At a somewhat deeper stratum, Kelvin’s blunder probably stemmed from a well-recognized psychological trait: The more committed we are to a certain opinion, the less likely we are to relinquish it, even if confronted with massive contradictory evidence. (Does the phrase “weapons of mass destruction” ring a bell?) The theory of cognitive dissonance, originally developed by psychologist Leon Festinger, deals precisely with those feelings of discomfort that people experience when presented with information that is inconsistent with their beliefs. Multiple studies show that to relieve cognitive dissonance, in many cases, instead of acknowledging an error in judgment, people tend to reformulate their views in a new way that justifies their old opinions.

The messianic stream within the Jewish Hasidic movement known as Chabad provided an excellent, if esoteric, example for this process of reorientation. The belief that the Chabad leader Rabbi Menachem Mendel Schneerson was the Jewish Messiah picked up momentum during the decade preceding the rabbi’s death in 1994. After the Rabbi suffered a stroke in 1992, many faithful followers in the Chabad movement were convinced that he would not die but would “emerge” as the Messiah. Faced with the shock of his eventual death, however, dozens of these followers changed their attitudes and argued (even during the funeral) that his death was, in fact, a required part of the process of his returning as the Messiah.

An experiment conducted in 1955 by psychologist Jack Brehm, then at the University of Minnesota, demonstrated a different manifestation of cognitive dissonance. In that study, 225 female sophomore students (the classical subjects of experiments in psychology) were first asked to rank eight manufactured articles as to their desirability on a scale of 1.0 (“not at all desirable”) to 8.0 (“extremely desirable”). In the second stage, the students were allowed to choose as a take-home gift one of two articles presented to then from the original eight. A second round of rating all eight items then followed. The study showed that in the second round, the students tended to increase their ratings for the article they had chosen and to lower them for the rejected item. These and other similar findings support that idea that our minds attempt to reduce the dissonance between the cognition “I chose item number three” and the cognition “But item number seven also has some attractive features.” Put differently, things seem better after we choose them; a conclusion corroborated further by neuroimaging studies that show enhanced activity in the caudate nucleus, a region of the brain implicated with “feeling good.”

Kelvin’s case appears to fit the cognitive dissonance theory like a glove. After having repeated the arguments about the age of the Earth for more than three decades, Kelvin was not likely to change his opinion just because someone suggested the possibility of convection. Note that Perry was not able to prove that convection was taking place, nor was he even able to show that convection was probable. By the time radioactivity appeared on the scene another decade later, Kelvin was probably even less inclined to publish a concession of defeat. Instead, he preferred to engage in an elaborate scheme of experiments and explanations intended to demonstrate that his old estimates still held true.

Why is it so difficult to let go of opinions, even in the face of contradictory evidence that any independent observer would regard as convincing? The answer can perhaps be found in the way the reward circuitry of the brain operates. Already in the 1950s, researchers James Olds and Peter Milner of McGill University identified pleasure centers in the brains of rats. Rats were found to press the lever that activated the electrodes placed at these pleasure-inducing locations more than six thousand times per hour! The potency of this pleasure-producing stimulation was illustrated dramatically in the mid-1960s, when experiments showed that when forced to choose between obtaining food and water or the rewarding pleasure stimulation, rats suffered self-imposed starvation.