Does time exist? - Andrew Zimmerman Jones

翻译人员: Leonard Au 校对人员: Adam Lee

（时间是什么？）

The earliest time measurements were

人类最初衡量时间的方法，

observations of cycles of the natural world,

就是观察自然世界的周期。

using patterns of changes from day to night

他们用朝暮之间和季节之间 的变化模式来制作日历。

and season to season to build calendars.

More precise time-keeping, like sundials

后来出现了更精确的计时方法， 比如日晷、机械钟，

and mechanical clocks, eventually came along

to put time in more convenient boxes.

让计时变得更方便。

But what exactly is it that we’re measuring?

但是，我们衡量的到底是什么呢？

Is time something that physically exists,

时间究竟是真正存在的一个物体，

or is it just in our heads?

还是一个只在我们大脑中存在的概念？

At first the answer seems obvious—

乍看之下，答案似乎很明显：

of course time exists;

时间当然是存在的；

it constantly unfolds all around us,

它时时刻刻在我们周围流逝着，

and it’s hard to imagine the universe without it.

很难想象宇宙没了时间 会变成什么样子。

But our understanding of time started

但是，我们对时间的理解 因为爱因斯坦而变得复杂了。

getting complicated thanks to Einstein.

His theory of relativity tells us that time

根据他的相对论， 每个人都会经历时间的流逝，

passes for everyone, but doesn’t always pass

但是时间流逝的速度 随着场合的不同而变化。

at the same rate for people in different situations,

like those travelling close to the speed of light

比如，速度将近光速的人，

or orbiting a supermassive black hole.

或者绕着巨大黑洞打转的人。

Einstein resolved the malleability of time

爱因斯坦解决了时间可塑性的问题，

by combining it with space to define space-time,

他把时间和空间结合起来， 定义了时空的概念。

which can bend, but behaves in consistent, predictable ways.

时空可以转弯，但它表现得一致且可预测。

Einstein’s theory seemed to confirm that time

爱因斯坦的理论似乎证实，

is woven into the very fabric of the universe.

时间是贯穿在宇宙的结构中的。

But there’s a big question it didn’t fully resolve:

但是有一个重要问题 是它没能完全解决的：

why is it we can move through space in any direction,

为什么我们在空间里 可以往任何方向移动，

but through time in only one?

在时间里却只能往一个方向移动呢？

No matter what we do, the past is always,

不管我们做什么， 过去永远都已经成了过去。

stubbornly, behind us.

This is called the arrow of time.

这个现象叫做“时间之箭”。

When a drop of food coloring is

如果把一滴食用色素滴进一杯水，

dropped into a glass of water,

we instinctively know that the coloring

我们本能地就知道 色素会从那一滴里渗透出来，

will drift out from the drop,

eventually filling the glass.

最终把整杯水染色。

Imagine watching the opposite happen.

想象一下相反的情况发生。

Here, we’d recognize time as unfolding backwards.

我们会意识到，时间正在往反方向进行。

We live in a universe where the food coloring

在我们这个宇宙中， 食用色素会在水中扩散，

spreads out in the water,

not a universe where it collects together.

而不会聚集在一起。

In physics, this is described by

这个原理在物理学中 叫做热力学第二定律：

the Second Law of Thermodynamics,

which says that systems will gain disorder,

每个系统会随时间失去秩序，

or entropy, over time.

或者说，系统的熵会增加。

Systems in our universe move from order to disorder,

我们宇宙中的系统 会从有秩序变得无秩序。

and it is that property of the universe

正是宇宙的这个属性，

that defines the direction of time’s arrow.

定义了时间之箭的方向。

So if time is such a fundamental property,

那么，既然时间是个如此基本的属性，

it should be in our most fundamental equations

它就应该出现在形容宇宙的 最基础方程式中，不是吗？

describing the universe, right?

We currently have two sets of

目前，物理学有两套方程式控制着。

equations that govern physics.

General relativity describes the

广义相对论形容的是巨大物体的行为，

behavior of very large things,

while quantum physics explains the very small.

量子物理学解释的是微小物体的行为。

One of the biggest goals in theoretical physics

理论物理学这半个世纪以来的最大目标之一，

over the last half century has been reconciling

就是把两者协调起来， 形成一个根本的“万物理论”。

the two into one fundamental “theory of everything."

There have been many attempts

已经有许多人尝试这么做，

—none yet proven—

却没有一个理论已被证实，

and they treat time in different ways.

而且它们处理时间的方法都不一样。

Oddly enough, one contender called the Wheeler-DeWitt

奇怪的是，有一个叫做 惠勒-德维特方程式的理论，

equation, doesn’t include time at all.

居然不把时间包含在内。

Like all current theories of everything,

就像所有万物理论一样，

that equation is speculative.

这个方程式只是猜测而已。

But as a thought experiment,

但是，作为思想实验，

if it or a similarly time-starved equation

如果这类不包含时间的 方程式正确的话，

turned out to be true, would that mean

是不是代表时间 在最根本层面上是不存在的呢？

that time doesn’t exist, at the most fundamental level?

Could time just be some sort of illusion generated

我们是不是因为对宇宙的感知受到限制， 才会产生时间的幻觉？

by the limitations of the way

we perceive the universe?

We don’t yet know, but maybe that’s

我们目前仍不清楚， 但是这种想法可能是错误的。

the wrong way of thinking about it.

Instead of asking if time exists as a fundamental property,

与其探讨时间是不是基本属性，

maybe it could exist as an emergent one.

倒不如探讨它是不是涌现性属性。

Emergent properties are things that don’t exist

涌现性属性不存在于一个系统的 个别部分，

in individual pieces of a system,

but do exist for the system as a whole.

但是它存在于该系统的整体。

Each individual water molecule doesn’t have a tide,

个别水分子是不会产生潮汐的，

but the whole ocean does.

但整个海洋会有潮汐。

A movie creates change through time by using

一部电影呈现时间流逝的方法，

a series of still images that appear to have a fluid,

就是利用一系列静止图像，

而这些图像之间似乎 有着流通、持续的变化。

continuous change between them.

Flipping through the images fast enough,

如果图像的翻看速度够快的话，

our brains perceive the passage of time

我们的大脑就会从静止图像的顺序

from the sequence of still images.

感测出时间的流逝。

No individual frame of the movie changes

电影中的个别画面都不会变化，

or contains the passage of time,

而且也不包含时间的流逝。

but it’s a property that comes out of how

但是时间的属性来自于 一系列画面之间的串连。

the pieces are strung together.

The movement is real, yet also an illusion.

电影中的动作是真实的，但也是虚幻的。

Could the physics of time somehow be a similar illusion?

在物理学上， 时间是不是同样也是幻觉呢？

Physicists are still exploring these and other questions,

物理学家还在探讨这类问题，

so we’re far from a complete explanation.

要得到完整的解释，还要等上好久，

At least for the moment.

至少以目前来看是这样。