Reference: Einstein’s 1920 Book
Section XXI (Part 2)
In What Respects Are the Foundations of Classical Mechanics and of the Special Theory of Relativity Unsatisfactory?
Please see Section XXI at the link above.
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Summary
In Classical Mechanics, and also in the special theory of relativity, reference bodies that maintain inherent uniform rotation are disregarded. Therefore, a new basis for physics is required that includes uniformly rotating reference bodies.
In rotating bodies radial acceleration is involved. Such a basis would obviously be conformable to the general principle of relativity.
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Final Comments
Classical mechanics refers to motion in a straight line only. But its laws may be generalized for curved motion. Curved motion exists in rotation that involves radial acceleration. Because there is acceleration, it must be balanced by inertia. When there is natural inertia there is also a field. Therefore, the curved motion shall bring a gravitational field into existence.
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