Conspiracy theories are curious things.
They can pop up out of nowhere, like the one about Barack Obama setting up FEMA concentration camps in which to imprison Republican voters. They can be durable stand-bys, like the one about HAARP being a secret earthquake weapon — which conspiracy theorists pounced on to try to make mileage out of the earthquakes in Japan and Christchurch this year.
Dr Neil Levy, a philosopher and principal researcher at the Florey Neurosciences Institutes, says there are several things that contribute to belief in conspiracy theories.
One is our tendency to overestimate our own ability to understand events. Another is our lack of appreciation of how in modern society, much knowledge isn't the product of lone individuals or institutions (who might easily be mistaken or dishonest) but the product of deeply interconnected systems. These different streams of knowledge and evidence come together to create a knowledge base that is remarkably sound.
One example of this is GPS satellites. Few of us on our own would have the know-how to test Einstein's theory of general relativity to see if it really is true, much less the ability to design GPS satellites and the rockets that launch them. Yet here we are with GPS satellites orbiting all around us, using Einstein's theory to direct pizza delivery drivers to our door. (And, of course, there are still cranks who claim that Einstein was wrong).
''It is a perennial temptation to think that one can do better than the distributed network of experts,'' Levy says. ''Though the distribution of cognitive labour is something that goes quite far back in human evolution, it is far more pervasive than we are evolved to deal with. We expect to have some grasp on how things work.
''Today we can't have more than the shakiest grasp (if that) in many areas, no matter who we are: the knowledge is too specialised and detailed for us to acquire. Given we have this expectation (which generates what has been called the illusion of explanatory depth), we find it difficult to take things on trust.''
Levy says it isn't necessarily irrational to believe in conspiracies because, after all, conspiracies do exist.
''I think there is a slow slide into irrationality: as the number and the (apparent) independence of the sources who support the official story increases, so does the irrationality,'' Levy says.
''What separates a conspiracy theorist about 9/11 from someone who accepts the official story is the number of independent agencies they must believe are in on it. Maybe there is an elite group within the CIA who could be relied upon to plant explosives and keep quiet about it (though in this age of leaks I wouldn't count on it), but the conspiracy theorists require that the engineers' associations who have rejected their claims that the buildings can't have been destroyed by planes are in on it, as are many journalists, and firefighters and (others).
''Things are even worse with the moon landing, given the literally thousands of people in NASA who would have needed to be bought off.''
All in all, Levy says, you rarely do better by rejecting the ''official'' story.
''In complex societies we are all in relations of epistemic dependence: we simply cannot hope to cut ourselves off from the distributed systems of knowledge production (media, government, economists, academia) and come to a better understanding of the world,'' he says.
''I think that for many conspiracy theories, the explanation of why they are accepted is very similar to the explanation of why people reject climate change and evolution: a mistaken and hubristic belief that a lone blogger (or a small network of bloggers) can do better at explaining events than thousands of well-qualified experts.''
What do you think? Are you a conspiracy believer, or do you know people who are? Which conspiracy theories do you find the most plausible, and which do you think are just silly? If you do believe in a particular conspiracy theory, what kind of evidence would it take to make you reconsider your belief?
Around the science webs:
Carl Zimmer looks at the German E. coli outbreak
David Gorski looks at fashionable toxin silliness
Clastic Detritus rounds up some of the week's best geology blogging