Notion of Absolute Clock Synchronization in SR
in [Relativity]
|
From: harald on 19 Mar 2010 05:23 On Mar 18, 11:27 pm, va...(a)icmf.inf.cu wrote: > On 18 mar, 10:49, harald <h...(a)swissonline.ch> wrote: > > > On Mar 18, 3:04 pm, va...(a)icmf.inf.cu wrote: > > > > On 17 mar, 10:34, harald <h...(a)swissonline.ch> wrote: > > > > > On Mar 17, 3:34 pm, va...(a)icmf.inf.cu wrote: > > > > > > On 16 mar, 17:20, harald <h...(a)swissonline.ch> wrote: > > > > > > > On Mar 16, 3:30 pm, va...(a)icmf.inf.cu wrote: > > > > > > > > On 15 mar, 05:53, harald <h...(a)swissonline.ch> wrote: > > > [..] > > > > > > > > > > E-sync means that the ELAPSED times of both clocks correspond, as well as > > > > > > > > > the readings at some time. E-sync'd clocks remain in synch. > > > > > > > > > Thanks for the elaboration. But more precisely: e-synched "perfect", > > > > > > > > "stationary" clocks remain in sync (if at the same gravitational > > > > > > > > potential). Now, let's hope that the OP will understand this. :) > > > > > > > > (Hello Harald, nice to meet you again). > > > > > > > In the ECI frame of GPS all the clocks remain synchronized, even if > > > > > > > they have different velocities and gravitational potentials. Then, > > > > > > > taking into account that huge experimental evidence, I dont see any > > > > > > > other alternative that to accept that absolute clock synchronization > > > > > > > exists in SR with the following meaning. Once perfect and stationary > > > > > > > clocks are e-synchronized in some inertial frame, they remain showing > > > > > > > the same time lecture at any local instant in all the others inertial > > > > > > > frames. Of course, that equal time lecture does not correspond to > > > > > > > the local time in each of the others inertial frames, where according > > > > > > > to SR rules, the now moving clocks (all with the same velocity) are > > > > > > > running slower than the local perfect and stationary e-synchronised > > > > > > > ones. > > > > > > > > RVHG (Rafael Valls Hidalgo-Gato) > > > [..] > > > > > The topic of this thread is concerned with the fact that according to > > > > all inertial reference systems in which the inertial reference system > > > > with its synchronized clocks is moving, those clocks are out of sync > > > > with each other (see also below). > > > > > > I mentioned the ECI of GPS, taken for granted that the e- > > > > > synchronization method of all its clocks is well-known. Let us > > > > > remember that all the moving clocks show the unique ECI time, > > > > > corresponding to the same time that a similar clock at rest in the > > > > > relevant ECI point would show. If now we consider the ECI moving at a > > > > > constant velocity with respect to an (imaginary) inertial frame B, > > > > > Note: the ECI "frame" itself is already an imaginary frame... > > > > I dont understand why you consider the ECI an imaginary frame. > > > The whole Earth is rotating relative to it; there isn't any material > > frame that is pretended to be "in rest". > > I have a doubt here about what do you mean by material frame. A stiff thing made up of atoms (such as earth, wood, steel or concrete). [..] > > > Yes, an inertial observer at rest in the moving system (moving GPS > > > satellite) appreciates all ECI clocks out of synchronism, but who > > > care that? > > > OK, perhaps I misunderstood what you tried to communicate - in which > > case I don't know what it was! > > I prefer to put the emphasis in what we are in agreement now. Our own > ideas can be evolving somewhat in the time. > > > In fact, you here agree with the SRT claim that clock synchronisation > > (along x) is "relative", in the sense that it is meant. > > Yes, without any doubt synchronization is relative to the inertial > frame you select to do it. But let us take some care here, I > distinguish a real inertial system (the centre of mass one associated > to some well-determined body set) from an imaginary one (as all of > them in the 1907 Minkowski view). > > > > I feel now very happy with your very valuable reference to 1905 > > > Einstein first paper on Relativity. Now we can make real the imaginary > > > inertial frame B identifying it with a moving GPS satellite (the real > > > inertial frame B is the centre of mass one corresponding to the > > > satellite and all bodies in its interior). > > > You can choose it as you wish, according to SRT (as long as it isn't > > rotating, which is incompatible with GPS satellites!). > > An inertial frame can never be rotating. The space belonging to the > ECI (or any other inertial frame) has always all its points at rest. > > > Consider now the inertial Solar System (the centre of mass one of all > > > its bodies). In principle, we can synchronize clocks in all its > > > planets, showing all of them the same unique time defined by 1905 > > > Einstein. > > > It is "unique" for the solar system, just as the pair of shoes that I > > wear are "unique" for me... > > I dont think so. You can change your shoes, but not the unique time > corresponding to the Solar System as long as it is maintained as a > closed one (I forgot to mention explicitly that basic condition when > talking about real inertial frames). Sure we can - we can set t=0 whenever we want, and also choose our time standard. > > Of course, this time is not an absolute one, but maybe > > > something similar to it was in the mind of the OP of this thread when > > > choosing its title. > > > Perhaps - but it looked as if he was still trying to understand the > > basics. > > (Some final comments) > I appreciate a lot this new contact with you. If I remember well, in > the last one (how many years ago?) you said that my Hierarchical > Inertial Frame (HIS) concept was a mix of different theories, > including the Newtonian one. I continue thinking that 1905 Einstein > discovered an absolute (and total, owed to ALL fields that can be > present) potential energy measured by a variable rest mass (depending > on position). Well, this is not the adequate place to talk about all > these things. In reality, I address them now in order to be able to > introduce a possible absolute time, the principal topic in this > thread. > What if we consider a sequence of real inertial frames, each one with > a body set that includes de previous one?( Earth, Solar System, Galaxy, > ). How far can we run in that hierarchy of HIS? One can choose any inertial reference system that one likes and link that to others. If you want to set or define (free to choose!) "absolute time" and "space", then one uses the same time and space coordinates everywhere (such as astronautes do) and one has to correct for the assigned speed in experiments. You may thus do that for "hierarchies" or other things of your liking. Note that the Earth's and solar "frames" are only approximately "inertial" in the SRT sense, which shows up in for example stellar aberration. > If we have a finite > number of bodies in our Universe, the sequence is finite and we would > have all the right to denote as absolute time the one corresponding > to the highest hierarchy last HIS. And if our Universe has infinite > number of bodies, in all ways we can talk at least about an absolute > time as a limit. It's always possible to conventionally assign an "absolute time" standard, just as we already have a "universal time" standard. Cheers, Harald
From: Inertial on 19 Mar 2010 09:12 "GSS" <gurcharn_sandhu(a)yahoo.com> wrote in message news:0247493d-e874-4864-ae9f-a3e8b4c299be(a)q21g2000yqm.googlegroups.com... > On Mar 18, 8:49 pm, harald <h...(a)swissonline.ch> wrote: >> On Mar 18, 3:04 pm, va...(a)icmf.inf.cu wrote: > .... >>>>>>>> Thanks for the elaboration. But more precisely: e-synched >>>>>>>> "perfect", >>>>>>>> "stationary" clocks remain in sync (if at the same gravitational >>>>>>>> potential). Now, let's hope that the OP will understand this. :) >> ..... >>> Of course, this time is not an �absolute� one, but maybe >>> something similar to it was in the mind of the OP of this thread when >>> choosing its title. >> >> Perhaps - but it looked as if he was still trying to understand the >> basics. >> >> Harald > > Maybe yes, I am still trying to understand the intricacies of clock > synchronization under SR regime. Its not that hard > Let us consider two identical precision atomic clocks, positioned at > points A and B, separated by a distance of about 30 km along east- > west direction, on the surface of earth. As you are talking SR, you must be assuming that the surface of the earth is an inertial frame (so we'll ignore it rotating, or orbitting, and ignore gravity). > Assume the two clocks A and B > are mutually synchronized through Einstein convention such that the > time taken, T_ab, by a laser pulse to propagate from A to B (as > measured from the clock readings of B and A) is the same as the time > taken, T_ba, by a laser pulse to propagate from B to A. Which is, of course, obviously true. > That means, > T_ab - T_ba = 0 which indicates e-synchronization of the two clocks. Only if that is what the clocks show. The fact light takes the same time to travel the same distance at the same speed doesn't make the clocks synchronized. > In your opinion, will this synchronization remain valid at least for a > 24 hour period? That is, if we take to and fro signal propagation time > readings at hourly intervals, will all readings show, > T_ab - T_ba = 0 It will be valid forever, if they remain at rest in the inertial frame. > Perhaps you may like to call this mutual synchronization of clocks A > and B as the 'local clock synchronization' valid in the local or lab > frame of the two clocks. If you want to. > Kindly explain the procedure for e-synchronization of the same two > atomic clocks A and B in the ECI or the GCRF frame. How exactly will > it be different from the local clock synchronization in practical > terms? The clocks would have to be at rest in those frames. If not, then you can of course have a whole series of appropriate clocks that ARE at rest in the frame you want (so A and B will be comoving past those clocks), and chose a time on those clocks (say 12:00), and whichever rest clocks A and B are adjacent to when those rest get to 12:00, copy that time to A and B. Then A and B will be in sync in that frame, and show the same time in that frame. But they won't be measured as ticking at the correct rate, so they will get more and more out of synch with other rest clocks they pass. > Since the two clocks under consideration are simultaneously known to > be co-moving in the solar system at about 30 km/s, you may kindly > explain the procedure for e-synchronization of the same two atomic > clocks A and B in the solar system BCRF frame. The clocks would have to be at rest in that frame. (Or see above) > How exactly will it be > different from the local clock synchronization in practical terms? No different at all. But the same clocks are not going to be both at rest in more than one (non-eqivalent) inertial frame. > Going one step still further,the two clocks under consideration are > simultaneously known to be co-moving in the Galactic reference frame > at about 200 km/s. Kindly explain the procedure for e-synchronization > of the same two atomic clocks A and B in the Galactic reference frame. The clocks would have to be at rest in that frame. (Or see above) > How exactly will it be different from the local clock synchronization > in practical terms? No different at all. But the same clocks are not going to be both at rest in more than one (non-eqivalent) inertial frame. > For the sake of simplicity of discussions, you may completely neglect > the gravitational effects on clock synchronization and only account > for the SR effects. Good .. this is all very trivial.
From: Sue... on 19 Mar 2010 09:52 On Mar 19, 4:52 am, GSS <gurcharn_san...(a)yahoo.com> wrote: > On Mar 18, 8:49 pm, harald <h...(a)swissonline.ch> wrote: > > > On Mar 18, 3:04 pm, va...(a)icmf.inf.cu wrote: > .... > >>>>>>> Thanks for the elaboration. But more precisely: e-synched "perfect", > >>>>>>> "stationary" clocks remain in sync (if at the same gravitational > >>>>>>> potential). Now, let's hope that the OP will understand this. :) > > ..... > >> Of course, this time is not an absolute one, but maybe > >> something similar to it was in the mind of the OP of this thread when > >> choosing its title. > > > Perhaps - but it looked as if he was still trying to understand the > > basics. > > > Harald > > Maybe yes, I am still trying to understand the intricacies of clock > synchronization under SR regime. > > Let us consider two identical precision atomic clocks, positioned at > points A and B, separated by a distance of about 30 km along east- > west direction, on the surface of earth. Assume the two clocks A and B > are mutually synchronized through Einstein convention such that the > time taken, T_ab, by a laser pulse to propagate from A to B (as > measured from the clock readings of B and A) is the same as the time > taken, T_ba, by a laser pulse to propagate from B to A. That means, > T_ab - T_ba = 0 which indicates e-synchronization of the two clocks.. Physical light paths are specifically excluded from the convention and no clock mechanisms are described. The basis is stipulations and conclusions of mathematicians. http://en.wikipedia.org/wiki/Einstein_synchronisation http://en.wikipedia.org/wiki/Coordinate_time What we can test physically is this: << the four-dimensional space-time continuum of the theory of relativity, in its most essential formal properties, shows a pronounced relationship to the three-dimensional continuum of Euclidean geometrical space. In order to give due prominence to this relationship, however, we must replace the usual time co-ordinate t by an imaginary magnitude sqrt(-1) ct proportional to it. Under these conditions, the natural laws satisfying the demands of the (special) theory of relativity assume mathematical forms, in which the time co-ordinate plays exactly the same rôle as the three space co-ordinates. >> http://www.bartleby.com/173/17.html That is just a formal way of stating that physical phenomena is independent of the coordinate system used to describe it. Nothing more. Nothing less. See also: "Tensors" http://farside.ph.utexas.edu/teaching/em/lectures/node111.html Sue... [...] > > GSS
From: valls on 19 Mar 2010 12:39 On 19 mar, 04:23, harald <h...(a)swissonline.ch> wrote: > On Mar 18, 11:27 pm, va...(a)icmf.inf.cu wrote: > > > > > > > On 18 mar, 10:49, harald <h...(a)swissonline.ch> wrote: > > > > On Mar 18, 3:04 pm, va...(a)icmf.inf.cu wrote: > > > > > On 17 mar, 10:34, harald <h...(a)swissonline.ch> wrote: > > > > > > On Mar 17, 3:34 pm, va...(a)icmf.inf.cu wrote: > > > > > > > On 16 mar, 17:20, harald <h...(a)swissonline.ch> wrote: > > > > > > > > On Mar 16, 3:30 pm, va...(a)icmf.inf.cu wrote: > > > > > > > > > On 15 mar, 05:53, harald <h...(a)swissonline.ch> wrote: > > > > [..] > > > > > > > > > > > E-sync means that the ELAPSED times of both clocks correspond, as well as > > > > > > > > > > the readings at some time. E-sync'd clocks remain in synch. > > > > > > > > > > Thanks for the elaboration. But more precisely: e-synched "perfect", > > > > > > > > > "stationary" clocks remain in sync (if at the same gravitational > > > > > > > > > potential). Now, let's hope that the OP will understand this. :) > > > > > > > > > (Hello Harald, nice to meet you again). > > > > > > > > In the ECI frame of GPS all the clocks remain synchronized, even if > > > > > > > > they have different velocities and gravitational potentials.. Then, > > > > > > > > taking into account that huge experimental evidence, I dont see any > > > > > > > > other alternative that to accept that absolute clock synchronization > > > > > > > > exists in SR with the following meaning. Once perfect and stationary > > > > > > > > clocks are e-synchronized in some inertial frame, they remain showing > > > > > > > > the same time lecture at any local instant in all the others inertial > > > > > > > > frames. Of course, that equal time lecture does not correspond to > > > > > > > > the local time in each of the others inertial frames, where according > > > > > > > > to SR rules, the now moving clocks (all with the same velocity) are > > > > > > > > running slower than the local perfect and stationary e-synchronised > > > > > > > > ones. > > > > > > > > > RVHG (Rafael Valls Hidalgo-Gato) > > > > [..] > > > > > > The topic of this thread is concerned with the fact that according to > > > > > all inertial reference systems in which the inertial reference system > > > > > with its synchronized clocks is moving, those clocks are out of sync > > > > > with each other (see also below). > > > > > > > I mentioned the ECI of GPS, taken for granted that the e- > > > > > > synchronization method of all its clocks is well-known. Let us > > > > > > remember that all the moving clocks show the unique ECI time, > > > > > > corresponding to the same time that a similar clock at rest in the > > > > > > relevant ECI point would show. If now we consider the ECI moving at a > > > > > > constant velocity with respect to an (imaginary) inertial frame B, > > > > > > Note: the ECI "frame" itself is already an imaginary frame... > > > > > I dont understand why you consider the ECI an imaginary frame. > > > > The whole Earth is rotating relative to it; there isn't any material > > > frame that is pretended to be "in rest". > > > I have a doubt here about what do you mean by material frame. > > A stiff thing made up of atoms (such as earth, wood, steel or > concrete). > > [..] > > > > > > > > > Yes, an inertial observer at rest in the moving system (moving GPS > > > > satellite) appreciates all ECI clocks out of synchronism, but who > > > > care that? > > > > OK, perhaps I misunderstood what you tried to communicate - in which > > > case I don't know what it was! > > > I prefer to put the emphasis in what we are in agreement now. Our own > > ideas can be evolving somewhat in the time. > > > > In fact, you here agree with the SRT claim that clock synchronisation > > > (along x) is "relative", in the sense that it is meant. > > > Yes, without any doubt synchronization is relative to the inertial > > frame you select to do it. But let us take some care here, I > > distinguish a real inertial system (the centre of mass one associated > > to some well-determined body set) from an imaginary one (as all of > > them in the 1907 Minkowski view). > > > > > I feel now very happy with your very valuable reference to 1905 > > > > Einstein first paper on Relativity. Now we can make real the imaginary > > > > inertial frame B identifying it with a moving GPS satellite (the real > > > > inertial frame B is the centre of mass one corresponding to the > > > > satellite and all bodies in its interior). > > > > You can choose it as you wish, according to SRT (as long as it isn't > > > rotating, which is incompatible with GPS satellites!). > > > An inertial frame can never be rotating. The space belonging to the > > ECI (or any other inertial frame) has always all its points at rest. > > > > Consider now the inertial Solar System (the centre of mass one of all > > > > its bodies). In principle, we can synchronize clocks in all its > > > > planets, showing all of them the same unique time defined by 1905 > > > > Einstein. > > > > It is "unique" for the solar system, just as the pair of shoes that I > > > wear are "unique" for me... > > > I dont think so. You can change your shoes, but not the unique time > > corresponding to the Solar System as long as it is maintained as a > > closed one (I forgot to mention explicitly that basic condition when > > talking about real inertial frames). > > Sure we can - we can set t=0 whenever we want, and also choose our > time standard. > From your last answer I deduce that we dont share a common interpretation about what is the time defined by 1905 Einstein. Let us take two very well-known real inertial systems, the ECI and the Solar System (SS). Let me ask you a very crucial question. Can be two GPS clocks (for example one in a satellite and another in the Earths surface) e-synchronized with respect to the ECI and at the same time also e-synchronized with respect to the SS? The essential difference between the (1905 Einstein) times of two different inertial systems has no relation at all with the totally arbitrary selection of initial instants and time standard units in both systems. > > > > > > > Of course, this time is not an absolute one, but maybe > > > > something similar to it was in the mind of the OP of this thread when > > > > choosing its title. > > > > Perhaps - but it looked as if he was still trying to understand the > > > basics. > > > (Some final comments) > > I appreciate a lot this new contact with you. If I remember well, in > > the last one (how many years ago?) you said that my Hierarchical > > Inertial Frame (HIS) concept was a mix of different theories, > > including the Newtonian one. I continue thinking that 1905 Einstein > > discovered an absolute (and total, owed to ALL fields that can be > > present) potential energy measured by a variable rest mass (depending > > on position). Well, this is not the adequate place to talk about all > > these things. In reality, I address them now in order to be able to > > introduce a possible absolute time, the principal topic in this > > thread. > > What if we consider a sequence of real inertial frames, each one with > > a body set that includes de previous one?( Earth, Solar System, Galaxy, > > ). How far can we run in that hierarchy of HIS? > > One can choose any inertial reference system that one likes and link > that to others. If you want to set or define (free to choose!) > "absolute time" and "space", then one uses the same time and space > coordinates everywhere (such as astronautes do) and one has to correct > for the assigned speed in experiments. You may thus do that for > "hierarchies" or other things of your liking. Note that the Earth's > and solar "frames" are only approximately "inertial" in the SRT sense, > which shows up in for example stellar aberration. > I prefer to wait for your answer to my previous question before comment your last one. > > If we have a finite > > number of bodies in our Universe, the sequence is finite and we would > > have all the right to denote as absolute time the one corresponding > > to the highest hierarchy last HIS. And if our Universe has infinite > > number of bodies, in all ways we can talk at least about an absolute > > time as a limit. > > It's always possible to conventionally assign an "absolute time" > standard, just as we already have a "universal time" standard. > Repeating my previous comment. RVHG (Rafael Valls Hidalgo-Gato) > Cheers, > Harald- Ocultar texto de la cita - > > - Mostrar texto de la cita -- Ocultar texto de la cita - > > - Mostrar texto de la cita -- Ocultar texto de la cita - > > - Mostrar texto de la cita -
From: GSS on 19 Mar 2010 14:25
On Mar 19, 6:12 pm, "Inertial" <relativ...(a)rest.com> wrote: > "GSS" <gurcharn_san...(a)yahoo.com> wrote in message > ...... > >> Let us consider two identical precision atomic clocks, positioned at >> points A and B, separated by a distance of about 30 km along east- >> west direction, on the surface of earth. > > As you are talking SR, you must be assuming that the surface of the earth is > an inertial frame (so we'll ignore it rotating, or orbitting, and ignore > gravity). > No, I meant to ignore gravity effects only. >> Assume the two clocks A and B >> are mutually synchronized through Einstein convention such that the >> time taken, T_ab, by a laser pulse to propagate from A to B (as >> measured from the clock readings of B and A) is the same as the time >> taken, T_ba, by a laser pulse to propagate from B to A. > > Which is, of course, obviously true. > >> That means, >> T_ab - T_ba = 0 which indicates e-synchronization of the two clocks. > > Only if that is what the clocks show. The fact light takes the same time to > travel the same distance at the same speed doesn't make the clocks > synchronized. > >> In your opinion, will this synchronization remain valid at least for a >> 24 hour period? That is, if we take to and fro signal propagation time >> readings at hourly intervals, will all readings show, >> T_ab - T_ba = 0 > > It will be valid forever, if they remain at rest in the inertial frame. > Will it still be valid for ever, if they remain at rest only in the local or lab frame fixed on the surface of earth? What do you think is the effect of earth rotation on the mutual e-synchronization of two clocks in the lab frame? >> Perhaps you may like to call this mutual synchronization of clocks A >> and B as the 'local clock synchronization' valid in the local or lab >> frame of the two clocks. > > If you want to. > >> Kindly explain the procedure for e-synchronization of the same two >> atomic clocks A and B in the ECI or the GCRF frame. How exactly will >> it be different from the local clock synchronization in practical >> terms? > > The clocks would have to be at rest in those frames. > > If not, then you can of course have a whole series of appropriate clocks > that ARE at rest in the frame you want (so A and B will be comoving past > those clocks), and chose a time on those clocks (say 12:00), and whichever > rest clocks A and B are adjacent to when those rest get to 12:00, copy that > time to A and B. Then A and B will be in sync in that frame, and show the > same time in that frame. But they won't be measured as ticking at the > correct rate, so they will get more and more out of synch with other rest > clocks they pass. I don't think you really mean what you write. Do you seriously think there are some atomic clocks that are actually at rest in the ECI or BCRF frames? Or can you ever make any atomic clock ever at rest in the ECI or BCRF frames? > >> Since the two clocks under consideration are simultaneously known to >> be co-moving in the solar system at about 30 km/s, you may kindly >> explain the procedure for e-synchronization of the same two atomic >> clocks A and B in the solar system BCRF frame. > > The clocks would have to be at rest in that frame. (Or see above) > But how? >> How exactly will it be >> different from the local clock synchronization in practical terms? > > No different at all. But the same clocks are not going to be both at rest > in more than one (non-eqivalent) inertial frame. > >> Going one step still further,the two clocks under consideration are >> simultaneously known to be co-moving in the Galactic reference frame >> at about 200 km/s. Kindly explain the procedure for e-synchronization >> of the same two atomic clocks A and B in the Galactic reference frame. > > The clocks would have to be at rest in that frame. (Or see above) > What I make out from your response is that two clocks A and B considered above, can be e-synchronized in ECI or BCRf or Galactic reference frames only if these clocks can be brought to rest in these frames. Since it is practically impossible to bring the two clocks (at rest on the surface of earth) to rest in ECI or BCRF or Galactic reference frames, it implies that it is practically impossible to mutually e-synchronize the two clocks in any of these inertial reference frames. That means two atomic clocks A and B can be mutually e-synchronized only in their local or lab frame and none else. All talk of e-synchronizing two or more atomic clocks in different inertial reference frames in relative uniform motion, is just hypothetical day dreaming or gedanken. Do other relativity experts agree? GSS >> How exactly will it be different from the local clock synchronization >> in practical terms? > > No different at all. But the same clocks are not going to be both at rest > in more than one (non-eqivalent) inertial frame. > >> For the sake of simplicity of discussions, you may completely neglect >> the gravitational effects on clock synchronization and only account >> for the SR effects. > > Good .. this is all very trivial. |