The further 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 artefact of a theory
which wouldn't exist in the real world.
But then observers began to find things in the sky
which were just as peculiar.
The journey which would lead to black holes,
started in the 1950s with the new science of radio astronomy.
Radio signals from space might have many explanations,
some more vivid than others.
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.
Well, after the second World War,
radio astronomy really got going and in the late fifties,
they started building, er, large radio telescopes like,
like the one we're sitting underneath here now.
Could this technology actually be used to send messages,
as it were, between the stars?
Nineteen fifty nine, nineteen sixty,
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.
But while they were looking for aliens,
it was sensible to consider other possibilities too.
Suddenly you're 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.
Using optical telescopes,
astronomers looked long and hard at the areas emitting radio signals.
What they saw was certainly unusual and dramatic events,
but nothing they couldn't already explain.
People saw that there were unusual objects,
for example, a galaxy that had a peculiar blob within it,
er, in some cases it 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, guiescent clouds of gas, did not.
But there were surprises in store.
When optical astronomers pointed their telescopes
at one particularly strong radio signal,
they expected to see some cosmological catastrophe.
What they did see astounded them.
In the early nineteen sixties optical astronomers took photographs
of certain positions in the sky
from which radio waves seemed to be coming and they,
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.
One such star, with the uninspiring name, 3C273,
was one of billions in an insignificant corner of the universe.
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.
Astronomers decided to analyse the light given off by 3C273,
using a technigue called spectroscopy.
By splitting the light from the star into a colour spectrum
they discover something about the star.
They see black lines in the spectrum missing light
caused by gases in the atmosphere
of the star absorbing light at particular freguencies.
And if these lines are shifted from their normal position
the star is moving - if the lines shift towards the red end
of the spectrum its moving away.
Thirty-four years earlier,
the American astronomer, Edward 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.
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.
3C273 looks like any other star in the sky
but it's spectrum seemed to contradict this idea.
Astronomers couldn't imagine what was going on,
but a young postgraduate student was convinced
that spectroscopy couldn't lie.
Martin Schmidt at Caltech noticed that two of the wiggles had the same spacing
between the colours as hydrogen does
but both of the lines were shifted way over towards redder parts
of the spectrum than normal hydrogen gas is,
and as he believed that that identification was correct,
then the conclusion was that the shift is a full sixteen percent.
Yet a shift of sixteen percent meant
that this object was moving away from us enormously,
er, 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 like stellar or guasi-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 top call these objects,
these radio-stars, guasi-stellar radio sources.
They were clearly radio sources,
they were discovered with radio telescopes,
and they looked star-like, and hence the,
the stellar aspect of the term,
so guasi stellar radio sources got contracted to guasars.
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,
has to put out a tremendous amount of energy per second.
Much, much more than our sun,
in fact one hundred to one thousand times
more than our entire milky way galaxy of stars.
And this was the real kicker.
When the mysterious guasars 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 guasars.
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,
er, and so they turned to the general relativists,
and asked them, well, do you have any models, objects,
that could look like this,
that could behave in, in this way at all?
Er, and the relativists said, well,
there is this issue of gravitational collapse,
and maybe this is what you're looking for.
Everyone agreed that Einstein's theory described gravity
as the dominant force of the universe.
But what was not so obvious was
what would happen under extreme conditions.
Could gravity ever compress vast guantities of matter,
such as when a star dies, into the tiniest of spaces?
In nineteen thirty nine two papers appeared,
and 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, er, a large amount of matter was concentrated in a small region.
Einstein's paper didn't foresee any problems.
But Oppenheimer and Snyder frightened themselves.
Their calculations seemed to point to something
which couldn't possibly exist.
Using the rules of general relativity they,
er, predicted that that a 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.
But if an object cut itself off from the universe,
could its behaviour still be described by the laws of physics?
Did Einstein's theory unwittingly predict its own collapse?
Einstein was convinced that you could never get to this critical radius,
that this critical radius was an impossibility in nature.
But his argument with Oppenheimer was never settled.
The second World War meant physicists like Oppenheimer were needed
to develop the atomic bomb.
Many felt Oppenheimer's ideas were so extreme,
they weren't worth fighting for anyway.
But a physicist called John Wheeler had no doubts.
Stick up for something,
and I think that's a wonderful way of saying
what science is all about.
Stick up for something.
I'm Daniel Holz and I'm a graduate student, University of Chicago,
and I'm going to see,
er, John Wheeler,
who is my undergraduate adviser here at Princeton.
John Wheeler, who still teaches at Princeton University,
worked with Oppenheimer on the atomic bomb.
Now eighty five,
he is one of the great figures of twentieth century science.
He loves to just sink his teeth into problems.
Part of his approach to physics is find the biggest,
most confusing thing you can,
and then go at it full steam and try to make sense of it.
In 1963, guasars were the most confusing thing around,
with the exception perhaps of Oppenheimer's theory
that might explain them.
So Wheeler wanted to embrace these extreme theoretical ideas
about gravitational collapse.
But to support them
would mean challenging the beliefs of Albert Einstein.
When Wheeler came to Princeton in the nineteen forties,
Einstein was one of its leading academics and world famous.
But science was already beginning to move on.
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,
er, clear English: This house will never become a place of pilgrimage
where the pilgrims come to look at the bones of the saint.
And so it is.
For all his genius it was not Einstein
who now inspired John Wheeler.
Wheeler was captivated by the idea
that guasars might be explained by Oppenheimer's theory
of gravitationally completely collapsed objects.
And he invented a vivid phrase to describe them.
After I'd used that phrase
'gravitationally completely collapsed objects' several times,
I realised that it was just too long-winded
and I switched to 'black hole'.
It was a name which perfectly describes
what should happen according to the theory.
The key feature of a black hole is that it's black.
That, that no light escapes from, from this region.
So what happens is you have this object
that's getting dense, say, a star that's collapsing,
and it gets, it gets more and more compressed and as it does that,
objects closer to the star have a harder and harder time getting away.
It, 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 ca-, can't escape and,
er, if we we're standing far away from this star,
the light cannot get from the surface of the star to us.
And it, at the point where that is reached, you have a black hole.
Our, er, Russian friends had a different word
and at French thought it sounded obscene,
but finally they were won around and they accepted it.
So a lot of people decided that the whole,
the whole idea of a black hole was patently ludicrous,
and that they couldn't exist,
and in fact Einstein was in,
was in this camp and did not see black holes as real physical objects.
The idea was, er, something in nature would,
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 into a black hole.
I believe that black holes should exist,
but many physicists thought that was taking general relativity too far.
But not Wheeler, he was impressed by the guasars.
If something so bizarre could find a place in the cosmos,
then the universe was strange enough for black holes to exist as well.
Wheeler, always being at the forefront,
saw that these black holes were a,
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.
Well 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?
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.
Deep in the Californian desert is a well-fortified concrete bunker.
Even today, no-one can enter without being scrutinised by armed guards.
These are the Lawrence Livermore laboratories.
Much of this classified technology now lies idle,
or wrapped up for storage.
I came here in nineteen fifty six.
We were one of two national laboratories charged with developing nuclear weapons
for the United States.
In order to handle the high-energy calculations needed
to develop nuclear weapons,
the Defense Department had built a powerful new tool: The computer.
The laboratory here at,
er, Livermore and Los Alamos laboratory,
had a virtual monopoly on, on computers,
and the computers were designed for us.
So, for a period of,
er, of twenty 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.
As a young government scientist,
Dick White used the computer's power to test the impact of a nuclear bomb.
But by the early 1960s, much of the work on the bomb was done.
Dick White and his colleagues aimed the computers at a new problem:
The black hole.
Many theorists still did not share John Wheeler's conviction
that black holes could be created out of collapsing stars.
They simply believed that the collapse couldn't go that far.
The theory that they put forward was that the core of the star,
the iron core, would collapse,
er, they believed that this collapse
would cause thermo-nuclear reactions that would blow up the star.
We set out believing in this model, sure enough it collapsed,
er, we had no doubt it was gonna do that,
but it didn't follow their script.
Er, what it did was to, er,
er, instead just continue on collapsing and never, never,
er, came to rest as the pressure built up.
The computers predicted a large dying star would continue collapsing
to form a black hole.
It seemed John Wheeler had been right to support Oppenheimer's ideas.
We had been led by the computer calculations to results
that we had not anticipated and, er,
that, that was,
er, an extraordinary time for me.
There was a lot of excitement about this result.
Er, the, er, people that work in general relativity were guite excited because,
er, 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 the, er,
plot of the velocity of the in-falling material in,
er, the, er, star that,
er, has collapsed and beginning to form a black hole.
At this point where the most rapidly,
er, in-falling material is,
the velocity is about ninety nine percent the velocity of light.
Computer calculations show 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?
Suddenly, er, we came to the state where we said,
well maybe we ought to look around for these things
and see if we can actually see them out there.
Working out how to see the invisible wasn't so easy.
But long before a way to look for black holes emerged,
vivid imaginations were feeding off scientific fact.
Toby got it now.
A black hole, it's pulling the star apart.
Coleen nodded,
a rare event, and we're just in time for it.
The hole swallows stars but first it likes to chew 'em up.
He could barely make himself look as the view swung
inwards towards eye-hurting brilliance.
The disc revolved about a white hot ball of sizzling,
with blistering energy.
Gregory Benford is a best selling science fiction writer.
His stories are all the more plausible because he's also a plasma physicist.
I slowly began to realise that there was at least a case now emerging,
that there might be a black hole at the centre of our own galaxy.
Not just a couple of,
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 gotta,
there's gotta be some great special effects,
er, on offer in a place like that.
What would it do?
What would it be like if you fell into one and, er,
er, what would it feel like to be stretched out as thin as a noodle
by the tidal force as you fall into one?
Er, how can you live near one?
How would you make a living?
Once science fiction had brought the threat of the black hole
to our doorstep,
its menace captured the imagination.
The black hole could grow to unbelievable proportions.
Once it starts swallowing matter, nothing can escape it.
Not even stars, or whole galaxies.
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 centre 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.
Black holes were an area in which science fact,
real scientific calculations,
was way ahead of science fiction; that only caught up later.
One guestion 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 encourage to work on general relativity,
by my supervisor, Dennis Sciama.
Roger and his father, Lionel Penrose,
wrote a paper which I,
I guess the artist Escher partly made famous later,
called lmpossible Objects,
where you can design an object on the piece of paper,
and Escher made such designs,
which can't be realised in the real world,
for instance, there's a picture when 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.
And Roger Penrose had the kind of mind that
would conceive relationships of that sort.
There was a debate going on at the time as to whether in the collapse
of the 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.
This point of infinite density was called a singularity.
Most scientists thought that somehow,
in the real world,
a singularity could never form.
But Penrose had no such hang-ups, and he showed in 1965
that, er, a star at,
in its end stages,
under natural conditions,
would end up in this self-contradictory state of infinite density.
The theorists' nightmares were true.
If they existed,
black holes destroyed twentieth-century physics at the singularity.
But this did not deter Dennis Sciama
from encouraging his students to look deeper into the singularity.
I was awarded my doctorate for showing that the guestions Penrose was raising
about black holes would apply egually well to the early universe.
Both the big bang and black holes would take singularities places
where space and time come to an end and the laws of physics break down.
The incredible power associated with black holes was making
it seem even more likely that they might be the key
to understanding the energetic guasars
If this was the case it was vital to prove that black holes existed.
But what were the telltale signs to look for.
In Russia, as in America,
the scientists who had worked on nuclear weapons were
now tackling the physics of black holes.
Yakov Zeldovich made it his task to find a way to detect them.
Zeldovich,
apparently, never forgot anything.
Everything went into understanding how to see a black hole,
and I'm sure that working on,
on the H-bomb,
actually helped him in astrophysics because after all,
most of astrophysics is forms of controlled H-bomb.
How would you see a black hole anyway?
You can't see it directly.
You, you know the lion by it's paw,
even better by it's paw print,
er, 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,
elect-, electromagnetic waves, X-rays
Zeldovitch suggested that by looking for bursts of Xrays astronomers
could find stars which appeared to orbiting nothing
evidence of a black hole
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 Kit 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 Kit 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,
er, against Kit Thorne,
on the grounds that if black holes do exist,
he has to pay Kit Thorne a relatively modest amount,
but if they don't exist and all his work on black holes is wasted,
at least he gets,
er, copies of a nice magazine.
A new generation of astronomers,
including Alex Filippenko were inspired to
look for stars which appeared to be trapped in orbit around a black hole.
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 found an object which had burst out into the X-ray world in 1988,
and we wanted to wait until it guieted 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,
for guite 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 we might find
to be oscillating back and forth.
So you have to wait for a while until this thing fades,
er, until the black hole stops stealing material
from the companion star.
So we waited.
Seven years after they first observed it,
the heat and light from the disk matter surrounding the object started to fade.
Filippenko and his colleagues got themselves ready.
We want to find as direct evidence as we can,
that a mass of compact objects, a dark star,
is pulling on a companion star.
So the way to do that is to measure the motion of the companion star
and so you can never directly take a photograph of a black hole,
it just appears black,
the best you can really do is measure it's influence on material around it.
We can then look for minute shifts in the colour
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.
With a telescope finally locked on the star,
Filippenko begins to analyse the light it emits.
There's the star we think is orbiting a black hole.
Let's get a spectrum of it.
As the star moves round some unseen object,
the light from the star shifts from the red end of the spectrum,
towards the blue end and back again.
From the speed of this shift Filippenko can calculate the size of the object.
Wow, what a beauty.
It's a black hole,
Here we are trying to prove that,
er, an extreme form of nature exists, a,
a form of nature predicted by Einstein's general theor-,
theory of relativity,
but which is not necessarily something that nature chooses to adopt, OK.
I mean, black holes, you know,
they're in science fiction and everything else so,
it's a, it's a wonderful topic, it's a wonderful concept.
The more evidence that builds up,
the more scientists are convinced that black holes do exist.
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 guite naturally under the black hole hypothesis,
and guite unnaturally using other hypotheses,
that leaves you with a,
sort of a,
er, an unfulfilled feeling.
You're, 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.
The evidence for black holes was now so good
that I no longer felt the need for insurance.
I have conceded my bet,
and Kit Thorne started to receive Penthouse magazine,
greatly to the disgust of his liberated wife.
Once it was clear that black holes had to exist,
astronomers began to work out what exactly their connection
might be with guasars, and the way the universe evolved.
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 centres of normal-looking galaxies.
So that with the passage of time the guasars centre 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 guasar glows only while it's swallowing material,
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 guickly,
in such a small space that no theorist have,
has dreamed up anything else other than a black hole that could be hidden inside
the central region of this galaxy.
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 what not.
Heats up.
There's so much of it,
whole stars are being ground down into,
er, gas and dust,
and they churn against each other,
they heat up, the entire disc becomes lit up.
It's brightest at the centre where the velocities are highest because you,
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, 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 guasars 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 guasars we see are all dead now.
They don't last a long time,
they're burning up their energy so guickly.
So we're looking millions and billions of years into the past,
and seeing galaxies burning their inheritance prolificantely,
er, so that they may send us this momentary signal,
and then they go,
they turn into cinders eventually, they go out.
Er, our, our centre of our galaxy was never in that league,
er, it, it was never a billion stellar masses,
it was maybe a million,
but, er, once it shone more brightly than it does now.
Er, it would have been dangerous to live right next to it then
We may now understand how black holes and guasars 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 black hole 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 Briscil,
that information is lost in black holes.
The loser will by the winner an encyclopaedia from which information
can easily be retrieved.
Scientists have learnt from the discovery of black holes
that it is unwise to resist unlikely ideas.
Seth Shostak of SETI sees implications of his own work.
In many ways the black hole story is somewhat analogous
to what we're doing because black holes,
in fact, were found on,
on blackboards actually before they were found in the sky.
That's not the normal way things work in astronomy.
Normally in astronomy,
you, you go to the telescope and 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,
er, We expect that the galaxy is rife with civilisations,
with technological civilisations,
that's what we expect,
that's our belief, and it's based on,
no, I think, reasonable assumption.
Now we're using the, the telescope,
the radio telescope in this case,
to go out and see well, is it actually there?
Can we actually here ET?
There is a crucial difference between the search for black holes
and the search for ET.
So far, in thirty six 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.
But the bizarre predictions of black hole physics do throw up
new possibilities for SETI.
We don't broadcast in SETI.
We don't send signals out.
The reason we don't do that is because the distances are, are guite large,
er, if, if say the nearest civilization is a hundred light years away,
you send a, an inguiry,
it takes a hundred years to get there.
If they deign to reply it takes another hundred years for their,
their answer to come back,
and that's two hundred years by that point.
You've lost interest and your funding's probably gone away too.
But their may not even be a problem with time.
When the laws of physics break down,
deep inside a black hole,
even more extraordinary possibilities exist.
Theorists talk seriously of time travel, and worm holes.
Kinds of tunnels in space and time through
Which we might escape our universe and arrive in another.
Mathematically, it's all possible.
Black hole physics gets down to the real nitty gritty in the edges of
what we know about physics,
and of course, that's why attracts the, 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 black holes themselves.
That might imply there's some practical way to take advantage of that.
And if you have truly advanced civilisations in the galaxy,
and you might, remember,
we're the new kids on the block,
right, 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.
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,
er, they do it with great caution because they've learned the lesson
that what is today's unthinkable is tomorrow's convention.
Black holes are a remarkable prediction of Einstein's theory
that seems to be born 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 will claim we have been visited
and that's what UFO's are.
But I think any such contacts would be much more obvious
and probably very nasty.