Human sperm vs. the sperm whale - Aatish Bhatia

比一比：人類精子與抹香鯨有什麼不同—艾提使·巴提亞 (Aatish Bhatia)

譯者: You-Chieh Wu 審譯者: Regina Chu

In 1977, the physicist Edward Purcell

1977 年，一位名為 愛德華·珀塞爾的物理學家

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

計算出，如果你把一個細菌往前推

然後任由它去

it will stop in about a millionth of a second.

它會在一百萬分之一秒內停住

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

在這段期間，它所前進的距離

將會少於一個原子的寬度

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

這樣的事實對於精子來說也是適用的

且對其它的微生物也是一樣

It all has to do with being really small.

這是因為它們都非常小

Microscopic creatures inhabit a world alien to us,

微生物所生存的世界 是我們無法想像的

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

對它們來說 光是游過一英吋的水

都是一件非常困難的事

But why does size matter so much for a swimmer?

但是為什麼尺寸大小 對泳者如此重要呢？

What makes the world of a sperm so fundamentally different

是什麼因素使得精子的世界

和抹香鯨的世界

from that of a sperm whale?

有著如此巨大的不同呢？

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

為了找尋答案，我們必須潛入

流體的物理學之中

Here's a way to think about it.

讓我們用這個方式來思考一下：

Imagine you are swimming in a pool.

想像你在一個泳池裡面游泳

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

裡面只有你以及一大群的水分子

Water molecules outnumber you a thousand trillion trillion to one.

水分子的數量是你的

千萬億萬億倍

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

所以，用你龐大的身體

來推動它們使你前進，是很容易的

but if you were really small,

但如果你的體積很小

say you were about the size of a water molecule,

小到跟一個水分子差不多的時候

忽然之間 就像你在擠滿人的泳池中

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

要游泳一樣

in a pool of people.

和輕鬆的揮舞穿梭在

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

微小的分子中有所不同

now every single water molecule

現在，每一個水分子

is like another person you have to push past

都像是一個人，你必須推擠他們

to get anywhere.

才能到達其它地方

1883 年，物理學家奧斯鮑恩·雷諾

In 1883, the physicist Osborne Reynolds

figured out that there is one simple number

發現了一個簡單的數

that can predict how a fluid will behave.

能夠預測流體的特性

It's called the Reynolds number,

我們稱之為雷諾數

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

雷諾數建立於幾個簡單的性質上

像是泳者的尺寸

its speed, the density of the fluid,

游動速度

流體的密度

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

以及流體的

黏度或稠度

這意味著

What this means is that creatures of very different sizes

這些尺寸不同的生物

inhabit vastly different worlds.

都生活在完全不同的世界裡

For example, because of its huge size,

例如說，抹香鯨因為其巨大的尺寸

a sperm whale inhabits the large Reynolds number world.

而生存在一個

大雷諾數的世界裡

If it flaps its tail once,

牠只要揮動一次尾巴

it can coast ahead for an incredible distance.

就可以往前滑行一段十分遙遠的距離

Meanwhile, sperm live in a low Reynolds number world.

另一邊來說

精子生活在一個低雷諾數的世界中

If a sperm were to stop flapping its tail,

若是精子停止揮動它的尾巴

it wouldn't even coast past a single atom.

它連一個原子的距離都無法超越

要想像精子的情況

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

you need to bring yourself down to its Reynolds number.

你必須將自己置入

它所對應的雷諾數當中

Picture yourself in a tub of molasses with your arms moving

試想你泡在一整大罐糖蜜中

而你手臂能揮動的速度

about as slow as the minute hand of a clock,

和時鐘上的分針一樣緩慢

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

這樣你就能感同身受

精子所對抗的是什麼

So, how do microbes manage to get anywhere?

那麼，微生物究竟是如何移動的呢？

Well, many don't bother swimming at all.

事實上，有許多微生物根本不用游泳

They just let the food drift to them.

只需要等食物漂過來就可以了

This is somewhat like a lazy cow

這就像是一隻懶惰的牛

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

等著靠近它嘴邊的那些草生長回來

But many microbes do swim,

但許多微生物是要游泳的

and this is where those incredible adaptations come in.

而這就是許多令人驚嘆的 適應方式會出現的原因

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

其中一種招數就是

改變它們「槳」的形狀

By cleverly flexing their paddle

藉由巧妙的伸縮彎曲

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

以在擺動的過程中

製造更多向前推進的力量

single-celled organisms like paramecia

於是像草履蟲這樣的單細胞生物

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

就有辦法在

一大群的水分子中前進

But there's an even more ingenious solution

但除此之外，細菌與精子

arrived at by bacteria and sperm.

還有更精巧的方法

Instead of wagging their paddles back and forth,

它們不以前後擺動「槳」的方式前進

而是以螺旋的方式運動

they wind them like a cork screw.

Just as a cork screw on a wine bottle

像是開酒瓶的螺絲錐那樣

converts winding motion into forward motion,

將旋轉的運動轉換成向前的運動

these tiny creatures spin their helical tails

這些微小生物轉動著螺旋尾巴

to push themselves forward

來使其向前推進

in a world where water feels as thick as cork.

而在它們的世界中 水就像軟木塞一樣的硬

Other strategies are even stranger.

其他的方式就更奇怪了

Some bacteria take Batman's approach.

有些細菌使用蝙蝠俠的方法

They use grappling hooks to pull themselves along.

用抓鉤來拉動自己

They can even use this grappling hook

而抓鈎更可以用來

當成彈弓，將自己彈射向前

like a sling shot and fling themselves forward.

Others use chemical engineering.

其它的使用化工的方法

H. pylori lives only in the slimy, acidic mucus

幽門螺旋桿菌只在我們

胃裡的酸性黏液中生存

inside our stomachs.

It releases a chemical that thins out the surrounding mucus,

它們釋放化學物質

將環繞的黏液變薄

allowing it to glide through slime.

從而使之在黏液中滑行

Maybe it's no surprise

或許你就不會驚訝

that these guys are also responsible for stomach ulcers.

這些傢伙也和胃潰瘍

脫不了關係

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

所以，當你很仔細很仔細

近距觀察我們的身體與這個世界

你就會看見各式各樣的小生物

you can see all sorts of tiny creatures

finding clever ways to get around in a sticky situation.

找尋聰明的方法

來對付麻煩的情況

Without these adaptations, bacteria would never find their hosts,

如果沒有這些適應方式的話

細菌將永遠無法找到它們的宿主

and sperms would never make it to their eggs,

且精子也永遠都無法遇到卵子

which means you would never get stomach ulcers,

這代表著你將永遠都不會得到胃潰瘍

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

但也代表著，你從最初就不會出生

(Pop)