We're going to focus on questions where you can't learn the answers because they're unknown.

我們接下來要著重於那些你找不到答案的問題，因為它們是未解之謎。

I used to puzzle about a lot of things as a boy, for example: What would it feel like to be a dog?

我還是個小男孩的時候，常常對很多事情感到困惑；舉例來說，如果我變成一隻狗，那會是什麼感覺？

Do fish feel pain?

魚會感覺到痛嗎？

What about insects?

那昆蟲呢？

Was the Big Bang just an accident?

宇宙大爆炸理論只是一場意外嗎？

Is there a God?

世界上真的有上帝嗎？

And if so, how are we so sure that it's a He and not a She?

如果真的有，那我們怎麼能確定祂是男生而不是女生？

Why do so many innocent people and animals suffer terrible things?

為什麼有這麼多無辜的人和動物遭受可怕的事物？

Is there really a plan for my life?

我的人生真的早就註定好了嗎？

Is the future yet to be written, or is it already written and we just can't see it?

未來還沒被寫出來，還是其實未來早就被寫好了，只是我們無從得知？

But then, do I have free will? I mean, who am I anyway?

然後，我真的有自由意志嗎？我想說的是，我到底是誰？

Am I just a biological machine?

我會不會只是一個生物機器？

But then, why am I conscious? What is consciousness?

那麼，為什麼我有意識？什麼是意識？

Will robots become conscious one day?

機器人有可能有意識嗎？

I mean, I kind of assumed that some day I would be told the answers to all these questions.

我認為，我相信有一天會有人告訴我這些答案。

Someone must know, right?

一定有人知道，對吧？

Guess what? No one knows.

猜猜事實是什麼？其實沒人知道。

Most of those questions puzzle me more now than ever.

其中許多問題讓我現在更感到困惑。

But diving into them is exciting because it takes you to the edge of knowledge, and you never know what you'll find there.

但是深入思考這些問題，讓我感到興奮，因為思考過程會帶你去到知識的邊緣。而你永遠不會知道你會在那裡找到什麼。

So, two questions.

來吧，兩個問題。

Questions that no one on Earth knows the answer too.

地球上沒有任何人知道答案的問題。

How Many Universes Are There?

世界上有幾個宇宙呢？

Sometimes when I'm on a long plane flight, I gaze out at all those mountains and deserts and try to get my head around how vast our Earth is.

有時候搭長途飛機，我眺望那些山群和沙漠，試著理解我們的地球有多大。

And then I remember that there's an object we see every day that would literally fit one million Earths inside it: the sun. It seems impossibly big.

於是我就想到有個物體我們每天都會看見，大概可以裝進一百萬個地球，就是太陽，它看起來無限大。

But in the great scheme of things, it's a pinprick, one of about 400 billion stars in the Milky Way galaxy, which you can see on a clear night as a pale white mist stretched across the sky.

但若宏觀而論，它就只是宇宙上的一個小點，是銀河系四千億顆星星中的其中一員，在晴朗的夜晚，你可以清楚的看到銀河，橫跨天空淡淡的一條白色霧般光帶。

And it gets worse. There may be 100 billion galaxies detectable by our telescopes.

更誇張的是，宇宙中可能有一千億個銀河可以被我們用望遠鏡看見。

So if each star was the size of a single grain of sand, just the Milky Way has enough stars to fill a 30-foot by 30-foot stretch of beach three feet deep with sand.

所以如果每個星星的大小都像一粒沙一樣，銀河有剛好足夠的星星填滿一個長寬各三十呎三呎深的沙灘。

And the entire Earth doesn't have enough beaches to represent the stars in the overall universe.

地球所有的沙子都比不上整個宇宙裡恆星的數量。

Such a beach would continue for literally hundreds of millions of miles.

大概要綿延幾億哩的沙灘才裝得下。

Holy Stephen Hawking, that is a lot of stars.

噢！Stephen Hawking，有這麼多星星耶！

But he and other physicists now believe in a reality that is unimaginably bigger still.

但是他和其他物理學家現在認為真相可能超乎想像的大。

I mean, first of all, the 100 billion galaxies within range of our telescopes are probably a minuscule fraction of the total.

也就是說，首先，我們的望遠鏡能觀察到一千億個銀河系可能只是全部宇宙的一小部分。

Space itself is expanding at an accelerating pace.

宇宙正在加速擴大中。

The vast majority of the galaxies are separating from us so fast that light from them may never reach us.

大部分的銀河系都是快速的遠離我們，快到他們的光線根本到不了我們這裡。

Still, our physical reality here on Earth is intimately connected to those distant, invisible galaxies.

但是，在地球上的物理現象和那些遙遠、看不見的銀河系有緊密關聯。

We can think of them as part of our universe.

我們可以將他們視為宇宙的一部份。

They make up a single, giant edifice obeying the same physical laws and all made from the same types of atoms --electrons, protons, quarks, neutrinos -- that make up you and me.

整體屬於一個獨立、巨大的架構，遵循同一個物理定律，由相同型態的電子、質子、垮克、微中子，組成你跟我。

However, recent theories in physics, including one called string theory, are now telling us there could be countless other universes built on different types of particles, with different properties, obeying different laws.

然而，最近的物理理論，包含其中一個叫做「弦理論」，告訴我們可能有數不清的宇宙，而且每個宇宙是由不同的粒子組成的，還有不同的特性、遵循不同的定律。

Most of these universes could never support life, and might flash in and out of existence in a nanosecond.

大部分的宇宙沒辦法發展生命可能只存在一微秒就消失。

But nonetheless, combined they make up a vast multiverse of possible universes in up to 11 dimensions, featuring wonders beyond our wildest imagination.

然而，這些宇宙都是多元宇宙的可能性之一，有高達十一個空間維度有超出我們所能想像的奇妙性質。

The leading version of string theory predicts a multiverse made up of 10 to the 500 universes.

而弦理論最先進的版本預測一個多元宇宙是由 10 的 500 次方個宇宙組成。

That's a one followed by 500 zeroes!

那有五百個零在1後面！

A number so vast that if every atom in our observable universe had its own universe.

這是一個太大的數字，即使每一個粒子在我們可看見的宇宙中擁有自己的宇宙。

And all of the atoms in all those universes each had their own universe, and you repeated that for two more cycles, you'd still be at a tiny fraction of the total.

而在那些宇宙中的每一個粒子又有他們自己的宇宙，你只要這樣不斷重複兩輪以上，你得到的仍是總數的一小部分。

Namely, one trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillionth.

也就是只有一兆、兆、兆、兆、兆、兆、兆、兆、兆、兆、兆、兆、兆、兆、兆分之一。

But even that number is minuscule compared to another number: infinity.

但即使是這樣的數字和無窮大比起來也只是一小部分。

Some physicists think the space time continuum is literally infinite and that it contains an infinite number of so-called pocket universes with varying properties.

有些物理學家認為所謂的時空連續體就是無窮大的，裡面包含了無數個所謂的「口袋宇宙」有著各式各樣的性質。

How's your brain doing?

你還跟著上嗎？

Quantum theory adds a whole new wrinkle.

量子理論帶來全新的可能。

I mean, the theory's been proven true beyond all doubt, but interpreting it is baffling.

這些理論已經被證實為真但是卻難以解釋。

And some physicists think you can only un-baffle it if you imagine that huge numbers of parallel universes are being spawned every moment.

有些物理學家認為唯一的解讀方式為是從很大數量的單一平行宇宙在每個時間點誕生。

And many of these universes would actually be very like the world we're in, would include multiple copies of you.

而這些單一宇宙，多數與我們所在的世界非常像，每個單一宇宙可能都有一個你。

In one such universe, you'd graduate with honors and marry the person of your dreams, and in another, not so much.

也許在其中一個單一宇宙的你，從名校畢業，還和你的夢中情人結婚，但是在另一個單一平行宇宙，卻沒有這麼幸運。

Well, there are still some scientists who would say, hogwash.

還是有些科學家認為這簡直是鬼話連篇。

The only meaningful answer to the question of how many universes there are is one.

這些科學家認為，有多少個宇宙的最合理解答只有一個。

Only one universe.

就是只有一個宇宙。

And a few philosophers and mystics might argue that even our own universe is an illusion.

還有一些哲學家和神秘主義者主張我們的宇宙其實只是一個幻象。

So, as you can see, right now there is no agreement on this question, not even close.

因此，如你所見，截至目前為止要取得一個統一的結論還早得很。

All we know is the answer is somewhere between zero and infinity.

我們目前只知道，正確的答案應該介於零到無窮大之間。

Well, I guess we know one other thing.

我想我們還知道了另一件事情。

This is a pretty cool time to be studying physics.

也就是現在是研究物理學的最佳時機。

We just might be undergoing the biggest paradigm shift in knowledge that humanity has ever seen.

因為物理學正在經歷人類有史以來最重大的知識典範轉移。

Why Can't We See Evidence of Alien Life?

為什麼我們找不到外星生命的證據？

Somewhere out there in that vast universe there must surely be countless other planets teeming with life.

在廣大宇宙之外的某個地方一定有數不清的星球富有生命。

But why don't we see any evidence of it?

但是為什麼我們找不到證據呢？

Well, this is the famous question asked by Enrico Fermi in 1950: Where is everybody?

這是Enrico Fermi在1950年所提出的一個相當著名的問題：每個人到底在哪裡？

Conspiracy theorists claim that UFOs are visiting all the time and the reports are just being covered up, but honestly, they aren't very convincing.

陰謀論者聲稱幽浮隨時隨地都來拜訪，只是相關報導都被掩蓋，但老實說，這一點都不具有說服力。

But that leaves a real riddle.

但那留下了一個謎。

In the past year, the Kepler space observatory has found hundreds of planets just around nearby stars.

過去幾年，克卜勒太空望遠鏡已經找到數百個行星在鄰近的星球。

And if you extrapolate that data, it looks like there could be half a trillion planets just in our own galaxy.

如果從數據來推論，很有可能有五千億個行星在我們的銀河系裡。

If any one in 10,000 has conditions that might support a form of life, that's still 50 million possible life-harboring planets right here in the Milky Way.

如果有萬分之一個星球有適合任何生物的環境，那就有五千萬個行星，可能存有生命就在銀河系裡面。

So here's the riddle: our Earth didn't form until about nine billion years after the Big Bang.

來看看這道謎題：我們的地球在宇宙大爆炸以後的九十億年才形成。

Countless other planets in our galaxy should have formed earlier, and given life a chance to get underway billions, or certainly many millions, of years earlier than happened on Earth.

在我們銀河系裡，應該有很多行星更早就形成了，且有機會孕育生命，幾十億，或至少比地球上的最原始的生命早了幾百億年。

If just a few of them had spawned intelligent life and started creating technologies, those technologies would have had millions of years to grow in complexity and power.

如果有幾個行星已經孕育了具有智慧的生命，並且開始創造科技，那些科技會有足足幾百萬年發展它的複雜度和影響力。

On Earth, we've seen how dramatically technology can accelerate in just 100 years.

地球上我們已經見證了科技可以如何在短短一百年間急遽加速。

In millions of years, an intelligent alien civilization could easily have spread out across the galaxy, perhaps creating giant energy-harvesting artifacts or fleets of colonizing spaceships or glorious works of art that fill the night sky.

何況是幾百萬年，一個高智慧的外星文明絕對已經將觸角伸到銀河系外面；說不定還創造了巨大的產能機器，或是殖民艦隊，甚至是填滿夜空的閃閃發亮藝術品。

At the very least, you'd think they'd be revealing their presence, deliberately or otherwise, through electromagnetic signals of one kind or another.

至少，你知道他們揭開他們自己神秘的面紗，故意地或是無心地透過電磁信號或是其他種方式。

And yet we see no convincing evidence of any of it.

但是我們還沒找到合理的證據。

Why?

為什麼？

Well, there are numerous possible answers, some of them quite dark.

因為有無數個可能的答案，其中有些聽起來蠻恐怖的。

Maybe a single, superintelligent civilization has indeed taken over the galaxy and has imposed strict radio silence because it's paranoid of any potential competitors.

可能有個高度文明的地方已經掌管整個銀河系，還讓無線電無法回報，因為不想讓其他可能的競爭者發現。

It's just sitting there ready to obliterate anything that becomes a threat.

它就只是蓄勢待發的要消除任何可能構成威脅的事物。

Or maybe they're not that intelligent, or perhaps the evolution of an intelligence capable of creating sophisticated technology is far rarer than we've assumed. After all, it's only happened once on Earth in four billion years.

也有可能他們並沒有那麼聰明，或者是智商演化到能夠創造複雜的科技，根本就不像我們想像的那麼容易。畢竟地球四十億年來只發生過一次。

Maybe even that was incredibly lucky.

可能只是運氣問題。

Maybe we are the first such civilization in our galaxy.

也許我們是銀河系第一個擁有文明的星球。

Or, perhaps civilization carries with it the seeds of its own destruction through the inability to control the technologies it creates.

又或者是文明帶著毀滅的種子來摧毀它製造的科技。

But there are numerous more hopeful answers.

不過現在出現了比較多有用的答案。

For a start, we're not looking that hard, and we're spending a pitiful amount of money on it.

首先，我們其實並沒有那麼認真地尋找，而且我們只花了很少的錢在上面。

Only a tiny fraction of the stars in our galaxy have really been looked at closely for signs of interesting signals.

在我們銀河系中，只有一小部分的行星曾經被仔細看過是否有不一樣的訊號。

And perhaps we're not looking the right way.

也許我們沒有用對方法。

Maybe as civilizations develop, they quickly discover communication technologies far more sophisticated and useful than electromagnetic waves.

也許是因為某個文明發展的時候，他們就立刻發現更厲害的傳播科技遠比電磁波更精密、有用的傳播科技。

Maybe all the action takes place inside the mysterious recently discovered dark matter, or dark energy, that appear to account for most of the universe's mass.

也許這些事情都發生在神秘不可測的近期發現的暗物質裡面，或是暗能量，那些說明宇宙大部分組成物的東西。

Or, maybe we're looking at the wrong scale.

或是我們根本就找錯方向了。

Perhaps intelligent civilizations come to realize that life is ultimately just complex patterns of information interacting with each other in a beautiful way,

也許高度文明認清生命最終只是資訊的複雜型式，和彼此用一種美麗動人的方式互動。

And that can happen more efficiently at a small scale.

這在小範圍中比較有可能發生。

So, just as on Earth clunky stereo systems have shrunk to beautiful, tiny iPods, maybe intelligent life itself, in order to reduce its footprint on the environment, has turned itself microscopic.

因此，就像是地球上笨重龐大的音響設備已經搖身一變成為美麗、方便攜帶的多媒體撥放器，這些可能的文明生物，為了隱藏足跡，讓自己小到只有顯微鏡才看的到。

So the Solar System might be teeming with aliens, and we're just not noticing them.

所以事實上，太陽系可能充滿了外星生物，只是我們沒有注意到而已。

Maybe the very ideas in our heads are a form of alien life.

也許在我們腦中迸生的想法，也是外星生物的一種形態。

Well, okay, that's a crazy thought.

好吧，我知道這是個瘋狂的想法。

The aliens made me say it!

是那些「外星生物」讓我這麼說的！

But it is cool that ideas do seem to have a life all of their own and that they outlive their creators.

但是「想法」好像是真的生命，他們甚至比他們的創造者還活得長久。

Maybe biological life is just a passing phase.

也許生物生命只是一個一閃即逝的物體。

Well, within the next 15 years, we could start seeing real spectroscopic information from promising nearby planets that will reveal just how life-friendly they might be.

在接下來十五年間我們可以看到分光鏡下的資訊，關於鄰近星球擁有友善生命的可靠消息。

And meanwhile, SETI, the Search for Extra-Terrestrial Intelligence, is now releasing its data to the public so that millions of citizen scientists, maybe including you, can bring the power of the crowd to join the search.

同時，SETI，外星智慧生命搜尋計畫現在正向大眾釋出資料，所以數百萬個科學家，可能你也是其中一個，可以加入這個搜尋計畫，影響群眾。

And here on Earth, amazing experiments are being done to try to create life from scratch, life that might be very different from the DNA forms we know.

在地球上，驚人的實驗正在試圖從搔抓中製造生命，這種生命的基因型態可能和我們所知的有很大的不同。

All of this will help us understand whether the universe is teeming with life or whether, indeed, it's just us.

這些實驗都會幫助我們了解這個宇宙是否富含生命；或是，其實就只有我們。

Either answer, in its own way, is awe-inspiring,

不管哪種答案都值得敬畏。

Because even if we are alone, the fact that we think and dream and ask these questions might yet turn out to be one of the most important facts about the universe.

因為即使只有我們，我們的思想、夢境，還有問這些問題的能力可能是宇宙中最重要的一件事。

And I have one more piece of good news for you.

我還有另一個好消息要告訴你。

The quest for knowledge and understanding never gets dull.

求知和理解知識的過程，永遠不無聊。

It doesn't. It's actually the opposite.

絕對不會，而且正好相反。

The more you know, the more amazing the world seems.

你知道的越多，這個世界看起來就更令人驚艷。

And it's the crazy possibilites, the unanswered questions, that pull us forward.

而且正是這些瘋狂的可能性、未解的謎題讓我們不停往前進。

So stay curious.

所以記得要保持一顆好奇的心！