observed matter
1% of critical density is visible matter (stars & gas)
nucleosynthesis in early universe
~5% of critical density is ordinary matter (protons & neutrons)
gravitational effect in galaxies & clusters of galaxies
~30% of critical density is matter
accelerating expansion
~70% of critical density is dark energy
inflationary model, fluctuations in background radiation
100% of critical density total
Summary:
5% ordinary matter
1% visible
25% extraordinary matter (dark)
70% dark energy
visible universe is only the tip of the iceberg!
29 x's more dark matter than visible!
5 x's more extraordinary matter than ordinary!
universe is dominated by dark energy!
has mass but emits little or no light
detected by gravitational effect
What is it?
MACHOs(Massive Astrophysical Compact Halo Objects)ordinary matter (must be < ~5%)
e.g. planets, white dwarfs, neutron stars, black holes
WIMPs
(Weakly Interacting Massive Particles)neutrinosextraordinary matter
hypothesized sub-atomic particles
do they exist?
extraordinary matterwe know they exist in large numbers
don't have nearly enough mass to account for 25%
Dark Energy
opposes gravity to cause expansion to accelerate
smoothly distributed
detected by measuring expansion rate in the past using distant supernovas
expansion decelerated at first, then began accelerating
What is it?
cosmological constant ? = energy of empty space ("vacuum")quintessence ? = energy field, as during inflation
new physics ?
Links - Dark Energy:
www.space.com
Discover
Science News
SNAP satellite
Physics Today
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