Imagine a world you could trust--really trust-- where truth was transparent and juries, police, locksmiths and gossip columnists were largely overthrown. Human society would be orderly, boring and as alien as an anthill.

This is the promise and the threat of a machine that could read minds. The hoary polygraph has never filled the bill. It measures not thoughts but only the indirect physiological consequences of thoughts--blood pressure and respiration, among others--that hint that a subject may be lying. The result, critics charge, is false positives--an honest answer misjudged as a lie--and false negatives--a lie misjudged as the truth. The courts have long ruled polygraph findings inadmissible as evidence. Just last October the National Research Council damned the device as a "blunt instrument," of little use in ferreting out criminals, spies and terrorists.

This article was originally published with the title Mind Readers.

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