  This white paper is an explanation of Ben and Dave's TARDIS time machine,
written for laypeople who are interested in time travel, but have no technical
knowledge of Einstein's Theory of General Relativity.
  The first part of this paper is an introduction to the pertinent ideas from
Einstein's theory of curved spacetime, followed by a review of other popular
time machine spacetimes. We begin with an introduction to curvature and
lightcones. We then explain the Alcubierre Warp Drive, the Morris-Thorne
wormhole, and the Tipler cylinder.
  We then describe the Traversable Achronal Retrograde Domain in Spacetime
(TARDIS), and explain some of its general properties. Our TARDIS is a bubble of
spacetime curvature which travels along a closed loop in space and time. A
person travelling within the bubble will feel a constant acceleration. A person
outside of the TARDIS will see two bubbles: one which is evolving forwards in
time, and one which is evolving backwards in time. We then discuss the physical
limitations which may prevent us from ever constructing a TARDIS.
  Finally, we discuss the method through which a TARDIS can be used to travel
between arbitrary points in space and time, and the possible dangers involved
with exiting a TARDIS from the wrong side.
  Before we begin, would you like a Jelly Baby?
