I am gonna try to explain relativity without light or maxwell's equation. Light or Maxwell's equation or electromagnetism has nothing to do with relativity. a) The speed of light (and not light itself - note the difference) has something to do with it. b) The fact that M&M used light to find the speed of ether and failed has something to do with it. c) The fact that it was observed that Maxwell's equation is not invariant under galliliean transformation has something to do with it. But conceptually even if there is no electromagnetic force or light in the world, special relativity still holds good and newton's equations are wrong. Ok what is special relativity? It hinges on one principle, which we need to take for granted. The principle of equivalence: a)There is a train which moving at 50 miles/hr and a physicist is inside this train. b)There is a train which moving at 40 miles/hr and a physicist is inside this train. c)There is a kid standing in the platform and is pushing a slab of wood horizontally with constant force. Let us assume no friction. Both the physicists looks at the slab and works out the laws of physics and they both should come up with the same laws of physics governing the horizontal motion of the slab. Let me further explain: We provide the physicists with the some measurements for them to figure out laws of motion. a) Constant Force of the push acting on the ball - F b) The path traced by the block is calculated by each physicist by observation from their respective trains. c) m - Inertial :) Mass of the block before the boy kicked the block. What was thought before relativity was that both physicists will come up with. F= d(mv)/dt (Newton's Laws) where v is the instantaneous velocity calculated from the path of the block by each physicist. The problem was their measurements were inaccurate. If they had performed a really accurate measurement, the equation which they would have got would have been different from Newton's laws (which I couldnt write here as I dont know how to write equations in this text box). Both of them would have got the same einstein's modified equations. Question: But we thought and accepted newton's laws as it obeyed equivalence principle.What happened to that? It still obeys equivalence principle, but under galiliean transformation of frames of references.The new Einstein equation doesnt obey the equivalence principle based on galilien transformation, but the one based on lorentz transformation. Yes.They changed the laws of motion and the equivalence principle at one stroke, but not in that order.So that both again tally. In elementary school, we would have learnt kinematics and then dynamics. The galiliean and lorentz transformation belong to kinematics. The newton's and einstien laws belong to dynamics (which involve force). So we all learnt wrong kinematics(galileo) and wrong dynamics(newton).But both negatives worked well to safegaurd the equivalence principle. Now we have the correct kinematics(lorentz) and correct dynamics(einstien). That is all to it.No Light!! ------------------------- But then I thought relativity had something to with light???!!! In the whole argument I havent brought the subject of light at all. Light which in turn pointed to maxwell's equation was the actual percursor for the train physicists of our world to start thinking whether they actually did their motion (kinematics) measurements acurately. Maxwell's equations wasnt invariant under galilean transformation based equivalence principle. This puts newton and maxwell at odds. Who was right? This indirectly put Galileo and Lorentz at odds.Who was right? Rather the question is which team was right? (Maxwell and Lorentz) new age team or (Galileo and Newton) old wise men team? We all know Eienstien judged that the New Age team won with the support of M&M team of experimenters as they proved that an object which moved at the speed of light, moved with the same velocity when observed from both trains. This result is inconsistent with Galilean Kinematics, but worked well with Lorentz Kinematics. Incidentally the object which moved with the speed of light was light itself(photons). The subtle point here is that, it could have been any object and also u didnt need to actually go in the speed of light to find out that galiliean kinematics is wrong and we could have done well with any object which went in a speed atleast close to light (close enough for the measuring instruments to detect the discrepancy). So maxwell's equations and light were only helpers in finding the basic problem in kinematics and dynamics. They werent necessary as in if we had accurate instruments we could have unravelled this problem without having no knowledge of light or maxwell's equations or for that matter even without knowing the speed of light. To take it further and bring home my point more. Let us assume maxwell's equations and speed of light were discovered after we discovered special relativity. What would have happened? The constant in the lorentz transformation and einstien's equation of motion would have been named 'l' (in the name of lorerntz) instead of 'c' :) as no one would have known that light travelled at that speed or no one would have known the constant in maxwell's equations. Then later when they would have discovered laws of electrodynamics, they would recognized that the lorentz constant 'l' actually is the speed of light 'c' or the constant in maxwell's equation 'c' and world would have marvelled at that coincidence :). My intention: Special Relativity is about the laws of physics which is one layer below the laws of forces or interaction. It is like the stage for dancers(other laws) like electrodynamics and gravitation. Is the shape of the stage, based on the shape of the dancers? This is a profound question, which some answers I would say in general theory of relativity. A fundamental question I am working now on: Are there any other transformations apart from lorentz, which will satisfies invariancy of both maxwell's equation and einstiens equations and also satisy the velocity measurements (atleast to the level of accuracy we are able to measure now).