Talk:Speed of light

Template:WP1.0

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 of 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)

Only a fool would call such a discovery by hindus as a co-incidence!!How can such a stuff be something irrelevant to this topic??sun means light,you guys are so ignorant about Hinduism and everything and think that you know everything.I strongly recommend to include this in the topic. — Preceding unsigned comment added by Shaardu (talk • contribs) 13:14, 11 June 2011 (UTC)

What wiki guidelines say? Its very apparent that the speed of light (i.e. part of sun) was accurately declared by Sayan. Ganesh J. Acharya (talk) 03:03, 7 July 2011 (UTC)

Again, it becomes a valid inclusion in the article sun in any case. Ganesh J. Acharya (talk) 04:06, 7 July 2011 (UTC)

Dear Mr. Ganesh J. Acharya, Here is my thought, if you blow air into the balloon, it expands of course. If you blow balloon with air, you are providing potential energy. The air inside obviously has high pressure than the air outside. So the potential energy is stored as difference in air pressure (you can imagine so). And when you release the air, the pressure difference makes the air to blow out, which is nothing but the conservation of energy (potential energy to kinetic energy of air molecules). My argument is that, the balloon has expanded and retained to its original position, so that the displacement (I'm considering vectorial quantity) in regard with time is zero. Coming to Sun, the Sun is not travelling at 186,413.22 miles per second as you have mentioned. This would be against relativity. May be the Rig-Vedic people didn't know relativity so didn't mention its sunlight. Sunlight is just an EM radiation over the visible range. You can say that they are just emitted by the sun's chemical reactions but not a part of it. Shriram (talk) 07:48, 7 July 2011 (UTC)

Various guidelines apply here, including WP:UNDUE, Wikipedia:Exceptional claims, WP:SECONDARY. To include this claim we would need an exceptional secondary reliable source. That: a) confirms this claim. b) puts this claim in a proper historical context. TR 08:58, 7 July 2011 (UTC)

In those days or for that matter even today Sun is seen as a living soul. If you start illuminating by yourself like Sun and your parts (rays emitted) move at 186,413.22 miles per second which a Risi sees and admires with the above words would that be wrong?Ganesh J. Acharya (talk) 03:06, 10 July 2011 (UTC)

Irrelevant.TR 10:22, 10 July 2011 (UTC)

Ganesh, you are perfectly entitled to your religious beliefs but they have no place in a scientific article. If you want to add this interpretation of a religious text to Wikipedia, I suggest that you look for a more appropriate article. Martin Hogbin (talk) 10:53, 10 July 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)

I'M SURE THERE IS AN ERROR ON THE LEFT WITH YOUR GROUP AND PHASE VELOCITY ANIMATED GRAPHIC. THE SPEED OF THE ENVELOPE IS THE GROUP VELOCITY NOT THE PHASE. — Preceding unsigned comment added by 188.28.239.158 (talk) 10:09, 26 September 2011 (UTC)

What error? The green dot is anchored to the maximum of the envelope and labelled as the group velocity, and the blue dot is anchored to a point where φ = π/2 and labelled as the phase velocity.
― A. di M.​_plé​^dréachtaí 19:30, 26 September 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

If the image included that distance, maybe. But the new image and the caption still wouldn't add anything to the understanding of the article. The current image/caption combo that is there is concise and informative. Just adding one more calculation/distance/time duration wouldn't really improve that. ScottSteiner ✍ 10:22, 16 April 2011 (UTC)

Removal of "in vacuo" in lede

Are we really proposing that the speed of light is constant regardless of the medium it is travelling through. Those first couple of sentences conflate the speed of light and c but it seems clear that it is the speed of light rather than the constant that is the subject there. Crispmuncher (talk) 00:25, 11 May 2011 (UTC).

The physical constant c, called the speed of light, is by definition exactly 299,792,458 m/s. The speed at which light propagates in a medium is less than c. The article is correct, with the above information given in more detail in the first two paragraphs.--JohnBlackburne^words_deeds 00:33, 11 May 2011 (UTC)

I understand the distinction, but it seems clear to me that the subject of the first sentence (and therefore by extension the second, which refers to "it") is the speed of light, not c. Therefore the "in vacuo" clarification is necessary. We shouldn't be talking about it as a fundamental constant without clarification either, for that matter. Crispmuncher (talk) 01:01, 11 May 2011 (UTC).

The first sentence reads "The speed of light, usually denoted by c, is a physical constant important in many areas of physics.". I'm not sure how you can come to the conclusion that it is not about the physical constant c, called the speed of light.TR 05:49, 11 May 2011 (UTC)

Because if for the sake of clarity we remove the subclause (which should not affect wider sentence structure) the sentence starts "The speed of light is..." How then, can it not be about the speed of light? Crispmuncher (talk) 15:05, 11 May 2011 (UTC)

Even without the subclause, it is clear that it is about the physical constant called "the speed of light". (Cause that is pretty much literally what the first sentences says.) So, yes it is about "the speed of light". Yet, it is not about the speed at which light propagates, as is clarified somewhat further in the opening paragraph.TR 15:20, 11 May 2011 (UTC)

Personally, I'd much rather have a clarification early on than until the fourth sentence. c is the speed of light, in vacuum, and that is a very important fact (whoever wrote in vacuo needs to be trouted). Also, currently, the second sentence reads like the speed of light is c regardless of the medium, which is simply false. I'd clarify it as soon as possible, preferably in the first sentence. Something like

The speed of light in vacuum, 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 of all massless particles and associated fields—such as electromagnetic radiation such as light—in vacuum, and it is predicted by the current theory to be the speed of gravity (that is, gravitational waves).

Headbomb {talk / contribs / physics / books} 16:09, 11 May 2011 (UTC)

I agree that this is an improvement. Count Iblis (talk) 16:30, 11 May 2011 (UTC)

Me too. I was WP:BOLD and changed it, since it doesn't hurt, and we can save the fine distinction that c is not only "the speed of light in vacuum" anymore, though is equal to it, for later. Also, I thought it was necessary to use SOME of the excerpted ref in the lede to remove the immediate question which otherwise arrises of why the speed of light is EXACTLY some value in m/sec. Answer: because we fiddle with the metre to require that it be so, having picked and fixed our arbitrary standard of time (which is easier to do, since there are so many good frequency standards out there for various processes). SBHarris 16:37, 11 May 2011 (UTC)

why light slows in a medium

I think this article misses the important point of why the speed of light is lower in a medium, or, how light travels in a medium. —Preceding unsigned comment added by 84.120.147.185 (talk) 07:54, 23 May 2011 (UTC)

The propagation of light is not the subject of this article. The subject of this article is the constant c, the only relevant point is that light does not always travel at that speed, even though it is called the "speed of light". Why that is so, is a topic for another article, such as light or maybe refractive index.TR 09:09, 23 May 2011 (UTC)

Er... There already is a section Speed of light#In a medium. ― A. di M.​_plé​^dréachtaí 10:27, 23 May 2011 (UTC)

Recent changes

I have just undone changes made by User:Drift chambers to the lede. The main reasons were that it broke the formatting of the lede, undoing the version currently there arrived at by consensus on this talk page, as well as adding a nonsensical sentence. As they were so disruptive and added nothing of value I had to revert.--JohnBlackburne^words_deeds 12:50, 20 September 2011 (UTC)

from http://www.britannica.com/EBchecked/topic/559095/speed-of-light. (re-worded) The speed of light refers to the rate of change of distance of light waves in motion through varying substances. Drift chambers (talk) 14:13, 20 September 2011 (UTC)

I'm sorry but the sentence you added, which I quote below in full, was simply nonsensical. The EB is a tertiary source, not a reliable secondary one, so should not be used anyway but you have clearly misunderstood it and the topic. --JohnBlackburne^words_deeds 15:08, 20 September 2011 (UTC)

The speed of light is the value calculated for the time taken for light to travel from a source emitting energy within the visible spectra to a hypothetical observer, an example is the light from the star known as the sun to an observers position within or upon earth.

Speed of light broken?

Might be worthy of note. http://www.bbc.co.uk/news/science-environment-15017484 --92.30.2.203 (talk) 19:16, 22 September 2011 (UTC)

Definitely worth mentioning, but with a caution that this needs more research. Pine^talk 21:35, 22 September 2011 (UTC)

Wait until it's properly sourced; a reliable scientific source. There's far less to it than some of the more excited headlines out there.--JohnBlackburne^words_deeds 21:40, 22 September 2011 (UTC)

John, you know not what you speak of. Return to your chalkboard. LaRouxEMP (talk) 21:42, 22 September 2011 (UTC)

Just read the articles, not just the headlines. From the BBC article

"we are not claiming things, we want just to be helped by the community in understanding our crazy result - because it is crazy".

I.e. the scientists know it is wrong to jump to conclusions. It's not a published result, never mind peer reviewed. It's the press trying to create headlines.--JohnBlackburne^words_deeds 22:22, 22 September 2011 (UTC)

There’s also this report, which gives an exact figure of 300,006 kps. But it then gets into extremely murky waters when it describes this figure as "6 kps faster than the speed of light". They’ve taken the exact known speed 299,793.458, rounded it up to 300,000, then subtracted this from 300,006, to arrive at a 6 kps difference. As mathematicians, they’d make good journalists. It’s impossible to tell from this article whether the newly measured speed is 299,793 + 6 = 299,799, or whether the 300,006 speed is correct, in which case the difference is not 6 kps but 300,006 – 299,793 = 213 kps. So much for quality science reporting. -- Jack of Oz ^{[your turn]} 23:04, 22 September 2011 (UTC)

A pretty good summary from Ars reports the 'news', gives various reasons to be sceptical, and says the results won't be made public until tomorrow when it will be easier to see what the fuss is about.--JohnBlackburne^words_deeds 23:18, 22 September 2011 (UTC)

There is also this experiment Minos (http://arxiv.org/pdf/0706.0437v3) which seems to suggest neutrinos can go faster than light, by roughly the same amount as in the CERN Opera experiment. Maybe empty space is not really transparent to light, but slows it down slightly so it cannot go the true speed limit. And I guess neutrinos aren't slowed in the same way? Doubledork (talk) 00:08, 23 September 2011 (UTC)

That's actually be theorised for quite some time; indeed, it is the basis of the theory underlying the Scharnhorst effect. Crispmuncher (talk) 00:18, 23 September 2011 (UTC)

Of course we do - Scharnhorst effect. hydnjo (talk) 03:32, 23 September 2011 (UTC)

I have replaced the BBC-ref with the arxiv source. DVdm (talk) 05:30, 23 September 2011 (UTC)

By the way, fwiw, see "Why CERN’s claims for faster-than-light neutrinos is wrong." DVdm (talk) 11:30, 23 September 2011 (UTC)

I suspect he may soon be very embarrassed he didn't double check that in his rush to get it out. I'm an electronics engineer, not a theoretical physicist, and it took me no more than five minutes to dismiss it. His whole argument is premised on the difficulty knowing exactly when the neutrinos are actually emitted, and he contends that the error is much greater than that used in the Opera paper. However, while he devotes his entire paper to the 500kHz coarse structure he completely neglects to account for the 200MHz fine structure. Opera are using a much more refined model of the neutrino emission than he is: that is why they can claim greater precision than he suggests.

That doesn't prove the Operas findings of course, but it does disprove Costella's assertions. Crispmuncher (talk) 16:27, 23 September 2011 (UTC).

He himself retracted it. Now it's titled “Why OPERA’s claim for faster-than-light neutrinos is not wrong”. :-)
― A. di M.​_plé​^dréachtaí 21:10, 26 September 2011 (UTC)

(Though I'm surprised that now he's that confident that the experiment is right–more than almost all physicists I've talked to.)
― A. di M.​_plé​^dréachtaí 00:40, 28 September 2011 (UTC)

I think the current article has the balance about right. We should mention the news that a reputable laboratory has results that suggest FTL travel but is should only be in the FTL section, not the lead. We should not add any more detail or discussion until the result is confirmed, if that happens. Martin Hogbin (talk) 17:18, 23 September 2011 (UTC)

Would anyone object to the removal of the following statement from the article:

One possibility is that the scientists overlooked that neutrinos travel through the Earth and not around the Earth’s circumference; taking such a "shortcut" shortens the travel time between CERN and LNGS by just about the right amount.

It's unreferenced and is pretty much WP:OR (the original citation was to a blog, and while it's an interesting observation, it doesn't reach the level of a reliable source or a notable explanation for the results). 107.10.43.91 (talk) 04:01, 25 September 2011 (UTC)

I agree. The Italians would have to be pretty stupid not to have considered the fact that neutrinos travel in straight lines thru the Earth. I also some speculation about extra dimensions, especially the part that it is the "current suggestion". Roger (talk) 05:56, 25 September 2011 (UTC)

Agreed. In fact, the experiment was actually done by firing the neutrinos THROUGH the Earth. There's no overlooking here. — Preceding unsigned comment added by 220.255.1.69 (talk) 08:30, 25 September 2011 (UTC)

I’m more a social scientist than a physical scientist and I was concerned that the way neutrinos travel through the Earth could be overlooked from what I understand about human thinking. Most fundamental particles that scientists study can’t pass through the Earth and that is the type of thing that can be overlooked, I overlooked it till I read the blog. I was worried that scientists from other organisations seeking confirmation might overlook that as well and scientists might waste research time studying something that isn’t happening. I don’t know if neutrinos are travelling faster than light or not, I know scientists should ask CERN if they took into account that neutrinos travel through the Earth. Incidentally the Schlafly blog Conservapedia isn’t highly regarded over relativity, see Conservapedian relativity. Proxima Centauri (talk) 09:26, 25 September 2011 (UTC)

They may have overlooked something, but they definitely didn't overlook that. Also, I guess the relative difference in length between a straight line and a great circle from CERN to LNGS is much more than 2.5×10⁻⁵.
― A. di M.​_plé​^dréachtaí 10:11, 25 September 2011 (UTC)

I get an arc to chord ratio of 1.0005466, given a distance between emitter and detector of 730 km, as the archivx article reports, and earth radius of 6378.1 km, i.e. the great circle distance would be 730.399 km.--agr (talk) 23:59, 26 September 2011 (UTC)

Superluminosity of c?

I was thinking about today's OPERA findings (disclaimer: IANAPP, I Am Not A Particle Physicist) and its possible implications, if the experiment is confirmed valid. Now if indeed a neutrino traveled at velocity greater than lightspeed, my understanding is that should result in a paradox (or a contradiction) within special relativity. Now special relativity is so fundamental, that something has to be broken. What if it is just that c (the universal top speed) is different from that of speed of light in a vacuum by an amount detected in this experiment (0.002%), and there is a hypothetical "universal web of aether" slowing down all interactions, except neutrinos (who have very few interactions anyway). Causality, which I find soothing, in special relativity would not be broken, but it would hold that c > v_light. The true value for c given by this experiment would be in the neighborhood of 299,799,922 m/s. Could we have missed such tiny inaccuracy, or have there been experiments (eg. E=mc² experiments) that should have detected this anomaly with c = 299,792,458 m/s? If not, could such experiment be devised? --hydrox (talk) 18:18, 23 September 2011 (UTC)

The first thing I thought when I heard that was that there must have been some kind of glitch with the measurement, and a part of me still hopes/believes that, but apparently people have known about this and trying to figure out what was wrong for years. On Monday I'm attending a talk about that by someone who has worked in that experiment, so I'll see what they think might be going on. If such a result was confirmed (e.g. a different experiment got similar results), it would imply... I dunno what, but it would have to be some really crazy stuff.
― A. di M.​_plé​^dréachtaí 19:18, 23 September 2011 (UTC)

There really is no point in speculating about this. It should be evident to anyone reading this article that a confirmed case of matter or energy travelling faster than c would have profound implications. At the moment we do not have that, we have a news story that is extremely relevant to this article and should therefore, in my opinion, be mentioned in this article in the relevant section. Beyond that we must wait and see. There have been similar claims before that have turned out to be errors. Martin Hogbin (talk) 08:36, 24 September 2011 (UTC)

Indeed. Even the authors themselves say, “Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.” Hey, I might quote that in the article.
― A. di M.​_plé​^dréachtaí 11:32, 24 September 2011 (UTC)

IANAPP either, but the report claims Sigma 6. I think this is extraordinarily significant, so that it is scientifically accepted to regard it as a discovery, not a signal deviation. The report is signed by 174 scientists, so they either risk their reputation en masse, or have valid reasons for their claim. Still it might be some as yet undiscovered systematic error, so let's wait and see... Rursus dixit. (^mbork³!) 09:17, 24 September 2011 (UTC)

Systematic error isn't that unlikely, the way they needed to correctly calculate the time of flight using different clocks at different locations is extremely difficult to get right. Also, this is the first experiment in which this is done to such an accuracy, so there is no well established routine that they could adopt knowing that it would give the desired result. Count Iblis (talk) 18:33, 24 September 2011 (UTC)

Replying to my above hypothesis that c > v_light. I calculated the cumulative error due to an incorrect value of c in GPS. The oldest GPS satellite currently in use is Navstar 2A-01, launched about 21 years ago. If GPS receivers were calculating the clock drift aboard this satellite with an incorrect value of c (0.99998c), it would result in an error of about 14,746 ns in 21 years, corresponding to a positioning error of over 4.4km. More recent satellites, like those launched in 2009, would still be off by at least 0.4km. So GPS seems to prove that Einstein's c has to be equal to the speed of light in a vacuum to a relative accuracy far below 0.002%. --hydrox (talk) 00:03, 25 September 2011 (UTC)

Just a thought

The 'neutrino' news has prompted me to wonder if we should have something like this in the article.

Because of its fundamental significance to physics, the speed of light continues to be a subject of speculation and investigation. From time to time, reputable laboratories have published results which have initially appeared to show energy, matter, or information travelling faster than light. Because of the significance that these results would have if confirmed they are often widely reported in the media. To date no such observations have been confirmed, and in cases where investigations have been complete the results have been found to be due to errors or misunderstandings. For these reasons, media claims of superluminal effects should be treated with caution until confirmed by the scientific community Martin Hogbin (talk) 09:20, 24 September 2011 (UTC)

I don't think this could fit in the article. After all, it boils down to a warning about media claims, so the essence would be off-topic in the article. I think such a warning could at best belong on top of the talk page, but I'm not sure. O.t.o.h. we already have a tag something like {{recentism}}:

DVdm (talk) 09:40, 24 September 2011 (UTC)

I realise that the "upper limit on speeds" section has to be greatly simplified for people like me to understand it - but in view of the Opera neutrino speed experiment, I have to ask the following question: given that the measured speed of the neutrinos is only a little faster than the speed of light (around 1000 Km/s IIRC), is it not possible that light travels a little less quickly than the physical maximum speed limit? New Thought (talk) 11:54, 25 September 2011 (UTC)

Yes that is possible, along with many other things but it is not our job to speculate here. Please read the section that I have now put in bold above. If and when there is a confirmed result, scientists will start to propose theories to explain it. Martin Hogbin (talk) 12:16, 25 September 2011 (UTC)

FWIW (& perhaps somewhat related) - Harvard Physicist Lisa Randall Seems To Have Presented A Worthy Perspective On All This - Enjoy! :) Drbogdan (talk) 16:10, 25 September 2011 (UTC)

I also have the feeling that the new speed is just a "correction" of the 1983 standard, that due to the age and the possibly gravitational mistakes, was just less accurate that the today neutrino measures... just my opinion. — Preceding unsigned comment added by 95.236.123.84 (talk) 18:02, 25 September 2011 (UTC)

• also, read here : http://arxiv.org/ftp/arxiv/papers/1109/1109.4897.pdf

they are really talkin about 20 cm ???? are they kidding ???? it looks an enourmous distance...for me. bah. — Preceding unsigned comment added by 95.236.123.84 (talk) 20:20, 25 September 2011 (UTC)

"In 1905, Albert Einstein postulated that the speed of light in vacuum was independent of the source or inertial frame of reference,"

Wasn't Maxwell first to postulate that? — Preceding unsigned comment added by 193.62.111.31 (talk) 14:32, 26 September 2011 (UTC)

No, just like in case of Einstein and Dirac, the equation Maxwell discovered was smarter than himself. Count Iblis (talk) 14:39, 26 September 2011 (UTC)

You have to be careful with terms like "postulate" since they are frequently misinterpreted. A postulate is not a conclusion nor even a hypothesis. A postulate is a precondition. This appeared to be the case even before Einstein started work on SR and for the purposes of developing the theory he accepted it without question. This is the starting point for SR, not a conclusion of it. Crispmuncher (talk) 15:13, 26 September 2011 (UTC).

A sense of "postulate" is "propose the existence of" and that seems to be the sense used here. And it was Maxwell that first postulated the constant speed of light (in 1898 I believe), which is necessarily independent of inertial frame of reference. — Preceding unsigned comment added by 193.62.111.31 (talk) 15:50, 26 September 2011 (UTC)

Maxwell died in 1879. Yes, he said that the speed of light and other electromagnetic waves was independent of the source, and that had been common knowledge for a long time when Einstein said it in 1905. The current text is misleading and should be fixed. Roger (talk) 17:14, 26 September 2011 (UTC)

Put Maxwell was hardly the first to propose this. The idea that light should travel at a speed independent of the source is inherent to any wave approach to light and thereby goes back at least as far as Huygens and probably further. For this reason the sentence does not claim that he was the first to do so.TR 16:13, 27 September 2011 (UTC)

How is it misleading? Here is the full sentence

In 1905, Albert Einstein postulated that the speed of light in vacuum was independent of the source or inertial frame of reference, and explored the consequences of that postulate by deriving the theory of special relativity and showing that the parameter c had relevance outside of the context of light and electromagnetism.

It does not say he was the first to think the speed of light was independent of its source or the frame: after all that's what the Michelson–Morley experiment strongly suggested. He was though the first to work out a theory that explained it.--JohnBlackburne^words_deeds 17:35, 26 September 2011 (UTC)

No, Einstein was not the first to work out such a theory. See Lorentz ether theory. The sentence is misleading because Einstein was not the first with either the postulate or the theory. Roger (talk) 20:08, 26 September 2011 (UTC)

Should we replace with

"In 1865, James Clerk Maxwell postulated that the speed of light in vacuum was independent of the source or inertial frame of reference. Lorentz explored the consequences of that postulate by deriving the theory of relativity and showing that the parameter c had relevance outside of the context of light and electromagnetism. Einstein later adopted this into the "special" theory of relativity."

I am at least sure about the Maxwell part. This article is about the speed of light, not relativity, and Maxwell gets the credit for that. (I was the IP OP I made a user name) 이방인 얼라이언스 (talk) 15:18, 27 September 2011 (UTC)

I have just restored the sentence on Einstein and relativity that was removed: Although others did work before Einstein he is largely credited with the discovery of SR, which established our modern understanding of the speed of light and its significance in Physics. I kept the information about Maxwell with a slight reworking of the information that was added about him. I'm aware though this makes that paragraph a bit longer in an already long lead, which could do with editing for length if anyone can find a way.--JohnBlackburne^words_deeds 22:40, 27 September 2011 (UTC)

Yes, Einstein is usually credited with SR, but this article is about the speed of light. The speed of light was known to be constant and important before Einstein, and the article should reflect that. I disagree with your change. Roger (talk) 00:02, 28 September 2011 (UTC)

It now has Maxwell's insight, but he did not establish the theoretical basis for the speed of light being constant, or its significance as not only the speed of electromagnetic waves but it's importance as a more general physical constant due to special relativity.--JohnBlackburne^words_deeds 00:18, 28 September 2011 (UTC)

Einstein's postulate was that the speed of light was independent of the source. Maxwell certainly did establish the theoretical basis for that. Your description of the postulate is inaccurate, and the rest of the sentence describes things done by others before Einstein. Roger (talk) 04:28, 28 September 2011 (UTC)

Your going to need to provide reliable secondary sources for your claims.TR 07:58, 28 September 2011 (UTC)

We don't need a reliable source for the fact that 1865 is before 1905. 이방인 얼라이언스 (talk) 12:21, 28 September 2011 (UTC)

We need a RS that someone discovered (special) relativity before Einstein.--JohnBlackburne^words_deeds 12:57, 28 September 2011 (UTC)

Here is Lorentz in 1904 showing (for the second time) "that the parameter c had relevance outside of the context of light and electromagnetism."[2] Since this article is about c (or the speed of light?), not "special" relativity (whatever that is), I think we should credit Lorentz here. 이방인 얼라이언스 (talk) 13:02, 28 September 2011 (UTC)

Furthermore, the constant c, which had been widely accepted since Maxwell and was used by Lorentz, is necessarily independent of inertial frame of reference. In fact that is the definition of "constant" - "independent of other things"; so the article phrase "Albert Einstein postulated that the speed of light in vacuum was independent of the source or inertial frame of reference" gives credit where it is not due. 이방인 얼라이언스 (talk) 13:33, 28 September 2011 (UTC)

That's not a secondary source, but leaving that aside that's Lorentz writing about the effect on solid bodies of "their motion through the aether", so repeating the same mistake of others before him. It was Einstein's insight that there is no privileged frame, so no ether, and all frames are relative to each other, from which with the constancy of the speed of light he was able to derive the laws others had arrived at and much more.--JohnBlackburne^words_deeds 13:43, 28 September 2011 (UTC)

Well, ignoring the aether is a good move and doubtless can be mentioned in the "special relativity" article. However, the sentence "In 1905, Albert Einstein postulated that the speed of light in vacuum was independent of the source or inertial frame of reference, and explored the consequences of that postulate by deriving the theory of special relativity and showing that the parameter c had relevance outside of the context of light and electromagnetism." simply gives credit where it is not due.

• Maxwell was the first to "[postulate] that the speed of light in vacuum was independent of the source or inertial frame of reference"
• Lorentz was the first to "[explore] the consequences of that postulate by [...] showing that the parameter c had relevance outside of the context of light and electromagnetism." 이방인 얼라이언스 (talk) 14:12, 28 September 2011 (UTC)