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If you look deep into the night sky,

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you see stars,

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and if you look further, you see more stars,

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and further, galaxies, and 
further, more galaxies.

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But if you keep looking further and further,

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eventually you see nothing for a long while,

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and then finally you see a
faint, fading afterglow,

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and it's the afterglow of the Big Bang.

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Now, the Big Bang was an era in the early universe

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when everything we see in the night sky

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was condensed into an incredibly small,

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incredibly hot, incredibly roiling mass,

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and from it sprung everything we see.

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Now, we've mapped that afterglow

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with great precision,

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and when I say we, I mean people who aren't me.

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We've mapped the afterglow

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with spectacular precision,

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and one of the shocks about it

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is that it's almost completely uniform.

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Fourteen billion light years that way

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and 14 billion light years that way,

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it's the same temperature.

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Now it's been 14 billion years

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since that Big Bang,

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and so it's got faint and cold.

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It's now 2.7 degrees.

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But it's not exactly 2.7 degrees.

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It's only 2.7 degrees to about

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10 parts in a million.

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Over here, it's a little hotter,

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and over there, it's a little cooler,

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and that's incredibly important
to everyone in this room,

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because where it was a little hotter,

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there was a little more stuff,

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and where there was a little more stuff,

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we have galaxies and clusters of galaxies

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and superclusters

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and all the structure you see in the cosmos.

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And those small, little, inhomogeneities,

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20 parts in a million,

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those were formed by quantum mechanical wiggles

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in that early universe that were stretched

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across the size of the entire cosmos.

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That is spectacular,

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and that's not what they found on Monday;

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what they found on Monday is cooler.

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So here's what they found on Monday:

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Imagine you take a bell,

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and you whack the bell with a hammer.

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What happens? It rings.

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But if you wait, that ringing fades

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and fades and fades

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until you don't notice it anymore.

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Now, that early universe was incredibly dense,

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like a metal, way denser,

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and if you hit it, it would ring,

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but the thing ringing would be

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the structure of space-time itself,

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and the hammer would be quantum mechanics.

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What they found on Monday

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was evidence of the ringing

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of the space-time of the early universe,

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what we call gravitational waves

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from the fundamental era,

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and here's how they found it.

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Those waves have long since faded.

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If you go for a walk,

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you don't wiggle.

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Those gravitational waves in the structure of space

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are totally invisible for all practical purposes.

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But early on, when the universe was making

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that last afterglow,

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the gravitational waves

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put little twists in the structure

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of the light that we see.

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So by looking at the night sky deeper and deeper --

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in fact, these guys spent
three years on the South Pole

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looking straight up through the coldest, clearest,

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cleanest air they possibly could find

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looking deep into the night sky and studying

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that glow and looking for the faint twists

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which are the symbol, the signal,

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of gravitational waves,

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the ringing of the early universe.

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And on Monday, they announced

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that they had found it.

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And the thing that's so spectacular about that to me

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is not just the ringing, though that is awesome.

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The thing that's totally amazing,

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the reason I'm on this stage, is because

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what that tells us is something
deep about the early universe.

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It tells us that we

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and everything we see around us

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are basically one large bubble --

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and this is the idea of inflation—

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one large bubble surrounded by something else.

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This isn't conclusive evidence for inflation,

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but anything that isn't inflation that explains this

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will look the same.

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This is a theory, an idea,

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that has been around for a while,

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and we never thought we we'd really see it.

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For good reasons, we thought we'd never see

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killer evidence, and this is killer evidence.

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But the really crazy idea

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is that our bubble is just one bubble

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in a much larger, roiling pot of universal stuff.

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We're never going to see the stuff outside,

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but by going to the South Pole
and spending three years

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looking at the detailed structure of the night sky,

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we can figure out

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that we're probably in a universe
that looks kind of like that.

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And that amazes me.

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Thanks a lot.

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(Applause)