From the BBC:
Albert Einstein thought the three dimensions of space were linked to time – which serves as a fourth dimension. He called this system space-time, and it’s the model of the Universe that we use today.
But Einstein also thought it was possible to fold space-time, creating a shortcut between two distant locations. This phenomenon is called a wormhole, and it can be visualised as a tunnel with two openings, each emerging at different points in space-time.
Wormholes might exist naturally in the cosmos; indeed, scientists in Russia are trying to use radio telescopes to detect them. But using wormholes for time travel won’t be straightforward.
Indeed not. Unless everything is absolutely determined, some wise person from the future has already gone back through a wormhole and altered the present so that we can’t go anywhere. Lee Smolin of the Perimeter Institute says time travel is probably impossible:
“If what’s real is the present moment and the past is only real in the sense that there are memories and records of it in the present, and the future is still to exist… there’s nowhere to go.”
But a colleague, Neil Turok, invokes quantum mechanics.
“I think it’s clear to me that there is some probability of us going backwards in time,” he says. “In quantum physics, nothing is impossible – particles travel through walls!” More.
Sure they do, but do they travel back into the mediaeval era?
It’s fun thinking about this stuff though.
See also: Is time travel a science-based idea? (2017)
Apparently, a wormhole is our best bet for a time machine (2013)
Does a Time Travel Simulation Resolve the “Grandfather Paradox”?