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THIS WILL CONTAIN SPOILERS FOR DONNIE DARKO (2001)
Recently, I watched the 2001 film Donnie Darko. As a side note, I really enjoyed the movie and I think you should watch it, but that’s not the point of this article. In the movie, our main character, Donnie Darko, experiences some strange events. He sees visions of a giant rabbit creature named Frank, he narrowly dodges death by falling jet engine, and at the end, it seems that he time travels back to the start of the film. Time travel is brought up several times before this, one of the most obvious being when Donnie asks his science teacher if it is possible. The teacher tells him that one would need to find a wormhole, basically a shortcut, through space-time, allowing for a “vessel” to travel through, and arrive at a different point in space and time.
Of course, this begs the question, is that possible? You’ve probably heard of wormholes, but as a reintroduction, Einstein (and others) explained that our universe is a “fabric” of space-time, and published his field equations, which are “solved” by descriptions of space-time in some situation, such as around a stationary sphere, or a spinning sphere. There is a special solution to these equations which hypothetically, presents the possibility of a wormhole. This would, in theory, allow for a bridge across spacetime, connecting two distant points, allowing for near-instantaneous travel across distances that would take years, centuries, or millennia to cross even at the speed of light. Now, if you’ve watched Interstellar (or watched my review of it), you’ve seen that form of travel as moving through space instantaneously. But, considering that wormholes bridge space-time, it may also be possible to use them to travel through time.
However, this does not come without its drawbacks. First of all, we don’t know where any wormholes are, and we’re not exactly sure if we can make one. Secondly, even if we had a wormhole, it would probably be tiny and have such strong gravity that anything near it would be ripped to shreds, not dissimilar from a black hole. Assuming that you can somehow get past all of those restrictions, you should be able to move across space and time.
Now, it may be better to consider a few more plausible ideas, though still very complicated, and very far away. We find our way back to Einstein, this time to his theory of special relativity. He tells us that the speed of light is constant in every frame of reference, and this has various consequences. At or near the speed of light, time will move slower compared to someone at rest (someone who is not moving).
The best way I understand this is that if you take a flashlight at rest and shine it on a mirror, the light will bounce there and back to you in a straight line. If you do the same thing on a moving train, it will appear to you that the light did that same thing, went straight there and back. However, to someone at rest looking onto that train, the light starts at one point, then as the train moves right (could be any direction), the light also moves in that direction, taking a diagonal path, then bouncing back, again along a diagonal path. Because the light took a diagonal path for the observer, but a straight path for the person on the train, the Pythagorean theorem tells you the light moved further for the observer, but since Einstein tells us the speed of light is constant, more time must have passed for the observer than the train person. Here's a diagram I drew from the observer’s perspective
Now, we are nowhere near moving at the speed of light, much less being able to pinch a hole in spacetime to create a wormhole, but as Donnie Darko’s teacher said, it is conceptually, all there. Honestly, the form of time travel in Donnie Darko is not super accurate, and I don’t think the expectation should be that it is. It’s still an excellent movie, even if it’s not as scientifically accurate as Interstellar. I hope you enjoyed learning about time travel, and if you’re in the mood for a movie, I’d recommend Donnie Darko.
https://en.wikipedia.org/wiki/Einstein_field_equations
https://en.wikipedia.org/wiki/Special_relativity
https://www.scientificamerican.com/article/can-time-travelers-reach-the-past-via-wormholes/
https://www.nytimes.com/2022/10/10/science/black-h