|Sonoma State University||J.S. Tenn|
Assumptions of homogeneity, isotropy lead to expanding or contracting models. Einstein introduces cosmological constant Λ to allow static universe.
Slipher: Spiral nebulae have large blueshifts and redshifts. This supports idea that they are external galaxies.
Hubble: Except for a few nearby nebulae, velocities of recession are proportional to distances. v = H0d H0 = 550 (km/s)/Mpc 1/H0 = 1.8 Gyr
Lemaître expands on his 1927 proposal that the Universe began a finite time ago with an explosion, but he omits "Hubble Law" from his 1931 translation.
|1950s||Baade revises distance scale: H0 = 275 1/H0 = 3.6 Gyr|
|1960s||Quasars are found; they are more abundant at high redshifts than at low.
Most cosmologists agree that the universe is evolving.
|1970s||Sandage & Tammann: H0 = 50 1/H0 = 20 Gyr
de Vaucouleurs, others: H0 = 100 1/H0 = 10 Gyr
“Standard Model” explains most observations.
Abundances of He, D support standard model.
Average density = 0.1 critical density.
Particle physics and cosmology interact.
|1980s||Guth, others: Inflationary model solves many problems, requires “flat” universe.
Simulations of early universe require cold dark matter. What is it? Is there enough to make the universe “flat?”
Huge structures are found. Is the universe really homogeneous?
COBE finds some structure in CMB.
Deuterium abundance measured. Agreement with big bang nucleosynthesis requires baryon density ≅ 0.05 critical density.
Motions of galaxies require total matter density (baryon + ?) ≅ 0.3 critical density. To get “flat” universe cosmologists assume cosmological constant, now thought of as pressure of vacuum.
HST observations of supernovae: H0 = 67 ± 10, expansion is accelerating, Λ ≠ 0.
SuperKamiokande experiment: muon neutrino has a small mass.
SNO confirms that neutrinos have mass. The total mass of neutrinos may equal that of stars.
WMAP measures fluctuations in CMB over entire sky. Best fit to WMAP data combined with measurements of type Ia SN and Baryon Acoustic Oscillations in the galaxy distribution: Universe is “flat,” baryon density = 0.0462 ± 0.0015, dark matter density = 0.233 ± 0.013 (and it’s cold), remaining 0.721 ± 0.015 is ascribed to “dark energy.” Also H0 = 70.1 ± 1.3, age of universe is 13.73 ± 0.12 Gyr, and first stars formed between 100 and 400 million years after the expansion began. [These numbers, announced in 2008, represent five years of WMAP observations.]
MiniBooNE experiment at Fermilab confirms that there are only three kinds of neutrinos.
NOTE: Gyr = billion years = 109 years = Ga (giga-annum), all values of the Hubble parameter H0 are in (km/s)/Mpc, and densities are fractions of the critical density, i.e., values of omega. “Flat” means Euclidean.
|Another history of cosmology, by Prof. Richard McCray of the Univ. of Colorado|
and another, from the American Institute of Physics Center for History of Physics
|Astronomy 350 Cosmology||Cosmology Books and Links|
|Please send comments, additions, corrections, and questions