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? Jason > The effects of time dilation are dependent on relative speed. But whether > I bring the clocks together moving one of them at either 1 meter/second or > 1 mm per year, they will still appear synchronized to the person on the > ground. You can calculate the time dilation effects of moving at 1 meter > per second over the ship's length of 100 meters, it won't account for the > 266.85 nanoseconds of clock descynrhonization that the observer on the > ground sees. > > The effect is more related to length contraction than anything. If you see > a length contracted object, you are simultaneously seeing "older" and > "newer" parts of that object, the rear part of the object will be newer in > time, while the forward part of the object will be the older part of the > object. Consider the observer on the ground watching the rocket gradually > slow. The entire part of the rocket is slowing at the exact same rate, but > by the time it stops both clocks will again be perfectly synchronized. > This resynchronization cannot be explained in terms of time dilation or > different relative velocities. > > There are no "older" or "newer" parts of an object, because there is no > such thing as an absolute time. Time is a purely local phenomenon: > apparent clock rates are affected by relative motions. > > Because of general relativistic effects, slowing the rocket will cause the > clock rates at the front and rear of the rocket to be different, so they > will not remain synchronized, even if that concept made any sense in the > first place. > > > However, it can be explained in terms of objects in spacetime being > 4-dimensional, and viewing acceleration or deceleration as the rotation of > those 4-dimensional objects. (which also explains the phenomenon of length > contraction) > > > 4-dimensional space-time is a construct that sometimes has heuristic > value, but it cannot be said to be the 'explanation' for anything. The only > explanations that SR gives are in terms of the effects of Lorentz > transformations. When we introduce general relativity, we see that Lorentz > symmetry is only ever a local effect, so 4-dim space-time becomes > insignificant. > > 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. > -- 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.
