Is Trans-Planckian Censorship a Swampland Conjecture?
  During an accelerated expansion of the Universe, quantum fluctuations of
sub-Planckian size can be stretched outside the horizon and be regarded
effectively classical. Recently, it has been conjectured that such
horizon-crossing of trans-Planckian modes never happens inside theories of
quantum gravity (the trans-Planckian censorship conjecture, TCC). We point out
several conceptual problems of this conjecture, which is in itself formulated
as a statement on the restriction of possible scenarios in a theory: by
contrast a standard swampland conjecture is a restriction of possible theories
in the landscape of the quantum gravity. We emphasize the concept of swampland
universality, i.e. that a swampland conjecture constrains any possible scenario
in a given effective field theory. In order to illustrate the problems clearly
we introduce several versions of the conjecture, where TCC condition is imposed
differently to scenarios realizable in a given theory. We point out that these
different versions of the conjecture lead to observable differences: a TCC
violation in another Universe can exclude a theory, and such reduction of the
landscape restricts possible predictions in our Universe. Our analysis raises
the question of whether or not the trans-Planckian censorship conjecture can be
regarded as a swampland conjecture concerning the existence of UV completion.
