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HORGAN: My faith is based on common sense, Paul, and on science itself. As science advances, it imposes limits on its own power. Relativity theory prohibits faster-than-light travel or communication. Quantum mechanics and chaos theory constrain our predictive abilities. Science's limits are glaringly obvious in particle physics, which, as Steven Weinberg describes [in the Visions issue], seeks a "theory of everything" that will explain the origin of matter, energy and even space and time. The leading theory postulates that reality arises from infinitesimal "strings" wriggling in a hyperspace of 10 (or more) dimensions. Unfortunately, these hypothetical strings are so small that it would take a particle accelerator the size of the Milky Way to detect them! I am not alone in fearing that string theorists are not really practicing science anymore; one leading physicist has derided string theory as "medieval theology." Paul, here is persuasive evidence of science's plight.
HOFFMAN: Yes, but who is to say that all these scientific theories won't ultimately be replaced by ones with greater explanatory power? Galileo and Newton thought their laws of motion were the cat's pajamas, explaining everything under the sun and many things beyond, but 2 1/2 centuries later a Swiss patent clerk toppled their notions of space and time. Obviously, Galileo and Newton did not foresee what Einstein found. I think it's ahistorical to assert that in the future there will never be an Einstein of, say, the mind who will be able to pull together a theory of consciousness. And even if it's true that some of the big unanswered questions of science may never be answered, a lot of new and exciting science could still come from overturning truths that we now take for granted. Robert Gallo, the AIDS researcher, once told me that at the end of the 1970s, he was at a conference where a prominent scientist confidently summed up the truths of biomedicine--such truths as: epidemic diseases are things of the past, at least in so-called developed nations; a widespread outbreak of infectious disease is impossible unless the microbe is casually transmitted; the kind of virus found in animals known as the retrovirus doesn't exist in man; and no virus causes cancer in humans. By the end of the 1980s, these four truisms had hit the dustbin. Or take a more recent example: the newfound plasticity of the human brain. Until a year and half ago, it was a dogma taught in every medical school in the country that the adult human brain is rigid, that its nerve cells can never regenerate. Now we know our brains do have the ability to generate new cells--a discovery that may not only open up a new understanding of the brain but also lead to novel treatments for a host of brain disorders.