A conversation between Lee Smolin and Stephen Wolfram

hi everyone okay so this is the uh the next episode in our continuing discussions with interesting folk and uh today we have lee smallin who is a physicist who i have known off and on for a very long time and uh works primarily at the perimeter institute in university of waterloo so let's see so lee i i think we probably first met probably around 1980 sometime like that maybe 40 something years ago and so so what were you at that point i remember you were doing all kinds of physics i didn't understand and a certain amount of artistic type stuff as i recall what what were you what were you working on back in those days i don't remember anything artistic although i have done artistic stuff since i was working on quantum gravity i've always been working so how did you get into quantum gravity um i it's the same way i got into physics i was first interested in architecture and so i since i was a little bit ahead in math i wanted to build buildings which were generalizations of geodesic domes in which i could take arbitrary curved surfaces and build a structure out of them so i knew a little differential geometry and i developed a program to triangulate sort of general curved surface that i would give it a call before and i was a high school dropout so i was sort of playing around with those kinds of stuff i was very influenced by um some of the architects around that time and there's one guy whose name i'm not remembering but i'm sure you'll know bug mr fuller sure did you meet him did you did you meet him yes i met him a few times and so um i was using the public library and one day i well where where where did you grow up oh this is in cincinnati ohio okay and i had been there was a chef i had been taking physics books home general relativity and so forth but to learn the the differential geometry to do the structural calculations and i noticed that there were a lot of chapters on general relativity so i got interested and one day i took home a book of essays about einstein edited by schlib you probably know him albert einstein philosopher scientist yeah and it had an essay by einstein called autobiographical notes and i just read that in one sitting basically one evening and i it said something went off and a little voice came and said i could do that now i had never taken a physics class it was a high school dropout i had for those days some computer skills but only nothing compared to what people of that age have mostly but so so when you were writing something to triangulate surfaces what was was that like a fortran program or something and so did you i mean so the i mean buckminster fuller was very big on this whole tensegrity you know these this sort of structures meat geometry was that the kind of thing you were into or is it more than pure geometrical how do you take the surface and make it discrete type thing yeah this is a i you know i didn't know when i asked this question i had no idea what the answer would be and this wasn't one of the answers i was expecting so that's that's that's really really cool okay well i only understood much later when i was interviewed by a journalist dennis overby and he said you know you're doing now in quantum gravity exactly what you were doing when you were a high school dropout with architecture and in a way it's true anyway i really got a mission from einstein einstein was very clear that physics was in not a very good state and it was quantum mechanics which he didn't believe and he felt we need uh completed with her better theory and there was a relationship between physics and space and time and quantum physics so in that evening i got a kind of mission because i somehow and i'm not i'm talented at some level but i'm not deeply deeply talented as a mathematician but somehow i got this strong sense i could do that with knowing nobody who did it right well einstein always used to say that he was very challenged as a mathematician i know i know exactly what he feels like because as you try and build these theories and it turns out you need to wheel in all kinds of fancy mathematics it's uh it's a different level but so so that essay must have been written by einstein in like the early 50s maybe yes and and then you must have been reading it sometime in the 70s exactly early 70s but so that was a time when you know in physics particle physics was getting very big general relativity was still not you know it was kind of an out in the boonies type field yes but so so but but so wait okay so you have we're triangulating these surfaces that is charming that you've been triangulating services all your life i find that some things that i did when i was like those kinds of ages are also what i've been doing all my life um but uh but did you ever end up actually building architectural structures and things no i had a little company that was going to build garages and pool covers and things like that out of geodesic domes stretched but luckily nobody actually enjoyed me so wait a minute a pool cover why is a geodesic dome why is a dome a good pool cover it's not i see okay fair enough it's not a good pool cover i'm curious how did you get the kind of entrepreneurial you know start accounting i mean how well do you like 16 or something at this point is that 15 16. i had no entrepreneurial talent or interest but my father said if you're going to be a dropout you've got to get a job you've got to get some kind of job my father was an engineer and so since i wasn't able to find a job i invented this company but i i have no entrepreneurial instincts anyway what was very lucky was that being the architecture had gotten me into a college which was a very innovative college that had just been founded two years before hampshire college oh yeah right when i decided i wanted to do physics i didn't know what i didn't know anything about it i took one class i my mother was a professor of playwriting at the university of cincinnati so i could take free classes so i took a graduate course in general relativity from paul esposito which was my first physics class and um and i i got some of the basics in a very primitive kind of form from him and then i wanted to to be a physicist so what i didn't know anything from anything so i got the course catalog from mit a friend of my parents lend it to me and i just went through there and wrote down all the courses i would want to take try to invent an education for myself but meanwhile i went back to hampshire on the way to mit and i stopped there and discovered that they had hired a physicist who was her bernstein who was a great pedagogue as a theoretical physicist i just totally locked out i spent the afternoon with him and it was very clear that he could be my teacher and that was very important because i was very undisciplined i had lots of ideas i could read a page of mathematics and understand it but i couldn't prove anything so i was way out of my practical knowledge and herb took me under his wing and was really really hard on me for three years and never said anything nice always told me i was dumb and inadequate and couldn't do this stuff so i worked really really hard and got skills and then i got into graduate school and then what sorry i got into graduate school because i was abused so much always but so i'm curious when hampshire college was that young i mean you know it's always interesting when educational organizations sort of that are somewhat experimental start up they usually attract a very interesting crowd of students how how big was hampshire college at that point and what were they was it in fact an interesting crowd of students it wasn't it wasn't interesting it was i was in the third class which was 200 students and how many were doing physics i mean were there a lot doing sort of sciency things or was it more liberal artsy humanities types no the discovery was that it worked much better for science than anything else that they're sort of focused on cases rather than survey knowledge the individual instructions so forth worked really well in science so there was another physicist with john dell who went to became a relativist and went to the university of maryland and so forth and we worked a lot together and there were a couple of mathematicians who were i think they're running across him yeah yeah right but but so i mean hampshire had some kind of project based maybe still does have some kind of project-based strategy for for learning is that right yes so what was so so when you were in that that what were your projects were you doing a bunch of general activity projects um my project was to learn qed from the first book of um bj bourquin and drama that was a project i also i was a joint student in philosophy and so my philosophy projects interestingly enough were a paper on foundations of quantum mechanics and a paper about the mind body problem in which i and this was purely accidental but i basically advocated of you which is now called wrestling wrestling or something like that momentism what is that what is that point of view that's the point of view um that at all matter has an inside aspect which can only be somehow quote experienced in an outer aspect which obeys the laws of physics it was a cheap way to pretend to be a monast while you were a duelist but the duelist part the ex fact that you had conscious experiences in no way affected the application of the laws of physics that's called pan psychism anyways well at least that's that's one version yeah i've always you know i've come to some of those ideas in a very very different way and um yeah it always confuses me when people say this is the name for this set of ideas and then it's like yeah it's anyway but but but so okay so then you learned qed you've learned philosophy you already learnt general relativity so at that time in general relativity people were you know things like you know the cursed solution was probably 10 years old or something at that time i mean it was still pretty early days in terms of people's understanding of general arts over there yes and what was the state of i mean at that time and the group of people working on general activity my impression was it was a very nice group of people but a rather small group of people is that a correct impression i think that's right so i went to my first conference my first year and it was a relativity conference in new york city and i and it happened that i met everybody somehow i met one person it wasn't does he say that large of a group um and i met one of roger's students and then i met raja and then i met penrose is that roger penner yeah and i met the dewitts i met very briefly bryce dewitt and steve hawking so it was a wonderful experience and i met david finkelstein who made a tremendous impression on me no idea who he was do you understand david finkelstein's work because i've always felt that he had just a lot of really interesting things to say and i look at his books and i'm like and i've talked to him a bunch of times and it's like this sounds interesting and then one thing he told me which which really uh sort of he said you've got to realize that i've written about the same thing multiple times and sometimes i don't agree with what i wrote earlier he had this idea the way he expressed it to me when i met him was i don't believe that god can understand infinity so i don't believe that god can do calculus god can sum and manipulate logic and but god cannot do calculus and i just thought he was some crazy guy he showed me finance checkerboard and years later i was introduced to him by lenny suskin as the person many most respected and i just thought he was a kind of street person office you know just because he has a long beard no no that that that would be unfair well no but he talked in this totally mystic way about he was trying his scientific method was to imagine he was god and try to invent the world the way god would with god's limitations and that's that's the way he talked all the time but the thing that that among the things that he did was discover what a black hole was so the schwarzschild the edington tinglestone coordinates which edington never understood are the way to understand what a black hole is and what the causal structure is right right it's funny that you talk about the god's eye view because the previous coordinate system for the schwa solution and so on had been actually was more of a god's eye view than anything finkelstein coordinates it's kind of funny um but but so so in in that crowd of relativists was john wheeler part of that crowd or was he not um not so much in that area excuse me i he certainly was but i didn't meet him then i met him no i'll tell you when i met john wheeler when i applied to princeton for graduate school so they called me to interview me and they gave me an appointment with john wheeler and now and on the way to the appointment they showed me for some reason my folder and i read some of the recommendations for myself because i had it i was just standing there in the hallway with my folder what do you do and somebody had written a recommendation that said that i was philosophical and somebody and somebody had drawn a big red circle around that and said sounds like one of johnny's boys i trusted ran faster than i i didn't want i didn't understand him i didn't he was just these slogans it was the problem is my parents had grown up around mystics and i knew i was negatively inclined to people who had that kind of personality structure so i didn't understand what was interesting about john wheeler so many years later i went to harvard just something else i intuited was that nobody understood very much about quantum gravity but these gage field people really understood something about an interesting class of theories and with the standard models so i went to harvard to be with the people who invented the standard model even though they had no interest in quantum gravity and they told me so right right but so i'm curious just coming back to something you said there i mean you said your parents were involved with mystics and so on what what kind of with some particular brand of mysticism and things or the guru chief work it's called the witch gurchief work and it's no shame if you've never heard of it they were a very small group led by a guy from russian armenia in the first half of the 20th century but they influenced a small number of filmmakers and dancers and writers and so forth and we can talk about it another time all right that's a different but but so but okay so mysticism and you know you had experience with mysticism which most people don't usually get and so when you ran into physicists like like david finkelstein who who had that vibe that that wasn't a didn't i mean i'm curious what was buckminster fuller's vibe was he like a practical architect or was he more of a kind of a mystical type person no he was this very american type of we can do it we can just go out the world and fix things so his story was that his life was failing who lost his job and he had no education because he dropped out of college and he was very sad and took a walk by the river in chicago and all of a sudden the thought came to him that if his life was otherwise not worth anything he could see how much one he could make it an experiment and see how much one person could do to improve life for people so that's and that was his motto he just went around inventing things which he thought would be an important part of relieving poverty and attacking environmental problems and things like that but so you know he he kept on using this weird dymaxion brand and things but but how did he get into jdc domes how did he get into that kind of geometry type thing and he had i don't really know i mean i've looked at his geometry book it's it's all handmade i mean he made it up on himself i think he was i think he was had a brilliance of being able to work that way but um and he was the worst poet in the universe he actually published some books in poetry about progress and so forth and anyway but so okay so so back to back to you in the in the um when was it must have been mid 70s mid 1970s or something by this point i started graduate school in 76. okay so which was right at the time when there was you know 1973 was when asymptotic freedom was discovered that must have been all the rage at harvard and so on at that time exactly but but so and um who did you work with at harvard well i didn't work with anybody but i was under the supervision of stanley desert who of course was one of the great people in quantum gravity so he's the d for adm formalism is that right and sydney coleman was my extensive advisor although he delegated everything to stanley and there were great people there with undoubtedly great people steve weinberg was there shelly glashow a tough taught taunt there for a year people came through like sasha polycov and ken wilson and there were young people there um who were also very good in among the post-docs who were a little bit older than me but um i could learn a lot from so it's a great environment and i just took the attitude that i'm going to steal as much of this technology as i can to use it to try to make a quantum theory of gravity and and since uh since that was new so the idea of applying it to quantum gravity that was new i kind of left out in the sense that there was this wide open range that was not that i could start to fill so i made a lattice theory of quantum gravity which wasn't a great quantum gravity but it was it it was a candidate that was my first paper but so was that was that was that a time when ken wilson was really pushing the lattice gauge theory thing was it kind of a a wilson gauge theory-ish type approach or something different yes wilson and i had been very influenced sasha polikov came by and gave a talk and also ken wilson's talk those two talks tremendously fired me up but so so when you try and put gravity on a lattice in that way does it i mean does it have the same kinds of issues that it has when you try and do finding diagrams and things or does it i mean what what goes why haven't we heard of lattice i mean you know usually when people talk about sort of simulations of quantum gravity it's with triangulations and so on more dynamical triangulations not just put it on a lattice what goes wrong with that this is a hypercubic lattice and i use the mcdowell man's reaction which was it was particularly adapted to that um the structure of the lattice breaks all the gauge symmetries i see okay which which i didn't understand at the time i wrote that paper but shortly after i finished the paper i started to think about hamiltonian methods and i then i realized that the whole thing we've done was we've done i done was was very very naive also i met bryce dewitt at a summer school and he was talking with him for a few hours i understood that i had not put in correctly the breaking of the diffumorphisms or the generator and so forth but so at that time people like steve weinberg i mean steve weinberg had written his book about gravitational cosmology he'd been involved a bit in early universe stuff i don't think he cared about quantum gravity i don't think he ever i mean i don't remember like in his gravitational cosmology book i don't think he even mentioned quantum gravity maybe as a maybe as a couple of pages of discussion or something is that he did have an important idea about that same time i think he published in 78 which is now called asymptotic safety he had the idea that the theory was protrudingly not normalizable but there would be fixed points of normalization group which would be off of the zero point where the gaussian fixed point is and you could define the theory in terms of tuning it to a surface which which went into the critical point and he published that in something like 78 and either and i think the next year or yeah i know it was when i was still at harvard but i didn't publish it so quickly i used a one over n expansion to try to isolate that the possibility of that um not truly a critical point so that was so that was like was like one over n in in the matter fields or one over n in some sort of generalized gravity or something it was one over n in the matter fields and it was enough to uncover the basic difficulty with those theories which i think has never been addressed which is that there is an asymptotically safe theory which is also normalizable which is the r plus lambda plus miles tension squared plus r scalar squared that's perturbedly normalizable and it has a non-trivial fixed point and it lacks unitarily and doesn't work at all it basically it's a fake how does it manage to how do you even set up a theory that doesn't have unitarity oh you sneak you you know you you write it in the euphilian formulation and then you i see you say um let's pretend about how the singularities in the plane are going to move around when you go back to laurencia i see okay so you were at this point you'd done sort of a lattice approach you tried to do a one over n approach this is like um and what was what was i mean is is that story for you at that time a try different methods to try and see whether there's a way to to get a theory of quantum gravity and a bunch of different methods or what was the what was the trajectory yeah so the trajectory was um i worked i had a number of other things i worked on um i got interested in the other side of the problem which was the semi-classical hawking radiation under radiation and so forth and i was very interested in that this is sort of in the two three years after graduate school and i wrote a paper about those issues which i i actually think is my best paper very few people have read it but what is the so what is that paper tell us about that paper you know i'll come back to it because it will take as far afield let me take the narration and then we'll go back to that um but it anyway it got me acquainted with that whole side of the subject which being educated by particle physicists who didn't know anything about quantum gravity i wasn't going to get this is sort of in my starting in my postdoc years and then there were theories with propagating torsion all sorts of complicated i i did the dumb thing that people do and they don't know what else to do which is to study the complications of the problem you understand rather than the simplifications of it and i played around with supersymmetry and supergravity some of this was with john dell but then um something interesting happened which which is that string theory was invented well it was not it had been invented a lot earlier it was reinvented it was reinvented and i a lot of my friends and people i knew jumped into this and i looked at it and said that doesn't make any sense and i've what we call background independence it was not background independent it was very background dependent and so i started with a mathematician friend lewis crane to start to try to make a background independent approach to strength view and most of this was never published but we spent a couple of years on and off trying to do that and so i do and this comes from wilson and the polycarp and all their methods on loops so the idea was to write polycon's idea was always to express qcd as a field theory on the functionals of loops which you imagine where the harmonies of the s of the sc3 or sc2 connection so so is that i mean should one think about that if one's doing fluid dynamics is that like writing fluid dynamics in terms of vorticity and things like that is that kind of a an analogy yes so what what the my original approach to lattice stage theory in hand and which i was interested in some of these other things we played with was the idea that the metric and the connection were independent variables and therefore i saw ways to study operators based on loops of electric or magnetic flux with the gravitational field and with lewis we were developing the algebras of such operators and trying to use them as a basis for string theory not truthfully so that didn't work but then abaya ashtakar invented it's not really true somebody else invented obviously invented but i developed to the extreme this approach based on the cairo connection and all the tools that lewis and i had developed were that we're just sort of ready to attack that idea of his idea but so to try to understand i mean so so this is for example in your idea for string theory this was a a different set of degrees of freedom a different sort of coordinate system for strings which would instead instead of a string propagating on a background it would be intrinsic representation of the string in terms of some kind of loop variables was that was that kind of the idea yes and was that something so so uh what i mean and there would be some lagrangian or something for this for this intrinsic loop thing and was it expected to be a field theory or this was a quantum mechanic so this was a classical a field theory no quantum field theory but on a space of loops so so then when you see the famous you know pants diagrams or something for strings your idea was that what you would be representing was those those loops joining and so on directly is that that kind of the notion yes so does that work in the end i mean has somebody actually done that now or is that um is that still unpublished i think that loop planar gravity does construct that representation where the states are functionals and graphs and so forth we can come to it there are things it does in my opinion and things it doesn't do but um but so okay so so back to to the beginnings of loop quantum gravity so this is this is what year now just to this is like mid-1980s or something or whatever what's that 1986. a bai published his paper on the classical formulation of this in december of 85 and immediately i'm working on it i'm trying to get some friends together to work on it by putting in the the kind of technical toolkit that we had from studying so can you just describe for i mean so what was the what do you now see as having been the core idea of that paper the paper we wrote no the the ashtakar paper i mean the idea of the astrakar paper was completely classical it was let me say it and he he went at it in a very insane um terror inducing way let me say just what's true the easiest way which which was that which which was a few papers forward from that this in some sense is a paper of ted jacobson and i but take the action for general relativity and write it in what's called the fobansky form i'm sorry the palatini form which is to write it separately as a function of the connection and the metric and then when you vary the connection its field equations give you back that the connection is actually the metric connection the christopher symbol so hold on a second i mean the normal you know normally it's r squared of g is you know the standard einstein hilbert action so there is so you could take that that r and write it out in terms of a bunch of christopher symbols and things or what what what's the what is this i i've i've heard of this palatine action but i have to admit i don't remember what it is what what um so the basic idea is that whereas hilbert and einstein wrote the action as a function of the metric where when there occurred a connection they put in the christopher symbol as a function of derivatives of the metric okay instead you have the metric and the connection as independent fields so there are additional field equations and they turn out to be the equations that say that the connection is the christopher connection made from the metric plus some other pieces and the other pieces will help you to do things like couple to to fermions but so let me just understand that so i mean the the naive way of thinking about differential geometry is the metric sort of is telling you everything and you should be able to derive from the metric the connection the christopher symbols the curvature etc etc etc but so this is now a different this is saying let's consider the christopher symbols as dynamical variables on their own is that yes and so so so it is a different physical theory it's a theory where i mean so so just to give an analogy in engaged field theory um you would have the analog of the chrystofel symbols is the gauge fields yes and and so normally and in you know in standard gauge field theory you know gluons and things like that are thought to be things in themselves what's the i mean in in in gravity well so so what's the analogy there i mean so is this how is that a different what will be the theory that is like einstein hilbert for gage field theory and then what is this different kind of thing where the where the where the christopher symbols are dynamical degrees of freedom well we to hold that question for five minutes okay two more steps okay okay first of all we're going to if you want a couple deferments we decompose the metric into frame fields this is just another way of expressing the information in the metric you give at each point four fields which are orthogonal four vectors which are orthogonal according to the metric and that's a different way to code the metric now um now look at the action and it's got terms like this e wedge e wedge the curvature tensor r which is again the curvature tensor just of the connection field so it looks just like a yang mills theory with e wedge e wedge the young mills field string and then you can write e to the fourth and that's really the cosmological term and so on and now i want you to do something really crazy which is um if you know something about which i'm sure you do the structure of lorenz group you can write it as you can write this double cover as sl2c and that you can break up into two commuting pieces a left-handed piece which gives the chiral rotations of left-handed neutrinos and the right-handed piece and they commute with each other so i want you to see the massless neutrinos right and i mean that requires yes and i want you to cut that action in half and you'll see that it is separately a term in the left-handed chiral connection that su-2 group which acts only on left-handed formulas and another plus another function which is this canonical conjugate of right-handed form connections a couple right-handed formulas and then the following is what ted jacobson and i have discovered which was so weird and then we'll get you a bye is cross out one of those terms and then you've got a complex action for a complex variables and it turns out that that's why that's still the einstein equation that is the uh if you're willing to insist on real functions being real so you complete everything but that's left-handed by adding its complex conjugate you only need half the fields the left half of the field moreover i'm going to have you do one more thing and then i'm going to tell you why the result is time is um the frame fields always exist turns out in the action in a structure called eyg which is a two form which which it has its own chirality its complex conjugate is its chiral of other half so we want you to write to every place there's an e y g write a b which is this left-handed two-form left-hand is helpful to form and we want to we want you to write the action as a function of the left-handed connection in these b's and the first thing that shocks you is that there's you have to put in a kind of lagrange multiplier field to make it work and its field equations say you build the bees back from the e wedges so you just have the b's the connection and the matter and and this lagrange multiplier field and that equation um which i can write for you in a minute is purely cubic and the simplest possible thing that you can write so whereas the einstein equations you know normally are infinite order and you have to expand and evaluate one over the determinant of the metric and the square root of that this is an equation written in terms of forms which is the action is purely cubic and the field equations are purely quadratic so there are many advantages if we're going to try to make that a quantity so hold on a second i'm just trying to understand the intuition behind this i mean it it it feels very wrong to take something and say i'm only going to consider the left chiral components or something yes it feels like you've only got you know you'd only have left circularly polarized gravitational waves or some weird thing like that yes what what is the physical interpretation of saying you only i mean is is it is it that the i mean or it would be like in fluid dynamics saying you're only going to consider vortices that go in one direction but maybe maybe the degrees of freedom of space time are enough that only considering the vortices in one direction you can kind of turn it around and look from the other side and it all works okay how should one how should one think about that um the taking the complex conjugate to define the real versions of metric is more powerful because all the complication is expressed a lot of complication is expressed in a statement of what's a real field so i see so so by forcing it to be real you are effectively adding back the degrees of freedom that you took out when you said i'm only going to consider the left chiral component or something yeah i mean it's like in you know when you do quantum field theory you know you would always write you know here's the lagrangian plus hermitian conjugate is that is that kind of the thing that you're doing in this case yes yeah yes um and um so so the remarkable thing that you're saying which i have to admit i didn't know so that's a is that when you write things in in terms of these variables what was a determinant in a square root and so on becomes a pure polynomial in those variables and a love and low order polynomial okay and that and it is a mathematical identity that that low order polynomial thing in terms of those variables is equivalent to the standard einstein hilbert action yes yes and there are no like boundary terms or something where you you know you're effectively doing integration by parts or something or or oh it's not there are the boundary conditions are beautiful because the boundary conditions that you have to add to that structure are ex are exactly trans simon theories of the connection on the back on the on the connection pulled back into the boundary so we can make use of a lot of structure and a lot that people know about schmidt simon's quarter simon's theory so that's that's very helpful um there's another thing you can say about that action which is i said this a term where we use a lagrange multiplier to make a field equation on the b's whose solution is that there exists a's uh e's the frame fields which are such that b is e one g so b if you don't introduce that equation then you have a theory which is just a function of the b's and the a's and no e's ever occur and that's a very interesting equation here in its own right it's a topological field theory so it can be used to measure the topology of manifolds and it's something that we can write the partition function for in exact form since there are not local degrees of freedom and there's a lot known about that and then what we're telling you is general relativity is is a projection of that path in the group that insists on those conditions so that easiness but so what is the physical interpretation of lagrange multiplies um the the physical interpretation is you have a path integral which is true in some sense trivial or at least exactly expressible and we want you to go into the measure of that path integral and remove some terms from the sounds and then it's no longer a topological field theory but it is a candidate for an action for generativity and one can bring in lots of tools that you wouldn't have known about to to understand fair enough but so you say it's a candidate for an action for general relativity but but you're so it is no longer something which is mathematically sort of equivalent to i mean because of because of what what what when you do that mathematical derivation from einstein hilbert to you know decomposing it in terms of these other degrees of freedom and so on where is the place where you're having to make assumptions that are essentially physical assumptions well in the classical theory it's fine i mean the assumption i didn't tell you about is that you have to to make sure you get to einstein's theory you have to assume that these frame fields and these b fields are non-degenerate otherwise they'll produce you solutions that don't have enough structure to reproduce general relativity as well as the solutions for general relativity for the quantum theory it's what does non-degenerate mean um the determinant of the these b fields are not zero and what's the physical interpretation of that um the structure is breaking down in a way that may be interesting but doesn't isn't a theory of metrics so so when they're degenerate like that you can't produce a metric from it somehow there's the volume has gone to zero or something or what what's the um the volume has gone to zero we know the output from the line and so so now you have a functional integral the functional integrals has many there are many heuristic beautiful things about functional integrals but if you really want them to be the foundation of your theory you have to show they converge and there is uh really common people show anything about path integrals i didn't think people could show very much mathematically about path integrals at the best of times yes i agree with you okay the state of the art is some formal results and then a number of numerical results which which have the natural mathematical language here is the representation theory of groups that is you can put everything that involves functionally integrating over gage fields into functionally integrating over a dual which is representations that's called the pedal vial theorem or something like that that if you have a harmonic analysis on space and connections which converges you can convert the basis where the states are functions of the connection for a basis where states are functions of polynomials basically okay so that's again that's a loop story again that's going from the from the underlying differential geometry to some kind of loop representation right which which has these wonderful among the few things that are straightforward and simple to compute are things like the operators which measure the energy the area of faces and these turn out to have computable structure so women with the area of a face would normally be like in in regi calculus or something the what is what is the physical interpretation of the area of a face so you have to define the face yeah so let's say we're going to use do we say we're talking about the hilbert space in the neighborhood of a black hole and we're going to use the horizon of the black hole as the space where as the this the thing we hold on to when we define some observables so one of the observables we can define is the area of the horizon and implement that on these hilbert spaces and it has a discrete spectrum which which we can compute with some work but so that spectrum i mean involves things like hbar and so on presumably i mean where does that where does that come into this whole i mean this is a path integral where the the weighting of the path integral is the standard quantum field theory e to the i times the action weighting type thing is that that the idea but but so actually now i'm curious i'm sorry you said you would could explain later what you think what your best ever paper about walking radiation and so on is so since you've since you've mentioned black holes we have to ask again about that what what was that paper oh the the main idea in that paper was that when people did relativity and computed the unreal factor variations of it or the hawking effect they always made the following assumption there are classical physics there are special frames of reference which are inertial frames and in quantum field theory there's special frames of reference which are minimal radiation frames yes and they assumed that they were the same and that's where all how all the results were generated that is that's how you tied the vacuum of the quantum field theory to particular asymptotic regions or researches of symmetry but that all were those all were assumptions and so i wanted to play a kind of equivalence principle game and see how much i can argue from just those as stated as assumptions as sort of trying to find an expression for uh mark's principle well it's interesting so so i mean just to recap i mean the the basic idea you know you have creation operators or something that represent the presence of you know the things that create particles and in the presence of a background you know uh comp you know curvature in the background space time the form of those creation operators changes but the assumption is that the at at infinity when you're far enough away from sort of all of the black hole stuff that's going on that those uh the the creation operators of the quantum field agree with the creation operators of the quantum field in a in a standard flat vacuum is that right and my point was that everybody just assumes that's true but we should come out and make a principle of it because the principle is that the asymptotic states that in some sense sufficiently far away from what's going on that the vacuum is the vacuum so to speak yes and and how does that so so in mark's principle i mean the the well okay so now i'm curious i mean like if you have a rotating setup or something which was the kind of the the place where what an earth happens to that idea of sufficiently far out everything is just the ordinary vacuum the rotating case is hard and doesn't follow the usual expectations okay if you remember dennis yama and um i knew dennis well yes yes yes he worried a lot about things like this but okay so so your result was your idea was have it be a principle that that quantum fields sufficient what was the ideas quantum field sufficiently far away from curvature or something will always will actually be the ordinary quantum field so what what what was the analog of the equivalence principle um and it's embarrassing that you remember your own paper that learned your own best paper but what was it something like that you could always uh that by i mean because the equivalence principle would say you can always substitute with acceleration and so on you know you could always you could always put put a different gravitational field there and maybe you would have a principle that would say you can get sort of an arbitrary deformation of the quantum field with a gravitational field is that is that yeah but that's not the way i see it the way i stated it was there are two techniques to locate some preferred frames or preferred states of motion one of them is where we measure accelerations we follow galileo in his ship in venice and we look at the birds flying and the bees rushing around and we figure out what the inertial flame is wait a minute i don't know that story about galileo what is that story oh it sounds like a story that's in his two new sciences he's a beautiful beautiful paragraph about in which he introduces the principle of inertia and does it right and does it very beautifully but and it talks about gondolas in venice or something or well being in a ship and going below decks so that you couldn't see oh how the ship was moving okay so that's where galilean invariants came from i didn't know that i didn't know that it's a beautiful it's a beautiful passage and so um and i said there's another way to find the preferred set of frames which is look measure the energy produced by by your frame um like particle production like how much particle production there is and the principle was that these two frames should coincide to leading order because the equivalent principle is a leaving order statement so women so you're saying that's an interesting idea so you're saying look at the particle content instead of saying i've got an accelerating frame it's got a weird particle content say use the particle content as the way to decide it's inertial or something like inertial if there is no particle content in it is that the yes but then the the the idea is that we say oh wow they are the same frames not to the curvature effects and that was the principle that they should do the same thing that's interesting okay the i yeah that sounds like an intuitively useful principle but but um uh okay yeah so let's go should we should i finish the on this story yes please please the loop quantum gravity story because that's the yeah right so the little quantum gravity story um let me just edit to my eyes a little bit my sense is that there's a lot of it which is very elegant which presents an interesting picture of how we might think about quantum space and time um there's a toolkit which is rather wonderful and one of the things that i endlessly don't understand is why i mean there are lots of people who go around saying loop on gravity is inadequate and that's fine and we should make another theory but they should steal our toolkit we have a great tool yeah i think i think several people working on our project are trying to do exactly that so that's the that's that's all but my sense is that and i have friends who get very angry at me when i say this but i think i think actually something is basically what i think of string theory where i think of dynamical triangulations what i think of causal sets these different approaches they have beautiful features which explain why some people are enthusiastic about them and they have persistent problems which no matter what you do you don't get by and which are worrying so i think unfortunately none of the things on the table are plausible plausible to me candidates for the quantum theory of gravity they may be plausible for describing some limits or some corners and regimes but we don't have the whole thing yet no the thing that i found exciting is i you know i've only known kind of a lay person's knowledge of all these different different approaches to quantum gravity right and so you know in our efforts to pursue sort of our lower level machine code kind of thing i had no expectation that it would connect with any of these existing areas what turns out to be the case is it seems to connect with all of them well i can say more accurately causal set theory definitely causes dynamical triangulations definitely loop quantum gravity don't know yet that would be you know i think it will be the case spin networks almost certainly string theory not so clear but probably but you know what what seems to happen is that you know in something like causal sets it's like you know the original causal set theory is just throw down a bunch of events in random places what we have is sort of an algorithmic way to generate where those events should be and that's that means that you can use all the technology of causal set theory which says given that you have a distribution of events here's what happens but now we have a way to explain why the events should be that way and i i would sort of suspect that the same kind of you know connection would exist with luke chrono gravity except i certainly don't understand look quantum gravity well enough to be able to see that but but that's um uh you know and that's i think it's a you know i i certainly didn't see this particular direction emerging of you know there's all this technology that's been produced and by the way what seems to be the case i'm again my currently perhaps naive point of view the machine code that we have seems to connect to all of these approaches that is it's not saying oh causal sets was right dynamical triangulations was wrong spin networks was whatever it seems to be that all of them end up being you know different descriptions different degrees of freedom so to speak um and you know unable to describe what you know is ultimately the same kind of thing so i you know which is kind of neat because it could have been the case that you know some group of people were just off working on something that just made absolutely no sense and you know had no foundation but i don't think that's the case it sounds like you have the same prejudice i have the same belief and what i also think is an opportunity once we see things that way is that we can understand what are the limits where the string theory begins to talk to us and what are the limits where these other areas being determined and first of all that suggests a lot of physics to think about second of all you realize there are some limits that are unexplored and so there's work to do which is organized by that right well i i certainly have some ideas about that but but i'm curious in in when you look at loop chronogravity if you were going to say i mean like like for us for for the models that we have there is a somewhat definite way one could imagine making a sort of space-time microscope a gravitational microscope so to speak where one can you know like in fluid dynamics usually we're looking at you know continuum fluids but there are experiments we can do where we can see the molecular dynamics so similarly you know we can sort of have we have ideas at least about what kinds of experiments you might do that would see through to the molecular dynamics of space-time so to speak and i'm curious in loop quantum gravity are there what would be the type of thing that you would expect to see where you know i mean okay at some level yeah i mean if like for example for a fluid uh you know one might have okay so so an analogy might be you know kamagarov's theory of of turbulence where things are everything is represented in terms of eddies and you have this whole cascade of eddies going down to small scales and so on should one think of is there a situation a very kind of bizarre naive question perhaps but you know in i've always wondered is there an analogy to turbulence and gravity yes and if you if you think about it in terms of you know you it sounds like you're thinking about things almost in terms of eddies do you have intuition about that that's that's really good questions i don't have much intuition um mostly because i don't know much about fluid dynamics of turbulence but yeah there is there's a lot that's interesting about that and i but i i i i also don't think it's hard to see what what the quantum gravity needs so may i just say it's just a few things what are the persistent issues we have one of them is if you think about it almost everything we know is at the limit of small g h bar let's keep c fixed so g h probably gives the planck area which is why we have all these areas and volumes which we can measure at the point scale so we control quantities that are in units of pr powers of g h bar but g over h rather h bar over g is where the energy lies so in other words by by looking only at quantities in gh bar we can talk about geometry but we can't talk about dynamics there's no place to write a hamiltonian which comes out in the units of gh barton naive question because i don't know the dimensions of g properly what what are the dimensions of g h bar is there a length or something is it a length squared okay so so that's a that's a plank area-like thing yes but we don't really have an an as a nice statement for the energy of what we imagine is that dynamics consists of local moves on those triangulations on those discrete structures and we know a lot about some asymptotic forms of those local moves so we can write partition functions and dominant contributions partition functions and so forth but we can't really honestly talk about energy as something which is happening in the theory so i think that's a huge issue well so just just to understand the um i mean in in in traditional i mean is is the theory initially a theory of pure gravity there's no matter in the in the theory originally is that correct that doesn't i prefer to have matter all the time but that's okay so so usually energy i mean obviously you know the energy momentum tensor has a contribution from mata fields it has a contribution from gravitational fields usually is when you say there isn't energy in the theory is that i mean usually you can you can at least say that there's a bunch of the of t new that comes from the gravitational field is that not something that can be done in this case not easily i see there are a few special cases where energies end up related to areas for example if you're in a frame of reference of an observer held just above the horizon of a black hole then you're you see in action a hamiltonian which has a term in the area of that horizon and that's been used by eugene and bianchi and alexandra perez and just a few other people but mostly let me just listen to mostly their the technologies that i think we want are have to do with computing energy and it's how energy evolves dynamically so i think we've got a corner of something we've neglected things in powers of h bar ovg related to that classical generality has a positive energy theorem and that's very important for the physics of gravity and it's not of the form of the integral of something positive over manifold the energy is very implicit in general activity and but we have no access to that quantum mechanically we don't have to my knowledge we don't have a way of stating a positive energy so you know it might be helpful in in our kind of theory right the you know you've got these hypographs that represent the structure of space and they have this uh evolution that's based on rewriting hypergraphs and so on in our models one of the surprises is that energy is very there's a very simple interpretation of energy if you look at the causal graph of the um you know of update events in this hydrograph and you look at the causal edges in that in that causal graph then energy is simply the flux of causal edges through space like hypersurfaces the interpretation of that is effectively it is it's roughly measuring the amount of activity in this network so i would be curious i mean in in what you're describing so so just to understand the dynamics i mean you have these essentially discrete loops but your dynamics is is what is the dynamics well is is there an interpretation of it in terms of of some kind of discrete process or is it just you're saying this is the partition function this is the path integral or whatever and and then it's traditional kind of you know doing a path integral type thing no so here's what we know about the path interval um imagine that we describe everything in terms of four-dimensional triangulations so that means that we have a lot of four simplicities around tied together in different ways going up a four-dimensional volume so this is like graduate calculus or like something like that yes yes and um and the boundaries of these four syntheses are three-dimensional geometries and they are typically triangulated by tetrahedra and we do a pack integral over all the ways to connect these things up plus the areas of the surfaces and um and that's and and that's all from the geometry side but i mean but that kind of thing like networks and things like that that is a that's a you know that's a a kind of a a way of giving a measure on this space of possible configurations that's not as such a dynamics i mean like like in our kind of models there's a definite dynamics it's just time evolves and something happens at every step in time yeah so now that i didn't tell you i know so the dynamics for a particular dynamics is push forward that quantum geometry dimensional geometry by putting four simplices down at places wherever you like because we're going to do a path integral so we're going to sum over all the ways to build a four-dimensional manifold by putting four simplices down and labeling when you have this a spatial space like tetrahedra they attach to other space like tetrahedra and be careful about the not changing locally the signature and each time you add a force implies you multiply by a certain factor which i can tell you what it is um there's the 10 j symbol which represents an integer 10 j i know about 9 j i don't know about 10 j okay so the 10 j i think i can get this right maybe i mean the 9j but we'll see we have um a tetra we have a fourth simplex a four syntax has five tetrahedron in it ten surfaces 10 dual surfaces and that should add up to [Music] the the degrees i'm starting to fade because the way the ten that i'm interested in are the ten dual faces which give the edges of the duals the dual triangle okay and we pile these up and we're going to sum over the values of the lengths of the dual triangulation and the volumes using the this we also have an operator at the vertices where five tetrahedra come together which measures space-time volume so one thing i'm curious about i just to understand the sort of intellectual landscape so there are spin networks there's the thing you're describing so i mean spin networks grow out of quantum mechanics and grow out of the theory of combining mensa and so on what you're describing is is you know how do you see the analogy between what you're talking about and the spin network idea well so the split network idea the three-dimensional states are described by spin networks su 2 skin networks and the that is that sound sums you over all different geometries assuming certain things about the topology which are stuck together when we put in the four symphyses we are putting in eigenstates of the lorenzian geometry and the representations there are actually the representations of sl2c and so there are these infinite dimensional representations and so what we're summing over in some sense we're holding the su-2 spins on the boundaries fixed and we're summing over the sl2c spins that meet the boundary and we have a particular condition which relates the representations of su-2 to the representations of sltc and so naively wait a minute i mean naively the because there are i mean you can index representations of the rotation group by just discrete indices the j's and so on for for you know in the punk array group right there's there's momentum p which is which is not quantized in the same way and not bounded there's not quantized in the same way is what you're saying that there's a continuous degree of freedom associated there's some other continuous degree of freedom that is not some discrete you know group uh you know thing that's like a like a uh you know compact lead group representation thing is that that kind of the idea yes exactly so let me say this because i've only recently really understood this because i was going somewhere else when all my friends were doing this but sl2c is not a compact group it's lorenz group and the physics if we want it to be lorenz invariant we have to respect this structure and when we're building four symphyses using representations the same way that we build a spin network using representations and give that the dual geometry so a four valence node and a spin network is dual to a tetrahedron and so forth if we want to represent space-time we need to have physics florence and variant and we therefore need the unitary representations of lorenz group which are infinite dimensional and they're labeled by by continuous by real numbers or conflicts which are essentially momentum yes is that right yes yes but there's a long way in that and then essentially and then let me here's something that i find very beautiful in both the cases um the i said that if you leave off the cons the certain constraints you've got a topological field there in both the euclidean and lorenzi case and i argue that if we're going to impose these constraints that change you from the topological field theory into general relativity the place to impose them is the measure and the path integral the measure of summing over all these pins so i the functions i put in there are functions that if you sum over everything because of the recursion relations of 10 j and 6j symbols the recursion relations just show you that there's no dependence on anything apart from the boundaries okay so what the theory asks you to do to make general relativity a theory with local degrees of freedom is not touch anything but the representation summed over in the euclidean phase the representations are labeled by j left and j wright and you sum over all of them with no relation between them that's like saying that the theory breaks down totally into a left-handed bunch of your right hand a bunch of sounds baron crane said if you add the condition that you're only going to choose the representations so that j left is equal to j right that's general relativity and then you have to make an argument in the lorenzian case the the corresponding statement is a little bit more interesting so let me say where it comes from and then say how it's projected and then i that would probably be enough so in um in sort of thinking about quantum gravity um we think a lot about boosts and areas because boost scenarios together define these chiral subgroups of the lorenz group basically the left-handed fields are those where you're boosting as you're making a left-handed rotation and the anti-self blue ones are the ones where you make a right-handed rotation while you boost and so those are those each defined representations now what we want you to do is choose a representation such that there's a relationship between the left-handed the left-handed representation the right-handed representation that reflects in a simple way and it is several lines of algebra but reflects the fact that we're summing either over the left chiral rotations or the right kind of rotations but nothing else notice out of the possible members of the lorenz group one can sum over we're restricting ourselves to those right and now let me show you and that we claimed is general relativity and now let me say something very cute and then i'll shut up because it's apparently saturation for many of us um assuming for me when you say that the left-handed constraint tells you that there's a certain amount of boost say in the z-direction which is related to a certain amount of rotation you really have picked up canadian sorry excuse me zed is a yes go ahead i'm around the right axis so you take the z-axis and you're interested in representations where it's constant how much you boost when how much you rotate but it's not hard when you so we want to impose that as a constraint and let me just do a little interpretation um the rotation is related to the spatial su2 and this is their representations are associated to areas so we really have an operator here that says there's an area you're on some surface in spacetime and we're measuring an area and the area is proportional to a boost now there's a constant of proportionality that i forgot to tell you about that we snuck in there which is called the emergency parameter so let's just sneak it in there so the area is related to this parameter times a certain amount of boost but the boost is a boost in energy so what that really is is a boost what we really mean by a boost is boost a hamiltonian which generates boost so we're saying a measurement of the area over here is like measuring the boost energy with some parameters and setting them equal to each other at least in the expectation value but the boost energy if we think of the under effect the boost hamiltonian is related to the acceleration times the regular hamiltonian and when you work all that out and i'm now cutting some corners you have a statement of the first law of thermodynamics that is if you assign entropy to the area that you defined here yeah i get it and energy boosts energy crossing the horizon with some parameters put in here this geometrical statement becomes the first law of thermodynamics by the first law as an energy conservation yes yes but so so you're saying that okay so in your interpretation energy you're saying that the the this area there is an inex the area is essentially generated by boosts that correspond to energy that is that the the that as you look at the forward evolution of areas if you look at the space like hyper surfaces that somehow these successive states of these little micro these little elementary areas are the things that are produced by essentially these little little tiny boosts is that kind of the idea yeah so i'm saying that tds so if we use the fact that the area is related to the entropy then there's something in a change in the areas of change in the entropy yeah is related to an energy input i get the idea but i mean what you're effectively saying there if i understand correctly is you're thinking you've got these space-like surfaces which are which are sort of triangulated and then what you're saying is to generate the next space like hypersurface you are you are thinking about that as something like a a sort of an elementary boost of one of these areas is that right yes so so i mean that's that's that's quite charmingly related to i mean in in our kind of setup basically you have this hypograph and at every at every moment what's happening is pieces of that hypograph are being rewritten so it's not the same it's not represented in the same kind of way as you're talking about it's not represented in terms of loops and things it's represented i mean we usually think about it in terms of of pure uh well i i guess hyperedges i i bet there's somebody who's who's uh who's who's on this zoom here probably understands this much better than me but but um uh but but i mean in um uh for us you can think about kind of time evolution is the consumption of hyper edges turning into other hyperedges for you it sounds like time evolution is the turning of one elementary area into another elementary areas is that right yes well that's interesting well that's interesting that's that's very uh that's that's very nice so so in your setup your your notion of the progress of time is i mean because usually in path integrals and usually in sort of space-time formulations of things time doesn't have a particularly special status um in in your setup does time end up having a pretty special status or it's some i let me confess and separate two things i've been giving a schematic of how loop quantum gravity could recover known physics and basically the name of what i was doing is there's a beautiful paper in 1995 by ted jacobson where he relates the laws of thermodynamics to the einstein equations and i'm claiming that observation is built into the geometry that we learned was in the interesting evolution law in sort of these spins from states and that generates a certain attitude towards time and so forth and i'm happy to talk about that but i should put a warning that my own views on time have run much ahead of that and are more radical and maybe maybe we should talk about that for a few minutes because just uh since i mean i i have very definite views of time that have kind of emerged from my adventures and i don't know whether um i mean you know in in um for me kind of the primary thing about time is this kind of inexorable process of computation that is sort of an irreducible process and that is kind of the the the the measure of something having been achieved by the progress of time and i'm curious what what what do you think you know how do you think about time what what what do you think time is so to speak well so this is remarkable it's almost it's somewhat the same thing but without the words about computation but maybe if you force us to the wall we'll we'll admit to thinking about computation so this is the two people i've worked most with this are marina cortez and kelly verde and the picture is that the world is in always in process of being built we're not interested in what exists we're interested in what happens and what happens we see in an ontology of events and what an event is so the only observers we are interested in is observers inside the universe we're not just in external observers and our ex for us an observer is an event or some generalized event and what is an event an event is a place where a number of quanta coming from the past or even define that as where they come from as the past needing and making a decision about sending some quanta onward to the future yes and what what we call those things token event graphs that's our that's our name for that that um uh yes beautiful and our and when we think about how those processes happen um some things which are originally indefinite become definite in the process of an event for example um if an event and this is part well let me just say if i am a guiding event or i am an event here and i want to think about an event in the future that is the state of possible children or grandchildren of mine then i use hilbert space in quantum states because the future is indefinite if i'm describing my past i just use an ordinary description because we know what the past was you need to be introduced to multi-way systems they are a very beautiful way to think about the kinds of things you're talking about and they make it a lot less okay but but but now i want to hear about your way of thinking about it yes well so interestingly enough this evolved over a long set of conversations with talia verde and one of the things we discovered is that if you dig enough into the history of quantum mechanics a lot of people are saying that well schroninger heisenberg freeman dyson most eloquently a number of other interesting people are saying this bragg brad says the futurist quantum in the past is classical and heisenberg says the quantum description the hilbert's faith that's that's different that that's not i mean the that way of describing things is not similar to things that we've described at least not so far as i can see but i but i'm curious i mean in in okay i'm i'm skeptical about that being the right way to think about it but but but let's but but but so your concept is that i mean for us we can make these these graphs that have you know we've got events going on they consume certain inputs they generate certain outputs and i don't know what well okay so so if we think about that kind of graph which it sounds like you're also thinking about what is the difference between that graph i mean that graph seems like it's essentially a time symmetrical thing what's the um uh you know where does the where does the kind of difference between past and future come in in that kind of interpretation um the it's it's subtle oh and sometimes i get confused about it but because i've tried to think about the past the one that would be symmetric in past and future but let me put it aside because i i haven't made that work the way i would want it to so in the asymmetry let me maybe make a comment about that because you know that's the old story of the second or thermodynamics basically is is how do you you know how do you deal with the fact that and what i've come to understand i mean i finally understood that sometime in the 1990s i thought about it for ages the you know the key thing about what is a plausible observer you know the main thing you have to do to explain the difference between past and future in thermodynamics is to understand that you can't set up some initial state that is a bizarrely constructed thing so that it will show anti-thermodynamic behavior such an initial state is not realistically constructable similarly for the observer the observer isn't a maxwell's demon-like thing that is noticing all these micro details of molecules the observer is just noticing certain kinds of coarse aspects of the of the structure and i think you know the thing that that um uh you know i've kind of understood is that when you think about the process of evolution as a computation this business about what observers have to do they have to outrun the computation in the system itself so they have to essentially do very sophisticated computations to be able to set up that correct initial condition and if you assume that the observer is computationally bounded that's not something they can do and that's why you observe thermodynamic behavior and so on so i'm curious when you made a statement that you think of events as being like observers i don't think of that i think of observers as being things that make equivalence classes of events that coarsely make equivalence classes of events and that the individual events themselves are way below the level of something that an observer is sensitive to so i'm curious if you have a different point of view about that i thought no not today not to know um what what we've been struggling with is something like so so let me back up if we if we have a causal structure we have an event in the causal structure it has a causal past yep and the recent cause of past can be represented as related to things which are true at the event so i think of an event just the mathematical formalism i like to use now is a two-sphere with some punctures and the punctures are where a live like quanta arrived at the celestial sphere you need to draw some causal graphs yes okay fair enough you've basically got a graph and you're you're thinking of representing that graph in terms of sort of an embedding of that graph in which there's a two-sphere around every node of the graph and you're looking at where the where the graph edge is pokes through the two sphere yeah right and the the job of so first of all i want to say that that quote what's real because like john bell i want to say what's real what's real is the information about its past that every observer has that every event sorry has it it has some unambiguous knowledge represented by punctures and labels on the two sphere about its recent past and i want to say that those those are real so i find that very bizarre for several reasons okay so so you know in my way of thinking about things and i suspect also in your way of thinking about things in terms of these you know the loop quantum gravity approach what's in a sense real is just the connectivity graph the embedding of that graph and saying you know what lat long of the two sphere this particular edge is going through is not something that i would expect to be a you know i would expect to be that that to be some kind of gauge choicey type thing not a um not something that is any real feature of the physics of what's going on but are you saying that the actual geometry the latitude longitude you know saying this causal edge went through at you know 30 degrees north 16 degrees west or something that that matters in what's going on it's a representation okay but does it does it yeah i mean there may be a concrete representation like when i do a graph you know when i draw a graph i generate a graph in you know wolfram language and it renders in in some notebooks somewhere and it's going to render in a particular form with particular you know with the nodes laid out in particular places but i don't imagine that that layout beyond being useful for me as a human understanding what what's going on in that graph i don't imagine that layout to be significant but okay so you but you're saying you you are you are caring about that graph embedding you it matters to you what the actual what the actual layout of the edges is yes okay and i am i'm positing that's what's real is for all the events the collection of those two spheres with labels on them and that i call the the views of every event has a view so so for me it would be for us it would be there's an event it has a past light cone that past light cone is a big chunk of causal graph which is you know a chunk of causal graph that is defined by a graph basically that's just a piece of graph we don't say what the embedding of that graph is we just know that that graph has certain connectivity but you're saying in addition to the graph structure you say there's also an embedding that you care about and embedding in in three plus one dimensional space time i don't care about in them okay i've been i've said something honestly i don't care about the embedding okay fair enough so so so you are really so you're saying the the past history of this event is defined and i would certainly agree with this is defined by the causal graph by the by the past like cone by the causal graph that lives in that past light cone yes okay and every event has to make a decision which is to make a partition of the energy that's been given it and sends some quanta forward at some particular angles with some distribution of the energy and momentum that's been given it i understand it's like a scattering event it's kind of like in particle physics it would be a scattering event of um um right yeah i mean i think in in our models it isn't as complicated as that in our models there isn't a serious scattering amplitude in our models what we say is that that there are certain set of events that can happen and all of them happen and so and all of them happen in different branches of this multi-way graph and they correspond to different possible histories of the universe and and so in other words rather than saying of a given event let's look at the micro probabilities for that individual event we're saying where you're saying look at each event and as i understand it you're saying look at each event and for that particular event it has a certain scattering amplitude and that event has certain probabilities of putting quanta out in these directions in those directions and so what what we're saying is so that so in a sense that will be kind of like a mean field theory of what we're talking about because what we're talking about is to say there are certain events that are possible we will essentially generate out this multi-way graph as we call it of all possible such configurations of events and we could we could represent that at least approximately by saying each event has certain probabilities but what we're actually saying is we're looking at all possible this really giant computational structure that is the the sequence of all possible sequences of events so to speak um but but okay so i so what what you're saying is you're you're looking it's a sort of probabilistic theory where at each event at each elementary event there is the and you're representing your representation of the world is in terms of these quanta that's actually surprisingly close to what we're talking about because for us every causal edge represents a certain the the flux of a causal edge through a space-like surface represents one unit of elementary energy so in fact in that sense for us causal edges are energy i mean which i think is the same as what you're saying i mean so for i mean i think for you perhaps for for us the the flux of a causal edge is a flux of energy um whereas i think you're saying perhaps uh maybe you're saying the same thing because you're saying that that at one of your events you have do you have some energy conservation principle at the events yes okay so that that's i mean for us it's a little bit more complicated because what we're saying is that the flux of causal edges through a space like hyper surface represents energy but knowing what the density of that what you know for a flux you have to have a density you have to have some kind of area measure and that's a slightly complicated thing to work out and that requires kind of thinking about generality and so on but but okay so so so then okay so in that model you have essentially a boltzmann-like molecular chaos story about what's past and what's future that is so so what i was saying about the preparation of the initial state is important if you could prepare an initial st i mean how do you imagine that the initial states are being prepared i don't imagine that's that's very interesting okay fair enough i mean so but but your model should have a boltzmann equation basically your model should have an equilibrium configuration like if if what you have is quanta coming in quanta going out that's just like you know that's just like the standard setup for the boltzmann equation what's that it's a gas yeah right right but and by the way it's not self-evident that the gas limit would work i mean that's something you'd have to establish right i mean it could be you know does it matter because the whole assumption of a gas is that the the outgoing quanta as you're calling them are uncorrelated i mean that's the that's essentially the um and if the thing is actually a liquid or a solid that's not true i mean that that's not a good approximation so why do you think i mean that's an interesting question why do you think that space-time viewed in this way is more like a gas than a liquid and is it the case perhaps that in some extreme situations of high curvature and so on that in your picture it wouldn't be the right thing to think about it as a gas rather than a liquid yes and what's happening here is that we've gone into the part of the theory that's not completely developed and not published so my answers are getting bigger what's that my answers are getting better that that's fair yeah right no i mean i'm but but to me i mean it is interesting that the intuition that you seem to have i mean i i i think your intuition is fairly similar to what we're talking about except that our model is simpler much simpler i mean it is similar in conception but considerably more complicated in in actually working out its consequences although the good news is that because we can leverage all this technology that's been built in causal sets in higher category theory et cetera et cetera we've actually made really good progress in untangling what the consequences actually are which is which is kind of nice yes that is can i tell you the one trick that we found which might be worth something for you so you know the causal set program has a problem showing the emergence of a classical space time to in wishes and beds in which its history is in bed yeah i think i think jonathan gorad who's been working on our project wrote this paper about algorithmic causal sets which i think the causal set people feel is a is a pretty big step forward in untangling that issue so i suspect you you may have a similar way of untangling that issue we have a very easy way to untangle that issue which i'm surprised other people haven't noticed so there's another theorem and notice here says if you have a uniform direction in space there's a corresponding conservation law but there's an inverse notice here and it goes something like this if you have a dynamics of momenta so everything i've been saying is there isn't a physical an embedding in space but they these objects are carrying definite units of energy and momentum so there's a combinatorial framework on which you've pasted there's no embedding in space-time but you've pasted copies of momentum space at the different events and you have ways of transferring energy and momentum among the different events and you enforce the conservation line now here's a little trick a conservation is going to be a delta function in your partition function it will be a delta function of the conservation law and you can write that as introduce a lagrange multiplier and z and let's write that as the integral over z of e to the i z dot the conservation law that gets all these zeds into your path interval and these zeds live in the inverse of momentum space and basically you can show that if you can solve all those conservation laws then each conservation law is like a little piece of a mentoski space-time with a few events on it and if you can solve all of the equations that's generated then basically you tie yourself together those little fragments tie into a minkowski space in the same dimension of your human space so it's a it's a kind of simple way to make sure that you generate a big minkowski in space from this is basically the inverse of medicine yeah i understand i mean but what you're saying is i mean usually when people do in causal sets they do you know poissonian sprinkling of events and what you're saying i think there is that there is by by there's some kind of phase fluid of events and there is some that some kind of some kind of conservation or about the phase fluid of events forces a makovskiyan structure is that that kind of the and you can see it in our papers it's quite explicit that's nice that's nice i mean that so so essentially what you're saying is that corners of the poisson sprinkling should not be reached because in fact there's essentially a phase fluid of events that just wouldn't wouldn't be able to extend in that direction yes there oh it's interesting stuff we are probably running out of time which is a shame because this has been um a lot of a lot of interesting things discussed i i'm i i am curious to ask one one question about kind of the the structure of science okay which is the whole you know you've been you were involved in the founding of the perimeter institute is that right or you you were were you its first director or no that was close what was the i just don't know the the history and i you know it's um what caused the perimeter institute to exist i mean was it was it in was a large part of it related to science that you've done or was it was it did it have some independent reason to the story is steven the story is really interesting um and it's it's not what you would expect what caused permanent institute to be done is michael lazaridis having invented the blackberry and finding himself very very wealthy compared to anything that he could understand decided to become a supporter of science he was a he was a drop out of engineering school and so our founding story is that and he was one of two individuals who were essential the other one was just finishing a phd in theoretical physics and deciding this was howard burton decided that he wanted to leave academic science and so he sent cvs to a number of places including research in motion saying give me something interesting to do i know i could go work on wall street or bay street and make a good living but can you give me something interesting to do that uses what i know and picked up the phone and called him and said with we're happy to interview you with research in motion but if you're really crazy meet me tonight at dinner at such and such a dino and i've got something to show you and mike unfolded his vision of making a scientific institution and you have to understand neither knew what they were doing howard at least is about to get a phd but he's never run anything who is this person who is the second howard burton you've never heard of him nobody's ever heard of him and but for some reason he was exactly the right person so as they talked mike offers him the job of basically the first director and which is insane and you can appreciate how i think it's great it's some yeah okay and howard said i have to think about it mike said take the weekend to think about it because if you say yes this is the last free weekend you'll have in several years and how well this was in toronto howard went to there's a boardwalk called the beaches the next day and thought for a few hours and sat down and wrote mike an email which was the conception of the institute the scientific focus the organization even the name the strategy to make this et cetera it was like in a 10-page email and somehow howard was exactly the right person what was his phd about what was howard's ph.d about it who who had he worked with um paul broadman who is who's at the university of wyoming okay so okay so he was interested in quantum gravity so did he was he an enthusiast of your work or was he did he have a particular sort of direction of quantum gravity that he was interested in no well yes and no his he for somehow and i don't know how why he was so smart but one of the principles that he enunciated at the beginning is one of friendly competition if you're going to go into it's not worth going to any area it's not capable of giving rise to a breakthrough if you go into an area where you're going to try and make a breakthrough you hire a number of people on different sides of the controversies and issues and you make sure that everybody feels simultaneously paid attention to and supported and completely insecure because there was no there's no mandate that says that there's going to be quantum gravity at a certain time period everything is on the table everything has to be demonstrated we don't have any fake parameters here by progress we mean real progress by grateful real breakthrough and so that's why we have stream theorists and partner information people looking at quantum gravity and us none of us would come from the blue planet gravity world still work completely in it and so forth um and the idea was to set up a sort of camp of friendly opposition so what was the i mean so you know mike who i i've never met we've exchanged an email but i've never met him so so i mean you know he's running business he's run a business for a long time and i know a little bit about running businesses too and you know there's certain kinds of things one thinks about like what are the objectives you know what what do we how do we figure out you know what what project are we trying to achieve so when when premature institute was set up was there some similar kind of there is an objective this is what the objective is or was it more we're just going to make this melting pot where there are different scientists doing different things i think that mike was he was always he had several objectives one is which he did not directly impose but he it was imposed in some of the first hiring and so we had for better worse an advisory committee and this was that there is a breakthrough to be made in quantum foundations in quantum mechanics that will lead to new technology this was always his mantra he would say it doesn't justify it we just want to do the pure science but as a businessman and somebody who thinks about the future of industry in canada we need we don't have enough innovation we need a breakthrough which is native here but quantum gravity wouldn't be i mean for me it's like it's a few hundred years to go from i would have thought actually i i now realize that i'm wrong about that but i had thought you know from quantum gravity to technology is a few hundred years not a few you know not a few years so to speak what was what was my experience you don't want a few years if it's a few years thing then industry can support it itself because you can make it you can justify an investment in it so mike wanted to say what are the furthest deepest problems and let's get the best people and give them everything they need to focus on so that so his but so his original concept was and it's been quite i think from what my impression i've never visited perimeter i've never had the never been in the right place at the right time so to speak but my impression is that as a kind of piece of regional development so to speak it's been pretty successful i mean in terms of of defining a you know of economic development um and and so on but but so that was part of the plan from the beginning so to speak it wasn't kind of let's just go and do this thing that is sort of uh you know reaching for the stars so to speak of of uh figuring out a quantum theory of gravity it was it was more let's do something that will bring technology and innovation to canada is that is that right green is a funny word he wanted to shame the politicians okay because he says they he didn't like the base support for basic science in canada yes did that work you know it put us in a very difficult position for the best of reasons which is that we were so much better resourced than anybody in physics in canada that we we came under a lot of skepticism and envy especially you give the job of directing this thing to a kid who has no experience so what happened to that kid that kid must not be a kid anymore what's happened to him now well that's a sort of sad story but you'll probably well i'll be interested in your comment on it um the kid it was amazing he was smart he you know as as we opened um we had a sort of double system which very few people understood one one of them is that of course all decisions are seconded by the board and the director reports to the board and proposes which is the way that the natural way that that you would do this kind of thing i now understand that i didn't understand i learned a lot i didn't understand that then within the walls of the institute we had a very open democracy with no hierarchy and lots of stuff that was sort of a radical experiment in academic self-governance why does this remind me of hampshire college somehow was this a recreation of the idol and i was the one who was very interested in structure like i went to oxford and cambridge and i talked to the old guys who knew what the rules really were because you know all these places are self-governing and they function on constitutions that are 500 years old and like you mean the oxford and cambridge college isn't there yes do they actually have constitutions i didn't know they had them king's college for example has the constitution oh how interesting and um so we ran by consensus for a few years but there was this secret which is that in the end howard it was howard's judgment now that went there was an advisory committee that went to the advisory committee on the board now howard was smart enough to figure out that after only a year or two that he was smart enough to actually hire good academics because people are really simple-minded that is we had all these fancy advisories for many people and they would sit there at our great extent expense and say what you really want to do is hire very good people and at some point you figured out that that's true and what it means that that's true um so there are a lot of things that howard did well and the the a lot of good decisions were made early and it grew very fast and flourished now howard made a mistake so he and mike were very close and ate breakfast together once or twice a week and mike was not that much older than howard so it was it's it went very well and we really did develop a atmosphere of cooperation in which the different areas we tried to support each other in doing the best and we were very careful and slow about higher so we did a lot of things right and it was going well one of the issues was of course tenure mike was against tenure howard was against tenure i was against tenure um but so there were a bunch of people like probably you who quit tenured jobs to go work there well there were three of us raymond rob myers and myself and what we discovered is that you can trade tenure for being a founder because there's nothing there's no experience like that but you can also have the confidence that you know if if all failed you could go back and get another professor job if you don't have that confidence it's kind of a bad sign i don't know if i had that confidence or not or cared but it was clear to me an opportunity of a lifetime and um but it doesn't work years down the line years down the line you can't offer somebody the experience of being a founder and then tenure was always decisive so our science advisory committee pushed strongly on the board and at some point tenure was dropped was added to son that's a that's a financially complex thing oh my god no um and i look at it and i mean i'm not on the finance committee but i can add and there's the standard thing to worry about and which is you you would die i didn't think we should have tenure if we had tenure i thought we should make it very restrictive to a small proportion of the faculty because what happens is we now have 20 of our own faculty then there are some borrowed mixed etc but let's talk about the pure cases and 16 of us have tenure and there's sort of four poor gonna get tenure pretty soon and that's it and we're we're well paid and um and we're expensive and we're hard to get rid of and it's it's a it's a real issue but i don't understand the finances of that because in you know if you live long and never retire you know there is a presumably there is a fixed endowment for the for the organization and how does that work i mean in other words you would be that that seems like a very complicated thing yes and it is and let's let's come back to that let me tell you the story of what happened to howard because he made a mistake this is my point of view i mean howard is a friend of mine this is not what he says happened but this is what i observed um and it has to do with politics and i don't know how much you know about canadian politics almost nothing but go ahead it's somewhat analogous to british politics that doesn't help me much but yeah go on yeah i i can guess but please go on anyway perimeter was the project clearly something this so another thing that mike was that was explained to mike by howard and other people who got on the board is you don't just say i want to found an institute and put a hundred something million dollars in the bank account and let it run until the bank account dries out which was actually his original vision what you do is you go to governments and you say i'll put this in if you put that in and so a deal which was sort of one to one to one of federal funding provincial funding and private funding where the private funding mostly came from endowment was established and this is a thing that that people who knew enough to do it set up at the very beginning and and was an important thing and anyway we were tied to the liberal party which is sort of something well anyway it's the center left party and wasn't was in power then and the finance minister who shepherded us through became the prime minister for a few years and there was an election coming up his name was paul martin and they were going to lose and it was going to be taken over by the conservatives and so here's the story this year um mike comes to howard and says can you advise me i've got paul martin is coming to toronto he's going to announce a number of science innovation projects he wants to use our stage to do that and among that is going to be a 50 million dollar addition to our funding from the feds and in exchange for that he wants me on the platform next to him while he's making these announcements and howard says to mike don't do it because that government is going to lose and it will look like you're nailing for a misfortune to the dying ship of the liberal elections and it looks coming the whole thing looks like a desperate attempt to buy votes so mike said with his loyalty and i have loyalty in the room so he went and stood next to paul martin not a perimeter his agenda but somewhere else simultaneously howard published an ipad in the toronto newspaper saying i am the director of perimeter institute and i would like to thank paul martin for this pledge of support but this is a cheap craze and political act which is desperate given the fact that they're all about to lose yipes and as the director approved institute i can't just let this go by literally so my view is that that's when howard lost his gentleman what what did howard have a political acts to grind as well or did he just was he just i mean did he have an actual opinion between these politicians and things surely he was liberal but he was apparently already in contact with the leading people in the conservative party and he why did he think why did he think it was important to stick his neck out on this issue because he had an agreement from the liberals to give the same 50 million if he stood independent because he had a deal with the conservatives so in other words he wrote that op-ed to as as part of sort of tipping the scale against the liberals somehow yes i see so he got kind of pulled into the swirl of the politics of the whole thing yes and he thought he could feed its control sorry he thought what he thought he could keep it under control and no it was fantastic because a couple a week or so after that i'm i'm in the building his secretary calls me and says there's a gentleman so and so um in the building he came here to have a meeting with howard and he has an hour free i had met him somewhere and some something for better education and he wants to meet you for a t cell and i don't remember this guy's name but he was the mentor to the person who was about to become prime minister and he was meeting there already with howard two weeks before the election to negotiate how the conservatives would embrace the project did they in the end yes i see but that kind of but but but and so why did howard who had you know done this slightly peculiar sticking his neck out thing on behalf of those politicians did they get him ousted for some reason or what was the what was the dynamic i think well what happened is that the new prime minister came to announce his science and technology budget at perimeter after the election after he was prime minister and we had a prime minister reception and for this and howard spoke on the stage and introduced everybody and five minutes after the prime minister left the building the vice chair of the board marched howard up to his office and fired him and so what was the political i mean what was the board heavily entangled with the politic with with the country politics yeah but first of all mike felt betrayed my fellow stabbed in the back this is all my reconstruction yeah yeah right so i'm curious when when mike was i mean was mike involved with the science of perimeter or was he mostly kind of the the global vision of do something important in physics i mean was was he actually like does he understand loop control gravity and things i mean is that the level of um of involvement i mean he's he's smart he's a good engineer he used to hang around i could know and he knew enough to he knew enough to understand setting up tensions and so he set up an advisory committee which from my point of view had too much influence but they were very good people so before he hired well me i rob we were the first two of the first three hired he had spent a lot of time with chris aisha roger penrose um etc and how it had set up all these meetings so that and mike is uh he's sometimes wrong in my opinion but he's a very good judge of character so why did he pick quantum and quantum gravity and things like that why was that i mean it's not the most obvious thing for a telecom oriented engineer to to get excited about oh no it is because um first of all quantum gravity is the coolest thing but he already knew about quantum information requirement computers and um raymond was our third hire and when we hired vermont we understood that that should really be a separate institute for quantum computing and that was put at the university of waterloo we were never actually at the university of oregon we're completely independent which is very important so do you think in the end that mike has been happy i mean it's been what how long has been 20 years or something that they um has this is it you know i i it's always the thing i'm curious about when people spend some chunk of their fortune on some you know intellectual kind of thing in the end are they excited about it or are they like oh those those intellectuals went off those academics went off and did something kind of random and didn't really do much for me but what's it very proud of him and i see him for lunch or dinner every once or twice a year so we're not friends but we we keep uh let me mention the counter case because mike was a co-ceo which was one of the things that doomed perimeter remote research in motion and his co-ceo um was don back baby or something or other big yeah yeah the silly okay who was a business harvard business school graduated so forth and belcili wanted also to make an institute and it's across the street from us it's in oh well it's in political theory and social sciences and so forth i had no idea what's it called the about survey school for international relations okay and roughly speaking it's a disaster that is about silly what mike knew about leadership and how to set up something jim never understood at all and jim set up a school and there was some institutes connected with it in which they were never good they were never the best people appointed in roles of governance there was a lot of parking of canadian intellectuals who needed work um there was much closer connection with the politics of the country the subject matter some sounds like it lends itself to that i mean quantum gravity is not usually a political platform yes yes but um it just i mean they have also a beautiful building i think not quite as good as ours but you know an architectural building which like us got uh metal and i forget queens does your building have judaism domes in it by any chance or did not not manage to was quantum gravity not enough in the in the mind of the architect to end up with triangulations they played with it they played with it but it's not there's a whole history to that also um anyway what was interesting is that there have been some good students who came a handful of good students to my knowledge who came out of the silly school but it was a tremendous waste of resources and the good faculty that they managed to hire left got acrimonious and left and it's interesting it is interesting and mike never he never at least to me came and said i think you should hire x rather than why um except when it was the case of the director when it was as chair of the board it was his direct responsibility to hire a new director but so i mean is is the main thing that mike has been pleased about the fact that he's managed to bring innovation to canada or is it more the kind of you know oh we got this particular science result and you know his funding was responsible for that happening i don't know he's not you'd have to ask him i mean what he's doing now he's disconnected from us he's disconnected from research in motion and he does basically venture capital in quantum technologies i see i see but but so that's interesting so i mean in in so does is perimeter now sort of you know it's a government-funded self-sufficient kind of thing or it's or it's living off it it's it's invested its endowment and it's living off the investment wow so do they let the do they let the scientists be involved in the investment or is there some completely separate investment group that is um is figuring that stuff out i always i always think it's interesting at universities that have elaborate economics departments and finance departments and so on do they let those people mess with the endowment or not would not be good to let me mention um there is a investment chair of investment subgroup of the board of directors and they are they are no matter how esteemed our people are they are principally retired ceos and so forth of the major banks of canada so they they could they pick on you know that's interesting we should we have gone way beyond the time that we had we had said we would go so i'm i'm um but uh this is this has been quite fascinating and um uh let's keep talking and we come as soon as i can invite a visitor i've never been to perimeter it's been one of those someday so i get so your building doesn't have gd6 domes but it does have award-winning architecture of some kind yes yes and it's great we have two billions the original one in my opinion was a great building okay and that was that that's that's the the young lee who might have been an architect speaking on that in that um the first architecture um bank shields and perrault anyway come and see it and see what you all right okay sounds sounds like a good thing and um yeah well we yeah and and you should you should drop in if you're in boston sometime there i hope to be going to toronto again right yeah we'll see we'll see what happens in the world you know the funny thing for me is that because i've been a remote ceo for well now it's what 31 32 years that this um this whole everybody doing everything remotely was like okay now everybody's doing the same thing i've already been doing so i it's i felt kind of guilty um it's um uh you know in in um um uh for how little affected time all right we should we should wrap up i see a very nice comment here on our chat from david chester saying thanking you lee and describing you as the architect of reality that's a that's a good tag line that's a beautiful thing and it's very flattering and it's not true [Laughter] that's nice all right we should we should wrap up so very nice to chat and thank you very much lee great see you very soon

Channel: Wolfram

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Id: J73kNUugfP4

Length: 145min 55sec (8755 seconds)

Published: Thu Sep 30 2021