The last form of FTL travel that we’ll dig into seems the least scientific. For 55 years, Doctor Who has chronicled the adventures across time and space of the Doctor and his/her human companions. Their means of transportation? A big blue box known as the TARDIS (Time and Relative Dimension in Space) that can take them anywhere, and anywhen, they want to go.
Built (or, rather, grown) by an ancient species known as Time Lords, TARDISes are more magical than the tech of Star Trek. As the Doctor has himself explained, his means of transport can get a little “wibbly wobbly, timey wimey.” There does seem to be some sort of delay on the way — it’s more hyperdrive than jump drive. But essentially the TARDIS disappears here, flies through the Time Vortex, and reappears there. That’s all you really need to know.
Or is it? It turns out even the TARDIS has more of a theoretical basis than the hyperdrive.
In 2013, physicists Benjamin K. Tippett and David Tsang published a paper proposing a theoretical means of creating an actual retrograde-capable time machine: a way to travel to your own past. The title of the paper: Traversable Achnronal Retrograde Domains in Spacetime (check the acronym, nerd).
Tippett and Tsang describe a bubble of spacetime containing a time-traveler entering a Closed Timelike Curve (essentially the same as an Einstein-Rosen bridge). Within that curve, the traveler can go anywhere on his or her own timeline, while within the bubble time seems to pass normally.
The two physicists even theorized that timelike curves could be split and connected, opening up the possibility of traveling not just along your own timeline — but anywhere in time and space.
All of which could make the TARDIS the winner of the theoretical faster-than-light travel stakes. With apologies to Han Solo, going point five past light speed may seem impressive, but there’s nothing faster than arriving before you set off in the first place.
Realism Rating: 1/5, and that’s being generous. For now the TARDIS is just wibbly wobbly, timey wimey, spacey wacey.