Number 370, May 6, 1998 by Phillip F. Schewe and Ben Stein
LOOKING FOR ANTI-QUARKS INSIDE PROTONS. Consider a proton zipping through the lab. Only about 30% of its momentum is taken up by valence quarks (two "up" and one "down" quark), the nominal constituents of the proton. Gluons, which keep the quarks attached to each other, account for 50% of the momentum. And the rest, the other 20% of a proton's momentum, is take up by virtual particles which pop pairwise into and out of existence on short-term loan from the vacuum (sometimes referred to as the "Fermi sea"). Like a reclusive tiger photographed at a waterhole with a tripwire camera, one of these virtual particles can be viewed if it is struck at just the right moment by a probe particle from a high-energy beam. In this way, the anti-up and anti-down quark population of protons has been systematically studied in a scattering experiment at Fermilab (contact Paul Reimer of Los Alamos, firstname.lastname@example.org, 505-667-0145). In general the prevalence of anti-u and anti-d quarks is about equal, except for cases where the struck quark has low momentum; then anti-d's outnumber anti-u's considerably. (Hawker et al., Physical Review Letters, 27 April.)
PHYSICS TODAY MAGAZINE CELEBRATES ITS 50TH ANNIVERSARY this month with, among other features, winning entries from a contest which asked for a news report of an imagined research breakthrough of the future. The essays are as follows. (1) Gordon Kane (Michigan) reports, in the year 2011, on the discovery of particles at the Large Hadron Collider with masses of 950 and 1900 GeV, which theorists interpret as being evidence for two new spatial dimensions. (2) Paul Grant (Electric Power Research Institute) describes the development (in the year 2028) of a DNA- related polymer which remains superconducting above 600 K.(3) Jack Watrous (NumerEx, in Albuquerque, NM) describes an era (the year is 2048) when the government is concerned about the spreading power of robot technology based on recombinant DNA, programmable protein folding, and autonomous computing; rumors of sentient ribonucleic robot colonies has anti-cybernetic watchdogs worried. (Physics Today, May 1998.)
DO CATHEDRAL GLASSES FLOW? Reportedly some stained glass windows from 12th century cathedrals are thicker at the bottom than at the top, suggesting that glass is a liquid which flows (albeit slowly) downward under the force of gravity. Surprisingly, the scientific literature on this point is scant, and Edgar Zanotto at the Federal University of Sao Carlos in Brazil (email@example.com) investigated this issue by modeling several different kinds of glass. He determines that if glass flows it must do so on a time scale of billions of years and not mere centuries. Zanotto points out that glass vases several thousands of years old do not show the effect of any downward flow. He argues that some cathedral glasses might be larger at the bottom because of the old manufacturing process in which the glasses were blown into cylinders and then flattened manually. (American Journal of Physics, May 1998.)
CORRECTION: The best artificial vacuum was reported in the original version of Update 369 as corresponding to a spacing between residual atoms of about 1 mm. Several labs have done better: Gerald Gabrielse of Harvard, for example, achieves a vacuum of 5 x 10-17 torr, corresponding to about 2 atoms per cm3.
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