Einstein's elevator thought experiment Were there any background theories for Einstein's elevator thought experiment which developed the equivalence principle?
Can Newton's equivalence principle (the equality of inertial and gravitational mass) be considered a "background theory" or an "unproblematic phenomena"?
 A: Were there any background theories for Einstein's elevator thought experiment which developed the equivalence principle. Can Newton's equivalence principle (the equality of inertial and gravitational mass) be considered a "background theory" or an "unproblematic phenomena"?
I’m not aware of any background theories other than that Einstein interpreted the equivalence of gravitational mass and inertial mass  (which was already known) as being a fundamental unique property of the gravitational field giving all bodies the same acceleration. I believe I read the idea initially came to him in thinking about being weightless in a free falling elevator. But the thought experiment was more fully described it in his book “Relativity: The Special and General Theory” was for a person in a compartment without a gravitational field present but with the compartment accelerating. The person would have no way of knowing if he were in an accelerating compartment, or a compartment at rest in a gravitational field.
Hope this helps.
