Name: 【TED-Ed】什麼是熵？- 傑夫-菲利普斯 (【TED-Ed】What is entropy? - Jeff Phillips)
Uploaded: 2021-01-14T07:24:36.000Z
Duration: 5 min 20 s

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

在化學和物理學中有個關鍵概念

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

有助於解釋是此非彼的物理現象

奶油為什麼會在咖啡裡散開來？

It's entropy, and it's notoriously difficult to wrap our heads around.

這是「熵」的概念，非常難以理解

Entropy is often described as a measurement of disorder.

有個說法常把熵 用來衡量不規則的程度

That's a convenient image, but it's unfortunately misleading.

例如，下列哪種情形比較不規則呢？

a cup of crushed ice or a glass of room temperature water?

一杯碎冰，還是一杯室溫的水？

So here's another way of thinking about it through probability.

另一種理解熵的方法是透過機率

This may be trickier to understand, but take the time to internalize it

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

which are comprised  of six atomic bonds each.

In this model, the energy in each solid is stored in the bonds.

這模型裡的能量存在固體的原子鍵裡

Those can be thought of  as simple containers,

可以把原子鍵想成簡單的能量容器

which can hold indivisible units of energy known as quanta.

裡面裝著不可分割的 能量單位「量子」

The more energy a solid has, the hotter it is.

It turns out that there are numerous ways that the energy can be distributed

and still have the same  total energy in each.

Each of these options  is called a microstate.

每一種能量分佈方式稱為一「微態」

For six quanta of energy in Solid A and two in Solid B,

假如固體甲有六個量子，而乙有兩個

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

當然還有其它分派八個量子的方式

For example, all of the energy could be in Solid A and none in B,

例如，固體甲擁有八個量子 而固體乙一個也沒有

If we assume that each microstate is equally likely,

如果假設每種微態發生的機率相等

we can see that some of the energy configurations

have a higher probability of occurring than others.

That's due to their greater number of microstates.

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

熵直接衡量每種能量分佈狀態的機率

What we see is that the energy configuration

in which the energy is most spread out between the solids

這兩個固體的能量最分散的時候

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

Low entropy means  the energy is concentrated.

To see why entropy is useful for explaining spontaneous processes,

為要理解怎樣用熵解釋自發過程

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

It continuously moves between  neighboring bonds.

而是持續在相鄰的原子鍵中移動

Because of the distribution  of microstates,

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

in which the energy is maximally  spread out,

there's a 13% chance that it will return to its starting point,

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

還有 8% 的機率 固體甲會增加能量

Again, we see that because there are more ways to have dispersed energy

and high entropy than concentrated energy,

高熵值的微態總數 比能量集中的還多

That's why if you put a hot object next to a cold one,

這就是為什麼把熱的物體 和冷的物體擺一起

the cold one will warm up and the hot one will cool down.

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

也有 8％ 的機率 熱的物體會變得更熱

Why doesn't this ever happen in real life?

為什麼現實生活裡沒發生這種情形？

Our hypothetical solids only had six bonds each.

我們的模型假設 只有六根原子鍵的固體

Let's scale the solids up to 6,000 bonds and 8,000 units of energy,

如果增加到 6,000 根原子鍵 和 8,000 個單位能量

and again start the system with three-quarters of the energy in A

初始狀態仍是甲有四分之三的能量

Now we find that chance of A spontaneously acquiring more energy

就會發現甲自發獲得更多能量的機率

Familiar, everyday objects have many, many times more particles than this.

日常熟知物體的粒子數遠比這多得多

The chance of a hot object  in the real world getting hotter

所以現實世界裡 熱的物體變得更熱的機率

because these states have more dispersed energy than the originals.

都是因為這些狀態的能量 比原先狀態的更分散

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

並不是某種神秘的力量 驅使系統傾向微調至更高的熵值

It's just that higher entropy is always statistically more likely.

而是因為統計上高熵值更可能發生

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

這就是為什麼熵又被稱為時間之箭

If energy has the opportunity to spread out, it will.

如果有機會分散能量，就會分散能量