A constant speed of light in all reference frames? Surely you can't be serious.
in [Relativity]
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From: rotchm on 5 Mar 2010 14:01 > > Length has an operational definition that uses the integer 299792458. > > This definition implies/makes the speed of light constant. > > This was not the definition used at the time of Einstein. This > definition was put into effect many years later It was the definition used long before Einstein. It is just that it took ~ 100 years for it to be acknowledged and ratified as a standard (definition). See for instance Poincare's work and the "Telegraphers synch procedure" ( before 1900) aka, Poincare synch/Einstein synch procedure. > ... after it had long been > observed that the speed of light does not depend on your choice of > reference frame. Read for instance Poincare's works in the ~ 1900. He mentions that the speed of light depends on the choice of the reference frame ( on the choice of the definitions). It is well understood today that our "Laws" ( the way we express them) depend on the choice of definitions.
From: jbriggs444 on 5 Mar 2010 14:17 On Mar 5, 1:54 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: [discussing the scenario in which two clocks symmetrically accelerate toward each other and this is observed from the point of view of one of the clocks] > Your initial assertions are correct. Both will report a slow down.... > During part of the trip. And a different slowdown during a different > part of the trip. I should correct myself here. The part I wrote about "a different slowdown during a different part of the trip" was an erroneous reference to a scenario in which a clock is reporting the Doppler shift that is _seen_ (i.e. without accounting for transit delays). In such a scenario, the clock sees an interval after it has accelerated and before its peer has accelerated and then a second interval after the peer has accelerated. The Doppler shifts for the intervals are, of course, different. In the scenario at hand we are trying to discuss what is _observed_ (i.e. accounting for transit delays and adopting particular standards of simultaneity) What is _observed_ is only a single interval during which the two clocks are in constant relative motion, not two such intervals. [From an "observed" point of view, the period when the peer clock remains motionless does not fall within the interval of the journey. Instead, it is in the relative past]
From: mpalenik on 5 Mar 2010 15:07 On Mar 5, 2:17 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: > On Mar 5, 1:54 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: > [discussing the scenario in which two clocks symmetrically accelerate > toward each other and this is observed from the point of view of one > of the clocks] > > > Your initial assertions are correct. Both will report a slow down..... > > During part of the trip. And a different slowdown during a different > > part of the trip. > > I should correct myself here. > > The part I wrote about "a different slowdown during a different part > of the trip" was an erroneous reference to a scenario in which a clock > is reporting the Doppler shift that is _seen_ (i.e. without accounting > for transit delays). In fact, what I was trying to describe to Ste was the effects that are specifically not due to Doppler shifting, as I was specifically making the point that the predictions of SR for time dilation are mathematically different than those which are due to the observed rate of change on a ticking clock to transit delays. > > In such a scenario, the clock sees an interval after it has > accelerated and before its peer has accelerated and then a second > interval after the peer has accelerated. The Doppler shifts for the > intervals are, of course, different. > > In the scenario at hand we are trying to discuss what is _observed_ > (i.e. accounting for transit delays and adopting particular standards > of simultaneity) No, that's not actually what we were talking about at all. > > What is _observed_ is only a single interval during which the two > clocks are in constant relative motion, not two such intervals. [From > an "observed" point of view, the period when the peer clock remains > motionless does not fall within the interval of the journey. Instead, > it is in the relative past] The relevant quantity was the time that each clock displays after the two are brought into comoving frames, which once again, depends on the frame that they are brought into. And yes, as the clocks accelerate, due to Doppler effects, they will each see an apparent change in the other clock's rate that brings it's reading into what it is supposed to be for whichever frame they are accelerating into. But I fear if Ste reads any of this, he's going to slip back into his whole "relativity is due to propagation delays" thing again. Let's tackle one problem at a time.
From: jbriggs444 on 5 Mar 2010 15:47 On Mar 5, 3:07 pm, mpalenik <markpale...(a)gmail.com> wrote: > On Mar 5, 2:17 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: > > > On Mar 5, 1:54 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: > > [discussing the scenario in which two clocks symmetrically accelerate > > toward each other and this is observed from the point of view of one > > of the clocks] > > > > Your initial assertions are correct. Both will report a slow down..... > > > During part of the trip. And a different slowdown during a different > > > part of the trip. > > > I should correct myself here. > > > The part I wrote about "a different slowdown during a different part > > of the trip" was an erroneous reference to a scenario in which a clock > > is reporting the Doppler shift that is _seen_ (i.e. without accounting > > for transit delays). > > In fact, what I was trying to describe to Ste was the effects that are > specifically not due to Doppler shifting, as I was specifically making > the point that the predictions of SR for time dilation are > mathematically different than those which are due to the observed rate > of change on a ticking clock to transit delays. Ok good. So we're both not talking about that. > > In such a scenario, the clock sees an interval after it has > > accelerated and before its peer has accelerated and then a second > > interval after the peer has accelerated. The Doppler shifts for the > > intervals are, of course, different. > > > In the scenario at hand we are trying to discuss what is _observed_ > > (i.e. accounting for transit delays and adopting particular standards > > of simultaneity) > > No, that's not actually what we were talking about at all. > > What is _observed_ is only a single interval during which the two > > clocks are in constant relative motion, not two such intervals. [From > > an "observed" point of view, the period when the peer clock remains > > motionless does not fall within the interval of the journey. Instead, > > it is in the relative past] > > The relevant quantity was the time that each clock displays after the > two are brought into comoving frames, which once again, depends on the > frame that they are brought into. In the scenario in question they are not brought into co-moving frames (whatever that means -- the notion of things being "brought into" frames is very questionable) They are brought _TOGETHER_. The time displayed on each clock when they become adjacent is an _observable_. It's not frame dependent. The numbers don't change if you decide to adopt a different frame of reference. You take a snapshot of the clocks side by side and you look at the numbers. There is no ambiguity. All frames get the same answer. Even the frame in which the two clocks are mutually at rest.
From: mpalenik on 5 Mar 2010 15:55
On Mar 5, 3:47 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: > On Mar 5, 3:07 pm, mpalenik <markpale...(a)gmail.com> wrote: > > > > > > > On Mar 5, 2:17 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: > > > > On Mar 5, 1:54 pm, jbriggs444 <jbriggs...(a)gmail.com> wrote: > > > [discussing the scenario in which two clocks symmetrically accelerate > > > toward each other and this is observed from the point of view of one > > > of the clocks] > > > > > Your initial assertions are correct. Both will report a slow down.... > > > > During part of the trip. And a different slowdown during a different > > > > part of the trip. > > > > I should correct myself here. > > > > The part I wrote about "a different slowdown during a different part > > > of the trip" was an erroneous reference to a scenario in which a clock > > > is reporting the Doppler shift that is _seen_ (i.e. without accounting > > > for transit delays). > > > In fact, what I was trying to describe to Ste was the effects that are > > specifically not due to Doppler shifting, as I was specifically making > > the point that the predictions of SR for time dilation are > > mathematically different than those which are due to the observed rate > > of change on a ticking clock to transit delays. > > Ok good. So we're both not talking about that. > > > > > > > > In such a scenario, the clock sees an interval after it has > > > accelerated and before its peer has accelerated and then a second > > > interval after the peer has accelerated. The Doppler shifts for the > > > intervals are, of course, different. > > > > In the scenario at hand we are trying to discuss what is _observed_ > > > (i.e. accounting for transit delays and adopting particular standards > > > of simultaneity) > > > No, that's not actually what we were talking about at all. > > > What is _observed_ is only a single interval during which the two > > > clocks are in constant relative motion, not two such intervals. [From > > > an "observed" point of view, the period when the peer clock remains > > > motionless does not fall within the interval of the journey. Instead, > > > it is in the relative past] > > > The relevant quantity was the time that each clock displays after the > > two are brought into comoving frames, which once again, depends on the > > frame that they are brought into. > > In the scenario in question they are not brought into co-moving frames > (whatever that means -- the notion of things being "brought into" > frames is very questionable) They are brought _TOGETHER_. All I can say is read what I originally wrote again. BTW, "together" is ambiguous. Together can mean comoving or it can mean "they pass each other." Each of those warrants a different answer. |