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狭义相对论#1:为什么相对论这么难? – 译学馆
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狭义相对论#1:为什么相对论这么难?

Why is Relativity Hard? | Special Relativity Chapter 1

大家好 我是亨利
Hi, this is Henry.
本视频是《狭义相对论》系列的第一集
And this is the first in a series of videos about Special Relativity.
本视频显然与学术课程不同
This is definitely not an academic course
但它会是针对单一话题的纵深探索
but it’s going to be a more in-depth and developed exploration of
而不是典型的一集就完事儿的“分钟物理”视频
a single topic than a typical standalone minute physics video.
我做这个系列的视频是因为
I’ve been greatly inspired and
我一直受到好友Sanderson的启发和强烈要求
heckled to do this by my friend grant Sanderson
Sanderson是3Blue1Brown的主持人
of 3Blue1Brown who set the standard
他的视频很有水准
for this kind of thing with his
他的视频系列是关于
excellent series series’es?
微积分学 线性代数
on calculus and linear algebra,
而我们要谈的是狭义相对论
so special relativity.
狭义相对论是物理学上
Special relativity is one
最流行 最著名的概念
of the most popularly famous ideas in physics.
它由爱因斯坦提出 是与光速 时空间有关的理论
It’s the thing that Einstein figured out about the speed
狭义相对论的公式是E=mc²
of light and space and time and e equals mc-squared.
它改变了我们对宇宙的认知
It changed our understanding of the universe and
只要懂一些基本的代数和几何
its core ideas are accessible in principle to
就能大体上了解狭义相对论的核心观点
anyone who understands some basic algebra and geometry.
不懂微积分学也完全没问题
You don’t even need to know calculus.
但是尽管如此
And yet in spite of this
狭义相对论仍然是一门
special relativity is one of the subjects in physics
让大多数人非常困惑的物理学科
that confuses the most people and
很多情况下
in many cases
人们甚至把物理学内容都想得和它一样难
turns them away from physics altogether.
我认为
I think in part
部分原因是 在物理学中
this is because special relativity is not quite a
狭义相对论没有庞大到
big enough subject to ever get its own full
发展成为一门独立学科
class in physics departments.
教学大纲上可能有经典力学
You might see classical mechanics
量子力学 电磁学
or quantum mechanics or electromagnetism or
还有对广义相对论的介绍
intro to general relativity on a course syllabus.
对现代物理学的大部分内容来说
But it’s surprisingly rare to see special relativity,
相对论是基本的构件
even though relativity is an essential building block
但教学大纲上有关狭义相对论的内容却少之又少
upon which most of the rest of modern physics depends.
狭义相对论的内容一般会被压缩到几天
Special relativity is typically relegated to just a few days squeezed
安排在其它物理课的开头或最后
into the beginning or end of other physics courses.
但狭义相对论让人困惑的主要原因是
However, the more important reason special relativity
不知为何它总是引入
confuses so many people is that it’s almost always introduced
大量复杂的代数公式
confusingly with lots of complicated algebraic equations
比如∆x ∆x(x是质数) 平方根
with delta xs and delta x primes and square roots
一会儿要除
which sometimes you divide by and
一会儿又要乘
sometimes you multiply by and
你一直在费心弄清一团糟的符号逻辑
all the while you’re scrambling to figure out where in all this symbol logical
空间和时间的根本性质
mess they’re hiding a supposedly mind-blowing insight
可能就隐藏在让你眼花缭乱的公式背后
about the fundamental nature of space and time.
但狭义相对论没这么难
Special relativity doesn’t have to be that way.
我认为 多年来 之所以狭义相对论的解释如此复杂
And I think the complicated explanations have only survived this long
仅仅是因为爱因斯坦就是这么做的
because they’re how Einstein did it.
但爱因斯坦是专业物理学家
But he was a professional
他正在攀登一座陡峭的智慧高峰
physicist climbing an intellectual mountain up its steepest face.
而且我不认为
And I don’t think that we should require
学习狭义相对论的每个人都得
everyone who learns about special relativity now to have
沿着爱因斯坦的老路走下去
to follow the same path Einstein did.
尤其是现在 更没必要了
Especially not now
因为我们有漂亮又简单的几何方式来解释它
that we have super beautiful and simple geometric ways of explaining it.
后来我们基本上摸清了
Essentially we figured out afterwards that there’s a
一个更简单的方式来攀爬这座高峰
much easier way to climb the mountain than what
通过这种方式及其提示
Einstein did, a way that you could probably
你甚至能够自己弄清其中的奥妙
even figure out on your own, given the right prompting.
从根本上说
And it’s that
这真的是一种用来理解空间和时间的
fundamentally beautiful simple geometric way to understand space
迷人的 简单的几何方式
and time that I want you to leave
我希望大家看完本系列的视频后能够学以致用
with after watching this series of videos.
如果一切顺利的话
If all goes well, hopefully you’ll gain some intuition
我希望你能对狭义相对论的定义 原因 正确性
for what special relativity really is, why it works
有一个直观的把握
why it’s right,
而且我希望你明白你之前听到的所有悖论
and why all those paradoxes you’ve probably
其实根本算不上悖论
heard about aren’t paradoxical at all.
他们只是你用兵不当造成小失败后的困惑
They’re just easy confusions to stumble
你本不该用平方根大军发起攻击的
into when you’re attacking things with an army of square roots.
刚开始学习狭义相对论时需要一些脑力
This is going to require some mental effort from your end.
举个贴切的例子吧
There’s a very real
学习相对论某种程度上就是
mathematical sense in which learning special relativity is kind
之前你一直以为地球是平面
of like living your entire life thinking the earth is flat.
然后渐渐了解地球其实是圆的
And then learning that the earth is actually round.
圆形的地球
A round Earth isn’t actually
事实上并不难想象
that complicated of a thing to picture
不就是个球嘛
I mean, it’s just a ball.
但是当你试着习惯这个概念
But trying to get used to that idea,
然后真正接受它
to really take it in and figure out how your day-to-day
并且深刻体察眼前的地球不是平的
experiences on this flat seeming surface of the earth —
即适应地球是圆的这个新概念
how they fit into this new round earth idea —
这个过程肯定要花费一定的脑力
that would certainly take some mental effort.
然而 这是一种完全不同的脑力
It is, though, a totally different kind of mental effort
不同于将许多数字塞进复杂的平方根公式里
from plugging lots of numbers into complicated square root formulas
但最终 付出总是会有收获的
and ultimately, much more worthwhile.
我是说 最后你对地球是圆的这个概念
I mean you probably have a pretty good
能有相当好的直观把握
intuition about round Earth concepts,
比如你一直向东走会发生什么
like what happens if you just keep walking east and
以及地球在月亮上的投影形状
what’s the shape of the Earth’s shadow on the moon
这些都无需用球极坐标系作复杂的计算
without having to do complicated calculations in spherical polar coordinates.
事实上我们要将这个类比推演到极致
In fact we’re gonna take this analogy to the extreme.
就像你能用手转动地球仪
Just like a globe is a really useful
让眼睛探索地球是圆形到底是什么意思
hands-on visual way to explore what it means for the earth to be round
因为地球仪的外观是以球形呈现的
because a globe comes with roundness built-in.
我设计并制作了一个可以亲手操作的
I’ve designed and had built a hands-on
空间时间模型 来解释狭义相对论
space-time globe that has special relativity built in.
它并不像地球仪一样简单
It’s not quite as simple as a globe globe
因为这个狭义相对论模型和地球仪比起来有点儿怪诞
because special relativity is a little weirder than roundness.
但是我希望
But the thing I like
通过这个铝制的机械时空模型
about this machined aluminum space-time
对时空进行物理上的直观呈现
globe is that it’s a physical
让你对狭义相对论有一个深入了解
manifestation of the intuition that I hope you develop for special relativity.
我们将通过这个模型亲自动手感受
We’re going to use it to gain a hands-on understanding
双胞胎悖论 长度收缩 时间膨胀
of the twins paradox, length contraction, and time dilation,
以及为什么光速是谁都不能赶超的 等等
why nothing can go faster than light, and much more.
希望你能观看我的下一个视频
I hope to see you in the next video.
当你等待相对论系列的下一个视频新鲜出炉的时候
And while you’re waiting for the next special relativity video to come out
欢迎你来访问本视频系列的赞助商:Brilliant.org
you might want to check out this video’s sponsor: Brilliant.org
这里有很多物理和数学方面的互动测验 小课程
a site full of interactive quizzes and mini courses on physics and math.
你可能听过我之前说过的这样的话:
As you’ve probably heard me say before, if you want to
如果你想深入理解物理学
understand physics deeply,
你就必须彻底想清楚相关概念
you really have to think through ideas
还要自己解决问题
and solve problems yourself.
而Brilliant能让你学之有方
And Brilliant offers a great way to do just that —
你可以学习一个新话题 比如神经网络
either by learning a new topic, like neural networks
然后用你学到的代数学的知识试着解决问题
practicing problem solving in an area you already know,
或者
like algebra or
你可以在这里玩一些趣味智力游戏
solving tricky puzzles, like this one.
如果你决定购买高级权限
If you decide to sign up for
解锁该网站的所有课程和测验
premium access to all of their courses and quizzes,
那么请通过这个网址brilliant.org/minutephysics进入
you can get 20 % off by going to
因为“分钟物理”的观众能享受八折优惠
brilliant.org/minutephysics.
在此说明一下 因为这个网址加了minutephysics的扩展域名
Again, that’s brilliant.org/minutephysics,
这样Brilliant就知道你是本视频的观众啦
which lets Brilliant know you came from here.

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视频概述

本视频是《狭义相对论》系列课程的第一集,主要对这门课程做了一个简单的介绍。接下来的课程将带你摆脱微积分的困扰,用基本的代数和几何理解狭义相对论。

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视频来源

https://www.youtube.com/watch?v=1rLWVZVWfdY

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