史蒂芬·霍金于3月14日故世了，人类痛失了一位宇宙学巨擎。霍金在物理学界最享有盛名的成就，是他关于宇宙形成的几大假说。然而他对未来也曾有过不少预测。

霍金对人类的未来总体上并不乐观，为了纪念他的去世，我们现在就来回顾一下他对人类将何去何从的几大预言。

霍金的末日说

首先是“末日”这个宏大的话题。近些年，霍金深信人类迫切地需要进入太空，因为“向太空扩张或许是人类自我拯救的唯一途径”。

2016年末，霍金曾说，人类大概只剩下一千年左右离开地球的“窗口期”。但是不到半年，霍金就改口称，这个窗口期离现在只有不到一百年了。在他看来，气候变化、“迟早会来”的小行星撞击、人口过量增长、流行病的威胁、核大战和生物战争等都是有可能导致人类灭绝的重大危机。

这几个月里到底发生了什么事，让霍金认为人类在地球上可生存的时间大大缩短了？当然，特朗普当选美国总统可能也是令他感到悲观一个重要因素。

霍金曾表示：“我们已经接近了全球变暖变得不可逆的临界点。特朗普的做法（退出《巴黎协定》）会将地球推向深渊，变得像金星一样，成为一个气温高达250度、天上下硫酸雨的星球。”

霍金谈人工智能

和伊隆·马斯克等人一样，霍金对所谓“通用人工智能”的威胁也是忧心忡忡。“通用人工智能”并非指现在常见的那种仅针对一个或几个任务而设计的AI程序，而是指可以自我进化、自我完善的人工智能程序，等到它发展一定程度，人类最终会被它赶尽杀绝，由机器人彻底取代我们。

霍金对人工智能的看法也并非完全是负面的。他指出，人工智能技术也有可能帮助我们摆脱疾病和贫困，甚至在一定程度上逆转气候变化的损害（当然他在其他场合还说过，气候变化可能使地球在600年内变成一个“大火球”）。

“人工智能的发明可能是人类文明史上最重大的事件，也有可能是人类文明史上最可怕的事件，不过我们现在还不知道。”他去年曾这样说。

（需要注意的是，有一句流传甚广的话据传是霍金所说——“知识的最大敌人不是无知，而是拥有知识的错觉。”霍金很可能从没说过这句话。）

人类何去何从？

好吧，这样看来，为了躲避死亡酸雨和“终结者”机器人，我们只有宇宙逃亡这一条路了。那么哪里才是霍金眼中理想的“第二地球”呢？

过去十年，霍金一直呼吁在月球和火星建立殖民地。不过这两个地方只是人类进入太空的跳板和补给站。霍大爷已经把我们的目的地钦定了，那就是离我们最近的恒星系——半人马座阿尔法星（没错，我们就是要在三体人打过来之前，先抢了他们的老窝）。

两年前，霍金与投资人尤里·米尔纳以及一支科学家团队合作，打算设计一种能承受太空飞行的计算机芯片，在太阳帆的辅助下向三体星系发射。这个叫做“突破摄星”的项目简直是“阶梯计划”的完美复原，目的是将这些探测器发往三体星系，就近拍摄该星系的图像传回地球，以便于人类评估该星系是否适合人类殖民。

当然，半人马座阿尔法星虽然是离地球最近的恒星系，但毕竟路程还是太遥远了。“突破摄星”计划的原理是希望利用100亿瓦的高能激光束，将这些纳米飞船加速到光速的五分之一。科学家认为，以这样的速度航行，纳米飞船或许能在我们的有生之年打个来回，使我们一窥三体星系的真实图景。

霍金或许永远看不见“突破摄星”计划的成果了。但是或许我们能看到那一天。（又或许老爷子的脑细胞会随着“阶梯计划”一起上路，在漫长岁月的某一天，像云天明一样，从三体星系给濒临绝境的人类文明指点一线生机。谁知道呢？）

译者：朴成奎

Stephen Hawking, the titan of cosmology who passed away Wednesday at the age of 76, made his name hypothesizing about the past—all of it. However, he also had plenty to say about the future.

His was not generally a very sunny outlook, but, in honor of his passing, it’s only right to revisit what he saw on our collective horizon.

Doomsday

Let’s start with the big one, then: Hawking had in recent years been convinced that humanity needs to get into space with a fair amount of urgency, because “spreading out may be the only thing that saves us from ourselves.”

In late 2016, Hawking reckoned humanity has about 1,000 years left on Earth. Half a year later, he cut that to 100 years, because of climate change, “overdue” asteroid strikes, excessive population growth, and the threat of epidemics. Oh, and nuclear or biological war.

What changed over those months to so drastically shorten humanity’s Earthbound future? Well, Donald Trump got elected as U.S. president, for one thing.

“We are close to the tipping point where global warming becomes irreversible. Trump’s action [pulling out of the Paris Climate Agreement] could push the Earth over the brink, to become like Venus, with a temperature of two hundred and fifty degrees, and raining sulphuric acid,” Hawking said.

Artificial intelligence

Along with the likes of Elon Musk, Hawking was one of the most prominent voices warning of the dangers of so-called general artificial intelligence—AI that isn’t just designed for a narrow task, but that can improve itself to a point where a new superintelligence leaves humanity in the dust, and robots ultimately replace us.

Hawking’s views on AI weren’t entirely gloomy, though. He also noted that the technology could help us get rid of disease and poverty, and reverse climate change damage (something that he otherwise predicted would turn Earth into a “ball of fire”within six centuries).

“Success in creating effective AI could be the biggest event in the history of our civilization. Or the worst. We just don’t know,” he said late last year.

(This is an apt moment to note that a phrase often attributed to Hawking—”The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.”—probably wasn’t his.)

Where to go?

Alright, so we need to flee death-rain and killer robots. Where is Hawking’s “Planet B”?

For the last decade, Hawking had been calling for colonies on the Moon and on Mars. But those are just staging posts—the physicist had his eye on the closest star system to ours, Alpha Centauri.

A couple years ago, Hawking joined a team of scientists and investor Yuri Milner to design computer chips that could fly through space, aided by a super-thin sail. The Breakthrough Starshot program aims to send these “interstellar sailboats” out as probes, in order to return imagery from Alpha Centauri that might give us clues as to likely locations for colonization.

Yes, Alpha Centauri is very, very far away, but the idea here is to propel these nanocraft using a 10 gigawatt light beam trained on their sails. Travelling at a fifth of the speed of light, the probes might be able to make the two-way trip within a few decades, the scientists hope.

Hawking will never get to see that plan come to fruition. But who knows? Perhaps we will.