05
Jul
12

Was the Ferry Scene in the Dark Knight Really a Prisoner’s Dilemma?

I was thinking about Batman a little bit today and how much I wanted to see the one coming out in a few weeks.

This made me think back to the second Batman and the ferry scene. Many people label it as an instance of really smart philosophical sensitivity in a film. It’s a thought experiment isn’t it? Yes, and I was happy to see it in the film.

However, I don’t think the situation is really a prisoner’s dilemma. Rather, it’s just a simple example of direct competition or rivalry. If there’s only one apple and we can fight for possession of it, then whoever wins will be better off, but that doesn’t mean we’re in a prisoner’s dilemma. It just means we’re fighting over the single apple.

Let me be more precise. Usually a prisoner’s dilemma indicate an example in which individual rationality leads to collective irrationality, i.e., that total social utility is lost because of the parameters of the game. But in the ferry example, if both sides to cooperate and don’t blow each other up, they will both die at the end of the time limit. This would lead to less total happiness than if one side had detonated so that they would get to live in perpetuity (or at least beyond the specific ferry situation). So, if one side had quickly detonated the other ferry, not only would they have been better off (they would live and the other boat would explode) but society would be better off as well. The people who did the detonating would get to live and return to their loved ones.

One thing also that makes the ferry situation a little different than ordinary prisoner’s dilemma is the way that options are dominated. Usually, the way a prisoner dilemma is understood is that one option is dominant over the other. What this means is that by picking the dominant option, one always does better. If you don’t confess, then I should confess because I’ll go free and you’ll be punished. If you are going to confess, then I should STILL confess, otherwise I’ll go away for much longer than if I don’t cooperate.

In the ferry example though, if I know you’re going to detonate me, then none of my choices matter anyway. All detonating will do is just bring me with you, which won’t make ME any better off. So, strictly speaking, detonating is not the dominant strategy. However, I might look at the situation this way: if the other person denotes, it doesn’t matter what I do, so I should think about the case in which they don’t detonate. And in that case, I should detonate first to survive the Joker’s set up. So, on the off chance you don’t detonate, I should just detonate. So in a way detonating is kind of the dominant option. But critically, detonating does not cause a loss in total social welfare, but rather preserves it.

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1 Response to “Was the Ferry Scene in the Dark Knight Really a Prisoner’s Dilemma?”


  1. July 24, 2013 at 6:11 pm

    So this is what I understand: because detonation annihilates (at least) 1 ferry, its passengers can’t decide either way. They’re dead! So the circle isn’t complete. In Prisoner’s Dilemma – even in the simultaneous version – deciding to rat out doesn’t preclude a choice / reprisal by the other party. Interesting.


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