Known physics defeated by simple puzzle?
in [Relativity]
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From: PD on 15 Feb 2010 11:53 On Feb 15, 10:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 15 Feb, 15:18, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 14, 1:42 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > No takers for this simple question then? > > > > Consider this setup: > > > > S1 D2 > > > > D1 S2 > > > > We've got sources S1 and S2, paired with detectors D1 and D2. They're > > > all mechanically connected, so that a movement in one of them > > > produces > > > a movement in all the others - in other words, their relative > > > distances are always maintained. Each source is transmitting a > > > regular > > > pulse of light to its counterpart detector (so S1 is transmitting to > > > D1, etc.), and both sources are transmitting simultaneously with each > > > other. > > > > Now, we calculate that a pulse has just been emitted from both > > > sources, and we suddenly accelerate the whole setup "upwards" (i.e. > > > relative to how it's oriented on the page now) to near the speed of > > > light, and we complete this acceleration before the signals reach > > > either detector. > > > > Now, do both detectors *still* receive their signals simultaneously, > > > or does one receive its signal before the other? And are the signals > > > identical, or do they suffer from Doppler shifting, etc? > > > In what frame do you want the answer? > > The frame into which the set-up is accelerating, or the frame from > > which the set-up is accelerating? > > The answer is dependent on that choice. > > The answer will be according to an observer that is attached to the > setup and is equidistant from both detectors. And remember, the > acceleration is complete before the detection occurs. OK, first of all, this is not an inertial reference frame, because it is accelerating. This is the reason why I gave you two choices of inertial reference frame, neither of which is the noninertial reference frame you've chosen. I can certainly give you an answer for the noninertial reference frame you've chosen: they do not arrive at the same time, and yes, they are frequency/wavelength shifted. I don't know whether you want the explanation for WHY this is so. To do so would entail first looking at it from the two inertial reference frames mentioned, then we'd discuss the principle of equivalence. PD
From: PD on 15 Feb 2010 11:55 On Feb 15, 10:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 15 Feb, 15:18, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 14, 1:42 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > No takers for this simple question then? > > > > Consider this setup: > > > > S1 D2 > > > > D1 S2 > > > > We've got sources S1 and S2, paired with detectors D1 and D2. They're > > > all mechanically connected, so that a movement in one of them > > > produces > > > a movement in all the others - in other words, their relative > > > distances are always maintained. Each source is transmitting a > > > regular > > > pulse of light to its counterpart detector (so S1 is transmitting to > > > D1, etc.), and both sources are transmitting simultaneously with each > > > other. > > > > Now, we calculate that a pulse has just been emitted from both > > > sources, and we suddenly accelerate the whole setup "upwards" (i.e. > > > relative to how it's oriented on the page now) to near the speed of > > > light, and we complete this acceleration before the signals reach > > > either detector. > > > > Now, do both detectors *still* receive their signals simultaneously, > > > or does one receive its signal before the other? And are the signals > > > identical, or do they suffer from Doppler shifting, etc? > > > In what frame do you want the answer? > > The frame into which the set-up is accelerating, or the frame from > > which the set-up is accelerating? > > The answer is dependent on that choice. > > The answer will be according to an observer that is attached to the > setup and is equidistant from both detectors. And remember, the > acceleration is complete before the detection occurs. Following up: Since you've mentioned your interest is in finding out the essence of the postulates used in special relativity, you should know that those postulates make statements about what is true in *inertial* reference frames, not the sort of accelerating frame you've just mentioned.
From: Ste on 15 Feb 2010 12:47 On 15 Feb, 16:27, dlzc <dl...(a)cox.net> wrote: > Dear Ste: > > On Feb 15, 4:34 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > On 15 Feb, 03:04,dlzc<dl...(a)cox.net> wrote: > > > > > Now, do both detectors *still* receive their > > > > signals simultaneously, or does one receive > > > > its signal before the other? > > > > S2 should get its signal first. The path length is > > > shorter, due to the acceleration. Acceleration is > > > not really part of SR, and your imaginary setup > > > isn't helping. > > > Forget the imaginary setup. The purpose of my > > questions are to establish and distill out the > > essential truths that are captured in relativity. > > They are called "postulates". Their number is two: > 1) physics is the same for all inertial observers > 2) the equivalence principle > Other theories derive the constant local speed of c. And the logic- > set of mapping problem-space to solution-space has a long and hoary > tradition (aka. mathematics). > > > It doesn't matter that no real device in the Universe > > could conceivably carry out such an acceleration. > > It does if one starts depending on instantaneous signal transmission > via "perfectly rigid structures". You aren't quite there yet, but > there was significant deformation of the structure you placed your > emitters and detectors on, causing ringing to boot (oscillating > distances), and you simply don't care about it... It's not that I don't care about it, or even that I wasn't aware of it. What I'm trying to get at is the essence of relativity. If that requires pasting in absurdly high assumptions for the rigidity of this setup and its acceleration, then fine.
From: Ste on 15 Feb 2010 12:50 On 15 Feb, 16:55, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 15, 10:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 15 Feb, 15:18, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Feb 14, 1:42 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > No takers for this simple question then? > > > > > Consider this setup: > > > > > S1 D2 > > > > > D1 S2 > > > > > We've got sources S1 and S2, paired with detectors D1 and D2. They're > > > > all mechanically connected, so that a movement in one of them > > > > produces > > > > a movement in all the others - in other words, their relative > > > > distances are always maintained. Each source is transmitting a > > > > regular > > > > pulse of light to its counterpart detector (so S1 is transmitting to > > > > D1, etc.), and both sources are transmitting simultaneously with each > > > > other. > > > > > Now, we calculate that a pulse has just been emitted from both > > > > sources, and we suddenly accelerate the whole setup "upwards" (i.e. > > > > relative to how it's oriented on the page now) to near the speed of > > > > light, and we complete this acceleration before the signals reach > > > > either detector. > > > > > Now, do both detectors *still* receive their signals simultaneously, > > > > or does one receive its signal before the other? And are the signals > > > > identical, or do they suffer from Doppler shifting, etc? > > > > In what frame do you want the answer? > > > The frame into which the set-up is accelerating, or the frame from > > > which the set-up is accelerating? > > > The answer is dependent on that choice. > > > The answer will be according to an observer that is attached to the > > setup and is equidistant from both detectors. And remember, the > > acceleration is complete before the detection occurs. > > Following up: Since you've mentioned your interest is in finding out > the essence of the postulates used in special relativity, you should > know that those postulates make statements about what is true in > *inertial* reference frames, not the sort of accelerating frame you've > just mentioned. I accept that.
From: Ste on 15 Feb 2010 13:06
On 15 Feb, 16:53, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 15, 10:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 15 Feb, 15:18, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Feb 14, 1:42 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > No takers for this simple question then? > > > > > Consider this setup: > > > > > S1 D2 > > > > > D1 S2 > > > > > We've got sources S1 and S2, paired with detectors D1 and D2. They're > > > > all mechanically connected, so that a movement in one of them > > > > produces > > > > a movement in all the others - in other words, their relative > > > > distances are always maintained. Each source is transmitting a > > > > regular > > > > pulse of light to its counterpart detector (so S1 is transmitting to > > > > D1, etc.), and both sources are transmitting simultaneously with each > > > > other. > > > > > Now, we calculate that a pulse has just been emitted from both > > > > sources, and we suddenly accelerate the whole setup "upwards" (i.e. > > > > relative to how it's oriented on the page now) to near the speed of > > > > light, and we complete this acceleration before the signals reach > > > > either detector. > > > > > Now, do both detectors *still* receive their signals simultaneously, > > > > or does one receive its signal before the other? And are the signals > > > > identical, or do they suffer from Doppler shifting, etc? > > > > In what frame do you want the answer? > > > The frame into which the set-up is accelerating, or the frame from > > > which the set-up is accelerating? > > > The answer is dependent on that choice. > > > The answer will be according to an observer that is attached to the > > setup and is equidistant from both detectors. And remember, the > > acceleration is complete before the detection occurs. > > OK, first of all, this is not an inertial reference frame, because it > is accelerating. > This is the reason why I gave you two choices of inertial reference > frame, neither of which is the noninertial reference frame you've > chosen. > I can certainly give you an answer for the noninertial reference frame > you've chosen: they do not arrive at the same time, and yes, they are > frequency/wavelength shifted. Actually Paul, I just want to add another clause to this. What happens if, still before the detection occurs, the whole setup decelerates back to the same velocity as it started with. So the whole setup has moved, but at the time of the detection, the setup is not moving relative to its original frame. I assume that they still arrive at different times, but does the Doppler shifting remain? |