Brian Greene: We have found, over the last hundred years,

that a very fruitful way

of thinking about the universe,

is to allow for the possibility

that left-right, back-forth, and up-down,

the three dimensions that we all are immersed within,

we move through freely in day-to-day life...

We have found it useful to imagine

that there may be more than those three dimensions

of space.

And, we have found that, at least theoretically,

using mathematics, if you engage

that possibility of more than

three dimensions of space,

certain problems of physics, all of a sudden,

admit to a solution.

And this is an idea that goes

all the way back to the early part

of the twentieth century, around roughly 1920,

when a German mathematician Theodor Kaluza

was studying Einstein's theory of gravity,

it's called the General Theory of Relativity,

and he found, rather surprisingly,

that if he imagined applying

Einstein's insights not to a universe

with three dimensions of space,

which is what Einstein had in mind,

but into one with four dimensions

of space with time included

in both approaches. He found that

he could find a framework

that put together the laws of gravity,

and the laws of electromagnetism,

in one theoretical package. So, he found a way of unifying

the then known laws of physics.

You move through the world, and you want to give some information

about your location.

You have to give a street,

a cross street, and a height, a floor number.

If you want to meet somebody, that would be the data

that you need to give.

The ideas of these higher dimensional theories

would be that that's not enough information.

You have to give those three pieces of information

plus more to really nail down where you are.

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A very natural question, when confronted with this strange idea,

of more than left-right back-forth and up-down, is

well we immediately see those three dimensions,

why don't we see the others?

And this is a real puzzle. It's a real problem

that people have come up with very interesting

and creative solutions for.

If the math of your theory is suggesting more dimensions

but you don't see them, where are they hiding?

And one of the places that they may be hiding

is in plain sight.

It may be that those other dimensions are all

around us just like the three that we know about,

but they're tightly curled up, to a very very small size.

So tiny, that we can't see it with the naked eye

or even with our most powerful equipment to date.

And, often people get confused 'what do you mean by a small,

curled up dimension?'

And all I mean by that is, if you're a little tiny ant,

and you're walking along one of these tiny dimensions

you circle around back to your starting point very quickly

you can't go very far in that dimension

because it curls back in on itself.

Like, a sphere, or like a little tiny circle

and you go around it you come back to your

starting point, and if that circle or that sphere

is so tiny that we don't have the visual acuity to pick it out,

those dimensions can be all around us, and yet be invisible.

So according to these ideas if I, you know, if I take my hand

and I sweep it in front of my face, I wouldn't just be moving in the

obvious dimensions that we can all see with the naked eye,

I'd also be in some sense moving around those other

tiny dimensions, I'd just be returning to my starting point

over and over again so quickly that on average, I wouldn't even

have recognized that I took the journey at all.

To me the most exciting thing that one can do with one's life, really

is try to, get some sense of how we got here.

Where did the universe come from? Where did life come from?

Where does consciousness come from?

These are the big questions, that frame existence.

And, what we are doing in physics and in string theory in particular,

is trying to answer one of those.

The real motivation, the driving force behind what we do

behind these ideas of extra dimensions and strings and quantum mechanics

and general relativity we are all trying to figure out

where the universe came from.

And the current laws of physics, remarkably, take us back to a

fraction of a second after the beginning.

But the current laws breakdown. So we are really working hard

to find laws that don't breakdown under any circumstance

no matter how extreme.

The early universe was very hot, it was very dense

it was a very violent arena.

We want laws that can cope with that arena,

allowing us to peer back using mathematics

and understand what happened at time zero.

That, to me, would be a remarkable achievement if our species can get to the

point where we can say:

Here's how the universe began, here's why there's a universe at all.

The notion of before the big bang, could be a meaningless question.

It could be that time comes into existence with the bang itself,

and, asking questions 'what happened before?'

doesn't make sense because the notion of before doesn't apply

that is certainly a possibility, but I am certainly open to other possibilities.

For instance, some of the theories that we're working on today suggest that

the big bang was not the actual beginning

of the universe in the grandest sense of the term,

but rather was an interesting event that gave rise to our part of the big cosmos

but there could be other big bangs happening here, there, other far flung places

throughout space,

so the big bang may simply be an interesting event but not the starting

event.

So, the notion of what happened before it may be perfectly well-defined,

and, using our mathematics, we may even be able to describe what it was

like

in those "pre" big bang eras, those pre big bang arenas.

Will we ever observationally be able to probe those realms if they exist?

Maybe not. Probably not.

But I don't think that's any cause to say that it's not in the realm of science

or it's not worth studying or thinking about.

Because one of the key things that's often lost is, when you're testing a theory,

you don't need to test every single prediction of the theory,

you need to test enough of the predictions that you gain confidence that the theory is

a good guide to the nature of reality and then if that theory tells you things about

realms that you can't see, like a realm before the big bang, you're actually learning

about that realm,

even though you can't test it or see it.

These kinds of ideas are really helping us gain the deepest insight into the

very nature of reality.

And I don't know how long it takes.

A hundred years, a thousand years, whatever. When our picture of reality shifts,

when we thought there were three dimensions and there are more

or when we thought that time was universal and we learned that it isn't.

Or when we learned that space is flexible as opposed to the previous Newtonian version

of it being this unchanging stage,

these shifts in our basic understanding of reality,

do begin to infiltrate the way we think of ourselves

and the way we picture how we fit in, to the grand scheme of the cosmos.

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