The Cosmic Triangle: Revealing the State of the Universe

Abstract

The "cosmic triangle" is introduced as a way of representing the past, present, and future status of the universe. Our current location within the cosmic triangle is determined by the answers to three questions: How much matter is in the universe? Is the expansion rate slowing down or speeding up? And, is the universe flat? A review of recent observations suggests a universe that is lightweight (matter density about one-third the critical value), is accelerating, and is flat. The acceleration implies the existence of cosmic dark energy that overcomes the gravitational self-attraction of matter and causes the expansion to speed up.

36 pages, 8 eps figures, use epsfig.sty, final draft of paper to appear in Science 284, 1481-1488, (1999) Change to CMB plot, Fig. 6 (third MSAM data point corrected) Addition of second CMB plot with more recent data added Minor typo in figs. 1 and 2 corrected