It's one of our most important tools, and holds a prominent place in many ancient philosophies and religions.

這是我們最重要的工具之一，在很多古哲學和古宗教中占有很顯著的地位。

The ancient Greeks believed that fire–along with earth, water, and air–was one of the four essential elements that made up the world.

古希臘認為，火，土，水和氣是組成這個世界的四個基本要素。

We now know that the world's a lot more complicated, with over a hundred elements of matter which can be combined in a tremendous variety of ways.

現在，我們知道世界的構成其實是更加復雜的，由上百種物質組成，而同時這些物質又可以以無數種不同的方式結合。

This might leave you wondering where fire fits in. What exactly is fire?

那這就讓你感到奇怪了，火是從哪里來的，具體是什么東西呢？

Watching a flame dance through the air, you might conclude that fire's a gas, like oxygen or carbon dioxide.

看到空氣中的跳動的火苗，你可能會覺得火是一種氣體，像氧氣，二氧化碳那類的。

It's not. Fire can burn fuel that's a gas, or a liquid, or even a solid–as in the case of glowing charcoal.

其實不是。火可以使氣體，液體甚至是固體燃料燃燒-比如燃燒的木炭。

But the fire itself isn't any of these things.

但是火本身并不是這些東西的任何一個。

In fact, fire isn't any thing at all.

實際上，火沒有自身的形態。

It's not its own type of matter; it's something that matter can do.

它不是物質，但卻起到一些物質的作用。

Fire is a chemical reaction.

火是一種化學反應。

A fire needs oxygen and some kind of fuel.

火是需要氧氣和某種燃料共同作用的。

This fuel–whether it's candle wax, wood, or gasoline–usually contains big molecules that have carbon atoms inside them.

這些燃料不管是石碏、木頭還是天然氣通常都會含有大量的碳分子。

You can think of these molecules as little containers of energy.

你可以將這些分子想象成小小的儲能體。

When they're allowed to combine with oxygen, this energy is released as heat and light.

當它們與氧氣結合時，這些能量就會作為光和熱釋放。

Fire is a rapid chemical reaction known as oxidation.

火是一種快速的氧化化學反應。

Inside a fire, oxygen molecules break bigger molecules apart into carbon dioxide and water vapor.

在火中，氧分子將更大的分子氧化成二氧化碳和水蒸汽，火中的所有光和熱都來自于含碳的大分子同氧氣的結合。

All the heat and light of a fire comes from big, carbon-based molecules combining with oxygen.

火所有的熱和光來源于碳分子和氧氣結合的反應。

So what is fire? It's not the fuel or the oxygen or the heat or the light.

那么到底什么是火？它不是燃料，不是氧氣，也不是光和熱。

Fire is what happens between all these things. It's a chemical reaction.

火就是它們之間所產生的一種化學反應。