My current work in progress, Timekeepers, is about time travel. Like most time travel fiction, it’s got time travelers jumping into various historical epochs and doing stuff. But there are some interesting corollaries to this kind of fictional technology.
Think about it. My protagonists jump about in time, from 2018, to 1066, to a million years ago in the Pleistocene. But, while their “timepieces” displace them in time, they always wind up on earth. Nothing remarkable, right? That happens all the time in this kind of fiction, from H.G. Wells to the ones on TV just last season.
Here’s the thing, though. Everything moves.
The solar system is moving in an orbit about the galactic core. In fact, it’s moving pretty fast: about 515,000 miles per hour. This means that from 1066 to 2018, the solar system has moved 0.73 light years. Thus, when our time travelers “jump” from 2018 to 1066, they not only “instantly” travel in time, in order to stay “on earth,” they must also “instantly” travel that same distance in space, 0.73 light years. Of course, what “instantly” means in a universe of time travel is a question in and of itself. On the other hand, relativity pretty much erases the notion of simultaneity, so time travel or not, we know time doesn’t follow intuitive rules.
It gets worse. My characters “jump” 1.4 mega-years back to the Pleistocene but stay on earth. When they do this, they have also traveled over a thousand light years.
The inevitable conclusion is that a time machine is also a faster-than-light drive. Of course, we all know it’s impossible to travel faster than light, so the logical conclusion is that time travel is also impossible.
On the other hand, we all enjoy stories that include faster-than-light drives, so impossibility isn’t really a problem with fiction. Except fiction, unlike the real world, has to at least make sense.
So there’s an issue for a author writing about time travel. It seems incumbent to find an “explanation” for staying on earth’s “world-line” when “jumping” in time. The explanation needs to be plausible, although it can’t be “scientifically accurate” since time travel itself is surely impossible. My idea for this novel is that they are traveling in a gravity well that’s carving out a path in space-time. It’s not implausible that the least-energy path back to 1066 is along this path. So, when my time travelers “jump,” they are following the path to the past carved out by Earth.
Do I believe in that explanation? Well, no. But I don’t believe in time travel either. This at least passes the sniff test, if you don’t think about it too much.
The other paradox with time travel involves “changing the past” and erasing the future. That’s a common plot element in time travel fiction, and it’s in my novel, too. But a plot turning point in my novel is what I think is a new idea about what “really” happens if someone “changes” the outcome of one of history’s turning points. The idea is tied to some real ideas in physics that arise in quantum mechanics.
Since it’s part of the climax to the novel, you’ll have to read the my book to learn about that.