Natural Science Forum / Physics / Relativity / July 2006

Rich non-arbitrary topological change may occur in a relativistic
vacuum space-time that violates chronology at every point, such that
every closed timelike curve (CTC) is ``censored" by passing through a
wormhole's event horizon. A Cauchy-like surface may exist through which
all timelike curves pass once and only once before crossing an event
horizon. All CTCs in a time-orientable space-time must pass through a
wormhole; otherwise the CTC could be deformed as a CTC to a
non-time-orientable point. Therefore, if all wormholes have event
horizons, there is chronology protection against uncensored CTCs, and
the universe is safe for those historians who cannot see through event
horizons. An indicator of a space-time's completeness which is
conformally invariant, unlike geodesic completeness, is that no causal
boundary exists, or equivalently that the entire space-time is a
chronology violating set. Such ``causally complete" space-times fail to
satisfy assumptions of the topological censorship theorem and a wide
range of singularity theorems.

If a wormhole's two mouths are nearby, its event horizon as a one-way
membrane causes the wormhole to propagate, mimicking the behavior of a
photon. If the two mouths are not nearby, they mimic the behavior of a
fermion and its anti-particle. Energy-momentum conservation implies
that these pseudo-photons can be created or destroyed only in multiples
of 2 (similar to results of Gibbons and Hawking), and that their
destruction creates gravitational waves. The time-reversed phenomenon
would be a collision of (non-planar) gravitational waves that creates
entangled pseudo-photon pair.