ASTR 5 Lecture Notes - Lecture 1: Cosmic Microwave Background, Rubber Band, Radiography
Document Summary
This is because there has only been a finite amount of time for them to travel. Therefore, our universe must have evolved, it had a start. Observed doppler shifts of galaxies: hubble makes a major discovery of the 20th. Paradox: 1/h = 4 x 10^17 seconds = 13. 5+/-0. 5 billion years ago, expansion started! We don"t have a good enough radio receiver to detect it. When it cooled to the same temperature as a star"s surface, neutral hydrogen atoms could finally survive (380,000 years after the big bang). This is called recombination", so at that time the universe became transparent, after which photons traveled in uninterrupted straight lines. Protons and neutrons stabilize: at t=1 second, the universe was a hundred billion degrees celsius, hotter than the center of a supernova, nuclear fusion reactions begin to take place throughout the entire universe (ex: heavy hydrogen/deuterium, helium)
