The dust bunnies that built our planet - Lorin Swint Matthews

譯者: Lilian Chiu 審譯者: Helen Chang

Consider the spot where you’re sitting.

想像你現在所坐的這個點。

Travel backwards in time

時間旅行回到過去，

and it might’ve been submerged at the bottom of a shallow sea,

這個點有可能是位在 一片淺海的底部，

buried under miles of rock,

被數英里的岩石給掩埋，

or floating through a molten, infernal landscape.

或者漂浮在熱熔的地獄環境。

But go back far enough—

但，如果回到夠久的過去——

about 4.6 billion years,

大約四十六億年前，

and you’d be in the middle of an enormous cloud of dust and gas

你會身處在塵埃和氣體 構成的巨型雲霧中，

orbiting a newborn star.

繞著新生的星體運轉。

This is the setting for some of the biggest, smallest mysteries of physics:

這是最大、最小物理學之謎 所發生的環境，這個謎就是：

the mysteries of cosmic dust bunnies.

宇宙塵兔之謎。

Seemingly empty regions of space between stars

在星體之間，看似 空無一物的宇宙區域，

actually contain clouds of gas and dust,

其實有著氣體和塵埃所形成的雲，

usually blown there by supernovas.

通常是被超級新星炸到那裡去的。

When a dense cloud reaches a certain threshold called the Jeans mass,

當雲的密度高到達 「金斯質量」這個門檻值時，

it collapses in on itself.

它自己就會崩塌。

The shrinking cloud rotates faster and faster, and heats up,

縮小的雲會越轉越快速， 溫度跟著上升，

eventually becoming hot enough to burn hydrogen in its core.

最終熱到足以燃燒 它核心區域的氫。

At this point a star is born.

在這個時點，星體就誕生了。

As fusion begins in the new star,

當新星中的融合開始，

it sends out jets of gas that blow off the top and bottom of the cloud,

它就會噴射出氣體， 將雲的頂部和底部吹掉，

leaving behind an orbiting ring of gas and dust called a protoplanetary disk.

留下繞行的環狀氣體和塵埃，

稱為「原行星盤」。

This is a surprisingly windy place;

這個地方風大得驚人；

eddies of gas carry particles apart, and send them smashing into each other.

氣體旋渦會把粒子帶開， 讓它們互相碰撞。

The dust consists of tiny metal fragments, bits of rock, and, further out, ices.

塵埃包含了小型的 金屬碎片、小堆岩石，

在更外圍還有冰。

We’ve observed thousands of these disks in the sky,

我們已經觀察到天空中 有數千個這種星盤，

at various stages of development

處在不同的發展階段，

as dust clumps together into larger and larger masses.

塵埃結在一起，質量越來越大。

Dust grains 100 times smaller than the width of a human hair stick to each other

比人類頭髮的寬度還要小一百倍的 塵埃粒子會彼此黏在一起，

through what’s called the van der Waals force.

讓它們相黏的力量 叫做「凡得瓦爾力」。

That’s where a cloud of electrons shifts to one side of a molecule,

此時，電子雲就會 轉移到分子的一邊，

creating a negative charge on one end, and a positive charge on the other.

在一端創造出負電荷， 另一端創造出正電荷。

Opposites attract, but van der Waals can only hold tiny things together.

異性相吸，但凡得瓦爾力只能夠 將微小的東西結合在一起。

And there’s a problem: once dust clusters grow to a certain size,

有一個問題：一旦塵埃群 成長到了某個大小之後，

the windy atmosphere of a disk should constantly break them up

星盤大氣中的風很大，

經常使這些塵埃群彼此相撞而散開。

as they crash into each other.

The question of how they continue to grow is the first mystery of dust bunnies.

它們如何持續成長， 是塵兔的第一個謎。

One theory looks to electrostatic charge to answer this.

有個從靜電電荷來解答的理論。

Energetic gamma rays, x-rays, and UV photons

高能加馬射線、X 光、UV 光子

knock electrons off of gas atoms within the disk,

在星盤中將電子 從氣體原子中打掉，

creating positive ions and negative electrons.

創造出正離子和負電子，

Electrons run into and stick to dust,

電子碰到塵埃就會黏住塵埃，

making it negatively charged.

讓它帶負電。

Now, when the wind pushes clusters together,

當風把塵埃群推到一起時，

like repels like and slows them down as they collide.

同性相斥，且當它們 相撞時會讓它們慢下來。

With gentle collisions they won’t fragment,

輕輕碰撞不會讓它們破碎，

but if the repulsion is too strong, they’ll never grow.

但如果相斥太強， 它們就永遠不會成長。

One theory suggests that high energy particles

有一種理論指出，高能粒子

can knock more electrons off of some dust clumps,

能把更多電子從塵埃團中給除去，

leaving them positively charged.

讓塵埃團帶正電。

Opposites again attract, and clusters grow rapidly.

異性相吸，塵埃群就會快速成長。

But before long we reach another set of mysteries.

但，不久，我們又 碰到了另一組謎。

We know from evidence found in meteorites

從隕石找到的證據顯示，

that these fluffy dust bunnies eventually get heated, melted

這些蓬鬆的塵兔最終 會被加溫、熔化，

and then cooled into solid pellets called chondrules.

接著冷卻，成為固態顆粒， 叫做隕石球粒。

And we have no idea how or why that happens.

我們不知道這是怎麼發生的， 也不知道為什麼發生。

Furthermore, once those pellets do form, how do they stick together?

此外，一旦那些顆粒真的形成了， 它們要如何黏在一起？

The electrostatic forces from before are too weak,

之前的靜電力太弱了，

and small rocks can’t be held together by gravity either.

小岩石無法靠引力就結合在一起。

Gravity increases proportionally to the mass of the objects involved.

物體間的引力 和物體的質量成正比。

That’s why you could effortlessly escape an asteroid the size of a small mountain

那就是為什麼你可以毫不費力， 光靠雙腿產生的力量，

using just the force generated by your legs.

就脫離小山大小的小行星。

So if not gravity, then what?

如果不是引力，那是什麼？

Perhaps it’s dust.

也許是塵埃。

A fluffy dust rim collected around the outside of the pellets

在顆粒外部集結的蓬鬆塵埃外緣

could act like Velcro.

可能會有魔鬼沾的功能。

There’s evidence for this in meteors,

在隕石中有找到相關證據，

where we find many chondrules surrounded by a thin rim of very fine material–

我們發現許多隕石球粒被薄薄一層 非常好的材質給包住——

possibly condensed dust.

有可能是高密度的塵埃。

Eventually the chondrule pellets get cemented together inside larger rocks,

最終，隕石球粒的顆粒會在 更大的岩石中被黏結起來，

which at about 1 kilometer across

這些岩石大約有一公里寬，

are finally large enough to hold themselves together through gravity.

終於，這些顆粒因此就夠大， 足以用引力持續結合在一起了。

They continue to collide and grow into larger and larger bodies,

它們繼續碰撞， 成長成更大的物體，

including the planets we know today.

包括我們現今所知的行星。

Ultimately, the seeds of everything familiar–

最終，我們熟悉的一切——

the size of our planet, its position within the solar system,

我們行星的大小， 在太陽系中的位置，

and its elemental composition–

以及組成的元素——

were determined by an uncountably large series of random collisions.

其根源是由一大連串 隨機撞擊所決定的。

Change the dust cloud just a bit,

若塵雲有稍微改變一點點，

and perhaps the conditions wouldn’t have been right

也許就不會有對的條件

for the formation of life on our planet.

讓我們的星球上出現生命了。