Talk:Speed of light

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Expansion VS SOL Limit

Is there any possible way, that someone could put together a nice addition for the front page on how the Universe is expanding faster than the speed of light? I think this information should be shown in greater detail because it shows a very big flaw in the argument that the Speed of Light is absolute.

Thank you. —Preceding unsigned comment added by 68.96.242.243 (talk) 01:49, 13 February 2011 (UTC)

Speculative interpretation or a religious text, not a scientific result at all.

Wouldn't [1] have helped readers realize the mention of Speed of Sun-light being clearly present accurately in the 1300's? Again I wanted to know why one cannot cite quotations from the religious texts?Ganesh J. Acharya (talk) 05:39, 21 February 2011 (UTC)

I had cited the following

Sayan. a (c. 1315-1387) while commenting on Rigveda stated "tatha ca smaryate yojananam. sahasre dve dve sate dve ca yojane ekena nimis.ardhena kramaman. a namo stu ta iti" which when translated is [O Sun,] bow to you, you who traverse 2,202 yojanas in half a nimesa", this speed turns out to be 186,413.22 miles per second which being near to the speed of light, is speculated to be speed of light it self. Src: http://www.ece.lsu.edu/kak/sayana.pdf, (accessed 15 Feb 2011), the referenced information is accessed from Indian Journal of History of Science, vol. 33, 1998, pp. 31-3 Ganesh J. Acharya (talk) 05:41, 21 February 2011 (UTC)

That sources doesn't appear to me to be claiming that they knew or estimated the speed of light, just that there was a numerological coincidence and some astronomy traditions that were lost and worth investigating. Dicklyon (talk) 06:40, 21 February 2011 (UTC)

Yes, out of who knows how many big numbers in historic texts it's one that can be made close to the speed of light. But it's not an estimate or calculation of the speed of light, and making that connection is pure speculation by the writers of that paper, relying on unconvincing assumptions about the precise sizes of the units involved.--JohnBlackburne^words_deeds 10:44, 21 February 2011 (UTC)

ok, again the reference is talking about "speed of light" and may be they are speculating. But then as per what guidelines of wikipedia it should not be included. Ganesh J. Acharya (talk) 06:11, 22 February 2011 (UTC)

The reference is actually arguing that Sayana is in all likelihood not referring to the speed of light , but to the speed of the Sun as it transverses the sky. This makes the interpretation of this text off-topic in this article. More so, since, whatever what was meant, this phrase seems to have had no influence on the historical development of the subject. Inserting a phrase like "some scholars have suggested that some phrase in the Sarayana may be interpreted as giving a value of the speed of light" would give undue weight to a singular interpretation of a religious text.TR 08:57, 22 February 2011 (UTC)

I agree, this text is not appropriate here. Martin Hogbin (talk) 09:24, 22 February 2011 (UTC)

• Is sun-light part of sun? even if it is written sun in travelling, is it wrong?
• Currently we could have a preconceived mindset that sun and its light are different. Why do we see them different?
• If I blow a balloon, does the balloon travel while it expands, or it does not travel?Ganesh J. Acharya (talk) 12:59, 22 February 2011 (UTC)

I don't see how the speed at which the sun transverses the sky, and the spee butd of the light travelling from the sun to us could be seen as the same thing, especially since the two are perpendicular. Nor do I see how it is relevant to discuss that on this page, since it has nothing to do with improving the "speed of light" article.TR 13:08, 22 February 2011 (UTC)

even in case of balloon if I reduce my size to that of an atom I will see balloon's sub atomic particles and space. But we still call these particles to be part of the expanding balloon and say the balloon is travelling?Ganesh J. Acharya (talk) 04:12, 25 February 2011 (UTC)

Rounded speeds

What is the point in having speeds rounded to 1 significant figure? Surely it would be better to have them to at least 3 or 4? I tried doing this but my edits were reverted on the grounds that it was intentional. Xtremerandomness (talk) 23:17, 22 February 2011 (UTC)

The article gives both extremely accurate figures and, in the "Approximate values" section, rounded ones that will be convenient and sufficient for many readers and casual purposes. Hertz1888 (talk) 23:31, 22 February 2011 (UTC)

People are perfectly capable of rounding figures to one or two significant figures in their heads. It's far easier for the majority to do that than to make the few looking for a more accurate figure have to delve through the article at large. Xtremerandomness (talk) 23:33, 22 February 2011 (UTC)

In my experience, that's not so true. Most people who have grown up since the demise of slide rules are relatively clueless about significant figures, and get distracted by digit values as if they mean something more than they do. The conventional rounded values are what we should be using in contexts where simple info is appropriate; the more-exact or exact numbers have their place, too. Dicklyon (talk) 04:23, 23 February 2011 (UTC)

I would disagree with you on that one - almost all people understand that these values are best rounded to 1 or 2 significant figures in most instances, even if they wouldn't know what a "significant figure" was if it was mentioned in conversation. Why not include 'metres per second' in the 'approximate values' section for the ease of others too? It is inconsistent not to do so. This is on top of the fact that it is not fair to patronise the community, presuming that they are unable to work out for themselves what is useful, whilst telling those that do need the more accurate information that they have to search through the article. I couldn't find them all in one place, so for some it would be quite a pain for them to have to do so. Xtremerandomness (talk) 14:06, 23 February 2011 (UTC)

299,792,458 is 300 million when rounded to three significant figures. --137.43.105.17 (talk) —Preceding undated comment added 14:17, 23 February 2011 (UTC).

Common misunderstanding should be cleared up in the article

I believe that it's a common and misguiding understanding that one light year is one year's worth of travel. Won't a paragraph or footnote emphasizing the perspective - ie to the traveler, it's teleportation as no time passes, to the viewer, it's one year? I know if I was just explained this at a young age I would have understood it and not had to wonder about it for the best part of 10 years. —Preceding unsigned comment added by 196.210.241.222 (talk) 22:28, 18 March 2011 (UTC)

It's just a distance, not a year's worth of travel, but how far light goes in a year. Like any other distance, if you could travel it at the speed of light, no time would pass for you. Dicklyon (talk) 06:14, 19 March 2011 (UTC)

I think WP should explain about this kind of thing but I am not sure whether this is the best place to do it. There is a fundamental problem with explaining things like relativity in the non-technical manner preferred by WP and this is that ordinary language is not able to adequately describe the subject. Intuitive understandings of terms like 'time' and 'distance' are based on our everyday, non-relativistic experience and are bound to be misleading. That is why we have to talk in technical terms like 'proper length' and 'coordinate time' if we want to discuss the subject in any detail. Martin Hogbin (talk) 10:03, 19 March 2011 (UTC)

It's definitely not the most obvious place to reference this; "Light year" does however references a unit of time "Year". Sure, clarify that it's a distance; I certainly find it notable that "year" has altered significance depending on the perpspective, being a fundamental property of light, seldomly explained simply...

change to c?

"Speed of light" is a bit misleading, as it makes it seem like light dictates everything else in the universe. c isn't really the "speed of light", it's just the maximum speed at which anything can travel in our universe. Light doesn't always travel at c, and not everything that can travel at c is light. I think this should at least be made clear in the article. Serendi^podous 09:03, 28 March 2011 (UTC)

From your question I infer that you think that the article does not make this clear?TR 11:11, 28 March 2011 (UTC)

No I don't think it does. Certainly not the first few paragraphs, which place the emphasis onto the particles, rather than the structure of the universe, which is what c is really about. Serendi^podous 11:47, 28 March 2011 (UTC)

But c is not really about the structure of the universe either. From a relativity perspective, c is just a gauge freedom of the metric with it's only physical significance being the fact that it has a finite value (rather than being zero or infinite).TR 13:37, 28 March 2011 (UTC)

[quibble] “not everything that can travel at c is light”, well, last time I checked the only massless particles were photons and gluons, and it's not like gluons by themselves can “travel” at all. :-) Gravitation too, of course. Shouldn't comment when I'm not fully awake yet.[/quibble] Anyway, I think I once proposed something along the lines of “this constant was named "speed of light" because it is the speed at which electromagnetic radiation travels in vacuum, but it has since been shown to have a much broader significance” (well, not with such a lousy wording), but I can't remember exactly what became of that. --A. di M. (talk) 11:55, 28 March 2011 (UTC) (amended at 12:00, 28 March 2011 (UTC))

The lead makes this pretty clear to me.

The speed of light, usually denoted by c, is a physical constant important in many areas of physics. Light and all other forms of electromagnetic radiation travel at this speed in empty space (vacuum), regardless of the motion of the source or the inertial frame of reference of the observer. Its value is exactly 299,792,458 metres per second (approximately 186,282 miles per second). In the theory of relativity, c interrelates space and time, and appears in the famous equation of mass–energy equivalence E = mc². It is the speed of all massless particles and associated fields in vacuum, and it is predicted by the current theory to be the speed of gravity (that is, gravitational waves) and an upper bound on the speed at which energy, matter, and information can travel.

No? Headbomb {talk / contribs / physics / books} 12:48, 28 March 2011 (UTC)

Maybe rearranging the sentences could “solve” the OP's problem, like this:

The speed of light, usually denoted by c, is a physical constant important in many areas of physics. Its value is exactly 299,792,458 metres per second (approximately 186,282 miles per second). It is the speed of all massless particles and associated fields in vacuum, and it is predicted by the current theory to be the speed of gravity (that is, gravitational waves) and an upper bound on the speed at which energy, matter, and information can travel. Light and all other forms of electromagnetic radiation travel at this speed in empty space (vacuum), regardless of the motion of the source or the inertial frame of reference of the observer. In the theory of relativity, c interrelates space and time, and appears in the famous equation of mass–energy equivalence E = mc².

(Or some other permutation thereof.) --A. di M. (talk) 13:17, 28 March 2011 (UTC)

That is certainly much better, though I would reemphasise the first line:

The speed of light, usually denoted by c, is a physical constant important in many areas of physics. Its value is exactly 299,792,458 metres per second (approximately 186,282 miles per second). It is the maximum speed at which all energy, matter, and information in the universe can travel. It is the speed not only of light but of all massless particles and associated fields in vacuum, and it is predicted by the current theory to be the speed of gravity (that is, gravitational waves). Such particles travel at c regardless of the motion of the source or the inertial frame of reference of the observer. In the theory of relativity, c interrelates space and time, and appears in the famous equation of mass–energy equivalence E = mc².

Serendi^podous 13:28, 28 March 2011 (UTC)

That would work for me (although some others may disagree, god knows how much we have discussed different perturbations of that paragraph.) Minor quibble, the start of the sentence "It is the speed not only of light but of" suggests that the reader should already know that light travels at that speed, which is not particular good form for an encyclopedia. TR 13:46, 28 March 2011 (UTC)

Well the article is called "Speed of light"; the reader pretty much goes into the text with that idea in mind. Serendi^podous 13:59, 28 March 2011 (UTC)

I agree with TR; that bothers me as well: it's not like light has already been mentioned (except in the phrase “speed of light” itself). How about “It is the speed of all massless particles and associated fields–including electromagnetic radiation such as light–in vacuum, and it is ...”? --A. di M. (talk) 14:44, 28 March 2011 (UTC)

OK, that works. Serendi^podous 15:09, 28 March 2011 (UTC)

Incorrect statement

I have deleted the words in bold from this quote from the article because they are clearly wrong. The speed of sound waves is independent of the motion of the source but not that of the observer relative to the medium. "The speed at which light waves (or any wave for that matter) propagates in a vacuum (or otherwise) is independent both of the motion of the wave source and of the inertial frame of reference of the observer. This is a property of waves, be they electromagnetic (light waves or radio waves) or even mechanical (sound waves)." Martin Hogbin (talk) 17:16, 12 April 2011 (UTC)

Right hand side info bar needs fix

There's a problem considering the info bar at the top right corner. The numbers should not be represented using commas, as they are wrong when mathematically expressed. Spaces should be used instead. Even though they are correct in at least USA, they are incorrect in many, many other countries. This causes misunderstanding and qualifies as a reason to change them. Many people tend to read the English page of a Wikipedia article, too, for better and more information even though their English and their understanding of English text wouldn't be so good (Small, trivial things, like using commas, like this article does.). It's not nice when you, for example, lose points for your presentation because you copy pasted one small part of the text and it caused misunderstanding. That's a bad example, I know, but it's still one reason, and who hasn't copy pasted from Wikipedia? Was it one small line or huge section... FinFihlman (talk) 14:10, 14 April 2011 (UTC)FinFihlman

Commas are overwhelmingly the most common character used for this in English, and this is the English Wikipedia. There are non-native speakers around, but this doesn't mean we shouldn't be using e.g. actual to mean ‘real’ because the cognate words in many other languages mean ‘current, present’, does it? See WP:MOSNUM#Delimiting (grouping of digits). ― A. di M.​_plé​^dréachtaí 23:40, 14 April 2011 (UTC)

File:Sun to Earth.JPG caption revert

I have reverted the change by 67.161.54.63 which added the following to the main image caption: "Moonlight takes about 1.17 seconds (average distance) to reflect from the Moon to the Earth." While that may be true, the addition, which brings it from one line to three, adds little to the understanding of the image which wasn't already present. Without a distance from the Earth to the Moon, it is less informative than what was already there and appears to violate the succinctness portion of WP:CAPTION. Furthermore, there is already an image displayed further down showing how long it takes moonlight to reach Earth. It was almost immediately undone by the user who added it. Are there any objections to reverting it back to its original form? ScottSteiner ✍ 09:10, 16 April 2011 (UTC)

I agree with all of that and have restored it. It would be misplaced anywhere, especially so in the lead/infobox image.--JohnBlackburne^words_deeds 09:44, 16 April 2011 (UTC)

Scott, would adding (to the image) the Earth - Moon distance be productive? -161