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Physics Colloquium,
April 5, 2005
THE COSMIC TRIANGLE: REVEALING THE STATE OF THE UNIVERSE
Neta A. Bahcall
Princeton University
The Cosmic Triangle provides a way to represent the past, present, and future
state of the Universe. Our location within the Cosmic Triangle is determined by
the answers to three fundamental questions:
- How much matter is in the Universe?
- Is the Universal expansion rate slowing down or speeding up?
- Is the Universe flat or curved?
By combining recent observations of clusters of galaxies, distant supernovae, and the cosmic microwave background radiation, we find evidence indicating that we live in a lightweight Universe, with mass-density only about 25% the critical density needed to halt the Universal expansion. The observations indicate that the expansion rate of the Universe is speeding up, due to 'dark energy' that opposes the attractive force of gravity and causes the expansion rate to accelerate. The observations indicate that the Universe is flat, with no significant space curvature. These observations determine the evolution and the ultimate fate of the Universe, suggesting a Universe that will expand forever, growing ever larger, colder and darker. The measurements and their
implications for the cosmological model of our Universe will be discussed.
3.30 p.m., Smith Laboratory, Room 1005
Refreshments served at 3:00 p.m., Atrium PRB
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