In statistical mechanics, we routinely deal with phase spaces of 6 x number of molecules in a gas sample. In physics, four dimensions are actually quite modest. It is just another sort of space that happens to transcend simple visualization. There is no easy way to draw a picture of a four dimensional spacetime. So when we add the extra dimension of time we generate a four dimensional spacetime. So far we have described how a two dimensional space is combined with the one extra dimension of time to generate a three dimensional spacetime, such as shown above in the figures. When we clean things up a little, we have a spacetime. Now we stack them up into the third dimension. Orbiting the sun in the three dimensional space around the sun in the course of a year, which will look like: For such a motion covers the same distance in the same time. The zig-zag line is a light signal bouncing back and forth between these two ends.Ī point that moves inertially, that is, a point that moves uniformly in a straight line in space is represented by a straight line in a spacetime. In the figure, a moving rod is represented by the trajectories in spacetime of its ends. If it is moving, it will intersect each instantaneous space at a different spot a moving body is presented by a line inclined to the vertical.Ī standard convention (that I will usually use) is to represent trajectories of light signals by lines at 45 o to the vertical. To see why it is vertical, recall that it has to intersect each instantaneous space at the same spot. In this spacetime, a small body at rest will be represented by a vertical line. The snapshots taken at different times are then stacked up to give us a three dimensional spacetime. It is easiest to imagine this if we start with a two dimensional space. We build a spacetime by taking instantaneous snapshots of space at successive instants of time and stacking them up. Quite puzzling relativistic effects could be comprehended with ease within the spacetime representation and work in the theory of relativity started to be transformed into work on the geometry of spacetime. This was their representation in spacetime. Minkowski explored a way of visualizing these processes that proved to be especially well suited to disentangling relativistic effects. You have to play out a little movie in your head. But you cannot just look at the figure and see the effect. The difference matters a great deal, since it is a manifestation of the key effect of the relativity of simultaneity. In one case, the events of the reflections of the signal are evenly spaced in time. Recall how tough it is to keep track of events at the ends of the rod. Now describe the same system from a different frame of reference. ![]() ![]() Take the simple case of a rod with a light signal bouncing back and forth between its ends. If you haven't already noticed, these motions can become rather complicated to visualize. ![]() So far all our discussions in special relativity have involved the motion of bodies in space over time.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |