Time Travel - Where not when.

The problem with time travel in fiction . . .

You may be surprised to find that this article is not about time travel, not really anyway. Most time travel movies focus on the mechanism of the 'time' part of time travel and conveniently forget the real problem.

Let's take an example that most people will be familiar with. In the movie 'Back to the Future', Marty and Doc fire up the DeLorean, accelerate past 88 mph and boom, they travel from 1985 back to 1955 and appear in exactly the same place. So much so, that in the later movie, the train tracks even line up across the years! This is repeated throughout the franchise and many other time-travel movies. There is a fundamental assumption that nothing has moved, that everything is locked in place over time. Sadly for the realists among us this couldn't be much further from the truth! In reality, in 1955 the Earth would have been nowhere near where it was in 1985, and Marty and Doc would have appeared in the cold dead vacuum of space. Not great for the story in fairness.

The obvious movements of the Earth that we are all familiar with are:-

• The Earth spins on its axis (once every 24 hours, although there is some complexity here not worth mentioning). A day!

• The Earth rotates around the sun (in approximately 365 days and a ¼) A year!

  
  

That's more than enough movement to be a problem for a time machine that only travels through time. A craft that can travel in time and space could presumably travel to the destination after the time travel bit, That's if these were all of the variables, as they are relatively 'small' distances and could be calculated and presumably traversed.

Except, that's not the end of the problem.

• The Solar System rotates around our galaxy, the Milk Way (in approximately every 230 Million years)

• The Milky Way is moving within the local group of galaxies (toward the Andromeda galaxy) at a speed of over 500km per second.

  
  

and finally . . .

• The general expansion of the Universe!

  
  

If you add all of that up, that's a lot of movement. So the real question is, how do you define our position in the Universe?

A coordinate system needs two things to work as the movie Stargate explained. It needs some coordinates in however many dimensions we are working in, and we need an origin.

All coordinates are relative to something, whether it's the Greenwich Meridian, the Sun, or something else. It is fine for a local system to define where the chemist is, your location on a road, even a spaceship travelling to the nearest star. There is always a nearby fixed point to use as a reference. But when it comes to determining an absolute position in the Universe you're stuffed because there is no overall fixed point, no origin.

By definition, there is no fixed point in a relative universe.

Once you've time-travelled you may have a long journey to get to your destination after the time travel bit. This assumes that you haven't materialised in the middle of a star or any other celestial body. As most of space is empty this is probably not the main issue.

Ironically, by the time you travel to the place you were aiming for, chances are it will be a different time period by the time you get there. After all, space is big. Very big.

With some sci-fi magic, it's not hard to imagine a craft that can solve these problems: its the TARDIS.

The TARDIS can travel in time and space. It was built by some super clever Time Lords with access to the Time Vortex and presumably some equally clever calculations that can work out absolute positions in space based on time. Perhaps there's an underlying fabric to the Universe that would allow a fixed origin that we haven't found yet.

Well maybe, but it wouldn't be easy! But then, of course, the Time Lords as their name suggests, have solved the slightly tricky problem of time travel to begin with.

There is another way around it in sci-fi-land that works for some stories: the classic wormhole that acts as a gateway to a shortcut through space-time, like a tunnel. This means there is a defined entry and exit point which presumably moves with the rest of the Universe like any other object with mass.

So great, ignoring the enormous amounts of energy needed to create one of these (more than is contained in the entire Universe according to one article), this does at least solve our coordinate problem. A craft can pop in and out of a wormhole like driving down a road and coming off at the correct exit. Perhaps. However, from a storytelling point of view, it is incredibly limiting, clunky, and ultimately no fun at all!