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.