![]() ![]() Two observers in relative motion disagree on the timing of the two events and on the associated synchrony of the clocks. So far we have said nothing about the order in time of these two events. The B-event at the B-end of the platform coincides with the setting of the B clock to 0. The A-event at the A-end of the platform coincides with the setting of the A clock to 0. We can describe the effect without them as follows. Signals themselves are not an essential part of the effect and they can be distracting. The account above uses light signals merely as a means to enable the two observers to determine the time order of the events. The effect just described is the relativity of simultaneity. Relativity of Simultaneity without Light Signals In fact clock A is set ahead of, that is, earlier than clock B, for it reads "0" earlier than clock B. Therefore the new observer will judge the clocks at A and B not to be properly synchronized. These two events are not simultaneous for the new observer. The clocks at A and B show the same time "0" when the flash events happen at each. ![]() ![]() The light postulate: both light flashes must move at the same speed that is, each must require the same time to cover the same distance. The two events were not simultaneous, according to the new observer. That is, the flash at A happened earlier than the flash at B. So if the two arrive at the same moment, the lightįrom A must have left earlier than the light from B to give it greater time to cover the greater distance to get to the midpoint. What is the new observer to make of this? For the new observer, the light from A must cover a greater distance to catch up with the receding midpoint and the light from B must cover a lesser distance to arrive at the midpoint rushing towards it. Nonetheless, the two signals arrive at the midpoint at the same moment. It is rushing away from light coming from A and rushing toward the light coming from B. Once again there will be two flashes and light from them will propagate towards the observer at the midpoint of the platform. ![]() For that new observer, the platform moves rapidly and, in the animation, in the direction from A towards B. Who moves relative to the platform along its length. Now consider this process from the point of view of an Earlier times are depicted lower in the figure. That is what the platform observer judges since, as the animation shows, both clocks read "0" when the flashes occur at each location. If both clocks show the same reading at the events of the two flashes, then we would judge the two clocks Imagine also that there are clocks located at A and B. Noticing that they arrive at the same moment and that they come from places equal distances away, the observer will decide that theĪnother outcome is closely related. Let us imagine that they arrive at the same moment, as they do in the animation below. The light propagates from these events to the observer. At either end, at the places marked A and B, there are two momentary flashes of light. Imagine a long platform with an observer located at its midpoint. There is a quick way to see how this comes about. (And until you do, nothing quite makes sense!) Using Light Signals to Judge the Time Order of Events Once you grasp it, everything else makes sense. However, as we explore more deeply, you will see that this is the central adjustment Einstein made to our understanding of space and time in special relativity. At first this will seem like just another of the many novel effects relativity brings. If one observer thinks that two events are simultaneous, another might not. Observers in relative motion disagree on the timing of events at different places. When Einstein first hit upon special relativity, he thought one effect of special importance, so much so that it fills the first section of his "On the Electrodynamics of Moving Bodies." It is the relativity of simultaneity. What the Relativity of Simultaneity is NOT.Relativity of Simultaneity without Light Signals.Using Light Signals to Judge the Time Order of Events. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |