1. How the Universe got its Spots Edmund Bertschinger MIT Department of Physics

2. Outline Introduction: the Big Bang Cosmic Microwave Background Radiation A sonogram of the early universe What have we learned? Outstanding questions

3. NASA/WMAP Science Team

5. 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?

6. Measuring the Afterglow of the Big Bang Wilkinson Microwave Anisotropy Probe (WMAP) Launched: Summer, 2001 (NASA/WMAP Science Team)

7. The Cosmic Microwave Background Radiation From COBE (1994) to WMAP (2003) NASA/WMAP Science Team

8. 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

9. WMAP Actual Sky Maps Top: Foregrounds removed. Bottom: 41 GHz NASA/WMAP Science Team Our View Before WMAP

10. 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 gasAnimationAnimation Fluctuations in radiation == Sound waves! –Light as sound?! Yes! Cosmic redshift: Doppler shift in an expanding universe

11. The Sonogram in Numbers: Angular Power Spectrum Top: Temperature fluctuations vs. angular scale Bottom: Cross- correlation of temperature and linear polarization vs. angular scale

12. 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

13. We are not made of the same type of matter as most of the Universe!

14. The WMAP results greatly improve our estimates of cosmic parameters. Four years ago, cosmologists proposed an accelerating universe. WMAP (in green) strongly confirms this.

15. NASA/WMAP Science Team We have seen the seeds of cosmic structure animation

17. Outstanding questions What is the dark energy? –Is it the “cosmological constant?” –What new physics acts on cosmic scales to produce this substance? What is the dark matter? Can we now fully understand the formation of galaxies?