Objections II

Some points about time travel made earlier either here or on the Logic of Time Travel blog might bear repetition. If they do not, then I apologize.

World-Lines In Wells, Blish And Anderson

The Time Traveler begins by stating that material objects extend through four dimensions and that only immaterial mental existences move along the fourth dimension. This unscientific Platonic-Cartesian mind-body dualism is repeated in James Blish's The Quincunx Of Time.

Both The Quincunx Of Time and Poul Anderson's Time Patrol series refer to world-lines which are four-dimensional entities. Time Patrol timecycles do not move along the fourth dimension but disappear at one set of spatiotemporal coordinates and appear at another. In The Quincunx Of Time, a vessel called a world-line cruiser does (somehow) travel from 8873 to 8704 along a planetary world-line.

Motion Through Time?

(i) If all three-dimensional objects do move uniformly along a fourth dimension, then what do they move in relation to?

(ii) Motion along a fourth dimension would take time. Therefore, that dimension would not itself be time.

(iii) If the Time Traveler or Jack Havig not only moves but also accelerates along the fourth dimension, then he leaves everyone and everything else behind, arrives in a void and has to wait for the rest of the universe to catch up.

(iv) This is a reductio ad absurdum argument. We do not move through time. Motion through space takes time which is the relationship between a position moved from and a position moved to.