It should be noted that while the subject of this paper is silly, the analysis actually does make sense. This paper, then, is a serious analysis of a ridiculous subject, which is of course the opposite of what is usual in economics.

He goes on to develop the First Fundamental Theorum of Interstellar Trade:

When trade takes place between two planets in a common inertial frame, the interest cost on goods in transit should be calculated by using time measured by clocks in the common frame, and not by clocks in the frames of the travelling spacecraft.

As promised, this does make sense. What a fascinating paper.