Why physicists refuse to measure the one-way speed of light directly?
in [Relativity]
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From: xxein on 13 Jan 2010 20:20 On Jan 11, 6:48 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > Sam Wormley wrote: > > On 1/11/10 12:01 PM, glird wrote: > >> On Jan 11, 11:22 am, Sam Wormley wrote: > >>> Physics FAQ: How is the speed of light > >> measured? > >> [snip] > >>> http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html > > >> I looked and found this written therein: > >> "At this time there are no direct tests of length contraction, as > >> measuring the length of a moving object to the precision required has > >> not been feasible. There is, however, a demonstration that it occurs: > >> "A current-carrying wire is observed to be electrically neutral in > >> its rest frame, and a nearby charged particle at rest in that frame is > >> unaffected by the current. A nearby charged particle that is moving > >> parallel to the wire, however, is subject to a magnetic force that is > >> related to its speed relative to the wire. If one considers the > >> situation in the rest frame of a charge moving with the drift velocity > >> of the electrons in the wire, the force is purely electrostatic due to > >> the different length contractions of the positive and negative charges > >> in the wire (the former are fixed relative to the wire, while the > >> latter are mobile with drift velocities of a few mm per second). This > >> approach gives the correct quantitative value of the magnetic force in > >> the wire frame. This is discussed in more detail in: Purcel, > >> Electricity and Magnetism. It is rather remarkable that relativistic > >> effects for such a tiny velocity explain the enormous magnetic forces > >> we observe." > > >> It is rather remarkable that DESPITE THIS EXPERIMENTAL confirmation > >> of Lorentz's length contraction, present physics still denies that it > >> really happens. > > >> glird > > > Depends on the observer! "Really Happening" is what one measures. > > And moreover, no matter what observers measure, this "length contraction" NEVER > affects the object itself. As that is what a "real contraction" would mean, it's > clear that this length contraction is not a real contraction OF THE OBJECT. > > So one must be careful in how one phrases statements about "length contraction". > There are too many possible meanings of "real" to be able to use that word > without saying what one means by it. > > Tom Roberts- Hide quoted text - > > - Show quoted text - xxein: You lose.
From: xxein on 13 Jan 2010 20:27 On Jan 11, 5:29 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > kenseto wrote: > > one-way isotropy is not a direct measure of the value of the > > one-way speed of light. Why? You can have 200,000 Km/sec isotropy or > > 300,000 Km/sec isotropy. > > No. It is true that tests for isotropy do not directly measure the value of the > speed. But once they demonstrate isotropy then the value of the one-way speed > involved can only be equal to the KNOWN value for the round-trip speed of light > in vacuum. After all, the round-trip paths used in such measurements consist of > two one-way paths in series. > > > Besides, since they performed experiments to measure for one-way > > isotropy why didn't they report the value of one-way speed of light > > for those same experiments? > > Because, as I keep telling you and you keep ignoring, most tests for isotropy > cannot obtain a value for the speed. Such experiments are optimized for > measuring the anisotropy, and generally do this with difference techniques, not > by measuring the value of the one-way speed and then subtracting values. > > You might have heard of the Michelson-Morley experiment. It > measures the anisotropy in the round-trip speed of light, but > is completely incapable of providing a value for the speed > of light itself. > > If you would LEARN something about the subject and STUDY the experiments, you > would know all this already. > > Tom Roberts xxein: Ever hear of time dilation? Where do you suppose that fits into |c| anisotropy?
From: xxein on 13 Jan 2010 20:34 On Jan 11, 12:48 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > kenseto wrote: > > Why physicists refuse to measure the one-way speed of light directly? > > You confuse "refuse" with an inability to do so accurately enough to be useful. > > The problem with any one-way measurement is that the systematic errors are > large. So large that competing theories cannot be distinguished via this method. > > For round-trip measurements the situation is quite different. From pre-1983 > measurements it is known that the round-trip speed of light in vacuum in any > earthbound laboratory is within 1 meter/sec of the currently defined value. That > is, after all, the rationale behind the redefinition of the meter. > > > The answer: [...] > > Ken's "answer" is nonsense. But yes, today the International Standards > Organization defines the speed of light in vacuum to be constant, and they > define the meter in terms of the speed of light and their definition of the second. > > [You REALLY don't understand this, and like a hamster in a wheel > you keep re-tracing old steps without getting anywhere.. Don't > expect me to respond until you LEARN something about this.] > > Tom Roberts xxein: You don't understand either. You just play that you are a brick wall.
From: xxein on 13 Jan 2010 20:46 On Jan 11, 2:54 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > GogoJF wrote: > > Tom: Why can't you use my concept of the "Light sandwich experiment", > > that I proposed in this paper? http://www.wbabin.net/physics/gogo4.pdf > > Because that approach ASSUMES that the one-way speed of light is isotropic! That > is inherent in this statement: "Since the clock is stationed exactly in between > Omni light sources A and B, Omni light sources A and B are illuminated at > precisely the same time at tA and tB." > > Given that the one-way speed is isotropic, then its value > MUST be the same as the two-way speed. There is no ambiguity in > measuring the latter, and we know its value. > > Claiming "it is impossible to measure the one-way speed of light" is a rather > gross overstatement -- one can clearly do so with two clocks and a measured > distance between them. Note that it INHERENTLY requires two clocks to make a > one-way measurement, and that requires that the two clock be synchronized -- > there's the rub! > > What is impossible is to divorce the result of such a measurement from the > method of synchronizing those two clocks. But one can synchronize two clocks in > ANY manner whatsoever, which implies that one can obtain ANY answer whatsoever > from such a measurement. > > Your paper chose to use one of Einstein's methods to synchronize > the two "Omni light sources" A and B. That's a reasonable method, > but it is not unique. > > It should be clear that using Einstein's synchronization method (any of them; > they are all equivalent) will GUARANTEE that the one-way speed of light will be > measured to be c. Note also that slow clock transport in an inertial frame is > equivalent to Einstein's methods. > > [Your quote from Croca requiring 100 meter paths is woefully > outdated. Detectors now exist with resolutions of a few > picoseconds.] > > [Also: The links to "poincare-curse" are all dead.] > > Tom Roberts xxein: It sounds like you are saying that a Doppler effect is as fictitious as time dilation, length contraction and a force due to gravitation. Oh, where is the wicked witch, Dorothy?
From: eric gisse on 13 Jan 2010 20:50
Da Do Ron Ron wrote: > eric gisse suggested: >>I'd suggest reading about it. > > Look, if it were that damn simple, why would > Andie panic & plonk, and why would Uncle Tom > and PDiddy take the A train? Androcles is stupid, that's why he doesn't understand. > > I have read about it, extensively, which is > precisely why I put the question to Tom. So you don't understand and want someone to explain it to you? Fair enough, at least you are more up front about it than others. What part do you have difficulty with? > > Perhaps you, Gisse, can help Tom answer? Tom Roberts does not need, and probably doesn't wish for, me to speak for him as he seems somewhat capable of doing it himself. > > ~~RA~~ |