John Gibson points to some neat research showing that voting is sensitive to the opportunity cost of doing so and infers that not voting might well be rational.I don't think it's as clear as this.
If voting is rational it comes down to a comparison of the costs with the consumption benefits.
This, however, is true only if we identify rationality with instrumental rationality. But there are, as Robert Nozick pointed out in his best book, two other conceptions of rationality which better justify voting.
One, which arises from Newcomb's problem, is evidential expected utility. You might believe that your decision to vote will affect the outcome not because it will be the decisive vote, but because your choosing to vote will be evidence that people like you will also choose to vote.Your voting then brings thousands of votes out.
Voting is like a Schelling focal point; it's an action people undertake in the belief that others will do so. In the days before mobile phones, people in Leicester would often meet under the clock tower; the clock tower was a focal point. And often, the real world solution to the classic prisoners' dilemma is to keep quiet; not grassing is a focal point. (Social norms are focal points.)
The second conception is symbolic utility. Some things we do not because they make sense in selfish cost-benefit terms, but because they symbolize - maybe just to ourselves but maybe to others - the type of person we are. For many people, voting is rational not because it changes the outcome of the election, but because it's a way of reminding ourselves that we are socially-engaged citizens.
Why do people go on protest marches? Why do so many countries ban drugs? Why don't we euthanize unhealthy old people? The answer lies not in cost-benefit thinking, but in symbolic utility.
I don't say this to say that voting is or is not rational. I do so to point out that rationality has more conceptions than Gradgrindian economists sometimes think.