PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 631 April 2, 2003 by Phillip F. Schewe, Ben Stein, and James Riordon
It may be highly improbable, but it cannot be ruled out, according to a new analysis that explores the idea of "hybrid singularity." As science fiction fans know, anyone who wishes to fall into a black hole and re-emerge at some distant location or even an another universe would have to go through a forbidding region inside the black hole known as a "space-time singularity." Traditionally this means negotiating a region of infinite density exerting destructive, tide-like distortions on any "extended object" such as a spaceship, molecule, or anything that is not truly point-like. Physicists now suspect this picture is incomplete and that a second and potentially milder type of singularity might exist. Known as a "Cauchy horizon singularity," it would impart only finite tidal distortions on extended objects.
The kinder, gentler singularity should only develop when a regular stream of matter or energy falls into the hole. Previous analyses have considered only streams that were brief bursts. But long-duration "non-compact" streams of radiation, like the cosmic microwave background, can also fall into the black hole. In a more comprehensive analysis that takes these "non-compact" sources into account, Lior Burko of the University of Utah (burko@physics.utah.edu) explores how a black hole's interior is affected by such infalling radiation. If the non-compact sources are weak, Burko shows, a hybrid singularity forms: a strong sector (inevitably destructive) and a weak sector (finite tidal distortions). Conceivably, a spaceship entering through the weak sector could travel unscathed to another part of space-time. If the perturbations due to non-compact sources are large, however, Burko shows that the singularity ends up being strong, and destructive, everywhere in the black hole. Whether black hole singularities in our universe are strong-only or hybrid in nature depends on incompletely known cosmological parameters (such as the expansion rate of the universe and the nature of dark energy). Several factors may ultimately rule out the possibility of hyperspace travel. They include: (1) the possibility that "weak" sectors may still be much too hazardous for travel; (2) overwhelming effects on the black hole from actual non-compact sources and (3) a working theory of quantum gravity, which may reveal other factors that rule out hyperspace travel. But for now, Burko says, the possibilities are open. (Burko, Physical Review Letters, 28 March 2003)
