Dark Matter And the Ultimate Fate of the Universe

since the beginning of human sentient sentence an ability to think about things cogitate people have always sat outside at night looked up into dark sky look up and in the dark looked at the Stars looked at the PAMP planets and wondered where does this come from where is it going what does it mean what's it composed of where will it fit in how do we fit in and out of that long string of human development human evolution thinking pondering it's really only in the last decades we're not talking about hundreds of thousands of years it's only in the last decades that we've been able to really quantify study analyze test measure the parameters that we need to understand these issues the field as you know is cosmology the study of the universe its birth its presence its future its possible death and its composition as we've gone into this what you'll hear tonight is that the composition of the universe and what's in it what makes it run is not only interesting it's bizarre some of the biggest most fundamental problems in all of science lies right in the heart of cosmology and it's our great fortune that one of the world's premier cosmologists as a member of our department of physics here at UCSD Kim Greist studied at University of California at Santa Cruz he's also done postdoctoral research with some of the world's most eminent cosmologists both at the University of California Berkeley and the University of Chicago and not to take anymore of his precious time I would like to introduce Kim to tell you about this strange and wonderful universe that we live in thank you thank you all for coming so what is the dominant material in the universe and what is the ultimate fate of the universe let me repeat those two questions what is the dominant or typical material in the universe and what's the fate of the universe those two questions might seem completely unrelated to you but they're actually very closely linked and that's what I really want to talk to you about tonight is first of all the answers to those questions and how they are linked now it might be surprising to you that with all the current technology that we have and all the current science that we do not know the answer to the first question what's the dominant material in the universe personally I find just as amazing that we probably do know the answer to the second question which is what is the ultimate fate of the universe so that's what we're going to work toward tonight but let's start by going through a little tour of what is in the universe okay so I'm gonna start just by what do you see out there an inventory of the universe so as marked demons was saying humans for thousands of years have looked up at the sky and said what's there and what's there is stars this actually happens to be from Australia and if you happen to live there you could see these little smudges they large and small Magellanic Clouds which actually are nearby galaxies they'll figure in our story a little later but if you just look randomly with your eyes you can see probably about five thousand stars humans somehow are always had the intuition that there's a lot more than five thousand stars up there and with the advent of telescope to prove that and being able to zoom in telescopes technology has been such a a mover in the in the in cosmology because it's allowed you to do things and answer questions that you haven't been able to that you'll be able to ask for thousands of years but now only answer so if you were using a telescope you look around and say okay what other kinds of things are in in space so you mostly see stars but you also see things like this is the the great nebula in Orion as you walk out tonight you'll be able to three see the three bright stars of Orion's belt and looking at those come down and you'll see the three stars of Orion's sword this is the middle sort middle star of his sort it's not a star at all this is a cloud of gas in which a bunch of stars is being formed this is the placental material being blown away actually after the formation of stars so we see stars and we see also clouds of gas from which stars are being born okay what else do we see looking around we also sees things like this the Crab Nebula this is a an exploded body of a star that went supernova about a thousand years ago and after the star had finished its life it exploded and all its material came a ghost shot back into the galaxy to become yet another generation of stars all the iron and carbon all the iron and heavy elements in the galaxy in this room came in fact from supernovas like this that's where it all comes from and that that shows you actually that the Sun is a second solar system as a second generation object so you see gas and junk coming off of stars but mostly you just see stars you see stars however in different form a in different kinds of groupings okay that that Orion Nebula after it formed would leave a little cute little compact group of stars called an open cluster after a few hundred million years though those stars were kind of drift apart and wander away and lose the brothers and sisters but this is a globular cluster of stars this is a family of stars this is what happened in the deep dark history of the universe when when different things happen this is a million stars all jammed into say about a few light years in fact only so this is these form very close together very compact and they're so compact that they've been this family of stars all formed together has managed to stay together over the entire 12 14 billion years of our galaxy some of the oldest stars we know are in these glass clusters okay and our galaxy has several thousands of these things wandering around relics of that ancient past okay so we see groups of stars like this too but notice that what we're seeing so far is just star so to answer the question what's the galaxy what's the dominant material of the universe we would be guessing about this point stars we also see things like this this is the great spiral nebula in Andromeda you can see this with your naked eye is a little smudge now what are you actually seeing here but you're actually seeing are a lot of stars that are nearby us and then something that's milky and fuzzy maybe some other things that are a long ways away okay these things have been known for centuries but people didn't know what they were okay it turns out now that what they are are groups of a hundred billion stars like our own at a very far distance away this one is two million light years away okay but so we see galaxies galaxies comes from the Greek word milk and that's why they you know called it that I guess does it look like milk to them so pretty much everywhere you see on the sky you see stars and then some of these different kinds of objects but there's one place on the sky that's different and that's been known about for thousands of years and that is the Milky Way it's itself this great band of white that goes across the sky if you've been out to the desert in the summer you've seen it again notice for thousands of years debated for hundreds of years and it's it's got this kind of white milky stuff with this dark clunky junky stuff all over it and what is it you know well again don't wait to find out in astronomy is to build a bigger better telescope and zoom in to see what it is okay so let's zoom in and let's see if we can see what it is if we zoom in by a lot we see that it's cotton candy or something okay well we haven't zoomed in enough so let's zoom in to this little region here some more and now those of you at the front can finally start to see that what you're seeing are thousands billions in fact of individual stars what you're seeing is an incredibly crowd crowded bunch of stars and there are about a hundred billion stars in our galaxy so by zooming in we actually are managed to prove that that Milky Way that band of stuff across the sky is actually just a bunch of stars okay so the explanation of that Milky Way picture is that we live in a concentration of stars it looks a lot like those spiral galaxies I was showing you we're all moving around somehow okay and this this actually also makes you think that when you see something like this that what you're seeing in fact is something a lot like our own Milky Way galaxy and so if this was our Milky Way galaxy this is an external galaxy of course but it's like ours we're living in a star out here and we look toward the Milky Way we're looking in toward here we're seeing that crowded star field in there we're all going around maybe a half a million miles an hour okay that can be measured all these stars are going for many years for for centuries people didn't know what these spiral nebulae were but then again with the advent of telescopes you can zoom in and see that in fact identify the Stars and now with Space Telescope Hubble Space Telescope our best way of zooming in currently you can zoom in and you can pick out the individual big stars and then prove that this thing here is actually again just a bunch of stars does anything change as you move out further in space well how do you move out further in space well in astronomy it means you get a big telescope and you look you zoom in and so you often see things like this these are spiral galaxies just like ours but now at a much bigger distance and they come in groups they come in families galaxies we found that stars come in families but galaxies themselves come in families like that there are places in the sky that are very unusual like this one one of my favorite pictures this is there's only like one star in this picture these are all galaxies this is the Coma Cluster of galaxies and these this is very far away millions of light years hundreds of millions of light years and this is probably about the size of our Milky Way galaxy okay so there are thousands of galaxies these big central CD galaxies have have obviously eaten dozens or hundreds of other galaxies for lunch okay and they're in the midst of eating other ones you can see them being ripped to shreds these big ones pull in so you find big clusters of galaxies but again the essence of this is just a bunch of stars are moving in galaxies under the influence of gravity finally what what you can do with the premiere instrument the Hubble Space Telescope in which NASA did is to say let's just take a blank area sky well you'll see anything and stare at it for a long time and see what's there so they took an area of sky about the size of a grain of sand being held at arm's length and they spent 10 days of the Hubble Space Telescope taking an images of that and adding in all the light that comes this is the deepest image ever make made it's probably the most expensive image ever made as well actually and here's what here's a quart there's a partion of the Hubble Deep Field that as its called there there's there's only two stars that you can see here are three but everything else is a galaxy and what you're seeing now are nearby galaxies will nearby everything here is far away this was a blank area of sky okay these guys are medium distant galaxies but even these little tiny things are very very far away galaxies and because in astronomy looking out in space is looking back in time you're actually seeing galaxies as they're starting to form here and they look weird they look different and that's what you would expect because you're seeing the history of galaxy formation okay so but the whole picture is that there's a lot of stars and galaxies so our picture of the what the universe isn't is a bunch of galaxies separate each one separated by millions of light years and there's an important ingredient I haven't talked about yet they're all moving away from each other they're all expanding now one thing astronomers can do as easily as take pictures and images is to measure speeds they use the Doppler technique which is the same technique the police prefer when they want to find how fast your car is what they do it's very common throughout all of astronomy actually and in fact this is for this is a slide for looking for extrasolar planets but the idea is here the idea is that a yellow star gives out light of a very peculiar frequency many different peculiar frequencies as that star moves toward you that light gets shifted to shorter wavelengths the frequencies change and that's called blue shifting if that same star is moving away from you that same light would get shifted to red redder frequencies and so by very precisely measuring the frequency changing the frequency shift either redshift or blueshift one can measure the speed that's exactly what the little computer and the police car does when it wants to know how fast you are it measures the shift the redshift or blueshift of you're coming toward or away of your car and figures out then how fast you're going so we're very good at measuring speeds and so if you actually went back to this Hubble Deep Field picture so people have gone out and spent enormous amounts of time measuring the speeds of almost every object in this picture and in fact they're all moving away from us sometimes at tremendous speeds at tremendous speeds and by now millions of galaxies speeds have been measured and the the observation is they're all moving away from us at enormous speeds okay so the universe is an expanding a bunch of galaxies now but what I've said is actually missing an important ingredient because in fact there's something there besides what we've seen so far part of the subjects of the talk the dark matter how do people know that's there well they actually it's the same idea here's a picture a nice picture of a galaxy and if you're a astronomy nerd you would say okay this is probably a bunch of stars going around in a circle let me check that by using this Doppler technique I'm really good at that I can measure the speeds here here here here and what do I expect I expect the speeds here to be coming toward me right and I expect the speeds there to be going away from me or vice versa depending on which way it's turning so people have gone out and measured these kind of galaxies actually thousands of them and they find out how fast it's going around they said oh it's going around at a half a million miles an hour good hey that's the same speed that we're going around in the Milky Way now in fact that's a very serious problem and the reason is if you actually take how much light is in this galaxy and you know how much star how much stars how much light starts give off you know how much mass stars are you can actually very accurately calculate how many stars are in this galaxy or in the Milky Way galaxy or any galaxy it's pretty easy to do this and you say okay how much mass are in those stars you find that there's not nearly enough mass to keep this stuff bound there's you off by a factor of at least ten and in fact the Sun moving around the galaxy if all there was in them toward the Milky Way there are stars that we see we would just be flying right out of the galaxy right now okay there's no way there's enough gravity in those stars to hold us into the galaxy of the Milky Way and the same is true of this galaxy NGC 45-65 the amount of speed just is way too big in fact in science you can do that you can do the reverse people do this you can use the speeds to measure the maths this is how we get the mass of the Sun for instance by measuring the speed of the earth around the Sun you can get a very precise calculation of the of the Sun that's that's how we get it so people got have gone out then on these galaxies and said okay let's figure out the mass and they've said hmm there's a problem the mass in this galaxy is not coming from the stars it's off by if there's something else giving us at least 10 times more mass so what we had to do then not because we like to but because we believe the laws of physics and the measurements that have been repeated and checked and if you didn't check is realized that a galaxy does not look like what I told you it looks more like this a friend of mine tried to keep make a nice artistic version you know there's the galaxy but then there's an extended dark halo that contains almost all the mass maybe a factor of 10 the way I explained it to myself it's more like this there's the galaxy and there's a dark halo and when you look at these pictures you should be thinking if you really are wanting to know what's really out in the universe it's not that beautiful pictures that's not the main story the main story is whatever this mysterious dark stuff is that's completely dominating the gravity and if I went back to that cluster of galaxies with a thousand galaxies all moving different ways it turns out that they're moving a thousand kilometres a second they're moving way too fast for the masses of those individual galaxies and again people can use different techniques and discover the actual mass in those clusters there's a huge ball of mysterious dark matter that somehow is the dominant material here so the story here is that somehow most of the dominant most of the material of the universe is unknown okay so the answer to the question then it's not stars then the dominant stuff of the universe is the dark matter the mysterious dark matter at least ten times more than stars so so is this important does it does it does it matter that most of the stuff of the universe we don't know what it is or is dark well I don't think it affects the stockmarket much but if you're interested in what is the reality of of the substances of the universe you would like to find out what that stuff is and in fact I'm going to come back to that and some various ideas people have on how to figure out what is this stuff that is making up this huge dark halo but they're actually before that is another even more fundamental reason why we want to know about what the dark matter is not actually what it is but how much and what its basic form is and the reason is is that how much and what its basic form is determines the fate of the universe so why is it that the that this dark matter somehow determines the fate of the universe well in the 1910s Einstein wrote down his theory of general relativity this replaced Newton's law of gravity and it was the first theory that was capable of actually being applied to the whole universe so you know you have this theory that can apply to the whole universe because it wasn't just objects in the universe it actually was a theory of space and time and he couldn't resist he said wow let's try it so he he solved for the universe and he did not like what he saw what he found what he found was that the universe was either expanding or contracting now in night in 1916 or something like that one he did this the universe was thought to be static they didn't know about these spiral galaxies moving away okay and they just thought they just they had measured the Doppler shift of the Stars and they're not all expanding so he said man this great theory I have you know it's been tested you know on gives Mercury's orbit it gives light bending such a good theory I'd hate to just throw it out because it doesn't agree with data it must be wrong so he went back to his theory and he looked at it said can I change it can I modify it now his theory depends upon his theory originally depended upon two numbers the first thing was the Hubble constant which is the current expansion rate how fast things are moving apart second number was called Omega that was the amount that was the matter density in the universe in other words the amount of mass in the universe that's one of the numbers that his theory depend upon now whatever he did with those two numbers it was going to be either contracting or expanding so he said that's not it he noticed then that there was it was mathematically allowed to add a third number into his theory it was like a a weird universal constant that would be this kind of a universal negative pressure that would fill all of space and time he called this the cosmological constant term and he noticed that if he put this bet it was allowed mathematically in the in the theory so he can put it in there fine and if he adjusted the number just right he didn't know what these other numbers were okay because they hadn't had measurements but he'd realized that he could balance the other two numbers off this number and get a universe that was static so he said voila published when he sent that theory out soon after of course Edwin Hubble working in Los Angeles with measuring the redshifts of these galaxies and discovering that in fact they were expanding and when einstein said daddy said ah I should not have put that in and he called the cosmological constant the biggest blunder of his scientific career but he was probably really thinking was man I could have predicted the expansion of the universe and gotten famous but anyway that third that third quantity the cosmos a constant is allowed and it really is a measurement problem what is its value he sent it to zero most people sent it to zero because you don't have until you have a measurement but really it was just an unknown number and in one sense the last 70 years since that of cosmology are trying to measure those three numbers there are extremely difficult numbers to measure what's really remarkable and what's what why I'm talking about this in part is because I would say within the last three years two of those numbers have been measured and enough of them have been measured so that we know the fate of the universe the fate of the universe is determined by the values of those three numbers this theory what it really gave us a long time ago but now very well tested is a theory that allowed us to make lots of testable predictions it said for instance that the universe had to be expanding and that meant it had to be smaller in the past and that said that led straight to the Big Bang it contains the Big Bang if the Big Bang is there then you have lots of predictions about what should be coming out of the early universe because we can predict amount of elements coming out of the universe you could all different kinds of radiation how galaxies form how structure forms all this should be contained in this theory and what we've seen for the last few decades is that so many of these predictions are just being tested because with better telescopes you can go out and look for this and find these things and this theory is just really incredible so far this theory matches with observation perfectly and this theory the Einstein's general theory of relativity as applied to the whole universe seems to be an accurate description of the world we live in we don't use it because we like it we use it because there are now thousands of experiments that agree with it and there's no alternative out there that that agrees as well as it does ok but we still need to know the values of these numbers the Hubble constant which now in the last say five years has been measured I could tell it to you but it's not units that are very interesting the thing that's not so well known still is the total amount of matter it turns out that that won't matter so much for us case because what is been measured very recent in the last two three years is the cosmological constant this is the energy of the vacuum the energy of empty space and it's known to not be zero now so another thing this theorem that this theory does by the way is is explain to you things like the expanse in the universe in a way that are probably different than you imagine and I just wanted to stop here for a second and explain to you what the expansion of the universe is like people are walking around have a wrong conception of this they think there was a bomb that went off sometime it in the distant past somewhere and it exploded and that we're coming out of it and that's the big bang okay that's not at all what the Big Bang was like okay a much better analogy would be a raisin bread you take a loaf of bread with raisins in it you stick it in the oven and it rises and all the raisins move apart the raisins are like the galaxies and the bread is like space okay so the expansion of the universe is much more an expansion of space itself the galaxies that we're seeing all flying apart from us they're not actually in a certain sense they're sitting at rest with respect to their local space okay and what's happening is the entire space is getting bigger and so that's much more what the expansion is so there was no center to the Big Bang and it didn't happen it happened at a certain time in the past but there everything's moving away from us but we're not in a special location and that can be shown by this little demonstration which I kind of like so here's a bunch of blue dots that represent some galaxies and now a little while later the universe expands they've turned red that just means later time and now they're a little bit farther apart okay now let's suppose you happen to be sitting on one galaxy like that one right there okay now you just sat there as it went from blue to red you stayed still all the other galaxies moved and got a little bit further away so it looked like this so you're sitting there and all the all the gap red galaxy's is the same galaxy little later I moved away so to you it looks like what does it look like it looks like you're the center of the universe and everybody is moving away from you you start to get paranoid but in fact even if you had been this guy here it would have looked the same because here you stat there this other person and so every - every person every galaxy the universe - seems to be the center of the expansion this is how the Big Bang works you can write down the mathematic mathematics for this very beautifully inside the theory of general relativity and it just makes it very clear how these things all work okay now I said the fate of the universe depends upon certain numbers and that these numbers are somewhat known now here's how it works here's how it works this this explains the fate of the universe in a sense what's happening in Einstein's theory is you have an expansion and if there's no cosmological constant and there's enough matter Omega matter bigger than one that's given in certain units such that this is true in fact so it's just it's a standard way of doing it then they doubt the gravity of all the mass the universe slows the expansion down and eventually that expansion will stop and it'll start and the universe will start to contract once that happens once you go past that point there's nothing to stop it and you go toward a Big Crunch in that case what the eventually all the galaxies we would run into us and all the atoms would run into us and we would all be squashed our entire galaxy would have be squashed into something smaller than Adam there's nothing to stop that big crunch from happening it's the Big Bang in Reverse okay so that would happen if there was enough matter however if the cosmological constant was zero and matter was not enough then the expansion rate is fast enough that there's not enough matter to slow it down the universe expands forever okay so this these two cases and what happens then well in that case well eventually the Sun goes out well actually eventually even before the Sun goes out some turns into a red giant and swallows mercury and then Venus and then burns earth to a crisp and then then it runs out so but the Sun goes out all the stars go out eventually you run out of hydrogen fuel and in this kind of thing it's a it's a cold end now in fact all these situations assume that there's no vacuum energy if a vacuum enter vacuum energy is very weird now if I take a box full of stuff and I make the Box bigger and I don't put more stuff in it the density of stuff goes down so the universe as it expands full of matter as it gets thing the density goes down and so the the force of those this thing and it goes down the vacuum is not like that if you take the vacuum and you make a bigger box with a vacuum you have more vacuum so you have a runaway situation going if you've got energy in the vacuum every time the universe expands you've got more vacuum and so you actually got a runaway expansion happening and in this case the universe is not slowing down at all it's expanding faster and faster and faster and faster the remarkable result of the last few years is by looking at distant supernovas it looks like the universe is expanding faster now than it was in the past it looks like the expansion is accelerating and that we are in the case of this thing and in which case it doesn't matter what Omega matter is if you've got anything in the vacuum that's enough you're you've got the runaway happening this is kind of a pretty odd situation this was not expected but we have to live with what nature tells us people are now checking these experiments they made maybe they'll find flaws in them so far no one's found any flaws so and it does fit with several other experiments as well so this looks to be the fate an expansion that goes faster and faster forever in this in this case what happens to us well it's very much like this case the Sun eventually runs out of fuel except it's a little weirder because we have things expanding faster and faster which means galaxies that we now see will eventually be moving away from us faster than the speed of light okay well in general relativity that's allowed but of course what's is just moving away from you faster than the speed of light you can't see it anymore you know it's outside your horizon but that seems to be the case is that basically what we're going to do is basically lose pieces of the universe as they move outside of our horizon so this death is not only cold it's very lonely will be end up with just our little local group of galaxies that remains after a while and then they'll all be dead and that'll be it what is the mysterious stuff we have okay what is the mysterious dark matter that is the dominant material of the universe well we know the answer to what the dominant stuff of the universe is it's some kind of vacuum energy at this point and in fact I didn't write it here but it gives you an Omega of about 0.7 so something like 70% of this critical density is right now today seems to be the vacuum weird as that is the other 30% well stars and everything you can see a way down at about 0.007 okay so stars are not a very important component of this galaxy of the universe when you actually add up things if you add dark matter in galaxies and clusters of galaxies you come to an Omega of 0.3 okay so the picture is you have roughly about 0.7 in vacuum about 0.3 in mysterious dark matter and some little tiny fraction in stars which are made of atoms and stuff that we know this has recently this whole picture has recently gotten a very interesting conformation from measurements of the microwave background which which measure the sum of all the Omegas vacuum plus matter plus stars and everything and the answer they find is about one that works perfectly 0.7 plus 0.3 plus something tiny is about one so this picture is starting to fit together which is really weird in cosmology usually in cosmology these numbers have like I said they've been looked for for 70 years and they haven't been agreement for the first time almost all the number almost all the measurements agree but I want it but what is now we still have a major books I want a major unsolved problem here because we have vacuum stuff which is pretty weird but thirty percent of what the stuff the universe is made out of is something now we don't know what it is I drew it as some kind of dark cloud around the galaxies you know is it Darth Vader or mismatched socks what could it be the truth of the matter is it could be almost anything because if you stick stuff out in the middle of space and it doesn't shine it's hard to see we see the shining stuff only and so we've built our whole subject of astronomy and cosmology on light coming signing stuff and it turns out unsurprisingly perhaps in retrospect that that's not the dominant stuff so people are very interested in finding out what it is and asteroids you ask astronomers what could it be well it could be black holes lots of black holes or Jupiter's if you will as you walk out tonight you look up in the sky and you'll see Jupiter it's quite near the moon it's the big bright thing you're the moon it's bright the only reason that's bright is its its reflected light from the Sun you take Jupiter and you stick it out in the middle of the galaxy it's dark it's not shining hardly at all and you need a lot of them you need about ten thousand Jupiter's for every Sun but if you filled the galaxy with those things you would not see them okay so maybe that's what the dark matter is astronomers could say particle physicists on the other hand say actually we have a much better idea we have this whole theory of the Big Bang we have theories of particle we actually can calculate particles left over from the Big Bang and there are many different types of particles weakly interacting massive particles is a whole class of different actual particles which give you an Omega of around point three left over from the Big Bang and they say that's much more likely now to tell you the truth these guys are probably right now in part because of an experiment I involved in that basically show that this is not the dominant dark matter this is true is a pretty cool idea it's almost the ultimate Copernican revolution not only aren't we not only are we not at the center of the universe we're not even made of typical stuff atoms are not the dominant kind of stuff in the universe it's some mysterious particle that would be going right through our buck they'd be going right through our body now this room would be filled with wimps okay there'd be billions of them going through your body but they're weakly interacting which means they just go right through there so they slip right through the spaces of the atoms and that would be the dominant stuff that we would be like some little ripple on top of okay this is not such a far-fetched idea it's actually probably true weird as it may seem so people would like to know how to how can you test that hypothesis well people who are looking very hard for the wimps the best way to test the hypothesis would be to actually catch one somehow now we know that even though they're weakly interacting weakly means that they go right through the earth typically without hitting them but if they came out of the Big Bang they must have some interactions and so you can calculate that very occasionally a wimp will come in and bump an atom and then that atom will bump other atoms and so there's probably a dozen groups of scientists now throughout the world who have taken crystals of material very pure material they've cooled it down to almost absolute zero you cover it with radio pure copper archeological lead paraffin all sorts of electronic stuff you stick it a mile underground and you instrument it and you wait to see if this kind of thing will happen okay so there's a probably a dozen groups that have done this they have yet to find a signal actually one group does claim a signal but no one else believes them so I'm with the people who don't believe them I looked at their data and it's it's funny they want to they want it so bad you know but it's a method that may actually work in in detecting these wimps and if it would be fantastic if it works if they find these particles than they would have found the dominant material of the universe okay now more active than that are the particle physicists who are going to go out and say why bother why trying to find the ones that are floating through the galaxy let's just build them let's make them and in fact if you look at the science justifications of the main particle accelerators this is CDF at Fermilab see the little guy there these are big accelerators this is Aleph at Geneva and this is d0 also at Fermilab and one of the main justifications are to look for these wimps they say we want to create the wimps you know we're gonna try to do it they're jamming together particles and huge energies trying to create new particles and they're because the particle theories say that these wimps could exist and if it is they can tell them how to reduce it so my bet is that if actually wimps are discovered these guys may do it because they're very serious about looking for them but again no detection yet so it's something to keep your eyes out for in the newspaper and stuff if people discover these things that would be a fantastic discovery of what the dominant material of the universe is now I took a different approach I said well let's try to look for the easy things first not the wimps but let's try to look for the macho's the the Jupiter's or black holes or these things and here's an idea that bodom pitch in ski from Princeton had in 1986 so he said look at if the dark halos made of some kind of Jupiter's or black holes or something they're moving all around well that's true and if you're watching a star here say in the Large Magellanic a nearby galaxy occasionally one of these dark objects will go right in front of it okay now what would happen if a black hole goes in front of a star most people get this answer wrong you think oh it's suck up the light right right it doesn't block the light it actually serves as a magnifying lens and amplifies and makes a star appear brighter and you can actually calculate this very easily using general relativity it's kind of fun and you can show that it act like a lens you can actually build a glass model of this kind of lens and look look around and see what people would look like so but this gives a technique then if you can monitor millions of stars in the nearby galaxies you can actually look for this effect so a group of us set out to do this about eight years ago you need your own telescope here's the one that we use in Australia we had complete use of it for eight years and so what we do is we look at this this is a picture of the Large Magellanic Cloud not very good there's many more stars here that you can't see unfortunately because of the contrast in the image so you take an image a five-minute exposure using our special telescope this will give us about a half a million stars then we move over and take another exposure another all night long and this way we can get the brightnesses of maybe 20 million stars a night using computers to analyze it then what we do is we look through all those stars every night we do this for many years and see whether any of those stars got brighter and dimmer in just the way that the gravitational lensing effect would say and if the dark matter consisted of black holes or Jupiter's or any kind of macho type thing we should see this signal okay so this was this is what we proposed to do this is what we did so well here's a typical image there's a half a million stars here you've got five minutes to measure the brightness of all of them because then you got to take another picture and you do that all night long so it's a lot of data but computers can do things like that you know so we search through and sure enough in 1993 we found this thing which says this is the brightness as a function of time it went flat like a normal star it got brighter just as predicted by that Einstein formula in both the red and the blue band and this is the first example of gravitational microlensing that was discovered and this was a macho event this showed that in fact out in somewhere in the dark halo something some dark object went in front of a star and magnified it just as we predicted so that caused a lot of excitement in the beginning the footprint of dark matter and the Department of Energy called me up and said you know what funding all these stupid wind searches is everything for them to look for anymore haven't you guys found the dark matter and I said oh no I said of course not we've found a few events we don't know how much dark matter that represents he said oh okay and they continue to send to fund the WIMP searchers you have to help your friends out or you're in big trouble so in fact what we've done recently now is spent the last several years doing a very careful calibration of our experiment we've now found maybe 17 of these micro lensing events and we know how our experiment reacts and in fact we can now say with assuring that that the that the Dark Matter whatever it is is not entirely made of any kind of macho type object okay so that's our new result that we're actually announcing at the a a at the American Astronomical Society meeting today fact that was announced but we do find that a 20% of the dark matter being made of some kind of much of stuff there's a very reasonable fit to our data it also means of course that the wimps people these particle idea has gotten much more secure we've by eliminating the main contender what is the dark matter then there's 80 percent of it at least out there that nobody knows what it is so that's pretty weird so I think my conclusions then really are just that the last few years has really seen a zeroing in on the primary basic parameters of cosmology this model it works so well is having less knobs to turn and so we are going to have to live with what it is there now this it'll be tested more and more of course as more and more people do more observations and in science we're always willing to throw at any theory in fact that's what scientists live force to be the one who discovers that the basic theory is wrong so far this theory is working great the dominant stuff in the universe it's actually seems to be the vacuum pretty weird the dominant material stuff still completely unknown but many many active search is underway so that's really that sums up pretty much everything I wanted to say and won't we stop and have some questions yeah it could have been a star in front of a star actually calculated how likely that was and because stars can lend the stars and we see too many just be stars lensing themselves so it's it's a Texan it's a numerical number because that's certainly a possibility yes unfortunately the probability is so small the probability the reason we have to monitor so many stars is any given lens has only one chance in a million of any given source was only one chance in a million so if it lenses one it's almost very unlikely what I didn't show from my picture is how precise that alignment has to be it has to be very precise Einstein actually was asked about this lensing effect and he calculated and said yeah it's there he says but you'll never see it you'll never get two stars lined up that perfectly the only reason we're getting it is because we're imagining the entire halo full of dark matter and our monitoring 30 million stars it's computer pilots technology that's made it Paulina no it's a good question his question was if you really want more universes than one you know one is not enough for you then don't you really want the Big Crunch because then you had you know nothing then you have the Big Bang then you have the Big Crunch that made a lot of sense I find that very attractive myself but in fact in quantum field theory there are many speculative their theories about how the universe begins and in fact the universe can begin as a quantum fluctuation even with it even within this universe we could have another universe forming okay that these are speculative ideas but in the theory of general relativity and in since we don't know the quantum field theory of at the fundamental level that's possibility so there are other ways to have many universes well if in the theory that we're stuck with right now it's the fact that there's an enormous amount of vacuum between us and those distant galaxies and that space it spells itself is expanding so they're not actually they're speeding up only because they're sitting at rest with respect to themselves their local space and we are but the there's just a lot of extra space being created between they didn't actually measure the vacuum energy what they did is they measured the expansion rate as a hit as a function of history so they looked back in the in the past and saw how fast the universe is expanding and they look now and they see that it's expanding faster in the eins then they're using the Einstein theory and in the Einstein theory the only way that works is if you have a vacuum energy nobody knows what a macho is if it's a black hole then it then it would have a Hawking type temperature which is basically zero if it's a brown dwarf it would have a brown Dorf it's a Jupiter so we depend on what it was the we don't need another universe to account for the accelerating expansion there's but nothing rules out the possibility of other universes what we define the universe at is at what we define the universe as is all the stuff that we could ever see okay so that's the universe there could easily be and in generality it's easy to write down mathematical solutions for lots of extra universes that we just don't happen to see they can be there but they can't have any effect on us either so this extra universes would have no effect on the expanding of this universe you okay it's not not well determined people would think of it that's probably 100 GeV a hundred times the mass of the proton proton up to a thousand would be a good guess for I'm now thinking of the neutralino from supersymmetry which is probably the most popular wouldn't candidate neutrinos are different than wimps though they are also weakly interacting particles so the first wimp was a neutrino but you should know with a big mass but that has been ruled out as a possibility now because neutrinos are well understood now so what was the other thing so they're not good candidates anymore for the wimp the wimp has to be some new particle and has not yet been discovered well in normal quantum field theory we make up lots of new particles it's easily to do it we give them different quantum properties so yeah they're probably some new particle like a neutrino that like a new type of quark that no one's ever heard of something like that it's a very natural wimp lots of possibilities certainly a lot of stuff from this goes into science fiction I've read science fiction novels that have contain ideas that I came up with actually but there is there are a couple of cases however where the reverse is true as well there was in fact Carl Sagan in writing his contact book contacted John wheeler and asked some questions that led John wheeler to invent some kinds of wormholes that are actually mathematically useful so it has occasionally worked the other way it's almost always we're trying to figure stuff out in the science fiction people read what we do in fact no because we can still see the microwave background which was when atoms formed so the first thing to wink out if you will will be the the remnant of the Big Bang so I mean some cosmologists get up to say get up and say and this is going to happen soon so you have to fund cosmology now he didn't talk about vacuum energy he talked he saw it purely as a is a constant that was consistent with the symmetries that he used to drive his theory it's the modern particle physicists who think about vacuum energy we have lots of particle theories all of which have vacuum energy we're very comfortable with it it just turns out that's exactly the same thing as the cosmological constant it's not only a it's a is in a sense it's a fudge factor it's a part of quantum field theory that's not well understood and people used to like to set it to zero because they didn't know what else to set it to it couldn't calculate it it's an uncountable number this really is a big challenge for particle physics now it's the same explanation you take a container and you expand it you're going to get more energy I mean weird stuff yeah that it's got a negative pressure that's called the negative pressure which is an effect of this thing it's straight out of gel relativity it's in there well there's no theoretical reason not to have them except that there's no pretty theory that does it so yeah there's no since we don't know what they are if you're free to make any theory you want you could make that third to me well people look really hard for neutral molecular hydrogen that's hard to see you look for it in 21 centimeter people have come up with ideas that it's this fractal you know if you you know they've gone to the point of saying okay how am I going to have to do it to prevent it from being seen and there are some very bizarre fractal needle ways of doing it and maybe you can do it but there's actually another reason that I didn't talk about which is a little comes out of Big Bang nucleosynthesis the amount of deuterium in the universe shows in fact that it can't be made of baryons the dark matter it's another line of reasoning I didn't have time for so I'm very convinced that whatever the dark matter is it's not normal atoms no because we look for for dark matter exactly through absorption and we know it's not there so I mean it could do a tiny bit but not significantly because to tell you the truth the those galaxies I showed you there are better galaxies that have small amounts of tracer material way out from where you see the stars you see the molecular hydrogen and in fact it's those speeds that give you the strongest constraints and it's the detailed measurements that show you that in fact most of the mass is outside where the visible stars are so it's other tracers besides those stars you find very rare stars or molecular hydrogen clouds yeah wimps would be created probably created before the protons and the neutrons before we taught before the regular stuff like us made of atoms would be the wimps oh yeah I mean I actually started out by doing wimp calculations from my thesis so let's thank professor

Channel: University of California Television (UCTV)

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Keywords: matter, physic, science, universe

Id: 9fIrmjxlT18

Length: 57min 54sec (3474 seconds)

Published: Fri Feb 29 2008