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