Re: Inertial vs gravitational mass

[Calvin Kalman <KALMAN@VAX2.CONCORDIA.CA>]

> At 17:51 -0700 1/21/03, Nathaniel Davis wrote:
>  >
>  >Why is inertial mass always equal to gravitational mass?
>  >
>  This was the
> finding of the Eotvos experiment, done in the early years of the 20th
> century, and the possibility that it might not have been true was the
> cause of the excitement over the possible "fifth force" a few years
> back. There may be some insights into this buried in general
> relativity, but since GR is based on the postulate that gravitational
> and inertial mass are the same thing, any insights might well end up
> being tautological.

This was a great puzzle to Newton. He was very concerned about
experimentally verifying this point and did a series of experiments
comparing identical  pendula with bobs containing different
materials. He also felt that there should be a reason for the
equality, but had no idea what why it was so. Eotvos "redid" the
experiments and around 1950 Dicke and collaborators "redid" them
exceptionally great accuracy. In a sense the General theory of
relativity explains the result, but you could also say that it is an
axiom of the general theory found in the principal of equivalence. I
would say the best explanation is Einstein's gedanken experiment
comparing motion in an elevator accelerating upwards  with gravity.


Best wishes


                     Calvin


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