Ch. 23 - Cosmology Part 2. The Beginning & the End. Skip Forward to 1964.
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The Beginning & the End
Penzias & Wilson discover isotropic emission at λ=7.35 cm. If a blackbody, T=3±0.5 K. Penzias talks on the phone to B. Burke, who heard from Ken Turner about a talk by P.J.E. Peebles (Princeton) who had predicted the universe would be filled with a 5 K radiation.
Discovery of the Cosmic Background Radiation (CBR).
1940s - Gamow, Alpher & Hermann, interested in nucleosynthesis, suggest that long ago the universe was hot & dense enough for the present heavy elements to be produced - BIG BANG,
1948 - Alpher & Hermann showed that a hot expanding universe should produce radiation redshifted to look like a T=5 K blackbody. However, this big bang model failed to correctly predict abundances of the heavies. Model largely forgotten by many, especially since….
1957 - Burbidge, Burbidge, Fowler & Hoyle (B2FH) demonstrated how heavies could be produced in stars.
1964 - Zel’dovich and (independently) Hoyle & Taylor realize that B2FH cannot make all the He we see today, but could have been made earlier.
R. Dicke (Princeton) realizes that the universe had to have been hotter in the past, and that the radiation could be detected today.
Peebles calculates necessary conditions for making lots of He but few heavies
Roll & Wilkinson make detector to observe 10 K radiation originally predicted by Dicke & Peebles
(Nucleosynthesis & radiation compete (γ-rays break up nuclei). Too little radiation ⇒too much nucleosynthesis. Too much radiation ⇒ too little nucleosynthesis. The CBR and He abundance today determine the state of the early universe.)
Before Dicke, Roll & Wilkinson complete their measurements, Dicke gets a call from Penzias regarding Peebles work.
Result: 2 Papers
Observations: “A measurement of excess antenna temperature at 4080 Mc/sec” Penzias & Wilson. (“… possible explanation is given by Dicke, Peebles, Roll & Wilkinson in a companion letter in this issue.”)
Theory: Dicke, Peebles, Roll & Wilkinson
1976 - Wagoner, Fowler & Hoyle work out “complete” Big Bang theory.
(Aside - Hoyle’s contribution here is “interesting” as he was a proponent of the Steady State model. He coined the term “Big Bang” as a derogatory term.)
Earliest observations seemed to deviate from a single-T blackbody.
A puzzling but exciting period of theoretical fantasies ensued……..
COBE Spectrum of the Universe - first 7 minutes of data (FAXed copy of version presented at AAS meeting)
Spectrum = Blackbody with T=2.726 K Dicke gets a call from Penzias regarding Peebles work.
Isotropy Measurement: after removal of Milky Way and Dipole Anisotropy (due to motion of Earth toward Virgo, etc.) Isotropic to within 1 part in 3x10-5.
Later (after years of accumulating data) higher-order anisotropies reported with ΔT/T~4.8±1.5x10-6.
The temperature and density fluctuations pointed toward the transition from a smooth big bang to the clumpy universe we have today.
Measured baryonic density ~ 0.05ρc.
Measured dark matter density ~ 0.3 ρc
So, ρmatter~ ρc to within a factor of ~3 today.
So at the time of recombination (z~1000) Ω=1 to within 1 part it 103, at the time of nucleosynthesis Ω=1 to within 1 part in 1012, and at the Planck time Ω=1 to within 1 part in 1060!
Coincidence?! Maybe Ω=1 precisely??? WHY???????
SN Ia Programs: Anisotropy (due to motion of Earth toward Virgo, etc.)
Other SN Ia data Anisotropy (due to motion of Earth toward Virgo, etc.) ⇒ H0=74±4 implying t0=12 Gyr for the best-fit region.
Results of WMAP: Anisotropy (due to motion of Earth toward Virgo, etc.)
k=0 (ΛCDM models)
t0=13.4 ±0.3 Gyr
What is the Λ-term?
Time variable “Dark Energy” with equation of state w≡p/ρ?
Pure cosmological constant Λ (w=-1)
Phantom Energy (w<-1) leading to “Big Rip”?
Current best estimate of w=-1.0 ±0.2
from Caldwell et al. 2003, PhRvL, 91, 1301.
Flatness problem: Why was Ωinitial so close to unity?
Isotropy (horizon) problem: How did distant locations of the universe, never in thermal contact, “know” how to be at the same temperature?
Monopole problem: GUTs predict production of magnetic monopoles, etc. - none ever detected.
Reionization of the Universe Anisotropy (due to motion of Earth toward Virgo, etc.)