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PPT : The Discovery of the Cosmic Microwave Background Radiation
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Cosmology in the Early 20th Century
* Prior to the 20th Century cosmology was the study of objects in the universe, not the physics of the universe as a whole.
* Einstein published General Relativity in 1915 which established a theoretical framework for understanding the universe as a whole.
* There was one cosmological fact – The night sky is dark (Olber’s paradox).
* Einstein ignored it and introduced the “cosmological constant” to allow a solution for an infinite static universe . Einstein’s biggest blunder?
* In 1925 Hubble showed that the Andromeda Nebula and other similar nebulae are separate galaxies, not part of the Milky Way.
* In 1929 Hubble and Humason formulated the redshift-distance law for Galaxies -> expanding or Big Bang universe.
Hubble Diagram 1929
* Cosmological Principle
* Red shift results from light traveling through expanding space.
* Hubble did not sample a large enough volume.
* The Hubble Constant derived from this data is 5x too large.
* The Earth was known to be older than the implied age of the universe
* Bondi, Gold and Hoyle proposed the steady-state theory.
The Andromeda Nebula (Galaxy)?
* Looking out from the earth, we saw the solar system, the Milky Way galaxy and other galaxies, mostly in clusters.
* All of these are gravitationally bound and do not expand with the universe.
* People were beginning to realize that in galaxies and clusters of galaxies, the motions imply more mass than is seen – Dark Matter.
Early Bell Labs Communication Satellite Work
* In 1955 John Pierce published a paper in ‘Jet Propulsion’ titled “Orbital Radio Relays”
* In 1957 Sputnik was launched and then in 1958 NASA proposed launching the 100’ diameter Echo balloon made of , 0.0005” aluminized mylar to measure the forces in orbit.
* Bell Labs proposed using Echo as a first communications satellite.
* The return signal would be weak, so they would combine two Bell Labs inventions to form a low noise receiving system.
o A traveling wave ruby MASER amplifier (the loweswt noise amplifier available)?
o A large horn-reflector antenna
* Echo was launched and used as a microwave relay in 1960. Eisenhower’s voice was transmitted by JPL and received at Crawford Hill
* Telstar was the first active communications satellite, launched in 1962
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