Followup to: Stranger Than History, Robin's post What Evidence Ease of Imagination?

I've been pondering lately the notion of "absurdity" - wondering what exactly goes on in people's minds when they utter the adjective "absurd" or the objection "Absurd!"

If there is an absurdity heuristic, it would seem, at first glance, to be the mirror image of the well-known representativeness heuristic. The less X resembles Y, or the more X violates typicality assumptions of Y, the less probable that X is the product, explanation, or outcome of Y. A sequence of events is less probable when it involves an egg unscrambling itself, water flowing upward, machines thinking or dead people coming back to life. Since human psychology is not a pure structure of quantitative probabilities, it is easy to imagine that the absurdity heuristic is separate from the representativeness heuristic - implemented by separate absurdity-detecting brainware.

I suspect people may also be more sensitive to "absurdity" that invalidates a plan or indicates cheating. Consider the difference between "I saw a little blue man yesterday, walking down the street" versus "I'm going to jump off this cliff and a little blue man will catch me on the way down" or "If you give me your wallet, a little blue man will bring you a pot of gold." (I'm thinking, in particular, about how projections of future technology are often met by the objection, "That's absurd!", and how the objection seems more violent than usual in this case.)

As Robin observed, a heuristic is not necessarily a bias. The vast majority of objects do not fall upward. And yet helium balloons are an exception. When are exceptions predictable?

I can think of three major circumstances where the absurdity heuristic gives rise to an absurdity bias:

The first case is when we have information about underlying laws which should override surface reasoning. If you know why most objects fall, and you can calculate how fast they fall, then your calculation that a helium balloon should rise at such-and-such a rate, ought to strictly override the absurdity of an object falling upward. If you can do deep calculations, you have no need for qualitative surface reasoning. But we may find it hard to attend to mere calculations in the face of surface absurdity, until we see the balloon rise.

(In 1913, Lee de Forest was accused of fraud for selling stock in an impossible endeavor, the Radio Telephone Company: "De Forest has said in many newspapers and over his signature that it would be possible to transmit human voice across the Atlantic before many years. Based on these absurd and deliberately misleading statements, the misguided public...has been persuaded to purchase stock in his company...")

The second case is a generalization of the first - attending to surface absurdity in the face of abstract information that ought to override it. If people cannot accept that studies show that marginal spending on medicine has zero net effect, because it seems absurd - violating the surface rule that "medicine cures" - then I would call this "absurdity bias". There are many reasons that people may fail to attend to abstract information or integrate it incorrectly. I think it worth distinguishing cases where the failure arises from absurdity detectors going off.

The third case is when the absurdity heuristic simply doesn't work - the process is not stable in its surface properties over the range of extrapolation - and yet people use it anyway. The future is usually "absurd" - it is unstable in its surface rules over fifty-year intervals.

This doesn't mean that anything can happen. Of all the events in the 20th century that would have been "absurd" by the standards of the 19th century, not a single one - to the best of our knowledge - violated the law of conservation of energy, which was known in 1850. Reality is not up for grabs; it works by rules even more precise than the ones we believe in instinctively.

The point is not that you can say anything you like about the future and no one can contradict you; but, rather, that the particular practice of crying "Absurd!" has historically been an extremely poor heuristic for predicting the future. Over the last few centuries, the absurdity heuristic has done worse than maximum entropy - ruled out the actual outcomes as being far too absurd to be considered. You would have been better off saying "I don't know".