David Malament's (1977) well-known result, which is often taken to show the uniqueness of the Poincare-Einstein convention for defining simultaneity, involves an unwarranted physical assumption: that any simultaneity relation must remain invariant under temporal reflections. Once that assumption is removed, his other criteria for defining simultaneity are also satisfied by membership in the same backward (forward) null cone of the family of such cones with vertices on an inertial path. What is then unique about the Poincare-Einstein convention is that it (...) is independent of the choice of inertial path in a given inertial frame, confirming a remark in Einstein 1905. Similarly, what is unique about the backward (forward) null cone definition is that it is independent of the state of motion of an observer at a point on the inertial path. (shrink)

In this paper a method is proposed for empirically determining simultaneity at a distance within the special theory of relativity. It is argued that this method is independent of Einstein's signalling method and provides a basis for denying the conventionality of distant simultaneity.

The objective of this article is to provide a formalism to deal with the special theory of relativity (STR, in short) as riewed by Reichenbach, according to which STR involves an ineradicableconventionality of simultaneity. One of the two postulates of STR asserts that, in empty space, the one-way speed of light relative to inertial frames is constant. Experimental evidence, however, is related to the constancy of the round-trip speed of light and has no bearing on one-way speeds. Following Reichenbach's viewpoint, (...) we relax the second postulate of STR, abandoning the constancy of the one-way speed of light to the more realistic one asserting the constancy of the round-trip speed of light. This, in turn, results in a formalism to deal with Reichenbach's special theory of relativity (RSTR, in short) in which the two one-way speeds of light in empty space, C±, in the two senses of a round-trip are arbitrarily selected in such a way that their harmonic mean is the measurable round-trip speed of light, c. Experimentally, RSTR and STR are indistinguishable and, hence, represent the same physical theory. It is only the formalism that we use to deal with STR which is extended in RSTR to accommodate the immeasurability of one-way velocities. The usefulness of the proposed formalism to study special relativity is demonstrated. (shrink)

Thought experiments are described in which the one-way velocity of light appears as a physical quantity. A rotating shaft is used to define distant synchrony for a system of clocks along the shaft. In this context Einstein's definition of distant simultaneity is seen as based on a physical assumption (and not merely on an overwhelmingly sensible choice in a range of conventional possibilities).

The Reichenbach-Grunbaum thesis of the conventionality of simultaneity is clarified and defended by developing the consequences of the Special Theory when assumptions are not made concerning the one-way speed of light. It is first shown that the conventionality of simultaneity leads immediately to the conventionality of all relative speeds. From this result, the general-length-contraction and time-dilation relations are then derived. Next, the place of time-dilation and length-contraction effects within the Special Theory is examined in the light of the conventionality thesis. (...) The slow-transport method of synchrony is then examined in the light of these results and is shown not to provide an adequate method of uniquely determining the one-way speed of light. Finally, the general ε -Lorentz transformations for events along the x-axis are derived from three principles: the round-trip light principle, the principle of equal passage times, and the linearity principle. These principles are shown to be independent of one-way velocity assumptions, and thus may form the basis of a Special Theory of Relativity without distant simultaneity assumptions. (shrink)

In this paper, I elucidate the main points involved in the question of the non-triviality of the conventionality of simultaneity within the kinematics of special relativity. I argue that there is an important distinction to be made between the inherited component and the sui generis component of the conventionality of simultaneity. The factual core of the kinematics of special relativity is explored, and it is shown that the Round-Trip Clock Retardation effect obtains if, and only if Winnie's Passage Time Principle (...) holds. Some consequences of this fundamental fact are then explored. In particular, Grunbaum's view that the epistemological conventionality of simultaneity is logically prior to the physical inter-frame relativity of simultaneity is found to be based largely on what I call the inherited component of the former. Finally, a question is raised as to the very self-consistency of the claim, made by Ellis and Bowman, that standard signal synchrony and slow-transport synchrony are logically independent. In some concluding remarks, the author's general agreement with Grunbaum's conception of bridled conventionalism is indicated. (shrink)

A number of physical processes and experimental procedures are listed which appear to be inexplicable in the context of the conventionality thesis of Reichenbach and Grünbaum. Distant synchrony can be produced by procedures based on the free displacement or rotation of elastic solids. Results are expected to agree with Einstein's definition of distant synchrony (by means of light signals, assuming isotropy). The one-way velocity of light can be measured using a rotating shaft, slotted disks, and one stationary clock.

In 1977, David Malament proved the valuable technical result that the simultaneity relation of standard synchrony $\epsilon=\frac{1}{2}$ with respect to an inertial observer O is uniquely definable in terms of the relation κ of causal connectibility. And he claimed that this definability undermines my own version of the conventionality of metrical simultaneity within an inertial frame.But Malament’s proof depends on the imposition of several supposedly “innocuous” constraints on any candidate for the simultaneity relation relative to O. Relying on Allen I. (...) Janis’s 1983 challenge to one of these constraints, I argue that Malament’s technical result did not undermine my philosophical construal of the ontological status of relative metrical simultaneity. Furthermore, I show that (a) Michael Friedman’s peremptorily substantivalist critique of my conception, which Malament endorses, is ill-founded, and (b) if Malament had succeeded in discrediting my own conventionalist version of metrical simultaneity, he would likewise have invalidated Einstein’s pioneering version of it. (shrink)

The Reichenbach-Grunbaum thesis of the conventionality of simultaneity is clarified and defended by developing the consequences of the Special Theory when assumptions are not made concerning the one-way speed of light. It is first shown that the conventionality of simultaneity leads immediately to the conventionality of all relative speeds. From this result, the general-length-contraction and time-dilation relations are then derived. Next, the place of time-dilation and length-contraction effects within the Special Theory is examined in the light of the conventionality thesis. (...) The slow-transport method of synchrony is then examined in the light of these results and is shown not to provide an adequate method of uniquely determining the one-way speed of light. Finally, the general ε -Lorentz transformations for events along the x-axis are derived from three principles: the round-trip light principle, the principle of equal passage times, and the linearity principle. These principles are shown to be independent of one-way velocity assumptions, and thus may form the basis of a Special Theory of Relativity without simultaneity assumptions. (shrink)

This paper is a response to the "panel discussion of simultaneity by slow clock transport in the special and general theories of relativity" ("philosophy of science", 36, (march, 1969), Pp. 1-81) which arose out of a paper by brian ellis and peter bowman on "conventionality in distant simultaneity", ("philosophy of science", 34, (june, 1967), Pp. 116-36). It is argued that the basic disagreement between the pittsburgh panel and us is an epistemological one. In particular, Our concept of a good physical (...) reason is radically different from the pittsburgh panel's. For us the known existence of a number of concordant, Isotropic, And logically independent criteria for distant simultaneity, And the non-Existence of any known discordant but isotropic criteria for distant simultaneity is a good physical reason for choosing one of these criteria. For the pittsburgh panel it is not. (shrink)