Sean Carroll - Is Time Real?

Shawn I desperately want to understand what reality is and my physicist friends tell me that the way to start is to assume that time is not real that seems to me bizarre yeah you're right to think that but I'm not sure you're talking to the right visitor okay well now I am but it's a very natural thing to on both sides time is obviously real in the sense that we use it all the time you can't even make a centum throughout invoking or some notion of time right past present future in fact dictionary researchers have shown that the word time is the most used noun in the English language so certainly something about time is real what physicists who say time might not be real really mean is that it might not be fundamental huh that is to say that when we dig down into the laws of physics we realize that time is not one of the crucial objects crucial concepts that we require to make sense of reality now even that is actually completely unclear at this moment the best theories we have of reality right now do include the notion of time in them it is not an illusion it is not emergent it is not a fake it is really there it is one of the fundamental things that we need so the question is once we finally understand everything well we have a better theory of everything in which time disappears and opinions differ my personal belief is that time is actually going to survive that once we understand the best possible theory of nature time will be a big part of it okay well if we look at time there may be three components the sense of a now which which makes the past really past and the future really hasn't happened yet and now whatever that means is the only reality second is maybe a flow of time that we sense there's movement and third is a direction that it's going forward as far as our perceptions are concerned and so in each of the three of those how does the concept of whether time is fundamental or not survive one of the things that is really confusing about time is that we use the same word to mean different things okay in fact this is one of I'm Stein's great great when he realized in special relativity that time as used to denote moments in the history of the universe is completely different from time as used to measure duration for my personal self so the time that I measure as I travel with my watch throughout the universe is not the same as the time we used to say the Big Bang happened 13.7 billion years ago they're related to each other in an obvious way and in fact he figured out exactly how they are related to each other if Isaac Newton had been correct then they simply would have been the same thing Einstein showed that there are two different things the time you experience the time we use to slice the universe into moments and then you have this difference between past and future and that's a bigger puzzle that we're still working on we think we understand the basics of it we think that it all comes down to not the fundamental laws of physics but the particular configuration the universe is in right now if you were Aristotle if you were pre Isaac Newton you wouldn't have thought that there was a question to be answered you would have thought there was the past there was the future these are different obviously but Isaac Newton comes along we develop our sense of the laws of physics and the difference between the past and future disappears this is a puzzle now now there is a puzzle where there wasn't one before how do you get the manifest fact that the past is different from the future out of the deep down laws of physics and we have lots of ideas along those lines but we're just not sure what the complete picture looks like all right well look we have these two massive ways of understanding the world that came up in the early part of the 20th century relativity and quantum mechanics and in relativity time seems to be this static four-dimensional so-called block universe where every coordinate in space and time is fixed and in quantum mechanics where time seems to really be flowing and real and is set and you got to integrate the two a lot of different ways but time can't be both at the same time where can they well I think it can be both at the same time I think time can be both existing equally well in the past present future and have the appearance to us of becoming beside like a married bachelor it is not quite like that it's more like athletic scholarship something that seems contradictory at first but once you understand it it begins to make sense so this is the job not at Caltech that's right this is the job of physics and philosophy to take things that are in tension not directly contradicting each other but things that seem to be pointing in different directions and to reconcile them so quantum mechanics has its own problems of interpretation and I think that even before we get to quantum mechanics there is a problem of the arrow of time versus the block universe the block universe idea is Einstein advocated it very strongly but it certainly goes back to Newton and Laplace the idea that if you knew everything there was to know about the universe right now you can make a perfect prediction about what would happen in the future and a perfect Retro diction of what had happened in the past what happens at every moment in the universe according to this idea is implicit in every other moment of the universe and it's a wonderfully beautiful idea an incredibly powerful it gives rise to the clockwork universe metaphor but we have to reconcile that with for instance the idea that I can make a choice about what having for dinner tomorrow we have to reconcile that with the feeling that we are flowing through time with the manifest fact that we can remember yesterday but we cannot remember tomorrow the wonderful thing about recent investigations as they point toward a single unified explanation for all these differences between the past in the future and that unified explanation is based on the famous celebrated second law of thermodynamics the fact that entropy increases this or universe ages entropy is a measure of the disorganization the disorderliness of the universe in the past things were more orderly in the future they're becoming more disorderly by itself that's not a surprise right I mean no one leaves their house a mess locks the doors and expects to come back the next day it all cleaned up right houses don't clean themselves up they do tend to dirty selves up well almost automatically this is a well-known feature of how the world works the surprising thing is that that basic feature of the world the tendency for things to become messy is really responsible for all of the differences between the past and the future even the fact that I can decide right now to have French food tonight rather than Italian food but I can't decide to have had French food last night well so what does that mean in summary to the concept of time what it means is that the apparent intrinsic difference between past and future is only apparent we believe we treat the past differently from the future but the laws of physics don't and the answer is not that we don't understand the laws of physics it's that we live in a particular universe we don't live in any old universe we live in one that started very very orderly if the universe had started in a state of maximal disorder sort of the most likely configuration to start in then there would truly be no distinction between past and future but what that means is there could be no free will there could be no choice there could be no memory there can be no metabolism no aging no evolution or there could be no living beings there could be no conscious thought so we live in a very particular configuration of stuff that features a strong arrow of time and we're putting together a picture where it all stems from a common cause

Channel: Closer To Truth

Views: 275,620

Rating: 4.8822103 out of 5

Keywords: Sean M. Carroll (Academic), Robert Lawrence Kuhn, Closer to Truth, Time, General Relativity (Field Of Study), Philosophy (Field Of Study), Physics (Field Of Study)

Id: FVINOl0Ctfk

Length: 8min 17sec (497 seconds)

Published: Tue Oct 15 2013