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文章評論 |
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作者：stinger |
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留言時間：2012-02-27 09:39:45 |
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Wudaxiong,
I basically said that you ARE a real scientist! If Star-wing denies you again I will fight for your reputation!
This stupid website has tons of problems, but Zhuang Rui said no problem! I could not even click the simplified Chinese button - always give me an error!
Hats Off! |
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作者：stinger |
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留言時間：2012-02-27 09:35:28 |
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き
这?#35748;痷и常ぃ種狦琍ò说い国没Τ学產и璶蠢诅〨
http://dingo.care2.com/photos/1/1694a.gif |
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兔子老兄，抱歉上文的回帖有計算錯誤，我把距離差當作光線傳播的總距離來算了。正確的計算過程如下。
假定圓盤周長3米，轉動速度是1米/秒。
則，光線走過3米距離所要的時間為 3/3E8 = 1.E-9 秒。
在這個時間段內，圓盤轉動距離大約是 1*1E-8 = 0.01微米。也就是說，順着轉動方向行進的光線比逆向行進的光線多走大約0.02微米的距離。
所以，如果用光纖作試驗，纏繞10圈左右，其距離差就會達到0.2微米，這個距離對可見光來說(波長0.5微米)，足以產生干涉效應
更一般性的計算公式參見 http://en.wikipedia.org/wiki/Sagnac_effect
以上的解釋建立在光速不變的假設之下，結論與特殊相對論的預測相符，看來並沒有什麼問題。
真正的問題，也是長久以來爭論不休的問題，是這樣的。
假如有一輛高速行進的列車，一個人站在列車中央，同時向前後發出光線，他看到的應該是光線同時到達車頭和車尾。而站台上的人呢，看到的則是光線先到達車尾後到達車頭，這就是特殊相對論。
依此原理，如果一個人站在旋轉圓盤上，在他看來，兩束光線的傳播距離是相等的，因此不應該產生相位差。這就似乎和特殊相對論的預測結果不符。
對於這個矛盾，人們解釋說，旋轉圓盤坐標系不是慣性系，因此特殊相對論已經不適用，需要用一般相對論，考慮加速度效應來解釋，但具體的定量計算結果仍很難得出。 |
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作者：stinger |
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留言時間：2012-02-27 08:06:19 |
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MichelsonGalePearson experiment
From Wikipedia, the free encyclopedia
The MichelsonGalePearson experiment (1925) is a modified version of the Michelson-Morley experiment and the Sagnac-Interferometer. It measured the Sagnac effect due to Earth's rotation, and thus tests the theories of special relativity and luminiferous ether along the rotating frame of Earth.
[edit]Experiment
The aim, as it was first proposed by Albert Abraham Michelson in 1904 and then executed in 1925, was to find out whether the rotation of the Earth has an effect on the propagation of light in the vicinity of the Earth.[1][2] [3] The Michelson-Gale experiment was a very large ring interferometer, (a perimeter of 1.9 kilometer), large enough to detect the angular velocity of the Earth. Like the original Michelson-Morley experiment, the Michelson-Gale-Pearson version compared the light from a single source (carbon arc) after travelling in two directions. The major change was to replace the two "arms" of the original MM version with two rectangles, one much larger than the other. Light was sent into the rectangles, reflecting off mirrors at the corners, and returned to the starting point. Light exiting the two rectangles was compared on a screen just as the light returning from the two arms would be in a standard MM experiment. The expected fringe shift in accordance with the stationary aether and special relativity was given by Michelson as:
where is the displacement in fringes, A the area in square kilometers, ϕ the latitude (41 46'), c the speed of light, the angular velocity of Earth, the effective wave-length used. In other words, this experiment was aimed to detect the Sagnac effect due to Earth's rotation.[4][5]
[edit]Result
The outcome of the experiment was that the angular velocity of the Earth as measured by astronomy was confirmed to within measuring accuracy. The ring interferometer of the Michelson-Gale experiment was not calibrated by comparison with an outside reference (which was not possible, because the setup was fixed to the Earth). From its design it could be deduced where the central interference fringe ought to be if there would be zero shift. The measured shift was 230 parts in 1000, with an accuracy of 5 parts in 1000. The predicted shift was 237 parts in 1000. According to Michelson/Gale, the experiment is compatible with both the idea of a stationary ether and special relativity.
As it was already pointed out by Michelson in 1904, a positive result in such experiments contradicts the hypothesis of complete aether drag. On the other hand, the stationary ether concept is in agreement with this result, yet it contradicts (with the exception of Lorentz's ether) the Michelson-Morley experiment. Thus special relativity is the only theory which explains both experiments[6]. The experiment is consistent with relativity for the same reason as all other Sagnac type experiments (see Sagnac effect). That is, rotation is absolute in special relativity, because there is no inertial frame of reference in which the whole device is at rest during the complete process of rotation, thus the light paths of the two rays are different in all of those frames, consequently a positive result must occur. It's also possible to define rotating frames in special relativity (Born coordinates), yet in those frames the speed of light is not constant in extended areas any more, thus also in this view a positive result must occur. Today, Sagnac type effects due to Earth's rotation are routinely incorporated into GPS.
[edit]References
^ Michelson, A.A. (1904). "Relative Motion of Earth and Aether". Philosophical Magazine 8 (48): 716719.
^ Michelson, A. A. (1925). "The Effect of the Earth's Rotation on the Velocity of Light, I.". Astrophysical Journal 61: 137. Bibcode 1925ApJ....61..137M. doi:10.1086/142878.
^ Michelson, A. A.; Gale, Henry G. (1925). "The Effect of the Earth's Rotation on the Velocity of Light, II.". Astrophysical Journal 61: 140. Bibcode 1925ApJ....61..140M. doi:10.1086/142879.
^ Anderson, R., Bilger, H.R., Stedman, G.E. (1994). "Sagnac effect: A century of Earth-rotated interferometers". Am. J. Phys. 62 (11): 975985. Bibcode 1994AmJPh..62..975A. doi:10.1119/1.17656.
^ Stedman, G. E. (1997). "Ring-laser tests of fundamental physics and geophysics". Reports on Progress in Physics 60 (6): 615688. Bibcode 1997RPPh...60..615S. doi:10.1088/0034-4885/60/6/001.
^ Georg Joos: Lehrbuch der theoretischen Physik. 12. edition, 1959, page 448 |
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作者：stinger |
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留言時間：2012-02-27 07:51:53 |
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Reference:
Sagnac effect
In 1913, Georges Sagnac showed that if a beam of light is split and sent in two opposite directions around a closed path on a revolving platform with mirrors on its perimeter, and then the beams are recombined, they will exhibit interference effects. From this result Sagnac concluded that light propagates at a speed independent of the speed of the source. The motion of the earth through space had no apparent effect on the speed of the light beam, no matter how the platform was turned. The effect had been observed earlier (by Harress in 1911), but Sagnac was the first to correctly identify the cause.
This Sagnac effect (in vacuum) was theoretically predicted by Max von Laue already in 1911. He showed that such an effect is consistent with stationary ether theories (such as the Lorentz ether theory) as well as with Einstein's theory of relativity. It is generally taken to be inconsistent with a complete ether drag; and also inconsistent with emission theories of light, according to which the speed of light depends on the speed of the source. |
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作者：stinger |
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留言時間：2012-02-27 05:12:45 |
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五大兄，
謝謝你！
我似乎覺得這就是光速可變和以太存在的證據了。但我沒有足夠的技術知識說明。 |
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這是個有意思的話題。
純粹按照光速來算，兩條光線繞一圈走過的距離如果產生干涉效果(可見光波長為0.5微米左右)，其時間差為1E-14 sec, 在這個時間內圓盤轉動的位移顯然小於0.5微米。因此不是牛頓力學能解釋的。
由於這是一個非慣性系統，光速在不同系統間切換時可能產生因加速度而導致的相對論效應。當然我也沒法解釋清楚，值得繼續思考。 |
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作者：stinger |
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留言時間：2012-02-26 21:53:11 |
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FYI：
＂Sagnac 效應可以說是物理學上饒有興趣的一個課題。一方面它的實驗事實既簡單又肯定，沒有人懷疑過；另一方面它的理論解釋卻是爭論了近百年的問題，現在也沒有停止。所以 Vigier稱它為物理學一個沒解決的基本問題[9]。
不少著名科學家都參加了對 Sagnac 效應的討論，如朗之萬[10]、朗道[11]、楊振寧[12]和 Vigier[9] 等。而它的理論解釋有經典理論（以太論）、狹義相對論、廣義相對論、Doppler 效應等不下十多種[13]。其中最簡單、最直接的解釋無疑是經典理論，即光速隨接收器運動而變化。另一個比較被接受的是朗道的由於牽涉到旋轉的廣義相對論的解釋。朗道提到象在一切穩定場中一樣，在旋轉物體上的鐘不可能在所有點都被單值地校準。當沿着任何封閉曲線進行鐘的校準並回到出發點時，我們得到一個時間，這個時間與原來的時間的差值就是 Sagnac 效應.＂ |
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作者：stinger |
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留言時間：2012-02-26 21:50:15 |
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五大兄，
先謝你前來！
我同意哪個力無關。
但你解釋光的干擾變化是由於二個方向走的光距離不同？這有問題了。
首先，光速一秒鐘饒地球七圈半，這麼點差距怎麼可能量的出來？
其次，光源不論在哪，速度不變。你的話隱含承認伽里略變換。
最後，這個現象的解釋百年來有十多種，從來沒統一過，包括很多明人的。你如何解釋你的如此肯定結論？
商榷 |
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Criolis力是另外一種效應，與此無關，因為光子無質量。 |
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鏡子轉動起來後，正向光線和逆向光線走過的距離是不相等的，所以產生相位差和干涉效應。 |
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作者：stinger |
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留言時間：2012-02-26 20:37:08 |
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http://zh.wikipedia.org/wiki/%E7%A7%91%E9%87%8C%E5%A5%A5%E5%88%A9%E5%8A%9B |
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作者：Rabbit |
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留言時間：2012-02-26 20:22:24 |
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