The idea of a working time machine is one of those increasingly few ideas from sci-fi which really has no basis in reality.
That said, some people aren't giving up yet.
A new documentary ('How To Build A Time Machine' by Jay Cheel) looks set to be a fascinating look at two men who are still working on making their own breakthroughs in time travelling technology.
One of these men is Ronald Mallett, a physicist whose father died of a heart attack when he was a young boy. As a result he has apparently dedicated his career to building a time machine - or at least working on the physics behind one - to try and save his father.
Mallett has argued - without, it has to be said, much support - that with sufficient energy a laser could create a 'closed timelike curve' that might make travel into the past possible.
He wrote in a 2003 paper: "Exact solutions of the Einstein field equations are found for the exterior and interior gravitational field of an infinitely long circulating cylinder of light. The exterior metric is shown to contain closed timelike lines."
Indeed his story has been told before and gained widespread attention, most notably in a 2007 episode of the American radio show and podcast This American Life.
The other half of Jay Cheel's film focuses on a different character altogether. Rob Niosi is building a time machine too, but instead of physics and maths he's using wood, steel and hard work. His project is actually just a replica of the Time Machine prop from the famous George Pal movie, and while it was supposed to take just three months it's so far 11 years in - without any end in sight.