Talk:Speed of light/Archive 4

message: To be honest, I'm not convinced the mnemonics section is very encyclopaedic; do people feel that it enhances the quality of the article, or should we get rid?  Thanks — Alan✉ 21:15, 23 January 2007 (UTC)
replies: text: I don't know, maybe leave just one, or maybe not. I'm for removal too, since people who wants to learn by heart the speed of light are rare (personal opinion). Certainly, this shouldn't be section 2 of the article. Dravick 01:42, 24 January 2007 (UTC)
replies: text: It's kind of neat to have such a mnemonic. That being said, when I was a physics major in first-year physics we used rounded numbers. People who need the exact number probably have it programmed into their desktop Crays by now.  But I think any mnemonics should be preserved for posterity in a footnote or other brief mention near the end of the message. P0M 02:28, 24 January 2007 (UTC)
replies: text: Okay, thanks for the responses.  I'll relegate them (or one of them) to a footnote.  — Alan✉ 20:48, 26 January 2007 (UTC)
replies: text: On second thoughts -- even the existing footnote references are to serious material; a 'mnemonic' reference would be conspicuous among them by its comparative lack of seriousness.  I'll just delete, as I can't see any way to include them that fits in with the content and style of the rest of the article.  — Alan✉ 20:58, 26 January 2007 (UTC)
thread_title:  mnemonics 

message: It says in the main article that the speed of light is 299,792,458 metres per second... When in fact it's that many KILOmeters per second... Someone should really fix that.... Seriously.
:Erm, not it isn't. The majority of physics undergrads knwo that the speed of light ~ 3E8 m/s. As the article says, 299,792,458. Which is the same as 299,792.458 km/s. Note comma in one, decimal point in the other. In localities where the comma is the decimal separator, then it would be written as 299.792.458 m/s or 299'792'458 m/s or 299.792,458 m/s or 299'792,458 m/s. To avoid decimal separator confusion, the speed of light is 299792458 m/s. Three hundred thousand kilometres per second, or three hundred million metres per second. Google Speed of light and look at Google Calculator if you don't believe me. Stannered 23:24, 28 March 2007 (UTC)
thread_title:  The actual Speed of Light 

message: According to data in the article Huygens' value is "better" than Newton's. If we use equatorial Earth radius 6378135 m and assume data from article - Huygens (?): 2000 Earth radii per minute, we get about 212,600 km/s, Newton (Optiks, 1704): 33.2 Earth radii per second, we get about 211,750 km/s. Obviously Huygens' value is better, or am I missing something? Also Boscovich in 1758 gave estimated value 20,000 Earth radii per 1/8 hour (~ 450 s) and 283.470 km/s, what is even better. --xJaM 03:35, 8 February 2007 (UTC)
replies: text: Newton and Huygens's values are virtually identical, according to the article.  I don't think it is worth distinguishing one as "better" than the other, when they are within 1% of each other, yet more like 30% from the true value.  You are right though, Huygens' value is slightly better.  In regards to Boscovich's value, keep in mind that it was determined about 80 years after Newton's value.  I have removed the incorrect wording from the article. Grokmoo 04:11, 8 February 2007 (UTC)
replies: text:  Yes, I uderstand that both values are almost identical - but just a sentence in the article said differently. I've added Boscovich's value not regarding directly to Huygens's or Newton's estimations, but just for an information (that might be included in the article). Yes, I know that it was estimated so late, but it is still a very good one, since a.u. at that time was not yet measured so good. Cassini measured a.u. in 1672 (109.8×109 m - parallax of Mars at oposition, Cassini, Flamsteed, 1672, 138.4×109 m - declination of Mars), and the first pretty satisfying measurement of a.u. was made in 1769 during the transit of Venus (153.9 and 148.2×109 m) - 11 years after Boscovich's estimation, which gives for a.u. around 127.6×109 m. --xJaM 01:56, 10 February 2007 (UTC)
replies: text:  Ok, everything looks good.  Thanks for the heads up on the error. Grokmoo 17:13, 16 February 2007 (UTC)
thread_title:  Huygens' and Newton's estimations 

message: Does anyone know why the definition went with 299792458 instead of a nice round 300000000?  was it just to keep everyone from having to junk their exisiting meter sticks? —The preceding unsigned comment was added by 216.70.247.242 (talk) 22:42, 12 February 2007 (UTC)
thread_title:  Question on definition 

message: "If this is true, an object may travel at the speed of light, but it will not travel through space when this is done, as no time will pass while it is at the speed of light."
The above sentence, which appears in the article, is either contradictory in itself, or implies some kind of speed-of-light travel of objects which occurs, but not through space. If an object is traveling at the speed of light, but it is not traveling through space, where is it traveling? If "no time passes", it should be specified FOR WHAT or WHOM, or for the entire universe. Is this non-passage of time a way of saying that the event of faster-than-light travel doesn't actually occur? Or does it mean the TRAVELER or TRAVELING OBJECT experiences no passage of time? Also, if "no time passes", would not this object be permanently frozen in time, as no events could occur to it to change its circumstance? If no force can act upon it, since it is outside of time, would it therefor be an irresistable force? An unmoveable object? Is this an accepted theoretical phenomenon? Does the sentence mean that the object will in fact travel at the speed of light, but for a period of time exactly equal to zero? Does this make sense, or is it sophistry, or is it a kind of thought experiment? This sentence needs clarification, correction, or removal. --4.239.0.189 18:12, 23 February 2007 (UTC)
replies: text: Ugh.  I think this wording should be removed from the article entirely.  If you look at the equations for the Lorentz transformations, you see that they indicate that no time will pass for an object traveling at the speed of light.  This, in some sense, implies that for  a light particle, all events actually occur simultaneously.  Note that this is only for the light particle itself, not for an outside observer traveling at less than the speed of light (relative to what he is observing).  The light particle is not really "outside of time" in the sense you are thinking, but yes, the wording in this section is not really clear.  In fact, I think the whole section could really use a good rewrite.  I'll mull this over for a couple days, and then hopefully have something better to put down. Any other contributions will be very welcome. Grokmoo 02:14, 24 February 2007 (UTC)

text: I agree. The idea of "traveling" when delta T = 0 and delta x,y,z = 0 is a total distortion of the idea of moving or traveling. If one observes cases of things that move at speeds closer and closer to c, one will observe their clocks going slower and slower, but their perception will be that less and less time passed while they were going a very great distance.   P0M 02:39, 24 February 2007 (UTC)
thread_title:  Contradictory (?) sentence in Sec. 3.2 - Technical impossibility of hyper-light-speed travel 

message: The current text says that light moving through a medium other than a complete vacuum is actually a "light-like hybrid of electromagnetic waves and mechanical oscillations of charged or magnetic particles such as electrons or ions, whereas light in the strict sense is a pure electromagnetic wave."  What is the reader supposed to make of this odd formulation? "Hybrid" is a biological term and is not helpful in guessing at what the writer was trying to say. The picture it paints in my mind is that of light in empty space hitting the window of a space craft (for instance) and suddenly turning into some sort of conjugal combination of electromagnetic waves traveling along with mechanical oscillations of various kinds of subatomic or atomic entities. 
Somebody who has a thorough grounding on this subject should rewrite the quoted material so that it accurately communicates the correct understanding of the change in measured speed.P0M 05:21, 24 February 2007 (UTC)
thread_title:  Another imperfection 

message: "Changes of gravity, however, warp the space the light has to travel through, making it appear to curve around massive objects."  Is it more accurate to say it "appears to curve" or simply that "it does"?69.119.13.218 20:59, 12 March 2007 (UTC)
replies: text: The problem is that light always goes straight, and what "curves" is the space it travels through. Or, to put it another way, light always takes the shortest trip between two points.  If we graph the positions of Earth and stars we think we know where to set our "gunsight" so that at a certain time of the day or night the gunsight will exactly line up on the star. Then we find that when the light has to skim by our sun on the way to earth the distant star is no longer where we expected it to be.  Do we say that light in this case has selectively changed its nature so that it curves through empty space? Or do we say that light goes in a "shortest distance" path, but what is the "shortest distance" changes in the presence of a massive object like the sun? Light does not have mass, so we cannot say that the sun "pulls" the light out of its normal path. 
The idea that gravity is an attraction explains why Mars stays in orbit around the sun, but it does not explain why something massless would be "attracted" by the mass of the sun. The idea that "gravity" is a misconception may be a very productive idea because space curvature explains what was previously called "mass attraction" but it also explains "curving" of light's path. P0M 03:46, 24 March 2007 (UTC)
replies: text: In classical optics you have fermat's principle stating that light chooses the path that takes the least amount of time. I think this works for gravitational lensing to. As in coordinate time (although not in proper time) light goes slower close to massive objects. I would not try to change the article though, since the current formulation is the standard one.Agge1000 00:38, 12 November 2007 (UTC)

text: "Massless" means that were the particle stationary, it would have no mass (see rest mass). You're not going to find a stationary photon, hence why it is massless (crudely). However, it has an energy, and that energy can be translated into a mass by E=mc^2 (or more accurately, E^2 = m^2 c^4 + p^2 c^2). So you can think of gravity applying to this equivalent mass, hence bending the light. Or, more accurately, you can indeed think of space-time curving. Mike Peel 05:14, 19 April 2007 (UTC)
replies: text: In this case, treating photons as massive particles influenced by strictly newtonian gravitation will only yield half the measured bending (that Eddington found in his famous experiment)Agge1000 00:56, 12 November 2007 (UTC)
thread_title:  Gravitational Lensing 

message: You completely misunderstand the velocity addition formula. 
The correct interpretation goes like this:
Take three observers. A, B, C. Let A observe the speed of B. Let this speed be VB. Also, Let A observe C, too and let the result be VC. Now, at the same time let B observe C and let the result be V. The velocity addition formula describes the relationship between these measurements:
VC=(VB+V)/(1+VB*V)(for the sake of simlicity c is 1 now.)
Your greatest mistake is that you identify the velocities of the right side of the equation with the measuremnts of A, the observer "in rest". No, only one of these variables belongs to A's observation, the other one belongs to B.
Let us now work out yor problem: Two space ships, B and C approach each other. Their speed measuremnts have to be the same, only the sign is and has to be different: Say V=-0.9, that is B sees C approaching him. The sign is negative because the direction of C is opposite. What does a A see? It depends on his relative motion. We may assume that VB=0,9. That is A sees B running towards C at 0.9.
The velocity addition formula tells now that VC=0. Which is correct. This means that if A sees B running away at a speed 0,9 and B sees C approaching him at a speed of 0.9, then A must see C standing still.
But this is not what you wanted. What you wanted was: A sees B running in the same direction as C. A's measurement on B is VB=0.9 and B's measurement on C, V=0.9 then VC is not VB+V but (VB+V)/(1+VB*V)
::That's not what the article wants.
Please reconsider your interpretation or I will change the whole paragraph. Then you can appeal to the saint moderators. —The preceding unsigned comment was added by Zgyorfi (talk • contribs) 10:06, 18 March 2007 (UTC)
replies: text: I don't know the history of the article, but it currently uses the word "speed" to describe all the variables, and speeds are always positive. That's more than enough for an article on the speed of light. Melchoir 02:03, 20 March 2007 (UTC)
replies: text: The way you you fixed it looks fine to me. There are multiple occurrences of the word "velocity" in that section, but your way of phrasing things should make what is going on clear enough for the general reader. P0M 02:42, 20 March 2007 (UTC)
thread_title:  Error in the main text 

message: If the observer in S\! sees an object moving along the x\! axis at velocity w\!, then the observer in the S'\! system, a frame of reference moving at velocity v\! in the x\! direction with respect to S\!, will see the object moving with velocity w'\! where
:w'=\frac{w-v}{1-wv/c^2}.
This equation can be derived from the space and time transformations above.
Now, this is the formula that applies to your situation. You'd better try to understand rather than referrring to authorities. 
Signature: I am not and never will be politically correct enough to follow your rules. My signature is my username, which is not hidden. Report to the inquisition if you like.
My, we've all expended quite a bit verbiage, and a wee bit of vitriol, to address something that didn't need correction.  The main text clearly states (stated) that these are speeds.
Signature:  I am not politically correct, but that has nothing to do with my being civil, courteous, or considerate, or with keeping the agreement I made to abide by the guidelines when signing onto Wikipedia so I'll sign John N. 23:26, 26 March 2007 (UTC)
thread_title: Composition of velocities

message: I am considering posing the following paragraph to the main page, so please reply with constructive criticism.
In mathematical notation we write concerning speed  v=d/t where v, d and t are v velocity, distance and time respectively. 
v=d/t Implies that t=d/v.  
Since according to the Principle_of_relativity  it is forbidden to travel faster than the speed of light, instead of writing t=d/v we could write t=d/(c-vn). We define vn =c-v. This would produce a singularity for time at the speed of light. 
This would imply that we could write (c-vn) =d/t. This would symbolize that Velocity an object having Invariant mass is undefined at the speed of light. 
Where appropriate, c=299,792,458 m/s.
71.156.91.18 00:20, 3 April 2007 (UTC)
replies: text: Hi, and thanks for posting this here first before trying to edit the article.  Note that according to your derivation, with t = d / (c - vn), and vn = c - v, we end up with t = d / v, which is the same as the Galilean definition you use above.  This does not produce a singularity for v = c.  For the correct derivation of how this goes, you should check out Lorentz transformation.  Also, note that there are many possible transformations that satisfy the singularity property you are talking about.  However, the standard Lorentz transformation is picked, because it is in fact derived from the underlying Minkowski space metric. Grokmoo 18:14, 3 April 2007 (UTC)
thread_title:  Speed of Light and mathematical Notation 

message: "In metric units, c is exactly 299,792,458 meters per second (1,079,252,848.8 km/h)."
hi, i was going over your page and i noticed that this part is wrong. your information on the speed of light is correct at the m/s stage, but your km/s calculation in wrong. it should be about 17,987,547.48 km/h not 1,079,252,848.8 km/h. 
299,792,458 X 60 /1000 = 17,987,547.480
Ochosi 23:22, 4 April 2007 (UTC)
replies: text: You forgot to multiply by 60 again (times 60 for seconds to minutes, then again for minutes to hours). – mcy1008 (talk) 23:35, 4 April 2007 (UTC)
thread_title:  Speed of light in your top section is wrong 

message: The photo captioned "A line showing the speed of light on a scale model of Earth and the Moon" does not make any sense.  Can someone come up with a better photo? Davidwr 00:29, 29 April 2007 (UTC)
replies: text: I think it would be better if it showed a 3D globe of the earth with atmosphere, dark space and a 3D moon. Then it showed a finite beam of light leaving the earth's domain and hitting the moon. It also would be nice to have a clock running in micro-seconds. --Marvin Ray Burns 02:24, 29 April 2007 (UTC)
replies: text: I stole the existing photo and added a distance-scale so at least it makes sense now.  Feel free to do a 3D one.  Davidwr 04:50, 29 April 2007 (UTC)
replies: text: It wasn't a photo, it was an animation. The new diagram isn't an animation (as far as I can tell). Stannered 09:47, 29 April 2007 (UTC)
replies: text: I restored the old animation. EdwardLockhart 12:27, 29 April 2007 (UTC)
replies: text: Thanks. I've reverted the other article that used this same image. Davidwr 21:52, 29 April 2007 (UTC)
thread_title:  Earth/Moon photo makes no sense 

message: the speed of light [is] precisely 299,792,458 m/s ... the speed of light is about 186,000 miles (about 299 338 km) per second
This looks very odd.  I suggest just saying about 186,282 miles per second  .  --Occultations 23:41, 18 May 2007 (UTC)
replies: text: Good point. Done. Dravick 23:51, 18 May 2007 (UTC)
thread_title:  <i>299,792,458 m/s</i>, but <i>about 299 338 km per second</i>? 

message: Footnotes 6 and 7 are dead links. Thus they should either be fixed or removed. --Trakon 10:46, 31 May 2007 (UTC)
replies: text: Actually it looks like I meant 7 and 8. --Trakon 09:27, 7 June 2007 (UTC)
thread_title:  Dead Links 

message: I deleted language to the effect that using c to denote the speed of light derives from constant. The one cited essay speculates that c may alternatively derive from constant, but acknowledges grudgingly that celeritas is the widely accepted derivation. Weber's constant isn't the speed of light. Further, with all the constants floating around, the idea that any one constant would appropriate the initial letter of constant as a symbol is far fetched. We should go with the consensus derivation. Finell (Talk) 04:49, 1 August 2007 (UTC)
replies: text: I've reverted your change, although it might be reworded yet again to note that c for constant was only the original usage and now generally means celeritas. — Joe Kress 07:49, 1 August 2007 (UTC)
thread_title:  ''c'' is for ''celeritas'' 

message: The standard physics nomenclature for this physical constant is "speed of light in vacuum", see for exampel NIST. I think wikipedia should adhere to to standardized physics nomenclature, to avoid endless discussions and redirects. I propose to rename this article. /Pieter Kuiper 18:11, 8 August 2007 (UTC)
replies: text: Please do not rename the article. Wikipedia's naming convention on en:WP is to use the name that the typical English language Wikipedia user would be most likely to use. In this case, that name is Speed of light. Only a specialist might ever think to add "in vacuum". The current, very long-standing name of this WP:FA is also shorter, and therefore easier to type into a search box, than what you propose. A redirect from "speed of light in vacuum" is not necessary (although it wouldn't hurt); if someone were ever to enter "speed of light in vacuum" in the search box, this article tops the list of articles that is returned with 100% relevance. Also, the article in not exclusively or even primarily about the named physical constant; it is more broadly about the phenomenon, its history, underlying theory, etc. On the other hand, correct terminology should be used in the body of the article. Finell (Talk) 21:41, 8 August 2007 (UTC)
replies: text: OK, I understand your points. I will create the redirect then, which will make a name change of these article more difficult. Thank you for taking the time to respond to my suggestion. /Pieter Kuiper 21:58, 8 August 2007 (UTC)
thread_title: Standard nomenclature: speed of light in vacuum.

message: I'm using Linux & Firefox so it may be a upper-/lowercase problem. Does it look OK in Windows?
Johnmuir 09:44, 11 August 2007 (UTC)
replies: text: I have no clue what your technical problem is. The image works fine as a thumb (I use Opera on a winXp - also works with Netscape) I'll try it on the computer lab machines w/ie later. Without thumbing the image the caption dissappears. Do you have any problems with other thumbed images? Does anyone else have the same problem? Thumbed images are preferred as it allows user pref to control the size when set at default. Vsmith 02:48, 15 August 2007 (UTC)

text: It's a common problem that .svg images don't display thumbnails. Unfortunately, the issue is hard to predict, reproduce, or fix. The move to a .svg in this article is fairly recent, which probably explains why more readers haven't complained. I recommend using raster files until the issue is solved (and I'll do so here). Melchoir 03:29, 15 August 2007 (UTC)

text: It looks fine now - the last change was successful. I'd be pleased to help on the general problem if I can. (Testing, programming or similar, but I'm not a graphics expert.) Johnmuir 19:25, 15 August 2007 (UTC)
replies: text: That would be great! Unfortunately, I don't know if there's any centralized discussion yet. I'm sure the problem must lie in the MediaWiki software, not Wikipedia's implementation, and I don't do work outside of Wikipedia myself, but you could always ask Wikipedia:Village pump (technical) for guidance. Melchoir 21:59, 15 August 2007 (UTC)
thread_title:  The Light Cone image does not show up 

message: Using Opera, it's more like 3 seconds. IE timing seems more plausible. Since this is apparently browser dependant, I move that the comment should be corrected, or the graphic removed. —Preceding unsigned comment added by PoorLeno (talk • contribs) 
:I agree. Apart from the timing problems, the graph is annoying and distracting. Jaho 01:30, 23 August 2007 (UTC)
thread_title:  graphic doesn't time 1.2 seconds 

message: I found this article . Maybe we can add something like that into the article? Oidia (talk) 12:14, 21 August 2007 (UTC)
thread_title: Possible to travel faster than speed of light

message: Speed of Light is a song by Stratovarius. I'm not english and i've not time enought to make the desambiguation page. Please, could someone else do it?
Thanks.   —The preceding unsigned comment was added by 213.60.158.76 (talk) 07:36, August 23, 2007 (UTC) 
:Done. — Joe Kress 02:14, 25 August 2007 (UTC)
replies: text: Speed of Light is also a song by OMD, Teenage Fanclub, and probably dozens of other bands. So it seems like a disambiguation page is better than linking to every single song with the name by every minor band who's made one (not to mention other possible uses).WildElf (talk) 17:31, 28 November 2007 (UTC)
thread_title:  There must be a Disambiguation 

message: Why does light travel at a constant speed? What governs this? Structure?
Kazuba 16:16, 10 November 2007 (UTC)
replies: text: The structure of spacetime within general relativity requires that there be one speed that all massless particles travel at.  Why general relativity is true (as far as we can tell), and why light is massless (as far as we can tell), are questions I don't think there are good answers to at the moment. -- SCZenz (talk) 18:51, 27 November 2007 (UTC)
thread_title: It may be a dumb question but..How come?

message: But Geraldomanchego (above) shouldn't be so sorry, he is not alone.  I have talked to many people who labor under this misconception.  I wonder if we need to add a Problems With Speed Exceeding c section to this article to gently usher or transition readers who steadfastly adhere to Newtonian physics into Relativistic physics.  Can someone clearly articulate the problems with speed beyond c?  John (talk) 19:44, 24 November 2007 (UTC)
thread_title:  Do we need a section on "Problematic Implications of V > c" 

message: a sprinter running 100 meters in 10 secondds  —Preceding unsigned comment added by 209.254.12.73 (talk) 21:38, 26 November 2007 (UTC)
replies: text: Gents, This page is intended for discussion of approaches to improve this article, not general questions and discussions about speed of light.  The[Reference Desk] is available for that.John (talk) 17:58, 27 November 2007 (UTC)
thread_title:  speed 

message: This is from something that we talked about today in my physics class. Please correct me if I'm wrong, or making incorrect assumptions.
If we use the time dilation equation:
T = T ' / sqrt(1-(v2/c2))
And assume that you are traveling at the speed of light. In this case, I am talking about light, so you can consider v=c. This makes the equation inoperable. So could you say that light itself does not have observe time? And that it does not move over time, but instead moves instantaneously? If this is the case, then the little animation showing light moving from the earth to the moon is incorrect. If this assumption that has been made is incorrect, then what really happens with the time dilation for light? —Preceding unsigned comment added by Kurt1288 (talk • contribs)  19:47, November 30, 2007
:The animation is fine. No matter what you would perceive if you could ride a photon, the light's speed in the reference frame of the animation is c and not infinity. Melchoir 01:31, 1 December 2007 (UTC)
replies: text: It would be helpful if you could phrase your thoughts in more concrete terms. What should the animation depict? Melchoir 09:26, 1 December 2007 (UTC)

text: A couple of things, first, the animation is just an animation.  Just as if you were to turn on a flashlight and shine it to a wall, that's the same concept as this little animation.  Second, as far as I know, it is when matter approaches the speed of light that these so called "rules" (originally from special realativity I think) apply. Light itself is Not matter, so light is beyond this restriction that is placed on matter.  Third, special relativity is just a strong human theory.  From other sources, I have heard that it is possible for matter to travel faster than light, and it is done constantly in other places in the universe.  One strong credible source (in my humble opinion) is Mr. L. Ron Hubbard.  Remember, our technology is only a few millineums old,  And we have yet to actually test Einsteins thoery.  Good luck in your physics class.  --DreHectik (talk) 20:47, 27 December 2007 (UTC)
thread_title:  About the Earth to Moon animation 

message: Locally the speed of light is always c but what is the average speed of light for light reaching us from distant stars (if earth based clocks are used)? Far away from stars and galaxies the speed should be higher than in our solar system due to the higher gravitational potential. (I am not interested in effects due to space-curvature or expansion of space just the effect due to gravitational potential) Perhaps there is some number on this speed that could be included in the article.Agge1000 (talk) 15:42, 8 December 2007 (UTC)
thread_title: Speed of light in interstellar space