Physics News Update, Number 386

Number 386, August 26, 1998 by Phillip F. Schewe and Ben Stein

BLACK HOLES CANNOT SERVE AS PORTALS TO OTHER UNIVERSES. That is the conclusion of Shahar Hod and Tsvi Piran (tsvi@vms.huji.ac.il, 011-972-2-6584233), two Hebrew University physicists who have performed the first detailed calculations tracing a black hole from the prelude of its formation to the development of its inner structure. Black holes have such large amounts of gravity that they irretrievably attract all objects that are closer than a point-of-no-return known as the event horizon. As Roger Penrose and Stephen Hawking first showed, the insides of black holes must contain a singularity, which in its simplest form is a region of infinite density. Associated with a singularity is a boundary known as a "Cauchy horizon" beyond which it becomes impossible to predict the future trajectory of a particle with any reliability. Previously, some theorists have suggested the possibility that matter passing through the Cauchy horizon may encounter an "asymptotically flat" region, a region of relatively weak gravity such as our own, and then travel to other universes rather than get caught in a singularity. However, Hod and Piran have now supported previous indications showing that these Cauchy horizons are unstable; small disturbances in the black hole instantly transform them into singularity regions. In fact, their calculations suggest that generic black holes contain two singularities that are connected to each other so that all infalling matter reaches one or the other. (Hod and Piran, Physical Review Letters, 24 August 1998)

TURBULENCE IN SOAP FILMS. Understanding the mystical swirls of the Great Red Spot of Jupiter and the majestic flows of the Atlantic Ocean can be enhanced by studying the patterns in the humble soap film, the thin slab of water sandwiched between two layers of soap molecules (surfactants). The fluid in soap films moves principally in two spatial dimensions, just like the aforementioned geophysical flows. Researchers at Los Alamos (Peter Vorobieff, 505-667-8090) have performed the first quantitative measurements of the properties throughout an entire soap film, rather than at just one or several points, which was previously the case. They added highly reflective titanium dioxide particles to the fluid, and snapped pictures with a digital camera, obtaining detailed images of thousands of points of the fluid every 160-300 microseconds. Sending the film through a comb, they produced a turbulent flow and measured such quantities as vorticity--essentially the measure of the fluid's swirling motion, with faster-moving and more tightly curving swirls leading to greater vorticity values. From this they determined the enstrophy (vorticity squared) and found evidence of "enstrophy cascade," in which energy was transferred from larger- to smaller-sized eddies before being dissipated there. This experiment paves the way for using soap films to further study 2D turbulence. (Rivera et al., Physical Review Letters, 17 August 1998; See Image at Physics News Graphics. Also see Los Alamos writeup on this topic.)

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