There is still a growing body of evidence that something is missing in our inventory of the contents of the universe. The big question is, what is the nature of this non-luminous ( or under-luminous) stuff, and how much is there in the universe? Last year, in 1994, a new round of experiments by physicists showed that neutrinos have a definite non-zero mass. Since there are as many of these as there are photons in the cosmic microwave background radiation, they may contribute as much as 30% of the total mass density needed to make the universe 'critical' with an Omega = 1.
Some of the expected 'dark matter' can be made to go away if we adopt a non-zero Cosmological Constant in the universe. This might also help the current incompatibility between the age of the universe dated from the expansion rates implied by the two galaxies observed by the Hubble Space Telescope, and the ages of the oldest globular cluster stars.
Since 1998, astronomers using distant supernovae have begun to detect that the universe's expansion is accelerating just as though there is a cosmological constant force present in space. By combining the supernova data and the cosmic background data from balloon observations, in the above plot, it is becoming very clear that Omega is very close to 1.0; that dark matter and baryonic luminous matter (Omega-m) account for 30% of this, and that a cosmological constant of 70% of Omega is consistent with the two independent sets of data. In general, the astronomical community now seems pretty convinced from over 20 years of studies using many different techniques, that there is a cosmological constant present and lots of cold dark matter. The purple intersection region above shows the area of overlap between the different estimates. Clearly, a universe with no cosmological constant ( lambda = 0) is excluded, just as one in which Omega is 100% lambda with no/little matter. The best range is for Dark Matter to be about 30% and Lambda about 70% with ranges of about 20-40% and 60-80% respectively. The NASA, MAP mission will refine these numbers to 1% accuracy by 2002.
Copyright 1997 Dr. Sten Odenwald
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