Chronology Protection in String Theory

[Vincent A. Maeder]

Cf. Disturbing Implications of a Cosmological Constant, Lisa Dyson, Matthew
Kleban, Leonard Susskind, Journal of High Energy Physics, 0210 (2002) 011
"In this paper we consider the implications of a cosmological constant for
the evolution of the universe, under a set of assumptions motivated by the
holographic and horizon complementarity principles. We discuss the ``causal
patch" description of spacetime required by this framework, and present some
simple examples of cosmologies described this way. We argue that these
assumptions inevitably lead to very deep paradoxes, which seem to require
major revisions of our usual assumptions."
http://arxiv.org/abs/hep-th/0208013


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From: KXX4493553 at aol.com [mailto:KXX4493553 at aol.com] 
Sent: Friday, September 19, 2003 12:38 AM
To: pynchon-l at waste.org
Subject: FWD: Chronology Protection in String Theory 



Chronology Protection in String Theory

Authors: Lisa Dyson
Comments: 17 pages. References added, typos corrected

Many solutions of General Relativity appear to allow the possibility of time
travel. This was initially a fascinating discovery, but geometries of this
type violate causality, a basic physical law which is believed to be
fundamental. Although string theory is a proposed fundamental theory of
quantum gravity, geometries with closed timelike curves have resurfaced as
solutions to its low energy equations of motion. In this paper, we will
study the class of solutions to low energy effective supergravity theories
related to the BMPV black hole and the rotating Wave--D1--D5--brane system.
Time travel appears to be possible in these geometries. We will attempt to
build the causality violating regions and propose that stringy effects
prohibit their construction. We will show how the geometry is corrected and
that, once corrected, causality is preserved. We will track our chronology
protection proposal in the dual conformal field theory. The absence of
closed timelike curves in the geometry coincides with the preservation of
unitarity in the conformal field theory. The agent of chronology protection
for the geometries studied here mirrors the enhancon mechanism, a mechanism
string theory employs to resolve a class of naked singularities. 

http://www.arxiv.org/abs/hep-th/0302052

  kwp