A Brief History of Time Page #5

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that the area

of the event horizon...

actually was the entropy

of a black hole.

But there was one fatal flaw...

in Bekenstein's idea:

If black holes

have an entropy...

they ought to have

a temperature.

And if they have

a temperature...

they ought

to give off radiation.

But how could they

give off radiation...

if nothing can escape

from a black hole?

As it turned out...

Bekenstein

was basically correct...

though in a manner

far more surprising...

than he or anyone else

had expected.

As he gradually lost

the use of his hands...

he had to start developing...

carefully choosing

research projects...

that could be tackled

and solved...

through geometrical arguments

that he could do pictorially in his head.

And he developed a very powerful

set of tools nobody else really had.

So in some sense,

when you lose one set of tools...

you may develop other tools,

but the new tools...

are amenable to different kinds

of problems than the old tools.

And if you're the only master

in the world of these new tools...

that means certain kinds of problems

you can solve and nobody else can.

My work up to 1973...

was in general relativity...

and was summarized in a book

I wrote with George Ellis called...

The Large Scale Structure

of Space-Time.

Even then, it was difficult

for me to write things down...

so I tended to think

in pictures and diagrams...

that I could visualize

in my head.

I remember

visiting Stephen and Jane...

at their home in Cambridge.

After supper in the evening...

when it was time

for Stephen to go to bed...

Jane insisted and Stephen acquiesced...

I guess this was standard...

that Stephen make his way up...

I've forgotten whether it was

one flight of stairs or two... alone...

and this was a period

when he could no longer walk.

The way he got up the stairs was,

he grabbed hold of the pillars...

that support the banister

and pulled him up with the strength...

pulled himself up the stairs

with the strength of his own arms...

dragging himself up...

from the ground floor

up to the second story...

in a long, arduous effort.

Jane explained that...

this was an important part

of his physical therapy...

to maintain his coordination...

and strength

as long as possible.

At first it was

sort of heartrending...

to watch what appeared to be the agony

of pulling himself up the stairs...

until I understood

it's just part of life...

pulling himself up

the stairs like that.

General relativity

is what is called...

a classical theory.

It predicts

a single definite path...

for each particle.

But according

to quantum mechanics...

there is an element

of chance or uncertainty.

A particle does not have...

just a single path

through space and time.

Instead, there is

an uncertainty principle...

according to which

both the exact position...

and velocity of a particle

can never be known.

I began investigating...

the effect quantum mechanics

might have...

on particles near a black hole.

I found that particles

could escape...

from a black hole...

that black holes

are not completely black.

At first I didn't believe it.

But when I redid

the calculations...

I couldn't get

the effect to go away.

I met Martin Rees, and he was

shaking with excitement...

and he said, "Have you heard?

Have you heard..."

what Stephen has discovered?

"Everything is different!

Everything is changed!"

I was still unsure of my discovery...

so I only told

a few colleagues...

but word soon spread.

Roger Penrose

phoned up on my birthday.

He was very excited

and went on so long...

that my birthday dinner

got quite cold.

It was a great pity,

because it was goose...

which I'm very fond of.

To me it's a miracle, 'cause it's

a complicated and messy calculation.

We can now do these things

very much better...

and it's more transparent

what happens.

But out of this messy calculation,

he showed that black holes...

aren't black with this

quantum mechanical effect.

There was a residual radiation.

Stephen came to a meeting...

and people were flabbergasted.

I remember someone saying,

"You must be wrong, Stephen.

I don't believe a word of it."

I once said

that I was unhappy...

with the explanation given in terms

of negative energy particles being created.

But I feel this is part

of the controversy of science.

You must have the give and take,

and I'm delighted to be a part of that.

That's what makes it fun.

If you all sat down and said,

"Oh, lovely"...

when you do have

niggling questions in your mind...

that's not doing

a service to science.

But I was not antagonistic

to it in any way...

except for that one time

when I questioned.

I finally convinced myself...

that black holes radiate...

when I found a mechanism

through which this could happen.

According

to quantum mechanics...

space is filled

with virtual particles...

and antiparticles...

that are constantly

materializing in pairs...

separating,

coming together again...

and annihilating each other.

In the presence

of a black hole...

one member of a pair

of virtual particles...

may fall into the hole...

leaving the other member

without a partner...

with which to annihilate.

The forsaken particle

appears to be radiation...

emitted by the black hole.

And so black holes

are not eternal.

They evaporate away

at an increasing rate...

until they vanish

in a gigantic explosion.

Quantum mechanics has allowed

particles and radiation...

to escape

from the ultimate prison...

a black hole.

Einstein never accepted

quantum mechanics...

because of its element

of chance and uncertainty.

He said,

"God does not play dice."

It seems that Einstein

was doubly wrong.

The quantum effects

of black holes...

suggest that not only

does God play dice...

he sometimes throws them...

where they cannot be seen.

He says himself...

that, uh...

he wouldn't have got to where he is

if he hadn't been ill.

And I think

that's quite possible...

because it's like Johnson said:

The knowledge you're to be

hanged in the morning...

concentrates

the mind wonderfully.

And he has concentrated

on this in a way...

I don't think he would have,

because he took a great interest...

in a lot of things in life...

and I don't know that he'd have

applied himself the same way...

if he'd been able to get around

as he used to do, so in a way...

No, I can't think anyone's lucky

having an illness like that, even so.

But it's less bad luck for him

than it would be for some people...

because he can so much

live in his head.

When I lived with the Hawking family,

I would usually get up...

around 7:
15 or 7:30

and take a shower...

and then read in my Bible some

in the morning and pray...

and then go down at 8:15

to get Stephen up.

And at breakfast I would often tell him

what I'd been reading in the Bible...

hoping that this would eventually

have some influence.

So then we would go into work...

and usually we'd go in and see

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