Please read the book, "The Meaning of Relativity" by Einstein and the references as follows:

References
1. On Criticisms of Einstein’s Equivalence Principle, Phys. Essays 16 (1), 84-100 (March 2003).
2. Space Contractions, Local Light Speeds, and the Question of Gauge in General Relativity, Chinese J. of Phys. (Taipei), 41 (4), 233-343 (August 2003).
3. Misunderstandings Related to Einstein’s Principle of Equivalence, and Einstein’s Theoretical Errors on Measure-ments, Phys. Essays 18 (4), 547-560 (December, 2005).