I did not think that Paul Krugman was still writing academic papers. Nor have I seen any evidence in the last decade that he still has any sense of humor.
This article extends interplanetary trade theory to an interstellar setting. It is chiefly concerned with the following question: how should interest charges 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.
A quick look at the acknowledgments, however, clears things up. The original manuscript was written in July 1978, when Krugman was an active researcher and being a curmudgeon wasn’t part of his professional identity.