The Fabric of the Cosmos

UNIVERSE OR MULTIVERSE? PBS Airdate: November 23, 2011.

Lying just beneath everyday reality is a breathtaking world,

where much of what we perceive about the universe is wrong.

Physicist and best-selling author Brian Greene

takes you on a journey that bends the rules of human experience.

Why don't we ever see events unfold in reverse order?

According to the laws of physics, this can happen.

It's a world that comes to light

as we probe the most extreme realms of the cosmos,

from black holes

to the Big Bang

to the very heart of matter itself.

I'm gonna have what he's having.

Here, empty space teems with ferocious activity.

The three-dimensional world may be just an illusion.

And there's no distinction between past, present and future.

But how could this be?

How could be we so wrong about something so familiar?

Does it bother us? Absolutely.

There's no principle built into the laws of nature

that says that theoretical physicists have to be happy.

It's a game-changing perspective

that opens up a new world of possibilities.

Coming up,

what if new universes were born all the time...

In this picture, the Big Bang is not a unique event.

And ours was one of numerous parallel realities?

Somewhere there's a duplicate of you and me and everyone else.

Are we in a universe or a multiverse?

The Fabric of the Cosmos, right now on NOVA.

New York City.

They say there's nowhere else like it, home to 8,000,000 people,

countless structures, monuments and landmarks, every one of them, unique.

Or so we think.

Uniqueness is an idea so familiar, we never even question it.

Experience tells us people and objects are one of a kind.

Why else would we visit museums and collect great masterpieces?

Yet a new picture of the cosmos is coming to light,

in which nothing is unique.

Not that the world's great masterpieces are fakes;

Instead, I'm talking about something far more profound:

A new picture of the cosmos that

challenges the very notion of uniqueness,

one in which duplicates are inevitable.

And that's just the beginning.

There might be duplicates not just of objects,

but of you and me and everyone else.

But if this new picture is right, where are these duplicates

and why haven't we ever seen them?

The answer may lie outside our universe.

There was a time when the word "universe" meant

"all there is", everything.

The notion of "more than one universe",

"more than one everything", seemed impossible.

But perhaps, if we could go beyond our Solar System, beyond the Milky Way,

even beyond other distant galaxies, past the end of the observable universe,

we'll find

that there's more,

a lot more,

that our universe is not alone.

There may be other universes.

In fact, there might be new ones being born all the time.

We may actually live in an expanding sea of multiplying universes,

a "multiverse".

If we could visit these other universes,

we'd find that some might have basic properties of nature so foreign

that matter as we know it couldn't exist.

Others might have galaxies, stars, even a planet that looks familiar

but with some surprising differences.

And if there are an infinite number of universes in the multiverse,

somewhere there's a place where almost everything is identical to ours,

except for the slightest details.

Like maybe there's another Brian Greene

who ends up in a different line of work.

If the multiverse is indeed infinite, then one is going to have to confront

a lot of possibilities that are very hard to imagine.

There will be other places where there will be Alan Guths

who look and think and act exactly like me,

as well as many where there will be Alan Guths who look and think

almost exactly like me, but with some small differences.

Is it science? Is it a part of metaphysics?

Is it just philosophy? Is it religion?

Physicists tend not to ask those questions, they just say,

"Let's follow the logic".

And the logic seems to lead there.

However unfamiliar and strange the multiverse might seem,

a growing number of scientists think it may be the final step

in a long line of radical revisions to our picture of the cosmos.

That is, there was a time when we thought that the Earth

was at the center of the cosmos,

and that everything else

revolved around us.

Then, along came scientists like Galileo and Copernicus.

And they showed us that it's the Sun, not the Earth

that's at the center of our Solar System.

And our Solar System?

It's just a little neighborhood in the outskirts of a gigantic galaxy.

And our galaxy?

It's one of hundreds of billions of galaxies that make up our universe.

Now, all of these ideas sounded out- rageous when they were first proposed,

but today, we don't even question them.

The idea of a multiverse may be similar.

It simply may require a drastic change in our cosmic perspective.

On the other hand, some scientists think that the multiverse

is nothing but a dead end for physics.

I'm very uncomfortable with the multiverse.

To become solid science it's got a lot of growing up to do.

You know, it exists in the same way that, you know, angels might exist.

We have to make our bets, and I think, right now,

the multiverse is a pretty good bet.

I think there's a good chance that the multiverse is real,

and that a hundred years from now people might be convinced that it's real.

So, where did this idea come from and what's the evidence for it?

Well, several surprising discoveries suggest that

we really may be part of a multiverse.

The first of these discoveries

has to do with the generally accepted theory of the origin of our universe:

The Big Bang.

According to this theory, our universe began some 14 billion years ago

in an intensely violent explosion.

Over billions of years, the universe cooled and coalesced,

allowing the formation of stars, planets and galaxies.

As a result of that explosion, the universe is still expanding today.

But if you could run the history of our universe in reverse,

all the way back to the beginning,

you'd find that the Big Bang theory tells us nothing about

what sent everything hurtling outward in the first place.

It's called the Big Bang theory,

but the one thing that it really says nothing about at all

is the bang itself.

It says nothing about what banged, why it banged,

or what happened before it banged.

So, what fueled that violent explosion?

What force could have driven everything apart?

The quest to figure that out would bring scientists

face to face with the multiverse.

One physicist whose work unexpectedly helped lay the foundation

for the multiverse idea is Alan Guth.

Today, he's a professor at M.I.T., but back in 1979,

Guth and a colleague, Henry Tye, were pursuing a new idea

about how particles might have formed in the early universe.

Henry suggested to me that we should maybe look at whether or not

this new process that we were thinking of

would influence the expansion rate of the universe.

Guth and Tye hadn't set out to investigate the expansion rate

of the universe in the first moments after the Big Bang,

but Henry Tye's question caused Guth

to review their calculations one more time.

I stayed up quite late that night

and went over the calculations very carefully,

trying to make sure everything was correct.

As the night wore on, Guth discovered something extraordinary

in the equations describing how new particles

might have formed in the early universe.

I came to the shocking conclusion that these new-fangled particle theories

would have a tremendous effect on the expansion rate of the universe.

The kind of process Henry and I were talking about would drive the universe

into a period of incredibly rapid exponential expansion.

What Guth found in the math was evidence that

in the extreme environment of the very early universe,

gravity can act in reverse.

Instead of pulling things together, this "repulsive" gravity

would repel everything around it, causing a huge expansion.

I immediately became very excited about it

and scribbled out the calculation in my notebook.

And then at the end I wrote "spectacular realization"

with a double box around it.

So, I realized that, if it was right, it could be very important.

By discovering this repulsive gravity,

Alan Guth had unintentionally shed light on the very beginning of the Big Bang.

Described mathematically, this force was so powerful

it could take a bit of space as tiny as a molecule

and blow it up to the size of the Milky Way galaxy,

in less than a billionth of a billionth of a billionth of a blink of an eye.

After this incredibly short outward burst,

space would continue to expand more slowly, and cool,

allowing stars and galaxies to form just as they do in the Big Bang theory.

Guth called this short burst of expansion "inflation",

and he believed it explained

what set the universe expanding in the first place.

The powerful, repulsive gravity of inflation was the bang in the Big Bang.

But despite having made a momentous breakthrough,

Alan Guth had an even more pressing concern.

I had no idea what my employment might be.

I was really looking for a more permanent job.

The inflationary universe scenario looks very exciting...

So I went on, actually, a pretty long trip, giving talks about this.

Suddenly this idea caught on.

Talks about inflation were packed with people from all areas of physics.

Lots of astrophysical theorists, including me, got very enthusiastic.

It was a very, very exciting time.

If you have a really good idea that allows other people

to move the field forward, people are going to pay attention.

An amazing feeling that, suddenly I had crossed that gap

from being an unknown post-doc to being one of the major players.

And

it was very hard to absorb, but it certainly felt good.

One reason inflation was so exciting was that it made predictions

that could be tested through observation.

Scientists realized that if the theory were correct,