Einstein's Universe (1979) - full transcript

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."