After applying an absolute synchronization, frame A and frame B each measure the one way light speed isotropically at c. Which one is at rest with the ether at absolute zero velocity?harrylin said:
It would be a violation of SR, which insists upon symmetry, although not LET, whereby we could tell an absolute frame since the two synchronization methods would not conform and we would no longer have symmetry between frames. Presumably the absolute frame in that case would be the one and only frame where light would still be measured isotropically, while all others produce an offset.Q-reeus said:
grav-universe - my understanding is SR and LET are indistinguishable in any operational sense. The talk has been though that a differential in c is allowed in principle in both theories, but since one-way measurements relying on some clock sync scheme are unobtainable, it could never be found. What I am toying with is an idea for determining difference in one-way speed that uses no clock sync. Not fully worked out, but as time permits may post on it.grav-universe said:
Q-reeus said:
grav-universe said:
They are if all frames are completely symmetrical, which so far they appear to be. LET covers a broader scope than SR, however. SR only works if all frames are symmetrical, while LET does not necessarily require it.Q-reeus said:
That would be interesting, but you would still need something physical to base the synchronization upon by which to measure the one way speed, whether it requires one clock or two clocks or no clocks. In that case you are really just comparing two physical systems to see if they conform. That is basically what yuiop's setup does, comparing the natural synchronization of a spinning arm to a synchronization using light.
Well, by asymmetrical I mean, like with the spinning arm for instance, once the arm is spinning, we measure it to be slightly oval-shaped. Presumably then, only one frame would measure a perfect circle. Otherwise we are not really discussing an absolute time per say, as might be applied between frames, but only within frames according to some natural synchronization, and that same synchronization would apply equally and symmetrically to every frame. But you are right, synchronization itself is relative, figuratively speaking, so you have convinced me to drop the word "absolute" as applied to the synchronization method, especially since its meaning can apparently be taken different ways. Although in that respect, even if an ether exists, measurements can still be taken "relative" to the ether, depending upon how one thinks about it, so all can be considered relative with or without an ether, just adding one more universal entity to be relative to, similar to how one might measure relative to the CMB, even if it were to alter our measurements in some way. However, more than just being relative, two such "natural" synchronizations, as with light and rotation, must really be precisely the same as clock settings would be determined from either, otherwise they do not conform to the frame in the same way for both methods and we could determine the one frame where they do. Not that it would matter much if we did, though, since there is nothing in physics that would ultimately prevent it except a postulated principle of symmetry within and between frames, but otherwise there is no reason it couldn't occur.harrylin said:
Sorry but cannot follow your logic here. Clocks can be made to read anything we wish, but that's beside my point entirely.harrylin said:
Harald - Not sure if you have worked as a consultant or whatever in GPS, but chucking in 'ECI frame' without explanation had me scrambling for one.
Got lucky first Googling attempt: http://en.wikipedia.org/wiki/Earth-centered_inertial. Now could you please explain just how the GPS situation involving orbiting satellites has a bearing on an effectively inertial lab frame where we are working with some fixed (unspecified for now) apparatus, apart from occasionally reorienting the apparatus direction?Not sure if you are referring to an 'aether wind' or such, but LET still gives the same results as SR even here.grav-universe said:
Will have to go back and check what yuiop was actually proposing (never got much interested till now). But obviously some kind of physical comparison has to be made - no 'mind powers' stuff here!
Considering ourselves stationary and we are in a ship while another ship is traveling away from us along the x-axis at v, if the ether physically contracts the ship along the line of motion and slows the ship's clocks and natural processes, each by precisely by a factor of sqrt(1 - (v/c)^2), then the ship observers will also measure the same isotropic speed of light, the same relative speed for us, and the same length contraction and time dilation when measuring the length of our ship and our clocks when using their own contracted rulers and slowed clocks. Since the measurements are precisely the same from either frame, we would not know if we were the ones that are stationary to the ether and the other ship is moving through it or the other way around. The mathematics is consistent where each frame measures precisely the same things of the other. However, that is just one condition in LET that allows symmetry within and between frames, so that we cannot identify the frame of the ether, the same as with SR. The length contraction and time dilation are two factors that can be made unknown variables in LET, though, so complete symmetry is not the only solution.Q-reeus said:
Will have to go back and check what yuiop was actually proposing (never got much interested till now). But obviously some kind of physical comparison has to be made - no 'mind powers' stuff here!
We're in perfect harmony here.grav-universe said:
Meaning I take it length and time wrt the 'absolute' or 'locally absolute' aether frame, as we have just agreed that between any two inertial frames the transformation relations are 'fixed'.The length contraction and time dilation are two factors that can be made unknown variables in LET, though, so complete symmetry is not the only solution.
harrylin said:
The relations for the transformations are fundamentally fixed in variable form regardless of the kinematic theory for how the universe operates, whether it be SR or LET or anything else. Let's say we are stationary in a ship within our own frame and an identical ship passes us in the opposite direction along the x axis, identical in the respect that they measure the same proper length d of their ship as we do of ours. Both ships synchronize the clocks at the front of their ships to T=0 upon passing, when the fronts coincide, which is the origin of each frame. According to our frame, the other ship's clocks are ticking slower by a factor of z, their rulers and ship are length contracted by a factor of L, and they have synchronized so that to us, the clock at the rear of their ship reads a greater time than the front clock by tl, so the other frame is synchronized with an additional time of tl per length L d. An event then occurs according to our frame at coordinates t, x. According to the other frame, the event would occur at x - v t, but their rulers are also contracted, so they measureQ-reeus said:
Q-reeus said:Sorry but cannot follow your logic here. Clocks can be made to read anything we wish, but that's beside my point entirely.
Harald - Not sure if you have worked as a consultant or whatever in GPS, but chucking in 'ECI frame' without explanation had me scrambling for one.
chinglu1998 said:
Understand what you're getting at I think - it's only the inter-frame measure product x't' that's 'invariant' for a given relative frame velocity, and either factor x' or t' could vary arbitrarily within that, so L can vary arbitrarily. Problem I see here is that SR Doppler shift is known to high precision - that fixes the t' part (the t'= y (t - v x / c^2)), thus forcing....grav-universe said:
Thanks for your response. I appreciate a worldwide navigation system needs a standardized reference frame to work from - ECI in this case. Knowing next to nothing about the actual workings of the GPS network, am thinking when you refer to a relative speed of c-v, this translates as a Doppler shift measurement, inferring relative velocity between that satellite emitter and terrestrial GPS receiver (or extended by computation to some other physical reference object). If I recall right there is normally four such satellites always in view to accurately 'quadrangulate' position and speed. That of itself doesn't allow one-way light speed measurements. As you put in #51, we know SR postulates that (one-way) c is an invariant in any frame, whether light is being emitted within that frame, or received from a source in that or any other frame.harrylin said:
Q-reeus said:
Q-reeus said:
As things stand you've got me confused, hopefully just a case of unspoken qualifications. In #31 "And yes, truly measuring the one way speed of light is indeed tantamount to measuring absolute velocity.", which I took as saying it was an impossibility. but then in #50 "The relative speed (also called "closing speed") of radio waves and a GPS receiver at rest on the Earth is c-v. This is merely an example that a nominal difference of one-way speeds can be measured..." - Gift's paper was I thought arguing just that. Let's bypass all the technical intricacies of how GPS works and consider physics in some nominally inertial lab frame. A basic consequence of a real nonreciprocal one-way c : from the fundamental relation c = lambda*f, if f is fixed any nonreciprocal c automatically means a nonreciprocal lambda in that frame. This regardless of whether the light source is within that or another frame. Do you agree with this? And contrary to the consensus viewpoint, lambda variation is at least in principle readily measurable (see below).harrylin said:
Thanks for that link - more details on one-way tests than the Baez site.
Not so - see below.
Found the 1986 paper by Silvertooth - seems OK in principle. Interested though in any actual detailed critique you may know of. A very similar style of differential phase type test was performed by C Navia et al, referenced in the above link. Interesting that the only criticism leveled there was one of sloppy technique - but nothing about fundamental theoretical inadequacy.The Silvertooth experiment there also looked for effects on phases, and was also discredited on theoretical grounds (the alternative theory could not explain the claimed results either). If I correctly recall (for I have now no time to redo the analysis), waves (from one side as well as from two sides) interfere the same when in motion as in rest - perhaps someone else can eventually correct me and elaborate.
That was from #42. I would now have to agree with grav-universe on that point: SR by the 2nd postulate forbids one-way c variation, whereas LET implicitly requires it. My assumption was LT's automatically compensate in both theories. That's only true for two-way measurements and 'normal physics' which depends on invariant two-way c. Hence one-way tests are crucial to distinguish between SR and LET - and differential phase type measurements are perfectly capable in principle of doing that - as per c = lambda*f discussed above. How so? Well my proposed twin fibers setup for one. A nonreciprocal lambda equally stretches/compresses lambda along both lines - and the associated node locations that for sure can be measured; just a question of required sensitivity. Another even simpler example, not very sensitive but 'for sure' in principle - a single match terminated line containing one or more sections of a very low Q almost '1/4 lambda' transmission cavity. Won't go into the details here, but not hard to show that any non-reciprocity in c and thus lambda will result in a corresponding reflection phase and amplitude variation. Once we see past the false dilemma of 'clock sync' and realize phase methods completely bypass this issue, 'impossibility of one-way c measurement' now looks pretty stupid imho. I've done a 180 degree flip on outlook here. Desperately resisting being sucked into a SR/LET theoretic dispute BH!
The only difference between LET and SR is a philosophical one; LET claims that nature operates on a single unidentifiable absolute ether rest frame in which we are almost always moving with respect to, while SR claims that every inertial observer can consider himself to be at rest in, what amounts to, the absolute ether rest frame. There can be no test that can distinguish between the two.Q-reeus said:I would now have to agree with grav-universe on that point: SR by the 2nd postulate forbids one-way c variation, whereas LET implicitly requires it. My assumption was LT's automatically compensate in both theories. That's only true for two-way measurements and 'normal physics' which depends on invariant two-way c. Hence one-way tests are crucial to distinguish between SR and LET - and differential phase type measurements are perfectly capable in principle of doing that - as per c = lambda*f discussed above. How so? Well my proposed twin fibers setup for one. A nonreciprocal lambda equally stretches/compresses lambda along both lines - and the associated node locations that for sure can be measured; just a question of required sensitivity. Another even simpler example, not very sensitive but 'for sure' in principle - a single match terminated line containing one or more sections of a very low Q almost '1/4 lambda' transmission cavity. Won't go into the details here, but not hard to show that any non-reciprocity in c and thus lambda will result in a corresponding reflection phase and amplitude variation. Once we see past the false dilemma of 'clock sync' and realize phase methods completely bypass this issue, 'impossibility of one-way c measurement' now looks pretty stupid imho. I've done a 180 degree flip on outlook here. Desperately resisting being sucked into a SR/LET theoretic dispute BH!
That's what I've thought till now. As for LET reference frame, 'absolute' need not mean that as such - I'm rather partial to an increasing view that CMBR provides a reference gauge for a 'locally absolute' rest frame. Think of the analogous 2D balloon model - any point locally stationary on the skin can serve as a local rest frame, though no globally 'absolute rest frame' is possible. But really I think it gets down to whether non-reciprocal c is in principle detectable - currently I would say yes - via properly designed one-way differential phase measurements. If you know of a reference that can shoot that idea down, please post it!ghwellsjr said:
Q-reeus said:
Yes it was listed early on in the thread, but I never got to read all of it myself. They claim clock synch is no barrier to making one-way tests, and quote Clifford Will to that effect. On the other hand these reviewers deny it can truly be done; ie. 'one-way' is always de facto 'two-way': http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#one-way_tests"ZapperZ said:
Amazing coincidence - precisely same thing happened to me (Microsoft automatic update = unwelcome reboot!) Ditto way overdue for sleep here too.harrylin said:
Q-reeus said:
Q-reeus said:Amazing coincidence - precisely same thing happened to me (Microsoft automatic update = unwelcome reboot!) Ditto way overdue for sleep here too.
EDIT: In #55 "Another even simpler example, not very sensitive but 'for sure' in principle - a single match terminated line containing one or more sections of a very low Q almost '1/4 lambda' transmission cavity. Won't go into the details here, but not hard to show that any non-reciprocity in c and thus lambda will result in a corresponding reflection phase and amplitude variation." That was just outright wrong and is withdrawn unreservedly. Reflection always implies a two-way measurement!
).Just knew it had to be something like that; glad we see eye to eye on that one! Meanwhile I've had an epiphany event of sorts.harrylin said:OK. Just a short precision about my unclear explanation: with "nominal c-v" I meant that that measurement is merely a result of the observer's reference and synchronization -> you can transform it away to v=0 in which case you obtain isotropic light speed (see dictionary.com, "nominal"
Cheers, Harald