Outside your window nothing seems to be happening,

窗外看起來一切正常

yet the plane continues to rattle you and your fellow passengers as it passes through turbulent air in the atmosphere.

但飛機繼續穿越亂流層時，你和其他乘客持續聽到飛機發出的咯咯聲。

Although it may not comfort you to hear it,

聽到這種聲音，可能無法舒緩你緊張的心情

this phenomenon is one of the prevailing mysteries of physics.

不過這個現象是物理學中最有名的謎團之一。

After more than a century of studying turbulence,

經過一百多年對亂流的研究後

we've only come up with a few answers for how it works and affects the world around us.

對於它是如何運作，以及如何影響我們周遭的世界，我們只找到了一點點答案。

And yet, turbulence is ubiquitous, springing up in virtually any system that has moving fluids.

亂流其實無所不在，幾乎在任何有流體的系統中，它都會出現。

That includes the airflow in your respiratory tract.

這包含你呼吸道裡的氣流。

The blood moving through your arteries.

你動脈裡流動的血液。

And the coffee in your cup, as you stir it.

還有你杯子裡攪拌著的咖啡。

Clouds are governed by turbulence,

亂流是雲的統治者

as are waves crashing along the shore and the gusts of plasma in our sun.

就連打上岸的海浪，和太陽中離子形成的陣風也是一樣。

Understanding precisely how this phenomenon works would have a bearing on so many aspects of our lives.

如何明確地了解這個現象發生的原因，實在是與我們的生活息息相關。

Here's what we do know.

以下是我們確定知道的。

Liquids and gases usually have two types of motion:

液體和氣體通常有兩種移動方式：

a laminar flow, which is stable and smooth;

一種是層流，移動時穩定且平順

and a turbulent flow, which is composed of seemingly unorganized swirls.

一種是亂流，由許多雜亂無章的漩渦所組成。

Imagine an incense stick.

想象一下線香 。

The laminar flow of unruffled smoke at the base is steady and easy to predict.

底部平坦的煙霧層流，穩定且易於預測。

Closer to the top, however,

然而，接近頂部

the smoke accelerates, becomes unstable,

煙霧上升速度加快，變得不穩定

and the pattern of movement changes to something chaotic.

移動模式變得混亂。

That's turbulence in action,

這就是移動中的亂流

and turbulent flows have certain characteristics in common.

亂流有一些共同的特徵。

Firstly, turbulence is always chaotic.

首先，亂流總是混亂無秩序的。

That's different from being random.

但這種混亂又非完全不受拘束的。

Rather, this means that turbulence is very sensitive to disruptions.

相反的，亂流對於干擾非常敏感。

A little nudge one way or the other will eventually turn into completely different results.

不同的干擾，即便只是輕微的，最終也會造成完全不同的結果。

That makes it nearly impossible to predict what will happen,

這使得亂流幾乎無法預測

even with a lot of information about the current state of a system.

即使有很多資訊可以偵測到目前氣流狀態，但是亂流仍然難以預測。

Another important characteristic of turbulence is the different scales of motion that these flows display.

另一個很重要的亂流的特徵，就是這種氣流有不同的強度。

Turbulent flows have many differently-sized whirls called eddies, which are like vortices of different sizes and shapes.

亂流裡有很多大大小小的漩渦，形成不同形狀和大小的渦流。

All those differently-sized eddies interact with each other,

這些大小不同的漩渦彼此相互作用

breaking up to become smaller and smaller

分裂變得越來越小

until all that movement is transformed into heat,

直到所有的運動在一個稱為「能量串跌」的過程中

in a process called the “energy cascade."

轉化為熱量。

So that's how we recognize turbulence–

這就是我們所認識的亂流 –

but why does it happen?

但為甚麼亂流會發生呢？

In every flowing liquid or gas there are two opposing forces:

在每個流動的液體或氣體中，都存在著兩種相反的作用力：

inertia and viscosity.

慣性和黏性。

Inertia is the tendency of fluids to keep moving,

慣性使液體持續流動

which causes instability.

也是造成不穩定性的原因

Viscosity works against disruption,

黏性是一種阻力

making the flow laminar instead.

使其流動趨向平穩。

In thick fluids such as honey,

像蜂蜜這種濃稠的液體裡

viscosity almost always wins.

黏性通常大於慣性。

Less viscous substances like water or air are more prone to inertia,

像水或空氣這種較少黏性的物質，通常是慣性大於黏性

which creates instabilities that develop into turbulence.

而慣性會造成不穩定性，然後演變成亂流。

We measure where a flow falls on that spectrum

我們使用雷諾數來估算

with something called the Reynolds number,

一個流體是處在穩定或混亂的狀態

which is the ratio between a flow's inertia and its viscosity.

雷諾數是流體的慣性與黏性的比值。

The higher the Reynolds number,

雷諾數越高

the more likely it is that turbulence will occur.

亂流發生的機率就越高。

Honey being poured into a cup, for example,

舉例來說，蜂蜜倒入一個杯中的雷諾數

has a Reynolds number of about 1.

大概是 1。

The same set up with water has a Reynolds number that's closer to 10,000.

水倒入杯中的雷諾數則將近 10,000。

The Reynolds number is useful for understanding simple scenarios,

雷諾數可以幫助我們了解在單純環境下的流體

but it's ineffective in many situations.

但是在許多時候，雷諾數是無用的。

For example, the motion of the atmosphere is significantly influenced

例如，地心引力和地球轉動等

by factors including gravity and the earth's rotation.

皆為影響大氣層流動的重要因素。

Or take relatively simple things like the drag on buildings and cars.

或拿些相對簡單的事為例，像是建築物和車子的阻力。

We can model those thanks to many experiments and empirical evidence.

藉著許多實驗和經驗的證據，我們可以模擬出類似的情況。

But physicists want to be able to predict them through physical laws and equations

但就像我們能模擬行星運行軌道或電磁場一樣

as well as we can model the orbits of planets or electromagnetic fields.

物理學家想要用物理定律和方程式來預測亂流變化。

Most scientists think that getting there will rely on statistics and increased computing power.

大多科學家認為，想要達成這個目標，必須依靠統計數據，和增強計算能力。

Extremely high-speed computer simulations of turbulent flows

利用超級電腦模擬亂流

could help us identify patterns that could lead to a theory

可以幫助我們辨認亂流不同的模式，進而發展出一套理論

that organizes and unifies predictions across different situations.

這種理論可以將各種預測加以整合。

Other scientists think that the phenomenon is so complex

但其他科學家認為亂流現象太過複雜

that such a full-fledged theory isn't ever going to be possible.

要有這麼完整的理論是不可能的。

Hopefully we'll reach a breakthrough,

希望未來我們能有所突破

because a true understanding of turbulence could have huge positive impacts.

因為真正地了解亂流，將對我們極有幫助。

That would include more efficient wind farms;

包括了更高效的風力發電場

the ability to better prepare for catastrophic weather events;

更有效地因應極端惡劣的天氣

or even the power to manipulate hurricanes away.

甚至包括操控颶風的能力。

And, of course, smoother rides for millions of airline passengers.

當然，還有為飛機上眾多乘客帶來更平穩的飛行旅程。

Despite how difficult it is to explain turbulence mathematically,

儘管用數學方法來解釋亂流非常困難

Vincent Van Gogh was able to capture it with a sounding accuracy

但文森．梵谷卻能夠在他的代表性畫作「星夜」中

in his iconic painting "The Starry Night".

精準地將它描繪出來。

Watch this video to learn more about the surprising man behind his masterpiece.

請觀看這部影片，透過他的傑作來更多的了解這個鬼才。