Talk:Speed of light
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Speed of light in space
I have been trying to find out the speed of light in space as opposed to a vacuum. Since a vacuum should have a temperature of 0 K and space has a temperature of 2.7K, the speed of light should be different for both. So what is the speed of light in space and what factors are involved in its calculation.
- I believe that the the definition of c as the speed of light in a vaccuam refers only to the fact that no matter particles are present in the path of light. Temparature has no part to play here. The speed of light does not depend on temparature.
- NOTE: This does not mean light would travel at the same speed in matter in different temparatures. The temparature affects the density of matter, does affecting the speed pof light. 59.93.161.76 12:06, 28 Mar 2005 (UTC)
History of the measurement of the speed of light (vandalism?)
The first two paragraphs of the "History of the measurement of the speed of light" section are
- The first quantitative estimate of the speed of light is seen in Indian vedic scholar Sayana's commentary on the Rigveda, one of the main Hindu scriptures. It says sun light travels 2202 Yojanas in a half Nimesa. Yojana is an ancient unit of length. Arthasastra defines it as being equal to 8,000 dhanus, which is equivalent to 9 miles. A nimesa is an ancient unit of time that is equal to 16/75 seconds. Thus 2,202 yojanas in half a nimesa is equal to 185,794 miles per second after conversion. The modern estimate of the speed of light is 186,281.7 miles per second.
- It is to be noted that Bhatta Bhaskara (probably in 10th century) made the same statement in his commentary on Taittiriya Brahmana, another Hindu Veda . He says this to be an old tradition.
This sounds pretty suspicous to me. I think that these two paragraphs should be removed (or at least good references should be added). --Jochen 13:46, 15 Mar 2005 (UTC)
- Yes, that was also my first reaction. However, there are quite some references to "2202 yojanas" on the internet, including arXiv e-print physics/9804020 (http://uk.arxiv.org/abs/physics/9804020), a paper by Subhash Kak of Louisiana State University titled "The speed of light and Puranic cosmology". I did not read the paper, but it looks serious to me. -- Jitse Niesen 15:09, 15 Mar 2005 (UTC)
- Your suspicions were justified. The units in question were not the same for all time periods and places, and experts' opinions differ about how long exactly they were.
- [1] (http://1stholistic.com/Prayer/Hindu/hol_Hindu-metrics-of-time.htm) says: one day is 8*6*25*10*5*3 nimesas. Since that is 180.000, a nimesa is 12/25s or 6/25s (if "day" is the bright half only, which is improbable since this would mean half a day has 8 dandas, but all the other sources say half a day is 4 dandas. So I'll ignore this.) Farther down the site says that a nimesa is 16/75s.
- [2] (http://www.indolink.com/Forum/Arts-Culture/messages/5311.html) says that a nimesha is 8/15s, plus, farther down, one "day" (having 12 hours) is either 4*6*15*15*5*3 or 4*7*15*15*5*3 nimeshas.
- Now we got the following nimesha/nimesa candidates:
- 0.213s
- 0.457s
- 0.48s
- 0.533s
- [3] (http://banglapedia.search.com.bd/HT/K_0303.htm) says that experts are divided on the size of a yojana - but it is between 6 and 9 miles. If we assume that this is the international mile, which is 1,6 kilometres (there are several others), then that is between 9,6 and 14,4 km.
- [4] (http://www.nios.ac.in/sc10/ch1sc5.htm) says it is 10 km.
- Finally, [6] (http://www.lovearth.net/108.htm) says that the speed Sayana was talking about was the speed of the sun, not light.
- Combining the possibilities, we get for the speed of the sun:
- 79, 82, 88, 91, 92, 96, 118, 132, 138, 198, 206 oder 297 millions of m/s.
- If we assume a longer or shorter mile, the candidates multiply further.
- This is a typically pseudoscientific pick-and-choose trick. If you are flexible enough you can find lots of such "coincidences". "Speed of sun? surely he means speed of light. Hmm... let's take this yojana and this nimesha, and we are spot on!"
- So Sayana was probably guessing, and he was wrong. Is anybody against deleting the paragraph now? --Hob Gadling 08:25, Mar 17, 2005 (UTC)
- Thanks for the research. Perhaps we should mention that Indian scholars wrote about the "speed of the Sun", but the size of the units is uncertain: for certain sizes of the units, the "speed of the Sun" is uncannily close to the modern definition of the speed of light, but other choices for the units produce a "speed of the Sun" which is different from the speed of light by a factor of up to 3 (4?). -- ALoan (Talk) 11:55, 17 Mar 2005 (UTC)
Hob Gadling's research seems convincing to me, including the conclusion "Sayana was probably guessing, and he was wrong". And 'guesses' about the speed of the sun seem irrelevant for the history of 'measurements' of the speed of light. Therefore I will remove the paragraphs in question. --Jochen 01:10, 19 Mar 2005 (UTC)
According to the standard measurement of yojana and nimesa used by Sayana in his books it is spot on. Even if we ignore that, it is still a valid estimate of the speed (which may have been close by a factor of upto 4). We don't know enough of the history of how he came up with the figure - for all we know it could've been a measurement that was undocumented or lost? I may agree that it may not belong in the 'History of Measurements' section but I find "Sayana was guessing and he was wrong" extremely arrogant. Does a figure like 2202 seem like a 'guess'? and even if he was close by a factor of 4, is it still a guess? In a period where Europe was grasping at theories like - light is due to the presence of something, light has infinite/possibly finite speed - is Sayana not even worth mentioning? (Indian astronomy was too advanced to believe Sayana estimated the sun to travel that fast.)
- You are misquoting Hob Gadling. --Jochen 19:49, 21 Mar 2005 (UTC)
- Indeed. You forget that Sayana was talking about the speed of the sun, not light. Also, what reason do you have for calling the values that lead to the right figure "standard"? On top of that, measurements don't fall from the sky. The first real measurements (Roemer etc.) were widely off, but we know that the method was sound. From Sayana, we don't have any data. No method, no error bars, only a single number given in dubious units and applied to the wrong object.
- Also, "Indian astronomy was too advanced to believe Sayana estimated the sun to travel that fast" is not an argument. Our astronomy is even more advanced, but if you ask an arbitrary non-astronomer, even a very wise one, for the speed of the sun (relative to what, by the way? the next fixed star? the core of our galaxy?), you will earn blank stares or guesses. And: Was Indian language so un-advanced that there was no word for "light"?
- "Does a figure like 2202 seem like a 'guess'?" Then call it a figure derived from numerological fantasies. People are not automatically right about everything just because they are long dead or from far away, or remembered as wise. Newton, Kepler, and Copernicus wrote a lot of gobbledigook, and there is no reason to assume that Sayana was any better.
- Regarding the context of the Sayana quote: There are some people who desperately search the old Indian writings for quotes that allow the interpretation that the writers knew a lot of things Western culture found out only recently. This has yielded lots of fruit. With the type of flexibility I outlined above, this can be done for any other culture, and the same was done for other cultures. According to pseudoscientists, the Parthians had batteries, the Egyptians had lightbulbs (a gift from the aliens), the Greeks had computers, the Africans had everything the Greeks later stole from them, and the Atlanteans invented by Plato had everything else. I guess one of the reasons is that some non-European people want smart ancestors to prove that they are not worse than European people. But they are already not worse. Europe becoming dominant was a coincidence, as Jared Diamond wrote in Guns, Germs, and Steel. Europe was lucky. --Hob Gadling 10:56, Mar 22, 2005 (UTC)
Europe was not just lucky. It also colonized a large part of the world for the last few centuries. In the context of India, the 'declared' intent of it's British colonial rulers was to engineer/perpetrate an 'awe' for European superiority, in order to keep the masses subjugated (not to mention the post-colonial British believed in their superiority). A few narrow-minded missionaries (no offense intended to the religion) also had a vested interest in the same. In addition to impoverishing a wealthy nation, they appropriated and destroyed traditional education systems (which was flourishing by British accounts http://www.swaraj.org/shikshantar/_disc5/00000049.htm) and replaced it with a glorified European version. In other words, they were practising Eurocentrism and had the means to enforce it.
'some non-European people want smart ancestors to prove that they are not worse than European people'
I consider that a biased and simplistic assumption on the intentions of people trying to search for the sciences within their cultures. What non-European cultures are probably seeking is acknowledgment that there are other cultures that have made significant contributions to the sciences. Some Indians atleast are trying to reclaim the science of their ancestors. For an example, see the patent controversy section in Neem.
Some accepted facts:
Around 100 BC (not sure about the 'accepted' dates), India's Taxila University was noted for Science, Medicine (Indian medicine included surgery) and the Arts.
Although the modern study of philosophy is dominated by the Greek Philosophy, Indian philosophy was known to encompass most of that thought and more.
The decimal system, algebra as it's used today originated in India.
- Didn't want to trumpet Indian acheivements but I think I see a condescension in "But they are already not worse."
I performed a random survey on guesses (diff age groups, all college graduates) for the speed of light. I found the following 'guesses' - 15,000 miles/sec, 2800 miles/sec (10 million miles/hour), 36 miles/sec (193,000 ft/sec) and ~2miles/sec (10 times the speed of sound - BTW this was Galileo's guess too). I would encourage you to try it too.
Can you also point me to other 'guesses' from the pre-Roemer days? Gobbledigook is fine too, since what I am attempting to put in this page is alleged to be the 'same'. In the absence of any data, Indians did not make the assumption that he measured it, but you don't hesitate to make the assumption of a numerological fantasy.
Sayana's number has also been validated (units and all) by Subhash Kak, Professor in the Dept of Electrical and Computer Engg in Louisiana State University, if that will lend it any credibility. I believe he mentions that Sayana used the same conversion for yojana & nimesa consistently ('standard') in his book.
And finally, if you read the Wikipedia criticisms on the book you mentioned Guns, Germs and Steel, you will note the charges of racism and also
"It makes little attempt to explain relatively recent geographic transitions in technology, power and wealth; in particular the rise of Europe and the decline of south-west Asia since about 1500 AD." - Pranathi
As an Indian who still lives in India, I will like to add a few words. I believe this discussion has been tainted by the eternal disease of debates, extremism in order to counter-attack. It is not true that aAncient Indians measured things, a guess is far more logical. However, to do this properly you have to understand how most Ancients(of any culture) found their wisdom. When you see a right fact, you tend to assume it was arrived at by following a scientific 'cause-effect' chain. Most of the times this is not true. It is usually a process of trial and error. Ancients did not find the disease-curing capablities of herbs by braking them into their chemical compositin and then studying the effects these chemicals had on cells. They just kept trying herbs at random till they found one that worked. However, dismissing them doesn't do either. I should say that a factor of even 5 in accuracy is remarkable. It has also been mentioned that he talked about the speed of sun. How do we know this? If anyone can give me the original Sanskrit from Rigbed(the first recorded Indian liturature, BTW) then I could check to see what the translation is and if there are any disputes among scholars about the meaning of words. -Molu
Molu, Sayana wrote -
Tathā ca smaryathe yojanānām sahasre dve dve sate dve ca yojane ekena nimishārdhena kramamāna
in his commentary on the 4th verse of the hymn 1.50 of Rgveda on the sun. The verse in the Rgveda does not mention any numbers.
With worst case scenario of #s presented by Hob Gadling, the figure is off by a factor of 3.75. I made it 4 to fend off further arguments and now you made it 5. Let's go back to the 3 :)..
Also, Sayana was from the 14th century - not exactly ancient. If 5th century Aryabhata could give periods of planets wrt the sun, an accurate ratio of earth's rotation to lunar obits etc, is it not possible that him & his successors had gone beyond trial and error? - Pranathi 25th Mar
Two points, Pranathi i)It's just a tiny bit more difficult to measure the speed of light than it is to measure the velocities of massive stellar bodies. Just look at the time europeans found stellar phenomenons and the time when they measured the speed of light with any accuracy. However, it may be possible that Sayana carried out some approximate measurement(such as the gunshot-between-observers-on-hills experiment). ii)Sayana was from the 14th century? Then how possibly did his verse get on the Rigved? Things said by a man as late as the 14th century has no buisness in the Rigvedas. If your time estimation is right, there is the possiblity of Sayanas verses being introduced to the Rigvedas much later by unscruplous priests. Very disturbing! I'll try to resolve whether the verse definitely refers to the sun and to nothing else. 59.93.160.46 17:28, 27 Mar 2005 (UTC)
I am not trying to prove that he measured it, rather I am refusing to make assumptions. I am arguing (to So Sayana was probably guessing, and he was wrong) that a guess not "more" probable than a measurement - not knowing where he got the data from & going by the accuracy of the #. Secondly, Sayana's verse is a commentary on a verse in the Rigveda. It's not a verse in the Rgveda - the original verse has no relation to this topic except that it is in praise of the sun. --Pranathi 21:19, 27 Mar 2005 (UTC)
Oh! I wasn't paying attention, I didn't notice you said commentary. Anyway, without hard facts this discussion is leading nowhere. For all we know, little green aliens from Alpha Centaurio may have come and told the Speed Of Light to Syan!\n59.93.161.76 11:59, 28 Mar 2005 (UTC)
Hello all, sometimes the internet is quite useful: the rig veda is for example at [7] (http://www.sacred-texts.com/hin/rigveda/), Sayana's commentary is at [8] (http://www.srivaishnava.org/scripts/veda/rv/rvtop.htm), so we can actually check what this is all about. Should we? Well, let's see. Verse 1.50 is at [9] (http://www.sacred-texts.com/hin/rigveda/rv01050.htm). It states (relevant verses selected)
- 4 Swift and all beautiful art thou, O Surya, maker of the light, Illuming all the radiant realm.
- 5 Thou goest to the hosts of Gods, thou comest hither to mankind, Hither all light to be beheld.
- 6 With that same eye of thine wherewith thou lookest brilliant Varuna, Upon the busy race of men,
- 7 Traversing sky and wide mid-air, thou metest with thy beams our days, Sun, seeing all things that have birth.
and so on. This is clearly about the sun ("maker of the light", "thy beams"). An alternative translation together with Sayana's commentary is at [10] (http://www.srivaishnava.org/scripts/veda/rv/rvtop.htm):
- 1.050.04 You, Su_rya, outstrip all in speed; you are visible to all; you are the source of light; you shine throughout the entire firmament. [Smr.ti states that the sun moves 2,202 yojanas in a half a winkle of the eye; jyotis.kr.t = giving light to all things, even to the moon and the planets, by night; for, they are of a watery substance from which the rays of the sun are reflected (like a mirror in a door-way reflecting sun's rays, to light up a chamber); metaphysical explanation: sun is the supreme spirit, who enables all beings to pass over the ocean of existence, who is beheld by all desiring final emancipation, who authors true light, and who illuminates everything through the light of the mind].
Again, this is clearly about the sun ("sun's rays", "authors true light"). Why do these "some" think that this would be about the speed of light? The source really only states that the sun moves 2,202 yojanas in half a winkle of the eye. After this, does anybody still think that the paragraph in question really improves an article about the speed of light and should stay in? --Jochen 21:26, 31 Mar 2005 (UTC)
- Yes, I still think it should be mentioned. I think that everybody agrees that verse 1.50.4 of the Rig Veda is about the Sun; the question is what Sayana's comment is about. The translator of the quote that Jochen gave, thinks it is about the speed of the Sun, Kak thinks it is about the speed of light because it would otherwise be inconsistent with what the Indians thought that the distance Earth-Sun is. I do not know the philosophy and physics of that time to gauge the strength of Kak's argument, but he seems a serious scholar and I think his interpretation should be mentioned. -- Jitse Niesen 13:57, 1 Apr 2005 (UTC)
Faster than c : Improper handling
This question has been raised before, but I still feel that it must be raised again. The writer states with assurance that recent experiments have shown group velocities to exceed c. I beg to differ. These experiments are some of the most debated ever in the history of science and many would go as far to question the moral velues and/or sanity of those advocating speeds greater than c. For example, recently the book "Faster Than The Speed Of Light" brought to light the ridicule faced by the author for propounding his theory. Nature even refused to publish his article for proposing something that challenges the foundations of one of the centurys two greatest theories advanced by a man who is often considered the impersonification of mordern physics, not to mention a Nobel laureate. Whether chnges do occur faster than the speed of light in vaccuam is a highly controversial issue and the author has no right to make the unaware reader believe that his next door neighbour regularly exceeds c. I request permission to make some minor changes to the section so the dispute among the scientific community is more clearly reflected.
Recently, some very strong evidence have emerged supporting the almost supernatural byproduct of Quantum Mechanics known as the Doppleganger Effect, the insteanteneous reflection of changes in one particle in another which implies transfer of information(since the state of a particle is definitely information). A compromise used by the Relativists to counter this is that c can not be exceeded in the 4 ordinary dimensions. However information may travel at c through extra dimensions curled up too small to be noticed(10/11 dimensional supergravity) so that it appears to exceed c.
- I am not aware of much controversy surrounding the experiments showing that the group velocity may exceed c. The group velocity is not the velocity of a physical object, hence such experiments do not contradict the relativity theory. The theory mentioned in "Faster than the speed of light" is very different: it does contradict relativity theory and it is not accepted by most scientists. I do not understand which experiments you are referring to in your second paragraph, but I guess it has something to do with quantum entanglement.
- You do not need any permission to change the article, you can just go ahead and change it. However, be prepared that your changes may be undone; in fact, this is quite likely if you don't support it by references to the literature. -- Jitse Niesen 20:07, 25 Mar 2005 (UTC)
Ancient theory: light is emitted from the eye
From the article: "One of the ancient theories of vision is that light is emitted from the eye, instead of being reflected into the eye from another source.*
How did this theory explain darkness? --Lakefall 18:24, 10 Apr 2005 (UTC)
- Dunno, but maybe that's why it's not so popular anymore. Wile E. Heresiarch 00:08, 11 Apr 2005 (UTC)
- Obviously it isn't popular, but I just wonder how anyone, no matter how ancient, could have come up with a theory about light, which doesn't explain darkness. So I suppose either it did try to explain darkness somehow or their concept of "light" didn't have anything to do with luminance. In the latter case they weren't even talking about the same light we are, but rather about the speed of vision or something like that. --Lakefall 18:24, 12 Apr 2005 (UTC)
- Actually, the Greek idea was pretty insightful as a theory of visual perception, since it addressed the question of how something can be overlooked for a while but be seen when looked for. An awful lot of seeing happens in the brain -- an active process, not a passive one. Hunter 23:05, 17 Apr 2005 (UTC)
- If light came from the eye, then looking into a mirror would make you blind. Ancient "theories" are generally bullshit. --Kvuo 00:44, 4 Jun 2005 (UTC)
- Hey, it seemed obvious with the available evidence they had at the time... I suspect they treated colours, brightness and so on as intrinsic properties of items, and considered light as something that went from your eye, sniffed out the state of the colour variable, and then reported back appropiately.--Fangz 15:40, 4 Jun 2005 (UTC)
"Einstein's constant"
Hello everyone. The intro says that c is called "Einstein's constant". I don't remember ever seeing that usage in any physics book or article. The term seems to be associated with a certain Kenneth Brecher; see for example [11] (http://newton.ex.ac.uk/aip/physnews.484.html). Maybe we can move "Einstein's constant" out of the intro and into some section farther down; the term doesn't get enough traction, sfaict, to warrant mention right at the top. Anyone want to weight in here? Regards & happy editing, Wile E. Heresiarch 00:08, 11 Apr 2005 (UTC)
Measurement of the Speed of Light - Ole Rømer
Rømer observed that Io revolved around Jupiter once every 42.5 hours when Earth was closest to Jupiter. He also observed that, as Earth and Jupiter were moving apart, Io's revolution seemed to take longer.
This statement is ambiguous because it implies that the movement of the Earth away from Jupiter is what makes Io's observed orbital period longer. The Speed of Light in a vacuum is constant and not affected by the movement of the observer or the subject.
Rømer made his observations by taking a previously measured time for Io's orbit about Jupiter, and making a schedule so he could observe the eclipses. He noted that Io was eclipsed earlier than the schedule predicted when the Earth was close to Jupiter, but was late when it was far away. Therefore, whether the Earth was moving toward or away from Jupiter was largely irrelevant, it was their distance apart and its affect on his schedule that he observed and measured.
- Good point, we should clear up that ambiguity. Please feel free to adjust the text accordingly if you have not already done so. Regards & happy editing, Wile E. Heresiarch 14:11, 12 Apr 2005 (UTC)
Roemer time-lag not similar to Doppler effect
From the article (about Roemer's detection of a variable time-lag in the occultations of Io): "These observations are akin to what today is known as the Doppler effect."
This statement is not correct. It is not the relative velocity of the two systems (Earth and Jupiter/Io) that is causing the time offset, but instead simply the distance between them, combined with the finite speed of light.
Reference to a Doppler effect is undesirable in this astronomical situation because of the potential for confusion with red shift (which is precisely a Doppler effect) or with the aberration effect that Bradley used for this purpose (which could reasonably be said to be akin to the Doppler effect, since both are velocity-based).
The effect is more like echolocation, or perhaps a closer analogy would be the determination of the speed of sound by measuring the differences in thunder delays between lightning flashes to points at known distances. But I do not see an analogy close enough that I think it enhances the article. Hunter 23:10, 17 Apr 2005 (UTC)
Relativity in Quran
I deleted the link Relativity in Quran (Islam) (http://islam.speed-light.info/relativity_quran.htm) because the explanation on that page is not sound. Specifically (this probably does not make sense unless you read the web page), even if the interpretation of Quran 32.5 that light travels the same distance in one day as the moon in 12000 orbits is correct, the distance travelled by the moon in one period is not computed correctly. The page says that the moon travels 3682.092 km/hr relative to the earth, and finds via an unintelligible reasoning that you have to multiply this number with 0.8915645 to get the speed outside gravitational fields, "relative to the stars". I don't know what exactly they mean with this phrase, but if it's relative to the centre of the Milky Way, then this is clearly incorrect since the sun travels with the much higher speed of 217 km/s (see Sun). -- Jitse Niesen 14:55, 26 Apr 2005 (UTC)
Communications "Beam of Light" Image
A few days ago I removed the animated image in the "Communication" section (See here). It's being animated adds very little information, in fact seems to add nothing, and is also animated on a fast loop, making it very distracting whilst attempting to read text around it. I removed it stating the reason, and suggested that it be replaced by a static version if it must be in there. Perhaps a static step-by-step image (i.e. in the style of a) signal sent out b)signal reflected etc ). Either way, It really doesn't need to be animated.
It was reverted the next day by the images author, for the reason "revert removal" - which suggests to me was purely for vanity reasons. What do people think? Does it add anything to the article being animated and does anyone else think it is a distraction? If there are no objections I'll remove it again in a couple of days with a note to the effect. - Xgkkp 18:58, 3 Jun 2005 (UTC)
- The dimensions of the Earth, the Moon and the distance between them are proportional to the real world but on a smaller scale. And the beam of light is animating at approximately the same speed a beam of light travels the Earth to the Moon in the real world. That's why it is crucial this image is animated. That's the whole point. Perhaps this could be made clearer in the image's caption. This is not a vanity issue. —Cantus…☎ 19:37, Jun 3, 2005 (UTC)
- On such a tiny scale, I really doubt that relative sizes matters. Also I'd be hesitant to suggest that people can't imagine/understand what the phrase "Houston had to wait nearly 3 seconds" means in the preceeding paragraph. Why couldn't it be a static image with the relative sizes? Xgkkp 19:53, 3 Jun 2005 (UTC)
- Yeah, that was pretty obvious I thought. I think it should have a static version in the article that links to the animated version, like a thumbnail links to a large version. - Omegatron 19:53, Jun 3, 2005 (UTC)
- This does seem like a good solution Xgkkp 17:49, 4 Jun 2005 (UTC)
- For what it's worth, I find the animated image useless and distracting, and I can't see the point of linking a noninformative static image to a noninformative animation. Why can't we just erase the image in question altogether? Wile E. Heresiarch 02:05, 5 Jun 2005 (UTC)
I turned the "distracting" animation into a link. This should hopefully solve the issue for everybody. —Cantus…☎