(audience chatters)
- [Presenter] Good evening,
ladies and gentlemen.
Welcome to Cal Performances.
Tonight's performance is
brought to you in part
by our season sponsor, Wells Fargo Bank.
Please take a moment to
turn off your cell phones,
and as a reminder, the use of
recording devices and cameras
of any kind is not
permitted in the theater.
Thank you and enjoy the performance.
- Good evening.
(audience applauds)
For those of you who don't know me,
I'm Robert Birgeneau,
Chancellor of UC Berkeley,
but for tonight's event, more importantly,
professor of physics.
It's my great pleasure to welcome you
to the J. Robert Oppenheimer
Lecture in Physics.
Berkeley has a long tradition
of being a world-leading
center of scholarly activity
and of bringing to campus
the very finest minds
to address us in a public forum
on great intellectual challenges.
It is this Berkeley tradition
of great learning and public service
that the Department of Physics
has arranged for tonight's lecture
to be given by world-renowned
scholar Stephen Hawking.
Professor Hawking has extracted,
has, pardon me, attracted, not,
he's also extracted
great physics, but he's,
(audience laughs)
attracted extraordinary
interest from around the world
for his work on quantum
theories of the cosmos.
We here at Berkeley are no exception
to the world's fascination
with this extraordinary scholar
as witnessed not only
by the complete sellout
of Zellerbach Hall,
but also by the fact that Wheeler Hall,
where this event is simulcast,
is also completely sold
out, just extraordinary.
(audience applauds)
It is with deepest pleasure that I,
on behalf of the entire campus
and surrounding community,
welcome Professor Stephen
Hawking to Berkeley.
(audience applauds)
As many of you will know,
this year, the College
of Letters & Science
introduced On the Same Page,
a program asking all of our
freshmen to read a common book.
That book was Stephen Hawking's
and Leonard Mlodinow's
A Briefer History of Time.
Faculty and students from
many different disciplines
took part in discussing this book.
In fact, even the
chancellor, namely myself,
was invited to participate,
and last Thursday, I held
a small discussion group
with a number of our freshmen,
embarrassingly one of
whom at the age of 18
turned out to understand quantum gravity
much better than I did.
(audience laughs)
I'd now like to invite
professor Mark Richards,
the executive dean of the
College of Letters & Sciences
and dean of physical
sciences to come forward
and tell you more about
this wonderful project
and how Berkeley is a
leader in educating students
through unique opportunities
such as the Oppenheimer Lecture, Mark.
(audience applauds)
- Thank you very much,
Chancellor Birgeneau.
I can assure you that Chancellor
Birgeneau is here tonight
mainly for the physics.
I'm here as representative
of the College of Letters & Science,
and this is a very special occasion
on which we're inaugurating a new program,
as the chancellor said,
called On the Same Page.
And I want to take just a few minutes
to describe this program
because it's very relevant
to the events tonight.
Now the College of Letters & Science
is actually most of the University
of California, Berkeley.
That is, most of the faculty,
most of the students,
most of the departments you think of
like physics and math and
biology and economics,
anthropology, history, music, literature.
We teach 58 languages here
and we have 38 departments in L&S.
It's a very big place.
As you might imagine,
for an entering freshman,
can be somewhat of an
intimidating experience.
And we've been working very hard
in the College of Letters & Science
to make it feel a bit smaller
and a little bit more friendly
for the entering freshmen.
There are a number of programs
that we're very proud of,
for example, the Freshman Seminar series,
where we strive to create a
seat for every entering freshman
to have a close experience with faculty
in classes of size 15 to 20
on whimsical subjects sometimes.
Also the Discovery courses
which are our flagship breadth courses
taught by our very finest
instructors for entering freshmen.
And also undergraduate research programs
to complement this more
intimate experience
with the faculty, the great
faculty of UC Berkeley,
and our goal is also
for all undergraduates
to have this research experience.
On the Same Page is a new
program in this direction.
The idea has actually
been around for some time,
bouncing around among the L&S deans.
But last May, when Professor
Cohen was successful
in inviting Stephen Hawking to
be the Oppenheimer lecturer,
it was just too good an
opportunity to pass up.
You're all probably familiar
with Professor Hawking's
famous popular book
called A Brief History of Time.
Very widely purchased,
perhaps not as widely read or understood
in its initial formulation.
(audience laughs)
There's a new version of this book,
I happen to have a copy here,
called A Briefer History of Time,
in which Professor Hawking has teamed up
with Leonard Mlodinow,
who among other things
is writer of the Star
Trek, The Next Generation
and Feynman's Rainbow
and also happens to be a
Berkeley PhD in physics
and a resident science writer at Caltech.
Also at this time, when we were thinking
that this might be a
good book and a good way
to start the Freshman Seminar program,
one of the closest friends
of the College of Letters &
Science stepped up to the plate
as a donor and offered to
buy a copy of this book
for every freshman and
entering transfer student
at UC Berkeley this year,
and they all received this, thank you.
(audience applauds)
So this November, all of our freshmen
received a copy of this
wonderful book in their mailboxes
for light reading over their holidays.
Now On the Same Page has meanings
on at least three different levels,
the obvious meanings being on
the same page with the author,
being on the same page
with your fellow students
and your faculty colleagues,
but also on the same metaphorical page
because in future years we might well have
playwrights or composers or filmmakers
instead of just plain old book authors
to be the the feature of this program.
Now I want you all to think about
the last time you read a really great book
and then imagine that all of your friends
had just read the same
book and then imagine
that you could freely
attend discussion sessions
with world-renowned experts
on every conceivable aspect of that book
and then imagine that you also
would have the opportunity
to hear the author lecture
and to meet the author.
This is the experience
that we hope to create
for all the L&S students,
beginning with their freshman year
and continuing each year
until their graduation.
And the message is very clear.
Welcome to Berkeley, a
place of challenging ideas,
a forum for diverse ways of interpreting
and experiencing the world around us,
and also an arena in which
great universal themes
are explored and questioned.
Certainly this year's author and subject
make for a fitting beginning
for On the Same Page.
It's not too hard to be interested
in things like the origin of the universe
and the fundamental nature of time.
So I want to thank Professor Hawking
for helping us make
this a very special year
in the College of
Letters & Science at Cal.
I'm also very happy to announce
that the L&S deans have already
selected next year's book.
Are you waiting?
(audience laughs)
It's Lincoln at Gettysburg
by author Garry Wills,
his brilliant political, historical,
and literary analysis of
Lincoln's famous speech
that recast the struggle for
freedom and human dignity
at a critical moment in
our nation's history.
All of our freshmen, all of our faculty,
and hopefully our students
and our colleagues
and our friends in the community
will be on the same page
with Lincoln and Garry
Wills next September.
And this will be also co-sponsored
as an event with Cal Performances
and Zellerbach Auditorium.
So I want to close by thanking you all,
everyone here in Zellerbach,
everyone out there in Wheeler Auditorium
that is also sold out with
closed-circuit broadcast,
and everyone out there on the webcast,
for helping us inaugurate On
the Same Page this evening.
I want to thank Robert Cole,
the director of Cal Performances,
for being our partner this
year and in future years,
Marjorie Shapiro, the chair
of the physics department
and her colleagues, for
sharing Stephen Hawking
and the Oppenheimer lecturer
with us this evening,
and also special thanks
to staff members Alex
Schwartz and Mary Olmstead
who helped to make this
event possible this evening.
So without further ado, let
me introduce Marvin Cohen.
Marvin Cohen is a highly distinguished
theoretical physicist himself,
holder of the very prestigious position
of University Professor in
our physics department here,
and he will introduce
Professor Hawking, thank you.
(audience applauds)
- Thank you, Mark.
It has been a great pleasure
for me to serve on the
Oppenheimer Lecture Committee.
Since its inception in 1988, 1998,
we've been privileged to
have outstanding theorists
speaking in the series.
It started with our first
speaker who was Murray Gell-Mann.
Then we had Kip Thorne,
Freeman Dyson, Frank Yang,
Michael Fisher, our own Bruno
Zumino, Robert Laughlin,
and tonight our 10th
lecturer is Stephen Hawking.
In the early lectures, before
introducing the speaker,
I would say something about Oppenheimer
and the history of his
involvement with our department.
However in recent years,
I've just described the current events
related to Oppenheimer.
For those of you who are interested
in learning more about Oppenheimer
and the connection to Berkeley,
there is considerable
information on the web
and there are a number
of books on Oppenheimer.
In 2005, we celebrated
the World Year of Physics.
The idea was to get
everybody into physics.
And it was the 100th anniversary
of the Einstein marvelous year of 1905,
and in that year Einstein
did extraordinary work
on the sizes of molecules,
that was his thesis,
on Brownian motion, on relativity,
and that's when he wrote down
that little e equals mc squared thing.
(audience laughs)
You see it all over Telegraph on t-shirts.
(audience laughs)
And he also did his research
on the photoelectric effect,
for which he later won the Nobel Prize.
The physics community around the world
participated in many projects
particularly to try to
interest high school students
and to reach the public, so
it was a year of outreach.
And many projects were repeated
again last year in 2006,
and they've continued to 2007.
And there's been a
considerable effort worldwide
to try to maintain this
level of excitement
to see whether or not we
can get people to realize
that physicists are people too
and that it's a wonderful
field to work in,
and I view the Oppenheimer Lecture series
as part of this effort.
Now activities related to Oppenheimer
intensified during this period
and in the past few years,
and several new books
appeared about his life
and about the Manhattan Project.
A recording of a speech by Oppenheimer
just months after the
first atomic bomb test
was found by the American
Philosophical Society
in their archives,
and we had the opportunity
here in Berkeley
to hear this speech.
The San Francisco Opera
presented the first performance
of the opera Doctor Atomic
about Oppenheimer and the
first atomic bomb tests.
There were discussions
about Oppenheimer on campus,
about ethics and science
and about physics.
I participated in some of
these, and I was very impressed
by the large interest of our community.
Now one area of physics
in which Oppenheimer made
seminal contributions
is associated with objects
that later became called,
later were called black holes.
Stephen Hawking is also known
for his seminal work in this area,
and like Oppenheimer, he is widely known
by the public at large.
And the mention of his
name is also a catalyst
for initiating intellectual
and stimulating discussions.
As I indicated, we have tried
to make the series of lectures
exciting and accessible
despite the technical
nature of the lectures.
There were talks on
quarks and quasiparticles,
symmetries and supersymmetries,
galaxies and strings,
and these were given by gifted lecturers,
using pictures and equations
and logical arguments
in an attempt to convince
us all, you and us,
that we can understand much
of what nature is about
using these tools.
Tonight, we are very fortunate
to have the opportunity
to continue our physics outreach program
with an Oppenheimer lecture
presented by Professor Stephen Hawking,
who is at Cambridge University
where he joined the department
of applied mathematics
and theoretical physics in 1973.
Since 1979, he has held the post
of Lucasian Professor of Mathematics.
This chair was once held by Isaac Newton.
Professor Hawking has
visited Berkeley before
and he's lectured here in the past.
I first met him in 1988
when he spent time here
as a Hitchcock lecturer.
He gave talks and
interacted with many of us,
both scientifically and socially.
His technical lectures
for members of our faculty and students
on cosmology and astrophysics
were usually focused
on subjects he was currently working on
such as black holes.
In addition, we were fortunate
to have him give general public lectures
on slightly broader subjects
like tonight's lecture,
which is on a fairly broad subject,
the origin of the universe.
(audience laughs)
It's not easy for me
as Chair of the Oppenheimer Lecture series
to come up with a stimulating speaker
who can excite both an
academic and public audience.
For this reason, I was particularly happy
when Stephen agreed to come.
This was about four years ago
when we met at London's Heathrow Airport.
I was coming from Edinburgh
and he was going to China.
I was complaining about being tired
from my short flight from Edinburgh,
while he was calmly eating lunch
with the look of someone
enjoying the anticipation
of another adventure, and I felt guilty.
I was reminded of this again recently
when I read an article about
Stephen's current plans.
When I turned 65, I thought
that maybe I should retire
and play checkers in the
sun and things of this kind.
In contrast, Stephen turned 65 this year,
and he has decided to
take a zero gravity ride
out of Cape Canaveral
(audience laughs)
in a so-called vomit comet.
(audience laughs)
During his flight, he will experience
the feeling of being weightless
and also the feeling of
being very very heavy.
I understand this event
is planned for next month.
And if that isn't enough, in 2009,
Stephen plans a longer and higher flight
in a space plane being developed now
to reach an altitude of 75 miles.
When he's not on a space mission,
Stephen Hawking does research,
he lectures to broad audiences,
and he writes very popular books.
He's an inspiration to those
who feel they are challenged
and limited in some way,
and that includes all of us.
Right now, I feel more
challenged than anyone here
because I have to think of next
year's Oppenheimer Lecture.
(audience laughs)
And this is going to be a
very hard act to follow.
So please join me in
welcoming Stephen Hawking.
(audience applauds)
(machine beeps)
- [Aide] Any questions?
- [Stephen] Can you hear me?
- [Audience] Yes.
(audience laughs)
- [Stephen] According
to the Boshongo people
of Central Africa,
in the beginning, there was only darkness,
water, and the great god Bumba.
One day, Bumba, in pain
from a stomach ache,
vomited up the sun.
The sun dried up some of
the water, leaving land.
Still in pain, Bumba vomited up the moon,
the stars, and then some animals,
the leopard, the crocodile, the turtle,
and finally man.
This creation myth, like many others,
tries to answer the questions we all ask.
Why are we here?
Where did we come from?
The answer generally given
was that humans were of
comparatively recent origin
because it must have been
obvious even at early times
that the human race was improving
in knowledge and technology.
So it can't have been around that long
or it would have progressed even more.
For example, according to Bishop Usher,
the book of Genesis placed
the creation of the world
at nine in the morning
on October the 27th, 4004 BC.
(audience laughs)
On the other hand, the
physical surroundings,
like mountains and rivers,
change very little in a human lifetime.
They were therefore thought
to be a constant background
and either to have existed
forever as an empty landscape
or to have been created at
the same time as the humans.
Not everyone, however,
was happy with the idea
that the universe had a beginning.
For example, Aristotle,
the most famous of the Greek philosophers,
believed the universe had existed forever.
Something eternal is more
perfect than something created.
He suggested the reason we see progress
was that floods or other natural disasters
had repeatedly set civilization
back to the beginning.
The motivation for believing
in an eternal universe
was the desire to avoid
invoking divine intervention
to create the universe and set it going.
Conversely, those who believed
the universe had a beginning
used it as an argument
for the existence of God
as the first cause or prime
mover of the universe.
If one believed that the
universe had a beginning,
the obvious question was what
happened before the beginning?
What was God doing
before he made the world?
Was he preparing hell for
people who asked such questions?
(audience laughs)
The problem of whether or not
the universe had a beginning
was a great concern
to the German philosopher Immanuel Kant.
He felt there were logical contradictions
or antimonies either way.
If the universe had a beginning,
why did it wait an infinite
time before it began?
He called that the thesis.
On the other hand, if the
universe had existed forever,
why did it take an infinite
time to reach the present stage?
He called that the antithesis.
Both the thesis and the antithesis
depended on Kant's assumption,
along with almost everyone
else, that time was absolute.
That is to say, it went
from the infinite past
to the infinite future
independently of any universe
that might or might not
exist in this background.
This is still the picture
in the mind of many scientists today.
However in 1915, Einstein introduced
his revolutionary general
theory of relativity.
In this, space and time
were no longer absolute,
no longer a fixed background to events.
Instead, they were dynamical
quantities that were shaped
by the matter and energy in the universe.
They were defined only
within the universe,
so it made no sense
to talk of a time before
the universe began.
It would be like asking for a
point south of the South Pole.
It is not defined.
If the universe was
essentially unchanging in time,
as was generally assumed before the 1920s,
there would be no reason
that time should not be
defined arbitrarily far back.
Any so-called beginning of the
universe would be artificial
in the sense that one
could extend the history
back to earlier times.
Thus, it might be that the
universe was created last year,
but with all the memories
and physical evidence
to look like it was much older.
This raises deep philosophical questions
about the meaning of existence.
I shall deal with these
by adopting what is called
the positivist approach.
In this, the idea is that
we interpret the input
from our senses in terms of
the model we make of the world.
One cannot ask whether the
model represents reality,
only whether it works.
A model is a good model
if first it interprets a
wide range of observations
in terms of a simple and elegant model,
and second, if the model
makes definite predictions
that can be tested and possibly
falsified by observation.
In terms of the positivist approach,
one can compare two
models of the universe,
one in which the universe
was created last year
and one in which the
universe existed much longer.
The model in which the universe existed
for longer than a year
can explain things like identical twins
that have a common cause
more than a year ago.
On the other hand,
the model in which the
universe was created last year
cannot explain such events.
So the first model is better.
One cannot ask whether the
universe really existed
before a year ago or just appeared to.
In the positivist approach,
they are the same.
In an unchanging universe,
there would be no natural starting point.
The situation changed radically however
when Edwin Hubble began
to make observations
with the 100-inch telescope
on Mount Wilson in the 1920s.
Hubble found that stars
are not uniformly
distributed throughout space,
but are gathered together
in vast collections called galaxies.
By measuring the light from galaxies,
Hubble could determine their velocities.
He was expecting that as many galaxies
would be moving towards
us as were moving away.
This is what one would have in a universe
that was unchanging with time.
But to his surprise, Hubble found
that nearly all the galaxies
were moving away from us.
Moreover, the further
galaxies were from us,
the faster they were moving away.
The universe was not unchanging with time
as everyone had thought previously.
It was expanding.
The distance between distant galaxies
was increasing with time.
The expansion of the universe
was one of the most important
intellectual discoveries
of the 20th century or of any century.
It transformed the debate
about whether the
universe had a beginning.
If galaxies are moving apart now,
they must have been closer
together in the past.
If their speed had been constant,
they would all have been
on top of one another
about 15 billion years ago.
Was this the beginning of the universe?
Many scientists were still unhappy
with the universe having a beginning
because it seemed to imply
that physics broke down.
One would have to invoke
an outside agency,
which for convenience one can call God,
to determine how the universe began.
They therefore advanced theories
in which the universe was
expanding at the present time
but didn't have a beginning.
One was the steady state theory
proposed by Bondi,
Gold, and Hoyle in 1948.
In the steady state theory,
as galaxies moved apart,
the idea was that new galaxies
would form from matter
that was supposed to be
continually being created
throughout space.
The universe would have existed forever
and would have looked
the same at all times.
This last property had the great virtue,
from a positivist point of view,
of being a definite prediction
that could be tested by observation.
The Cambridge Radio Astronomy
Group, under Martin Ryle,
did a survey of weak radio
sources in the early 1960s.
These were distributed fairly
uniformly across the sky,
indicating that most of the
sources lay outside our galaxy.
The weaker sources would
be further away on average.
The steady state theory
predicted the shape
of the graph of the number of sources
against source strength.
But the observations showed
more faint sources than predicted,
indicating that the density
sources was higher in the past.
This was contrary to the basic assumption
of the steady state theory,
that everything was constant in time.
For this and other reasons,
the steady state theory was abandoned.
Another attempt to avoid the
universe having a beginning
was the suggestion
that there was a previous
contracting phase,
but because of rotation
and local irregularities,
the matter would not all
fall to the same point.
Instead, different parts of the matter
would miss each other,
and the universe would expand again
with the density remaining finite.
Two Russians, Lifshitz and Khalatnikov,
actually claimed to have proved
that a general contraction
without exact symmetry
would always lead to a bounce
with the density remaining finite.
This result was very convenient
for Marxist Leninist
dialectical materialism
because it avoided awkward questions
about the creation of the universe.
It therefore became an article of faith
for Soviet scientists.
When Lifshitz and Khalatnikov
published their claim,
I was a 21-year-old research student
looking for something to
complete my PhD thesis.
I didn't believe their so-called proof
and set out with Roger Penrose
to develop new mathematical techniques
to study the question.
We showed that the
universe couldn't bounce.
If Einstein's general theory
of relativity is correct,
there will be a singularity,
a point of infinite density
and spacetime curvature
where time has a beginning.
Observational evidence to confirm the idea
that the universe had
a very dense beginning
came in October 1965,
a few months after my
first singularity result
with the discovery of a faint background
of microwaves throughout space.
These microwaves are the same
as those in your microwave oven,
but very much less powerful.
They would heat your pizza only
to minus 271.3 degrees centigrade,
not much good for defrosting the pizza,
let alone cooking it.
(audience laughs)
You can actually observe
these microwaves yourself.
Set your television to an empty channel.
A few percent of the snow
you see on the screen
will be caused by this
background of microwaves.
The only reasonable
interpretation of the background
is that it is radiation left over
from an early very hot and dense state.
As the universe expanded, the
radiation would have cooled
until it is just the faint
remnant we observe today.
Although the singularity
theorems of Penrose and myself
predicted that the
universe had a beginning,
they didn't say how it had begun.
The equations of general relativity
would break down at the singularity.
Thus, Einstein's theory cannot predict
how the universe will begin,
but only how it will
evolve once it has begun.
There are two attitudes one can take
to the results of Penrose and myself.
One is to that God chose
how the universe began
for reasons we could not understand.
This was the view of Pope John Paul.
At a conference on
cosmology in the Vatican,
the pope told the
delegates that it was okay
to study the universe after it began,
(audience laughs)
but they should not inquire
into the beginning itself
because that was the moment of creation
and the work of God.
I was glad he didn't realize
I had presented a paper at the conference
suggesting how the universe began.
I didn't fancy the thought
of being handed over
to the Inquisition like Galileo.
(audience applauds)
The other interpretation of our results,
which is favored by most scientists,
is that it indicates that the
general theory of relativity
breaks down in the very
strong gravitational fields
in the early universe.
It has to be replaced by
a more complete theory.
One would expect this anyway
because general relativity
does not take account
of the small-scale structure of matter,
which is governed by quantum theory.
This does not matter normally
because the scale of
the universe is enormous
compared to the microscopic
scales of quantum theory.
But when the universe is the Planck size,
a billion trillion
trillionth of a centimeter,
the two scales are the same
and quantum theory has
to be taken into account.
In order to understand the
origin of the universe,
we need to combine the
general theory of relativity
with quantum theory.
The best way of doing so seems to be
to use Feynman's idea
of a sum over histories.
Richard Feynman was a colorful character
who played the bongo drums
in a strip joint in Pasadena
and was a brilliant physicist
at the California Institute of Technology.
He proposed that a system got
from a state A to a state B
by every possible path or history.
Each path or history has a
certain amplitude or intensity,
and the probability of the
system going from A to B
is given by adding up the
amplitudes for each path.
There will be a history
in which the moon is made of blue cheese,
but the amplitude is low,
which is bad news for mice.
(audience laughs)
The probability for a
state of the universe
at the present time is given
by adding up the amplitudes
for all the histories
that end with that state.
But how did the histories start?
This is the origin
question in another guise.
Does it require a creator to
decree how the universe began,
or is the initial state of the universe
determined by a law of science?
In fact, this question would arise
even if the histories of the universe
went back to the infinite past,
but it is more immediate
if the universe began
only 15 billion years ago.
The problem of what happens
at the beginning of time
is a bit like the
question of what happened
at the edge of the world
when people thought the world was flat.
Is the world a flat plate
with the sea pouring over the edge?
I have tested this experimentally.
I have been round the world
and I have not fallen off.
As we all know,
the problem of what happens
at the edge of the world
was solved when people realized
that the world was not a flat
plate, but a curved surface.
Time, however, seemed to be different.
It appeared to be separate from space
and to be like a model railway track.
If it had a beginning, there
would have to be someone
to set the trains going.
Einstein's general theory of relativity
unified time and space as spacetime,
but time was still different from space
and was like a corridor,
which either had a beginning
and end or went on forever.
However, when one combines
general relativity
with quantum theory, Jim
Hartle and I realized
that time can behave like
another direction in space
under extreme conditions.
This means one can get rid of the problem
of time having a
beginning in a similar way
in which we got rid of
the edge of the world.
Suppose the beginning of the universe
was like the South Pole of the Earth
with degrees of latitude
playing the role of time.
The universe would start as
a point at the South Pole.
As one moves north, the
circles of constant latitude,
representing the size of
the universe, would expand.
To ask what happened before
the beginning of the universe
would become a meaningless question
because there is nothing
south of the South Pole.
Time, as measured in degrees of latitude,
would have a beginning at the South Pole,
but the South Pole is
much like any other point,
at least so I have been told.
I have been to Antarctica,
but not to the South Pole.
The same laws of nature
hold at the South Pole
as in other places.
This would remove the age-old objection
to the universe having a beginning,
that it would be a place where
the normal laws broke down.
The beginning of the universe
would be governed by the laws of science.
The picture Jim Hartle and I developed
of the spontaneous quantum
creation of the universe
would be a bit like the
formation of bubbles of steam
in boiling water.
The idea is that the
most probable histories
of the universe would be like
the surfaces of the bubbles.
Many small bubbles would appear
and then disappear again.
These would correspond to mini
universes that would expand,
but would collapse again while
still of microscopic size.
They are possible alternative universes,
but they are not of much interest
since they do not last long enough
to develop galaxies and stars,
let alone intelligent life.
A few of the little bubbles, however,
with grow to a certain size
at which they are safe from recollapse.
They will continue to expand
at an ever-increasing rate
and will form the bubbles we see.
They will correspond to universes
that would start off expanding
at an ever-increasing rate.
This is called inflation,
like the way prices go up every year.
(audience laughs)
The world record for inflation
was in Germany after the first world war.
Prices rose by a factor of 10 million
in a period of 18 months,
but that was nothing compared to inflation
in the early universe.
The universe expanded
by a factor of million trillion trillion
in a tiny fraction of a second.
Unlike inflation in prices,
inflation in the early
universe was a very good thing.
It produced a very large
and uniform universe,
just as we observe.
However, it would not
be completely uniform.
In the sum over histories,
histories that are very slightly irregular
will have almost as high probabilities
as the completely uniform
and regular history.
The theory therefore predicts
that the early universe
is likely to be slightly non-uniform.
These irregularities would
produce small variations
in the intensity of the
microwave background
from different directions.
The microwave background has been observed
by the map satellite and
was found to have exactly
the kind of variations predicted.
So we know we are on the right lines.
The irregularities in the early universe
will mean that some regions
will have slightly higher
density than others.
The gravitational attraction
of the extra density
will slow the expansion of the region
and can eventually cause
the region to collapse
to form galaxies and stars.
So look well at the map
of the microwave sky.
It is the blueprint for all
the structure in the universe.
We are the product of quantum fluctuations
in the very early universe.
God really does play dice.
We have made tremendous
progress in cosmology
in the last 100 years.
The general theory of relativity
and the discovery of the
expansion of the universe
shattered the old picture
of an ever-existing
and everlasting universe.
Instead, general relativity
predicted that the universe
and time itself would
begin in the Big Bang.
It also predicted
that time would come to
an end in black holes.
The discovery of the
cosmic microwave background
and observations of black holes
support these conclusions.
This is a profound change in
our picture of the universe
and of reality itself.
Although the general theory of relativity
predicted that the universe must have come
from a period of high
curvature in the past,
it could not predict how the universe
would emerge from the Big Bang.
Thus, general relativity on its own
cannot answer the central
question in cosmology,
why is the universe the way it is?
However, if general relativity
is combined with quantum theory,
it may be possible to predict
how the universe would start.
It would initially expand
at an ever-increasing rate.
During this so-called inflationary period,
the marriage of the two theories predicted
that small fluctuations would develop
and lead to the formation
of galaxies, stars,
and all the other
structure in the universe.
This is confirmed by observations
of small non-uniformities
in the cosmic microwave background
with exactly the predicted properties.
So it seems we are on our way
to understanding the
origin of the universe,
though much more work will be needed.
A new window on the very early universe
will be opened when we can
detect gravitational waves
by accurately measuring the
distances between spacecraft.
Gravitational waves propagate freely to us
from earliest times, unimpeded
by any intervening material.
By contrast, light is scattered many times
by free electrons.
The scattering goes on until
the electrons freeze out
when the universe is 300,000 years old.
Despite having had some great successes,
not everything is solved.
We do not yet have a good
theoretical understanding
of the observations that the
expansion of the universe
is accelerating again after a
long period of slowing down.
Without such an understanding,
we cannot be sure of the
future of the universe.
Will it continue to expand forever?
Is inflation a law of nature,
or will the universe
eventually collapse again?
New observational results
and theoretical advances
are coming in rapidly.
Cosmology is a very
exciting and active subject.
We are getting close to
answering the age-old questions.
Why are we here?
Where did we come from?
Thank you for listening to me.
(audience applauds)
(audience applauds)
- Professor Hawking has agreed
to answer some questions,
and so we gathered a few of
the most popular questions
and there were five.
And my job is to read all five questions,
and he will answer all five questions
with one extended answer.
Some of these questions bear
on things he's already said,
but you have to realize
the questions were made
in advance of his talk.
Question one, do we know for
certain how the universe began?
Question two, the problem for most people
in trying to grasp all this
is if the Big Bang began at all,
what was before the Big Bang?
I'm afraid I'm gonna end up in hell.
(audience laughs)
Question three is how will
the universe end and when?
Question four, you say
your goal is simple,
a complete understanding of the universe,
and the question goes on to say
why is it as it is and
why does it exist at all?
How close are we and
can science ever answer,
and this is in big letters,
why it exists in the first place?
And question five is a very good one.
What are the pressing big
questions that are left?
Professor Hawking.
(machine beeps)
- [Stephen] We are thoroughly
sure the universe began
with a period of accelerating expansion.
This is called inflation
because the size of the universe grows
in the way prices go up in some countries.
The inflation in the early universe
is much more rapid than
our financial inflation.
The universe expanded
by a factor of a million trillion trillion
in a tiny fraction of a second.
Inflation in the size of the
universe is a good thing,
unlike inflation in prices.
It would produce a very large
and very smooth universe
with just the right amount of irregularity
to account for the formation
of galaxies, stars,
and ultimately, human beings.
How did this inflation start?
How can one describe the universe
at the beginning of time?
I now think I can show how the universe
was spontaneously created out of nothing
according to the laws of science.
The universe exists
because general relativity
and quantum theory allow
and require it to exist.
If I'm right, the
universe is self-contained
and governed by science alone.
In time, we can hope to
understand it completely.
We have long enough as the
universe should last forever.
(audience laughs)
Eternity is a very long time,
especially towards the
end, as Woody Allen said.
(audience laughs)
Thank you.
(audience applauds)
