The fundamentals of space-time: Part 2 - Andrew Pontzen and Tom Whyntie

时空基本原理: 第二部分- Andrew Pontzen and Tom Whyntie

翻译人员: Qingqing Mao 校对人员: Xiaoou Chen

Light: it's the fastest thing in the universe,

光：宇宙中最快的东西

but we can still measure its speed

但我们依然有办法测量它的速度

if we slow down the animation,

如果我们把画面放慢，

we can analyze light's motion using

我们可以使用时空图来分析光的运动

a space-time diagram,

which takes a flipbook of animation panels,

就像从侧面来看一页页的手翻书

and turns them on their side.

In this lesson, we'll add the single experimental fact

在这堂课里，我们将补充一个实验事实

that whenever anyone measures just how fast light moves,

当任何人测量光的速度的时候

they get the same answer:

都会得到相同的结果

299,792,458 meters every second,

每秒299 792 458米

which means that when we draw light

这意味着

当我们把光画在时空图上时

on our space-time diagram,

it's world line always has to appear at the same angle.

光的世界线必须总是呈现相同的角度

But we saw previously that speed,

但是，我们之前看到

or equivalently world line angles,

速度，即世界线的角度

change when we look at things from

会随着不同观察者的视角而改变

other people's perspective.

To explore this contradiction,

为了弄清这个矛盾

让我们来看看如下情况

let's see what happens if I start moving

如果我开始移动

while I stand still and shine the laser at Tom.

而我站在这里朝着汤姆发射激光

First, we'll need to construct the space-time diagram.

首先，我们需要构造时空图

Yes, that means taking all of

这意味着

the different panels showing the different moments in time

取出对应每一个时刻的每一帧图片

and stacking them up.

然后把它们叠在一起

From the side, we see the world line

从侧面我们看到激光的世界线

of the laser light at its correct fixed angle,

有着固定的、正确的角度

just as before.

就和早先的一样

So far, so good.

目前为止一切顺利

But that space-time diagram represents Andrew's perspective.

但是这个时空图展示的是安德鲁的视角

What does it look like to me?

从我的视角来看是什么样的呢？

In the last lesson, we showed

在上一课里

how to get Tom's perspective moving all the panels

我们展示了如何得到汤姆的视角

只需把所有的图片平移一点

along a bit until his world line is completely vertical.

直到汤姆的世界线完全垂直

But look carefully at the light world line.

但是仔细看看光的世界线

The rearrangement of the panels

平移所有图片的话

means it's now tilted over too far.

会使得光的世界线倾斜过度

I'd measure light traveling faster than Andrew would.

我所测得的光速将会快于安德鲁所测得的

But every experiment we've ever done,

但是我们所做过的所有实验

and we've tried very hard,

我们所有的努力

says that everyone measures light to have a fixed speed.

都表明光速是恒定的

So let's start again.

让我们重新开始

In the 1900s, a clever chap named Albert Einstein

在19世纪00年代，有个聪明的家伙叫爱因斯坦

worked out how to see things properly,

他想出了如何从汤姆的视角

from Tom's point of view,

来正确地看待问题

while still getting the speed of light right.

而同时依然能得到正确的光速

First, we need to glue together the separate panels

首先我们需要把分离的画面都粘合起来

into one solid block.

粘成完整的一块

This gives us our space-time,

于是我们有了时空

turning space and time into

将时间和空间

one smooth, continuous material.

变成一整块平顺连续的材料

And now, here is the trick.

现在，变戏法的时候到了

What you do is stretch your block of space-time

你要做的是

沿着世界线拉伸你的整块时空

along the light world line,

then squash it by the same amount,

然后在垂直于世界线的方向上

but at right angles to the light world line,

同等数量地压缩时空

and abracadabra!

唵嘛呢叭咪吽！

Tom's world line has gone vertical,

汤姆的世界线变得垂直了

so this does represent the world from his point of view,

所以这代表了他眼中的世界

but most importantly,

但是最重要的是

the light world line has never changed its angle,

光的世界线从未改变角度

and so light will be measured by Tom

所以汤姆所测量的光速

going at the correct speed.

也是正确的光速

This superb trick is known as

这个杰出的戏法叫做

a Lorentz transformation.

洛伦兹变换

Yeah, more than a trick.

这可不是骗人的把戏

Slice up the space-time into

重新将时空分割为一幅幅画面

new panels and you have

你将得到物理上正确的动画

the physically correct animation.

I'm stationary in the car,

我静止坐在车里

everything else is coming past me

所有东西都朝我移来并经过我身边

and the speed of light

而光速依然

works out to be that same fixed value

是那个恒定的速度

that we know everyone measures.

和所有人测量的光速一样

On the other hand,

而另一方面

something strange has happened.

有些奇怪的事情发生了

The fence posts aren't spaced a meter apart anymore,

围栏柱子的间隔不再是一米了

and my mom will be worried

而我妈妈会担心

that I look a bit thin.

我看起来瘦了

But that's not fair. Why don't I get to look thin?

这不公平！为什么我看起来没瘦？

I thought physics was supposed to be the same

我以为物理学对每个人都是一样的

for everyone.

Yes, no, it is, and you do.

的确是一样的，你也看起来瘦了

All that stretching and squashing

所有这些，时空的拉伸和压缩

of space-time has just muddled together

把我们之前认为的

what we used to think of separately

独立的时间和空间

as space and time.

都混合到了一起

This particular squashing effect

这个特别的压缩效应

is known as Lorentz contraction.

被称为洛伦兹收缩

Okay, but I still don't look thin.

好吧，可是我依然看起来不瘦

No, yes, you do.

不，你的确看起来瘦了

Now that we know better about space-time,

现在我们对时空有了更多的了解

we should redraw

我们应该重新画出

what the scene looked like to me.

我眼中的情形是怎么样的

To you, I appear Lorentz contracted.

对你来说，我表现出洛伦兹收缩

Oh but to you, I appear Lorentz contracted.

而对你来说，我表现出了洛伦兹收缩

Yes.

对

Uh, well, at least it's fair.

好吧，至少这是公平的

And speaking of fairness,

说到公平

just as space gets muddled with time,

不仅空间被时间搅浑

time also gets muddled with space,

时间也被空间搅浑

in an effect known as time dilation.

有个效应叫做时间膨胀

No, at everyday speeds,

虽然在日常的速度下

such as Tom's car reaches,

比如汤姆的车速

actually all the effects are much, much smaller

实际的效应非常非常地小

than we've illustrated them.

比我们刚才展示的要小得多

Oh, yet, careful experiments,

然而精密的实验

for instance watching the behavior of tiny particles

比如观察微小的粒子

whizzing around the Large Hadron Collider

在大型强子对撞机里的运动

confirmed that the effects are real.

确认了这些效应是真实存在的

And now that space-time is

既然现在时空已是被实验验证的事实

an experimentally confirmed part of reality,

we can get a bit more ambitious.

我们的野心可以更大一些

What if we were to start playing

我们是否可以开始

with the material of space-time itself?

考虑时空本身的性质？

We'll find out all about that in the next animation.

我们会在下一个动画里找到答案