‘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 travelers, complete with champagne and a banner saying, ‘Welcome time travelers’.
None showed up, in case you were wondering.
But could a time machine actually be possible? Doctoral student Caroline Mallary, at the University of Massachusetts Dartmouth has published a design for a real, working time machine (which is nothing like a modified DeLorean, sadly).
But it won’t be easy to build, says Gaurav Khanna, Professor of Physics, University of Massachusetts Dartmouth, writing for The Conversation.
Khanna says, ‘Mallary’s model consists of two super long cars – built of material that is not exotic, and have positive mass – parked in parallel. One car moves forward rapidly, leaving the other parked. Mallary was able to show that in such a setup, a time loop can be found in the space between the cars.
‘If you suspect there is a catch, you are correct. Mallary’s model requires that the center of each car has infinite density. That means they contain objects – called singularities – with an infinite density, temperature and pressure.
‘Moreover, unlike singularities that are present in the interior of black holes, which makes them totally inaccessible from the outside, the singularities in Mallary’s model are completely bare and observable, and therefore have true physical effects.
‘Physicists don’t expect such peculiar objects to exist in nature either. So, unfortunately, a time machine is not going to be available anytime soon.’