Have you read about this theory before? A time traveler wants to visit the past, say November 5th, 1955. So he enters his Delorean, speeds up to 88 miles per hour, and bang! He finds himself in outer space, cause he forgot that the Earth is moving and has not yet arrived in that spot in space. There’ll be no rescue in sight for the next twenty years. Now he’s alone in space without a suit, and the end of this movie is tragic.
This popular theory comes from the fact that Earth drifts at an impressive 2.6 million kilometers per day in its orbit around the Sun. While the Sun itself circles the black hole at the galaxy's center with a speed of approximately 828,000 kilometers per hour. So our planet travels in a spiral path throughout the Milky Way. In the past, it was hundreds of thousands of kilometers away from the place we are at this exact moment.
If you then consider time travel as time shifts while maintaining a fixed position, then yes, a time traveler would end up in outer space. Now, this is a pickle, isn’t it? Well, luckily, our time traveler lives in a universe where Einstein’s theory of relativity rules.
Yes, I’m about to explain the CORRECT physics of time travel, knowing very well that time travel to the past is impossible. Because this is the science of fiction, and that’s what we do—speculate over the unreality.
Newton vs. Einstein
As I said before, for a time traveler to end up in outer space we must change the time variable while keeping the position fixed. And this is such a Newtonian way to think!
Although our common sense is indeed very much Newtonian, we live in a relativistic world. Time and space are relative to the observer, and the notions of movement and locked positions are ill-defined.
The greatest difference between Newton’s theory of gravitation and Einstein’s general relativity is that for Newton time has nothing to do with the three spatial coordinates, length, width, and height.
In the classical, Newtonian mechanic, time and space are of different natures. Space is the environment in which we live, the three-dimensional place everything lies. And time is the measure of a system’s evolution. From this perspective, it is perfectly possible to stand still in place while traveling through time (who hasn’t had a moment of stand-by to observe time goes by?).
For Einstein, on the other hand, we cannot dissociate time from space. There’s no way to walk through time or space alone. Future and past are written in space-time coordinates.
So deep down, even if you are motionless in one place, you know you are moving. There is no fixed position in the universe, no privileged observer. Everything is moving relative to something. Although we can stay still relative to Earth, Earth moves and takes you with it.
Past and future events should be causally connected. Any other point in space-time that does not belong inside the past or future light cones of events cannot be said to happen either in the future or the past. So going back in time in this thread of causally-connected events would lead us to past Earth and not outer space.
Time traveling to the future!
Funnily enough, this idea of a time traveler ending up in outer space is more connected to a trip to the past. With the same hypothesis, if you enter a time machine to go a second into the future, you would end up several kilometers above sea level or deep down inside the planet, depending on where in the world you are. (In the book The Time Machine, H.G. Wells avoided this issue by fixing the machine on Earth’s surface. This was 20 years before Einstein formulated his general theory).
It is weird to think that traveling to the future would result in a traveler in outer space. We all know we are time-traveling to the future, so it becomes more intuitive to assume that jumping a second ahead would not result in being buried alive or free-falling from the stratosphere. So there is no reason to assume that going to the past would be different.
That’s it for today, folks.
Let’s agree to not break any more laws of physics than necessary and consider traveling in time a journey through a path causally connected to the present that links past Earth to future Earth.
See you next post!
Carla Ra is a scientist by day, sci-fi writer by night.
You can check out her anthology ARTIFICIAL REBELLION here.