How the Universe got its SpotsHow the Universe got its Spots
Edmund Bertschinger
MIT Department of Physics
Outline
• Introduction: the Big Bang
• Cosmic Microwave Background Radiation
• A sonogram of the early universe
• What have we learned?
• Outstanding questions
The Big Bang
• The Universe as we know it began 13.7 billion years ago in an explosion so powerful that space itself was propelled outwards.
• Even atoms could not exist in this hot fireball.
• 380,000 years after the bang, H atoms formed
• 200 Million years later, the first stars formed
How do we know?
Measuring the Afterglow of the Big Bang
WilkinsonMicrowaveAnisotropyProbe(WMAP)
Launched:Summer, 2001
(NASA/WMAPScience Team)
What is the Microwave Background?
The cosmic microwave background radiation is the thermal (blackbody) radiation emitted by the hot dense gas formed in the Big Bang.
It was discovered by Penzias and Wilson in 1965; they received the Nobel Prize in 1978.Animation
WMAP Actual Sky Maps
Top: Foregrounds removed. Bottom: 41 GHz
NASA/WMAP Science Team
Our View Before WMAP
A cosmic sonogram
• The Big Bang began with a burst of near-exponential expansion: cosmic inflation
• Quantum mechanical fluctuations in energy made ripples in the gasAnimation
• Fluctuations in radiation == Sound waves!– Light as sound?! Yes!
• Cosmic redshift: Doppler shift in an expanding universe
The Sonogram in Numbers:Angular Power Spectrum
Top: Temperature fluctuations vs. angular scale
Bottom: Cross-correlation of temperature and linear polarizationvs. angular scale
What have we learned from these spectra?
• Age, size, and curvature of the universe– 13.7 Billion yr, consistent with infinite Euclidean space
on scales of 50 Billion lt-yr
• Contents of the universe: bizarre!– 4% atoms (almost all Hydrogen and Helium)– 23% cold dark matter (elementary particles as yet
undiscovered on Earth) detected by its attractive gravity– 73% mysterious “dark energy” (we’re not even sure of
the physics of this substance!) detected by its repulsive gravity causing the cosmic expansion to accelerate
• Hydrogen was re-ionized about 200 Myr after BB
The WMAP results greatly improve our estimates of cosmic parameters.
Four years ago, cosmologists proposed an accelerating universe.
WMAP (in green) strongly confirms this.
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