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Hi, this is Henry, and this is the first in a series of videos about special relativity.
大家好，我是亨利，这是狭义相对论系列视频的第一集。
This is definitely not an academic course,
这绝对不是一门学术课程,
but it's going to be a more in-depth and developed exploration of a single topic than a typical standalone minute physics video.
但和一般的单集minute physics视频相比，这一系列的视频将更加深入地探索这一个主题。
I've been greatly inspired and heckled to do this by my friend Grant Sanderson of Three Blue One Brown
我受到了我朋友Grant Sanderson极大的启发，
who set the standard for this kind of thing with his excellent series on calculus and linear algebra.
他在微积分和线性代数方面的一系列视频都很棒，并为这类视频设定了一个标准。
So, special relativity. Special relativity is one of the most popularly famous ideas in physics.
狭义相对论。 狭义相对论是物理学中最著名的观点之一。
It's the thing that Einstein figured out about the speed of light and space and time and equals mc-squared.
它是爱因斯坦计算出关于光速、空间以及E=mc²的理论。
It changed our understanding of the universe and its core ideas are accessible in principle
它改变了我们对于宇宙的理解，原则上，任何具备代数和几何知识的人
to anyone who understands some basic algebra and geometry. You don't even need to know calculus.
都能理解其核心思想。你甚至不需要知道微积分。
And yet in spite of this, special relativity is one of the subjects in physics that confuses the most people
尽管如此，狭义相对论仍然是物理学中最让人困惑的学科之一
and in many cases turns them away from physics altogether.
甚至都把他们给吓跑了。
I think in part, this is because special relativity is not quite a big enough subject to ever get its own full class in physics departments.
我认为部分原因是，狭义相对论的内容并没有多到可以在物理系单开一门课程。
You might see classical mechanics or quantum mechanics or electromagnetism or intro to general relativity on a course syllabus
你或许会在课程大纲里看到经典力学、量子力学、电磁学或广义相对论入门
but it's surprisingly rare to see special relativity,
但很少会看见狭义相对论，
even though relativity is an essential building block upon which most of the rest of modern physics depends.
尽管相对论是现代物理学其余大部分所依赖的基础。
Special relativity is typically relegated to just a few days squeezed into the beginning or end of other physics courses.
狭义相对论通常被压缩成几天的课程，被放在了其他物理课程的开始或最后。
However, the more important reason special relativity confuses so many people,
但狭义相对论让这么多人感到困惑的一个更重要的原因是
is that it's almost always introduced confusingly with lots of complicated algebraic equations with Delta X's
它老是引入一堆带着Delta X's、Delta X Prime's
and Delta X Prime's and square roots, which sometimes you divide by and sometimes you multiply by,
以及平方根的复杂公式，一会儿除，一会儿乘，
and all the while you're scrambling to figure out where in all this symbol logical mess they're hiding
并且你要一直努力弄清楚这些乱七八糟的符号背后
a supposedly mind-blowing insight about the fundamental nature of space and time.
何处隐藏着令人兴奋的对空间和时间基本性质的洞见。
Special relativity doesn't have to be that way.
狭义相对论不必如此。
And I think the complicated explanations have only survived this long because they're how Einstein did it.
我认为复杂解释存在这么久的原因是因为爱因斯坦就是这样做的。
But he was a professional physicist climbing an intellectual mountain up its steepest face.
但他是一位攀爬智慧最巅峰的专业物理学家。
And I don't think that we should require everyone who learns about special relativity
并且我认为我们不应该要求每一位学习狭义相对论的人
now to have to follow the same path Einstein did.
现在都必走爱因斯坦走过的路。
Especially not now that we have super beautiful and simple geometric ways of explaining it.
尤其不是现在，因为现在我们有了非常漂亮和简单的几何方法来解释它。
Essentially we figured out afterwards that there's a much easier way to climb the mountain than what Einstein did,
后来我们发现其实有比爱因斯坦更简单的登山方法，
a way that you could probably even figure out on your own, given the right prompting.
只要给予正确的提示，你甚至可以用这种方法自己找出答案。
And it's that fundamentally beautiful simple geometric way to understand space and time
那就是我希望你在看完本系列视频后留下的
that I want you to leave with after watching this series of videos.
本质上美丽简洁的理解时空的几何方式。
If all goes well, hopefully you'll gain some intuition for what special relativity really is, why it works, why it's right,
如果一切顺利，你将获得一些概念，关于什么是狭义相对论，为什么它能用，为什么它是正确的
and why all those paradoxes you've probably heard about aren't paradoxical at all.
以及为什么你听说过的那些悖论根本就不是悖论？
They're just easy confusions to stumble into when you're attacking things with an army of square roots.
当你用一堆平方根的来解决问题时，很容易陷入一片混乱。
This is going to require some mental effort from your end. There's a very real mathematical sense
这需要废一些脑力。在数学意义上说，
in which learning special relativity is kind of like living your entire life thinking the earth is flat,
学习狭义相对论就像是一辈子都认为地球是平的，
and then learning that the earth is actually round.
然后再学习地球其实是圆的。
A round earth isn't actually that complicated of a thing to picture, I mean, it's just a ball, but trying to get used to that idea,
圆圆的地球并不是一种难以想象的画面，就是个球形，但要习惯这个概念
to really take it in and figure out how your day-to-day experiences on this flat seeming surface of the earth--
打心眼里接受它并弄清楚你在看起来是平面的球面上的日常经验
how they fit into this new round earth idea-- that would certainly take some mental effort.
是如何如何融入这个新的球形地球思想的—这当然需要些脑力。
It is, though, a totally different kind of mental effort from plugging lots of numbers into complicated square root formulas
不过，这是一种完全不同的脑力劳动，不需要把大量的数字代入复杂的平方根公式中
and ultimately, much more worthwhile.
但结果更加值得。
I mean you probably have a pretty good intuition about round Earth concepts,
我的意思是你可能对圆形地球的概念有很好的直觉
like what happens if you just keep walking east and what's the shape of the Earth's shadow on the moon
比如如果你一直往东走，会发生什么以及无需在球坐标下进行复杂的计算，
without having to do complicated calculations in spherical polar coordinates.
就能想象出地球在月球上的阴影是什么形状。
In fact we're gonna take this analogy to the extreme.
事实上，我们将把这个类比发挥到极致。
Just like a globe is a really useful hands-on visual way to explore what it means for the earth to be round
就像地球仪一样，它是一种非常实用的直观方式，可以用来探索地球是圆的
because a globe comes with roundness built-in, I've designed and had built a hands-on space-time globe that has special relativity built in.
因为地球仪就是球形的，我设计并做了一个内置狭义相对论的时空地球仪。
It's not quite as simple as a globe globe because special relativity is a little weirder than roundness.
它不像一个地球仪那样简单，因为狭义相对论比球形更奇怪一点点
But the thing I like about this machined aluminum space-time globe is that
但我喜欢这个加工铝制时空球的地方在于
it's a physical manifestation of the intuition that I hope you develop for special relativity.
它是狭义相对论直觉的一种物理表现，并且我希望大家能具备这种直觉。
We're going to use it to gain a hands-on understanding of the twins paradox, length contraction, and time dilation,
我们将用它来获得孪生佯谬、长度收缩以及时间膨胀
why nothing can go faster than light, and much more. I hope to see you in the next video.
为什么没有物体可以超过光速等等的交互理解。希望下期视频也能看到大家。
