What is dark matter?  What is one observation as evidence that dark matter should exist?  Explain.  No credit for single word responses.

Suppose an electron in an atom drops from energy level 4 to energy level 2. What happens to the lost energy?

According to the quantum model, which of the following best describes an electron in an atom?

A positively charged particle in the nucleus of an atom is a . A particle of light is a .

What is cosmic inflation?

How can we know the Sun’s atmosphere contains neon vapor?

According to General Relativity, what is gravity?

Suppose an electron in an atom jumps from energy level 2 to energy level 4. Where does the extra energy come from?

According to experiment, which interpretation correctly describes the fundamental nature of reality?

Suppose you are on a spaceship flying toward Earth at 0.9c, where c is the speed of light. In your frame of reference your ship is 10 meters long (front-to-back). How long is your ship, as measured from Earth’s surface?