User:HM. Alamgir

2nd Postulate: The reference frame is important in describing the theory of relativity. In our whole discussion in the comprehensive regard we place `observer’ instead of `reference frame’ such that its origin is coincided always by him. Thus `the moving reference frame’ is regarded here as `the moving observer’ and `the rest reference frame’ as `the rest observer’. By major spacetime it is meant here the spacetime located at infinite distance away from the observer or the central spacetime of the universe where an enormous object should be visible to him even in its least dimensions. All inertially moving observers (rest or moving) refer the same about that visible object that it is as like as rigidly connected to each of their respective frame i.e. it is at rest with respect to each of their respective reference frame/observer. In their regard its position vector remains approximately unchanged as long as they move in classical uniform velocity. It is in agreement with the 1st postulate of the special theory of relativity by Sir A. Einstein. Because both of the inertial moving as well as rest observers sees the same phenomenon referring the position of the Sun or any other infinity distant star that any infinity distant visible object seems to be rigidly connected to each of its respective observer/reference frame(inertially moving or rest). Here `the position vector’ or `the rigidity’ may be regarded as so-called `law of physics’ which remains the same with respect to all inertial moving or rest observers describing the position of the infinity distant visible object(major spacetime) under observation. If these observers wouldn’t move inertial i.e. if they move along a remarkable curvature, if they spin being at the same position or if they spin along with their translatory motion they couldn’t see that infinity distant visible object as rigidly connected to their respective reference frame/observer accordingly. In other words, in that case the position vector of the same infinity distant visible object would vary in time with respect to its respective reference frame/observer. Inertial moving observer’s imagination that infinity distant visible object seems to him as rigidly connected to his moving frame is given frequently as a familiar evident example through our whole discussions on the comprehensive relativity.$$$$