Talk:Speed of light: Difference between revisions

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	== Semi-protected edit request on 3 October 2022 ==

	{{Edit semi-protected\|Speed of light\|answered=yes}}

	Insert the following sentence to the proper line of "Increases accuracy of c redefinition og the metre and second"

	'After similar experiments found comparable results for c, In 1973, the Consultative Committee of the Definition of the Metre determined the speed of light in vacuum to be c= 299 792 458±1.1 m/s by using the average of vacuum wavelength of several laboratories and the frequency of methane-stabilized He-Ne lasers.

	<Ref>
	J. Terrien, Wavelength standards, optical frequency standards, and the velocity of light, Nouv. Rev. Optique, 1973, t. 4, no 4, pp. 215-220, Bureau International des Poidset Mesures, Pavillon de Breteuil, F-92310, Sevres
	Comite International des Poids et Mesures, Comite Consultatif pour La
	Definition du METRE, 5e Session-1973 (13-15 Juin), Bureau international des Poids et Mesures, Pavillonde Breteuil, F-92310, Sevres
	3 392 231. 3955 pm; an average of values reported by several laboratories( NBS (the National Bureau of Standards; It became the National Institute of Standards and Technology, or NIST, in 1988), NRC (the National Research Council Canada ), and BIPM (the International Bureau of Weights and Measures)).
	88 367 181 627±50 kHz; measured by the US National Bureau of Standards in Boulder, Colorado

	The End. ] (]) 07:19, 3 October 2022 (UTC)
	:] '''Not done:''' please provide ] that support the change you want to be made.<!-- Template:ESp --> I couldn't grasp your formatting for the sources. ] (]) 11:31, 24 October 2022 (UTC)

	== Speed of light in a medium ==

	The "in a medium" section states:"However, this represents absorption and re-radiation delay between atoms, as do all slower-than-''c'' speeds in material substances".<br>
	I am specifically thinking of the speed of light in transparent material such as glass or diamond. If that statement is true, wouldn't we expect the re-radiation to be emitted in random directions, scattering the light more and more as it travels through the material, making these materials not transparent at all? Doesn't the fact that we can see a clear picture through a glass pane, of what is on the other side, disprove that there is absorption and re-radiation, but instead that there is some other mechanism?<br>
	Assuming that there is absorption by an electron, and some very small amount of time (dt) later, some re-radiation by the same electron, wouldn't this electron be in a slightly different angular position, in relation to the atom core, that small amount of time (dt) later? and therefore causing the re-emission to be at a slightly different angle? ] (]) 12:27, 9 November 2022 (UTC)
	:]. The talk page is for improving the article by reference to reliable sources, not for personal speculations. ] (]) 22:13, 29 December 2022 (UTC).
	::The argument is well founded. Hopefully I can provide acceptable sources. If you look at the "see also" material ] "Microscopic explanation" section provides an explanation directly contradicting the statement in question.
	::I've seen a user removing this sentence which got reverted because lack of the source, which is fair enough, but hopefully other well written wiki section is okay.
	::The statement itself does not provide a citation as well. I couldn't track down this information. I think it is true for those exotic materials and extreme light slowing down, but not for general light propagation through materials, especially not for refraction in transparent materials.
	::I also found a video from Fermilab that says that bouncing off atoms is specifically not the reason why light slows down in water. It is due to EM field interactions in material. The argument is exactly the same as from Dhrm77, even if one could argue absorption and reemission is not exactly scattering the logic still holds up because it's still bouncing off atoms just with even more delay - https://www.youtube.com/watch?v=CUjt36SD3h8&t=171. In a follow up video there is an exact explanation of refraction which is in full agreement with the "Microscopic explanation" of refractive index article - https://www.youtube.com/watch?v=NLmpNM0sgYk&t=517s
	::The "slower than c" speed in those materials are not due to single photon-atom interactions like emission and absorption or scattering but due to EM wave interactions between the light and material, the resulting wave looks like a wave with lower propagation speed. It's not any kind of "delay between atoms" at all. ] (]) 00:49, 4 June 2023 (UTC)


	== michelson morley experiments? ==

	I think the Michelson-Morley experiments should be added in this wiki. Please adivse. ] (]) 21:40, 1 July 2023 (UTC)

	:See ] <span style="font-variant:small-caps; whitespace:nowrap;">] {] · ] · ] · ]}</span> 22:04, 1 July 2023 (UTC)

	== kilometres per hour to be consistent ==

	The speed of light is approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour.
	The metric measurement should include 1.08 billion kilometres per hour, to be consistent with metric and imperial examples. ] (]) 07:36, 5 September 2023 (UTC)

	== Is this part accurate in History? ==		== Is this part accurate in History? ==
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	== Why not also include an accurate description of c in miles per second? ==		== Why not also include an accurate description of c in miles per second? ==

			186282.3970512 mi/s, to be fairly accurate.
	186282.3970512 mi/s, to be fairly accurate. ] (]) 06:55, 22 February 2024 (UTC)

			== Speed of light in vacuum ==

			Misplaced Pages should get rid of all occurrences of the phrase "speed of light in vacuum". There is only one speed of light, which is a universal constant. Also the speed of light doesn't change if not in vacuum. ] represents the real speed of a photon, and that doesn't change. Only ] is changing, causing the optical effects that mislead people. But this very article is explaining the same in the section ]. ] (]) 13:24, 20 May 2024 (UTC)

			:If you have a reference for your point of view please share it. ] (]) 15:15, 20 May 2024 (UTC)
			::@] shouldn't this work the other way around? I don't want to add anything. I want something to be removed which has no reference. ] (]) 15:52, 20 May 2024 (UTC)
			:::The article has rather a lot of mentions of the speed of light in vacuum that are supported by references to ]. Merely in ], we have {{tqb\|Sometimes {{Math\|''c''}} is used for the speed of waves in any material medium, and {{Math\|''c''}}<sub>0</sub> for the speed of light in vacuum.<ref name=handbook>See, for example:
			* {{Cite book
			\|last=Lide \|first=D. R.
			\|year=2004
			\|title=CRC Handbook of Chemistry and Physics
			\|url=https://books.google.com/books?id=WDll8hA006AC&q=speed+of+light+%22c0+OR+%22&pg=PT76
			\|pages=2–9
			\|publisher=]
			\|isbn=978-0-8493-0485-9
			}}
			* {{Cite book
			\|last=Harris \|first=J. W. \|year=2002
			\|title=Handbook of Physics
			\|url=https://books.google.com/books?id=c60mCxGRMR8C&q=speed+of+light+%22c0+OR+%22+date:2000-2009&pg=PA499
			\|page=499
			\|publisher=Springer
			\|isbn=978-0-387-95269-7
			\|display-authors=etal}}
			* {{Cite book
			\|last=Whitaker \|first=J. C.
			\|year=2005
			\|title=The Electronics Handbook
			\|url=https://books.google.com/books?id=FdSQSAC3_EwC&q=speed+of+light+c0+handbook&pg=PA235
			\|page=235
			\|publisher=CRC Press
			\|isbn=978-0-8493-1889-4
			}}
			* {{Cite book
			\|last=Cohen \|first=E. R. \|year=2007
			\|title=Quantities, Units and Symbols in Physical Chemistry
			\|url=https://books.google.com/books?id=TElmhULQoeIC&q=speed+of+light+c0+handbook&pg=PA143
			\|page=184
			\|edition=3rd
			\|publisher=]
			\|isbn=978-0-85404-433-7
			\|display-authors=etal}}</ref> This subscripted notation, which is endorsed in official SI literature<ref name=BIPM_SI_units>{{SIbrochure8th\|page=112}}</ref> ....}} I find the idea that we would deny the current definition of the metre rather disturbing. ] (]) 16:20, 20 May 2024 (UTC)
			::::This is what I was talking about from the beginning. You are confusing two different concepts as well. ''c''<sub>0</sub> has a place in physics. In one place. Optics. In case of refraction the phase velocity is used for calculations, because the phase of light is shifting constantly if travelling in a medium which is not vacuum. Every other area of physics is using the universal constant ''c'', which can be calculated using ]. By the way the ] article also says "Photons are massless particles that always move at the speed of light when in vacuum." which is plain wrong. Photons are unable to travel slower then ''c''.
			::::If you think that Misplaced Pages is correct in its current state, than I won't say anything more. ] (]) 16:58, 20 May 2024 (UTC)
			:::::I fixed the ] article thanks. ] (]) 20:20, 20 May 2024 (UTC)
			:::@] You asked that all occurences across Misplaced Pages to be changed. I think we better discuss a reference for your claim first. You pointed to one section, ], but it has sources so you need to explain why they should be removed. ] (]) 16:58, 20 May 2024 (UTC)
			::::Understanding should be the key here. Please look at this . After watching it you will have the urge searching for references, too. ] (]) 17:10, 20 May 2024 (UTC)
			:::::That's a great video. But it's not news, sorry. It explains the atomic model of the index of refraction. Based on this video I recommend no changes. ] (]) 17:58, 20 May 2024 (UTC)

			* In the literature:
			::{\| class="wikitable" style="text-align: center"
			\|-
			! Google Search !! Scholar !! Books
			\|-
			\| "Speed of light in vacuum"
			\|
			\|
			\|-
			\|}
			: Getting rid of the term would be spectacularly against Misplaced Pages's mission. - ] (]) 19:41, 20 May 2024 (UTC)

			{{reflist-talk}}

			:If the speed of light is always the same, then ] shouldn't exist. ] (]) 09:24, 21 May 2024 (UTC)

			:The existence of Cherenkov radiation is already mentioned at the end of {{section link\|Speed of light#In a medium}}. <span style="box-shadow:2px 2px 6px #999">]]</span> 10:16, 21 May 2024 (UTC)

			== Speed of light in literature ==

			I think there needs to be a section about speed of light in popular culture somewhere, namely the teleportation gimmick used areas like in Star Wars and Kingdom Hearts. The disambiguation mentions a few examples but not this article. ] (]) 00:00, 15 October 2024 (UTC)

			:We already have a page on ] and one on ] and on ]. ] (]) 01:32, 15 October 2024 (UTC)

			:A fairly well-known old science-fiction story where the speed of light plays a prominent role is "]" by Philip Latham. The speed of light actually remains the same, but other things change, resulting in the doom of the universe... ] (]) 07:41, 15 October 2024 (UTC)

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Is this part accurate in History?

Quote:

Connections with electromagnetism

In the 19th century Hippolyte Fizeau developed a method to determine the speed of light based on time-of-flight measurements on Earth and reported a value of 315000 km/s (704,634,932 m/h).

His method was improved upon by Léon Foucault who obtained a value of 298000 km/s (666,607,015 m/h) in 1862. Kailandosk (talk) 01:06, 18 November 2023 (UTC)

Are you suggesting our article may not be correct or proposing that it include conversions to km/h at that point, and in either case, why? NebY (talk) 11:07, 18 November 2023 (UTC)

There's a definite discrepancy in number of significant digits between the quoted metric and traditional measurements... AnonMoos (talk) 13:10, 18 November 2023 (UTC)

Indeed, but the values in parentheses aren't in the article. If we wanted to include them, we could use {{Convert}}, which would probably round them appropriately automatically, and wouldn't abbreviate miles to "m" either, but I don't see why we'd want to include such conversions in that part of the article anyway. NebY (talk) 13:46, 18 November 2023 (UTC)

I added the parenthesis. It's just a conversion to m/h that I made, just to show how different they are & to convert it into U.S. terms. Kailandosk (talk) 00:15, 24 December 2023 (UTC)

I'm not sure if 315000 or 298000 km/s is correct. I feel it's 315000 km/s, but I'm not sure. Kailandosk (talk) 18:04, 25 November 2023 (UTC)

Why not also include an accurate description of c in miles per second?

186282.3970512 mi/s, to be fairly accurate.

Speed of light in vacuum

Misplaced Pages should get rid of all occurrences of the phrase "speed of light in vacuum". There is only one speed of light, which is a universal constant. Also the speed of light doesn't change if not in vacuum. Group velocity represents the real speed of a photon, and that doesn't change. Only phase velocity is changing, causing the optical effects that mislead people. But this very article is explaining the same in the section Speed of light#In a medium. Lustakutya (talk) 13:24, 20 May 2024 (UTC)

If you have a reference for your point of view please share it. Johnjbarton (talk) 15:15, 20 May 2024 (UTC)

@Johnjbarton shouldn't this work the other way around? I don't want to add anything. I want something to be removed which has no reference. Lustakutya (talk) 15:52, 20 May 2024 (UTC)

The article has rather a lot of mentions of the speed of light in vacuum that are supported by references to reliable sources. Merely in Speed of light#Numerical value, notation, and units, we have

Sometimes c is used for the speed of waves in any material medium, and c₀ for the speed of light in vacuum. This subscripted notation, which is endorsed in official SI literature ....

I find the idea that we would deny the current definition of the metre rather disturbing. NebY (talk) 16:20, 20 May 2024 (UTC)

This is what I was talking about from the beginning. You are confusing two different concepts as well. c₀ has a place in physics. In one place. Optics. In case of refraction the phase velocity is used for calculations, because the phase of light is shifting constantly if travelling in a medium which is not vacuum. Every other area of physics is using the universal constant c, which can be calculated using Maxwell's equations. By the way the Photon article also says "Photons are massless particles that always move at the speed of light when in vacuum." which is plain wrong. Photons are unable to travel slower then c.

If you think that Misplaced Pages is correct in its current state, than I won't say anything more. Lustakutya (talk) 16:58, 20 May 2024 (UTC)

I fixed the Photon article thanks. Johnjbarton (talk) 20:20, 20 May 2024 (UTC)

@Lustakutya You asked that all occurences across Misplaced Pages to be changed. I think we better discuss a reference for your claim first. You pointed to one section, Speed of light#In a medium, but it has sources so you need to explain why they should be removed. Johnjbarton (talk) 16:58, 20 May 2024 (UTC)

Understanding should be the key here. Please look at this video. After watching it you will have the urge searching for references, too. Lustakutya (talk) 17:10, 20 May 2024 (UTC)

That's a great video. But it's not news, sorry. It explains the atomic model of the index of refraction. Based on this video I recommend no changes. Johnjbarton (talk) 17:58, 20 May 2024 (UTC)

In the literature:

Google Search	Scholar	Books
"Speed of light in vacuum"	67,400	68,200

Getting rid of the term would be spectacularly against Misplaced Pages's mission. - DVdm (talk) 19:41, 20 May 2024 (UTC)

References

See, for example:
- Lide, D. R. (2004). CRC Handbook of Chemistry and Physics. CRC Press. pp. 2–9. ISBN 978-0-8493-0485-9.
- Harris, J. W.; et al. (2002). Handbook of Physics. Springer. p. 499. ISBN 978-0-387-95269-7.
- Whitaker, J. C. (2005). The Electronics Handbook. CRC Press. p. 235. ISBN 978-0-8493-1889-4.
- Cohen, E. R.; et al. (2007). Quantities, Units and Symbols in Physical Chemistry (3rd ed.). Royal Society of Chemistry. p. 184. ISBN 978-0-85404-433-7.
International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 112, ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16

If the speed of light is always the same, then Cherenkov radiation shouldn't exist. AnonMoos (talk) 09:24, 21 May 2024 (UTC)

The existence of Cherenkov radiation is already mentioned at the end of Speed of light § In a medium. Dr Greg talk 10:16, 21 May 2024 (UTC)

Speed of light in literature

I think there needs to be a section about speed of light in popular culture somewhere, namely the teleportation gimmick used areas like in Star Wars and Kingdom Hearts. The disambiguation mentions a few examples but not this article. Jordf32123 (talk) 00:00, 15 October 2024 (UTC)

We already have a page on Teleportation and one on Teleportation in fiction and on warp drive. Johnjbarton (talk) 01:32, 15 October 2024 (UTC)

A fairly well-known old science-fiction story where the speed of light plays a prominent role is "The Xi Effect" by Philip Latham. The speed of light actually remains the same, but other things change, resulting in the doom of the universe... AnonMoos (talk) 07:41, 15 October 2024 (UTC)

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