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Summary
For decades, astronomers' observations have indicated that some elusive "dark matter" provides most of the gravity needed to keep the stars from flying out of the galaxies. In recent years, cosmologists' studies of the afterglow of the big bang, the cosmic microwave background, have indicated that dark matter makes up 80% of all matter in the universe. Now, many physicists expect that within 5 to 10 years they will finally discover particles of dark matter—that is, if they haven't already done so. Data from three experiments all suggest that physicists have glimpsed dark matter particles much less massive than they had expected, or so argues a group of theorists at Fermi National Accelerator Laboratory. Physicists working on other experiments say their results rule out such particles, but the Fermilab group contends that a realistic look at the data and the uncertainties shows no fatal contradictions.
