Paul Krugman’s Theory of Interstellar Trade:

This paper extends interplanetary trade theory to an interstellar setting. It is chiefly concerned with the following question: how should interest rates on goods in transit be computed when the goods travel at close to the speed of light? This is a problem because the time taken in transit will appear less to an observer traveling with the goods than to a stationary observer. A solution is derived from economic theory, and two useless but true theorems are proved… This paper, then, is a serious analysis of a ridiculous subject, which is of course the opposite of what is usual in economics