Seth Lloyd - The Physics of Eternity

Seth when we try to think about the universe at the beginning of the universe the end of the universe but time is this enormous quantity as we look forward we can look back and see maybe a finite time the Big Bang for 13.8 billion years ago but going forward it just seems like an unknown maybe an infinite number what what can physics tell us about this concept of eternity don't hold your breath I can see it's the main thing that it tells us it's true what you say Robert is interesting that physics actually does throw a light on the notion of eternity I mean physics has given us new insights into your time and and time in physics is some kind of more tangible thing than it is philosophy in general it's part of the fabric of our reality and so time and space are two parts of of the same thing in some sense and as you say our current picture of the universe is a time effectively began 13.8 billion years ago and may continue forever that current observation says will continue forever okay that's kind of hard to wrap our minds about our brains are puny finite things that time is infinite but physics tells us more so for instance because existence and thought and life takes energy then and it also degrades that energy it takes free energy and creates entropy then the amount of resources that we have locally to actually do things like be alive or no maybe not live forever ourselves that doesn't sound like such a good idea but you know have maybe our genes go on for a while perhaps our ideas go on for a little longer and maybe our bits live forever you know that requires energy and energy is constantly degrading so it's an interesting open question whether life or even something like life could go on forever frankly the universe looks pretty bleak if you look at current predictions for the dim distant future sure but if you go on forever in any capacity one of the complexities that happens is that you have an infinite amount of time and all these particles even if they get more dispersed an infinite number of things can happen in fact everything happens and if it's really an infinity everything happens and in for the number of times there seems to be something deeply wrong about that but it's hard to figure out what that wrong thing is well there's nothing wrong with you know if you have an infinite future and a finite set of things that can happen and stuff keeps happening by god everything is going to happen in a certain number of times there's nothing nothing particularly wrong about that in fact it's sort of nice but it does raise some some knotty problem so if everything happens an infinite number of times then why is it that we think that we're near the beginning of the universe so it looks right now that yeah 13.8 billion years ago the Big Bang occurred and this might very well be the beginning of the universe but if everything happens an infinite number of times and how do we not know that this is just an illusion and that we're like kajillions of years along in the history of the universe and it's just some kind of random accident that it appears that it looks like the Big Bang happened 13.8 now this is the so-called Boltzmann's brain problem where how do we know we're not just this random fluctuation that came into existence for a microsecond or a nanosecond and then get a blow out of existence absolutely yeah I mean this is the so Ludwig Boltzmann the famous 19th century physicist came up with exactly this problem while studying the increase in entropy he said well the universe starts off where any physical system that starts off in a state of very low entropy which means which means disorder right so it's a very ordered system entropy is low interest rate you have very much ordered right so beginning the energy that you have is very ordered and it's what's called free energy so it's available for use then as time goes on the energy degrades it becomes which is energy that's not so useful and then eventually when everything becomes heat and is the same temperature you have the maximum disorder this is the state of maximum entropy the so-called heat and death of the universe but what Boltzmann pointed out is that you have this initial state going from low entropy at stage of going to high entropy and then as you go to get to this point of high entropy you could exist forever at a state of high entropy but with very unlikely fluctuations we'll take you back down to states of low entropy a gap and the lower the entropy the more unlikely the fluctuation but as both them pointed out since this is going on for infinite time if you look at the number of times along this plate what place were people you know say find themselves in a state of low entropy as we do right now online 13.8 billion years for the Big Bang then the vast majority in fact that all but one of these times is just some like random fluctuation so both Swan concluded from that oh we must just be like grains and rose out of like some random fluctuation in the universe doesn't exists now this is wrong by the way but but it's a compelling argument at least when false one first put it forward in the late sorry the late 18-hundreds so where do you pinpoint the mistake the mistake is saying that the prior probability of being where we are now considered on a beautiful cliff above the beach with the waves crashing the background 13.8 billion years after the beginning of the universe and a particularly fine epic of the universe it is so that this is just one time but all these other times because they're an infinite number of them Boltzmann assigned them infinite weight that said their prior probability is 1 whereas the prior added up together added up together as one to me this is this is a misunderstanding of how one assigns prior probabilities in science in science we have different hypotheses and so let's compare this two hypotheses one that ok it's 13.8 billion years for the universe it's a beautiful day in the island of Vieques and and they were the hypothesis you and I are just a random fluctuation none of that stuff is really out there we're just going to revert to nothingness in the in a nanosecond right that's the alternative hypothesis now what boss Minh did he said this second one has probability one prior probably one of this first one is prior probability tiller so suppose we assign you know the the hypothesis that it really is 13.8 billion years after the beginning of universe probability 1/2 to the minus 300 that's a big number it's like they're not two to three hundred is the number of particles in the universe is a teeny probably but it's a finite probability and let's assign this other probability one minus two so it's almost and then we start looking around well the Boltzmann brain prediction says what do we see next what we see next is corollary nothing you know everything just goes away in a mess of like heat death of the universe but oh that didn't happen suddenly the hypothesis that it's actually 13.8 billion years since the beginning the universe we actually are sitting on the cliff in vak this stub becomes like a lot more proceso with every nanosecond that we continue to exist as opposed to being different Boltzmann's brains that keep coming into existence through going out of existence but that's an alternative hypothesis right we're saying that becomes a less likely one than the more simple hypothesis that there is continuation and in fact given I gave you this very tiny number was like a very one of the tinier numbers that I could think of off the spur of the moment you know one out of the number of particles are small so even just the fact that we survive for one nanosecond already if the Boltzmann great hypothesis is wrong and that the purposes that we really are here on the beam is right

Channel: Closer To Truth

Views: 32,966

Keywords: Seth Lloyd, Closer To Truth, Physics, Eternity, Future, Immortality, Cosmos, Cosmology, Cosmic Inflation

Id: cX-9E9Fy2OI

Length: 8min 13sec (493 seconds)

Published: Mon Apr 04 2016

Reddit Comments

[u/Jasper1984]

Ftr, i didn't get my Boltzman brain comment(here) from this.

Video isn't so bad. Though i am hesitant about things that might sound smart to people but isn't so much, or about the other videos that mix in things that really have strongly varying actual solidity..