Cosmology - The cosmic triangle: Revealing the state of the universe

The cosmic triangle is introduced as a way of representing the past, presen t, and future status of the universe. Our current location within the cosmi c triangle is determined by the answers to three questions: How much matter is in the universe? Is the expansion rate stowing 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), i s accelerating, and is flat. The acceleration implies the existence of cosm ic dark energy that overcomes the gravitational self-attraction of matter a nd causes the expansion to speed up.