In this paper, we show that a restricted form of time travel both accords with special relativity kinematics and avoids several prima facie objections. We argue that such time travel provides a reasonable way to interpret certain phenomena which can readily be described, and the analogues of which have already been observed at the level of elementary particle reactions. We then describe how a time-traveling object could measure itself, and demonstrate how, in the appropriate circumstances, such an experiment could convince (...) a theorist who insisted on a single criterion for length measurements that his standard had itself changed in length. The same experiment can shed light on the possibility of detecting a universal expansion; and we show that, given certain experimental results, one must conclude that every member of a class of time travelers has changed in length simultaneously, though perhaps only while going backwards in time. (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)

About twenty years ago, philosophers debated the verifiability of the statement “Last night everything doubled in size.” It seems that universal nocturnal expansion would double our rulers and tape measures making the size change indiscernible. I think that there is an internal analogue to the question “Did everything double in size last night?” The question “Did my preferences double in intensity last night?“ also raises problems of verification.