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Recommendaton for Clarifying Special Relativity

  1. Jun 20, 2013 #1
    This thread is intended to replace the previous thread that I established (and was closed), because the img link was inadvertently corrupted.

    I was hoping to generate interest among the mentors (and the more prominent contributors to this subject) in preparing something like a Fact Sheet or FAQ clarifying the elements of Special Relativity Theory. PAllen and Fredrik have made very useful contributions to the subject and have identified the root source of the problem we have had in the past in discussing foundational issues of special relativity. They have pointed out that some of us have been operating on different basic conceptions of what elements of Einstein’s SR discussions actually constitute The Theory of Special Relativity as it is should be understood.

    Perhaps an august team representing the PF stance on this subject could develop a summary of the situation in order to avoid future confusion of the type that has precipitated the kinds of misguided discussions that have taken place in the past.

    The diagram below is not offered as a form to be adapted—it is intended merely as a stimulus to motivate a team of seasoned PF mentors and established authoritative PF contributors to come up with some sort of presentation that clarifies the relationships among the various theories and interpretations.

    Last edited: Jun 20, 2013
  2. jcsd
  3. Jun 20, 2013 #2


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    One issue from the get go is that 'Einstein's presentation' of SR evolved through discussion and contribution of others. Initially, it did not emphasize the metric or spacetime; later it did. Spacetime diagrams were little used in SR treatments until circa 1950s (after Einstein died). Einstein never used lines of simultaneity for non-inertial observers. Einstein never enunciated any concept resembling a 'simultaneous space' carried by a general observer, in any presentation I've seen. (Personally, I like some of these innovations [space time diagrames], but not others [treating lines of simultaneity as if they had any objective significance]).

    Thus, I don't think focusing on Einstein's presentation is important for a physics forum. We would get bogged down in history, relative emphasis of different documents, and even which translations to give weight to (since almost all of his scientific writings were in German). I suspect there would also be a tendency to read our own pedagogical biases into Einstein's writings.
  4. Jun 21, 2013 #3

    PAllen, it seems to me that what you have just described illustrates all the more the benefit of some kind of PF clarification of the relationships among the various concepts you allude to. In four years of an Undergraduate physics program followed by two years of physics Master’s program, then three years of the physics Doctorate program, I don’t recall being exposed to any distinction between Einstein’s presentation of special relativity and what would be considered on this PF as a valid characterization of The Special Theory of Relativity (of course I may not have been paying attention). And in looking back in my old Rindler text book through the foundational discussions of Einstein’s concepts, I don’t find those distinctions (other than Rindler’s pointed remarks about the explicit exclusion of LET from Einstein’s theory). Now, if after all of my exposure to special relativity, I can be confused throughout extended series of posts here, I just imagine that there must be many other visitors to the forum, who have not had extensive formal exposure to SR, who might well be even more confused than I.
  5. Jun 21, 2013 #4


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    Perhaps your lack of exposure to these distinctions is an indication of their relative importance.
  6. Jun 21, 2013 #5


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    Subtle, and if you're saying what I think you're saying, I agree.
    Does SR need 'clarifying' ?
    No doubt some people find this stuff edifying but for me the words 'dancing, 'angels' and 'pin' come to mind.
  7. Jun 21, 2013 #6


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    Are you really confused? Or do you just not like the answer you have repeatedly gotten, which basically amounts to: the only block on your chart that we talk about here on PF is the one that says "falsifiable elements only"?
  8. Jun 21, 2013 #7
    I'm certainly not confused now. The situation has been made quite clear. But, although it is clear to you PF SR experts, it will not necessarily be clear to visitors to the forum.

    The point of this thread has nothing to do with whether I like or dislike the views of others on the subject of foundational physics. The comments offered have not always been consistent, and, as an example, I'm not the one who presented the confusing narrative that LET is an interpretation of Einstein's special relativity. I understand the context now (as shown in the block diagram of my initial post). It should not be assumed that any visitor to the forum should understand this. It would be more natural, in this example, to assume that Einstein's SR excludes LET, since Einstein's writings and text books like Rindler's are so explicit about this.

    Hopefully, the chart makes the relationships in this regard quite clear now. But, This has not been obvious throughout many of the discussions.

    But, the point of this thread is not to rehash old arguments and I have no interest in pursuing the subject further. If it is felt that my suggestion has no merit--fine. It was only a recommendation.
  9. Jun 21, 2013 #8
    I think there are several problems with your diagram. First, Einstein's 1905 presentation did not "explicitly exclude" a Lorentzian ether interpretation. It simply said that the identification of a unique frame as the "rest frame of an ether" will prove superfluous. There's a difference between saying something is superfluous and saying it is explicitly excluded. Second, Einstein's presentation did not include any non-falsifiable elements. He was remarkably careful to give operational meanings to all his statements (which is not to say his presentation couldn't have been improved). Third, the one-way speed of light in terms of coordinates in which "the equations of Newtonian mechanics hold good" is an empirical fact, and this is all that special relativity claims, so you shouldn't say this is a non-falsifiable feature of special relativity. Fourth, the expression "Abstract Math Interpretation" doesn't make any sense. A physical theory isn't just math, it requires a correspondence with sense impressions and operational measures (at the very least).
  10. Jun 21, 2013 #9


    Staff: Mentor

    What percentage of forum visitors have raised questions similar to yours? My sense is that it's a very small percentage, but I may be wrong.
  11. Jun 21, 2013 #10
    One thing I learned from writing FAQ's or fact based articles is that there are several challenges to consider.

    1) What types of questions is the FAQ designed to answer, (a sequential list like a flow chart helps)
    2) Where to draw the line on alternate model/proposals/interpretations as opposed to concordance/textbook views (this part is sometimes tricky to control)
    3) images and supportive links reliability on a long term basis (broken links are frustrating to a reader)
    4) keeping the article as short and as informative as possible (lol personal experience taught me just how tricky that is)
    5)level of understanding suitable to a large body of readers ( its easy to get too technical, but a good article needs the technical details, so its a juggling act)

    just some things to consider in your writing,
  12. Jun 21, 2013 #11
    Never Mind

    Never mind.
  13. Jun 22, 2013 #12
    Good start! As already mentioned, Einstein's presentations evolved in the course of time. His early presentations corresponded somewhat with your middle presentation, similar to his other "annus mirabiis papers": the mathematical consequences of a combination of observations. In fact he stuck to discussing falsifiable elements (top balloon). Of course he did give "physical interpretations" of the result, but those were again limited to measurement predictions. Your presentation on the right was perhaps first given by Minkowski. I suggest to replace "Einstein" by "Minkowski", which will steer the reader in the direction of Minkowski Spacetime diagrams etc.

    PS. while it is impossible to please everyone, the first balloon could be improved as follows: Includes falsifiable assumptions only (the speed of light is isotropic by definition).
    - http://www.fourmilab.ch/etexts/einstein/specrel/www/
    Last edited: Jun 22, 2013
  14. Jun 22, 2013 #13
    Thanks for the comment, harrylin (especially your polite but accurate tone). I must concur in your observations. You are of course correct to point out that ideas about his own theory evolved over time (as also immediately pointed out by PAllen), so that my characterization was inaccurate in that respect. I actually had not consciously passed over this fact—out of habit, when characterizing Einstein's ideas, I just normally include those expressed from the early ‘20s on (and certainly the late ‘40s and early ‘50s). I probably should not have presented them in that context, at least without qualification. And again you correctly attribute one of the most significant ideas coming out of the special theory to Minkowski, where I, again out of habit, lump Minkowski’s in with Einstein (from Einstein’s book: “…These inadequate remarks can give the reader only a vague notion of the important idea contributed by Minkowski. Without it the general theory of relativity, of which the fundamental ideas are developed in the following pages, would perhaps have got no further than its long clothes.”). And it apparently took Einstein a while to endear himself to Minkowski’s idea.

    It kind of reminds me of a recent visit I had with my old relativity advisor. He was a new PhD graduate himself, fresh out of the University of Texas (perhaps a Wheeler student--although Wheeler may not have taken on students at UT), when I entered the PhD program. He commented that as he gets older he is beginning to think more and more about ideas underlying physics. And I think that is what many look for when they come to this forum. But of course that does not mean we should cater at the expense of watering down the theory to the point of presenting inaccurate representations.
    Last edited: Jun 22, 2013
  15. Jun 22, 2013 #14
    Just to bring the diagram into closer agreement with Harrylin's suggestions. Again, this is not a recommendation to use this diagram. It is only to motivate interest in creating a FAQ

    . LETvsSR_Diagram2_zpse69a2099.png
    Last edited: Jun 22, 2013
  16. Jun 22, 2013 #15
    I have a question about this. I think numerous experiments have been conducted that support isotropy for space with very high precision (I believe those tests were all conducted for light traveling one way). However, do those results guarantee the one-way speed of light has been shown to be falsifiable?
  17. Jun 23, 2013 #16
    First a few comments:
    - I should not have omitted "one-way" there, sorry for that. MMX happened to be about speed of light isotropy as well, the two-way kind.
    - with "Einstein's later presentation" you apparently mean after 1922, as his opinion swayed in all directions until at least then (for example, 1920: "The ether of the general theory of relativity is transmuted conceptually into the ether of Lorentz if we substitute constants for the functions of space which describe the former, disregarding the causes which condition its state."). Minkowski's opinion was certainly more straightforward and constant.
    - perhaps your middle interpretation could be called the "shut up and calculate" (non-)interpretation.

    Concerning the measurement of one-way light speed isotropy we had many discussions here and there is also an overview article in Wikipedia with many references:

    Einstein was very sharp when in 1905 he made the one-way speed of light isotropic "by definition". Two years later he reformulated it even better, IMHO:

    "We [...] assume that the clocks can be adjusted in such a way that
    the propagation velocity of every light ray in vacuum - measured by
    means of these clocks - becomes everywhere equal to a universal
    constant c, provided that the coordinate system is not accelerated." (translation by A.Beck)
    - original here: http://www.soso.ch/wissen/hist/SRT/E-1907.pdf

    For SR to work, it must be possible to define an isotropic one-way speed of light wrt any inertial reference system of choice -because the two-way speed is isotropic. It is the free choice of the operator to set the clocks such that the subsequently measured one-way speed of light in all directions becomes isotropic wrt to that system.
    Last edited: Jun 23, 2013
  18. Jun 26, 2013 #17
  19. Jun 26, 2013 #18


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    Why? Such discussion is great for 'history of science' and philosophy. How often do discussions of electromagnetism as physics focus on textual analysis of Maxwell's papers? Or Schrodinger's, Heisenberg's, etc. for QM? For learning and understanding current understanding of science, current textbooks and papers are the relevant material- they define what current understanding is.

    In the case of Einstein, a several of his papers have stood the test of time as still being relevant learning materials (especially SR, less for GR). However, in a science forum they stand on their merits as relevant explanatory papers, not primarily because Einstein wrote them.
  20. Jun 26, 2013 #19


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    Here's one of my favorite quotes on relativity (bold emphasis by me)...
    (my previous uses of this quote)

    Similarly, we don't focus on Bohr's presentation when we talk about Quantum Mechanics, or Newton's presentation for Mechanics, or Maxwell's presentation of Electromagnetism.

    (Note... it's "focus" not "ignore"... some historical and philosophical motivation is important... but clarity of what the final [or at least current] viewpoint is more important... and should be the target of the "focus".)

    [PAllen was quicker to respond.]
  21. Jun 26, 2013 #20

    I think that on this forum it should look like this:
    (I'm not sure about the LET part, nor how that should or can work, but I do know that anything below 'Lorentz Trantsformations' is on this forum considered philosophy.)
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