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	Speed of light is a featured article; it (or a previous version of it) has been identified as one of the best articles produced by the Misplaced Pages community. Even so, if you can update or improve it, please do so.
[REDACTED]	This article appeared on Misplaced Pages's Main Page as Today's featured article on October 29, 2004, and on August 16, 2022.
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Photons faster than the speed of light

Researchers managed the speed limit of light "inside hot swarms of charged particles, fine-tuning the speed of light waves within plasma to anywhere from around one-tenth of light's usual vacuum speed to more than 30 percent faster." (source: sciencealert.com) — Preceding unsigned comment added by 151.34.70.250 (talk) 13:59, 2 September 2022 (UTC)

That source says this is about group velocity, and this Misplaced Pages article already states that group velocities greater than c are possible, and have been achieved before. -- Dr Greg  talk  14:24, 2 September 2022 (UTC)

Thank you, but the current WP article not the group velocity affirm that "fine-tuning the speed of light waves within plasma to anywhere from around one-tenth of light's usual vacuum speed to more than 30 percent faster." 30 percent faster seems to be a relevant experimental result. — Preceding unsigned comment added by 87.15.179.76 (talk) 19:21, 2 September 2022 (UTC)

This is not a comprehensible use of the English language. Try again? JBL (talk) 20:48, 2 September 2022 (UTC)

Sorry, there was a typo. The current WP article doesn't affirm that "fine-tuning the speed of light waves within plasma to anywhere from around one-tenth of light's usual vacuum speed to more than 30 percent faster.

In the same way, nothing similar is said within the article titled group velocity. To say that someone has achieved a group velocity that is 30 percent faster than the speed of light, seems to be relevant for the WP article. — Preceding unsigned comment added by 151.46.32.41 (talk) 15:45, 4 September 2022 (UTC)

We have an entire section on Faster-than-light observations and experiments|Faster-than-light observations and experiments and it begins See also: Faster-than-light and Superluminal motionThe experiment you mention is just one instance in a large field of study. WP:NOTNEWS applies to the continual flow of scientific experiments and demonstrations too. NebY (talk) 16:08, 4 September 2022 (UTC)

Ok, thanks for your help. I misunderstood that my link was a summary of a peer-reviewed scientific paper instead of a part of a continous flow of scientific news. — Preceding unsigned comment added by 151.38.251.187 (talk) 18:06, 4 September 2022 (UTC)

Semi-protected edit request on 15 September 2022

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Copying one letter 50.29.238.62 (talk) 05:45, 15 September 2022 (UTC)

 Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format and provide a reliable source if appropriate. EnIRtpf09b 05:59, 15 September 2022 (UTC)

Semi-protected edit request on 3 October 2022

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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. Suh, Hosuhng (talk) 07:19, 3 October 2022 (UTC)

 Not done: please provide reliable sources that support the change you want to be made. I couldn't grasp your formatting for the sources. Aaron Liu (talk) 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".
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?
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? Dhrm77 (talk) 12:27, 9 November 2022 (UTC)

WP:Not a forum. The talk page is for improving the article by reference to reliable sources, not for personal speculations. Xxanthippe (talk) 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 https://en.wikipedia.org/Refractive_index "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. 83.21.29.156 (talk) 00:49, 4 June 2023 (UTC)

michelson morley experiments?

I think the Michelson-Morley experiments should be added in this wiki. Please adivse. 82.174.79.67 (talk) 21:40, 1 July 2023 (UTC)

See Speed_of_light#"Luminiferous_aether" Headbomb {t · c · p · b} 22:04, 1 July 2023 (UTC)

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