A blend of Science and philosophy teases out the paradoxes surrounding whether it will ever be possible to slip back and forth between the ages.

Time Travel is a curious thing. Imagine having the whole of history at your very finger tips; it would be easy to travel back to the day when JFK was shot, to discover if it really was Lee Harvey Oswald behind the assassination and reveal the identity of that troubling ‘Babushka Lady’, or to hop over to ancient Egypt to watch the pyramids being made, or discover the meaning behind Stonehenge. The possibilities are endless, but so is time, and any talk of time travel, or travelling backwards in time at the very least, opens up all sorts of troubling questions and complexities.

In ‘Time Machine Tales: The Science Fiction Adventures and Philosophical Puzzles of Time Travel’, Paul J Nahin delves into questions surrounding time travel as presented through the world of science fiction. A science writer by trade, Nahin takes a philosophical seat here, leaving behind the dreary equation-filled technical notes of the past in favour of colourful anecdotes from favourites including Arthur C Clarke and Isaac Asimov, interjected with thoughts and theories of leading physicists. Quite fitting, perhaps, as not so long ago, talk of travelling through time was relegated solely to realms of science fiction.

As excited as many sci-fi fanatics might get at the thought off hopping forward or backwards in time, for the most part such ideas have been dismissed as implausible. After all, the basic premise of travelling backwards in time inverts the cause and effect paradigm by which we all understand life, by demanding backwards causation. Today though, talk of time travel is a much more respectable business. As Nahin points out, the only reason time travel seems so implausible is because there is no rational scientific theory to explain it.

To put this into context, in 2013 Professor Brian Cox announced that time travel is theoretically possible, but only into the future, and that once in the future, it is impossible to go back. This is due to Einstein’s special theory of relativity (hypothesised in 1905 – it’s old news now), which states that when an object approaches the speed of light, time within the object slows down. The idea being that the closer a rocket ship travels relative to the speed of light, the slower the seconds pass by on a watch worn by an astronaut compared to that of an identical one back on Earth. Of course, no technology exists today that would be able to take someone very far into the future – the energy required would be astronomical – but it has already been done, albeit on a very small scale, by Russian cosmonaut Sergei Krikalev, who spent 803 days, 9 hours and 39 minutes in space and returned to Earth 0.02 seconds into his own future.

With the right explanation, time travel doesn’t seem so far-fetched after all. Not so, though, with the idea of travelling to the past.

Backwards travel conjures up far more issues, not least the cumulative audience paradox. This is the idea that, if backwards travel were possible, there would be untold numbers of time tourists present at the crucifixion of Christ, the assassination of John Lennon, the battle of Battenberg, the birth of Prince George and any other historic event that anyone could ever have even the slightest interest in. Of course, as Nahin points out, the absence of temporal visitors is an objection to the actuality of time travel, and not the possibility of it. It could be, as many science fiction writers have suggested, that in the future, there are certain rules forbidding time travel to the past.

If it seems impossible, though, why are we so obsessed with talk of time travel? The answer is simply because, although we believe it to be impossible, it has not yet been proven to be impossible, and many are simply not satisfied with this. Professor Stephen Hawking has said that he believes there is new physics yet to be discovered that will forbid would be time travellers from travelling up and down the centuries – but until such a discovery is made, and proven, the conversation is likely to continue.

This is an unusual book, falling somewhere into the murky depths between philosophy and physics. Nahin approaches the science fiction of the past using current discussion from leading physicists and philosophers, to create a book which will make you pause, think, and quite possibly probably scratch your head as you try to contemplate the reality of time machines crashing into themselves, the implications of the bootstrap paradox, and the mind-bending characteristics of a Möbius strip.

This review was first published online for E&T magazine