I’ve always wanted to invent a time machine so I could whip back in time to stop Hitler before he did anything evil. Of course there are a couple of problems. First is I’d be joining the back of a LOOONG queue. The other is that our friend Albert Einstein tells us it’s impossible.
But even if a time machine could be built, nobody’s really figured out what it entails. Here’s the deal.
Science fiction is rife with stories about time travel, variously either as social commentary, H. G. Wells style, or as cautionary tales – witness Ray Bradbury’s wonderful A Sound of Thunder. Invent a time machine, go back in time and change the past – and you’d better watch out.
Of course, if things change so you don’t exist, then you can’t have invented the time machine. Which means you didn’t go back in time. Therefore you do exist, so you did invent the time machine and… Yah.
Or there’s Harry Harrison’s hilarious Technicolour Time Machine, about a movie maker who uses a time machine to cut production costs on his period drama by going back to the actual period. What I’m getting at is that there’s a gaping great hole in all of this. And it’s an obvious one.
Suppose you COULD time travel. Suppose you’d built a machine to do it. You decide to whip back twelve hours. And promptly choke to death in the vacuum of deep space.
What gives? The problem is that everything in space is moving. Earth is rotating. Earth also moves around the Sun, which itself is orbiting the galaxy, which itself is moving as part of the Local Group, and so forth. We don’t notice or even think about it because we’re moving with the Earth. If we take Earth as our reference point, it’s fixed relative to us. And that leads us to imagine that time machines are NOT moving through space – Wells, in particular, was quite explicit that his time machine was fixed and time moved around it.
But actually, a time machine that did this – that stayed ‘still’ relative to Earth would have to move through space, because Earth is moving.
Let’s reverse that for a moment. What say your time machine doesn’t move in space at all. You move back and forth through time, but your absolute spatial position is fixed. Not relative to Earth, but relative to the universe.
You leave your lab and leap back 12 hours. Earth won’t be there – it won’t have arrived. Leap forward 12 hours – same thing, only Earth’s moved away. If you’ve only moved a few seconds, you might find yourself plunging from a great height (aaaargh!). Or buried deep in the Earth (choke).
So for a compelling time-machine story you need to have a machine that not only travels anywhere in time, but also anywhere in space. And, of course, any relative dimensions associated with both. That’s right. A machine that travels anywhere through time and relative dimensions in space.
Heeeeeey, wait a minute…
Copyright © Matthew Wright 2014