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Talk:History of the metre

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I have started this page by copying the relevant section from the Speed of light article. The referenced need copying. Martin Hogbin (talk) 10:35, 30 July 2010 (UTC)

Premature

This article has been planted here without careful consideration of its content. Although an article on this topic is desirable, this very preliminary version requires a lot of work. That can be accomplished here, or the article can be resubmitted when various editors have prepared a more adequate presentation. Brews ohare (talk) 13:45, 30 July 2010 (UTC)

I had begun an article along these lines at this link. Brews ohare (talk) 14:35, 30 July 2010 (UTC)

I'm not looking. If you want to improve this article then work on it here. otherwise this article is likely to be deleted. --Michael C. Price 06:31, 31 July 2010 (UTC)

Not a POV fork

The statement below is copied to the deletion request page.

When I started this article it was intended to allow detailed discussion of this topic that, in my opinion, was not suitable for the Speed of light or even the Metre articles. I also hoped to move some of the detailed discussion and disagreement from the Speed of light article on this subject to a more appropriate place where those interested could discus the issues involved.

It was not my intention to start a POV fork and in particular it was not my intention to create an article in which an alternative or personal POV could be presented, or in which the Speed of light arbcom decision on tendentious editing could be circumvented.

Brews, having looked through this article after your edits, I notice that, in addition to adding much useful detail, you have taken the opportunity to add some of the contentious material that you tried add to the Speed of light article. I hope you will cooperate with other editors in ensuring that this page represents a consensus view in the subject. Martin Hogbin (talk) 10:17, 31 July 2010 (UTC)

Martin, I'm sorry to say this, but how could you have expected this article to evolve any differently than it is, given the cast of characters who you know so well? Now instead of one battleground, we have two. If there is any legitimate place for this article in Misplaced Pages, and I do not believe that there is, it must be confined to the specific reasons for the change in definition and its effect on use of the metre in labs. Any discussion of the effect on the speed of light, or the speed of light as a physical constant, belongs in the Speed of light article, and is a content fork here (regardless of the original intent). Likewise, the history of the accuracy and methodology of measuring the speed of light belongs only in the Speed of light article, and is a content fork (and unreasonable duplication of content that will lead to inconsistent treatment) here. UGH!!—Finell 20:52, 31 July 2010 (UTC)
Finell: It is not possible to enlarge upon a topic without introducing it. Brews ohare (talk) 05:12, 1 August 2010 (UTC)
Sorry if I have created a monster but the argument on the Speed of light article should now subside as the text on this subject is reduced to a sentence or two.
Regarding excessive duplication of the material that properly belongs in the SoL article it should be deleted from here. Martin Hogbin (talk) 10:41, 1 August 2010 (UTC)

Conversion factor?

Although one source (at least) uses the term 'conversion factor' for the speed of light, I do not think this statement is particularly useful, or indeed relevant to this article.

I think it would be better to say that the SoL is a dimensional physical constant and therefore its numerical value is determined by the choice of units. Because of the new definition of the meter, this dimensional constant now has a fixed numerical value in SI units. We might say something like it is now used a conversion factor between the SI units of time and length. Martin Hogbin (talk) 11:26, 31 July 2010 (UTC)

I'm confused by what you're saying - can you rephrase your last sentence? A missing "as" perhaps? --Michael C. Price 12:55, 31 July 2010 (UTC)
Yes.Martin Hogbin (talk) Martin Hogbin (talk) 16:01, 31 July 2010 (UTC)

Martin: I believe you have identified some semantical issues here that might be worth looking into. They may lead to a more complete exposition of the philosophy in Jespersen in his section “Relate all measurements to time”. His formulation of this objective of standards people involves these words you have selected: “And measuring length in terms of time is a prime example of how defining one unit in terms of another removes a constant of nature by turning c into a conversion factor whose value is fixed and arbitrary.” I believe Sydenham says “Thus, the speed of light as a numerical value, is not a fundamental constant”, which I take as a way to say that the numerical value could be defined to be any number whatsoever, and that value is to be distinguished from the 'speed of light' as a physical phenomenon. Maybe it would be a useful exercise to try to express this goal, that of reduction of the number of necessary standards and introduction of more defined values, using different terminology? Brews ohare (talk) 15:13, 31 July 2010 (UTC)

Yes, I think that would be good. Martin Hogbin (talk) 16:01, 31 July 2010 (UTC)

In this connection, the separation of the numerical value from the 'speed of light' as a physical phenomenon is related to the question of how one checks for the answers to questions about the ‘physical phenomenon’ (such as those that arise in quantum gravity, e.g.) when the ‘numerical value’ is a defined quantity beyond measurement. I am not trying to say that it cannot be done, but that an explanation of how it is done is useful. Brews ohare (talk) 15:26, 31 July 2010 (UTC)

I do not understand what you mean. The 'speed of light' as an abstract concept is just that, an abstract concept. To make it any more than that a system of units is required and if you choose to base one of those units in the speed of light then the SoL will clearly have a fixed value in that system of units.

I'd guess that questions bout the 'speed of light' as a physical phenomenon have to be phrased in terms of comparisons, rather than numerical values. For example, the isotropy of the 'speed of light' as a physical phenomenon is checked by looking at the ratio of its value in one direction with that in another. It is done, for example, by spinning a resonator and monitoring its resonance frequencies as a function of angle. Its constancy over time is about the ratio of today's value with yesteryear's. And so forth. Brews ohare (talk) 15:42, 31 July 2010 (UTC)

The questions you pose cannot be answered in any fundamental sense. Even the One-way speed of light cannot be measured. Martin Hogbin (talk) 16:00, 31 July 2010 (UTC)
Well, suppose the resonator experiment is done. For example Test of the isotropy of the speed of light using a continuously rotating optical resonator. If a variation is found, and one has scrupulously eliminated the obvious sources of error like the effect of rotational forces on the geometry, one is left with two choices: the metre is longer in some directions than in others (the SI units language) or the speed of light is anisotropic. I suppose that the theoretical understanding would decide whether the anisotropy was due to (say) quantum gravity effects upon the phenomenon ‘speed of light’ or some other cause. Brews ohare (talk) 16:37, 31 July 2010 (UTC)
That is right. This is really just the MMX only better. There is no way to tell if the apparatus is longer when it is pointing in one direction than when it is pointing in another of if the (two-way) speed of light is anisotropic. In the end it is just convention.
There is no need to consider quantum gravity, for which there is no workable theory, you can get enough unintuitive results from GR which is a well verified theory.
The use of quantum gravity is just a hypothetical with an associated WP link. Herrmann et al. cite 3 or 4 other such theories that employ local Lorentz violations. Brews ohare (talk) 17:53, 31 July 2010 (UTC)
Brews, I presume that you know the difference between an established theory of physics and stuff that you find on the internet? Martin Hogbin (talk) 20:08, 31 July 2010 (UTC)
If (hypothetically) quantum gravity explained quantitatively that the phenomenon ‘speed of light’ varied with angle, and the resonator experiment showed that same variation, then one has shown conclusively that the c in the SI units is simply a conversion factor an arbitrary number determined by the deliberations of the CGPM, only historically related to the actual phenomenon ‘speed of light’. Of course, from a logical standpoint that is already understood to be the case, but the experiment shows that the isotropy of the selected numerical value is not "accidentally" also imitating the behavior of the actual phenomenon ‘speed of light’. Brews ohare (talk) 17:00, 31 July 2010 (UTC)
I do not know what you mean by 'simply a conversion factor'. We can choose to use it as a conversion factor from seconds to metres if we wish. Martin Hogbin (talk) 17:24, 31 July 2010 (UTC)
I struck out this term and replaced with another. Brews ohare (talk) 17:48, 31 July 2010 (UTC)
No, what such an experiment would show is that the current definition of the metre is not unambiguous, leading to a similar situation as when it was discovered that the spectrum line of Krypton used to define the metre pre-1983 was assymmetric, and thus did not have a well defined wave length, even though that wavelength of that spectrum line had an exactly defined value. In this situation, strictly speaking the speed of light still has a defined exact value, but the length of a metre depends in what direction you measure.TimothyRias (talk) 18:52, 31 July 2010 (UTC)

Timothy: Yes I agree entirely. Brews ohare (talk) 19:29, 31 July 2010 (UTC)

Regarding the term conversion factor: Wheeler “a mere conversion factor...a factor that arose out of historical accident..with no deeper physical significance. ” Brews ohare (talk) 19:29, 31 July 2010 (UTC)

You keep saying the same thing, that the numerical value has no special significance. We all know that, because it is a dimensional constant. Martin Hogbin (talk) 20:08, 31 July 2010 (UTC)
Yup, and even some dimensionless constants are arbitary. E.g. 1000 metres to a kilometre.--Michael C. Price 21:38, 31 July 2010 (UTC)

Martin: Sorry if I wasn't clear; the point was that Wheeler uses the term conversion factor that you don't like to use. Brews ohare (talk) 23:06, 31 July 2010 (UTC)

How can the speed of light be monitored in a system where it has a defined value?

IMO this section has no place here. First, the title is ridiculously long. Second, the answer is just "it would appear as a recalibration".

Let's just stick to the topic of the article name, and not give everybody an excuse to delete the article.

--Michael C. Price 17:54, 31 July 2010 (UTC)

Michael: Clearly the rotating resonator experiment was done. It is cited by 50+ other articles, indicating a sustained interest among the scientific community. Its espoused purpose is to determine how narrowly the isotropy can be limited. That will ultimately reflect upon a variety of conjectures about local Lorentz invariance. The value of c in SI units cannot be "recalibrated" to obtain anisotropy; instead it would be amended to include angle corrections. How can this discussion be out of place here? Brews ohare (talk) 18:04, 31 July 2010 (UTC)

So? The recalibration has an angular dependence. This article is not a collection of any and all related questions about the speed of light. Ignore this and you'll see the article deleted by Finnell and others. Wait and see. --Michael C. Price 18:11, 31 July 2010 (UTC)

As I predicted . I'm going to delete the whole section. Possibly say something about recalibration. --Michael C. Price 19:49, 31 July 2010 (UTC)
Michael: So, title the subsection "Possible recalibrations?". The point here is the following: the special theory of relativity depends upon establishing various properties of the speed of light. For example see Frauser et al.. It seems to me to be a very probable question among readers as to how these tests can be carried out when the so-called "speed of light" is defined to be 299 792 458 metres per second. It is apparent that any such tests become reinterpreted as what you call "recalibrations" . Of course, any such recalibration requires some theoretical explanation, for example, does the recalibration mean the special theory is only approximate, even locally? It doesn't help clarity to avoid the term "speed of light" and bury it under the term "recalibration" as though it was some kind of minor adjustment. Brews ohare (talk) 18:39, 31 July 2010 (UTC)
Are there any sources that explicitly link the 1983 redefinition with possible anisotropy? If not then we must delete this section. Please just stay focussed on the article topic, OK? --Michael C. Price 18:46, 31 July 2010 (UTC)
There's plenty of garbage incorrect WP:SYNTH in the preceding sections as well. From "History": The speed of light, usually denoted c nowadays, has been subject to investigation for millennia. However the nature of c, as a universal physical constant, was only established by the development of special relativity in 1905. This left the value of c, as with all physical constants, as a subject of further refinement by measurement.; from "Consequences": The effect of this definition gives the speed of light in vacuum an exact value in metric units, namely 299,792,458 metres/second. This can be regarded as a conversion factor between the second and the metre. Because the second is defined in terms of atomic transitions that can be measured accurately, the new definition, being a ratio of measured times, allows for a definition of the metre with greater accuracy in practical measurement than one based on a ratio of lengths determined using a fringe count of interference patterns.; in "Increased accuracy and redefinition of the metre": The introduction of many sources required a methodology for comparison. The wavelength of the sources could be compared, but using interferometry to measure wavelengths was subject to some serious errors. On the other hand the measurement of frequencies had become very good. As all believed that frequency and wavelength were related by the speed of propagation, it was evident that a comparison of the frequencies of sources was tantamount to a comparison of wavelengths, but more accurate. The only issue was to insure that the speed of propagation was the same in all such comparisons, which led to the adoption of the speed of light in vacuum as the standard of speed of propagation. In 1975, considering that similar measurements of c agreed with each other and their uncertainty was comparable to that in the realization of the metre
All of the quoted phrases are at best misleading, at worst completely incorrect. Physchim62 (talk) 18:54, 31 July 2010 (UTC)
Okay, specifics please. Start from the top. What's your problem with However the nature of c, as a universal physical constant, was only established by the development of special relativity in 1905.--Michael C. Price 18:59, 31 July 2010 (UTC)

Michael: I am not tied to any of this stuff. Change it around if you like. At least some of it is inherited verbiage that I may not agree with myself. Brews ohare (talk) 19:09, 31 July 2010 (UTC)

My point is that there is so much that is simply wrong that it would be better to start again from scratch: my preference would be in the relevant section(s) of Metre, which certainly need improving. Let's try to get something out of this by improving an existing (and very important) article rather than creating a new one. What was "wrong" with the 1960 definition of the metre? How did we find out about it? What was done to correct it? Those are the three basic questions (for me, at least). Physchim62 (talk) 19:21, 31 July 2010 (UTC)

It would be helpful if a list of what specifically you think is "wrong" were provided. Vague allegations don't improve my clarity of mind, and probably would carry over to any revisions. Brews ohare (talk) 19:32, 31 July 2010 (UTC)

Physchim62, I'm not seeing what you say "is simply wrong". Again, specifics, please. And again, this isn't in metre for the same reason it isn't in speed of light: too much detail for them since it lies at the intersection of the two. I really fail to see what all the fuss is about. --Michael C. Price 19:42, 31 July 2010 (UTC)
Physchim62, this was the reason that I set up this page, so that Brews' rather idiosyncratic views on certain matters could be discussed here rather than causing a great stir on the SoL or Metre pages. That is still no reason to allow bad physics on this page though. Martin Hogbin (talk) 20:13, 31 July 2010 (UTC)
Martin: Although it may be fashionable to say so, I object to my views being called idiosyncratic; so far as I can see nothing I've said is unsourced or peculiar to myself. If you think differently, please itemize. Brews ohare (talk) 20:34, 31 July 2010 (UTC)

How can the properties of light be tested if c has a defined value?

The section below was removed as being off-topic. As I think the question in the header is perfectly natural and in fact has come up over and over again, I would like some explanation as to why this subject is off-topic. I'm inclined to think it is simply fear of the AfD that is the cause of this deletion. Brews ohare (talk) 20:41, 31 July 2010 (UTC)

The special theory of relativity is posited to apply locally even in the general theory of relativity, and the definition of the metre explicitly states that the ‘time-of-flight’ realizations of the metre must be restricted to distances short enough that general relativistic corrections are not significant. The special theory is based upon a number of postulates concerning properties of the speed of light. In the present SI units system where the speed of light has a defined value of c = 299,792,458 m/s exactly, how can these tests of relativity be pursued as measurement methods become more and more precise? And as measurements explore more deeply the properties of light, what is their effect upon the definition of the metre?

The constancy of the speed of light can be monitored by observing the back-and-forth time-of-flight of light over a fixed distance, for example. Naturally, this is an experimental measurement, and subject to three possible errors (at least): first, the accuracy with which the time can be measured, second the accuracy with which the length can be maintained at a fixed value, and third the accuracy with which the medium of propagation can be held constant. An uncertainty is whether the length of the path changes with time (for example, as the universe expands, there is evidence that distances change; see Metric expansion of space) and whether the time provided by the standard of time changes (see Fine structure constant). Much more mundane factors can change the fixed length, for example, a bar changes length with temperature, flexure (changes in bending because of changed gravitational field or movement of supports), and so forth. These effects are small, but the anticipated variation in the speed of light is really small, so very extreme care must be taken in looking at all the possible sources of uncertainty.

The isotropy of the speed of light can be monitored using a rotating resonator. Should it happen that such an experiment in the future demonstrated an orientation dependence of the resonant frequencies of the resonator, in the SI units that would translate into a metre that had different lengths in different directions, and the standard for the metre would have to be amended to specify corrections to measurements based upon their orientation. That would not mean that the value of c in SI units would have to be altered. However, the underlying cause of the anisotropy would have to be explained, and conceivably a theory such as quantum gravity (say) might explain that observed anisotropy as an anisotropy of the physical phenomenon ‘speed of light’.

  1. “that in the context of general relativity, the metre is considered a unit of proper length. Its definition, therefore, applies only within a spatial extent sufficiently small that the effects of the non-uniformity of the gravitational field can be ignored (note that, at the surface of the Earth, this effect in the vertical direction is about 1 part in 10 per metre). In this case, the effects to be taken into account are those of special relativity only.” The Metrologia (1997) 34, pp. 261-290
  2. Bertfried Fauser, Jürgen Tolksdorf, Eberhard Zeidler (2007). Quantum gravity: mathematical models and experimental bounds. Birkhäuser. p. 21. ISBN 3764379774.{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. Sven Herrmann, Alexander Senger, Evgeny Kovalchuk, Holger Müller, and Achim Peters (2005). "Test of the isotropy of the speed of light using a continuously rotating optical resonator" (PDF). Phys Rev Lett. 95: 150401. doi:10.1103/PhysRevLett.95.150401.{{cite journal}}: CS1 maint: multiple names: authors list (link)

This subsection can be beefed up with more experimental references and book discussions, but it hardly seems off-topic to ask how the properties of the “speed of light” are to be discovered when c has an exact value. Brews ohare (talk) 20:49, 31 July 2010 (UTC)

Find a source that makes that link. It seems you still fail to understand basic Misplaced Pages policy. --Michael C. Price 21:27, 31 July 2010 (UTC)

What link are you looking for? Are you simply asking for a verbatim reference here as a time-honored scheme to resist material you have a dislike for? Brews ohare (talk) 21:34, 31 July 2010 (UTC) BTW, WP policy is not to knock down perfectly valid exposition on the pretext of requiring verbatim confirmation of obviously relevant points. Brews ohare (talk) 21:36, 31 July 2010 (UTC) Which things do you doubt?

  • That continued tests of special relativity are being made?
  • That they involve the speed of light?
  • That a defined value of c in the SI system is compatible with such tests?
  • That a reasonable source of confusion is that c has a defined numerical value, and yet the properties of the speed of light still can be measured?

Or is it your stance that you agree with all these points (your answer is that they are not questions, but facts) but that WP policy ties your hands and (sadly) requires a source that assembles them all in one place? Brews ohare (talk) 21:40, 31 July 2010 (UTC)

I've already answered your questions; you're just not listening (clue: focus, relevance, sources). Obviously you didn't spend your time in the cooler reading the Wiki policy pages (which I mostly agree with, BTW). --Michael C. Price 21:55, 31 July 2010 (UTC)
My opinion is that these issues don't fit well in an article about "the 1983 redefinition of the metre". But to address the issue here, if new physics is discovered that makes the original definition of the metre ambiguous, then that simple means that the definition will be amended. Compare his with the way we measure time. We know that moving clocks tick at a different rate than stationary clocks. This is a relevant factor in GPS and this is corrected for.
But because there are no such issues for the metre right now, you can't make an issue about specific things like potential violations of Lorentz invariance. I could just as well invoke other issues, like mixing of photons with axions, the fact that according to QED, light actually does not travel at c in external electromagnetic fields, that you can have dark matter particles with a very small magnetic moment that will cause a small aniotropy in the speed of light (because the Solar system moves at about 220 km/s in the galactic frame) etc. etc. You can find references for all these facts, but none of these consider this as a problem for the definition of the metre. Count Iblis (talk) 22:03, 31 July 2010 (UTC)
Count Iblis: You bring up a number of potential issues that I was unaware of. I agree that none of these are presently a problem for the metre, and that anyway, however they turn out, the metre will not change except to better specify what the ideal circumstances are under which the metre will be observed. As you know that would be only to add to a laundry list of requirements that grows longer all the time. The point of this subsection, although it has yet to be recognized that way, is not to suggest that there are real serious problems requiring immediate attention. The point of the subsection is that having a fixed defined value for c does not preclude investigation of the properties of the phenomena that is the speed of travel of light. That should be an obvious point, and it also should be obvious that a defined value for c will lead to confusion about whether these experiments can actually be done. The reader may suspect, as did Eddington, that the use of a net with 5" mesh will lead to the assessment that no fish exist that are less than 5" in size. To spell that analogy out, the definition of c as an exact value well may lead to the impression that any test of whether light is isotropic, dispersionless, etc. is placed beyond test by that definition. Brews ohare (talk) 22:20, 31 July 2010 (UTC)
What is placed beyond test is the defined value of c, not any experimental investigations. Brews ohare (talk) 22:28, 31 July 2010 (UTC)
As Wheeler says: “What will be the effect of future, still better, measuring technique? ...will that improvement in precision change the speed of light? No. ...we have to expect that the speed of light will remain at the decreed figure of 299,792,458 meters per second...” Brews ohare (talk) 23:11, 31 July 2010 (UTC)

Reply to M Price: Although these pages often are full of rhetorical devices, my questions above that you did not answer were posed in earnest as an attempt to engage you in dialog. I am not playing a debating game, and do not appreciate being fobbed off with some airy rebuttal that has no content. Brews ohare (talk) 22:31, 31 July 2010 (UTC)

I'm not interested in engaging in dialogue with someone who just doesn't listen. --Michael C. Price 04:15, 1 August 2010 (UTC)

Brews, I am not sure what you are trying to say here but you seem to be confusing and misunderstanding certain concepts. If you are saying, 'Does the new definition of the metre change reality?, the answer is 'No, of course it does not'. What it changes is the way we have currently chosen to measure some aspects of reality.

We can always do experiments and we must always be prepared to get results that we do not expect but how those results might be interpreted is to some degree a matter of choice. Forget quantum gravity, there is no theory of that subject that makes any testable predictions, according to the very well established theory of general relativity the current definition of the meter could already lead to some strange results if used inappropriately. Luckily the people at CGPM have though of this and have defined the metre as a unit of proper length. Have a read of this Martin Hogbin (talk) 17:24, 1 August 2010 (UTC)

Does the definition preclude some measurements?

I wrote a new subsection that I hope is clearer about my concerns. Brews ohare (talk) 00:16, 1 August 2010 (UTC)

I have removed the entire section per WP:OR. This is 99.9% original research. The only thing that is not, is the footnote "The isotropy of the speed of light can be monitored using a rotating resonator". I don't think that deserves a section of its own. DVdm (talk) 09:22, 1 August 2010 (UTC)
DVdm: Although you view this section as original research, you haven't explained why you think this section is original research. The purpose and claim of the section is simply to say that the 1983 decision does not prevent any experiments, even though it does result in units where the speed of light is a defined constant. Do you disagree with that claim?
It also suggests that this point could be a source of confusion, and attempts to make clear just how such confusion can be avoided. You may disagree that this point can be confusing, but that is your own personal clarity on the matter, and needn't apply to everyone. Do you expect a source that suggests that this can be a confusing point? How about Wilkie's article cited in the intro? Why do you imagine so much is written about this definition?
Can you explain further what is OR in this section, and why you object to it? Brews ohare (talk) 10:19, 1 August 2010 (UTC)
There is nothing to be explained beyond what is said in WP:OR. DVdm (talk) 10:26, 1 August 2010 (UTC)

DVdm: I've asked for clarification because I do not understand your viewpoint. It would be helpful if you would explain your stance, rather than simply making an assertion. Perhaps the addition of some sources on issues you debate, or some rewording would fix matters. For reference in your reply, the subsection is provided below. Brews ohare (talk) 10:33, 1 August 2010 (UTC)

Does the definition preclude some measurements?
The special theory of relativity is based upon a number of postulates concerning properties of the speed of light. In the present SI units system where the speed of light has a defined value of c = 299,792,458 m/s exactly, can these postulates continue to be tested as experimental technique improves? For example, does the definition of c as an exact value mean that any test of whether light is isotropic, dispersionless, etc. is placed beyond test, by definition? The answer is: ‘No. What is placed beyond test is the defined value of c, not any experimental investigations.’
For example, consider the hypothetical observation of anisotropy. In the SI system of units, the anisotropy would take the form of the metre having different lengths in different directions. Of course, a standard of length cannot be allowed to be uncertain in this way, so the effect of this hypothetical observation would be a change in the definition of the metre, to add a directional correction. At the same time, however, the explanation of this anisotropy would be attempted by improvements in theory, and quite possibly the successful explanation would be that the physical phenomenon of the speed of travel of light was anisotropic. The physical phenomenon of the speed of travel of light must be kept separate in our thinking from the numerical value of c in the SI system of units. (This distinction might be a good reason to use the symbol c0 for the SI conversion factor instead of c, as is recommended by the CGPM.)
In sum, tests of the special theory of relativity, for example, are not impeded by an exact definition of c in the SI system of units. The experiments show up as tests of the adequacy of the definition of the metre. Any necessary changes in this definition due to future experimental results will be accompanied eventually by theoretical explanations, and these theories may indeed invoke as yet undiscovered properties of the speed of travel of light.
Brews, I repeat: there is nothing to be explained beyond what is said in WP:OR. If you don't understand what is explained there, you should not be editing articles here. DVdm (talk) 10:43, 1 August 2010 (UTC)

DVdm: What I understand is that you cannot make any specific connections between WP:OR and the text above, and so refuse to do so. Brews ohare (talk) 11:25, 1 August 2010 (UTC)

I second DVdm's view. Brews, stop behaving like a baby that has to be spoonfed everything. Read WP:OR and inwardly digest, for heaven's sake. --Michael C. Price 11:31, 1 August 2010 (UTC)

With this it has become clear to me that Brews ohare should not be allowed to edit articles on Misplaced Pages. After all this time he acts as if he still has wp:NOCLUE about one of the most basic policies of Misplaced Pages. I am speechless. DVdm (talk) 11:36, 1 August 2010 (UTC)

I'd take these comments as violations of one of the WP:Pillars, namely WP:Civil, an unfortunate response to a simple request to connect some dots. If you are more able to understand WP:OR than I, go ahead and apply it to the above text. Point out what needs to be sourced, and is not. Brews ohare (talk) 12:06, 1 August 2010 (UTC)

RfC: Is the following proposed subsection WP:OR?

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Does WP:OR apply to the subsection appended to this request on Talk:Redefinition of the metre in 1983, and if so what needs to be sourced? Brews ohare (talk) 12:42, 1 August 2010 (UTC)

The paragraphs follow below:

Does the definition preclude some measurements?
Does the definition of c as an exact value mean that any test of whether light is isotropic, dispersionless, etc. is placed beyond test, by definition? The answer is: “No. What is placed beyond test is the defined value of c, not any experimental investigations.” For example, the special theory of relativity is based upon a number of postulates concerning properties of the speed of light. In the present SI units system where the speed of light has a defined value of c = 299,792,458 m/s exactly, nonetheless these postulates can continue to be tested as experimental technique improves.
To illustrate how the properties of light may continue to be examined within the 1983 decision, consider the hypothetical observation of anisotropy in the propagation of light. In the SI system of units, anisotropy would take the form of the metre having different lengths in different directions. Of course, a standard of length cannot be allowed to be uncertain, so the effect of this hypothetical anisotropy would be to change the definition of the metre, by adding a directional correction. At the same time, however, the explanation of this anisotropy would be attempted by improvements in theory, and one might conjecture that the successful explanation could involve an anisotropic propagation of light. In any event, the fundamental physical phenomenon of the propagation of light must be kept separate in our thinking from the numerical value of c in the SI system of units. (Separation of these notions might be a good reason to use the symbol c0 for the SI conversion factor instead of c, a practice recommended by the CGPM.)
In sum, tests of the special theory of relativity, for example, are not impeded by an exact definition of c in the SI system of units. The experiments take the form of tests of the adequacy of the definition of the metre. If there are any necessary changes in this definition due to future experimental results, they will be accompanied eventually by theoretical explanations, and these theories may indeed invoke, if need be, as yet undiscovered fundamental properties of the propagation of light.

References

  1. ^ Bertfried Fauser, Jürgen Tolksdorf, Eberhard Zeidler (2007). Quantum gravity: mathematical models and experimental bounds. Birkhäuser. p. 21. ISBN 3764379774.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ The isotropy of the speed of light can be monitored using a rotating resonator: see Sven Herrmann, Alexander Senger, Evgeny Kovalchuk, Holger Müller, and Achim Peters (2005). "Test of the isotropy of the speed of light using a continuously rotating optical resonator" (PDF). Phys Rev Lett. 95: 150401. doi:10.1103/PhysRevLett.95.150401.{{cite journal}}: CS1 maint: multiple names: authors list (link) Cite error: The named reference "isotropy" was defined multiple times with different content (see the help page).
  3. Adams, S (1997). Relativity: An Introduction to Space-Time Physics. CRC Press. p. 140. ISBN 0748406212. One peculiar consequence of this system of definitions is that any future refinement in our ability to measure c will not change the speed of light (which is a defined number), but will change the length of the meter!
  4. Rindler, W (2006). Relativity: Special, General, and Cosmological (2nd ed.). Oxford University Press. p. 41. ISBN 0198567316. Note that improvements in experimental accuracy will modify the meter relative to atomic wavelengths, but not the value of the speed of light!
  5. Tom Wilkie (Oct 27, 1983). "New Scientist". 100 (1381). Reed Business Information: 258 ff. ISSN 0262-4079. From now on, if a physicist should somehow discover that light is travelling faster than we had thought, then the metre will be lengthened automatically to restore the defined value of the speed of light. {{cite journal}}: |chapter= ignored (help); Cite journal requires |journal= (help)
  6. Edwin F. Taylor, John Archibald Wheeler (1992). Spacetime physics: introduction to special relativity (2nd ed.). Macmillan. p. 5. ISBN 0716723271. What will be the consequences of a future, still better, measuring technique?...will that improvement in precision change the speed of light? No. Every past International Committee on Weights and Measures has operated on the principle of minimum dislocation of standards; we have to expect that the speed of light will remain at the decreed figure of 299,792,458 meters per second, just as the number of meters in a mile will remain at 1609.344. Through the fixity of this conversion factor c, any substantial improvement in the accuracy of defining the second will bring with it an identical improvement in the accuracy of defining the meter. Is 299,792,458 a fundamental constant of nature? Might as well ask if 5280 is a fundamental constant of nature.
  7. A Brillet and JL Hall (1979). "Improved laser test of the isotropy of space". Phys Rev Lett. 42 (9): 549 ff. {{cite journal}}: Unknown parameter |month= ignored (help)
  8. E Richard Cohen (1988). "Variability of the physical constants". In Venzo De Sabbata, V. N. Melnikov (ed.). Gravitational measurements, fundamental metrology, and constants; NATO Advanced Study Institutes series v.230. Springer. p. 93. ISBN 9027727090. Although as the result of this definition, the quantity c cannot change, it is still possible to ask if the speed of light can change. To answer this question it is necessary to have a theory of the propagation of electromagnetic waves. With such a theory one might postulate...some operationally observable mechanism that could lead to detectable changes in the speed of light.

Notes

  1. For example, the Michelson-Morely experiment sought to compare the speed of light in various directions, and when no difference was found the Fitzgerald contraction was postulated to account for it within the aether theory by making the lengths different in different directions. This length difference was rendered unnecessary by the theory of relativity. In a reversal of history, if a difference in the speed of light actually were found today (at a much more refined level of accuracy), in contradiction to the special theory of relativity, the roundtrip time-of-flight length measurements in different directions would be different, indicating the lengths in different directions were different in SI units. In the rotating resonator approach to measuring anisotropy, “length variations of this cavity – whether accidental or cosmic – appear as variations of laser wavelength. They can be read out with extreme sensitivity as a frequency shift...”

Observation

The above paragraphs say nothing controversial. Brews ohare (talk) 12:42, 1 August 2010 (UTC)

Comments on RfC

  • Please add comments here with a leading asterisk
What needs sourcing? Brews ohare (talk)
the whole of it: you can't just take a few choice facts from different sources and build an argument around it. That's OR.--JohnBlackburnedeeds 14:30, 1 August 2010 (UTC)
John: Your description of these paragraphs is incorrect. They present a very simple fact, the ability to carry out all the experiments that one used to do, despite the SI defined value for c, and illustrates that fact with the isotropy experiments cited, which are ongoing today. There is nothing more to it than that. If you read more into it, perhaps you can point out what wording is ambiguous or liable to misinterpretation? Brews ohare (talk) 15:19, 1 August 2010 (UTC)
If there is to be any objection to these paragraphs, it should be that it expresses something obvious. However, that appears not to be the case. Brews ohare (talk) 15:25, 1 August 2010 (UTC)
Having no guidance form the critics, I have sourced just about every sentence. Brews ohare (talk) 16:08, 1 August 2010 (UTC)
  • Yes, well actually I am not sure if OR is the right term. The paragraph in question is a rambling essay mixing a number of things that are correct but do not need saying with a naive view of physics that means very little. Martin Hogbin (talk) 16:48, 1 August 2010 (UTC)
The OR arises from the synthesis, i.e. the drawing together valid sources to write I'm not sure exactly what but something not given in the sources. That it's poorly written and makes little sense, rather than drawing clear conclusions with a clear POV, makes no difference. The point of WP:OR is that anything written by editors which draws conclusions other than those given in the sources is OR, precisely because without the conclusions being in reliable sources there's no way to be sure if it's Nobel prize worthy insight or juvenile ramblings. That's why we insist on sources, and any reasoning not given in sources is OR.--JohnBlackburnedeeds 19:51, 1 August 2010 (UTC)
Again, John, what is the synthesis you speak of? Vague generalities are great for political speeches intended to seem to say something, but are not useful here. Brews ohare (talk) 20:18, 1 August 2010 (UTC)
Martin: Well, at least you are on the right track in saying OR doesn't fit the objections. However, I don't understand the characterization as "rambling". The lead sentence says precisely what is to be discussed. The second paragraph gives a pertinent example with references to the literature. and the last paragraph is a succinct summary. These paragraphs do not say "a number of things" but one thing (experiments still can be done even though c has a defined value), with an example, and a summary. If it seems rambling (or as Blackburne says, "unclear") I'd submit that it is because you expect to find something there that isn't (maybe some diatribe about modern physics?), and so get lost trying to find the arguments you expect, in place of reading the arguments actually made. Brews ohare (talk) 20:29, 1 August 2010 (UTC)
So your point is that experiments can still be done, after the speed of light is fixed by definition? Yes, of course they can. I do not think anyone is challenging that. Martin Hogbin (talk) 21:32, 1 August 2010 (UTC)
Yes, Martin. As I said, the segment is obvious. However, there does exist confusion on this point, as the segment says. Brews ohare (talk) 23:44, 1 August 2010 (UTC)
To make the point clear, it helps to notice that because c is fixed, as umpity sources say, any refinement in measurement of the properties of the propagation of light are reflected in the metre. So, in particular, anisotropy in propagation (if it occurred) would show up in anisotropy in length (also cited). Brews ohare (talk) 23:48, 1 August 2010 (UTC)
What would an experiment that appeared to show anisotropy in the speed of light tell us? That depends very much on what the experiment was. If, for example, it was an experiment to compare the speed of light round a closed path in one direction with its speed in the other direction, it might tell us that the apparatus was in a rotating frame. If it compared the speed of light in an upward direction with that in a downward direction it would tell us that there is gravity on Earth and that GR describes it well. If an interferometric measurement in space showed an anomaly in the speed of light it might tell us that we have detected gravity waves, another verification of GR. None of these have much to do with the definition of the metre, which is a unit of proper length.
If, on the other hand, an anomaly in the speed of light that could not be explained by our current theories of physics was detected experimentally then something would have to change. A new theory maybe or perhaps just a modification to an old one. Exactly how this might affect the current definition of the metre would depend on what was discovered. Maybe the frequency of the light would be specified, maybe some kind of correction for some new effect would be needed, maybe the speed of light standard would be abandoned in favour of something else, maybe our whole concept of distance would need to be revised. Who can tell? Speculation about the anisotropy of the speed of light and its effect on the definition of the metre is completely pointless. Martin Hogbin (talk) 14:12, 2 August 2010 (UTC)
Martin: You've made some good points about measurements and theory. But I'd like to say as gently as possible that this is not what the subsection is about. The object is to explain to the naïve that just because c0 has a fixed value beyond measurement does not mean that the fundamental properties of light are beyond study. An example is provided in the second paragraph of very particular studies done relevant to isotropy. The point of the example is not to laud the experiment, but to show that experiments about light are still ongoing, and that if one wishes to describe them in SI units they are phrased as searching for differences in lengths in different directions, that is, a positive outcome would lead to an anisotropic metre unless the definition were amended to incorporate a directional correction. I think you have become drawn into a discussion of the types of experiments and their possible interpretations, and that is not what the example is selected to illustrate. Brews ohare (talk) 15:05, 2 August 2010 (UTC)
If all you want to say is that the current definition has no power to make light travel at the speed we tell it to that is so obviously true that it does not really need saying in any great detail. I see three classes of possible future experiment being possible possible, those that refine the delineation of the meter, those that are outside the scope of the meter definition, and those that will change everything. Which need a detailed explanation here? Martin Hogbin (talk) 15:27, 2 August 2010 (UTC)
An interesting formulation. I find the literature to so easily confuse the "exact speed of light" with c0 that something needs to be said, even if it is obvious to you. Your three categories of measurements may not be mutually exclusive. If you want to talk about that, I'd suggest another subsection. This one has only a very simple goal. Brews ohare (talk) 16:33, 2 August 2010 (UTC)
What i do not understand is which of my three categories do you want to give details of in the article. Or do you claim there is another category? Martin Hogbin (talk) 17:15, 2 August 2010 (UTC)

Hi Martin: That is an interesting question. You are thinking harder about this than I have.

My stance was just that choosing a unit of speed didn't mean that light traveled at that speed (a point you regard as trivial), particularly if the speed of light depends on a variety of parameters that we don't know about and therefore have omitted from the definition of the metre. Therefore, an experiment using a particular realization of the speed of light doesn't necessarily realize the standard unit because these hidden variables are not controlled for. I interpreted that as showing up as failure of the metre to be uniquely defined as we discover these hidden variables, because extra conditions would have to be attached to its definition to insure that the realization would produce the unit. Obvious examples are isotropy, dispersion, and less obviously, the volume of the universe.

Help me out with other kinds of examples. Brews ohare (talk) 17:34, 2 August 2010 (UTC)

I have started a section below to discuss this subject further. Martin Hogbin (talk) 17:52, 2 August 2010 (UTC)

More discussion

  • The problem with this section is that it is trying to answer a question without referring to a source that asks and treats the said question. Instead it tries to answer the question by arguing based on facts drawn from other sources. This technique is very usual for scientific writing (you might even go as far as to say that it is the cornerstone of scientific writing.), but is unacceptable on wikipedia. The reason is that in scientific writing there is reason to assume that the author is competent in interpreting his sources (and there is peer review to check that he is), moreover in the case of scientific journals the readership can also be expected to be able to interpret the quoted sources. In the case of[REDACTED] neither is the case, there is no way to know if an editor is a specialist in the field, or just some cranky teenager, nor can it be expected of the general reader to interpret the given sources. As such, articles should keep interpretation of sources to a minimum, and more importantly directly cite sources for their conclusions. Brews, I repeatedly noticed in your writings that this point about[REDACTED] policy has not quite come across with you. Many times have I seen you stick a whole battery of refs on a statement, none of which directly dealt with the statement to be sourced, but where to statement should (according to you) follow from this collective of sources. I really do hope, you start to understand what this policy means and more importantly why it exists in first place. It might prevent a lot of hardship and drama and save you a lot of energy. This is not meant as a personal attack, rather it is meant as very well meant advice.TimothyRias (talk) 09:30, 2 August 2010 (UTC)
Hi Timothy: I do appreciate your taking the time to explain matters carefully. Let me see whether this analysis applies to the segment above, by pulling it apart to identify whether indeed this criticism applies. To do that, let me state the various points and examine the evidence brought to bear.
  • Does the definition of c as an exact value mean that any test of whether light is isotropic, dispersionless, etc. is placed beyond test, by definition?
Is this question asked and answered by a source? Yes, it is. I haven't dredged up all such sources. One is E Richard Cohen, quoted in the piece. The question also is asked (but never answered) by Wilkie “Does the new standard mean that we will be unable to detect ” One example of this question is that of isotropy, treated in the second paragraph. The Michelson-Morely experiment as done today using the analysis of relativity is another way to test relativity itself, and two sources are cited referring to measurements of isotropy using a rotating resonator by means of detecting dimensional changes in the cavity via a shift in frequency. They clearly ask and answer that particular version of the question. So I'd say the question doesn't originate with me, and neither do the answers. So your first concern is put aside, do you agree?
  • The summary says, in effect, that questions about propagation of light are turned into questions about the definition of the metre by the new definition. That point has been cited in the first paragraph, referring to four sources: Adams, Rindler, Wheeler and Wilkie all of whom point out that refinements in c don't affect c0. It is established in the example of isotropy by reference to Brillet and Hall, but also applies to later work using rotating resonators like the cited Herrmann et al. These authors specifically refer to the changed length of the resonator as a function of orientation. Evidently, the idea here is that the length didn't really change, but the frequency shifts indicating an apparent change, which they actually think is a test of the isotropy of light propagation. Other interpretations are that the metric of space is anisotropic. In any case, the point is that tests can be made, and if they proved to establish a real effect, the metre would be different in different directions. I believe this point to be adequately sourced.
  • The object of this section is not to preach to the choir, but to explain to the naive that just because c0 has a fixed value beyond measurement does not mean that the fundamental properties of light are beyond study. Do you disagree with the thesis?
I hope you might engage in some detail here as to how you would present this simple matter? Brews ohare (talk) 12:59, 2 August 2010 (UTC)
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