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The Cosmic Triangle: Revealing the State of the Universe

N. Bahcall, J. P. Ostriker, S. Perlmutter, P. J. Steinhardt

astro-pharXiv:astro-ph/9906463

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.

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