You can’t turn a phone booth into a Gallifreyan contraption that is bigger on the inside and traverses thousands of years’ worth of space wars, but there could be another way for time travel to cross from the universe of sci-fi to science.
Shooting through the cosmos at light speed can take us into the future. What scientists want to know now is how to go in reverse. UMass Dartmouth grad student Caroline Mallary has published a new study in the journal Classic and Quantum Gravity that describes a deceptively simple way of pulling off an effect similar to a time machine, and it might just turn physics on its head.
To get how such a (theoretical) time machine would work, you first have to understand the concept of time loops. Einstein’s theory of general relativity allows time to warp enough to actually fold in on itself, producing a phenomenon in which you would only go so far into the future until you were thrown back into the past and had to live the same events all over again. It’s kind of like déjà vu.
Remember Miss Peregrine’s Home for Peculiar Children? The time loop that kept those peculiar kids living through the same day in 1940 for decades is what Einstein would call a “closed time-like curve” or CTC, a by-product of travel faster than the speed of light, and the closest thing physicists can refer to as a time machine. Except not everyone believes in time loops. The research of physicists like Kip Thorne and Stephen Hawking was supposed proof that these phenomena are impossible.
Altering the past can change an entire series of events that haven’t even happened yet. Hawking’s Chronology Protection Conjecture backs that up with its conclusion that nature does not allow for any changes to its past, which keeps any sort of weird paradoxes from happening in the future. If you went back in time and murdered your grandfather by slipping arsenic in your tea, you would essentially be erasing yourself from existence.
Some argue that exotic matter, or matter with negative mass, must be present in order for a time loop to be possible—except exotic matter has never actually been known to exist.
Back to Mallary’s groundbreaking study. She has actually created a (theoretical, again) model to catapult yourself backward in time, no exotic matter required. All you need are two cars parked in parallel and one to speed forward while no one pushes the gas on the other one. Do that, and you can find a time loop in the space between cars.
Of course, there is one catch to this. You might not need exotic matter, but you do need a singularity, an object with infinite density, temperature, and pressure, in each car. These types of singularities need to be completely exposed and observable. The singularities that lurk in the middle of black holes wouldn’t work because they are totally inaccessible from the outside. The singularities Mallary proposes aren’t even believed to exist in nature.
Until something that we couldn’t imagine has its existence proven, we’re probably not going to see this time machine anytime soon, even though it is supposed to work. But it does prove the physicists are going to have to redefine their reasons for why time loops can’t happen.
At least for now, it’s back to the TARDIS.