Carlo Rovelli on physics and philosophy

[Music] [Applause] thank you for joining us it's lovely to have you here thank you it's wonderful finally being back to pi after this long absence well thank you for coming and i i was struggling with ways to introduce you to our to our audience because there's so many things you know uh theoretical physicist and author and world traveler and philosopher so i decided i didn't want to introduce you i want you to tell me pretend i'm a stranger on a plane and i just sat down next to you and i buckled up and i say hey what do you do for a living ah that way i would say hi my name is carlo i was born in italy and i go around i talk with people i have ideas i try to do them what about you i talk to people like you trying to figure out what they do so it's a good thing we're sat next to each other on this plane um you didn't mention theoretical physics uh is that because uh what you consider yourself doing is more just talking to people about a variety of stuff if you have to uh uh define me what i am primarily i'm definitely a theoretical physicist and the rest of the things that i do uh part motivating part around that so so my competence if i have any it's in theoretical physics um i don't like to define myself even in front of myself so um i like to keep you know things open and when i started writing books for the large public um i there was a moment in which i was telling myself wait a minute are you just turning into a writer instead of a scientist and and then i realized that this is a meaningless question i'm just doing what i'm doing and things are connected the only meaningful question is how much how many hours i devote for one and the other that's my bill right well i ask partly because you're you're currently you have a position in london ontario at the rotman uh school of philosophy which seems at least on the surface to be a strange place for a theoretical physicist to be a uh can you explain what you're doing at a school of philosophy i talk with philosophers i love to talk with philosophers because i think it's useful for physics um i have this convention since long time i was interested in philosophy since uh i've been interested in philosophy since i was a kid i guess during when i was a student in studying physics i also continued to study philosophy and i think that the clear-cut separation is a bit artificial and it's damaging for both disciplines how so well first of all of course uh not all physics uh needs to talk with philosophy in fact most of it does not need philosophy if you have to you know solve the maxwell equations for a certain antenna you just i happily ignore philosophers for that particular problem and and a lot of physics is is just concrete specific problems um but of course there's a part of physics which is not to apply knowledge uh that we have for solving problems is to find out what is the knowledge we have at the basis and that part uh it's the kind of things that you know einstein maxwell newton or galileo boltzmann were doing or heisenberg um and that kind of activity uh traditionally were was done by people who were schooled in philosophy i mean iceland had deep knowledge of philosophy and so heisenbergen certainly newton galileo i mean he was avid reader of aristotle um because this there's a mistake in the understanding of physics and science in general science is just collecting data and writing equations that predict this data i mean that's just a little part of it the largest part of it is figuring out a set of notion concept in a concept of structure how to think about that when you go from you know the ptolemic to the copernical system you don't just collect data and and make you you rearrange the order of the world in a different way and you do the same when that's what iceland did this was maxwell fired id that heisenberg did and boltzmann and so on so the core problems in fundamental physics today like quantum gravity the problem in which i am do require the same kind of rethinking the conceptual basis of a discipline and the philosophers are very good in that not because they solve the the problem of physics i mean the relativity was found by iceland the physicist but it's a physicist was who was talking listening to what the philosophers were saying um philosophy has a capacity of critical thinking which is very deep has uh imagination could also come out with completely different ways of thinking about reality sometimes crazy we don't care about them but that's not the point sometimes very useful sometimes i think theoretical physicists come up with ideas of reality that strike me as crazy too and sometimes they do sometimes even perhaps too much crazy and they should listen to philosophers who say wait come on don't exaggerate guys are there certain open questions in physics that you think would most benefit from input from philosophers yes and they they change of course uh because physics is a process and uh and uh and right now uh the number of uh of open questions where philosophical thinking philosophical clarity is is useful some of them for instance have to do with time uh in in trying to write a quantum theory of gravity of course uh space and time change have to change because now we're looking at the quantum property of space and time and we have so many prejudices about how space should do should be and how time should be and a careful philosophical analysis of what we know i find it useful that's one of the things i'm exchanging with philosopher in touch with even in in in simple things we one very well known problem about time is that um the past is different from the future and so what's the root of this difference between past and future is that something intrinsic in time by itself or not and the answer is not just academic well yeah it is academic but the the the question is important because if we want to understand more understand how quantum gravity works we have to get clarity about these things so the nature of time is it's one the nature of the observer is another one we now are in this funny situation with quantum mechanics which is a fantastically good theory but it's formulated in terms of an observer so why do we need a do you need a guy with a phd in physics to formulate uh you know understand how the things work no i mean things work by themselves without an observer so how to make sense of that and these are questions that physicists have been struggling with and they are and they will come up with a solution i think solutions are being debated around the table um a philosopher can listen contribute and and provide perspective i was struck when i i have your book here uh reality is not what it seems about quantum gravity and we'll get more into quantum gravity but what struck me most was the book essentially begins with the ancient greeks quantum quantum gravity and loop quantum gravity are relatively new fields of physics but to explain them you went back thousands of years can you tell us what what inspired you to go so far back to bring us to the present of quantum gravity that book um reality is not what it seems it's uh it's actually the first popular book that i wrote about science and uh uh i i wrote it quite late after so many people had told me why didn't you write a book bubble a book about quantum gravity uh it was at least 20 as the people were telling me that and pushing and some publishers also come on carlo you you're right nice why don't you write the people you have these beautiful science but you're right about that um also because people are sick and tired with strength theory it just can't strengthen anymore so let's do some good quantity um but i didn't know how to do it because uh how do you tell quantum gravity to to people right i mean you have to to digest generativity you have to change quantum mechanics it's a long story so i for long i hesitated because i wanted to do physics and not waste time writing then i started considering the idea but i couldn't find the the right way and then it just it was a flash uh i had so many things to do but i couldn't organize them and i mentioned in one of the preface of my books and i don't remember which edition i was driving from from italy to france where i had moved at the time and in the middle of the night and then i said well i need to explain this concept i need to explain this concept i need to explain this concept i need to tell the reader what is a field uh is electric field it's not clear i need to tell you what exactly we mean by geometry it's not what we use it's subtle and it tells a leader that particles are not precisely particles so there's some discreteness some granularity and then i started thinking where maybe i should say when these ideas were born so the ideas needed to understand if i tell how they were born and suddenly the entire history the narration came in front of my my mind and of course i just talked about democritus right i talk about galileo i talk about faraday talking maxwell what problem they wes addressing how they come out with that particular solution and why we're using this notion now and how this notion build up changed and came all the way to the quantum gravity you know and this is evolution of the world at the time of the heart in the renaissance this idea that this is rest extends and then newton comes and says okay i got the world is a space time passes and there are some little stones that move around with forces that's the hello and then fahrenheit comes i don't know wait wait you're missing something there's a field okay and max will put order in the field and then uh eisen comes and says look the space and the time are actually mixed so you should not have two different things you should think to talk about another space time a space time and then i instantaneously later realized that the space time is a field wow occur now we connect the notion of field space time and quantum mechanics connect the notion of a particle with a field so unless you go through the the way these things developed you don't get them i think so i i decided to write a book without details but with a core flow of ideas that's how it works and when that when that epiphany hit you while driving i know what happened after that you know what happened after that i got a ticket because you were driving too fast because i was driving fast it was it was it was an empty in the night highway i was so excited so excited the first chapter is going to be seen and there's somebody here and i look at the speedometer where you don't know how you call it in english and i'm going you know 180 kilometers per hour on the highways oh no so i i i had to pull poo poo on the side and the the policeman what the hell did we do and i was you know i just told him i said i'm sorry i just was going extremely fast the reality was i was not even in a hurry uh i just uh got an idea how to write a book and was so happy with that i just didn't was excited excited and the policeman said okay good luck with your book and let me go you let you go yeah i'm dying to use that excuse someday you know oh no i was speeding because i figured out how to write a book about quantum gravity i don't think it will work for me but i'm glad it worked for you yeah it's good to know that word i have a question um a lot of what you're talking about it seems that it's very fundamental this idea of unlearning things both when you're writing books to encourage your readers to unlearn some things or even in your research i think that when we're thinking about something we can be stuck in certain ways of conceptual thinking or be making some assumptions and not even realize it are there certain strategies that you've learned perhaps from philosophers that encourage you to challenge your conceptual ways of thinking oh that's a very good question i don't know the answer um the the the the premise of your question are i think the most fundamental point about learning the difficulty of learning is not to uh to learn something new that's easy the difficulty of learning is to unlearn what we think we know we are all deeply convinced that we are right about the way we see the world everybody including myself and so um so we just don't give up easily the ideas we have and we don't learn unless we give up you wrote once that science is born from an act of humility is do you mean by humility the the idea that we can accept that we don't know everything that but even stronger the idea that what we think we know we might be wrong and so what we don't know is so much more and so large that we shouldn't rely so much on what what you know yeah i think humility there is this beautiful letter by newton newton was arrogant pretentious uh perfectly aware that he was the greatest thinker of his time three centuries later we still think he's a great thinker maybe in science of all the times he was aware of that and at the end of his life he writes this letter he says i don't know how the others are looking at me or will be looking at me but i myself look at myself like a kid playing with uh little peoples on the on the shore in front of the ocean of our ignorance and that's why he succeeded in being newton i think because he was perfectly aware that there was uh everything to be discovered and uh so he was both arrogant and humble at the same time exactly the mixture of that you can be arrogant with respect to the others you am humble with respect to your rugging your ignorance and the fact that um that we might be right we might be wrong i've been reading this summer uh because we're doing an audiobook in english uh galileo greatest book which is the dialogue of the two sis maximum sisters maximum assistant of the world um it's it's a fantastic book it's a book that convinced you humankind in fact that the earth is moving and it's this is uh spinning and it's going around the sun and uh it has all the arguments for the earth to move but reading its surprise is that the arguments are just a few pages the large part of the book is to convince the reader that it's possible to question what he um give granted it's all about look you think that but that might not right and give an example given give a thing it's only when three-quarter into the book say okay now you're open to the people i haven't argued anything i've just told you consider alternatives only at that point he brings argument for the movement of the earth which by the way are wrong i'm mistaken we know that this yes but nevertheless he convinced the world not by giving good argument in fact he isn't wrong but by showing that uh it there's nothing wrong in accepting that uh something completely obvious to you is it's not right but that was not your question your question will what's a strategy we can go into for for not being trapped in our own beliefs and i don't i don't know i think it's because we are and scientists are like everybody else right and uh more than being aware of that keep repeating to ourselves that i don't i don't know what's right for you yeah doing so do you remember a moment in your earlier life when when maybe physics or science itself sort of revealed to you this um this new way of looking or unlearning things you may have known um open your eyes to new possibilities was there a sort of a epiphany there or was it a series of of uh happening it was a series of happening starting from when i was a student uh i fell in love with science late when i was already a university student in in physics and in in studying modern physics uh it was a series of shocks like oh my god somehow reality is not what it seems that became the title of my book so it was a strong experience at that time is that a is that a phrase that you've had in your mind for a long time before the book came out that reality is not what it seems is that sort of the realization you had those years ago the concept yes for sure somebody grew with me in various manners the phrase itself i'm not sure i think it came from the text of the book and then i picked it up because i think it represented what was going on um we were talking about you mentioned quantum gravity before and there's a line in your book uh seven brief lessons on physics it's just such a simple short line there is a paradox at the heart of our understanding of the physical world um and that paradox is essentially the root of quantum gravity that paradox between general relativity and quantum mechanics can you can you elaborate a bit more on why that's a paradox what what paradox we're struggling with and why we need a solution to it yes uh i believe it is it is an apparent paradox uh but it's a strikingly paradoxical the way it looks um and uh i think the way i described that book i'm not um it's what a student of physics learns when he goes to school at the university uh and he just minimally thinks think um because you go to to classes on quantum mechanics and and you get to explanation of the world and the world is about all about discreteness i think uh you know the the light light is photons it's just discrete particles uh the the the mentally particle bits of things everything is in bits and and and and and and chunks it's probabilistic things jump from one to another um and uh and there is this strange interactive thing uh for which in quantum mechanics you predict how things interact with one another so you you say okay that's the way reality is i mean okay god did reality that i mean we don't know what she thinks so she why but that's where and then you go to the other class or this other teacher that teaches you about general relativity and this is you know equally immense fundamental successful theory and the universe is continuous it's perfectly continuous there's nothing probabilistic there is you know deterministic equations of motion everything is perfectly um objective out there you can write the history of space time in a single equation and then say wait a minute i mean either one or the other they kind of i mean my teachers stop talking to one another haven't talked to them for 30 years and they're both professor of physics with a phd in tenure um so it's really two totally different images of how reality works and you know god can be complicated i don't know but not so self-contradictory the world is either this way or the other way or some way which is compatible with both but what is the one that is compatible with both and speaking of quantum gravity as part of this show we collect questions from other listeners and a mutual friend of ours carlo lynching chen she's a postdoctoral researcher in brussels belgium she sent in a question for you oh fantastic hi carlo this is lin ching so in our quest for a theory of quantum gravity do you think we will need new fundamental principles that both quantum mechanics or general relativity have not yet revealed to us and what is your strategy for finding them out thank you that's a great question she's fantastic um and it follows immediately from what you were asking before uh the answer i have i'm not sure but that the answer on which i'm working is no no to the question uh do you think there is some fundamental principle that will be missing and i think that this the idea that oh we're missing something crucial fundamental down there is just wrong the the point is that we have to take seriously what we learn with quantum mechanics and seriously what we learn about generativity and bring them together and they do go together they just have to rearrange thing and to to understand that uh um so i i'm a very conservative guy from this perspective i don't believe we need something new by a supersymmetry with other worlds many dimension breaking allowance invariance of correction to quantum mechanics nature has been saying no to all the attempts to test this alternative hypothesis so far so i don't see any evidence that we're missing something it's just that uh generativity it's about space-time so it's the shape of space-time shape of space and the shape of time which means how different clocks move respect to one another and how meters measure geometry and that's quantum and so we have to uh understand the quantum properties of time and the quantum property of space and you know that's radical so the the assumption is conservative but if you follow up this is completely radical because it means it's a continuous space that you thought was forget about it the time evolution in a single variable forget about it you have to replace the the usual way of thinking space usually is thinking time is something consistent with quantum mechanics but not this quantum mechanic in space-time quantum mechanics of space-time so for instance you have to have a mathematics and a physical intuition that allows you for having quantum superposition of space times plural of geometries like there is a shredding a cat that can be uh both awake and sleep or somebody said that a lie and and alive i like your version better yeah i like cats yeah exactly so introducing quantum mechanics can be both awake and sleepy uh and sleeping and and so in the same sense space can have a shape and also another shape in a superposition of the two of course this requires imagination finding the right concept to talk about that that's also a philosophy comes in useful and right mathematics and i think there are i mean loop quantum gravity is an example of a theory that attempts to do that we don't know if it is right it's very conservative and that's why the answer to lychee question is is no so there's no other principle to be added but it's completely radical then because it forces us to rethink the basic notions and you mentioned evidence when you were giving this explanation looking for evidence to support various theories of quantum gravity what kind of evidence would you be looking for i think that recently there have been a lot of evidence that helps us and in science evidence is never definitive it's always indications like in life by the way um so it's not that you kill theory it's very rarely that you really really kill a theory with a with an experiment but you create problems to a theory and when you have too many problems you look somewhere else um and there have been a lot of these things recently uh the strongest and the most um unexpected for many people has been the absence of low energy supersymmetry there was a big part of the community that was completely convinced sort of 99.9 percent that subassimity was going to be detected by the large hydraulics right with lh lhc and it wasn't it was a shock there was title of the journals like you know this is a crisis of physics of course it's not the crisis of physics it's only the crisis for those who expected it right which is not physics it's just a school a particular school of thought but that's nature talking and when nature talking we should listen i think um another example it's um uh breaking a lot of loyalty environments the the symmetry at the basis of uh iceland especially which is law and samarians um some people thought this was very also that was like super simple it was a very good very nice idea you can make the proper quantum quality easier if you don't have a lawrence environment so people try to write theories which break lawrence and variance and and and might be quantum gravity theories uh so this was tested tested 10 years of 15 years now of astrophysical observations and all the expected signs of breakthrough zero so once again nature talks as far as we know nature is saying no no no guys that's not the right way to look for the solution so i think nature is giving indication i mean a lot of people expect a negative cosmological constant you know even today there is a large part of the community that continues to do calculations and calculations with the negative cosmological causes called ads cft ads means antidesister experiences a space with an effective negative cosmological concept except that the cosmological concept has been measured by the astronomers by the cosmologists in a very convincing way they got the nobel prize the ones who did that and it's positive so once again i think my interpretation my reading of that as a scientist i mean i might be wrong i know it might be wrong but my reading of that is that nature is talking listen that's not the right direction so what will nature say to you how will nature speak to you to advance loop quantum gravity say what signs are you looking for uh there are two or three directions where me and many of my colleagues are looking into um for the moment zero so we have no negative response for nature but we don't have any positive responsibility can you explain that a bit we don't know so so there's nothing that has come as a contradiction to what we expected but there is nothing that has come to uh confirm predictions of the theory either so i cannot say that the gravity is confirmed in any sense it's a tentative theory it's just out on the table and let's see so where could the confirmation could come from i see three possible direction one is early cosmology there's a lot of literature papers and papers written so the universe we know come out to the big bang the very early moment at the beginning of its life is deep into quantum gravity regime so that's where quantum gravity should play a role and uh a lot of colleagues have applied loop quantum gravity to describe what happens there it seems to be working and to see if one can predict a effect of what happened there that can be tested in the cosmic background radiation it's possible people working measurements getting more precise i hope they will convert to something useful but for the moment there's nothing that's one the second one is black holes i'm working with black holes loop contour gravity is consistent very much with the idea that a black hole evaporates that's hawking great realization the black will evaporate they become smaller smaller and then at the end they don't just disappear pop out of existence but there's a remnant uh which is a white hole so it's a there's a quantum gravity transition a jump they must jump quantum mechanics into from a black hole to a white hole with a little throat but a huge inside and then this white hole slowly things come out the information slowly come out leaves for a very long time and this so this is a scenario it's a possibility uh it might have astrophysical consequences these are being explored virus group including london the people i'm working with um is one of this possibility which i'm particularly attracted to which is that these little things that float around in the universe this ram black or remnants which are white holes are actually dark matter that's what a component of darmac if so it might be that we've already observed something we just haven't recognized it right okay dark matter being another great puzzle of modern dark matter is it's a it's a big puzzle and that's the opposite of the quantum gravity puzzle because it's not a puzzle in our understanding it's a pathway you know what we see so we we look the universe around us and we see galaxy star or clouds of hydrogen all sorts of stuff and then there is this stuff out there you're not even sure stuff i mean there's some something that produces effect out there we see the gravitational effect of these things and we have quite convincing evidence that is not usual matter it's not just atoms or molecules or protons or neutrinos or photons is something else and it's a lot it's quite as much normal matter and dark matter even more dark matter than and nobody knows what it is so it's fantastic is this you know people who say that we're close to the end of physics and close to the theory of everything come on guys we don't even know what we see around us so dark matter is really a question we have a lot of possible explanations but too many and known non confirmed non really credible i like the black hole ones because it does not rely on any new assumption you can say oh dark matter is some new kind of particle we haven't seen yet uh while if there's black holes it's just generativity right so something we know exists but i don't know it's an open fashion it's funny you said it's a mystery we don't know and that's fantastic and that you know that's not always the case in a lot of professions where the lack of knowledge about something is something you're excited about you know are you glad that physics is nowhere near being complete oh infinitely so of course of course yeah otherwise it would be boring right imagine what a disaster if we got somebody wrote okay i got it everything this is the final equation of everything but that's what you're going for no no no is it quantum gravity not sort of that grand unifying theory no it's a step on the way okay it's just figuring out what's the quantum property of space and time i mean then with so much more i'm not i'm not working for a theory of everything i'm working just for the next step in understanding what's right so what would be beyond quantum gravity and our understanding or um one once we've figured out the quantum nature of spacetime does that open up new questions or help us answer old ones um you're referring to fundamental physics right because of course there are plenty of questions if you're not fundamental physics like you know what is consciousness or how thunderstorm really works which we figure out yet but in fundamental physics um after suppose loop quantum gravity is confirmed okay i i with a colleague uh margie's custody we have an experiment which we proposed which might even be doable in 10 years or so which would actually test the discreteness of time predicted by loop quantum gravity so suppose this can be done okay and bingo the right numbers that because loop control gravity predicts that space is discrete right it's granola nothing continuous is really granular like light is made by photons spaces make this grain of space but also time uh has which is i expect it has this gradle and and uh we have an idea of perhaps with some slight advancing technology not excessive can be could be tested now suppose this come out right okay bingo loop control gravity is correct proof right numbers are there now what well now we still have a universe described by a funny standard model where the weak interaction and the strong interactions are completely separated described by similar theories but not really unified in any way um gravity described by still another theory 19 parameters of the standard model with who chose them why why three generation why um we have suppose with quantum gravity we figure out big bang and what seems likely that it was not the initial explosion was a bounce it's an idea not just studied by various people but our universe is the result of a previous one yeah so there was something some universes was collapsing in some sense under its own weight it gets to the sort of maximal compression where the quantum gravity comes in it bounces and what you see as a big bang is this bounce i think it's a reasonable hypothesis it seems to be more reasonable than a big bang but we don't know suppose we figure this out have we solved everything no of course i mean what was what the collapsing universe coming from i mean what was there yeah it's a little bit it seems today so impossibly difficult to figure out what was in the collapsing universe but you know at the time of my grand grandfather it was seemed impossible to discover what was the chemical composition of jupiter yeah i mean it was considered unsolvable problem i mean now we know in jupiter everything even you know there were ants there we would have seen that so uh science finds new problems and uh and grows at all levels and no if their mysteries is not a reason of sadness is a reason of joy because a new thing to discover uh it's a beauty of understanding you're still like isaac newton playing with pebbles on the vast sea of what we don't know absolutely and regarding this you know general idea of working in a field where you maybe don't yet have evidence for or against it it just reminds me of something you write about in your book the seven brief lessons when you're talking about einstein's theory you write about how a lot of times something very important is kind of considered useless at the time when it's developed one example you gave is that riemann's work that was generalizing gauss's explanations was considered useless at the time but it was then a fundamental piece of einstein's theory um so it seems that this is very crucial to work on things where we don't actually know exactly what the application will be or exactly how long it will be but i'm wondering if you think that physicists need to find in general some kind of a balance between working on problems where we have an idea of the time horizon for the applications versus working on these problems where we don't really know where it will lead yes obviously there is a balance to be to be searched there um i think if you look at this from uh from from the main hall of perimeter this is the same city how to find balance but if you look at it on the large scale um 99.9 of the money put into research worldwide is to practical applications um and the tendency is to to go more for practical applications and that's a disaster i think because uh of course we need practical education right we need people who study chemistry of material because we need a certain material for something like healing people and replacing bones i'm just defending um so applied science is great but to um to concentrate resources toward applied science so much as is that today i think it's a it's a disaster we need people who are uh who do the kind of pure science or fundamental science or basic science i mean all these words are emphasized all of them namely don't think about application just forget applications um because somehow our our science is built upon a number of key results obtained through the centuries if you look at each of one no one was looking for application and if he had looked for application at his own time he wouldn't have got there so it's obvious that we need to um to just ask the question what's behind things what's how can i understand better at the fundamental level um applications will come out sometimes fortunately sometimes unfortunately because sometimes applications are to kill people and to make war um so you're the organizer of a research initiative called the quantum information structure of space time and this brings together theorists experimentalists and philosophers can you tell us why you think it's so useful to bring together that group of people and what you're trying to answer through this initiative yeah uh thank you for this question a quantum information structure space time the short name is kiss kiss written with a queue but we like this um it's a big consortium with big grant um mostly used for supporting young people for stocks um a group of pi here in fact two groups of the ice are part of it and there are about dozens of groups all over the world from hong kong to to mexico to california and the aim is to bring together uh two communities or actually three communities the two communities are quantum information and quantum gravity and the idea is that uh quantum gravity people have been using quantum information notions or beginning to use in various ways and quantum information people are starting thinking about how quantum information works in space and time let me say this way and so the same problems are being addressed for a completely different perspective and the third community is philosophers because this dialogue opens fundamental questions like uh what we're saying before the direction of time the nature of what is information what we mean by information and in in quantum gravity it's a theory which is not written in space-time so in some some space-time have to be re-thought to come out on the theory in some way and these are philosophical questions so these are different communities which are being um broke together and in uh in june uh this year there will be not far from pi in london ontario so it's just a short drive from pi a conference um bringing together this and it's a conference that we have is organized a standard conference with you know speeches and a few questions why do you say that um each half day we'll have a few 10 15 minutes very short flash presentations and then a couple of hours of open discussion uh everybody with everybody in which the different opinion of being is a good chair who sort of tries to balance and and follow so um discussion comparison point of view because there are these communities quantum information quantum gravity and philosophers who look at these things uh which have different ways of viewing the same thing so we want to compare and of course learn from these differences are there frustrations that tend to come up when people with such different backgrounds and education are trying to discuss a topic with each other yeah absolutely because because you the things you you know you give for granted then person who's good scientists come to you and say you're wrong and that's frustrating and uh and then but that's great because i think that's um that's how the process of uh knowledge works and we learned from experiments but we even more learn from continuous exchange of perspective and the more we we listen to other perspectives and that's a that's a great opportunity i think because quantum information has boomed for various reasons in the last [Music] decade probably there are very good ideas there which i think are relevant for gravity on the other hand the pure quantum information are not aware that some of the things that they are struggling with have already been addressed by quantum gravity right so there is a there's really a dialogue to start here and and the philosopher are interested in both uh and have things to say about both so i hope that this dialogue and three based not just in presentation but in discussion will work and i look forward to that i'm sorry after two years of lockdown of pandemics and people staying at home uh how have you felt distinctly the the absence of in-person gatherings with other researchers and scientists getting together in the same place a little bit yes a little bit yes um it has for me this has not been dramatic because we're all on the internet we're not on zoom but being always on zoom is also painful and uh this morning finally the first day i'm back in p.i.s so long finally i was with a young colleague lamina japan in front of a blackboard the writing things that say no wait it's not this is not oh what a pleasure it was so long this didn't happen and from reading the website for this kiss initiative it seems that a major goal is to deepen the understanding of information could you just tell us what you think of information as meaning and why you think that information is so fundamental yes information is a very tricky world word because uh um the spectrum of meanings is very wide um extremely wide so it's also when when talking about information uh people often get confused because in in the debate in a dialogue people mean different things and you go from the from the most complex one i mean you have information about your father of course i know a lot about my father to the most basic one which is uh um my little card here uh contains so many megabytes of information okay obviously the two are connected somehow but the two are very different completely different about your father is something that has to do with meaning in that case without even emotions but certainly is interpreted information in some sense so it has to do um something something something that needs to be decoded that can be translated while the in in the case of the memory card just counting something is a number of countings and things i counted the number of atoms or cantinam or something um in this spectrum um i think that the what is interesting is exactly the spectrum that it goes has so many um uh possible meanings but what the most interesting is the basic one and the basic one there's a there's a very simple notion of information which is purely physical which is correlation when two two uh two things know about one another if you glue two things uh if one point one direction the other also points that direction so if you have information about one you if you know one you know the other one so one has information about that meaning that there is a correlation between the two that's a basic no transformation it's purely physical nothing mental nothing um no no meaning no significance no no no that's basic enough information and i think this natural information is fundamental not because the world is made by information it was made by staff by variable by think switcher but because the world is made by relations the properties of things are relative to something else so if you want to describe the structural world you're always talking about how one thing affects another one so how they get correlated to the other one so immediately you can quantify how much things affect one another by using the notion of information and this means not information is a increasing of the world but it's a key ingredient of our thinking about the world we're thinking about the variables and um i think quantum mechanics itself can be largely talked in this way i've been thinking this since back in the 90s when i started thinking about the notion of mechanics um and because of that i think in quantum gravity also um it could be a fundamental role to think about information systems have about one another but once we go into this way of thinking about physics not as how systems are but our system have information about that how they're correlated then it's easier to um understand as a continuity to the most complicated notion of information the one about your father or your father right so the mental is not so far away from the physical now because we start taking the physical from the right perspective from which is easier to reconstruct the more complicated notion of information meaning for instance we talk about memory traces and we build that more and more complicated so it's a very versatile rich confusing but key notion for understanding the world information because the world is made by relations not by things i i in reality is not what it seems uh there's a passage that i love i even told you about it after i read it because you you go through so much of the book explaining the historical context of quantum gravity and explaining the concepts in very easy to follow terms which i appreciate and then late in the book you say um if dear reader you have found the journey so far a little rough hold on tighter because we're now flying between voids of air and then you get into your new ideas which you said if if the ideas seem confused it's uh because the person with the confused mind is me you're yourself that's first of all that's something i don't often see in popular science books is the warning to the reader like it's okay to be shaken by this it's okay to not fully get it um so you gave this warning and then you use expressed ideas that you personally don't have a full concept of can you explain a little bit about what's what that's like going into territory that is less historically sound and more speculative and putting your putting your own ideas out on the line like that um yeah i think that um uh there is a lot about the world that is we understand and this is what we we don't understand and it doesn't make more much sense to do what we too often do in my opinion which is to pretend that we understand the part we don't understand um [Music] maybe it's just my education on my way i mean it's certainly university professors that teach lecture and physics um they shouldn't pretend that they know everything about it they don't know about it and they may be wrong i mean they will be teaching things which are wrong so they should say look this is what you understand this is what i understand and be aware that this be something wrong and if there's something confusing um it might well be because it is confusing and it might well because uh or because a person is confused or because the community is confused a good example is quantum mechanics quantum mechanics is a 100 years old spectacularly successful used in technological applications everywhere but it's still confusing and the fact is confusing may be good because it may be that we still haven't got something some right way of looking at it so let's say it's confusing not hide it and i think this makes also things easier for the student at the university or for the reader of a book who is not presented this you know smooth white clean uh piece of stone say this is it period no i mean we are humans uh science is a human activity like everything else dirt is imprecise their whole system so i think it's better to present what it is i think i i connected with the idea that you yourself are struggling with these ideas and you know some when you read a book by an expert on any subject you assume the expert knows everything and for you to say later in the book you know here's what i'm grappling with it helps i think it helps the reader understand that this is a difficult complex yeah my book my books are a little bit different uh in spirit um from most popular science books because they also are aimed as a slightly different audience and in fact i've remarked from the reactions that i i get that the typical reader of science book likes my books less and the people who like my book are at both the the two others the two extreme sides are either people who know zero about science or people who know a lot about science and and i understand the reason because i think that these two extreme categories when i'm when i'm talking about about what i do the typical science book um it's uh written for somebody who want to know more and more and more and more and more about some domain okay so you give more details you get more information say oh and we know that and we know that and we know that and we know that and uh you know there are kids nerds that really want to know more more and more about the neutrinos and all the possible details about that um i don't do that zero i i do the opposite i take away i take away i take away i strip away as much as possible trying to reduce to what seems to be the core that we have understood about something and to present it in a way that it stays together it holds on and allows the reader to understand what it is and what seems to me the the real thing we have understood and then of course this those who know nothing about science they like it because they're great i can i get to the idea and those who know a lot about science also like it because they say oh wow that's a good way of doing things maybe i didn't think this way maybe i was thinking the other way that's a new perspective on things and a lot of my best colleagues tell me ah i read your book wow i didn't i didn't think about this way of putting it great great i've learned so um we're gonna tell his name but even my greatest enemy the chief of the opposition you know band theoretical physics was a nobel prize winner sent a message to me saying fantastic the little book i loved it right so this is but the student of physics server just studied that at school reads what i'm saying it knows because wait a minute i mean you just there's all missing here i got a an email i say you talk about quantum mechanics in the same lesson you don't even mention the schrodinger equation i thought yeah that's right i don't actually show you the question but that's not the core story so um so yes and this connects to your question what you were saying before because uh to do that you need to understand something all the way through so once we have totally digested something then you can just bingo in one place down to the essence to the essence yeah right i mean take um copernicus if you read the book of copernicus you know it's 300 pages of calculations detail geometry perspective it's horrendously complicated in the eggplant and the the he has he he has the the the ap cycles still and this and this and that and to make this complicated the moon is complicated uh what is it 400 years have gone from copernicus now we have digested everything right can say two lines thirst is spinning and is moving around is orbiting around the sun that's what copernicus has clarified okay so it's totally clear it's strange if you think about we're actually moving it's revolutionary it changes everything the earth is valid like the others but it can be said in two lines once we've really understood something at the end we can say it into lines in a way that has it as it really and the people understand what it is so my ambition but we're not there would to do the same i just did with copernicus the same with you know standard models especially tv generativity quantum mechanics quantum filthy or equal to gravity yeah you said in uh one piece you wrote um sometimes dreams come true i felt there was a story about the adventure of physics that had to be told but i thought people were not interested but you were wrong you were dead wrong because a lot of people were interested you know millions of people have read your book it's translated into dozens of languages what do you what do you think you got wrong about estimating people's interest in the subject matter i don't know i didn't i was just not just me wrong the the seven with lesson physics is a was printed in uh 5 000 copies yeah at the beginning so that was the estimate of the publisher that was going to sell do you think it was because you whittled down to the essence and you left out the equations no i think no i think it's because i um [Music] mostly because of the last chapter of the seventh i think that's what made the book so it's a book that is not just about physics it's a book that tries to go down to the essence and then ask the question all right so what does it mean for us how does it um reflect on the way we see ourself we see ourself and the way we um we think about the material the physical world and our uh let me use this strong word spiritual world and i think that let me tell you my my interpretation of that it's a i and my friends and many people around me share a view of the world which is not much known by a large majority of the population and it's a view of the world that is neither um you know the world is made by little atoms bouncing with one another and that's it so you know emotions the sense of lies whatever that's that comes later is neither that is not it but it's neither um you know the material world is irrelevant there is a spiritual world with uh you know god morality and thing and that's that's what the reality is somehow a lot of people are unhappy with both because they don't believe the spiritual world too much anymore because we're in a secular society which doesn't hold anymore for a large number of people and less and less and less but neither uh people find convincing a sort of cold and ground scientism which has no hold for uh for meaning promotion for um for our aim for what we are as as thinking and and desiring and suffering so the fact that somehow uh people find in my book a perspective of the two things can very well stay together and there's no contradiction between one another is what a lot of people jumps in and say oh but then there are people who can you know think what matters for me is my emotions but also there's nothing in contradiction with fundamental science there i think that this is bringing together that make people react and regarding this goal that you have in your writing of getting to the essence of a concept i would think this would be uniquely challenging when you're talking about something like time because the average person will probably talk about time at least once in a typical day so there must be a lot that you need to strip away because the average person has a lot of assumptions that they're making about this word time can you tell us about what that process was like when you're describing time yeah i mean absolutely i i wrote a book just uniquely entirely about about time that was not a it wasn't easy to write book because exactly for the reason you um you you're asking and you're pointing to and when i decide how to write this book i exactly ask myself this question and so the the first half the longest half of the book is just one by one one chapter after chapter demolishing something we give granted for time and on on on good grounds on things we know so we think that time has this property and you know it seems obvious to that that's the way we think and now i tell you it's not the case and i'll show you why we know it's not the case so the first part of the book it's in part it's just a way of telling boltzmann theory of telling ice and special activity putting the various pieces of the story together but not just for talking about physics for talking look what this imply with respect to our notion of time special activity definitely changes our notion of time um notion of present everywhere in the universe doesn't hold but it's hard to think the world without a notion of present and we're in the universe the question what is going on right now on andromeda galaxy is meaningless there's no meaning in what is going on right now there's no now in andromeda so they're asking what is going on here in beijing i mean no we're not in beijing so they're not here in beijing eugene is elsewhere so so to the the the book was designed exactly to address what you are saying to take away one by one the suppositions of people that the people give for granted in science and as some of my colleagues which are very reflective and uh you know the written book there is absolutely nothing they learn because they have gone through that and a lot of my colleagues that teach special activity they never have stopped in thinking what actually they're teaching and i think that's wrong i mean that's physics is interesting because um you tell us something about the world not just because you write equations and then you make prediction and it matches with what you measure and are you yet at a stage where you can give this one or two sentence definition that's the core of what time is no with time it's very complicated and and the reason is exactly because we haven't got to the end of understanding it there are there are things about time which i think we're generally confused a lot of things we have figured out with total clarity like the non-existence of a present everywhere in the universe um but there are issues about um how to think about time in a fully consistent way with everything we know which i don't think we'll figure out even the direction of time is is is complicated because we have connected it to entropy to the microscopic description but there are definitely holes in our understanding in my opinion i i found um that book the order of time to be to really make my brain meld and squish in other directions i i found it i was listening to the audio book and at one point i was rushing somewhere and something you said something you wrote about time made me think why am i rushing anywhere rush is an illusion i also so i appreciated your writing of that book i also really liked benedict cumberbatch reading it to me that was a that was a nice experience uh boy it helps when these concepts are i've been listening to his voice and saying wow who wrote this wonderful thing that's too good for certainly not me he has a way of making it um comprehensible but also uh it's like it's talking to you and telling you in a like a friend it's quite wonderful yeah but we actually have another student question about your books we want to introduce that yeah we have a this question was sent in by a phd student here at perimeter this is matt duchen a student at iqcn perimeter i'm running how did you first get started into writing science books and how's that writing helped your own research do you find writing a technical paper or a more accessible book more challenging what's what's trickier a detailed scientific paper or a popular piece of science writing for a general audience probably a book for a general audience why is that because roughly you write a paper a scientific paper after you figure something out so you just get confused in a problem and uh and uh either alone or with some somebody else in physics we were mostly in little groups of two or three intermedical physics you sort of come out and some point is clear and then you write it down and you write it down what you have understood so the writing is relatively easy i'm picky i'm complicated in writing scientific articles i try to write them clear so i spend time writing and rewriting rewriting perhaps more than um what i should or could but the writing is you're you're you know what you're saying exactly while when you're writing a book you still don't know what you're saying you're picking up what you're saying in the writing itself so for me it's it's complicated and and writing for me it's a complicated process so it's not um my books are the result of a large number of revision in that large number of cancellations take away a lot because they say oh this is this is not useful for what comes and that's just um superfluous so sorry take away and then i the same phrase i rewrite it 10 times no that's not clear i mean is there a way to say it better so so it's that's that's a hard master writing for me i was just going to say for you it seems that this must be particularly challenging because you're not just writing a book for the general public as you said you're hoping that your book will be influential for the general public and also for experts in the field even though the material is not technical or maybe doesn't rely on math so i would assume writing something that can be a good fit for both of those audience this must be very challenging yes it is and i have these two readers in mind the super expert one who knows everything and and and the one who knows nothing which is good because uh thinking that the super expert one is what you know warns me for not saying something which now if i say that he's gonna complain and and and thinking about the the you know the prototypical grandmother who doesn't know anything um uh stops me from saying things oh that's too complicated i mean how can anybody get this point so i always have to um struggle so so this simplifies because you give me guidance but yes uh it's it's also complication try because i i'm i'm putting my own ideas in the books mostly because it's my own perspective of things written about quantum mechanics algoland which is entirely from perspective heisenberg born iraq rather than from the perspective of schrodinger so it's taken quantum mechanics because i think it's the most interesting thing i'm not the only one but there are people who think different you think no no no no it's all about the wave equation schrodinger equation the wave function evolving that's all there is i think that's wrong so i i give a different perspective so it's a my books are a way of defending the perspective but but the two things help one another because uh in the moment in which you try to explain something simple you get clarity yourself i mean for me it's not an exercise it's an exercise of science i feel i'm doing science when i'm when i'm doing that i'm clarifying my mind and reading at the great masters who are better than me i mean reading galileo when he write his books it seems to me he's doing exactly the same thing i mean he's talking to people that's a book written for the cultivated person of the european renaissance in the seven late in the 17th century not for his colleagues astronomers because it explains things one by one but obviously it's debating with his colleagues astronomers in the book is making the subtle points of the argumentation proving him right and them wrong in that book so he has doing both things and that's what makes this that book so great now of course i'm not galileo and i'm not writing the dialogue of the two great systems but is this kind of uh popular science which i'm other people are doing no not which is presenting ideas in a way which are comprehensible to defend these ideas which i'm trying to do are you working on any books now sorry are you working on a book now yeah i am but i'm not sure i should talk about that um are you always working on one book or another no no i have not been writing for for one year or more i just stopped completely uh i'm under strong pressure of course from publishers and things for writing more and now i've i've i i think i've i there's something i want to do let me just give you this i am i'm not covering a large portion of physics i want to do the narration tell the story of how you a theoretical physicist like me get into a specific problem get fascinated by the problem work through and come out with some ideas and struggling on so whether this particular thing is right or wrong is irrelevant i want to tell how is theoretical science in the doing is it sort of humanizing the process of putting out yes yes making it relatable to non-sign yes yes let's show what is actually going on including um you know changing mind and realizing things didn't work well uh i don't actually have any further questions we've kept you for more than an hour i believe wonderful um so thank you so much for uh for chatting with us um i'll just ask a question i always ask um people when i interview them what keeps you up at night these days what problems or challenges are rolling around in your brain um [Music] a very uh i last night i was awake it was a relevant question yeah yeah absolutely um there is a beautiful experiment thing quantum gravity fact is being proposed and uh there are some people who are questioning the way to think about that and uh i think they're wrong so i'm i'm trying to find out the a right theoretical description of this experiment and in doing that it's uh it's fun because it's basic physics but it's um uh it's uh it's a writing thinking that you in a new ways and there are technical issues technical problems so i keep going around this these things here so it's not a big huge question it's a very small specific question well we'll have to have you back another time so you can tell us tell us the results of that so thank you again this has just been a pleasure thank you very much that was very nice [Music] you

Channel: Perimeter Institute for Theoretical Physics

Views: 52,169

Keywords: physics, theoretical, perimeter, institute, canada, ontario, science, stem, quantum gravity, philosophy, Seven Brief Lessons on Physics, The Order of Time, Reality is Not What it Seems, Conversations at the Perimeter, physics podcast, podcast, Carlo Rovelli

Id: ZSv0cMfxsqk

Length: 75min 21sec (4521 seconds)

Published: Wed Jun 01 2022