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Gravitational Waves – Listening to Spacetime · Talking Science

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So we are digging into a massive stack of astrophysical
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research for today's deep dive. We've got historical
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analyses of Albert Einstein's original 1916 papers,
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plus operational blueprints and data logs from
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the LIGO observatories. And some of the latest
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cosmological surveys mapping out binary star
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systems, right? Right, exactly. And our mission
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today is to understand this monumental shift
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in human history that happened back in September
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of 2015. To really set the stage for why this
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specific date is so huge, I want you to think
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about what it's like to watch a movie. Specifically,
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like, a silent movie. Yes, a silent film. I mean,
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you can follow the plot, you see the sweeping
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landscapes, you watch the actors' expressions
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and the explosions. Can we get the gist of the
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story? Yeah, you become incredibly skilled at
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interpreting the universe of that film purely
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through the light bouncing off the silver screen.
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But then, you know, one day you walk into the
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theater, and for the very first time, someone
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actually turns on the speakers. Oh, wow, that's
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a huge shift. It is. You actually hear the blast.
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You feel the bass rumble in your chest. The medium
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just fundamentally transforms from a visual observation
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into a completely immersive physical experience.
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That analogy perfectly captures humanity's relationship
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with the cosmos up until 2015. Really? Yeah.
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I mean, for our entire existence as a species,
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every time we looked up at the night sky, we
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were essentially watching a silent movie. Just
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collecting light. Exactly. From our naked eyes
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to the most advanced massive telescopes ever
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constructed, we were only ever doing that one
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single thing. collecting light. Whether it was
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like visible light or infrared or x -rays, it
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was all just different flavors of light. Right,
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but in 2015, we didn't just get a clearer picture
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of the sky. We built an ear to actually hear
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the universe. We detected gravitational waves.
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We did. And today, we're going to unpack exactly
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how this discovery happened. We'll demystify
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a hundred -year -old prediction and explore the
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most violent cosmic collisions imaginable. And
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the best part is, we're going to do all of this
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without you needing a PhD in astrophysics. Absolutely.
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So let's start with the foundational concept
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here. To understand how the universe can create
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a wave, you first have to understand the medium
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those waves are traveling through. Okay, so the
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ocean they're swimming in, so to speak. Right.
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And that requires rewinding about a century to
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Einstein's theory of general relativity, which,
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you know, completely rewrote our understanding
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of gravity. Because before Einstein, the prevailing
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view... which goes all the way back to Isaac
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Newton, was that gravity was this invisible,
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instantaneous magnetic tether pulling objects
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across empty space. Yeah, like a giant invisible
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string connecting the Earth to the sun. Right,
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which works well enough for basic calculations.
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It does, but Einstein realized it was fundamentally
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incomplete. He proposed that space and time are
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not just this empty, passive theater where events
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take place. They aren't separate things. Exactly.
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They are woven together into a single, dynamic,
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four -dimensional fabric known as spacetime.
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Spacetime, right. And what you and I experience
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as gravity isn't a pull at all. It's simply the
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bending and curving of that spacetime fabric
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by massive objects. Now, I remember from high
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school physics the classic textbook analogy for
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this. You imagine space as a stretched out...
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trampoline right oh yeah the rubber sheet analogy
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yeah and if you place a heavy bowling ball in
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the center it creates this deep dip right and
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then if you roll a smaller marble nearby its
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path just naturally curves inward toward the
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bowling ball It's not being magnetically pulled
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or anything. Right, it's just following the curve
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of the fabric itself. Exactly. But I always felt
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that analogy was a bit of a cheat because it
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only explains the space part. It completely ignores
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the time part of space -time. Well, yeah, that
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is the inherent flaw of trying to use a two -dimensional
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rubber sheet to explain a four -dimensional universe.
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It falls a bit short. It does. A much better
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way to visualize gravity as geometry is to think
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about walking on the Earth. Okay, how so? Well,
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if you and I stand at the equator, say, a thousand
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miles apart, and we both walk perfectly straight
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north, our paths start out completely parallel.
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Right, we're just walking straight ahead. But
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as we keep walking, because the Earth is curved,
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we eventually bump into each other at the North
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Pole. Oh, right. And there was no mysterious
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magnetic force pulling us together. We just followed
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straight lines on a curved surface. Exactly.
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And when we apply this to time, it gets even
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more fascinating. Because massive objects warp
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the entire fabric, so they also warp time. Yes.
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The closer you are to a massive object, the slower
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time passes for you relative to someone further
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away. Wait, really? Like noticeably slower. Well,
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for us, it's tiny, but this isn't just theoretical.
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The GPS satellites orbiting the Earth right now
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actually experience time at a slightly faster
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rate than the phones in our pockets. Because
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they're further out from Earth's gravity well.
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Right. And if engineers didn't program those
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satellites to constantly correct for that time
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warp, GPS navigation would completely fail within
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a single day. Wow, that completely shifts the
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perspective. I mean, when you drop your keys
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on the kitchen floor, they aren't being magically
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pulled down by the Earth. Not at all. Your keys
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are just coasting down the geometrical dip that
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the Earth has made in both space and time. You've
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got it. And the sources highlight that this isn't
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some fringe theory. It's one of the most rigorously
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tested and confirmed models in the history of
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science. Which brings us to the massive problem
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this creates for physicists. Yeah. Because if
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we accept this premise that reality itself is
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a flexible, dynamic grid. It logically follows
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that grids don't just bend. They bounce. Well,
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if you disturb them violently enough, they shudder.
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Oh, they ripple. Exactly. Einstein realized that
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if you take immensely heavy objects and accelerate
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them violently, they should send ripples spreading
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outward through the fabric of the universe at
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the speed of light. Okay, so these are the gravitational
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waves. Yes, but these ripples don't just pass
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through space like a sound wave moving through
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the air. What do they do? They physically stretch
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and squeeze the space itself as they pass. Wait,
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hold on. Let me stop you there because I really
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want to make sure I'm fully wrapping my head
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around the mechanics of this. Sure, go ahead.
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If a wave stretches and squeezes the space itself
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and we are inside that space. Yes. That means
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it stretches and squeezes everything in it. Like
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that means it stretches and squeezes you, the
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listener, right in your chair. Like a momentary
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invisible funhouse mirror just washing over you.
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That is the literal. Physical reality of a gravitational
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wave. That is wild. It is. As it washes over
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Earth, the physical distances in one direction
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momentarily grow a tiny bit longer, while the
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distances in the perpendicular direction shrink
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a tiny bit shorter. And then it just snaps back
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to normal. Yep. Space wobbles. Okay, I have to
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push back a little on the scale of this, though.
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Yeah. Because space is notoriously stiff. Right?
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Extremely stiff. I mean, it takes the entire
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mass of the Earth just to keep my keys on the
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floor. So to make the literal fabric of the universe
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wobble in a way that we could ever hope to notice
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from across the cosmos. Takes a lot of energy.
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Yeah, what could possibly be heavy enough and
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violent enough to shake the universe like that?
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To shake the universe, you need the most extreme,
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unimaginable engines of destruction in nature.
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Okay, like what? Well, for the waves we've managed
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to detect, the source is almost always the collision
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of black holes. Ah, black holes. Right. These
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are the corpses of massive stars that have completely
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collapsed under their own weight. And they're
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super dense, right? Unbelievably dense. They
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curve spacetime so deeply that not even light
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can escape their geometry. They are the ultimate
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cosmic heavyweights. Exactly. Now... Picture
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two of these monsters locked in a binary orbit.
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Okay, so they're circling each other. Right,
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and over millions of years as they orbit, they
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are actually churning up space -time, bleeding
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energy out into the cosmos in the form of these
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waves. And because they are losing energy...
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Their orbit shrinks. Yes, they get closer and
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they spiral faster and faster. It's the ultimate
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death spiral. It really is. In the final fractions
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of a second before they collide, these two objects,
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each weighing perhaps 30 times more than our
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entire sun, are whipping around each other an
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astonishing 100 times a second. 100 times a second?
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For something that huge? I know, it's hard to
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fathom. And when their event horizons finally
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touch and they merge into a single larger black
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hole, a portion of their combined mass is converted
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entirely into raw energy. Just radiated out as
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gravitational waves. Exactly. The data logs from
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our sources put numbers on this that frankly
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defy human comprehension. They really do. I read
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that for a fraction of a second, that final collision...
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radiates more power in the form of gravitational
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waves than all the shining stars in the entire
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observable universe combined. It's true. I just
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want the listener to pause and let that sink
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in. More power output than all the galaxies we
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can see, shining all at once. And it is entirely
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invisible. It is pure, violent shaking of space
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-time. That is terrifying and amazing. It is
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the most powerful event nature can muster. But
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here is the great cosmic irony that plagued Einstein.
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What's that? Because these specific cataclysms
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usually happen more than a billion light years
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away, by the time that universe -shaking ripple
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travels across the cosmos and reaches Earth,
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it has faded to an almost impossibly faint tremor.
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Oh, so it's practically nothing by the time it
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gets here. Right. Einstein himself actually doubted
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we would ever, ever be able to detect it. I can
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see why he doubted it, honestly. Especially because
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of the fundamental measurement problem we touched
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on earlier. The ruler problem. Yeah. If the wave
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stretches and squeezes everything, it stretches
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and squeezes any ruler or measuring instrument
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we could possibly build. Exactly. Like if my
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ruler stretches by 10 % at the exact same time
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the table I'm measuring stretches by 10%, the
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table still looks like it's exactly one ruler
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long. The change is completely masked. So how
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do you measure the invisible when your tools
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are changing size too? You abandon physical rulers
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completely. You have to use something that space
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-time cannot stretch, which is the speed of light.
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Ah, okay. And this brings us to LIGO, the Laser
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Interferometer Gravitational Wave Observatory.
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LIGO? I've heard of this. Yes. The brilliance
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of LIGO is in its design, specifically the mechanism
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of an interferometer. How does that work? It
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consists of two incredibly long vacuum tunnels,
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each four kilometers in length, arranged perfectly
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at a right angle to each other. Kind of like
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a giant letter L. Exactly like a giant L. And
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that shape is deliberate because of how gravitational
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waves stretch space in one direction while squeezing
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it in the perpendicular direction. So if a waves
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washes over that giant facility, one tunnel is
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going to momentarily stretch while the perpendicular
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tunnel compresses. Spot on. To measure this,
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scientists split a highly precise laser beam
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and send half of it down one tunnel and half
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down the other. At the end of each tunnel is
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a mirror that bounces the light back to the starting
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point. And because the tunnels are perfectly
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identical in length, The two laser beams return
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at the exact same moment. Yes, and the peaks
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and valleys of their light waves line up perfectly,
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but in opposite phases, meaning they completely
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cancel each other out. Oh, wait. This is exactly
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how noise -canceling headphones work. That's
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a perfect analogy, yeah. Right, because those
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headphones listen to the sound wave of, say,
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an airplane engine, and they produce a sound
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wave that is exactly inverted. And when the two
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waves meet, they destroy each other. Leaving
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total silence. So LIGO is doing this with light.
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When the universe is quiet, the lasers cancel
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each other out and the detector just sits in
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total darkness. That mechanism is the key to
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the whole machine. Because the moment a gravitational
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wave passes through the Earth, it stretches one
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tunnel and squeezes the other. So suddenly, one
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laser beam has a slightly longer journey and
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the other has a slightly shorter one. Exactly.
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They no longer return at the exact same time.
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They no longer cancel each other out. And in
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that tiny mismatch, a flash of light hits the
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detector. You got it. That flash is the signal.
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Which sounds pretty straightforward in theory.
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But we really have to talk about the sheer microscopic
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scale of the measurement happening here. Oh,
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it's staggering. Yeah, because when we say one
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tunnel gets longer, we aren't talking about inches
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or even millimeters, right? Or even close. After
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traveling a billion light years, the wave is
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so unbelievably faint that the change in the
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four kilometer tunnel's length is thousands of
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times smaller than the nucleus of a single atom.
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It is literally smaller than a proton. That is
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insane. The source text actually offers an analogy
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that puts this in perspective, and I love this.
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Let's hear it. It says it is the equivalent.
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Of measuring the distance from Earth to the nearest
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star, Proxima Centauri. Which is over 24 trillion
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miles away, just for the record. Right, 24 trillion
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miles away. And being able to detect if that
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massive distance changed by the width of a single
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human hair. It's almost impossible to comprehend.
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Achieving that level of sensitivity is arguably
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one of the most fiendishly difficult engineering
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challenges. humanity has ever overcome. I mean,
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to measure a change smaller than a proton, you
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have to isolate those mirrors from literally
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everything else in the world. Right, because
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any tiny bump would ruin it. Exactly. They had
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to account for the vibrations of trucks driving
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on highways miles and miles away. They had to
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account for ocean waves crashing on distant coastlines.
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They even had to cool and stabilize the mirrors
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to prevent the quantum thermal jitter of the
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atoms inside the glass from ruining the measurement.
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That is serious dedication. It took decades of
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relentless effort by a global collaboration of
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thousands of scientists to filter out all that
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noise. And the payoff for all that obsession
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finally came on September 14, 2015. Yes, it did.
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They had built two identical Lego detectors located
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thousands of kilometers apart, right? One in
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Washington state and one in Louisiana. And that
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was to ensure that a localized vibration, like,
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I don't know, a local earthquake or a truck.
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Wouldn't trick them. Exactly. If it happens in
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both places, it's real. Right. Yeah. And on that
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day, both detectors, separated by thousands of
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miles of Earth, recorded the exact same microscopic
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shiver at almost the exact same time. It was
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the unmistakable signature of two black holes
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colliding over a billion years ago. A century
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after he wrote down the equations, Einstein was
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proven completely right. It is such a beautiful
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synthesis of theoretical genius and engineering
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mastery. But, you know, what makes this discovery
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so vital isn't just ticking off an old prediction
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on a checklist. No. No, it fundamentally transforms
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our relationship with the cosmos because it gives
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us a brand new sense. Like we talked about with
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the silent movie. Right. Before 2015, every single
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astronomical tool we had relied on light. But
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black holes, by definition, give off no light.
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Exactly. To every telescope we had ever built,
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a black hole collision was a completely invisible
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event. We were utterly blind to it. We were blind
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to the most violent events in the universe. But
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gravitational waves are not light. They are the
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physical shutter of reality. So they allow us
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to perceive events that are shrouded in total
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darkness. Yes. That is why astrophysicists say
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we have gone from only seeing the universe to
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finally being able to hear it. And what's wild
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is that they actually translate these spacetime
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wobbles into an audio file. They do. It's so
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cool. Because these whales have a frequency of
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vibration. Just like sound waves, scientists
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can take the laser data and basically run it
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through a speaker. Yeah, the frequency of those
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merging black holes creates a distinct, faint
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chirp sound. A chirp? Yeah, it goes from a low
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pitch to a high pitch very quickly as the black
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holes spiral faster and faster right before the
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final pop of the merger. That is amazing. You
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can go online and actually listen to the space
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-time death cry of two black holes from a billion
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years ago. You really can. And that 2015 detection
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was just opening the door. Since then, the detectors
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have been upgraded, and we've felt dozens of
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these cosmic collisions. Oh, so it wasn't just
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a one -off. Not at all. And most importantly,
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we've detected a completely different kind of
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event, which is the collision of neutron stars.
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OK, let's define neutron stars because they operate
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very differently than black holes and they are
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really crucial to this story. They are. A neutron
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star is the collapsed core of a massive star
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that went supernova. But it's not a black hole.
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No. Unlike a black hole, which is essentially
16:37
just an extreme warp in empty space, a neutron
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star is actual physical matter. Just incredibly
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dense matter. Exactly. Gravity has crushed the
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star so intensely that the electrons and protons
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have literally merged. It's essentially a city
16:52
-sized atomic nucleus. Wow. It is so incredibly
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dense that a single teaspoon of neutron star
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material would weigh billions of tons. So because
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they are made of physical matter, matter. When
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two neutron stars get caught in a death spiral
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and smash into each other, they don't just warp
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space. No, they create a colossal physical explosion.
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So there's light involved. Exactly. They emit
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a massive burst of light across the entire electromagnetic
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spectrum while simultaneously sending out powerful
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gravitational waves. And in 2017, we actually
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caught one of these collisions, right? We did.
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burst of gamma rays coming from the exact same
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region of the sky. That is so cool. It was like
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finally getting the picture and the sound at
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the exact same time in our cosmic movie theater.
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It burst the era of multi -messenger astronomy.
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Multi -messenger meaning light and waves. Right.
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By having both the physical wave and the light.
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We solved mysteries that neither sense could
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answer alone. Like what? Well, for example, we
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learned that the violent collision of neutron
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stars is the actual cosmic forge where the universe's
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heavy elements are created. Oh, like gold and
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silver. Yes. The gold in the jewelry you might
18:07
be wearing right now? the platinum in our electronics,
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they were all forged in the catastrophic smash
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-up of neutron stars. That is unbelievable. Yeah.
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We literally saw the light of gold being created
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while feeling the physical shockwave of the blast.
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Exactly. We observed it happening in real time.
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It's incredible. We started this deep dive with
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a mission to understand how humanity went from
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seeing the universe to feeling it. And we've
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covered a lot of ground. We really have. We explored
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how space -time is... We unpack the unimaginable
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energy of merging black holes. And the mind -boggling
18:49
engineering required to build lasers capable
18:51
of measuring a stretch in reality smaller than
18:54
a proton. And the craziest part. The field of
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gravitational wave astronomy is still in its
18:59
absolute infancy. Really? Oh, yeah. We've only
19:02
just turned the speakers on. But as detectors
19:04
get more sensitive, the implications become staggering.
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What's next? Up to this point, we've been talking
19:09
about detecting waves from dying stars and black
19:12
holes. But if we can eventually put interferometers
19:16
in space, which is a project currently in development
19:18
called LISA, we could theoretically detect gravitational
19:22
waves that are much older and much lower in frequency.
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How old are we talking? Millions of years. We
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could look past the stars entirely. Wait, what
19:32
do you mean? You see, when we use light to look
19:34
deep into the universe, we hit a wall. We can
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only see back to about 380 ,000 years after the
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Big Bang. Because before that, the universe was
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a dense, superheated plasma. Right. It was opaque.
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Light literally could not travel through it.
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But gravitational waves don't care about plasma.
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Exactly. They pass through everything unimpeded.
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The Big Bang itself, the ultimate violent expansion
19:57
of space -time, would have unleashed a torrential
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flood of primordial gravitational waves. And
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those waves are still traveling. Those waves
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are still washing over us right now. If we can
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build an ear sensitive enough, we won't just
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be listening to the death of stars. We could
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literally hear the exact moment of the universe's
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birth. Wow. That is profound thought to end on.
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I mean, for all of human history, we looked up
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at the night sky and it looked so serene. So
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peaceful. Yeah, we thought the universe was mostly
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quiet and still, simply because we only had our
20:26
eyes open. But it was never quiet. No, it wasn't.
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We have been sitting in the middle of a roaring,
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chaotic ocean of cosmic collisions since the
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dawn of time. So next time you step outside and
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look up at a seemingly quiet night sky, ask yourself.
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What invisible waves are washing over you right
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in that very moment, bringing echoes of a billion
20:46
-year -old storm?