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How Infrared Lasers Could Improve the Future of Gravitational Wave Detection · The Quark Side - Quantum Physics Podcast

• 0:01
  Speaker 1: Welcome to the Quarkside Quantum Physics Podcast, an exploration of
• 0:05
  Speaker 1: the fundamental structure of reality, where quantum laws govern matter, energy,
• 0:11
  Speaker 1: and information. Here, uncertainty is a feature, not a flaw,
• 0:16
  Speaker 1: and understanding begins at the smallest scales.
• 0:27
  Speaker 2: Imagine trying to feel a vibration coming from millions of
• 0:32
  Speaker 2: light years away.
• 0:33
  Speaker 3: Which is just, I mean, it's almost impossible to even conceptualize. Right.
• 0:36
  Speaker 2: Not hearing a sound, not seeing a flash of light,
• 0:39
  Speaker 2: but actually feeling a physical vibration from across the universe.
• 0:43
  Speaker 3: Yeah. From entirely across the cosmos.
• 0:45
  Speaker 2: The sheer audacity of even attempting that is wild, but
• 0:48
  Speaker 2: humanity is actually doing it. We are building machines that
• 0:51
  Speaker 2: measure changes in distance that are a thousand times smaller
• 0:55
  Speaker 2: than the width of a single proton.
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  Speaker 3: It really is one of the most absurd engineering feats
• 1:00
  Speaker 3: we've ever attempted.
• 1:01
  Speaker 2: So today we are going to explore how we are
• 1:04
  Speaker 2: upgrading our ability to listen to the universe's most massive collisions,
• 1:09
  Speaker 2: like black holes, neutron stars, all of it.
• 1:11
  Speaker 3: Exactly.
• 1:11
  Speaker 2: And our mission is to figure out how solving this
• 1:14
  Speaker 2: incredibly delicate, bizarre engineering puzzle right here on Earth is
• 1:18
  Speaker 2: going to let us hear the oldest black holes out there.
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  Speaker 3: It's a huge step forward for astrophysics.
• 1:24
  Speaker 2: Okay, let's unpack this scale first because, I mean, the
• 1:26
  Speaker 2: human brain just isn't built to comprehend something a thousand
• 1:29
  Speaker 2: times smaller than a proton.
• 1:30
  Speaker 3: No, not at all. We just don't have a frame
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  Speaker 3: of reference for it. Right.
• 1:33
  Speaker 4: So if you really think about it, measuring that kind
• 1:35
  Speaker 4: of distance is like standing in your backyard, looking up
• 1:38
  Speaker 4: at the night sky, and trying to measure the exact
• 1:41
  Speaker 4: width of a microscopic dust mite that is just sitting.
• 1:44
  Speaker 2: On a rock on the moon.
• 1:46
  Speaker 3: That is, yeah, that is actually an incredibly accurate analogy.
• 1:50
  Speaker 3: It is a staggering scale to try and wrap your
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  Speaker 3: head around.
• 1:53
  Speaker 2: It just sounds like sci-fi.
• 1:54
  Speaker 3: It does. But to ground your analogy in the physical
• 1:57
  Speaker 3: reality of how we are actually pulling this off, you
• 2:00
  Speaker 3: have to picture the hardware involved.
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  Speaker 2: Okay.
• 2:02
  Speaker 3: We are talking about massive mirrors. They weigh 40 kilograms,
• 2:06
  Speaker 3: which is about 88 pounds each.
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  Speaker 2: So these are huge.
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  Speaker 3: Huge. These aren't, you know, your standard bathroom mirrors. They
• 2:12
  Speaker 3: are heavy, highly engineered cylinders of ultra pure glass. Wow.
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  Speaker 3: And they sit exactly four kilometers, so two and a
• 2:20
  Speaker 3: half miles apart, from each other. inside these incredibly long
• 2:23
  Speaker 3: vacuum tubes.
• 2:25
  Speaker 2: So you have these 88-pound glass cylinders, two and a
• 2:28
  Speaker 2: half miles apart, just perfectly suspended in pitch darkness.
• 2:32
  Speaker 3: That's the setup. They act as the ultimate cosmic tripwire.
• 2:36
  Speaker 2: A tripwire?
• 2:36
  Speaker 3: Yeah.
• 2:37
  Speaker 2: I like that.
• 2:38
  Speaker 3: Yeah, they're suspended there in a complete vacuum, totally isolated
• 2:42
  Speaker 3: from the outside world, just waiting for a ripple in
• 2:45
  Speaker 3: space-time itself to pass through the Earth and jostle them.
• 2:48
  Speaker 2: And these ripples come from massive collisions, right?
• 2:51
  Speaker 3: Exactly. When massive objects in deep space, like two black holes, collide,
• 2:56
  Speaker 3: they send out gravitational waves.
• 2:58
  Speaker 2: Right, which aren't sound waves.
• 3:01
  Speaker 3: No, not at all. They are actual physical ripples that
• 3:04
  Speaker 3: stretch and squeeze the very fabric of space as they
• 3:08
  Speaker 3: travel outward at the speed of light.
• 3:10
  Speaker 2: And by the time those ripples travel for like a
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  Speaker 2: billion years and finally reach Earth, that stretching is unimaginably tiny.
• 3:18
  Speaker 1: It is.
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  Speaker 3: Which is why we need the tripwire.
• 3:21
  Speaker 2: Makes sense.
• 3:22
  Speaker 3: We bounce a main science laser back and forth between
• 3:25
  Speaker 3: these 88-pound mirrors over that 2.5-mile stretch. Uh-huh. Because the
• 3:29
  Speaker 3: speed of light is constant, we know exactly how long
• 3:32
  Speaker 3: it should take the light to make that round trip.
• 3:34
  Speaker 2: Right. The timing is locked in.
• 3:35
  Speaker 3: Precisely. So, if a gravitational wave passes through the Earth,
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  Speaker 3: it stretches the space between the mirrors by that fraction
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  Speaker 3: of a proton.
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  Speaker 2: And the laser catches that change.
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  Speaker 3: Yes. The distance changes. The laser light's travel time shifts
• 3:50
  Speaker 3: ever so slightly. And the tripwire is triggered. We've essentially
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  Speaker 3: heard the collision. Okay.
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  Speaker 2: I have to admit, though, I'm lost on one thing
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  Speaker 2: right out of the gate.
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  Speaker 3: Sure. What's that?
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  Speaker 2: If these detectors are already built and they are already
• 4:02
  Speaker 2: successfully acting as this cosmic tripwire measuring fractions of a proton,
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  Speaker 2: why are we talking about upgrading them? It sounds like
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  Speaker 2: they already do the impossible.
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  Speaker 3: It's a fair question. It really comes down to reach.
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  Speaker 2: Reach, like how far out we can hear.
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  Speaker 3: Exactly.
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  Speaker 1: Mm-hmm.
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  Speaker 3: Right now, we can hear the loud, relatively recent collisions
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  Speaker 3: in our immediate cosmic neighborhood. Okay. But to listen further
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  Speaker 3: out into the universe, you know, to hear fainter, smaller,
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  Speaker 3: or much more ancient collisions from the very dawn of
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  Speaker 3: the cosmos, the detectors need to be exponentially more sensitive. Ah,
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  Speaker 3: I see. So the next evolution involves swapping out the
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  Speaker 3: current mirrors for new ones. They feature what is called
• 4:42
  Speaker 3: a low-noise crystalline mirror coating.
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  Speaker 4: No way.
• 4:45
  Speaker 2: When you say low noise, I assume you don't mean
• 4:47
  Speaker 2: acoustic noise, right? Because they are in a vacuum tube.
• 4:50
  Speaker 2: There is no sound.
• 4:52
  Speaker 3: You're right to clarify that.
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  Speaker 4: Yeah.
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  Speaker 3: When physicists talk about noise in this context, they mean
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  Speaker 3: thermal noise, heat.
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  Speaker 2: Heat makes noise?
• 5:01
  Speaker 3: Well, at a microscopic level, the atoms inside any material
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  Speaker 3: are always jittering around.
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  Speaker 2: Just constantly vibrating.
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  Speaker 3: Exactly. That jittering is thermal energy. So if the atoms
• 5:11
  Speaker 3: on the surface of your mirror are jittering, That creates
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  Speaker 3: microscopic fluctuations on the mirror's surface itself.
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  Speaker 2: Oh, I get it. So to a laser trying to
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  Speaker 2: measure a proton-sized change in distance, the jittering atoms look
• 5:24
  Speaker 2: exactly like a gravitational wave.
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  Speaker 3: That's it. It completely blurs the signal.
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  Speaker 2: So the mirror is basically vibrating itself and drowning out
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  Speaker 2: the universe.
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  Speaker 3: That is a very good way to look at it.
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  Speaker 3: So the new crystalline coatings are fundamentally structured differently.
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  Speaker 2: How so?
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  Speaker 3: Their atomic structure is much more rigid and ordered. That
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  Speaker 3: drastically reduces the internal thermal jittering. It essentially quiets the
• 5:48
  Speaker 3: mirror down so we can hear those fainter signals.
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  Speaker 2: Okay, so we swap out the glass for the new
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  Speaker 2: crystalline mirrors, and boom, we can hear the edge of
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  Speaker 2: the universe.
• 5:57
  Speaker 3: If only it were that easy.
• 5:59
  Speaker 2: Right. I know it's not that simple, because there is
• 6:02
  Speaker 2: this bizarre obstacle standing in the way of the upgrade.
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  Speaker 3: There really is.
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  Speaker 2: Because before we can even turn on the main science
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  Speaker 2: laser to listen to the cosmos... These 88-pound mirrors have
• 6:13
  Speaker 2: to be completely at rest and perfectly locked in place, right?
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  Speaker 3: They do. And this is where the engineering gets incredibly punishing.
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  Speaker 2: Punishing is a good word for it.
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  Speaker 3: I mean, you can't just hang an 88-pound mirror on
• 6:26
  Speaker 3: a wire and expect it to stay still. The Earth
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  Speaker 3: is a terribly noisy, vibrating place.
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  Speaker 2: Right, like a truck driving on a highway five miles
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  Speaker 2: away would shake the ground enough to ruin a measurement
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  Speaker 2: that small.
• 6:38
  Speaker 3: Oh, it is actually much worse than a truck. Really? Yeah,
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  Speaker 3: even the ocean waves crashing on a shoreline hundreds of
• 6:45
  Speaker 3: miles away from the observatory create enough continuous seismic vibration
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  Speaker 3: to completely blind these mirrors.
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  Speaker 2: Hundreds of miles away. That is insane.
• 6:55
  Speaker 3: It is. So we have to actively counteract that constant rumbling.
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  Speaker 2: And how do we do that?
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  Speaker 3: The system used to freeze these mirrors in place against
• 7:04
  Speaker 3: the movement of the Earth is called arm-length stabilization, or
• 7:07
  Speaker 3: we just call it the locking system.
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  Speaker 2: Wait, so if the ground beneath it is always moving,
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  Speaker 2: how does that actually work? How do you lock something
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  Speaker 2: that heavy?
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  Speaker 3: It relies on a hyper-precise feedback loop. We use a
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  Speaker 3: secondary laser, specifically a green laser light, that bounces off
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  Speaker 3: the mirrors to constantly measure their exact position.
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  Speaker 2: Okay, a green laser.
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  Speaker 3: Got it. And that green laser feeds data into a
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  Speaker 3: computer thousands of times a second.
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  Speaker 2: Wow, so it's constantly monitoring.
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  Speaker 3: Continuously. The computer calculates exactly how the mirror is swinging
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  Speaker 3: due to seismic noise. And then it sends signals to
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  Speaker 3: tiny magnetic actuators pushing against the mirror. Oh, wow.
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  Speaker 2: So the computer is actively pushing back against the ocean
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  Speaker 2: waves in real time.
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  Speaker 3: Exactly. The actuators nudge the mirror microscopically to perfectly cancel
• 7:54
  Speaker 3: out the Earth's vibrations.
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  Speaker 2: So it brings it to a standstill.
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  Speaker 3: Right. Bringing the mirror to a complete dead stop and
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  Speaker 3: holding it at that exact four kilometer distance.
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  Speaker 2: Which brings us to the ultimate paradox of this upgrade.
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  Speaker 3: The big bottleneck.
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  Speaker 2: Yeah, so we have this locking system that relies on
• 8:10
  Speaker 2: a green laser to act as the sensor, right?
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  Speaker 3: Correct.
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  Speaker 2: And we have these incredible new super sensitive crystalline mirrors.
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  Speaker 2: But the problem is that these new crystalline coatings actually
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  Speaker 2: absorb the green laser light.
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  Speaker 3: They do. The new coating is completely incompatible with green light.
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  Speaker 2: Wait, so if the mirror absorbs the light instead of
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  Speaker 2: reflecting it, does the whole stabilization process just fall apart?
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  Speaker 3: It completely falls apart.
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  Speaker 2: Okay, let me try to visualize this. Is this like
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  Speaker 2: trying to balance a heavy spinning plate on a rigid stick,
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  Speaker 2: but suddenly your stick turns into a wet noodle because
• 8:41
  Speaker 2: the plate just absorbed all its strength?
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  Speaker 3: That's a great analogy, actually. What's fascinating here is that
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  Speaker 3: the stabilization system needs the green light to bounce back
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  Speaker 3: so the computer can feel where the mirror is.
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  Speaker 2: Like the rigid stick. Right.
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  Speaker 3: If the crystalline coating absorbs the green light, the system
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  Speaker 3: gets no feedback. The stick turns to mush.
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  Speaker 2: The computer goes blind.
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  Speaker 3: Yes. The computer goes blind. The actuators don't know when
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  Speaker 3: to push. and the mirror just starts swinging wildly from
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  Speaker 3: the seismic noise.
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  Speaker 2: So the whole thing is just useless?
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  Speaker 3: Well, it actually gets worse.
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  Speaker 2: Worse? How can it be worse than useless?
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  Speaker 3: Because when the mirror absorbs that laser light, the light
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  Speaker 3: doesn't just disappear. That energy is converted into heat. Oh, no.
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  Speaker 2: And we literally just talked about how heat is the
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  Speaker 2: ultimate enemy here.
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  Speaker 3: Exactly. The localized heat from absorbing the green laser causes
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  Speaker 3: the crystalline mirror coating to physically expand and warp.
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  Speaker 2: So the laser's melting it?
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  Speaker 3: Essentially, yes. It melts a microscopic dent into the surface
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  Speaker 3: of your perfect mirror, which completely ruins that proton-level precision.
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  Speaker 4: Oh, wow.
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  Speaker 2: So the pursuit of a better, quieter mirror accidentally blinded
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  Speaker 2: the machine's ability to hold itself still.
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  Speaker 3: It did. We built a better ear. But in the process,
• 9:55
  Speaker 3: we broke the neck that holds the ear steady.
• 9:57
  Speaker 2: That is incredibly frustrating.
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  Speaker 3: It is, but... it's common in cutting-edge science. We often
• 10:02
  Speaker 3: think of astrophysics as this purely theoretical, high-minded discipline where
• 10:07
  Speaker 3: people are doing complex math on chalkboards to solve the
• 10:09
  Speaker 3: mysteries of spacetime.
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  Speaker 2: Right, like Einstein sitting in a room thinking about gravity.
• 10:13
  Speaker 3: Exactly. But in reality, it's not. Unlocking the cosmos almost
• 10:18
  Speaker 3: always comes down to fixing a hyper-specific localized materials problem
• 10:22
  Speaker 3: right here on Earth.
• 10:24
  Speaker 2: So our ability to map the universe is currently stalled
• 10:27
  Speaker 2: by how a specific crystal reacts to green light.
• 10:30
  Speaker 3: That was exactly the bottleneck.
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  Speaker 2: Okay, so since we can't use the green light with
• 10:34
  Speaker 2: the new mirrors because they just eat it up and warp,
• 10:38
  Speaker 2: how in the world do we keep these 88-pound mirrors
• 10:40
  Speaker 2: perfectly still across two and a half miles?
• 10:43
  Speaker 3: Well, a team of researchers led by Dr. Jian Liu
• 10:46
  Speaker 3: at the University of Western Australia, they're part of the
• 10:49
  Speaker 3: OSGRAV team, they figured out a brilliant workaround.
• 10:52
  Speaker 2: What did they do?
• 10:54
  Speaker 3: They realized that if green light is the problem, they
• 10:57
  Speaker 3: needed a color of light that the new crystalline coatings
• 11:00
  Speaker 3: would completely ignore.
• 11:01
  Speaker 2: Something that just bounces right off.
• 11:03
  Speaker 3: Right. A light that would bounce off the surface without
• 11:06
  Speaker 3: leaving any energy or heat behind.
• 11:08
  Speaker 2: And what color was that?
• 11:09
  Speaker 3: They found it in the infrared spectrum. They developed an
• 11:13
  Speaker 3: entirely new locking scheme using infrared light.
• 11:16
  Speaker 2: Specifically, I think it was 1596 nanometers, right?
• 11:18
  Speaker 3: That's exactly right. 1596 nanometers. To the new crystalline mirrors,
• 11:22
  Speaker 3: this specific infrared wavelength is perfectly fine. The coating doesn't
• 11:26
  Speaker 3: absorb it at all. It reflects it beautifully.
• 11:28
  Speaker 2: Okay, so problem solved. The infrared laser bounces back perfectly,
• 11:32
  Speaker 2: feeds the computer, and you get your arm length stabilization.
• 11:35
  Speaker 3: Well, not quite. Why not?
• 11:37
  Speaker 2: I know what people listening are thinking right now because
• 11:39
  Speaker 2: I'm thinking it too.
• 11:40
  Speaker 3: Let's hear it.
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  Speaker 2: If the new mirrors reflect infrared perfectly and the main
• 11:44
  Speaker 2: science laser, the one that actually listens for the gravitational waves,
• 11:48
  Speaker 2: is also an infrared laser, why is this complicated? Why
• 11:51
  Speaker 2: not just have the main laser lock the mirrors itself?
• 11:55
  Speaker 3: The very logical question. The short answer is that the
• 11:57
  Speaker 3: main science laser operates at a completely different infrared wavelength.
• 12:01
  Speaker 2: Oh, really?
• 12:02
  Speaker 3: Yeah. It operates at 1064 nanometers.
• 12:05
  Speaker 2: Okay, but it's still infrared.
• 12:06
  Speaker 3: It is. But you can't just use it to lock
• 12:08
  Speaker 3: the mirrors from a dead stop. Because the main laser
• 12:11
  Speaker 3: is incredibly powerful.
• 12:13
  Speaker 2: Like too strong to use for a delicate job.
• 12:15
  Speaker 3: Precisely. If the mirrors are swinging wildly and you hit
• 12:18
  Speaker 3: them with the full power of the main science laser,
• 12:21
  Speaker 3: it creates a chaotic optical resonance that actually pushes the
• 12:24
  Speaker 3: mirrors around and makes the swinging worse.
• 12:27
  Speaker 2: Oh, wow. Is that like trying to stop a swinging
• 12:29
  Speaker 2: pendulum by blasting it with a fire hose?
• 12:32
  Speaker 3: That is exactly what it's like. You need a gentler
• 12:36
  Speaker 3: secondary laser, the locking laser. to grab the mirror, slow
• 12:40
  Speaker 3: it down, hold it steady, and then hand control over
• 12:43
  Speaker 3: to the powerful main laser once everything is perfectly still.
• 12:46
  Speaker 2: But wait, so we have two different wavelengths. The new
• 12:49
  Speaker 2: locking laser is 1,596 nanometers, and the main science laser
• 12:54
  Speaker 2: is 1,064 nanometers.
• 12:56
  Speaker 3: Correct.
• 12:57
  Speaker 2: If mismatched frequencies are the problem, why not just build
• 13:01
  Speaker 2: a main science laser that also runs at 1,596 nanometers
• 13:04
  Speaker 2: so they match?
• 13:06
  Speaker 3: Well, the main 1064 nanometer laser is a highly customized,
• 13:10
  Speaker 3: multi-million dollar piece of hardware.
• 13:12
  Speaker 2: Ah, it's a money issue.
• 13:14
  Speaker 3: Money and infrastructure. The entire observatory's optical layout, all the sensors,
• 13:19
  Speaker 3: the vacuum interfaces, it is all perfectly tuned to that
• 13:23
  Speaker 3: specific 1064 nanometer light.
• 13:26
  Speaker 2: So you'd have to rebuild the whole place.
• 13:28
  Speaker 3: Exactly. Rebuilding the entire core of the billion dollar observatory
• 13:32
  Speaker 3: just to match a new locking laser wasn't an option.
• 13:35
  Speaker 3: we had to adapt the locking mechanism to fit the
• 13:37
  Speaker 3: existing infrastructure.
• 13:39
  Speaker 2: Okay, so what does this all mean in practice? We
• 13:42
  Speaker 2: have two different lasers running at two completely different frequencies,
• 13:46
  Speaker 2: and they need to seamlessly pass control of an 88-pound
• 13:50
  Speaker 2: mirror suspended two and a half miles away. I mean,
• 13:52
  Speaker 2: this sounds like the most stressful relay race imaginable.
• 13:56
  Speaker 3: The relay race analogy is a really apt way to
• 13:58
  Speaker 3: describe the handover process.
• 14:00
  Speaker 2: Let's walk through this race. So, The infrared locking laser
• 14:04
  Speaker 2: runs the first leg, getting the mirror perfectly stabilized.
• 14:07
  Speaker 4: Right.
• 14:08
  Speaker 2: Then it has to pass the baton to the main
• 14:10
  Speaker 2: measuring laser so the actual listening can begin.
• 14:13
  Speaker 3: Exactly.
• 14:14
  Speaker 2: But if they are running at different speeds, or in
• 14:17
  Speaker 2: this case different frequencies, they are going to drop the baton.
• 14:21
  Speaker 2: They can't communicate, right?
• 14:22
  Speaker 3: Right. The computer won't be able to read them both
• 14:24
  Speaker 3: simultaneously to make the switch. The mirror will lose its
• 14:27
  Speaker 3: lock and will start swinging all over again.
• 14:30
  Speaker 2: So how do they keep from dropping it? I read
• 14:32
  Speaker 2: that the researchers used special crystals to somehow translate the frequencies.
• 14:36
  Speaker 3: They did.
• 14:37
  Speaker 2: Do these crystals act as the synchronization zone on the track?
• 14:41
  Speaker 2: You know, that painted box where both runners have to
• 14:43
  Speaker 2: be moving at the exact same speed so the handoff
• 14:45
  Speaker 2: is perfectly smooth?
• 14:47
  Speaker 3: They absolutely serve as that synchronization zone. If we connect
• 14:50
  Speaker 3: this to the bigger picture, the researchers used special nonlinear
• 14:54
  Speaker 3: crystals to physically manipulate the light itself.
• 14:57
  Speaker 2: How does that work?
• 14:59
  Speaker 3: They take a small portion of the 1,596 nanometer locking
• 15:02
  Speaker 3: light and a small portion of the 1064 nanometer main
• 15:06
  Speaker 3: laser light, and they run both of those invisible beams
• 15:09
  Speaker 3: through these special crystals. Okay. The crystals combine and convert
• 15:14
  Speaker 3: those different frequencies to produce green light.
• 15:16
  Speaker 2: Wait, hold on. I need to push back on this.
• 15:18
  Speaker 3: Go ahead.
• 15:20
  Speaker 2: Converting frequencies. You mean taking two invisible infrared lasers and
• 15:26
  Speaker 2: physically turning them into a visible galaxy?
• 15:29
  Speaker 3: Yes, that's exactly what happens.
• 15:32
  Speaker 2: That sounds like alchemy. How does a crystal just change
• 15:35
  Speaker 2: the fundamental nature of light?
• 15:37
  Speaker 3: It does sound like magic, but it's an entire field
• 15:39
  Speaker 3: of physics called nonlinear optics.
• 15:41
  Speaker 2: Okay, I'm listening.
• 15:43
  Speaker 3: Think of the crystal as an optical mixing board. Under
• 15:46
  Speaker 3: normal conditions, light beams just pass right through each other.
• 15:49
  Speaker 4: Right.
• 15:50
  Speaker 3: But inside the very specific atomic lattice of a nonlinear crystal,
• 15:54
  Speaker 3: the incoming photons of light are forced to interact.
• 15:57
  Speaker 2: Oh. Interesting.
• 15:59
  Speaker 3: The crystal essentially takes the energy of the incoming infrared photons,
• 16:03
  Speaker 3: combines them, and emits new photons that have a higher energy.
• 16:07
  Speaker 2: And higher energy means?
• 16:10
  Speaker 3: Higher energy means a shorter wavelength, which shifts the invisible
• 16:13
  Speaker 3: infrared light right up into the visible green spectrum.
• 16:16
  Speaker 2: Wait, wait, wait. Green light? But we just established like
• 16:19
  Speaker 2: 10 minutes ago that the whole problem started because the
• 16:21
  Speaker 2: new emitters hate green light. They absorb it and warp.
• 16:24
  Speaker 3: They do. But here's the genius of it. This conversion
• 16:29
  Speaker 3: into green light isn't happening out in the main vacuum
• 16:31
  Speaker 3: tubes where the precious crystalline mirrors are hanging.
• 16:33
  Speaker 2: Where is it happening?
• 16:35
  Speaker 3: This is happening entirely internally on a small optical bench
• 16:38
  Speaker 3: safely inside the control room. Oh, whoa.
• 16:42
  Speaker 2: Okay, I see.
• 16:43
  Speaker 3: By converting samples of both infrared signals into the exact
• 16:46
  Speaker 3: same frequency of green light inside the control room, the
• 16:49
  Speaker 3: computer can directly compare them using standard, highly sensitive green
• 16:53
  Speaker 3: light sensors.
• 16:54
  Speaker 2: So it forces the two lasers to speak the same language.
• 16:56
  Speaker 3: Yes. It forces them to synchronize perfectly.
• 17:00
  Speaker 2: That is brilliant.
• 17:01
  Speaker 3: And once they are synchronized, once both runners are perfectly
• 17:04
  Speaker 3: matched in the handover zone, the computer smoothly dials down
• 17:08
  Speaker 3: the power of the locking laser while dialing up the
• 17:10
  Speaker 3: power of the main laser.
• 17:12
  Speaker 2: And the baton is passed.
• 17:13
  Speaker 3: Passed perfectly. The mirror never even knows what happened.
• 17:16
  Speaker 2: That is truly mind-bending. They used the very color of
• 17:20
  Speaker 2: light that was causing the problem to solve the problem,
• 17:22
  Speaker 2: just by moving where that color exists in the system.
• 17:25
  Speaker 3: It is an incredibly elegant workaround. And the operational reality
• 17:29
  Speaker 3: here is that this handover is unimaginably delicate.
• 17:33
  Speaker 2: I can imagine.
• 17:34
  Speaker 3: Dr. Lee's team didn't just theorize this on a chalkboard.
• 17:37
  Speaker 3: They built it and proved it works. They demonstrated they
• 17:41
  Speaker 3: could achieve a fully stable handover from the locking laser
• 17:44
  Speaker 3: to the main laser in about 60 seconds.
• 17:47
  Speaker 2: 60 seconds. Wait, why is that specific time frame so important?
• 17:53
  Speaker 3: Because... The moment of transition, when both lasers are pushing
• 17:56
  Speaker 3: on the mirror, is highly unstable.
• 17:59
  Speaker 2: So you want it over as fast as possible.
• 18:01
  Speaker 3: Exactly. The faster you can complete the handoff securely, the
• 18:05
  Speaker 3: less chance there is for seismic noise to break the lock.
• 18:08
  Speaker 3: A 60-second transition is actually much faster and more reliable
• 18:12
  Speaker 3: than the previous green light system ever was.
• 18:14
  Speaker 2: Oh, wow. So they improved the speed, too.
• 18:17
  Speaker 4: Yes.
• 18:18
  Speaker 3: And they proved it wasn't just a fluke by repeating
• 18:20
  Speaker 3: this rapid handover successfully over several days of rigorous testing.
• 18:25
  Speaker 2: Okay, so a 60-second baton pass using an infrared optical
• 18:29
  Speaker 2: mixing board is undeniably cool. But let's talk about the results.
• 18:33
  Speaker 3: Sure.
• 18:34
  Speaker 2: What does this mean for the actual physical precision of
• 18:37
  Speaker 2: the machine? Because we started this conversation talking about a
• 18:40
  Speaker 2: thousandth of a proton.
• 18:41
  Speaker 3: Right. Well, the margin of error they maintained during this
• 18:44
  Speaker 3: new infrared locking method is almost unfathomable.
• 18:48
  Speaker 2: Give it to me.
• 18:49
  Speaker 3: Based on the data from those days of testing, the
• 18:52
  Speaker 3: measurement error between the lasers during the lock was estimated
• 18:55
  Speaker 3: to be about one tenth the width of an atom.
• 18:58
  Speaker 2: I need to stop and just let that sink in.
• 19:02
  Speaker 2: One tenth the width of a single atom.
• 19:09
  Speaker 3: Measured continuously.
• 19:10
  Speaker 2: Here's where it gets really interesting. Across an entire four kilometer,
• 19:15
  Speaker 2: two and a half mile laser arm. That is the
• 19:18
  Speaker 2: margin of error while pushing back against the vibration of
• 19:22
  Speaker 2: ocean waves.
• 19:23
  Speaker 3: Yes. That is the level of stability they achieved.
• 19:27
  Speaker 2: Numbers like that, they stop feeling like math. If our
• 19:32
  Speaker 2: error margin is a tenth of an atom over two
• 19:34
  Speaker 2: and a half miles, how does that translate to what
• 19:37
  Speaker 2: you and I will actually see in the news?
• 19:39
  Speaker 3: It's a huge shift.
• 19:40
  Speaker 2: Like, does this mean we'll find things we didn't even
• 19:42
  Speaker 2: know existed?
• 19:44
  Speaker 3: It buys us a much deeper view of the universe.
• 19:46
  Speaker 3: Think of it this way. The reason we want to
• 19:48
  Speaker 3: install those new low-noise crystalline mirrors in the first place
• 19:51
  Speaker 3: is because they are intrinsically quieter.
• 19:54
  Speaker 2: Right, less of that thermal atomic jittering.
• 19:56
  Speaker 3: Exactly. But we couldn't use them because we couldn't lock them.
• 20:00
  Speaker 3: By solving the locking problem with this incredible one-tenth of
• 20:03
  Speaker 3: an atom precision, we can finally install those mirrors.
• 20:07
  Speaker 2: We basically unlocked the hardware upgrade.
• 20:09
  Speaker 3: We did. And with those new mirrors successfully installed and locked,
• 20:13
  Speaker 3: the detector's sensitivity will completely skyrocket.
• 20:16
  Speaker 2: And that lets us hear further.
• 20:18
  Speaker 3: This directly advances humanity's ability to discover and study cosmic
• 20:22
  Speaker 3: events that are currently completely invisible to us.
• 20:25
  Speaker 2: Like what?
• 20:26
  Speaker 3: We will be able to detect the collision of ancient
• 20:29
  Speaker 3: black holes that happened so incredibly far away and so
• 20:33
  Speaker 3: early in the formation of the universe that their gravitational
• 20:36
  Speaker 3: waves are just too faint for our current glass mirrors
• 20:38
  Speaker 3: to pick up.
• 20:39
  Speaker 2: So we are essentially building a better time machine that
• 20:43
  Speaker 2: can hear further back into the history of the cosmos?
• 20:45
  Speaker 3: That is exactly what it is. And we will also
• 20:48
  Speaker 3: be able to listen to distant neutron stars colliding.
• 20:51
  Speaker 2: Why are neutron stars so important?
• 20:53
  Speaker 3: Those specific collisions are crucial because they are the cosmic
• 20:56
  Speaker 3: forges that create the heaviest elements in the universe.
• 20:59
  Speaker 2: Like what kind of elements?
• 21:01
  Speaker 3: Like the gold in your jewelry or the platinum in
• 21:03
  Speaker 3: your electronics.
• 21:04
  Speaker 2: Wait, really?
• 21:05
  Speaker 3: It does. But right now... Unless a neutron star collision
• 21:09
  Speaker 3: happens relatively close by in cosmic terms. The tiny ripples
• 21:13
  Speaker 3: it makes are completely lost in the thermal background noise
• 21:16
  Speaker 3: of our own detectors.
• 21:17
  Speaker 2: Ah, the jittering.
• 21:18
  Speaker 3: Right. This new infrared locking scheme strips away that noise.
• 21:22
  Speaker 3: It clears the path.
• 21:23
  Speaker 2: So, you know, every time you scroll through your news
• 21:26
  Speaker 2: feed and you see a headline about some massive reality-altering
• 21:29
  Speaker 2: cosmic discovery?
• 21:30
  Speaker 3: Like the sound of two black holes colliding billions of
• 21:33
  Speaker 3: years ago?
• 21:34
  Speaker 2: Yeah, exactly. Or mapping where all the gold in the
• 21:36
  Speaker 2: universe comes from. You have to remember what's really happening
• 21:39
  Speaker 2: behind the scenes.
• 21:40
  Speaker 3: It's all engineering. It is.
• 21:42
  Speaker 2: You are reading about the triumph of tiny, incredibly grounded
• 21:46
  Speaker 2: engineering fixes. We only get to understand the macro universe,
• 21:50
  Speaker 2: the colossal, mind-breaking scale of deep space, by mastering the
• 21:55
  Speaker 2: absolute micromechanics of things right here on Earth.
• 21:58
  Speaker 3: It is the ultimate synthesis of the large and the small.
• 22:01
  Speaker 2: It really is.
• 22:02
  Speaker 3: I mean, The universe is constantly broadcasting information in every
• 22:06
  Speaker 3: conceivable way. It's vibrating. It's radiating. It's stretching the fabric
• 22:10
  Speaker 3: of space-time itself.
• 22:12
  Speaker 2: But we just can't hear it.
• 22:14
  Speaker 3: Not without the tools. We are deaf and blind to
• 22:17
  Speaker 3: it until we literally invent the right physical materials, the
• 22:21
  Speaker 3: right glass, the right coatings, the right nonlinear crystals to
• 22:25
  Speaker 3: actually catch those signals.
• 22:26
  Speaker 2: It all comes down to mastering the exact wavelength of
• 22:29
  Speaker 2: an infrared light or figuring out how to use a
• 22:31
  Speaker 2: crystal to synchronize two lasers in 60 seconds without dropping
• 22:35
  Speaker 2: the baton.
• 22:36
  Speaker 3: Exactly right.
• 22:37
  Speaker 2: It is wild to think that our understanding of the
• 22:40
  Speaker 2: infinite is entirely bottlenecked by the materials we can build
• 22:44
  Speaker 2: with today.
• 22:45
  Speaker 3: It's humbling, honestly. It is.
• 22:47
  Speaker 2: Which leaves me with this final thought for you to
• 22:49
  Speaker 2: just sort of mull over. If upgrading to better mirrors
• 22:53
  Speaker 2: required a complete reimagining of the colors of light we use,
• 22:57
  Speaker 2: and required us to invent new ways to use crystals
• 23:00
  Speaker 2: just to keep our earthly instruments stable, what other hidden
• 23:03
  Speaker 2: signals in the universe are currently washing right over us?
• 23:06
  Speaker 3: Oh, that's a profound thought.
• 23:08
  Speaker 2: Right. I mean, we are sitting here, so proud of
• 23:10
  Speaker 2: our infrared lasers and perfectly quiet mirrors. But what if
• 23:15
  Speaker 2: the next great cosmic secret is already here, pulsing through
• 23:18
  Speaker 2: the room you are sitting in right now, just waiting
• 23:21
  Speaker 2: for humanity to invent the right color of technology to
• 23:24
  Speaker 2: finally tune into it?
• 23:25
  Speaker 3: It really makes you wonder.
• 23:27
  Speaker 2: It does. Something to think about the next time you
• 23:29
  Speaker 2: look up at the moon and wonder just how small
• 23:31
  Speaker 2: of a detail you're missing.