"hawking: the farther we probe into the universe, the more remarkable are the discoveries we make." "much of my work has been concerned with the mysteries of black holes." "many people dismiss black holes as just an artifact of the theory, which wouldn't exist in the real world." "but then observers began to find things in the sky which were just as peculiar." "narrator: in the end, scientists would find some very peculiar things -- impossibly bright objects blazing from the distant past, and forces of impenetrable darkness." "the first thing they found was signals, radio waves from space." "astronomers tuned in in search of aliens." "man: well, my name is seth shostak, and i'm a an astronomer at the seti institute here in lovely mountain view, california." "the acronym "seti" stands for search for extra-terrestrial intelligence." "now, that "i" on the end means we're not looking for extraterrestrial life, but we're looking for intelligent life." "that means they can hold up their side of the conversation, if you will." "after the second world war, radio astronomy really got going." "and in the late '50s, they started building large radio telescopes, like the one we're sitting underneath." "could this technology actually be used to send messages, as it were, between the stars?" "in 1959, 1960, the first experiments were made using this kind of technology -- a big radio telescope -- to try and eavesdrop on any civilizations that might be nearby." "narrator:" "no aliens found, granted, but there was no mistaking the signals." "shostak: suddenly, you were getting these clear radio views, so you knew that in that direction there's a very strong source of radio waves." "you would tell your friend the optical astronomer, and they would go use a big telescope, like the palomar 200-inch telescope, or something similar, and they would point it in that direction." "narrator: where the universe emitted a radio signal, optical astronomers now trained their gaze." "what they saw defied explanation." "but at first, its significance eluded them." "man: people saw that they were unusual objects." "for example, a galaxy that had a peculiar blob within it in some cases was found to emit radio waves." "whereas a normal-looking, boring-looking galaxy did not." "or, for example, a cloud of gas that had all sorts of little striations in it, and looked as though it might be exploding -- those were precisely the objects that seemed to emit radio waves." "whereas more normal, quiescent clouds of gas did not." "narrator: gradually, the strange evidence mounted." "when observers turned their telescopes on the source of particularly strong radio signals, they expected to see cosmological catastrophes." "instead, they were left with cosmic questions." "filippenko: in the early 1960s, optical astronomers took photographs of ctain positions in the sky from which radio waves seemed to be coming, and they just saw nothing unusual." "there was just the usual smattering of stars, and there was no obviously exploding star, no turbulent cloud of gas, nothing seemingly unusual -- just normal stars." "and this perplexed the astronomers." "narrator:" "take the case of 3c273, a star of no particular distinction." "it hardly seemed worth notice, that is, until observers began to look a little closer." "filippenko: 3c273 in the constellation virgo looked just like a star, yet we know that ordinary stars don't emit radio waves, and so this was highly, highly unusual." "narrator: using a technique called spectroscopy, astronomers studied the light emitted by 3c273." "when you take a spectrum of an ordinary star, that is when you pass the light through a prism and break it up into a rainbow, you can see small dips, small wiggles in the spectrum." "and those are the wiggles that are produced by atoms, by gases in the atmosphere of those stars that are absorbing some of the light." "and by identifying the pattern of these lines, these little wiggles that appear in a star, you can deduce whether the atmosphere of the star has hydrogen or helium and oxygen -- things like that." "but if that pattern is shifted toward redder colors, then you deduce not only that the star has hydrogen or other common elements, but also that the star is moving away from you." "hawking:" "34 years earlier, the american astronomer, edwin hubble, had used spectroscopy to discover that the universe is expanding." "distant galaxies are moving away from us." "the spectrum of 3c273 was about to tell us even more." "filippenko:" "the spectrum of 3c273 didn't fit any patterns of normal gases that have been observed in normal stars." "and so this really befuddled astronomers." "not only was the object emitting radio waves profusely, but it had this really strange spectrum that couldn't be matched with any known type of gas." "narrator: a star's spectrum is its signature, and this one was an aberration." "it was enough to leave many astronomers confounded." "but for one, 3c273 was a revelation." "he was convinced spectroscopy couldn't lie." "filippenko:" "martin schmidt at caltech." "noticed that two of the wiggles had the same spacing between the colors as hydrogen does, but both of the lines were shifted way over toward redder parts of the spectrum than normal hydrogen gas is." "and if he believed that that identification was correct, then the conclusion was that the shift is a full 16%." "yet a shift of 16% meant that this object was moving away from us enormously fast, and had to be" "one or two billion light years away." "so, no way could it be a normal star or even a peculiar magnetic star in our own galaxy." "it had to be some sort of a strange object that looks stellar or quasi-stellar simply because it's so, so far away, and yet it's enormously bright." "so this really caught people by surprise, and a few people, i think, had a hard time believing that anything so relatively bright could be so far away." "astronomers decided to call these objects, these radio-stars, quasi-stellar radio sources." "they were clearly radio sources -- they were discovered with radio telescopes -- and they looked star-like, and hence the stellar aspect of the term." "so "quasi-stellar radio sources" got contracted to "quasars."" "martin schmidt concluded that it must be, intrinsically, an extremely powerful source -- an exceedingly bright object intrinsically -- because to appear as bright as it does in the sky, yet be so far away," "it has to put out a tremendous amount of energy per second -- much, much more than our sun -- in fact, 100 to 1,000 times more than our entire milky way galaxy of stars." "and this was the real kicker." "hawking: when the mysterious quasars were discovered, i was just beginning my post-graduate research." "my work was to lead me to study things even more mysterious -- black holes." "i was dealing with einstein's general theory of relativity, and this seemed, to some physicists, a promising place to look for an explanation of the quasars." "astronomers and astrophysicists wanted an explanation for how these strange objects could behave in this extraordinary way -- how they could produce so much energy, and yet be so small." "and so they turned to the general relativists, and asked them," ""well, do you have any models for objects" ""that could look like this, that could behave in this way at all?"" "and the relativists said," ""well, there is this issue of gravitational collapse, and maybe this is what you're looking for."" "narrator: gravity is the dominant force in the universe." "this tenet of einstein's was irrefutable." "but there was no such consensus about what would happen under violent conditions, like the death of a large star." "einstein wondered, could its gravitational collapse crush its vast quantities of matter into the tiniest of points?" "dowker: in 1939, two papers appeared." "one was by einstein himself, and one was by the american physicist, robert oppenheimer, and his co-worker, snyder." "they discussed what would happen when a large amount of matter was concentrated in a small region." "narrator: einstein rejected the prospect of infinite collapse." "but oppenheimer and snyder's calculations made the conceptual leap." "dowker: using the rules of general relativity, they predicted that that massive object would undergo catastrophic gravitational collapse and would reach a critical radius at which it seemingly cuts itself off from the rest of the universe." "narrator: for many, the idea of a star descending into such an abyss was unthinkable -- all the more so when the view was shared by the greatest living scientist." "dowker: einstein was convinced that you could never get to this critical radius, that this critical radius was an impossibility in nature." "narrator: the controversy was short-lived for now." "with the second world war, oppenheimer's talents were needed elsewhere, developing the atomic bomb." "his earlier work languished, dismissed by peers as a radical departure from einstein." "but oppenheimer had convinced one colleague, john wheeler." "stick up for something." "and i think that's a wonderful way of saying what science is all about." "stick up for something." "man: i'm daniel holz, i'm a graduate student at the university of chicago, and i'm going to see john wheeler, who was my undergraduate adviser here at princeton." "narrator: for holz, these periodic visits with his mentor are a privilege." "at age 85, john wheeler is still a luminary of 20th century science." "holz: he's certainly one of the greatest physicists alive, and he's contributed in important ways in many different aspects of physics." "he's had fresh ideas that have pushed the very edges of our knowledge." "he loves to just sink his teeth into problems." "part of his approach in physics is, find the biggest, most confusing thing he can, and then go at it full steam and try to make sense of it." "narrator: wheeler was witness to a remarkable chapter in the annals of physics." "he worked with oppenheimer on the atomic bomb." "but before that, when wheeler arrived at princeton in the 1940s, einstein was the most eminent member of the faculty." "in 1963, the controversy about collapsing stars was rekindled by the discovery of quasars." "wheeler had a difficult choice between two convictions and two cherished colleagues." "though he differed with einstein, he recalls him fondly." "wheeler: he was kind enough to invite me to bring my graduate students around to his house one day for tea." "one of those students, joe callaway, said," ""professor einstein, when you're no longer living, what will happen to this house?"" "and einstein's face was a study -- deep wrinkles, a wonderful smile and laugh," "and his beautiful voice with a bit of a german accent, but in clear english " ""this house will never become a place of pilgrimage where the pilgrims come to look at the bones of the saint."" "[ laughter ] and so it is." "narrator: wheeler was never one to shy away from controversy." "to him, the notion of extreme gravitational collapse was the stuff of inspiration." "and at oppenheimer's bidding, he took up the cause." "in fact, the idea was predicted by the laws of general relativity." "but to einstein, in this case, there was just so far his own theory could go before it defied reality." "wheeler: he seemed to have a psychological block against considering collapse." "i don't know why." "narrator: the truth is, even earlier theorists had no such misgivings." "as early as the 18th century, the mathematician pierre laplace pondered the possibility." "oppenheimer went on to calculate the mathematics, but wheeler coined the name." "wheeler:" "after i'd used that phrase," ""gravitationally completely collapsed object,"" "several times, i realized that it was just too long-winded, and i switched to "black hole."" "narrator: the name stuck." "a black hole, by definition, is a place where gravity is so great, it engulfs everything around it." "holz: the key feature of a black hole is that it's black, that no light escapes from this region." "so what happens is you have this object that's getting dense, say, a star that's collapsing, and it gets more and more compressed." "as it does that, objects close to the star have a harder and harder time getting away." "in some sense, the gravitational pull is stronger and stronger." "if you keep on extrapolating that, the object gets more and more dense." "at some point, you reach the stage where even light can't escape, and if we we're standing far away from this star, the light cannot get from the surface of the star to us." "at the point where that is reached, you have a black hole." "wheeler: our russian friends had a different word, and the french thought it sounded obscene, but finally they were won around and they accepted it." "so a lot of people decided that the whole idea of a black hole was patently ludicrous, and that they couldn't exist." "in fact, einstein was in this camp and did not see black holes as real physical objects." "the idea was something in nature would prevent a black hole from forming -- as you tried to put all this mass in one place, some mysterious force would come out and always prevent you from actually getting that much mass" "that you would actually end up collapsing to a black hole." "hawking: i believed that black holes should exist, but many physicists thought that was taking general relativity too far." "narrator:" "wheeler had another agenda in embracing the unlikely premise of black holes." "quasars had become a nagging mystery." "could it be, he wondered, that one phenomenon could somehow explain the other?" "holz: wheeler, always being at the forefront, saw that these black holes were a windfall for explaining all sorts of astrophysical observations, and would become very important in our understanding of the world." "and so he was egging everyone, urging everyone on to join in exploring this vista that opened up this landscape of science." "what can we do with these black holes?" "what are the implications for them?" "how will this affect the way we look at our universe?" "hawking: many of us were beginning to think there might be large numbers of black holes in the universe." "but that depended on what happened in the giant explosions that occur at the end of the life of massive stars." "narrator: in the scrublands of central california is a facility where scientists produced some of the most important weapons of our time." "even today, it is a compound shrouded in secrecy." "the lawrence livermore national laboratory still buzzes with important scientific work." "but some of its technology, outdated now after the cold war, lies idle, awaiting the day it will be scrapped or carted away." "among its guarded prizes is a powerful tool the defense department helped create, the first supercomputer." "its purpose -- to help make the elaborate calculations needed for nuclear weapons." "dick white was one of the first scientists to use it." "white: i came here in 1956." "we were one of two national laboratories charged with developing nuclear weapons for the united states." "the laboratory here at livermore, and los alamos laboratory, had a virtual monopoly on computers." "the computers were designed for us." "so for a period of 20 years, the development of computers depended on the existence of these labs." "it opened up to us the possibility of calculating things that we could not even think of doing before." "narrator: at first, white needed the computer's power to test each new generation of the bomb." "but by the early '60s, the work was largely done, so white and his colleagues aimed their computer at a new problem, black holes." "many theorists still didn't believe in them." "they envisioned a very different outcome for a large star." "a massive supernova would blast it into oblivion." "white: the theory that they put forward was that the core of the star, the iron core, would collapse." "they believed that this collapse would cause thermonuclear reactions that would blow up the star." "we set out believing in this model." "sure enough it collapsed." "we had no doubt it was going to do that, but it didn't follow their script." "what it did was to instead, just continue on collapsing, and never came to rest as the pressure built up." "narrator: white confirmed that a large dying star would continue collapsing and end up as a black hole." "it seems wheeler and oppenheimer had been right." "white: we had been led by the computer calculations to results that we had not anticipated, and that was an extraordinary time for me." "there was a lot of excitement about this result." "the people that worked in general relativity were quite excited, because in a way, it said, well, the things that they had been talking about for years -- very supermassive condensed stars with big gravitational fields -- may indeed exist." "this is a plot of the velocity of the in-falling material in a star that has collapsed" "and beginning to form a black hole." "at this point, where the most rapidly in-falling material is, the velocity is about 99% the velocity of light." "hawking: computer calculations showed that at least some explosions of stars would form black holes." "but if nothing can get out of a black hole, how could we detect one?" "narrator: sighting the unseeable wasn't going to be easy." "except, that is, for a select breed of thinker, science fiction writers." "black holes were just too hot an idea to pass up." "man: toby got it now." ""the black hole?" "it's pulling the star apart?"" "colleen nodded." ""a rare event, and we're just in time for it." ""the hole swallows stars, but first it likes to chew them up."" "he could barely make himself look as the view swung inwards towards eye-hurting brilliance." "the disc revolved about a white-hot ball, sizzling with blistering energy." "narrator: gregory benford is a best-selling author." "his science fiction is remarkably convincing, because he also happens to be a physicist." "benford: i slowly began to realize that there was, at least, a case now emerging that there might be a black hole at the center of our own galaxy -- not just a couple of times the mass of the sun," "but a thousand times, or a million times, and that prospect thrilled me." "i thought, wow, there's got to be some great special effects on offer in a place like that." "what would it do?" "what would it be like if you fell into one, and what would it feel like to be stretched out as thin as a noodle by the tidal force as you fall into one?" "how can you live near one?" "how would you make a living?" "narrator:" "in science fiction, black holes became the ultimate cosmic monster." "they could weigh as much as a billion suns." "they could swallow matter whole, even stars, and once one starts moving in for the kill, there's no stopping it." "benford: it becomes compact, massive, and therefore able to, if it were to encounter something else, able to eat some more matter." "it becomes the eater of all things, because nothing survives it." "if this happens, as is most probable, at the center of the galaxy where the stars are more concentrated, there's more dust and gas, then that's where you would probably first make black holes," "and then that's where the feeding trough is." "they start to eat the surroundings." "hawking:" "black holes were an area in which science fact, real scientific calculations, was way ahead of science fiction." "that only caught up later." "one question many science fiction writers speculated on was, what would happen inside a black hole?" "computer calculations couldn't be trusted for this, because they would become inaccurate in the extreme conditions." "but the answer was supplied by a mathematician called roger penrose, who, like me, had been encouraged to work on general relativity by my supervisor, dennis sciama." "roger and his father, lionel penrose, wrote a paper, which i guess the artist esher partly made famous later, called "impossible objects,"" "where you can design an object on a piece of paper -- and esher made such designs -- which can't be realized in the real world." "for instance, there's a picture where the steps go round in a circuit, but they're always going down as you keep going round." "you then end up where you began, and yet you've been going down all the way." "and you can draw something which suggests that." "but in fact, you couldn't construct it in the real world." "roger penrose had the kind of mind that would conceive relationships of that sort." "narrator:" "penrose grasped concepts no computer ever could." "but his imagination also took him to a conclusion other scientists were desperately trying to avoid." "oppenheimer's idea of gravitational collapse was strange enough." "now penrose was claiming the awesome power unleashed in that collapse would break the known laws of physics." "sciama: there was a debate going on at the time as to whether, in the collapse of a star in it's late stages, it would achieve infinite density in the central region." "if the theory says it reaches infinite densities, then in a certain sense the theory has broken down and there would be a contradiction." "the theory would not be self-consistent." "if our best theory of gravitation is not even self-consistent, then we have a crisis in physics." "the theory of relativity contains in itself the seeds of its own decay." "narrator:" "it's called a singularity... a point of infinite density." "most scientists thought it utterly impossible." "sciama: but penrose had no such hangups, and he showed in 1965 that a star in its end stages under natural conditions would end up in this self-contradictory state of infinite density." "so the whole space-time has gone pathological." "narrator: it was a physicist's nightmare." "in a black hole, matter could actually exit the known universe." "time and space drew to a close, and physics as we know it became meaningless." "still, dennis sciama encouraged his students to delve deeper." "sciama: stephen said to me, in a certain sense, the universe is like a big star -- of course, the universe is expanding -- if in your mind you reverse the sense of time," "then the universe is collapsing." "it's a bit like a collapsing star, a very large star." "should i work on that?" "hawking:" "i was awarded my doctorate for showing that the questions penrose was raising about black holes would apply equally well to the early universe." "both the big bang and black holes would contain singularities, places where space and time come to an end, and the laws of physics break down." "narrator:" "singularities, it seems, are cauldrons of staggering energy." "in black holes, they can consume everything in their path." "with the big bang, a singularity willed the whole universe into being." "and what else, scientists wondered, could be behind the force unleashed in quasars?" "sciama: they were actually applying einstein's theory, not just to mathematical or mathematically dominated situations on paper," "but to actual objects in the sky that were exploding." "in fact, a quasar is the most violent explosion we know of other than the big bang itself." "narrator: in russia, as in america, scientists who had worked on nuclear weapons were now tackling the unlikely physics of singularities." "but first they had to prove these black holes, immense yet hidden, really existed." "one set out to find the invisible, yakov zeldovich." "benford: zeldovich, apparently, never forgot anything." "everything went into understanding how to see a black hole." "i'm sure that working on the h-bomb actually helped him in astrophysics, because after all, most of astrophysics is forms of controlled h-bombs." "how would you see a black hole anyway?" "you can't see it directly." "you know the lion by its paw, or even better by its paw print." "that's less dangerous than actually approaching a lion." "so he said, suppose you've got two stars going around like this, and one of them is a black hole, say this little one right here." "this black hole has a powerful gravitational influence, and it can actually suck the gas off the surface of this other star." "first it gets torn apart by tidal forces as it tries to orbit the black hole." "then these shred it, smears it around, and the parts bump into each other -- they begin to grind upon each other." "the density is fairly high, and they heat up." "they heat up, they give off emission -- electromagnetic waves, x-rays, visible, infrared -- and from that we can see this disc of hot material." "that's one way to see a black hole indirectly." "the most gaudy way is if you've got a black hole that is really spending its energy account." "meanwhile, magnetic fields have been dragged into this giant salvage dump, perhaps, at the center of a galaxy." "these magnetic fields tend to get ordered, and they go like this." "they come out of the accretion disc and peel away outside." "this set of straight field lines, perpendicular to the disc, means that material, if it gets really hot, can take off along these field lines, and head on out all the way -- perhaps with enough energy to blow off the field lines," "and to take off and leave the galaxy, in which case you have a bright stream of well-ordered material, like water out of a fire hose, spewing out into intergalactic space, and radiating, because it's still hot." "it's got lots of energy." "that we call a galactic jet." "and if you see two of them, then it's clear evidence that there is a kind of an interesting symmetry at the center of a galaxy." "you get two discs -- sorry, you get one disc, and you get two jets." "and those -- a double pair of jets is, of course, the most beautiful thing to find." "hawking: observational evidence was beginning to come, but was still very uncertain." "i didn't want to see all my work on black holes go to waste." "so i made a bet with kip thorne, who had been a student of john wheeler." "one suspects that it was more an insurance policy by steve, rather than what he really believed." "because he bet with kip thorne -- claiming that black holes did not exist in nature, even though they existed in theory, and he bet one year of penthouse against four years of private eye against kip thorne" "on the grounds that if black holes do exist, he has to pay kip thorne a relatively modest amount, but if they don't exist, and all his work on black holes is wasted, at least he gets copies of a nice magazine." "narrator: while hawking was hedging his bets, the evidence for black holes was starting to mount." "galactic jets had been sighted." "but this still wasn't proof." "there was no guarantee the emissions came from black holes." "so a new generation of astronomers tried a different tact." "they began to look for stars that might be trapped in orbit around a black hole." "for alex filippenko, the search was on." "filippenko: you choose the ones that are the most likely candidates." "and those, by the hypothesis of zeldovich and others, were the x-ray-emitting stars." "so we find an object which had burst out into the x-ray world in 1988." "we wanted to wait until it quieted down at x-ray energies, because, along with the x-ray outburst, you get an outburst of optical light, radio light, everything." "and so what happens is, for quite a while, the matter which is being dumped into the black hole glows so much at all wavelengths that it completely dominates the light from the star, which you might find to be oscillating back and forth." "so you have to wait for a while until this thing fades, until the black hole stops stealing material from the companion star." "so we waited." "[ alarms buzz and ring ] narrator:" "they waited a long time." "after seven years, the object they believed to be a black hole began to quiet down, leaving the companion star circling it in stark relief." "filippenko and his team were ready." "filippenko: we want to find as direct evidence as we can that a massive compact object, a dark star, is pulling on a companion star." "so the way to do that is to measure the motion of the companion star." "since you can never directly take a photograph of a black hole, it just appears black, the best you can really do is measure its influence on material around it." "we can then look for minute shifts in the color of the light coming from this star, and if these shifts are found, and they go back and forth periodically, then that's an indication that something is tugging on the star," "because stars on their own don't just go around, going back and forth, or going around in circles in the sky." "by newton's laws, there has to be something tugging on them in order to induce that motion." "narrator: with his telescope finally witness to the companion star, filippenko can analyze its light." "okay, there's the star we think is orbiting a black hole." "let's get a spectrum of it." "narrator: as it orbits, its spectrum shifts." "by the amount of that shift, filippenko can measure the speed of the star, and the gravitational effect the object it's circling is exerting." "the bigger the pull, the bigger the object." "wow, what a beauty." "it's a black hole, at least five times the mass of the sun." "here we are, trying to prove that an extreme form of nature exists, a form of nature predicted by einstein's general theory of relativity, but which is not necessarily something that nature chooses to adopt." "black holes -- they're in science fiction and everything else, so it's a wonderful topic, it's a wonderful concept." "narrator:" "as the evidence builds, scientists have become convinced black holes do exist." "filippenko: clever theorists can come up with many explanations for individual objects." "but when you find a whole collection of objects, all of which collectively show the same phenomenon, that can be explained quite naturally under the black hole hypothesis and quite unnaturally using other hypotheses where you conjure up special conditions" "for each of these different objects, that leaves you with an unfulfilled feeling." "you're thinking up a new theory for every object, and it just doesn't sit well, you know, it doesn't seem right, it doesn't feel right." "yet, when you have a whole class of objects which are behaving the same way, and are well explained with one simple theory, that gives you some confidence that what we're really seeing is a black hole." "hawking:" "the evidence for black holes was now so good that i no longer felt the need for insurance." "i conceded my bet, and kip thorne started to receive penthouse magazine, greatly to the disgust of his liberated wife." "narrator: in the passing of one mystery comes the answer to another." "could black holes power the brightest beacons in space?" "filippenko: quasars appear to be denizens of the early universe, they just don't exist nowadays." "yet, if they are powered by material falling into a black hole long ago, back when the universe was young, then it seems reasonable that their remains exist here today in the centers of normal-looking galaxies." "so that with the passage of time, the quasar's center gradually used up all the gas and other material in its vicinity." "it stopped eating this material, and hence it faded with time, because the quasar glows only while it's swallowing material." "so a natural conclusion was that nearby normal-looking galaxies might have very massive centers, which do not appear active anymore simply because there's no material for them to swallow." "astronomers have found evidence of stars moving around very rapidly in the central region of what appears to be a completely boring and inactive galaxy " "where material seems to be going around so quickly in such a small space that no theorist has dreamed up anything else other than a black hole that could be hidden inside the central region of this galaxy." "so black holes appear to form in the centers of galaxies." "and in particular, large galaxies appear to preferentially harbor black holes at their centers." "benford: the disc revolved about a white-hot ball, sizzling with blistering energy." ""why is everything so hot?"" ""friction -- all that stuff" ""orbiting tighter and tighter around the hole " ""it rubs up against other stuff," ""gas, dust, and whatnot -- heats up."" "there's so much of it." "whole stars are being ground down into gas and dust, and they churn against each other, they heat up, the entire disc becomes lit up." "it's brightest at the center where the velocities are highest, because the velocity gets higher and higher and higher the closer you get to the black hole." "this big shining disc, not a compact disc, a cosmic disc, is visible at immense distances, because it shines particularly out in the directions perpendicular to the disc of the galaxy across the whole universe." "that's what we believe quasars are." "the discs and their surrounding environment, which also gets heated up by all this radiation shining out toward us from the far past, because the quasars we see are all dead now." "they don't last a long time." "they're burning up their energy so quickly." "so we're looking millions and billions of years into the past, and seeing galaxies burning their inheritance prolificately," "so that they may send us this momentary signal." "and then they turn into cinders eventually, they go out." "our center of our galaxy was never in that league." "it was never a billion stellar masses, it was maybe a million, but once it shone more brightly than it does now." "it would have been dangerous to live right next to, then." "hawking: we may now understand how black holes and quasars are related, but there is plenty of mystery left." "strange as it may sound, i have found that things can get out of black holes." "on a microscopic scale, there is always a bit of uncertainty in the speed of a particle." "this means that particles can travel faster than light and can escape from a black hole." "other people call this hawking radiation, but i don't feel i can use the term." "many physicists believe that this radiation will be completely determined by what fell into the black hole, but i think the radiation will be random and will not carry any information about what fell in." "i therefore have another bet with kip thorne on it, but this time he and i are on the same side." "we bet against another physicist, john friscil, that information is lost in black holes." "the loser will buy the winner an encyclopedia from which information can easily be retrieved." "narrator:" "the confirmation of black holes has taught scientists it's unwise to resist unlikely ideas." "seth shostak of seti sees implications for his own work." "shostak: in many ways, the black hole story is somewhat analogous to what we're doing, because black holes, in fact, were found on blackboards, actually, before they were found in the sky." "that's not the normal way things work in astronomy." "normally, in astronomy, you go to the telescope, you find something you hadn't expected, and then you try and explain it." "but black holes, they were found by theoreticians years before anybody had any hope of finding them with a telescope." "well, here we have the same thing in seti." "we expect that the galaxy is rife with civilizations, with technological civilizations." "that's what we expect, that's our belief, and it's based on, i think, reasonable assumption." "now we're using the telescope, the radio telescope in this case, to go out and see, well, is it actually there?" "can we actually hear e.t.?" "narrator: but there's one crucial difference between the discovery of black holes and the search for e.t." "shostak: so far, in 36 years of listening, we have not heard a single, confirmed peep from the cosmos." "i mean, that's a fact, that's the bottom line." "narrator: still, seti enthusiasts are patient." "the question is, will their cosmic counterparts be, as well?" "shostak: we don't broadcast in seti." "we don't send signals out." "the reason we don't do that is because the distances are quite large." "if the nearest civilization is 100 light years away, you send an inquiry, it takes 100 years to get there." "if they deign to reply, it takes another 100 years for their answer to come back, that's 200 years by that point." "you've lost interest, and your funding has probably gone away, too." "narrator: while we await some faint murmur from far away, our imaginations are carrying us to the very brink of the universe." "today, theorists talk seriously of time travel and what they call "worm holes,"" "elusive tunnels in space and time, through which we could escape our universe and slip into another." "mathematically, it's all possible." "shostak:" "black hole physics gets down to the real nitty gritty, the edges of what we know about physics." "and of course, that's why it attracts the top theoreticians, because it's a chance to make that breakthrough." "you're going to unknown territory." "there are suggestions that this speed limit on communication and transport, the speed of light, you can't go faster than the speed of light, and you can't send information faster than the speed of light." "but the physics of black holes suggest, although it's still uncertain, that there may be other ways to send information using the physics of black holes, or using black holes themselves." "that might imply there's some practical way to take advantage of that." "and if you have truly advanced civilizations in the galaxy, and you might, remember, we're the new kids on the block, the earth has been here four or five billion years, but the galaxy has been here at least twice that long," "so there may be some civilizations that are very, very much more advanced than we are." "they may be taking advantage of that, and it may be that we're sitting around with our radio receivers hoping to get signals, and all the really interesting traffic is being communicated in a way that we're not yet aware of." "but it also has led to predictions that are so strange as to be held in -- well, they're obviously suspect." "i mean, the idea of time travel, the idea that you can somehow drop into a worm hole and come out in possibly even another universe -- that is such a bizarre idea, and yet it's this," "these probings on the frontier that sometimes present you with a completely new way of looking at things that make the biggest progress." "so, of course, everybody will pay lip service to the fact that yes, these bizarre predictions coming out of black hole research -- yes, well i'm not sure i believe in time travel, or being able to drop into a black hole" "and go to another universe -- that doesn't sound right to me." "but they do it with great caution, because they've learned the lesson that what is today's unthinkable is tomorrow's convention." "hawking: black holes are a remarkable prediction of einstein's theory that seems to be borne out by our observations." "but the theory may allow even more extraordinary possibilities, like rapid intergalactic transit or time travel." "if it does, why haven't we been visited by aliens or tourists from the future?" "of course, some people would claim we have been visited, and that's what ufos are." "but i think any such contacts would be much more obvious and probably very nasty."