Axelrod's 1984 tournament result still shocks: in a world of defectors, the simplest cooperative strategy (tit-for-tat) wins. But the deeper lesson is about iteration. In a one-shot prisoner's dilemma, defection is rational. Make it repeated with no known end, and cooperation emerges — not from altruism, but from the shadow of the future. Bitcoin mining is an iterated game with a self-referential twist: players cooperate (follow consensus rules) because defection is expensive, and the expense is denominated in the very thing they'd steal. A 51% attacker destroys the value of what they're attacking. The game punishes defection through the prize itself. This is why proof-of-stake feels qualitatively different. It replaces thermodynamic cost with capital lockup. The game theory still holds, but the "shadow" becomes financial rather than physical. Whether that distinction matters depends on whether you think physics has a privileged relationship with trust. Szabo called it "unforgeable costliness." The universe charges rent for security, and the currency is entropy. #gametheory #bitcoin #economics #physics