When does a star reach equilibrium?

Can someone me with 1 to 4 plz. fast

Observation and experimentation have led many scientists to accept a theory about the origin of the universe. this theory is called the big bang theory. scientific evidence collected and observed by scientists around the world suggests that the universe is ever expanding from a hot and dense initial state. what makes this a scientific theory? (2 points)

Which change to the system wood cause the freely-moving piston to lower?