Brian Clegg - Time travel : Ten Short Lessons

Time Travel
Ten Short Lessons

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Ten Short Lessons

Brian Clegg

Johns Hopkins University Press

Baltimore

First published in Great Britain in 2021

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Few television shows have had the lasting appeal of Doctor Who, first broadcast in 1963 and, despite a hiatus, still going strong over fifty years later. I can still remember the sense of mystery when the first episode went out in the days of black-and-white TV. It was quite different from anything else Id seen in my young life. And, dramatically, the series was launched during a week that was branded on the memories of anyone old enough to remember it.

At 12.30 p.m. Central Standard Time on 22 November 1963 in Dallas, Texas, US President John F. Kennedy was assassinated. TV broadcasts in many countries came to a standstill. At 5.15 p.m. in the UK the next day, the first episode of Doctor Who was broadcast. A combination of power cuts and the shadow of Kennedys assassination meant that many missed that first episode, so it was rebroadcast the following week. But what made the launch of Doctor Who particularly poignant as a series that arrived at such a definitive point in history was that the stand-out feature of the show was time travel.

In part, time travel opened up new vistas. As well as exploring alien planets, the Doctor and his companions could visit historical events. The BBC envisaged this originally as an educational opportunity, though it soon became clear that a visit to the past or future opened up dramatic possibilities and any educational element was given a light touch. Equally, time travel made it possible to explore paradoxes when, for example, it became feasible to go back in time before a disaster and change things so that it never happened. In practice this has rarely featured in the programme, but time travel is a tempting snare for the imagination.

These paradoxical possibilities would feature more strongly in some Hollywood ventures into time travel, from Back to the Future to Looper and beyond and, of course, in literary classics such as Ward Moores Bring the Jubilee and Douglas Adams Life, the Universe and Everything. But, generally speaking, the audience for science fiction has taken time machines to be a fun convention that allowed for an illusory ability to be played out, because the assumption for many was that time travel would never be possible in reality.

Although science fiction, unlike fantasy, tries to stick to what is physically possible, it has always featured a handful of special conventions where something that is believed to be infeasible is allowed to happen. The rules allow these unlikely concepts to be introduced, after which the storyline has to follow what is practical within the known world. An early example of this was in the H. G. Wells novel The First Men in the Moon. Wells introduced an imaginary substance, cavorite, which blocked gravity. But once he had brought this impossible invention into the storyline, the consequences moved forwards logically.

Such frequently used cheats have included faster-than-light travel, hyperspace, force fields or shields, tractor beams and, of course, time travel. And in most of these cases, it is hard to see how the technology or concept could ever be made real. But time travel is the exception that proves the rule. Because, remarkably, Einsteins theories of relativity have made it clear that making a time machine is more a matter of engineering challenges than physical impossibilities. Time travel is real and is happening right now.

Travelling through time has a seductive appeal for practically everyone. Who wouldnt be fascinated by a visit to the past? Admittedly, it would be a problem if you worked in the gambling industry: there would be no future in lotteries or betting if anyone could pop back and place a bet on a certain outcome. But for the rest of us, its a beguiling prospect. History and archaeology have their limitations. It would be amazing to be able to watch or take part in great events from history and see what really happened, or to see living dinosaurs striding across the Earth, no doubt turning palaeontology on its head. For that matter, on a personal level it would be transformative to have the chance to see dead relatives again, to revisit things you never got the chance to say. And then theres the future whether that be dark or bright. The reality of things to come would be science fiction come alive, a heady plunge into a speculative world.

So lets take a step beyond the Doctor, Doc Brown and all those time-travelling fictional characters and take a real-world trip in the fourth dimension.

Clearly any real body must have extension in four directions: it must have length, breadth, thickness, and duration.

H. G. WELLS (1895)

Its no surprise that time travel crops up regularly in fiction, but it is quite shocking to learn that it can be done for real. In one sense, we all travel in time. Our conscious moment of the present seems to tick forwards, gliding from hour to hour and day to day. And, thanks to memory, we can slip back into the past, revisiting another time even if memory is now recognized as a mental construct that inaccurately recreates what once was. Yet this picture of time travel seems like cheating. Its not what we hope for. Its a bit like saying we are physical travellers sitting in a chair at home because the planet Earth is constantly in motion around the sun. Thankfully, though, its only the beginning.

This is because true time travel the ability to move to a time other than the present based on science and technology is real. There is nothing in the laws of physics that prevents time travel, and the science behind it has been experimentally proved many times over. We can, with H. G. Wells time traveller, take on a journey in a fourth direction that is different from the spatial three. A trip through the dimension of time.

Every experience you have involves movement through space. It may be your body moving, or something more subtle: you couldnt see, for example, without photons of light moving from the source to your eyes, breathe without air molecules moving into your lungs or even think without the movement of electrical impulses in your brain. And all movements involve some elapse of time: nothing can move instantaneously. Thats a reality that was challenged in the fifth century BC by an ancient Greek philosopher called Zeno. According to Zeno and the Eleatic school, change and movement were nothing more than illusion. Zeno illustrated this viewpoint with a number of paradoxes.