Information not only about the Hubble constant but also about gamma ray bursters, gravitational lenses, Chandra X-ray Observatory, and other interesting topics.
See the NASA site at http://www.hubbleconstant.com for astronomy news on the scale and size of the Universe, and on other contemporary topics.
[Comments by Alex Filippenko, University of California at Berkeley, who will be coauthor with me of the second edition of Journey Through the Universe]
Much to everyone's surprise, very recent (1998) measurements suggest that the expansion rate of the Universe might actually be *increasing* with time, rather than decreasing! Two independent teams of astronomers have measured the apparent brightness of supernovae at high redshifts, and the distances derived from them are larger than expected in a universe decelerated by the pull of gravity. In fact, they are more distant than expected even in the case of a virtually empty universe which expands with a constant speed. If the speed of a given galaxy is increasing with time, space itself must have a long-range repulsive property, somewhat like "antigravity" -- but we hesitate to use this term because it has nothing to do with matter or antimatter, and it cannot be locally utilized for levitation or other strange feats. Instead, the effect might be produced by some sort of "strange energy" in the Universe, like that which is believed to have led to a rapid inflationary epoch at very early times. It is essentially the "cosmological constant" that Albert Einstein introduced to counter the attractive force of gravity and thereby achieve a static universe, but later renounced as the biggest blunder of his career.
Although this discovery is tentative, and must still be verified with completely independent techniques, its consequences are quite attractive. First, the derived expansion age of the Universe is about 14 billion years (assuming a Hubble constant of 65 km/s/Mpc), consistent with the revised ages of the oldest globular star clusters (11-14 billion years). Second, the global geometry of the Universe appears to be nearly flat, in agreement with the predictions of the inflation theory of the early Universe. Moreover, the Universe could actually be shaped like an enormous beach ball, with an unmeasurably large radius of curvature; we do not need to settle on the infinite, negatively curved universe implied by measurements of the average matter density alone. This is more consistent with current suspicions that the Universe might have begun as a quantum fluctuation out of nothing: a spatially finite fluctuation is much easier to imagine than an infinite one!
Note that if the expansion of space continues to accelerate, the Universe will easily expand forever, despite perhaps being formally "closed" (positively curved) like a beach ball. This differs from models in which space doesn't have a repulsive property and a closed universe definitely must end with a "big crunch."
A Nature of the Universe Debate, in memory of David Schramm, was held in Washington,
DC, on 4 October 1998. The title was: "The Nature of the Universe: Cosmology
Solved?" Speakers were:
P. James E. Peebles, an astrophysical cosmologist's viewpoint
Michael S. Turner, a particle cosmologist's viewpoint
Owen Gingerich, introductory talk
Joseph I. Silk, introductory talk
Margaret J. Geller, moderator
Details are available at:
http://antwrp.gsfc.nasa.gov/debate/debate98.html
