- 2 days ago
This video explores LIGO (Laser Interferometer Gravitational-Wave Observatory), a massive, highly precise experiment designed to detect gravitational waves (1:20-2:10). Einstein predicted these ripples in space-time 100 years ago, but scientists originally thought they were impossible to measure due to their incredibly small size (2:53-3:45).
Key Highlights of the LIGO Experiment:
The Machine's Scale: LIGO consists of two 4-kilometer-long concrete tubes arranged in an L-shape, located in remote deserts (0:05-0:19).
How it Works: Lasers are fired down these arms, bouncing off some of the smoothest mirrors ever made (11:14-11:53). When a gravitational wave passes, it squeezes and stretches space, slightly altering the laser's path, which is detected by a flicker of light (5:27-5:40).
Extreme Precision: The detector must measure changes 10,000 times smaller than a proton (3:52-3:59), requiring vibration isolation 10 billion times more still than the ground (13:00-13:14).
Results and Future:
First Detection: After years of silence, LIGO detected the first gravitational wave in September 2015, caused by two merging black holes 1.3 billion light-years away (14:26-15:42).
Nobel Prize: This groundbreaking discovery earned the scientists the Nobel Prize and opened a new era of astrophysics (15:23-15:28).
Future Upgrades: New, larger observatories are planned to increase sensitivity and hear even further into the universe (16:48-17:11).
Key Highlights of the LIGO Experiment:
The Machine's Scale: LIGO consists of two 4-kilometer-long concrete tubes arranged in an L-shape, located in remote deserts (0:05-0:19).
How it Works: Lasers are fired down these arms, bouncing off some of the smoothest mirrors ever made (11:14-11:53). When a gravitational wave passes, it squeezes and stretches space, slightly altering the laser's path, which is detected by a flicker of light (5:27-5:40).
Extreme Precision: The detector must measure changes 10,000 times smaller than a proton (3:52-3:59), requiring vibration isolation 10 billion times more still than the ground (13:00-13:14).
Results and Future:
First Detection: After years of silence, LIGO detected the first gravitational wave in September 2015, caused by two merging black holes 1.3 billion light-years away (14:26-15:42).
Nobel Prize: This groundbreaking discovery earned the scientists the Nobel Prize and opened a new era of astrophysics (15:23-15:28).
Future Upgrades: New, larger observatories are planned to increase sensitivity and hear even further into the universe (16:48-17:11).
Category
😹
FunTranscript
00:00Ready?
00:00Right here, out in the middle of the desert,
00:03miles from any city, are huge concrete tubes
00:07that are part of a giant machine
00:09running the most precise experiment
00:12humans have ever built.
00:14This experiment is happening inside two tubes,
00:17each four kilometers long.
00:19And inside each tube, there's a big metal pipe.
00:22And at the end of each pipe,
00:23scientists place some of the smoothest mirrors ever made.
00:27And then they fire a powerful laser
00:29that gets split down each tube,
00:31bouncing back and forth and back and forth,
00:33building up power,
00:34until they bring those beams back together
00:37to detect something that just a hundred years ago
00:40scientists said was impossible to find.
00:44Finding it took hundreds of scientists
00:46and over a billion dollars.
00:49But what exactly did we find?
00:51And what's the cutting edge we're finding now
00:54that makes those same scientists want to build
00:56an even bigger one?
00:59Let's go.
01:09Right now, I'm here,
01:11in the control room of this giant machine.
01:14Hey everyone.
01:15Hi everyone, how are ya?
01:16I've seen you on the internet.
01:17Yeah, I'm Cleo, great to meet you.
01:19This machine is known as the
01:21Laser Interferometer Gravitational Wave Observatory,
01:24or just LIGO.
01:26And that is Mike, the head of LIGO.
01:28The reason this machine is such a big deal
01:30is that up until now, for all of human history,
01:34everything that we know about the cosmos
01:36has been from waves of light and particles
01:39that just happen to come our way.
01:41But it turns out there are other ways to sense our universe.
01:46Think about it this way.
01:47Imagine that you're in a jungle and you can only see.
01:51Think about what you know about what's around you.
01:53Now, with this machine, it's like all of a sudden we can suddenly hear.
02:00Think about what you know now about what's around you.
02:03That's why LIGO was built.
02:05To create a way to hear our universe.
02:09And with this machine, our hearing is getting better, fast.
02:12It's as though a few years ago we could only hear the universe yelling.
02:16And now we can hear it murmuring.
02:19But when scientists started building this machine back in the 90s,
02:23it was thought of as high risk, high reward.
02:25Because it was all based on a prediction made by Albert Einstein 75 years before.
02:31Imagine for a second that two enormous stars 100 light years away from us collide.
02:39What happens here on Earth?
02:41Well, at first, nothing.
02:43We don't see it.
02:44We don't feel it.
02:45But Einstein predicted that massive things warp space and time around them.
02:51And that's what we call gravity.
02:54So when these two massive stars collide,
02:57Einstein said that not only do they produce an explosion of light,
03:01but they make ripples that stretch and squeeze space and time.
03:06And those ripples move outward like a wave.
03:10A gravity wave.
03:12A gravitational wave.
03:15And Einstein predicted that these gravitational waves travel at the same speed as light.
03:20So after 100 years, that light from that collision hits us.
03:24And so do these waves.
03:25But think about what that means.
03:28It implies that everything we know, you, me, the space between us, all of reality as we know it,
03:35is getting stretched and squeezed.
03:38And we never feel it.
03:40But 100 years ago, this was all just a theory.
03:43Gravitational waves.
03:44Most physicists believe that even if Einstein were right, it would be too hard to actually prove.
03:50That's because based on Einstein's predictions, this stretch or squeeze would be 10,000 times smaller
03:57than the size of a proton.
04:00To put that into perspective, trying to measure that is like trying to measure the distance from here
04:06to the nearest star, four light years away, and watching that distance change by the width of a human hair.
04:15That's why we had to build this insane machine.
04:19It's a giant measuring stick.
04:21But if everything is getting stretched and squeezed, including your measuring stick,
04:26how would you get an accurate result?
04:28No, seriously, how would you do it?
04:30Turns out the measuring stick and this are the key.
04:34Because what if you used something that we know has a constant speed, right?
04:38Like light.
04:39And you shoot it down your measuring stick.
04:41You could calculate how long it takes the light to go down and bounce back.
04:45So if the distance changes, the time the light would take would change too.
04:49That would work in principle.
04:51But actually doing this is insanely hard.
04:56So this is what they built.
05:00I'm walking around next to LIGO's measuring sticks right now.
05:05That's what these concrete arms are.
05:07The way this works is laser light is sent out here and then splits into two,
05:11speeding down these identical arms.
05:13Then hits mirrors at the end and gets reflected back.
05:17Now normally, the arms are perfectly aligned so that the waves of light cancel each other out,
05:22resulting in no light hitting the detectors.
05:25But if that mysterious, stretchy, squeezy wave comes through,
05:29it would change the length of the arms, shift the laser beams ever so slightly.
05:36And on the detector, you should see a flicker.
05:43The longer the measuring stick, the easier to measure the change.
05:46Except the harder to build it in the first place.
05:50LIGO's measuring sticks are four kilometers long.
05:53So long, they need to correct for the curve of the Earth.
05:57The curvature of the Earth is such that, you know, if we launch the light from the corner station,
06:03at the ends, the fall off of the curvature of the Earth is about four feet.
06:08Now, time to go inside.
06:10The suspense is building.
06:13Oh, cool.
06:15This is a big deal.
06:16Very few people get to go inside here.
06:17I was so excited.
06:19Except there were a lot of spiders.
06:20Yeah, widows.
06:21That's the main thing I'm worried about.
06:22Less excited about that.
06:24Now we are inside the concrete tube.
06:27This is the beam pipe.
06:28And inside the beam pipe is 10,000 cubic meters of nothing.
06:33And when I say nothing, I mean there are fewer particles in there than the International Space
06:37Station flies through because they sucked them all out.
06:41And the reason they did that is to make sure the only thing in there is the laser.
06:45We're going off to this clean room space.
06:47So we have several different layers to protect ourselves.
06:51I think I look great.
06:52Busted down.
06:53Wow, you look cool.
06:56That's a good thing about $700 glasses.
07:00Why do we have to wear these glasses?
07:02Because the laser that we use is invisible.
07:05And if it hits you in the eye, you're not, you won't blink.
07:08It will blind you and you can start hearing popping first, which is your blood vessels
07:12popping before your field of vision goes cloudy.
07:15Okay, I'm going to wear the glasses just in case.
07:18Inside this is the laser, where the whole experiment starts.
07:21But if I were to open up this pipe, you wouldn't see it because it's an infrared laser.
07:26Its wavelength lies just outside the spectrum that you can see.
07:29We sense this as heat.
07:31Right now, at the beginning here, only 60 watts of power goes into the experiment.
07:35That's actually a lot.
07:36My little laser pointer here is probably .005 watts.
07:41So this is already 12,000 times more powerful, and it's not even close to its max power.
07:47Once the laser travels down the arms, it hits the mirrors at the ends.
07:50And on its way back, it hits more mirrors, bouncing back and forth within the arms
07:54300 times on average before hitting the detector, building up the laser power to 400 kilowatts.
08:01That's 80 million times more powerful than my little laser pointer.
08:05But this extreme power has a purpose.
08:07More light equals more sensitivity.
08:10And more bouncing means a longer distance the light travels.
08:13A longer measuring stick increasing the total travel distance to 1,200 kilometers,
08:19which makes any little change easier to measure.
08:22But pulling this off is even harder than you think.
08:26They have to line this laser up with incredible accuracy.
08:31That's what they're doing here at this crazy looking table.
08:35But to look any closer, I need to put on some special gear.
08:42Why do we look like this?
08:44Why are we gowned up?
08:45It's definitely not to protect us.
08:47It's because we're just dirty, right?
08:49Like our skin, our eyelashes, our sneezing, our coughing.
08:53I touched my glasses after wiping my hands.
08:55So now I need to wipe my hands again.
08:57This is serious business.
08:58Even the tiniest speck of dust on these optics could ruin the whole experiment.
09:02So to limit that chance, they only open up these chambers about once a year
09:05to make sure that everything is perfectly aligned.
09:08It's extremely rare to get to go inside.
09:11And once it's all aligned, the laser exits here and enters the arms.
09:16Oh my god!
09:17Do you see it?
09:20That's the coolest thing.
09:21And while I was here, I learned the most fun way to explain
09:25what they're doing with this machine.
09:26Has anyone asked you to do the LIGO dance yet?
09:28No!
09:29Okay, one hand up in the air, one hand out to the side.
09:34Gravitational waves coming towards us.
09:36This one goes down, this one goes big.
09:38This one goes big, this one goes little.
09:40And then it goes faster and faster and faster and faster.
09:42And that is what's happening.
09:45But it's doing it 10 to the minus 22 meters.
09:51So they set up this incredible experiment.
09:53But if anything jostles it, it messes the whole thing up.
09:57My favorite story about this is how scientists at LIGO
09:59found a very weird source of noise.
10:02Himiko, why did ravens cause an issue at LIGO in 2018?
10:07Here's the deal.
10:07Back in 2018, frost formed on these pipes that were part of the cooling system
10:12at the end of one of the detector four kilometer arms.
10:15The ravens, clever as they are, found the icy pipes and started pecking at them.
10:20That tapping created little vibrations that interfered with the laser readings
10:24underneath, causing those glitches in the agibemis data.
10:26This is Miko.
10:28It's like Clippy, but way smarter.
10:30Actually, hold on, let me show you.
10:32There's a secret way to turn it into.
10:33There we go, Clippy!
10:34I like talking to it because it helps me figure out what's most interesting about a story.
10:38Like I can have a conversation and then I can go into the transcripts and find sources
10:42and figure out what I thought was most cool. Miko, how did they solve the raven problem?
10:46Well, the team got a little creative.
10:48They insulated those pipes so that condensation couldn't form and freeze anymore,
10:53which means no more frosty treats for the ravens and no more data glitches caused by their tapping.
10:59If you want to chat with Miko, you can scan this QR code or use the link in my description.
11:02And make sure to ask how they deal with airplane noise at LIGO.
11:06It's a whole thing.
11:07Thanks, Miko. Back to the story.
11:08So now that the laser is lined up, it's flying down the arms and it's hitting these mirrors.
11:14But remember, we're trying to measure something smaller than a proton.
11:18So these can't just be any mirrors.
11:20These are some of the smoothest, most reflective mirrors in the world.
11:25These things are huge.
11:27The main mirrors at the ends of the arms weigh 40 kilograms.
11:31And making them takes work on four continents over multiple years.
11:34Wait, but that doesn't look like a mirror.
11:37You can see right through it.
11:39That's because these mirrors need to be coated with dozens of layers of different materials
11:43to optimize their reflectiveness.
11:46But now they definitely don't look like regular mirrors.
11:49And that's because they're not made for visible light.
11:51They're made to reflect the infrared light of the laser.
11:55And on top of that, they're polished to be unbelievably smooth.
11:59Normal people think that their fridge surface is flat, stainless.
12:03Yeah.
12:03But it turns out that if you were to take your fingernail or something and rub across it,
12:06it has a peak to valley shape, right? All flat surfaces do.
12:09But those peaks and valleys won't work for the laser.
12:12Those peaks and valleys will distort our detector laser waveform.
12:16A typical mirror in your bathroom is about 90 to 95% reflective.
12:20But these mirrors reflect 99.9999% of the infrared light that hits them.
12:26That means that practically all of this powerful laser light can keep on bouncing
12:30back and forth along these tubes, measuring their length for any changes.
12:35So now we've got our powerful laser, our insanely long arms,
12:38our super smooth mirrors all aligned.
12:40But there's one more thing that could ruin everything.
12:44What if you do all of this incredibly delicate work and then a truck drives by?
12:50The whole thing could get ruined if the ground that it's on doesn't stay still.
12:55And by still, I mean a kind of stillness that you and I have never known.
13:01So the natural movement of the ground that we're standing on is about a nanometer,
13:07you know, a billionth of a meter.
13:09That means our mirrors have to be made 10 billion times more still
13:13than the ground we're standing on.
13:15This machine is 10 billion times more still than the normal still ground.
13:25What does that even mean?
13:28They did it by creating an insanely complex suspension system
13:31that isolates those mirrors and counteracts any vibrations,
13:35even hanging them by strands of glass about four times thicker than a human hair
13:42and yet stronger than steel.
13:45The details of the engineering here are incredible.
13:49And what really blows my mind is that they did all of this work
13:54on basically a bet that Einstein was right.
13:58So they build this crazy machine and then they turn it on.
14:02And nothing.
14:04For 10 years, no flicker.
14:07The detector stays silent.
14:08They don't see a single gravitational wave.
14:11Brutal.
14:11We didn't see anything in those first science runs.
14:14We didn't see any gravitational waves at all.
14:16But they kept going, making the machine better and better,
14:20more and more sensitive until in September 2015,
14:23they turn on the newer, better, advanced LIGO.
14:27And almost immediately, three days later, they finally see.
14:33And that flicker, it actually looked like this.
14:38Yep.
14:39It's a bump on a chart.
14:40They call it a chirp.
14:41But how did they know that that chirp was actually a gravitational wave?
14:46Maybe it was just a truck going by.
14:48That's why, 3,000 kilometers away, in a totally different place with none of the same trucks,
14:55they'd built a whole nother one.
14:58That's right.
14:59There are two of these enormous, crazy machines working together to check each other's work.
15:05And that second machine saw the chirp too.
15:07After all this work, and all this building, and all this genius human effort,
15:13a hundred years, almost to the day after Einstein predicted it,
15:18we saw our first gravitational wave.
15:23For those scientists, it meant that they'd just won the Nobel Prize.
15:29And for all the rest of us, it meant a totally new era.
15:34Eventually, they figured out that those first waves they detected
15:37were caused by two black holes merging 1.3 billion light-years away.
15:43It was a huge impact, causing massive waves.
15:46A cosmic yell, basically.
15:48And it turns out that the universe yells a lot.
15:52We've made 294 detections to date.
15:55And right now we get them about once every three days or so.
15:58We've now heard more black holes colliding, creating even bigger ones.
16:02Stars smashing and exploding,
16:05telling us where many of the elements on Earth come from.
16:08These sounds let us officially measure the speed of gravity and the expansion of the universe.
16:15We first understood light.
16:17And then we manipulated it.
16:19We're now right at the beginning of understanding gravity.
16:23Just imagine what we could do if we could manipulate that.
16:28When LIGO first started listening to the universe, they could only hear this far.
16:32And they didn't detect anything.
16:34Then, here's how far they could hear in 2015, making their first detection.
16:38And today, LIGO can reach more than a thousand times more space than it originally could.
16:44And the best part is, we're only just getting started.
16:47They're working on new, bigger machines, like this one in Europe.
16:51It's a triangle with three 10-kilometer-long arms buried underground.
16:56And in the US, there's another plan for one called Cosmic Explorer, an L-shape.
17:01But instead of 4-kilometer arms, they want 40.
17:05Those observatories would expand our hearing to close to the edge of the observable universe.
17:11Humans are astonishing.
17:13We gave ourselves, and every person after us, a new sense.
17:19We might be the first living species ever to sense the universe in this way.
17:26The universe has been talking to us this whole time, and we can finally hear it.
17:33So now, the question is, what will we hear next?
17:37If you believe that there should be more optimistic science and tech stories, subscribe.
Comments