Lec31 - Possible models of universe Does Gravity alone...

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Unformatted text preview: Possible models of universe Does Gravity alone Influence Universe’s Expansion? • Recent observations of white dwarf supernovae in very distant galaxies have yielded unexpected results. • Remember, white dwarf supernovae make very good standard candles. • Supernovae are apparently fainter than predicted for their redshifts. • At a given cosmological redshift • galaxies should be closer to us… i.e. shorter lookback time …for greater Universal mass densities • these supernova are farther back in time than even the models for an ever- expanding (coasting) Universe predict • This implies that the Universal expansion is accelerating ! • there must be an as yet unknown force which repels the galaxies • a dark energy Four Models for the Future of the Universe 1. Recollapsing Universe: the expansion will someday halt and reverse 2. Critical Universe: will not collapse, but will expand more slowly with time 3. Coasting Universe: will expand forever with little slowdown 4. Accelerating Universe*: the expansion will accelerate with time *currently favored Some say the world will end in fire, Some say in ice. From what I’ve tasted of desire I hold with those who favor fire. But if it had to perish twice, I think I know enough of hate To say that for destruction ice Is also great And would suffice.- Robert Frost 23. The Beginning of Time Carl Sagan (1934 – 1996) American astronomer Somewhere, something incredible is waiting to be known. 23.1 Running the Expansion Backward • How can we presume to understand the conditions that existed in the early universe? Our goals for learning: The Creation of Matter • The early Universe was filled with radiation & subatomic particles. • We’ve seen matter converted to energy… • but Einstein’s famous equation is a two-way street!...
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This note was uploaded on 02/01/2012 for the course PHYS 133 taught by Professor Staff during the Fall '08 term at University of Delaware.

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Lec31 - Possible models of universe Does Gravity alone...

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