THE PRISONER'S DILEMMA

When is it worth trusting someone? as the saying goes trust makes way for treachery but it is true.

Here is a puzzle that provides an answer.

Two prisoners are suspected of having carried out a crime together the maximum sentence for the crime is 10 years. The two suspects have been arrested separately and each is offered the same deal,  If he confesses that they both committed the crime and his accomplice remain silent, the charges against him will be dropped.  But the accomplice will have to serve the full 10 years if both he and his accomplice remain silent. There will only be circumstantial evidence which nonetheless puts both men behind bars for 2 years. But if both he and his accomplice confess to the crime they are both to be sentenced to 5 years in prison.

The suspects cannot confirm how should they react under questioning. 

Should they trust each other?

This is the so-called prison dilemma a classic conundrum in game theory. The two suspects both lose if they opt for the most obvious solution, ie put themselves first they get a 5 year sentence each.

Far better if each one trusts one another.  If they remain silent then they get a 2 year sentence. Note: If only one of the suspects confesses then the sentence is 10 years for the other suspect the confessor is freed.

In the 1979 the political scientist Elroid Rod organised the tournament in which 14 academic colleagues play 200 rounds of the prisoner's dilemma against one another in order to work out the best strategy. He found that in the first round it is best to co-operate with your accomplice, trust him in the second round. Do what your accomplice did in the previous round by initiating his moves he will follow you.

 You can't shake hands with a clenched fist, Gandhi