CMB
Suggested Reading: Ryden, Chapter 9
1934, Richard Tolman, blackbody radiation in an expanding
universe cools but retains its thermal distribution and
remains a blackbody
Flux
1941, Andrew
AndrewMcKellar,
McKellar,excitation
excitationof
ofinterstellar
interstellarCN
CN
doublet absorption lines gives an effective temperature of
space of ~2.3K
McKellar, PDAO, 7, 251 (1941)
Wavelength (Å)
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~109K 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.
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 ...
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)
1965,
Roll
& Wilkinson,
detect
radiation
background
3.2cm,
1965,
Roll
& Wilkinson,
detect
thethe
radiation
background
at at
3.2cm,
"with
amplitude
consistent
with
Penzias
&1966
Wilson
blackbody
7 MARcH
LETTERS
amplitude
consistent
with
Penzias
& Wilson
forfor
blackbody
ALwith
REVIEW
spectrum;
isotropic
to
10%
spectrum;
isotropic
to
10%
of
cold
ble I)
t of
nts
of erments
perexpersure
lo '4-
(fl
V)
QJ
I- eCL
O
K ~lO
l6
P R I NC E TON
(3.5
(3.
O
i
& Wilkinson,
(1965)
Roll Roll
& Wilkinson,
PRL PRL
(1965)
tA
0XxE lO-is
O p
0Z~
g)
0 O-20
tO
l
in
and
l
to
nsisemthe
great-
ng-wave-
ex-
the
lo'
IO
IO
WAVELENGTH
!0
I
(c m
'
)
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.
1966-1967, 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)
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!]
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!]
CMB - Main Observational Results
2. isotropic, better than ~10-3
CMB - Main Observational Results
3. anisotropy, 10-3 level, dipole, kinetic effect
v~370km/s
our motion w.r.t. the CMB frame
CMB - Main Observational Results
4. anisotropy, 10-5 level, primordial
Planck Satellite
COBE
WMAP (Wilkinson Microwave Anisotropy Probe)
CMB - Main Observational Results
5. weak polarization, 10-7 level
primordial (grav. waves) [not detected yet/BICEP2?]+reionization
COBE
WMAP (Wilkinson Microwave Anisotropy Probe)