¿Deben los intereses computarse según el tiempo propio del transportista o según los relojes de un sistema inercial? Esta interesante pregunta da origen a two useless but true theorems, examinados en este paper. Transcribimos el

First Fundamental Theorem of Interstellar Trade: When trade takes place between two planets in a common inertial frame, the interest costs on goods in transit should be calculated using time measured by clocks in the common frame, and not by clocks in the frames of trading spacecraft.