Notion of Absolute Clock Synchronization in SR
in [Relativity]
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From: Tom Roberts on 25 Mar 2010 13:42 GSS wrote: > On Mar 22, 8:45 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: >> note there is no inertial frame in which these >> clocks are synchronized, and that is usually a prerequisite for calling them >> "synchronized". Your measurements and operations are clear, but applying the >> word "synchronized" to this is not so clear. > > If you cannot apply the word "synchronized" in this case, which other > word, you think, is more appropriate? We apply words in order to simplify the task of referring to common objects and tasks. This technique has no major or common use, and I see no reason to make up a special word for it. > At any instant, when TAI time is t1, if each one of the two 'ideal' > clocks A and B show the same time t1, shouldn't we call them > 'mutually' synchronized, irrespective of the reference frame in which > we may consider them to be located at that instant? Clock synchronization is INHERENTLY frame dependent. That is, a given pair of clocks can be synchronized in one AND ONLY one inertial frame; they are not synchronized in any other inertial frame. Your specific case is different from this and has no such inertial frame, so it does not meet the usual definition of "synchronized" as used in modern physics. > Why should the physical state of the two clocks > being 'in synchronization', change when we refer their location to ECI > or BCRF or the Galactic frame? Because the world we inhabit behaves that way. I cannot help it if you do not like this fact. Synchronization is not a "physical state", it is merely a human convention. That is, no natural phenomenon depends on how humans happen to set the parameters of systems they call clocks. > Choice of a reference frame is our > 'human' artifact, and this choice must not influence a physical > phenomenon of two clocks being 'in synchronization' or 'not in > synchronization'. There is no "physical phenomenon" corresponding to clock synchronization. Just like choice of coordinates (reference frame), selection of synchronization technique is also an arbitrary human choice, as is the choice of the inertial frame in which to apply it. > Isn't this awkward situation a consequence of equally awkward second > postulate of SR? Not at all! It is a direct consequence of the way the world works. SR merely MODELS this, it does not "dictate" or "cause" it. This is physics, and we are MODELING the world, not "creating" it. > Since physically no atomic clock can ever be at *rest* in the ECI > frame, This is false. A clock at either earth's south or north pole is at rest in the ECI frame. Such clocks do not actually exist, of course. > do you mean to imply that in order to synchronize the clocks A > and B (at rest on the earth surface) in the ECI frame, their time > offsets will have to be physically altered or adjusted to suit the > computations of SR? I mean that in order to be synchronized in the ECI, they must be synchronized in the ECI. That is, their time offsets must be adjusted so this is true. This is no different from synchronization in any other inertial frame. The method you described does NOT do this. Note also that earth's surface is irrelevant, it is earth's geoid that matters; in most places on land, the surface is well above the geoid. Tom Roberts
From: Sue... on 25 Mar 2010 16:14 On Mar 25, 1:42 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > GSS wrote: > > On Mar 22, 8:45 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > >> note there is no inertial frame in which these > >> clocks are synchronized, and that is usually a prerequisite for calling them > >> "synchronized". Your measurements and operations are clear, but applying the > >> word "synchronized" to this is not so clear. > > > If you cannot apply the word "synchronized" in this case, which other > > word, you think, is more appropriate? > > We apply words in order to simplify the task of referring to common objects and > tasks. This technique has no major or common use, and I see no reason to make up > a special word for it. > > > At any instant, when TAI time is t1, if each one of the two 'ideal' > > clocks A and B show the same time t1, shouldn't we call them > > 'mutually' synchronized, irrespective of the reference frame in which > > we may consider them to be located at that instant? > > Clock synchronization is INHERENTLY frame dependent. That is, a given pair of > clocks can be synchronized in one AND ONLY one inertial frame; they are not > synchronized in any other inertial frame. Your specific case is different from > this and has no such inertial frame, so it does not meet the usual definition of > "synchronized" as used in modern physics. http://en.wikipedia.org/wiki/Coordinate_time http://en.wikipedia.org/wiki/Einstein_synchronisation > > > Why should the physical state of the two clocks > > being 'in synchronization', change when we refer their location to ECI > > or BCRF or the Galactic frame? > > Because the world we inhabit behaves that way. I cannot help it if you do not > like this fact. Synchronization is not a "physical state", it is merely a human > convention. That is, no natural phenomenon depends on how humans happen to set > the parameters of systems they call clocks. << * invariance with respect to time translation gives the well-known law of conservation of energy >> http://en.wikipedia.org/wiki/Noether%27s_theorem#Applications > > > Choice of a reference frame is our > > 'human' artifact, and this choice must not influence a physical > > phenomenon of two clocks being 'in synchronization' or 'not in > > synchronization'. > > There is no "physical phenomenon" corresponding to clock synchronization. Just > like choice of coordinates (reference frame), selection of synchronization > technique is also an arbitrary human choice, as is the choice of the inertial > frame in which to apply it. > > > Isn't this awkward situation a consequence of equally awkward second > > postulate of SR? > > Not at all! It is a direct consequence of the way the world works. SR merely > MODELS this, it does not "dictate" or "cause" it. This is physics, and we are > MODELING the world, not "creating" it. http://en.wikipedia.org/wiki/Lorentz_ether_theory > > > Since physically no atomic clock can ever be at *rest* in the ECI > > frame, > > This is false. A clock at either earth's south or north pole is at rest in the > ECI frame. Such clocks do not actually exist, of course. > > > do you mean to imply that in order to synchronize the clocks A > > and B (at rest on the earth surface) in the ECI frame, their time > > offsets will have to be physically altered or adjusted to suit the > > computations of SR? > > I mean that in order to be synchronized in the ECI, they must be synchronized in > the ECI. That is, their time offsets must be adjusted so this is true. This is > no different from synchronization in any other inertial frame. The method you > described does NOT do this. Note also that earth's surface is irrelevant, it is > earth's geoid that matters; in most places on land, the surface is well above > the geoid. Sue... > > Tom Roberts
From: Inertial on 25 Mar 2010 19:04 "Sue..." <suzysewnshow(a)yahoo.com.au> wrote in message news:7002e36e-90de-4611-be76-88e5699b136a(a)h18g2000yqo.googlegroups.com... > > http://en.wikipedia.org/wiki/Lorentz_ether_theory We are discussing SR .. not LET. Try to keep up Sue and keep your quote-mining and link-mining relevant.
From: GSS on 29 Mar 2010 05:17 On Mar 25, 10:42 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > GSS wrote: > ... >> At any instant, when TAI time is t1, if each one of the two 'ideal' >> clocks A and B show the same time t1, shouldn't we call them >> 'mutually' synchronized, irrespective of the reference frame in which >> we may consider them to be located at that instant? > > Clock synchronization is INHERENTLY frame dependent. That is, a given pair of > clocks can be synchronized in one AND ONLY one inertial frame; they are not > synchronized in any other inertial frame. Agreed that a given pair of precision atomic clocks A and B (separated by constant distance S) can be synchronized in ONE AND ONLY ONE inertial reference frame. But is there any restriction on the choice of THAT inertial reference frame? Specifically, can we practically (not through gedankens) synchronize two clocks A and B in an inertial reference frame in which they are known to be in uniform MOTION (and not at rest)? Let us consider four identical precision atomic clocks A,B, and C,D, located on earth geoid such that A and C are positioned side by side while B and D are also positioned side by side as shown below. A..............................................B <-----------------S----------------------------> C..............................................D Let us set their 'initial times' or their timing offsets by using the GPS service such that when the GPS time is t1 (UTC), all of the four clocks A, B, C and D read t1 (within the limits of timing resolution as available with current cutting-edge technology). Now, using the term 'synchronized' as approved in 'SR' standards, can you say that the clock pairs (A,B), (C,D), (A,C), and (B,D) are mutually *synchronized* in ECI frame, even though these clocks are not at rest in ECI and are moving with non-uniform velocity in the ECI frame? Let us now consider 'the' pair of clocks C and D as 'in motion' in BCRF. Without using any gedanken, kindly explain how will you mutually synchronize the clocks C and D in BCRF in practical terms? Will you physically alter the timing offsets of the clocks C and/or D to *match* with the computed requirements of SR? If you do manage to practically 'synchronize' the clocks C and D in BCRF, obviously their synchronization with clocks A and B will get broken. Then we should be able to say that the clocks A and B are mutually synchronized in ECI frame while the clocks C and D are mutually synchronized in BCRF. You are requested to kindly clarify if there is any practical method of *checking* or verifying that clocks A and B are indeed mutually synchronized in *ECI reference frame* and the clocks C and D are indeed mutually synchronized in *BCRF*. Will this practical method of *checking* the mutual synchronization of these clock pairs be frame dependent or common for both pairs? GSS > >> Why should the physical state of the two clocks >> being 'in synchronization', change when we refer their location to ECI >> or BCRF or the Galactic frame? > > Because the world we inhabit behaves that way. I cannot help it if you do not > like this fact. Synchronization is not a "physical state", it is merely a human > convention. That is, no natural phenomenon depends on how humans happen to set > the parameters of systems they call clocks. > >> Choice of a reference frame is our >> 'human' artifact, and this choice must not influence a physical >> phenomenon of two clocks being 'in synchronization' or 'not in >> synchronization'. > > There is no "physical phenomenon" corresponding to clock synchronization. Just > like choice of coordinates (reference frame), selection of synchronization > technique is also an arbitrary human choice, as is the choice of the inertial > frame in which to apply it. ...... >> do you mean to imply that in order to synchronize the clocks A >> and B (at rest on the earth surface) in the ECI frame, their time >> offsets will have to be physically altered or adjusted to suit the >> computations of SR? > > I mean that in order to be synchronized in the ECI, they must be synchronized in > the ECI. That is, their time offsets must be adjusted so this is true. This is > no different from synchronization in any other inertial frame. The method you > described does NOT do this. Note also that earth's surface is irrelevant, it is > earth's geoid that matters; in most places on land, the surface is well above > the geoid. > > Tom Roberts
From: Paul B. Andersen on 29 Mar 2010 16:57
On 29.03.2010 11:17, GSS wrote: > On Mar 25, 10:42 pm, Tom Roberts<tjroberts...(a)sbcglobal.net> wrote: >> GSS wrote: >> ... >>> At any instant, when TAI time is t1, if each one of the two 'ideal' >>> clocks A and B show the same time t1, shouldn't we call them >>> 'mutually' synchronized, irrespective of the reference frame in which >>> we may consider them to be located at that instant? >> >> Clock synchronization is INHERENTLY frame dependent. That is, a given pair of >> clocks can be synchronized in one AND ONLY one inertial frame; they are not >> synchronized in any other inertial frame. > > Agreed that a given pair of precision atomic clocks A and B (separated > by constant distance S) can be synchronized in ONE AND ONLY ONE > inertial reference frame. But is there any restriction on the choice > of THAT inertial reference frame? Specifically, can we practically > (not through gedankens) synchronize two clocks A and B in an inertial > reference frame in which they are known to be in uniform MOTION (and > not at rest)? > > Let us consider four identical precision atomic clocks A,B, and C,D, > located on earth geoid such that A and C are positioned side by side > while B and D are also positioned side by side as shown below. > > A..............................................B > <-----------------S----------------------------> > C..............................................D > > Let us set their 'initial times' or their timing offsets by using the > GPS service such that when the GPS time is t1 (UTC), all of the four > clocks A, B, C and D read t1 (within the limits of timing resolution > as available with current cutting-edge technology). Now, using the > term 'synchronized' as approved in 'SR' standards, can you say that > the clock pairs (A,B), (C,D), (A,C), and (B,D) are mutually > *synchronized* in ECI frame, even though these clocks are not at rest > in ECI and are moving with non-uniform velocity in the ECI frame? Yes. Clocks showing UTC (or GPS-time which is the same but for a known offset) are synchronized in the non rotating ECI-frame. That means that they are all simultaneously showing the same time _in the non rotating ECI-frame_. Be however aware that the ECI-frame - Earth Centred Inertial frame is a misnomer in this context. It is no inertial frame because space-time is curved, and the curvature is essential. So you cannot use Einstein's synchronization method to define simultaneity (except for between clocks on the same gravitational potential). You could say that simultaneity is defined by the Schwarzschild time coordinate. Since clocks on the geoid, using the SI definition of a second, are running slow compared to Schwarzschild time by a factor of (1.0 - 6.9692842E-10), UTC and GPS-time is defined such that simultaneity is defined (at least in effect) by the Schwarzschild time coordinate, but all clocks should run slow by the factor above relative to Schwarzschild time. > Let us now consider 'the' pair of clocks C and D as 'in motion' in > BCRF. Without using any gedanken, kindly explain how will you mutually > synchronize the clocks C and D in BCRF in practical terms? The same way as clocks on the geoid are synced to the UTC/GPS, that is by compensating for what is called the 'Sagnac effect.' Basically this is to use the difference between the speed of light in the 'reference frame' and the speed of the clocks in same. That is the same as considering the speed of light to be c +/- v in the 'ground frame', where v is the speed of the clocks in the 'reference frame'. The speed of the Earth in the BCRF is ~ 3E4m/s. You would of course have to consider Earth's rotation, the relative position of the clocks compared to their velocity in the BCRF etc. But it could be done. Due to the rotation of the Earth the clocks wouldn't stay in sync in the BCFR for long, though. > Will you > physically alter the timing offsets of the clocks C and/or D to > *match* with the computed requirements of SR? If you do manage to > practically 'synchronize' the clocks C and D in BCRF, obviously their > synchronization with clocks A and B will get broken. Then we should be > able to say that the clocks A and B are mutually synchronized in ECI > frame while the clocks C and D are mutually synchronized in BCRF. Right. > > You are requested to kindly clarify if there is any practical method > of *checking* or verifying that clocks A and B are indeed mutually > synchronized in *ECI reference frame* This 'checking' is made on a more or less continuously basis. Look up TAI-time, and how TAI clocks are kept in sync. > and the clocks C and D are > indeed mutually synchronized in *BCRF*. Will this practical method of > *checking* the mutual synchronization of these clock pairs be frame > dependent or common for both pairs? Much harder. What would you consider to be a valid 'check'? > GSS >> >>> Why should the physical state of the two clocks >>> being 'in synchronization', change when we refer their location to ECI >>> or BCRF or the Galactic frame? >> >> Because the world we inhabit behaves that way. I cannot help it if you do not >> like this fact. Synchronization is not a "physical state", it is merely a human >> convention. That is, no natural phenomenon depends on how humans happen to set >> the parameters of systems they call clocks. >> >>> Choice of a reference frame is our >>> 'human' artifact, and this choice must not influence a physical >>> phenomenon of two clocks being 'in synchronization' or 'not in >>> synchronization'. >> >> There is no "physical phenomenon" corresponding to clock synchronization. Just >> like choice of coordinates (reference frame), selection of synchronization >> technique is also an arbitrary human choice, as is the choice of the inertial >> frame in which to apply it. > ..... >>> do you mean to imply that in order to synchronize the clocks A >>> and B (at rest on the earth surface) in the ECI frame, their time >>> offsets will have to be physically altered or adjusted to suit the >>> computations of SR? >> >> I mean that in order to be synchronized in the ECI, they must be synchronized in >> the ECI. That is, their time offsets must be adjusted so this is true. This is >> no different from synchronization in any other inertial frame. The method you >> described does NOT do this. Note also that earth's surface is irrelevant, it is >> earth's geoid that matters; in most places on land, the surface is well above >> the geoid. >> >> Tom Roberts -- Paul http://home.c2i.net/pb_andersen/ |