phizzicsphan Posted January 17, 2017 Report Share Posted January 17, 2017 In reading Reinhardt et al. 2007 (testing time dilation using lithium ions moving in a storage ring) closely it appears to me that their use of the Einstein synchronization convention may render their result (finding no violation of predicted time dilation under special relativity) a self-proving tautology. That is, by assuming that the two-way speed of light is constant, which is the key assumption for Einstein synchronization of distant clocks, which they seem to have used to synchronize their lasers, this leads to their necessary finding that time dilated. Can others weigh in on this? Here's the paper: https://www.evernote.com/l/AAWGqbXyUYtN ... LiUNw_6VXg Quote Link to comment Share on other sites More sharing options...
OceanBreeze Posted January 17, 2017 Report Share Posted January 17, 2017 Good question. I think what you are really getting at is What Components Are Necessary for an Experiment to Be Valid? One of those components is something that remains constant. Physical constants can be obtained through calculation or measurement, and include such things as Avogadro’s number, pi and the speed of light. You are absolutely right in thinking that constancy of light speed can be shown as a direct consequence of velocity time dilation, and conversely velocity time dilation can be verified as a consequence of the constancy of the speed of light. Thus, the seeming tautology you mentioned. However, the speed of light has been measured often and very accurately, using many different experimental methods, to the point that scientists accept the constancy of the speed of light as an axiom; that is, it has been experimentally verified, but it is not proven in any theoretic sense. Getting back to the specific experiment described by Reinhardt et al, it was a modern variation of the Ives–Stilwell experiment. In such experiments the contribution of relativistic time dilation is determined by measuring the relativistic Doppler shift, or transverse Doppler effect (TDE), of light. The TDE is separated from the usual longitudinal Doppler shift by the use of saturated spectroscopy. The advantage of saturated spectroscopy is it reduces the product of the two transition frequencies of the moving ion beams (V1 V2) to Vo^2, which greatly reduces the dependency on exact values of V1 and V2, which of course are clock dependent. My understanding is this does not completely eliminate the two-way speed uncertainty, and the problems of clock synchronization; it does constrain it a very low value. Quote Link to comment Share on other sites More sharing options...
phizzicsphan Posted January 17, 2017 Author Report Share Posted January 17, 2017 Thanks for these reflections. It seems, however, that we can't have just "a little" tautology. It's like being pregnant, an all or nothing kind of thing. If the exact values of V1 and V2 are clock dependent then we are committing methodological tautology from the outset: putting the answer in at the beginning through our choice of clock synchronization. So by assuming the isotropic two-way speed of light with our choice of clock synchronization aren't we determining the result? Am I wrong on this? Quote Link to comment Share on other sites More sharing options...
OceanBreeze Posted January 17, 2017 Report Share Posted January 17, 2017 I can't say that you are wrong, I think your objection is valid. I will say that some experimental error is always present, no matter how carefully it is run. But we do not draw solid conclusions from just one experiment. If I am not mistaken, there have been several versions of Ives-Stilwell run by several different experimenters and not all of them using the same method of synchronization. All of the results are comparable. Quote Link to comment Share on other sites More sharing options...
phizzicsphan Posted January 18, 2017 Author Report Share Posted January 18, 2017 (edited) My concern is that it's no so much experimental error as built-in methodological error, again forcing the result measured rather than the result being an actual independent phenomenon. So even though these Ives-Stillwell type experiments, and other tests of time dilation, seem to be getting more and more accurate results, what they're actually measuring is a more and more accurate methodological tautology. Edited January 18, 2017 by phizzicsphan Quote Link to comment Share on other sites More sharing options...
OceanBreeze Posted January 18, 2017 Report Share Posted January 18, 2017 I am not qualified to judge the value of these experiments, and nobody on the planet would give a hoot if I did. :zip: Quote Link to comment Share on other sites More sharing options...
phizzicsphan Posted January 18, 2017 Author Report Share Posted January 18, 2017 Well, I would give a hoot :) I appreciate the feedback. I look forward to anyone else's insights on this issue. Quote Link to comment Share on other sites More sharing options...
phizzicsphan Posted January 18, 2017 Author Report Share Posted January 18, 2017 And I think you are qualified in fact. What I'm getting at is a logical/scientific issue that anyone who reads the paper can decide for him/herself. Are the experimenters guilty of methodological tautology or not? I've emailed one of the authors to ask similar questions but no response yet. Quote Link to comment Share on other sites More sharing options...
sanctus Posted January 18, 2017 Report Share Posted January 18, 2017 I do not see it as a tautology, it being what OceanBreeze says here:You are absolutely right in thinking that constancy of light speed can be shown as a direct consequence of velocity time dilation, and conversely velocity time dilation can be verified as a consequence of the constancy of the speed of light. Thus, the seeming tautology you mentioned. Reason is we have a theory built on two axioms (speed of light is constant and there is no preferred reference frame) which then predicts stuff (eg. time dilation). So it is of type "given A then B", if B seems to imply A, it is not surprising since B is derived from A but this does not prove A-->no circularity. It is not "A because of B" and "B because of A", just "given A then B"... Quote Link to comment Share on other sites More sharing options...
sanctus Posted January 18, 2017 Report Share Posted January 18, 2017 O, skipped through the paper and re-read your first post, it seems that you are after consequences of their experimental setup, rather than "philosophy of science"...to that (experimental setup) I also do not feel I know enough to reply. Quote Link to comment Share on other sites More sharing options...
phizzicsphan Posted January 18, 2017 Author Report Share Posted January 18, 2017 santus, it's not so much "given A, then B" as "by assumption A we are preordaining result B," at least insofar as I can determine from reading the paper's details. That is, by using the Einstein clock synchronization procedure to synchronize the lasers that are then used to measure the speeds of the lithium ions in the storage ring, the experiments are putting in by hand the time dilation effect. This is the case because Einstein synchronization assumes two-way isotropic speed of light no matter the speed of the observe. Since nothing else in the universe behaves in this way, time dilation must result in order to keep the speed of light constant. Alternatively, if we did not assume the two-way isotropic speed of light then we wouldn't be seeing any time dilation. Thus the result obtained was preordained by the assumptions used in the experimental setup. Does that make sense? Or do you disagree? Quote Link to comment Share on other sites More sharing options...
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