‘If time travel is possible, where are the tourists from the future?’ Stephen Hawking asked in A Brief History Of Time.
Hawking also famously staged a party for time travellers, complete with champagne and a banner saying, ‘Welcome time travellers’.
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Writing in Forbes, astrophysicist Ethan Siegel of Lewis & Clark College says that people would need to construct a wormhole and move one end of it at the speed of light.
Then (in theory) you could step through it and arrive at a point backwards in time, Siegel says.
The problem is that to do so, you’d need negative mass/energy particles (which have never been discovered) – oh, and you need to make a black hole.
But if you can do that, you can travel in time, Siegel says in Forbes’ Starts With A Bang blog.
Siegel writes, ‘If this negative mass/energy matter exists, then creating both a supermassive black hole and the negative mass/energy counterpart to it, while then connecting them, should allow for a traversable wormhole.’