(音乐)
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.
在学校,普通的一天里, 无尽的时间要花在怎么去回答问题上, 但是现在,我们不这么做了。 我们将把目光放在那些你不能够学到答案的问题上, 因为它们是未知的。 我曾经在孩童时期对很多事情都有疑惑, 比如说,做一只狗会有什么样的生活呢? 鱼会感觉到疼痛么? 昆虫会不会呢? 难道宇宙大爆炸仅仅是个意外么? 上帝真的是存在的么? 如果存在的话,我们怎么能够确定上帝是男的还是女的呢? 为什么世界上这么多的无辜的人和动物要遭受一些可怕的事情? 我的生活真的是被计划好的么? 未来是还没被决定的呢, 还是说未来是已经被写好了的,只不过我们看不见? 然后,我有自由的意志么?我到底是谁呢? 我仅仅是一台生物机器么? 然后,我为什么会有意识呢?意识又是什么东西? 机器人以后也会有意识么? 我是说,我稍微假设一下,在某一天 我会有这些问题的答案, 那么肯定是有人知道答案的对吧? 你猜猜?没有人知道。 大部分这些问题带给我的困扰与日俱增。 但是探索这些问题答案的过程真的很有趣 因为它带你到了知识的边缘,你永远不知道你将在那里发现什么。 所以,这里有两个问题—— 这两个问题地球上没有人可以回答出来。 (音乐)世界上有多少的宇宙呢? 有时候, 当我坐在远途飞行的飞机上, 我会向外俯瞰那些山川和沙漠 然后尝试着猜测我们的地球到底有多广袤无垠。 接着我记得我们每天都能看见一个物体的出现, 它还可以装进一百万个地球: 太阳。它看起来真的是不可思议般的大! 但是在浩瀚的宇宙中,它不过一个针孔大小而已, 是银河系中四千亿星星的一员, 正如你可以在晴朗的晚上 看到满天的星星好似淡淡的白雾 然而更令人惊叹的是, 通过天文望远镜我们可以 探测到大约一千亿个的星系。 所以如果每个星星都是沙子中的一粒的话, 仅仅银河系就有足够的星星让 一个30英尺长30英尺宽的沙滩 盖上3英尺厚。 整个地球上的沙滩甚至还不能 代表宇宙中所有的星星。 这样的一个沙滩会大约绵延几亿英里长。 天啊,史蒂芬 霍金,这可是超级多的星星啊! 但是他还有其他物理学家现在相信事实上 还会比现在的大不知道多少,完全没法想象。 我的意思是,首先,这些我们可以观测到的一千亿星系 可能不过是总数的很小一部分。 空间现在仍在在加速拓展。 绝大部分的星系 正在以一个比光还要快的速度离我们而去,他们的光都不可能到达地球。 但是,事实上我们地球上的物理现象 是和那些遥远的看不见的星系有着很密切的关系。 我们可以把它们看作宇宙中的一部分。 它们组成了一个巨大的宏伟建筑物 所有的建筑物里的物质都遵循相同的物理定律,由相同的微粒组成, 原子, 电子,质子, 夸克,中微子——那些形成了我们的微粒。 然而,物理学最近的理论显示,包括弦理论, 告诉我们世界上可能会有数不完的其他宇宙 由不同于我们的宇宙的微粒组成, 有不同的性质,遵循不同的规律。 大部分的宇宙可能永远不能产生生命, 或者生命在一纳秒内存在然后消失了。 但是,无论如何,它们组成了巨大的多元宇宙, 可能一共有11维, 在我们的想象力之外创造着奇迹。 领先的弦理论预测一个多元宇宙 可以组成10的500次方个不同的宇宙。 就是1后面跟著500个0, 这个数字是如此之大以至于我们观测宇宙中的 每个原子都有自己的宇宙, 所有的宇宙中的所有原子都有 自己的宇宙。你再重复 两次同样的循环,你得到的仍然是 总数的一小部分, 也就是大约10的180次方分之一。 即便是这个数字, 相比另一个数字也是小数目: 无限。 部分物理学家认为时空连续到几乎是无限的 它包括了无限的所谓的子宇宙 和所有的可能。 你的大脑现在怎么样了? 量子理论给了我们一个全新的视野。 我的意思是,这个理论证明了所有的疑惑, 但是证明和解释起来却非常的困难, 有些物理学家认为要解释疑惑就 必须要你想象世界上有无数的平行宇宙 在每个瞬间都在像产卵一样分化, 这些宇宙中有许多会跟我们所在的世界很相似, 并且会有多个你这个人的副本。 在这些宇宙中,你会以荣誉学位毕业 并且嫁给一位梦中情人, 而在另一个宇宙中的你,活的不那么好。 好吧,仍然会有一些科学家会说,这是废话。 这里唯一有意义的回答:世界上有多少宇宙的答案是一个。 仅仅一个宇宙。 有少部分哲学家和神学家 会说即便我们的宇宙也是幻觉, 不真实存在的。 所以,你可以看到,现在 世界上没有对于这个问题的统一回答,甚至还没有可以回答的迹象 我们只知道这个答案介于0到无穷大之间。 让我们来说一下另一件事。 这是一个非常有趣的学习物理的机会。 我们可能正在经历人类史上 最大的知识范例变动。 (音乐)为什么我们看不到外星人的迹象? 在浩瀚宇宙的某一处, 肯定会有个地方会有无数的星球在大量的孕育出生命。 但是为什么我们就看不到那些迹象呢? 这个著名问题在1950年由Enrico Fermi提出: 其他生命到底在哪里? 阴谋论的理论家认为不明飞行物经常飞到地球来 并且有关的报告被隐藏了,但是说实话,这个并不能令人信服。 但这就留下了一个谜。 在过去的时间里,开普勒空间瞭望台 发现了几百颗行星在恒星附近环绕。 如果外推一下这个数据, 这好像是有5000亿个行星 在银河系中。 如果有万分之一的行星有条件 孕育生命,这依然有 五千万适合生命的行星。 这仅仅是在银河系。 所以这个谜就是:我们地球的存在 是在大爆炸的九十亿年之后。 无数的银河系内其他行星会在地球之前形成 并且让生命可以进化。 它们要比地球早几十亿年,或者最起码早几百万年 就已经出现了。 如果只有一少部分生命进化出了有智慧的 和可以创造科技的生命, 那些科技将会有几百万年的时间 去发展出对应的复杂度和能力。 在地球上, 我们见证了科技在仅仅100年内 是怎样急剧发展的。 在数百万年内,一个有智慧的外星文明 肯定可以轻易地发展到银河系的每一个角落, 或许发明了巨型能源捕获机这样的东西。 或者是殖民飞行舰队 或者是充满了夜晚天空的辉煌艺术作品。 至少你想它们也会 把它们的存在,有意或无意的, 通过一种或其他的电磁信号告诉我们。 但是现在没有充分证据显示有任何一种文明。 为什么呢? 这里会有很多可能的答案, 其中有些相当消极。 可能一个非常有智能的文明 已经占领了整个银河系并且故意把辐射波屏蔽了, 因为它们害怕潜在的竞争对手。 他们可能就坐等去消灭 任何可能成为隐患的东西。 或者它们还不够聪明, 或者可能在进化出一个 能够创造复杂科技的智能生物 是远比我们想象的要难。总而言之, 在40亿年智能生物至此只在地球发生过一次。 或许这是巧合的巧合。 或许我们是银河系内第一个有如此程度文明的。 或者,可能 文明携带毁灭自己文化的种子 这些种子通过以不能控制自己科技进步的方式衍生着。 但这里有更多充满希望的答案。 作为开始,我们没有努力去搜索它们,我们只是花了很少一部分钱而已。 仅仅是银河系中的很小一部分行星 被我们仔细研究了它们的使我们感兴趣的信号。 或许我们没有找对方向。 可能一个文明发展得 太快以致于它们使用一些 比电磁波更加复杂有用的信号。 可能所有的活动都是在谜一般的 最近发现的暗物质里发生的。 或者是揭示了宇宙大部分质量的暗能量, 或者 可能我们找错了大小范围。 可能智能文明意识到了 生命最终不过是复杂的信息模式 互相以一种美丽的方式作用于其他个体, 它们可能在更小的情况下表现的更加有效率。 所以,就像笨重的音响系统变小了, 变成精致小巧的ipods;或者是智能生物本身变小, 这样可以减少在环境中留下的足迹,让他们变成微观物体。 所以,在太阳系可能充满了外星人,只不过我们没发现而已。 可能我们脑中的那个想法就是一种外星生命的形式。 好吧,真是一个疯狂的想法。 外星人让我说的。 但这个好想法的确有自己的一套生命的解释 而且它们比它们的创造者活得更久。 可能生命体只是一个转瞬即逝的阶段。 好吧,在未来的15年内, 我们可以开始看到真正的光谱学信息 从附近有希望的行星开始去揭示一个星球有多适合居住。 另一方面,有个叫做"搜寻外星智能生物"的组织,也叫SETI, 现在把自己的数据公之于众, 这样成百万计的科学家,可能也包括你, 可以发动群众的力量去加入这个搜索。 并且在地球,人们在做一种神奇的实验 去寻找随机创造出生命, 而且它们的DNA会跟我们有很大不同。 所有的这些会让我们了解 这个宇宙是不是充满了生命 或者,真的,只有我们。 任何一个答案,就它们本身而言, 都是令人惊讶的, 因为即便只有我们存在, 这些思考与梦想,这些疑问本身, 可能会变成宇宙中最重要的事实之一。 我还有一个好消息给你。 对知识的渴望不会让你生活乏味, 不但不会,还会反过来。 你知道的越多,对你来说这个世界就越神奇。 还有这些疯狂的可能性还有没回答的问题, 它们使我们向前。