Human sperm vs. the sperm whale - Aatish Bhatia

精子 vs. 抹香鲸 - Aatish Bhatia

翻译人员: Justine Bai 校对人员: Qiwen Lu

In 1977, the physicist Edward Purcell

1977年，物理学家爱德华·珀塞尔 (Edward Purcell)

calculated that if you push a bacteria and then let go,

计算出，如果你推动一个细菌

然后任它而去，

it will stop in about a millionth of a second.

它将在大概一百万分之一秒内停止运动。

In that time, it will have traveled less than the width of a single atom.

在这样短的时间内，它运动的距离

小于一个原子的宽度。

The same holds true for a sperm and many other microbes.

这种情况适用于精子

和其它很多微生物。

It all has to do with being really small.

它们都必须非常小。

Microscopic creatures inhabit a world alien to us,

微生物栖生在一个完全不同于我们的世界，

where making it through an inch of water is an incredible endeavor.

对它们来说，渡过一英尺水

都将极其困难。

But why does size matter so much for a swimmer?

不过为何大小对于“游泳者”如此重要呢？

What makes the world of a sperm so fundamentally different

是什么使得精子的世界

与抹香鲸的世界

from that of a sperm whale?

有着完全不同呢？

To find out, we need to dive into the physics of fluids.

为了找到答案，我们需要潜入

流体的物理世界。

Here's a way to think about it.

试着从这个角度来想一下

Imagine you are swimming in a pool.

想象你在一个游泳池里游泳

It's you and a whole bunch of water molecules.

有你和一大堆的水分子

Water molecules outnumber you a thousand trillion trillion to one.

水分子的数量级是你的

千万亿万亿倍

So, pushing past them with your gigantic body is easy,

所以，你庞大的身躯很容易

在它们中间前行

but if you were really small,

但是如果你非常小的话

say you were about the size of a water molecule,

小到和水分子差不多的话，

突然之间，就变成你在一游泳池的人

all of a sudden, it's like you're swimming

中间游泳。

in a pool of people.

不同于轻松地在一堆

Rather than simply swishing by all the teeny, tiny molecules,

小小的分子中挥动游弋，

now every single water molecule

现在每个水分子

is like another person you have to push past

都像另一个人，你必须推动划过他们

to get anywhere.

才能到达别的地方

1883年，物理学家奥斯本·雷诺 (Osborne Reynolds)

In 1883, the physicist Osborne Reynolds

figured out that there is one simple number

计算出一个简易的常数，

that can predict how a fluid will behave.

可以预知流体的表现能力。

It's called the Reynolds number,

这个常数叫做“雷诺数”，

and it depends on simple properties like the size of the swimmer,

它适用于简单的个体，

比如“游泳者”的大小、

its speed, the density of the fluid,

游的速度、

流体的密度、

and the stickiness, or the viscosity, of the fluid.

以及流体的

黏度或稠度。

这意味着

What this means is that creatures of very different sizes

大小不同的生物

inhabit vastly different worlds.

生活在完全不同的世界。

For example, because of its huge size,

比如，由于极其巨大

a sperm whale inhabits the large Reynolds number world.

抹香鲸生活在

大雷诺数世界。

If it flaps its tail once,

它拍打一下尾巴，

it can coast ahead for an incredible distance.

可以向前游很远。

Meanwhile, sperm live in a low Reynolds number world.

同时，精子生活在

低雷诺数世界。

If a sperm were to stop flapping its tail,

如果精子停止摇动尾巴，

it wouldn't even coast past a single atom.

它向前的距离不会超过一个原子。

想象一下变成精子是什么样的

To imagine what it would feel like to be a sperm,

you need to bring yourself down to its Reynolds number.

你需要把自己放到

它所在的雷诺数中。

Picture yourself in a tub of molasses with your arms moving

想象自己在一罐蜜糖中，

你挥动手臂的速度

about as slow as the minute hand of a clock,

和分针一样慢，

and you'd have a pretty good idea of what a sperm is up against.

你就能明白

精子对抗的是什么

So, how do microbes manage to get anywhere?

那么，微生物是如何移动的呢？

Well, many don't bother swimming at all.

许多根本不考虑游泳。

They just let the food drift to them.

它们让食物带着前行。

This is somewhat like a lazy cow

就像一头懒牛

that waits for the grass under its mouth to grow back.

等着它嘴下的那块草长回来。

But many microbes do swim,

但有些微生物会游泳，

and this is where those incredible adaptations come in.

它们有惊人的适应性。

One trick they can use is to deform the shape of their paddle.

其中一个方式就是

改变纤毛的形状。

By cleverly flexing their paddle

灵巧地弯曲纤毛

to create more drag on the power stroke than on the recovery stroke,

可以使动力

大于阻力。

single-celled organisms like paramecia

单细胞生物，比如草履虫

manage to inch their way through the crowd of water molecules.

就可以在

水分子中前行。

But there's an even more ingenious solution

还有更绝的，

arrived at by bacteria and sperm.

就是细菌和精子的方法。

Instead of wagging their paddles back and forth,

它们并不把前后摆动纤毛，

而是旋转着，就像螺旋拔塞。

they wind them like a cork screw.

Just as a cork screw on a wine bottle

同酒瓶中的螺旋拔塞

converts winding motion into forward motion,

将旋转运动转化成向前运动一样，

these tiny creatures spin their helical tails

这些微小的生物旋转着螺旋状的尾巴

to push themselves forward

使自己向前，它们世界中的水

in a world where water feels as thick as cork.

它们世界中的水同瓶塞一样硬。

Other strategies are even stranger.

另一种办法更加奇怪。

Some bacteria take Batman's approach.

一些病毒选择了蝙蝠侠的方法。

They use grappling hooks to pull themselves along.

它们用抓钩将自己拉起。

They can even use this grappling hook

甚至还能

像弹弓一样将自己弹过去。

like a sling shot and fling themselves forward.

Others use chemical engineering.

另一些用化学方法。

H. pylori lives only in the slimy, acidic mucus

幽门螺旋杆菌只在胃中的

inside our stomachs.

酸性粘液中生活。

It releases a chemical that thins out the surrounding mucus,

它们释放一种化学物质

使周围的粘液变薄，

allowing it to glide through slime.

从而划过粘液。

Maybe it's no surprise

并不奇怪，

that these guys are also responsible for stomach ulcers.

这些家伙也要对

胃溃疡负责。

So, when you look really closely at our bodies and the world around us,

所以，当你近距离观察

我们的身体和这个世界，

你可以看到各种各样的小生物

you can see all sorts of tiny creatures

finding clever ways to get around in a sticky situation.

用聪明的方法

应对棘手的情况。

Without these adaptations, bacteria would never find their hosts,

如果不去适应，

细菌找不到寄主，

and sperms would never make it to their eggs,

精子也遇不到卵子，

which means you would never get stomach ulcers,

这意味着你也不会得胃溃疡，

but you would also never be born in the first place.

但你最初也不会出生。

(Pop)