In an interview with Good Morning Britain today, he expressed concern about the "definite swing to a right wing, more authoritarian approach" in US politics and the emergence of President Donald Trump.
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While Hawking said America was "still a place I like and admire in many ways", he was uncertain about returning.
"I would like to visit again and talk to other scientists, but I fear that I may not be welcome," he said, while also pointing to the President's environmental policy as a key area of concern.
"He should replace Scott Pruitt at the Environmental Protection Agency," Hawking said. "Climate change is one of the great dangers we face, and it's one we can prevent. It affects America badly, so tackling it should win votes for his second term. God forbid."
Hawking said Trump had been elected by those "who felt disenfranchised by the governing elite in a revolt against globalisation".
The scientist also discussed Brexit and said the leaving the European Union "threatens Britain's status as a world leader in science and innovation".
He warned against a hard Brexit, saying: "That would leave us isolated and inward-looking. Instead, we should retain as many links as possible with Europe and the rest of the world, particularly China."
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Last year, Hawking said Brexit may be too "complex" a situation, even for him. He told the Prime Minister in November: "I deal with tough, mathematical, complex questions every day, but please don't ask me to help with Brexit."
On a more positive note, Hawking also revealed he's planning a trip to space, after Sir Richard Branson offered him a seat on his Virgin Galactic spacecraft.
Hawking said: "My three children have brought me great joy - and I can tell you what will make me happy, to travel to space."
"I thought no one would take me but Richard Branson has offered me a seat on Virgin Atlantic, and I said yes immediately," he said.
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In an interview with ITV's Good Morning Britain on Monday, British scientist Stephen Hawking claimed that he fears he "may not be welcome" in the United States now that Donald Trump is President. Hawking was particularly critical of the appointment of Scott Pruitt as head of the Environmental...
Stephen Colbert trashed President Donald Trump’s proposed rollback of Obama-era environmental regulations on Tuesday.
The “Late Show” host mocked the... Huffington Post - PoliticsAlso reported by •Daily Record