The world according to Snafu - Time Travel

A recent post referring to the novel 'The Time Traveller's Wife', prompted me to think about time travel.  As a long term Science Fiction reader, I have always been fascinated by time travel stories. As far as I am aware time travel was first fictionalised by H G Wells, although I could be wrong, but it has since been a major part of the SF genre.

It presents all kinds of wonderful possibilities for writers, paradox, discovery, solving crimes and mysteries, parallel timelines and an opportunity to write an historical novel with modern characters. Mark Twain used that theme when he wrote 'A Connecticut Yankee in the Court of King Arthur' and many writers followed.
The paradox theme of time travel has fascinated a lot of people, for instance the one about shooting your grandfather so that you are not born is usually trotted out, but some have gone as far as being your own grandfather. In the 1940s Heinlein wrote one along those lines called ‘All you Zombies’ and another less incestuous paradoxical story, ‘By his Bootstraps’  both of which are circular in time.

Heinlein used the pseudonym of Anson MacDonald for several of his earlier short stories

Some writers have looked at the way in which altering events in the past will change the present, nicely done in Ray Bradbury’s ‘ A sound of Thunder ‘ where it occurred accidentally.  This was made into an abysmal movie; enough said.  The movie series ‘Back to the Future’ involved a lot of deliberate changes occurring in time giving rise to different futures. Many stories deal with unexpected changes to history and some where you cannot change it at all, and so anything you do is already accounted for in history. This idea has occurred regularly and is an important concept in many novels. Moorcock’s ‘Behold the Man’, Ward Moore's 'Bring the Jubilee' and John Boyd’s ‘The Last Starship From Earth’, all rely on the idea that the past is set and if you go back you are not changing it but making it happen the way it should.

Interfering with history brings about victory for the North in the civil War

On TV, Dr Who is a constant time tourist but never seems to change time much. In a recent episode the idea that committing suicide would get you out of a tight spot since you would remove the paradoxical time loop in which you are trapped and come back to life, something that Poul Anderson used long before in his time travel stories in the 1950s.

One of the more unlikely ideas, often embedded in the main plot, is an object that has no origin. The moving story by Richard Mathewson, ‘Bid Time Return’ has one of these, the main character is unexpectedly given a watch by a very old lady. Later in the narrative, but earlier in time, he gives it to her when she is a young woman after he travels back in time. Giving it to her means that she can give it back to him when she meets him as an old lady and so it becomes a paradox, since it has no proper origin.

These objects are often called a ‘bootstrap paradox’, generally thought to have derived from Heinlein’s By His Bootstraps, where a notebook has a similar history in that story. His older self gives it to his younger self to teach him what he needs to know to become his older self…
Recently Time travel has featured in children's stories, some of which are well worth reading.

Time travel can be dangerous if you go back to WWII

Change the future and avoid a war, or cause a war we can survive, which is best choice for the H Bomb Girl?

Like the more recent 'The Time Traveller's Wife' the hero in this novel can travel in time without a time machine

One theme which occurs now and then is a time war, where the protagonists attempt to write each other out of history by changing their past, often on a cosmic scale. A good example of this is Fritz Leiber’s ‘The Big Time’, but many others have written on the same theme and the Terminator movies are based around this kind of warfare.

The spiders and the Snakes fight it out using humans as foot soldiers recruited from throughout all of Earth's history, but all the action in this great little novel takes place in an R&R facility away from the battle front.

 In several stories time police exist to protect against random changes brought about by illegal time travellers and in Asimov’s 'The end of Eternity' the organisation ‘Eternity’ is regulating history by making changes that are supposed to create a better future.

An elite force patrol the timelines looking for time crimes with some unexpected twists

He is ordered to change her past, but Harlan knows this will erase his lover from history because she would never be born, so he cannot bring himself to change her timeline, instead together they end Eternity

So much has been written on the subject by many well-known writers, but very few of them have acknowledged that to travel in time, you must also travel in space because the Earth is moving.  Just moving in time is going to strand you in an empty vacuum nowhere near the planet Earth. Dr Who occasionally remembers this but more often than not the writers ignore it.

An unusual time travel story by James Tiptree jr, a woman writer by the way, recognises this in her ‘The Man Who Walked Home’. This intriguing story is written so that it takes a while for the reader to understand what is actually taking place as the story unfolds. This is one of the few that takes into account that time and space is inseparable.

 In the comic 2000AD, in a 1980’s episode, one of the characters had a ‘time bomb’, not a timed explosive device, but a device which warped you a few minutes through time. The result was that you were suddenly dumped into outer space, because the Earth had moved on whilst you were in the time warp.

This use of space-time is very rare, most time travellers just pop up in the same place on the Earth as if it was not moving during the elapsed time that you have just short circuited. Some rationalise this by saying that you are moving with the Earth and so that your relative motion is retained, but that implies that you and the Earth are travelling through time together. If you are fixed in place with the earth’s movement, you will simply be frozen in place until you arrive at the new time. This would be kind of annoying for us normal travellers, because the earth would be littered with frozen time travellers hanging around like statues until their timer pings and they come back to life.
If as time travel stories suggests, you vanish and reappear retaining your original motion you would be still heading in the particular direction the Earth had been going before you jumped and because the Earth circles the sun, its direction is changing hour on hour, you would be flying away at a tangent.
The Earth is rotating too, so ignoring the other movement of the Earth, if you want to arrive in the same place, you can only jump in exact multiples of 24 hours, a few minutes’s difference would make you end up in Cornwall instead of Essex or vice versa, but it is not even that simple. Consider time travelling ahead one day. When you arrive, we could assume you would still be moving in the same direction the Earth was going when you left, but you will only have been moving this way for a few subjective seconds that you experience during the time jump, whilst the Earth has kept on going for a whole day and it is moving at about 30km per second around the sun. Since its orbit is a curve, you will now be heading out from Earth’s orbit and so be several miles away from the ground.

You would do well to have started out with either a parachute or a hang glider strapped to you. Attempting a time jump for more than a day and you would need some kind of re-entry vehicle with ablative tiles on it or you would burn up as you plummet down to earth. Travelling backwards in time to go back a day and you could reappear inside the Earth’s core, which would be a bit unfortunate. Assuming you do more or less keep pace with the Earth, if you try to go back in time for a year, you would meet the Earth coming at you like a train. Not cool. Move in time one hundred years either into the future or the past and you would be in deep space with the Earth millions of miles away and hopelessly out of reach.
If somehow you can cancel out the movement problems and arrive in the same place and time of day, if you start at midday and jump six months to the same time of day, you would arrive standing on your head, since the place you started from is now on the far side of the sun and facing your finishing point.

Scientists did not coin the term Space-time for nothing. They are closely related, you cannot do anything without spending some time on doing it. Even reaching for the ketchup on the dinner table involves time. As close as it is to you, it is still separated by time. You can only ever see it as it was a few picoseconds ago, because even light needs some time to reach you. To move it takes more time, whilst both your hand and the ketchup exist at the same time it still takes time for you reach it and pour it out. So everything around you is removed from you in both space and time, showing there is a strong link between the two. Nothing takes no time when moving through space, likewise moving in time displaces you in space.

So time travel is not as straightforward as it seems and to jump in time and land in the same place on the ground would require a lot of movement in space too, with some very complicated calculations to find your way to the place the Earth is/was when you arrive. The most practical time machine you could build would have to be a space-ship as well. You could then head for an empty spot in the solar system where it would be safe to emerge at the end of the time jump, having calculated what is/was in the vicinity at the time you intend to travel to. You would not want to arrive where another object was/is when you arrive. Once you have jumped through time, you would then have to fly your space-ship-time-machine to the new position where the Earth has moved on to, or come from, depending on which way you are going in time. The length of journey to the earth would depend on how far you have jumped through time and could be a considerable distance if you have travelled far in time. So the time jump would need to be a space jump too. Of course, you could call this space-ship-time-machine a ‘Time and Relative Dimension In Space’ machine, the initials of which makes the word TARDIS.
Now where have I heard that before?

So the creators of Dr Who did understand the problem once, but time travel seems to have lost some of the science in science fiction.