What is entropy? - Jeff Phillips · TED-Ed
了解熵的概念，解释物理过程的方向性，如冰融化、奶油扩散等。适合练习科学词汇和理解抽象概念。
There's a concept that's crucial to chemistry and physics.
有一个概念对化学和物理学来说至关重要。
It helps explain why physical processes go one way and not the other: why ice melts, why cream spreads in coffee,
这有助于解释为什么物理过程总是朝某个方向发展，而不会朝相反方向进行：为什么冰会融化，为什么奶油会扩散到咖啡中。
why air leaks out of a punctured tire.
为什么空气会从被刺穿的轮胎中泄漏出来？
It's entropy, and it's notoriously difficult to wrap our heads around.
这就是所谓的“熵”（entropy），它极其难以被我们理解。
Entropy is often described as a measurement of disorder.
熵通常被描述为一种衡量系统无序程度的指标。
That's a convenient image, but it's unfortunately misleading.
这确实是一张很“方便”（即易于理解）的图片，但遗憾的是，它具有误导性。
For example, which is more disordered - a cup of crushed ice or a glass of room temperature water?
例如，哪一个状态更“无序”（即更混乱）：一杯碎冰，还是一杯室温下的水？
Most people would say the ice, but that actually has lower entropy.
大多数人可能会选择“冰”，但实际上冰的熵值更低。
So here's another way of thinking about it through probability.
那么，这里有一种通过概率来思考这个问题的新方法。
This may be trickier to understand, but take the time to internalize it and you'll have a much better understanding of entropy.
这可能有点难以理解，但请花时间仔细思考并真正将其内化到自己的认知中，这样你就能对“熵”这个概念有更深刻的理解了。
Consider two small solids which are comprised of six atomic bonds each.
假设存在两种小型固体，每种固体都由六个原子键构成。
In this model, the energy in each solid is stored in the bonds.
在这个模型中，每种固体中的能量都储存在化学键中。
Those can be thought of as simple containers, which can hold indivisible units of energy known as quanta.
这些可以被视为简单的容器，它们能够容纳被称为“量子”的、不可分割的能量单位。
The more energy a solid has, the hotter it is.
固体所含的能量越多，其温度就越高。
It turns out that there are numerous
原来，这样的例子其实有很多。
ways that the energy can be distributed in the two solids and still have the same total energy in each.
能量可以在这两种固体中以不同的方式分布，同时每种固体的总能量仍然保持不变。
Each of these options is called a microstate.
这些选项中的每一个都被称为“微型国家”（microstate）。
For six quanta of energy in Solid A and two in Solid B, there are 9,702 microstates.
当固体A中含有6个能量量子，而固体B中含有2个能量量子时，系统总共有9,702种可能的微观状态（即微观构型）。
Of course, there are other ways our eight quanta of energy can be arranged.
当然，我们的这八个能量量子还可以以其他方式排列组合。
For example, all of the energy could be in Solid A and none in B, or half in A and half in B.
例如，所有的能量都可能集中在物质 A 中，而物质 B 中没有任何能量；或者，一半的能量在物质 A 中，另一半在物质 B 中。
If we assume that each microstate is equally likely, we can see that some of the energy configurations have a higher probability of occurring than others.
如果我们假设每个微型国家出现的概率都是相同的，那么就会发现某些能量配置出现的概率比其他配置要高。
That's due to their greater number of microstates.
这是因为它们的微观状态数量更多。
Entropy is a direct measure of each energy configuration's probability.
熵是衡量每种能量构型出现概率的直接指标。
What we see is that the energy configuration in which the energy is most spread out between the solids has the highest entropy.
我们所观察到的是：当能量在固体内部最为均匀分布时（即能量分布最为分散的状态），系统的熵值最高。
So in a general sense, entropy can be thought of as a measurement of this energy spread.
从广义上讲，熵可以被看作是对这种能量分布情况的度量。
Low entropy means the energy is concentrated.
低熵状态意味着能量高度集中。
High entropy means it's spread out.
高熵状态意味着能量或物质分布得非常均匀（即处于高度分散的状态）。
To see why entropy is useful for
要理解为什么熵在某些情况下是有用的……
explaining spontaneous processes, like hot objects cooling down, we need to look at a dynamic system where the energy moves.
在解释诸如热物体冷却这类自发过程时，我们需要研究一个能量在不断流动的动态系统。
In reality, energy doesn't stay put.
实际上，能量并不会一直停留在某个地方（或某个状态）。
It continuously moves between neighboring bonds.
它在相邻的化学键之间不断移动。
As the energy moves, the energy configuration can change.
当能量发生转移时，其能量状态（即能量配置）也可能发生变化。
Because of the distribution of microstates, there's
由于微观状态的分布情况，因此……
a 21% chance that the system will later be in the configuration in which the energy is maximally spread out,
系统有 21% 的概率会处于一种能量分布最为均匀的状态。
there's a 13% chance that it will return to its starting point, and an 8% chance that A will actually gain energy.
它有 13% 的概率会回到起始位置，还有 8% 的概率 A 会真正获得能量。
Again, we see that because there are more ways to have dispersed energy and high entropy than concentrated energy,
我们再次发现：由于能量分散状态（高熵状态）比能量集中状态存在更多的可能性，因此自然界更倾向于出现能量分散的状态。
the energy tends to spread out.
能量倾向于向外扩散（即从高密度区域向低密度区域传递）。
That's why if you put a hot object next to a cold one, the cold one will warm up and the hot one will cool down.
这就是为什么当你把一个热物体放在一个冷物体旁边时，冷物体会变暖，而热物体会变冷的原因。
But even in that example, there is an 8% chance that the hot object would get hotter.
但即使在这个例子中，那个高温物体仍有 8% 的可能性会变得更热。
Why doesn't this ever happen in real life?
为什么这种事情在现实生活中从来都不会发生呢？