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Marc R. Reinganum, "Is Time Travel Impossible? A Financial Proof", Journal of Portfolio Management 13(1):10-12, Fall 1986.

Current economic conditions rule out the possibility of past, present, or future time machines. The interest rate would always be zero if time travel were possible, because of the arbitrage opportunities that time travel would permit. Positive rates of interest are positive proof that time travel, unlike space flight, is pure fantasy.

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