什么是熵？ - 杰夫·菲利普斯：英语精读讲义

There's a concept that's crucial to chemistry and physics. 短語搭配

有一个对化学和物理学至关重要的概念。

It helps explain why physical processes go one way and not the other. 講解

它有助于解释为什么物理过程是单向的而不是反向的。

Why ice melts,

为什么冰会融化，

why cream spreads in coffee,

为什么奶油会在咖啡里散开，

why air leaks out of a punctured tire.

为什么空气会从被扎破的轮胎里漏出。

It's entropy,

它就是熵，

and it's notoriously difficult to wrap our heads around. 習語

出了名的难以理解。

Entropy is often described as a measurement of disorder. 表達脈絡

熵经常被描述为混乱程度的量度。

That's a convenient image,

这是一个很方便想象的画面，

but it's unfortunately misleading.

但遗憾的是它有误导性。

For example,

举个例子，

which is more disordered?

哪个更混乱？

A cup of crushed ice

是一杯碎冰

or a glass of room temperature water?

还是常温下的一杯水？

Most people would say the ice,

大多数人会说是冰，

but that actually has lower entropy.

但其实它的熵更低。

So here's another way of thinking about it, 表達脈絡

所以我们换个方式来思考，

through probability.

通过概率。

This may be trickier to understand,

这可能更难理解，

but take the time to internalize it, 短語搭配

但花点时间去消化它，

and you'll have a much better understanding of entropy. 語法

你会对熵有更深刻的认识。

Consider two small solids,

假设有两个小固体，

which are comprised of six atomic bonds each. 用詞

每个由六个原子键组成。

In this model,

在这个模型中，

the energy in each solid is stored in the bonds.

每个固体中的能量都储存在化学键里。

Those can be thought of as simple containers, 短語搭配

它们可以被看作是简单的容器，

which can hold indivisible units of energy,

能够容纳不可分割的能量单位，

known as quanta. 文化背景

也就是量子。

The more energy a solid has,

一个固体拥有的能量越多，

the hotter it is.

它的温度就越高。

It turns out that there are numerous ways that the energy can be distributed in the two solids 講解

事实证明，能量在这两个固体中有很多种分布方式，

and still have the same total energy in each.

同时各自还能保持相同的总能量。

Each of these options is called a microstate. 文化背景

每一个这样的组合都被称为一个微观状态。

For six quanta of energy in solid A

对于固体A中有6个能量量子

and two in solid B,

和固体B中有2个量子的状态，

there are 9,702 microstates.

总共有9702个微观状态。

Of course,

当然，

there are other ways our eight quanta of energy can be arranged.

我们这8个能量量子还有其他的排列方式。

For example,

比如说，

all of the energy could be in solid A

所有的能量都可以集中在固体A中，

and none in B,

而B中没有，

or half in A and half in B.

或者一半在A，一半在B。

If we assume that each microstate is equally likely, 語法

如果我们假设每个微观状态发生的可能性相等，

we can see that some of the energy configurations have a higher probability of occurring than others. 短語搭配

我们就能看到，某些能量分布方式比其他方式发生的概率更高。

That's due to their greater number of microstates. 短語搭配

这是因为它们拥有更多的微观状态。

Entropy is a direct measure of each energy configuration's probability.

熵是对每种能量分布发生概率的直接量度。

What we see is that the energy configuration in which the energy is most spread out between the solids 語法

我们发现，能量在固体之间最分散的分布方式，

has the highest entropy.

具有最高的熵。

So in a general sense, 表達脈絡

所以从广义上讲，

entropy can be thought of as a measurement of this energy spread.

熵可以看作是这种能量分散程度的量度。

Low entropy means the energy is concentrated.

低熵意味着能量是集中的。

High entropy means it's spread out.

高熵意味着它是分散的。

To see why entropy is useful for explaining spontaneous processes 講解

要明白为什么熵能用来解释自发过程，

like hot objects cooling down,

比如热的物体变凉，

we need to look at a dynamic system where the energy moves.

我们需要看一个能量发生移动的动态系统。

In reality,

实际上，

energy doesn't stay put. 習語

能量不会原地不动。

It continuously moves between neighboring bonds.

它会在相邻的化学键之间不断移动。

As the energy moves,

随着能量的移动，

the energy configuration can change.

能量的分布状态也会改变。

Because of the distribution of microstates,

由于微观状态的分布规律，

there's a 21% chance that the system will later be in the configuration 語法

系统接下来有21%的几率会进入某种状态，

in which the energy is maximally spread out. 短語搭配

在这种状态下，能量最大程度地分散开来。

There's a 13% chance that it'll return to its starting point 短語搭配

有13%的几率它会回到初始状态，

and an 8% chance that A will actually gain energy.

还有8%的几率A实际上会获得能量。

Again,

再一次，

we see that because there are more ways to have dispersed energy and high entropy 語法

我们看到，由于拥有分散能量和高熵的方式

than concentrated energy,

比集中能量的方式更多，

the energy tends to spread out.

能量总是倾向于分散。

That's why if you put a hot object

这就是为什么如果你把一个热的物体

next to a cold one,

放在一个冷的物体旁边，

the cold one will warm up

冷的会变热，

and the hot one will cool down.

而热的会变凉。

But even in that example, 語法

但即便是那个例子，

there is an 8% chance that the hot object would get hotter.

热物体变得更热的几率也有8%。

Why doesn't this ever happen in real life?

为什么这在现实生活中从未发生过呢？

It's all about the size of the system. 短語搭配

这全都取决于系统的规模。

Our hypothetical solids only had six bonds each.

我们假设的固体每个只有六个化学键。

Let's scale the solids up to 6,000 bonds 短語動詞

让我们把固体放大到6000个键

and 8,000 units of energy.

和8000个能量单位。

And again,

并且再说一次，

start the system with three quarters of the energy in A

初始时让四分之三的能量在A中，

and one quarter in B.

四分之一在B中。

Now we find that the chance of A spontaneously acquiring more energy 用詞

现在我们发现A自发获得更多能量的几率

is this tiny number.

是这样一个微乎其微的数字。

Familiar everyday objects have many, 語法

我们熟悉的日常物体拥有比这

many times more particles than this.

多得多得多的粒子。

The chance of a hot object in the real world

在现实世界中一个热物体

getting hotter is so absurdly small, 語法

变得更热的几率荒谬地小，

it just never happens.

它就是绝不会发生。

Ice melts, 表達脈絡

冰融化，

cream mixes in,

奶油融入，

and tires deflate

轮胎漏气，

because these states have more dispersed energy than the originals.

是因为这些状态比初始状态具有更分散的能量。

There's no mysterious force nudging the system towards higher entropy. 習語

并没有什么神秘力量在推动系统走向更高的熵。

It's just that higher entropy 語氣意圖

只是更高的熵

is always statistically more likely.

在统计学上总是更有可能发生。

That's why entropy has been called time's arrow. 習語

这就是为什么熵被称为时间之箭。

If energy has the opportunity to spread out, 語法

如果能量有机会分散开来，

it will.

它一定会。