Nearly every religion in the world has some interpretation of them, and from our earliest myths to the latest cinematic blockbusters, the dead keep coming back.

所有世上的宗教幾乎都有不同的生死觀，從遠古的神話到最新的賣座鉅片，死而復生總是最熱門的題材。

But is resurrection really possible?

但「復活」真的可能發生嗎？

And what is the actual difference between a living creature and a dead body, anyway?

而活生生的生物和屍體又有什麼差別呢？

To understand what death is, we need to understand what life is.

為了瞭解何謂「死」，我們得先探討何謂「生」。

One ancient theory was an idea called vitalism, which claimed that living things were unique because they were filled with a special substance, or energy, that was the essence of life.

「生機論」為一個古老的理論，主張生物之所以獨一無二是因為，體內有種特殊物質或能量，也就是生命的本質。

Whether it was called qi, lifeblood, or humors, the belief in such an essence was common throughout the world.

無論稱這種物質為「氣」、「血」或是「體液」，世界各地對於這種物質的想法相當普遍。

And still persists in the stories of creatures who can somehow drain life from others, or some form of magical sources that can replenish it.

而且仍有人相信那些留存於故事中能吸取別人「生命」的生物，或相信有些神秘的物質能夠使生命回春。

Vitalism began to fade in the Western world following the Scientific Revolution in the 17th century.

在 17 世紀的科學革命後，「生機論」在西方世界開始逐漸式微。

René Descartes advanced the notion that the human body was essentially no different from any other machine, brought to life by a divinely created soul located in the brain's pineal gland.

笛卡兒提出一項看法，人體基本上跟機器沒有兩樣，由神創的靈魂提供生命，而靈魂位在大腦的松果體。

And in 1907, Dr. Duncan McDougall even claimed that the soul had mass, weighing patients immediately before and after death in an attempt to prove it.

1907 年 Duncan McDougall 醫師甚至認為靈魂有重量，為了證明理論，他測量了人體死亡前後的體重。

Though his experiments were discredited, much like the rest of vitalism, traces of his theory still come up in popular culture.

雖然如同殘存的生機論一樣，McDougall 醫師的實驗倍受質疑，但在流行文化中仍能找到此論點的蹤跡。

But where do all these discredited theories leave us?

但這些受到質疑的理論都會被遺忘嗎?

What we now know is that life is not contained in some magical substance or spark, but within the ongoing biological processes themselves.

我們現在知道的是，生命不包含在一些神奇的物質或能量中，而是存在於本身正在進行的生物過程中。

And to understand these processes, we need to zoom down to the level of our individual cells.

為了了解這些過程，我們需要放大到細胞等級來看。

Inside each of these cells, chemical reactions are constantly occurring, powered by the glucose and oxygen that our bodies convert into the energy-carrying molecule known as ATP.

我們的身體會轉化葡萄糖和氧氣成攜帶能量的分子——也就是 ATP，它們會提供能量使每個細胞中都在不斷地發生化學反應。

Cells use this energy for everything from repair to growth to reproduction.

細胞會利用這種能量來做任何事，從修復至增長繁殖等。

Not only does it take a lot of energy to make the necessary molecules, but it takes even more to get them where they need to be.

不僅需要大量的能量來製造必需的分子，還需要更多的能量將這些分子送到需要的地方。

The universal phenomenon of entropy means that molecules will tend towards diffusing randomly, moving from areas of high concentration to low concentration, or even breaking apart into smaller molecules and atoms.

普遍的熵現象意指，分子將趨向於隨機擴散，從高濃度移至低濃度的區域，甚至會分解成更小的分子或原子。

So cells must constantly keep entropy in check by using energy to maintain their molecules in the very complicated formations necessary for biological functions to occur.

因此，細胞必須不斷地用能量控制熵，使熵的分子處於非常複雜的構造，才能使生理功能可以發揮。

The breaking down of these arrangements when the entire cell succumbs to entropy is what eventually results in death.

當整個細胞再也無法抵抗熵時，這些機制會開始瓦解，最後導致生物死亡。

This is the reason organisms can't be simply sparked back to life once they've already died.

這就是一旦生命體死亡，就無法起死回生的理由。

We can pump air into someone's lungs, but it won't do much good if the many other processes involved in the respiratory cycle are no longer functioning.

我們可以輸送氧氣至生物的肺部，但如果包含在呼吸週期的其他過程都失效的話，注入再多空氣也是無濟於事。

Similarly, the electric shock from a defibrillator doesn't jump-start an inanimate heart, but resynchronizes the muscle cells in an abnormally beating heart so they regain their normal rhythm.

同樣的，心臟電擊器的電擊無法重啟沒有生命的心臟，但可使心跳異常的心肌細胞重新同步，恢復正常的跳動。

This can prevent a person from dying, but it won't raise a dead body, or a monster sewn together from dead bodies.

這可以拯救瀕臨死亡的人，但無法讓人死而復活，更別說讓一隻由屍體縫製而成的怪物產生生命了。

So it would seem that all our various medical miracles can delay or prevent death but not reverse it.

所以，儘管有各種醫學奇蹟可以延遲或預防死亡，但我們無法逆轉死亡。

But that's not as simple as it sounds because constant advancements in technology and medicine have resulted in diagnoses such as coma, describing potentially reversible conditions, under which people would have previously been considered dead.

但也不能一概而論，因為不斷進步的醫學跟技術診斷出可能可逆的狀況，例如昏迷，這種情況在以前發生的話，病患會被判定死亡。

In the future, the point of no return may be pushed even further.

在將來，生命的盡頭可能會變得更長。

Some animals are known to extend their lifespans or survive extreme conditions by slowing down their biological processes to the point where they are virtually paused.

我們知道，有些動物為了延長壽命或在惡劣環境下存活，會減緩生理機能使其幾乎趨向停止。

And research into cryonics hopes to achieve the same by freezing dying people and reviving them later when newer technology is able to help them.

而人體冷凍技術的研究希望能藉由冷凍奄奄一息的人達到相同的效果，當有更先進的科技能幫助他們時，再將他們復活。

See, if the cells are frozen, there's very little molecular movement, and diffusion practically stops.

你看，如果細胞被冷凍，就只會有非常細微的分子運動，而且擴散也幾近停止。

Even if all of a person's cellular processes had already broken down, this could still conceivably be reversed by a swarm of nanobots, moving all the molecules back to their proper positions, and injecting all of the cells with ATP at the same time, presumably causing the body to simply pick up where it left off.

即使一個人的所有細胞代謝過程都已經瓦解，這情況仍可由一群奈米機器人來反轉，將所有分子移回至適當的位置，也同時將 ATP 注入所有細胞內，這也許可以讓生命體重新運作。

So, if we think of life not as some magical spark, but a state of incredibly complex, self-perpetuating organization, death is just the process of increasing entropy that destroys this fragile balance.

所以如果我們認為生命並非某種神奇的火花，而是極其複雜且自我延續的組織狀態，那麼死亡只是破壞這個脆弱平衡的熵增過程。

And the point at which someone is completely dead turns out not to be a fixed constant, but simply a matter of how much of this entropy we're currently capable of reversing.

一個人完全死亡的關鍵點，不再是一個固定的常數，而是我們目前能夠逆轉多少熵的問題。