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Summary
By studying Type Ia supernovae, exploding stars visible at distances so vast that they represent earlier epochs of cosmic history, astronomers are getting a look at the ultimate fate of the universe. By comparing the brightness of these beacons--an indicator of their distance--with the rate at which cosmic expansion is carrying them away, two groups of observers are now closing in on the rate at which cosmic expansion has changed over time. Early results suggest that high matter density is slowing the universe's expansion, and that the cosmos contains hundreds of times more mass than can be seen as stars and galaxies--a conclusion that may conflict with other clues suggesting a low-density universe (see p. 36).
