Katie Mack - Death of a Universe

coming out this morning to hear about this very cheerful topic so I've been thinking a lot lately about the end of the universe the ultimate destruction of all reality and what's the what that's going to look like and how we can find out what's coming and part of the reason that I'm thinking about that is because I'm writing a book so you fell by this book when it comes out in 2020 it's called the end of everything I have to mention that I'm sort of contractually obliged but anyway so I'm gonna talk a little bit about that and I'm gonna start with a poem 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 it had to perish twice I think I know enough of hate to say that for Destruction ice is also great and would suffice this is the famous poem by Robert Frost from 1920 of course we know the answer now it's fire it's definitely fire the world will end in fire in only a few million years actually the Sun will have expanded and and heated up enough to boil off the oceans of the earth make leaving the earth a lifeless charred husk of rock after that the Sun will expand even farther it'll engulf the orbits of Mercury and Venus probably the earth will spiral in at some point around there it'll soften outer layers the earth will end in fire it will be definitely fire dead okay but that's you know that's just the earth that's a few billion years I'm more interested in this I'm a cosmologists I study the universe I'm interested in how all of this will end this is an image from the Hubble Space Telescope a beautiful view of our cosmos with tens of thousands of galaxies visible here like each one of these little tiny dots is a galaxy a collection of millions or billions of stars possibly with their own planets and civilizations who knows I want to know how this is all going to come to an end okay so in this talk I'm gonna go through a few possibilities so we've got the Big Crunch he death big rip and vacuum decay I'll talk about those for now in preparing for this talk I thought I should take a little public survey and see how people feel about all of these so I went on Twitter and asked which which of these scenarios would would be more personally rewarding for for the audience and and I got 4000 responses and they chose wrong okay so they 37% preferred the Big Crunch which is not the right answer I've really the vacuum decay is so much cooler and you'll see why but anyway I thought I should let you know so we'll start with the Big Crunch okay so this is a sort of old idea this is one of the least likely ways for the universe to come to an end as far as we know from our current physics but back in like the 80s and 90s it was it was thought to be you know reasonably probable and basically what happened was we were looking at the out of the universe and we're noticing the you know the the galaxies are moving apart from each other the universe is expanding okay the idea is that the Big Bang happened something happened that started off the expansion of the universe and since then the universe has been getting bigger and bigger and the way it gets bigger is that the galaxies and the things in the universe get farther apart from each other oops yeah and as that happens basically the empty space in between galaxies is getting larger and so we looked at out at the universe and we saw the expansion of the universe and we thought okay so what's gonna happen next is it going to keep expanding forever or is it going to turn around at some point and the question there is between the balance between the sort of expansion set off by the Big Bang and the gravity of all of the stuff of the universe and and we didn't know the answer and so for a long time it was thought that after a while you know the the expansion will go for a while and then it'll start to reverse and the galaxies will start to come together again and get more and more compact and then at some point in the the distant future you'll have a situation where galaxies are sort of crowding in and and the universe is becoming a more compact space and what you would see as that happens is you would start to see more collisions of galaxies and we see collisions of galaxies all over the sky we see galaxies coming together with their gravity and getting mixed up and so this is one of the first things that would happen if the universe were going to do a Big Crunch if it were going to all come back together and although it's unlikely now that the Big Crunch will happen we do get a bit of a taste of that in a few billion years because this this galaxy here is coming right for us so this is the Andromeda galaxy it's probably a little bit more massive than our galaxy although there's some debate about whether or not it might be closer to the same than we thought and it's coming for us at about 110 kilometers per second and in about 4 billion years it will collide with with our Milky Way and it'll be really cool to see when that happens I mean we'll all be dead obviously the earth will be dead but maybe you know maybe we can leave like a little webcam or something and and this is what would see something like this so we'd see the the galaxy composer it would start to interact with our galaxy you'd get this in this picture you see all this sort of red this red these red blobs that you'd get a lot of star formation as the as the gas and dust of those galaxies come together form new stars it might ignite the black holes in the Centers of the galaxies you get stuff pouring into the black holes and create Jets coming out of the black holes in the Centers of galaxies really cool and in the end you'd end up with a sort of less interesting blob of stars after it all sort of settles down but the the thing about this is that this is probably not going to really mess up the solar system I mean there it'll be dead but but it'll still be around you know and the the this will still be rather sudden and the Sun will be okay because when galaxies collide generally the stars move right past each other there's so much empty space even in galaxies but the Big Crunch isn't like that because with the Big Crunch yeah the galaxies come together and stuff but the other thing that happens is that all of the radiation from the stars and all of the radiation left over from the Big Bang starts to get compressed in a smaller and smaller space as the universe is condensing and so one of the really cool things that you learn when you study the Big Crunch is what you learn what kills the stars and that is okay so you know this is a picture of our Sun from it may you can look at pictures of the Sun like real time on the internet now which is kind of amazing these amazing images from these satellites what kills the the stars in the Big Bang in the Big Crunch is that the radiation gets so strong just in the universe in the ambient space in the universe that ignites the surfaces of the stars and and the surfaces of the stars themselves sort of detonate at that point the planets you know there's no hope but but it would be it would be really cool just everything would sort of catch fire okay so so that's probably not going to happen the most likely thing is actually the heat death based on what we know about the universe right now and the idea behind the heat death is that you know the universe is expanding and it's going to keep expanding and keep expanding and keep expanding because there's something in the universe that's making the universe expand faster there's something that's balancing out the gravity of all the stuff pulling the universe together and balancing out out and over balancing it there's there's something in the universe that makes the universe expand faster we call it dark energy we don't know what it is but whatever it is it's sort of stretching out the space between galaxies and it's coming to dominate the universe that as it goes as it continues to expand the universe each galaxies will get more and more isolated until eventually our galaxy our little group of galaxies the the sort of conglomeration of us and Andromeda left over in trillions and trillions of years we'll be alone in the cosmos because everything else would be so far away pulled away by the expansion the universe that we won't be able to see it anymore and so each little island of structure will be isolated and eventually the stars will burn out and the particles will decay the black holes will evaporate and everything will just kind of fade to black that's called the heat death it's called the heat death because the the term heat in that in that term actually comes from the idea of disordered energy so as the particles decay and as the universe becomes empty all this left is a little bit of sort of a tiny background of radiation at something like 10 to the minus 48 kelvins very very cold background of radiation that's just uniform throughout the universe just Heat and you can't do anything with a uniformly distributed heat and so all structure will end all order will end and it'll just be this maximum entropy state of nothingness so that's that's the heat death and that that assumes a cosmological constant so because they tell you this because it could get worse so so cosmology Wisconsin is this idea that Einstein came up with as a way to balance out the gravity of everything in the universe because when Einstein Einstein it's time he thought the universe was static and so he knew that all the galaxies are pulling on each other so they should just all come together there should be an immediate Big Crunch and so he had to put in something in the equations to balance that out and so he put in something called the cosmological constant they could kind of push everything away and keep it static and when he found out that the universe was expanding he got rid of that term but now we need something to push the galaxies to make them expand faster faster and so it's cosmological constant and the thing about a cosmological constant the the constant part is the density so if you have the density of stuff in the universe versus time you know the the density of matter goes down as the universe is expanding the density of radiation goes down even faster but the cosmological constant just stays constant if you have a box this big full of cosmological constant you make it twice as big now you have twice as much cosmological constant it's weird stuff but what that means is that over time it'll just completely dominate the universe and there will be really nothing left aside from from the cosmological constant cuz everything else gets diluted and it doesn't but that's for for a cosmological constant in particular kind of dark energy but there are other kinds of dark energy that that don't do this sort of flat thing they they actually kind of go up over time and that's called phantom dark energy and that leads to something called a big rip now a big rip is worse than the heat death because in a big rip when the galaxies are being pulled apart from each other there's so much dark energy in the universe it's so powerful that it doesn't just remove it doesn't just make the dick galaxies more distant from each other it starts to expand them from within like currently in the expansion of the universe as we understand it we're not getting any bigger but the universe around us the spaces between things are getting bigger in a big rip in a phantom dark energy universe leading to a big rip the the sort of bonds that hold together structure would themselves be overcome by the dark energy because in big rip universe in a phantom dark energy universe you have box of fan of dark energy you make that box twice as big now you have more than twice as much dark energy and there's a there's a lovely illustration that NASA made of what would happen in a big rip that that I really like so you have the expansion and then pimping the galaxies get pulled apart now just just to give you an idea of how we study this there's there's a parameter that we study having to do with the balance of density and pressure of the stuff made in the universe called the of state parameter this w and I tell you this because the cosmological constant gives you a W equals exactly minus one that's how you define a cosmology with monseñor that's it's one of the properties of it the the pressure and the density sort of exactly balanced each other in this written in this way and phantom dark energy is a cosmological constant of anything at all less than minus one so so cosmic constant is exactly that number anything at all less than that number is phantom dark energy destroys the universe of the big rip so when that when the big rip was first sort of hypothesized they there was a really amazing paper that came out they calculated exactly what would happen when if if you had a w of let's say minus three-halves okay just as an example and so they made this this timeline of doom so they say start with like the things that have already happened you know galaxies form atoms form and then you know they they figure out that the big rip would be at thirty-five billion years from the beginning in the universe and so 1 billion years before that galaxy clusters go away 60 million years before Milky Way is gone then things speed up a lot three months before the solar system is unbound 30 minutes before the earth explodes and then 10 to the minus 19 seconds right before the end the the atoms are dissociated and everything is ripped apart and the universe is destroyed during during this big rip but that's for that's for three-halves W equals three house which is a really really large negative number and we can calculate we can measure W by doing things like we have this this Planck satellite that's looking at the Cosmic Microwave Background the the afterglow of the Big Bang itself and studying the properties of that and we can measure W to to a great precision with with these kinds of measurements combined with others and what we're hoping for is W equals exactly minus one what we actually measure is that so a little bit less than minus one but within the Arab right so it's it's it's minus one within the error of the measurement so far but it'd be the best fit value is actually a little bit less but it's okay because if the big rip is coming it's not coming for a very long time we have at least 120 billion years before we have to worry about this so so you can rest easy it'll it'll be awhile and this you know we're constantly refining this number so so we don't really know yet um but that's a big rip but the last one vacuum decay is cool because it could happen at any time technically so so this is an idea that it's been around for a while I think at least since the the 70s or 80s and it's this idea that the that the universe could kind of destroy itself in a sort of bubble of quantum death I'll explain that um so so it's been over it's it's this idea that there's more than one kind of state of the cosmos the state of the fundamental vacuum of space and we could transition between those two states possibly and for a while it was sort of just this this curiosity and in the acquaintance but then something happened which is that we discovered the Higgs boson this is the large how this is an event display from the Large Hadron Collider showing you know protons smash together create this debris it's measured by by these detectors and we learn about the standard model of particle physics we learn about the properties of subatomic particles and we discovered the Higgs boson this sort of final missing piece of our best model of particle physics yet the standard model and when we discovered it it told us the the vacuum decay is possible but but I'm getting out of myself but let me just start with the standard model okay so this is the standard model of particle physics it's a beautiful set of it's a theory that tells us what's what the particles of the universe are and it's it's been fantastically successful in predicting all kinds of experiments and interactions and it's got a set of particles plus that one the Higgs boson discovered in 2012 very exciting so we'll just walk you through what these are so there's the the quarks these are the purple ones the quarks are particles that are constituents of protons and neutrons so if you take two up quarks on a down quark you get a proton two down quarks and an up quark you get a neutron then there's the green ones here the leptons these are the the electron and the neutrinos the electron of course is the thing that goes around the nucleus of an atom although once you learn quantum field theory and stuff you learn it's more of a sort of cloud of electron probability nough sand wave functions and things but it's a sort of constituent of the atom on the right there the red those are the gauge bosons these are things that are responsible for the fundamental forces of nature so you have the photon that does the electromagnetic force the gluon that holds things together inside inside nuclei it's it's the thing that does the strong force the strong nuclear force then there's the W and the Z bosons that do the weak force the weak nuclear force and by studying the properties of all of these particles the the standard model of particle physics we can learn about the the fundamental nature of the cosmos the fundamental nature of the sort of universal vacuum in which we live and specifically by measuring the Higgs boson and the top quark we can learn something about that and so we can make this graph this is a graph from 2012 shortly after the Higgs boson was discovered and for different values of the Higgs mass and the top quark mass you end up in regions of stability or instability or places where the equations don't make sense and what we found by measuring these numbers is that we're right there so that's that's a metastable spot that means that the universe is stable for now at the moment but it's not stapled forever it's sort of an unstable equilibrium and what that what that means in terms of you know what here's a sort of schematic of what that means okay so this is a schematic of two different states of the universe where each state gives you different sort of laws of physics different constants of nature okay and you can think of it as these are little valleys in some energy space and you know we live in one of these values valleys right and the higher one is the false vacuum the lower one is the true vacuum because the false vacuum is sort of the less stable state and the true vacuum is where things are much more stable because this lower energy and that's sort of where everything would settle right so what that plot showed us that that metastable state means that we're in a false vacuum which means that if you had a high enough energy event happen somewhere in the universe it could kick us right over into the true vacuum and that would be bad because the true vacuum has different constants of nature than the false vacuum constants of nature things like the the charge of the electron or the mass of the particles or even the the strength of gravity sometimes and so so if you take the the molecules that you're made of and you put them into a true vacuum state those molecules don't hold together anymore total destruction right but luckily the energy it would take to kick us over that Hill is just phenomenal right like way higher than any kind of energy we can make with with a Collider way higher than any particle collisions we've ever heard of just just totally unreachable that energy so you might think okay we're safe like technically we're in a true vat of false vacuum but we can't possibly get over that hill unfortunately the universe is also fundamentally quantum mechanical which means that if you're if you're over here in one little Valley you can just like quantum tunnel right over to the other one which means that at any point in space there's some problem that at that point in that time there will be some little quantum event that will kick that little bit of space into the true vacuum and because the true vacuum is a lower energy state it's sort of preferable which means that that little bit of true vacuum will want to expand so what that looks like so let's say you have this this event happens over here you get this bubble of true vacuum expanding through the universe and it's expanding at the speed of light and this this bubble wall has some kind of energy associated with it the energy it would take to get over that hill which means that the bubble wall if it comes out you would just incinerate you immediately and because it's expanding at the speed of light if you're over here like you're not gonna see it's coming there's just no way and then once it passes you know does incinerates you and then it creates this true vacuum everything falls apart and a total destruction right so this this idea has been around for a while as I said and there's is a paper from 1980 by Coleman de Lucha which which I really like it has this beautiful piece of physics poetry in it now I want to share it with you now this this in this paper just before this this bit that I'll quote you they went through and they calculated what would happen to that bubble of true vacuum once it forms and they calculated that in the model they were working with that that bubble of true vacuum once it forms would be gravitationally unstable and it would just collapse completely so first you know first there's the wall of destruction and then there's there's the atoms can't hold together and then total collapse and so and so they they did those calculations and then they say this is disheartening they say the possibility that we're living in a false vacuum has never been a cheering one to contemplate vacuum decay is the ultimate ecological catastrophe in a new vacuum there are not only there are new concepts in nature after the vacuum decay not only is life as we know it impossible so is chemistry as we know it however one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain if not life as we know it at least some structures capable of knowing joy this possibility has now been eliminated so so I should say that you know those calculations from the 80s there are some uncertainties in that and it's possible that the new vacuum would not immediately collapse once it forms it's probably still not possible we could survive in it but you know some structure is capable of knowing joy but but there are a couple of reasons that you really shouldn't worry about vacuum decay aside from the obvious there's nothing you could do about it you wouldn't see it coming also it's not like anybody's gonna miss you it's the whole universe it's gone so like it's fine but aside from that you know these calculations that the idea that we're living in a metastable state come from careful measurements of the standard model of particle physics and and although the standard model of particle physics has been massively successful in terms of all the experiments we've ever done everything we've ever seen we know it's not the whole story because when we look at sort of a pie chart of what the universe is made of we see that most of the universe is dark energy and dark energy does not fit in the standard model of particle physics it's not part of that picture it's something else then then most of the matter in the universe is dark matter which also does not fit in a standard model of particle physics we don't have a particle in that picture that makes the dark matter that we that we observe the the invisible stuff that holds galaxies together doesn't seem to be in that in that model the entire standard model of particle physics lives here in this little 4.9% slice of the universe that we can even remotely understand so everything that we've ever observed and all of these calculations are based on this little bit that that we can do experiments with so maybe there's something in the rest of this that says that we're not gonna at any moment transition to true vacuum state maybe there's some kind of thing that'll tell us that that there's some other possibility for how the universe will end that that that you know maybe it'll be some other really interesting story and in the meantime you know I'm working on trying to understand the rest of this pie chart and figuring out sort of what it all means and where we're going so thank you I think we have time for some questions if if we want if anybody has questions about the universe and we're all going as are there better endings from from the research into this other stuff I mean it depends on what you mean by better I mean unfortunately there there doesn't seem to be any scenario that's the seriously discussed in the literature that has the universe not end right so so so like there doesn't seem to be anything anyway for for things to just keep going and and given that you know it's not it's not gonna end well but but there are other possibilities for things that for things outside of these these four that I talked about one of the ones that's discussed a lot is the idea that that we live on a kind of brain which is a brain is like short for membrane it's a kind of limited space and then there's another one separated from us by a higher dimensional space and then they could like collide and then come apart again and then collide again have this like cyclic model of collisions of different brains across this higher dimensional space and that's something that that we might learn more about by studying dark dark energy maybe dark matter has something to do with with one of these things but I mean mostly mostly the name of the game is studying how the universe is expanding trying to get a better model of quantum gravity is something that unites the theories of gravity with the theories of the fundamental particles so that we know what what these things are and then that might tell us more about the structure of the larger universe but but I haven't I haven't seen anything that that gives us like a gentle a gentle end so it's it's it's it's gonna be unpleasant I think no matter which way it goes you mentioned black holes evaporating yes what's that yeah yeah that's really cool okay um so okay so this is this is an idea that came from Stephen Hawking actually the idea is that though black hole is you know the remnant of a star that's collapsed on itself and created this kind of singularity in space where nothing can escape from it though you'd have to move Traveler than the speed of light to escape from a black hole you can't do that but Stephen Hawking calculated that there's there's this way in which sort of quantum mechanical effects on the edge of the black hole can create particles sort of out of the vacuum in a sense that can leave the black hole and carry away some of its mass and this is called Hawking radiation and so basically all black holes that have some radiation that comes off of them at some tiny level it's it gets brighter as the black hole gets smaller but that kind of carries away the mass of these black holes and so if you leave if you leave a black hole alone long enough it will eventually radiate so much that it will disappear but it'll take a really long time so black holes that are something like 10 to the 15 grams so about the mass of a mountain if they were formed at the very beginning of the universe they would just now be evaporating so it takes it takes a while and more massive black holes would take longer to evaporate so so that's something that's that's been talked about for a while fun fact about black hole evaporation is that there have been some recent papers showing that that as buckles are evaporating if they're if they're small enough to be doing that just before they completely disappear they might trigger vacuum decay and destroy the universe so so it may be the you know that if you leave a black hole long enough it destroys the universe we don't know yet but I'm working on a paper about that at the moment it's kind of fun um what are some differences between cosmic inflation and the big grip because they're both very they seem to be both processes where the universe expands very quickly you're out of control yeah yeah so so cosmic inflation is there's there have been a lot of comparisons between cosmic inflation and dark energy the sort of dark energy dominated universe so cosmic inflation universe is one in which the universe is expanding very rapidly in very much the same way that a universe dominated by dark energy would expand rapidly but but the the big rip is a slightly different situation in which in that it's it's a more powerful expansion so whatever is whatever it is that's causing a big rip if it happens the span of dark energy would be would be different from what we imagine inflation to be a sort of more destructive but but I should say you know we don't we don't know for sure that inflation happen we don't know exactly what it did we just there we have a lot of evidence that there was a rapid expansion a beginning the universe but we don't know how it worked or what what made it happen dark energy dark matter it's out there why isn't it here so so yeah dark matter if it's out there is here it's passing through us all the time the the amount of dark energy that we would have in this room would be about about a third the mass of a proton per cubic centimeter and it would be passing through us right now at something like a couple hundred kilometers a second as the earth moves through the solar system and through the galaxies so so the idea is that the galaxy is kind of embedded in this a cloud of dark matter and we're moving through it all the time it's just it just seems to be very very hard to detect so whatever the dark matter is it seems to be a kind of particle that doesn't interact easily with the kind of materials we use for detectors it has mass so if you get a lot of it together it can be very important gravitationally but it doesn't seem to do much in terms of the sort of particle interactions at least not to the level that we've detected in terms of dark energy it would also be here but the end the the density of it is also very small and so it's only in spaces where the density of everything else is very very low that it can be sort of important quick question so if time varies in space-time based on gravity and acceleration throughout the universe mm-hmm how do you have one reference of time that you're saying like oh this will happen in 10 billion years or something so in the sort of speed at which time passes can vary depending on where you are and what you're doing and stuff like that but when I when I say something like you know 120 billion years from now I'm referencing specifically the time as we would measure it on earth but also it there are very few situations in which it makes much of a difference at all how how quickly time passes especially since 120 billion years is a very rough number and so it's so in most cases for cosmic timescales those things tend not to tend not to really factor in but if you're if you're doing sort of precision things or if you're talking about you know being really close to a black hole versus not then it then it can make a really big difference I think maybe you like one more question okay so the question is w you told us about -1 or a little bit less than minus 1 yeah but the error bars allow a little bit greater than minus 1 yeah yeah so so that's yeah so that's another possibility so that number W if it's anything less than 1/3 that sorry if there's anything less than minus 1/3 then you get accelerated expansion and so a cosmological constant is exactly minus 1 anything between that and minus the third is is just accelerated expansion driven by something else that would also give you something like a heat death below minus 1/3 gives you a big rip and but and so there are a lot of I should say also that W is sort of assuming that it's constant that the the W number is constant there are kinds of dark energy that change over time where the dark energy might sort of not be doing anything for a while and it might turn on at some point or there are even models where dark energy and dark matter interact with each other in some ways so there are a lot of different possibilities but for simplicity if you if each one has just a constant W then then anything between you know from from minus 1/3 or lower would give you the kind of expansion that we see I think I think maybe I need to finish up but yeah ok well thank you [Applause]

Channel: NECSS

Views: 17,449

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Keywords: science, skepticism, necss, astrophysics, astronomy, cosmology

Id: HETBNk1Dq-g

Length: 37min 27sec (2247 seconds)

Published: Tue Jul 24 2018