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.