On a typical day at school, endless hours are spent learning the answers to questions, but right now, we'll do the opposite. We're going to focus on questions where you can't learn the answers because they're unknown. I used to puzzle about a lot of things as a boy, for example: What would it feel like to be a dog? Do fish feel pain? How about insects? Was the Big Bang just an accident? And is there a God? And if so, how are we so sure that it's a He and not a She? Why do so many innocent people and animals suffer terrible things? Is there really a plan for my life? Is the future yet to be written, or is it already written and we just can't see it? But then, do I have free will? I mean, who am I anyway? Am I just a biological machine? But then, why am I conscious? What is consciousness? Will robots become conscious one day? I mean, I kind of assumed that some day I would be told the answers to all these questions. Someone must know, right? Guess what? No one knows. Most of those questions puzzle me more now than ever. But diving into them is exciting because it takes you to the edge of knowledge, and you never know what you'll find there. So, two questions that no one on Earth knows the answer to. (Music) [How many universes are there?] 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. 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. 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. And it gets worse. There are maybe 100 billion galaxies detectable by our telescopes. 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. And the entire Earth doesn't have enough beaches to represent the stars in the overall universe. Such a beach would continue for literally hundreds of millions of miles. Holy Stephen Hawking, that is a lot of stars. But he and other physicists now believe in a reality that is unimaginably bigger still. I mean, first of all, the 100 billion galaxies within range of our telescopes are probably a minuscule fraction of the total. Space itself is expanding at an accelerating pace. The vast majority of the galaxies are separating from us so fast that light from them may never reach us. Still, our physical reality here on Earth is intimately connected to those distant, invisible galaxies. We can think of them as part of our universe. 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. 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. Most of these universes could never support life, and might flash in and out of existence in a nanosecond. But nonetheless, combined, they make up a vast multiverse of possible universes in up to 11 dimensions, featuring wonders beyond our wildest imagination. The leading version of string theory predicts a multiverse made up of 10 to the 500 universes. That's a one followed by 500 zeros, a number so vast that if every atom in our observable universe had its own universe, 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, namely, one trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillionth. (Laughter) But even that number is minuscule compared to another number: infinity. 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. How's your brain doing? Quantum theory adds a whole new wrinkle. I mean, the theory's been proven true beyond all doubt, but interpreting it is baffling, and some physicists think you can only un-baffle it if you imagine that huge numbers of parallel universes are being spawned every moment, and many of these universes would actually be very like the world we're in, would include multiple copies of you. In one such universe, you'd graduate with honors and marry the person of your dreams, and in another, not so much. Well, there are still some scientists who would say, hogwash. The only meaningful answer to the question of how many universes there are is one. Only one universe. And a few philosophers and mystics might argue that even our own universe is an illusion. So, as you can see, right now there is no agreement on this question, not even close. All we know is the answer is somewhere between zero and infinity. Well, I guess we know one other thing. This is a pretty cool time to be studying physics. We just might be undergoing the biggest paradigm shift in knowledge that humanity has ever seen. (Music) [Why can't we see evidence of alien life?] Somewhere out there in that vast universe there must surely be countless other planets teeming with life. But why don't we see any evidence of it? Well, this is the famous question asked by Enrico Fermi in 1950: Where is everybody? 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. But that leaves a real riddle. In the past year, the Kepler space observatory has found hundreds of planets just around nearby stars. And if you extrapolate that data, it looks like there could be half a trillion planets just in our own galaxy. 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. So here's the riddle: our Earth didn't form until about nine billion years after the Big Bang. 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. 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. On Earth, we've seen how dramatically technology can accelerate in just 100 years. 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. At the very least, you'd think they'd be revealing their presence, deliberately or otherwise, through electromagnetic signals of one kind or another. And yet we see no convincing evidence of any of it. Why? Well, there are numerous possible answers, some of them quite dark. 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. It's just sitting there ready to obliterate anything that becomes a threat. 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. Maybe even that was incredibly lucky. Maybe we are the first such civilization in our galaxy. Or, perhaps civilization carries with it the seeds of its own destruction through the inability to control the technologies it creates. But there are numerous more hopeful answers. For a start, we're not looking that hard, and we're spending a pitiful amount of money on it. Only a tiny fraction of the stars in our galaxy have really been looked at closely for signs of interesting signals. And perhaps we're not looking the right way. Maybe as civilizations develop, they quickly discover communication technologies far more sophisticated and useful than electromagnetic waves. 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. Or, maybe we're looking at the wrong scale. Perhaps intelligent civilizations come to realize that life is ultimately just complex patterns of information interacting with each other in a beautiful way, and that that can happen more efficiently at a small scale. 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. So the Solar System might be teeming with aliens, and we're just not noticing them. Maybe the very ideas in our heads are a form of alien life. Well, okay, that's a crazy thought. The aliens made me say it. But it is cool that ideas do seem to have a life all of their own and that they outlive their creators. Maybe biological life is just a passing phase. 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. And meanwhile, SETI, the Search for Extraterrestrial 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. 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. All of this will help us understand whether the universe is teeming with life or whether, indeed, it's just us. Either answer, in its own way, is awe-inspiring, 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. And I have one more piece of good news for you. The quest for knowledge and understanding never gets dull. It doesn't. It's actually the opposite. The more you know, the more amazing the world seems. And it's the crazy possibilities, the unanswered questions, that pull us forward. So stay curious.
在學校尋常的一天裡 永遠沒有盡頭的時間 花在學習問題的解答上 但是現在我們要反過來做 我們將關注於你無法 學到答案的問題上 因為答案還沒有人知道的 我在孩童時期曾經對很多事情感到不解 例如當狗會是什麼樣的感覺? 魚會感覺到疼痛嗎? 那昆蟲又怎樣呢? 「宇宙大爆炸」僅是個意外嗎? 上帝真的存在嗎? 如果真的有-我們如何確定 祂是男生而非女生呢? 為什麼會有這麼多無辜的人類和動物 遭受到悲慘的事情? 我的生命中真的有命數嗎? 未來是否還沒註定好呢? 還是未來早已註定好了 而我們不過無從得知而已 不過話說回來我有自由意志嗎? 我是指我到底是誰呢? 我僅僅是一台活生生的機器嗎? 不過話說回來我為什麼會有意識呢? 意識又是什麼東西呢? 機器人哪天也會變成有意識的嗎? 我彷若在假設未來的某一天 會有人告訴我所有這些問題的答案 肯定有人知道答案對吧! 你猜怎麼著-沒有人知道的 大部分的問題困惑著我更甚以往 但是探索這些問題是很有趣的 因為它會帶你到知識的盡頭 而你永遠不知道你會在那裡發現到什麼 因此由兩個地球上沒有人 知道答案的問題來做開端吧! (音樂) [有多少個宇宙存在呢?] 有時候當我坐在遠途飛行的飛機上時 我會向外凝視那些山脈和沙漠 嘗試著猜測我們的地球到底有多巨大 接著我想到一個我們每天 都看得到的東西 恰恰可以裝進一百萬個地球-就是太陽 它應該是大到不切實際了 其實不過也只是滄海一粟罷了 只是銀河系四千億顆星星的其中之一 這些星星你可以在晴朗的夜晚看到 如同白茫的霧氣般在天空延展 還有更不堪的事 或許只有一千億個的星系是可以被 我們的天文望遠鏡所探測到的 假設每個星星是 一粒沙子的大小的話 僅僅銀河系就有足夠的星星 以沙子填出 30 乘 30 平方呎大 3 呎深的沙灘 整個地球上的沙灘甚至還不足以 代表全宇宙中所有的星星數 這樣的一個沙灘將會綿延數億英里長 天啊!史蒂芬.霍金 這可是超級多的星星啊 但是現在他和其他物理學家相信實際上 仍然還要比現在所知多上不知道多少 首先天文望遠鏡掌握到的一千億個星系 可能只是總數裡極小的部分 太空正以加速度擴展中 絕大部分的星系正迅速離我們而去 它們所發出的光線可能永遠到不了地球 我們地球上的物理現象 仍舊緊密地與那些遙遠的、 見不著的星系有關聯 我們可以把它們看做是 我們的宇宙的一部分 它們組成了一個巨大的體系 遵循著相同的物理法則 而且全部都是由與構成了你和我 相同的原子、電子、質子、 垮克、中子所組成 然而包括「弦理論」在內的近期物理理論 告訴了我們可能有著 無以計數由不同粒子、 帶有不同屬性所建立、 遵循不同法則的其他宇宙存在 大部分的宇宙可能永遠不能供養生命 而且其誕生與消滅可能只在豪微秒以內 不過無論如何它們總算一起構成了 可能多達11次元空間的巨大多元宇宙 我們最奔放的想像力也勾不著之奇景 「弦理論」最主流之版本預測出由 10 的 500 次方個宇宙構成一個多元宇宙 就是 1 後面帶著 500 個 0 一個如此龐大的數字 如果我們可觀測到的宇宙裡 每粒原子都有自己的宇宙 以及在所有那些的宇宙中全部的原子 各自有自己的宇宙 你再重複兩輪同樣的推演 你仍將會是總數的一小部分而已 也就是 1 /10 的 180 次方 (笑聲) 即便是這個數字與另一個數字 相比還是微不足道:無窮 部分物理學家認為時空 連續體確實就是無窮大 而且那包含了無窮帶有不同屬性 名喚"自成一格之宇宙"的東西 你的大腦還能運作吧? 「量子論」添加了全新的問題進來 該理論已經從所有的 質疑聲中被證實為真了 不過我是指釐清它很容易讓人搞糊塗 有些物理學家認為 只有當你想像著龐大數量的平行宇宙 在每個時點又誕生了出來 而且多數的那些宇宙將會確實 非常類似於我們所在的世界 還會包含繁多個你本人的翻版 這樣你才可能不搞混 在其中一個宇宙你會光榮地畢業、 以及與你的夢中情人成婚 而在另一個宇宙中的你就沒那麼好了 也還是有一些科學家可能 會說這是一派胡言 對於有多少宇宙存在這個問題 只有一個有意義的答案 那就是僅僅一個宇宙而已! 有少部分哲學家和神秘力量信奉者 會說就連我們的宇宙也不過是個幻像 所以如同你所能知道的 對於這個問題現在仍沒有一個共識 還差的遠呢! 我們只知道這個答案 介於零到無窮之間 我認為我們還知道另一件事情 這是絕佳的時候來學習物理 我們可能正在經歷人類有史以來 知識上最大的思維方式轉變 (音樂) [為什麼找不到外星生命的跡象呢?] 在浩瀚宇宙的某一處 肯定有無數的其他星球充斥著生命體 但是為什麼我們看不到任何跡象呢? 「恩里科‧費米」在 1950 年 提問了這個著名的問題: 「外星人都在哪兒呢?」 密謀論主義們聲稱不明飛行物體 亦即「幽浮」不時光臨到地球 而且有關的報告、報導都被掩蓋了 不過老實講他們也不是很有說服力啦 但是這留下了一個真正的謎團 去年裡克卜勒太空望遠鏡 又在一些恆星週邊發現了數以百計的行星 如果你用那些資料估算一下 光我們銀河系就很可能 有 5000 億顆的行星 假使一萬顆裡有任何一顆行星 有著能供養某型態生命的條件 在銀河系裡面 依然還有五千萬顆 可能蘊藏生命體的行星 所以謎團在這裡 地球直到「宇宙大爆炸」90 億年 之後才開始形成 在我們的星系中有無數星球 應該形成於更早之前 給予生命體現蹤的機會 早於地球出現生命體之前的 數十億年或數千萬年 如果只有一小部分孕育出過智慧生命 並且創造出科技 那些科技早已有數百萬年的時間 來提升複雜性和力量 在地球上 我們已經見識到科技可以如何 突然間單單在一百年內加速發展 在數百萬年裡一個高智慧的外星文明 肯定可以輕易地流傳遍整個星系 或許創造出巨型的採收能量裝置 或者是太空船殖民艦隊 或是可以填滿夜空的美麗藝術作品 最起碼你會認為 不論刻意與否 應該有透過某種電磁波訊號 或是其他方式顯露出它們的存在 但是我們還找不到任何有力的證據 為什麼呢? 是這樣啦,有許多可能的答案 其中有一些很令人絕望 也許單一超智慧文明 已經確實掌控了銀河系 而且實施嚴格的電波靜音 因為它會對任何潛在的競爭對手擔憂不已 它就是已經坐等著要徹底摧毀 會變成威脅的任何東西 或者它們也許沒那麼有智慧 又或許創造精密科技的智慧能力進化 遠比我們所設想的更難得 四十億年來終究只發生過一次 就是在地球上 也許就連這次已是無比地幸運了 或許我們是本星系中的第一個智慧文明 或者有可能文明帶有無力控制 其所創造出之科技的自我毀滅因子 不過還是有很多充滿希望的答案 首先我們並沒有認真在搜找 我們現在只花極少的金錢在這上頭 在我們星系只有一小部分星球 真的曾經被仔細觀察過 值得玩味之訊號的跡象 或者是我們沒有找對方向、用對方法 也許當文明在發展時 他們很快地就發現了遠比電磁波 更精密、更有用的通訊科技 也許所有的動作都發生在最近才被發現 如謎般的暗黑物質或是暗黑能量之中 那看起來佔了整個宇宙的絕大多數 或者可能我們找錯了大小範圍 也許智慧文明理解到生命最終 只用美妙的方式 以複雜之資訊彼此互動 這種互動溝通在小規模下變得更有效 因此就如同地球上笨重的立體音響 已縮小成美麗輕巧的 iPod 或許智能生命體為了減少在環境中 留下的足跡已經將自己變得微不可察 因此太陽系也許滿是外星人 我們就只是無法察覺到它們而已 可能我們腦中的此刻的想法就是 一種外星生命的形式 好啦,這真是個瘋狂的想法 是外星人讓我這麼說的 不過這實在很勁爆 說想法似乎全都有各自的生命 而且比想出它們的人更長壽 也許生理生命只不過是個過渡的階段 在未來十五年裡我們有可能看到 來自有良機的鄰近行星之真實光譜資料 那將顯現它們可能有多麼迎合生命 同時「搜尋天外文明計畫」亦即 SETI 現在正對普羅大眾開放它的資料 因此可能也包括你在內的 數百萬平民科學家 能把群眾的力量帶進這個研究中 而在地球上已經做過了試著憑空 創造出生命的神奇實驗 此生命可能與我們所知的 DNA 型式非常不一樣 這所有一切將會幫助我們瞭解 到底宇宙是充滿生命體 或者確實就只有我們而已 兩個答案各有千秋都令人敬佩 因為就算我們是唯一的智慧文明 我們思索、夢想、問這些問題的現實 可能會變成宇宙中最重要的事實之一 而且我要再多給你一則好消息 追求知識和理解永遠不會乏味 不但不會還恰恰相反 你知道的越多 這個世界就似乎越神奇 其中荒唐的可能性和尚未有答案的問題 催促著我們向前進 所以持續好奇吧!