The speed of light on the Earth and in the gravity-free space

Abstract

The metric for describing the spacetime geometry of a charged and rotating source in general relativity is the Kerr-Newman metrics, and it is an appropriate one to discuss the movement on the Earth. It is explicit that the velocity of light we measure is dependent on the rotation and net charges of the Earth, and usually the measurements are less than it in the really free space, at infinity or the gravity-free space, as long as the net charges of the Earth are less than 1.4x10^19 C. According to this, the velocity of light in the really gravity-free space should be corrected. When we adopt the coordinate time at infinity as the unified time at each measurement placement on the Earth, it is 0.2085 m/s slightly larger than what we identify in vacuum on the Earth, 2.9979458x10^8 m/s. The calculations also show the tiny deviation on the speed of light along the longitudinal direction between two poles and the equator, and it also exists deviation between the left-handed circularly light and the right-handed circularly one in the equator. We also discuss the difference on the speed of light in the local reference frame by using the proper time.