Thought some here might find this interesting . . .
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 843 October 18, 2007 by Phillip F. Schewe www.aip.org/pnu RELATIVISTIC THERMODYNAMICS. Einstein*s special theory of relativity has formulas, called Lorentz transformations, that convert time or distance intervals from a resting frame of reference to a frame zooming by at nearly the speed of light. But how about temperature? That is, if a speeding observer, carrying her thermometer with her, tries to measure the temperature of a gas in a stationary bottle, what temperature will she measure? A new look at this contentious subject suggests that the temperature will be the same as that measured in the rest frame. In other words, moving bodies will not appear hotter or colder. You*d think that such an issue would have been settled decades ago, but this is not the case. Einstein and Planck thought, at one time, that the speeding thermometer would measure a lower temperature, while others thought the temperature would be higher. One problem is how to define or measure a gas temperature in the first place. James Clerk Maxwell in 1866 enunciated his famous formula predicting that the distribution of gas particle velocities would look like a Gaussian-shaped curve. But how would this curve appear to be for someone flying past? What would the equivalent average gas temperature be to this other observer? Jorn Dunkel and his colleagues at the Universitat Augsburg (Germany) and the Universidad de Sevilla (Spain) could not exactly make direct measurements (no one has figured out how to maintain a contained gas at relativistic speeds in a terrestrial lab), but they performed extensive simulations of the matter. Dunkel ([EMAIL PROTECTED] ) says that some astrophysical systems might eventually offer a chance to experimentally judge the issue. In general the effort to marry thermodynamics with special relativity is still at an early stage. It is not exactly known how several thermodynamic parameters change at high speeds. Absolute zero, Dunkel says, will always be absolute zero, even for quickly-moving observers. But producing proper Lorentz transformations for other quantities such as entropy will be trickier to do. (Cubero et al., Physical Review Letters, 26 October 2007; text available to journalists at www.aip.org/physnews/select) NUCLEAR SYRUP. A new measurement of how long it takes certain nuclei to fission into large fragments suggests that the *liquid-drop* model of the nucleus should be replaced with a *nuclear syrup*model. Fission is the most dramatic form of radioactivity, when a nucleus loses not merely a small fragment-such as an electron, gamma ray, or an alpha particle-but actually splits in half. The fission of many nuclei has been studied through the years, most famously uranium-235. As early as 1939 Niels Bohr and John Wheeler tried to model the nature of fission by saying that the nucleus is like a drop of water in which the tendency of the drop to fly apart is checked by the force of surface tension; something like this, they said, kept a nucleus intact until such time as the rapid oscillations of an unstable nucleus became so large that the *surface tension* normally keeping the nucleus together was overcome. Sometimes as a prelude to fission, the nucleus relieves some of its instability and effectively reduces its internal *nuclear temperature* by flinging out neutrons or gamma rays. In fact, the lifetime for fission has been indirectly measured by observing those cast-off neutrons. The results suggest that the old liquid-drop model was off by a factor of ten or so in predicting lifetimes. Some scientists have begun to think that an additional stickiness in the nuclear substance is at work, which slows up the fission process. An experiment at Oak Ridge National Laboratory has probed this proposition by creating several fissionable nuclei artificially with heavy-ion beams bombarding a tungsten target; the projectile and target nuclei temporarily fuse together, travel a short distance through the tungsten crystal, and then fission. The spacing of the atoms in the crystal is used as a reference to measure the recoil of the composite nucleus before fission. According to team member Jens Andersen of the University of Aarhus in Denmark ([EMAIL PROTECTED], 45-8942-3713), the Oak Ridge experiment suggests that the fission lifetimes are even longer (an additional factor of ten to one hundred) than those derived with the more indirect neutron-emission method. This could imply that the nuclear shape does not oscillate as rapidly as a water droplet would but instead deforms very slowly like a drop of syrup. (Andersen et al., Physical Review Letters, 19 October 2007; journalists can obtain the text from www.aip.org/physnews/select) *********** PHYSICS NEWS UPDATE is a digest of physics news items arising from physics meetings, physics journals, newspapers and magazines, and other news sources. It is provided free of charge as a way of broadly disseminating information about physics and physicists. For that reason, you are free to post it, if you like, where others can read it, providing only that you credit AIP. Physics News Update appears approximately once a week. AUTO-SUBSCRIPTION OR DELETION: By using the expression "subscribe physnews" in your e-mail message, you will have automatically added the address from which your message was sent to the distribution list for Physics News Update. If you use the "signoff physnews" expression in your e-mail message, the address in your message header will be deleted from the distribution list. Please send your message to: [EMAIL PROTECTED] (Leave the "Subject:" line blank.) -- Ronn! :) _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
