On Sat, Dec 29, 2018 at 9:50 AM Jason Resch <[email protected]> wrote:
> On Fri, Dec 28, 2018 at 4:09 PM Bruce Kellett <[email protected]> > wrote: > >> From: Jason Resch <[email protected]> >> >> >> Clock desycnhronization is a different phenomenon and has a different >> cause and explanation than time dilation. >> >> Because of the relativity of simultaneity in SR, clock synchronization is >> not a global phenomenon -- it depends on the way in which the clocks are >> synchronized. So clocks synchronized by one method in one frame will not >> necessarily be synchronized in different frames. The time read on such >> clocks is local only, so will they will not necessarily agree when they are >> brought together. >> > > You would agree that two atomic clocks in the same reference frame, 100 > meters away synchronized by a flash of light exactly in between them are > synchronized, right? > > Now assume there are two clocks each in both the front and rear of the > rocket, as well as a 5th clock exactly in the middle. Roughly this is as > follows: > > > Clock1-----------------------Clock3-----------------------Clock4 > Clock2----------------------------------------------------Clock5 > > Clocks 2, 3, and 5 are atomic clocks, which count the number of vibrations > of some atom per second, and increment the nanosecond counter displayed on > the clock face when it has seen enough vibrations of that atom. Clocks 1 > and 4 are not atomic clocks, but are mere counters. Every time clock 3 > measures a vibration of the atom, it sends a light pulse to a sensor in > clock 1 and clock 4. Clock 1 and clock 4 count these light pulses, and > when there have been enough light pulses to represent a nanosecond, they > too increment the nanosecond counter on the clock face. > > At some time = 0, the rocket is at rest, and clock1 and clock4 are set to > 0, then clock 3 turns on and sends the light pulses and clocks 1 and 4 > begin counting. The moment clock1 counts 1, clock2 is activated and sets > its counter to 1, and thereafter counts the vibrations of its own atom > under measurement. Likewise, the moment clock 4 measures its first light > flash, clock 5 is activated and begins counting its own atom's vibrations. > > Do you agree at this point, all 5 clocks are synchronized, within their > own reference frame? > > Now what happens from an external frame as this rocket accelerates to 0.8 > c in the direction facing rightwards? Outside this frame, one will see the > light flashes take slightly longer to reach clock4 which is moving away > from the light source of clock3, while clock1 will begin receiving the > light flashes slightly faster the absolute number or difference in timings > is proportional to both the length separating the clocks, as well as the > absolute speed of the rocket. This results in a permanent discrepancy > between clocks 1 and 4. > > Now what of clocks 2 and 5? Do they not remain in complete agreement with > their local "light flash counting clocks" throughout this process? > > What happens when the rocket comes to a rest, from the perspective of the > external at-rest observer, do the clocks not all resynchronize? > > Can not everything in this experiment be explained in terms of special > relativity? > No, not if the rocket changes velocity at some point. That brings GR into the picture. But I think I disagree overall: the relativity of simultaneity in SR means that clocks that are synchronized in some way will not necessarily be synchronized in some other frame. So rockets synchronized at the ends of a moving rocket will not necessarily be synchronized when brought together in some other frame. There are some similarities with the twin paradox here -- clocks disagree because they have followed different spacetime paths. Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
