You may not realize it, but from the moment you got out of bed today
你或许没有意识到，但从你今天起床的那一刻
to the point where you sat down to watch this video, you've essentially been swimming.
到你坐在这里观看这个视频，从本质上说，其实你是在游泳。
Why? Because air is a fluid just like water.
为什么？因为空气是流动的，就像水一样。
It has waves and eddies. It flows.
它也有波浪和漩涡。它会流动。
And when you push air out of the way, it rushes around you into a wake.
当你在空气中破浪而行，它会在你的后面形成漩涡。
So why don't we notice it most of the time?
那么我们为什么大部分情况下都意识不到它？
We commonly think of air as empty space.
我们通常会把空气当作真空。
But while one cubic centimeter of interstellar space,
但是，一立方厘米的外太空空间，
the volume in the tip of your pinky finger, contains roughly one atom,
相当于你小拇指指尖大小的体积，大约只会包含一个原子，
the same volume of air has about 10 quintillion molecules.
同样体积的空气有10×10的18次幂个分子。
If that sounds hard to wrap your head around,
如果你对这个数量级没有概念，
it happens to be about the same as the number of insects alive on the planet,
这大约相当于地球上所有昆虫的数量，
all crawling, climbing, and flying over each other in an enormous, tightly packed swarm.
那么一大群爬来爬去、飞来飞去的虫子，紧密地堆积在一起。
When this swarm of molecules runs into things,
当这些分子相互撞击，
it exerts a force, pressing against the boundaries of the fluid, like water pressing against the glass of a bottle.
它们向周围的边界施加压力，就像水对玻璃杯壁施加的压力。
This is known as air pressure.
这就是所谓的大气压。
And while air is lighter than water, all those molecules still get pretty heavy,
尽管空气比水要轻，这些分子还是具有相当的重量，
with the total air filling a typical school gym, weighing about as much as an adult elephant.
一个标准体育馆内所有的空气，重量相当于一头成年的大象。
So when you walk into a gym, how come you're not immediately crushed by the elephant of air in the room?
那么当你走进体育馆的时候，怎么没有被里面的空气大象压垮呢？

Well, first of all, because most of it is pressing on the floor and the walls,
首先，空气的压力大部分施加在地板和墙壁上，
and the part that is pressing on you is pushed back by the pressure inside you!
落在你身上的压力被你体内的压力抵消了！
You see, the air, as well as the water and everything else,
你看，空气就和水及其它
that fills our bodies exerts an amount of pressure equal to that of the air outside.
我们体内的物质一样，它们也在施加一定的压力，与外部空气的压力相同。
Of course, this is no accident.
当然，这并非凑巧。
It's precisely what allows us to survive in the normal atmosphere,
正是因为这个原因，我们才得以在大气中存活，
and what makes it more difficult at high altitudes or deep water.
但是在高海拔和深水中我们就能感受到压力。
And we normally don't feel the air pressing on us because it's generally uniform.
通常情况下我们感受不到压力，因为它们基本上是相等的。
So even though different amounts of air molecules are hitting you at different times,
所以，尽管在不同的时间有不同数量的空气分子撞击到你，
the swarm is so thick that all those little differences average out.
但由于数量实在太大，这种小小的差异无法体现出来。
What happens when air pressure isn't uniform?
如果空气的压力不一致将会如何？
This means that the molecules are pushing harder in one region of air than another,
这说明空气分子的压力在一个地区强过另外一个地区，
driving the air flow from the higher pressure region to the lower.
导致空气从高压区流向低压区。
We feel this flow directly as wind, and the pressure systems that meteorologists
我们最直接的感受是刮风，气象学家经常谈到的压力系统，
are always going on about are responsible for other weather changes, from the mundane to the catastrophic.
是各种天气变化的主要原因，从日常的天气到灾难性的天气。
But differences in air pressure do more than just let us complain about the weather; they're the very reason we're alive.
但是，气压之间的差别，其作用不仅仅是让我们抱怨坏天气；它恰恰是我们得以生存的原因。
We breathe by lowering the pressure in our lungs, allowing air to rush in.
我们降低肺里的气压才可以呼吸，让空气得以进入。
So the next time you take a deep breath, think of the unfathomable number of air molecules you're commanding to move.
所以下次你做深呼吸的时候，想想那些无数的空气分子在听你调遣。
We look up at the night sky to ponder the infinity of space,
我们仰望夜空，思索宇宙的无限，
but unless you're watching this video from that deep space,
但除非你是在外太空看这个视频，
there are more air molecules in and around your body than there are grains of sand in all the world's beaches and deserts,
有更多的空气分子围绕在你身边，它们的数量比地球上所有的沙滩和沙漠中的沙子，
stars in the visible universe, or both of those numbers combined.
以及天上可见的星星数量，加起来还要多。
The vastness of the universe is right in front of you and inside you.
广阔的宇宙就在你眼前，也在你的身体里。