Full Idea
Einstein came to general relativity from the principles that the laws of nature are the same in all frames of reference.
Gist of Idea
General relativity assumes laws of nature are the same in all frames of reference
Source
report of Albert Einstein (works [1915]) by Frank Close - Theories of Everything 5 'Cosmological'
Book Reference
Close,Frank: 'Theories of Everything' [Profile Books 2017], p.101
A Reaction
I wish physicists would tell us a bit more about the ontological status of the 'laws of nature'. Presumably they are not supernatural, so there is an aspect of nature which is constant in all frames of reference. Explanation please.