Yes, the problem. Because there is only one. ;)
I don’t even remember how we got on the subject, but something in a conversation with Prairie last night got me rambling on about the biggest problem I have with time travel stories. As fun as they are, there’s always been one thing that bugged me about them — though, admittedly, it’s most likely because in the majority of instances, worrying about it would essentially negate the possibility of the story working at all.
Essentially, it’s that while what makes the story fun is the ability to travel temporally, nobody ever seems to take into account the need to travel spatially as well.
The Earth rotates at a little over 1000 miles per hour. It also orbits the sun at around 67,000 miles per hour. Our solar system is moving through the galaxy at approximately 447,387 miles per hour. Our galaxy is moving at roughly 1.34 million miles an hour through the universe. So, assuming that those are all the variables we have to work with (that is, assuming that time is a constant within our universe, and that there is nothing “outside” our universe to measure its relative speed), we travel (very) roughly 6,679,393,200 miles per second relative to our universe.
So, were I to invent a time machine and move myself one second back in time, I’d end up popping back into the normal time stream somewhere more than six and a half billion miles away from where I started! Needless to say, I’d be incalculably lucky to end up arriving anywhere that would allow me to survive — most likely, I’d just end up floating out in the vacuum of space somewhere.
Any feasible time machine, then, would somehow have to ensure that the traveler was able to move temporally while remaining stationary spatially relative to their starting point, and not to the universe as a whole.
Tricky.
Not that that keeps me from enjoying time travel stories anyway, of course. But there’s always this niggling little voice in the back of my head…