“Is Time Travel Impossible?” by Marc R . Reinganum in The Journal of Portfolio Management v 13 (1986) #1 (Fall), pp. 10-12, argues that, were time travel possible, the effects on financial markets would be discernible as a zero rate of interest. Granted that we seem to approach that rate to-day, as technocrats attempt to push on a string to keep the economy moving, but these effects should have been observed on previous markets as well.One of the recurring presumptions of comic books, and of movie serials is that formulæ and mechanisms have to be created from the ground up if a unique physical instantiation is lost. But Mr Phelps will surely have very little research or development ahead of him.