The universe is expanding - so, at one time, it was very small.
Cosmic Background Radiation
Knowing how fast light travels allows us to determine how far apart things in the universe are, and how old they are.
Knowing the life cycles of stars gives us an understanding of the formation of solar systems, and how long this takes.
The Red Shift
Galaxies were forming 10-15 billion years ago.
Based of half-lives of radioactive elements, we can determine the relative ages of things within our solar system.
Hubble's Law
This shows when objects are moving away from you, because of the changes to the color of light.
Stellar Formation and Evolution
Quasars
Radioactive Decay
The universe was once very hot, and has cooled off over time.
Speed of Light
