TEDxSF - Dr. Alex Filippenko - Dark Energy and the Runaway Universe

Aleksei Filippenko is an American astrophysicist and professor of astronomy at the University of California Berkeley his research focuses on supernovae and active galaxies at optical ultraviolet and near-infrared wavelengths Filippenko developin runs the Katzman automatic imaging telescope which conducts the Lick Observatory supernova search he was a member of both teams that discovered the accelerating expansion of the universe propelled by mysterious dark energy and is frequently featured on History Channel's the universe programs Filippenko received a Bachelor of Arts in physics from the University of California Santa Barbara and a PhD in astronomy from the California Institute of Technology please welcome dr. Alex Filippenko to be here this afternoon my talk will be on 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 what is the size of the universe is it infinite or does it wrap around itself somehow what is the age of the universe we now know the universe is 13.7 billion years old very old but not infinitely old what will be the fate of the universe will it continue to expand forever or will it someday reverse its motion and come crashing bang back in on itself how will the universe end and we're also interested in the basic building blocks of the universe the galaxies gigantic collections of hundreds of billions of stars gravitationally bound together stretching across tens or even hundreds of thousands of light-years we live in one such galaxy the Milky Way which would look much like this one if we could see it from the outside there are galaxies throughout the universe here's one of my favorite photographs from the Hubble Space Telescope part of what's called the Hubble Ultra Deep Field now this is a tiny but representative part of the sky imagine a grain of sand or a small pebble held at arm's length imagine how small that looks that's the fraction of the sky represented by this photograph yet you can see there are thousands of galaxies there most of those little blobs are other galaxies not stars in our own galaxy extrapolated over the whole sky we estimate that there's something like 100 billion galaxies and that's just in the parts of the universe that we can see we now think the universe extends far far beyond those parts we can see and everywhere it's filled with galaxies how did they form how do they evolve with time these two are among the central questions of cosmology so it's a really fascinating field now among the general public present company excluded there's considerable 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 do sound similar but cosmology and cosmetology differ by an ET cosmetology has an extra ET like the extra-terrestrial but to give you an example of this confusion here's a copy of an ad that a colleague placed in my mailbox some time ago make cosmology your career training and supervision and hairstyling blow-drying permanent waves combing and frosting scalp cuts where to go style style cuts basic cuts fur through there information and interviews call that number now classes started last March but I'm sure there will there will be such classes in the upcoming quarter or semester so if you want to do as I and many of my colleagues have done and get to the cutting edge of this field you should take a course like this yeah well I'm sorry these guys need a course not only on their own subject but a course on spelling and proofreading because in addition to foo they're here you see hair flying up there anyway a central figure in this field was Edwin Hubble who in the late 1920s looked at other galaxies and found that moving away from us and at a given time right now the more distant galaxies are moving away from us faster than the nearby galaxies so here we are the Milky Way galaxy and all the other galaxies are moving away with the more distant ones moving faster than the nearby ones the universe is expanding and we're not at the center it's not that other galaxies don't like us and that we smell or something or maybe these other galaxies or lactose-intolerant you know Milky Way galaxy lactose-intolerant no we think that this is a property of a uniformly expanding universe let me give you an example here's a one-dimensional universe made out of a rubber tube that's space and ping-pong balls those are the galaxies they don't expand galaxies are gravitationally held together so that they don't expand as the universe expands you can see that from the perspective of say the orange ping-pong ball all the others move away so it thinks it's at the center but the same can be said for any other ping-pong ball each one sees the others moving away and indeed the more distant ping-pong balls from any given ping-pong ball move faster than the nearby ones because every bit of space expands and the greater the amount of space there was to begin with the greater is the total expansion and this works for a finite universe or one that's infinite so in fact we live in a uniformly expanding universe with no unique center now with today's great telescopes we've measured the current rate of expansion of the universe it's just some value and you might think that's all there is to know but in fact there isn't there there is something more to know and that is the change in the rate of expansion with time after all the universe has galaxies with mass and these galaxies pull on other galaxies so they should slow down they should retard the rate of expansion just as when I toss this Apple up the mutual gravitational attraction between the Apple and the earth slows it down indeed if it slows it down enough it'll stop and then come crashing back down so if the universe is sufficiently dense then the expansion rate will slow down so much that someday the universe will stop expanding and then Rika laps in on itself ending in a very dense hot state the opposite of the Big Bang we call it the Big Crunch or the NAB Gib that's big bang backwards right Big Bang can now give however it could be that the universe is not sufficiently dense to ever halt the expansion it could be that there's not enough matter per unit volume to slow down the expansion to a complete halt in that case the universe would keep on expanding forever that's analogous to heaving this Apple so fast that it escapes from the earth that never comes back now gravity keeps on pulling on it keeps on slowing it down but never brings it to a stop and never brings it back in on itself that would be an eternally expanding universe one that becomes ever colder darker and more dilute we would like to know the fate of the universe what will it do in the future and we can figure it out by examining the past history for example if the universe has been slowing down quickly with time then it will someday stop reverse its motion and come crashing back down however if we examine the past history and find that the universe has been slowing down very little then in fact it'll expand forever it's like a universe expanding faster than the escape velocity it's kind of like an apple thrown at greater than the escape velocity from Earth so if you were to examine the past history you could in principle predict the future now how do you examine the history of the expansion rate well you can look to great distances galaxies that are a billion light years away or four billion light years away or nine billion light years away are seen not as they are right now but as they were 1 billion 4 billion 9 billion years ago it takes time for light to travel from one place to another you see the Sun as it was a little over eight minutes ago not as it is right now even the typical bright stars you see you see as they were some tens or hundreds of years ago light doesn't travel instantaneously fast so if we look at galaxies that are very distant we are effectively looking back in time we're looking at a movie of the history of the universe and encoded in the light from those galaxies is information about the expansion rate of the universe as it was long ago well how do we determine distances of galaxies how do we know that this galaxy is safe for a billion light-years away if we can find a star in it whose power whose luminosity whose earth we know and look at how bright it appears to be we can determine the distance of that star okay this is just the same way that you determine the distance of an oncoming car at night you look at how bright the headlights appear to be and you've calibrated the true power of the headlights of a car of known distance but normally ordinary stars can't be seen in galaxies you need a special star a supernova an exploding star only a small minority of stars explode at the end of their lives our Sun won't but those that do become millions or even billions of times the power of our Sun and can be seen at vast distances here you can see a star a single star exploding in that galaxy becoming the equivalent of 1 billion suns again if our Sun were to do this and it won't then sunblock of 50 just wouldn't cut it it wouldn't protect you you'd need sunblock or supernova block of about a billion well the point is is that we have by now found and studied explosions of this sort in galaxies of known distance some galaxies are sufficiently nearby that we can see relatively ordinary stars look at how bright they appear compare them with how luminous they really are figure out their distance and hence the distance of the galaxies in which they're located if we find some exploding stars in galaxies of known distance and measure how bright they get that's like calibrating the power of the headlight of the nearby car that's your comparison okay and then you can go and look at very distant galaxies search for supernovae within them look at how bright they appear to be thus calculate their distance and thus know how far back in time you are looking so roughly fifteen years ago two teams formed to find very distant supernovae and measured their distances I actually was at one time a member of both teams but my primary affiliation with was with this one the high redshift supernovae search team and the upshot of both teams which announced their results in 1998 was that these distant exploding stars that were found were very very faint incredibly faint now you might say well yeah but they're in these very distant looking faint small galaxies you expect the supernovae to be faint that's true but these were fainter than they had any right to be suppose the universe for just one second old and I tossed this Apple in one second the Apple reaches some distance from my hand but it's been slowing down because of Earth's gravity if Earth's gravity were weaker than in one second that Apple would travel farther because it wouldn't slow down as much if earth weren't present at all and there were no other forces the Apple wouldn't slow down at all and in one second it would get to an even greater distance well what we found was that the Apple the supernova the galaxies in which they're located are at a greater distance than they could have reached had they not been slowing down at all in other words it almost looks as though those galaxies have been accelerating away from us if you attached a rocket to the Apple and you go like that then it can get to a greater distance in a given time than it could reach at a constant speed so instead of measuring an anticipated deceleration a slowing down we seem to have measured an acceleration of the universe a speeding up with time in the past four or five billion years in the headline that came out was astronomers see a cosmic anti-gravity force at work we use this term anti-gravity hesitantly because people asked us can we attach the stuff whatever it is to our cars and levitate over San Francisco traffic jams no we cannot I'm sorry anyway that was February 1998 by the end of the year the editors of Science magazine proclaimed this to be the single most important discovery in all areas of science that year because it seemed to be so fundamental and the caricature of Einstein looks surprised here not because he's blowing universes out of his pipe you may not have known but that's where universes come from from the pipes of theoretical physicists but rather he's surprised because the single universe is expanding faster and faster with time he's doubly surprised because he has a sheaf of papers here on which there's an equation lambda equals 8 pi G Newton's constant times the density of the vacuum they might say the density of the vacuum why did they invite this guy from berserk Li to give a TEDx talk you know you were taught on your mother's knee that the vacuum is zilch zero nothing how can it have a nonzero density well first of all I'm just the messenger Einstein came up with idea and the reason he came up with idea way back in 1917 is that at that time people thought that the universe is static neither collapsing nor expanding yet to counteract the force of gravity between two galaxies you would need some sort of a repulsive effect acting in the opposite direction with exactly the same magnitude the same amount just as gravity is pulling down in this Apple if my hand is pulling up on it with an equal force it remains stationary if one or the other dominates then the Apple moves well Einstein didn't like this it seemed like a fudge factor an arbitrary fudge factor and there was no experimental evidence in laboratories for this weird repulsive effect this cosmological constant and it implied a nonzero repulsive energy of the vacuum so you never like this 12 years later Edwin Hubble discovered that the universe isn't static after all it's expanding so the whole physical and philosophical motivation for the cosmological constant vanished Einstein renounced it supposedly as the biggest blunder of his career so here he is sad that he ever introduced the cosmos constant what have we done we've resurrected the idea not to give a static universe but one which on the largest scales over billions of light years is expanding faster and faster with time so here in this room the down-arrow dominates in our solar system the down-arrow dominates in our Milky Way galaxy the down-arrow dominates but over hundreds of millions or billions of light years the up-arrow begins to dominate and it accelerates the expansion of the universe instead of his biggest blunder it could have been his greatest triumph and he might be quite surprised if he were alive right now so what is this stuff what is the weird stuff that's accelerating the universe it's certainly not the visible stars and galaxies they all exert an attractive force there's also dark matter in the universe okay it also exists exerts an interactive effect we just don't know exactly what it is but it's pervasive in the universe this has to be something new we call it dark energy perhaps regrettably because if there's one equation people on the street know it's e equals MC squared so I'm repeatedly asked is dark energy the same thing as dark matter no dark matter pulls dark energy whatever it is pushes and this stuff over the whole volume of the universe is the dominant stuff of the universe almost 3/4 of the matter energy content of the universe is this dark energy and we don't know what it is most of the rest is dark matter and we don't know what that is either we're made of atoms we're made out of the 4% that's normal and the point four percent that's easily visible we're the debris of the universe the afterthought of creation that's not to say you're not important you are to yourselves and your loved ones but you are not made of the dominant stuff of the universe and we don't know exactly what that dominant stuff is it could be all sorts of weird quantum fluctuations or something but there are hundreds of ideas and theoretical physicists are now working on them it's a cottage industry trying to figure out what the dark energy is some say it's the most important unsolved problem in all of physics well you might say maybe the data are on maybe the interpretation is wrong if it's we're only based on supernovae I would agree but now 12 years later there's a lot of other evidence that either the universe is filled with dark energy of a repulsive sort or Einstein's general theory of relativity is wrong on the largest scales also a very exciting conclusion part of the evidence comes from a baby picture of the universe a picture of the universe when it was only 380,000 years old analyzing all these little fluctuations in density and temperature also suggests that there's a new component to the universe also those fluctuations grow with time under the influence of gravity forming galaxies and clusters of galaxies and superclusters of galaxies and the voids in between them as seen in this computer simulation what you get when you include dark matter and dark energy is better agreement with the observed distribution of galaxies and clusters of galaxies in the universe than if you were to ignore the presence of dark energy so there's a lot of evidence now pointing to this dark energy we think it's real or relativity is wrong so what will be the future of the universe well if the dark energy remains dominant and repulsive the universe will expand forever faster and faster and faster with time a runaway universe but of course since we don't know what the dark energy is maybe it's sign will change in the future and it might become gravitationally attractive nevertheless Robert Frost apparently knew of the two possibilities an eternally expanding universe ending up cold and dark like ice or a collapsing universe one ending up dense and fiery and hot like fire he wrote the poem 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 it had to perish twice I think I know enough of hate to say that for Destruction ice is also great and would suffice so Frost would prefer the rikka lapsing you but if you had to perish twice than one eternally expanding ending an ice would be okay and that's perhaps appropriate given his name Robert Frost well to conclude let me give you a call to action we can use astronomy and cosmology as a hook to get kids interested in technology most of them won't become astronomers that's probably a good thing but they'll go off into applied fields in engineering in computer science but the hook is astronomy and cosmology so spread the word about this wonderful stuff moreover there's an amazing puzzle waiting to be answered what is the nature of the dark energy as I said some people think it's the number one problem in physics today and it may provide a clue to the ultimate goal of theoretical physics a unified quantum theory of gravity thank you very much

Channel: TEDx Talks

Views: 42,037

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Keywords: ted, ted talk, Filippenko, tedx, Alex, ted talks, tedx talk, tedx talks, ted x

Id: -gAtPyEu0G4

Length: 21min 23sec (1283 seconds)

Published: Mon Dec 13 2010