Name: 重力波の発見-60のシンボル (Gravitational Waves Discovery - Sixty Symbols)
Uploaded: 2021-01-14T10:27:40.000Z
Duration: 13 min 13 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

I guess the first thing to say is they're a consequence of general relativity that

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when you get as far as writing down the equations of general relativity and start

trying to solve them you find that some of the solutions involve these wave solutions.

They're distortions of the spacetime that propagate out. -I mean they're important

for lots of reasons they're important because they are a prediction of general

relativity so actually if you then detect them you've found further

confirmation that general relativity is actually right. -Whenever matter

passes by through some region of spacetime it will distort the spacetime just like

you would distort water when if you put your fingers through water and waves

propagate out this is a propagation of the spacetime itself, so the spacetime is

propagating out at the speed of light. -But also because in principle at least

they open up an entire new window on the universe, everything, almost everything we've done

in astronomy, barring a few cosmic rays and neutrinos, has been mediated through

light - we've used light to figure out what's going on in the universe. Having

an entirely new way of detecting what's going on out there in the universe is a

very exciting thing for astronomers because it - it opens up all sorts of new avenues for

As the Earth goes around the Sun then the spacetime is distorting around the Earth

and that's propagating out in waves in all directions.

[Brady off Camera] Do those waves have nothing to do with for example why the moon is attracted to the Earth?

[Prof. Copefield] No - no they're different gravit- that- that's a different aspect, sometimes

we call them gravitational waves, but they're different here these are the-

the tides don't exist because of the nature of gravitational waves propagating.

You've got the Earth going around the Sun and then you've got the Moon going around the Earth.

These are very massive objects, right, and so there's a net attraction just due to

the pure mass of these objects and that's where the tides come from the

large mass of the Moon and the even larger mass of the Earth and as they go

around the water that's on the Earth gets distorted by the changing

gravitational field due to the huge mass of the Moon and the Earth.

But on top of that there's like a secondary effect going as the Moon

is going around it's causing ripples in the spacetime and it's those ripples -

these are minuscule ripples that are propagating out - and it's those that

recently were detected not from the Moon but from two massive, supermassive

two massive black holes that were orbiting each other and so they

distorted the spacetime enough that these waves that propagated out -

they could be detected here on Earth. -I said space is expanding and contracting,

but the amount that space is expanding and contracting by is absolutely

minuscule. So this big result that came up with this thing that they detected - the amount

by which space was expanding over the many kilometers of their detector was

less than the diameter of the nucleus of an atom. So it's an absolutely tiny - infact

that's why we don't - sort of notice them going past 'cause if they were big effects, you know you'd see

kind of space doing all sorts of weird things. But because they're so tiny we just don't see them.

It's just amazing, I mean the numbers involved, the timing involved -

it's a spectacular event so - a billion light years away - four hundred and fifty megaparsecs away -

So a billion years ago, two black holes which were each of them thirty times the mass

of the Sun, okay? Which is unusual apparently in its own right to get this kind of

combination. They were orbiting, they'd been orbiting each other

for probably millions of years anyway. -They have to be bound together because they

were in orbit around one another and it's actually quite complicated because -

so the way you get massive black holes is you have some very massive star

exploding in a supernova, and unless that supernova is set up very carefully, if

you imagine you had a pair of binary stars in orbit around one another -

one of them goes supernova - if you're not very careful that's gonna

unbind the system because you've lost a whole load of mass, there's all sorts of energy

being transferred between one and the other - so somehow the two manage to stay

When first one went supernova and then a bit later the other one went supernova -

probably tens to hundreds of thousands of years later the other one went supernova.

Alternatively, possibly, if both of these stars were in a cluster they might actually have

individually been separate stars and at some point in the subsequent

evolution they might have actually got sufficiently close together that they'd end up

capturing each other and end up in a binary system that way. So it is a little bit of

a mystery how you make these two massive black holes - fairly massive,

not supermassive black holes - in orbit around one another in the first place, but there are

at least kind of plausible mechanisms for doing it. -So they're doing this for millions

and millions of years and then in the final - I think it's .2 of a second -

first they're coming closer and closer together. They start going so rapidly

around one another that it begins to approach the speed of light in fact

something like sixty percent of the speed of light.

These are 30 solar mass black holes. As they're coming closer and closer, when they're

about, I think, 350 kilometers apart they basically start merging together.

Amazingly, from just looking at the kind of signal they detect they can learn a

great deal about the kind of black holes it actually was, how the amplitude

changes over time, how the frequency of the signal changes over time. So in

this case they're fairly confident that one of them was a 29 solar mass black hole

and the other one was a 36 solar mass black hole -

they got sort of errors of 1 or 2  solar masses on each one -

but they were both 30 to 40 solar mass black holes. So those are the

kind of black holes which are probably the end states of very massive stars,

although they are actually on the high side even for very massive stars.

Remember we've talked about this intricate link between the matter and the

spacetime. Just imagine - try to imagine - these two huge objects.

What they're doing to the matter, to the spacetime around it, as they- and the

spacetime must be going 'oh my god what's happening here' and it's flipping

up and down, up and down and they're just generating - these waves are beginning to

propagate out. 350 kilometers, we should find a distance, what, to London? Then you got two

30 solar mass black holes sort of orbiting one another in this region and so they're

going at close to the speed of light. So the the spacetime in which it's

revolving must be going - is having huge distortions associated with it.

And so it begins to send out gravitational waves - they've been happening

all the time but at a much lower amplitude because they've not been

feeling this effect, like this. And then these two black holes keep coming in together and they merge.

And what happens is when you've got two black holes they'll merge into a bigger black hole.

So one of them is 29 solar masses, the other one is 36 solar masses.

If you add those two together you get 65 solar masses, so you would think by merging

these two together you make a 65 solar mass black hole. Turns out they can also tell

you what the mass of the black hole ended up with was. Again, just by looking at the

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重力波の発見-60のシンボル (Gravitational Waves Discovery - Sixty Symbols)

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massive

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matter