There is a good-news-bad-news rhythm to the introduction of any pervasive new technology. With cellular telephones, for instance, the good news came with the explosive growth of the industry itself, which by November 1992 had recorded its 10 millionth customer. Three months later came the bad news: David Reynard, bereaved husband, appeared on “Larry King Live” with the remarkable accusation that cell-phone use had caused the brain tumor that killed his wife. Reynard, not surprisingly, was suing the cell-phone companies he held responsible. With that single anecdotal incident, Reynard set in motion a health scare that continues to play in the press and our societal subconscious to this day. If history is any indication, it will continue indefinitely. I can make this prediction free of concern about whether cell-phone use is truly carcinogenic. If it’s not, in fact, our anxiety-and the amount of press that fuels this anxiety-is likely to last considerably longer. Such is the nature of fear and the nature of science, and the inability of the latter to dispel the former.

The noteworthy aspect of fear is that its shelf life is considerably longer when the object of fear is a threshold phenomenon-invisible, at the limits of detection, if not simply a figment of the imagination. This preternatural quality is crucial because both science and the human intellect have evolved to handle the material world with relative ease. After all, when automobiles kill tens of thousands of Americans each year, the mechanism of our demise is relatively obvious, as it is with guns. Anxiety is not the issue. Caution is. If science manages to unambiguously identify the agent of an illness, as happened with the AIDS virus, the shadow of impending doom is dispelled by the light of knowledge, and the medical research establishment marches off to deal with it. The rest of us, or most of us, alter our behavior accordingly and the prophylactic industry flourishes. But we don’t, by and large, panic.

If no immediate cause of death or illness can be identified, or if no mechanism links the alleged agent of our woe directly to the illness or death-as was the case, for instance, with electromagnetism from power lines, silicone seeping from breast implants or, at least so far, genetically manipulated agricultural products-then fear sets in like ice on a pond, and an entirely different set of societal forces go to work.

This is where science fails us. The primary problem is that science is incapable of proving a negative. Over the years, researchers have looked at the effects of electromagnetic radiation at cell-phone-like frequencies on cells (the biological kind) in petri dishes and on lab animals and even humans, without coming up with any particularly believable evidence that cell phones themselves would be harmful. But here’s the catch: No matter how ingenious and copious the experiments, they could no more prove that cell phones do not cause cancer than they could prove the nonexistence of God. “It is scientific only to say what is more likely and what less likely,” as Richard Feynman put it, “and not to be proving all the time the possible and impossible.” When it comes to what is more or less likely, however, everyone has a different opinion on how to weigh the odds. That the scientific community and the lay public do so by different standards of evidence is made obvious by the common belief in phenomena-from UFOs, ESP and ghosts to the continuing incarnation of Elvis-that are not considered likely by most working scientists.

This proving-a-negative problem comes with an important corollary: Experimental science is also inherently incapable of achieving perfection. The experiment does not exist, nor will it ever, that can unambiguously throw up zeros across the board simply because the phenomenon it has set out to study is nonexistent. Rather, if done honestly, it will result in a range of values around zero, and the midpoint of this range is even likely to be above zero-a positive result, in the lingo-because it will reflect a host of subconscious factors that will push researchers to be slightly optimistic rather than rigorously detached. For those who want to believe that the phenomenon is real, the existence of these positive results, however close to zero, will constitute all the evidence they need.

This is simply a fact of human nature, one that Francis Bacon, the Abner Doubleday of experimental science, pointed out 400 years ago when he created the scientific method as a tool to overcome our inherently delusional thinking. “The human understanding still has this peculiar and perpetual fault of being more moved and excited by affirmatives than by negatives,” Bacon wrote, “whereas rightly and properly it ought to give equal weight to both; rather, in fact, in every truly constituted axiom, a negative instance has the greater weight.” Those of us who believe in ESP, for instance, do so because we have anecdotal evidence that it does exist, despite the decades of scientific experiments that suggest it does not.

As a result, little or nothing is needed in a scientific vein to initiate health scares, and even less to perpetuate them indefinitely. Indeed, they become inevitable and play themselves out with a certain relentless predictability. Their procession from meaningless beginnings to full-blown national anxiety could be dictated by a flowchart or programmed with simple software.

Imagine that researchers from Laboratory A decide to study the possibility that cell phones cause cancer, assuming for the sake of argument that the hypothesis is false. If the researchers do their study well and find insufficient evidence of carcinogenicity, the story ends. Until, that is, Laboratory B gets involved. These researchers are likely to be slightly less detached than their predecessors. After all, they would not have chosen this line of research had they not believed, in effect, that the work of Laboratory A left open a window of doubt. If these researchers now perform their experiments less rigorously, or interpret their data less rigorously, then they are likely to publish an article suggesting that cell phones may cause cancer. Or if not Lab B, than Lab C, or D, ad virtually infinitum.

This report will be picked up by the press because even the hint of a suggestion that some aspect of everyday life may cause illness or death constitutes news. This is not just the way of the press, it’s human nature, as Francis Bacon made clear. (A recent example is the coverage of a study on exposure to household levels of radon gas that was published in the June issue of the American Journal of Epidemiology. Over the years, a dozen studies have failed to show that household levels of radon increase cancer risk. When the 13th was published claiming the opposite, the newspaper headlines read: “University of Iowa Study Says Radon Greater Risk Than Thought Before.” The Iowa scientists, of course, said they simply used better techniques than their predecessors. They may be right, but the odds are against them.)

When the press publishes such reports, the relevant federal agencies have no choice but to get involved. If they do not, consumer-protection groups will accuse them of taking a cavalier approach to public health. The same goes for the relevant industry. To do nothing is to invite public reproach. Now both the agencies and the industry will respond publicly that little or no scientific evidence exists to support the claims, but they will also admit that the threat can’t be ruled out. Either or both will allocate money to do proper scientific studies. If these studies unambiguously identify a mechanism by which cell phones cause brain tumors, we have a real public health threat on our hands, and the authorities are mobilized. End of fear. We stop using our cell phones, or we stop using them in a way that could be dangerous.

If these studies come up negative, however, the scientists will report that their data suggest it is unlikely cell phones cause cancer, perhaps highly unlikely. They will also admit, if they are rigorously scientific, that they cannot rule out an effect. This may satisfy the public, the consumer protection groups and even the press, although the smart money would bet against it. As one consumer advocate put it in a recent news article on the cell-phone scare: “People just want to know whether phones are safe or not, yes or no.” Neither-the scientifically appropriate response-eases no one’s anxiety.

One other factor will come into play at this point. Experts refer to it as an epidemic of selection. We inevitably search for explanations when tragedy hits. The unfortunate individuals who have had brain tumors or have seen their loved ones succumb, as did David Reynard, will look for explanations and may seize on those that they read about in the newspapers-cell phones, for instance. The news reports on the possibility that cell phones cause cancer are likely to suggest to thousands of victims and their families that cell phones were the cause of their illness. (A number of liability lawyers will come to the same conclusion.) They will start advocacy groups and lobby Congress, and when industry-funded studies come up empty, they will suggest that the industry scientists involved had no motivation to find the truth. When cooler heads suggest that such cover-ups are unlikely, that even cell-phone company employees use cell phones and that these scientists are probably no more likely than you or I to allow innocent people to die needlessly for the sake of a modest paycheck, they will point to the cigarette industry as proof that this has happened before and so it may be happening again. As congressmen realize that votes are on the line, they will push the relevant government agencies to do more studies. But no amount of studies will resolve the residual ambiguity, will allow the scientists to say cell phones are definitively safe. The leftover uncertainty perpetuates itself indefinitely.

Eventually the anxiety-of-the-decade will fade, to be replaced in our minds and our newspapers by a more up-to-date apprehension. It would be nice to think that eventually we’ll outgrow the cycle, but I have to defer here to my late mother, who was a lay expert on anxiety. The time to really worry, she used to say, is when things seem so good you have nothing to worry about.