“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 travelers”.
None showed up – but time travel itself might actually be possible, according to one astrophysicist (although it won’t be easy, and it involves alarming forces like supermassive black holes).
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.”