Stephen Hawking: Master of the Universe (2008) - full transcript
Stephen Hawking wants big answers
to big questions.
How can we understand the universe?
Is it arbitrary,
or is there a grand design?
Do we still need a God?
In 1988,
Stephen Hawking wrote an
unlikely but sensational bestseller
and became an instant celebrity.
In the book, he promised
we'd soon have the ultimate answer,
a Theory of Everything, that
explained how the universe began.
This film tells the story
of what happened next,
Hawking's 20-year struggle
to fulfill his dream,
and the extraordinary events
of his personal life.
Today, almost completely paralysed,
Hawking is tantalisingly close
to his goal.
It seems that he
and his fellow physicists
may be about to discover the secret
of the universe's beginning.
Stephen Hawking's record-breaking,
bestselling book,
A Brief History Of Time, has made
him an international celebrity.
But time is precious
to a man who clicks out sentences
at three words a minute.
Hawking was diagnosed
with motor neurone disease in 1963,
when he was a PhD student.
Doctors gave him two years to live.
For 40 years,
he's defied their predictions.
With a string of major discoveries
to his name,
he's become the world's
most famous scientist.
But being a celebrity
can have its drawbacks.
This is our fans.
Professor Hawking's fans.
Huge, incredible piles of mail.
Their imaginations
are extremely interesting.
Um...
You get people who write in
about time wormholes,
about spacecraft,
alien invaders, teleporting.
How can Professor Hawking possibly
comment on all these theories?
It's not possible.
But we do try and interest
some of the students sometimes.
Slowly, word by word,
click by click,
Hawking continues towards
a complete theory
of the fundamental processes
of our cosmos -
his Theory of Everything.
His focus now
is the very moment of creation,
the birth of our universe.
But to crack that
involves making sense
of the least understood force
in nature.
My recent experience
of weightlessness demonstrates
how well we understand
gravity on the human scale.
But we must understand gravity
as it affects individual particles.
Stephen Hawking is like
a cosmic crime scene investigator.
He's trying to understand something
that happened 13.7 billion years ago
- the Big Bang.
He's turning over all the remnants
of the explosion
and trying to fit them
back together again.
The fragments are all the matter
and forces of nature
we see around us today.
But one piece refuses to fit.
Gravity.
As human beings, we don't notice
anything strange about gravity.
But if it had been any stronger,
the universe as we know it
could never have existed.
Space would have been pulled
back in on itself,
obliterating any possibility
for planets and stars to form.
There are four forces in nature,
and gravity seems to be strangely
weaker than the other three,
as physicist Michio Kaku explains.
We see four fundamental forces
of the universe today.
Gravity, which holds the Earth,
the sun and the solar system together,
the electromagnetic force
which lights up our cities
and the internet and laser beams,
and also the two nuclear forces.
But why should there be
four fundamental forces?
We think that at the instant
of creation,
these four forces meld together
into a single force,
a super force.
At the Big Bang, everything was one.
But as the universe cooled,
four forces emerged.
Electromagnetism
and the two nuclear forces
which controlled atoms
and radioactivity
all seemed to be about
the same strength.
But the fourth force, gravity,
isn't just a bit weaker...
..it's vastly weaker.
As Professor Lisa Randall
of Harvard University demonstrates,
the electromagnetic forces
in a tiny magnet
can easily overwhelm
a mountain range.
It turns out that gravity
is many, many orders of magnitude
weaker than the other forces.
Surely gravity
doesn't seem that weak
when you're climbing up a mountain,
but with an incredibly tiny magnet,
I can pick up this paper clip
with the tiny magnet.
Is that amazing? Well,
this tiny magnet is competing
against the gravitational force
of the entire Earth.
At a fundamental level,
the force of gravity is much weaker
than the other forces.
But the problem is,
we don't understand where
this huge discrepancy comes from.
And it's this discrepancy
that's stopping Hawking
achieving his dream.
He can't create a Theory
of Everything until he can explain
what happened to gravity
at the moment of the Big Bang,
when the universe was tiny.
If we want to know what happened
when the universe began,
we have to have a theory
that can describe gravity
on a very small scale.
Hawking has struggled for decades
to solve this problem.
But now he's in a race.
The final breakthrough
may well come from someone else.
Physicists love to explain how
our universe arose and how it works.
We understand enormous amounts,
but when asked,
how did it all come to be,
we don't have one single answer, yet.
In 1988, Stephen Hawking's book,
A Brief History Of Time,
was published.
Few expected it
to be such a runaway success.
I remember reading the draft
of his book
on a train journey to Beijing,
and...well, to be honest,
when I read the book,
I certainly did not anticipate
that it was going to be
the bestseller it really was.
Overnight, Hawking became
a household name.
He was in great demand.
My first guest tonight's
a truly remarkable man,
regarded by many as a genius.
Professor Stephen Hawking.
But the pressure of fame
took its toll on his marriage.
Hawking had set out to write a book
that would carry his message
to a wider audience,
and make him a bit of cash
to help pay
for the expensive specialist care
he needed.
But he never anticipated the upset
it would cause in his personal life.
After years of caring for Hawking alone,
his wife Jane suddenly found herself
surrounded by nurses and assistants.
In an interview in 2000,
Hawking's youngest son Timothy
recalled how,
when he was nine years old,
his life was turned upside down.
It changed things completely.
Lots of new people coming into
the house, wandering in and out.
The front door was always open.
I think my mum found it hard,
because nurses started treating
our house as their own home.
You know, taking baths,
helping themselves to food,
and our house
was turning into a hospital.
It started to unsettle
the balance of the family.
Suddenly, my dad seemed
to become a lot more outgoing
with people outside the house.
He was starting to let
his hair down in some ways.
He started buying Beatles CDs
and stuff, and...
you know, having parties.
In fact, he could also,
of course, be more independent
now that he had his nurses,
and that actually made
his life easier,
which meant that he didn't have
to be with my mum 24 hours a day.
Two years after
his book's publication,
Hawking and his wife Jane
were separated.
In 1995, he married his nurse,
Elaine Mason.
I am marrying the woman I love.
And the world waited eagerly for his
much-vaunted Theory of Everything.
When the Brief History Of Time
first came out,
I think physicists
were fairly hopeful
that we would have this final
theory of everything,
maybe within just a few decades.
In 1988, there was certainly
cause for optimism.
Only gravity had to be explained
and brought into the fold.
Back in the 1970s,
Hawking had already given physics
an inkling of how it might work.
By applying quantum mechanics to the
edge of the black holes in the 1970s,
I was able to revolutionise
our understanding of them.
Hawking had proved it was possible
to unite the theories
of the very large -
stars, planets and gravity -
as originally proposed in
Einstein's Theory of Relativity,
and blend in some of the theory
of the very tiny
- of atoms, quantum mechanics.
To extend our understanding further,
we need to bring quantum mechanics
into the heart of the black hole.
By joining the theories of the large
and the tiny in a limited way,
Hawking had utterly changed
our picture of black holes.
He showed they chew up our universe,
but then explode,
giving off vast amounts
of energy and material
that eventually forms new stars.
Physicists were fascinated.
It was as if Hawking
had pulled down a wall.
Suddenly, the theorists
of the very large
and the theorists of the very small
had something to talk
to each other about.
If Hawking could find a connection
between the large and the tiny
in black holes,
there must be more.
Surely a single theory
of the universe could be found
that would include
how gravity worked,
both now,
and at the universe's beginning.
The race was on.
Hawking first became enthused
about an idea called super symmetry.
Super symmetry is based on the
notion that before the Big Bang,
when the universe was
just a single point,
everything including gravity
was merged with perfect symmetry
into one almighty super force.
We think that
at the instant of creation,
there was a super force,
a master force, a single force
that governed the properties
of this dot-like universe,
but then the universe began to expand
and the force cracked.
When the universe began,
the super force
was entirely symmetrical.
It was made of the same stuff
and it all behaved in the same way.
But then, as it expanded,
this symmetry started to break.
In the milliseconds after
the Big Bang,
forces flew off in all directions,
and the universe
became messy and uneven.
Gravity and all the other parts
of nature we see today
are the irregular,
imperfect descendents
of the original symmetry.
The theory of super symmetry
solved part of the problem
Hawking had with gravity.
Now the whole of nature,
including gravity,
could be unified with the Big Bang
by one set of equations.
But there was still a problem.
If gravity was unified with
everything else at the Big Bang,
why did it become
so very weak afterwards,
compared to the other forces?
The brightest minds, like Hawking
and Princeton professor Ed Witton,
were trying to work out how the
perfection of super symmetry broke
and ended up
as the world we see today.
Imagine sitting down
at a dinner table.
There's a glass to your left,
and there's a glass to your right.
So the arrangement of the table
has a symmetry
between left and right,
at least for the glasses.
It works fine if everybody
picks up the glass on the left,
or if everyone picks up
the glass on the right.
But a mixture,
where everybody sits down
and ends up with the glass,
breaks the symmetry.
You all pick the glass from the
left or the glass from the right.
That's an example
of what physicists call
spontaneous symmetry breaking.
And it's ubiquitous
in the real world,
both for the electrons
in a piece of iron,
and for the early universe
settling down from the Big Bang.
Explaining why the universe
had settled down the way it had
was the next problem
Hawking had to solve.
Super symmetry made lots of sense,
but there seemed to be
no particular reason
why gravity should end up so weak.
Much work still needed to be done,
but Hawking's ability to communicate
was slowing down drastically.
Today, it is a constant effort.
I'm gonna demonstrate
using a hand switch,
which is what Professor Hawking used
to use until about two years ago.
Now, he uses a menu system,
which is basically
a big screen full of words.
And when he presses the switch once,
you see this highlighted section
that goes up and down.
That's actually selecting
which part of the screen
he wants to speak from.
So if you press it
and then press it again
while it's over the top half,
it's now worked out that
he wants to say something
in the top half of the screen.
And if you press it a third time
on the right line,
it'll go along that line,
and a fourth time
lets you select a letter.
And now we've got a whole screen
full of words
beginning with Q and R,
and you can do the same thing again,
and you can select a word.
That's how he builds up a sentence
word by word,
or if he wants to speak a word
that isn't in the list,
he can do it
letter by letter as well.
Throughout the '90s,
at only four words a minute,
Hawking worked away
at the problem of gravity.
but cutting-edge physics
became increasingly dependent
on complex maths,
and Hawking was reliant
on students and colleagues
to perform computations.
Thank you very much.
The next big breakthrough
came not from Hawking,
but from a colleague
just down the corridor in Cambridge.
Professor Michael Green
is one of the big hitters
in what is known
as super string theory,
or string theory for short.
It suggests that all the particles
and forces of nature
are actually vibrating little
string-like objects,
and it seems to magically solve
the problem of gravity
that Hawking is struggling with.
One of the remarkable things
about string theory
is that it necessarily
includes gravity,
and in fact, in the earliest days
of string theory,
people were trying to formulate a theory
which did not include gravity.
They didn't understand that string
theory necessarily included gravity.
String theory is
a radically different way
of looking at our universe.
In string theory,
the entire universe,
including space, time
and even gravity,
are made up of tiny,
string-like objects
that only appear to us
to be different particles
because of the different ways
they vibrate.
LUTE STRUMMING
VIOLIN BOWING
BASS GUITAR PLUCKING
The theory suggests that our world
is just a giant mesh
of vibrating strings.
String theory brings the theories
of the very large and the very small
together beautifully.
Einstein's Theory of Relativity
describes a universe
where space bends and curls,
just like pieces of string.
Quantum mechanics says particles
are wavy and fuzzy,
a concept well-expressed
by vibrating strings.
First of all,
each vibration of the string
corresponds to a particle.
Therefore, string theory
is a quantum theory.
The jumble of particles we see
is nothing but the jumble of notes,
vibrating on a string.
But when the string moves
in space and time,
it forces space and time to curl up,
and that's why we have
precisely Einstein's equations.
Because string theory can encompass
both the tiny quantum world
and the vast world of space,
it looked like it might hold the answer
to the problem of gravity
that was so tormenting Hawking.
But it was not Hawking
who saw the possible solution.
It was that chap down the corridor,
Michael Green.
Here in Aspen, Colorado,
he and his colleague John Schwarz
finally cracked
how to make gravity fit the theory.
We were making progress, we felt,
in understanding how string theory -
or super symmetrical
string theories,
which we called
super string theory
to understand
how super string theory works.
But in the early '80s,
there was very little interest
in our work.
People were pursuing other,
somewhat related,
but other directions,
and so we were convinced that what
we were doing was quite important,
and we found it rather puzzling
that there wasn't more interest
from our colleagues.
It sort of culminated,
as I remember it,
essentially in one day,
when suddenly everything fell...
all the jigsaw, pieces of the
jigsaw puzzle came together.
And it was a really unusual
feeling for both of us.
Green and Schwarz
had made a huge breakthrough.
When the news came of the
Green-Schwarz calculation,
that was like a thunderclap,
and I was pretty sure
life would never be the same again,
at least not professional life.
Green and Schwarz's version
of string theory
not only included gravity,
but it had an amazing explanation
for why gravity is so weak now.
The reason?
The universe is made up
of 11 dimensions.
It may sound like science fiction,
but even Stephen Hawking
is prepared to admit
it might be right.
String theory is the only candidate
for a theory of everything
that has a certain symmetry
that physicists believe in,
but have not yet observed.
If it is not found,
we will have to think again.
Hawking had spent decades
leading the quest
for a theory of everything.
Now, someone else
had made the vital next step,
a great step into
a multi-dimensional universe.
During my lifetime,
we have discovered
many of the laws
that govern the universe.
But we don't yet understand
how they all fit together
or why they seem to be
finely adjusted to allow life.
Stephen Hawking has spent 45 years
trying to create
a theory of everything.
His main stumbling block
has been finding a way to explain
how gravity arose in
the white heat of the Big Bang,
and why it's so weak.
Now the elusive answer
seems to have come from elsewhere.
String theory has been
developed for 20 years now.
The latest version is called M-theory,
and almost all physicists
have huge hope for it
as a theory of everything.
But to explain gravity's weakness,
the theory has to be constructed
in nine, ten, even 11 dimensions.
It sounds like science fiction,
but string theorists believe
those extra dimensions to be real.
But what does that actually mean?
In string theory,
in addition to the three space
dimensions that we're familiar with,
sideways, up and across,
there are some extra dimensions.
In the simplest
versions of the theory,
we say there are
six extra dimensions,
which we don't see directly
in the physical world.
But nevertheless they could be there.
We can't see the extra dimensions
because they're outside
our 3D universe.
Some could be bigger
than our three dimensions.
Our entire universe could be
sitting inside a higher dimension.
We could be a bit like fish in a tank,
unaware of the world outside,
unaware of the extra dimensions.
Today we physicists
believe that we are the fish,
we spend all our lives
in three dimensions,
going forward, backward,
left, right and up and down,
not realising that there
could be other dimensions,
other universes, other ponds.
Perhaps as many as 11 dimensions
in a multiverse of universes.
Some people say, "Well, what's
at the edge of the universe?"
Is there a wall that says,
"The end of the universe,
do not pass go.
This is it folks."
The answer is no.
Think of the way Columbus
handled that question.
People said, "Columbus,
if the earth is round,
then what happens
when you fall off the edge?"
And then Columbus said,
"There is no edge,
cos you just keep on
going around in a circle."
So in two dimensions,
the earth is infinite,
you can spend all your time
going in a circle,
but in three dimensions,
the earth is a ball. It's finite.
In the same way our universe
looks infinite in three dimensions.
You can go anywhere and
there's no wall out there,
but in four dimensions, in hyperspace,
perhaps it's just a pond.
But extra dimensions do not have
to be bigger than our 3D universe.
Some could be tiny.
They could be curled up
so small we don't notice them
and that may explain
why gravity is so very weak
if Harvard professor
Lisa Randall's work is correct.
It could be that
at every point in space
there are these curled-up
extra dimensions,
looking somewhat
like these doughnuts do.
It's hard to imagine because the idea
is that if there are
two curled-up extra dimensions,
curled-up into a doughnut shape,
or we call it a torus,
there could be one of these doughnuts
at every point in space,
and it could be
a higher dimensional doughnut
which is hard to draw
and even harder to eat,
but it could be that there are even
more curled-up extra dimensions in this way,
and that,
what this illustrates is that
at every point in space
we have one of these doughnuts.
And we may not have seen
these extra dimensions
because they are too small
for us to measure.
Physicists now believe
that the tiniest, immeasurably
small points in space
may actually conceal
curved-up extra dimensions.
And that would affect
how we perceive gravity.
The idea from string theory
is that gravity is not
weirdly weak after all,
it's just that we don't
experience it fully.
It may be as strong as all
the other forces in the universe
but its effects are weakened
by having to make its way
through extra dimensions.
It's a bit like distant music,
fighting its way through
a noisy environment.
BLURRED MUFFLED MUSIC
Maybe that's why gravity is so weak
because most of gravity flies
into hyper space and disperses
and we only see the remnants.
That's why when you hear this music
it's very, very faint,
cos most of the music has gone
in a different direction
and we only hear the remnants.
Extra dimensions
act a bit like a showerhead.
Up close to the tiny extra
dimensions, gravity is strong,
but as you move away
it gets very weak, very quickly.
The final piece in
the theory of everything
is potentially hovering
over the last hole in the jigsaw.
The holy grail is within reach.
If string theory is correct,
then gravity is as strong as all
the other forces in our universe
but just feels weak
because it's fighting its way
through extra dimensions.
The trouble is nobody,
not even Hawking,
has any idea whether
any of this is true or not.
Super symmetry, string theory,
M-theory, extra dimensions
- they all exist...
on paper.
There is a little evidence
that some of the particles
predicted by super symmetry exist.
As yet, there's no hard proof
the rest are any more
than elegant theories.
But we may be standing
on the brink of a huge breakthrough.
Particle physics has made fabulous
advances in the last 20 years.
By colliding particles
at the kinds of energies
that would have been
around at the Big Bang
we have unified three of the four forces.
Gravity still refuses to be tamed
but, perhaps, not for long.
Hawking's optimism
in his professional life
is matched only by the strength
he displays in his personal life.
His second marriage,
to his nurse Elaine Mason,
started to unravel in 2004.
For the second time in
their ten-year marriage,
the police started an
investigation into alleged abuse.
Members of his nursing staff claimed
he had been virtually abandoned
outdoors to suffer sunstroke.
But claims were met with
counter-claims and withdrawals.
Throughout,
Hawking steadfastly refused
to criticise his second wife.
However, in late 2006,
Hawking filed for divorce.
Relations with his first family
now seem to have resumed on
a normal, civilised basis.
Last year,
Hawking co-authored a children's
book with his daughter Lucy.
The subject?
Physics, of course.
Using physics to explain how
our universe came about
has been Stephen Hawking's
lifelong obsession.
String theory might
be the answer he seeks
and, now, there's an outside chance
that we're about to find evidence
which will finally tell us
how the universe began.
At CERN, near Geneva in Switzerland,
they're building the biggest
experiment ever conceived.
The Large Hadron Collider
works by firing subatomic particles
in opposite directions
around a 16 mile tunnel.
They hit each other
at nearly the speed of light.
The energies involved
replicate the conditions
that were around in the early universe.
In theory, the machine
is not quite powerful enough
to explore what gravity was like
at the exact moment of the Big Bang.
Or is it?
Trying to unify gravity with
the other forces in nature
would involve an experiment with
incredibly high amounts of energy.
That would be far beyond the capacity
of any machine we have ever built
but if string theory is correct,
help may be on hand
from extra dimensions.
Amazingly, there is a possibility
that we will see
extra dimensions at CERN.
The evidence for that would be
tiny exploding black holes,
something Hawking himself predicted.
So you might ask the question,
"Is it possible that by colliding
particles in an accelerator
you could actually
produce little black holes?"
You might indeed.
And the answer is maybe.
Black holes can be any size,
even as tiny as an atom.
If gravity really is seeping into
our world through extra dimensions,
like water out of a shower head,
then incredible things
might happen at CERN.
If two particles meet right
next to the shower head
where gravity is strongest,
they might suddenly form
a mini black hole.
Once you get within the distance
associated with these extra dimensions,
then gravity goes up more fast
as distance decreases.
That's what's allowing you
to form the black holes more easily.
But Hawking's work on black holes
predicts that
they would explode very quickly.
And if the black holes were
formed in the Large Hadron Collider,
they would be very noticeable.
It's been said that they would
shine like a Christmas tree
and you would be able, not only
to detect the black holes,
you would be able to detect
the evaporation of the black hole
as predicted by Hawking.
Such a result
would be a double whammy.
For the first time ever
there would be experimental evidence
to back up Hawking's theories
about black holes.
Hawking might even get a Nobel prize,
and there would be strong evidence
that extra dimensions are real,
and that string theory
is really on the road
to a theory of everything.
You would produce extra particles,
particles that can travel
into the extra dimension.
And if we see those particles
it would be strong evidence
that extra dimensions actually exist.
The big switch on
at the Large Hadron Collider
is waited for with bated breath
by the whole of physics.
It might well fundamentally
change our view of our universe,
and shed light on the big questions
that Hawking has always
sought answers to.
For Stephen Hawking
it will be yet another reminder
of our true place in the vast cosmos.
We once thought we were at
the centre of the universe.
Then we thought the sun was.
Eventually we realised
we were just on the edge
of one of billions of galaxies.
Soon we may have to humbly accept
that our 3D universe is just one
of many multi-dimensional worlds.
So after a lifetime of trying to answer
the big questions about existence,
what does the universe
look like to Stephen Hawking?
"Can we now see where we came
from and where we are going?
I am tempted to say that science
is about ever-expanding horizons,
and that new discoveries
only help us to frame questions
in more and more accurate ways."
However, there is more
to the answer than that.
Stephen Hawking is dogged
in his determination.
He has lived 45 years longer
than his doctors predicted.
He may soon lose the use
of his vital facial muscles
and become totally paralysed.
None of it seems to phase him.
I think Stephen faces
in his thoughts
absolutely every scenario
he could possibly face.
He's not afraid of
any scenarios really.
I mean,
he's an incredibly brave person
and a huge risk taker.
You know, he's got a really...
incredible appetite for life.
Just about the only area in his life
where Hawking is a stick-in-the mud
is his world-famous voice.
It's a voice
that was cobbled together
from a 1980s
telephone answering system.
The card was actually
first designed for a sort of...
automated telephone use.
This was back in the 1980s
when that was a really,
really difficult thing to do,
and it was a cutting
edge synthesiser at the time.
'Can you finish in ten minutes?'
He could have a voice
that is more realistic,
more easy to understand,
and would use less power
and wouldn't break so often.
But the one he has
is recognised all over the world
and it's the one he wants to keep.
Thank you very much.
So what does the universe
look like to Stephen Hawking?
Remarkably
he's one of the few scientists
who've tried to do more than compute
what happened at the Big Bang,
and how it evolved afterwards.
He's proposed why the Big Bang
happened in the first place.
The universe is governed
by two kinds of laws
laws of evolution which determine
how the universe develops in time
given its state at one time,
and boundary conditions
which determine the initial state.
So far, almost all scientific effort
has been devoted
to finding laws of evolution.
But Jim Hartle and I proposed
the "no boundary condition"
as the only reasonable initial
condition for the universe.
Hawking's "no boundary condition"
is his most radical suggestion
to date.
It's a proposal, not a theory,
but it is based on strong science.
Hawking's universe
did not have a beginning,
but bizarrely
it has also not existed for ever.
The best analogy Hawking can give
is that of bubbles,
but without the man to blow them up.
Hawking thinks that
the universe spontaneously arises.
Time begins when the universe begins.
It goes on expanding, perhaps for ever.
In Hawking's mind,
our universe has no creator.
It came out of nothing
and exists all on its own.
It's the ultimate free lunch...
..although Hawking did think
of making some cash out of it.
Maybe Hartle and I should
have patented our idea,
and have charged everyone
royalties for their existence.
And interestingly,
many within physics are coming
round to Hawking's radical view.
Within the 11 dimensions
of string theory,
some scientists think our universe
could be just one of many 3D blobs.
In string theory,
it's possible that
there may exist entirely separate
giant sheets of space.
String theorists
call them membranes,
or "branes" for short
and suggest that 3D universes
can form on them.
This is where we reach
the end of our understanding.
And now, even the world's
greatest physicists start guessing.
It could be that matter,
the stuff we know about,
is actually stuck,
or lives, on the surface of a brane.
And the idea that we are stuck
to one of many membranes
raises the distinct possibility
that membranes may clash
out there in the greater universe.
If we are just one brane,
maybe there are many other branes.
There could be other branes
elsewhere which we're unaware of.
Each of these branes
would in some sense
correspond to a different universe,
and maybe these branes
would even occasionally collide.
One of the ideas that's been
proposed is that the Big Bang
explosion 14 billion years ago
originated as a collision of branes.
Not only is it possible
to make such a theory,
but it's got some
attractive features,
because it can explain
why gravity appears to be so weak.
It's all pretty heady stuff.
It's the kind of thing
physicists dream about,
and it's all a long
way off being proven.
But for Hawking it's the search
that gives his life meaning.
During my lifetime,
we have discovered many of the laws
that govern the universe,
but we don't yet understand
how they all fit together
or why they seem to be finely
adjusted to allow life.
I am confident that
we will resolve these mysteries,
and I think the years ahead
will be a golden age of discovery.
Stephen Hawking
may not have single-handedly
created a theory of everything,
but he's come within a whisker.
He may be almost
completely paralysed,
but that hasn't stopped him
being a tireless explorer.
Soon, this master of the universe
will be off on his travels again.
Hawking plans to be on the first
commercial flight out into space.
As always, there's a reason
for his adventure.
I think we are acting
with reckless indifference
to our future on planet Earth.
At the moment,
we have nowhere else to go.
But in the long run,
the human race shouldn't have
all its eggs in one basket
or on one planet.
I just hope we can avoid
dropping the basket until then.
Subtitles by Red Bee Media Ltd
to big questions.
How can we understand the universe?
Is it arbitrary,
or is there a grand design?
Do we still need a God?
In 1988,
Stephen Hawking wrote an
unlikely but sensational bestseller
and became an instant celebrity.
In the book, he promised
we'd soon have the ultimate answer,
a Theory of Everything, that
explained how the universe began.
This film tells the story
of what happened next,
Hawking's 20-year struggle
to fulfill his dream,
and the extraordinary events
of his personal life.
Today, almost completely paralysed,
Hawking is tantalisingly close
to his goal.
It seems that he
and his fellow physicists
may be about to discover the secret
of the universe's beginning.
Stephen Hawking's record-breaking,
bestselling book,
A Brief History Of Time, has made
him an international celebrity.
But time is precious
to a man who clicks out sentences
at three words a minute.
Hawking was diagnosed
with motor neurone disease in 1963,
when he was a PhD student.
Doctors gave him two years to live.
For 40 years,
he's defied their predictions.
With a string of major discoveries
to his name,
he's become the world's
most famous scientist.
But being a celebrity
can have its drawbacks.
This is our fans.
Professor Hawking's fans.
Huge, incredible piles of mail.
Their imaginations
are extremely interesting.
Um...
You get people who write in
about time wormholes,
about spacecraft,
alien invaders, teleporting.
How can Professor Hawking possibly
comment on all these theories?
It's not possible.
But we do try and interest
some of the students sometimes.
Slowly, word by word,
click by click,
Hawking continues towards
a complete theory
of the fundamental processes
of our cosmos -
his Theory of Everything.
His focus now
is the very moment of creation,
the birth of our universe.
But to crack that
involves making sense
of the least understood force
in nature.
My recent experience
of weightlessness demonstrates
how well we understand
gravity on the human scale.
But we must understand gravity
as it affects individual particles.
Stephen Hawking is like
a cosmic crime scene investigator.
He's trying to understand something
that happened 13.7 billion years ago
- the Big Bang.
He's turning over all the remnants
of the explosion
and trying to fit them
back together again.
The fragments are all the matter
and forces of nature
we see around us today.
But one piece refuses to fit.
Gravity.
As human beings, we don't notice
anything strange about gravity.
But if it had been any stronger,
the universe as we know it
could never have existed.
Space would have been pulled
back in on itself,
obliterating any possibility
for planets and stars to form.
There are four forces in nature,
and gravity seems to be strangely
weaker than the other three,
as physicist Michio Kaku explains.
We see four fundamental forces
of the universe today.
Gravity, which holds the Earth,
the sun and the solar system together,
the electromagnetic force
which lights up our cities
and the internet and laser beams,
and also the two nuclear forces.
But why should there be
four fundamental forces?
We think that at the instant
of creation,
these four forces meld together
into a single force,
a super force.
At the Big Bang, everything was one.
But as the universe cooled,
four forces emerged.
Electromagnetism
and the two nuclear forces
which controlled atoms
and radioactivity
all seemed to be about
the same strength.
But the fourth force, gravity,
isn't just a bit weaker...
..it's vastly weaker.
As Professor Lisa Randall
of Harvard University demonstrates,
the electromagnetic forces
in a tiny magnet
can easily overwhelm
a mountain range.
It turns out that gravity
is many, many orders of magnitude
weaker than the other forces.
Surely gravity
doesn't seem that weak
when you're climbing up a mountain,
but with an incredibly tiny magnet,
I can pick up this paper clip
with the tiny magnet.
Is that amazing? Well,
this tiny magnet is competing
against the gravitational force
of the entire Earth.
At a fundamental level,
the force of gravity is much weaker
than the other forces.
But the problem is,
we don't understand where
this huge discrepancy comes from.
And it's this discrepancy
that's stopping Hawking
achieving his dream.
He can't create a Theory
of Everything until he can explain
what happened to gravity
at the moment of the Big Bang,
when the universe was tiny.
If we want to know what happened
when the universe began,
we have to have a theory
that can describe gravity
on a very small scale.
Hawking has struggled for decades
to solve this problem.
But now he's in a race.
The final breakthrough
may well come from someone else.
Physicists love to explain how
our universe arose and how it works.
We understand enormous amounts,
but when asked,
how did it all come to be,
we don't have one single answer, yet.
In 1988, Stephen Hawking's book,
A Brief History Of Time,
was published.
Few expected it
to be such a runaway success.
I remember reading the draft
of his book
on a train journey to Beijing,
and...well, to be honest,
when I read the book,
I certainly did not anticipate
that it was going to be
the bestseller it really was.
Overnight, Hawking became
a household name.
He was in great demand.
My first guest tonight's
a truly remarkable man,
regarded by many as a genius.
Professor Stephen Hawking.
But the pressure of fame
took its toll on his marriage.
Hawking had set out to write a book
that would carry his message
to a wider audience,
and make him a bit of cash
to help pay
for the expensive specialist care
he needed.
But he never anticipated the upset
it would cause in his personal life.
After years of caring for Hawking alone,
his wife Jane suddenly found herself
surrounded by nurses and assistants.
In an interview in 2000,
Hawking's youngest son Timothy
recalled how,
when he was nine years old,
his life was turned upside down.
It changed things completely.
Lots of new people coming into
the house, wandering in and out.
The front door was always open.
I think my mum found it hard,
because nurses started treating
our house as their own home.
You know, taking baths,
helping themselves to food,
and our house
was turning into a hospital.
It started to unsettle
the balance of the family.
Suddenly, my dad seemed
to become a lot more outgoing
with people outside the house.
He was starting to let
his hair down in some ways.
He started buying Beatles CDs
and stuff, and...
you know, having parties.
In fact, he could also,
of course, be more independent
now that he had his nurses,
and that actually made
his life easier,
which meant that he didn't have
to be with my mum 24 hours a day.
Two years after
his book's publication,
Hawking and his wife Jane
were separated.
In 1995, he married his nurse,
Elaine Mason.
I am marrying the woman I love.
And the world waited eagerly for his
much-vaunted Theory of Everything.
When the Brief History Of Time
first came out,
I think physicists
were fairly hopeful
that we would have this final
theory of everything,
maybe within just a few decades.
In 1988, there was certainly
cause for optimism.
Only gravity had to be explained
and brought into the fold.
Back in the 1970s,
Hawking had already given physics
an inkling of how it might work.
By applying quantum mechanics to the
edge of the black holes in the 1970s,
I was able to revolutionise
our understanding of them.
Hawking had proved it was possible
to unite the theories
of the very large -
stars, planets and gravity -
as originally proposed in
Einstein's Theory of Relativity,
and blend in some of the theory
of the very tiny
- of atoms, quantum mechanics.
To extend our understanding further,
we need to bring quantum mechanics
into the heart of the black hole.
By joining the theories of the large
and the tiny in a limited way,
Hawking had utterly changed
our picture of black holes.
He showed they chew up our universe,
but then explode,
giving off vast amounts
of energy and material
that eventually forms new stars.
Physicists were fascinated.
It was as if Hawking
had pulled down a wall.
Suddenly, the theorists
of the very large
and the theorists of the very small
had something to talk
to each other about.
If Hawking could find a connection
between the large and the tiny
in black holes,
there must be more.
Surely a single theory
of the universe could be found
that would include
how gravity worked,
both now,
and at the universe's beginning.
The race was on.
Hawking first became enthused
about an idea called super symmetry.
Super symmetry is based on the
notion that before the Big Bang,
when the universe was
just a single point,
everything including gravity
was merged with perfect symmetry
into one almighty super force.
We think that
at the instant of creation,
there was a super force,
a master force, a single force
that governed the properties
of this dot-like universe,
but then the universe began to expand
and the force cracked.
When the universe began,
the super force
was entirely symmetrical.
It was made of the same stuff
and it all behaved in the same way.
But then, as it expanded,
this symmetry started to break.
In the milliseconds after
the Big Bang,
forces flew off in all directions,
and the universe
became messy and uneven.
Gravity and all the other parts
of nature we see today
are the irregular,
imperfect descendents
of the original symmetry.
The theory of super symmetry
solved part of the problem
Hawking had with gravity.
Now the whole of nature,
including gravity,
could be unified with the Big Bang
by one set of equations.
But there was still a problem.
If gravity was unified with
everything else at the Big Bang,
why did it become
so very weak afterwards,
compared to the other forces?
The brightest minds, like Hawking
and Princeton professor Ed Witton,
were trying to work out how the
perfection of super symmetry broke
and ended up
as the world we see today.
Imagine sitting down
at a dinner table.
There's a glass to your left,
and there's a glass to your right.
So the arrangement of the table
has a symmetry
between left and right,
at least for the glasses.
It works fine if everybody
picks up the glass on the left,
or if everyone picks up
the glass on the right.
But a mixture,
where everybody sits down
and ends up with the glass,
breaks the symmetry.
You all pick the glass from the
left or the glass from the right.
That's an example
of what physicists call
spontaneous symmetry breaking.
And it's ubiquitous
in the real world,
both for the electrons
in a piece of iron,
and for the early universe
settling down from the Big Bang.
Explaining why the universe
had settled down the way it had
was the next problem
Hawking had to solve.
Super symmetry made lots of sense,
but there seemed to be
no particular reason
why gravity should end up so weak.
Much work still needed to be done,
but Hawking's ability to communicate
was slowing down drastically.
Today, it is a constant effort.
I'm gonna demonstrate
using a hand switch,
which is what Professor Hawking used
to use until about two years ago.
Now, he uses a menu system,
which is basically
a big screen full of words.
And when he presses the switch once,
you see this highlighted section
that goes up and down.
That's actually selecting
which part of the screen
he wants to speak from.
So if you press it
and then press it again
while it's over the top half,
it's now worked out that
he wants to say something
in the top half of the screen.
And if you press it a third time
on the right line,
it'll go along that line,
and a fourth time
lets you select a letter.
And now we've got a whole screen
full of words
beginning with Q and R,
and you can do the same thing again,
and you can select a word.
That's how he builds up a sentence
word by word,
or if he wants to speak a word
that isn't in the list,
he can do it
letter by letter as well.
Throughout the '90s,
at only four words a minute,
Hawking worked away
at the problem of gravity.
but cutting-edge physics
became increasingly dependent
on complex maths,
and Hawking was reliant
on students and colleagues
to perform computations.
Thank you very much.
The next big breakthrough
came not from Hawking,
but from a colleague
just down the corridor in Cambridge.
Professor Michael Green
is one of the big hitters
in what is known
as super string theory,
or string theory for short.
It suggests that all the particles
and forces of nature
are actually vibrating little
string-like objects,
and it seems to magically solve
the problem of gravity
that Hawking is struggling with.
One of the remarkable things
about string theory
is that it necessarily
includes gravity,
and in fact, in the earliest days
of string theory,
people were trying to formulate a theory
which did not include gravity.
They didn't understand that string
theory necessarily included gravity.
String theory is
a radically different way
of looking at our universe.
In string theory,
the entire universe,
including space, time
and even gravity,
are made up of tiny,
string-like objects
that only appear to us
to be different particles
because of the different ways
they vibrate.
LUTE STRUMMING
VIOLIN BOWING
BASS GUITAR PLUCKING
The theory suggests that our world
is just a giant mesh
of vibrating strings.
String theory brings the theories
of the very large and the very small
together beautifully.
Einstein's Theory of Relativity
describes a universe
where space bends and curls,
just like pieces of string.
Quantum mechanics says particles
are wavy and fuzzy,
a concept well-expressed
by vibrating strings.
First of all,
each vibration of the string
corresponds to a particle.
Therefore, string theory
is a quantum theory.
The jumble of particles we see
is nothing but the jumble of notes,
vibrating on a string.
But when the string moves
in space and time,
it forces space and time to curl up,
and that's why we have
precisely Einstein's equations.
Because string theory can encompass
both the tiny quantum world
and the vast world of space,
it looked like it might hold the answer
to the problem of gravity
that was so tormenting Hawking.
But it was not Hawking
who saw the possible solution.
It was that chap down the corridor,
Michael Green.
Here in Aspen, Colorado,
he and his colleague John Schwarz
finally cracked
how to make gravity fit the theory.
We were making progress, we felt,
in understanding how string theory -
or super symmetrical
string theories,
which we called
super string theory
to understand
how super string theory works.
But in the early '80s,
there was very little interest
in our work.
People were pursuing other,
somewhat related,
but other directions,
and so we were convinced that what
we were doing was quite important,
and we found it rather puzzling
that there wasn't more interest
from our colleagues.
It sort of culminated,
as I remember it,
essentially in one day,
when suddenly everything fell...
all the jigsaw, pieces of the
jigsaw puzzle came together.
And it was a really unusual
feeling for both of us.
Green and Schwarz
had made a huge breakthrough.
When the news came of the
Green-Schwarz calculation,
that was like a thunderclap,
and I was pretty sure
life would never be the same again,
at least not professional life.
Green and Schwarz's version
of string theory
not only included gravity,
but it had an amazing explanation
for why gravity is so weak now.
The reason?
The universe is made up
of 11 dimensions.
It may sound like science fiction,
but even Stephen Hawking
is prepared to admit
it might be right.
String theory is the only candidate
for a theory of everything
that has a certain symmetry
that physicists believe in,
but have not yet observed.
If it is not found,
we will have to think again.
Hawking had spent decades
leading the quest
for a theory of everything.
Now, someone else
had made the vital next step,
a great step into
a multi-dimensional universe.
During my lifetime,
we have discovered
many of the laws
that govern the universe.
But we don't yet understand
how they all fit together
or why they seem to be
finely adjusted to allow life.
Stephen Hawking has spent 45 years
trying to create
a theory of everything.
His main stumbling block
has been finding a way to explain
how gravity arose in
the white heat of the Big Bang,
and why it's so weak.
Now the elusive answer
seems to have come from elsewhere.
String theory has been
developed for 20 years now.
The latest version is called M-theory,
and almost all physicists
have huge hope for it
as a theory of everything.
But to explain gravity's weakness,
the theory has to be constructed
in nine, ten, even 11 dimensions.
It sounds like science fiction,
but string theorists believe
those extra dimensions to be real.
But what does that actually mean?
In string theory,
in addition to the three space
dimensions that we're familiar with,
sideways, up and across,
there are some extra dimensions.
In the simplest
versions of the theory,
we say there are
six extra dimensions,
which we don't see directly
in the physical world.
But nevertheless they could be there.
We can't see the extra dimensions
because they're outside
our 3D universe.
Some could be bigger
than our three dimensions.
Our entire universe could be
sitting inside a higher dimension.
We could be a bit like fish in a tank,
unaware of the world outside,
unaware of the extra dimensions.
Today we physicists
believe that we are the fish,
we spend all our lives
in three dimensions,
going forward, backward,
left, right and up and down,
not realising that there
could be other dimensions,
other universes, other ponds.
Perhaps as many as 11 dimensions
in a multiverse of universes.
Some people say, "Well, what's
at the edge of the universe?"
Is there a wall that says,
"The end of the universe,
do not pass go.
This is it folks."
The answer is no.
Think of the way Columbus
handled that question.
People said, "Columbus,
if the earth is round,
then what happens
when you fall off the edge?"
And then Columbus said,
"There is no edge,
cos you just keep on
going around in a circle."
So in two dimensions,
the earth is infinite,
you can spend all your time
going in a circle,
but in three dimensions,
the earth is a ball. It's finite.
In the same way our universe
looks infinite in three dimensions.
You can go anywhere and
there's no wall out there,
but in four dimensions, in hyperspace,
perhaps it's just a pond.
But extra dimensions do not have
to be bigger than our 3D universe.
Some could be tiny.
They could be curled up
so small we don't notice them
and that may explain
why gravity is so very weak
if Harvard professor
Lisa Randall's work is correct.
It could be that
at every point in space
there are these curled-up
extra dimensions,
looking somewhat
like these doughnuts do.
It's hard to imagine because the idea
is that if there are
two curled-up extra dimensions,
curled-up into a doughnut shape,
or we call it a torus,
there could be one of these doughnuts
at every point in space,
and it could be
a higher dimensional doughnut
which is hard to draw
and even harder to eat,
but it could be that there are even
more curled-up extra dimensions in this way,
and that,
what this illustrates is that
at every point in space
we have one of these doughnuts.
And we may not have seen
these extra dimensions
because they are too small
for us to measure.
Physicists now believe
that the tiniest, immeasurably
small points in space
may actually conceal
curved-up extra dimensions.
And that would affect
how we perceive gravity.
The idea from string theory
is that gravity is not
weirdly weak after all,
it's just that we don't
experience it fully.
It may be as strong as all
the other forces in the universe
but its effects are weakened
by having to make its way
through extra dimensions.
It's a bit like distant music,
fighting its way through
a noisy environment.
BLURRED MUFFLED MUSIC
Maybe that's why gravity is so weak
because most of gravity flies
into hyper space and disperses
and we only see the remnants.
That's why when you hear this music
it's very, very faint,
cos most of the music has gone
in a different direction
and we only hear the remnants.
Extra dimensions
act a bit like a showerhead.
Up close to the tiny extra
dimensions, gravity is strong,
but as you move away
it gets very weak, very quickly.
The final piece in
the theory of everything
is potentially hovering
over the last hole in the jigsaw.
The holy grail is within reach.
If string theory is correct,
then gravity is as strong as all
the other forces in our universe
but just feels weak
because it's fighting its way
through extra dimensions.
The trouble is nobody,
not even Hawking,
has any idea whether
any of this is true or not.
Super symmetry, string theory,
M-theory, extra dimensions
- they all exist...
on paper.
There is a little evidence
that some of the particles
predicted by super symmetry exist.
As yet, there's no hard proof
the rest are any more
than elegant theories.
But we may be standing
on the brink of a huge breakthrough.
Particle physics has made fabulous
advances in the last 20 years.
By colliding particles
at the kinds of energies
that would have been
around at the Big Bang
we have unified three of the four forces.
Gravity still refuses to be tamed
but, perhaps, not for long.
Hawking's optimism
in his professional life
is matched only by the strength
he displays in his personal life.
His second marriage,
to his nurse Elaine Mason,
started to unravel in 2004.
For the second time in
their ten-year marriage,
the police started an
investigation into alleged abuse.
Members of his nursing staff claimed
he had been virtually abandoned
outdoors to suffer sunstroke.
But claims were met with
counter-claims and withdrawals.
Throughout,
Hawking steadfastly refused
to criticise his second wife.
However, in late 2006,
Hawking filed for divorce.
Relations with his first family
now seem to have resumed on
a normal, civilised basis.
Last year,
Hawking co-authored a children's
book with his daughter Lucy.
The subject?
Physics, of course.
Using physics to explain how
our universe came about
has been Stephen Hawking's
lifelong obsession.
String theory might
be the answer he seeks
and, now, there's an outside chance
that we're about to find evidence
which will finally tell us
how the universe began.
At CERN, near Geneva in Switzerland,
they're building the biggest
experiment ever conceived.
The Large Hadron Collider
works by firing subatomic particles
in opposite directions
around a 16 mile tunnel.
They hit each other
at nearly the speed of light.
The energies involved
replicate the conditions
that were around in the early universe.
In theory, the machine
is not quite powerful enough
to explore what gravity was like
at the exact moment of the Big Bang.
Or is it?
Trying to unify gravity with
the other forces in nature
would involve an experiment with
incredibly high amounts of energy.
That would be far beyond the capacity
of any machine we have ever built
but if string theory is correct,
help may be on hand
from extra dimensions.
Amazingly, there is a possibility
that we will see
extra dimensions at CERN.
The evidence for that would be
tiny exploding black holes,
something Hawking himself predicted.
So you might ask the question,
"Is it possible that by colliding
particles in an accelerator
you could actually
produce little black holes?"
You might indeed.
And the answer is maybe.
Black holes can be any size,
even as tiny as an atom.
If gravity really is seeping into
our world through extra dimensions,
like water out of a shower head,
then incredible things
might happen at CERN.
If two particles meet right
next to the shower head
where gravity is strongest,
they might suddenly form
a mini black hole.
Once you get within the distance
associated with these extra dimensions,
then gravity goes up more fast
as distance decreases.
That's what's allowing you
to form the black holes more easily.
But Hawking's work on black holes
predicts that
they would explode very quickly.
And if the black holes were
formed in the Large Hadron Collider,
they would be very noticeable.
It's been said that they would
shine like a Christmas tree
and you would be able, not only
to detect the black holes,
you would be able to detect
the evaporation of the black hole
as predicted by Hawking.
Such a result
would be a double whammy.
For the first time ever
there would be experimental evidence
to back up Hawking's theories
about black holes.
Hawking might even get a Nobel prize,
and there would be strong evidence
that extra dimensions are real,
and that string theory
is really on the road
to a theory of everything.
You would produce extra particles,
particles that can travel
into the extra dimension.
And if we see those particles
it would be strong evidence
that extra dimensions actually exist.
The big switch on
at the Large Hadron Collider
is waited for with bated breath
by the whole of physics.
It might well fundamentally
change our view of our universe,
and shed light on the big questions
that Hawking has always
sought answers to.
For Stephen Hawking
it will be yet another reminder
of our true place in the vast cosmos.
We once thought we were at
the centre of the universe.
Then we thought the sun was.
Eventually we realised
we were just on the edge
of one of billions of galaxies.
Soon we may have to humbly accept
that our 3D universe is just one
of many multi-dimensional worlds.
So after a lifetime of trying to answer
the big questions about existence,
what does the universe
look like to Stephen Hawking?
"Can we now see where we came
from and where we are going?
I am tempted to say that science
is about ever-expanding horizons,
and that new discoveries
only help us to frame questions
in more and more accurate ways."
However, there is more
to the answer than that.
Stephen Hawking is dogged
in his determination.
He has lived 45 years longer
than his doctors predicted.
He may soon lose the use
of his vital facial muscles
and become totally paralysed.
None of it seems to phase him.
I think Stephen faces
in his thoughts
absolutely every scenario
he could possibly face.
He's not afraid of
any scenarios really.
I mean,
he's an incredibly brave person
and a huge risk taker.
You know, he's got a really...
incredible appetite for life.
Just about the only area in his life
where Hawking is a stick-in-the mud
is his world-famous voice.
It's a voice
that was cobbled together
from a 1980s
telephone answering system.
The card was actually
first designed for a sort of...
automated telephone use.
This was back in the 1980s
when that was a really,
really difficult thing to do,
and it was a cutting
edge synthesiser at the time.
'Can you finish in ten minutes?'
He could have a voice
that is more realistic,
more easy to understand,
and would use less power
and wouldn't break so often.
But the one he has
is recognised all over the world
and it's the one he wants to keep.
Thank you very much.
So what does the universe
look like to Stephen Hawking?
Remarkably
he's one of the few scientists
who've tried to do more than compute
what happened at the Big Bang,
and how it evolved afterwards.
He's proposed why the Big Bang
happened in the first place.
The universe is governed
by two kinds of laws
laws of evolution which determine
how the universe develops in time
given its state at one time,
and boundary conditions
which determine the initial state.
So far, almost all scientific effort
has been devoted
to finding laws of evolution.
But Jim Hartle and I proposed
the "no boundary condition"
as the only reasonable initial
condition for the universe.
Hawking's "no boundary condition"
is his most radical suggestion
to date.
It's a proposal, not a theory,
but it is based on strong science.
Hawking's universe
did not have a beginning,
but bizarrely
it has also not existed for ever.
The best analogy Hawking can give
is that of bubbles,
but without the man to blow them up.
Hawking thinks that
the universe spontaneously arises.
Time begins when the universe begins.
It goes on expanding, perhaps for ever.
In Hawking's mind,
our universe has no creator.
It came out of nothing
and exists all on its own.
It's the ultimate free lunch...
..although Hawking did think
of making some cash out of it.
Maybe Hartle and I should
have patented our idea,
and have charged everyone
royalties for their existence.
And interestingly,
many within physics are coming
round to Hawking's radical view.
Within the 11 dimensions
of string theory,
some scientists think our universe
could be just one of many 3D blobs.
In string theory,
it's possible that
there may exist entirely separate
giant sheets of space.
String theorists
call them membranes,
or "branes" for short
and suggest that 3D universes
can form on them.
This is where we reach
the end of our understanding.
And now, even the world's
greatest physicists start guessing.
It could be that matter,
the stuff we know about,
is actually stuck,
or lives, on the surface of a brane.
And the idea that we are stuck
to one of many membranes
raises the distinct possibility
that membranes may clash
out there in the greater universe.
If we are just one brane,
maybe there are many other branes.
There could be other branes
elsewhere which we're unaware of.
Each of these branes
would in some sense
correspond to a different universe,
and maybe these branes
would even occasionally collide.
One of the ideas that's been
proposed is that the Big Bang
explosion 14 billion years ago
originated as a collision of branes.
Not only is it possible
to make such a theory,
but it's got some
attractive features,
because it can explain
why gravity appears to be so weak.
It's all pretty heady stuff.
It's the kind of thing
physicists dream about,
and it's all a long
way off being proven.
But for Hawking it's the search
that gives his life meaning.
During my lifetime,
we have discovered many of the laws
that govern the universe,
but we don't yet understand
how they all fit together
or why they seem to be finely
adjusted to allow life.
I am confident that
we will resolve these mysteries,
and I think the years ahead
will be a golden age of discovery.
Stephen Hawking
may not have single-handedly
created a theory of everything,
but he's come within a whisker.
He may be almost
completely paralysed,
but that hasn't stopped him
being a tireless explorer.
Soon, this master of the universe
will be off on his travels again.
Hawking plans to be on the first
commercial flight out into space.
As always, there's a reason
for his adventure.
I think we are acting
with reckless indifference
to our future on planet Earth.
At the moment,
we have nowhere else to go.
But in the long run,
the human race shouldn't have
all its eggs in one basket
or on one planet.
I just hope we can avoid
dropping the basket until then.
Subtitles by Red Bee Media Ltd