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Cosmic Microwave Background
Looking back in time
Matter-Radiation Densities in Universe
Dark Energy Dominated Universe
Cosmic Microwave Background
• Discovered by Arno Penzias and Robert Wilson• They were studying the Milky Way’s emission
of microwave (radio) wavelengths.• As they tried to calibrate their antenna, they
were bothered by a “background hiss” that they could not escape.
• The hiss was like static and came from everywhere – weak and detectable at any time of the day.
Cosmic Microwave Background
• The source of the “radio noise” was absolutely uniform, from all directions, and unchanging in time.
• Penzias and Wilson, after conversing with scientist working on roughly the same problem at Princeton, came to the conclusion that the mysterious static was the fiery creation of the universe itself.
Cosmic Microwave Background
– It is the remains from the days early on when the universe was radiation (high-energy gamma rays) dominated – before matter “vanquished it.”
– This won them the 1978 Nobel Prize.• Before Penzias and Wilson, researchers had
predicted the existence and properties of the microwave background (as early as the 1940s). – The Princeton scientists had predicted that the
gamma radiation would have been redshifted as the universe expanded.
Cosmic Microwave Background
• The CMB can be thought of as a “fossil remnant” of the primeval universe.