Wang / Sagnac Devices
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From: doug on 22 Oct 2009 21:35 Jonah Thomas wrote: > doug <xx(a)xx.com> wrote: > >>Jonah Thomas wrote: >> >>>"Androcles" <Headmaster(a)Hogwarts.physics_p> wrote: > > >>>>The bigot Tom Roberts stops looking at the beamsplitter and says >>>>emission fact can't work because there is no phase shift at the >>>>beamsplitter, but Sagnac doesn't have a detector at the >>> >>>beamsplitter,>the camera is actually off the turntable. >>> >>>> http://commons.wikimedia.org/wiki/File:Sagnac-Interferometer.png. >>> >>>I see your picture appears to put the detector at the edge of the >>>turntable and hanging over the edge. Did they really do it with the >>>detector not moving? That would be a very interesting result. >>> >>>I see now why you want to look at the phase shift after the >>>beamsplitter. In that picture, the distance traveled after the >>>beamsplitter is a little bigger than the radius of the platform, and >>>more than a quarter of the distance the light travels in opposite >>>directions. Sure, that's enough to make a difference if the light is >>>getting out of phase over that distance. It doesn't look obvious to >>>me why the effect for that linear distance would be proportional to >>>the speed of the rotation, though. > > > The problem is, if Sagnac is a special case of Wang, then the phase > shift is propotional to two things -- the speed that the detector moves, > and also the length of the path in the direction of movement. The latter > has no necessary relationship to the length of the beamsplitter. What > happens inside the beamsplitter is a confounding variable. It can be > varied independent of the factors people believe in, and it is not > observed to cause results that vary from the factors people believe in. > So it cannot be the whole Sagnac effect and probably does not happen or > the experiments are controlling for it. Because otherwise it would be a > source of variation that is not actually observed. > > >>>After all, in the same diagram the direction of the light source is >>>shown. It not quite tangent to the circle, facing backward. So >>>according to emission theory, why would we expect the light to >>>travel at c+v anywhere in this apparatus? The light will start out >>>traveling a little faster than c-v. Unless the mirrors and lenses >>>and such change that speed, it will keep that same speed all the way >>>around the mirrors in both directions and past the beam-splitter and >>>into the interferometer. Whatever argument works to explain the >>>Sagnac effect for other theories of light, would explain it for >>>emission theory at least for this case. >>> >>> >>> >>>>So even if you and Jonah Thomas are taken in by his prejudice in >>>>favour of SR, he's really just another incompetent babbling fool >>>>and isn't knowledgeable at all. He's never read Einstein's paper, >>>>he advocates "Spacetime Physics", a crappy publication that >>>>skips over Einstein's faulty math. >>> >>>I wouldn't recommend that people read Darwin to understand >>>evolution. If Einstein had bad math and somebody since has fixed it >>>up, that's just fine. After all, it took hundreds of years for >>>mathematicians to fix the holes in Newton's calculus. If they >>>haven't fixed up Einstein's stuff but just made it harder to see the >>>holes then boo. >>> >> >>Remember that you are talking to Androcles, the retired almost >>engineer who has his hatred of Einstein to keep him going. >>He has no clue what relativity is about but he knows that he >>does not like it. Einstein's work is now presented differently >>than it was a century ago but the basis is the same and it needed >>no fixing up. There is also the century of experiments which all >>support it. > > > When I started to pay attention to problems in Einstein's original paper > various people pointed me to a later Einstein paper which they said was > better written and which cleared things up. If we've had a hundred years > to learn better how to derive SR and how to teach it, and we are no > better than Einstein in 1920, then something is very wrong. Your ignorance of the science of the last century is not a problem with science. Study some of it. > > In the last hundred years explanations have been found for the various > self-contradictions and failures of SR, so the problems have either been > fixed or covered over. There are no contradictions or failures of SR in its domain of applicability. There was nothing to fix. There's no need to pretent there were never any > problems if the problems have been resolved. Point out a problem is you think there was one?
From: Darwin123 on 22 Oct 2009 20:55 On Oct 21, 11:11 am, Darwin123 <drosen0...(a)yahoo.com> wrote: > On Oct 19, 8:13 pm, Jonah Thomas <jethom...(a)gmail.com> wrote: > > > Darwin123 <drosen0...(a)yahoo.com> wrote: > There is an effect in Sagnac cavities where the nodes and the > antinodes are locked in place by hysteresis in the metal reflectors. > The Sagnac effect vanishes when this happens. I read an article > describing what causes it and how to remediate it. This is a material > property, and is considered a defect in the apparatus. If metals > didn't have hysteresis type properties, it wouldn't happen. This hysteresis effect is caused by surface plasmons. Hence, it is an effect restricted to metallic mirrors. The microscopic details of the Sagnac experiment are interesting. However, they are unnecessary for understanding relativity. The kinematics of relativity are scale invariant. The constitutive properties of the materials are not scale invariant. I think what Wang was a bit naive. Basically, he discovered that the introductory textbooks don't discuss many interesting details of the Sagnac cavity. However, I don't think he discovered a violation of relativity. He discovered optical engineering.
From: Jonah Thomas on 22 Oct 2009 22:49 "Inertial" <relatively(a)rest.com> wrote: > "Jonah Thomas" <jethomas5(a)gmail.com> wrote > [snip] > >> >> >> >>Doppler shift is a change in observed frequency. > > No, the formula gives a definition. The vague descriptions do not. > > You seem confused by the concept of a definition for a term (ie what > the phrase means), and a formula that gives a value for it (ie how to > calculate the value for it). > > You need to have both, of course. You need to know how to calculate > the value in specific instance .. and you need to know what the value > you just calculated actually means. Sure, but what it means *is* how you measure it. You can come up with theories to explain it that are compatible with the measurements, but the actual definition of each term *is* what you do to find it. The theoretical explanations are secondary. > >> Regardless .. Doppler shift is an effect on the observed wavelength > >> and/or frequency due to motion of source and/or observer. For > >light> in SR (and as observed) one only needs to consider the > >relative motion> of source and observer, and both wavelength and > >frequency are> affected. > > > > If the speed of the wave is constant, then both wavelength and > > frequency have to be affected. > > Maybe .. maybe not. For light, according to SR, yes By definition, if speed equals wavelength times frequency. > > If the wavelength is constant then speed and > > frequency have to be affected. > > All that follows form the relationship between frequency, wavelength > and speed, of course. Yes, exactly. > > It depends. > > Exactly .. it does all depend .. which is why I have described it as > above. > > Saying Doppler shift is just an effect on frequency (as you did > originally) is misleading. It can also affect wavelength. Which is > why is the point I was trying to make. If it's defined on frequency and you extend it to wavelength, you are making implicit assumptions. You'll get correct results as long as those assumptions hold up. > Perhaps rather than "Or wavelength .. Or both" I should have more > correctly said "or both frequency and wavelength" .. as Doppler will > always affect frequency, but may or may not affect wavelength. That's how I'm thinking of it right now. Given a medium which controls the speed of the waves, doppler must affect both. Without a medium all bets are off but doppler might easily still affect both.
From: bz on 22 Oct 2009 22:32 tominlaguna(a)yahoo.com wrote in news:bqs0e5lqmuqtjqft1lvurh8ui21i974qp0@ 4ax.com: > Almost correct. For example, in the situation where a mirror is > moving normally toward a source at velocity v, the mirror will > experience the light as arriving at c + v. Upon reflection, the light > will be traveling at c + 2v with respect to the source; and, as you > state, at c + v with respect to the mirror. Easily tested by experiment: a) Two parallel mirrors, moving toward and away from each other (one attached to the voice coil of a loud speaker, or plated onto a surface of a quartz crystal). b) laser beam bouncing back and forth between the mirrors many times. If the bounce is n times, then the final velocity of the light exiting from the pair of mirrors should be c+n*v and c-n*v Should be an easy 'high school physics lab' test. If you demonstrate light is ballistic, you will earn a nobel prize. From a previous post of mine, several years ago [paraphrased] At 10000 cm/s peak rate of motion for the mirror (447 mph), and aiming for c+/- 1%, we need 1.5e4 reflections. Keep the mirrors close together, lets say 0.1 cm (about 40/1000 th of an inch, the path length would be about 15 meters. Over that distance, the beam divergence for a good laser should be small enough to allow such an experiment, making sure we have the right reflection at the output end, if our laser beam is about 0.01 mm in diameter, we need mirrors that are about 15 cm long. I don't see any reason that experiment can not be done. [unparaphrased] So, you just need to send pulses through the pair of mirrors, and measure the speed of the output pulse by seeing how long it takes to go by two detectors spaced a known distance apart. A +/- 1% variation in the speed of light should be rather noticable. Good luck. -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set.
From: Jonah Thomas on 22 Oct 2009 23:00
doug <xx(a)xx.com> wrote: > Jonah Thomas wrote: > > When I started to pay attention to problems in Einstein's original > > paper various people pointed me to a later Einstein paper which they > > said was better written and which cleared things up. If we've had a > > hundred years to learn better how to derive SR and how to teach it, > > and we are no better than Einstein in 1920, then something is very > > wrong. > > > > In the last hundred years explanations have been found for the > > various self-contradictions and failures of SR, so the problems have > > either been fixed or covered over. > > There are no contradictions or failures of SR in its domain of > applicability. There was nothing to fix. > > There's no need to pretent there were never any > > problems if the problems have been resolved. > > Point out a problem is you think there was one? To you? Whatever for? You would deny it and argue that it never existed, you would misunderstand and confuse the issue. I have better things to do than argue with fanatics. And anyway it's of purely historical interest. Einstein's mistakes are no more important than Darwin's mistakes or Newton's mistakes provided they've been fixed. |