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.
The TARDIS bubble explainedA 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.
A simple spacetime diagram
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.