Good news, Doctor Who fans! A pair of physicists have proposed a spacetime geometry where Doctor Who’s TARDIS would actually be capable of traveling both forward and backward through space and time. This kind of spacetime could actually exist in our own universe, meaning the TARDIS — if such a craft was ever created — might actually have a scientific leg to stand on. In fact, given the scale of the universe, some semblance of the Doctor and his TARDIS might already exist, somewhere out there in the great wide expanse.

The research paper (Traversable Achronal Retrograde Domains In Spacetime — yes, really) was written by Ben Tippett and David Tsang of the Gallifrey Polytechnic Institute and Gallifrey Institute of Technology. The institutions don’t exist, but the physicists are real — and Tippett was the physicist who brought us the Unified Theory of Superman’s Powers back in 2009, if you remember that. In the paper, Tippett and Tsang propose a spacetime geometry where retrograde time travel (traveling back up your own time stream) is possible.

A spacetime geometry is when spacetime — i.e. the fabric of the universe where everything has happened, happens, and will happen in the future — is arranged into a certain shape. This is a very complex topic, but put simply, space consists of three dimensions (X, Y, Z), and time adds a fourth dimension. Spacetime tries to find a mathematical model/setting that accounts for scientific theories, such as general and special relativity. As such, there are lots of different proposed spacetime geometries — the most famous of which are Euclidean and Minkowski space, which are the mathematical settings for general and special relativity, respectively.

To allow for retrograde time travel, you need a spacetime geometry where the time dimension curves around, back in on itself. When spacetime is convoluted in such a way — it’s called a closed timelike curve (CTC) — you can theoretically hop from your current space and time to another point in space and time. (A lot like a wormhole, actually — which, incidentally, is exactly what that “time vortex” (pictured above) at the start of every Doctor Who episode is.) In Tippett and Tsang’s paper, from what I can tell (I am not a physicist), the TARDIS (spacecraft) creates a Traversable Achronal Retrograde Domains In Spacetime (TARDIS!) bubble — a bubble consisting of a closed timelike curve — and then uses that to travel around space and time with reckless, bow-tie-and-tweed-wearing abandon.

If all that sounds a bit too complex, the same physicists have also published The Blue Box White Paper, which attempts to explain their TARDIS bubble in layman’s terms. The above diagram, for example, demonstrates a simple two-dimensional spacetime.

So, there you go: All you Whovians out there can now tell your friends that the Doctor could actually exist in our universe. In fact, given the sheer scale of the universe — how big it is, how long the universe will exist for before it dies, land the number of habitable planets — it’s fairly likely that Time Lords actually already exist. Or will exist in the future.

Now read: The downside of traveling quickly through space and time: Annihilating whole star systems when you arrive

Research paper: arXiv:1310.7985 – “Traversable Achronal Retrograde Domains In Spacetime” [Free PDF]



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