Thursday, May 19, 2022, 16:00
online only
(for the zoom link contact michael.spira@psi.ch, johannes.schlenk@psi.ch or
antonio.coutinho@psi.ch)
Fabio Costa, University of Queensland
Abstract:
Given a time machine, could you travel back in time to kill your past
self? If not, what would prevent it? By allowing closed time-like
curves, general relativity takes such questions from the realm of
speculative fiction to that of physics: Moving along a closed time-like
curve (CTC), an object could travel back in time and interact with its
past self. This possibility makes the usual formulation of physical laws
in terms of initial conditions problematic: not only certain initial
conditions appear to lead to logical inconsistencies, but the very
notion of "initial" is ill-defined, in the presence of CTCs. I will
present a general rationale for formulating physics in such exotic
space-times. I will discuss in particular models that are locally in
agreement with classical physics, namely where observers acting in local
space-time regions can perform arbitrary classical operations. I will
show an example of non-trivial time travel, where three agents can
interact in such a way to be all in the future and in the past of each
other, while being free to perform arbitrary local operations and
without giving rise to any paradox. I will briefly comment on a quantum
extension of the formalism.