Talk:Speed of light

Skip to table of contents

This is the talk page for discussing improvements to the Speed of light article.
This is not a forum for general discussion of the article's subject.

Put new text under old text. Click here to start a new topic.
New to Wikipedia? Welcome! Learn to edit; get help.

Article policies

Find sources: Google (books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL

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 Wikipedia community. Even so, if you can update or improve it, please do so.

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

Article milestones
Date	Process	Result
August 17, 2004	Featured article candidate	Promoted
December 7, 2008	Featured article review	Demoted
November 21, 2009	Peer review	Reviewed
January 25, 2010	Featured article candidate	Not promoted
October 12, 2010	Peer review	Reviewed
December 20, 2010	Featured article candidate	Promoted
March 19, 2022	Featured article review	Kept
Current status: Featured article

‹See TfM›

Physics: Relativity Top‑importance

	Physics portal This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics articles
Top	This article has been rated as Top-importance on the project's importance scale.
	This article is supported by the relativity task force.

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".

Archives

Archive 1 (Up to end of 2004)
Archive 2 (2005 – July 2006)
Archive 3 (July 2006 – end of 2006)
Archive 4 (2007)
Archive 5 (2008)
Archive 6 (Jan 2009 – Feb 2009)
Archive 7 (Feb 2009 — July 2009)
Archive 8 (July–Aug 2009)
Archive 9 (August 2009)
Archive 10 (Aug–Sept 2009)
Archive 11 (Sept–Oct 2009)
Archive 12 (Oct–Dec 2009)
Archive 13 (Nov 2009 – May 2010)
Archive 14 (May–Aug 2010)
Archive 15 (Aug–Dec 2010)
Archive 16 (Feb 2011 – Apr 2014)
Archive 17 (Jan 2014 – )

This page has archives. Sections older than 90 days may be automatically archived by when more than 4 sections are present.

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]