Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001kcs..confe...5f&link_type=abstract
Presented at the KITP: Colloquium Series, May 23, 2001, Kavli Institute for Theoretical Physics, University of California, Santa
Physics
Scientific paper
Type la (hydrogen-deficient) supernovae have enormous potential for thedetermination of fundamental cosmological quantities. Relatively low-redshift Type la supernovae demonstrate that the Hubble expansion islinear , that the Hubble constant has a value of 65 +1- 2 km/s/Mpc(statistical uncertainty), that the bulk motion of the Local Group isconsistent with the COBE result, and that the properties of dust in othergalaxies are similar to those of dust in the Milky Way. The light curvesof high-redshift (z = 0.3-1) supernovae are stretched in a mannerconsistent with the expansion of space; similarly, their spectra exhibitslower temporal evolution (by a factor of 1 +z) than those of nearbysupernovae. Our most important conclusion is that the expansion of theUniverse is accelerating, perhaps due to the presence of vacuum energy,also referred to as Lambda or Einstein's "cosmological constant." Thus,Einstein seems to have been right after all, but for the wrong reason (andwith the incorrect numerical value for Lambda). We derive a currentdynamical age of 14 +1- 2 billion years for the Universe, consistent withthe ages of globular star clusters. Moreover, combining our results withexisting measurements of the cosmic microwave background radiation, wefind a best fit for the normalized matter density and vacuum energydensity in the Universe of about 0.3 and 0.7, respectively. With a sumclose to unity, this agrees with the value predicted by most inflationarymodels for the evolution of the Universe, and indicates that the Universeis flat (Euclidean geometry) on large scales. A number of systematiceffects (dust, evolution) might be affecting our results and will bediscussed, but so far they don't seem to eliminate the need for nonzeroLambda. Most recently, analysis of a supernova at redshift 1.7 providesfurther support for acceleration, rather than some other astrophysicalsystematic effect.
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