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  • At about six o'clock in the morning on September 14, 2015,

  • scientists witnessed something no human had ever seen:

  • two black holes colliding.

  • Both about 30 times as massive as our Sun,

  • they had been orbiting each other for millions of years.

  • As they got closer together,

  • they circled each other faster and faster.

  • Finally, they collided and merged into a single, even bigger, black hole.

  • A fraction of a second before their crash,

  • they sent a vibration across the universe at the speed of light.

  • And on Earth, billions of years later,

  • a detector called the Laser Interferometer Gravitational Wave Observatory,

  • or LIGO for short,

  • picked it up.

  • The signal only lasted a fifth of a second

  • and was the detector's first observation of gravitational waves.

  • What are these ripples in space?

  • The answer starts with gravity,

  • the force that pulls any two objects together.

  • That's the case for everything In the observable universe.

  • You're pulling on the Earth, the Moon, the Sun, and every single star,

  • and they're pulling on you.

  • The more mass something has, the stronger its gravitational pull.

  • The farther away the object, the lower its pull.

  • If every mass has an effect on every other mass in the universe,

  • no matter how small,

  • then changes in gravity can tell us about what those objects are doing.

  • Fluctuations in the gravity coming from the universe

  • are called gravitational waves.

  • Gravitational waves move out from what caused them,

  • like ripples on a pond,

  • getting smaller as they travel farther from their center.

  • But what are they ripples on?

  • When Einstein devised his Theory of Relativity,

  • he imagined gravity as a curve in a surface called space-time.

  • A mass in space creates a depression in space-time,

  • and a ball rolling across a depression will curve

  • like it's being attracted to the other mass.

  • The bigger the mass,

  • the deeper the depression and the stronger the gravity.

  • When the mass making the depression moves, that sends out ripples in space-time.

  • These are gravitationl waves.

  • What would a gravitational wave feel like?

  • If our bodies were sensitive enough to detect them,

  • we'd feel like we were being stretched sideways

  • while being compressed vertically.

  • And in the next instant,

  • stretched up and down while being compressed horizontally,

  • sideways,

  • then up and down.

  • This back and forth would happen over and over

  • as the gravitational wave passed right through you.

  • But this happens on such a minute scale that we can't feel any of it.

  • So we've built detectors that can feel it for us.

  • That's what the LIGO detectors do.

  • And they're not the only ones.

  • There are gravitational wave detectors spread across the world.

  • These L-shaped instruments have long arms,

  • whose exact length is measured with lasers.

  • If the length changes, it could be because gravitational waves are stretching

  • and compressing the arms.

  • Once the detectors feel a gravitational wave,

  • scientists can extract information about the wave's source.

  • In a way, detectors like LIGO are big gravitational wave radios.

  • Radio waves are traveling all around you, but you can't feel them

  • or hear the music they carry.

  • It takes the right kind of detector to extract the music.

  • LIGO detects a gravitational wave signal,

  • which scientists then study for data about the object that generated it.

  • They can derive information, like its mass and the shape of its orbit.

  • We can also hear gravitational waves by playing their signals through speakers,

  • just like the music a radio extracts from radio waves.

  • So those two black holes colliding sounds like this.

  • Scientists call this slide whistle-like noise a chirp,

  • and it's the signature of any two objects orbiting into each other.

  • The black hole collision was just one example

  • of what gravitational waves can tell us.

  • Other high-energy astronomical events will leave gravitational echoes, too.

  • The collapse of a star before it explodes in a supernova,

  • or a very dense neutron stars colliding.

  • Every time we create a new tool to look at space,

  • we discover something we didn't expect,

  • something that might revolutionize our understanding of the universe.

  • LIGO's no different.

  • In the short time it's been on,

  • LIGO's already revealed surprises,

  • like that black holes collide more often than we ever expected.

  • It's impossible to say, but exciting to imagine,

  • what revelations may now be propagating across space

  • towards our tiny blue planet and its new way of perceiving the universe.

At about six o'clock in the morning on September 14, 2015,

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TED-ED】重力波とは何か?- アンバー・L・スチューバー (【TED-Ed】What are gravitational waves? - Amber L. Stuver)

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    osmend に公開 2021 年 01 月 14 日
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