Context: Classical statistical mechanics requires the existence of h (but does not define its value). Eventually, following upon Planck's discovery, it was recognized that physical action cannot take on an arbitrary value. Instead, it must be some multiple of a very small quantity, the "quantum of action", now called the Planck constant. Classical physics cannot explain this fact. In many cases, such as for monochromatic light or for atoms, this quantum of action also implies that only certain energy levels are allowed, and values in between are forbidden.

Question: Classical statistical mechanics requires the existence of what?
Answer: h

Question: What was realized after Planck's discovery?
Answer: that physical action cannot take on an arbitrary value

Question: What is the Planck constant formerly known as?
Answer: quantum of action

Question: Regarding atoms, what does the Planck constant imply?
Answer: that only certain energy levels are allowed

Question: Regarding atoms, what are values in between certain energy levels considered by the Planck constant?
Answer: forbidden

Question: Following Planck's discovery, what was realized about values of physical action?
Answer: physical action cannot take on an arbitrary value

Question: The Planck constant initially was given what name?
Answer: the "quantum of action"

Question: How is the proportional nature of the Planck constant explained?
Answer: Classical physics cannot explain this fact

Question: For certain cases of light or atoms, what does the quantum of action yield?
Answer: only certain energy levels are allowed, and values in between are forbidden.

Question: What does modern statistics mechanics not define the value of?
Answer: Unanswerable

Question: What is not required to exist in modern statistics mechanics?
Answer: Unanswerable

Question: What does the Planck Constant negate?
Answer: Unanswerable

Question: What is the Planck constant incorrectly known as?
Answer: Unanswerable

Question: Which science is the proportional nature of the Planck constant fact?
Answer: Unanswerable