Transcript Big Bang

Big Bang
Radio Noise
Theory
• Hubble’s law suggests that
any initial radiation would
be extremely redshifted.
• If there was start to the
universe then the
radiation would have a
blackbody spectrum.
Experiment
• In 1964 Penzias and
Wilson measured
background radio noise.
– Cosmic microwave
background
• The intensity was
consistent with blackbody
radiation at 3K.
Hot Radiation
• If the universe had a
beginning there would
be a start – Big Bang.
• An initial burst of
light would be as hot
as a star.
– Not as hot as a
plasma
– About 3000 K
Stretching Light
• As the universe expands the
wavelength of light stretches.
– Burst of light: 3000 K
– Peak radiation:1 micron
– Visible light
• Today the universe is 1000
times larger.
– Temperature: 3 K
– Peak radiation : 1 mm
– Microwaves
1 wavelength, small universe
1 wavelength, expanded universe
COBE
• In 1989 NASA launched
the COBE satellite.
– Measure far infrared
spectrum
– Black body temperature
2.728 K
Anisotropy
• COBE measured
fluctuations in the CMB.
– One part in 100,000
– Eliminate Earth’s
motion
– Remove Milky Way
noise
• The CMB is anisotropic –
different by direction.
WMAP
• The Wilkinson Microwave
Anisotropy Probe was
designed to measure the
CMB.
– Launched in 2001
– Ended 2010
• WMAP measured five
microwave frequency
bands.
More Precise
• WMAP improved
COBE’s measurements.
– Blue 2.7249 K
– Red 2.7251 K
• The anisotropy points at
the fraction of matter of
different types.
– Ordinary matter 5%
– Cold dark matter 23%
– Dark energy 72%
Age of the Universe
• The Hubble constant is related to the age of the universe.
– H0 = (73.5 km/s)/Mpc; 1 Mpc = 3 x 1019 km
– 1/H0 = 4 x 1017 s = 13.7 billion years
• This is consistent with the most distant quasars.
• The Planck satellite is measuring the CMB with more
precision.