---
author: Big Think
date: '2026-05-12'
guest: ''
layout: post.njk
source: https://www.youtube.com/watch?v=68DgpdnjBEg
speaker: Big Think
tags:
- time
- spacetime
- relativity
- entropy
- physics
title: 时间的本质：从牛顿到爱因斯坦的物理学之旅与熵增之谜
summary: 本文深入探讨了时间的本质，对比了牛顿力学中绝对时空观与爱因斯坦相对论中统一的四维时空观。文章解析了电磁学如何引入光速恒定这一革命性概念，以及广义相对论如何将引力解释为时空曲率。最终，通过熵增定律，揭示了时间单向性的深层物理原因——宇宙始于一个特殊的低熵状态，并持续向高熵演化，这赋予了我们对过去有记忆而对未来有预期的独特体验。
insight: ''
draft: true
series: ''
category: tech-trends
area: tech-engineering
project: []
people:
- Sean Carroll
companies_orgs: []
products_models: []
media_books: []
status: evergreen
---
### 时间的单向性：物理定律与客观现实的悖论
物理学的基本定律，无论是基于牛顿的经典时空观，还是爱因斯坦的相对论，都表现出一种时间上的对称性——它们能够同样准确地预测过去和未来。这意味着，在理论层面，时间没有明确的“方向”。然而，在我们的日常经验中，时间显然具有明确的方向性：我们能清晰地回忆起昨天发生的事情，却只能模糊地预测明天，我们拥有过去的记忆，却从未有过关于未来的“记忆书”。这种时间方向性的感知，并非源于物理学的基本定律本身，而是源于宇宙中众多事物集体行为的特殊开端。物理学家兼哲学家 **Sean Carroll** 解释了这一现象的本质。
Original English
One thing that is true even in Newtonian
ways of thinking about space and time or
in Einsteinian ways of thinking about space and
time is that these fundamental laws work forward
and backward in time. Knowing everything about
the universe at one moment predicts the past
as well as the future. That's because what we
think of as the fundamental laws of physics do
not have a directionality to time. They treat the
past and future the same. But there's clearly a
direction to time in the world. I remember what I
was doing yesterday. I might guess what I'm going
to do tomorrow, but I don't remember it in the
same way. I have no photographs or memory books
of the future. What is going on with that? And
the answer is it's not the fundamental laws of
physics. It's the collective behavior of many,
many things in the universe that start out in a
special state. I'm Sean Carroll. I am a physicist
and philosopher at Johns Hopkins University,
host of the Mindscape podcast, and also author
of a bunch of books, most recently the biggest
ideas in the universe series, including
spacetime in motion and quant and fields.
### 牛顿力学：绝对时空的基石
**艾萨克·牛顿** 是一位杰出的思想家，他创立的经典力学深刻地改变了我们对世界的认知。在他构建的物理学体系中，空间和时间被视为独立存在且绝对的实体。这意味着，宇宙中不存在一个“首选”的位置或参照系。无论你在宇宙何处，或是以何种速度运动（只要是匀速），物理定律的运作方式都是相同的，这一点由**伽利略**提出并被牛顿采纳。然而，尽管没有首选的运动状态，牛顿理论依然假定了存在一个普适的、所有观察者都同意的空间距离和时间点。无论是在地球上还是在遥远的星系，一英里或一个瞬间的概念被认为是普遍一致的。
Original English
What is the nature of time?
Isaac Newton, you may have heard, was a smart
fellow. And one of the interesting things when you
invent a whole new way of doing physics, if you're
right and it becomes successful, then later on
people kind of take it for granted. They're like,
"Yeah, this is how the world works or whatever."
But at the time, you're still very careful. And
and Newton was himself super duper careful about
all the assumptions that went into his theory
and what their implications were and so on.
One part of classical mechanics is the idea of
space and time both separately existing and being
absolute. There is a meaningfulness to that. There
is no preferred position in the universe. You can
be anywhere you want. The laws of physics work the
same. There's not even a preferred velocity to the
universe. This was figured out by Galileo and
Newton kind of took it on board. If you started
everything moving at 1 mile per hour to the left,
the world will look exactly the same. There's no
actual frame of rest that you can measure. But
there is space and there is time and everyone
agrees on what those two things mean. When I say
I am one mile away from a certain other point,
everyone in the universe agrees you are one mile
away. Yes, that is correct. When I snap my fingers
and say at the moment I snap my fingers a certain
thing is happening in Los Angeles everyone agrees
that indeed at that moment that's a well-
definfined concept to say what is happening
at some point far away not just Los Angeles but
Alpha Centtory or the Andromeda galaxy. Turns out
those assumptions are not quite right and it was a
journey to get there as it often is.
### 电磁学革命：光速恒定的挑战
19世纪，随着**电磁学**的兴起，物理学界开始面对对牛顿绝对时空观的挑战。**詹姆斯·克拉克·麦克斯韦**在前人如**法拉第**和**安培**等人的基础上，整合了电场和磁场这两大基本力场的规律，形成了描述电磁现象的统一方程组。这些方程不仅解释了电和磁的相互作用，还惊人地预测了电磁波的存在，并计算出其传播速度——即**光速**。然而，麦克斯韦方程组与牛顿力学存在一个根本性的矛盾：牛顿力学不承认任何“首选速度”，而麦克斯韦方程组却明确指出了一个普适常数——光速。无论观察者如何运动，测得的光速值始终相同，这令当时的物理学家们困惑不已，他们尝试了各种复杂的理论来解释这一现象。
Original English
It started in
the 1800s with the invention of electromagnetism.
So there are all these new phenomena that people
were thinking about since Ben Franklin flew
his kite and studied lightning coming down. It
was James Clark Maxwell who put the whole story
together after work by people like Faraday and
Aier and so forth. And what he realized is there's
two fields pervading the universe, an electric
field and a magnetic field. and he wrote down some
equations that these fields obey and they sort of
play with each other and push around charged
particles and things like that. People were
very happy at the existence of electromagnetism.
They started thinking about what it all meant and
what they realized is that the sort of way that
space and time are treated in Maxwell's theory
of electromagnetism is different than the way
they are apparently treated in Newton's theory.
In particular, Maxwell's equations predicted a
special velocity. There's no special velocity in
Newtonian mechanics. Every velocity is created the
same. Maxwell says there is something called the
speed of light. It is the speed at which waves in
the electromagnetic fields move. And naively, you
look at the equations and everyone measures the
same value for the speed of light. It's a constant
of nature. How can it possibly be the case that
everyone measures the same speed for light even if
they're moving with respect to each other? So for
a long time, for decades, people physicists bashed
their heads against this problem. They came with
very elaborate schemes to get rid of it.
### 爱因斯坦的狭义相对论：时空的统一
面对光速不变的难题，**阿尔伯特·爱因斯坦**在1905年提出的**狭义相对论**给出了革命性的解释。他大胆地假设，电磁波并非是某种介质中的波动，而是自身就构成了存在的实体。他认为，方程预言的“人人测得光速相同”并非需要回避的异常，而是宇宙的本质属性。要认真对待这一事实，就必须彻底重构我们对空间和时间的认知。两年后，爱因斯坦的前教授、数学家**赫尔曼·闵可夫斯基**提出了关键性的数学框架：空间和时间不再是相互独立的绝对概念，而是融合成了一个单一的四维实体——**时空（spacetime）**。在**闵可夫斯基时空**中，不同的观察者会根据他们相对运动的方式，以不同的方式划分出各自的“空间”和“时间”。因此，在某个时刻发生在遥远地方的事件是否“同时”发生，不再是一个客观的绝对事实，而是取决于观察者的测量。尽管爱因斯坦起初对闵可夫斯基的数学表述不以为然，但这种将空间和时间结合起来的视角，为他后来构建包含引力的广义相对论奠定了至关重要的基础。
Original English
And it
was Einstein, Albert Einstein in his great paper
in 1905 who first said you should get rid of the
idea of these waves traveling through a medium.
You should think of the electromagnetic waves as
really being the thing that exists. And when the
equations tell you everyone measures the speed
of light the same, that's because they do. Take
that seriously. All you have to do is entirely
rejigger your thoughts about what space and time
are. And in fact, it wasn't until two years later
when Herman Mmanovsky, who was a mathematician
who had been one of Einstein's professors, said,
"You know, the right way to think about Einstein's
theory is to say that space and time aren't
separate anymore. To imagine there's one thing
called spacetime, and different people, different
observers moving in different ways through the
universe will divide it up into space and time
differently. There's no objective true fact about
when I snap my fingers now what's happening light
years away. That's going to depend on who's doing
the observing and who is doing the measuring. It
can all be explained very beautifully by imagining
a single four-dimensional spaceime instead of
separate space and time. Einstein himself was not
impressed by this move. Einstein was a hilarious
character because he was a physicist's physicist.
He was very mathematically adept. You know, don't
believe the stories that Einstein wasn't good
at math in school. He was very good at it, but
he wasn't in it for the math. He was in it for the
physics. So, he learned as much math as he needed.
And when Benovsky says, "I have some new math
that unifies space and time based on Einstein's
theories," Einstein himself is like, "I don't need
that. That's like extra mathematical nonsense."
He soon changed his mind because it turns out that
that move from space and time being separate to
being combined is super useful going forward,
including 10 years later, he would invent his
general theory of relativity that include gravity
into the space-time story.
### 广义相对论：引力即是时空几何
狭义相对论成功地统一了空间和时间，但如何将**引力**纳入这个新的时空框架，成为了爱因斯坦面临的下一个巨大挑战。牛顿的万有引力定律，一个关于质量之间吸引力的平方反比定律，虽然极其成功，却与狭义相对论中不存在绝对静止参照系和光速不变的原理不兼容。爱因斯坦尝试了几种方法，最终意识到他需要采取一种更为“戏剧化”的方式。他观察到，所有物体在引力作用下都会以相同的速率下落（如**伽利略**的实验所示），无论其质量大小。这表明引力效应在局部区域会“消失”，因为所有处于自由落体状态的观察者都无法区分自己是处于引力场中还是在加速运动。由此，爱因斯坦构想了一个革命性的理念：引力并非是一种作用在时空之上的“力”，而是**时空本身几何性质的体现**。
他借鉴闵可夫斯基的时空概念，提出时空是一个动态的四维结构，其几何形状（曲率）会受到其中物质和能量的分布影响而发生弯曲和变形。我们所感受到的“引力”，实际上就是物体沿着这种弯曲时空中的“测地线”（最短路径）运动的表现。1915年，爱因斯坦完成了**广义相对论**，将引力这一基本自然力，通过时空几何的语言，完美地整合进了物理学的宏大图景之中。
Original English
When Einstein put
together what we now call the special theory of
relativity, the idea that there's no preferred
standard of rest in the universe, but also
everyone thinks the speed of light is the same.
All you have to do is imagine ultimately that
space and time are glued together. That was a
radical reworking of the framework of physics. You
know, Newton's idea of separate space and separate
time absolute and agreed upon by everyone had been
there for hundreds of years. And when you do that,
when you say, okay, I'm going to completely
invent space and time in part because I want
to match this wonderful theory. We have Maxwell's
theory of electricity and magnetism. You have to
go back to everything that was a success in your
previous way of doing things and say does it still
work? The biggest success of Newtonian classical
mechanics was gravity. The famous inverse square
law of gravity. Newton posited that if you
have two objects with two different masses,
they have a gravitational force that will pull
them together that diminishes as one over the
square of the distance between them. And that
simple rule plus the framework of Newtonian
mechanics is enough to match exactly what you see
in the sky in terms of the planets moving around.
It's enough to launch a rocket and get it to the
moon. So Einstein comes along and says, "Well,
okay, can I make a version of Newton's theory of
gravity that is compatible with my new theory of
special relativity?" And after trying, he said,
"No, I can't. You have to do something much more
dramatic." And what he realized is that gravity is
a special force of nature. You know, Maxwell talks
about electricity and magnetism. If I want to know
what the electric field is at one point in space,
it's very easy to do. I put a positively
charged particle, a negatively charged particle,
they get pushed in opposite directions by the
electric field. But Einstein realized that
every particle reacts the same way to gravity.
If I have a very heavy particle and a very light
particle and I drop them, Galileo showed that they
drop at exactly the same rate. They're not pushed
around in a different way. So because of that,
gravity seems to disappear if you only look at it
in a tiny region of the universe. If you were in a
sealed box and you were dropping things and going,
"Oh, I have gravity here." You don't know that for
sure. Maybe you're in a rocket ship and the rocket
is accelerating and you're being tricked into
thinking you have gravity. So Einstein, because
he's Einstein, he's very smart. You know, you or I
would go, "Huh, that's interesting." But he says,
"I think what that means is that gravity is not
a force on top of spacetime. It's a feature of
spacetime itself." What feature could it be? Well,
my ex-professor Minkovsky says that spacetime has
a geometry. It's one combined thing, and there
are equations telling me how particles move in it.
Maybe that geometry is curved. Maybe it's not like
a flat tabletop like uklitian geometry. Maybe it's
warped and bent and dynamical and changes in
response to the existence of mass and energy
and things like that. It's a it's a good idea to
have. It takes you a lot of effort and a lot of
mathematical work to figure it out. So 10 years
later in 1915, Einstein finally completes what
we call the general theory of relativity. In the
general theory of relativity says spaceacetime
is a four-dimensional thing. That four-dimensional
thing has a geometry. It's pushed around by matter
and energy. And we experience the curvature of
spacetime as the force of gravity.
### 时空几何的推论：双生子佯谬与时间膨胀
当空间和时间被统一成一个整体——时空后，这意味着它们之间的关系变得更为密切，并且观察者在时空中的不同“路径”会产生不同的时间累积。在空间中，两点之间的距离通常是我们想象中的最短路径，即直线。然而，在时空中，这个类比稍有不同：**最短路径（直线）对应的是时间最长的累积**，而最长路径则对应时间累积的减少。
这引出了著名的**双生子佯谬（Twin Paradox）**。设想一对双生子，其中一人留在地球，另一人乘坐接近光速的飞船进行星际旅行并返回。尽管两人同时出发，但旅行归来的宇航员双生子会比留在地球上的双生子年轻。这是因为旅行的双生子沿着一条弯曲的时空路径前进，经历的时间累积比留在原地（近似直线穿越时空）的双生子要少。需要强调的是，这并不是说旅行者身上的“时钟”变慢了；在任何局部参考系下，时间流逝的速度始终是每秒一秒。而是说，由于他们采取了不同的时空轨迹，最终累积的总时间产生了差异。
同样，在**广义相对论**中，强**引力场**也会导致时空弯曲，从而影响时间的累积。身处强引力场（例如靠近黑洞）的人，所经历的总时间将比远离引力源的人少。电影**《星际穿越》（Interstellar）**中对这一现象进行了精彩的视觉化呈现，展示了时间在强大引力作用下显著变慢的效应。
Original English
When Einstein
and Minkovsky figured out that space and time are
both two different ways of slicing up spaceime,
what does that mean? What does that mean like
in our guts, right? What does it visually
or measurably imply? You know, in space there's
something called the distance between two points.
If you say, you know, I'm here in Washington DC
and a friend of mine is in Los Angeles, there's
a distance between those two cities and we all
agree on what that distance is because implicitly
we're imagining the shortest distance path, right?
The straight line that connects these two points.
But of course, if you actually travel between
these two cities, you won't exactly necessarily
take that much distance because you're going to
go right and left. You're not going to go exactly
on a straight line. So in space, we're all very
very used to the idea that different paths have
different lengths, even if they start and end at
the same point. In special relativity, now that
space and time are unified, what that means is
that time is like that. The time you personally
measure on your wristwatch is very analogous
to the distance that you travel moving on some
path. What that means is that rather than being
a universal thing that everyone agrees on, time
depends on the trajectory you take through the
universe. The most famous example of this is the
twin paradox. You imagine two twins. They don't
have to be twins, but it's more vivid if they are
because you think of twins as being the same age.
Okay? One twin just doesn't move, just stays home.
This is the lazy twin. And they get older like
the rest of us all do. The other twin hops in a
rocket ship that moves out very close to the speed
of light. You need to move close to the speed of
light to feel the effects of relativity and then
comes back. And so they left at the same time.
They were the same age. They come back to the same
point in space and the same point in time. But the
twin who traveled is now younger. The twin who
traveled has experienced less time than the twin
who stayed home. And the reason why is because
they took different paths through spaceime.
Space and time are similar to each other but not
exactly the same. That's why in space the shortest
distance path is a straight line. But in time the
longest time path is the straight line. The twin
who stays stationary and doesn't move, that's
moving in a straight line through spacetime,
that's the one that feels more time pass before
the other twin comes back. When people hear
this stuff about relativity and moving through
space and things, what they want to say is, "Oh,
so you're saying that time moves more slowly when
you're traveling near the speed of light?" No,
I do not want to say that. I very much do not want
to say that. What is the rate at which time moves?
It is 1 second per second. You're being tricked
by your use of the English language because you
move through space and it makes perfect sense
to say I am moving at 1 meter/s or 2 meters/s
or whatever. The rate at which you move is the
number of distance you travel per unit time. But
the amount of time you travel per unit time is
always one. Now that accumulated time along two
different trajectories can be different. That's
the origin of something like the twin paradox. Or
when gravity comes into the game, the amount of
total time you experience will be less if you're
deep in a gravitational field than if you're out
there in interstellar space where gravity is not
that important. So in general relativity, being
in a strong gravitational field is much like
moving out there close to the speed of light.
If you had someone stay back here on Earth,
someone else go near a black hole, for example. A
black hole is the strongest kind of gravitational
field you can have. Don't go in to the black
hole because then you can't come back out. But
if you go near it and then you come back, you
will be younger than the person who just stayed
behind. You will have experienced less time.
Your wristwatch is still clicking at one second
per second, but the accumulated amount of time is
different because you have taken a different path
through curved spacetime. In Interstellar, the
Christopher Nolan movie, this was wonderfully
illustrated. Kip Thorne, who is a Nobel Prize
winning physicist, was the executive producer
and one of the instigators of that movie, and he
put all of his physics knowledge in there about
wormholes and black holes and gravity and time
travel. So up until the very last scenes when
they're in the library and everything goes
haywire, all the physics in that movie is
completely respectable.
### 时间之箭的根源：熵增定律与宇宙的开端
尽管物理学的基本定律在时间上是可逆的，但我们体验到的时间却具有明确的单向性：我们拥有过去的记忆，却无法预知未来；我们只会变老，而不会变年轻。这背后的根本原因，并非来自于物理定律本身，而是源于宇宙的**集体行为**，特别是它起始于一个极其**特殊的低熵状态**。
**熵（Entropy）**，是19世纪提出的一个概念，用来衡量一个系统的**无序度、随机性或混乱程度**。**热力学第二定律**明确指出，在任何孤立系统中，熵总是随时间增加。这是因为，一个系统有无数种方式处于高熵（混乱）状态，而只有极少数方式处于低熵（有序）状态。宇宙之所以展现出时间的方向性，是因为它从一个极度有序、低熵的初始状态开始，并且一直在朝着高熵状态演化。这个宇宙起源的低熵状态本身是一个未解的宇宙学之谜。正是这种熵的持续增加，使得我们能够形成关于过去的记录（记忆），见证衰老过程，并感受到时间沿着一个特定方向流动。
Original English
One thing that is true
even in Newtonian ways of thinking about space
and time or in Einsteinian ways of thinking about
space and time is that these fundamental laws work
forward and backward in time. Knowing everything
about the universe at one moment predicts the past
as well as the future. That's because what we
think of as the fundamental laws of physics do
not have a directionality to time. They treat the
past and future the same. But there's clearly a
direction to time in the world. I remember what I
was doing yesterday. I might guess what I'm going
to do tomorrow, but I don't remember it in the
same way. I have no photographs or memory books
of the future. I was younger. I will always be
older in the future. What is going on with that?
And the answer is it's not the fundamental laws
of physics. It's the collective behavior of many
many things in the universe that start out in a
special state. It goes back to the idea of entropy
from the 1800s. The idea of the disorderliness of
a system, the randomness, the disorganization. And
entropy increases with time. That's the famous
second law of thermodynamics. Why does entropy
increase with time? Because there are more
ways for a system to be arranged in a high
entropy configuration than a low entropy one by
definition. And the universe started in a very
special low entropy state. Nobody knows why that
is true. This is a mystery to cosmology. But the
entropy of the universe was very very low to start
and it's been increasing ever since. and us having
memories of the past but not the future. The
ability to have records, the fact that we age in
the same direction. This is all because entropy is
increasing in one direction rather than the other.
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