Original subtitles

All Texas. What?

All Texas. All Texas, yes, I know.

Might care to look at that, Peter.

What is it? Oh...

"The essence of a man like me lies just in

"what he thinks and how he thinks,

"not in what he does or suffers."

The time had come for the rank amateur

to try to grasp the way Einstein thought.

Yes, said Nigel Calder, the writer,

my journey was really necessary.

There's the observatory now.

What, those two little white whatever they are?

That's right.

Well, the third one I can see now.

Yes, they're the domes.

They, keep a look out for aircraft

so as not to zap us with their laser beam.

Are you serious? Quite serious.

They wanted me to speak Einstein's words and

make the odd space flight, but mostly just to attend to

the theory of relativity.

I was promised a tale of how our perceptions of space

and time and color are distorted

according to where we are and how we're traveling.

Amid such relativity, Einstein found

reliable laws governing atoms, planets, stars

and all creation.

Yes, an escort. Perhaps to make quite sure I didn't

Funk the cerebral adventure they had in store for me.

Very nice flying. Thank you very much indeed.Thanks.

On my arrival, I knew only that Albert Einstein was

a gentle genius whose reasoning anticipated

our world of nuclear energy and space flight.

The Big Bang. The black hole.

Things I'd only heard about.

My tutors were to be leading experts,

assembled in this remote corner of Texas, for my benefit,

and of yours.

Our guides through Einstein's Universe.

Dennis Sciama, here, is a theorist

concerned with the overall nature of the universe.

Roger Penrose, he pioneered the modern theory

of black holes. You've heard of them.

Yes, yes, I have,

without understanding what they are.

Well John Wheeler, here, said they had to exist

and named them black holes as a matter of fact.

He's very much a grand old man of theoretical physics.

I see. Oh, there's some more... Oh, yes.

And Wallace Sargent, here, thinks he's discovered a huge black hole.

Well he looks as if he's photographed

just at the moment of discovery, doesn't he?

Quite pleased with himself. Yeah, with everything.

Irwin Shapiro, you'll hear how he's been

getting radar echoes from the planets. USTINOV: Yes.

And Sidney Drell's a theorist from the

high speed world of subatomic particles.

Gracious! And Ken Brecher, here, he's checked

some of Einstein's basic assumptions

with very precise astronomical tests.

A formidable range of expertise but they, they look friendly enough.

I then became aware that there might be

more to those motorcycles than met the eye.

As we journeyed into the mountains,

Calder told me that the Theory of Relativity burst upon the world

more than 70 years ago

when Special Relativity proclaimed

the curious effects of high-speed motion.

General Relativity, he said, followed later

as Einstein's Theory of Gravity.

But we were to take them in the reverse order and

approach the bewildering distortions of time

by way of a gravitational black hole.

I'm just nosing in towards the black hole... now.

For our celebration of Einstein's Relativity

and the famous formula that powers the universe,

the venue was the McDonald Observatory of the University of Texas

and the observatory's main telescope was our window on Einstein's universe.

With a light gathering mirror a 107 inches wide,

it's not the largest in the world but

a very impressive instrument all the same.

Oh, it's charming. Isn't it though?

Yes. Quite a telescope.

Already I found a posse of relativists at my shoulder

and affording us the use of the telescope to embellish

our little seminar was the director of the observatory, Harlan Smith.

See the gigantic counterweight here.

That's merely a counterweight?

Yes, many people ask what that's for but it's just dead weight.

The air was decidedly thin on the mountain top.

They bring you up here, getting you in some sense closer to the stars I suppose,

and then present you with stairways at every turn.

More steps? More steps.

You're standing very close to one of the portholes which the light can emerge.

We can put an instrument on there to analyze the light.

Becomes a main collecting mirror.

But it's also interesting to see the control console down there.

It's really remarkably small for all the functions it does.

You mean that's the dashboard for this?

That's all it takes.

Well this is McDonald and this kit peak. This one...

They did everything to help a greenhorn understand

modern astronomy in it's Einsteinian modes.

And that's a tracking station in Madrid, the Bond telescope...

So basic are Einstein's ideas to modern knowledge

that confirming them is now a global industry.

When I prowled through the observatory it seemed like a set

for some drama in space, and in a sense it was.

About science, Einstein and I had only this in common,

we both hated the way it was taught to us at school.

He transcended that... I drowned in it.

John Wheeler began my rather belated rescue.

Thanks to you not being a scientist,

we're all going to have to give this account

the simplicity that Einstein would have loved.

Where do you think we should the account, John?

With gravity?

Nothing could be better.

Everyone has to deal with it every day.

Gravity.

Well let's see what the astronauts made of gravity

on the moon.

I'm very proud to have the opportunity here to play postman.

What could be a better place to cancel a stamp than right here at Hadley Rille.

I, I remember this from the time...

Now in my left hand I have a feather...

In my right hand a hammer.

I guess one of the reasons,

we got got here today was because of a

gentleman named Galileo, a long time ago,

who made a rather significant discovery

about falling objects in gravity fields.

And we thought that where would be a better place to confirm his

findings than on the moon.

And, so, we thought we'd try it here for you.

And the feather happens to be, appropriately, a falcon feather

for our falcon.

And I'll drop the two of them here and hopefully

they'll hit the ground at the same time.

How about that?

I have here a hammer and a bird's feather.

How about that?

If you were Galileo,

how would you in the light of that, try to persuade

people that everything falls at the same rate?

Difficult.

Difficult. Air resistance is a whole problem isn't it?

So it's such a wonderful thing that air resistance

for objects like this doesn't count so much.

Fantastic.

What a feat for Galileo to realize

that everything falls at the same rate.

But for Einstein it was a still greater

act of imagination to realize

that the reason those things all move the same,

they get their moving orders from the same piece of space,

it's not the distant Earth,

it's the space right where they are.

"There came to me the happiest thought of my life.

"Consider someone in free fall, for example,

"from the roof of a house.

"There exists for him during his fall

"no gravitational field."

And Einstein really tells us that gravity is an illusion.

I can toss, across to Dennis, a ball

and that arc looks as real as anything could be.

And I can toss a ball across to Sid

and the arc looks as real as anything could be.

But Einstein tells us that the arc is a pure illusion.

If we could only cut away

this grid with a welder's torch from underneath us

and all fall freely,

then, as I toss that ball, it would

move in a beautiful straight line.

Einstein tells us that in a local,

freely falling frame, there is no gravity.

Einstein would have loved to see those astronauts in Skylab.

They were weightless. They were in free fall.

Einstein's great idea,

all objects fall

because they get their moving orders right from space.

Skylab had no power in orbit and no force acted on it.

It went just as straight as possible through space.

But space is warped around the earth.

So Skylab could end up and did end up going in a circle.

Warped space was Einstein's style of thinking.

Moving about in warped space

is no more mysterious than traveling

about in these mountains.

You just can't go in a straight line.

To go in a straight line you must go down on the plain.

Well, like everything else, light, it seems,

responds to gravity.

And so space is warped.

Coaxing me over that fence was Irwin Shapiro.

One of the important questions we have to decide is whether something

is straight or warped. How can we do that?

We need some frame of reference.

For example, if you were to look at

this line of posts and trying to decide

whether they were straight or not, how would you do it?

Well, you'd presumably, look along it.

I think I could have told from there but it's almost straight.

Right. You squinted along it and really,

your frame of reference was the light rays

and that's a very good technique, however you can get fooled

if the light itself gets bent.

For example, water bends light

and we can illustrate that here with these two rulers. I put these two rulers

in the water and ask you to decide whether

the bottom one or the top one is actually straight.

Well, since water bends light,

the bottom one looks straight and obviously isn't.

That's right. See, when we pull it out,

when they're out of the water, you can see clearly that the

bottom one is the one that's bent and the top one is the straight one.

In fact, if you look from the earth at light from a star beyond the sun,

the sun's gravity bends the light of the star as it grazes it's limb.

And so, the position of the star appears to change.

Einstein calculated the bending of light

using this idea of curved space.

As seen from the earth,

certain fixed stars appear to be in the neighborhood of the sun

and can be observed during a total eclipse of the sun.

At such times these stars ought to appear to be displaced outwards

from the sun as compared with their apparent position in the sky when

the sun is situated at another part of the heavens.

A ray of light going past the sun undergoes a deflection of

1.7 seconds of arc.

That prediction, in 1915,

led to world fame for Einstein.

In fact, there was a total eclipse of the sun in 1919

and a team of British astronomers

went to observe this total eclipse in the tropics.

And here's a plate taken from that expedition,

of the sun during the total eclipse. This is a negative

so you don't see the sun at all,

it's a blank field...

...and these black striations are the solar corona.

And very tiny black dots

are the stars in the field of view.

And the relative positions of these stars were

measured very accurately and compared with corresponding measurements

of a photograph taken of the same stars

when the sun wasn't in the field of view

and the results showed the star positions shifted

during the total eclipse

in approximate agreement with Einstein's predictions

and certainly quite different

from what Newton would have predicted.Oh.

Newton, forgive me.

You found the only path barely open in your time

for a man of the highest powers of thought and ordering.

The concepts which you created still guide our thinking in

physics even today although we now know

that they will have to be replaced by others,

farther removed from the realm of direct experience,

if we aim at a deeper understanding of relationships.

Nowadays, we needn't await a total eclipse of the sun

to attempt to make measurements of the deflection of light,

we can use radio waves.

According to Einstein's theory,

radio waves, just like light and

x-rays or any other light-like radiation,

is predicted to behave the same way under the influence of gravity.

Instead of ordinary stars in our galaxy,

with radio waves we observe the much more distant objects called quasars.

Just like the visible stars,

quasars seem to change position

in the sky when the sun comes into line with them.

With the radio technique,

we can also achieve far better accuracy.

The most accurate measurements were done

at the National Radio Astronomy Observatory in Greenbank, West Virginia.

This experiment confirmed Einstein's prediction for the bending

to within about one percent.

Powerless, then, to question that gravity bends light,

we tried our skills with an impressionistic model of warped space.

They urged me to believe that the

distortions of space due to a massive body like the sun

could shape the course of lesser objects like the planets.

The table maker gratuitously added

bottomless pits of gravity,

black holes that would swallow an unskillful ball.

Black holes aren't getting much to eat today.

Einstein wouldn't be happy if we didn't tell you his story

in the simplest words.

Space tells matter how to move and matter tells space how to curve.

That's it.

Throw this ball past the sun.

That's light

changing its direction,

but not through some mysterious force acting through space

but through the warping of space itself.

Or put a planet

into orbit around the sun and watch it go.

And where does it get it's moving orders from?

Not from that sun

but from the space right where it is.

Or put Skylab

into orbit around the earth

and ask those people on Skylab what do they see.

They get their moving orders

from space itself, right there, where it is.

Einstein's wonderfully simple picture of it all.

Or the moon going around the earth.

Pull the earth away,

unwarp space and the moon will fly off.

Happy to go in a beautiful straight line.

But cosmic space isn't, after all, a distorted tabletop.

I bared my misgivings to Dennis Sciama.

How on earth, or rather, how in the universe can nothingness have shape?

That is indeed a difficult question

and the Greeks struggled with it very much.

They had a geometry of their own

and light, responding to that geometry,

would move in straight lines.

That's not at all the case in Einstein's theory.

He uses a different geometry from the Greeks.

A geometry in which space is warped and light responding to that geometry

doesn't move in straight lines but is bent.

And a planet responding to that geometry would move,

let's say, in a circle around the sun.

Einstein himself was very concerned to stress

this difference from the old geometry and he tried to make it plain to all of us.

On the basis of the general theory of relativity,

space, as opposed to what fills space,

has no separate existence.

There is no such thing as empty space,

that is space without a gravitational field.

The geometrical properties of space are not independent but they are determined by matter.

It seemed that either Newton's force of gravity or Einstein's warped geometry,

would keep the planet circling in the same stately fashion.

But who was right?

In Einstein's theory,

the orbits are predicted to be slightly different

than they are in Newton's theory.

For example, let us consider a single planet in orbit about the sun.

In Newton's theory, this planet would be predicted to follow an elliptical path,

that is a path sort of like a stretched out circle.

And in Newton's theory this path would be followed continually,

ad nauseum, following the same elliptical path all the time.

Whereas in Einstein's theory,

this path actually swivels around.

That is the ellipse rotates very slowly in space.

Near the sun, gravity's a little stronger in

Einstein's theory than in Newton's.

So close in, the planet teeters for a moment before climbing away.

This different prediction of Einstein's theory

actually cleared up a nineteenth century mystery

about the orbit of the planet Mercury,

the closest one to the sun.

The ellipse corresponding to the orbit of Mercury is not stationary

with respect to the fixed stars, but rotates

exceedingly slowly.

The value obtained for this

rotary movement is 43 seconds of arc per century.

This effect can be explained

by classical mechanics only on the assumption of hypotheses which have

little probability.

On the basis of the general theory of relativity,

it is found that the ellipse of every planet

must necessarily rotate in this manner.

In the late 1960s

we used the Haystack radio telescope in Massachusetts

to measure the swivel of Mercury's orbit.

This telescope is enclosed in a ray dome to protect it from the wind and the sun.

What we did was use this radio telescope

with an attached radar system to send pulses of radio energy

towards Mercury and to detect the echoes.

In fact, although the power in the transmitted radar signals

is about 500,000 watts,

enough to supply the electrical needs of a small town,

the echo we detect is so weak

that its power is even less than that expended by an average housefly

crawling up a wall at the rate of only a millimeter per millennium.

By measuring these echoes from Mercury, periodically

over several years, we were able to detect the swivel of Mercury's orbit

because the echo delay is different for a swiveling than for a non-swiveling orbit.

Our results confirmed Einstein's prediction to within one percent.

There's an amazing object that's been discovered in

the sky that swivels in its orbit far more than Mercury does.

This object illustrates beautifully Einstein's relativistic effect.

The object is called a binary pulsar.

An object lying far off among the stars, the binary pulsar,

was evidently quite invisible.

By what new ingenuity could they track its orbit?

Kenneth Brecher patiently explained.

Imagine a rapidly moving vehicle coming down the road... A motorbike say.

As it comes towards you, you hear a high pitched roar.

When it passes you, the pitch drops

with a change in frequency according to whether

the source of sound is coming towards you or going away.

That's the Doppler Effect.

The same thing happens with light or with radio waves.

Police speed traps use Doppler radar.

It sends out radio waves that

bounce off the vehicle and come back with a higher frequency.

The faster you're going the more the frequency is changed.

The Doppler Effect is an unbeatable way of measuring relative speed.

Now imagine an object, circling, giving out its own radio pulses.

You'd find the frequency rising and falling repeatedly.

You could tell it was circling even if you couldn't see it.

Completely out of sight among the stars there's an orbiting pulsar.

It's nature's gift to the relativist.

A pulsar is a collapsed star, a neutron star we call it,

which ticks like a very accurate clock

emitting regular beeps of radio energy.

This particular pulsar changes its beep rate

in an eight hour cycle as it sweeps forwards and backwards.

But did you discover this binary pulsar?

No, I didn't discover the pulsar but all of us who are working on

relativity and astrophysics are incredibly excited about it.

It's a unique object and a unique opportunity to

test the laws of general relativity in a very precise way.

It's being studied at the Arecibo radio observatory in Puerto Rico.

Joe Taylor and Russell Hulse of the University of Massachusetts discovered it

and Taylor has been checking up on it every few months ever since.

We're right on source? Yeah.

Following errors? No.

Thank you. Good.Okay.

Hello, everything still going all right?

Yeah, fine.

One of the marvelous things about it is the changes are so predictable

that when they switch on the pulsar always clocks in right on cue.

The pulsar is in a very tight, fast orbit

around another collapsed star that's not directly detectable.

And the pulsar's orbit changes in the Einsteinian manner.

It swivels 30,000 times faster than Mercury's orbit does, four degrees a year.

The binary pulsar's very nice evidence for Einstein's effect.

But really, to milk it for all it's worth in confirming relativity,

Taylor still has years of work to do.

And in fact there's some things still more exciting in prospect,

which is that as the binary pulsar goes round,

according to Einstein, it radiates gravitational waves.

The result of that would be that the orbital period would change slowly

and Joe Taylor is trying to detect this change.

In fact, just the other day,

Joe Taylor sent me a new manuscript of his in which he claims to

begin to measure this effect and it does seem to fit Einstein's theory very well.

These gravitational waves that Einstein predicted

are ripples of warped space.

And with the help of a computer, theorists have made movies of gravitational waves

that ought to pour out from violent events

like the collapse of a star.

And there's an interesting kinship, isn't there, between gravitational waves

and the familiar tides of the sea

that are raised on the earth by the warped space around the moon.

We're a long way from the sea here so we can't actually see

the ocean moving up and down the way it does in a spectacular

fashion on the coast but, as a matter of fact, at this observatory

they have measured how the rocks of the earth move under the moon's influence.

They move up and down by as much as a foot twice a day.

Unsettling to think of the earth heaving like that.

But the force of the tides gave a certain palpability to warped space.

Wheeler then offered me a warped miniature table and a jar of quicksilver.

You'll notice that you have

one of the blobs of mercury pulled right out, stretched out

and nothing is a more beautiful illustration of a tide effect than that.

What you can, if you'd like to,

to illustrate that gravitational waves

are also tides,

is take that blob of mercury and jiggle it

and you notice it changes its shape, first this way and then that way

and there just isn't a more beautiful illustration

of what a gravitational wave is

than the tidal stretching of that little blob of mercury

or the tidal stretching of a gravitational wave detector.

One of the things that interests me most about the whole thing

is the push it's going to give to technology,

because looking for gravitational waves,

we have to get down to what everybody calls the quantum limit of measurement,

and that's a new thing in the world,

and it's going to mean new kinds of equipment

that show up all over the map.

Engineering, biology, medicine... What have you.

You can try to detect very slight ringing

in great super cool metal cylinders like the one at Stanford in California.

In Glasgow, they have a different method.

Look at some of the details of the optical systems down in here.

Ronald Greaver uses laser beams

that shuttle to and fro many times.

And that's to measure shifts in the position of different masses,

shifts that might be caused by gravitational waves washing through the earth.

But it's incredibly delicate.

They're getting ready to look for movements far, far smaller than the width of an atom

between masses mounted about

30 feet apart.

It's possible that stars going round one another very rapidly can be detected.

It's possible that violently exploding star like supernovae will be detected

and it's even possible that objects falling into massive black holes

will produce gravitational waves we can pick up.

And if any of those things happen,

we'll be seeing the effects Einstein predicted

of warped space propagating

actually with the speed of light.

The McDonald Observatory had its own laser

and after hearing about clever experiments in other places

I was to see one in progress myself.

We've put those waves of gravity behind us, Peter,

and come back to basic issues about gravity and orbits and warped space.

What they do here is shoot their laser at the moon

to check its distance and movements to within a matter of inches.

The moon's a heavy object

but the earth is heavier still

and they might respond differently in the sun's gravity.

Then, we might see the moon's orbit drifting a few feet closer to the sun

and Einstein would be wrong.

Fantastic sight of the moon.

The moon looked splendid.

No amount of scrutiny by science can efface its terrible beauty.

You probably want it back now, don't you, Robert?

Yes.Yes.

Very wise.

To reflect the laser pulses from the moon,

the Apollo astronauts

set down a series of corner cubes on the surface at various locations.

Exactly like the cubed corner I have here in my hand.

Take a look at it, you look in at this face,

and you'll see that no matter what direction the light enters the corner cube,

it has he remarkable property

of coming out again in exactly the same path, but in the opposite direction.

The Soviet Union

landed two Lunar HUD vehicles on the surface

of the moon and each of them carried an array of corner

reflectors that were built by the French.

And tonight we're going to try and get echoes back

from one of these Lunar HUD vehicles.

Lunar HUD 21, which you can see

in the upper right hand corner of the moon, over there.

Oh yes.

Eric Silverberg took up the story.

We fired the laser every three seconds

which produces an extremely intense pulse of

light that starts at the far end of the room and then expands

up through this tube hitting two reflections

and then more until it fills the entire mirror,

107-inch mirror, which gives us a very parallel beam of light

to send up to the moon.

We typically fire from 300 to 400 shots in each 45 minute period.

Since the laser pulse is about three feet long,

going up to the moon we can very accurately time how long it takes

to get there and back.

We always have to station an aircraft observer outside

the dome to keep track of any possible nearby aircraft because of the

intensity of the beam.

We're going to start ranging on the reflector now

and Robert will start firing at the Soviet, site.

His job is the most demanding

because he has to point the telescope

with an accuracy which is

equivalent to trying to hit a penny

at a distance of perhaps a mile.

And we help him out as much as we can

by putting a small red flash on the image of the moon in order

to, show him precisely where the beam is pointed.

In really good conditions we can get a return

back on the teletype perhaps every fifth or every tenth laser shot.

And when it happens they ring a bell

so that Robert knows precisely whether or not he's located at the right position.

But even with such precise measurements, it's not easy

to calculate the moon's orbit

because of the myriad of small effects that influence its motion.

My colleagues and I use the measurements made here at

McDonald to actually compute the moon's orbit to very high

accuracy and found it to agree very well with Einstein's claim.

So Einstein's theory has again

withstood another stringent test and rival theories

are put under much greater constraints if they're going to be in

accord with the behavior of nature.Fantastic.

I left them contentedly ringing the bell for Einstein while

tending a half-baked bun of comprehension in my brain.

I'd pictured the moon faithfully circling in the warped space

around the earth and the sun's gravity toying with our own great planet.

Einstein wouldn't be happy

if we didn't tell you his story in the simplest words.

Space tells matter how to move

and matter tells space how to curve.

Warped space didn't trouble me too deeply. I remembered how easily

any exercise in straight line geometry can be botched.

If the young Ustinov could bend the world...

Why not Einstein?

But to step onto the quicksands of Einsteinian time,

er, that was uncanny.

Unsuspectingly, I watched next morning as a visitor, John Engelbrecht,

measured the speed of light.

I'm generating the light pulse

with a sparker which I'm going to turn on here.

And that creates sparks, essentially, short beams of light

that travel across to the other dome

where we have the mirror

and the mirror reflects the beam of light into this

telescope right here, where we have a photo-multiplier tube

to pick up the light signal so that we can look at it

on the oscilloscope right here.

We measure the time interval

by measuring the distance

between the two blips on the oscilloscope where distance across the screen is time.

Looks like about 450 nanoseconds?

And the round-trip distance is 134 meters.

Yes.

Well it's not bad.

You've determined the speed of light this morning to be about

298 million meters per second.

An accuracy of about, oh about,

oh, about, one percent.

Um, the speed of light is in fact, Peter, known to, great accuracy.

It's one of the most precisely known numbers in all of physics.

The national Bureau of Standards in the United States

has a figure of about 299,792,457.4 meters per second.

Point four?

Well, the National Physical Laboratory in London

er, perhaps would disagree with the last figure.

Yes, I thought so.

Einstein was emphatic that a blast of light is

always a constant no matter what the motion of the source or the motion of the observer.

I've checked this, in fact, using not light but x-rays

which are a form of light but at very high energies.

In 1970, a satellite was launched off the coast of Kenya for the purpose

of doing x-ray astronomy.

It was called Uhuru.

It discovered and began observing a peculiar class of star.

An x-ray binary pulsar gives off regular bursts of x-rays

while orbiting at high speed around another star.

Now suppose that Einstein were wrong

and that x-rays go faster if they were launched

when the pulsar is moving towards the earth.

Then x-rays from that part of the orbit could overtake

x-rays that are coming from the other part of the orbit,

making a simple picture quite complicated.

For example, you could see the pulsar coming and going at the same time.

Peter, from my friend Ethan Schreier

at the Smithsonian Astrophysical Observatory,

who worked on the Uhuru satellite,

I got the following tracing of x-ray pulses

coming from the x-ray pulsar Centaurus X-3.

And as you can see by looking at these pulses,

they're absolutely regular.

Each pulse comes along at a specific time interval

and there are no spurious ghost pulses lying in between the pulses that we see here.

This is direct proof that the speed of light

is indeed independent of the velocity of the source.

I looked at three separate sources.

The most distant one, lying in the small Magellanic Cloud,

the light took 200,000 years to arrive at the earth

from that source.

And in all that time, the pulses emitted

when the pulsar came towards us, never

overran those that were emitted when it went away.

By more than a factor of perhaps a part in a billion.

To put it in earthly terms, that would be about the speed of a

turtle moving along the ground.

That's a very earthly term.

In deference to this evident obsession of Einstein's,

I accepted that in cosmic space the speed of x-rays

or visible light or radio waves, never varies.

But, dear me, how promptly that golden rule was broken.

If we send radio pulses

to another planet like Mercury or Venus

when they're on the other side of the sun from earth,

they can appear to be slowed down by the direct effect of the sun's gravity

on the waves as they pass near the sun.

It looks, from where we are, as if the sun's gravity

acts very like a lens, bending the light and slowing it down.

About fifteen years ago

it occurred to me that this increase in the travel time

was a direct consequence of Einstein's general theory of relativity.

In those days of increasing

science budgets and low rate of inflation

it took less than two years

to convert that idea into a very sophisticated radar

system which we installed on the Haystack telescope

to make these measurements on Mercury and Venus.

Now the actual predicted effect is very small,

it's only 200 millionths of a second out of a total round-trip time

of about 1,500 seconds or approximately

one part in 10 million.

And we were able to measure it with an accuracy

of approximately five or ten percent with this radar experiments.

Now, if we could turn to Mars...

You can't expect to make that image of Mars just now

because it's right on the far side of the sun

and it's close to the horizon.

But, maybe we'll get an impression.

Mars is now very near the far side of the sun

as we view it from Earth

and is in a good position to see this effect.

And in fact, the last time Mars was in this position,

we used radio waves sent to the Viking spacecraft

which we landed on the surface of Mars

to measure this predicted slow-down much more accurately.

And with such measurements we're able to verify

the predictions of general relativity on regard to the slow-down

to an accuracy of about one-tenth of one percent.

Okay, you say light slows down near the sun.

But Ken Brecher told us just now

that light seems always to go at the same speed.

I think, Peter, that as a theorist,

Roger Penrose here might resolve that contradiction for us.

Yes, well, you see, it really depends where the measurement is done.

If you measure the speed of light

as it appears at the surface of the sun

from here then it would seem as though it slows down.

It would seem as though the sun was surrounded by some sort of lens

that should not only slow the light but also bend the light.

But if you did the measurement at the surface of the sun

then you would get the same answer for the speed of light

as you get from the speed of light at the surface of the Earth.

We had come to the nub.

To keep his blessed speed of light always reading the same,

Einstein decided that time itself must slow down near a massive object.

So gravity has the apparent effect of reducing the speed of light

and slowing down time.

So if you imagined the extreme situation of a black hole

then light would be reduced to zero speed apparently

and time would apparently have been stopped completely at the surface.

Apparently?

Well, I feel awfully guilty asking this because I'm opening,

as they say here, a new can of peas,

but we've heard so much about black holes.

What is a black hole apparently?

Yes, well, according to Einstein's theory,

if you have the final fate of a very massive star,

would be an object so concentrated

that light itself couldn't escape from it.

The object collapses inwards and, signals,

light, any other kind of signal, any object,

cannot escape from this region

into which the star would collapse.

The black hole that results from the collapse of a star

several times the mass of the sun,

would be an object several miles in diameter.

But if you, say, imagined the Earth

compressed right down until it became a black hole,

the dimension would be a bit less than an inch or something like that.

That's the Earth? The Earth would have to be compressed

into that size to be a black hole. USTINOV: I see.

So, you shouldn't be candid.

- Don't worry. - I see.

Light at the surface of a black hole trying to escape

would hover there forever.

And judged by us, looking from a safe distance,

time there appears to stop.

You'd wait forever for the next tick of the clock.

A short distance away from the black hole,

time does seem to pass but rather slowly by our reckoning.

You can think of the black hole to be surrounded by shells

in which time runs progressively faster.

That's what happens in the immediate vicinity of a black hole.

But the effects on time extend for thousands of miles

with time getting gradually closer to what we regard as the normal rate.

If you imagine that little black hole

with the same mass as the Earth

and surround it by a sphere representing the Earth's surface,

where we live,

our clocks run at the appropriate rate.

There isn't really a black hole at the center of the Earth

but time at the Earth's surface

is so little just as if they were.

Compared with the very gradually increasing rates of time

way out in space high above the Earth's surface.

"The observer will interpret what he sees

"as showing that one clock

"really goes more slowly than another clock.

"So, he will be obliged to define time in such a way

"that the rate of a clock depends on where the clock may be."

Peter, the interesting thing about general relativity is that my clock,

whether I'm sitting here on the surface of the Earth,

whether I'm orbiting around a black hole,

will appear to me always to be running at the same rate.

The gravitational effects don't change the actual clockwork mechanism,

and don't affect it in any way.

Nonetheless, from your point of view,

you might see my clock running at a different rate

and we would appear to have time running at different rates.

We could correct for this, and general relativity in fact tells us

exactly how to do that,

um, but the, the clocks themselves

are in fact not disturbed by the gravitational field.

Yeah. I... I don't quite understand one thing

because obviously we are our own terms of reference

and therefore our clocks are our own terms of reference,

they become part of us.

If I take an airplane, as we all do and fly very high,

is there what is shown on the clock face

affected by the fact that I have flown high

or not, by the time I arrive?

Yes, it is in fact affected

and when you come back it will read differently from the identical clock

which you left behind which didn't take part in the airplane ride.

But although the clock reading is different when you come back on the ground,

the clock, once it's back on the ground

will continue to run at the same rate it used to run on the ground.

So that the difference in reading will then remain constant

as time goes on.

The important point is that this effect is not a psychological effect.

It's a genuine, measurable, physical effect.

In the last decade or so, extraordinarily accurate atomic clocks

have been made which are sensitive enough

to see these very small effects.

Such that, for example, the difference between

the rate of a clock running on the ground

and one running on the second story of a building

could be observed and measured very accurately.

Oh, so Big Ben's been wrong all the time

because it's at about the eighth floor?

I see. Right, it's gaining relative to your clocks.

My common sense was outraged, of course.

Yet, recent results have evidently smothered

all expert and inexpert doubts about Einsteinian time.

Sidney Drell set the scene.

The atomic clock is not just an instrument for scientific laboratories

to run their equipment with or part of their play equipment.

In fact, in everyday life it sets the time by which we live.

Here, one has a crystal oscillator

which keeps time relative to an atomic clock

which signal is being received here

with due allowance for the time it takes for light to bring the signal here.

Here is the time that it's reading out.

I notice that my own crystal watch

is two seconds slow by the time given there.

Well... Mine is six seconds out. That's terrible.

Well, this will go back to the maker.

Back in Washington, there sits the master atomic clock

against which all other time is referenced

for an international time standard.

The atomic clocks keep time to an accuracy

which approaches one second out of a million years.

That is how far they have come.

To understand the atomic clock

we have to now enter into the theory of atoms.

And this is another theory,

the theory of, how light is emitted and absorbed by atoms

and how light propagates with very sharply defined frequencies.

There's another, theory to which Einstein made

very enormous contributions.

Sometimes we think of the year 1905,

when Einstein was 26 years old,

as one of the miracle years of the world.

Because in that year when he was giving us special relativity, Peter,

he was also giving us the theory of light

occurring in discrete packages and with precise frequencies.

It was, in fact, with this work that in 1921,

he received the Nobel Prize,

when the relativity theory was still viewed as too mathematical,

too controversial and not really of practical importance.

This side of Washington, they keep the clocks

that directly answer your question, Peter,

about how time passes in an aircraft.

Karel Ally of the University of Maryland, and his colleagues,

put one set of atomic clocks aboard a US Navy airplane.

And this was starting in 1975.

And you remember, on the moon,

those man-made corner reflectors,

well, the aircraft carried one of them

to throw back yet more laser pulses.

Providing a link to another set of clocks

kept in a cabin on the ground for comparison.

The same types of atomic clock?

Yes, they're twin brothers in effect.

The prediction of general relativity

is that as you get higher above the ground,

the grip of gravity on time weakens

and your clock should run a little faster.

The laser flashes coming from base

serve to check the time recorded in the air

against the readings of the clocks on the ground

while the aircraft flew around and around Chesapeake Bay.

The ground radar kept track of it.

The aircraft's speed, by the way, also had a very small effect on time

by a quite different prediction of relativity

but the experimenters took that accurately into account.

Yes, I'm sure they did.

The main effect on time related to the aircraft's height.

At 35,000 feet,

the airborne clocks gained about three billionths of a second every hour,

and each flight lasted about 15 hours

and five flights like that accurately confirmed

the effect of gravity on time.

So Einstein's account of how the world works triumphs yet again.

"To punish me for my contempt for authority,

"fate made me authority myself."

And what's true of atoms and atomic clocks

is also true of atoms in ordinary objects like an apple.

And perhaps we could draw some of these threads together

by telling, how in a time shell,

starting at the top of a tree and moving into a time shell lower down,

an apple manages to accelerate in the way that's so familiar.

It's moving into shells, very fine shells,

of ever slowing time.

Its atoms are operating more slowly.

It seems to be losing internal energy

which has to reappear in some new form

and the form it takes is energy of motion.

So the apple is going faster and faster as it moves down

into slower and slower zones of time.

Until finally it hits the ground

and that energy of motion is destroyed.

Well, Nigel, just two little points I'd like to clarify

before we all go further into this adventure.

It seems to me that the apple has acquired such a particular status

with Newton, that perhaps one ought to realize

for uninitiated agriculturalists

that pears and grapes and, in fact, people are subject to the same laws,

that pears are not exempt.

Exempt from the action of gravity.

Well, certainly not, because,

especially since Einstein,

the emphasis in present thinking

is that gravity affects everything in just the same way.

And in the case of people

our atoms also are affected in that rate of operation

according to whether we're living down in the valley

or up on the mountain.

I found the propositions

of general relativity easy to state.

Gravity bends light and warps space.

Gravity slows down light and slows down time.

Bewilderingly simple, really, as their full meaning sank in.

You could think, if you dared, of visiting a black hole

and hovering there for a while.

And there in the slow running time shells close to the black hole,

perhaps only a few years would pass

while hundreds of years were passing on Earth.

Maybe you'd like to imagine yourself

as twin brothers testing this theory.

"The adventurous one is my twin brother, Peter,

"and my cautious one is... Albert."

And Peter wanted very badly to investigate this black hole.

He's always been reckless. You coming?

You silly boy.

It's going to be great up there!

That's certain.

How about that?

That's the last we've seen of Peter on this Earth anyway.

Would I dare make the imaginary journey

to the black hole now proposed?

Well... Why not?

Goodbye!

Goodbye.

Oh, do take care.

I shook the dust of the 20th century from my feet

as my imagination bounded towards the black hole.

I'm just nosing in towards the black hole now.

I'm just nosing in towards the black hole now.

Well...

At least that black hole has slowed down

the hectic pace of his life but I hope to God he takes care.

The rate of time seemed entirely normal to me, but on the Earth

it was evidently racing along.

The gravitational effects don't change the actual clockwork mechanism.

Nonetheless, from your point of view,

you might see my clock running at a different rate.

Pictures from the Earth showed the days

passing in a matter of minutes.

I saw who won the Grand National in 1990 but I shan't tell.

It was hard to make out what Albert was saying in mission control.

Anyway, your will is in spirit

and we'll be able to celebrate any moment now.

Yes!

A happy new century!

Happy day... Yeah.

Missed the bloody bottle!

I see, you look very spry, yes, you do.

Twenty-first century?

We're still 20 years off by my reckoning.

As years passed on Earth and only months on my spaceship,

my greatest concern was for Albert.

My twin brother was aging before my eyes.

As for me, I was only a few months older.

Well, it would appear that Mr. Einstein was right.

Eh, Peter?

As you can see, I'm still trying to look after you

in spite of...

Nurse...

It wasn't long before the Earth forgot all about me.

Time to go home.

Before I could even think

of playing Rip Van Winkle in the world of the 21st century,

there was one visit I had to make.

Alas, poor Albert.

Even in imagination, this time travel by means of gravity

seemed a joyless enterprise.

There was no method for retracing my steps through Einsteinian time

and returning to the 20th century.

We've talked about the warping of space

and about the effects of gravity on time, in space and time.

But relativists like to combine the two into space-time.

With time as being the fourth dimension.

"The non-mathematician is seized by a mysterious shuddering

"when he hears of four-dimensional things.

"By a feeling not unlike that awakened by thoughts of the occult.

"And yet, there is no more commonplace statement

"than that the world in which we live

"is a four-dimensional space-time continuum."

Here we are at a certain place in Western Texas.

And the time is half past eleven.

Put the two together...

I clap my hands, that's an event in space-time.

Now each of our lives is a series of such events strung together

into a world line in space-time.

And here we meet together, our world lines more or less intersect.

In order to get a picture of space-time,

it's convenient to think of space as represented as a two-dimensional flat plate

and that frees the third dimension to represent time.

Now, let us imagine an object which is stationary in our description.

Then this would be represented by a vertical straight line.

An object which is moving uniformly but with some velocity,

would be represented again by a straight line but now tilted over.

What about an object which is accelerating?

Then that would be represented by a curved line.

This is the world line of the object.

Now let's think of the sun,

that again, thinking of it as stationary

would be represented by a straight line

and the Earth, in orbit around the sun,

would be represented by a spiral line.

But then the Earth, as we know,

is in free fall and should therefore be represented

by as straight a line as you can draw.

And how is it that it's drawn as this spiral line?

Well, this is because the space-time is really curved.

Now, remember our deformed billiard table,

the space then would be warped in a certain way.

And as the space evolves to give us our space-time picture,

the whole space-time is slightly deformed.

And this is why the apparently curved picture

of a spiral motion of the Earth

is really as straight a line as you can have in this curved geometry.

And I gather that I feel the burden of gravity here on Earth

because I go against the grain of space-time.

Gravity feels the same as acceleration

but, according to Einstein, in an important sense,

gravity is the same as acceleration.

In a gravitational field things behave as they do

in a space free of gravitation.

If one introduces a reference system which is accelerated.

Do you want me to try it?

Try it. Never get off the ground with me in it.

What Einstein called a reference system which is accelerated

was for me a curiously dumpy helicopter

to be flown as delicately as possible.

I'd ridden some awkward steeds for the movies

but nothing quite as undignified as doctor's scales.

As the helicopter lurched upward, my weight increased.

Each brief acceleration adding pseudo-gravity.

Whenever we climbed steadily or hovered, my weight went back to normal.

And when the pilot let the machine accelerate downwards,

a nasty feeling that... "Oh! How the pounds melted away."

In some neglected slot machine of my mind

a penny dropped.

When a vehicle accelerates, lurching in one direction,

all its loose contents are left behind

and seem to fall in the opposite direction.

As the master said, "It's just like gravity."

Acceleration could also put me on different scales of time.

Stand by, Albert.

It's not only gravity that affects the rate of a clock

and sew the passage of time,

even motion can do that.

And Einstein showed that already in 1905,

ten years before he developed the general theory of relativity.

What Einstein showed was that if an observer

moves out into interstellar space at high speed

and finding himself amongst the stars,

then turns round and comes back at close to the speed of light,

while the journey for him will seem short,

for the people who stay at home

it will seem much longer.

For instance, he will find that he has aged less during that journey

than the person who has stayed at home.

A little lonely up here in space.

Long after I'd fired my motors to turn for home,

my twin brother Albert was still receiving signals

sent by me on the outward leg of the journey.

Again, time seemed to me to pass normally.

But it was in this melancholy phase of my return journey

that I observed poor Albert growing older by the hour.

Just as for the visit to the black hole,

this high speed relativistic flight plan

took me on a one-way ticket into the twenty-first century.

Although he lived before the space age,

Einstein made many imaginary journeys like this.

Gedanken experiments.

"Thought experiments," the physicists called them.

"One could imagine that the organism,

"after an arbitrarily lengthy flight,

"could be returned to its original spot in a scarcely altered condition

"while corresponding organisms which had remained in their original positions

"had long since given way to new generations."

Einstein said that many years ago,

but, people for many years didn't really accept that notion.

It, in fact, was the source of much argument

and was elevated at times into the notion of a paradox.

But now, with very fast moving atomic particles,

we have displayed this affect with extreme accuracy.

Most precisely, atomic particles in a storage ring at CERN,

so-called new mesons which normally live

a very fleeting fraction of a second,

perhaps a millionth or two millionths of a second,

have been shown to have their lives extended

by a factor of thirty or so

just by having them move at speeds very close to the speed of light.

Well, I understand that this is possible for particles

but it does sound rather like science fiction to me

and like fantasy, would it be...

Would it be really possible for this to happen?

For people, I mean.

Well, this is a matter of faith, not a matter of science.

There's nothing in principle, I believe, that stands in the way

of getting one up to speeds,

that are a significant fraction

of the velocity of light.

And, when one thinks of the incredible things

that we do with instruments these days,

measuring with accelerators that are many miles long,

timed to precisions of billionths of a second,

I would be the last to think it's impossible, and won't be done.

After all, we did send men to the moon and look

for how many centuries that seemed impossible.

Presumably, one of the great advantages there would be

if human beings ever attempted to travel between the stars,

that you not only gain in an apparent extension of life,

as compared with the Earth, but also you can travel greater distances

than you would think possible by normal reckoning of speeds from the Earth.

I would say it's not only an advantage, it's a requirement

because distances to other, stars,

and their presumed planets are so great that there's no way

we're going to ever explore them if we don't stretch out our lives,

our time scale.

It was one of Einstein's earliest ideas in relativity

that you could distort time and space just by traveling fast enough.

We've now left gravity and general relativity aside for a while

to hear instead about special relativity

and the strange effects of motion.

Now let's imagine that these bikes are capable of, say,

half the speed of light.

That's what their speedometers show anyway,

fractions of C, the speed of light.

What kinds of Einsteinian effects

can we illustrate with bikes like these?

Perhaps you should start with the simplest point of all.

From the point of view of the rider,

he's at rest and it's the landscape that's rushing towards him.

In Einstein's democratic universe,

that point of view is just as valid as yours or mine.

And then recall the Doppler effect,

the change in frequency in color of light.

An object rushing towards you looks blue because the light gets crowded together.

It has a higher frequency.

When it's going away it looks red because the light gets stretched out

and then it has a lower frequency.

I'd like to emphasize something there, Peter.

Compared with ordinary white light,

blue light has a higher frequency and more energy too.

But red light represents a low frequency and less energy.

Einstein made two important discoveries about the Doppler effect.

First, it doesn't make any difference who is said to be moving.

It's just the relative speed that counts.

Einstein's second discovery about the Doppler effect

is that when a high speed vehicle is just passing you,

strange things happen.

Imagine that you were quick enough to

photograph it with your camera.

You ready, Peter?

As the vehicle passes us by,

you'd think it would be neither red-shifted nor blue-shifted

because it's moving perpendicular to our line of sight.

But, in fact, it's slightly red-shifted.

What's more, it's rotated away from us.

Not shortened.

Many accounts of relativity would have the bike squeezed short.

No, it still appears to be undistorted

but slightly rotated away from us.

But from the point of view of the rider,

it could be very peculiar distortions of the scenery

if you rode past buildings, say, almost at the speed of light.

Perhaps the first thing you notice...

...is the building and the truck curve in a little.

Then, as you speed up, you see that they seem to be twisted towards you.

Indeed, as your speed increases closer and closer

to the speed of light, you start seeing the far sides of the building and truck.

You seem to be seeing right around the corners.

It's like walking through a rain storm

when your front gets wet and your back stays dry.

The light approaches you from unexpected directions.

Consider two bicycles coming at each other at close to the speed of light.

You might think that their combined speed,

the rate at which they are coming together,

is faster than light.

But from each rider's point of view, it's not like that at all.

Their combined speed, as they measure it,

always remains less than the speed of light.

Einstein launched his disconcerting ideas from very simple premises.

The riders demonstrated why time runs slowly in a fast moving vehicle.

They just rode in company and threw a ball to represent a signal,

a flash of light.

From their point of view, the light went straight across between them.

But from our point of view, as onlookers watching the bikes go by,

the signal went obliquely and on a longer path.

But light always moves at the same speed

so that the time it takes for the signal to go from there to here

takes longer from our point of view

than from the point of view of the riders.

So Einstein tells us

that their clocks in the moving frame

move slower than ours in exactly proportioned

of this line to this line.

High speed travel also makes you seem heavier.

Time for rapidly moving bikes slows down and it accelerates more sluggishly.

Mass means resistance to acceleration

and the bike's mass piles on as it gets near the speed of light.

In fact, it continues to grow more massive without limit

as it gets very close to the speed of light

so that, in fact, it never can go faster than light.

But from the point of view of the rider,

his mass seems the same as usual.

When Einstein realized just how much the way things look

depend on where you stand,

he also saw a danger.

Because, he reasoned, the laws of physics must be the same

for the rider, as for the fixed observer.

Special relativity was born brilliantly out of that requirement.

But the price Einstein exacted from us

was the scrapping of the old ideas about time.

Einstein realized that although each person's view of events

is a little different,

everyone's view is equally valid.

And yet we are observing, all of us, the same laws of physics.

And the touchstone for the reliability of physical laws

was Einstein's old obsession,

the speed of light remaining constant

amid all the commotion of the cosmos.

Now, because of its motion in orbit around the sun,

our Earth is traveling at a speed of about 30 kilometers a second.

If the principle of relativity were not valid,

we should expect the laws of nature

to depend on the Earth's direction of motion at any moment.

But the most careful observations have never revealed

any lack of prevalence of different directions.

This is a very powerful argument

in favor of the principle of relativity.

But Einstein's revelations shook the planet.

From the reasoning of special relativity

emerged a law of creation and destruction.

It was time for us to consider the realm of the atom,

where relativistic events are more usual than on the roads of Texas.

First, for real motorcycles,

the velocities are much too low

for the effects of relativity to be noticeable.

Even, with a spacecraft,

circling the Earth every 90 minutes,

the speeds are too low.

They're being moved, in fact, about one forty-thousandth the speed of light

and, their increase in mass due to motion

is less than one part in a thousand million.

Astronomers looking at distant stars and distant objects

are seeing systems moving with a substantial fraction of the velocity of light.

And when we enter the atomic realm,

we, enter into an area where

the relativistic effects are very noticeable.

Even on your television screen,

the electrons that paint the television screen,

are moving with perhaps 20 to 30% of the velocity of light.

And, thereby their mass is increased to the order of a percent or so.

Out at Stanford, at the linear accelerator center,

we produce the highest energy electrons in the world.

They come so close to the speed of light

that their mass is increased by a factor of 40,000,

compared to what they started with.

As a result of this very high velocity and high energy that they acquire,

their clocks are slowed down,

and they don't realize that they have moved

a full two-mile of our accelerator.

In fact, from the electron's point of view,

their clocks are moving so slowly

they think they have gone only two and a half feet

by the time they come to the end of the accelerator.

At the end of the accelerator, we also have a storage ring,

so-called sphere ring, where we smash the particles into one another.

We create new matter.

And in this way we can very accurately measure

the conversion of energy of motion into matter.

And into mass. And in this way confirm with great accuracy

the Einstein equation, E = mc2.

What an equation that is.

It looks so innocent.

E... Energy, M... Mass,

and C... Not the speed of light

but the square of the speed of light.

An enormous number.

So that a little mass is worth a lot of energy.

It's hard to appreciate

what an enormous leap of intuition and imagination

it took to come to this simple formula.

Einstein had been thinking, from the age of 16 to 26,

consistently about the nature of light and electromagnetic radiation

and almost as a by-product of his... Of his, thinking on this subject,

he came to the following conclusion,

that if you look at light, say, from the sun,

and if you were moving towards the sun,

as we've already discussed, the light would become bluer.

Now, the blue light has more energy than the white light we normally see,

and therefore, he reasoned, there must be more energy

apparently coming from the sun.

But if that energy is not drawn from any change in the motion of the sun,

it must mean that that energy is coming from the mass itself.

And so he concluded

that the mass of the sun itself is converted directly into energy.

He then made the enormous leap to generalize this result to all forms of energy.

In the 19th century, there had been energy of motion,

and energy of light, energy of heat, but not inter-convertible.

And so he came to the startling conclusion

that all mass and all energy are in fact equivalent.

"We are led to the more general conclusion

"that the mass of an object is a measure of its energy content.

"It is not impossible

"that with materials whose energy content is variable

"to a high degree, for example with radium salt,

"the theory may be successfully put to the test."

What Einstein is noting here is that the energy released in nuclear reactions

is so great that there is actually a measurable change

in the mass.

That can be detected and his formula can be verified.

The, nuclear burning together

with the Einstein relation, E=mc2,

solved a long-standing riddle,

namely, how is it that the stars, the sun,

can burn for billions of years without running out of, material?

This equation, E=mc2,

and the efficiency of nuclear burning,

were tested quantitatively in 1932,

by Cockcroft and Walton with their accelerator.

They verified it for the first time.

But it was a long time before any practical use was made of it.

Einstein was hounded out of Germany,

he came to Princeton,

where I had the pleasure of seeing him after his arrival.

But it was five years from that until that fateful day

when I went down to the pier in New York,

and a ship came in with Niels Bohr,

and the word of the discovery of the fission of uranium.

January 16, 1939,

and not long after that Einstein wrote that fateful letter

to Roosevelt with all its consequences.

"Extremely powerful bombs of a new type may thus be constructed.

"I understand that Germany has actually stopped the sale of uranium

"from the Czechoslovakian mines."

And it was hardly 200 miles from here across the desert,

that that first dramatic explosion took place

that brought us into the true atomic era.

Einstein, who set it all in train,

was appalled by the nuclear arms race.

It's ironic that this humble, gentle man who had been an avowed pacifist

should now be etched in the history of mankind as the father of nuclear weapons.

He believed, as do many today,

including many scientists who are familiar with

the devastating effects of these weapons,

that survival in a world with nuclear weapons

is one of the great challenges of our generation.

It was, I believe, his last official act,

to endorse a manifesto in 1955

with Bertrand Russell, which I believe you have here.

Yes.

"We appeal to you as human beings to human beings.

"Remember your humanity and forget the rest.

"If you can do so, the way lies open to a new paradise.

"If you cannot, there lies before you the risk of universal death."

I think, in talking about Einstein's great achievement,

we should really stress the fact that it lies at the basis of all life.

The nuclear weapons are only a small by-product

of human folly.

Even when I strike this match,

a minute amount of the mass is converted into energy.

If I took all the mass in this match,

and converted it into free energy,

there's enough energy here to lift the entire mountain,

on which we're sitting now, about ten feet off the ground.

This energy plays a role in the hum of a violin,

in the growing plants here, and in fact in the expansion of the universe.

All of astrophysics is about nature's attempt

to release the energy hidden in ordinary matter.

Energy defined by the equation E equals MC2.

So I learned to perceive the sun, hot enough in Texas,

as a natural nuclear furnace and a typical star.

Energy can create matter, so matter has hidden energy.

Falling down, like the apple, can liberate some of it.

So Wallace Sargent led me back to gravity,

saying it can overwhelm a star.

When the sun grows old, it will first of all

become a red giant, in which it becomes

much bigger and a little cooler than it is now.

At this time, the Earth will be consumed,

but fortunately, it will not happen for several more billion years.

After that, the sun will shrink and become a white dwarf

which is about the size of the Earth.

During this time, a lot of hidden energy will be released,

but not as much as has been released by

nuclear burning at earlier stages of its evolution.

Stars much more massive than the sun

end their lives as supernovae,

that is they undergo gigantic explosions.

During this event, the inner parts of the star

is driven inwards in an enormous implosion.

This forms a neutron star, which in turn becomes a pulsar.

The matter in the neutron star is extraordinarily dense,

and the atoms are crushed together,

and a substantial fraction of the hidden energy

originally in the star is set free.

Well, so neutron stars exist, but theoretical calculations tell us

that some thing of three times the mass of the sun can't exist as a neutron star.

It's a short step from a neutron star

to matter being crushed by implosion into a black hole.

In the case of a collapsed star, ten times the sun's mass,

the resulting black hole would be only about 40 miles across.

Nothing could escape from it, not even light.

Material falling into such a black hole

would liberate tremendous energy

just before disappearing into the hole,

giving out intense x-rays.

And these x-rays could be seen from the Earth,

and that's in fact how we could expect to detect such a thing.

Well, the x-ray source called Cygnus X-1

meets these specifications and may well be a black hole.

And it's sucking material apparently from a companion super giant star.

Well, now we're on Cygnus X-1.

What we can actually see here is the companion to the star.

Not the black hole itself.

The black hole is orbiting around the star that you can see.

This is a record of the extra emissions from Cygnus X-1.

And you see there's no regularity in it

as there would be if it were a neutron star.

No, they're not very regular, are they?

The quest for black holes was, for me,

the culminating proof that Einstein's theories

still inspire the very latest research.

It led us to distant galaxies of stars

as big as our own Milky Way, but erupting most violently.

In order to explain many of the phenomena out there in the universe,

we have to invoke enormous energy sources.

And it looks more and more as though black holes may be the only possibility

to provide such large sources of energy.

In this kind of theory, an enormous black hole with a mass

probably several billion times the mass of the sun,

sits at the center of the galaxy and releases energy

in some way, which we don't yet understand,

by swallowing entire stars and gas from the surrounding galaxy.

For the past couple of years, several of us

have been paying particular attention to the galaxy M87.

It's a very distinctive galaxy

with a jet of luminous matter poking out at one side.

M87 is a strong source of radio waves and also x-rays.

And all together, it's a very energetic galaxy.

Most of the work that we've done has been observations

at the Kitt Peak Observatory in Arizona

and at Palomar Observatory in California.

We've used a very sensitive light detector

brought out from London by Alec Boksenberg.

What we do is to look at slices of M87

at different distances from the center and use the Doppler shift

to tell how fast the stars in the galaxy are moving around.

What we find is that the stars in the very center of M87

are moving around much more rapidly than we would expect.

As far as we can see, they're moving fast

because they're orbiting around an invisible object.

But we can use the speeds of the stars

to estimate the mass of this invisible object.

It turns out to be about 5,000 million times as big as the sun.

Just about the kind of mass that we would expect for a black hole,

if it really is powering all the phenomena that we see in M87.

The problem is

that the volume you would expect for a black hole

of the mass that we think the one in M87 has is very small indeed.

And so, really, the problem is to try

and resolve much smaller angular distances.

Small, angular distances.

I suppose that's the penny at a distance of a mile again.

In order to try and do this, I've turned radio astronomer

and with colleagues used the radio telescopes

at Goldstone in California,

and at Madrid in Spain, 5,000 miles away.

The object is to try and get a telescope as large as the Earth

by means of which you can resolve very small distances.

I'd just like to know, at this juncture,

to what extent is all this a logical consequence of Einstein's work

or has it already taken off on its own?

Well, it was certainly not known to Einstein

that black holes would be a consequence of his work.

On the other hand, later work,

since Einstein died in fact, has pointed very clearly

to the fact that within his theory,

at least, within general relativity, one...

This is a very clear prediction of the theory.

And of course, independent of the actual nature

of the underlying object, we know that it has to

put out a great deal of energy because we see that directly.

And that implies huge underlying mass from E=mc2.

And of course the light that we get directly from the object

as analyzed by Wallace Sargent...

Well, they used the Doppler Effect

and didn't pose to us as photons.

So the richness of Einstein's ideas

bears on the entire range of actual observations of these objects.

A computer charted the fathomless warp of space

in an imagined collision between two black holes.

Our ancestors frightened themselves with dragons and hobgoblins,

we have Jaws and black holes.

In fact, at the dead center of a black hole,

I found that even Einstein's ideas falter.

Here, if general relativity can now be

adequately applied to the black hole itself

and a certain distance in, then it's possible to show

that even the theory itself predicts its own downfall.

And this is one of the things which was not appreciated before Einstein died.

Certainly, everything does get compressed into a very, very small region.

And there comes a point somewhere,

when new physics has to come in.

The argument really is at what point

and what new physics comes in.

Of course, when you're at states of very high density,

you can no longer deal with gravitation in isolation,

while the other forces of matter,

the strong nuclear forces, the weak forces of radioactive decay

and the electromagnetic forces.

Nor can you stay strictly within the realm of classical physics

and ignore the quantum ideas.

Yes, you're right.

It's ironic that Einstein, who was a founder of the quantum theory

through his discovery of the quantum of the photon,

which is the particle of light,

never felt comfortable, never felt satisfied

with that theory because of the element of uncertainty,

the element of chance that it brings in

to a description of the behavior of particles.

Apprehending more than I could possibly comprehend,

I listened like a child allowed to stay up late

to ideas that might surpass Einstein's.

On a theoretical front here, I might say that

it seems to me we're no closer to knowing where we're going.

They are the very beginnings of efforts

to make a super gravity theory,

a quantum theory that embraces gravity and the other forces of matter

that are all unified together in this great dream, the grand synthesis

that Einstein spent 30 years, the last 30 years of his life

trying to create and failed.

That in alone is a measure, a statement of how difficult the problem is.

When you get down to the size of an elementary particle,

the question is, does the concept of space and time

still apply at a smaller scale than this.

And I think most physicists would take the view

that it does apply and that it goes on

until you're down to a tiny fraction of the size of a particle.

But this sort of line that we're following is one which suggests

that perhaps things go wrong before that and the idea is that the point,

the concept of a point in space is not the primary concept.

This is only a mathematical artifact,

and that something a little closer to the idea

of a particle, although not actually a particle.

It's a thing that we call a twister,

which is, um... Well, it's something I couldn't explain in detail,

but the idea is that the concept of a particle

and of space itself are both things

which emerge out of this more primitive concept.

And this is the line we've been pursuing for many years now.

And one of the great problems is to see

how to tie it in with general relativity in a very clear way.

And there are some encouraging features,

but it's certainly not finished yet.

From the minutest quantities of space

to the immensities of the universe,

the director recognized the little boy in me

and he let me drive the big telescope across the sky.

Beautiful, isn't it? USTINOV: Yes, that's fantastic.

The rings of Saturn mapped for me

the warped space surrounding the giant planet.

As I scanned the Milky Way, Harland Smith reminded me

that the stars, billions of them, and including the sun,

all circle under their mutual gravity.

And we looked beyond our own galaxy

to similar whirlpools of stars far away in space-time.

To sample a few of the billions of galaxies

prepared me for contemplating the whole of Einstein's universe

and its presumed origin in the Big Bang.

And it was brought home to me

how Einstein's discoveries about space and time,

light and matter, all connect and make a girdle of the universe.

Could we pull Einstein's ideas all together.

Energy has mass and mass has energy.

And the mass of the sun, so gigantic,

has only to be burned up a little at a time

to provide us with all the heat and light and power

that we see here on Earth.

But that mass has more gravitational pull

that pulls light, bends it, pulls other stars,

and when stars start flying apart,

in the earliest days of the universe,

that gravitational pull slows down their outward flight.

The universe comes into being out of nothingness.

Matter, light, energy. All at once.

And this matter, this light and this energy,

all expand, get more dilute.

Contract into stars, galaxies, planets

and the whole thing goes on expanding,

getting bigger, farther apart,

and that's the phase we live in now,

as these galaxies are flying apart from each other.

But then comes the moment, we believe, down the line,

when they stop flying apart and their gravitational attraction

pulls them back together again.

The whole thing contracts, energies go up once more,

we get to a gigantic, big crunch.

In its pristine form, 60 years ago,

general relativity clearly required the Big Bang

for the birth of the universe.

But that melodramatic story conflicted with the astronomy of the day,

and Einstein doctored his equations to describe a more restful universe.

"In order to arrive at this consistent view,

"we admittedly had to introduce an extension

"of the field equations of gravitation,

"which is not justified by our actual knowledge of gravitation."

"The introduction of that cosmological term

"was the biggest blunder I ever made."

"Death alone can save one from making blunders."

In fairness to Einstein, just about the time that he made this remark,

astronomers' ideas of the universe were changing rapidly.

It was discovered about that time that not only

was there our Milky Way galaxy

but there were billions of other galaxies in the universe as well.

But more surprisingly, it was found that they were

rushing away from one another at enormous speeds.

This was discovered by means of the Redshift

that occurs in the spectrum of the light due to the Doppler shift

when things are moving away from us.

I'm using this particular machine to measure the Redshift of the galaxy.

This is the galaxy and this is the spectrum of the galaxy

under the nearby object which has no Redshift at all.

When I change the magnification,

here is a spectral line due to sodium.

And in the distant galaxy, the spectrum line is shifted towards the red

and from the separation of the two lines,

one can tell that, roughly, the Redshift is about 7000 kilometers per second.

This is one of the most important kinds of

measurements that astronomers make.

We often make Redshift measurements.

It was first discovered about 50 years ago,

and this led to the idea of the expanding universe.

Later, in 1965, a radio telescope in New Jersey

revealed that the whole universe,

even the apparently empty parts of the sky,

were aglow with radio emission.

This is apparently left over from the birth of the universe.

It's this particular discovery that makes the Big Bang theory

the dominant theory of cosmology at the present time.

They represented the expanding Einsteinian universe

by a balloon studded with galaxies.

They told me that it served as a note

of the entire universe with its space curving right back on itself

because of the gravity of all its contents.

And they induced a cooperative Texan bug to travel in it.

In sympathy with that cosmic bug,

my mind voyaged among the galaxies.

I couldn't really visualize the overall warping of cosmic space. Who can?

But I sensed that gravity might indeed close up the universe,

so that if I traveled far enough,

I should find myself coming full circle back to my starting point.

The bug has nowhere to go but around.

There's no end.

Nowhere at end to the universe.

It's closed universe

but unbounded universe.

Einstein's picture was the universe is closed.

At least that's what he wrote in the last edition

of his book published in the year of his death, 1955.

Today, of course, we don't really know how the evidence is.

Whether there's enough matter

to curve the universe up into closure.

But to predict, as Einstein did,

the expansion of the universe,

and to predict it correctly, and to predict it against all expectation...

So fantastic a thing... To my idea,

is the greatest prediction that mankind has ever made.

And to my mind, gives us more faith than anything that we could have,

that some day we'll find how the universe itself came into being.

I think it's quite right to have celebrated Einstein

out here on the far frontier of Texas.

Because not only is it the site of a major observatory...

And observatories are going to be

where Einstein's theories will have to be tested in the distant future...

But also, because we have all around us still,

the great frontier, the American West.

And this symbolizes, in a way, Einstein's general relativity

which is at the far frontier of the human mind.

The most beautiful thing that we can experience is the mysterious.

It's the only source of true art and science.

And he to whom this emotion is a stranger,

he who can no longer pause in wonder or stand rapt in awe,

well, he's already half dead.

His eyes are shut.

It was Einstein's passion to understand the universe.

For him, that understanding was the only real power,

and he did more to create it than any other man who's ever lived.

Well, that's a very large claim,

and I'm sure you're right, but would you agree with that, Wall?

Yes. Astronomers use Einstein's ideas all the time,

often without remembering who thought of them.

It's the ultimate distinction in science to be part of the furniture, like Newton.

You ask me if one can eventually express

everything in scientific terms.

Yes, it's possible, but it is useless.

It is as though one were to reproduce

Beethoven's Ninth Symphony in the shape of an air pressure curve.

I propose a toast to Albert Einstein.

One of our greatest heroes.

Musicians have Mozart, Beethoven.

We have Newton and Einstein.

And it's appropriate that most of our talk

has been about his physics, but we shouldn't forget the other side,

Albert Einstein the folk hero.

Though widely honored, he was a simple man who spurned

and shunned wealth, power and status.

A refugee on the run from Hitler,

he was a dignified and gentle symbol

of scientific inspiration that was a great

particular inspiration for young refugees

and immigrants interested in science.

The reputed grandfather of the atom bomb,

he was the moral leader of the efforts

to bring that dangerous and deadly application of E=mc2 under international control.

I propose a toast to the memory of Albert Einstein.

Hear, Hear. To Albert Einstein.

The most daring proposition in relativity is that the laws of nature

must remain the same at all places and at all times,

even in galaxies so far away

that their light has traveled for thousands of millions of years to reach us.

If so, Albert Einstein's own laws of nature,

conceived with pen and paper on the planet Earth,

hold good everywhere.

"What really interests me is whether God had any choice"

"in the creation of the world."