Nova (1974–…): Season 30, Episode 13 - The Elegant Universe: String's the Thing - full transcript
Now on NOVA,
take a thrill ride into a world
stranger than science fiction,
where you play the game
by breaking some rules,
where a new view of the universe
pushes you beyond the limits
of your wildest imagination.
This is the world
of string theory,
a way of describing every force
and all matter,
from an atom to Earth
to the end of the galaxies,
from the birth of time
to its final tick,
in a single theory...
A theory of everything.
Our guide to this brave
new world is Brian Greene,
the best-selling author
and physicist.
And no matter how many times
I come here,
I never seem to get used to it.
Can he help us solve
the greatest puzzle
of modern physics?
That our understanding
of the universe
is based on two sets of laws
that don't agree.
Resolving that contradiction
eluded even Einstein,
who made it his final quest.
After decades, we may finally be
on the verge of a breakthrough.
The solution is... strings...
Tiny bits of energy vibrating
like the strings on a cello,
a cosmic symphony
at the heart of all reality.
But it comes at a price...
Parallel universes
and 11 dimensions,
most of which you've never seen.
We really may live
in a universe with more
dimensions than meet the eye.
People who've said that there
are extra dimensions of space
have been labeled crackpots
or people who are bananas.
A mirage of science
and mathematics,
or the ultimate
theory of everything?
If string theory
fails to provide
a testable prediction,
then nobody should believe it.
Is that a theory of physics
or a philosophy?
One thing that is certain...
Is that string theory
is already showing us
that the universe
may be a lot stranger
than any of us ever imagined.
Coming up tonight...
We accidentally discovered
string theory.
The humble beginnings
of a revolutionary idea.
I was completely convinced
it was going to say,
"Susskind is the next Einstein."
This seemed crazy to people.
I was depressed, I was unhappy.
The result was
I went home and got drunk.
Obsession drives scientists
to pursue the holy grail
of physics,
but are they ready
for what they discover?
Step into the bizarre world
of "The Elegant Universe,"
right now.
Captioning sponsored by SPRINT,
MICROSOFT, the PARK FOUNDATION,
ALFRED P. SLOAN FOUNDATION,
NATIONAL SCIENCE FOUNDATION,
VOLKSWAGEN,
THE GEORGE D. SMITH FUND,
THE U.S. DEPARTMENT OF ENERGY,
THE CORPORATION
FOR PUBLIC BROADCASTING
and VIEWERS LIKE YOU
Corporate funding for NOVA
is provided by Sprint
and Microsoft.
Additional funding
is provided by:
Dedicated to education
and quality television.
Funding for "The Elegant
Universe" is provided by:
To enhance public understanding
of science and technology.
And by the National
Science Foundation,
where discoveries begin.
Additional funding is provided
by Volkswagen
and by:
and:
Major funding for NOVA
is also provided
by the Corporation
for Public Broadcasting
and by contributions
to your PBS stations from:
It's a little-known secret,
but for more than half a century
a dark cloud has been looming
over modern science.
Here's the problem.
Our understanding
of the universe is based
on two separate theories.
One is Einstein's
general theory of relativity.
That's a way of understanding
the biggest things
in the universe...
Things like stars and galaxies.
But the littlest things
in the universe...
Atoms and subatomic particles...
Play by an entirely different
set of rules
called quantum mechanics.
These two sets of rules are each
incredibly accurate
in their own domain,
but whenever
we try to combine them
to solve some of the deepest
mysteries in the universe,
disaster strikes.
Take the beginning
of the universe, the Big Bang.
At that instant, a tiny nugget
erupted violently.
Over the next 14 billion years,
the universe expanded and cooled
into the stars, galaxies
and planets we see today.
But if we run the cosmic film
in reverse,
everything that's now rushing
apart comes back together.
So the universe gets
smaller, hotter and denser
as we head back
to the beginning of time.
As we reach the Big Bang...
When the universe was
both enormously heavy
and incredibly tiny...
Our projector jams.
Our two laws of physics,
when combined, break down.
But what if we could unite
quantum mechanics
and general relativity and see
the cosmic film in its entirety?
Well, a new set of ideas
called string theory
may be able to do that,
and if it's right,
it would be one of
the biggest blockbusters
in the history of science.
Someday, string theory may be
able to explain all of nature...
From the tiniest bits of matter
to the farthest reaches
of the cosmos...
Using just one
single ingredient:
tiny, vibrating strands
of energy, called "strings."
But why do we have to rewrite
the laws of physics
to accomplish this?
Why does it matter
if the two laws that we have
are incompatible?
Well, you can think of it
like this.
Imagine you lived
in a city ruled not
by one set of traffic laws,
but by two separate sets of laws
that conflicted with each other.
As you can see, it would be
pretty confusing.
What the heck are you doing?!
To understand this place,
you'd need to find a way
to put these two conflicting
sets of laws together
into one all-encompassing set
that makes sense.
We work on the assumption
that there is a theory out there
and it's our job...
If we're sufficiently smart
and sufficiently industrious...
To figure out what it is.
We don't have a guarantee,
it isn't written in the stars
that we're going to succeed,
but in the end
we hope we will have
a single theory
that governs everything.
But before we can find
that theory,
we need to take
a fantastic journey
to see why
the two sets of laws we have
conflict with each other.
And the first stop
on this strange trip is
the realm of very large objects.
To describe the universe
on large scales,
we use one set of laws...
Einstein's general theory
of relativity,
and that's a theory
of how gravity works.
General relativity
pictures space
as sort of like a trampoline,
a smooth fabric that heavy
objects like stars and planets
can warp and stretch.
Now, according to the theory,
these warps and curves create
what we feel as gravity.
That is, the gravitational pull
that keeps the earth
in orbit around the sun
is really nothing more
than our planet following
the curves and contours
that the sun creates
in the spatial fabric.
But the smooth,
gently curving image of space
predicted by the
laws of general relativity
is not the whole story.
To understand the universe
on extremely small scales,
we have to use our other
set of laws... quantum mechanics.
And as we'll see,
quantum mechanics paints
a picture of space
so drastically different
from general relativity
that you'd think
they were describing
two completely
separate universes.
To see the conflict
between general relativity
and quantum mechanics,
we need to shrink
way, way, way down in size.
And as we leave the world
of large objects behind...
and approach
the microscopic realm,
the familiar picture of space
in which everything
behaves predictably
begins to be replaced
by a world with a structure
that is far less certain.
And if we keep shrinking,
getting billions and billions
of times smaller
than even the tiniest
bits of matter...
Atoms and the tiny particles
inside of them...
The laws of the very small,
quantum mechanics, say
that the fabric of space
becomes bumpy and chaotic.
Eventually, we reach
a world so turbulent
that it defies common sense.
Down here, space and time are
so twisted and distorted
that the conventional ideas
of left and right...
up and down...
even before and after,
break down.
There's no way to tell
for certain that I'm here...
or here...
or both places at once.
Or maybe I arrived here...
before I arrived here.
In the quantum world, you just
can't pin everything down.
It's an inherently
wild and frenetic place.
The laws in the quantum world
are very different
from the laws
that we are used to.
And is that surprising?
Why should the world of the very
small, at an atomic level...
Why should that world obey
the same kind of rules and laws
that we are used to in our world
with apples and oranges and
walking around on the street?
Why would that world
behave the same way?
The fluctuating, jittery picture
of space and time
predicted by quantum mechanics
is in direct conflict
with the smooth, orderly,
geometric model
of space and time
described by general relativity.
But we think that everything...
From the frantic dance
of subatomic particles
to the majestic swirl
of galaxies...
Should be explained by just
one grand physical principle,
one master equation.
If we can find that equation,
how the universe really works
at every time and place
will at last be revealed.
You see, what we need
is a theory
that can cope with the very tiny
and the very massive...
One that embraces both quantum
mechanics and general relativity
and never breaks down, ever.
For a physicist,
finding a theory
that unites general relativity
and quantum mechanics
is the holy grail,
because that framework
would give us a single
mathematical theory
that describes all the forces
that rule our universe.
General relativity describes the
most familiar of those forces...
Gravity.
But quantum mechanics
describes three other forces.
The strong nuclear force.
That's responsible
for gluing protons and neutrons
together inside of atoms.
Electromagnetism...
which produces
light, electricity
and magnetic attraction.
And the weak nuclear force.
That's the force responsible
for radioactive decay.
Every event in the universe,
from the splitting of an atom
to the birth of a star,
is nothing more than these four
forces interacting with matter.
Albert Einstein spent
the last 30 years of his life
searching for a way
to describe the forces of nature
in a single theory.
And now string theory
may fulfill
his dream of unification.
For centuries,
scientists have pictured
the fundamental ingredients
of nature...
Atoms and the smaller particles
inside of them...
As tiny balls or points.
But string theory proclaims
that at the heart
of every bit of matter
is a tiny, vibrating strand
of energy, called a string.
And a new breed
of scientist believes
these minuscule strings
are the key
to uniting the world of the
large and the world of the small
in a single theory.
The idea
that a scientific theory
that we already have
in our hands
could answer
the most basic questions
is extremely seductive.
For about 2,000 years,
all of our physics, essentially,
has been based on...
Essentially we were talking
about billiard balls.
The very idea of the string
is such a paradigm shift,
because instead
of billiard balls,
you have to use
little strands of spaghetti.
But not everyone is enamored
of this new theory.
So far no experiment
has been devised
that can prove
these tiny strings exist.
Let me put it bluntly:
There are physicists
and there are string theorists.
It is a new discipline,
a new, you may call it, tumor.
You can call it what you will.
They have focused
on questions which
experiment cannot address.
They will deny that...
These string theorists...
But it's a kind of physics
which is not yet testable.
It does not make predictions
that have anything to do
with experiments that
could be done in the laboratory
or with observations
that could be made
in space or from telescopes.
And I was brought up to believe,
and I still believe,
that physics is
an experimental science.
It deals with the results
to experiments
or, in the case
of astronomy, observations.
From the start,
many scientists thought
string theory was
simply too far out.
And, frankly, the strange way
the theory evolved
in a series of twists,
turns and accidents
only made it seem more unlikely.
In fact even its birth has been
turned into something of a myth,
which goes like this.
In the late 1960s,
a young Italian physicist
named Gabriele Veneziano
was searching
for a set of equations
that would explain
the strong nuclear force...
The extremely powerful glue
that holds the nucleus
of every atom together,
binding protons to neutrons.
As the story goes,
he happened on a dusty book
on the history of mathematics,
and in it he found
a 200-year-old equation,
first written down by a Swiss
mathematician, Leonhard Euler.
Veneziano was amazed to discover
that Euler's equations,
long thought to be nothing more
than a mathematical curiosity,
seemed to describe
the strong force.
He quickly published a paper
and was famous ever after
for this accidental discovery.
I see occasionally
written in books
that, uh... that this model
was invented by chance
or was, uh, found
in a math book,
and, uh, this makes me
feel pretty bad.
What is true
is that the function
was the outcome
of a long year of work,
and we accidentally
discovered string theory.
However it was discovered,
Euler's equation,
which miraculously explained
the strong force,
took on a life of its own.
This was the birth
of string theory.
Passed from colleague
to colleague,
Euler's equation ended up
on the chalkboard
in front of a young American
physicist, Leonard Susskind.
To this day
I remember the formula.
The formula was...
And I looked at it, and I said,
"You know, this is so simple
even I could figure out
what this is."
Susskind retreated
to his attic to investigate.
He understood that
this ancient formula described
the strong force mathematically.
But beneath
the abstract symbols,
he had caught a glimpse
of something new.
And I fiddled with it.
I monkeyed with it.
I sat in my attic, I think,
for two months, on and off,
but the first thing
I could see in it,
it was describing
some kind of particles
which had internal structure,
which could vibrate,
which could do things, which
wasn't just a point particle.
And I began to realize
what was being described here
was a string...
An elastic string,
like a rubber band or like
a rubber band cut in half.
And this rubber band could
not only stretch and contract
but wiggle.
And marvel of marvels,
it exactly agreed
with this formula.
I was pretty sure at that time
that I was the only one
in the world who knew this.
Susskind wrote up his discovery,
introducing the revolutionary
idea of strings.
But before his paper
could be published,
it had to be reviewed
by a panel of experts.
I was completely convinced
that when it came back,
it was going to say,
"Susskind is the next Einstein,
or maybe even the next Newton."
And it came back saying, "Nah,
this paper is not very good.
Probably shouldn't
be published."
I was truly
knocked off my chair.
I was depressed, I was unhappy.
I was saddened by it.
It made me a nervous wreck,
and, uh, the result was
I went home and got drunk.
As Susskind drowned his sorrows
over the rejection
of his far-out idea,
it appeared
string theory was dead.
Meanwhile, mainstream science
was embracing particles
as points, not strings.
For decades, physicists
had been exploring
the behavior
of microscopic particles
by smashing them together
at high speeds,
and studying those collisions.
In the showers
of particles produced,
they were discovering
that nature is far richer
than they thought.
Once a month there'd be
a discovery of a new particle...
The rho meson, the
omega particle, the B particle,
the B1 particle,
the B2 particle, phi, omega.
More letters were used
than exist in most alphabets.
It was a population explosion
of particles.
It was a time
when graduate students
would run through the halls
of a physics building
and say, "They discovered
another particle,
and it fit the theories,"
and it was all so exciting.
And in this zoo
of new particles,
scientists weren't
just discovering
building blocks of matter.
Leaving string theory
in the dust,
physicists made a startling
and strange prediction...
That the forces of nature can
also be explained by particles.
Now, this is
a really weird idea,
but it's kind of like
a game of catch
in which the players like me...
And me are particles of matter.
And the ball
we're throwing back and forth
is a particle of force.
It's called
a messenger particle.
For example,
in the case of magnetism...
The electromagnetic force...
This ball would be a photon.
The more of these
messenger particles, or photons,
that are exchanged between us,
the stronger
the magnetic attraction.
And scientists predicted
that it's this exchange
of messenger particles
that creates
what we feel as force.
Experiments confirmed
these predictions
with the discovery
of the messenger particles
for electromagnetism, the
strong force and the weak force.
And using these newly
discovered particles,
scientists were closing in
on Einstein's dream
of unifying the forces.
Particle physicists reasoned
that if we rewind
the cosmic film
to the moments
just after the Big Bang...
Some 14 billion years ago
when the universe was
trillions of degrees hotter...
The messenger particles
for electromagnetism
and the weak force
would have been
indistinguishable.
Just as cubes of ice melt
into water in the hot sun,
experiments show
that as we rewind
to the extremely hot conditions
of the Big Bang,
the weak and electromagnetic
forces meld together
and unite into a single force,
called the electroweak.
And physicists believe
that if you roll the cosmic film
back even further,
the electroweak would unite
with the strong force
in one grand superforce.
Although that has yet
to be proven,
quantum mechanics
was able to explain
how three of the forces operate
on the subatomic level.
And all of a sudden
we had a consistent theory
of elementary particle physics,
which allows us to describe
all of the interactions...
Weak, strong
and electromagnetic...
In the same language.
It all made sense, and, uh,
it's all in the textbooks.
Everything was converging
toward a simple picture
of the known particles
and forces...
A picture
which eventually became known
as the standard model.
I think I gave it that name.
Professors Sheldon Glashow,
Abdus Salam and Steven Weinberg.
The inventors
of the standard model...
Both the name and the theory...
Were the toasts
of the scientific community,
receiving Nobel Prize
after Nobel Prize.
But behind the fanfare
was a glaring omission.
Although the standard model
explained three of the forces
that rule the world
of the very small,
it did not include
the most familiar force.
Gravity.
Overshadowed
by the standard model,
string theory became
a backwater of physics.
Most people in our community
lost complete interest
in string theory.
They said, "Okay, that was
a very nice, elegant thing
but had nothing
to do with nature."
It's not taken seriously
by much of the community,
but the early pioneers
of string theory are convinced
that they can smell reality
and continue to pursue the idea.
But the more these diehards
delved into string theory,
the more problems they found.
Early string theory had
a number of problems.
One was that it predicted
a particle which we know
is unphysical.
It's what's called a tachyon...
A particle that travels
faster than light.
There was this discovery
that the theory requires
ten dimensions,
which is very disturbing,
of course,
since it's obvious that
that's more than there are.
It had this massless particle
which was not seen
in experiments.
So these theories
didn't seem to make sense.
This seemed crazy to people.
Basically, string theory
was not getting off the ground.
People threw up their hands
and said, "This can't be right."
By 1973, only a few young
physicists were still wrestling
with the obscure equations
of string theory.
One was John Schwarz,
who was busy tackling
string theory's
numerous problems,
among them, a mysterious
massless particle...
Predicted by the theory
but never seen in nature...
And an assortment of anomalies,
or mathematical inconsistencies.
We spent a long time trying
to fiddle with the theory.
We tried all sorts of ways
of making the dimension be four,
getting rid of
these massless particles
and tachyons and so on,
but it was always ugly
and unconvincing.
For four years,
Schwarz tried to tame
the unruly equations
of string theory,
changing, adjusting,
combining and recombining them
in different ways.
But nothing worked.
On the verge
of abandoning string theory,
Schwarz had a brainstorm:
Perhaps his equations
were describing gravity.
But that meant reconsidering
the size of these tiny strands
of energy.
We weren't thinking about
gravity up till that point,
but as soon as we suggested
that maybe we should be dealing
with a theory of gravity,
we had to radically change
our view
of how big these strings were.
By supposing that strings
were a hundred billion billion
times smaller than an atom,
one of the theory's vices
became a virtue.
The mysterious particle
John Schwarz had been
trying to get rid of
now appeared to be a graviton,
the long-sought-after particle
believed to transmit gravity
at the quantum level.
String theory had produced
the piece of the puzzle
missing from the standard model.
Schwarz submitted
for publication
his groundbreaking new theory
describing how gravity works
in the subatomic world.
It seemed very obvious to us
that it was right,
but there was really no reaction
in the community whatsoever.
Once again, string theory
fell on deaf ears.
But Schwarz
would not be deterred.
He had glimpsed the holy grail.
If strings described gravity
at the quantum level,
they must be the key
to unifying the four forces.
He was joined in this quest by
one of the only other scientists
willing to risk his career
on strings, Michael Green.
In a sense, I think,
we had a quiet confidence
that the string theory
was obviously correct,
and it didn't matter much
if people didn't see it
at that point.
They would see it down the line.
But for Green's confidence
to pay off,
he and Schwarz
would have to confront
the fact that
in the early 1980s,
string theory still had
fatal flaws in the math
known as "anomalies."
An anomaly is just
what it sounds like:
It's something that's strange
or out of place,
something that doesn't belong.
Now this kind of anomaly
is just weird.
But mathematical anomalies
can spell doom
for a theory of physics.
They're a little complicated,
so here's a simple example:
Let's say we have a theory
in which these two equations...
describe one physical property
of our universe.
Now, if I solve this equation
over here and I find x = 1,
and I solve this equation
over here and find x = 2,
I know my theory has anomalies
because there should
only be one value for x.
Unless I can revise my equations
to get the same value for x
on both sides,
the theory is dead.
In the early 1980s,
string theory was riddled
with mathematical anomalies
kind of like these,
although the equations
were much more complex.
The future of the
theory depended
on ridding the equations of
these fatal inconsistencies.
After Schwarz and Green battled
the anomalies in string theory
for five years, their work
culminated late one night
in the summer of 1984.
It was widely believed
that these theories
must be inconsistent
because of anomalies.
Well, for no really good reason,
I just felt
that had to be wrong,
because I... I felt string
theory has got to be right,
therefore
there can't be anomalies.
So we decided, "We got
to calculate these things."
Amazingly, it all boiled down
to a single calculation.
On one side of the blackboard,
they got 496.
And if they got the matching
number on the other side,
it would prove string theory
was free of anomalies.
I do remember, um...
a particular moment
when John Schwarz and I
were talking at the blackboard
and working out these numbers
which had to fit,
and they just had
to match exactly.
I remember joking with
John Schwarz at that moment,
because there was
thunder and lightning.
There was a big mountain storm
in Aspen at that moment,
and I remember saying
something like, you know,
"We must be getting pretty close
"because the gods
are trying to prevent us
completing this calculation."
And indeed they did match.
The matching numbers meant the
theory was free of anomalies
and it had
the mathematical depth
to encompass all four forces.
So we recognized
not only that the strings
could describe gravity
but they could also describe
the other forces,
so we spoke in terms
of unification.
And we saw this
as a possibility of realizing
the dream that Einstein had
expressed in his later years
of unifying the different forces
in some deeper framework.
We felt great.
That was
an extraordinary moment,
because we realized
that no other theory
had ever succeeded
in doing that.
But by now,
it's like crying wolf,
each time we had done something
I figured everyone's going to be
excited, and they weren't.
So I figured... well, by now
I didn't expect
much of a reaction.
But this time,
the reaction was explosive.
In less than a year, the number
of string theorists leapt
from just a handful to hundreds.
Up to that moment,
the longest talk I'd ever given
on the subject was five minutes
at some minor conference,
and then suddenly
I was invited all over the world
to give talks
and lectures and so forth.
String theory was christened
the "theory of everything."
In early fall of 1984, I came
here, to Oxford University,
to begin my graduate studies
in physics.
Some weeks after, I saw a poster
for a lecture by Michael Green.
I didn't know who he was,
but then again, I really
didn't know who anybody was.
But the title of the lecture
was something like
"The Theory of Everything."
So how could I resist?
This elegant new version
of string theory seemed capable
of describing all
the building blocks of nature.
Here's how.
Inside every grain of sand...
are billions of tiny atoms.
Every atom is made
of smaller bits of matter...
Electrons orbiting a nucleus
made of protons and neutrons...
Which are made of even smaller
bits of matter, called quarks.
But string theory says this
is not the end of the line.
It makes the astounding claim
that the particles making up
everything in the universe
are made
of even smaller ingredients...
Tiny, wiggling strands of energy
that look like strings.
Each of these strings
is unimaginably small.
In fact,
if an atom were enlarged
to the size
of the solar system...
a string would only be
as large as a tree.
And here's the key idea:
Just as different vibrational
patterns, or frequencies,
of a single cello string
create what we hear
as different musical notes,
the different ways
that strings vibrate
give particles
their unique properties,
such as mass and charge.
For example, the only difference
between the particles
making up you and me
and the particles that transmit
gravity and the other forces
is the way
these tiny strings vibrate.
Composed of an enormous number
of these oscillating strings,
the universe can be thought of
as a grand cosmic symphony.
And this elegant idea
resolves the conflict
between our jittery,
unpredictable picture of space
on the subatomic scale
and our smooth picture of space
on the large scale.
It's the jitteriness
of quantum mechanics
versus the gentleness
of Einstein's general
theory of relativity
that makes it so hard
to bridge the two,
to stitch them together.
Now, what string theory does,
it comes along
and basically calms the jitters
of quantum mechanics.
It spreads them out
by virtue of taking
the old idea of a point particle
and spreading it out
into a string.
So the jittery behavior is there
but it's just
sufficiently less violent
that quantum theory
and general relativity
stitch together perfectly
within this framework.
It's a triumph of mathematics.
With nothing but these tiny
vibrating strands of energy,
string theorists claim to be
fulfilling Einstein's dream
of uniting all forces
and all matter.
But this radical new theory
contains a chink in its armor.
No experiment can ever check up
what's going on
at the distances
that are being studied.
No observation can relate
to these tiny distances
or high energies.
That is to say, there ain't no
experiment that could be done,
nor is there any observation
that could be made
that would say
"You guys are wrong."
The theory is safe,
permanently safe.
Is that a theory of physics
or a philosophy?
I ask you.
People often criticize
string theory
for saying that
it's very far removed
from any direct
experimental test,
and it's... surely
it's not really, uh...
a branch of physics
for that reason.
And I... my response
to that is simply
that they're going
to be proved wrong.
Making string theory
even harder to prove
is that in order to work,
the complex equations require
something that sounds
like it's straight out
of science fiction:
extra dimensions of space.
We've always thought,
for centuries, that there
was only what we can see,
you know, this dimension,
that one and another one.
There was only three dimensions
of space and one of time.
And people who've said
that there were
extra dimensions of space
have been labeled
as, you know, crackpots
or people who were bananas.
Well, string theory
really predicts it.
To be taken seriously,
string theorists had to explain
how this bizarre prediction
could be true,
and they claim that the far-out
idea of extra dimensions
may be more down to earth
than you'd think.
Let me show you what I mean.
I'm off to see a guy who was
one of the first people
to think
about this strange idea.
I'm supposed to meet him
at 4:00 at his apartment
on Fifth Avenue and 93rd Street
on the second floor.
Now, in order to get
to this meeting,
I need four pieces
of information,
one for each of the three
dimensions of space...
A street, an avenue
and a floor number...
And one more for time,
the fourth dimension.
You can think about these
as the four dimensions
of common experience...
Left-right, back-forth,
up-down and time.
As it turns out,
the strange idea that there
are additional dimensions
stretches back almost a century.
Our sense that we live
in a universe
of three spatial dimensions
really seems beyond question.
But in 1919, Theodor Kaluza,
a virtually unknown
German mathematician,
had the courage
to challenge the obvious.
He suggested
that maybe, just maybe,
our universe has
one more dimension
that for some reason
we just can't see.
No, he says here,
"I like your idea."
So, why does he delay?
You see, Kaluza
had sent his idea
about an additional spatial
dimension to Albert Einstein.
And although Einstein was
initially enthusiastic,
he then seemed to waver
and for two years held up
publication of Kaluza's paper.
Eventually, Kaluza's paper
was published,
after Einstein decided extra
dimensions were his cup of tea.
Here's the idea.
In 1916, Einstein showed
that gravity is nothing
but warps and ripples
in the four familiar dimensions
of space and time.
Just three years later,
Kaluza proposed
that electromagnetism
might also be ripples.
But for that to be true,
Kaluza needed a place
for those ripples to occur.
So Kaluza proposed an additional
hidden dimension of space.
But if Kaluza was right,
where is this extra dimension?
And what would
extra dimensions look like?
Can we even begin
to imagine them?
Well, building
upon Kaluza's work,
the Swedish physicist
Oskar Klein suggested
an unusual answer.
Take a look at the cables
supporting that traffic light.
From this far away, I can't see
that they have any thickness.
Each one looks like a line,
something with only
a single dimension.
But suppose we could explore one
of these cables way up close,
like from the point of view
of an ant.
Now, a second dimension,
which wraps around the cable,
becomes visible.
From its point of view, the ant
can move forwards and backwards,
and it can also move clockwise
and counterclockwise.
So, dimensions can come
in two varieties.
They can be long and unfurled,
like the length of the cable,
but they can also be
tiny and curled up,
like the circular direction
that wraps around it.
Kaluza and Klein made
the wild suggestion
that the fabric of our universe
might be
kind of like
the surface of the cable,
having both big,
extended dimensions...
The three that we know about...
But also tiny, curled-up
dimensions, curled up so tiny,
billions of times smaller
than even a single atom,
that we just can't see them.
And so our perception
that we live in a universe
with three spatial dimensions
may not be correct after all.
We really may live in a universe
with more dimensions
than meet the eye.
So, what would these
extra dimensions look like?
Kaluza and Klein proposed
that if we could shrink down
billions of times,
we'd find one extra
tiny, curled-up dimension
located at every point in space.
And just the way an ant can
explore the circular dimension
that wraps around
a traffic-light cable,
in theory, an ant that is
billions of times smaller
could also explore this tiny,
curled-up circular dimension.
This idea that extra dimensions
exist all around us
lies at the heart
of string theory.
In fact, the mathematics
of string theory demand
not one but six
extra dimensions,
twisted and curled
into complex little shapes
that might look
something like this.
If string theory is right,
we would have to admit
that there are really
more dimensions out there,
and I find that
completely mind-blowing.
If I take the theory
as we have it now literally,
I would conclude that the
extra dimensions really exist.
They're part of nature.
When we talk
about extra dimensions,
we literally mean
extra dimensions of space
that are the same
as the dimensions of space
that we see around us.
And the only difference between
them has to do with their shape.
But how could these
tiny extra dimensions,
curled up into
such peculiar shapes,
have any effect
on our everyday world?
Well, according to string
theory, shape is everything.
Because of its shape,
a French horn can produce
dozens of different notes.
When you press one of the keys,
you change the note
because you change the shape
of the space inside the horn
where the air resonates.
And we think the curled-up
spatial dimensions
in string theory work
in a similar way.
If we could shrink down
small enough
to fly into one of these
tiny six-dimensional shapes
predicted by string theory,
we would see how
the extra dimensions
are twisted and curled back
on each other,
influencing how strings,
the fundamental ingredients
of our universe,
move and vibrate.
And this could be the key
to solving one of nature's
most profound mysteries.
You see, our universe is kind
of like a finely tuned machine.
Scientists have found that
there are about 20 numbers...
20 fundamental constants
of nature...
That give the universe the
characteristics we see today.
These are numbers like
how much an electron weighs,
the strength of gravity,
the electromagnetic force,
and the strong and weak forces.
Now, as long as we set the dials
on our universe machine
to precisely the right values
for each of these 20 numbers,
the machine produces
the universe we know and love.
But if we change the numbers
by adjusting the settings
on this machine
even a little bit,
the consequences are dramatic.
For example, if I increase
the strength of
the electromagnetic force,
atoms repel one another
more strongly,
so the nuclear furnaces that
make stars shine break down.
The stars, including our sun,
fizzle out...
and the universe as we know it
disappears.
So, what exactly in nature
sets the values of these
20 constants so precisely?
Well, the answer could be
the extra dimensions
in string theory.
That is, the tiny, curled-up
six-dimensional shapes
predicted by the theory
cause one string to vibrate
in precisely the right way
to produce what we see
as a photon
and another string to vibrate
in a different way,
producing an electron.
So according to string theory,
these minuscule
extra-dimensional shapes
really may determine
all the constants of nature,
keeping the cosmic symphony
of strings in tune.
By the mid-1980s, string theory
looked unstoppable.
But behind the scenes,
the theory was in tangles.
Over the years, string theorists
had been so successful
that they had constructed
not one but five different
versions of the theory.
Each was built on strings
and extra dimensions,
but in detail, the five theories
were not in harmony.
In some versions, strings
were open-ended strands;
in others,
they were closed loops.
At first glance,
a couple of versions even
required 26 dimensions.
All five versions
appeared equally valid,
but which one was describing
our universe?
This was kind
of an embarrassment
for string theorists,
because on the one hand,
we wanted to say
that this might be it...
The final description
of the universe.
But then in the next breath
we had to say,
"And it comes in five flavors,
five variations."
Now, there's one universe,
you expect there to be
one theory and not five.
So this is an example
where more is definitely less.
One attitude that people who
didn't like string theory
could take was
"Well, you have five theories,
so it's not unique."
This was a peculiar
state of affairs,
because we were looking just
to describe one theory of nature
and not five.
If there's five of them,
well, maybe there's...
smart enough people
would find 20 of them,
or maybe there's
an infinite number of them,
and you're back to just
searching around at random
for... for theories
of the world.
Maybe one of these
five string theories
is describing our universe.
On the other hand, which one?
And why... what are
the other ones good for?
But having five string theories,
even though it's big progress,
raises the obvious question:
If one of those theories
describes our universe,
then who lives
in the other four worlds?
String theory seemed
to be losing steam once again,
and frustrated
by a lack of progress,
many physicists
abandoned the field.
Will string theory prove
to be a theory of everything,
or will it unravel
into a theory of nothing?
On NOVA's Web site, go behind
the scenes with Brian Greene,
journey into the subatomic
world, play with strings,
picture other dimensions,
and much more.
To order this program
on VHS or DVD
or the book
The Elegant Universe,
please call WGBH
Boston Video at
1-800-255-9424.
Next time on NOVA:
Can string theory be saved?
Do we live in a world
of extra dimensions
with parallel universes
just beyond our reach?
The thrill ride continues
as Brian Greene pushes
physics to the limit
on the next episode of
"The Elegant Universe."
NOVA is a production
of WGBH Boston.
Corporate funding for NOVA
is provided by Sprint
and Microsoft.
Additional funding
is provided by:
Dedicated to education
and quality television.
Funding for "The Elegant
Universe" is provided by:
To enhance public understanding
of science and technology.
And by the National
Science Foundation,
where discoveries begin.
Additional funding is provided
by Volkswagen
and by:
and:
Major funding for NOVA
is also provided
by the Corporation
for Public Broadcasting
and by contributions
to your PBS stations from:
We are PBS.
take a thrill ride into a world
stranger than science fiction,
where you play the game
by breaking some rules,
where a new view of the universe
pushes you beyond the limits
of your wildest imagination.
This is the world
of string theory,
a way of describing every force
and all matter,
from an atom to Earth
to the end of the galaxies,
from the birth of time
to its final tick,
in a single theory...
A theory of everything.
Our guide to this brave
new world is Brian Greene,
the best-selling author
and physicist.
And no matter how many times
I come here,
I never seem to get used to it.
Can he help us solve
the greatest puzzle
of modern physics?
That our understanding
of the universe
is based on two sets of laws
that don't agree.
Resolving that contradiction
eluded even Einstein,
who made it his final quest.
After decades, we may finally be
on the verge of a breakthrough.
The solution is... strings...
Tiny bits of energy vibrating
like the strings on a cello,
a cosmic symphony
at the heart of all reality.
But it comes at a price...
Parallel universes
and 11 dimensions,
most of which you've never seen.
We really may live
in a universe with more
dimensions than meet the eye.
People who've said that there
are extra dimensions of space
have been labeled crackpots
or people who are bananas.
A mirage of science
and mathematics,
or the ultimate
theory of everything?
If string theory
fails to provide
a testable prediction,
then nobody should believe it.
Is that a theory of physics
or a philosophy?
One thing that is certain...
Is that string theory
is already showing us
that the universe
may be a lot stranger
than any of us ever imagined.
Coming up tonight...
We accidentally discovered
string theory.
The humble beginnings
of a revolutionary idea.
I was completely convinced
it was going to say,
"Susskind is the next Einstein."
This seemed crazy to people.
I was depressed, I was unhappy.
The result was
I went home and got drunk.
Obsession drives scientists
to pursue the holy grail
of physics,
but are they ready
for what they discover?
Step into the bizarre world
of "The Elegant Universe,"
right now.
Captioning sponsored by SPRINT,
MICROSOFT, the PARK FOUNDATION,
ALFRED P. SLOAN FOUNDATION,
NATIONAL SCIENCE FOUNDATION,
VOLKSWAGEN,
THE GEORGE D. SMITH FUND,
THE U.S. DEPARTMENT OF ENERGY,
THE CORPORATION
FOR PUBLIC BROADCASTING
and VIEWERS LIKE YOU
Corporate funding for NOVA
is provided by Sprint
and Microsoft.
Additional funding
is provided by:
Dedicated to education
and quality television.
Funding for "The Elegant
Universe" is provided by:
To enhance public understanding
of science and technology.
And by the National
Science Foundation,
where discoveries begin.
Additional funding is provided
by Volkswagen
and by:
and:
Major funding for NOVA
is also provided
by the Corporation
for Public Broadcasting
and by contributions
to your PBS stations from:
It's a little-known secret,
but for more than half a century
a dark cloud has been looming
over modern science.
Here's the problem.
Our understanding
of the universe is based
on two separate theories.
One is Einstein's
general theory of relativity.
That's a way of understanding
the biggest things
in the universe...
Things like stars and galaxies.
But the littlest things
in the universe...
Atoms and subatomic particles...
Play by an entirely different
set of rules
called quantum mechanics.
These two sets of rules are each
incredibly accurate
in their own domain,
but whenever
we try to combine them
to solve some of the deepest
mysteries in the universe,
disaster strikes.
Take the beginning
of the universe, the Big Bang.
At that instant, a tiny nugget
erupted violently.
Over the next 14 billion years,
the universe expanded and cooled
into the stars, galaxies
and planets we see today.
But if we run the cosmic film
in reverse,
everything that's now rushing
apart comes back together.
So the universe gets
smaller, hotter and denser
as we head back
to the beginning of time.
As we reach the Big Bang...
When the universe was
both enormously heavy
and incredibly tiny...
Our projector jams.
Our two laws of physics,
when combined, break down.
But what if we could unite
quantum mechanics
and general relativity and see
the cosmic film in its entirety?
Well, a new set of ideas
called string theory
may be able to do that,
and if it's right,
it would be one of
the biggest blockbusters
in the history of science.
Someday, string theory may be
able to explain all of nature...
From the tiniest bits of matter
to the farthest reaches
of the cosmos...
Using just one
single ingredient:
tiny, vibrating strands
of energy, called "strings."
But why do we have to rewrite
the laws of physics
to accomplish this?
Why does it matter
if the two laws that we have
are incompatible?
Well, you can think of it
like this.
Imagine you lived
in a city ruled not
by one set of traffic laws,
but by two separate sets of laws
that conflicted with each other.
As you can see, it would be
pretty confusing.
What the heck are you doing?!
To understand this place,
you'd need to find a way
to put these two conflicting
sets of laws together
into one all-encompassing set
that makes sense.
We work on the assumption
that there is a theory out there
and it's our job...
If we're sufficiently smart
and sufficiently industrious...
To figure out what it is.
We don't have a guarantee,
it isn't written in the stars
that we're going to succeed,
but in the end
we hope we will have
a single theory
that governs everything.
But before we can find
that theory,
we need to take
a fantastic journey
to see why
the two sets of laws we have
conflict with each other.
And the first stop
on this strange trip is
the realm of very large objects.
To describe the universe
on large scales,
we use one set of laws...
Einstein's general theory
of relativity,
and that's a theory
of how gravity works.
General relativity
pictures space
as sort of like a trampoline,
a smooth fabric that heavy
objects like stars and planets
can warp and stretch.
Now, according to the theory,
these warps and curves create
what we feel as gravity.
That is, the gravitational pull
that keeps the earth
in orbit around the sun
is really nothing more
than our planet following
the curves and contours
that the sun creates
in the spatial fabric.
But the smooth,
gently curving image of space
predicted by the
laws of general relativity
is not the whole story.
To understand the universe
on extremely small scales,
we have to use our other
set of laws... quantum mechanics.
And as we'll see,
quantum mechanics paints
a picture of space
so drastically different
from general relativity
that you'd think
they were describing
two completely
separate universes.
To see the conflict
between general relativity
and quantum mechanics,
we need to shrink
way, way, way down in size.
And as we leave the world
of large objects behind...
and approach
the microscopic realm,
the familiar picture of space
in which everything
behaves predictably
begins to be replaced
by a world with a structure
that is far less certain.
And if we keep shrinking,
getting billions and billions
of times smaller
than even the tiniest
bits of matter...
Atoms and the tiny particles
inside of them...
The laws of the very small,
quantum mechanics, say
that the fabric of space
becomes bumpy and chaotic.
Eventually, we reach
a world so turbulent
that it defies common sense.
Down here, space and time are
so twisted and distorted
that the conventional ideas
of left and right...
up and down...
even before and after,
break down.
There's no way to tell
for certain that I'm here...
or here...
or both places at once.
Or maybe I arrived here...
before I arrived here.
In the quantum world, you just
can't pin everything down.
It's an inherently
wild and frenetic place.
The laws in the quantum world
are very different
from the laws
that we are used to.
And is that surprising?
Why should the world of the very
small, at an atomic level...
Why should that world obey
the same kind of rules and laws
that we are used to in our world
with apples and oranges and
walking around on the street?
Why would that world
behave the same way?
The fluctuating, jittery picture
of space and time
predicted by quantum mechanics
is in direct conflict
with the smooth, orderly,
geometric model
of space and time
described by general relativity.
But we think that everything...
From the frantic dance
of subatomic particles
to the majestic swirl
of galaxies...
Should be explained by just
one grand physical principle,
one master equation.
If we can find that equation,
how the universe really works
at every time and place
will at last be revealed.
You see, what we need
is a theory
that can cope with the very tiny
and the very massive...
One that embraces both quantum
mechanics and general relativity
and never breaks down, ever.
For a physicist,
finding a theory
that unites general relativity
and quantum mechanics
is the holy grail,
because that framework
would give us a single
mathematical theory
that describes all the forces
that rule our universe.
General relativity describes the
most familiar of those forces...
Gravity.
But quantum mechanics
describes three other forces.
The strong nuclear force.
That's responsible
for gluing protons and neutrons
together inside of atoms.
Electromagnetism...
which produces
light, electricity
and magnetic attraction.
And the weak nuclear force.
That's the force responsible
for radioactive decay.
Every event in the universe,
from the splitting of an atom
to the birth of a star,
is nothing more than these four
forces interacting with matter.
Albert Einstein spent
the last 30 years of his life
searching for a way
to describe the forces of nature
in a single theory.
And now string theory
may fulfill
his dream of unification.
For centuries,
scientists have pictured
the fundamental ingredients
of nature...
Atoms and the smaller particles
inside of them...
As tiny balls or points.
But string theory proclaims
that at the heart
of every bit of matter
is a tiny, vibrating strand
of energy, called a string.
And a new breed
of scientist believes
these minuscule strings
are the key
to uniting the world of the
large and the world of the small
in a single theory.
The idea
that a scientific theory
that we already have
in our hands
could answer
the most basic questions
is extremely seductive.
For about 2,000 years,
all of our physics, essentially,
has been based on...
Essentially we were talking
about billiard balls.
The very idea of the string
is such a paradigm shift,
because instead
of billiard balls,
you have to use
little strands of spaghetti.
But not everyone is enamored
of this new theory.
So far no experiment
has been devised
that can prove
these tiny strings exist.
Let me put it bluntly:
There are physicists
and there are string theorists.
It is a new discipline,
a new, you may call it, tumor.
You can call it what you will.
They have focused
on questions which
experiment cannot address.
They will deny that...
These string theorists...
But it's a kind of physics
which is not yet testable.
It does not make predictions
that have anything to do
with experiments that
could be done in the laboratory
or with observations
that could be made
in space or from telescopes.
And I was brought up to believe,
and I still believe,
that physics is
an experimental science.
It deals with the results
to experiments
or, in the case
of astronomy, observations.
From the start,
many scientists thought
string theory was
simply too far out.
And, frankly, the strange way
the theory evolved
in a series of twists,
turns and accidents
only made it seem more unlikely.
In fact even its birth has been
turned into something of a myth,
which goes like this.
In the late 1960s,
a young Italian physicist
named Gabriele Veneziano
was searching
for a set of equations
that would explain
the strong nuclear force...
The extremely powerful glue
that holds the nucleus
of every atom together,
binding protons to neutrons.
As the story goes,
he happened on a dusty book
on the history of mathematics,
and in it he found
a 200-year-old equation,
first written down by a Swiss
mathematician, Leonhard Euler.
Veneziano was amazed to discover
that Euler's equations,
long thought to be nothing more
than a mathematical curiosity,
seemed to describe
the strong force.
He quickly published a paper
and was famous ever after
for this accidental discovery.
I see occasionally
written in books
that, uh... that this model
was invented by chance
or was, uh, found
in a math book,
and, uh, this makes me
feel pretty bad.
What is true
is that the function
was the outcome
of a long year of work,
and we accidentally
discovered string theory.
However it was discovered,
Euler's equation,
which miraculously explained
the strong force,
took on a life of its own.
This was the birth
of string theory.
Passed from colleague
to colleague,
Euler's equation ended up
on the chalkboard
in front of a young American
physicist, Leonard Susskind.
To this day
I remember the formula.
The formula was...
And I looked at it, and I said,
"You know, this is so simple
even I could figure out
what this is."
Susskind retreated
to his attic to investigate.
He understood that
this ancient formula described
the strong force mathematically.
But beneath
the abstract symbols,
he had caught a glimpse
of something new.
And I fiddled with it.
I monkeyed with it.
I sat in my attic, I think,
for two months, on and off,
but the first thing
I could see in it,
it was describing
some kind of particles
which had internal structure,
which could vibrate,
which could do things, which
wasn't just a point particle.
And I began to realize
what was being described here
was a string...
An elastic string,
like a rubber band or like
a rubber band cut in half.
And this rubber band could
not only stretch and contract
but wiggle.
And marvel of marvels,
it exactly agreed
with this formula.
I was pretty sure at that time
that I was the only one
in the world who knew this.
Susskind wrote up his discovery,
introducing the revolutionary
idea of strings.
But before his paper
could be published,
it had to be reviewed
by a panel of experts.
I was completely convinced
that when it came back,
it was going to say,
"Susskind is the next Einstein,
or maybe even the next Newton."
And it came back saying, "Nah,
this paper is not very good.
Probably shouldn't
be published."
I was truly
knocked off my chair.
I was depressed, I was unhappy.
I was saddened by it.
It made me a nervous wreck,
and, uh, the result was
I went home and got drunk.
As Susskind drowned his sorrows
over the rejection
of his far-out idea,
it appeared
string theory was dead.
Meanwhile, mainstream science
was embracing particles
as points, not strings.
For decades, physicists
had been exploring
the behavior
of microscopic particles
by smashing them together
at high speeds,
and studying those collisions.
In the showers
of particles produced,
they were discovering
that nature is far richer
than they thought.
Once a month there'd be
a discovery of a new particle...
The rho meson, the
omega particle, the B particle,
the B1 particle,
the B2 particle, phi, omega.
More letters were used
than exist in most alphabets.
It was a population explosion
of particles.
It was a time
when graduate students
would run through the halls
of a physics building
and say, "They discovered
another particle,
and it fit the theories,"
and it was all so exciting.
And in this zoo
of new particles,
scientists weren't
just discovering
building blocks of matter.
Leaving string theory
in the dust,
physicists made a startling
and strange prediction...
That the forces of nature can
also be explained by particles.
Now, this is
a really weird idea,
but it's kind of like
a game of catch
in which the players like me...
And me are particles of matter.
And the ball
we're throwing back and forth
is a particle of force.
It's called
a messenger particle.
For example,
in the case of magnetism...
The electromagnetic force...
This ball would be a photon.
The more of these
messenger particles, or photons,
that are exchanged between us,
the stronger
the magnetic attraction.
And scientists predicted
that it's this exchange
of messenger particles
that creates
what we feel as force.
Experiments confirmed
these predictions
with the discovery
of the messenger particles
for electromagnetism, the
strong force and the weak force.
And using these newly
discovered particles,
scientists were closing in
on Einstein's dream
of unifying the forces.
Particle physicists reasoned
that if we rewind
the cosmic film
to the moments
just after the Big Bang...
Some 14 billion years ago
when the universe was
trillions of degrees hotter...
The messenger particles
for electromagnetism
and the weak force
would have been
indistinguishable.
Just as cubes of ice melt
into water in the hot sun,
experiments show
that as we rewind
to the extremely hot conditions
of the Big Bang,
the weak and electromagnetic
forces meld together
and unite into a single force,
called the electroweak.
And physicists believe
that if you roll the cosmic film
back even further,
the electroweak would unite
with the strong force
in one grand superforce.
Although that has yet
to be proven,
quantum mechanics
was able to explain
how three of the forces operate
on the subatomic level.
And all of a sudden
we had a consistent theory
of elementary particle physics,
which allows us to describe
all of the interactions...
Weak, strong
and electromagnetic...
In the same language.
It all made sense, and, uh,
it's all in the textbooks.
Everything was converging
toward a simple picture
of the known particles
and forces...
A picture
which eventually became known
as the standard model.
I think I gave it that name.
Professors Sheldon Glashow,
Abdus Salam and Steven Weinberg.
The inventors
of the standard model...
Both the name and the theory...
Were the toasts
of the scientific community,
receiving Nobel Prize
after Nobel Prize.
But behind the fanfare
was a glaring omission.
Although the standard model
explained three of the forces
that rule the world
of the very small,
it did not include
the most familiar force.
Gravity.
Overshadowed
by the standard model,
string theory became
a backwater of physics.
Most people in our community
lost complete interest
in string theory.
They said, "Okay, that was
a very nice, elegant thing
but had nothing
to do with nature."
It's not taken seriously
by much of the community,
but the early pioneers
of string theory are convinced
that they can smell reality
and continue to pursue the idea.
But the more these diehards
delved into string theory,
the more problems they found.
Early string theory had
a number of problems.
One was that it predicted
a particle which we know
is unphysical.
It's what's called a tachyon...
A particle that travels
faster than light.
There was this discovery
that the theory requires
ten dimensions,
which is very disturbing,
of course,
since it's obvious that
that's more than there are.
It had this massless particle
which was not seen
in experiments.
So these theories
didn't seem to make sense.
This seemed crazy to people.
Basically, string theory
was not getting off the ground.
People threw up their hands
and said, "This can't be right."
By 1973, only a few young
physicists were still wrestling
with the obscure equations
of string theory.
One was John Schwarz,
who was busy tackling
string theory's
numerous problems,
among them, a mysterious
massless particle...
Predicted by the theory
but never seen in nature...
And an assortment of anomalies,
or mathematical inconsistencies.
We spent a long time trying
to fiddle with the theory.
We tried all sorts of ways
of making the dimension be four,
getting rid of
these massless particles
and tachyons and so on,
but it was always ugly
and unconvincing.
For four years,
Schwarz tried to tame
the unruly equations
of string theory,
changing, adjusting,
combining and recombining them
in different ways.
But nothing worked.
On the verge
of abandoning string theory,
Schwarz had a brainstorm:
Perhaps his equations
were describing gravity.
But that meant reconsidering
the size of these tiny strands
of energy.
We weren't thinking about
gravity up till that point,
but as soon as we suggested
that maybe we should be dealing
with a theory of gravity,
we had to radically change
our view
of how big these strings were.
By supposing that strings
were a hundred billion billion
times smaller than an atom,
one of the theory's vices
became a virtue.
The mysterious particle
John Schwarz had been
trying to get rid of
now appeared to be a graviton,
the long-sought-after particle
believed to transmit gravity
at the quantum level.
String theory had produced
the piece of the puzzle
missing from the standard model.
Schwarz submitted
for publication
his groundbreaking new theory
describing how gravity works
in the subatomic world.
It seemed very obvious to us
that it was right,
but there was really no reaction
in the community whatsoever.
Once again, string theory
fell on deaf ears.
But Schwarz
would not be deterred.
He had glimpsed the holy grail.
If strings described gravity
at the quantum level,
they must be the key
to unifying the four forces.
He was joined in this quest by
one of the only other scientists
willing to risk his career
on strings, Michael Green.
In a sense, I think,
we had a quiet confidence
that the string theory
was obviously correct,
and it didn't matter much
if people didn't see it
at that point.
They would see it down the line.
But for Green's confidence
to pay off,
he and Schwarz
would have to confront
the fact that
in the early 1980s,
string theory still had
fatal flaws in the math
known as "anomalies."
An anomaly is just
what it sounds like:
It's something that's strange
or out of place,
something that doesn't belong.
Now this kind of anomaly
is just weird.
But mathematical anomalies
can spell doom
for a theory of physics.
They're a little complicated,
so here's a simple example:
Let's say we have a theory
in which these two equations...
describe one physical property
of our universe.
Now, if I solve this equation
over here and I find x = 1,
and I solve this equation
over here and find x = 2,
I know my theory has anomalies
because there should
only be one value for x.
Unless I can revise my equations
to get the same value for x
on both sides,
the theory is dead.
In the early 1980s,
string theory was riddled
with mathematical anomalies
kind of like these,
although the equations
were much more complex.
The future of the
theory depended
on ridding the equations of
these fatal inconsistencies.
After Schwarz and Green battled
the anomalies in string theory
for five years, their work
culminated late one night
in the summer of 1984.
It was widely believed
that these theories
must be inconsistent
because of anomalies.
Well, for no really good reason,
I just felt
that had to be wrong,
because I... I felt string
theory has got to be right,
therefore
there can't be anomalies.
So we decided, "We got
to calculate these things."
Amazingly, it all boiled down
to a single calculation.
On one side of the blackboard,
they got 496.
And if they got the matching
number on the other side,
it would prove string theory
was free of anomalies.
I do remember, um...
a particular moment
when John Schwarz and I
were talking at the blackboard
and working out these numbers
which had to fit,
and they just had
to match exactly.
I remember joking with
John Schwarz at that moment,
because there was
thunder and lightning.
There was a big mountain storm
in Aspen at that moment,
and I remember saying
something like, you know,
"We must be getting pretty close
"because the gods
are trying to prevent us
completing this calculation."
And indeed they did match.
The matching numbers meant the
theory was free of anomalies
and it had
the mathematical depth
to encompass all four forces.
So we recognized
not only that the strings
could describe gravity
but they could also describe
the other forces,
so we spoke in terms
of unification.
And we saw this
as a possibility of realizing
the dream that Einstein had
expressed in his later years
of unifying the different forces
in some deeper framework.
We felt great.
That was
an extraordinary moment,
because we realized
that no other theory
had ever succeeded
in doing that.
But by now,
it's like crying wolf,
each time we had done something
I figured everyone's going to be
excited, and they weren't.
So I figured... well, by now
I didn't expect
much of a reaction.
But this time,
the reaction was explosive.
In less than a year, the number
of string theorists leapt
from just a handful to hundreds.
Up to that moment,
the longest talk I'd ever given
on the subject was five minutes
at some minor conference,
and then suddenly
I was invited all over the world
to give talks
and lectures and so forth.
String theory was christened
the "theory of everything."
In early fall of 1984, I came
here, to Oxford University,
to begin my graduate studies
in physics.
Some weeks after, I saw a poster
for a lecture by Michael Green.
I didn't know who he was,
but then again, I really
didn't know who anybody was.
But the title of the lecture
was something like
"The Theory of Everything."
So how could I resist?
This elegant new version
of string theory seemed capable
of describing all
the building blocks of nature.
Here's how.
Inside every grain of sand...
are billions of tiny atoms.
Every atom is made
of smaller bits of matter...
Electrons orbiting a nucleus
made of protons and neutrons...
Which are made of even smaller
bits of matter, called quarks.
But string theory says this
is not the end of the line.
It makes the astounding claim
that the particles making up
everything in the universe
are made
of even smaller ingredients...
Tiny, wiggling strands of energy
that look like strings.
Each of these strings
is unimaginably small.
In fact,
if an atom were enlarged
to the size
of the solar system...
a string would only be
as large as a tree.
And here's the key idea:
Just as different vibrational
patterns, or frequencies,
of a single cello string
create what we hear
as different musical notes,
the different ways
that strings vibrate
give particles
their unique properties,
such as mass and charge.
For example, the only difference
between the particles
making up you and me
and the particles that transmit
gravity and the other forces
is the way
these tiny strings vibrate.
Composed of an enormous number
of these oscillating strings,
the universe can be thought of
as a grand cosmic symphony.
And this elegant idea
resolves the conflict
between our jittery,
unpredictable picture of space
on the subatomic scale
and our smooth picture of space
on the large scale.
It's the jitteriness
of quantum mechanics
versus the gentleness
of Einstein's general
theory of relativity
that makes it so hard
to bridge the two,
to stitch them together.
Now, what string theory does,
it comes along
and basically calms the jitters
of quantum mechanics.
It spreads them out
by virtue of taking
the old idea of a point particle
and spreading it out
into a string.
So the jittery behavior is there
but it's just
sufficiently less violent
that quantum theory
and general relativity
stitch together perfectly
within this framework.
It's a triumph of mathematics.
With nothing but these tiny
vibrating strands of energy,
string theorists claim to be
fulfilling Einstein's dream
of uniting all forces
and all matter.
But this radical new theory
contains a chink in its armor.
No experiment can ever check up
what's going on
at the distances
that are being studied.
No observation can relate
to these tiny distances
or high energies.
That is to say, there ain't no
experiment that could be done,
nor is there any observation
that could be made
that would say
"You guys are wrong."
The theory is safe,
permanently safe.
Is that a theory of physics
or a philosophy?
I ask you.
People often criticize
string theory
for saying that
it's very far removed
from any direct
experimental test,
and it's... surely
it's not really, uh...
a branch of physics
for that reason.
And I... my response
to that is simply
that they're going
to be proved wrong.
Making string theory
even harder to prove
is that in order to work,
the complex equations require
something that sounds
like it's straight out
of science fiction:
extra dimensions of space.
We've always thought,
for centuries, that there
was only what we can see,
you know, this dimension,
that one and another one.
There was only three dimensions
of space and one of time.
And people who've said
that there were
extra dimensions of space
have been labeled
as, you know, crackpots
or people who were bananas.
Well, string theory
really predicts it.
To be taken seriously,
string theorists had to explain
how this bizarre prediction
could be true,
and they claim that the far-out
idea of extra dimensions
may be more down to earth
than you'd think.
Let me show you what I mean.
I'm off to see a guy who was
one of the first people
to think
about this strange idea.
I'm supposed to meet him
at 4:00 at his apartment
on Fifth Avenue and 93rd Street
on the second floor.
Now, in order to get
to this meeting,
I need four pieces
of information,
one for each of the three
dimensions of space...
A street, an avenue
and a floor number...
And one more for time,
the fourth dimension.
You can think about these
as the four dimensions
of common experience...
Left-right, back-forth,
up-down and time.
As it turns out,
the strange idea that there
are additional dimensions
stretches back almost a century.
Our sense that we live
in a universe
of three spatial dimensions
really seems beyond question.
But in 1919, Theodor Kaluza,
a virtually unknown
German mathematician,
had the courage
to challenge the obvious.
He suggested
that maybe, just maybe,
our universe has
one more dimension
that for some reason
we just can't see.
No, he says here,
"I like your idea."
So, why does he delay?
You see, Kaluza
had sent his idea
about an additional spatial
dimension to Albert Einstein.
And although Einstein was
initially enthusiastic,
he then seemed to waver
and for two years held up
publication of Kaluza's paper.
Eventually, Kaluza's paper
was published,
after Einstein decided extra
dimensions were his cup of tea.
Here's the idea.
In 1916, Einstein showed
that gravity is nothing
but warps and ripples
in the four familiar dimensions
of space and time.
Just three years later,
Kaluza proposed
that electromagnetism
might also be ripples.
But for that to be true,
Kaluza needed a place
for those ripples to occur.
So Kaluza proposed an additional
hidden dimension of space.
But if Kaluza was right,
where is this extra dimension?
And what would
extra dimensions look like?
Can we even begin
to imagine them?
Well, building
upon Kaluza's work,
the Swedish physicist
Oskar Klein suggested
an unusual answer.
Take a look at the cables
supporting that traffic light.
From this far away, I can't see
that they have any thickness.
Each one looks like a line,
something with only
a single dimension.
But suppose we could explore one
of these cables way up close,
like from the point of view
of an ant.
Now, a second dimension,
which wraps around the cable,
becomes visible.
From its point of view, the ant
can move forwards and backwards,
and it can also move clockwise
and counterclockwise.
So, dimensions can come
in two varieties.
They can be long and unfurled,
like the length of the cable,
but they can also be
tiny and curled up,
like the circular direction
that wraps around it.
Kaluza and Klein made
the wild suggestion
that the fabric of our universe
might be
kind of like
the surface of the cable,
having both big,
extended dimensions...
The three that we know about...
But also tiny, curled-up
dimensions, curled up so tiny,
billions of times smaller
than even a single atom,
that we just can't see them.
And so our perception
that we live in a universe
with three spatial dimensions
may not be correct after all.
We really may live in a universe
with more dimensions
than meet the eye.
So, what would these
extra dimensions look like?
Kaluza and Klein proposed
that if we could shrink down
billions of times,
we'd find one extra
tiny, curled-up dimension
located at every point in space.
And just the way an ant can
explore the circular dimension
that wraps around
a traffic-light cable,
in theory, an ant that is
billions of times smaller
could also explore this tiny,
curled-up circular dimension.
This idea that extra dimensions
exist all around us
lies at the heart
of string theory.
In fact, the mathematics
of string theory demand
not one but six
extra dimensions,
twisted and curled
into complex little shapes
that might look
something like this.
If string theory is right,
we would have to admit
that there are really
more dimensions out there,
and I find that
completely mind-blowing.
If I take the theory
as we have it now literally,
I would conclude that the
extra dimensions really exist.
They're part of nature.
When we talk
about extra dimensions,
we literally mean
extra dimensions of space
that are the same
as the dimensions of space
that we see around us.
And the only difference between
them has to do with their shape.
But how could these
tiny extra dimensions,
curled up into
such peculiar shapes,
have any effect
on our everyday world?
Well, according to string
theory, shape is everything.
Because of its shape,
a French horn can produce
dozens of different notes.
When you press one of the keys,
you change the note
because you change the shape
of the space inside the horn
where the air resonates.
And we think the curled-up
spatial dimensions
in string theory work
in a similar way.
If we could shrink down
small enough
to fly into one of these
tiny six-dimensional shapes
predicted by string theory,
we would see how
the extra dimensions
are twisted and curled back
on each other,
influencing how strings,
the fundamental ingredients
of our universe,
move and vibrate.
And this could be the key
to solving one of nature's
most profound mysteries.
You see, our universe is kind
of like a finely tuned machine.
Scientists have found that
there are about 20 numbers...
20 fundamental constants
of nature...
That give the universe the
characteristics we see today.
These are numbers like
how much an electron weighs,
the strength of gravity,
the electromagnetic force,
and the strong and weak forces.
Now, as long as we set the dials
on our universe machine
to precisely the right values
for each of these 20 numbers,
the machine produces
the universe we know and love.
But if we change the numbers
by adjusting the settings
on this machine
even a little bit,
the consequences are dramatic.
For example, if I increase
the strength of
the electromagnetic force,
atoms repel one another
more strongly,
so the nuclear furnaces that
make stars shine break down.
The stars, including our sun,
fizzle out...
and the universe as we know it
disappears.
So, what exactly in nature
sets the values of these
20 constants so precisely?
Well, the answer could be
the extra dimensions
in string theory.
That is, the tiny, curled-up
six-dimensional shapes
predicted by the theory
cause one string to vibrate
in precisely the right way
to produce what we see
as a photon
and another string to vibrate
in a different way,
producing an electron.
So according to string theory,
these minuscule
extra-dimensional shapes
really may determine
all the constants of nature,
keeping the cosmic symphony
of strings in tune.
By the mid-1980s, string theory
looked unstoppable.
But behind the scenes,
the theory was in tangles.
Over the years, string theorists
had been so successful
that they had constructed
not one but five different
versions of the theory.
Each was built on strings
and extra dimensions,
but in detail, the five theories
were not in harmony.
In some versions, strings
were open-ended strands;
in others,
they were closed loops.
At first glance,
a couple of versions even
required 26 dimensions.
All five versions
appeared equally valid,
but which one was describing
our universe?
This was kind
of an embarrassment
for string theorists,
because on the one hand,
we wanted to say
that this might be it...
The final description
of the universe.
But then in the next breath
we had to say,
"And it comes in five flavors,
five variations."
Now, there's one universe,
you expect there to be
one theory and not five.
So this is an example
where more is definitely less.
One attitude that people who
didn't like string theory
could take was
"Well, you have five theories,
so it's not unique."
This was a peculiar
state of affairs,
because we were looking just
to describe one theory of nature
and not five.
If there's five of them,
well, maybe there's...
smart enough people
would find 20 of them,
or maybe there's
an infinite number of them,
and you're back to just
searching around at random
for... for theories
of the world.
Maybe one of these
five string theories
is describing our universe.
On the other hand, which one?
And why... what are
the other ones good for?
But having five string theories,
even though it's big progress,
raises the obvious question:
If one of those theories
describes our universe,
then who lives
in the other four worlds?
String theory seemed
to be losing steam once again,
and frustrated
by a lack of progress,
many physicists
abandoned the field.
Will string theory prove
to be a theory of everything,
or will it unravel
into a theory of nothing?
On NOVA's Web site, go behind
the scenes with Brian Greene,
journey into the subatomic
world, play with strings,
picture other dimensions,
and much more.
To order this program
on VHS or DVD
or the book
The Elegant Universe,
please call WGBH
Boston Video at
1-800-255-9424.
Next time on NOVA:
Can string theory be saved?
Do we live in a world
of extra dimensions
with parallel universes
just beyond our reach?
The thrill ride continues
as Brian Greene pushes
physics to the limit
on the next episode of
"The Elegant Universe."
NOVA is a production
of WGBH Boston.
Corporate funding for NOVA
is provided by Sprint
and Microsoft.
Additional funding
is provided by:
Dedicated to education
and quality television.
Funding for "The Elegant
Universe" is provided by:
To enhance public understanding
of science and technology.
And by the National
Science Foundation,
where discoveries begin.
Additional funding is provided
by Volkswagen
and by:
and:
Major funding for NOVA
is also provided
by the Corporation
for Public Broadcasting
and by contributions
to your PBS stations from:
We are PBS.