crummer@AEROSPACE.ARPA (06/21/85)
From: Charlie Crummer <crummer@AEROSPACE.ARPA> > THE EFFECT IS SYMMETRICAL: > -All inertial frames of reference are equivalent, so instead of thinking > of B moving away from A at speed v, just think of A and B as moving away > from each other (or from a common middle point). This removes the false > lack of symmetry in the first phrasing > -A perceives B's time as being slower AND VICEVERSA, as long as they > continue to move away from each other. Not quite: As long as they continue to move relative to one another. > Conversely, if they were moving > towards each other they would perceive an "acceleration" of each other's > time. Not true. Time dilation is a function of v^2 so whether they approach one another with velocity v or recede from one another with that velocity the mutual dilation is the same. The directional information is lost once the velocity is squared. > This is simply the Doppler effect. A and B must be able to measure time > in order to compare, so say they use identical light sources and rely on > the period of the light (wavelength/c). A light source moving away seems > to have a longer periods (the "ticks" of the "clock" seem to take > longer) than an identical one on the observer's lap, hence the perceived > time dilation. The reason for each "tick" to take longer to arrive is > that it must cover a slightly longer distance than the preceding one. You are confusing Feynman's "light clock" with the Doppler effect. The light clock slows because the apparent distance travelled by the light pulse increases as a function of v^2. The Doppler effect, on the other hand, is a also a function of the angle between the wave number vector of the light and the velocity vector. Time dilation is not the Doppler effect. > This does not apply to the twin paradox, which is a non-symmetrical > situation, where one twin goes on a round trip, so his frame of > reference is non-inertial. True. --Charlie