The fundamentals of space-time: Part 1 - Andrew Pontzen and Tom Whyntie

时空基本原理: 第一部分- Andrew Pontzen and Tom Whyntie

翻译人员: Fen Guan 校对人员: Qingqing Mao

Space: it's where things happen.

空间描述事情在哪里发生

Time: it's when things happen.

时间描述事情什么时候发生

We can measure where things are

我们可以度量事情在哪儿

and when things take place,

在什么时间发生

but in modern physics,

但是在现代物理学

we realize when and where

我们发现时间和地点

are actually part of the same question.

事实上是同一个问题的不同方面

Because when it comes to understanding the universe,

因为当要了解宇宙

we need to replace three-dimensional space plus time

我们需要用一个概念

来代替三维空间加时间

with a single concept:

four-dimensional space-time.

四维时空

We'll explore and explain space-time

在这个动画系列里

in this series of animations.

我们将探索解释四维时空

Animations?

用动画？

Yeah.

是的

Well, we're not very animated are we?

好吧，但我们并没有怎么动，不是么？

Sure we are! Look, I can go from here to here.

我们当然在动，看，我从这儿到了那儿

Whoa! How'd you get from here to there?

哇！你怎么从这儿到那儿的？

How fast did you go?

你动得多快？

Did you run? Walk?

你跑的还是走的？

Did you even go in a straight line?

你是走的直线么？

Ah! To answer that, you'll need to make our cartoon physics

啊哈！要回答这个，你需要把我们的卡通物理

look more like physics physics.

变得更像真实的物理

You'll need more panels.

你需要更多图画

More panels, please!

请给更多图画

Okay, in each panel, Andrew's in a slightly different place.

好了，在每个图中，安德鲁在一个稍微不同的地方

So I can see each one records

每一张图记录了

where Andrew is at a different time.

安德鲁不同时间的位置

That's great. But it would be easier to see

非常好，不过如果我们剪开数以百计的图画

what's going on if we could cut out

然后堆在一起看

all the hundreds of panels and stack them up

就能更简单地看清发生了什么

like a flip book.

就像手翻书一样

Right, now let's flip through the book

好，来让我们快速翻这本书

so that we can see one panel after another

我们看到一个接一个的图画

getting through 24 in every second.

每秒24张

See! I told you it was an animation.

看！我说过这是个动画

Now you can see me walking along.

现在你能看到我是怎么走过去的

Drawing all those panels and putting them into a flip book

画出所有图然后放在手翻书里

is just one way of recording the way I'm moving.

是记录我移动的一种方法

It's how animation, or even movies, work.

这就是动画片，甚至电影的工作原理

As it turns out, at my walking speed,

结果发现，以我的步行速度

it takes two seconds to get past each fence post,

每两秒经过一个篱笆桩

and they're spaced four meters apart.

桩子间距4米

So we can calculate my velocity --

我们可以计算我的速度

how fast I'm moving through space - -

我在空间移动的速度

is two meters per second.

就是两米每秒

But I could've worked that out from the panels

但事实上不需要翻动画面

without flipping through them.

我也可以从那些画面里面算出速度

From the edge of the flip book,

从手翻书的侧面

you can see all of the copies of the fence posts

你可以看到篱笆桩的所有副本

and all of the copies of Andrew

还有安德鲁的所有副本

and he's in a slightly different place in each one.

他在每个里面处在稍微不同的位置

Now we can predict everything that will happen to Andrew

现在我们可以预测以每秒24页翻动时

when we flip through 24 pages every second,

安德鲁将会发生的事

including his speed of motion,

包括他的运动速度

just by looking.

仅仅通过看

No need to flip through at all.

不需要翻动

The edge of this flip book

这个手翻书的侧面

is known as a space-time diagram

就叫做安德鲁的行程的时空图

of Andrew's journey through, you guessed it,

你猜到了

space and time.

时间和空间

We call the line that represents Andrew's journey

我们把代表安德鲁的行程的线

his world line.

叫做他的世界线

If i jog instead of walking,

如果我用慢跑代替步行

I might be able to get past a fence post every second.

我可能每秒通过一个桩

He's not very athletic.

他不是那么有运动细胞

Anyway, when we look at this new flip book from the edge,

无论如何，当我们看这个新手翻书的侧边

we can do the same analysis as before.

我们可以做和之前相同的分析

The world line for Andrew jogging

安德鲁慢跑的世界线

is more tilted over

比他步行的世界线

than the world line for Andrew walking.

更加倾斜

We can tell he's going twice as fast as before

我们不用翻画就可以知道

without flipping the panels.

他的速度是原来的两倍

But here's the clever bit.

但再机智点

In physics, it's always good to view things from other perspectives.

在物理学中，多从其他角度看事情总是好的

After all, the laws of physics

毕竟，物理基本定律

should be the same for everyone

对每个人都一样

or no one will obey them.

或者说没有人能违背

So let's rethink our cartoon

重新审视这个卡通

and have the camera follow Andrew jogging along

让镜头跟随安德鲁一起慢跑

as the fence posts approach and pass behind him.

篱笆桩一一接近又被超过

Still viewing it as a flip book of panels,

同样将其看做手翻书

we don't need to redraw anything.

我们不用重新画所有图画

We simply move all of the cutout frames slightly

只是略微移动所有的画面

until Andrew's tilted world line

直到安德鲁的倾斜的世界线

becomes completely vertical.

变成竖直的

To see why, let's flip it.

为什么呢？来翻起来

Yes, now I'm stationery, just jogging on the spot,

对的，现在我是不动的，在固定点慢跑

in the center of the panel.

一直在图画的中间

On the edge of the flip book,

在手翻书的侧边图里

my world line was going straight upwards.

我的世界线是竖直的

The fence posts are coming past me.

篱笆桩经过了我

It's now their world lines that are tilted.

现在桩的世界线是倾斜的了

This rearrangement of the panels is known as a

这种图画的重新放置叫做

Galilean transformation,

伽利略变换

and it lets us analyze physics from someeone else's perspective.

它让我们从其他人的角度分析物理

In this case, mine.

在这个例子里，我的角度

After all, it's always good to see things from other points of view,

总之，多从其他角度看事物总是好的

especially when the viewers are moving

尤其当观察者

在以不同速度移动的时候

at different speeds.

So long as the speeds aren't too high.

只要速度不是太快

If you're a cosmic ray moving at the speed of light,

如果你是一束以光速移动的宇宙射线

our flip book of your point of view falls apart.

你看到的手翻书就跟不上了

To stop that from happening,

为了阻止这样的事发生

we'll have to glue panels together.

我们不得不把所有画面粘在一起

Instead of a stack of separate panels,

我们需要一个整块的时空

we'll need a solid block of space-time,

来取代画面的堆积

which we'll come to in the next animation.

我们将在下一个动画里解释这一点