- 1 day ago
In the middle of the desert, miles from any city, are two HUGE concrete tubes. They’re part of a giant machine running the most precise experiment humans have ever built…
Each tube is 4 kilometers long, and inside there’s a big metal pipe. And at the end of each pipe, scientists place some of the smoooooothest mirrors ever made. And then they fire a powerful laser that gets split down each tube, bouncing it back and forth… building up more and more power… until… they bring those beams back together… to discover something that just 100 years ago scientists thought was impossible to find!
Finding it took hundreds of scientists and over a billion dollars. But what did we find?? And what’s the cutting edge we’re finding NOW that makes those scientists want to build… AN EVEN BIGGER ONE?
Let me show you…
Chapters
00:00 What's the most precise experiment humans have built?
01:41 How do we know what’s out in the universe?
02:33 What if two stars collide?
03:41 What are gravitational waves?
6:34 What's inside the concrete tubes in the desert?
5:50 How did they build the Laser Interferometer Gravitational-Wave Observatory?
07:42 How does the laser experiment work?
09:20 What's the LIGO dance?
11:14 What are the most reflective mirrors in the world?
14:02 What happened when they turned on the laser machine?
15:17 Did we detect gravitational waves?
16:16 Can we manipulate gravity?
17:44 :)
Each tube is 4 kilometers long, and inside there’s a big metal pipe. And at the end of each pipe, scientists place some of the smoooooothest mirrors ever made. And then they fire a powerful laser that gets split down each tube, bouncing it back and forth… building up more and more power… until… they bring those beams back together… to discover something that just 100 years ago scientists thought was impossible to find!
Finding it took hundreds of scientists and over a billion dollars. But what did we find?? And what’s the cutting edge we’re finding NOW that makes those scientists want to build… AN EVEN BIGGER ONE?
Let me show you…
Chapters
00:00 What's the most precise experiment humans have built?
01:41 How do we know what’s out in the universe?
02:33 What if two stars collide?
03:41 What are gravitational waves?
6:34 What's inside the concrete tubes in the desert?
5:50 How did they build the Laser Interferometer Gravitational-Wave Observatory?
07:42 How does the laser experiment work?
09:20 What's the LIGO dance?
11:14 What are the most reflective mirrors in the world?
14:02 What happened when they turned on the laser machine?
15:17 Did we detect gravitational waves?
16:16 Can we manipulate gravity?
17:44 :)
Category
📚
LearningTranscript
00:00Ready?
00:00Right here,
00:01out in the middle of the desert,
00:03miles from any city,
00:04are 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,
00:20There's a big metal pipe.
00:22And at the end of each pipe,
00:23scientists place some of the smoothest mirrors
00:26ever 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,
00:41scientists said it 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
00:55want to build an even bigger one?
00:59Let's go.
01:10Right now, I'm here,
01:11in the control room of this giant machine.
01:14Hey everyone.
01:15Hi everyone, how are you?
01:16I've seen you on the internet.
01:17Yeah, I'm Cleo, great to meet you.
01:19This machine is known as the Laser Interferometer.
01:22Gravitational Wave Observatory.
01:24Or just LIGO.
01:26And that's 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 happened to come our way.
01:41But it turns out, there are other ways
01:44to sense our universe.
01:46Think about it this way.
01:47Imagine that you're in a jungle
01:48and 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
01:56we 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.
02:08And with this machine, our hearing is getting better, fast.
02:12It's as though a few years ago
02:13we could only hear the universe yelling.
02:16And now we can hear it murmuring.
02:19But when scientists started building this machine
02:21back in the 90s, it was thought of as high risk, high reward.
02:25Because it was all based on a prediction
02:27made by Albert Einstein 75 years ago.
02:31Imagine for a second that two enormous stars
02:35100 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
02:47warp 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
02:59an explosion of light,
03:01but they make ripples that stretch and squeeze space and time.
03:06And those ripples move outward.
03:09Like a wave.
03:10A gravity wave.
03:12A gravitational wave.
03:15And Einstein predicted that these gravitational waves
03:18travel at the same speed as light.
03:20So after 100 years, that light from that collision hits us.
03:24And so do these waves.
03:26But think about what that means.
03:28It implies that everything we know,
03:31you, me, the space between us,
03:33all 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,
03:48it would be too hard to actually prove.
03:51That's because based on Einstein's predictions,
03:53this stretch or squeeze would be 10,000 times smaller
03:57than the size of a proton.
04:00To put that into perspective,
04:02trying to measure that is like trying to measure the distance
04:05from here to the nearest star,
04:08four light years away.
04:09And watching that distance change
04:11by the width of a human hair.
04:14Yeah.
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,
04:24including your measuring stick,
04:26how would you get an accurate result?
04:28No, seriously.
04:29How would you do it?
04:30Turns out the measuring stick and this is the key.
04:34Because what if you use something that we know
04:36has 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
04:44to go down and bounce back.
04:45So if the distance changes,
04:47the 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.
05:04That's what these concrete arms are.
05:07The way this works is laser light is sent out here
05:09and 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
05:19so 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,
05:33shift 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,
06:00you 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,
06:34I mean there are fewer particles in there
06:36than the International Space Station flies through.
06:39Because they sucked them all out.
06:41And the reason they did that is to make sure
06:42the 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 won't blink.
07:08It will blind you and you can start hearing popping first,
07:11which is your blood vessels popping
07:13before your field of vision goes cloudy.
07:15Okay, I'm gonna 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.
07:24Because 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,
07:32only 60 watts of power goes into the experiment.
07:35That's actually a lot.
07:36My little laser pointer here is probably 0.005 watts.
07:41So this is already 12,000 times more powerful.
07:44And 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,
07:52bouncing back and forth within the arms 300 times on average
07:56Before 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 up this laser 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? Why 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. This 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.
09:06To 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 what they're doing with this machine.
09:26Has anyone asked you to do the LIGO dance yet?
09:28No!
09:29Okay.
09:30One hand up in the air.
09:32One hand out to the side.
09:34Gravitational waves coming towards us.
09:36This one goes down.
09:37This one goes big.
09:38This one goes big.
09:39This one goes up.
09:40And then it goes faster and faster and faster and faster.
09:42And that is what's happening.
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 found 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 detective four-kilometer arms.
10:15The ravens, clever as they are, found the icy pipes and started pecking at them.
10:19That tapping created little vibrations that interfered with the laser readings underneath,
10:24causing those glitches in the Igebanus data.
10:26This is Miko.
10:27It's like Clippy, but way smarter.
10:30Actually, hold on.
10:31Let me show you.
10:32There's a secret way to turn it into.
10:33There we go!
10:34Clippy!
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
10:41and find sources and figure out what I thought was most cool.
10:44Miko, 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 be just 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.
11:30And 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 to 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, it has
12:07a peak to valley shape, right?
12:08All 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 back and forth along these tubes,
12:31measuring their length for any changes.
12:34So now we've got our powerful laser, our insanely long arms, our 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.
13:06You know, a billionth of a meter.
13:09That means our mirrors have to be made 10 billion times more still than 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?
13:27They did it by creating an insanely complex suspension system that isolates those mirrors and counteracts any vibrations,
13:35even hanging them by strands of glass about four times thicker than a human hair and yet stronger than steel.
13:45The details of the engineering here are incredible.
13:48And what really blows my mind is that they did all of this work on basically a bet that Einstein
13:57was right.
13:58So they build this crazy machine and then they turn it on.
14:02And nothing.
14:04For 10 years, no flicker, the 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, more 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.
14:38Yup, it'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, there are two of these enormous, crazy machines working together to check each other's work.
15:05And that second machine saw the chirp too.
15:08After 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 were caused by two black holes,
15:39merging 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, telling 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.
16:48They're working on new, bigger machines, like this one in Europe.
16:51It's a triangle with three 10-kilometre-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 wanted 40.
17:04Those 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.
17:30And we can finally hear it.
17:33So now, the question is, what will we hear next?
17:38If you believe that there should be more optimistic science and tech stories, subscribe.
17:55And subscribe.
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