Conventionality of Simultaneity (from Stanford Encyclopaedia of Philosophy online = free source)
The debate about the conventionality of simultaneity is usually carried on within the framework of the special theory of relativity. Even prior to the advent of that theory, however, questions had been raised (see, e.g., Poincaré, 1898) as to whether simultaneity was absolute; i.e., whether there was a unique event at location A that was simultaneous with a given event at location B. In his first paper on relativity, Einstein (1905) asserted that it was necessary to make an assumption in order to be able to compare the times of occurrence of events at spatially separated locations (Einstein, 1905, pp. 38-40 of the Dover translation or pp. 125-127 of the Princeton translation; but note Scribner, 1963, for correction of an error in the Dover translation). His assumption, which defined what is usually called standard synchrony, can be described in terms of the following idealized thought experiment, where the spatial locations A and B are fixed locations in some particular, but arbitrary, inertial (i.e., unaccelerated) frame of reference: Let a light ray, traveling in vacuum, leave A at time t1 (as measured by a clock at rest there), and arrive at B coincident with the event E at B. Let the ray be instantaneously reflected back to A, arriving at time t2. Then standard synchrony is defined by saying that E is simultaneous with the event at A that occurred at time (t1+ t2)/2. This definition is equivalent to the requirement that the one-way speeds of the ray be the same on the two segments of its round-trip journey between A and B. Norton, J. 1986. "The Quest for the One Way Velocity of Light," British Journal for the Philosophy of Science 37, 118-120 (cited in the above). I have a later version of the Princeton translation mentioned. On 3 Jan, 01:56, archytas <[email protected]> wrote: > Stedman, G. E., "A Unidirectional Test of Special Relativity?" > American > Journal of Physics 40(19 72): 782-4. > Taylor, Edwin F. and John Archibald Wheeler, Spacetime Physics (San > Francisco: W. H. Freeman and Co., 1963). > Weinberger, H., and M. Mossel, "Theory of a Unidirectional > Interferometric Test > of Special Relativity," American Journal of Physics 39(1971): 606-9. > Winnie, John, "Special Relativity Without One-Way Velocity > Assumptions," > Philosophy of Science 37(1970): 81-99, 223-38. > > These were a few places I visited to make sure, if I am howling at the > Moon, I'm not doing so entirely naked. I have not found anyone > assuming MM not to be a round trip except you, though as Einstein > said, 'it would only take one'. I have since found a 1977 conference > addressing the matters - remember its "thinking principles" that > concern me, so I don't need to be up to date. One paper I only > currently have rough notes of has this: > In rebutting the claim that measurement of the ratio of electrostatic > units to electromagnetic units suffices to ascertain the one-way speed > of light, Adolf Grunbaum exhibits still > other ways in which prior synchrony conventions are involved. > According to Grunbaum, the proponent of that approach . . . begs the > question by his failure to see that the simultaneity > criterion based on the choice of e = 1/2 is used in the very > definitions of the physical quantities that enter into Maxwell's > equations and that these equations would be different for a different > choice of C, since then the various physical quantities would, in > general, have different relationships to one another. Thus, for > example, the first partial derivative of the electric field strength > with respect to one of the space coordinates represents a space > variation of simultaneous values of the quantity E .... In this way, > the simultaneity criterion e = 1/2 is presupposed in the very > equations which are used to define the electromagnetic and > electrostatic units of charge as well as in the experimental > determination of their ratios .... > All of these considerations make it evident that Maxwell's > electromagnetic theory is permeated with synchrony and one-way > velocity conventions. Einstein could hardly have been oblivious to > that fact. His 1905 paper on special relativity was entitled, "On the > Electrodynamics of Moving Bodies" ("Zur Elektrodynamik bewegter > Korper"), and it addressed itself to problems arising directly out of > Maxwell's equations (which we know). > > My interests in this may formalise into defeasible reasoning processes > and some simple statements on creativity that include theory being > under-determined by evidence (and our own inabilities to put the > evidence in theoretical context) - much of our action surely is. All > seems to rely on approximation, itself a complex and potentially > formalisable. > > 3 Jan, 01:03, archytas <[email protected]> wrote: > > > > > This is the quote from 'Einstein et al' from my records - I've been > > working on something completely different (fiction) in which Einstein > > has relevance. > > > If at the point A of space there is a clock, an observer at A can > > determine the time values of events in the immediate proximity of A > > by finding the positions of the hands which are simultaneous with > > these events. If there is at point B of space another clock in all > > respects resembling the one at A, it is possible for an observer at B > > to > > determine the time values of events in the immediate neighborhood > > of B. But it is not possible without further assumption to compare, > > in respect of time, an event at A with an event at B. We have so far > > defined only an "A time" and a "B time." We have not defined a > > common "time" for A and B, for the latter cannot be defined at all > > unless we establish by definition [Einstein's italics don't show here] > > that the "time" > > required by light to travel from A to B equals the "time" it requires > > to travel from B to A. (pp: 39-40.) > > > Just as a matter of interest, our old friend Descartes once wrote of > > the ancient and > > medieval belief in which light was generally believed to travel at > > infinite speed, that "for me this was so certain that if > > it could be proved false, I should be ready to confess that I > > know absolutely nothing about philosophy" (Holton, Gerald, > > Introduction to Concepts and Theories in Physical Science. 2nd > > ed., revised and with new material by Stephen G. Brush (Reading, > > Mass.: > > Addison-Wesley Publishing Co., 1973): 385-6. Warm up the time > > machine! Nothing like proving a Frenchman wrong! > > > Very recent experiments have fired lasers in all directions (in > > apparatus on a bed of air) and confirmed 'c' at 10 to the minus 20 for > > 10 of 18 or so criteria - this equipment may be improved to be able to > > detect the possible influences of dark matter on light speed. On MM I > > can only say I have found scores of work that assumes the > > perpendicular beams and round trip speed. It seems unlikely Einstein > > would have said the above if he did not think this was the case. My > > guess is the one way speed of light is a dead duck now, but it wasn't > > once. The problem of distant simultaneity or somesuch, as my fading > > memory allows. Maybe Socratus' 'hidden ether' can turn us to ideas of > > whatever spins in dark matter? Carlos will have the 'address' ... > > > Anyway, chin chin - I have two cans of Foster's in the fridge as a > > gift for repairing an old neighbour's television. My ancient > > soldering iron managed the slow clock trip of my legs to her house and > > I presume the 'amber nectar', though an Australian lie, has similarly > > survived the trip back. Did you know they don't use valves in tvs > > these days Georges? It was some shock to me, I can tell you! Had I > > been more rigorous in approach, I need not have had the back off the > > set, as I ended-up replacing the fuse trip-switch after I noticed the > > kettle for my tea was not working either. > > > On 2 Jan, 23:38, archytas <[email protected]> wrote: > > > > I have no doubt on the aether 'testing' failure stuff. Didn't we send > > > up some kind of 'evacuated lead balloon' some time ago to confirm some > > > kind of 'curved space drag'? (gleaned from cleaning my car's windows > > > with New Scientist) - none of this is about 'bringing back old > > > physics'. I'll see what I can codge together, but will say again, for > > > tonight, what I've put forward is about learning and how sound a > > > philosophical base we can put science on - and perhaps later any role > > > this has in actual science. In Socratus' context, I may be on about > > > what we might make of the term 'hidden ether', without just dismissing > > > it. > > > > On 2 Jan, 21:33, Georges Metanomski <[email protected]> wrote: > > > > > --- On Sat, 1/2/10, archytas <[email protected]> wrote: > > > > > > Einstein, Albert, et al, The > > > > > Principle of Relativity (New York: Dover > > > > > Publications) page 40 in my motheaten edition - on the > > > > > reference you > > > > > demand. Are we to take it you have taken up reading? > > > > > ============ > > > > G: > > > > I don't have this book. Could you, pls, quote the few lines about > > > > points A and B? I'm really interested. > > > > ================== > > > > Neil:> One experiment, amongst many on these 'dilettante' lines > > > > > was this: > > > > > (J. G, Small and R. E. Phelps) - a 'new' > > > > > version of the Michelson-Morley experiment (1970s). Instead > > > > > of > > > > > comparing > > > > > round-trip speeds, as the original experiment did, > > > > > =============== > > > > G: > > > > There were no "round-trips" in MM experiment. It was supposed to > > > > prove the Aether wind by sending, reflecting and comparing two > > > > beams, one parallel and one perpendicular to the earth surface, > > > > thus to the alleged wind. The experiment failed giving the C > > > > identical in both directions (within experimental error) thus > > > > killing the Aether hypothesis and providing first solid support > > > > to the SR. All improved versions of the experiment failed to > > > > prove the Aether and confirmed the invariance of C. > > > > > Many new and fantastic things happen in science. Why bother about > > > > obstinate trials to revive the Aether, or entangled acausality > > > > allegedly demonstrated by Aspect, whose technologically impressing > > > > experiment is totally meaningless. > > > > > Cheers > > > > Georges. -- You received this message because you are subscribed to the Google Groups "Epistemology" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/epistemology?hl=en.
