#3 A Brief History of Time - The expanding universe

Chapter 3:

1. Edwin Hubble and his red-shifted universe

   1. On a spectrum of star, light with longest wavelength appears at the red end, light with the shortest appears on the blue end

   2. When a star is moving away from us, the wavelength of the light it emitted will increase

   3. Edwin Hubble found out most galaxies appeared red-shifted, which means they are moving away from us

   4. The further the galaxy, the faster it is moving away

2. Microwave radiation

   1. The expansion of the universe meant that the glow of early universe should be so greatly red-shifted, it would appear to us now as microwave radiation

   2. In 1965, Arno Penzias and Robert Wilson discovered the radiation

3. Friedmann's 3 models of the expanding universe

   1. The universe is growing slowly and will eventually stop due to attractive forces between galaxies (space is finite and bent like Earth's surface)

   2. The universe is growing so rapidly that the gravitational attraction never stops it (space is bent like a saddle)

   3. The universe is expanding just fast enough not to collapse, and the speed of separation gets smaller but never 0 (space is flat)

4. "Dark matter"

   1. There should be a lot of unobservable matter to halt the expansion of the universe

5. Singularity

   1. It has an infinite curvature of space and time, our tools (rules in science) will not work at the singularity