Talk:Speed of light

After looking over the talk page archives, I can see that this has been debated repeatedly, but I can't for the life of me wrap my head around the logic that has led to the current situation in the infobox. Why are these values so dramatically reduced in precision compared to the exact figure of 299,792,458 m/s?

The primary argument in favor of the status quo seems to be that most visitors to the page won't need any more precision than that. In that case, why provide the 299,792,458 figure in the first place? Just say it's approximately 300 million, and anybody who wants more precision can click on the footnote to get it straight from the source. Wikipedia is a work of reference, and it should provide reference values. These numbers are not so complicated that they require dumbing down. And the article as a whole is clearly not written to be understood by people who would find such numbers overwhelming.

Let's say there are two types of people who come to this article looking for an imperial value for the speed of light: people who want to see 186,282 (or, to match the precision of the original value, 186,282.397), and people who will be satisfied with the precision level of 186,000. As it currently stands, the latter group will be okay, and the former will be annoyed that they have to do the calculation themselves. If more precision was added to the values in the infobox, the former group would be satisfied, and the latter would have the far simpler task of mentally replacing the "extraneous" digits with zeroes. Even if the former group is very small, which I doubt, providing more precision would be a net benefit to our readers.

Also, why are the approximate values cited to a high school algebra textbook? Surely, regardless of the chosen level of precision, converting the original value into other units falls under WP:BASICMATH and requires no citation. I can't see the cited page on Google Books, does it have something to say about the significant digits themselves? – Reschultzed (talk) 03:05, 22 July 2026 (UTC)Reply

About Talk:Speed_of_light/Archive_17#Precision_of_values_in_infobox 11 years ago there was a consensus to list converted values for the speed of light to 3 significant figures. You could propose a different approach but you need to get input.

I actually think there is a case for a different solution. List miles per second at six figures because the six figure speed of light in miles/second appears in a lot of old textbooks, then delete the other conversions altogether. There is no case for including them other than editor whimsy I guess.

In any case, I disagree with your claim about no citation needed. Unless we have a direct source, the conversion factor should be documented, ie via https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8, and the significant figures need to correspond to the arithmetic used. This is not WP:BASICMATH as you can see from https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors#B72. Johnjbarton (talk) 03:24, 23 July 2026 (UTC)Reply

One way to solve this problem is to just state the value in SI units. The speed of light as 299 792 458 m/s is the only useful number in all circumstances. There is no real need to express this and other values in debase units outside of SI, other than to waste time and energy just to pamper a minority of people not wanting to learn and know what the majority use and know. Ametrica (talk) 23:11, 11 October 2026 (UTC)Reply

> The speed of light in vacuum is a universal physical constant

This is a wish or theory at best, not a fact and so should not be presented as a fact! There is no way for mankind to explicitly verify that in each and every corner of the Universe, at any given time in the past, C was the same as in the present. Even if current scientific theory says so, the theory may or may not be correct in light of future experimental discoveries.

Thus BIPM / SI painted themselves into a corner by defining the meter as a derivative of C. If oscillation, slowing or quickening of C is ever discovered, they'd need to go back to the X-shaped rod, which is still kept in a safe. ~2026-48980-54 (talk) 00:06, 10 September 2026 (UTC)Reply

Right, if that is ever discovered, the world will happily go back to anything. Wikipedia reflects the current consensus, not any other possible future. - DVdm (talk) 08:59, 10 September 2026 (UTC)Reply

I think you are confused. The value of the speed of light is not relevant to any physics theory. The value is simply a conversion factor from natural units to International System of Units. It has no more meaning than the number "3" in the conversion from Tablespoons to Teaspoons. Its role in physics is to be part of chain of comparisons needed to compare data from different types of experiments. Sadly our current article misrepresents the sources on this issue. I will try to make some improvements. Johnjbarton (talk) 23:07, 10 September 2026 (UTC)Reply

The article has a sentence: In the early 1860s, Maxwell showed that, according to the theory of electromagnetism he was working on, electromagnetic waves propagate in empty space[152]... where source 152 is: See, for example:

• Giordano, Nicholas J. (2009). College physics: reasoning and relationships. Cengage Learning. p. 787. ISBN 978-0-534-42471-8. Extract of page 787
• Bergmann, Peter Gabriel (1992). The riddle of gravitation. Courier Dover Publications. p. 17. ISBN 978-0-486-27378-5. Extract of page 17
• Bais, Sander (2005). The equations: icons of knowledge. Harvard University Press. p. 40. ISBN 978-0-674-01967-6. Extract of page 40

However none of these sources are discussing Maxwell. It seems that these sources purport to verify "electromagnetic waves propagate in empty space" which is inappropriate since it would not have been possible for Maxwell to create "empty space". The links in these citations do not reveal any content. I think these sources should be removed. Johnjbarton (talk) 23:25, 10 September 2026 (UTC)Reply

The section "Role in physics" starts with 4 paragraphs on special relativity. Not all of that content is directly about speed of light. Special relativity has many counterintuitive and experimentally verified implications. is true and Terrell rotation is one of them but this kind of detail gets in the way of plainly describing the speed of light as a boundary for a "domain of validity" as described by

• Uzan, J. P. (2025). Fundamental constants: from measurement to the universe, a window on gravitation and cosmology: J.-P. Uzan. Living Reviews in Relativity, 28(1), 6.

The special theory of relativity explores the consequences of this invariance of c with the assumption that the laws of physics are the same in all inertial frames of reference. is an anthropomorphic repetition of the first paragraph and is not directly supported by the sources given (which are just sources on invariance of c in special relativity, no exploring discussed). This invariance of the speed of light was postulated by Einstein in 1905... is true but it is History, not directly related to "Role in physics".

If we say less about special relativity details we have more punch on "Role in physics". Johnjbarton (talk) 03:42, 12 September 2026 (UTC)Reply

Ok I went ahead. I think the result is more focused on the speed of light now. Johnjbarton (talk) 04:10, 13 September 2026 (UTC)Reply

The speed of light is a well defined constant, exactly c = 299792458 m/s, and it is a trivial matter to convert it to miles per second: Since this final value is exact and easily representable as such, I see little motivation to have the article only approximate it. @Johnjbarton et al. what do you think? —Quantling (talk | contribs) 13:44, 2 October 2026 (UTC)Reply

Presumably this relates to these edits, in which you changed

For example, in imperial units, the speed of light is approximately 186282 miles per second.

to

For example, in imperial units, the speed of light is 186282 ⁠39937/100584⁠ miles per second.

It's not immediately obvious why we should present such a precise formulation for a conversion that you describe as trivial. As WP:NOTEVERYTHING says, Information should not be included solely because it is true or useful, and its utility is in any case doubtful; someone wishing to carry out exact calculations in miles will find it trivial to use the exact values already provided together with routine conversions, whereas the form you provide is not easy to use in calculation and not otherwise meaningful for general readers. Most of all, this does not make the article easier to read or understand, but quite the opposite. NebY (talk) 14:10, 2 October 2026 (UTC)Reply

I agree that general readers don't need exact values, whether metric or imperial units, and that readers who want the exact values will likely want metric. But I don't see that providing the exact value in imperial units impedes any of these readers. On the other hand, by using a trivially little amount of space, the exact value provides information that some readers may be seeking and others will find interesting even though it is not of direct use to them. So, yes, the upside isn't dramatic, but the downside IMHO is even smaller. I'm seeing providing this exact value as a net win. —Quantling (talk | contribs) 14:56, 2 October 2026 (UTC)Reply

I agree with NebY, this unusual fractional form is distracting, not representative of sources on the topic, and has no practical value. Johnjbarton (talk) 16:00, 2 October 2026 (UTC)Reply

It's this type of useless and confusing crap that makes it a good reason to stop presenting outdated idiot units in Wikipedia and elsewhere. The speed of light expressed in SI units is perfectly suited for the entire population of the world. Those who don't know the value in SI units would have no need to know it at all. Ametrica (talk) 23:00, 11 October 2026 (UTC)Reply

Alas SI units are not sufficient for the entire world in its current state. —Quantling (talk | contribs) 00:53, 14 October 2026 (UTC)Reply

This edit request has been answered. Set the |answered= parameter to no to reactivate your request.

The following line:

The limit obtained depends on the model used: if the massive photon is described by Proca theory,^[1] the experimental upper bound for its mass is about ×10⁻⁵⁷ grams;^[2] if photon mass is generated by a Higgs mechanism, the experimental upper limit is less sharp, m ≤ 10⁻¹⁴ eV/c² (roughly 2×10⁻⁴⁷ g).^[1]

Has the typo that it says 'x 10^-57' but it should instead simply be '10^-57' or '1 x 10^-57', whichever fits. Sketch X7 (talk) 06:46, 15 October 2026 (UTC)Reply

 Done —Quantling (talk | contribs) 14:16, 15 October 2026 (UTC)Reply