Well, that didn't take long. After saying yesterday that I was going to stop searching for inspiration and let it come to me, up it pops up yesterday evening in the form of Horizon on BBC2. It was exactly the sort of scientific documentary I like - talking about outlandish theoretical physics and showing just how bizarre this universe of ours is. The subject last night? Time travel. And not any of your Doctor Who, jump-in-a-police-box malarkey (though the daleks did put in an appearance during the show and the closing titles were accompanied by the haunting strains of the Doctor Who theme), either. We're talking about real time traveling.
The first person to really consider what time was was Isaac Newton. He reasoned that time was constant, that it applied everywhere in the universe in exactly the same way. One unfortunate consequence of this view was that it meant that everything that ever happened was proscribed from the very beginning. I.e. we are nothing more than puppets acting out what was ordained at the beginning of time. Not a particularly appealing thought.
Then along came Einstein a couple of hundred years later and ripped that to shreds. According to his theory of relativity, time slows down as your speed increases. Suddenly, the prospect of time travel became real. If you set off into space and travel near the speed of light for a year before getting back to earth then the people you left behind might be ten years older. You would have traveled nine years into the future. How cool would that be? In fact, there are certifiable time travelers living on Earth, right now. There is a Russian cosmonaut who has spent more than 700 days on the spacestation Mir, traveling at upwards of 17000 mph. When he got back to earth again after his last trip, he had effectively traveled 1/50th of a second into the future. Not much, I'll grant you but he had traveled through time nonetheless.
The problem is, for 'viable' time travel to be made a reality, you would want to be able to travel back in time as well as forward and relativity says that would mean traveling faster than the speed of light, something that Einstein showed wasn't possible. So time travel was still just a fantasy after all.
That assumed that time travels along a straight line from beginning to end. A friend of Einstein's, Kurt Goedel, wondered what would happen if, instead, time looped. If it did then he showed that it would be possible to take a shortcut through spacetime and go back as well as forward. Unfortunately for him, for time to loop, the universe has to be spinning and our universe doesn't spin (though how we know that I've got no idea). His ideas inspired a whole load of other physicists to look for ways to 'get round' Einstein's requirement to travel faster than light in order to go back in time. Many of them have been successful and shown, mathematically, that it would be possible to do it. Again, there are downsides to these theories. The absolutely vast amount of energy needed to make them happen being one, the fact that a time machine wouldn't be able to travel back to a time before it was built being another (though this wasn't explained at all). So we're now in the position where time travel is theoretically possible but just isn't practical.
But there is another way to 'travel' through time. Instead of you going to the past, why not bring the past to you? Not really, of course but in a simulation. If computers continue to improve at the rate they have been doing for the last twenty or thirty years, it will eventually be possible to run a simulation of the past that would be so good it would be indistinguishable from the real thing, Even down to how the people in the simulation think. Of course, if you can run one simulation, you can run billions of them, to see what variations there are. And that raises a nasty question. Are we real or do we just exist in some future simulation of the past? And if it's the latter then are we like the 'real' us at all?
I'd like to think that the real me is the slim attractive one from the simulation next door.