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An introduction to the cosmic microwave background W. Hu
An introduction to
the cosmic microwavebackgroundW. Hu
"Big Bang" • Universe Began Hot and Dense• Expands and Cools
"Gravitational Instability"
• Galaxies ("Structure") from the self-attraction of primordial fluctuations
Cosmological Background
gravityW. Hu
Cosmological Expansion
Recession Velocity
Expansion Redshift
W. Hu
CMB Properties
• 3 degrees above absolute zero (-270˚C)
• mm-cm wavelength (1-10% microwave oven)
• 400 photons/cm (10 trillion photons/sec/cm )3
• Few percent of TV "snow"
• Temperature slightly different on differentparts of the sky (Wrinkled or anisotropic at 1 pt in 100000)
2
W. Hu
%CMB
Large–Angle Anisotropies
Actual Temperature DataReally Isotropic!
W. Hu
Large–Angle Anisotropies
dipole anisotropy1 part in 1000
W. Hu
Large–Angle Anisotropies
10º–90º anisotropy1 part in 100000
W. Hu
Very Brief History
Nucleo-Synthesis
LastScattering
GalaxyFormation
3 min 3x105yrs 5x109yrs
pnHe
e
CMBg
W. Hu
Gravitational Instability"Wrinkles" or Hills & Valleys
Accumulation in Valleys
Initial
After InfallW. Hu
Inflation to Structure Formation
PresentInflation
<10-35s 1010yrs
Gra
vita
tion
al In
stab
ility
Exp
onen
tial
Stre
tch
Lar
ge S
cale
Str
uct
ure
Gal
axie
sTime
Rap
idE
xpan
sion
W. Hu
Inflation to Structure Formation
PresentInflation
<10-35s 1010yrs
Gra
vita
tion
al In
stab
ility
Exp
onen
tial
Stre
tch
Lar
ge S
cale
Str
uct
ure
Gal
axie
s
Rap
idE
xpan
sion
Horizon
HorizonCrossingW. Hu
Inflation to Structure Formation
PresentInflation
<10-35s 1010yrs
Gra
vita
tion
al In
stab
ility
Exp
onen
tial
Stre
tch
Lar
ge S
cale
Str
uct
ure
Gal
axie
s
Rap
idE
xpan
sion
Horizon
HorizonCrossing
CMBObserver
LastScattering
3x105yrs
W. Hu
Large–Angle Anisotropies
10º–90º anisotropyseeing beyond the horizon
W. Hu
Understanding Maps
COBE's fuzzy vision
W. Hu
Understanding Maps
COBE's fuzzy vision
W. Hu
Understanding Maps
COBE's imperfect reception
W. Hu
Understanding Maps
Our best guess for the original map
W. Hu
Small–Angle Anisotropies
<1º anisotropyseeing inside the horizon
?
W. Hu
Small–Angle Anisotropies
Horizon
HorizonCrossingW. Hu
Small–Angle Anisotropies
Horizon
LastScattering
Present
3x105yrs 1010yrs
W. Hu
Small–Angle Anisotropies
CMBObserver
Horizon
LastScattering
Present
3x105yrs 1010yrs
W. Hu
Seeing Sound
Harmonic Features:Origin of Fluctuations
(Inflation?)
Fate of the Universe(Eternal expansion?Big Crunch?)
W. Hu
Music of Inflation
Present
Inflation
1010yrs
Exp
onen
tial S
tret
chR
apid
Exp
ansi
on
CMBObserver
Horizon
LastScattering
Present
3x105yrs
Fundamental
W. Hu
Music of Inflation
Present
Inflation
1010yrs
Exp
onen
tial S
tret
chR
apid
Exp
ansi
on
CMBObserver
Horizon
LastScattering
Present
3x105yrs
Overtones 1:2:3...
W. Hu
Current CMB Quilt
FIRS BAM SP91 IABPyth MSAM WD OVRO SuZIE(Sask)(COBE)Tene SP94 MSAM RING ATCAArgo
(CAT)QMAP MAXCOBE Pyth95 CATSask
10 100
110
20
40
60
80
100
l (multipole)
θ (degrees)
∆T (µ
K)
W. Hu – Sept. 1998
Curvature and Fate of Universe
Flat
Curved
Negative Curvature: Expand ForeverPositive Curvature: Big Crunch
W. Hu
Microwave Background Triumphs
Validation of
• Big Bang (Hot, Expanding Univ.)
Thermal SpectrumTemp. at early times
• Gravitational Instability (wrinkles galaxies)
Amplitude and Spectrum ofAnisotropies
W. Hu
Microwave Background Future
How Microwaves Ring
• Origin and Evolution of Structure (galaxies...)
Music of Inflation?
• Ultimate Fate and Global Propertiesof the Universe
Curvature, Content (dark matter)
W. Hu
