Journal of Applied Sciences Research, 4(1): 32-39, 2008 © 2008, INSInet Publication Corresponding Author: Md. Haider Ali Biswas, Mathematics Discipline, Khulna University, Khulna-9208, Bangladesh. Phone: 041-720171, Ext. 343 (Off.) E-mail: mhabiswas@yahoo.com 32 Review of the Theory of Relativity Tajuddin, Md. Haider Ali Biswas and Ariful Islam. 1 2 2 Primary Education, Sylhet Division, Sylhet, Bangladesh. 1 Mathematics Discipline, Khulna University, Khulna-9208, Bangladesh. 2 Abstract: This study is a review of the theory of relativity. Einstein devised the special theory of relativity in 1905. In special relativity Einstein kept some ideas in his subconscious mind which was very important for the modification of physics. Einstein mentioned in special relativity that the mass of a body increases with an increase of the motion of the body . In fact Einstein recognized acceleration instead [8] of momentum unknowingly. This idea was not incorporated in special theory of relativity. Classical mechanics was founded on rectilinear principles of motion. But Einstein observed that space-time is curved and all motions are curved . Einstein had an attempt to establish the curvilinear principle in physics but [1] he could not complete his works. In Time Dilation and Length Contraction Einstein developed some concepts with a number of anomalies. Actually time dilates and contracts due to the fluctuation of gravitational influence in different space-time. In principle of equivalence Einstein explained the gravitational and inertial mass are the same . But this explanation of principle of equivalence needs more [2] elaboration. Body possesses definite shape, size and density but it can only express mass with the help of gravitation. Beyond the gravitational field body is unable to express mass. This idea is not incorporated with the theory of principle of equivalence. Einstein formulated the general theory of relativity in 1915 combining special relativity, accelerated frame, principle of equivalence and gravitational fields. Einstein put forth three experiments for the proofs of the general theory of relativity. But the general theory which are based on assumptions beyond the principle of equivalence are not well substantiated . [2] Key words: Theory of Relativity, Time Dilation and Length Contraction, Rectilinear and Curvilinear Principle, Momentum and Acceleration, Principle of Equivalence. INTRODUCTION A century had passed since Einstein devised theory of relativity in 1905. In the meantime knowledge was exploded greatly. But physics did not reach the highest level. In view of present needs and expanded knowledge lots of criticism were made against different aspects of physics as well as relativity. Physics is not a static body of doctrine but a developing science . [9] About two thousand years back Greeks had a belief that the earth is static and all the heavenly bodies move around the earth. But in the seventeenth century Galileo by his newly invented telescope observed that the earth and the other planets move around the sun. The old ideas of static world were removed and the new ideas of spherical movement of the world took place. Spherical movement of the heavenly bodies is a natural phenomenon. But no reaction from Galileo and afterward was found about this phenomenon. Physics cannot overlook this phenomenon. Physics must have to incorporate this idea in its principle of motion. It was Einstein who found that time and space are curved and all motions are curved . According to general theory of relativity [1] all system of reference are equivalent with respect to the formulation of fundamental laws of physics . [7] As per above view a number of questions peep in the mind. Why do the planets move around the sun? Is this spherical movement a principle of nature? How do we get rectilinear motion? Is rectilinear motion a principle of nature? How do we get curvilinear motion? Do there be two principles of nature of opposite direction? Attempt has been made to review the different aspects of theory of relativity with a view to developing unification theory in the light of the above queries. Special Theory of Relativity: Einstein published five articles in 1905. Afterward these articles were known as special theory of relativity. There were inadequacies in classical physics. Special theory of relativity fulfilled a number of these shortcomings but still a lot of remained. Laws of classical mechanics do not hold good in analysing the velocity of elementary particles and the speed of objects involved are appreciable compared to the speed of light. Einstein formulated special relativity by taking the speed of light as the