Name: 光の速さは？ (How Fast Is Light?)
Uploaded: 2021-01-14T10:43:12.000Z
Duration: 7 min 11 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：

基礎受動態

This episode was made possible by generous supporters on Patreon.

It travels at 671 million miles per hour.

Whatever units you choose, that's crazy fast.

The fastest humans in history were the Apollo 10 astronauts at 0.006% the SOL.

The fastest human-made object was the Juno space probe at 0.025% the SOL.

Andromeda is hurtling toward the Milky Way Galaxy at 0.04% the SOL.

All of these are tiny fractions of that 671 million mph.

Physicists have only really gotten close to the speed of light with subatomic particles.

The record for a proton in the Large Hadron Collider is 99.999 999% the SOL.

I have a specially designed rocket just for this purpose.

We lost him during the Twins Paradox video.

Alright, now we have a Rocket Clone. Let's do this.

Say he gradually accelerates away from my space station.

How long will it take him to reach light speed?

See, accelerating a rest mass like a person or a rocket requires energy.

For example, a rocket transforms energy from its fuel into kinetic energy.

It will continue to accelerate as long as it burns fuel.

Even if he somehow managed to turn all of the energy in the observable universe

into kinetic energy for himself, he'd still only be going 99.999...

That's 100 nines after the decimal place, which is still not 100%.

It would literally take an infinite amount of energy over an infinite amount of time

to accelerate up to exactly the speed of light.

That being said, there are things in the universe that go at exactly light speed.

And that's any light from the spectrum, not just visible light.

But also gravitational waves and anything else without rest mass.

Anyway, that speed does exist, but the fact that it's impossible for massive

objects to reach it has a weird side effect.

No matter how fast you go, light will always be faster.

Light is so fast that it breaks our understanding of how speed works.

How can it always be going the same speed faster than you?

We're going to need a space-time diagram.

If you're not familiar with those, you should go check out this video first.

Alright, let's bring back Rocket Clone for another experiment.

If, instead of accelerating, he travels at steady speed his space-time path will look

Let's consider the part between my space station and, oh I don't know, Wolf 359.

They're about 8 light years apart and the trip takes about 14.5 years.

We know speed is space divided by time, so 8 light years divided by 14.5 years is

We can draw those measurements as a triangle, which makes the speed the tangent of an angle,

It's a hyperbolic tangent or “tanch” for short.

Switching from my point of view to Rocket Clone's is a hyperbolic rotation.

The space and time axes rotate in opposite directions

to line up with the observer taking the measurements.

That's called a hyperbolic rotation because the coordinates on each axis

The more his path is tipped from mine the faster he's moving according to me.

So let's look at a bunch of different speeds and see what happens.

Even the accelerated rocket from earlier approaches it.

字幕リスト動画再生

光の速さは？ (How Fast Is Light?)

weird

approach

constant

pattern