On Second Thought...

[ Fri. Jan. 2. 2009 ]

Scientists are supposed to change their minds when evidence undercuts their views. Dream on.

When politicians do it, they're tarred as flip-floppers. When lovers do it, we complain they're fickle. But scientists are supposed to change their minds. Having adopted their views on scientific questions— What killed the dinosaurs? Is the universe infinite?—based on a dispassionate evaluation of empirical evidence, they are expected to willingly, even eagerly, abandon cherished beliefs when new evidence undercuts them. So it is remarkable that so few of the essays in a new book in which scientists answer the question in the title, "What Have You Changed Your Mind About?", express anything like this ideal.

Many of the changes of mind are just changes of opinion or an evolution of values. One contributor, a past supporter of manned spaceflight, now thinks it's pointless, while another no longer has moral objections to cognitive enhancement through drugs. An anthropologist is now uncomfortable with cultural relativism (as in, study the Inca practice of human sacrifice non-judgmentally). Other changes of mind have to do with busted predictions, such as that computer intelligence would soon rival humans'.

Rare, however, are changes of mind by scientists identified with either side of a contentious issue. No one who rose to fame arguing that Alzheimer's disease is caused by sticky brain plaques and who has now been convinced by evidence that the plaques are mostly innocent bystanders, not culprits. No one who once pushed hormone replacement therapy to prevent heart attacks in menopausal women who now realizes that the drugs increase the risk of heart attacks (as well as stroke and breast cancer). No one who cast his lot with the theory that a killer asteroid sent the dinosaurs into extinction who now reads the impact-crater evidence as implicating worldwide volcanism instead. But really, we shouldn't be surprised. Proponents of a particular viewpoint, especially if their reputation is based on the accuracy of that viewpoint, cling to it like a shipwrecked man to flotsam. Studies that undermine that position, they say, are fatally flawed.

In truth, no study is perfect, so it would be crazy to chuck an elegant, well-supported theory because one new finding undercut it. But it's fascinating how scientists with an intellectual stake in a particular side of a debate tend to see flaws in studies that undercut their dearly held views, and to interpret and even ignore "facts" to fit their views. No wonder the historian Thomas Kuhn concluded almost 50 years ago that a scientific paradigm topples only when the last of its powerful adherents dies.

The few essays in which scientists do admit they were wrong— and about something central to their reputation—therefore stand out. Physicist Marcelo Gleiser of Dartmouth breaks ranks with almost every physicist since Einstein, and with his own younger self, in now doubting that the laws of nature can be unified in a single elegant formulation. Gleiser has written dozens of papers proposing routes to the unification of gravity and quantum mechanics through everything from superstrings to extra dimensions, but now concedes that "all attempts so far have failed." Unification may be esthetically appealing, but it's not how nature works.

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