It is, of course, difficult to decide whether someone is an expert in a field when you yourself are not, but certain clues will help you make this deci- sion. If the supposed authority claims to have knowledge of things that he or she could not possibly possess (for example, about private conversations the person could not have heard), then you have little reason to trust other things that person has to say. You know that he or she has no qualms about making things up. Furthermore, it is often possible to spot-check certain claims in order to make sure that they are correct. It may take one expert to determine another, but it often takes little more than good common sense and an unwillingness to be fooled to detect a fraud.
Even when it is clear that the person cited is an expert in the appropriate field, we can still ask whether the question is of the kind that can now be settled by an appeal to experts. One sign that a question cannot yet be settled by experts is that experts in that area do not agree with each other. It does not do much good to cite one authority in support of a claim if another authority with just as much expertise would endorse the opposite claim. Moreover, even the best experts sometimes simply get things wrong. For example, in 1932 Albert Einstein, who was surely an expert in the field, de- clared, “There is not the slightest indication that [nuclear] energy will ever be obtainable. It would mean that the atom would have to be shattered at will.” Just a year later, the atom was, in fact, split. Even so, a leading British physicist, Ernest Lord Rutherford, insisted that the splitting of the atom would not lead to the development of nuclear power, saying, “The energy produced by the atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moon- shine.”5 Given the knowledge available at the time, both Einstein and Rutherford may have been justified in their claims, but their assertions were, after all, more speculations than scientifically supported statements of fact. The lesson to be learned from this is that the best experts are sometimes fal- lible, and become more fallible when they go beyond established facts in their discipline to speculate about the future.