Dark Energy and the Runaway Universe

the same religion that's capable of hideous acts of destruction can also be capable of moments of healing and restoration and of hope but educate a girl and you educate her entire family there's a Sun within every person when that anger sets him write it write the letters but don't send them you never want to leave concrete proof of insanity Thank You Karl we are the probably the best kept secret in Santa Barbara County a very small organization two years ago we were me and now there are over 30 I would like to ask everyone who works for lco to just stand up so there's a that's a fraction of the gang there's actually 60 people around the world what we're doing is building a unique observatory it will consist of approximately 50 to 70 telescopes spread all over the world of various sizes and the idea is to make them available both to for our own staff to scientists from around the world and most particularly to children and we already have 2 2 meter telescopes which are quite quite large I mean they're much bigger than my wingspan they weigh about 28 tonnes and those are used most school nights by schoolchildren in the UK and in Europe and that's particularly because the telescope's are in Hawaii and Australia and it's dark there while it's light in Europe and we expect to expand this network so that schoolchildren here can come - for instance - here or in their classrooms and observe with telescopes so that's what we're about and we're having a good deal of fun and we sponsor this this lecture series and the idea is to bring a world-renowned astronomer who's done something extraordinarily important to this community once a year and to have both that astronomer work with the our people and the UCSB astronomers for a week and then to give a public lecture here and the subtitle on this lecture tonight is Goleta boy does good so I'll now introduce dr. crystal Martin from UCSB physics department who will introduce our speaker okay now on to the main event dark energy and the runaway universe Alex Filippenko is a professor at UC Berkeley where his research on exploding stars has won numerous awards and played a major role in the startling discovery that space is not only stretching but space is stretching faster and faster as time progresses alex is not only very well known for his research but is just a phenomenal lecturer he's won numerous teaching awards at Berkeley and just last year was named the National professor of the year you may have listened to some of his astronomy video lectures a 96 lecture series that's put out by the teaching company and thanks to the generosity of Las Cumbres Observatory our graduate students at UCSB got to hear several technical lectures from him this week and participate in discussions so tonight we're hoping to share with you some of the excitement and stimulation that we get from from just doing science and like you to extend a warm welcome to a Santa Barbara native Alex Filippenko well thank you very much crystal Curt Wayne and everyone else it's really been wonderful coming back here this is kind of like a homecoming I grew up in Santa Barbara went to Fairview Elementary School that doesn't exist I guess as such anymore Goleta Valley junior high and Dos Pueblos high school and then finally UC Santa Barbara and it's been amazing actually to see some of my teachers from all these schools progressively progressively back I haven't met anyone from Goleta Valley anyone here who taught me in Goleta Valley Jim private yes we'll we'll chat afterwards okay with the bright lights I can't exactly tell who you are but that's just an excuse I met Jim Stahl and a few others here and unfortunately you know senility must be creeping in or something because I recognized the face but couldn't quite say the name that doesn't mean you didn't make a profound impression on me you you did you know but my but my roots in physics and astrophysics were really seeded here at UCSB where I had some really wonderful professors and many of them are here today and as part of in particular the College of Creative Studies I was taught to defend my arguments and stand up on my feet and you know solve difficult problems and things like that and I found that that's been extremely useful throughout my career and that's something you actually don't get at many universities even small private colleges so it's been great fun visiting this week my voice is now hoarse because I'm coming down with a cold I've been talking to people non-stop but it's been worth it it's been really really great coming back I want to particularly acknowledge Wayne rosing and Las Cumbres Observatory for sponsoring this lecture series and for choosing me to be the second annual lecture Wayne is a remarkable guy if you if you don't know his history you can google quite literally Wayne rosing and find out all about him but he started this this amazing network of something like 60 telescopes that will the place throughout the world to monitor objects that need to be monitored sort of day and night but any at any given place you can only do it during the day so the idea is to have these telescopes throughout the world where somewhere it will be nighttime and and you'll be able to monitor these objects at night if I said that during the did I say during the day I mean it ago I didn't mean that listen to what I meant to say not to what I actually said that's what professors are taught to do right anyway so that's really great and if some sort of a crazy object goes off in the middle of the night somewhere you can redirect one of these telescopes to that object and yet useful data on it so he's a real visionary and his scientific director who's also here is is tim brown so i'd like to really extend my thanks to them for establishing this network here's one of the telescopes that's being produced by the biopsy OGT inc net net dot inc whatever and i toured their facilities today and was mightily impressed by what they've accomplished accomplished accomplished in just a year and a half so it's really really fantastic so anyway this talk tonight will be about cosmology now cosmology is that subset of astronomy that deals with the structure and evolution of the universe as a whole we're interested in some of the grandest questions when did the universe begin you know is it infinitely old we now think think it began something like 14 billion years ago how will it end what will its fate be far far in the future you know these are national magazine front cover stories now these magazines want to educate the public but of course they also want to make money and they make a lot of their money from newsstands sales not just from subscriptions and they will not choose a cover story that they don't think will sell but astronomy sells and in particular cosmology cells these are as I say the grandest questions is the universe infinite does it wrap around itself what is its overall structure and shape these are the kinds of questions we ask it's the kinds of questions that people have wondered about ever since their brains became sufficiently advanced to to conceptualize and you know such questions and then to think about how such questions might be answered we are also interested in cosmology in galaxies how they formed how they evolved with time here's a galaxy much like our own Milky Way galaxy it consists of hundreds of billions of stars gravitationally bound into this nice whirlpool shape in this particular case how did such things form and how do they evolve with time you might say well there's our Milky Way galaxy and maybe you've heard a few of others like Andromeda and the Whirlpool but you might not think that they're all over the place in fact galaxies are the fundamental building blocks of the universe just as stars are the fundamental building blocks of galaxies and one of my favorite photographs from the Hubble Space Telescope is this Hubble Ultra Deep Field this in fact is just part of it this is a small but representative sample of the sky if you hold up a small pebble or a large grain of sand at arm's length and imagine what fraction of the sky that grain of sand covers that's the fraction of the sky subtended by this photograph yet in this photograph there's something like one or two thousand galaxies like our Milky Way we can count them one two three four five six I could spend my whole hour doing that but it wouldn't be terribly interesting nevertheless you can see that astronomers have really cushy jobs we get paid for sitting around counting galaxies so it's really great yeah it's a that's I think the best kept secret anyway you look at this thing and you say alright there are one or two thousand galaxies how many galaxies are there spread throughout the sky we estimate that there's something like 50 to 100 billion galaxies accessible to great telescopes like the Hubble and that's just in the parts of the universe that we can see we now have good reasons to think that the universe is far far larger jet than just those parts that we can see and everywhere we look it is filled with galaxies how did they form how do they evolve with time fundamental questions indeed now before I move on let me point out that among the general public present company excluded there's often a misperception there's a confusion between cosmology the study of the structure and evolution of the universe as a whole and cosmetology the study of hairdos and facials they both have the same root cosmos all that there is or to make order of but they have bifurcated as have astrology and astronomy and in fact they're even spelled differently cosmetology is the same as cosmology but with an extra ET like the extra-terrestrial I'm not sure of the cosmic significance of that but write them down and cosmetology only differs from cosmology by an ET well of course they are fundamentally different now but to illustrate an example of this confusion let me show you of a copy of an ad that a colleague placed in my mailbox a few months ago make cosmology your career training and supervision in hairstyling blow-drying permanent waves coloring and frosting you laugh but these are all very important topics ok scalp treatments body and skin care style cuts basic cuts for further information and interviews call that number now classes started let you know in March but maybe you can join late or maybe there's a summer session or a fall session and you know if you want to get to the cutting edge of cosmology as I and my colleagues have done you need to take a course like this sorry about the very bad pun I couldn't I couldn't resist well these guys obviously need a lesson not on that not just on the differences between cosmology and cosmetology but in spelling and proofreading because in addition to futher here you notice hair slime you see that hair slime and coloring well that's okay that's the British spelling and my own thesis advisor at Caltech was British so I'll allow that but anyway okay pretty funny yeah these guys don't even know what it is they're teaching okay so a central figure in this field was Edwin Hubble after whom the Hubble Space Telescope is named and he made a number of startling discoveries the most important of which for the purposes of my talk this evening is that as was mentioned earlier the universe is expanding it's not just that the galaxies are zipping through some pre-existing space getting farther and farther from one another rather it's that space itself the fabric of space itself is expanding stretching with time getting bigger and bigger and there's ways we can tell the difference between space itself stretching and galaxies flying like bullets through a pre-existing space and it really is that the galaxies and you know are spreading apart because space is is growing and he came to this conclusion by passing the light of galaxies through a prism like this and measuring the rainbow or the spectrum of light from each galaxy and the spectrum tells us many many important things about galaxies like the chemical composition of the stars of which they are made and the typical temperatures of those stars and things like that but for my purposes here what's important about the spectrum is that it can tell you whether an object is moving toward you or away from you and also how quickly and this is someone analogous to the audible Doppler effect when a siren of a known pitch is going away from you it sounds low and when it's coming toward you it sounds high so if it zooms past he goes yeah like that you've all heard this effect now if you hear a siren that's going yeah yeah yeah it doesn't mean that the driver is drunk and going around in circles it just means that the siren itself doesn't have a constant pitch but you can still hear it go from a high-pitched er to a low-pitched ya okay and in a similar way light gets moved over to redder or longer wavelengths if the object is moving away from you and it gets moved or moved to shorter wavelengths or or wavelengths if it is moving toward you if the object is moving toward you so there's a red shift and a blue shift and what Hubble found is that basically just about every galaxy is red shifted but more interestingly the greater is the distance the current distance of the galaxy the greater is the redshift so here are some galaxies that are about sixty million light-years away and they're moving away from us at something like twelve hundred kilometers per second okay that's pretty fast that's breaking the local speed limit and here are some more distant fainter looking galaxies that are farther away okay and they're moving away from us even faster so at a given time right now all the galaxies basically are moving away from us except for those that are so close that they're gravitationally bound to ours but that's just a technicality so they're all moving away and those that are farther away from us right now are moving away faster so if you look from our perspective at a diagram it looks something like this here are all these galaxies and they're all moving away from us here we are and the more distant ones are moving faster than the nearby ones that alone is not evidence that the universe's expansion is accelerating it just means that the more distant ones have more space between us and them than the more nearby ones as I will illustrate in a minute but before I do so there's something rather strange about this diagram let me pause what's strange about it yeah we're at the center there we are you know is that likely the the is it something we said or do they not like us or or do we smell or maybe maybe all these galaxies are lactose-intolerant get a milk Milky Way lactose-intolerant yeah an eleven-year-old student told me that joke he came up with it during a public talk that I gave some years ago and I asked him for permission to use that joke and he gave it to me when I gave when I give similar versions of this talk at my home institution Berkeley or Cal I say are we from Stanford you know big rivals with do apologies for the probably many Stanford alumni that are here it's a very very fine institution of course just not quite as fine as Cal so okay well in fact we don't think we're in any special place in the universe we think that we live in a uniformly expanding space and no matter which galaxy you happen to be in you would see the others moving away with a speed that is proportional to their current distance so here's a very simple one-dimensional universe I'm told I shouldn't move around too much or else I'll go out of the camera field of view so I'll just stay right here but suppose I have this one-dimensional universe where the galaxies are these ping-pong balls and they don't expand by the way because they're gravitationally held so strongly that they don't experience the expansion of space but the space between them expands so if you put yourself on this yellow ball right here you see all the other ones moving away and the more distant ones move away faster than the nearby ones because there's more rubber between us and the more distant ones than there is between us and the nearby ones and in a given amount of time then all of that rubber stretches by a uniform amount per centimeter and so this more distant one moves farther away but that conclusion did not at all depend on which ping-pong ball I chose to be my home right it could have been the yellow one but it could have been any of these other ones next door right forgetting about the end of this rubber band here either the universe is infinite or wraps around itself so don't worry about the edge there is no edge but nor is there any unique Center at least not in any of the dimensions to which we have physical access if you don't like a one-dimensional universe take this one here an expanding loaf of raisin bread where all the dough has yeast uniformly spread through it and again forget about the edges it's either an infinite universe or it wraps around itself over a very very large radius and you let this thing bake for an hour let's say and let's say it doubles in size in an hour you can see that all the galaxies moved away from this one but oops but so so is the case for all the other galaxies from all the other galaxies you can see the same perspective all the galaxies move away and the more though there is to begin with the more it stretches and so it looks like these more distant gala these are moving away faster so none of them is at any unique center okay we live in a uniformly expanding universe with no unique center well you might ask how quickly is the universe expanding and with telescopes like the Hubble and Keck and other telescopes astronomers have now measured the speed of expansion pretty darn well depending on with whom you speak at something like plus or minus 5% something like that but the story doesn't end there in fact we expect the universe's expansion rate to change with time and that's because the universe is filled with stuff and stuff pulls on other stuff as mr. Newton told us many hundreds of years ago here you have this Apple you can't give a talk about gravity without using the proverbial Newtonian Apple so here I toss it in the air and the mutual gravitational attraction between the earth and the Apple causes the Apple to slow down in its upward trajectory in fact eventually it stops and comes crashing back down that's because of the gravity between the Apple and the earth so to the galaxies are pulling on one another and should be slowing down the expansion of the universe now if there are enough galaxies per unit volume then the force of all these galaxies on each other should be sufficient to halt the expansion someday and then cause the universe to wreak elapsed on itself and that's analogous to an apple thrown at a speed less than the escape speed from the earth it comes up and then it comes crashing back down so if you will this could be the Big Bang and then the Big Crunch Big Bang Big Crunch or you could say Big Bang NAB Gibb which is Big Bang backwards ok Big Bang Kanab give so if there's a lot of stuff in the universe there will someday be again AB Gib where the universe becomes hot and compressed again and all the galaxies and stars get destroyed but had I eaten my Wheaties this morning and if there were no ceiling here or air resistance and things like that I could in principle heave this Apple at a speed greater than the Earth's escape speed and it would never come crashing back down equivalently if the mass of the Earth were much smaller I could toss this Apple and it would never come crashing back down so in a similar way if the density of the universe if the number of galaxies per unit volume is sufficiently small then in fact the verse could expand forever having a fate very different from that of a Big Crunch instead of a hot compress state it would eternally expand becoming cold dim dark dilute I told you that one of the central questions of cosmology is what the fate of the universe is and so we would like to know this fate well okay how do we do that we have to look back into the history of the expansion and if the thing has not been slowing down very much then it's likely that it'll keep on expanding forever in fact it's not just a probabilistic argument you can set up equations and things but if you measure the speed of a as a function of time and it's been slowing down a lot then in fact it'll probably reach some maximum extent and then reverse in on itself so we would love to know what it's going to do and we can figure it out by looking back into the past history of the universe now you might say that's impossible how can you look back into the past we live right now after all but does anyone have a clue as to how maybe you could look back into the past anyone want to venture a guess physicists here who already know are excluded from this contest yes yeah he's got the right idea what's your name Phil Phil's got the right idea you look at progressively more distant objects and you see them as they were farther back in time and that's because light doesn't travel add an infinite speed it travels at a finite speed it's very fast it's about a foot per billionth of a second footprint on Oh second so you might think that's infinitely fast but it's not I'm seeing Phil as he was perhaps 20 billions of a second ago he might not even exist anymore oh he does you know I good for me I had a larger audience even better for him he's still on this Good Earth you see the Sun as it was a little over eight minutes ago because it takes eight minutes or so for the light to travel 150 million kilometres 93 million miles you see even the nearest stars in the sky as they were typically some tens of years ago because some there's some tens or hundreds of light years away but if you look at galaxies that are say a billion light years away and maybe that one's four billion light years and this one here might be nine billion light years and that little smudge there might be 11 billion light years away then basically you're seeing them as they were one four nine 11 billion years ago and encrypted in that light is information about the expansion rate of the universe as it was one four nine eleven billion years ago so you can look back in time and trace the expansion history of the universe now to do that you need accurate distances so how do you get distances of galaxies well the way astronomers normally do that at least for nearby galaxies is that they find a star in that nearby galaxy let's say that one let's call it Wayne and Wayne here has detailed properties just like those of a star that you've studied in our own galaxy and whose distance you know for example Betelgeuse here okay we happen to know just how powerful intrinsically Betelgeuse is and you might think all the stars are the same but they're not they're they're different you know there are different classes of stars and if you see that that star there is just like Betelgeuse and you know the true power of Betelgeuse then by comparing that star's apparent brightness with the known lumen or power of beetlejuice you can figure out the distance of that star and hence of the galaxy in which it's located this is essentially you're using the inverse square law of light a good example is that if you look at an oncoming car at night one way you judge its distance is by looking at how bright the headlights appear to be you've calibrated how bright the headlights are of a car of known distance nearby and you make this almost instinctive almost intuitive comparison you judge the distance of the car if you're not very good at doing this you shouldn't be driving at night okay maybe you're good at looking at the angular separation between the two headlights we also use that it turns out to judge the distance of the car but the idea is there okay so you might say okay that's fine for a nearby galaxy but these galaxies here are so distant but in fact the individual stars merge together and this galaxies might consist of a hundred billion stars but you can't see the individual stars and in this galaxy there it's even worse they've all merged together and in fact you can't see the individual stars so you might say this technique won't work for distant galaxies and you don't really know if that galaxy is four billion light years away or 3.5 or 4.2 you might say that you don't know the distance accurately enough to do this cosmological test to figure out how long the go you're looking and to you know retrace the expansion history of the universe but in fact there is one type of star that can be seen at distances of billions of light years anyone know what kind of star that is a supernova what's a supernova it's an exploding star that's right an exploding star I mean here's one our Sun will not do this fortunately it will die relatively quietly we'll still get burned you know I think global warming is bad now wait a couple of hundred million years and you know not that I'm saying we shouldn't do anything about it now but wait a couple of hundred million years and it'll be a lot worse okay so here's a star that exploded and some of these explosions can become several billion times the power of our Sun so if our Sun were to you'd need sunblock or supernova block of several billion in order to protect yourself fortunately we don't need to worry about the Sun doing this and so you won't see much super blow nova block you know two billion on sale and stores some of these things are tremendously powerful and in fact here you can see a star that brightens and at its peak it was about as bright as as the central billion or so stars in the nucleus of this galaxy and just last week some of you may have read about work that my team at berkeley did in identifying and studying the most powerful exploding star ever seen this is a nasa illustration this is we don't have such a detailed photograph of it but this thing was as bright at its peak as the typical brightest supernova that we've known and so it was ten times as bright as the typical brightest supernovae and it's light lasted that is remained bright a factor of ten longer so ten times ten is a hundred this thing emitted about a hundred times as much energy as typical luminous supernovae and here's a nasa animation of what we think happened before the star exploded it had this cosmic burp an outburst where it ejected two lobes of material and then the star exploded for real and produced a tremendously powerful explosion this was supernova 2006gy for those who are interested you can google it and find out more about it so that was a tremendously powerful explosion and we're still trying to figure out exactly what caused it but we think that there's a new mechanism that caused this particular type of explosion that was predicted forty years ago and this might be the first observed example of it now the supernova that I'm interested in for the purposes of this talk are not those really weirdo kinds that I just mentioned but rather a supernova called a type 1a where a weird kind of a star called a white dwarf similar to what our Sun will become in six or seven billion years gathers material from a companion star and reaches an unstable mass at which it explodes and these things explode at about the same mass in the same way and so they reach the same true brilliance the same power and you can use them in a sense as standard headlights or standard candles these white dwarfs are really weird stuff they're made out of a type of matter known as degenerate matter not because it's morally reprehensible or anything like that but rather that's just the term that quantum physicists give to this type of matter that's incredibly compressed and our Sun will become one of these things later on as I say but it won't blow up because as far as we can tell our Sun does not have a companion star from which to steal matter so we want to find these type 1a supernovae in galaxies of known distance in galaxies where measurements of stars like Wayne have already told us the distance normal stars so we already know the distance of this galaxy we measure the peak brightness of the supernova and then that combination of known distance and measured peak brightness gives us the true power or umph or luminosity of the supernovae we need to calibrate the headlight and they might be different there might be variations among them so you want to do this with a bunch of supernovae to make sure you've calibrated them correctly the more the merrier but these supernovae are rare a type 1a supernova might go off in a galaxy such as this once per century okay and it's really more like once for a couple of centuries let's say but let's say once per century or maybe twice per century a different kind of supernova will go off so I could be you know a really cruel adviser and have each of my students staring through the eyepiece of a telescope each and every night yours you know cuz I'm not gonna do this work right so have the students do it well you know they'd be students for fifty or a hundred years and meanwhile they'd be chained to the computer during the day doing calculations for me there are some crimes of course that are so egregious that even a tenured professor can get fired and that would be one such crime but you could look at thousands of galaxies and since these are statistically independent events if there's one supernova per century per galaxy if you look at thousands of galaxies there's going to be several tens of supernovae per year you can do that calculation so I could have the students looking around through the telescope at a bunch of different supernovae and once they found ten or twenty or something they would graduate and that would just take them a couple of years nevertheless this would be considered cruel and unusual punishment as well and so I'd probably be fired fortunately there's an easier way there's an easier way you don't have to look through the eyepiece all you need to do is take photographs of random galaxies and look for arrows and where there are arrows there are exploding stars you see it happened once twice three times four or five times by rigorous methods of mathematical induction I conclude that it must happen every time okay well okay if it were that easy you know we wouldn't give degrees for this kind of thing what we really do of course is we program robotic telescopes and Wayne rosing zel Co GT Network telescopes will be robotic to take pictures of galaxies over the course of many years but they take a picture of a given galaxy perhaps once a week and they compare the new picture with the old picture and usually there's nothing new in the new picture but sometimes there is something new and that gets flagged as a supernova candidate and my team has been operating one of these robotic telescopes successfully since around 1997 it's called the Katzman automatic imaging telescope partially funded by the Sylvia and Jim Katzman foundation and I'm extremely happy to report that Wayne rosing tabasco Foundation is also now a supporter of this telescope and indeed lco GT is using this to some extent as a model of how their telescopes their network their global network of telescopes will operate in the future so we have this thing at Lick Observatory it's about a two-hour drive from the Berkeley campus one hour east of San Jose and my associate Wade onli who's brilliant has programmed this thing to automatically night after night look at lots and lots of galaxies we look at maybe 1,200 per night over seven or eight thousand per week and then we start repeating the exposures and he's written all the software to do that and to make the comparisons of the new pictures with the old pictures and sometimes it's really quite obvious in the new picture there's this dot marked with an arrow well okay the arrow gets put in by the software but clearly in the old picture that thing wasn't there this is a star exploding in this galaxy 100 million light-years away it is about as bright as a star in our own Milky Way galaxy about a thousand light years away 100 million 1000 you can do the inverse square law if you wish to this is roughly a factor of 10 billion so I exaggerated a little bit but 4 billion is perhaps a more typical factor but I wanted to use round numbers so here perhaps the case is quite clear usually it's not so clear and there are supernova candidates that are flagged that end up being you know poorly subtracted stars like the star might not subtract well when you subtract one image from another or there might be asteroids flying through the field of view or there might be charged particles that hit our detector that masquerade as a star so I used the superior eye brain combination of undergraduate students to filter through the 50 to 100 supernova candidates that are found each night out of these twelve or fourteen hundred images and they determine which of these objects is most likely most deserving of follow-up most likely to be a supernova and those are the ones that we follow so my undergraduates get hands-on experience quite early this is rather old picture 2005 it's a bit cut off there that's okay I should I should update this picture but they're all in grad school now in fact he was a high school student at Berkeley high at the time that he was doing their research with my group and now he's an undergraduate at Harvard so that's pretty good so they get excited about the supernova discoveries and they get their names associated with the supernovae in the discovery telegrams and it's a really great educational tool and indeed with LC OGT school kids all over the world will be able to in principle look at pictures like this and for themselves identify exploding stars so it should be a great thrill for them I'm extremely happy to say that our group beats all others in the world at finding nearby exploding stars indeed there are six or seven competing groups in the world we find about half of all the nearby exploding stars and those other six groups combined find the other half so I'm really quite pleased with this record our first one was in 1997 when we were just getting started you might say that was a supernova of questionable integrity given its name supernova 1997 BS but in fact they are named an order of discovery a B C through Z a a a b a c through AZ ba and so on so you can figure out what number that was that year we then really got rolling setting a bunch of world records breaking our own world record many times we found the first supernova of the new millennium regardless of your definition of the new millennium not that that's astrophysically important but it was kind of cool anyway now we could find more of them we've stabilized in the mid-eighties here mid to low 80s we could find more by looking at each galaxy less frequently than simply observing more galaxies and we could find more if we were to devote some of our telescope more of our telescope time to the search rather than to the scientific follow-up of the supernova that we find but we want to really do some science with them so we actually spend only seventy or eighty percent of our time searching and we spend the rest of the time doing these follow-up observations and we search each galaxy roughly once a week in order to find the things when they are young and that's to maximize the science that we gain from these discoveries it's not all just about finding more and more of them I should say that having found of out 750 of them or so in the last ten years we can now determine a good rate for different kinds of super novae there are different ways that stars can explode in different kinds of galaxies and I have a fantastic student Jesse Lehmann who is doing that for his doctoral work right now he's a quadriplegic he had a skiing accident as a senior in high school but he decided to move on and have a positive outlook on life and he graduated with honors from the University of Maryland and then came to Berkeley for his graduate studies he can't move much of anything except for his head but he has a great brain and he can speak to his computer and programmed that computer and deal with very large data bases so I can't send him observing to the telescope nor can I have him doing pencil and paper theory but he can milk giant datasets and he's been doing a great job and you'll hear more from him in the future so we're gonna be publishing a great paper on supernovae rates pretty soon okay well through these studies and those done by my colleagues and at Harvard and Texas and other institutions we now have a pretty good understanding of nearby type 1a supernovae we'd like to have a better understanding so these studies are continuing but at least we have a good enough understanding that we can now go off and look for distant ones and do some real cosmology with them so we've calibrated the headlight so now here's part 2 of the talk there's been two teams that have historically been looking for high redshift or distant type 1a supernovae in order to trace the expansion history of the universe the one that I've been most closely associated with is the high Z or high redshift supernovae search team led by Brian Schmidt of the Australian National University the other one is the supernova cosmology project led by Saul Perlmutter of the Lawrence Berkeley Lab and he's also now a professor of physics at Berkeley I was part of this team for a while but just different cultures led me to switch teams they come in from a culture of high-energy particle physicists and I came from the culture of astronomers and we just do science in different ways neither one is better than the other they're just different and I was more comfortable doing sign the way I used to do it so it's been a generally healthy and spirited competition each team wanted to be first each team wanted to be best if one team was taking into account some sort of a subtle effect and the other team was not that other team would look bad so it was a good thing competition can be a good thing and contrary to popular belief our team leaders were not always at each other's throats this was a picture taken at Aspen where we had some discussions on super novae but generally it's been a spirited thing Brian and Saul now what we do is we use bigger telescopes this one happens to be in Chile at Cerro to Lolo inter-american Observatory and it's four meters in diameter and we take deep wide-angle pictures of the sky by deep I mean we look at faint galaxies not just the bright galaxies so in a picture like this you might see hundreds of galaxies even a thousand galaxies indeed there's very few stars in our own galaxy in this in this picture almost every blob you see is another galaxy and if you take a bunch of pictures across the sky over the course of a few nights if you do the math you find that you might be monitoring something like 100,000 galaxies so if you repeat those photographs three weeks later the odds are that among those 100,000 galaxies several dozen in fact will have blown up and we can find them again by subtracting one image from another here's just a small subset of one image taken on the 7th of April and the 28th of April you subtract this one from that one you get a bunch of noise every measurement process has noise associated with it but here cleverly placed in the middle of the square is something that looks like it might be significant a supernova candidate it might be something else it might be an asteroid flying through our field of view or something like that indeed there have been so-called Kuiper belt objects Pluto like things that fly through our field of view and we we throw them away they're garbage but one person's garbage is another person's gold of course you know all the hullabaloo about the Kuiper belt objects and how we don't consider Pluto to be a true planet anymore anyway we're looking for supernovae in here and image you can see a good image of that supernova candidate but it remains a candidate until a spectrum is taken and in fact the spectrum will tell us whether it's a supernova and whether it's a supernova of the right variety but these objects are so faint that we need the world's largest telescopes the two Keck 10-meter telescopes jointly owned and operated by Caltech and the University of California we need those to take spectra and here is the former director of the Keck telescopes Fred Chaffee sitting in the hole in the middle of this 10 metre diameter network of 36 hexagonal segments like a honeycomb usually he's not there while we're doing the observations that was just a PR shot his small pupils do not add significantly to the light gathering power of this telescope okay well when we get the spectrum and it turns out to be a type 1a supernova of the normal variety and all that kind of stuff well then in fact I'm a very happy camper and you can see them the real reason why we built observatories in Hawaii I live in Northern California where the water the ocean water is too cold for swimming and I like the beach just as much as anyone else so it's nice to go to Hawaii but all joking aside Hawaii is a wonderful place for these telescopes because of the stability of the atmosphere the darkness of the sky and other factors so it's a really great place well we find these supernovae we take spectra and then we follow up on the ones that are most promising and here we're coming to the punchline okay here are three faint distant galaxies in which there are three supernovae dutifully marked with arrows and these supernovae are faint really faint and you might say well big deal you were looking for faint distant supernovae in faint distant galaxies why are you so surprised well these guys are fainter than they have any reasonable right to be in any reasonable universe suppose the universe were one second old one second from the Big Bang okay and I toss this Apple after one second the Apple reaches some distance above my hands right but it's been slowing down if the Earth's gravity were weaker it wouldn't slow down as much and it would go higher in one second now I can't make Earth's gravity weaker but I can do the next best thing I can throw the Apple faster it's not quite the same thing but it's you know at least gives the same result so in one second the Apple gets farther if the gravity is weaker now suppose the earth were not present the Apple would have no reason to slow down in the absence of all other bodies in the solar system and then the universe just forget about them all the Apple would have no reason to slow down and so in one second it would reach an even greater distance right well what we're saying is is that the Apple the supernovae are at a greater distance than they could have reached even if they had not been slowing down at all so they're that they're at a greater distance than even with a constant speed so in the absence of other subtle effects which we did have to consider you know maybe the things look too dim because there's dust or gas in the way blocking some of the light like fog on a you know like headlights on a foggy night you'll overestimate the distance of the car if you don't take into account the fog right but in the absence of all these other effects which we did rule out one by one the obvious conclusion then is that if the thing looks fainter than expected then its distance is what farther away and so if even a constant speed wouldn't suffice what must have happened to the thing it must have accelerated so it's like you attach a rocket to this thing and it goes zoom like that oh man you know wrong answer we thought we were trying to measure the rate of slowing down of the universe and instead we find that it's speeding up that's really really weird you know it suggests some sort of a cosmic anti-gravity astronomers see a cosmic anti-gravity force at work you know accelerating the expansion of space and we use this term anti-gravity hesitantly because people ask us well can we attach this stuff whatever it is to our cars and levitate over LA traffic or Santa Barbara whatever you know no we can't attach the stuff to our cards as far as we can tell this stuff cannot be harnessed it is a property of space itself I'll tell you a little bit more about that in a few minutes and it's only anti-gravity in a sense it's not like there are two masses here and they kind of feel each other and they go away from each other no it's rather a property of space that causes space to expand faster and faster with time our team leader said Bren Schmidt said my own reaction is somewhere between amazement and horror amazement because this is not the answer we expected horror because we still weren't absolutely sure that were right but we had done many checks and cross checks a number of people in our team independently measured the data and came to the same conclusions and we felt that we should announce this result and we also knew that the other team is was on to something we didn't know what what they were on to but we figured they probably might have found the same effect so we really should announce it so in fact I was privileged for our team to announce this at a meeting in Los Angeles in late February 1998 and it was really fantastic but on our team the first person to realize what the data were trying to tell us was my postdoc at the time Adam riess he's now a professor at Johns Hopkins University and the end of 1997 was perhaps and the beginning of 98 was the most exciting time in my career because every once in a while he'd come to me he'd say you know you know here here's what the measurements are showing and I'd say you know Adam you know what did they teach you at Harvard he had in a grad student Harvard didn't they teach you to measure the brightness of stars correctly or so I was thinking I'm not sure I insulted him in this way but you know I was worried about the measurements as were other team members like Bob Kirchner who's been spending his sabbatical at Santa Barbara at the Kavli Institute but gradually we realized that the measurements had been done correctly and nanyem is now very very famous and correctly so here he is in in Time magazine by the end of 1998 the editors of science magazine proclaimed this to be the single most important discovery of science in science during the entire year in all fields of science and both both groups were credited with this and indeed had there not been two teams that reported this result I don't think the anyone would have believed it because you know they would have said well maybe you made some programming error and two plus two equals five that would have been a real embarrassment that doesn't him that doesn't give you more funding in science you know or maybe there was something subtle like we haven't taken into account this fog correctly or the properties of the fog are different or something weird is going on well that wouldn't have been such an embarrassment we would learn something about the universe that way and that's the way science progresses we never prove anything we can only get a better and better working model of the universe and reject competing hypotheses okay so you know we we were horrified that we might have made a mistake but we had done many cross checks and then you know two teams had the same result and we still didn't believe it near the end of 1998 but the editors told us that's okay many people have had a chance to check your results no one has found any clear errors in the measurements or in the interpretation either the universe is accelerating for some unknown reason or you found something interesting about the universe that you know will be figured out in the next few years but it will be nothing to be ashamed of and so we were very grateful that they honored us in this way now the caricature of Einstein is surprised here you might think that it's because he's blowing universes out of his pipe but in fact that's where universes come from they come from the pipes of famous theoretical physicists that's another lecture maybe some other day I can come back seriously though this is one universe which is speeding up in its expansion and that's hard to show in one still picture so he's surprised about that he's doubly surprised because he has this sheaf of papers where there's an equation lambda equals eight pi times G Newton's constant of gravity times the density of the vacuum he might say what in the world is this guy from berserk Lee telling us the density of the vacuum you were hopefully taught on your mother's knee that the vacuum is sheer emptiness nothing nothing goes on there it's got zero mass per unit volume or energy per unit volume so what does he mean by this crazy hypothesis of a nonzero than city well shortly after the development of the general theory of relativity Einstein introduced a mathematical fudge factor which he called the cosmological constant lambda because he realized that in his general relativistic universe as in the case of the Newtonian universe things should attract each other and even though the true nature of galaxies was not yet known at the time the spirit of what I'm about to say still holds Einstein figured that the universe should be collapsing in on itself because everything should be mutually gravitationally attracting everything else and since the sky wasn't falling and the astronomers at Mount Wilson Observatory said that the universe seems to be static Einstein included in his equations this fudge factor which does not make the equations mathematically wrong indeed one could say it generalizes the solutions however there were several problems this thing made the equations less aesthetically pleasing less mathematically beautiful and physicists are drawn by aesthetics to some degree moreover this thing suggested that the empty space is not empty after all it has some sort of an energy and of a repulsive variety and finally this repulsive stuff had to have exactly the same magnitude or sign as the attractive gravity so that are acting in the direction opposite of gravity it would exactly balance it so here I'm holding this Apple my upward pull on it exactly matches the force of gravity pulling it down so it's static if one of the two were to dominate the Apple would not be static ok so he had to make this thing arbitrarily tuned finely tuned to match effectively the force of gravity and there seemed to be no real reason that the stuff even if it were to exist would have this rather strange property so he did not like the cosmological constant and in fact twelve years later when Edwin Hubble discovered that the universe isn't static after all but rather is expanding the whole physical and philosophical motivation for such a weird energy disappeared and Einstein basically said to heck with the cosmological constant he renounced it he was sad that he had ever introduced because had he not done so he would have predicted that the universe is likely to be in some sort of a dynamic state not a static state and there were some other theoretical physicists who did make that prediction so here on stein is sad that he ever introduced the cosmological constant he never liked it even though it isn't mathematically wrong okay he renounced it what we have done 70 or 80 years later is we've said no the idea rather than being his biggest blunder he anecdotally said that this was the biggest blunder of his career rather than being the biggest blunder the idea of a non-zero energy of the vacuum that somehow it causes some sort of repulsion made it may have been in some ways his greatest triumph and his blunder was in giving this thing exactly the same magnitude or size as the attractive force of gravity giving you this very unlikely and in fact mathematically or physically unstable solution of a static universe it was this fine-tuning that was the blunder but the idea may have been his his greatest triumph because we've resurrected it and what we're saying is that though in this room gravity dominates and in this solar system and in our galaxy and in our cluster of galaxies gravity dominates on scales of billion light-years or more this up arrow dominates over the down arrow and so over the largest distances the universe is in fact accelerating spreading out faster and faster with time now I don't know what Einstein's reaction would be if he were alive right now to hear it to hear what we've discovered but maybe it would be something like this okay so anyway well the conclusion that we drew in 1998 was based on supernovae that were only about four or five billion light-years away so what we could say is that in the last four or five billion years the universe has been accelerating in its expansion but a reasonable question to ask is what was the universe doing in the first nine billion years of it's roughly 14 billion year life if this stuff whatever it is is a constant property of space then there's a very natural prediction you would expect that at early times the universe should have been slowing down in its expansion and the reason is pretty simple long ago the galaxies were closer together so their gravitational attraction for one another was stronger even Newton would have agreed with that and the repulsion was relatively weak because there wasn't much space between the galaxies okay so if this stuff has a certain amount for every little volume of space if the total amount of space between the galaxies is small then the repulsion the total repulsion will be small so plotting in a sense the strength of gravity versus time the strength of gravity was going down because the galaxies were spreading apart the cumulative effect of this repulsion was growing stronger with time as the galaxies spread apart and the volume of space became bigger and bigger and eventually then the two crossed and the universe started accelerating but while gravity was stronger than the anti gravity if you will the universe should have been slowing down with time okay so that's a clear prediction well we went off with the Hubble Space Telescope and found very distant type 1a supernova here's some of them they are six seven eight nine billion light-years away and lo and behold the measurements suggest that back then six seven eight nine billion years ago the universe was slowing down in its expansion and it's only in the last four or five billion years that globally this stuff has taken over and started accelerating the expansion of the universe so the universe went from deceleration to acceleration that's a change in the deceleration obviously you're slowing down then you're speeding up such a change mathematically is known as a jerk so in a sense we measured the cosmos to have gone through a jerk and the headlines that came out were the following a cosmic jerk that reversed the universe and here's my former postdoc Adam riess now you know how it is with large newspapers like the LA Times or the New York Times you rarely read the articles in their entirety you look at the headlines and you look at the pictures and if it looks especially interesting maybe you read the entire article so I started getting all these phone calls hey who's this jerk you work with who reversed the expansion of the universe well it says that reversed not who reversed and but but Adams mother was not very pleased by this juxtaposition it's also not the best picture of Adam but anyway he forgives me for showing it after all it was in the New York Times and you know any publicity in the New York Times is good publicity right so okay well that's kind of cool well then you might ask what is this stuff that we found is it the visible matter in the universe that makes up the galaxies no because all visible that matter that we know of gravitationally attracts other matter what about dark matter how many of you have heard of dark matter yeah a lot of people have heard of dark matter dark matter exists you know in abundance in clusters of galaxies like this in fact it's nine times as massive as the visible matter and we know it's there because if it weren't there the clusters of galaxies would be gravitationally unbound they would be zipping past each other and would not stay together and one of my heroes Fritz Zwicky of Caltech he died in 1974-75 he came to this conclusion that there's dark matter in the universe in the early 1930s but he was nearly uniformly ignored it's too bad he was a brilliant guy he made predictions about supernovae and stuff but he was largely ignored because his colleagues at Caltech didn't like him that's because he didn't think very highly of them he was arrogant he was abrasive he was brilliant but he was arrogant and abrasive and in fact legend has it that he referred to his Caltech colleague as spherical bastards because you know they're bastards anyway you look at them well this is this is not a good way to make friends okay if you go around calling your friends spherical bastards I don't think you're going to get very many dinner invitations so but but he did come up with dark matter but anyway dark matter pulls it doesn't push so it's not whatever this stuff is this stuff is something new and for want of a better term astronomers now call it dark energy and you hear about dark energy it's a great regret about term in my opinion because you know the most famous equation in all of physics is what e equals MC squared anyone on the street knows e equals MC squared they might not know what it means chances are they really don't know what it means but they will have heard the thing and so is dark energy in some way the same thing as dark matter no no no banish the thought they are completely different things dark energy is some sort of a weird thing with a positive energy but a negative pressure and the negative pressure is what in a sense stretches space and I don't claim to understand that Don Morrall fan Jim Hartle and other relativist that relativists at UCSB can explain to you if you wish to know but this negative pressure is what does this to the universe and so we call it we call it dark energy and this stuff is not a minor component of the universe 73% of the energy plus mass content of the universe is this dark energy and you know what we don't know what it is I would say we haven't a clue except that that doesn't quite tell the whole story there are hundreds of theories but we really don't know which one is correct one idea is is that it's the quantum fluctuations in the very vacuum of space itself we've known for decades that space isn't empty in fact it's teeming with activity and we can tell that it is because it ever so subtly affects the energy levels of the hydrogen atom and other atoms and those effects have been measured but it had been always assumed that over all the positive energy fluctuations effectively cancel negative energy fluctuations so there are negative energy ones to give you an energy of the vacuum that's precisely zero and this assumption had been made by theoretical physicists not because they had a good mechanism for such a cancellation but rather because if you don't assume such a magical cancellation the natural amount of this dark energy that you predict is so many orders of magnitude bigger than it could possibly be that you know we wouldn't exist we wouldn't be around right now if it were that big so physicists simply said for reasons yet to be figured out there is an exact cancellation of the positive and negative energy fluctuations well if the positive ones slightly outnumber the negative ones for a net positive energy remarkably enough it has the desired property of stretching space of having a rather large negative pressure but that's just one idea it's the simplest idea and the data right now are most consistent with that idea but theoretical physicists really don't like that idea and they're considering many other ideas and you will read about dark energy and the teams studying supernovae are now trying to quantify in more detail the expansion history of the universe in order to set observational constraints on what the dark energy might be that's what we're trying to do in the next ten years but there's a lot of it and we don't know what it is there's also a lot of dark matter and we don't know what this is in general we think it's some sort of an elementary particle leftover from the beginning of the universe the Big Bang a kind of a particle unlike a proton or a neutron the best candidates are the so called wimps weakly interacting massive particles but not a single one has ever been detected in a laboratory and that may or may not be a problem depending on with whom you speak the people who are doing the experiments say that's not yet a problem but of course they want to continue to get funded and this is this is very good research I don't mean to belittle it seriously unless we check all these possibilities we won't know but it is disconcerting to me at least that no particles of the WIMP variety have yet been found the atoms of which we consist constitute only 4% of the contents of the universe the remaining 96% is basically of unknown physical properties or origin that's kind of weird that's not true in this room okay but in the vastness of space most of which is mostly empty it's actually filled with this stuff okay here in this room we're dominated by these guys but only about a tenth of the four percent that is 0.4% consists of atoms that you can actually see atoms that glow or reflect light like stars or nebulae so not to diminish our importance but we are the debris of the universe the afterthought of creation okay and that's again to say that your it's not that you're not important you are to yourself your family your loved ones but I want to emphasize that we are not made of the dominant stuff of the universe the dominant stuff is the dark matter and we don't know what it is and especially the dark energy and we really don't know what it is so there's a lot to be done by the young students and postdocs and those of you who are still in in primary and secondary school so my license plate is let's see if you can figure it out dark in RG dark energy and the accelerating universe my wife Noelle came up with that she likes little word games like this so dark energy and the accelerating universe okay so so uh so you have this stuff dark energy and you might then ask what will be the fate of the universe let's get back to the question I originally posed well if the dark energy remains repulsive forever then it's quite clear that the universe will expand forever not just because it doesn't have enough matter to ever bring itself back but more importantly because it's dominated by this stuff that's making it expand faster and faster and faster with time but since we don't know what the dark energy is it's actually quite conceivable that it's sine will change in the future and become gravitationally attract indeed there's a historical precedent to this we think that all of the stuff of which we are made was once a dark energy like component that existed when the universe was a tiny tiny tiny fraction of a second old and that component inflated the universe from something almost arbitrarily small into something far far larger than what we can see indeed this inflation may have made the universe 40 orders of magnitude larger or more than the parts that we can see and this is a reasonable theory this is not the ramblings of a crackpot ok so indeed the analogy I like to give is that the ratio of all that there is the diameter of all that there is to the diameter of what we can see 14 billion light years in in all directions may be at least as large as the ratio of the diameter of all that we can see to the diameter of a proton now that proton is about yay big and I exaggerate quite a bit so our observed universe according to this theory may be a proton in all that there is okay and it's filled with these galaxies and so we think that a similar sort of dark energy may have inflated the universe into this gigantic gigantic thing okay and now we see a modern-day example of it and the theorists who had come up with this inflation theory they were told early on that well this looks nice but the problem is we've never seen any stuff that has these properties well maybe now we have seen stuff of this kind okay and so in a sense it's leading to a resurgence in interest in these kinds of theories the dark energy is important not just because we don't understand it but because most physicists would agree that to understand it we will require a unification of the two great pillars of modern physics general relativity on the one hand that deals beautifully well with the universe on the largest scales and quantum physics which deals beautifully with phenomena on atomic and subatomic and molecular scales they work beautifully in their respective domains but when you try to bring them together they're at war there or with one of their mutually inconsistent and it is thought that this is some sort of a phenomenon that can be only understood through some quantum theory of gravity be it string theory or some other competing theory so there's great excitement about this dark energy because it may lead to an observational test that would lead to the elimination of at least some categories of these theories any theory that categorically denies the possibility that the universe could be filled with some sort of stuff like this can be eliminated as being wrong and that's the spirit of science so how will the universe end well if the stuff remains attractive repulsive it'll it'll expand forever easily but going back to my analogy I forgot to say that the stuff that originally inflated the universe eventually turned into matter and antimatter and photons and the matter and antimatter eventually annihilated leaving a few little protons and stuff sitting around and we are the result of that whole process we used to be the dark energy that inflated the universe but eventually that dark energy became normal attractive matter so it could be that this stuff will do the same thing in which case the universe will wreak elapsed but if it remains gravitationally repulsive then the universe will expand forever faster and faster and faster and I encourage you afterwards after QA to look through some of the telescopes at galaxies and clusters of galaxies because if you want to see them with your very own eyes you've got to do this soon in the next few tens of billions of years because beyond that time the clusters of galaxies will have been whisked away to distances which make them too faint to see well too close Robert Frost apparently knew of these two possible fates for the universe he may not know no about of about anti-gravity but he knew that it might wreak elapsed into a fiery dense Big Crunch in a sense and ending in fire dense and hot and compressed or eternal expansion ending up cold and dark and dilute in a sense and ending in ice because he had this famous on fire and ice 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 you see Robert Frost would prefer this kind of a universe and ending in fire but if he had to perish twice eternal expansion and an ending in ice would be okay and that's perhaps appropriate given his name Robert Frost thank you very much and here thanks very much I know a lot of you are interested in this and this is really fantastic stuff you know crystal I think mentioned my video lecture series with the teaching company it covers cosmology and planets and all this sort of stuff in 96 half-hour lectures it was just re-released in a second edition I think it's on sale right now they're giving it away go to teaching company or teach cocom and you can get a lot more of this stuff but I'll be very happy to answer questions I see a bunch of hands raised yeah you can line up I guess but I'll take one while you're lining up and I'll be sure to repeat the questions so everyone hears it go ahead there in the back yeah the question is does it make me uncomfortable that dark energy has gone from heresy to dogma in a decade actually nine short years you know I go to talks and they start out with assuming the standard model of the dark energy plus dark matter dominated universe I I mean it's it sort of makes me uncomfortable but the point is is that there now a lot of independent methods several independent methods that lead to the same conclusion if they're only based on type 1a supernovae I would remain very nervous because it could be there there's something weird going on with a supernova maybe they used to be intrinsically dimmer and they look too dim because you know not because they're farther away or whatever but there's now a number of different techniques that lead to the same conclusion and some of those techniques are completely independent of supernovae moreover try as we might we can't find anything wrong with the supernovae and and it's the nature of science where if you have independent methods that give the same result your confidence and things grows and grows and grows and indeed it's now to the point where if you look at the large-scale structure of the universe the clusters and superclusters of galaxies and things like that and you ask where did they come from well we can see the echoes of the Big Bang the cosmic microwave background radiation and we can see tiny variations in the density of the matter back when the universe was not even 400 years old and you take those initial density fluctuations and you run them through huge computer models and we have fantastic computers now and you watch them grow and you model that growth with and without dark energy and in fact the observations better match the computer models if you include the dark energy you know that that's one of the forms of evidence okay and there's a number of them now and that's why I think it has gone to this acceptance does that mean we should forget you know about looking for possible things that have gone wrong no we should keep our eye out for that we should be village n't for that vigil vigilant for that so but we are now addressing what are the properties of the dark energy and your proposal you say okay I'm gonna try to figure out what the properties are set observational constraints on it hopefully in in those sorts of studies if the whole concept is wrong we'll figure it out but you can't get funding anymore if you just say well I want to test for the presence of dark energy because they'll people will say we really do think it's there why don't you test for what its properties might be and in the process if it's really not there hopefully that will become obvious so the nature of the question has changed yes or should it are there people lined up or should I just choose people Auguste pardon line up here okay you can well or whatever but it might be hard for people to leave their chairs so go ahead for now okay hopefully it was understandable good Yeah right right yes so here that basically what's being said and this is very perceptive in fact our bubble this expanding balloon here I've got just a two-dimensional example of a universe it's you know suppose you can go forwards and backwards and left and right but not in and out so this is an expanding universe I won't expand it too much otherwise I'll get a little bang you know but anyway it's expanding into some third dimension which is in fact the way I've defined it not part of this hypothetical universe and the questions is being asked is that suppose there's some grand or hyperspace where there are all sorts of little bubble universes floating around in a four dimensional bulk as we call it and indeed string theory and its various variations are seriously considering that our three spatial dimensions in one large and one time dimension at least the big ones we think there might be little spatial dimensions but anyway we are of a brain a membrane a B are a and E not a BA are AI n floating around in some bulk some bigger thing and there could be other membranes floating around there and there are indeed ideas where gravity can go from one of these things to another and maybe we're being pulled from from outside in a sense where outside is kind of a weird term I am no theorist okay I like to say that I know which end of the telescope to look through okay and there are many people here my colleagues from UCSB who know much much more about this than than I do but my impression as an impartial and not very knowledgeable observer at some of the conference that are held conferences that are held is that though that's a possibility that's actively being researched right now and indeed that possibility of other membranes is is really being a serious issue right now but but even the possibility that maybe they're pulling on us from the outside even that's being considered but that that is not a very likely solution and one reason is that in a sense it's you can measure these Microwave Background fluctuations that we see and it's kind of interesting we know that they have a particular physical size and that we can calculate in a way that doesn't really depend on the details of the early history the universe and so there's they're like meter sticks you know how long they are and you look at how big they appear to be in angular size and that relationship between how big they appear to be and how big they really are tells you the path the shape of the path of the light rays okay and it turns out the light rays are going along paths that you learned about in tenth grade geometry you know Euclidian straight lines so that means that the universe on largest scales that we can see is globally flat and according to the general theory of relativity that means that there is a certain energy density in the universe and let's call it one point zero for kicks well the visible matter and the dark matter are about point three in fact point two seven it's the atoms the 4% and the wimps if that's what they are the 23% that's point two seven and if the total is 1 then 1 minus point two seven by advanced mathematics last time I checked on my calculator was 0.73 okay so they are saying there's got to be another component of energy in the universe if general relativity is correct and the overall geometry of space is linked with the paths of light through that space so they're saying yeah there's a there's an energy there and moreover we can tell that that energy is not clumped in clusters of galaxies but rather has to be sort of more uniformly spread out and if it's uniformly spread out however it can't be light little particles like neutrinos because their presence would have messed up the formation of the largest-scale super clusters and voids and stuff in our universe so it's a it's a convoluted argument but the point is is that this energy we really think is there and does not have the properties of positively attractive gravity so we think that there's this energy but but that's not to say that general relativity is necessarily correct or that there aren't these other universes pulling on ours so you should become a theoretical physicist and study these things in more detail other yeah yes right there yeah yeah right yeah sure all right so that the question is how do we know that today's super novae that we've calibrated so well are the same as the ones five to nine billion years ago after the afterall the universe has changed a lot the white dwarfs themselves may not be made out of the same stuff there are more heavy elements nowadays than there used to be that's good for us we are made of the heavy elements by the way that are burst forth into the cosmos created by these explosions and ejected into the cosmos later on to become stars planets in life this is what Carl Sagan meant when he used to say that we are made of star stuff or star dust he didn't discover this but he said it very eloquently so indeed the white dwarfs may have been different and so we might be comparing things that are intrinsically say less luminous then than they are now so there are various ways we can look for differences okay for example in detail the spectrum of a distant supernova if it looks in detail the same as that of a nearby one then you know spectroscopy is an extremely powerful technique you can't get similar looking spectra without rather similar physical conditions or maybe you can have rather different physical conditions but there are other ways to test for that so spectroscopy is very quantitative and very good at telling you about the physics of what's going on but then you might say well maybe we're being fooled anyway so then I say okay you can look at supernovae in different galaxies that are nearby some galaxies have a larger proportion of young stars some have a larger proportion of old stars some have a larger proportion of stars that haven't produced many heavy elements yet other galaxies have lots and lots of heavy elements so the point is is that nearby type 1a supernovae occur in a variety of environments and some of those environments look much like the early universe back when there when stars were generally younger than they are now okay and and stars didn't have his name heavy elements as they do now well we can find galaxies where the stars are younger than most the stars now and where they didn't have as many heavy elements and so we can locally test by looking at these nearby supernovae how stars probably exploded back when the universe in aggregate form on average that is used to be different because we can find pockets of it in today's universe the universe on small scales in homogeneous we can find pockets that resemble the early universe so it's a thing we worry about a lot and it's exactly these kinds of tests that we're doing and so far we have not found any clear differences between the nearby ones and the and the distant ones but that's a it's an extremely good point that does worry us late at night okay yeah question over there yes so much your questions in that part of the room yes oh yeah the question is will the expansion someday go near or even exceed the speed of light yes absolutely I'm glad you asked that the expansion especially in an accelerating universe can easily exceed the speed of light but that is not a violation of Einstein's special theory of relativity because the special theory says that nothing can go through no signal no signal carrying information can go through a pre-existing space at a speed faster than that of light but space itself can expand faster than light so take this rubber band with the ping-pong balls on it very simply let's take two ping-pong balls that are more than 300,000 kilometers apart from each other yeah 300,000 or 186,000 miles if you prefer the inferior units and and suppose you have these two things more than 300,000 kilometers apart and now let's say you double the size of the universe so let's say you more than double the size of the universe in one second by telling each little bit of rubber to expand by a factor of 2 or more you can all agree to do that ok you can all come to this agreement they all do that so every a little bit of space more than doubles let's say so now these two ping-pong balls are more than twice that original distance apart that means they've moved more than 300,000 kilometers in one second therefore they have exceeded the speed of light but can you use that stretching of space to send a signal from one of those galaxies to another you cannot and in fact if you send a signal be it FedEx or carrier pigeons or even light in fact the signal will have a harder and harder time getting to the other galaxies if space is accelerating it in its expansion because the amount of remaining space is growing ever faster so the the signal will never get from here to there and so it's not a violation of relativity cool huh yeah ok there were questions right there near the side okay fair enough what relation did the Big Bang have with the Genesis has described in the Bible I think that the as scientists what we try to do is come up with a better and better working model of how the universe works how do how do objects behave within the universe how do they interact with one another and so on and and the properties of the universe what is the age of the universe and these kinds of things we don't really ask sort of what the purpose of the universe is or you know why you are here why why we are here and many physicists would even say that we can't even really ask what was around before the beginning because you can't really test that because there's this one universe and how can you test for what was before the beginning religious beliefs of course are based on faith and and tell you sort of how to conduct your life and and what your morals maybe should be and and what you might turn into after death and things like that and and these are beliefs based on faith and many scientists have many different faiths and in general they find no real conflict between their faith-based beliefs and what they're trying to do as scientists figure out what the laws wouldn't what are the physics are and so on and they treat the Scriptures more as a metaphor perhaps for how the universe was created or or as an allegory or something like that most would not take the Bible literally in the you know the universe was created in seven days and all that or even if you do you could say well back then what was a day maybe it was a billion years or something like that okay but most Sciences I would say even those that are very religious and there are many don't take what's called a literal interpretation of the Bible now you could say well what if we do take a literal interpretation then you would have to say that everything that we measure as scientists is just a figment of our imaginations or has been set up in precisely this way to make it look like the universe's fourteen billion years old to make it look based on the geologic strata that the earth is four and a half billion years old and so on and so forth it would all have to have been up and I cannot believe that a creator would design a universe in precisely such a way as to deliberately fool it arguably one of that creators most magnificent creations as far as we can tell now there may be other very intelligent creatures out there and there probably are but on this earth we are pretty magnificent and I just cannot believe that a benevolent creator would have done that so I reject the hypothesis that this has all been set up if you accept that it's been all set up then I could say well your whole life was just the last one one thousandth of a second and it's the whole thing is a figment of your imagination I cannot disprove that okay but it could be true I cannot disprove that all the geologic strata were laid down to fool us but I just don't think it's true but I cannot use science to disprove these hypotheses but nor can I use science to prove them so I would prefer to keep science and religion completely separate each has its own turf each asks questions that are best answered within its own domain and address different aspects of human life and and belief systems so I think in general then there's no conflict if you insist that the whole thing that everything that scientists measure is wrong then in fact there is a conflict but most scientists would say that there is no conflict between religion and science because they don't take things that literally okay that's the best I can do I would say yes yes the question is if parts are accelerating faster than the speed of light is it possible that the dark energy and dark matter reside beyond that boundary it's possible but that dark energy and dark matter would then not have any influence on space here because receding away from us faster than the speed of light no signal from that dark matter and dark energy could come over here in such a way as to affect us now it might be beyond the universe so to speak as I discussed an answer to one of the other questions but that's different from being in our universe but beyond what's called our horizon ok yes in the back there is there any relation between the space inside an atom you're saying and the dark energy in the universe well possibly I mean the the space inside an atom and everywhere else in fact does have these quantum fluctuations going on indeed that very slightly alters the energy levels of the electrons in an atom and and that's been measured more over the space between two highly conducting plates is different from the space outside of them and you can actually tell even though there's a vacuum between the plates and the vacuum outside the plates but those two vacu are different because remarkably enough the plates ever-so-slightly go together just by a little bit they just keep on going together because the energy out there is different from the energy inside but are those the dark energy we don't know if the dark energy is quantum fluctuations then indeed it would be intimately related to the stuff inside of atoms but although the data right now are most consistent with that hypothesis that the dark energy has something to do with quantum fluctuations of space itself of energy in space itself the there are a number of theoretical reasons for not liking that and this is what has led to a cottage industry of competing hypotheses many of them go by the generic name of quintessence sort of like the Aristotelian fifth essence okay so we don't know basically maybe in a few years we'll we'll have a better idea we'll have a better answer to your question yes oh yeah so do we think that there are other universes that exist or could develop we have no direct evidence for them but I personally speaking you know beyond just physics alone think that they do exist sticking just to physics if you think that inflation is a reasonable theory for our universe then in fact and raylene day at Stanford and and other people have shown how you could have this inflating region and in that region then the dark energy turns into normal stuff like you and me but other little parts of it due to quantum fluctuations keep on inflating and then most of those parts turn into normal stuff but little parts of that keep on inflating so you have universes in a sense budding off from one another I mean they're connected but they're for all intents and purposes they're disconnected because you could never communicate from one to another or if the universe began with quantum fluctuations out of some nothingness some pre-existing hyperspace or maybe the universe came into existence with the laws of physics it could have come into existence many times so all these things are reasonable deductions based on what we know in quantum physics okay and assuming this inflation is right these are in a sense reasonable extrapolations based on what we know but by their very nature those conclusions at least temporarily remove themselves from the realm of physics because we right now do not know of any way even in principle of testing for these other universes okay there may be some ways again you know feeling gravity from another one might be one way but you have to prove that that's a unique explanation for the phenomenon that you've observed so the problem is it's hard to test for these other universes but by their very nature you know they remove themselves from the realm of science but it might still be true that they exist and if you go a step further if you'll permit me there's another reason for thinking that these things might exist and some physicists really detest this kind of reasoning but I think used not to if you don't go too far with this kind of reasoning it has its utility it's sort of a principle known as the anthropic principle the idea is the following why is our universe so beautifully constructed to allow complexity to develop culminating as far as we know right now on this earth with humans ok although we will be replaced someday with even more presumably evolutionarily advanced beings if you look at seemingly random inconsequential constants of nature like the mass ratio of the proton to the neutron or the relative strengths of the gravitational force and the electromagnetic force and things like that you find that if you play around with these things and alter their values a little bit you come up with rather boring universes compared with the one in which we live for example universes that only have hydrogen or only have helium or only permit iron not the rich periodic table that we have not the rich molecules that we have but rather uninteresting universes and so you might say well maybe there's only one way to write down a self-consistent set of mathematical laws that govern the behavior of matter and everything else maybe maybe not maybe there's meant more than one mathematical way of doing it but suppose there's just one way but the constants of nature our random accidents in a sense there's no fundamental reason that the speed of light is what it is it just happens to be that way and an analogy is snowflakes snowflakes all have a fundamental hexagonal symmetry because of the structure of the water molecule but no two snowflakes look the same because of detailed because of differences in the detailed motion of the molecules right at the moment with when the snowflake was beginning to form so no two of them look alike if the physic constants were laid down by an effectively random process like snowflake formation and we don't know whether they were laid down this way or not but I'm speculating and that these ideas are not due to me other people much more eminent than I have been talking about this stuff so again it's not just some crazy dude from berserk Lee but anyway if the constants were dictated by a rather random accidents we call it spontaneous symmetry breaking and things like that then it could well be that in fact in other universes that the constants had different values and most of those universes are quite uninteresting compared to ours we call them stillborn some may be equally interesting or even more interesting but ours is one of the relatively rare interesting ones that allowed complexity to develop and not surprisingly we live in such a universe it's sort of like playing poker every hand is equally unlikely but according to the rules of poker some hands are better than others they are winning hands okay and so we by necessity live in a winning hand because we capitalized on it there may be many many more that are not winning hands and finally you could say as an analogy the ancient Greek philosopher thousands of years ago could have contemplated the nature of the earth and asked himself why does it look so special to allow us to exist if there is only one you know was it created for us well maybe it was that's not an unreasonable deduction but with or without a God the Greek philosopher could have said maybe bodies like this for whatever reason form with a variety of masses and a variety of distances from the stars around which they orbit and a variety of different properties some of which allow the existence of liquid water and so on and those that in which that those in which the conditions were conducive to the development of complexity culminating with life you know they had a chance to form life and the other ones had no chance or less of a chance or whatever and we then live in one of those good planets and so the philosopher could reasonably conclude not prove in any observational way that there is an ensemble of other bodies out there and that the earth does not have special properties necessarily by design but rather has special properties by accident and we necessarily developed in one of the worlds with special properties I'm sorry for the lengthy answer but that was such an interesting question that I wanted to do it yes oh yeah so how did the extra dimensions of string theory fit into the idea of dark energy well there's a number of ways the most fundamental I think is that to work these string theories theories that say that at the fundamental level all of the elementary particles are little packages of energy in the shape of a string or a membrane sort of flopping around vibrating and to get the mathematics to work out to resemble anything close to our universe you have to have the vibrations occur in multiple dimensions more than just the three that we see they're like seven or six depending on your version of string theory of additional dimensions most or all of which are cool curled up into tiny tiny scales that we cannot see so this sounds pretty crazy but it doesn't it's not necessarily crazy imagine you're a bird flying over a sheet of sandpaper from far above you see what looks like a two-dimensional flat sheet but if you swoop down and look at it under a magnifying glass you see that it has granularity it has a third dimension and that's a richer universe or a hose seen from far away ants going along that hose if it were truly one-dimensional would just sort of smack into each other and then they'd have to turn around kind of a boring existence but if that hose actually has a small circular dimension than two ants coming next to each other could say oh I'll just bypass this one and keep on going and the ants themselves might have two dimensional bodies and so on so you have a richer universe that way even though on the largest scales you don't notice those tiny dimensions but real they're really there so that's the premise of string theory okay that's one of the premises so how this could affect things is that if string theory ends up being the theory that unifies quantum physics and general relativity then as I said we think that this unification will lead to an explanation of the dark energy or conversely the properties of the dark energy will help in this unification process and so they will be then intimately related the dark energy will be perhaps the most obvious physical manifestation in today's low energy old universe of string theory yeah there was a question right there yes yeah globular clusters yeah thirteen point seven yeah yeah so the question is you know there are these beautiful clusters of stars called globular clusters yeah and they're they're up to 13 billion years old and we now think the universe is pretty close to thirteen point seven plus or minus 0.2 billion years old so that's older than the globular clusters it didn't used to be that way a decade ago there was still a problem a little bit more than a decade ago that the best derived ages for the globular clusters were bigger than the derived expansion age of the universe so how can some of the contents of the universe be older than the universe itself that's like saying that you're older than your mother okay it's sort of a physical impossibility unless you're dr. Spock or something like that you know so two things happened the ages of the globular clusters that were calculated back then had been too high they were thought to be 16 billion years old or something and they're more like 13 or 12 and moreover we now have a pretty accurate current expansion rate of the universe that's the hotel called Hubble constant and we have at least two a first-order approximation the expansion history it decelerated for the first nine billion years and then accelerated for the next five billion or so so you take today's expansion rate coupled with the expansion history and you calculate that the age is 13.7 billion years old and the globular cluster ages have gone down to 12 or 13 so suddenly there's this comfort zone and if you take spectra of the stars of globular clusters you find that indeed they have a very small proportion much smaller than that of the Sun of heavy elements that's because these were among the first generations of stars to form not the very first generation because these things are not completely devoid of carbon and oxygen and iron and the things we love because we're made out of them but the abundances are very low so what we think happened is that the first generation of stars formed two to three hundred million years after the Big Bang that polluted faced with heavy elements from which then new stars formed with a slight but nonzero abundance of these heavy elements and the kinds of supernovae that we think polluted space with these heavy elements may have been the super-duper supernova that I showed you near the beginning of my talk this one that exploded by a new kind of a mechanism and that's important if it's true because it means that the first generation of stars which theorists link were more massive on average than today's stars did not all go wonk and collapse to form black holes some of them successfully exploded ejecting newly synthesized heavy elements into the cosmos making it possible eventually for the earth and life and us to arise and if that isn't one of the most cosmically magnificent stories distort the story of our creation and emergence from the hydrogen and helium of the Big Bang then I don't know what a better story would be you know so yeah one more question okay how about over here yes ah that that's an interesting question that I said that clusters of galaxies are dense enough to be gravitationally bound but eventually on the largest scales you get to regions where the anti-gravity if you will dominates and what can that teach us about the future and also about the dark energy itself first this is one of the things that independently suggest the existence of dark energy by the way and it's a very clever argument beyond the clusters of galaxies they're the so-called super clusters they're very large they can be a hundred million light-years in diameter they're they're sufficiently weakly bound that in fact the dark energy is spreading them apart it turns out even though the dark energy is not spreading clusters of galaxies apart now it turns out that if there were no dark energy then photons or particles of light from the afterglow of the Big Bang the so called cosmic microwave background radiation entering one of these super clusters would gain some energy on its way in because it's going into an attractive region of space okay it's going into a super cluster of galaxies and so it gains some energy it's called a gravitational blue shift but then on the way out it would lose an equal amount of energy as a gravitational redshift leading to no net gain or loss of energy for those photons and so in the direction of the super clusters of galaxies you should see no variation in the microwave background caused by that intervening cluster but if the cluster is expanding faster than it should have because it's been acted upon by dark energy then during the time of flight of that photon the cluster expands its gravity weakens its so-called gravitational potential weekends if you want to get more technical and the gain of energy of the photon on the way in is greater than the loss of energy of the photon on the way out and so there's a net gain in energy and that region of space 13.7 billion light years away looks a little bit hotter than the surrounding regions okay this is called technically the integrated sax wolf effect and it has been noticed at a marginally statistically significant level I think it's real okay but it's it's a little bit dicey still but I think it's real and that's an independent confirmation that on the scale of the super clusters of galaxies in fact there is this dark energy that's acting upon them what that tells us about the future I would say so far not much well you know that those measurements alone don't tell us much but in conjunction with the other measurements we are getting more and more independent ways of measuring distances in the universe as a function of redshift volumes and the growth of large-scale structure and all those things together are determined by the detailed properties of the dark energy exactly how has it changed with time it looks to a first approximation as though the dark energy is a property of space that does not depend on time so unlike normal matter where you have a thousand particles in the box if you expand that box the density goes as one over the volume right double the volume the density is one-half as big well this stuff double the volume and the density remains the same yeah now maybe that's not true you know maybe it deviates a little bit from that but so far the observations seem to be indicating that and I can see the gears turning in many of your heads I just said that you double the volume and the density of the stuff remains the same but that means there's twice as much stuff is that's crazy right you're creating stuff out of nothing here's the rub okay this is a positive energy so it contributes the total positive energy of the universe indeed it helps make the universe spatially flat on large scales otherwise it would be negatively curved it would be kind of like a horse's saddle but this stuff kind of flattens it out so it's a positive energy and so there is a gravitational attraction of all the stuff for all the other stuff it's a gravitational attraction it's nonzero in fact it's quite big it's just that the pressure of this stuff is an even bigger quantity and it dominates over the gravitational attraction so overall the universe accelerates with time but the gravitational attraction cannot be ignored and it turns out that the magnitude the size of the gravitational attraction is exactly equal to but but negative of the amount of matter that you have in this dark energy so as the amount of dark energy grows the amount of gravitational attraction which can be thought of as a negative energy grows negative at the same rate and the two end up being zero the energy of the universe appears to be exactly or very close to zero and with a dark energy dominated universe that's a very natural result you're not creating something out of nothing it's like an apple it's kinetic or energy of motion is zero at least in my frame of reference here I can define its gravitational energy its potential energy to be zero so here it is zero plus zero is zero as I drop the Apple it clearly picks up energy of motion one two three four five units of kinetic energy but it's also picking up negative one two three four five units of potential energy gravitational energy which exactly balances the kinetic energy so I've not created nor have I destroyed energy in this process and I won't become rich and famous because I solve the energy energy problems of the world okay all I've done is I've dropped an apple okay so in a similar way the growth of the universe from dark energy conserves energy it's zero and the universe could have just started as some little quantum fluctuation so it's almost identically zero and as Alan Guth one of the originators of the inflation theory likes to say the universe may be the ultimate free lunch it's total energy is 0 is it flux it came out of nothing but fortunately for us there's a positive component to the energy you and I everyone else Berkeley UC Santa Barbara the kaveri institute l co GT but there's also a negative energy our attraction for everything else in the universe exactly balances the matter that you have talking about you know not leaving a footprint well there you go thank you so much I'll be happy to hang around a bit longer thank you very much you

Channel: University of California Television (UCTV)

Views: 177,561

Rating: 4.8791423 out of 5

Keywords: astronomy, super-novae, dark, matter, universe

Id: vPkGEVgOJK0

Length: 116min 6sec (6966 seconds)

Published: Thu Mar 13 2008