Your 70-year-old future self suddenly appears, urgently borrowing $10,000 cash with a written promise to repay "when you become me." They vanish with the money. Thirty years later, you finally build a time machine. As you prepare to travel back to your younger self, you discover the aged promissory note in your pocket. Your spouse argues this creates a paradox - if you repay the debt, you'd have no reason to time travel, but if you don't, you'll be violating your own contract. Debate: Does this constitute a binding agreement across timelines? Is the debt canceled since you ultimately paid yourself? Would not repaying make you a thief from yourself?