|
|
|
|
|
 |
文章评论 |
 |
|
|
作者：stinger |
|
留言时间：2012-02-27 09:39:45 |
|
|
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! |
|
|
|
作者：stinger |
|
留言时间：2012-02-27 09:35:28 |
|
|
き
这�认痷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 |
|
|
|
兔子老兄，抱歉上文的回帖有计算错误，我把距离差当作光线传播的总距离来算了。正确的计算过程如下。
假定圆盘周长3米，转动速度是1米/秒。
则，光线走过3米距离所要的时间为 3/3E8 = 1.E-9 秒。
在这个时间段内，圆盘转动距离大约是 1*1E-8 = 0.01微米。也就是说，顺着转动方向行进的光线比逆向行进的光线多走大约0.02微米的距离。
所以，如果用光纤作试验，缠绕10圈左右，其距离差就会达到0.2微米，这个距离对可见光来说(波长0.5微米)，足以产生干涉效应
更一般性的计算公式参见 http://en.wikipedia.org/wiki/Sagnac_effect
以上的解释建立在光速不变的假设之下，结论与特殊相对论的预测相符，看来并没有什么问题。
真正的问题，也是长久以来争论不休的问题，是这样的。
假如有一辆高速行进的列车，一个人站在列车中央，同时向前后发出光线，他看到的应该是光线同时到达车头和车尾。而站台上的人呢，看到的则是光线先到达车尾后到达车头，这就是特殊相对论。
依此原理，如果一个人站在旋转圆盘上，在他看来，两束光线的传播距离是相等的，因此不应该产生相位差。这就似乎和特殊相对论的预测结果不符。
对于这个矛盾，人们解释说，旋转圆盘坐标系不是惯性系，因此特殊相对论已经不适用，需要用一般相对论，考虑加速度效应来解释，但具体的定量计算结果仍很难得出。 |
|
|
|
作者：stinger |
|
留言时间：2012-02-27 08:06:19 |
|
|
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 |
|
|
|
作者：stinger |
|
留言时间：2012-02-27 07:51:53 |
|
|
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. |
|
|
|
作者：stinger |
|
留言时间：2012-02-27 05:12:45 |
|
|
五大兄，
谢谢你！
我似乎觉得这就是光速可变和以太存在的证据了。但我没有足够的技术知识说明。 |
|
|
|
这是个有意思的话题。
纯粹按照光速来算，两条光线绕一圈走过的距离如果产生干涉效果(可见光波长为0.5微米左右)，其时间差为1E-14 sec, 在这个时间内圆盘转动的位移显然小于0.5微米。因此不是牛顿力学能解释的。
由于这是一个非惯性系统，光速在不同系统间切换时可能产生因加速度而导致的相对论效应。当然我也没法解释清楚，值得继续思考。 |
|
|
|
作者：stinger |
|
留言时间：2012-02-26 21:53:11 |
|
|
FYI：
＂Sagnac 效应可以说是物理学上饶有兴趣的一个课题。一方面它的实验事实既简单又肯定，没有人怀疑过；另一方面它的理论解释却是争论了近百年的问题，現在也没有停止。所以 Vigier称它为物理学一个没解决的基本问题[9]。
不少著名科学家都参加了对 Sagnac 效应的讨论，如朗之万[10]、朗道[11]、杨振宁[12]和 Vigier[9] 等。而它的理论解释有经典理论（以太论）、狹义相对论、广义相对论、Doppler 效应等不下十多种[13]。其中最简单、最直接的解释无疑是经典理论，即光速隨接收器运动而变化。另一个比较被接受的是朗道的由于牽涉到旋转的广义相对论的解释。朗道提到象在一切稳定场中一样，在旋转物体上的钟不可能在所有点都被单值地校准。当沿着任何封闭曲线进行钟的校准並回到出发点时，我们得到一个时间，這个时间与原來的时间的差值就是 Sagnac 效应.＂ |
|
|
|
作者：stinger |
|
留言时间：2012-02-26 21:50:15 |
|
|
五大兄，
先谢你前来！
我同意哪个力无关。
但你解释光的干扰变化是由于二个方向走的光距离不同？这有问题了。
首先，光速一秒钟饶地球七圈半，这么点差距怎么可能量的出来？
其次，光源不论在哪，速度不变。你的话隐含承认伽里略变换。
最后，这个现象的解释百年来有十多种，从来没统一过，包括很多明人的。你如何解释你的如此肯定结论？
商榷 |
|
|
|
Criolis力是另外一种效应，与此无关，因为光子无质量。 |
|
|
|
镜子转动起来后，正向光线和逆向光线走过的距离是不相等的，所以产生相位差和干涉效应。 |
|
|
|
作者：stinger |
|
留言时间：2012-02-26 20:37:08 |
|
|
http://zh.wikipedia.org/wiki/%E7%A7%91%E9%87%8C%E5%A5%A5%E5%88%A9%E5%8A%9B |
|
|
|
作者：Rabbit |
|
留言时间：2012-02-26 20:22:24 |
|
|
|
|
