How Traveling Back In Time Could Really, Physically Be Possible

It's one of the greatest tropes in movies, literature, and television shows: the idea that we could travel back in time to alter the past. From the time turner in Harry Potter to Back To The Future to Groundhog Day, traveling back in time provides us with the possibility of righting wrongs in our own past. To most people, it's an idea that's relegated to the realm of fiction, as every law of physics indicates that motion forward through time is an absolute necessity. Philosophically, there's also a famous paradox that seems to indicate the absurdity of such a possibility: if traveling backwards through time were possible, you'd be able to go back and kill your grandfather before your parents were ever conceived, rendering your own existence impossible. For a long time, there seemed to be no way to go back. But thanks to some very interesting properties of space and time in Einstein's General Relativity, traveling back in time may be possible after all.

The place to startis with the physical idea of a wormhole. In our known Universe, we have tiny, minuscule quantum fluctuations in the fabric of spacetime on the smallest of scales. These include energy fluctuations in both the positive and negative directions, often very close by one another. A very strong, dense, positive energy fluctuation would create curved space in one particular fashion, while a strong, dense, negative energy fluctuation would curve space in exactly the opposite fashion. If you connected these two curvature regions together, you could — for a brief instant — arrive at the notion of a quantum wormhole. If the wormhole lasted for long enough, you could even potentially transport a particle through it, allowing it to instantly disappear from one location in spacetime and reappear in another.