Dark matter - what we're really made of | Michelle Thaller | TEDxBinghamtonUniversity

you I hope you will agree with me that we live in an extravagantly beautiful and vast universe the scale of it is something that not only inspires us but also humbles us a take for example a galaxy this is a fairly typical spiral galaxy and a galaxy like this is composed of about half a trillion stars 500 billion stars even more mass is in dust and gas and everything rotates around a common center that the Sun for example takes about a quarter billion years to go once around the Milky Way galaxy now n2n this galaxy is about a hundred thousand light years across Lightyear of course is an unit of distance as the distance light travels in one year going at 186,000 miles per second so it's about six trillion miles multiply that by a hundred thousand and you get a sense of how big a single galaxy is but in the universe there are scales far bigger than galaxies this for example is a lovely picture from the Hubble Space Telescope and amazingly every little blob you see in this picture is not a star but entire galaxies a galaxy of billions or hundreds of billions of stars there's about a little bit over a thousand galaxies in this image and it actually represents one of the deepest views into the universe we've ever taken some of these galaxies are on the order of 12 billion light-years away and that's really wonderful because what that means is that light took that long to travel to us when you look at a galaxy 12 billion light-years away you see it as it was 12 billion years ago so we have a ringside seat as astronomers to sit back and collect light and actually watch the universe in fold the history in front of us now it's worth mentioning okay 2,000 galaxies in this image alone how much of the sky does this rip represent there's all of these galaxies in the sky it may surprise you to know that this whole image the amount of sky on this is equivalent this is really true to looking at the eye of a needle held at arm's length against the sky so if you look through the eye of a needle in any direction on the sky you're going to see between a thousand and two thousand galaxies think about the amount of matter the amount of material in our universe amazingly right now we think all of this stuff is just a tiny bit of the whole this shows you we think the current energy content of our universe is and honestly this is a little embarrassing I want to explain to you why we would possibly believe something like this by energy content our universe is about 73% something called dark energy and this was discovered only about 10 years ago you may have heard the universe is expanding well it turns out it's not only expanding it's actually accelerating the galaxies are flying faster and faster apart all the time it takes a lot of energy to actually accelerate an entire universe we've made great strides in explaining what this mysterious energy is we've given it a name that's about as far as we've gotten the the reason we call it dark is just that it means we know nothing about it we're going to talk today more about the matter content of the universe and that's not a whole lot better all the matter that I just showed you the billions of galaxies we believe that everything that's made up of the stuff that we are made of regular matter makes up about 4% of the universe and it's even more depressing than that because all of the exciting stuff like stars galaxies planets all of that that's about 0.4% and the other 3.6 percent is just cold gas between the galaxies the remaining 23% is something called dark matter and this is a new form of matter that we have no idea again what it is hence the word dark as far as we know dark energy and dark matter are not related yet another reason not to let astronomers name anything it's very confusing but today we're going to talk about dark matter how could we possibly believe that everything we see is only about 4% of the matter of the energy of the universe now this actually goes back quite a ways and it's been annoying astronomers for quite some time other than this annoyed astronomers named Fritz Zwicky and Ricky in the 1930s began to study clusters of galaxies galaxies if they're close enough together can actually orbit around each other even collide together under the four of gravity despite the fact that the universe is expanding and it definitely is if galaxies are dense enough and close enough gravity can overcome the expansion of the universe and the wiki was studying clusters of galaxies all orbiting around each other what he found is that the speed of the galaxies was far too high these galaxies should just fly apart they shouldn't be clustering at all and when he did the measurement is a beautiful picture of a small cluster of galaxies from Hubble Space Telescope when he did the measurement he found that you needed about 80 to 90 percent more mass in these galaxies to account for them not flying apart he didn't know what this was he said well maybe it's some kind of missing mass some kind of dark matter that we don't know what it is yet in the 1960s Vera Rubin realized this problem was still true closer to home she was studying our own Milky Way galaxy and I mentioned that we all orbit the center of the Milky Way well the Sun is actually going so fast around the center of the Milky Way we should fly off into space instead there really is this mysterious unseen presence that binds the Galaxy together and both us and other spiral galaxies it's about the same there's about 80 to 90 percent more mass in them than we can account for by just adding up all the stars even estimating how much cold gas there would be between the stars so this is a pretty big problem at first we really didn't think there was anything necessarily very exotic about this dark matter we were just beginning to take pictures of distant galaxies maybe this missing material could be in a form of lots of cold gas between the stars cold gas even between the galaxies maybe it's lots of black holes black holes are collapsed dead stars the gravity is so intense it actually sucks in light no light coming from those could be lots of black holes out there there was actually a live a battle of the acronyms some people said that maybe all of this matter is contained in lots and lots of giant planets and they called them massive compact halo objects or macho's and there was a competing school that said well dunno maybe we're thinking about this all the wrong way maybe this dark matter is a type of new elementary particle we haven't found yet and they coined the term the weakly interacting massive particle or wimps so this was actually what we thought at first might be what the missing mass was made of the problem is over the last few decades we have made better and better telescopes and we now have been able to eliminate most of these things for example cold gas it turns out dark matter is not cold gas this is an all-sky image wrap this image all the way around you looking in all directions of the sky and the plant telescope can see extremely cold gas gas that is only a couple degrees above absolute zero any sort of normal cold gas between the stars and galaxies would show up on this survey and sure enough we found plenty of it that we'd never seen before but not enough to account for anywhere near the amount of matter needed for this missing mass problem it's not black holes you think that black holes would be very hard to observe because they don't give off any light of their own in fact what black holes do is that as matter falls into them the matter gets accelerated faster and faster around the black hole and black holes actually actually become little natural particle accelerators this is an x-ray map of the sky black holes heat gas up as it spirals into them before it falls in and they emit x-rays and we've done a wonderful survey now of the entire x-ray sky we have identified thousands of new black holes and we actually just by doing statistics think there are millions more we haven't discovered but once again all the black holes added up don't even help us by a fraction of a percent it's a tiny amount and unfortunately for the acronym people we now know it's not macho's it's not giant planets these are images from one of the deepest surveys of the sky we've done called the Sloan Digital Sky Survey with the Sloan survey we're actually filling in slowly the entire sky this is looking at the northern part of our galaxy and then the southern part of our galaxy we're not quite done with the whole sky yet but strip by strip we're finding thousands of these giant planets we call them brown dwarfs now we know of many of them we're doing census we understand exactly what the statistics are there is still nothing close to 90% of the mass so now we're left with this situation with all the lovely quote from Sir Carter Arthur Conan Doyle of Eeyore Sherlock Holmes once you eliminate the possible whatever remains no matter how improbable must be the truth we've eliminated all of the easy explanations - what all of this mass can be instead it must be something more exotic now this stuff is really dark not only does it not emit any light at any energy not radio waves not microwaves any sort of normal matter made of atoms would emit light in some way it doesn't reflect light it's very odd the the only thing that we can detect about dark matter is its gravity it holds galaxies clusters together it holds even single galaxies together and 100 years on the world's expert in gravity is still Albert Einstein Albert Einstein described gravity as a curvature of space and actually a curvature of time as well anything with mass curves space around it I actually am curving space a little bit around me something like the Sun does it a whole lot more and some of the better tests of Albert Einstein's theory involved the Sun to give you an idea this is a diagram where you actually see the Sun here in the middle here's earth not to scale luckily we'd be burned up but if you have a very sensitive telescope when you look at the edge of the Sun you actually see all of these stars kind of crowded up by the rim of the Sun and this was first observed during a solar eclipse when the sun's light was conveniently blocked out now we can observe it routinely it turns out that those stars crowded up by the rim of the Sun are actually physically behind the Sun their light should be blocked by the disk of the Sun between us and the star but the curvature due to gravity the Sun is creating a curvature of space which bends the light around it and we can see stars behind the Sun and what I assigned did is he could predict this angle absolutely perfectly if you know the angle that something is deflected you know the mass of the object that's creating that it works time and time again so here's what we're now doing this is a real picture from the Hubble Space Telescope it has not been modified and what you see here is a cluster of galaxies these are all galaxies orbiting around each other in the foreground and you'll notice there's kind of this weird blue it's actually a galaxy right here there's a similar one here is a similar one here and there are these strange streaked out arcs again this is a real picture from the Hubble not not changed what we now realize is that what we're seeing is a galaxy behind this cluster of galaxies and the light is being lens into multiple images and smeared out gravitational arcs we call them using this we're measuring the mass of the clusters of galaxies and finding out once again they contain about 90% more mass than we think they should here's a wonderful picture from Hubble you see all of these lenses all of these arcs caused by dark matter this is now how we find dark matter we look for these arcs and map dark matter using this so the plot thickens a little bit this is actually a cluster of galaxies that really is two groups of galaxies colliding together it's called the bullet cluster that's about a billion light years away and many many millions of light years across again pretty much everything you see in this frame our galaxy is except for a couple of foreground stars that got in the way now these two clusters of galaxies are flying through each other they're actually going to combine and make one big cluster and there's a lot of gas in between the galaxies that has gotten rammed together by the force of this collision when you look at the same frame in x-rays this is about the same scale actually this is from the Chandra x-ray Observatory all of this light you see here is million-degree gas gas between the galaxies that has been shocked and heated it actually bent into these beautiful shockwaves as these two galaxy clusters stick into one big galactic cluster but here's the problem this is a false color image and this is the same galaxy cluster we saw before in this case the kind of pink colored haze you see here is where we see that hot x-ray gas as the two galaxy clusters combined into one on either side where you see a blue coloring that's where we see the gravitational lensing that's where we don't see any matter but we see the evidence of gravity of dark matter and amazingly what seems to have happened is that as one galaxy came one galaxy cluster came this way and another came that way all of the galaxies and gas stuck smacked up against each other and the dark matter sailed right on through didn't interact with regular matter at all and so if you're ever feeling a little arrogant just to remind you the sort of your anti motivation poster what we now know is as far as dark matter goes you know congratulations most of the universe cannot be bothered to interact with you dark matter is seriously strange stuff now it's it's kind of fun to note that we actually have proof of dark matter from a very different type of astronomy this is back in the 1960s people named Penzias and Wilson had a microwave antenna that was looking at microwave sources of radiation in the sky and there was a problem with their antenna because everywhere they looked in the sky there was an underlying hiss there was noise in the background and no matter where they pointed the antenna it was exactly the same so of course you would figure that this sort of consistent noise means there's a problem with your telescope and the most likely explanation they thought was pigeons pigeon poo here's something for you to take home tonight trivia is a very good generator of microwaves and radio waves and so they trapped all the pigeons this is a pigeon trap but you can actually see in the Smithsonian Air and Space Museum they scooped out all the pigeon poo they turned their antenna back on and lo and behold that hiss was still there now it was very quiet very small in fact it correspondent to a temperature of microwaves of 2.7 degrees above absolute zero very very faint and and luckily somebody very quickly realized that this had been a specific prediction of the Big Bang Theory you see the Big Bang Theory said that once everything was much denser and hotter and in fact it was so hot and dense at one point about 13.7 billion years ago that the universe itself was opaque to light light was trapped in a soup of energy and matter and then there was a moment as the universe became less and less dense where light could actually freely fly and be released and the prediction of the Big Bang Theory is that this radiation today should be at 2.7 degrees we were detecting radiation from 13.7 billion light years away we now have mapped that radiation at first we thought it was entire smooth over the entire sky now we know there are small variations and these are two maps from our latest mission the colors the red and the blue show you areas where the microwaves are a little bit hotter and a little bit colder the difference between the hot and cold areas is less than one millionth of a degree this is a picture of the universe as it appeared 13.7 billion years ago when there was nothing but hydrogen almost all the same temperature and we realized that if we look very closely at these variations this is a sort of the whole thing kind of flattened out there's a pattern to the variations in this microwave background in fact we can actually see sound waves propagating through the entire universe we're modeling that now and the way sound waves propagate through something tells you something about its density sound travels faster through water than it does through air so using the microwave background we can actually track sound waves through the entire universe and find the density of the universe as a whole you know that old cliche about in space no one can hear you scream so 13.7 billion years ago the universe was dense enough they could have heard you scream and you would have been screaming because the temperature was about 4000 degrees so anyway um we by studying these sound waves going through the whole universe we realized something was damping them down quieting down these sound vibrations but whatever it was wasn't giving any contribution to the density of matter and when we did the math we found that whatever it was that was contributing that gravitational damping would be about ninety percent of the universe so another confirmation of dark matter when you run a computer simulation from the microwave background observations that we've taken if you run what Dark Matter might have done over 13.7 billion years with all of this mass attracting together you come up with this beautiful web-like structure this is an invisible scaffolding of our universe that makes up almost all the matter in the universe isn't it possible that this would affect the way regular matter would evolve over time in the universe and in fact sure enough this is a simulation of exactly that over time all of the hydrogen gas all the regular matter was attracted by the ground somebody of this dark-matter web underneath it things were brought together to form galaxies to form stars and planets over billions of years in this simulation we see galaxies drawing together from smaller galaxies forming bigger ones inside the galaxies stars forming none of that would have gotten started without that scaffolding of dark matter underneath that gravitational binding of the entire universe so is it possible the galaxies really look like this well yes in fact this is a professor of mine at Harvard he began to map yeah he began to map the distribution of the galaxies and he found that if he the Milky Way is here if you look out in distance galaxies seem to be forming voids and arcs and in fact now the farthest out we can see with the digital Sloan Sky Survey we can see that there is this beautiful web structure that the galaxies are forming and we don't know what's underneath except it has to be the dark matter it's now got us wondering really how much this has affected the history of the universe with our own galaxy cluster in the center looking out we see that all the galaxies are mapped on to this beautiful web so it seems like we need to find what this matter is we're hoping our friends at CERN at the Large Hadron Collider will get to energies that will actually create a Dark Matter particle until that happens it's still a mystery and this must have had a huge impact on the universe so when you think about how much matter is out there in a form that we can't see we're down to the question is the universe made of dark matter and the rest of us is doesn't matter so thank you very much and have a good night finding yourself you

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Keywords: english, technology, ted talk, ted x, united states, michelle thaller, education, Binghamton University, galaxy, ted, TEDxBinghamtonUniversity, nasa, tedx talk, history, tedx, ted talks, america, dark matter, tedx talks, science

Id: lYH_nFwMXRM

Length: 19min 46sec (1186 seconds)

Published: Thu Mar 07 2013