A Dark Forest First Attack Is Rational Only If the Attacker Accepts It as Its Last

Abstract

The Dark Forest argument holds that a civilization that detects another should strike it at once, so detection, and any transmission that invites it, is danger. Existing models make the detected civilization the object of the strike and play the strike on a roster the attacker knows; where they advise restraint, the advice rests on steps that fail in the cases it is for. This paper takes the object of hostility to be remaining uncontrolled capacity to warn or retaliate, on a roster no attacker ever knows to be complete. A first strike is rational only if the timing benefit of what it removes is at least the disclosure loss from every leftover that learns of it. A leftover able to bring about the attacker's destruction, by striking or by warning one who can, costs the attacker its whole stake, and the actors the attacker has never found are such a leftover that no strike removes. A Dark Forest believer that strikes first therefore accepts the strike as the last attack it will ever make; the strike is rational only if waiting would raise the cost of removing the target by about the attacker's whole stake. A transmission that reveals the sender gives a receiver a posterior over the sender's capacity, not a target, and proves that the sender can warn. A receiver need not be hostile; for one that is, the sender is a witness it must pay for, so a beacon delays every hostile that cannot be nearly sure of removing the sender's forces, and a free beacon harms its sender only through sure kill, whole-stake urgency, a receiver that fears no one the sender could warn, or an opening hidden from the sender. Messaging to extraterrestrial intelligence (METI) is judged by reach and by what a receiver must believe to act, not by fear of punishment, and a beacon deters by witnessing: the sender need not be able to strike anyone, only to tell someone who can.