Time, metaphysics of

7. The A-theory and special relativity

The other main objection to the A-theory is that it is prima facie inconsistent with the special theory of relativity (see Time §3). Given that the special theory is a well-confirmed scientific theory, and thus is very likely to be true, it is incumbent upon any proponent of an A-theory of time to show that the two theories can, in principle, be reconciled. According to the standard interpretation of the special theory, simultaneity does not obtain absolutely, but only relative to a frame of reference (see Relativity theory, philosophical significance of §3). It may be the case that e ₁ is simultaneous with e ₂ relative to one frame of reference, but relative to another, e ₁ is earlier than e ₂, and relative to yet another, e ₁ is later than e ₂. Furthermore, no one frame of reference is privileged. It follows that there is no frame-independent way of marking out all those events that are simultaneous with the present moment, and thus are themselves present. An event which is present relative to one frame of reference may be past or future relative to another frame of reference, and neither of these frames of reference has a claim to being ontologically privileged. Consequently, there is no absolute (frame-independent) distinction between past, present and future. Furthermore, if presentness confers ontological status on events, then existence itself becomes a frame-relative matter. An event might exist, because it is present, relative to one frame of reference, yet not exist, because it is past or future, relative to another. Some A-theorists (for example, Smith 1993) have attempted to reconcile their view with the special theory. Whether such attempts are successful is the subject of much contemporary debate (see Sider 2001; Saunders 2002; and Balashov and Janssen 2003).