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Leaving Earth -

For decades, the theoretical physicist had been telling humans to begin the process of permanently settling in other planets, which made headlines on various occasions.

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Leaving Earth -

Hawking claimed that humankind would eventually fall victim to a disaster so big that we would go extinct, maybe sooner rather than later.

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Leaving Earth -

In 2016, he told the BBC: "Although the chance of a disaster to planet Earth in a given year may be quite low, it adds up over time, and becomes a near certainty in the next thousand or 10,000 years.

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Colonizing other planets and solar systems -

To ensure the survival of humankind, Hawking believed we would have to actually colonize other planets and solar systems.

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Colonizing other planets and solar systems -

"Spreading out may be the only thing that saves us from ourselves. I am convinced that humans need to leave Earth," he said at a Norwegian science and arts festival in 2017.

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The rise of artificial intelligence -

Hawking saw the opportunities from the advances in artificial intelligence, but he also warned about the dangers.

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The rise of artificial intelligence -

In 2014, he told the BBC that "the development of full artificial intelligence could spell the end of the human race."

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The rise of artificial intelligence -

Hawking believed basic artificial intelligence developed so far had already proven very useful. For example, the tech he used to communicate incorporated a basic form of AI.

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The rise of artificial intelligence -

But Hawking feared the consequences of advanced forms of machine intelligence that could match or surpass humans.

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Gene editing -

In his posthumous collection of articles and essays 'Brief Answers to the Big Questions,' Hawking predicted that genetic editing techniques will give rise to a breed of "superhumans."

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Gene editing -

"I am sure that during this century, people will discover how to modify both intelligence and instincts such as aggression," he wrote.

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Gene editing -

"Once such superhumans appear, there will be significant political problems with unimproved humans, who won't be able to compete," he wrote. "Presumably, they will die out, or become unimportant. Instead, there will be a race of self-designing beings who are improving at an ever-increasing rate."

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The biggest threat to Earth -

In the same book, Hawking predicted that the number one threat to Earth is an asteroid collision, just like the one that killed the dinosaurs.

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The biggest threat to Earth -

However, "we have no defense" against that, Hawking wrote. On the other hand, he saw global warming as a more immediate threat.

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Climate change -

Hawking was particularly concerned of a so-called tipping point, where global warming would become irreversible.

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Climate change -

He also expressed concern about America's decision to pull out of the Paris Agreement in 2017.

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Climate change -

"Trump's action [pulling out of the Paris Agreement] could push the Earth over the brink, to become like Venus, with a temperature of 250 degrees and raining sulfuric acid," Hawking told the BBC.

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Climate change -

The UN's Intergovernmental Panel on Climate Change (IPCC) also warns of the potential risk of hitting climate tipping points, as temperatures increase.

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The Earth will turn into a ball of fire -

Hawking theorized that the planet would turn into a giant ball of fire by 2600 due to overcrowding and energy consumption. This would make Earth uninhabitable.

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The Earth will turn into a ball of fire -

"With climate change, overdue asteroid strikes, epidemics and population growth, our own planet is increasingly precarious," he told the BBC in 2017.

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The Earth will turn into a ball of fire -

This was one of the reasons why Hawking defended the idea of humans permanently settling on other planets.

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Alien contact -

Given that Hawking spent most of his life looking at space, it's not surprising that he reflected on whether there are other lifeforms out there.

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Alien contact -

There's even a whole field of science, known as SETI (Search for Extra-Terrestrial Intelligence) dedicated to listening for signals from intelligent beings elsewhere in the universe.

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Alien contact -

However, Hawking cautioned against trying to actively hail any alien civilizations that might be out there.

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Alien contact -

In 2010, he told the Discovery Channel: "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans."

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The best idea humanity could implement -

In 2010, when asked by Time magazine what scientific discovery or advancement he would like to see in his lifetime, Hawking replied with "nuclear fusion." This would be a new source of carbon-free energy, which melds two hydrogen atoms together to produce a helium atom and a lot of energy.

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The best idea humanity could implement -

"I would like nuclear fusion to become a practical power source. It would provide an inexhaustible supply of energy, without pollution or global warming," he said.

Sources: (BBC) (The Guardian) (World Economic Forum) (CNBC) (Time) (Discovery Channel)

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