CMB. Suggested Reading: Ryden, Chapter 9

Transcription

1 CMB Suggested Reading: Ryden, Chapter 9

2 1934, Richard Tolman, blackbody radiation in an expanding universe cools but retains its thermal distribution and remains a blackbody 1941, Andrew McKellar, excitation of interstellar CN doublet absorption lines gives an effective temperature of space of ~2.3K Flux McKellar, PDAO, 7, 251 (1941) Wavelength (Å)

3 1946, Gamow, to match observed abundance, nuclei should be built up out of equilibrium in hot early universe (high expansion rate, assume matter domination) 1948, Gamow, T~10 9 K when deuterium formed, argues for radiation domination in early universe; the existence of CMB 1948, Alpher, Bethe, & Gamow (αβγ paper), element synthesis in an expanding universe; calculations based on previous ideas 1948, Alpher & Herman, make corrections to previous results; state that present radiation temperature should be ~5K (close! but largely a coincidence; incorrect assumptions - neutron dominated initial state); no mention of the observability.

4 1957, Shmaonov, horn antenna at 3.2cm, find the absolute effective temperature of radio emission background 4±3K, independent of time and direction Early 1960s, Zel dovich, Doroshkevich, Novikov, estimate expected background temperature from helium abundance; realize Bell Labs telescope can constrain 1964, Hoyle & Tayler, essentially correct version of primordial helium abundance calculation (no longer pure neutron initial state; weak interaction for neutron vs proton) 1965, Dicke, Peebles, Roll, & Wilkinson, realize oscillating or singular universe might have thermal background; build detector to search; then they hear about the discovery of...

5 1965, Penzias & Wilson, antenna has isotropic noise of 3.5±1.0K at wavelength of 7.35cm; careful experiment (e.g., shooed away pigeons roosted in the antenna; cleaned up the usual white dielectric generated by pigeons); explanation could be that of Dicke et al. Nobel Prize in Physics (1978)

6 1965, Roll & Wilkinson, detect the radiation background at 3.2cm, with amplitude consistent with Penzias & Wilson for blackbody spectrum; isotropic to 10% (fl V) QJ I- e CL lo '4- K O O ~lo l6 ta 0 E lo-is XxtO O pg) Z~ 0 O-20 l P R I NC E TON (3.5 (3.i Roll & Wilkinson, PRL (1965) l lo' IO IO I WAVELENGTH (c m )!0 ' FIG. 2. Measurements to date of the microwave background radiation. The galactic radio background is extrapolated with a spectral index of n =0.5. This figure due to P. J. E. Peebles.

7 , Field & Hitchcock, Shklovsky, Thaddeus & Clauser, Thaddeus (following a suggestion by Woolf) independently show that the excitation of interstellar CN is caused by CMB (McKellar s 1941 observation explained!) 1970s, 1980s, ground, balloon, satellite observations 1990, NASA s COsmic Background Explorer (COBE) satellite confirms CMB as nearly perfect isotropic blackbody and discovers the anisotropies. John Mather & George Smoot Nobel Prize in Physics (2006)

8 CMB - Main Observational Results 1. nearly perfect blackbody spectrum of temperature T=2.73K Blackbody spectrum of CMB measured by COBE (1990) [error bars enlarged by 400x!]

9 CMB - Main Observational Results 1. nearly perfect blackbody spectrum of temperature T=2.73K Scott 1999 CMB dominates the energy density of radiation backgrounds Blackbody spectrum of CMB measured by COBE (1990) [error bars enlarged by 400x!]

10 CMB - Main Observational Results 2. isotropic, better than ~10-3

11 CMB - Main Observational Results 3. anisotropy, 10-3 level, dipole, kinetic effect v~370km/s our motion w.r.t. the CMB frame

12 CMB - Main Observational Results 4. anisotropy, 10-5 level, primordial Planck Satellite COBE WMAP (Wilkinson Microwave Anisotropy Probe)

13 CMB - Main Observational Results 5. weak polarization, 10-7 level primordial (grav. waves) [not detected yet/bicep2?]+reionization COBE WMAP (Wilkinson Microwave Anisotropy Probe)