Speed of Light: A universal Constant?
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From: Henri Wilson on 16 Apr 2005 17:31 On Sat, 16 Apr 2005 09:52:32 +0100, "George Dishman" <george(a)briar.demon.co.uk> wrote: > >"Henri Wilson" <H@..> wrote in message >news:tn8161hfhml9om3ec4sdat9a4bsgt22aqt(a)4ax.com... >> On Fri, 15 Apr 2005 14:26:34 +0100, "George Dishman" >> <george(a)briar.demon.co.uk> >> wrote: >... >>>The fringes don't move during rotation. For any >>>given speed, there is a fixed phase difference >>>introduced by the mechanism I illustrated. That >>>gives some pattern of fringes. If you then >>>rotate at a different (but still constant) >>>speed, that will give a different (but still >>>constant) phase shift, and hence it will also >>>give a static pattern of fringes but they will >>>have moved compared to the first pattern. >> >> well how can the thing be used to measure total rotation angle? >> Don't tell me the fringe movement is sensitive enough to involve >> an integration over time? > >That's right. That's why it they have only >become feasible with modern optical components >special fibre materials and digital integration. >Counters don't drift ;-) OK, let's say half a fringe deflection corresponds to a rotational speed of 1 degree per hour. The instrument reading fluctuates between between 0.4 and 0.6 of a fringe shift over a period of a 30 minutes. How much has the thing rotated at the end of that period? If 100 fringes corresponded to say 1 degree per hour then it might be possible to produce accurate results but is that the kind of movement you get? > >> That couldn't posibly produce the accuracies obtained by these >> gadgets. > >Most people take the technology for granted, >it's only when you look inside that you get >an idea of the problems had to be overcome. > >>>The relationship predicted by SR is that the >>>phase difference is proportional to the angular >>>speed, hence the displacement of the fringes is >>>also proportional to the speed. >> >> Well I reckon that is also the case using the ballistic principle. > >Yes, I said so two sentences below ... > >>> The fringes >>>would move at a constant rate for constant >>>angular acceleration. >> >> Yes. That is correct,,,which makes it pretty hard to calculate the >> total rotation over a long time period. > >Hard, but not impossible. That is the source >of one of the key specifcations. If you look >on the KVH site, the "TG-6000 IMU" is spec'd >at 10 degrees per hour drift while the others >are 1 degree per hour at constant (room) >temperature. > >>>The same arguments would apply to a Ritzian >>>version qualitatively, the only difference >>>being that the constant of proportionality >>>should be zero because the speed imparted due >>>to the motion of the source cancels the change >>>of path length. That is what I think you will >>>try to address. >> >> No, I say there is still a path length difference due to the >> different angles at each reflection.. > >Yes, I meant you will be addressing the zero >coefficient. Angles and speeds would be >aspects you could consider in solving that. OK, I'll keep working on it. > >George > HW. www.users.bigpond.com/hewn/index.htm Sometimes I feel like a complete failure. The most useful thing I have ever done is prove Einstein wrong.
From: Jim Greenfield on 16 Apr 2005 19:06 "George Dishman" <george(a)briar.demon.co.uk> wrote in message news:<d3qkqn$luu$1(a)news.freedom2surf.net>... > "Henri Wilson" <H@..> wrote in message > news:748161p3j4p7o776a6q3uq1ddlf7adi1l8(a)4ax.com... > > On Fri, 15 Apr 2005 15:32:14 +0100, "George Dishman" > > <george(a)briar.demon.co.uk> > > wrote: > >>1879 and 1926, Michelson In the famous experiment where Michelson measured the speed of light, his source was stationary, and frequency or wave lengths were not considered at all. A similar experiment, using the exact same principals, but with the source moving, has NEVER been done (vacuum). And until it is, c'=c+v will NOT be falsified (or afterwards) > >> > >>http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html > Back at the start of this conversation you > said of SR supporters: > > ----- Original Message ----- > From: "Henri Wilson" <H@..> > Newsgroups: sci.physics.relativity,sci.physics,sci.astro > Sent: Tuesday, March 22, 2005 11:24 PM > Subject: Re: Speed of Light: A universal Constant? > > > > You will find that whenever they cannot answer a difficult question, they > > will > > either resort to abuse and ridicule (...you don't understand relativity!) > > or > > they will disappear from the thread. > > I hope you consider this a "difficult question" > for supporters of ballistic light models. > However, if you "disappear from the thread" to > work on the VB program or solving the problem > I won't hold it against you ;-) (for Henri) I tried to email you privately, but am blocked. George and I have discussed his sagnac at length, and I arrived at position as follows: My understanding of George's arguement is that the point of interference changes, which is the basis on which the machine works, due to a change of time for the photons to complete their circuit(s), which is produced by the rotation of the plane. (OK so far, G?) But velocity is ALSO a factor of time, so it is a matter of INTERPRETATION only, as to whether time changes, or velocity does! I think that if G wishes to argue otherwise, he is defacto introducing the assumption that the DISTANCE factor in velocity altered also. That would be an unacceptable assumption to make George- to use postulates of SR to show SR correct ;-( So sleep tight, Henri, and leave G some free time to work on his animation which will show how time dilation occurs! Cheers George Jim G c'=c+v
From: bz on 16 Apr 2005 21:01 H@..(Henri Wilson) wrote in news:sh0361pepm96fke2tvbim51f1ftv4ntja9(a)4ax.com: > OK, let's say half a fringe deflection corresponds to a rotational speed > of 1 degree per hour. > > The instrument reading fluctuates between between 0.4 and 0.6 of a > fringe shift over a period of a 30 minutes. > > How much has the thing rotated at the end of that period? > > If 100 fringes corresponded to say 1 degree per hour then it might be > possible to produce accurate results but is that the kind of movement > you get? http://www.fesg.tu-muenchen.de/us/Docs/Ring-SPb04.pdf http://www.phys.canterbury.ac.nz/research/laser/ring_open.shtml -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+sp(a)ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
From: George Dishman on 17 Apr 2005 07:00 "Jim Greenfield" <jgreen(a)seol.net.au> wrote in message news:e7b5cc5d.0504161506.76630d7c(a)posting.google.com... > "George Dishman" <george(a)briar.demon.co.uk> wrote in message > news:<d3qkqn$luu$1(a)news.freedom2surf.net>... >> "Henri Wilson" <H@..> wrote in message >> news:748161p3j4p7o776a6q3uq1ddlf7adi1l8(a)4ax.com... >> > On Fri, 15 Apr 2005 15:32:14 +0100, "George Dishman" >> > <george(a)briar.demon.co.uk> >> > wrote: > >> >>1879 and 1926, Michelson > > In the famous experiment where Michelson measured the speed of light, > his source was stationary, and frequency or wave lengths were not > considered at all. Henri asked if an experiment had ever been done with light bouncing off a moving mirror and of course that was one of the first methods used to measure the speed of light. It wasn't exactly what Henri was looking for but it was the obvious answer to his question. It is a bit of an aside from the real topic, though related. > A similar experiment, using the exact same principals, but with the > source moving, has NEVER been done (vacuum). Yes it has Jim, the Sagnac experiment uses a moving source which is why Henri and I are discussing it. Henri understands the question and so did you a few months ago when we were discussing it by email. It has even been done in vacuum but in fact the version in a fibre is a better test since it removes possible concerns about remnant atmosphere. > And until it is, c'=c+v > will NOT be falsified (or afterwards) That seems to sum up some people's attitude, even AFTER it has been falsified, they will not admit it is false. > (for Henri) > I tried to email you privately, but am blocked. George and I have > discussed his sagnac at length, and I arrived at position as follows: > My understanding of George's arguement is that the point of > interference changes, which is the basis on which the machine works, > due to a change of time for the photons to complete their circuit(s), > which is produced by the rotation of the plane. (OK so far, G?) > But velocity is ALSO a factor of time, so it is a matter of > INTERPRETATION only, as to whether time changes, or velocity does! That is not correct. SR says the speed is c in the lab frame while Ritz says the light is launched ballistically at c relative to the source so the velocity is defined by the theory in both cases. This part is not in dispute. > I > think that if G wishes to argue otherwise, he is defacto introducing > the assumption that the DISTANCE factor in velocity altered also. We know that the distance in the lab frame is altered because the detector moves during the time of flight, and since we know the rate of rotation, we know how much it moves. The current discussion relates to how to calculate the exact path length using Ritz and whether any additional time delay effects are predicted other than distance/speed. > That > would be an unacceptable assumption to make George- to use postulates > of SR to show SR correct ;-( You still don't seem to follow the method Jim, we use the postulates of SR to make the SR prediction, we use the postulates of ballistic light theory to make its prediction. Then we see which one matches reality. Each theory can only use its own postulates to make its prediction. The question we are discussing is what prediction you get using ballistic theory. The launch speed is well defined but that together with conventional model of reflection gives a prediction of dt = 0 falsifying the theory. Henri and I are looking at the only poorly defined aspect, the reflection process, to see if an alternative model could resolve the problem. I don't think it can but that is the challenge. > So sleep tight, Henri, and leave G some free time to work on his > animation which will show how time dilation occurs! It might have to do one to illustrate how Huygens wavefront construction determines the angle of reflection in the case where the speed of the light is affected by bouncing off the mirror. George
From: George Dishman on 17 Apr 2005 07:28
"Henri Wilson" <H@..> wrote in message news:sh0361pepm96fke2tvbim51f1ftv4ntja9(a)4ax.com... > On Sat, 16 Apr 2005 09:52:32 +0100, > "George Dishman" <george(a)briar.demon.co.uk> wrote: >>"Henri Wilson" <H@..> wrote in message >>news:tn8161hfhml9om3ec4sdat9a4bsgt22aqt(a)4ax.com... .... >>> Don't tell me the fringe movement is sensitive enough to involve >>> an integration over time? >> >>That's right. That's why it they have only >>become feasible with modern optical components >>special fibre materials and digital integration. >>Counters don't drift ;-) > > OK, let's say half a fringe deflection corresponds to a rotational speed > of 1 > degree per hour. > > The instrument reading fluctuates between between 0.4 and 0.6 of a fringe > shift > over a period of a 30 minutes. > > How much has the thing rotated at the end of that period? If the rate due to rotation is exactly 0.5 and we see 0.4 to 0.6 then there is noise of +/-0.1. You don't say how often it is being measured but suppose this was 1800 readings so the +/-0.1 is for 1 second long measurements. Assuming the noise is Gaussian, the mean is 0.0 and the readings uncorrelated so the total will be 1800 * 0.5 = 900 and the error will be 0.1 * sqrt(1800) = 4.2 or 0.47% or equivalent to 0.5 +/- 0.0024 fringes. > If 100 fringes corresponded to say 1 degree per hour then it might be > possible > to produce accurate results but is that the kind of movement you get? I would need to know how many turns of fibre were used but I'll research that later, or maybe just guess for the purpose of illustration. I have some other stuff to do first but my gut feel is that it would be smaller than you suggest. Actual techniques are much more complex, the web page I gave a few posts back talked about it. For example at zero rotation, you have the same length in both paths since it is the same fibre so you are in the regime where there are no fringes but the uniform half brightness over the whole screen. The sensor is a photodiode or something like that which measures the brightness at the centre spot hence my earlier focus on point behaviour rather than fringes, and the change of brightness either side of zero speed is symmetrical hence an additional modulation is superimposed. There is also a possible ambiguity if the simple technique is used because a shift of 1/8 fringe is indistinguishable from a shift of 3/8 fringe (think of a sine wave). The maximum rate for the DSP3000 is 375 degrees per second so I would expect that is less than 1/4 fringe. The spec is here: http://www.kvh.com/pdf/DSP3000_5.04.pdf Note the output formats are rate (primary), incremental angle (change since some earlier orientation) and integrated angle. George |