什麼是熵？ - 傑夫·菲利普斯：英語精讀講義

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

有一個對化學和物理學至關重要的概念。

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

它有助於解釋為什麼物理過程是單向的而不是反向的。

Why ice melts,

為什麼冰會融化，

why cream spreads in coffee,

為什麼鮮奶油會在咖啡裡散開，

why air leaks out of a punctured tire.

為什麼空氣會從被扎破的輪胎裡漏出。

It's entropy,

它就是熵，

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

出了名的難以理解。

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

熵經常被描述為混亂程度的量度。

That's a convenient image,

這是一個很方便想像的畫面，

but it's unfortunately misleading.

但遺憾的是它具有誤導性。

For example,

舉個例子，

which is more disordered?

哪個更混亂？

A cup of crushed ice

是一杯碎冰

or a glass of room temperature water?

還是常溫下的一杯水？

Most people would say the ice,

大多數人會說是冰，

but that actually has lower entropy.

但其實它的熵更低。

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

所以我們換個方式來思考，

through probability.

透過機率。

This may be trickier to understand,

這可能更難理解，

but take the time to internalize it, 片語搭配

但花點時間去消化它，

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

你會對熵有更深刻的認識。

Consider two small solids,

假設有兩個小固體，

which are comprised of six atomic bonds each. 用詞

每個由六個原子鍵組成。

In this model,

在這個模型中，

the energy in each solid is stored in the bonds.

每個固體中的能量都儲存在化學鍵裡。

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

它們可以被看作是簡單的容器，

which can hold indivisible units of energy,

能夠容納不可分割的能量單位，

known as quanta. 文化背景

也就是量子。

The more energy a solid has,

一個固體擁有的能量越多，

the hotter it is.

它的溫度就越高。

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

事實證明，能量在這兩個固體中有很多種分佈方式，

and still have the same total energy in each.

同時各自還能保持相同的總能量。

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

每一個這樣的組合都被稱為一個微觀狀態。

For six quanta of energy in solid A

對於固體A中有6個能量量子

and two in solid B,

和固體B中有2個量子的狀態，

there are 9,702 microstates.

總共有9702個微觀狀態。

Of course,

當然，

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

我們這8個能量量子還有其他的排列方式。

For example,

比如說，

all of the energy could be in solid A

所有的能量都可以集中在固體A中，

and none in B,

而B中沒有，

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, 文法

如果我們假設每個微觀狀態發生的可能性相等，

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

我們就能看到，某些能量分佈方式比其他方式發生的機率更高。

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

這是因為它們擁有更多的微觀狀態。

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

熵是對每種能量分佈發生機率的直接量度。

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

我們發現，能量在固體之間最分散的分佈方式，

has the highest entropy.

具有最高的熵。

So in a general sense, 表達脈絡

所以從廣義上講，

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

熵可以看作是這種能量分散程度的量度。

Low entropy means the energy is concentrated.

低熵意味著能量是集中的。

High entropy means it's spread out.

高熵意味著它是分散的。

To see why entropy is useful for explaining spontaneous processes 講解

要明白為什麼熵能用來解釋自發過程，

like hot objects cooling down,

比如熱的物體變涼，

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

我們需要看一個能量發生移動的動態系統。

In reality,

實際上，

energy doesn't stay put. 慣用語

能量不會原地不動。

It continuously moves between neighboring bonds.

它會在相鄰的化學鍵之間不斷移動。

As the energy moves,

隨著能量的移動，

the energy configuration can change.

能量的分佈狀態也會改變。

Because of the distribution of microstates,

由於微觀狀態的分佈規律，

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

系統接下來有21%的機率會進入某種狀態，

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

在這種狀態下，能量最大程度地分散開來。

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

有13%的機率它會回到初始狀態，

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

還有8%的機率A實際上會獲得能量。

Again,

再一次，

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

我們看到，由於擁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.

能量總是傾向於分散。

That's why if you put a hot object

這就是為什麼如果你把一個熱的物體

next to a cold one,

放在一個冷的物體旁邊，

the cold one will warm up

冷的會變熱，

and the hot one will cool down.

而熱的會變涼。

But even in that example, 文法

但即便是那個例子，

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

熱物體變得更熱的機率也有8%。

Why doesn't this ever happen in real life?

為什麼這在現實生活中從未發生過呢？

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

這全都取決於系統的規模。

Our hypothetical solids only had six bonds each.

我們假設的固體每個只有六個化學鍵。

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

讓我們把固體放大到6000個鍵

and 8,000 units of energy.

和8000個能量單位。

And again,

並且再說一次，

start the system with three quarters of the energy in A

初始時讓四分之三的能量在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

現在我們發現A自發獲得更多能量的機率

is this tiny number.

是這樣一個微乎其微的數字。

Familiar everyday objects have many, 文法

我們熟悉的日常物體擁有比這

many times more particles than this.

多得多得多的粒子。

The chance of a hot object in the real world

在現實世界中一個熱物體

getting hotter is so absurdly small, 文法

變得更熱的機率荒謬地小，

it just never happens.

它就是絕不會發生。

Ice melts, 表達脈絡

冰融化，

cream mixes in,

鮮奶油融入，

and tires deflate

輪胎漏氣，

because these states have more dispersed energy than the originals.

是因為這些狀態比初始狀態具有更分散的能量。

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

並沒有什麼神秘力量在推動系統走向更高的熵。

It's just that higher entropy 語氣意圖

只是更高的熵

is always statistically more likely.

在統計學上總是更有可能發生。

That's why entropy has been called time's arrow. 慣用語

這就是為什麼熵被稱為時間之箭。

If energy has the opportunity to spread out, 文法

如果能量有機會分散開來，

it will.

它一定會。