Cox was later everybody relies on Canon EOS pools phones it seems completely similar and of course it's not the point is a wonderfully explaining by Newton the video between tibia where he says that his time not not the the stupid time that the cart and his total think about but he's but a mad time is not something to observe something we compute because we observed quantities like the angle of something oscillating we hand the angles and all that and what we observe is how this quantity changing on respect to the other and ours Newton says is very convenient to compute calculate guests find a variable T and describe everything how it evolved in T and have clocks think about rocks as set of things that evolve well together thinking of approximating this this invisible of T which means that of course we can describe the world without tea is very unconvenient in outside relativity is necessary in general relativity in fact in generativity use a coordinate time which is not connected to anything directly measurable is an arbitrary label so at elemental label Nature is not organized in terms of evolution in time I go back there's no time here how do we how do we work with time I thought I had a transference before sorry in this way here so time is in the in the boundary data is one of the variables a gravitational field one well the one you're using in that particular experiment you're interested in the case of the bouncing black hole just put yourself a some charge you may use and it's appropriate time between what you see the thing come here notice something coming out you want to compute that as a function of the mass so I think that there is no ops there is no really mystery of time like it was in the 60s when we learned we drove through the questions it can be worked out completely and the the arrival point isn't as a fundamental level we don't I'm variable having said so the question is what is the relation between this absence of fundamental time in the sort of just even algebra and and our experience of time well I think that the answer is that our experience of times is a lot of layers and we do find aspect of time at different layers when we describe the theory we go up to either specific approximation or more partial descriptions at the fundamental level of a different variant quantum field theory there is a LAN flow the flow of inaudible FISMA which are phenomenology modified by itself which is there it's that's part of it which is related to the terminal time and because the the inner flow is just an equivalence class of outer flows each one related to an ocean of air of energy and n o'clock so for every clock of every energy you have a possible notion of time when you have an equilibrium state which with with respect to that time so equilibrium states are related to toggle if you and so on so forth to go to a single unit time you have to go to the nonrelativistic limit there's no single unit time in in classical special relativity to go to orientation to this thing with the past from the future you have to go to low percent to be I mean there are traces only because entropy was low in the in the past so this is definitely something which is an open problem I believe that low pass definite is perspectival I have written about that I'm not going to convince you in one second there are books about that but this has nothing to do with fundamental time here and and to understand what is the thing about passing this sort of high daguerreian open space in the would do which is our sense of time this is not a problem for metaphysics this is a in people study the brain our brain works thanks to entropy that keep growing by using the traces and by building up as anticipation of the future so if we want to connect our experience experiencial time to physics we have to go to the side of the blade we cannot go into look into the question of undergrads there's nothing to do down there now books about time this is a fantastic book your brain is a time machine the narrow science and physics of of time so based on that you know in a context in which you are going to be and therefore you have traces and in which because of that you could have evolution will building a brain all these things happen which are a memory or anticipation which is what we call the flow of time mixing all this in a single story of you explain these doing dances when you actually know I mean this this this makes perfectly sense within a normal atomistic approximation and if you special relativity you go fast of course your own clock time is shorter and then your sense of time is going to be short so it's it is nothing consistent there are a lot of steps we understand badly here of course when why employers do because in the past the brain with so they haven't zeroed out but try to mix up this problem with these problems is a confusion in my opinion so moral law search in elementary physics what is not in elementary physics it's perfectly consistent to write a fundamental theory which doesn't have all the temporal aspects that we saw intuitively are attached to so what I mean we are very attached to up and down and in Newtonian physics you know up and down this doesn't confuses us we know the story in between it's a long story in between ok last and it's a very last point this was very much form Michele bit bull but since it's not here I just wanted to say the title of that since I closed the panoramic of what I think the concept or aspect is there is a deeply relational aspect in generativity the localization of something only means what what's around it general TV you don't localize things in space-time because the things you talk about are spacetime Jonas so black hole solution attraction solution is not somewhere it's somewhere once you have two black holes you can say where one has resurfaced and so the original is that you have the regions and you've boundary between regions now in quantum mechanics are very much the same structure of systems and interaction between systems it is my opinion which to do quantum gravity if you put these two things together you understand things much better namely you should identify the system the quantum system the more system with spacetime region and observer with its boundary and I like relational quantum mechanics is particularly designed to do to do that of course other ways of thinking to mechanics could work equally so a a company can experiment is also a preparation and a measurement and if you think in this term the the only thing you need is the amplitude from an initial state to a national another state you may do something with an amplitude you forbid the solution what what comes out that's my last slide and there's just a summary of everything you're saying I said in which I have the list of thing said at the beginning a little bit qualified we do not we don't have one to zero either through a gravity we do not know which is right and no no this is complete there are serious open problems in each one of them but I completely follow Steve in that we are working better if we don't do the thing that I myself do very often which is keep pointing out the limitation of the other theories you know they are there in all these theories we know that I don't know to take them going to finish limiting look what gravity as a landscape problem in string source of course I accept excetera there are limitations this is different from our prejudices that we have that we don't look at other theories there are theories calculations there let's be happy with that and we do have already some empirical evidence that rule out some theory favor disfavor assignments on so forth and this is gonna grow and that's I think it's a it's it's a half-full glass regarding philosophy I think that physical space contragravity definitely given perspectives that so to bring together like readies in classical general relativity the relational aspect of space that is in Newton and the cart with the material the the entity aspect of space which is Newton by understanding that Newton space is a field it's made by quanta and it's the continuous field is just a classical approximation of of its physical time I think one can perfectly well work in terms of computing position amplitude innovation within variables forgetting about any different fundamental time this seems very disorienting but it's because we are trying to put experience some time down to the point or anything where it's not its place we have to understand this tower properties of time how they come up at add value later at those levels and finally I just skipped sketched very recently I think there is a deeply sort of relational aspect both enjoying quantum mechanics that have to be merged to be able to work with welcome [Applause] we have a quick comment and a question well the comment is that in your slide at the beginning about prejudices you had asymptotic safety and the section on no it's no limit to to scale there are some pretty good arguments that if you measure scale in terms of the renewable eyes physical Planck length that asymptotic safety we'd see to a minimum land so it might be at least to be movable yeah or at least somewhere sitting this is a common criticism I'll have to check okay there's a bit catchy well I'm not sure there's a review of minimum length which is ping builder which include survivors as a bunch of references to that thank you the question has to do with time without time and in your loop formulation where you say that the time is intrinsic in the boundary I still don't quite understand what that means for normalization of wave functions if your boundary is something like the cosy surface then I can see how that intrinsic data would give you a normalization of your amplitudes but if it's not how do you determine normalization of transition amplitudes yes very good this is the this is the this is the key technical question for doing that in fact and the the fool answer is a bit long so let me give you the the key the key point if I measure the position of a particle I can ask a question which is what the probability of having the particle here rather than here or here or here and here right here or here everywhere in the universe and probability is always probability out of a set it's not probably by itself doesn't mean anything what is so if I ask the question where is the particle here as opposite to somewhere else of course I have to have a pervasive solution such that the sum of all the probability or everywhere in space is it's 1 so I need some sort of space like surface where I know for sure that the particle is now one can turn the question around and use the ask the question the following equation I have a detector here which is on here and say from and I know the initial state what is the probability that it clicks versus it does not click I'm going to alternatives clicks double-click and I don't need to know whether the particle is somewhere else I need to know that the sum of the two probabilities I have to one so now is this is a story I have my relevant table space and I have two subspaces one is the space with what I know and what is the space where I want to know whether it's yes or no and the ratio of the two dimensions essentially is the probability of that major given yes versus giving no that's the structure there are numbers work trying to do that but that's exactly the key the key technicalities [Music] yeah very good yeah I got the question they also is that I would dispute your first line this has been long debated and still now there are different opinions - typical champions of the opposite Penrose and who price Standard Oil atavistic quantum mechanics as it is usually formulated in textbooks as a time orientation is no doubt between between this measurement in this measurement the wavefunction is one of the past not one of the future but the predictions of standard textbook quantum mechanics do not have an orientation and I this is a strong statement namely if I make a sequence of experiments many many times is it release okay so I spin up spin like that spin like that extra factor that is a sequence of experiments and I told the results to you down and I give them to you and I ask you to reconstruct where the time goes in this direction of the structure you cannot it's a statement so therefore the predictions of quantum mechanics are key invariant exactly like prediction of classical mechanics the wave function in between its I think this is a strongest argument indicating that the wave function in between should not be taken ontological it's just that if we think that we know the past and not a future there the wave function is an information about the past and not the future so that's in my opinion the strongest argument for epistemic into position of the wave function rather than a realistic interpretation to logic interpretation of wave action now if you accept this which is disputed by some but I would say is agreed by most but but if you accept this then your question force namely quantum mechanics by itself properly formulated it's invariant under T going to minus T so is classical mechanics so is quantum gravity so is everything the only only only source we have of time orientation is this fact so far mysterious which entropy was known in the past universe and everything can be traced to that so I'm very sympathetic this idea that we shouldn't be looking into the quantum leader the experience of time so now you are right I mean whatever is the approach quantum gravity zesting theories of quantum gravity definitely you have these dynamics even if you pause it tomorrow in addition to the dynamics definitely there is a problem in explaining how is it that this tomorrow positive ID from the mental even my account might examine exactly because it's not really the same it's not that let's see I take it a matter for like the presence of the what the physical present of the laptop on your desk is causing my impression that there is lots of there we can't really apply this kind of this line of reasoning in according I mean speaking to the idea that you positive tomorrow at some fundamental so I totally agree with you on the other side you say yeah it's a multi-layer concept and you are giving here at least some time with an Army's biology brain science and maybe there is something that you are living out here in question yeah so when you say experience of experiential sorry time it's understood in terms of all this stuff so what do you really mean with understood because that's my problem I mean it's you know the gummy life problem of deciding to understand the relationship between primary qualities and secondary qualities it's team up there nobody really found the solution and so it seems that even if you refer to the Bryant's brain science and you try to ground your experience of time on brain science still do this which is not feel they feel your own subjective experience of time is not it's pretty much like the feeling of heat in the cup of coffee right you keep thinking okay how is it that the feeling all heat in my hand connects to the kinetic energy of the small occurrence of cup of coffee but there is something about experience beside the qualia which is which sounds to us in an ordinary way of simply irreducible to them statistical mechanics so when you say understood in English nights before that now it's gone so you mean so are you using some sort of deductive approach because it's not three I mean it's not it's a philosophical point yeah so I do think there are some aspects the perception of fire experience of time which which belongs more to the domain of qualia the secondary quality anyone listening here neuroscience yes she's on the other side yeah yeah so let me try to answer in as clearly as I can first when I said I wrote understood that and I mean it was understood I said it has to be understood it has to be some first wait wait first okay so let me be clear I'm not claiming that in this no you might have understood and in that case that would be very interested more yeah but this is not the main us the main also is that I do stand on the idea that there's a lot to understand from the brain science that is good the main point for me is not this one the main point is this whether this experience shown time has to do with neuroscience or has to do cashton in terms so your philosophy whatever you think about qualia because you don't for all possible reasons because you don't accept naturalism because whatever that's fine that's a nice it was going to grantee that's my point so if you want to add another line here and and which is larger philosophical problems about subjectivity so you send photos to Suites okay and I register as a points okay now I so I register something which will give me the defense but I see that the targets on its yeah this is a this is very similar to the to the to the the mental experiment that panels discussing the paper trying to make this point there is a very careful discussion of that in this book here you price time x ro and yes yes yes but really the point is that in in in from reading these questions you have to distinguish the case in which there is a time orientation in the question itself and the case in which there isn't so I gave an example in which you have at t1 t2 t3 t4 t5 t6 a sequence of spin measurement from which I would get the probabilities if in fact you can Eliza exactly also the your example it's very easy to come out with experiments where there is a time orientation but it's always clear that this is X parenting which you assume that in one of the two directions of time there was something peculiar right so if I give you many picture of an expanding gas it's very easy to find to see the direction of time right you got suspended that then in all your runs there was one end which was peculiar so you have to put yourself in a situation in which there is nothing peculiar at the end so for instance you do a a you make a sharp measurement of an eigenstate at the end and then something that does not commute and and then they said it's mathematical because the model square of the probability amplitude is this time reversal when you she's going to interaction oh no good fantastic the universe is not invariant and at t minus T the universe is Marya that CPT as far as we know so I should qualify the u.s. invited the t minus T provided that one in reverse the sense of the magnetic field will reverse the charge in Manhattan and so on suppose to something that confused David Albert which is the famous article saying that electromagnetism is not time reversal invariant and he standing in that and the reason is that if you take en be an evolving time and you take the same es MB annual backward they don't satisfy the max equation why because you have to switch B minus B for the special access fish but that's not what you're interested in exactly what if there is no resistance well fine even only for like microscopic scale or he said there is just like kid nor instance in the microscopic scale and offer there's emergence of in the the absence of a single time variable playing the same role as Newtonian time of the type of experience is already in classical general relativity I mean if you ever if you have to Gary this morning if you have two clocks two watches you put one up one down wait a little bit you came back together you compare them they have different meanings which one is tiny the one up or the one down see so in general TV there isn't a time where there are the meanings of a clock along each line there is a proper time so time is a concept that becomes way more complex the more you enlarge the the aerial phenomena that you are considering and in general TBT you can still define proper time and we know how to do that in two gravity you can talk about even for classic cars overfill every in front space is it when you write down the fundamental values that you you can't go because you need the I epsilon three confinement we now have to perform the iteration so wise and you don't have to go on the tour you have to give the direction of time so so isn't that a problem from the type of because you see what I mean is that you can say confusion [Music] although his answer is wrong just home because you have to keep the epsilon prescription if you want a meaningful so so for that reason I see there an appearance of the direction of time that food that you can perform calculations you don't in pieces so what I mean this is a picture of the kingdom which makes the price to pay is that exactly it's jobs yeah I epsilon versus - Alexia yeah I see what you're saying the the the military the question is rien sorry the we learn the with equation unlike the Schrodinger equation is visible so the propagators of we are not the other goes the propagator of the will integrate equation have both the forward in time and backward in time evolution so exactly so the questions how issue it's hidden in the fact that you're giving a about is a boundary states that you choose yeah yes you have somehow here you have to be the average position momentum time and energy and you choose the positive energy of the negative energy so if you start to a wave packet which is moving forward then it's its propagate on the propagates the forward part that works all the time so hamiltonian constraint of primary as I said so they don't freak about this there is no time evolution kilometer so are you saying that that is that concern and come kind of evidence yes non-existent at the fundamental as something needed for this with a pentagram so this is a if you want this is DB clearly thirty years later with more proper variables and instead of having a constraint we directly the the transition amplitudes but it's basically that in fact formally I mean you're not able to do that but to ative lis the this the the state the transition altitudes it should change the state a little bheem the this should be given by wheeler do it later if I forget all the infinities and the thing is true if you actually just want Navy surfer I make your question about the exploding black bowls I still don't really get why that should happen I mean if I have a star that's collapsing and gonna make a supernova there's some probability I guess that just before it forms a neutron star turns around and goes out the other way because the wave function has a small tail yeah that's out filming and not in going super neighs Jack all you're saying in other words what is what is making this thing bounce it seems like it can't possibly be the right okay good we we spent this summer discussing these things so let me give you my best last last the last understanding of this let let me take the worst-case scenario the suppression factor for this to happen is the one given naively by semi classical gravity so e to the minus the action over H bar reaction is M square the area just the dimension of H bar H bar G so from a microscopic black hole you have a suppression factor which is e to the M the mass of the black hole mainly the area of the blacks for over the Planck area so it's a dramatically suppression factor so it's not going to happen that's essentially what you're gonna see naive a semi-classical intuition tell us that Tammany does not happen from microscopic things good still this is gonna still happen later on in the following sense we let me fold in now what was disregarded before which is Hawking radiation so slowly sort of adiabatically the black hole becomes smaller and smaller as well as water as it becomes small it's mass get close to the Planck mass and the area gets close to the blank area so at some points and spread the factor so this suppression factor e to the minus n over N plug boost one so at some point is so small that is going to happen so you're imagining a long period of Hawking evaporation until it reaches a near the Planck size and then it explodes that's is a worst case scenario so in the worst case scenario in the sense it's the is if there's nothing enhancing this probability this phenomena is going to happen not when the thing is larger but when the thing has already been reduced to Planckian or bit more than Planckian size and this is very interesting because it tell us how the black hole ends that's what we all want to know like this is a story about how the black hole ends and in fact they tell us that what comes out is a white hole with a long tail and not a knot pops into nothing it's a white hole with a short throat but a long tail which takes a long time then to evaporate so even in the worst case scenario this is how the black hole end now separated from that where argument to say that the suppression is not as bad as e to the minus M square so this may happen before but you may say well this contradict my idea about microscopic object and I not sure my arguments are gonna convince you because they are indirect argument [Music] depending on the peoples of phenomenology most people in phenomenology takes this to happen between M Squared mm cube so they cover all possible cases and this will give signals in the in the highly high energy signals to essentially the photon trapped inside that come out if it is M Squared so if we are down to the most favorable and the most intuitive case which we are trying to compute the men struggling with it then M and T M Squared T Hubble time give M Squared the mass of a little planet and the dimension of millimeters centimeters which is where the fast radio bursts are so the first radio burst I the idea that this could be one of the component of faster diverse requires this happening much before Woking evaporation so that will be killed if if really the suppression is e to the minus M Squared the TV energy factors no so those are phenomenology range which is one one clarification regarding the time so you mentioned the direction of time evolution but then more basically the very notion of succession not being given together at the same time how does it fit in this is it is it taken care of by the internal flow I do I think this is even more basic that is presupposed from the start that there is such a thing as succession as opposed to everything being given at once I I don't have a clear answer to that you may talk with a lot about that but there is a key intuition countable and in fact that that the in quantum mechanics the element of the algebra the operators which are the event the thing that the single observer don't commute now doctor mute means that a before B or B before a different have different effects so there is a in written in the algebra something that does not commute which somehow a line has been suggesting look this is the this is a sort of first manifestation of temporality doesn't have all the property of time that and then remarkably a line has shown that this is a it's actually related to this in a flow in an algebra if you have a following manner now to go from there on it's a long story but I think this captures something core about the product no I just want to add one sort of philosophical comment about this issue of time you see we are used to attribute any variability in life to the passing of time I mean this is what we do you know if I since I had a teacher when I was in high school but not in high school - his konami code and once he asked me to go to the blackboard and yes you did this gesture and so we were doing kinematics and so he asked me what is the parameter so you know I scratch my head I was thinking perhaps the Xcode iterating and after a while I answer it's tired sit aside so so now now there is another viability which has been observed and confirmed incredibly well which is the viability quantum mechanics by viability I mean the following I mean that if you repeat the same experiment like a two-slit experiment or like one smooth experimental enough you will find a result which is actually under this is suit that there is a Swiss team which has made Hippolytus to fabricate hundred numbers by on a cell phone by using this principle and the system is so good that even if you do all the apaches extreme you will not be able to buy this and remember it will not be true for computer fabricating so there is a hot on nest in the quantum which is I believe to Troodon ability I believe that to use to attribute all the viability of height down all our equations in physics as d by DT because we are tribute all the variability to the passing of time and then we are surprised that when we have entangled photons and so on we cannot we can we say that there is a spooky action at a distance that actually have the hug between the two so what I believe is that we have to get rid of that prejudice that everything is a function of time and and we have to rely on this variability which is quantum ok and which as Kara has explained actually does generate a classical time when you take the thermal state so it it has a potential of actually being intact as a classical time but it's very subtle it's something which is thermodynamical and so on and so forth but what I am trying to say philosophically is that we are probably home to us tribute the variability to the passing of time that's a cheating that's a you are saying it as the Newton's you know of course it's very useful it makes it very nice and so on but probably feeling future it's a mistake I was confused by what he has said about the commutation relations and possible connection with the order of time because these commutation relation sorry that's about equal time saying which is behind the emergence of time from the non commutativity okay it's essentially the following it's essentially that you take a state statistical state and you evaluate it on a be okay of course in general the state is not a trace you will not get the same result as if you are very late it'll be a yeah but it turns out that there is a time evolution which which is due to tobita which we tell you that when you evaluate Phi of not on a unclear but on B and a transformed by certain operator which is evaluated at imaginary time then you get the same result and this is the key so the key is following the keys and when the algebra is so and this relation is exactly the relation between the eisenberg evolution and the Gibbs State see when you have the Eisenberg evolution you have the conjugacy by exponential ith a exponential minus i th okay on the other hand the equilibrium state is the place of exponential minus beta H times an observable now these two things are related exact the relational ontology so the point now is the following the point is that okay this relation is very simple in all the nine quantum mechanics but when you do not take quantum mechanics ordinary but when you take quantum mechanics with ignorance which is such a is a framework of Aldermen so what you do is you take an operator which is very subtle inside so it's like a subsystem if you wanted the world auto mechanic our system then it turns out that it doesn't evolution this evolution and it's infinitely more subtle than in the case of a single state layer as before but what it tells you is that because of the on commutativity they are gy is actually turning on itself and and this is an amazing fact you see this absolutely the base in fact and it turns on itself only because it's not visible that's the only reason why it turns on itself so okay reason why we know each other Calvin and I is that at some point we met and okay I had this so I'm since a long time but I didn't know any way to relate it to physics I applied which gonna feel silly nothing and and so I I bet Carlo Carlo was doing same type of talks I mean I I bother different like air doing his talk and but but then we talk together and at some point I explained this seventh wheel and he disappeared we're having dinner together car will disappear so I was saying okay by P I said something then he came back five minutes later and he showed me two papers that he had written one year before two years before and in these two papers he had found from philosophical thinking okay I I really found this viable for philosophical thinking he has found that in the formulation of quantum gravity were okay with a bit on Us Weekly vanishing and so far a lot of time so yet the idea of actually saying that you need a thermal state in order to get the time to recover a time so and if you have a Tamil state he had written an equation that or action actually was relating the tamil state to the time that equation was a semi-classical limit of my equation so then we got you know we got really fascinated by this because okay even if we don't say the kind dance that will be something there must be something behind this is what it's not a totally matter but the oh so really I think the philosophical idea which is behind it is that we are home to attribute every viability to the passing of time this is a consequence of a touch of our selection on our plane because this is the most efficient way to act in the external world but in fact you know we are in the quantum we are living in a quantum world and in the quantum world okay you know it since I'm all set up this is oh oh there is another way to state what you're saying yeah if you can see minus plus C or minus C it loose music but causality is not and the change of C 2 minus C has to be conceived in physics of continuity and causality is not symmetric because the same state of affairs yield same consequence at least in classic important yes but the cause is you can have different causes that year the same 8 okay so let me talk also to this one because it's a this is really the only guy who has clear ideas of that which I found it tricky reason I came back the philosophers I came back and I think the Philosopher's know it very well and I think he's right I mean it's one of the most well respected philosopher of science in the analytic tradition that was absolutely it started um I think it's what he says is - and you price agrees with that and I would say the large bunch of lawful science ability the questions of classical and forget quantum for the moment because the question of classical mechanics are invariant to the t minus T so as long as we talk about classical mechanics there is no sense in which comes ality has one direction rather than the other directions maybe even the state of affairs today you can equally well predict the past to the global to the future and as I Stein has pointed out the same is to impart the mechanics is a beautiful ice and paper there is uncertainty the future but given the state today if you want to know what happened the future there is a constant it now this dramatic clashes without experience of course and fact but it's a fact Russell Bertrand Russell wrote the notion of causality has disappeared from elementary physics is gonna go away from you know that Cupido go away from science and is remaining there just because like the monarchy in susan it's believed the to Donald no damage but it's not true but then of course in philosophy have been a big discussion cartridge and so on say wait a minute we think it of course all the time I mean you cannot ask them ask us to I mean that medical doctor what to think that of course isn't so the question is where does the notion of causality right by himself talk about common causes which were two things happening different places to be Pro common causes if there is a tsunami wave arriving to Island you think there is one earthquake even asked not in the future okay why not come across and there's only one possible answer to this question I believe and a lot of people live which is because I'm to be was low in the past so the existence of traces the orientation of the causal arrow that we use is there because we live in a strongly thermodynamically oriented situation of course that entropy girls is not mysterious at all because things the mysterious things is why decreases in the past and why why if we look back in the past something so I do think that the arrow of time which is implicit in causality which we use all the time in science sits solidly and uniquely on low past entropy as a fact in our universe now whether we put it as a postulate like David Albert passed apoptosis as an i political know of the Big Bang like Penrose violent I thought this is all whether we try to drive for something else I try to devise something else in this perspective on paper maybes good I don't know that's another attempt there is nothing else in in in the physics that distinguishes past from future and in particularly quantum mechanics it's not that it is possible future if not this past low end that's my strong conviction it would be the reverse yeah an argument comes from so it's known about so this clearly this is a course of set theory they posit causality yeah I mean the theory is formulated from point zero in a strongly kind oriented mother so they say it starts from that and then this happened then this happened that itself so they always have trees like crosses to deliver him so doesn't have to know you're right it doesn't have you're right yeah that's a way they told but that's not the weekend before yes there's an approach to the dynamics of your sense that it's not like you can define puzzle sets in terms of traffic and then it becomes and then becomes functional dependence upon oriented possibly or is a proposed dynamics for cause offsets or growth dynamics or case but here you know this case is her objection comes in and that's a crucial one I mean you might have a point or anything where there is a strong time orientation why causal said people not Steven on the support but how the hell that time oriented produces a time reversal invariant classical mechanics in which we live where time is strongly rendered so we're looking we're back at around three I mean even if down there there is some strong violation what's what what the story is I don't think it has to be so much oh it has more explanatory vote even if you pause it was strong another doesn't explain how easy then we experienced exactly exactly exactly yeah even if you pause it you cannot use it to to derive our stealing well you still have to feel the second so the entropy was low but the bound as the universe expands this bound gets relaxed so you have to get my [Music] holographic entity so that sense you you relate the arrows time revolution of the universe but you don't need a real fine tuning of the TC differently because as big as it could be later it would be large and bangles bangles are useless so perhaps we should stop here in a break and [Music]

Channel: ERC PhiloQuantumGravity

Views: 30,499

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Id: T2axJ_XCewc

Length: 122min 49sec (7369 seconds)

Published: Mon Dec 04 2017

Reddit Comments

[u/JRDMB]

Thanks, I really appreciate it when a conference posts the videos and slides of all the talks as this one on "Quantum Gravity: Physics, and Philosophy" did here. They even posted a conference booklet with a page or so on each talk. Lots of good talks there to get into in addition to this Rovelli one, as time permits. Thanks for posting.