Local Inertial Coordinate System and The Principle of Equivalence
  In this paper, the local inertial coordinate system is calculated through coordinate transformations from laboratory coordinate system. We derived the same free falling equations as those in General Relativity. However, the definitions of second and higher order covariant derivatives are different. Our results are different from the classic view of the principle of equivalence, and suggest that all the laws of physics in gravitational field can be given by doing coordinate transformations from local inertial coordinate system to lab coordinate system. 
Xin Zhang, Bin Xi