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Physics News Update
Number 399, October 26, 1998 by Phillip F. Schewe and Ben Stein

NONLOCALITY GETS MORE REAL. "Bell's Inequalities," the set of mathematical relations that would rule out the notion that distant quantum particles exert influences on each other at seemingly instantaneous rates, have now been violated over record large distances, with record high certainty, and with the elimination of an important loophole in three recent experiments, further solidifying the notion of "spooky action at a distance" in quantum particles. At the Optical Society of America meeting in Baltimore earlier this month, Paul Kwiat (kwiat@lanl.gov) of Los Alamos and his colleagues announced that they produced an ultrabright source of photon pairs for Bell's inequality experiments; they went on to verify the violation of Bell's inequalities to a record degree of certainty (preprint at p23.lanl.gov/agw/2crystal.pdf). Splitting a single photon of well-defined energy into a pair of photons with initially undefined energies, and sending each photon through a fiber-optic network to detectors 10 km apart, researchers in Switzerland (Wolfgang Tittel, Univ. Geneva, wolfgang.tittel@physics.unige.ch) showed that determining the energy for one photon by measuring it had instantaneously determined the energy of its neighbor 10 km away--a record set by the researchers last year but now demonstrated in an improved version of the original experiment. (Tittel et al., Physical Review Letters, 26 October 1998.) A University of Innsbruck group performed Bell measurements with detectors that randomly switched between settings rapidly enough to eliminate the "locality loophole," which posited that one detector might somehow send a signal to the other detector at light or sub-light speeds to affect its reading. (Weihs et al.,Phys. Rev. Lett., website at http://www.uibk.ac.at/c/c7/c704/qo/photon/_bellexp/)

TUMOR GROWTH CAN BE FRACTAL. A curve is fractal if when you look at segments of the curve it appears the same at many different scales of magnification. To be fractal means to be multiply indented, so much so that the curve is said to possess more than a one-dimensional nature. Some fractal curves are so "rough" that they are more like surfaces than lines. The rougher the curve the higher its fractal dimensionality. Scientists have previously found evidence for fractal behavior in curves describing heart fibrillation, forest fires, crystal growth, and many other systems. This applies now also to tumor growth. Antonio Bru of CIEMAT (Madrid) and his colleagues from several labs in Spain (011-34-1-346-6183, bruno@ibm1.ciemat.es) have studied the dynamical behavior of a series of rat brain tumors growing in petri dishes. The morphology results: the tumor profiles are super-rough, with a fractal dimension of 1.21. The dynamical results: the tendency for interface cells to duplicate turns out to be a function of local curvature. The researchers' aim in pinning down the tumor's mathematical parameters is the search for mechanisms that can control and possibly even stop tumor growth. (Bru et al., Physical Review Letters, 2 November 1998.)

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