---------- Forwarded message ---------- Date: Tue, 15 May 2001 14:28:08 -0400 (EDT) From: AIP listserver <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Subject: update.539 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 539 May 15, 2001 by Phillip F. Schewe, Ben Stein, and James Riordon (DE)CONSTRUCTING DIMENSIONS. What is space? We generally take space for granted. We exist within it, we move about, make measurements of it. It's there before anything else and it seems to be continuous. Furthermore, extra dimensions, beyond the three spatial dimensions we perceive, are mandated by modern string theories in the process of bringing quantum mechanics and general relativity together in a single theoretical framework. That we can't see these dimensions is usually explained by saying that they are curled up in some way. The customary prescription for discovering such dimensions is to study particle interactions at ever higher energies, which is equivalent to studying matter at ever smaller size scales. Now, three physicists want to re-examine the whole concept of space by coming from the other direction. As higher energies are probed, say Nima Arkani-Hamed (LBL, 617- 496-8188) Andrew Cohen (Boston Univ, 617-495-1988) and Howard Georgi (Harvard, 617-496-8293) dimensions may actually disappear, revealing themselves as only a property of particle forces at low energies. Imagine, for the moment, a number of copies of our four-dimensional (three space plus time) universe. Without interactions between them, these universes are inaccessible---we are ignorant of their existence. But further imagine a new set of forces, linking pairs of these universes. If these forces are similar to the strong nuclear (hadronic) force, which is strong at low energies but gets weak at high energies, relatively low energy experiments (although still high energy in the TeV range by today's standards) would detect these alternate universes while high energy ones would not. This connection between different universes at low energies, the ability to transfer information, and even travel among them, appears as a new dimension. This dimension was not present beforehand, but appeared dynamically. In other words, the new dimension comes into existence only through interactions among particles. At high energies these forces "melt" away, and the extra dimension disappears. The theorists suggest that even our familiar three spatial dimensions might come about in this way. Evidence for this kind of dynamical dimension would be the discovery, amid high energy collisions, of a finite series of new particles with a very specific spectrum of masses. (Physical Review Letters, 21 May 2001) COMPUTING WITH WAVES. Conventional computers do their jobs by using electrons as billiard-ball like particles to move around circuits and carry out the desired tasks. At last week's CLEO/QELS lasers/optics conference in Baltimore, a University of Rochester group (Ian Walmsley, 716-275-0312, [EMAIL PROTECTED]) presented a simple optical system that performs a database search of 50 items in a way that cannot be duplicated in any particle-powered computer. To do the search, the researchers use wave interference, the patterns that are created when two waves, such as light waves, combine. While their demonstration is not any more efficient than traditional database searches, it is the largest search performed with wave interference. It is a follow-up to a similar demonstration in an atom (Ahn et al., Science, 21 January 2000) and expands possibilities for "wave computing" which would be intermediate in power between classical computing and quantum computing. In addition, the Rochester group uses light, which is much easier to prepare and transport than atoms. In their demonstration, the researchers produce a single pulse of light carrying a spectrum of different colors, each containing a different bit of information. They split the pulse into two identical pulses each with half the intensity. One travels to an "Oracle," an optical element (an acousto-optic modulator) which for certain colors shifts their phase, the relative position of the peaks of the wave compared to other colors. Then they combine the Oracle pulse with the other, untreated pulse at a beamsplitter, which produces two output beams, each going in different direction. Only the components of the beam which have their phases changed travel toward a spectrometer and detector, enabling the researchers to read out the information and determine the location of the desired item in the database. (Paper QWB3; http://www.osa.org/mtg_conf/CLEO/) ____________________________________________________________________ "...where annual election ends, tyranny begins;" Thomas Jefferson & Samuel Adams The Armadillo Group ,::////;::-. James Choate Austin, Tx /:'///// ``::>/|/ [EMAIL PROTECTED] www.ssz.com .', |||| `/( e\ 512-451-7087 -====~~mm-'`-```-mm --'- --------------------------------------------------------------------
