Name: 宇宙についての誤解 (Misconceptions About the Universe)
Uploaded: 2021-01-14T10:25:42.000Z
Duration: 5 min 46 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：

様態の副詞

- There was a time when the universe was expanding so rapidly that parts of it were moving apart

from each other faster than the speed of light. That time is right now. A lot of people make

a big deal out of the fact that during inflation, right after our universe burst into existence,

the whole universe was expanding faster than light. Now, while that is true, it kind of

implies that the universe doesn't normally do that, and it does. I mean, if you pick

two points far enough apart in our universe, you can always find ones that are moving apart

from each other faster than light. That is simply due to all of the expanding space in

between. So our universe is now and has always been expanding faster than the speed of light.

But doesn't this violate Einstein's special theory of relativity that says nothing should

be able to move faster than light? Actually, no. Relativity says nothing can move through

space faster than light, but that doesn't stop space itself from expanding however it

likes. Now, it was Hubble in the late 1920s who made the observations of the night sky,

which led us to see that our universe is expanding. The further out in space he looked, the faster

the objects were moving away from us. So imagine a point so far out there that the average

recession velocity is the speed of light. I mean, if you think about it, it's going

to be the same distance in every direction. So that would form a sphere which we call

the Hubble Sphere. Everything beyond that sphere is moving away from us faster than

the speed of light. So common sense would say we would never be able to see the light

from those objects because of how fast they're moving away from us. But in fact, this is

not true. We can see those objects. To understand how this could work, picture a galaxy beyond

our Hubble Sphere. It's receding faster than light, it's in a super luminal region of space

from our perspective. So any light that emits in our direction, will actually be moving

away from us as time goes on. Well that doesn't sound very promising. But due to the accelerating

expansion of space, our Hubble Sphere is actually getting bigger. And if it gets bigger faster

than that light can get away, then at some point that light is going to travel from a

super luminal region of space into a subluminal region of space, and so it can start making

progress towards us. So we can detect it, so we can see that distant galaxy, which is

of course now even further beyond our Hubble Sphere, but we can see its light. We can detect

that it's there. This is remarkable. In fact, all of the photons we now receive from the

first 5 billion years of the universe, they were all emitted in regions of space that

were traveling, at the time, faster than the speed of light relative to us. The objects

that emitted them were, are, and always have been moving away from us faster than the speed

of light. But their light has entered our Hubble Sphere and had enough time to reach

us, and so we can see them. So the observable universe is larger than our Hubble Sphere.

It's actually limited by what's called the particle horizon. That is based on the amount

of time light has had to travel towards us since the beginning of time, that is 13.8

billion years ago as far as we can tell. Now because the universe has been expanding and

that expansion has been accelerating, things are much further out than 13.8 billion light

years away. I mean, the observable universe has a radius of over 46 billion light years.

The diameter is about 93 billion light years. That is a huge volume of things that we can

see. And 13.8 billion years ago, everything in that volume and everything beyond it that

we can't see would have been compressed into a tiny infinitesimally small point that we

call the singularity. Actually, no. I mean, that would be true if the universe is finite.

But if the universe is infinite, and it kind of looks like it is, then it was always infinite.

So the big bang would have happened literally everywhere. But if the universe has always

been infinite, then what is it expanding into? Well, it doesn't have to expand into anything.

I mean, it can expand into itself. That's the thing about infinity. You never run out

of it. This episode of Veritasium was supported by audible.com, a leading provider of audiobooks

with over 150,000 titles in all areas of literature, including fiction, non-fiction, and periodicals.

This week I wanted to recommend the book Hitchhiker's Guide To The Galaxy. It's one of my favorites

and it's a classic of the science genre. You know, people often ask me, why is the number

42 on the Veritasium logo? And that's because it's the answer to the ultimate question of

life, the universe, and everything. So if you haven't read this book yet, you should

definitely check it out, and in fact, you can download it for free by going to audible.com/veritasium,

or you can pick any other book of your choosing for a one month free trial. So I want to thank

Audible for supporting me and I want to thank you for watching.