The Evolution Of The Connotation Of The Principle Of Relativity

In refuting the questions raised by proponents of geocentric theory,Galileo proposed the principle of relativity of mechanics.But in his works the principle is naive,for he had no systematic theory of mechanics.After Galileo,Huygens studied collision problem using the principle of relativity as one of his basic assumptions.Building on the work of Galileo and Huygens,Newton treated the principle of relativity as a corollary,the fifth corollary,based on the concept of absolute space and his fundamental laws of mechanics.In the 1740s and 1750s,reference frames were introduced with the development of algebraic representations of motion.Furthermore,based on the absoluteness of the time parameter,the transformation relationship between the corresponding physical parameters in two reference frames which move uniformly in straight line with respect to each other of the same physical process is given.Today,this transformation relationship is known as the Galilean transformation.At the same time,Euler realized that the form of the dynamic equation(mainly Newton’s second law)was invariable under the Galileo transformation.By this time,the knowledge framework related to the relativity principle in classical mechanics is basically formed.In addition,Euler denied absolute motion,but retained absolute space and absolute time.In the middle and late 19th century,Inspired by the work of C.Neumann,L.Lange reformulated the law of inertia based on the concept of free material point and put forward the concepts of inertial time scale and inertial reference system.Thus,absolute space as a reference is eliminated,and the laws of mechanics are valid for all inertial frames of reference.In1904,Poincaré described the principle of relativity as one of the fundamental principles of physics.On the other hand,in the face of the contradiction between the principle of relativity of mechanics and the theory of electromagnetism,Einstein established a new theoretical framework based on the general validity of the principle of relativity and the assumption of the invariance of the speed of light,and obtained a new transformation relation between the inertial system corresponding to the principle of relativity: Lorentz transformation.Furthermore,in dealing with the theory of gravity,Einstein solved the problem of gravity through the generalized principle of relativity and equivalence principle.It can be said that whether classical mechanics or relativity,the core principle dealing with relativistic motion problems is the principle of relativity.And in order for the principle to be implemented,invariants or absolute parameters are needed which are common basis of different reference frames.In classical mechanics,this invariant is the absoluteness of simultaneity or absolute time.Relativistic transformation invariant is the speed of light,and its physical basis is electromagnetic theory.In a view of symmetry,relativity principle is one of the most important symmetry principles.It is generally considered that principle of relativity is the embodiment of space-time symmetry.In classical mechanics and special relativity,the Galilei and Lorentz transformations are related to global symmetry,whereas in general relativity,symmetry is only local,so the corresponding transformations are local or infinitesimal transformations.The illumination given by the principle of relativity is that we may never know what the real laws of the physical world are,but perhaps it is certain that the form of the theory does not depend on the relative motion of the frame of reference chosen by the researcher.