"stephen hawking:" "personally, i am sure that the universe began with a hot big bang, but will it go on forever?" "and if not, how will it end?" "i am much less certain about that." "the expansion of the universe spreads everything out, but gravity tries to pull it all back together again." "our destiny depends on which force will win." "and the influence of gravity in turn depends on what the universe is made of, and just how much of it there is." "it won't be easy to find out if, as we suspect, most of it is dark matter, stuff we can't even see." "narrator:" "in our age-old attempts to give the universe definition, we've often grappled with phenomena we could not see." "priya natarajan is an astrophysicist studying something that may be beyond our imagination." "but working with the unseen may be easier for her than many, for she once aspired to be a poet." "natarajan: there is this impression that everything the scientists do is very circumscribed, whereas it is not, because we are bringing the ways in which we perform a model, the ways ... the ingredients that we put in." "and the ways in which we choose to mix the ingredients has a lot to do with our individual creativity and our feelings and our sense and intuition of how things ought to be." "so it's almost like writing poetry, where you pick a particular poetic form." "for instance, you could pick the sonnet or you could pick the japanese haiku, which, each of these forms has a set of rules, so you operate within a set of rules, which is very much like the laws of physics" "that you operate within in a model." "but, then, inside the form or inside the model, there's a lot of freedom, there's a lot of choices you can make." "narrator:" "natarajan grew up in india." "her life changed when she was awarded a scholarship to cambridge university in britain." "here she's taken on a quest, as spiritual as it is scientific." "she ponders the ultimate destiny of the universe." "natarajan: we see the stars that shine in the galaxy, and we also have evidence that there is some gas in the galaxy, because we can see the light that's scattered off the gas." "but as it turns out, galaxies contain a lot more than just that." "narrator:" "natarajan owes her inspiration to a maverick astronomer named vera rubin, who, in the late 1960s, dared question a basic premise of astronomy." "natarajan: what vera rubin did in her work was map the speeds of stars at different distances from the center of a huge spiral galaxy." "narrator:" "vera rubin noticed something which defied accepted wisdom." "stars spinning around the center of galaxies were supposed to behave like the planets that orbit the sun." "they don't." "natarajan:" "with our solar system, you have the sun in the center and you have sort of the planets orbiting around." "and since the dominant gravity is that of the sun, the planets that are the outer planets, they move much slower than the planets on the inside." "so naturally what people expected to find was similarly in a galaxy, if you measure the speed of the stars away from the center towards the edge, you expect it to fall off." "and what vera rubin found, instead, when she actually measured that for a spiral galaxy, was that the speed stayed the same." "as she sort of mapped the speed of the stars from the inside out, all the way out to the edge, they stayed the same." "narrator: rubin was the first to pose a question that has baffled scientists ever since." "if all the stars in a galaxy move at the same speed, regardless of their distance from the center, then the center couldn't be the only source of gravity affecting them." "something else would have to be exerting a powerful force, something we simply can't see." "what she found was that in order to explain the speeds that she observed, she needed to have a lot more stuff in the galaxy than we see, and since the stuff is not visible and it's not emitting any light," "she coined the term "dark matter"" "to refer to that." "narrator: rubin had every reason to believe her discovery would be met with great excitement." "it was, though not the kind she might have expected." "natarajan: her announcement that there was dark matter associated with every individual galaxy was received with much skepticism, because of the far-reaching implications it had, and because, also, of the inferred percentage of dark matter." "from her work, she inferred that almost 90% of the mass in a spiral galaxy had to be dark." "narrator:" "rubin's findings suggested that the destiny of galaxies is governed by a vast and inscrutable network." "every galaxy is enveloped in dark matter, invisibly locking all the stars in its embrace with the gravity it exerts." "the black emptiness of space, it seems, isn't that empty after all." "99% of the universe could well be made up of dark matter, a sprawling, cosmic web." "for cosmologists like myself, it's crucial to know precisely how much dark matter there is in order to know what will become of the universe eventually." "natarajan: the total mass of our universe is what decides the fate of our universe, whether we continue expanding, or whether we stop and decelerate, or we turn around back on ourselves." "so the ultimate fate of what really happens to us depends on how well we have made an inventory of the mass in the universe." "and therefore, if such a large fraction is indeed dark, that has very important consequences." "hawking: few people now doubt that vera rubin was right." "dark matter determines the future of the universe." "to know our ultimate fate, we need to be sure that dark matter exists, and how much of it there is." "searching for the invisible is not for the faint-hearted." "when chris stubbs first told his colleagues he wanted to look for dark matter, they told him he was out of his mind." "that wasn't the way to a safe job." "there's an infinite amount of science to do, and i think the trick is to choose carefully what you spend your time doing." "and my taste, for a long time, has run towards fundamental problems that may be very difficult to address experimentally, but which have a very large impact on our understanding of the universe." "narrator: chris stubbs has made a career of shooting in the dark." "he's part of an international team of 18 scientists and 3 institutions, all with one improbable goal." "stubbs: we're carrying out an experiment to look for a particular kind of dark matter, which we call "machos," which is a shorthand that stands for "massive compact halo objects."" "the idea is that our galaxy has a big halo of dark matter around it that's made out of astronomical objects that, for one reason or another, don't shine like the stars that we see." "narrator: stubbs believes these strange vestiges of stars, their compressed corpses, litter the universe." "machos range from the size of the earth to 10 times that of the sun." "if they are the secret phantoms that govern the motion of stars, they would be most numerous on the fringes of galaxies." "hawking: it was the right place to search, but finding them would be like looking for a black bat on a dark night." "the one thing that he knew was that his subjects were fairly heavy." "and if they were heavy, they would have a gravitational effect on light passing nearby." "the macho-hunter turned to einstein's general theory of relativity to tell him how gravity affects light." "narrator: stubbs set out to find stealth stars in the dark reaches of space." "by shedding a little einsteinian light on them." "according to relativity, space and time can be thought of as one." "an object marks its place in the fabric of space-time with a dent, a pocket into which other objects that pass within its sphere must fall." "this is how gravity works, and nothing is immune to its power, not even light." "we're used to the idea that light travels in straight lines, and when space-time itself is curved, light still tries to travel in a straight line, but it can't, because space-time itself actually has shape and dents and warps in it." "so just like matter, light which is traveling in a space-time where there's some large massive object will actually be attracted to the object, and its path will be bent towards it." "this effect of the bending of light is what is used by astronomers in their search for machos in the halo of our galaxy." "stubbs: einstein's general theory of relativity tells us that light passing close to an object, like the sun or a lump of dark matter, is deflected ... it gets bent." "and the effect that a mass has on the light coming from a distant star or galaxy is just like putting a lens in front of the star." "it distorts the image, and it makes it appear brighter." "narrator:" "if a macho passes between us and a distant group of stars, they would brighten, then fade back to normal, a telltale sign of the macho's presence." "stubbs used the stars as a million cosmic spotlights, hoping one might flare, magnified by the chance sweep of a stray macho." "it was a painstaking hunt for a faint glimmer from something that may not even exist." "this is just before peak brightness." "it still stands out from the rest of the stars." "stubbs: our experiment has made more measurements of the brightness of individual stars than the entire cumulative history of astronomy combined, and we then sift through all of these records in order to find the one time in a million" "when a star gets brighter as a result of a macho traveling close to the line of sight between us and the star." "narrator:" "hours of patient observation, months of marshaling data ... a lot was riding on little more than a good guess." "stubbs: two years after we started the experiment, we were looking through the data, trying to understand how to analyze it, and much to our surprise found exactly what we thought we were looking for, in that we saw a star get brighter" "and then fainter again with exactly the signature that's predicted by general relativity." "okay, this looks like it definitely fits pretty well." "it's easy to draw a nice curve." "stubbs:" "our experiment has detected a previously unknown component of this galaxy." "it's a stunning result." "narrator:" "chris stubbs clinched it." "dark matter is no fantasy." "it's actually out there." "but a mystery lingers." "to power the fast rotation of stars vera rubin had detected would take a lot of dark matter." "it seems there are just not enough machos to account for that kind of colossal gravitational pull." "stubbs:" "the simplest point of view is that the machos are ordinary matter made up of the same material that exists in stars." "it just didn't happen to end up in stars." "and we think we know exactly how much ... we think we know how much ordinary matter there is in the universe, and it just isn't enough to solve the dark matter problem of the universe." "we need to find something else to account for more of the dark matter." "machos were big, so why not try something tiny?" "one candidate was a well-known particle, the neutrino." "this is produced in atomic bomb explosions, so it would also have been produced in the big bang explosion." "if it had a tiny mass of its own, it could be the dark matter, or it could be one of the so-called exotic particles whose existence was predicted by theory, but which were very hard to detect in reality." "perhaps they are actually out there, silently shaping the evolution of the universe." "narrator:" "professor carlos frenk believes small things can have a powerful influence, in the case of neutrinos and in the case of his son david." "frenk: i think there is a great parallel between the evolution of the largest system that we know of, which is the universe, and the evolution of the biological system, like a person or like my son." "i often wonder what are the factors that are going to influence the development of my son, whether he will be a physicist or a scientist, whether he will be a musician, or whether he will be anything else." "i don't quite understand what are the forces that are going to drive him in one direction or the other." "the universe, however, is simpler, because we have a much greater mastery over the laws that govern the evolution of the universe." "narrator: frenk is determined to reconstruct the way the young universe evolved into the universe we know today." "the most crucial piece of the puzzle is the most elusive ... the role played by dark matter." "david's science class relies on models." "it is the lot of the probing mind to require the concrete to envision concepts beyond our grasp." "so it is, for david's father." "frenk experiments with computerized representations of a universe largely unseen, from its elemental birth to the rich complexity we know today." "but his model will only work if he programs in the precise characteristics for dark matter." "he starts each recreation just a second after the big bang." "frenk: prior to that time, the universe was made up of a cosmic soup of elementary particles and radiation." "nothing else could exist in the midst of this tremendous heat." "but then, after about 100 seconds, the universe had cooled down a little bit to a mere 10 billion degrees, but this temperature is now low enough that the first thermonuclear fusion reactions can take place." "narrator:" "at that critical instant, according to frenk's scenario, a mysterious group of particles broke free from the pack." "long before the appearance of stars and galaxies, they swarmed into great clusters of dark matter." "these vast aggregates exerted a powerful gravitational pull on the remaining ordinary matter." "as the dark empire grew in tandem with the expanding universe, it reined in more and more ordinary matter, ultimately giving rise to the stars." "eventually, one billion years after the big bang, congregations of stars drew together to from the earliest galaxies." "frenk's tale was an epic one." "he had its framework by the early 1980s, but it was missing one crucial ingredient." "what was the dark matter?" "the idea that was around at the time was that the dark matter could consist of small elementary particles called neutrinos." "narrator: could this minute shrapnel from the big bang work as the dark matter in his model?" "frenk: that was a very trendy, fashionable idea, if you like, in those days, and it was the first concrete proposal we had for what the dark matter could be, and this was very significant." "and some people would say ..." "a very significant idea, and so people would say it signalled the beginning of a revolution in the way in which we study the universe, because for the first time, the neutrino hypothesis provided a concrete starting point" "that we could explore in an unambiguous fashion using the tools of evolutionary cosmology." "narrator: neutrinos stream through the universe at virtually the speed of light." "every second, about 100 trillion shoot straight through your body." "these tiny particles suffuse the universe, they are everywhere, yet they will slip through any barrier, so they're almost impossible to nab." "for particle physicists, no catch is more challenging." "their goal is to find out if neutrinos have mass." "without mass, they wouldn't have a gravitational effect, and they wouldn't be a candidate for dark matter." "in northern france, yves declais is leading an ambitious effort to reel in neutrinos." "declais:" "when you prepare your bait, when you have prepared your detector, when you have prepared your trap, you have to install it at the right place, and so you have to go where you think you will be able to detect neutrino," "where you will be right to get out some fish out from the river." "and after that, you have not only to wait, but you have to work, and you will see what will be the result." "you will see how many neutrino, how many fish you will get out from the river." "narrator: the best place to cast a line is already known." "neutrinos are produced where there's radioactive decay." "both are governed by the physics of nuclear reactions." "fred reines worked on the atomic bomb, then became the first neutrino hunter." "declais: he thought it was possible to see the flash of light produced by the introduction of a neutrino into some water detector, when you have the explosion of the bomb, and in order to detect this flash" "with respect to the natural background around." "but it was quite difficult to install such an experiment near an atomic bomb." "narrator: eventually, reines shifted his experiments to a safer source of neutrinos, a nuclear power plant." "in 1956, he became the first to trap a neutrino." "the achievement won him the nobel prize." "but reines wasn't able to learn if the neutrino had any mass." "that challenge now falls to yves declais." "like reines, he will stalk his tiny quarry in the bowels of a colossal furnace." "beside a nuclear power station is an underground bunker, shielded by the earth from the interference of cosmic rays." "declais: you have to be in the right place, very strong neutrino source in order to be able to see some interaction of these neutrino." "and you have, also, to protect your detector against the background." "and when you detect low-energy neutrinos, the main background comes from the sky, comes from cosmic rays, so you have to install your detector as deep as possible underground." "in this experiment we want to see if the nature of the neutrino change between the source of the neutrino and the detector one kilometer away." "and if the nature of the neutrino change during this path of one kilometer, we can demonstrate, we can prove that this is related to the existence of a mass for the neutrino." "it is a little bit complicated to compute, but it is a very, very simple system." "narrator:" "neutrinos, by definition, must have mass if they undergo a subtle distinguishable transformation." "declais and his team have already conducted a neutrino census nearby the reactor." "now they want to take a comparative tally here, two-thirds of a mile away." "you can see yours ..." "no, passed too quickly." "two events very far apart." "narrator: they want to see if there are fewer of the kind of neutrinos they clocked closer to the reactor." "the rest, then, would have undergone the telltale transformation by the time they traveled this distance, proving the particles have mass." "it may take years, but yves is persistent." "declais:" "this is really important for particle physics and also for cosmology and astrophysics." "one of the best candidates for the dark matter, for the missing matter in the universe, is the neutrino, if the neutrino has a mass." "even if the mass of the neutrino can be very tiny ... very, very, very small ... because the universe is completely filled by a lot of neutrino coming from the early universe, from the first three seconds of the universe." "narrator:" "meanwhile, carlos frenk wasn't waiting for word." "he kept hammering away at his digital reenactment of creation." "his approach was to assume neutrinos have mass, and see what kind of universe would result." "frenk: so we programmed our computer to follow the evolution of the universe in which the dark matter was made up of massive neutrinos, and that the aim was to produce in the computer a synthetic universe that we could then compare with the real thing." "so we programmed our computer up in this fashion, and let it churn away over christmas, and when we came back, we saw the first maps being generated by the computer." "here we have a recognizable universe, a credible universe, something that's made galaxies, something that's made galaxy clusters, something that is competitive vis-a-vis the real universe." "there was a great sense of elation, and the thought that we might have solved what was already, clearly then, and sadly still is today, the main unsolved problem in cosmology." "it was one of those feelings you have once in a lifetime, when you think you've really stumbled upon something major." "now, that was our first impression." "narrator:" "the impression was fleeting." "frenk was so elated to have concocted his own digital universe, at first he didn't notice a fatal flaw." "on closer inspection, his model for creation didn't quite look like the real thing." "and that was very depressing." "we thought for a while, for a few weeks, perhaps, that we really had found the key to the universe, and that key evaporated, and it was a terribly disappointing period." "narrator: in failure, there can be lessons." "in perseverance there can be results." "frenk wasn't about to give up." "frenk: it is paradoxical that we can understand the universe better than we can understand a tiny little part." "my son is an insignificant little speck in this gigantic universe, and yet i can understand the universe better than i can understand my son." "and so often i regard myself as being very lucky that i am a physicist, rather than a biologist or a psychologist." "they have a much tougher time than we do, because we deal with systems that are intrinsically simple." "biologists and psychologists deal with this much more complex, and in some ways magical world of humans, who are essentially unpredictable." "narrator: particle physicists urged a startling alternative, to replace the neutrino with an entirely hypothetical component." "frenk dubbed it "cold dark matter."" "his long struggle with neutrinos hadn't worked, but he had learned much in the process." "now, maybe, practice would make his model perfect." "frenk: our next step, then, was to change our starting assumption, and now take the dark matter to be composed of cold dark matter." "[ plays schumann's "melody" ]" "[ plays wrong notes ] frenk: i must say, we were very skeptical when we started this new project." "by then we had got slightly fed up with particle physicists trying to tell us astronomers what our universe was made of." "particle physicists are supposed to be working on something else, and they have no right to come and tell us astronomers what our universe is made of." "so our approach at first was really, frankly, cynical ... we started off saying, right, let's go and put these particle physicists right." "we ruled out neutrinos." "now let's go rule out cold dark matter as well, and get those guys off our backs so they can go and do their own thing with accelerators and we can keep on trying to understand how galaxies form." "[ playing schumann's "melody" ]" "frenk:" "what happened was that, these cold dark matter universes turned out to be far richer and far more interesting than we ever had any right to expect." "narrator: frenk's new model works at last, but there's a catch." "it relies on an invented particle, a symbol tapped out on a keyboard." "does cold dark matter exist?" "the burden of proof is on the experimentalists who now have to go and detect these particles." "and until that happens, then we cannot be by any means certain that this is a correct theory." "but if they do succeed, this really will be an outstanding achievement, and i think it's not an exaggeration to say that if the dark matter turns out to be an exotic elementary particle, this really will go down in history" "as one of the greatest scientific discoveries ever." "hawking: the evidence suggests that most of the universe is made up of something no one has ever seen." "by its very nature, cold dark matter has to be hard to detect." "finding a way to do so is one of the most difficult tasks in physics today." "narrator: now, in search of a particle that can't be seen, one that has only pure conjecture to vouch for its existence, a team of scientists has come to the mining country of northern england." "leading them is neil spooner." "spooner:" "it's fairly astounding that at the end of the 20th century, we actually don't know what most of the universe is made of ... not 90%, maybe even 99% ... and that it sort of" "puts one in, as a human being ... into some perspective that we ... the earth is not the center of the solar system, et cetera, and maybe we're not even the only life now." "and we're not even made of particularly common matter, in that we're not the typical matter that's around, because most of it's dark matter, which we don't know what it is." "narrator:" "spooner's first challenge was finding a way to glimpse the particles he was after." "as with neutrinos, the search for cold dark matter must be conducted underground, beyond the reach of cosmic rays." "his team is going to great lengths to find dark matter, and great depths." "spooner: it just happens that my father is a mining engineer by profession." "so i just asked him what was the deepest mine in britain, naively thinking it would be a coal mine, which would be useless for us because it would be quite difficult to work in the coal mine," "because of the safety aspect of it." "but it turned out that he looked it up, and it was boulby, which is a salt mine, which is ideal for us." "narrator: boulby mine is not only the deepest in britain, but in all europe." "the elevator bores into the ground for five long minutes, plummeting a mile below the surface." "at this depth, the air is 18 degrees hotter than at the surface, and choked with dust." "building delicate instruments that can stand up to these corrosive conditions was a daunting prospect." "spooner:" "it's a technological fight, trying to work deep underground in the salt mine, which is an environment which," "well, we're dealing with fairly intricate electronics, and we're trying to be clean." "and trying to do that in a mine is sort of very, very difficult." "narrator: deep in the earth, it's hard to tell the locals, working their picks and shovels, from the particle physicists mining for matter." "spooner: they all say, "have you found it yet?"" "we usually say, "not yet, but we're working on it."" "narrator: even though dark matter may occupy 99% of the universe, the particles spooner and his team are after are elusive." "they aren't known as "weakly interacting massive particles,"" "or "wimps," for nothing." "they meekly shun contact with anything else." "spooner:" "these particles are neutral." "they're not charged." "their interaction is like a sort of a billiard-ball effect if they interact, which mainly they don't." "but when they do, they just will strike an atom which will recoil." "so what we're looking for is these little recoils of atoms." "i'm talking about very small distances ... thousandths of a millimeter or so." "and as this atom recoils, it gives off some energy, in our case, light." "and you try and detect this light." "narrator: that glint would be so faint and evanescent that even slight radiation from surrounding rocks might mask it." "so the detector is further insulated within 200 tons of distilled water." "spooner: we're over a kilometer underground, so we've got rid of the cosmic rays, and then we're in the water, so we can screen off the stuff coming from the walls, and then we've got our detector in the middle," "sitting there waiting for a wimp." "our detector was a simple crystal, which gives off little bursts of light when struck by the particle." "we have to really amplify this light, because it's very low level." "seems to be okay." "spooner: we use this device called a photomultiplier to convert light into electrons." "these are then multiplied, and you get ..." "for every one that comes in, you get about a million coming out." "and that provides a nice, big signal, which you can then measure and record." "in the last year or two, we have made fairly significant progress." "we've improved our detectors such that we're now about 50 times more sensitive than anyone else was previously." "but we still need to get probably another 100 times better." "if we do that, then we should see them or we should not see them." "if we see them, then obviously that's very exciting, and maybe we've discovered what dark matter is, or what most of the dark matter is." "if we don't see them, that's also pretty exciting, because it's got to be something, and if it's not wimps, maybe it's not machos, and maybe neutrinos don't have mass." "we don't know, but it's got to be something." "so that would deepen the mystery." "frenk: if and when the dark matter ... or i should say, when the dark matter is discovered, because it's not a question that dark matter is there to be discovered and it will be discovered." "i can say that with complete certainty ... well, as complete as a scientist can ever do." "but when the dark matter is discovered, i think the whole jigsaw of our universe will fall into place." "we will understand not only why our universe looks the way it does, we will understand why there are galaxies, how they came to be, why there are planets, why there are stars, but we would also understand" "what the ultimate fate of our universe will be." "there are two possibilities." "if there's only a fairly small amount of dark matter, the universe will continue to expand forever, getting colder and colder, and more and more empty." "on the other hand, if there's a lot of dark matter, gravity will slow down the expansion of the universe and stop it eventually." "then the universe will begin to contract, and will end up in a big crunch, like the big bang in reverse." "from what we know now, it could go either way." "if i placed a bet, i think i know which fate i'd back." "but how would i collect after the big crunch?" "whichever way the universe eventually goes, its evolution is being affected by dark matter right now." "before we have even discovered what it's made of, some astronomers have begun mapping its effects." "woman: the challenge of mapping the universe is that you have to do it in three dimensions." "and human beings are very good at making two-dimensional maps." "it's the challenge of getting that third dimension and putting it in your head, being able to close your eyes and see in 3-d what's around you." "it's a challenge, but it's fun." "so i think we'll lay things out with the equator down here." "faber: when we first started this mapping business, it was very, very primitive, and people knew that there were clusters over there and a few over there and so on." "it was a little bit like stanley going to darkest africa." "he knew where the congo river was, and the nile maybe, but not much about anything else." "looks like it's over there." "narrator: exploring a dark continent of her own, sandra faber has spent years charting unknown terrain." "her mapping techniques have revolutionized the way we look at the universe and contemplate its future." "faber: what we're going to see here is three slices of the universe." "and earth is down here in this diagram, right here at the point." "and now we see the first slice being displayed like this." "each little black dot is a galaxy." "this was taken from the southern hemisphere, and now we see finally the third slice is coming up here." "what's interesting about these maps is that the galaxies are not uniformly distributed in space." "instead, what we see is that they tend to pile up along these walls." "some people have called them soap bubbles." "and then the insides of these spaces are called voids." "they're relatively empty of galaxies." "and, of course, this whole structure is expanding as the universe expands." "now, the question is, of course, why do the galaxies trace this beautiful large-scale structure?" "narrator: sandra's hunch was that this structure was created by the unseen influence of dark matter." "she set out to prove it with the most advanced telescopes in the world." "observing is almost mystical." "it's the act that really puts me in contact with the rest of the universe." "sitting there and accepting these photons, i imagine projecting myself back along that same path, and in some way, i know this sounds ridiculous, being in communication and communion with where they came from." "i often think if somebody's looking back at me, i wonder if their telescope is bigger than mine." "narrator: even through the most powerful instruments, galaxies millions and billions of light-years away appear as tiny specks." "yet faber's work demands the most exacting measurements, even of these far-flung galaxies." "so sensitive are the telescope's detectors that before each run they must be cooled with liquid nitrogen." "at over 300 degrees below zero, their very atoms are stilled." "faber: having checked everything out, we then walk into the control room off the dome." "gone are the days of standing in the cold." "we don't do that anymore." "we aim the telescope and we sit there and we wait, we expose." "ah!" "so this is our next observation." "what was this galaxy?" "this was ngc-5813." "5813, okay." "narrator:" "sandra and her colleagues developed their mapping technique to fathom the role dark matter plays in the architecture of the universe." "this looks different from our previous spectrum." "narrator:" "that dark matter governs the motion of individual stars, there's no question." "at stake is how it guides the paths of entire galaxies as they drift through space." "bit by bit, the data is falling together into an awesome portent of our galaxy's fate." "faber: suddenly it came to us that if we plotted all of these motions of galaxies, that an enormous region of space, including us, was moving roughly in parallel, like a big river of galaxies," "at the break-neck speed of 600 kilometers per second, and that was a definitely new thought for us." "that really struck us very strongly." "we said, what have we discovered?" "this is truly remarkable." "then we began to look at our survey in more detail, and we saw that, in fact, off in the distance there, towards which this great river was flowing, was a very large structure, which one of us later named" ""the great attractor,"" "and it turned out to be a very, very big supercluster, a super-supercluster of galaxies, and our motion towards that is due to its gravity." "it's pulling all of us in." "and at something like 50 to 100 billion years from now, our galaxy will be one of several thousand on an orbit in the great supercluster called the great attractor." "narrator: a staggering force, emanating from a huge concentration of matter, known and unknown, is relentlessly reeling us in across intergalactic space." "the fate of the universe is shaped by a vast sprawl of dark matter, by a cosmic specter drawing the galaxies together into clusters and superclusters, turning great patches of sky into empty voids." "faber: the way the dark matter clusters will affect exactly how galaxies form and how superclusters, voids, walls, and so on form." "dark matter is key." "it is controlling the motion of everything else." "it's making the galaxies form." "it's making the large-scale structure form." "it's in charge." "narrator:" "we can still only guess what dark matter holds in store for us." "and it seems not all great minds guess alike." "faber: well, currently, it looks as though there's not enough matter in the universe, quite, to retard the expansion." "if we had to bet right now, we'd probably bet that the universe will expand forever." "it's a fascinating idea." "if the universe expands forever, what will happen to it as it cools off?" "stars are gradually consuming all the gas in galaxies." "over time, it will all be used up." "those stars will burn and use up their fuel and die, become cold, dead remnants, white dwarves, maybe some black holes in there." "galaxies are ever merging to make yet larger structures, but will become ever dimmer as the stars in them die out." "and ultimately, even the very stuff of which stars are made ... the protons, neutrons, and so on ... will decay." "and it may be that the ultimate state of the universe is to have no matter at all ..." "a sea of elementary particles," "dead photons, and nothing else." "hawking: and the alternative of a big crunch is not much better." "a few years ago, when i was giving a lecture, i was asked not to mention the end of the universe, in case it depressed the stock market." "but i can reassure worried investors, either way, the universe is good for many billions of years more." "the end may be coming, but not just yet."