108 research outputs found
How dominant is the vacuum?
It would be hard to find a cosmologist today who does not believe that the
vast bulk of the Universe (ninety-five percent or more) is hidden from our
eyes. We review the evidence for this remarkable consensus, and for the latest
proposal, that the mysterious dark matter consists of as many as {\em four
separate ingredients}: baryons, massive neutrinos, ``exotic'' dark matter
particles, and vacuum energy, also known as the cosmological constant (Lambda).
Of these, only baryons fit within standard theoretical physics; the others, if
their existence is confirmed, will mean rewriting textbooks. New experimental
evidence has recently appeared for and against all four components, so that the
subject is in a state of turmoil and excitement. The past three years in
particular have seen the fourth (vacuum) component come into new prominence,
largely at the expense of the third (exotic dark matter). We conclude our
review by exploring the possibility that the energy density of the vacuum is in
fact so dominant as to leave little room for significant amounts of exotic dark
matter.Comment: 25 pp, 11 figs. References updated, expanded to match version in
press: Naturwissenschaften V. 88, Nr. 6 (2 July 2001
Scaling Relations for the Cosmological "Constant" in Five-Dimensional Relativity
When the cosmological "constant" is derived from modern five-dimensional
relativity, exact solutions imply that for small systems it scales in
proportion to the square of the mass. However, a duality transformation implies
that for large systems it scales as the inverse square of the mass
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