Why physicists refuse to measure the one-way speed of light directly?
in [Physics]
|
From: kenseto on 5 Feb 2010 15:04 On Feb 5, 1:12 pm, glird <gl...(a)aol.com> wrote: > On Feb 4, 11:45 pm, Jerry <Cephalobus_alie...(a)comcast.net> wrote: > > > > > > > On Feb 4, 8:30 pm, Rock Brentwood <markw...(a)yahoo.com> wrote: > > > An empirical science is supposed to be falsifiable. That means, first > > > and foremost, you must ALWAYS keep the language intact for counter- > > > factuals, regardless of whether they are true or not! Because when you > > > don't you've just introduced a hole in the rug where oversights can > > > slip in unseen that you can't even address or see (because the > > > conventions in place linguistically filter them out), much less > > > address. > > > One of the places oversights crop in with the flawed notational > > > conventions (e.g. "set c = 1", or as the ISO says, "set c-second/meter > > > = 299792458") is you lose meaningful and HIGHLY physically relevant > > > discussion about such issues as the variation of the permittivity > > > (plus, you get the apparent discrepancy above that 1 meter -> 0 as > > > time t -> 0). In fact, the variability of both permeability and > > > permittivity are precisely what the metric above imply -- not just for > > > electromagnetism, but also the gauge-theoretic analogue of epsilon and > > > mu for gauge fields. > > > I find the above line of argument to be unconvincing, perhaps > > even somewhat specious. Every choice of notational convention has > > at its basis a set of theoretical and/or practical assumptions, > > but the mere fact that one is necessarily forced to adopt one or > > another convention does _not_ preclude investigation into the > > validity of one's choice. > > For example, the definition of the kilogram in terms of a > > material standard, the International Prototype Kilogram (IPK), has > > _not_ precluded investigations on the stability of the IPK, which > > exhibits rapid, short term mass swings on the order of 30 ug > > when compared against the worldwide ensemble of prototype > > standards, and which been estimated to have lost on the order of > > 50 ug over the last century. > > Likewise, modern-day repetitions of the MMX are _not_ interpreted > > as checks on the dimensional stability of the cryogenic optical > > resonators employed in the most precise of these recent tests, > > even though the ISO definition of the meter would seemingly > > preclude any possibility of measuring anisotropies in the speed > > of light. > > Presumably the standard definition of a meter was that 1 meter is > the distance light travels in a vacuum in 1 second. Presumably the > standard definition of a second was that 1 second is the time it takes > light to travel one meter in a vacuum Given those two "definitions" > it is clear that the speed of light in a vacuum will always be c even > if it isn't. No....1 second is the duration for 9,192,631,770 periods of cs 133 radiation.
From: glird on 5 Feb 2010 17:23 On Jan 22, 10:50 am, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > >< Einstein described two basic methods to synchronize two clocks A and B at rest in a given inertial frame: A) Place a light source exactly midway between them. Arrange so the source simultaneously sends a light pulse (propagating in vacuum) direct to each clock, and make the clocks start ticking at the same indicated value when they receive the light pulse. B) Send a light pulse from A to B, and have B immediately return it to A (e.g. with a mirror). Adjust the clocks so the reflection at B occurs at an indicated time midway between the two times at A. {snip} Given one-way isotropy in the speed of light (guaranteed in SR by the second postulate), these two methods are equivalent, and always yield clocks that measure the speed of light to be isotropic. As no mention of which inertial frame was used, this applies in any inertial frame, thus ensuring invariance of the one-way speed of light.> Exercise 1 for readers: Find where he wrote item A in his 1905 STR paper. (Clue: It wasn't there.) Exercise 2 for readers: Without using his method of "synchronizing" the two clocks, show that the 2nd postulate suffices to assure isotropy in the speed of light in all directions. (Clue: If you adhere to his Minkowski- denied assumption, this is impossible,) glird
From: Tom Roberts on 5 Feb 2010 17:37 Rock Brentwood wrote: > The correct statement is: the speed of light in a "vacuum" (i.e. a > boost-invariant, rotation-invariant, translation-invariant medium) in > a flat Minkowski space is a constant. > > Correct though this may be, it is not physically relevant for two main > reasons: (1) there is no such thing as a vacuum, not even outer space, > and (2) the cosmos is not flat, as a space-time geometry. Nonsense. You need to learn how to think like an experimental physicist. Yes, Minkowski spacetime is a MODEL, not some "absolute truth" (or somesuch). To apply it one must COMPUTE how accurately the model applies to a given experiment. For EVERY ONE of the relevant experiments measuring the speed of light in vacuum, your claims are irrelevant. That is, the effect due to the residual gas in the vacuum, and the effect due to the curvature of spacetime, are both NEGLIGIBLE. Minkowski spacetime is a highly accurate model for many situations and experiments. That makes it "physically relevant" to them. Tom Roberts
From: PD on 5 Feb 2010 17:39 On Feb 5, 4:23 pm, glird <gl...(a)aol.com> wrote: > On Jan 22, 10:50 am, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > > >< Einstein described two basic methods to synchronize two clocks A and B at rest in a given inertial frame: > > A) Place a light source exactly midway between them. Arrange so the > source simultaneously sends a light pulse (propagating in > vacuum) > direct to each clock, and make the clocks start ticking at the > same indicated value when they receive the light pulse. > B) Send a light pulse from A to B, and have B immediately return it > to A (e.g. with a mirror). Adjust the clocks so the reflection > at B occurs at an indicated time midway between the two times at > A. > {snip} > Given one-way isotropy in the speed of light (guaranteed in SR by the > second > postulate), these two methods are equivalent, and always yield clocks > that > measure the speed of light to be isotropic. As no mention of which > inertial > frame was used, this applies in any inertial frame, thus ensuring > invariance of > the one-way speed of light.> > > Exercise 1 for readers: Find where he wrote item A in his 1905 STR > paper. > (Clue: It wasn't there.) > Exercise 2 for readers: Without using his method of "synchronizing" > the two > clocks, show that the 2nd postulate suffices > to > assure isotropy in the speed of light in > all > directions. > (Clue: If you adhere to his Minkowski- > denied > assumption, this is impossible,) > > glird The 1905 paper is not the be-all, end-all of relativity. If you were expecting that one paper to be the comprehensive compendium and reference for SR, I'm afraid you're barking up the wrong tree.
From: glird on 5 Feb 2010 20:44
On Feb 5, 5:39 pm, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 5, 4:23 pm, glird <gl...(a)aol.com> wrote: ><> Exercise 2 for readers: Without using his method of "synchronizing" the two clocks, show that the 2nd postulate suffices to assure isotropy in the speed of light in all directions. (Clue: If you adhere to his Minkowski-denying assumption, this is impossible,) > > > The 1905 paper is not the be-all, end-all of relativity. If you were > expecting that one paper to be the comprehensive compendium and > reference for SR, I'm afraid you're barking up the wrong tree. Woof!! P--...leeze try to do exercise 2 anyway... f u can gird |