Time Travel

You know how it is.  A car comes out of nowhere, and slam!, before you know it, it’s 1973.  Are you mad, in a coma, or back in time?

Time travel in science fiction, such as that from the BBC’s Life on Mars, is often genius.  And so it may become in science fact.

It all started in 1895 with The Time Machine.  H G Wells was, naturally, the first to realise that, if there’s one thing in this big new Universe you can’t tamper with, it’s time.  So, he tampered with it.  Figuring that space made up three dimensions, Wells volunteered time as the fourth.  And if you can move freely in 3D, why not also in time?

Time travel happens every day, of course.  Time’s arrow moves us forward as we experience a sequence of events.  And consider this: stargazing is a form of time travel.  Our Universe is so unimaginably vast that light from its outer limits takes longer than twice the age of the Earth to reach our telescopes.  The nearest star system, Alpha Centauri, is about 25 trillion miles off.  Light, the fastest thing known to science, takes more than four years even from those nearby suns to hit the naked eye.  So, we see the sky as it was in the past.

The truth is, if you think about this stuff long enough, your head can start to swim!  Since nothing happens instantaneously, and light takes time to reach the human eye, even a ship’s sail, for instance, emerging on the distant horizon is seen as it was a fraction of a moment ago.  This phenomenon would be far more obvious if the speed of light was much slower than its 186 000 miles per second (300 000 km per second).

The idea of time travel in fiction is usually one in which the alleged illusion of time’s arrow becomes (a) a confusion of time-hopping and causal relationships (Groundhog Day), or (b) a multiplicity of possible timelines (Back to the Future).  DCI Sam Tyler, from Life on Mars, was not the first to be unstuck in time.   Billy Pilgrim, the protagonist in Kurt Vonnegut’s wonderfully creative anti-war classic Slaughterhouse Five, is similarly unstuck, and Doctor Who is founded on the idea that time is a Wellsian dimension that can be traversed at leisure!

Wells’ invention of time as the fourth dimension came a full decade before Albert Einstein rewrote physics with his Relativity Theory.   And Einstein’s treatment of space and time as part of a four-dimensional spacetime has exploded into today’s conception of a multi-dimensional Universe.  String theory predicts that spacetime has 10 or 11 dimensions, but that our Universe, when measured along these additional dimensions, is subatomic in size.

Another piece of time travelling genius from science fiction is Carl Sagan’s Contact (1985).  The famous US astronomer sought expert advice of black hole expert Kip Thorne before making the film version of Contact (1997).  Sagan wanted to know whether black holes could be used to travel in time. Thorne’s advice: black holes are dangerous; use a WORMHOLE idea instead.  Indeed, Sagan’s enquiries about time travel sparked a whole new field of physics, with dozens of scientific papers by some of the world’s best physicists, including Kip Thorne himself and cosmologist Paul Davies who wrote How to Build a Time Machine (2001).

There are still technical issues before a wormhole time machine becomes a reality.  We’ve not yet found a wormhole, let alone learned how to control one.  But it’s a stunning fact that, early in the C21st, we have now reached a stage in our understanding of nature where time travel is even a bare possibility.

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