“The encounter could create a time paradox, the results of which could cause a chain reaction that would unravel the very fabric of the space time continuum, and destroy the entire universe!” This particular quote, uttered by Doc Brown in Back to the Future II, is an example of how common the phrase “space time continuum” is in science fiction and pop culture. As far as complicated science-y sounding phrases, it’s one of the best out there. But what is spacetime?
In 1905, Albert Einstein published his famous theory of special relativity. In his theory Einstein revealed that the laws of physics are the same for all non-accelerating observers (the principle of relativity). He also posited the groundbreaking idea that the speed of light in a vacuum is a universal constant. That means regardless of whether you’re moving toward or away from a light source, the light still travels at 300,000,000 meters per second
The revelations brought about by special relativity exposed a link between space and time. In our universe we have observed three dimensions of space (up/down, left/right, and forward/backward) and one dimension of time. When combined together you get a four-dimensional space known as the space-time continuum.
While solving his equations for general relativity (different from special relativity in the sense that the observers are now accelerating), Einstein found that immensely massive objects can cause a distortion in spacetime. One way of visualizing this distortion is to think of a large weight in the middle of a trampoline. The trampoline is warped by the weight, and a ball rolled along the outside of the trampoline will gradually be pulled into the center. This is what gives us gravity, and is what puts the planets in their orbits.
According to Einstein even light itself is not immune to the curvature of spacetime. His theory is supported by an observed astronomical phenomenon known as gravitational lensing. Gravitational lensing occurs when massive objects bend light, and in doing so act as a lens for objects lying behind. One of the clearest examples of lensing can be seen in observing a quasar in the Pegasus constellation, fittingly nicknamed Einstein’s cross. A super-massive galaxy sits between Earth and the quasar, and due to the galaxy’s distortion of spacetime four images of the quasar are visible as the light is bent.
Spacetime is related to another classic science fiction cliche, the wormhole. A theoretic passage through spacetime, wormholes were predicted by Einstein himself in 1935. While he was able to prove their existence in the mathematical sense, there have been no real-world wormhole observations as of yet. It’s possible that black holes could form the mouth of a wormhole, but this is still just one solution.
Hollywood has always loved to toss around scientific phrases, and while they’re usually far from accurate they can certainly be a whole lot of fun. Thanks to some meaningless science buzzwords, we got the famous “don’t cross the streams quotes” in Ghostbusters. But next time someone tells you that the space time continuum is in danger of unraveling, I wouldn’t get too concerned.