"Stephen Hawking's Universe" is made possible
by Alfred P. Sloan foundation to enhance public understanding
of the role of science and technology,
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the corporation for public broadcasting,
and viewers like you.
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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 certain 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.
To learn more about "Stephen Hawking's Universe,"
visit pbs online at the internet address
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