Immortality. In movies, kings are always searching for the secret to immortality.
长生不老。在电影里，国王们总是在寻找关于长生不老的秘密。
But is immortality really a good thing?
但是长生不老真的那么好么？
To a ten-year-old boy, one year is the same as 10% of his life.
对于一个十岁的男孩来说，一年相当于他一生的10%。
To his forty-year-old mother, one year is merely 2.5% of her life.
对于他的四十岁的母亲，一年仅仅是她一生的2.5%。
The same year, 365 days, can feel differently to different people.
都是一年，365天，会使不同的人有不同的感受。
If we live until we're 82, that's about 30,000 days.
如果我们一生能活82岁，也就是大约30000天。
If this boy lives for 30,000 years, a year to him could feel like a day.
如果这个男孩能活30000年，一年对他来说就相当于一天。
And if this boy's emotions sustain through the potential boredom of living for millions of years,
并且如果这个男孩的内心忍受着要度过数百万年的枯燥生活，
he might become extremely lonely and sad, knowing he has and always will outlive everyone he has ever loved.
他就可能变得极度孤独和悲伤，他了解他已经并且将要见证每一个爱他的人的离去。
But what if everyone were immortal?
但是，如果每个人都能长生不老呢？
Well, first off, Earth is only so big. So, where would we all live?
首先，地球只有这么大。那么我们该住到哪里？
"Excuse me!" "That's my face!" "Stop it!" "Pardon me." "Tight in here!"
“不好意思！”“那是我的脸！”“停！”“请原谅”“好挤啊！”
Do you remember what you did last year or when you were five?
你还记得你去年做了些什么吗？那五岁那年你做过的事呢？
How much of your past have you forgotten?
你的过去你已经忘记多少了？
If you have trouble remembering what you did when you were five,
如果你觉得记起五岁那年你做的事很困难，
how will you remember what happened if you were alive a thousand years ago? A million years ago?
你又怎么会记起一千年前你活着的时候发生的事？一百万年前？
We don't remember every single detail of our past
我们不记得我们的过去中的每一个细节，
because our brains have a limited capacity and we replace useless memories,
因为我们的脑容量有限，并且我们取代无用的记忆，
like middle school locker combinations, with relevant information.
就像中学柜子的排列顺序和其他类似的事情。
If this immortal boy finds a companion to fall in love with once every hundred years,
如果这个能长生不老的男孩找到一位伴侣，和她共度了一百年的时光，
he would have ten thousand girlfriends in a million years.
那么，在一百万年中，他就可以有一万位女朋友。
And how many of those ten thousand girls' names will he be able to remember?
不过在这一万个女朋友中，有多少个人的名字能被他记住？
This changes what a meaningful relationship means, doesn't it?
这改变了传统意义上的“关系”，不是么？
Another tricky thing about immortality: Human beings have not always looked the same.
另一个关于长生不老的有趣之处就是，所有的人并不是一样的。
This can be explained by Darwin's theory of evolution.
达尔文的进化论可以解释这一点。
For instance, if women find taller men more attractive,
比如说，如果女人们认为长的高的男人更加吸引她们，
then more tall men would mate and have children, putting more tall genes in the gene pool.
那么更多的高个男人就能找到伴侣并且生育后代，把更多的高个基因引入基因库。
That means, in the next generation, more children will have the genes to be taller.
这就意味着在他们的下一代中，更多的孩子会拥有高个基因并且长得高。

Repeat that process for a million years and the average height will be a lot taller than the average height today,
在一百万年中重复这个过程，平均身高就会比现在的平均身高高上许多，
assuming there's no natural disaster that wipes out all the tall people.
假设没有自然灾难除掉所有高个子的人。
Our ancestors were short, hairy apes.
我们的祖先很矮，是全身都是毛发的猿类。
We still have body hair, but we don't look like apes any more.
虽然我们也有体毛，但我们长的不再像猿类。
If you're the only person who is immortal, while everyone else keeps evolving, generation after generation,
如果你是唯一能长生不老的人，其他的人都在一代又一代的不断进化，
you will eventually look quite different than the people who surround you.
你最终会成为你身边人中的异类。
"Hi, how you doing?" If one of our ancestors, apes, is still alive today,
“嗨！你感觉怎么样？”如果我们祖先猿类中的一个如今还活着，
how many people will make friends with it instead of calling the Museum of Natural History?
又有多少人愿意和他做朋友，而不是戏称他为自然历史博物馆？
And one more physical consideration for immortality: Scars.
还有一个关于长生不老的身体上的顾虑：伤疤。
After all, immortality doesn't automatically translate to invincibility, it just means you cannot die.
毕竟，长生不老并不等同于不会受伤，它只代表你不会死。
But it doesn't guarantee what condition you'll be alive in.
但它无法确保你的身体条件的好坏。
Look at your body and count how many scars you have.
所以，看看你的身体，然后数一数你有多少道伤疤。
If you have made this many permanent scars within your life,
如果在你的一生中，你已经有了这些永久的伤疤，
imagine how much damage you would have if you were one thousand years old!
想象一下如果你能活一千岁，你还会有多少伤疤！
Now, there are approximately 185,000 amputation-related hospital discharges every year in the U.S.
在美国，每年大约有185000位截肢的病人出院。
These injuries are due to accidents or illnesses.
这些伤害源于事故或是疾病。
Certainly the percentage is low comparing to the total population if you only live for a hundred years.
当然，如果你只活100年的话，这个比例很低对于全体的人类而言是很低。
However, if you've been alive for over one million years, the odds of still having all your limbs are pretty slim.
但是如果你能活超过一百万年，你还拥有完整的肢体的可能性就会非常低。
What about little accessories, like your eyes, your nose, your ears, fingers or toes? What about your teeth?
那么，其他的小的器官，比如说你的眼睛、你的鼻子、你的耳朵、手指头或者脚趾头、你的牙齿，会怎么样呢？
What are the odds of you keeping your dental health for a hundred years? A thousand years? One million years?
在一百年中，一千年中，甚至一百万年中，你保持牙齿健康的概率有多大？
You might end up looking like a horribly scuffed-up Mr. Potato Head with missing pieces and dentures.
你可能最终看起来像一个被磨坏了的薯头先生，身体不再完整，还带着一副假牙。
So, are you sure you want to live forever?
那么，你还确定你想永远不死么？
Now, which superpower physics lesson will you explore next?
现在，你打算接着去研究哪门超能力物理课？
Shifting body size and content, super speed, flight, super strength, immortality, and invisibility.
是改变人体大小和成分，超级快的速度，飞行，神力，长生不老还是隐身。