Why do people believe things that science has proved untrue?

The world was going to end on Dec. 21, 1954, in a flood. But the cult members had no fear. They had faith, so they would be saved -- rescued by a spaceship and whisked away from God's wrath.

On Dec. 22, 1954, some of those cult members felt pretty foolish. But, to the shock of psychologist Leon Festinger, who had been studying the cult, others went the opposite way: They believed even more strongly than they had before the prophecy failed. In fact, to these true believers, the prophecy had not failed at all. They, the cult members, had managed to stop the flood with the power of their faith [source: Mooney]. That there was no flood was proof that they were right to believe.

In 1957, Festinger coined the term cognitive dissonance to describe what he had seen. It refers to the mental discomfort of facing inconsistency in one's thoughts, beliefs, perceptions and/or behaviors [source: McLeod]. He theorized that in this state of stress, the mind will tend seek a way to remove the conflict and restore cognitive harmony.

Most of us indulge this tendency to some degree. We all want to feel comfortable with our thoughts and actions, and it's a whole lot harder to change than it is to stay the same. We can see cognitive-dissonance theory at work in everyday life. A parent who believes her child to be brilliant believes the test he failed was poorly written, even though the rest of the class did fine on it. A man who catches his disheveled wife leaving a hotel with another man believes nothing happened, they just talked.

When an otherwise rational person holds an irrational belief in the face of significant evidence against it, cognitive dissonance is usually involved. How the mind facilitates this is a study in self-preservation, and it typically involves a mental tendency known as confirmation bias.

When there was no flood, no spaceship, no death and destruction, the cult members were faced with two possible "facts." Option No. 1: They were wrong to believe. Option No. 2: They were right to believe, because their faith stopped the flood.

In fact, for the most sincere believers, option No. 1 probably didn't enter the picture. And if it did, they probably would have immediately forgotten it.

Confirmation bias can explain everything from unbudging stereotypes to increasing political polarization. The theory goes: We are more likely to believe (or seek or remember or even notice) the "facts" that support our current viewpoints, and less likely to believe the ones that would require mental adjustment. The more deeply ingrained or self-defining or consequential the current viewpoint, the further the mind might go to ignore the new evidence that would disprove it [source: Arnold]. Attempts to debunk an irrational belief will tend instead to reinforce it, as the believer may have come to see his or her perseverance as heroic, as standing up to the "establishment" [source: Arnold].

While belief perseverance is not limited to the realm of science, when that new, threatening evidence takes the form of overwhelming scientific data, there are some approaches that work particularly well to keep the conflict at bay.

When a parent who refused to vaccinate due to the autism link, who spoke out publicly on the topic and even criticized his friends for following the schedule, is faced with overwhelming evidence that there is no link at all, he may determine that "evidence" to be the product of a far-reaching medical, governmental and corporate conspiracy to maintain high pharmaceutical-industry profits.

Creating a conspiracy is one of the easiest ways to reject evidence. Conspiracies by nature are irrefutable. It's all happening in secret. Anybody can be in on it. The data is faked. The photos are re-touched. The corporate-funded media will say anything.

It's not the only way, though, to validate a threatened belief. The collection of techniques that enable what has come to be called denialism is a varied bag of tricks.

In the case of Festinger's cult, the technique was "reinterpreting the evidence." This involves analyzing any new facts in such a way as to support the original belief. Before Dec. 21, the truth of their faith would be proved by the flood; after Dec. 21, the truth of their faith was proved by the absence of the flood. Similarly, when Andrew Wakefield's seminal study linking vaccination to autism was published in 1998, its presence in the prestigious British Medical Journal was proof of its legitimacy. In 2011, its retraction by that journal was proof of its legitimacy -- obviously, the pharmaceutical industry was frightened enough by the truth of the study to start throwing its weight around [source: CNN]. (Conspiracy can work in tandem with most other denial techniques.)

One can create standards of proof that science can't possibly meet, such as, "I'll believe that climate change is a result of human actions when I see proof that Earth has never undergone a temperature increase before."

One can seek out "experts" who support the irrational belief through pseudoscience, misinterpretations, misrepresentations and logical fallacies, as in "If smoking really caused lung cancer, everyone who smokes cigarettes would get lung cancer."

Pretty effective on their own, these (and all) belief-perseverance techniques have received a tremendous boost with the advent of the Internet. Those looking to maintain an irrational viewpoint need only perform a simple search to locate fellow believers, entire communities of them, and the "experts" who back it all up with appropriate jargon.

In the end, it's not about science at all. It's about avoiding the stress of unlearning, the possibility of regret or the shame of having been wrong. And so, in the interest of cognitive harmony, otherwise reasonable individuals believe vaccines can cause autism, human actions have nothing to do with climate change, smoking doesn't cause cancer, and the test, obviously, was wrong.

For more information on belief perseverance, denialism, and other theories of modern psychology, check out the links on the next page.