Alex Filippenko - How will the Universe End?

he received his PhD in astronomy from Caltech in 1984 and joined the UC Berkeley faculty in 1986 he has co-authored over 520 scientific publications and has won numerous prizes for his research Alex has won the top teaching Awards at Berkeley and in 2006 was named at the Carnegie case national professor of the year among doctoral institutions he has produced a 96 lecture astronomy video course with a teaching company and has co-authored an award-winning astronomy textbook Greg Laughlin is associate professor of astronomy and astrophysics from UC Santa Cruz he earned his bachelor's degree in physics from the University of Illinois and his PhD in astronomy and astrophysics from UC Santa Cruz his current research focuses on the dynamics of extrasolar planets and protoplanetary discs stellar evolution and most important for today's discussion the long term evolution of the universe greg has written a popular level book with colleague fred adams of the university of michigan entitled the five ages of the universe inside the physics of eternity our first speaker today is Alex Filippenko please welcome thanks very much Tucker and it's always a pleasure to participate in wonderful ninth year Wow and it's always a great set of topics my colleague Greg and I today we'll be discussing whether the universe will have a happy ending and there are many ways you could define happy or sad endings I think in the end neither of us degree disagrees with each other very much so this won't be so much a debate as it will be I think a discussion or a dialogue I don't know that I've come up with a definition of whether either of the potential endings will be happy or not and I'm not sure greg has either but we're here to discuss the possible future of the universe and the format we'll take is that each of us will have a little 15 or 20 minute presentation introducing some concepts and then we'll have a conversation with each other hoping to elaborate on some of the points and then the last half hour or so we'll have a Q&A with you so anyway we all know that the universe is not infinitely old it actually had a beginning about fourteen billion years ago and that is actually a fairly well determined number by now 13.7 plus or minus 0.2 or 0.3 something like that but a bigger question is you know will it have an end that is will it keep on expanding forever or will it someday Riko lapse into what you could call a a Big Crunch or if you started with a big bang you could say NAB Gibb which is a big bang backwards right Big Bang NAB Gibb now this this Time magazine headline makes a fairly definitive statement how the universe will end they were discussing some research that I had done with with our two teams studying the expansion history of the universe and at that time we thought we knew what the fate of the universe would be as I will discuss later probably more in the conversation with with Greg we're not we're now not so sure that the ultimate fate of the universe will be eternal expansion so probably they should have had a question mark after that title but in any case the universe might live a long and among the things we will discuss is the various physical processes that could occur while it's living a long time well I mentioned expansion let me at least give you the evidence for expansion it goes all the way back to the late 1920s and Edwin Hubble who noticed that basically with very few exceptions all the galaxies are moving away from ours and here are a bunch of galaxies in the Virgo cluster it's about 60 million light years away and it's zooming away from us at something like eleven or twelve hundred kilometers per second and moreover at a given time right now more distant galaxies are moving away from us as well but even faster than nearby galaxies that's not in and of itself evidence for an accelerating universe it's only evidence for a uniform the expanding universe which I'll be glad to elaborate on later on but basically he figured this out by sending the light of galaxies through a prism decomposing the light into a rainbow or a spectrum like this and from the spectrum you can tell whether the objects are moving away from you or toward you if they're moving away then the light from the spectrum tends to be shifted toward redder or longer wavelengths and if it's moving toward you then the light is shifted towards shorter wavelengths and the amount of the shift is proportional to the speed of recession or approach so here's the perspective from the point of view of of the Milky Way galaxy here we are and all the galaxies are moving away from ours and at a given time right now the ones that are farther away are moving faster than the ones that are nearby so before I move on let me pause because there's something very strange about this diagram what is it yeah we're at the center you know is it that they don't like us or our galaxy is it something we said or do we smell are all these other galaxies lactose intolerant get it Milky Way galaxy like this yeah or since I'm in a cow friendly crowd today I could say are we from Stanford now I know that yesterday's wonder felt Swiss held at Stanford it's a fine institution just not quite as fine as Cal but anyway now we don't think that that this indicates that we're at the center this just is indicative of a uniformly expanding universe and Greg will ask me about that later on in the conversation okay so however you don't expect the universe's expansion to be constant with time and this goes all the way back to to Newton Newton famously looked at the Apple you know the idea that it fell on his head is probably apocryphal but supposedly he was motivated by seeing this Apple fall and he looked at the moon and considered whether the moon and the Apple are being governed by the same force which he called gravity well when you toss an apple into the air the mutual gravitational attraction between the Apple and the earth slows the Apple down it comes crashing back down in fact if I don't throw it very fast or equivalently if the mass of the earth is large if the mass of the earth were small or if I threw it fast enough I could get it to you know escape from the earth that is go at a speed greater than the escape speed and in that case it would never come back down however gravity would always be acting upon the Apple and so it would always be slowing down in its expansion it just wouldn't slow down enough to ever come back okay so we expect the universe to be slowing down its expansion because there are galaxies in the universe and they're all pulling on one another and the question is or it was 10 years ago 15 years ago is the density of the universe sufficiently large to slow down the expansion of the universe so that it someday comes to a halt and comes crashing back down into a Big Crunch a hot dense compressed state or is the density the universe low enough that it'll keep on expanding forever albeit progressively more slowly with time okay in that case it would expand forever becoming cold and dark and dilute well a way to measure the or a way to predict the future of the universe is to measure the expansion history of the universe if it's been slowing down quickly then it will someday stop and reverse its motion if it hasn't been slowing down quickly then it will probably expand forever in fact it's not a probabilistic argument there are equations you can write down that will tell you plug in the observations and the aect and the equations will tell you whether it'll expand forever or not so you look at the expansion history and see whether it's been slowing down quickly now you might say we live right now how can we possibly measure the history of the expansion anyone want to venture a guess yeah look at different parts of state space why does that help you that's exactly right so the farther out you look the longer it took time to reach you because time the longer it took light to reach you because light doesn't travel infinitely fast a star that's ten light years away you were seeing as it was ten years ago a galaxy that's say four billion light years away you're seeing as it was four billion years ago one that's eight billion light years away you're seeing it eight billion years ago and so on so if you look at all these galaxies at different distances you're looking at them as they were at different times in the past and encrypted in that light is information about the expansion rate of the universe at those various times in the past 1 billion four billion eight billion years ago okay so then the question is well how do you know that this galaxy is four billion light years away and not 3.8 or 4.3 how do you know accurately enough what the distance is well you need accurate distances in order to get the correct look-back time and the way we look at these distant galaxies and get their accurate distances is by finding stars that explode inside them so here's an exploding star and this star might not be visible individually in that distant galaxy before the explosion see they're all merged together there are tens of billions of stars there you can't see individual ones but after it explodes you can see it easily on its own and very few stars explode at the end of their lives but some do and they shine with the power of a billion suns and see can see them billions of light-years away that's the idea and in particular we study the kind of explosion called a type 1a supernova where you have a white dwarf star a very weird kind of a star like what our Sun will become in about six billion years six or seven billion years but unlike our Sun this white dwarf is gravitationally bound to another star from which it can steal material and in some cases it can gradually accrete or swallow enough material such that its mass reaches an unstable limit of around 1.4 solar masses and at that point it undergoes a catastrophic nuclear runaway which makes it explode with about the same power at its peak as all of its brethren that is all of the stars that explode in this way explode with roughly the same peak power so if you can measure some of these things in nearby galaxies and look at how bright they get and if you know already the distance of this nearby galaxy through other techniques there are ways we have of determining distances of nearby galaxies so you measure the peak brightness you know the distance of that galaxy that allows you to calculate the true power of that type 1a supernovae knowing that you can then move on and find type what type 1a supernovae in distant galaxies make a comparison of their apparent brightnesses and hence get the distance and for the past 15 years or so there's been two teams working on this the high redshift supernovae search team and the supernova cosmology project their two leaders are Brian Schmidt of the Australian National University and Saul Perlmutter here at Berkeley contrary to popular belief they're not always at each other's throats and in fact it was generally as a healthy and spirited competition both teams wanted to be first both teams wanted to be best and that accelerated no pun intended progress in this field so what they did is they used big telescopes in the Southern and Northern Hemisphere's this happens to be the southern hemisphere they took deep pictures of the sky in those deep pictures there are thousands of galaxies you take many such deep pictures over the course of one night you're effectively looking at tens of thousands of galaxies three weeks later repeat those same fields in the sky take pictures of them and among those tens of thousands of galaxies quite a few a few dozen maybe will have produced a supernova of type 1a and here in fact as a small part of one of those fields imaged on the 7th of April 97 and then a 28th of April if you digitally subtract this image from that one you get a bunch of noise any measurement process has noise associated with it but in addition here cleverly placed in the middle of the photograph is something that looks like it might be real that's a supernova candidate a Hubble picture shows it very nicely a few weeks later my role on the team is to use the world's largest optical telescopes to get spectra of these little supernova candidates to see if they really are supernova the ones that are good and are of type 1a we follow we watch them brighten and fade and here they are here's three of them at peak brightness and here's the punchline I've at least my part of the presentation these supernovae are so faint that they are farther away than they had any right to be in a well-behaved universe Newtonian or even simple Einsteinian universe so let me give you an analogy suppose the Big Bang occurred one second ago and and I illustrate it with this Apple like this I can measure the distance of the Apple from my hand in one second and it's some distance but it's been slowing down of course right during its upward journey so if I were to decrease the mass of the earth and throw it with the same force through the Apple of the same force it would go up higher in one second because it wouldn't slow down as much no I can't decrease the mass the earth but I can do the next best thing I can throw the Apple faster which isn't quite the same thing but at least Apple gets farther in one second so it sort of illustrates the point if there were no earth at all and I throw the Apple the Apple would have no reason to slow down it would go at a constant speed in a constant direction forever that's just Newton's first law okay so it would get even further in one second so what we're saying is is that these supernovae and the galaxies in which they're located are like the Apple but the Apple was measured to be farther away than it could have gotten in one second even if it were not slowing down at all so it's farther than the distance that would have gotten even if there were no earth and unless there's some other effect yeah it's pretty crazy huh and that's unless there's some other effect which we were careful to worry about and great can ask me about it later or whatever what is one possible conclusion what is the obvious conclusion yeah it's accelerating instead of slowing down or even remaining constant it's like it you touch your rocket to it and go zoom then it can go further in one second then it would have had there been no gravity at all so that's the idea and the headlines that came out were that you know astronomers see a cosmic anti-gravity force at work we hesitate to use this word anti-gravity because members of the press say well can you use this stuff to levitate over Bay or cha bay area traffic jams you know attach it to your car or whatever no you can't do that we think this is an actual property of space itself but anyway it was kind of cool so by the end of the year 1998 the editors of Science magazine proclaimed this to be the single most important discovery in all areas of science that year which you know we were very pleased with the character caricature of Einstein is surprised here not because he's blowing lots of universes out of his pipe that's where universes come from there they come from the pipes of old theoretical physicists maybe this could be a future topic of the Wonder fest no I'm just kidding here he's he's he's surprised because this one University blew out of his pipe is expanding faster and faster with time not more and more slowly as most physicists had expected he's doubly surprised because he has a sheaf of papers here where there's an equation lambda equals 8 pi G Newton's constant of gravity times the density of the vacuum and you might say what's this guy from berserk Lee telling us about the density to vacuum you were taught on your mother's knee that the vacuum is zilch nothingness right how could it have anything but a nonzero but a zero density well what he postulated was that the vacuum might have a nonzero and repulsive density because he suggested that normal gravity would cause all the galaxies to pull on each other and so the universe if anything should be contracting because the Milky Way galaxy is pulling on other galaxies okay so he pause related without proof that there's some sort of a weird stuff pushing the universe out and he later renounced this idea when Hubble discovered that the universe isn't static after all Einstein thought it was static astronomers at his time thought it was static but later it was discovered that it's expanding after all in which case you don't need this weird stuff for which there was no experimental evidence and which implied that the density the vacuum was nonzero okay so here announce the ID said I was a Dumbo for forever suggesting it had I not done that I would have predicted that the universe is expanding or collapsing or doing something interesting well what we're saying is is that the cosmological constant or something like it exists but instead of exactly balancing on large scales the attractive force of gravity it's a little bit bigger than gravity when you go out go out the distances of a billion or more light-years okay here in this room obviously gravity dominates and in our solar system in our galaxy in our cluster of galaxies gravity dominates but over billions of light years of otherwise empty space this weird stuff now called dark energy grant dominates and it causes an overall acceleration of the universe so my 15 minutes are just about up let me just summarize by saying that this repulsive stuff is now thought to be about three-quarters of the total energy density component of the universe or a contribution to the universe 23% is dark matter of largely unknown type so 96% of the universe we don't really know in detail what it is okay we just know that it exists and whether it's gravitationally repulsive or attractive the stuff we're made of is just a small section of this pie and you know stiffness stuff might be some sort of quantum fluctuations I'll talk about that later or it might be something else but if this stuff remains repulsive forever then the universe will expand forever faster and faster and faster with time in fact in a while it'll start exponentiating in size in every any given interval of time or whatever the doubling time is it'll double and that's an exponentiation it's not quite doing that right now it's just accelerating right now but it's yet exponentiating but eventually it'll exponentiate if this stuff remains repulsive but we've since then learned because of fear is set stanford in other places that in fact the stuff might change sign in the future and if that's the case then the universe will wreak elapsed in a fiery hot Big Crunch so I don't know what the better fate is eternal expansion becoming ever colder darker more dilute stars will someday die out life as we know it will certainly die out maybe life as we don't know it won't die out but anyway that's a pretty depressing thought but that but the Big Crunch is a pretty unhappy ending - I would submit and I'm not sure which one of them is most unhappy but let me end by saying that Robert Frost might not have known about anti-gravity but he knew about these two possible fates of the four the universe REE collapse hot dense and ending in fire so to speak or eternal expansion cold dilute and ending in ice because he had this famous poem right fire and ice some say the end I'm sorry some say the world will end in fire some say in ice from what I've tasted of desire I hold with those who favor fire but if I had to perish twice I think I know enough of hate to say that for Destruction ice is also great and would suffice so frost would prefer this kind of a universe but if he had to perish twice eternal expansion and an ending and ice would be okay and that's perhaps appropriate given his name Robert Frost okay so that's my presentation now we'll go on to thank you as always Alex does a great job of sort of giving the big-picture overview so my car almost ran out of gas while I was driving up here from Santa Santa Cruz I stopped in Los Gatos and in Los Gatos it turns out that earlier this week they had a Halloween parade in which everybody dressed up their dogs in Halloween costumes and then paraded them through the streets and so I was realizing that the universe I may not have a happy ending after a home owner heard about that but but more to the point this is a picture that I took flying up out of San Jose on an early morning flight and if if you look at it for a moment you'll see that that that's the sort of sunlight reflecting off the clouds and then that is San Francisco and what a point are there on your Oh helps a lot they're running out of batteries no I'm not sorry you almost run out of gas so I guess we're good that's right it's it's and the universe is gonna kind of end up and low down there you go yeah so that's San Francisco right there and then we're literally sort of right here you know I drove up to get here and the thing I like about flying in air hot in airplanes is that you just barely get a sense for the curvature of the earth you just barely get a sense of the fact that that you're actually on a planet and I know that Alex spent a lot of money getting his demonstrations together for yeah I'm kind of a cheapskate so I brought a penny as my as my demonstration and it's a fake Apple it's a fake Apple no this is a real comprehending and so the earth is really like the largest thing that you can kind of get your your mind easily around and and even that it takes hours and hours to fly to Europe it's just earth is an enormous thing and so I also brought a grain of sand which I have between my thumb and my forefinger and a grain of sand is just about the smallest thing that you can see without magnification and it's just about the smallest thing that you could feel as well and so something that's always struck me is remarkable is that if you shrink the earth down by a factor of a hundred billion if you make a hundred billion to one scale model of the earth and the earth is about the size of a grain of sand and at that that scale the Sun is the size of a penny and a scale model is is for the earth and the Sun is holds if you hold the penny sort of as far as you can away from the grain of sand that's a good scale model for our inner solar system and you know there's all this stuff going on I had to turn off my cell phone because otherwise I would get a bunch of calls during this during this talk and we're all like totally doing off stuff nuclear power they're talking about in the last in the last talking it's sort of interesting to get perspective is it's really just like a grain of sand sitting at two arm's length away from a penny and then you know came back next week the grain of sand would have moved 150 second of the way around the penny it's really not very much happening at all if you really look at the big scale here's here's picture taken by one of the Apollo astronauts as they left the earth here's another picture taken by the Apollo astronauts of the earth and a crescent phase and this picture shows the planet Venus actually just starting to transit go in front of the Sun and so this gives a sense serve the scale of the Sun in comparison to a trust or a planet and this is actually a little bit of an exaggeration because Venus is closer to us than the Sun it but nevertheless it gives a sense of this sort of a huge scale of the Sun and how how it Dwarfs the earth but if we go out even further you know then you look out into the stars then in order to make the sort of distances between the stars really manifest you have to take the Sun which I've strung town to the sides of a penny and shrink that down to the size of grain of sand and so if you take the Sun and shrink it down to the size of a grain of sand then the nearest star is a few miles away the nearest star would be sitting over in San Francisco at that scale and that is always staggered me in fact that if the Sun is shrunk down to a size of a grain of sand then Alpha Centauri is three small sand grains sitting over in San Francisco the Sun is sitting here in Berkeley and and so when we look out at the night sky we're literally seeing sort of a field of stars that are literally like little bright grains of sand separated by literally miles this isn't our galaxy we are living inside of a spiral galaxy and this is a slightly more dramatic spiral galaxy than the one we're living in but it's not a bad approximation and when you see these pictures from the Hubble Space Telescope you know you're just sort of overwhelmed a galaxy like this contains about a hundred billion stars and so if we keep the sand grain size analogy going a hundred billion sand grains would easily fit in this lectern and so what you want to imagine if you make a scale model for a galaxy is that you're taking a hundred billion sand grains and you're spreading them out over a disc that's about thousand times the width of the United States taking a whole lectern full of sand and it's sort of dispersing it over the distance between here and the moon so it's an incredibly rarefied it's an incredibly low-density thing I think the most important thing to know about galaxies is that to the zeroth approximation to the first approximation even second or third approximation it's basically nothing there at all and that doesn't that doesn't square very well with these dramatic HST pictures I mean imagine that we were sort of out in space a few hundred thousand light-years away from this thing this thing would occupy almost that much of your field of view and so if it went we were really there it's incredible to go out at night and have that thing you know just like standing right up there have a gigantic spiral galaxy right there filling up a big chunk of the sky that would be amazing but it turns out that if if this thing was actually sitting there and you went out that night you wouldn't really be able to see it or you just barely be able to see just the faintest glow it would actually be dimmer than that certainly what you wouldn't be able to see it if the lights were this bright what's remarkable is that right now in the mid autumn constellation Andromeda is high in the sky we have a giant spiral galaxy that is filling about this much of our field of view literally directly overhead at night at this time of year this Andromeda galaxy and yet it's so dim that we can't really see it with our naked eye this thing is larger than the full moon in the sky sort of over its full extent and if we take a very long time exposure like a big telescope can do or like the Hubble Space Telescope can do then you see that this thing is actually a glowing spiral of stars but I think the thing to keep most in mind is that it's barely there at all it's like a grain grains of sand separated by miles and so when you're talking about the the universe I think it's always important to keep in mind with the universe's absolutely just mostly empty space Alex showed a picture of the Virgo cluster of galaxies the Andromeda galaxy is about two million light years away so when we look at this galaxy we're seeing light that left it two million years ago when you look out at the nearest stars in the sky you're seeing light that you know sort of was emitted during the clinton administration if you look at you know the average star that you see now with your with your eye in the skies probably a few hundred light you away and so that light was emitted back say during the Renaissance this light was emitted two million years ago and then the nearest cluster of big galaxies to our own galaxy is the Virgo cluster and the light from these galaxies was emitted about 60 million years ago so the dinosaurs were still roaming the earth when the light left these galaxies we're seeing them as through a time machine the way they were 60 million years ago and if we look on the largest scales this is actually a computer simulation a bright cluster of galaxies is like one of the sort of regions where there's a little bit of yellow sort of spotted in different parts of this this diagram this is a picture of sort of the large-scale structure of the universe over literally billions of light-years in size and these galaxies at this scale you can't see the individual galaxies and rather you see sort of clusters of galaxies like that Virgo cluster are arrayed in this huge filamentary structure and this this is really you know so when I think of the universe I think of this huge extraordinarily faint extraordinarily tenuous fill an entry structure where the filaments and especially where the filaments are joining are clusters of galaxies and what what alex has been you know in large part responsible for realizing over the last 10 years is that this whole thing is starting to basically come undone the expansion of space large-scale acceleration the expansion of space is starting to take all these filaments and really pull them faster and faster away from each other and this is going to have profound consequences for what happens in the extremely distant future this transparency isn't very good but what what this is showing here is a computer simulation that shows this sort of spidery network of galaxies and this scale here is roughly the distance from the Virgo cluster to where we are we're in sort of a backwater region of one of these filaments the Virgo cluster is sort of like a nexus where several filaments are coming together and over the next year a big G doesn't stand for a thousand dollars it stands for a billion years so this is 14 billion years after the Big Bang we had this sort of spidery filamentary structure that looks like this 54 billion years after the Big Bang this acceleration of the expansion has taken hold of all this stuff and like a balloon that's being expanded very rapidly if you can imagine this stuff is sort of painted on the surface of the balloon it just blown up and so this stuff that we can see now has been carried out of our field of view and after roughly a hundred billion years after the universe is about of order ten times older than it is now then our galaxy and the Andromeda galaxy will be left in a combined mess and all the other galaxies in the universe will have been inflated beyond our horizon so it's it's it's a remarkable thing universe is remarkable but remarkably large remarkably tenuous and it's it's in the process of being ripped apart and so it's very interesting to think about what that holds in store for the earth as a planet for the stars for the galaxies and it holds a lot in store for sort of big-picture questions and I've been kind of fascinated by this idea of does the universe have a happy ending I think that I'm interested in like what does a happy ending mean in fairy tales you know they all live happily ever after does that mean that they they're just everything was good for an indefinite period of time or they lived through their normal lifespan or they all got rich and they're driving Bentley's now I mean what does that what does that mean so I was hoping that that in thinking about that I think that's kind of a deep question and this this discovery of the expansion of the acceleration of the unit acceleration of the expansion of the universe is really brought that question to sort of an interesting perspective and so I hope that you know Alex and I can kind of talk talk this over a little bit and and then open the floor to discussion to sort of see how this can touch on sort of some really big picture issues so I guess I sit down now I don't know how often these wonderful turn into like a real debate where they like do they ever have like heated arguments onstage or is it all kind of like well what we thought we'd do was first have a half an hour or we kind of discuss things amongst what you know I asked Greg some things to clarify something isn't yes me and then the last half hour is that way you wanted Tucker right but that's okay so we won't quite take funny things yeah but we'll take questions later so I I wanted to ask you Greg a little bit more about what what sort of physics will happen to our son and our galaxy and other stars in a universe that lasts forever hmm you know I mean suppose this dark energy never becomes gravitationally attractive and we and we do exponentiate in size you've already talked about how in a hundred billion years there will be nothing left to see but can you tell us a little bit more about what's gonna happen to our son right right so so our son you know as most people know is is shining our son is in a delicate balance between its desire to collapse under its own weight and turn into a black hole and it's equally opposite and compulsive desire to explode Sunday the Sun is under high pressure and it would it would the gas pressure would like to explode and so the Sun is being held in this balance and the Sun has a problem because it leaks heat out all the time that's good for us on earth we bask in the sun's heat in the sun's light but because the Sun is forced to leak heat out of its surface it's also forced to regenerate that heat in order to maintain balance between pressure and gravity and it's doing that by fusing hydrogen into helium and it's been doing that for the last four-and-a-half billion years and the Sun is about half done fusing its central hydrogen into helium and so it's a bit like the situation where you're driving I'll say across the Santa Cruz Mountains and you see that the gas gauge is starting to get lower and lower and there's really two things that you can do one is you can sort of ease up on the gas and try to conserve fuel you know try to get to the next gas station and with some fuel still left in the tank the other thing that you can do is obviously the faster you get to the gas station the faster you can fill up and solve your problem so you can floor it and the Sun is basically taking that second option the Sun as it starts to run out of hydrogen in its center is fusing hydrogen at an ever-increasing rate and that will cause an ever-increasing luminosity from the Sun itself and within five six seven billion years the Sun will stop being the steady orange or yellowish orbit it is today and will swell to fill a large chunk of the inner solar system so the earth for instance is going to be neck-and-neck with being destroyed by the red giant Sun Sun will expand out to roughly the size of the Earth's orbit as it expands that will sort of lose mass and the sort of dramatic wind and that will cause the earth to sort of spiral out away from the Sun as the Sun gets larger and larger and it turns out it's really gonna be neck and neck it's not clear whether the earth will be subsumed into the Sun or whether the earth will just barely manage to escape the red giant Sun what is clear is the earth will get completely toasted by the Sun within a few billion years will experience a runaway greenhouse effect that will turn our planet into something like Venus and then even that atmosphere will be driven away this temperature on the surface of the earth will reach of order a thousand degrees or more so the prognosis for the earth is is is not particularly not particularly good yeah so I mean that's not very happy either no I basically can't think of a happy ending really about those shares of Google you own I should have bought when it was 400 per share but I thought oh it can't possibly go higher than this right but I shouldn't you should buy puts on Google anyway think about what a bringing Google up and the way that was facetious or not is I think actually might might be a very important point things are starting to happen on the earth that it's not clear whether it's happened anywhere in the universe up until now we here on the earth are starting to engage in directed processes if if you look at the San Francisco Bay Area and compare the city of San Francisco to what existed a few hundred years ago there's been an astounding and the best way to put it is geological processes occurred raised up all these skyscrapers we are literally transforming the surface of the earth and the processes that are fully competitive with geological processes and that's happening because we've tapped into what am i guess the scientific method is the best way to to to express that we have started to understand how the universe works a little bit of the universe is isolated itself and it's understanding how the mechanisms operate and I think that that really really is is going to play a major role in the future and I think that's tied in pretty closely to whether or not we have a happy ending yeah did you have questions you want to ask or should we just keep on I do have some do have some okay that's every now and then the school I teach the schools right each have lowered their standards and we're almost but not paid attention and let me teach philosophy and I'm there's a philosopher named Hume who stumbled upon or worked hard to find a very deep idea regarding the the laws of physics I teach physics you you guys do too in a sense what we when we talk about Newton's laws say the foundation of mechanics we're confident of their truth because of what we've observed in the past Newton's first law you mentioned an object goes in a straight line at constant speed unless acted on by an unbalanced external force but our belief in those laws all hinge on on the past on the fact that today and the future we think looks like the past the process of induction all of science is based on induction seeing something happened once and again and again and again and bleeding if it happens enough that it'll go on happening is there any way of dealing with the question of can we can we know that the laws of physics not just the the acceleration that the lambda factor say in Einstein's equations is there any way to know that whether the laws of physics themselves can be reliable in law on long timescales or even short ones oh that's a very interesting question maybe I'll address it first and then you can cancel them so what one one possibility for what this agent is that's accelerating the expansion the universe the so-called dark energy is that we are right now living in a state where one of the four forces presumably gravity because that's what's dictating the large-scale behavior of the universe is actually an amalgam of two other forces the the two forces are sort of unified unified right now in a symmetric way into this thing that we call a gravity but it's conceivable we have we have no evidence for this but I'm just throwing out one of the theorists ideas it's conceivable that this gravity should have by now broken down into two separate things two separate forces neither of which might resemble gravity but but because it hasn't yet broken apart into this state of broken symmetry it's in this unified state space is filled with with with equivalent residual energy this is sort of like super cooling water you can cool water below it's freezing point below T equals zero degrees Celsius and if you do it very carefully its kinetic temperature that temperature of the random molecular motions of the molecules will be below zero degrees Celsius so it should freeze but there's an additional amount of movement of the molecules so to speak which keeps them in a liquid state that's sort of a latent heat or the latent energy associated when you go from the liquid state to the solid state but in this case it's still in that liquid in it and it's just it keeps the liquid in a liquid form even though it would like to be at that temperature in a solid form okay and it's a form in a sense of broken symmetry so at today's temperature three degrees above absolute zero is the temperature of the universe it's conceivable that gravity should have broken apart into two other forces but somehow remains supercooled in this weird symmetric state and the dark energy is the energy associated with that symmetric state and if someday and that and that dark energy by the way in a counterintuitive way perhaps has these repulsive properties now if gravity someday decides to break apart into two distinct forces then you know if both of those look very different from what gravity looks like today then in fact Newton's laws of gravitation will will fail and and we will no longer be in this bound orbit around the Sun and the Sun might disperse I mean who knows I don't know what the universe will do because I don't know what each of these two forces will look like but it's quite conceivable that neither one will look like gravity and that would be an example of the laws of physics seemingly letting us down in the future changing from what we've known and loved in the past does that answer your question dresses it yeah sure I think the job yeah so your your question remind me um when Einstein was working in the Patent Office and Switzerland well at the time when he was developing his theory of relativity of special relativity he had a conversation with with his friend and in that conversation Einstein expressed the view that the one part of physics that he felt would not be overturned that will never be shown to be wrong is thermodynamics thermodynamics is is sort of a large and interesting field but it it basically is responsible for laws such as the increase in entropy the general increase in disorder over time and Einstein felt that while everything else was in some sense subject to revision he felt that that thermodynamics was was going to be in violet and there's there was a very interesting sort of proof or not proof but something that confirmed his ideas you know Einstein of course then went on to to develop a theory of general relativity and one of the inescapable consequences of the theory of general relativity is the formation of black holes the idea that if you have enough mass and the mass will collapse under its own weight and and and form a singularity that's that's that's cloaked by an event horizon and in the classical theory of general relativity if you shine light on a black hole the light just just goes into the black hole black holes literally completely black and thermodynamics states that if something is completely black that is something absorbs all the light that falls on to it and a black hole is a perfect example of that then it necessarily will radiate this very specific spectrum of energy anything that's completely black will process the radiation and give off what's known as a blackbody or thermal spectrum and so there was this conflict between Einstein's theory of general relativity which is one of the most extraordinary theories of the 20th century and thermodynamics and turns out now Stephen Hawking is famous for showing that black holes do indeed radiate it's ultimately Stephen Hawking is famous for showing that black holes radiate and evaporate and that sense shows that thermodynamic sort of carries the day and so I very much agree with that sentiment that the statistical laws of what happens when you have very very large numbers of things will continue to hold in our universe but I do think that that you know as we get better and better understanding like what alex is saying or the discovery of higher and higher energy processes many of the laws that seem to hold at low energies are subject to revision but I think that thermodynamics won't be how about one more question for me and then maybe folks could approach them the microphones or now if you like you've talked about the dimming of the universe say in roughly a hundred billion years the dimming of the galaxies at least the stars though in our own galaxy well at least some still be shining there have been some newly born stars some long-lived ones but I understand Greg you've worked in the dynamics of a long-lived galaxies yeah about near collisions that what what's the fate within our galaxy in the term order of a hundred billion years right so so over the next hundred billion years all the other galaxies will recede from do you except for the Andromeda galaxy we're we're actually orbiting around the Andromeda galaxy right now and in roughly five six billion years at about the same time that the Sun is turning into a red giant will collide with the Andromeda galaxy and that that collision when you look at a galaxy yeah yeah yeah so this is this is a supercomputer simulation that shows what happens when two spiral galaxies like the Milky Way and Andromeda interact and collide and you see that there's just this tremendous amount of stuff going on these are literally hundreds of billions of stars all interacting under their own gravity and taking these two highly ordered discs and just shredding them throwing out these tidal streamers and basically merging into what will end up as a single giant elliptical galaxy and when you look at it on this this sort of simulation you think oh my god that that's gonna be the worst thing that could yeah it makes the Sun turning into a red giant looks like small potatoes when you have a hundred billion stars colliding with another group of 100 billion stars but the thing to remember is that these galaxies the stars in these galaxies are like grains of sand separated by miles and so when you have one group of sand grains separated by miles colliding with another group of sand grains separated by miles you don't even notice it right as this is going on there will be about twice as many stars shining in the night sky and that's it as far as the earth is concerned that's it and one thing that can't happen is that the Sun may well get tossed out of the collision all right a lot of these stars are our sort sent down into the core some of them go into the central black hole some of them end up near the core and a lot of stars are tossed out if the Sun and the earth if the Sun gets tossed out the earth will get tossed out with it and if the universe continues to accelerate its expansion then the Sun and the baked planets are going to be isolated from all of the other galaxies and so a possible fate for our earth right here is that we survive the sun's red giant phase that you know we sort of have this baked planet orbiting a white dwarf remnant to the Sun that thing has been thrown out during this collision and we are utterly alone in space utterly alone to the sense that there are no other stars in the sky there are no galaxies there is nothing as far as literally you can see and that's a pretty desolate future a baked planet even the fossils right those fossils are going to get metamorphosed out of existence right think pressure it's going to destroy every trace that we were here if the Sun on the earth gets tossed out then they'll be utter desolation right there will be no evidence that we ever were around or that any life on earth was ever around or any evidence that there were ever any other stars or planets or anything that's pretty sad ending - I would say our conclusion I think Tucker is that the universe will not have a happy ending but I'm not so worried about global warming what's the problem just drive your home it will open it up for questions now generally yeah it hardly seems to matter anymore but I did have a question you described the the structure the distribution of matter and you characterized it as kind of a kind of a filament restructure what's the structure of the distribution of dark matter well it's pretty much the same there are voids and there are regions that are that are where it's more clumpy and the stars tend to form in the regions where the density of the dark matter is the highest because the dark matter also gravitationally pulls in the stuff of which stars are made neutrons and protons and regular sort of matter but there's no the voids aren't completely empty it's just that there's sort of a you know this distribution with with low-density regions and high density regions and the galaxies tend to form in the high density regions so it's sort of like if you're flying above a mountain chain and you can see that there's snow on the tips of the mountains but there's this huge underlying backbone the galaxies are just the snow at the tips of the of the mountains yeah yeah but that's that's exactly right and and I think that the interesting thing about dark matter is that because it's dark it's not shining and because it's not shining it's not dissipating energy and so dark matter dark matter collapses under its own weight it can't form a disc like our galaxy the disk of our galaxy is is is formed of stars that formed from gas clouds that could collapse and and and and have pressure and so dark matter because it can't collide will sort of you know stay in a more amorphous shape even when it collapses whereas is ordinary matter like the matter of the stars are of will tend to form disks so you can never have like a Saturn's disk made out of dark matter because the Dark Matter particle is basically a very hard time colliding with each other but by and large the dark matter and the ordinary matter really sort of follow the same structure on the very largest scales sorry I was struck by that computer simulation with the filaments in the galaxies at the net at the nexus where they they came together are the one minor question Aerith of filaments between the bright spots are those composed of stars I know that's a simulation but because as that network they just a bunch of stars that are not as you might say nice dance and that was a that's my question and I don't even know how to quite pose this but I remember is that elementary structure of the whole universe do you think of it that way if I recall as a considerable thought that mass itself might be I guess it's called an emergent property from the from the whole universe structure there I'm Way beyond that's the limit of my knowledge but I I got the impression that we can think of mass itself or energy as being a property of the universe as a whole rather people trying to explain various kind of for it and not force us into distance but I'll stop there because that's as far as I can go but can you come in a lab okay what you asked two questions and one is easy to answer and the other is hard to answer the one that's easy to answer is those simulations are showing a volume that's have ordered billions of light years on a side and so if you could zoom in and zoom in and look at the filaments you'd see that the filaments are not actually sort of solid or even continuous objects but rather of galaxies which in turn are incredibly low-density objects and so that film entry structure is sort of the way that the galaxies are organized on the largest scales and to get down to the size scale stars you'd have to zoom into the individual galaxies where you would be able to see that the galaxies themselves are composed of fields of stars now the second question on mass being an emergent phenomena within the universe I think that makes sense when one talks about the very earliest moments of the universe how the universe came into being what the nature of matter truly is you can start to ask that question but when you stand back on the largest scales the universe is sort of the structure in the universe is defined by the fact that there is matter there is stuff that can be converted back and forth to energy but which is in stable form and that's what's sort of giving the universe its overall structure I don't know if you want to take I can add a little bit to it you might be referring to this idea that the universe in the first tiny blink of an eye of its existence inflated by a gargantuan factor from an almost indescribable small little volume to arbitrarily large okay and it was driven we think by an energy that's reminiscent of the dark energy that's currently beginning to accelerate the universe but the energy density back then was much greater and it went whoosh much more quickly than it's going whoosh right now that energy that drove the inflation is exactly balanced by sort of a negative gravitational energy in other words everything attracts everything else and so to give you a simple example when I release this Apple from rest it gains energy of motion it gains kinetic energy but I'm not creating energy out of nothing because it's also gaining an equal negative gravitational energy negative one two three four five units of gravitational energy at the same time it's gaining positive 1 2 3 4 or 5 units of kinetic energy so the sum is 0 so this this weird dark energy like thing that drove the original inflation was a positive energy that was we think constant are nearly constant with time per unit volume and it made the universe become really big and you might think that that created a giant amount of energy and it did but it was exactly balanced by the negative gravitational energy of the attraction of every little bit of this stuff for everything else so remarkably enough these inflating universes are universes of basically zero energy it's just it's good that there's the positive part the dark energy and then the negative part its gravitational attraction for everything else eventually that form of dark energy decayed into matter antimatter photons and everything else we love then the matter and antimatter all hit each other and a little bit of matter was left over for reasons we don't completely understand and that's what we're made of right now we're made of the residual stuff that originally inflated the universe so in a sense the total mass and energy of the universe was and always has been or is and always has been zero but fortunately for us there are positive parts us and negative parts our attraction for everything else but the mass of the universe emerged from this dark energy or the in photon as it's sometimes called that that created this gigantic universe in the first place and what was there before the inflation you know could have been something arbitrarily small it could have been even and a quantum fluctuation out of a pre-existing nothing or maybe a quantum fluctuation out of a pre-existing universe and ours sort of budded off so to speak so in a sense the mass of the universe now emerged from whatever it was that made the universe as big as it is okay but it's a very hard question we don't know that what I just said is true it's speculative but but an interesting speculation so since according to thermodynamics entropy always increases would Krunch ending to the universe contradict that yeah that's a good question ya know I don't know the if you take an object like the Sun the Sun taken as a whole seems to engage in a decrease in entropy in the sense that the sun's final product is going to be a white dwarf which will end up in a highly ordered crystalline state at the end of the day and so when you look at the Sun as an evolving body you might think that at the end of the day this law of second six second law of thermodynamics has been violated but that's not the case because when you consider the universe as a whole all the radiation that the Sun has emitted and spewed out during its lifetime that creates far larger sort of end product of disordered and highly ordered remnant and so the reason why the question of the increase in entropy in a collapsing universe is is or is not a violation of the second law of thermodynamics is interesting because you're talking about the the universe as a whole and so I will state and I'm quite sure this is true is that second law of thermodynamics is not violated in that case the the sort of entropy of the stuff that is lining up in the Big Crunch is higher than the original entropy but unfortunately I don't have a good sort of analogy or even I don't almost be honest good understanding of exactly why that is the number of quantum states that you're left with during the the Big Crunch is going to be vastly vastly higher than the number of quantum states that existed during during the early Big Bang but I I don't I don't have the exact answer to why that is I believe the answer to that question is is is well understood but but I personally don't have it you yeah I don't either really the there are a number of arrows of time one of which is the thermodynamic arrow of time right how do you define which way time goes and some physicists said well it's the direction in which entropy keeps on increasing but but as Gregg said the the number of states number of possible states at the end is very large because one way to think about it is that you're you're squishing down the universe and you're creating all this high-energy radiation and if you just had a universe filled with radiation and only radiation that would be that the highest entropy possible in fact indeed in a universe that expense forever you have that and state as well well I don't completely understand like what Gregg said is why that state of entropy in the Big Crunch is clearly higher than the state of entropy that the universe was born in in the Big Bang yeah I think that's so it's a good question but it is I agree with Gregg it's it's it's well resolved by the theoretical physicists who have dealt with this in other words they don't feel that this is a problem yeah I don't know quite what the answer it is I think I think that another another way that that you can help to understand better understanding of it is the the Big Bang we often think is sort of cloak way of empty space and some sort of atom sitting there an empty space which exploded in reality that the Big Bang was everywhere and the basically if you take the expansion that's going on right now and run that clock backward then you find an increasingly dense universe and increasingly hot universe but it's always all enveloping and you always have a region beyond your horizon and so the process of the evolution of the universe through its initial hot dense phases out to some very cold phase and then back into a hot dense phase if we take a comoving volume of the universe then the amount of disorder that that creates will been dumped into other parts of the universe and so when you come back you are sort of have this this this accounting problem in that do you consider just the entropy of what was in your comoving volume in the sense with the Sun do you consider just the entropy of the Sun itself or do you consider the entropy of everything that is now in your causal horizon and what was beyond that and so this sort of law of thermodynamics when viewed on the the scale of the Big Bang as a whole and that perhaps the Big Crunch as a whole the universe there is something that's perhaps larger than your current horizon and so the universe is not a fixed system and you're able to dump entropy off into regions that you are no longer in to contact with and so I think that is the the key to that dilemma is how you do your accounting and the entropy had served the Metaverse they use a region beyond your causal horizon has increased whereas the entropy within your causal horizon may not necessarily have have increased as the Big Crunch recedes and the same thing is just like with the Sun turning into a white dwarf if the Sun is tossed out of the the galaxy and at the rest of the universe sort of inflates away and it's left all by itself then it really does look if you take an accounting of the total amount of entropy that the Sun is produced all that entropy is outside the Suns universe at the end of the day and so it seems that there's been a violation a second law of thermodynamics but if you account for everything that the Sun has ever been in contact with then you find out that that's not the case I think but that's the the resolution to to the second law problem for Rica lapsing universe a question here please well if I understand you well you know created all they'll and that concept because of you understand it that the galaxies and the stars were accelerating okay so I tend to believe it to think more or simply so like I believe that it's a lot like the aether theory the only present letter because Weiss couldn't be the answer just simple geometry if I believe if I remember correctly my physic is in college gravity is a field and it decreases the forces that generates according to the distance so if the galaxy is if the universe is expanding right now the distances is increasingly getting larger and larger so the force will be smaller so they al acceleration will be smaller because the mass is constant so why is not that a better explanation than creating a whole constant of land but the trouble is that as I try to explain the galaxies the supernovae are farther away than they would have been even if there were no gravity at all so it's not just that the deceleration is less than we expected it's as though there were no deceleration at all but even beyond that the things are farther away than than just that you know so I mean we take into account the inverse square law of gravity when when predicting the various future possibilities for the universe that's all taken into account the density of the universe is decreasing at least the the regular particle density is as the universe expands and you include all that it's just like when I toss the Apple the apples distance from the center of the earth is d is increasing and so the force is getting smaller you take that into account and you still find that the Apple will will always be slowing down never speeding up right at best it can go away from the earth at a constant speed as time approaches infinity but it can never go faster and faster with time and that's the that's the difficulty you need something to make the expansion go faster with time it's a bit like if you think that the pressure in your tire is is too high and so you open up the valve to let a bit of air out and if you were to do that and you find that as you let the air out then the tire gets more and more pressurized that's very analogous to what we're seeing with the whole universe so when the whole dark energy thing came and the accelerating universe it looked like you know it was gonna go on forever and you suggested that something has changed that maybe the thinking is that the sign might reverse what what has changed that right thinking different so when that headline came out you know reporters talked to us about our early discovery that the two teams had made of this accelerating expansion and at the time the theoretical models for what this dark energy might be were not yet very advanced okay this was kind of a new idea and so people said well this stuff is repulsive and it might even be just these quantum fluctuations in the vacuum which are occurring all the time and you know they actually affect very ever so slightly the structure of atoms you know but people figured all right there's a little bit of some of that or something like that that's causing this weird acceleration okay and so the number of models was fairly limited okay then a bunch of theorists came along and including Andre lean day at Stanford and they came up with other possibilities for what this dark energy might be not just vacuum quantum fluctuations but other things and among those other things are substances or energy fields that later on change sign gravitationally because they decay or change into something else and in answer to a previous question I actually gave an example of that I said that the in float on that dark energy that we think inflated the universe in the first 10 to minus 35 seconds of its existence and which was definitely very repulsive back then you could call it repugnant if you want but it was you know it was a repulsive it created an exponential expanding universe that's what made it very large in a very small amount of time it later decayed into normal matter antimatter and photons and all three of those things normal matter antimatter and photons are gravitationally attractive they are a type of energy which is gravitationally attractive rather than being a type of energy that's gravitationally repulsive because it has a weird property called a negative pressure we can go into that later if we have time so there's an example of a dark energy like field that later decayed or changed into something that grabbed it was that was gravitationally attractive and indeed if the current dark energy is of a similar sort and if it's total density plus the density of normal stuff that we know of exceeds one in certain units a certain critical amount if it exceeds one ever-so-slightly then when this stuff if it ever becomes gravitationally attractive when it does it'll start slowing down the universe and if and if there's enough of it it'll eventually cause it to come to a halt and rhe collapse and so now with with these additional theories we've come to the realization that though the dark energy is repulsive right now it might not forever stay that way and that's why we're still not sure whether that we will have eternal expansion or an ultimate Big Crunch neither of which I submit is a particularly happy ending sir okay well that's good because that just answered one of the two questions I want to ask so I'll direct my other question now to Greg when the Milky Way galaxy and Andromeda collide isn't it going to generate a tremendous burst of star formation a lot of new stars upset and also well you know the Sun gets hotter if we're in O'Neill colonies few billion years in the future can we just move them further away as the Sun gets warmed up yeah so so you that's absolutely true that the Milky Way still has quite a bit of gas that hasn't been turned into stars and Andromeda galaxy has somewhat less but a sizable amount and so when the galaxies collide you know as I was saying the stars just fly right through each other and sort of spin around in this joint gravitational field that they're producing but the gas does smack and when that happens that provides the conditions under which new stars can form very very vigorously when we look out in the universe and see galaxies in the process of colliding we see star formation just occurring at a tremendous rate they're called starburst galaxies and so there will be the last sort of baby boom of stars in the joint Milky Way Andromeda galaxies will occur in 6 billion years or so when the collision occurs and there'll be planets forming from those young stars there will be all sorts of interesting things going forward and then for the next trillion years or so there will always be sort of the same sort of density of stars in the night sky as stars like the Sun die and become red giants and then turn into white dwarfs and fade from view stars that are a little bit less massive than the Sun will sort of take their place the smaller star is the longer it takes to evolve and because there's many more stars of low mass than of higher mass like the Sun for about a trillion years or so you'll be always replacing the ones that are dying with more that are coming to the end of their lives and turning into red giants but then after about a trillion years that'll really shut down a drastic arena for a trillion years again send our O'Neil's colonies to already closely around red dwarfs exactly so the next trillion years if you envision sort of an Isaac Asimov style future for the galaxy of big snooze colonies and is this character was do is doing that as well yeah that's gonna work for about a trillion years there's there's enough stellar energy hydrogen fusing into helium that will keep things running in that kind of stage four of order a trillion years then you have to sort of change your style look it looks like in a century gonna have a space elevator and you know another century you get we the way things go the trillion sounds a long time the trouble is that after about a hundred trillion years even the lowest mass stars are certainly by a quadrillion years even the lowest dense mass stars will have burnt out and and so then there will be you know no recourse right there won't even be the low mass stars to to build colonies around it turns out it turns out actually that's almost right but not quite right there's also brown dwarfs and if you there's roughly as many brown dwarfs those are objects that aren't quite large enough to fuse hydrogen into helium and over this timescale quadrillions of years you'll occasionally have a collision between two brown dwarfs when brown dwarfs collide they don't bounce off each other it's really an inelastic collision and so two brown dwarfs can collide and make a merged object that's large enough to fuse hydrogen it's a bona fide star so it turns out if you do a detailed calculation for the next hundred or thousand quadrillion years there are always be about 50 stars shining in the joint Milky Way and dromeda galaxies that are being produced by this process but it really is true that that after 10 to 100 trillion years like you were saying that the huge wave of stars that have been formed during the early phases of galaxy's evolution those guys are all dying turning into white dwarfs and they are not being replaced in in any considerable number so things are really gonna change in the trillion years and you think that's you think that's scary in three minutes another wonderful log begins we have time for just one more question I'm afraid yes sir okay so some series such as that that there exist a mega mark multiple universe so in Kies there there are a lot of universe and they are actually interacting with each other I think most lots of discussions were chain for example the nature of the dark energy I noticed about the ending of our universe how it works if there actually several universe and actually actually interacting with each other well I think in most of the multiverse hypotheses the different universes don't actually interact with each other beyond the possibility that they bud off from one another select between you and me in a whole bunch of other dimensions a whole new universe could be sprouting off but we basically don't interact with those universes but that's one possible happy ending though life and other interesting things might cease in this universe new ones will spring forth in which this whole thing could could recur but I don't know that we interact with FEM do you do you know Greg with whether we enjoy other then you can have a very massive black hole which is spinning and so there exist solutions to the equations of general relativity in which you can i Papa sized having contact with regions that are outside of our causal horizon by entering rapidly spinning black holes that's something that struck me about being evolved in the extremely distant future is that the story is continuously changing I first started started thinking about the future about about ten years ago back in 1996 1997 and at that time Alex and his collaborators hadn't yet discovered that the the universe's expansion is accelerating and so my my friend Fred Adams and I wrote a book about everything that would happen in the future and large chunks of that book were just obliterated by the fact that the acceleration is is the expansion is accelerating and so at any given moment our view of the future is very much colored by our understanding of today talking about the extremely distant future is it an interesting and profitable way of working through our own understanding the laws of physics as we understand them but I think it's if one thing is absolutely certain it is that the future is going to be more interesting than we sort of envision it and it's going to be different than we envision it but that doesn't make the sort of viewing the long-term future it doesn't make it an empty endeavor because we learn a lot about the here and now and get a better sense of what we have by making these these extrapolations these these thought experiments I would say that Greg is being a bit modest when he says that large chunks those of the book were sort of destroyed I urge you to read the book because in fact many of the physical processes that he discusses like the decay of protons and the you know disruption of white dwarfs and the evaporation of black holes and all this kind of stuff will still occur in an accelerating universe in fact so it's still a very very relevant and interesting book before we thank our speakers pardon me I must remind the questioners they're very capable questioners as well as the speakers that Wonder fest needs a signature from each of you on a waiver form are these these videos can appear on the internet please thank the speakers and we'll get ready for next time you

Channel: Prometheus Unchained

Views: 9,566

Rating: 4.7735848 out of 5

Keywords: The Universe (TV Program), alex filippenko, the end of the universe, heat death, the end of the world, the end of the earth, the sun, astronomy, End, Ufo, Space

Id: dNydwuCTVMU

Length: 80min 58sec (4858 seconds)

Published: Sun Jan 12 2014