The world's most famous physicist has decided to go public with the answer to time travel. (Maybe so we can escape those aliens he warned were out to kill us?) Whatever the reason, Hawking offers advice for any of us thinking of trying to build a working time machine.
"I used to avoid talking about it for fear of being labelled a crank," wrote Hawking in the Daily Mail. "But these days I'm not so cautious."
So what has Hawking's big brain come up with?
If you were hoping that the much-talked-about wormholes might be the answer, sorry. According to Hawking:
I think a wormhole like this one can't exist. And the reason for that is feedback. If you've ever been to a rock gig, you'll probably recognise this screeching noise. It's feedback. What causes it is simple. Sound enters the microphone. It's transmitted along the wires, made louder by the amplifier, and comes out at the speakers. But if too much of the sound from the speakers goes back into the mic it goes around and around in a loop getting louder each time. If no one stops it, feedback can destroy the sound system.
The same thing will happen with a wormhole, only with radiation instead of sound. As soon as the wormhole expands, natural radiation will enter it, and end up in a loop. The feedback will become so strong it destroys the wormhole. So although tiny wormholes do exist, and it may be possible to inflate one some day, it won't last long enough to be of use as a time machine.
And as for a black hole? Those probably won't work either:
A supermassive black hole is a time machine. But of course, it's not exactly practical. It has advantages over wormholes in that it doesn't provoke paradoxes. Plus it won't destroy itself in a flash of feedback. But it's pretty dangerous. It's a long way away and it doesn't even take us very far into the future.
So what's the solution? Turns out you've got to feel the need—the need for speed!
If we want to travel into the future, we just need to go fast. Really fast. And I think the only way we're ever likely to do that is by going into space. The fastest manned vehicle in history was Apollo 10. It reached 25,000mph. But to travel in time we'll have to go more than 2,000 times faster. And to do that we'd need a much bigger ship, a truly enormous machine. The ship would have to be big enough to carry a huge amount of fuel, enough to accelerate it to nearly the speed of light. Getting to just beneath the cosmic speed limit would require six whole years at full power.
But before you get started on those time machine blueprints, you'd better get more details on Hawking's theories over at the Daily Mail.