The Big Bang Theory and Its Evidence: Practice Problem Solutions

1. It says the universe has been expanding and cooling for about 13.8 billion years, from a hot, dense state.

2. Georges Lemaitre; he was a Catholic priest.

3. A faint glow of microwaves from every direction, left over from when the early universe became transparent. Arno Penzias and Robert Wilson found it in 1964.

4. About 2.725 K. The ripples (about one part in 100,000) match the model and are the seeds of galaxies.

5. The CMB and the evolution of galaxies over time did not fit with a universe that always looks the same.

6. About 75% hydrogen and 25% helium by mass, which matches what is measured in old gas clouds. (Lithium is a puzzle.)

7. Any two of: what caused it; why the laws of physics are as they are; what dark matter and dark energy are; whether there was a 'before.'