The Prisoner's Dilemma

One of the most famous puzzles in game theory — the foundation of modern economics, evolutionary biology, and Cold War strategy.

You and an accomplice are arrested. The police separate you into two rooms — you can't communicate. Each of you is independently offered the same deal:

• Stay silent (cooperate with your partner), or
• Betray the other (testify against them).

The consequences depend on what both of you choose:

• Both stay silent → 1 year each (police only have minor charges).
• You betray, they stay silent → you walk free (0), they get 10 years.
• You stay silent, they betray → you get 10 years, they walk free.
• Both betray → 5 years each.

You're purely self-interested and want the fewest years for yourself. You'll never meet this person again.

What is the rational choice — stay silent, or betray?