Q&A The Physics and Philosophy of Time - with Carlo Rovelli

you say that unless we're there's an astronomical distance like Jupiter or something that we're basically all in the tight same time now how do you explain then if say I'm in San Francisco and it's 7:00 in the morning and you're in Rome and it's I don't know 4 o'clock in the afternoon or whatever the time is there and you seem like you're in the future to me but yeah I'm not your how do you explain this time difference or is it just a man-made thing good so let me think this question seriously um you presented this I'll be joking but it's look for long for many centuries people on earth didn't have to think that we are in the same temporal situation because there were no telephones there were no telegraph traveling was traveling by horse at the fastest way so every place at its own time and there was not even need to Accord clocks and in fact until the 19th century time in Bristol was different the time in London because midday twelve o'clock was when the Sun is at the same it in the Senate is in London half an hour of 20 minutes before I don't know land in Bristol right Sun goes so each place has its own time and you would count your horse go somewhere else and readjust your time right without any problem the very idea that we have to at the same time came only when telegraph and trains can come in and then people started debating could we can we agree on on a common way of time and for a while there was this suggestion that everybody would use London time of course the suggestion come from the British and people were not very happy about the rest of the planet and the Americans will be so and then say well that's everybody have its own time but this is gonna be a mess so then it was compromised so let's slice the planet in in how you see whose segments time segments and and at least we have the same time for we know exactly we jump on our so we are at most half an hour of something out of proper time and then clean you know trains and the need to have very precise timing and and so there were a number of project to synchronize the time between the train stations and this was already the end of the 19th cent with the beginning of the 20th century and there were some patents which were presented for the best way to synchronize clocks and in fact one of the patent offices where these patents were debated how to synchronize clock was in Bern Switzerland it was a young clerk there who was analyzing these patents how to synchronize clock his name was Albert his last name was Einstein and that's the port he was doing he was evaluating patents to how to synchronize clock between the train station of Europe in order to dot them out of time one another and the guy realized that to be precise this is totally impossible so in the moment in which Europe got together Europe I also mean Britain so in a moment in which so we all get together to say let's put the clock seriously at the same time in the same years i sterilize it that's impossible so you see there is a there's a crossover things there's a geographical thing there's a cultural thing there is a historical thing but the point is the final point is that saying at the same time doesn't make any sense if we want to go precise we have question over here yes hi that's great talk thank you very much you've been talking about a linear universal observable time and there's a three different there those are three things then it's not talking about so multiversal nonlinear and non-observable time lester that non-observable if you don't see time passing if you can't see things changing this time pass well the linearity of time is the fact that time is a single one-dimensional wine and something I said it's just not there no it's not if you don't see it then you don't know that it's massing right so the the observability of time is exactly what what motivated us in quantum gravity to get rid of the time variable all together somehow once you get confused about time you make one step back and say what we mean by time this mean what I observed in my clock and then you ask is the clock representing my theory and you say yes it is because in the clock in my theory there is the I can put that matter that describe the clock and how it changes so quantum gravity what you do is you only put observable time inside and you forget anything which is time with a capital T which is not the clock time so is it different to quantum physics where things can be in more places than one at once can you have more times in once the things goes together in in in in in standard quantum physics that the textbook quantum physics is it when you study at university the training equation there is a T variable but this is because that quantum physics assumes a Newtonian time and background time essentially you know so quantum field theory says anything you assume rock from space-time but it is a car generativity once you bring generativity in that's that's an approximation this T of the Schrodinger equation should go to disappear you want to replace it with a reading of your clock and with observable time okay well hello I have this like I find what you say about how the emotional aspect of time is what time is for humans and also about how that sort of the source of a lot of the suffering that we as humans go through so I'm wondering if you as a quantum physicists have a strategy for thinking about time to try and alleviate that emotional suffering as a quantum physics if you decide I don't have any differently as a human being as a human being I'll just you know try to deal with it and but in my little personal experience I think the best thing to do is to follow the advice of the Buddhist just accept it accept impermanence deeply fully and then you realize that life is wonderful nevertheless someone else down here about as gentleman just on the Isle here you can have to duck under time to get there they break it I was curious that you didn't really focus on aging or decay in your discussion around a full bunch you know I will thought that is from a human perspective the most obvious thing that you relate to because your brain decays you have fewer brain cells or you look at radioactive decay you see a clear change there how does that fit into the the four metrics that you described in a simple way at first at first sight in a horrendous complicated way if you want to go deeper in a simple way because at our scale where we can disregard the speed of light with and disregard quantum mechanics and so on and so forth we are immersed in the earth is clearly in a strongly entropy gradient because you know we get light from the Sun which is low entropy or this high energy photon and then they go out to - to the sky slow energy photon which is much higher entropy so we're in this flux and this flux the the biosphere is strongly time oriented so we live in this time orientation entropy keep growing we leave keep growing localized I was fed by the low entropy of of the Sun and the PS biosphere II strongly time-oriented and it's just the working of of entropy going it's a continuous disordering that's what that was abuse furies i think it's a mistake to think about life as a resistance thing entropy to grow life is a way for him to be to grow like a little fire birds so we are a strongly oriented phenomenon and ahsan oriented strong named to the phenomena we do things like burning and in particular aging and so on and so forth which is this is a particular physics of us which of course then becomes strongly emotionally meaningful to us aging and dying that's a simple answer so within physically make sense perfectly whatever going a complex answer is that things are not so easy because biologists tell us that there's no reason whatsoever living beings to die a priority bacteria to something some bacteria don't die okay the actual evolutionary origin of death is at some point and it's a big discussion in biology about that death has a purpose because it it super simply it's it's better for the for the species so again there is a evolutional reason for that we're just a piece of nature of nature for not following the law of increasing increasing entropy and the way to reflect emotionally to us it's because then we have our brain and so on and so forth am i answering or I'm just adding confusion to confusion however you're not asking me why why you're aging right up on the balcony up that you said the plants was their smallest amount of time possible yeah what would half a Planck length be then perfect yeah that's the right question um the if this is correct I strongly believe is correct but it's not something fully established in which we we take it serious so we have many experiment of them that we have almost no experiment of them but if this is correct the idea that you can slice time in smaller and smaller pieces is just wrong right the just units of time one bit of time is an unbreakable so to say a certain amount of time is to say how many units how many how many bits of it so the answer to what is half of Planck time is there isn't that in the world you could not find F half a long time yes yeah it seems to me it seems to me that everything that's ever happened is in the past and that everything that is yet to happen is in the future so almost by definition there is no present would you agree with that hey you're saying the present is very short but it's horrendously short yes its boundary between the yes is the boundary with the past and the future is very very short that's certainly true for the present in Newtonian physics no doubt and it's also true if you think of space-time as a big picture you have a slice and what's over it is it's the future and what's below it the past and the present is so thin that there's nothing in but that's not the way the world is designed right so in space-time the past is whatever is inside or a past like on so it's whatever can affect us whatever come in our past and the future is this other opposite things it's qohen obsess so in between the past and the future there isn't just a single line is a huge amount of time and nanosecond but five nanoseconds between you and me so in your life in the taste of your life is a huge amount of time which is your past for me the past for me now a huge amount of time there's a future for me now in a nanosecond which is neither past nor future if you leave the on Andromeda there will be green with antennas or whatever a million years of your life would be neither past nor future for me so the presence is all things were endlessly sick it's ice a special activity in the middle here I think there we go right in the middle high because you mentioned black holes yes gravitational forces I was wondering cos in space gravity is different and there is less friction I think if you think that not only time is different but because now there are humans in space if our perception of time is going to be different while we're there what do you mean by the question exactly it's our perception is going to be different because we as human are going to be in space yes going to be his face yeah I think that what we call time it's a multi-layered thing which depends on which to some extent the logic sense has been on our the space perception so whether the humans are not humans different because it's like colors right we see a color space which is three-dimensional red blue and yellow whatever this is only because we have three three different kind of receptor in our eye so the three dimensional the way the thing is colored it's only there because we humans see that way so things are not colored unless they're their units now if you if you if you ask how our perception of time is going to change the way we do interstellar traveling it seems to me compute obvious is gonna change because in the moment in which you know I'm my girlfriend is an astronaut she goes far away she comes back and she comes back ten years later for me but she has grown grown just one year she's still young I'm older so we're gonna get used to this growing a different speed okay or maybe she comes back far in the future a hundred years in my future I say oh my god my girlfriend is hunting me on your future I've lost her no no maybe I can get there I just go also I enrolled in an astronaut and and I go very very fast and come back in the future hey I love you we are back together in the future this is physics it's not science fiction I mean just an issue of money to build the starships and do that if you could go you said black holes black holes are slow earth of time very powerful right in fact a surface or to some extent the surface of black hole horizon is a place where if you the more close you go with a clock the amount slows down if you're very very near to black hole you stay there for a while you come out millions of year past outside so why call our Stoppers of time so just think that think the black hole something that goes from here very fast to the future in in a moment you go to the future so I figure if you could go near to a black hole we don't know where is the nearest black hole we know there's a huge black hole in the center of the galaxy but as far away but we know the galaxy's full of stellar black holes so maybe we're gonna see one not too far I hope that not me but my next generation somebody could be able to go there and then we'll have to rearrange our thinking of time taking to account this variability I think when thinking about gravity and the fabric of space-time should we now change that to space entropy would that make sense yeah well yeah that's one yeah absolutely that's one of the open problems in 3d of physics in fact is one of the most clearly defined in and a less traveled less studied problem to a graph is we try to write a some number of papers on that but we're not sure very fast um everything has entropy okay a gaseous entropy the letter magnetic light has end to be the heat inside a hot cavity and to be sauna same to behind having to be the gravitational field has entropy so space as entropy and so we are able to compute the entropy because we would precise computing to be of all the things except for space we don't know that how to do the thermodynamics of space-time itself it's one of the open problems in emphasis not only we don't know how to do the quantum mechanics of the gravitational field but we don't even know simple flow which is just simply the statistical mechanics the thermodynamics of so of space-time which is a gravitational field so the end of your space has to be multiplied but we don't we don't have a good definition of it so in in quantum mechanics as is this idea of measurement which has sort of an effect on what a particle is and sort of measuring the particle is what defines sort of whether by position or velocity and if it's not being measured it's sort of uncertain yeah where where it could be for example right so could time not just be a feature of the world being constantly sort of measured and that if there aren't particles interacting and being measured constantly that time is actually not defined and the time would come from this measurement okay so good a few steps and break the question in pieces definitely at least I'm strongly convinced that time being a variable like any other because this is always clock time that I would the other one is observable time it's a variable like any others who is a quantum mechanical variable so it works like any other so it's only become determinate when we measure it that's I'm convinced which is not a way to say that gravitational field it becomes a quantum object or anything else it's going to be quantized okay it's going to occur I haven't said so let me stick back to your question what you said is exactly what it is written in textbook about quantum mechanics which I think on which as you know there's a huge debate and strictly speaking obviously is meaningless right as what the universe know whether I'm measuring something or not I'm not on Andromeda it doesn't mean that nothing happens on Andromeda because none of us is measuring there obviously silly so I think and this is where opinions diverge how to make sense of that that's called the interpretation of quantum mechanics problem on which there open debates this summer I'm going to also to have a big public debate - with a knock so if you'll ossifer was wanting to petition quantum mechanic I have another one so we're going to debate publicly this is a British Association philosophy of science sponsoring this debate and it's an internal conference so that's to say it's a it's a it's a disgusting do we think about this is that the word measurement is wrong world the right word is interaction so when a system interact with another system not it's been measured by a physicist with a white thing you know male white with a PhD this does make no sense who is measured or good measure but a measurement happens when two system interact so the way we have to think about the world were not mechanically in my opinion is that we can think of the world split arbitrarily in subsystems and the way each subsystem behave is by being measured by others and so things become well-defined you were saying including time but interactions that's why when I was saying the microscopic picture is this flickering probabilistic thing that are actualized in each interaction fewer questions from this side of the room very quiet so I know you've been listening yes thank you very much for a wonderful talk I just wondered because you mentioned the Buddhist angle and I know that spirituality is always a bit strange when you link it to science but input ISM there is the belief that the universe has no beginning at all and I was just wondering given that time is a variable of the universe that we live in or the bubble that we live in does it even make sense the obsession that we have to find the beginning of everything is there an order like you said an absolute order which existed at a certain point and then it just changed I mean perhaps this obsession that we have comes from the fact that we are dominated by by a time yes yes certainly this is a possibility that this obsession with the beginning it's it's a wrong question right this is an old idea Stephen Hawking I've explored this idea in detail you say what's before the Big Bang is like asking what's north of North Pole it's just not the right question this is nothing and the Big Bang might be something like that when we see when we think of the universe as a whole we have this notion of cosmological time which is which it's not a wrong notion it's just one of these averaged approximations in which we disregard all this fine structure of the universe who give this very very wide view of the universe at large and in that sense we can choose one surface of now pretty arbitrarily and ask what happened it might be a soaking suppose for a while that this question goes this slicing goes wrong at some point there's no meaning before we're not sure and in fact today we don't know what happened BIGBANG right but there's a lot of work trying to apply quantum gravity to the Big Bang and the indications that I see and there's a quite big part of the community to think that is that know what's actually happening there is different this approximation can be continued and we can keep giving the story of what happened before the Big Bang and roughly the idea is that you can think of large universe compressing and contracting getting to a sort of minimal size and then bouncing up and that's what we call the Big Bang this bouncing of the of the going through a quantum phase and then reopening up and when we look back in time we're seeing at this bounds so a lot of people studying whether we can give a description of these bounds and see traces of that and that's another thing I hope before dying of knowing whether they whether we can properly think about before the Big Bang or not I don't know one more question somewhere up on the balcony yeah give us a wave so you can see how you are yes off you go so I understand that fields have quanta like the electromagnetic field and the photon but I've I've wondered does the what is the quanta of the field of space-time or is there just no such thing oh yes very such thing and in fact loop under gravity theory which which I work is the mathematical description of the quanta of space of quantum space-time the the you can think it's very mental chunk of space in some things this is the the the the Planck size elementary bits out of which space is is in there quanta there they're linked to one another and they're all this link and you follow this link and make you cross to make a loop that's the name loop quantum gravity come from now the key point crucial point is that you have to think of these bits this quantum of gravity not as things immersed in space so in the space and this quantity there they are spaces that we made up space themselves so we call space it's a collection of these connected one another and we what we call distance is sort of numbering of how many of these what we call town time is how they transform into one another continuous is the number of step of this transformation so these are quanta but they're not like particles not the particles of particle physical the quanta of the field the photons are the quanta of the little of the electromagnetic field but the photons are little chunks of energy that travel in space or the quant of gravity a little chunk of gravity of something which may current made up themselves spaces they don't live in space it's like this is a constant my analogy if you look at my my t-shirt is not a my t-shirt has threads in each if you take away the threads is not a t-shirt still there there's nothing so the t-shirt is just weaved by it by the threads so space itself is weaved by this interconnected quanta of gravity this is the core of look at the world right well we have run out of time whichever version of time you're using today in your head might have changed a bit in the past hour and a half so Carlo will be signing books outside and please let's give a huge thank you for this fabulous evening thank you you [Applause]

Channel: The Royal Institution

Views: 48,034

Rating: 4.8643274 out of 5

Keywords: Ri, Royal Institution, lecture, Q&A, time, the order of time, carlo rovelli, philosophy, physics

Id: NXcu0BlbTrM

Length: 29min 35sec (1775 seconds)

Published: Wed Jun 13 2018