If you look deep into the night sky,
you see stars,
and if you look further, you see more stars,
and further, galaxies, and further, more galaxies.
But if you keep looking further and further,
eventually you see nothing for a long while,
and then finally you see a faint, fading afterglow,
and it's the afterglow of the Big Bang.
Now, the Big Bang was an era in the early universe
when everything we see in the night sky
was condensed into an incredibly small,
incredibly hot, incredibly roiling mass,
and from it sprung everything we see.
Now, we've mapped that afterglow
with great precision,
and when I say we, I mean people who aren't me.
We've mapped the afterglow
with spectacular precision,
and one of the shocks about it
is that it's almost completely uniform.
Fourteen billion light years that way
and 14 billion light years that way,
it's the same temperature.
Now it's been 14 billion years
since that Big Bang,
and so it's got faint and cold.
It's now 2.7 degrees.
But it's not exactly 2.7 degrees.
It's only 2.7 degrees to about
10 parts in a million.
Over here, it's a little hotter,
and over there, it's a little cooler,
and that's incredibly important to everyone in this room,
because where it was a little hotter,
there was a little more stuff,
and where there was a little more stuff,
we have galaxies and clusters of galaxies
and superclusters
and all the structure you see in the cosmos.
And those small, little, inhomogeneities,
20 parts in a million,
those were formed by quantum mechanical wiggles
in that early universe that were stretched
across the size of the entire cosmos.
That is spectacular,
and that's not what they found on Monday;
what they found on Monday is cooler.
So here's what they found on Monday:
Imagine you take a bell,
and you whack the bell with a hammer.
What happens? It rings.
But if you wait, that ringing fades
and fades and fades
until you don't notice it anymore.
Now, that early universe was incredibly dense,
like a metal, way denser,
and if you hit it, it would ring,
but the thing ringing would be
the structure of space-time itself,
and the hammer would be quantum mechanics.
What they found on Monday
was evidence of the ringing
of the space-time of the early universe,
what we call gravitational waves
from the fundamental era,
and here's how they found it.
Those waves have long since faded.
If you go for a walk,
you don't wiggle.
Those gravitational waves in the structure of space
are totally invisible for all practical purposes.
But early on, when the universe was making
that last afterglow,
the gravitational waves
put little twists in the structure
of the light that we see.
So by looking at the night sky deeper and deeper --
in fact, these guys spent three years on the South Pole
looking straight up through the coldest, clearest,
cleanest air they possibly could find
looking deep into the night sky and studying
that glow and looking for the faint twists
which are the symbol, the signal,
of gravitational waves,
the ringing of the early universe.
And on Monday, they announced
that they had found it.
And the thing that's so spectacular about that to me
is not just the ringing, though that is awesome.
The thing that's totally amazing,
the reason I'm on this stage, is because
what that tells us is something deep about the early universe.
It tells us that we
and everything we see around us
are basically one large bubble --
and this is the idea of inflation—
one large bubble surrounded by something else.
This isn't conclusive evidence for inflation,
but anything that isn't inflation that explains this
will look the same.
This is a theory, an idea,
that has been around for a while,
and we never thought we we'd really see it.
For good reasons, we thought we'd never see
killer evidence, and this is killer evidence.
But the really crazy idea
is that our bubble is just one bubble
in a much larger, roiling pot of universal stuff.
We're never going to see the stuff outside,
but by going to the South Pole and spending three years
looking at the detailed structure of the night sky,
we can figure out
that we're probably in a universe that looks kind of like that.
And that amazes me.
Thanks a lot.
(Applause)