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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"?

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  • $\begingroup$ What do you mean by "background theories"?? Do you mean theories that historically preceded GR? Or are you asking about what kind of thinking led Einstein to the equivalence principle? Or something else? Please be specific. $\endgroup$ – N. Steinle Dec 31 '18 at 0:03
  • $\begingroup$ Both, for this question, were there any theories which helped develop the equivalence principle directly? Would inertial mass = gravitational mass be considered to be a theory which helped develop the equivalence principle? $\endgroup$ – Maths Dec 31 '18 at 0:06
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    $\begingroup$ Please update your question and expound upon these curiosities. Show us that you've done some investigating of your own, and you're more likely to get a good answer. $\endgroup$ – N. Steinle Dec 31 '18 at 0:16
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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.

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    $\begingroup$ Obviously, the galilean equivalence principle could be considered as a background theory? $\endgroup$ – N. Steinle Dec 31 '18 at 0:57
  • $\begingroup$ Thank you. Thank you @Bob D. If you don’t mind, please could you help with something else too. Norton presents the elevator thought experiment in argument form with premises and a conclusion as follows. Premise 1: In a box, an observer will see free bodies move identically when the box is uniformly accelerating in gravitational free space and when the box is at rest in homeogenous gravitation field. Premise 2: Einstein generalised this for all observable phenomena. Would you know what grounds he had for this strong generalisation (inductive logic)? Thank you $\endgroup$ – Maths Dec 31 '18 at 2:54
  • $\begingroup$ @N.Steinle Good point. Galileo showed experimentally that the acceleration of mass due to gravity does not depend on how much mass is involved. I think that led to the equivalence principle but I’m not sure it went so far as to explicitly state the equivalence principle $\endgroup$ – Bob D Dec 31 '18 at 3:52
  • $\begingroup$ @AnmolGrover Not sure what you mean by all observable phenomena. Galileo showed by experiment that the acceleration due to gravity does not depend on mass. Newton explained the phenomena that while increasing gravitational mass increases the gravitational force, it also increase inertial mass which resists change in motion (acceleration) and the two exactly cancel, but the result seemed to be a coincidence. Einstein eliminated the need to differentiate between gravitational and inertial mass by introducing the curvature of space time. In any case, prof Norton can explain it better than me. $\endgroup$ – Bob D Dec 31 '18 at 14:16

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