Physics News Update, Number 430

Number 430, May 26, 1999 by Phillip F. Schewe and Ben Stein

INSTANT HOLOGRAPHY Polaroid succeeded in creating instant photography, the appearance of an image very soon after exposure. Now scientists at the Risoe National Lab in Denmark (P.S. Ramanujam, p.s.ramanujam@risoe.dk, 011-45-4677-4507) have done the same for holography. They have devised a photosensitive polymer (azobenzene) in which blue-green laser light can record an image in a matter of nanoseconds without any chemical processing. Applications for this type of process would be 3D hologram movies, waveguides for instantly reconfigurable optical switching, and for tracking the movement of particles. (P.S. Ramanujam et al., Applied Physics Letters, 24 May 1999.)

HELIUM ATOMS SHOOT DOWN HOLLOW FIBERS in an experiment at the Australian National University (Maarten Hoogerland, maarten.hoogerland@anu.edu.au). Previously rubidium atoms had been sent down fibers (see Update 245) but alkali atoms are prone to stick along the way. The helium atoms can be detected more efficiently than the rubidium atoms, and they (like the rubidium) flow smoothly, (guided by "evanescent light" impinging upon the fibers from outside) since they have first been put into a long-lived excited state which is almost impervious to interactions with the walls of the fiber. Possible applications include atom interferometers useful for gyroscopes or gravity wave detectors (after all, the working substance of the interferometer, atoms, are sensitive to gravity), and for atom-optics handling of Bose-Einstein condensates. (Paper QTuH2, May 25, at the Conference on Lasers and Electro-Optics (CLEO) in Baltimore.)

THE TEMPERATURE OF THE WORLD is 14.0°C. At least that’s the global average surface temperature. The average for the northern hemisphere, 14.6°C, is somewhat warmer and the southern a bit cooler, 13.4. A team of scientists (contact Phil Jones, University of East Anglia, UK, p.jones@uea.ac.uk) has gathered data from across a 150-year record and from points around the globe looking for trends. This is what they found: Over the period 1861-1997 the average global temperature rose 0.57°C. The warmest years of the century have all occurred in the 1990s: 1998 (the warmest), 1997, 1995, and 1990. The two periods of greatest warming were 1925-1944 and 1978-1997. Much of the net warming occurred at night; for the period 1950-93, nighttime average minimum temperatures increased 0.18°C per decade while daytime average high temperatures increased 0.08°C per decade. (P.D. Jones et al., Reviews of Geophysics, May 1999.)

MEASURED VALUES FOR THE HUBBLE CONSTANT are converging nicely. At a press conference on May 25, Wendy Freedman of the Carnegie Institution reported a new value of 70 km/sec/megaparsec (with an uncertainty of 10%), down from a value of 80 reported back in 1994. She is one of the leaders of a group that uses the Hubble Space Telescope (HST) to track the light emission of Cepheid variable stars in nearby galaxies. Another Carnegie astronomer, Allan Sandage, has been a leader of a group that consistently measures a smaller value for the Hubble constant, the latest number being about 59, up from an earlier value of 57. Thus the observed Hubble constant, which is a measure of the overall expansion of the cosmos, is now providing an estimate for the age of the universe--about 12 billion years--that is no longer in contradiction with the apparent age of the oldest stars. (NASA press release, 25 May 1999.)