A Brief History of Time Page #4

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Wheeler coined, suddenly caught on.

Everybody adopted it,

and from then on...

people around the world...

in Moscow...

in America...

in England and elsewhere...

could know they were speaking

about the same thing.

And not only that,

but suddenly...

the whole range of concepts

got through to the general public...

and even science-fiction writers

all of a sudden...

could talk about it.

Tonight, my friends...

we stand on the brink

of a feat unparalleled...

in space exploration.

If the data

on my returning probe ship...

matches my computerized

calculations...

I will travel where no man

has dared to go.

Into the black hole?

In...

through...

and beyond.

Why, that's crazy!

Ha! Impossible!

As a massive star contracts...

its gravity becomes so strong...

that light can no longer escape.

The region from which

nothing can escape...

is called a black hole...

and its boundary is called

the event horizon.

One might say

of the event horizon...

what Dante said

of the entrance to hell...

"Abandon all hope,

ye who enter here."

I was once asked to actually...

be an adjudicator...

on an essay

of which the subject was...

"How to fall through

a black hole and live."

Now, the problem I had

was that I wouldn't know...

how to give out the prize...

because if I said,

"That looks like a good essay"...

the only real way

of showing this was right...

was to actually follow it,

to do the experiment and fall in.

But then, having fallen in...

I would assume taking the person

who wrote the essay with you...

the question would be,

how do you tell the rest of the world?

Do you take the prize in

that you give to them...

and what do they do with it

when they get to the center?

Believe me...

I've been waiting a long time

for someone like you...

to record this moment.

Thank you, Doctor.

Then I'm ready.

Ready to embark

on man's greatest journey.

Certainly his riskiest.

The risk is incidental

compared to...

the possibility to possess

the great truth of the unknown.

There...

long-cherished laws of nature...

simply do not apply.

They vanish.

And life?

Life?

Life forever.

If you were watching an astronaut...

foolhardy enough

to jump into a black hole...

at some time on his watch...

say, 12:
00...

he would cross

the event horizon...

and enter the black hole.

But no matter

how long you waited...

you would never see

the astronaut's watch reach 12:00.

Instead, each second

on the watch...

would appear to take

longer and longer...

until the last second

before midnight...

would take forever.

Thus, by jumping

into a black hole...

one could ensure that

one's image lasted forever.

But the picture

would fade very rapidly...

and grow so dim

that no one could see it.

As somebody disappears

into a black hole...

as seen from the outside,

it looks as though...

time actually slows down,

and the person who's moving...

at least he's thinking

he's moving...

he's perhaps talking

in his spaceship at a normal rate...

seems to slow down

and ends up being frozen...

in a particular position...

as seen by somebody

watching him from the outside.

And as seen from the outside,

you never see what happens after that.

The astronaut

wouldn't notice anything special...

when his watch

reached midnight...

and he crossed

the event horizon...

into the black hole...

until, of course,

he approached the singularity...

and was crushed into spaghetti.

One can fall

through this event horizon...

without feeling anything,

without noticing it.

After about a week of falling,

one begins to feel the pinch...

and one extends

longer and longer...

and gets slightly thinner.

And, of course,

one begins to get squeezed...

until one gets

very long and very thin...

and rather nasty.

By the end of two weeks, one's fallen right

into the center and is, of course, dead.

Before you lose sight

of the outer world...

you would see things happening

and see them at a greater rate...

so that it would look like

a firework display.

The frustration would be that,

although you would be able to see...

everything that happens in the future,

it would be going so fast...

that from a scientific point of view,

you'd have no time to analyze it.

You wouldn't be able

to take it in.

Eventually things

would be going off so fast...

and it would be so explosive

that you yourself would be...

destroyed by the explosion,

and that would be the end.

But it would be a very exciting way

to end one's life.

It would be the way

I would choose if I had the choice.

In the long history of the universe...

many stars must have burned up

their nuclear fuel...

and collapsed in on themselves.

The number of black holes

may be greater...

than the number

of visible stars...

which totals about

a hundred thousand million...

in our galaxy alone.

We also have evidence...

that there is

a very large black hole...

at the center of our own galaxy.

Friends ask me,

"Well, if a black hole is black...

how can you see it?"

And I say,

"Have you ever been to a ball?"

Have you ever watched

the young men...

dressed in their black

evening tuxedos...

and the girls

in their white dresses...

whirling around,

held in each other's arms...

and the lights turned low...

and all you can see

is the girls?

Well, the girl is

the ordinary star...

and the boy is the black hole.

You can't see the black hole

any more than you can see the boy...

but the girl going around

gives you convincing evidence...

"there must be something there

holding her in orbit."

One evening, shortly after

the birth of my daughter, Lucy...

I started to think

about black holes...

as I was getting into bed.

My disability makes this

rather a slow process...

so I had plenty of time.

Suddenly I realized...

that the area

of the event horizon...

must always increase with time.

The increase in the area

of the event horizon...

was very reminiscent

of a quantity called entropy...

which measures the degree

of disorder of a system.

It is a matter

of common experience...

that disorder tends

to increase with time...

if things are left

to themselves.

Jacob Bekenstein

came into the office one day.

"Jacob," I said...

"It always troubles me..."

when I put a hot teacup

next to a cold teacup.

I've increased, by letting heat

flow from one to the other...

the amount of disorder

in the universe.

But Jacob,

if a black hole swims by...

and I drop

both teacups into this...

"I've concealed the evidence

of my crime, have I not?"

Bekenstein's a man

of great integrity...

and he looked troubled,

and he came back to me later...

and he said,

"No, you have not..."

concealed the evidence

of your crime.

"The black hole records

what's happened to you."

Stephen Hawking

read the paper...

in which Bekenstein

announced this result...

thought it was preposterous...

and decided to prove

it was wrong.

My discoveries led

Jacob Bekenstein to suggest...

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