Humans have always been fascinated by time travel. Physicists have been trying to prove time travel possible for years, if only theoretically. Now, physicist Ben Tippett of the University of British Columbia, Canada, and astrophysicist David Tsang of the University of Maryland have come up with a model for a time machine that Tippett says is “mathematically possible.” They’ve nicknamed the model a Traversable Acausal Retrograde Domain in Space-time, or TARDIS, as a nod to the time-traveling sci-fi hero, Dr. Who. The results are published in Classical and Quantum Gravity.
In order to understand how such a machine would work, here’s a brief refresher on Einstein’s Theory of General Relativity. Einstein posited that the three spatial dimensions we are most familiar with—left-right, up-down and forward-backward—cannot be separated from the fourth dimension of time. In essence, they comprise a four-dimensional surface, “across which the stars and planets and all the rest of the matter in the universe tumble,” write Tippet and Tsang in a paper titled “The Blue Box White Paper,” when they first started contemplating their time machine. In addition, another key law of physics, known as Classical Energy Conditions requires two conditions: matter must be gravitationally attractive, and can never move faster than the speed of light. Any matter that defies either of those criteria is considered “exotic” or “unphysical.” So far, no such exotic matter has ever been discovered, but more on that later. In our understanding of the universe through Einstein’s theory, the planets and stars might appear to move through space in straight lines; however, when they come close to each other, space-time curves, bending the trajectories of these nearby planets and stars into ellipses.