When you go to science fiction school, one of the first things you learn about time travel is that time machines generally travel through time and not through space. That is to say that they travel forward and backward in time, but not from place to place (the TARDIS and DeLorean being exceptions to this).
This idea of moving through time and not space originates – as does the very concept of a time machine – in the work of H. G. Wells, and his 1895 novel “The Time Machine” provides the best example of how this movement through time works. As Wells’ time traveler pushes his lever forward and activates his machine, he stays routed to the spot but watches the world around him change as he moves forward through time at a faster rate. He sees a candle burn down in an instant. He eventually also sees his house being demolished around him, the destruction of human civilization, volcanoes, and lots of other crazy shit.
However, there is a problem with describing H. G. Wells’ time machine as “travelling through time and not space” because the Earth is in constant motion. If the machine remains in the same spot on the laboratory floor, it naturally follows that it must be in motion too. While it remains stationary relative to the surface of the Earth, it is in fact moving through space.
If the time machine were to stay in the exact same spot and not move along with the Earth as it does in Wells’ novel, the experience of the time traveler would be quite different. He would observe the Earth moving rapidly beneath him as it spins on its axis. Day would not turn to night, but every location along that latitude would whiz by. Of course, when you consider that the Earth is also continually in motion around the sun an additional dimension is added, meaning that the time traveler would actually spend much of his journey through time in the cold vacuum of space. Add to this the fact that the entire solar system is continually in moving relative to the rest of the galaxy and this whole “moving through time and not space” lark starts to look a little silly. The possibility of the time traveler ever ending up any near where he started from disappears entirely.
If you are cursing me for being pedantic right now, I don’t blame you. But I’m not pointing this out to detract from Well’s work, in fact The Time Machine is one of my favorite books. I actually think that adding this conundrum into a time travel story could pose some interesting questions, forcing time travelers to face different challenges and affording them new possibilities. Thinking in this way actually makes “moving through time and not space” seem like a very effective way of traveling through space relative to the Earth, the only problem being that the uncontrollable motion of the Earth would determine where you would end up.
Of course, it’s easier just to say that while the time machine doesn’t move of its own accord, it is still affected by the force of gravity. That’s fine. Why the hell not? Except that this causes more problems for the time traveler, like being struck in the face by a fast moving object. You see, if the time machine is affected by gravity, it follows that it must also be affected by external physical forces – physical contact with the ground being the only thing that would stop it being pulled towards the center of the Earth.
H. G. Wells was able to cleverly skirt around the issue of physical contact with external objects with this short passage implying that speed somehow made the molecules of both the machine and the time traveler immune to their touch:
“The peculiar risk lay in the possibility of my finding some substance in the space which I, or the machine, occupied. So long as I travelled at a high velocity through time, this scarcely mattered; I was, so to speak, attenuated—was slipping like a vapour through the interstices of intervening substances!”
However this did not address the issue of gravity and contact with the ground.
While Wells’ time traveler survives a number of catastrophes by remaining inside his machine, he might actually be more vulnerable to the dangers of the physical world because of it as he would have less time to react to them and be unable to move out of the way. This might be a problem when somebody decides to build a road through the space his laboratory once occupied, or when his housekeeper mutates into a ravenous Morlock. And let’s not forget the issue of whether he would be invisible or not. If not, he would look very strange indeed.
One possible solution to the conundrum of “travelling through time and not space” while still being effected by the force of gravity (and thus remaining in the same location relative to the Earth) might be to build a time machine in one of Earth’s Lagrangian points. This would allow the machine to phase out of reality in a way that it would not be affected by physical contact with other objects but also prevent it from plummeting into either the Earth’s core or the heart of the sun.
These are just some points for writers of time travel fiction to think about when plotting their stories. However you decide your time machine is going to work, and which ever laws of physics you decide to ignore, just remember that adding limitations like these can help make your science fiction concepts seem more realistic. For those of you who are thinking about building an actual time machine of your own, my advice would be to pack an oxygen tank and a parachute, just in case.
This article was written by Mark Ball.