Could human civilization eventually spread across the whole Milky Way galaxy? Could we move beyond our small blue planet to establish colonies in the multitude of star systems out there? This question's a pretty daunting one. There are around 300 billion stars in the galaxy, which is about 160,000 light-years across. So far we've sent a single spacecraft outside our solar system, trudging along at 0.006% of the speed of light. At that rate, it would take over 2.5 billion years just to get from one end of the galaxy to the other. And then there's the question of human survival. The gulf between stars is simply enormous. We couldn't live sustainably on most planets, and we require a lot of resources to stay alive. And yet, decades ago, scholars found that it's theoretically possible to not just spread human civilization across the galaxy, but to do so quite quickly, without breaking any known laws of physics. Their idea is based on the work of a mathematician named John von Neumann, who designed on paper machines that could self-replicate and create new generations of themselves. These would later come to be known as von Neumann machines. In the context of space exploration, von Neumann machines could be built on Earth and launched into space. There, the self-sufficient machines would land on distant planets. They would then mine the available resources and harvest energy, build replicas of themselves, launch those to the nearest planets, and continue the cycle. The result is the creation of millions of probes spreading outwards into the universe like a drop of ink in a fishbowl. Scholars crunched the numbers and found that a single von Neumann machine traveling at 5% of the speed of light should be able to replicate throughout our galaxy in 4 million years or less. That may sound like a long time, but when you consider that our universe is 14 billion years old, on a cosmic scale, it's incredibly fast - the equivalent of about 2.5 hours in an entire year. Creating von Neumann machines would require a few technologies we don't have yet, including advanced artificial intelligence, miniaturization, and better propulsion systems. If we wanted to use them to spread actual humans throughout the galaxy, we would need yet another technological leap - the ability to artificially grow biological organisms and bodies using raw elements and genetic information. Regardless, if in the last billion years an alien civilization created such a machine and set it multiplying its way toward us, our galaxy would be swarming with them by now. So then where are all these machines? Some astronomers, like Carl Sagan, say that intelligent aliens wouldn't build self-replicating machines at all. They might hurtle out of control, scavenging planets to their cores in order to keep replicating. Others take the machines absence as proof that intelligent alien civilizations don't exist, or that they go extinct before they can develop the necessary technologies. But all this hasn't stopped people from imagining what it would be like if they were out there. Science fiction author David Brin writes about a universe in which many different von Neumann machines exist and proliferate simultaneously. Some are designed to greet young civilizations, others to locate and destroy them before they become a threat. In fact, in Brin's story "Lungfish," some von Neumann machines are keeping a close watch over the Earth right now, waiting for us to reach a certain level of sophistication before they make their move. For now, all we have is curiosity and theory. But the next time you look at the night sky, consider that billions of self-replicating machines could be advancing between stars in our galaxy right now. If they exist, one of them will eventually land on Earth, or maybe, just maybe, they're already here.
人类文明能遍布银河系吗 我们能在这个小小的蓝色星球之外的 广袤星系建立殖民地吗 这个问题还挺吓人的 银河系有3000亿颗恒星左右 从一边到另一边的距离是160000光年 现在为止我们就发送了一艘宇宙飞船到太阳系外 以0.006%光速缓慢前行 以那个速度,得花不止25亿年 才能横跨一个星系 然后就有了这个人类生存的问题 恒星间的距离简直大无边际 在多数星球上我们都不能持续生存 而且我们需要很多资源才能存活下来 然而几十年前,学者发现从理论角度 在银河系传播人类文明不仅是可行的 而且还能很快实现 还不违背现有的物理定律 这个想法源于一名叫约翰·冯·诺依曼的数学家的研究 他在纸上设计了一台能进行自动复制和创造新一代的机器 他在纸上设计了一台能进行自动复制和创造新一代的机器 后来这些机器被称为冯·诺依曼机器 在太空探索的背景下 冯·诺依曼机器可以建在地球上 然后发射进太空 太空中,这种自给机器会在遥远的星球着陆 然后开采可用资源、搜集能量 进行自我复制 把复制的机器发射到最近的星球 然后不断循环这个过程 最后结果就是无数探测器 像水里的一点墨水一样不断向外在宇宙中蔓延 学者进行计算之后发现,一台冯·诺依曼机器 以5%光速飞行 要花400万年才能通过不断复制穿越银河系 听起来时间很长 但想到140亿岁高龄的宇宙 从宇宙尺度看来已经非常快了 也就是一整年里的两个半小时 造一台冯·诺依曼机器需要几项目前没有的新技术 造一台冯·诺依曼机器需要几项目前没有的新技术 包括先进的人工智能 微型化科技 更好的推进系统 如果想运用这些技术把人类送进银河系 我们还得需要另一项技术性飞跃 通过原始元素和基因信息来人为造出生物有机体和生物机体 通过原始元素和基因信息来人为造出生物有机体和生物机体 不管怎么说,如果过去10亿年间 有外星文明造出了类似的机器 通过不断复制的方式向我们驶来 我们的银河系应该已经到处都是这些机器了 但是那些机器在哪儿呢 一些天文学家,比如卡尔·萨根,说 聪明的外星人不可能建造自我复制机器 这些机器会在横冲直撞后失去控制 为了实现自我复制把星球洗劫一空 另外一些人认为这种机器不存在是因为 根本不存在智慧的外星文明 或者在他们发展出必要科技前就已经灭绝了 但这些想法并不妨碍人类想象,如果存在外星文明 将是怎样一番景象 科幻小说作家大卫·布林 描写了一个存在许多不同的冯·诺依曼机器并同时扩散的宇宙 描写了一个存在许多不同的冯·诺依曼机器并同时扩散的宇宙 一些机器跟年轻文明打招呼 另一些则定位年轻文明,并且在年轻文明成为威胁前将其摧毁 实际上,布林的小说“Lungfish"里面 一些冯·诺依曼机器正密切关注着地球 等我们成熟到一定阶段后 他们才采取行动 目前,我们有的只是好奇心和理论 但下次你仰望夜空时 想象无数自我复制的机器 正在银河系的恒星间穿梭 如果它们存在,最后一定会降临地球 也许,它们已经到地球了