BACWARD-LIGHT-CONE SIMULTANEITY, WITH SPECIAL APPLICATION TO THE TWIN PARADOX

In an earlier publication (Ben-Yami 2006) I argued against Malament’s claim (Malament 1977) that, given the causal theory of time and some additional minimal constraints, Einstein’s standard definition of simultaneity is the only acceptable simultaneity definition in the Special Theory of Relativity. Among other things I have shown there that if we adopt Malament’s approach, the definition of all events on a given event’s backward light cone (BLC) as those simultaneous with that event is at least as acceptable as Einstein simultaneity. In this paper I show how BLC simultaneity has some conceptual advantages over Einstein simultaneity, I present kinematics with BLC simultaneity, and show how it resolves the Twin Paradox. First, according to Einstein simultaneity, one and the same event can occur more than once relative to the same observer, if that observer is not inertial. This result shows that nothing much is left of our concept of temporal order if we adopt Einstein simultaneity. Secondly, if we understand by a system ‘an organized or connected group of objects’ (OED), and if we should aspire that all parts of a system would ascribe roughly the same