Why physicists refuse to measure the one-way speed of light directly?
in [Physics]
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From: glird on 5 Feb 2010 12:55 On Feb 4, 9:30 pm, Rock Brentwood <markw...(a)yahoo.com> wrote: > > The metric describing the universe is: > ds^2 = dt^2 - 1/c(t)^2 (dx^2 + dy^2 + dz^2) > where the speed of light c(t) is a function of time given (in a matter- > dominant era) as > c(t) = c (T/t)^{2/3} > where T represents the current time and c represents the speed of > light at time T. The "speed of light" is not "c(t)", it is "c". If your "c(t)" means "c, a function of t", then it is meaningless because the speed of light is NOT a function of t. If your c(t) means ct - as in Minkowski's "4th dimension"; then it isn't a speed at all. It is a distance. Given that c = # meters per second, = dx/dt; if you multiply that by t you get, (dx/dt)t = dx = # meters. snip > All the above considerations apply generally to gauge fields, with the > only modification being that the E and B fields now have an extra Lie > index (E^a, B^a: a = 1, 2, .... dimension of underlying Lie group), > and D and H have the indices in the lower position D_a, H_a, and > epsilon and mu are now matrices (epsilon_{ab}, mu^{ab}), while k > generalizes to the gauge group metric k_{ab} and 1/k to the inverse of > the gauge group metric k^{ab}. Outside of the word "Lie", which applies to most of Minkowski's concepts, that is purely abstract mathematics with no explanation as to how it relates to physical reality. > Since one normally assumes the gauge theory is given with an adjoint- > invariant metric, then for simple gauge groups, k reduces to a > multiple k_{ab} = (1/g^2) kappa_{ab} of the Killing metric. So, the > variability of epsilon translates into a variability of g -- which is > now proportional to t^{-2/3}. Sure. glird
From: glird on 5 Feb 2010 13:12 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. glird
From: PD on 5 Feb 2010 13:45 On Feb 5, 12:12 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 No. If you don't know, don't guess. You could look it up at nist.gov. > Given those two "definitions" > it is clear that the speed of light in a vacuum will always be c even > if it isn't. > > glird
From: glird on 5 Feb 2010 13:46 On Jan 19, 10:34 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > >< Well yes, one cannot assume what one is trying to establish. And yes, attempting to discuss "light speed invariance" divorced from a theory means nothing. So while no experiment has directly established one-way light speed invariance, the indirect evidence is quite solid. In particular, no known theory that does not have one-way light speed invariance is consistent with these experiments. I mean MEASURED invariance. There are theories in which the coordinates have both anisotropy and lack of invariance, but which are experimentally indistinguishable from SR. In short, for these theories their anisotropy and non-invariance precisely cancel out whenever real clocks and real rulers are used to measure the speed of light. Science is not about arbitrary "rules", but rather is about formulating and testing theories experimentally. SR has been extensively tested, and has not been refuted by any experiment within its domain of applicability. That's as good as it gets. > Here is the "bad" detail overlooked by Tom's "good": There are two mutually exclusive EXPLANATIONS of how the formulations (equations) work! Tom insists Minkowski's is right and ignores Einstein's contrary one. glird
From: Argir Pando Vasil Dobri Matea Karagorgovi on 5 Feb 2010 14:11
On Feb 5, 7:46 pm, glird <gl...(a)aol.com> wrote: > On Jan 19, 10:34 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > > >< Well yes, one cannot assume what one is trying to establish. And yes, attempting to discuss "light speed invariance" divorced from a theory means nothing. > > So while no experiment has directly established one-way light speed > invariance, > the indirect evidence is quite solid. In particular, no known theory > that does > not have one-way light speed invariance is consistent with these > experiments. > I mean MEASURED invariance. There are theories in which the > coordinates have both anisotropy and lack of invariance, but > which are experimentally indistinguishable from SR. In short, > for these theories their anisotropy and non-invariance > precisely cancel out whenever real clocks and real rulers > are used to measure the speed of light. > Science is not about arbitrary "rules", but rather is about > formulating and > testing theories experimentally. SR has been extensively tested, and > has not > been refuted by any experiment within its domain of applicability. > That's as > good as it gets. > > > Here is the "bad" detail overlooked by Tom's "good": > There are two mutually exclusive EXPLANATIONS of how the formulations > (equations) work! Tom insists Minkowski's is right and ignores > Einstein's > contrary one. > > glird c = const even in the case of (x = 0) / (t = 0) |