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This article appeared on Wikipedia's Main Page as Today's featured article on October 29, 2004, and on August 16, 2022.

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There is a request, submitted by ScientistBuilder (talk)ScientistBuilderScientistBuilder (talk) 17:18, 29 January 2022 (UTC), for an audio version of this article to be created. For further information, see WikiProject Spoken Wikipedia.[reply]

The rationale behind the request is: "The speed of light is central to physics fields including the Big Bang Theory, special relativity, general relativity, spectroscopy, optics, as well as real world applications such as signal processing and GPS networks".

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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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

Wikipedia 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)[reply]

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

@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)[reply]

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 $c$ ₀ for the speed of light in vacuum.^[1] This subscripted notation, which is endorsed in official SI literature^[2] ....

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

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 Wikipedia is correct in its current state, than I won't say anything more. Lustakutya (talk) 16:58, 20 May 2024 (UTC)[reply]

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

@Lustakutya You asked that all occurences across Wikipedia 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)[reply]

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)[reply]

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)[reply]

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 Wikipedia's mission. - DVdm (talk) 19:41, 20 May 2024 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

[handbook-1] 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.

[2] Lide, D. R. (2004). CRC Handbook of Chemistry and Physics. CRC Press. pp. 2–9. ISBN 978-0-8493-0485-9.

[3] Harris, J. W.; et al. (2002). Handbook of Physics. Springer. p. 499. ISBN 978-0-387-95269-7.

[4] Whitaker, J. C. (2005). The Electronics Handbook. CRC Press. p. 235. ISBN 978-0-8493-1889-4.

[5] 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.

[BIPM_SI_units-2] 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

[1]

[2]