Knocking on Heaven's Door - Lisa Randall [105]
For public policy, decision points can be even less clear. Public opinion usually occupies a gray zone where people don’t necessarily agree on how accurately we should know something before changing laws or implementing restrictions. Many factors complicate the necessary calculations. As the previous chapter discussed, ambiguity in goals and methods make cost-benefit analyses notoriously difficult, if not impossible, to reliably perform.
As New York Times columnist Nicholas Kristof wrote in arguing for prudency about potentially dangerous chemicals (BPA) in foods or containers, “Studies of BPA have raised alarm bells for decades, and the evidence is still complex and open to debate. That’s life: in the real world, regulatory decisions usually must be made with ambiguous and conflicting data.”51
None of these issues mean that we shouldn’t aim for quantitative evaluations of costs and benefits when assessing policy. But they do mean that we should be clear about what the assessments mean, how much they can vary according to assumptions or goals, and what the calculations have and have not taken into account. Cost-benefit analyses can be useful but they can also give a false sense of concreteness, certainty, and security that can lead to misguided applications in society.
Fortunately for physicists, the questions we ask are usually a lot simpler—at least to formulate—than they are for public policy. When we’re dealing with pure knowledge without an immediate eye to applications, we make different types of inquiries. Measurements with elementary particles are a lot simpler, at least in principle. All electrons are intrinsically the same. You have to worry about statistical and systematic error, but not the heterogeneity of a population. The behavior of one electron is representative of them all. But the same notions of statistical and systematic error apply, and scientists try to minimize these whenever feasible. However, the lengths to which they will go to accomplish this depends on the questions they want to answer.
Nonetheless, even in “simple” physics systems, given that measurements won’t ever be perfect, we need to decide the accuracy to aim for. At a practical level, this question is equivalent to asking how many times an experimenter should repeat a measurement and how precise he needs his measuring device to be. The answer is up to him. The acceptable level of uncertainty depends on the question he asks. Different goals require different degrees of accuracy and precision.
For example, atomic clocks measure time with stability of one in 10 trillion, but few measurements require such a precise knowledge of time. Tests of Einstein‘s theory of gravity are an exception—they use as much precision and accuracy as can be attained. Even though all tests so far demonstrate that the theory works, measurements continue to improve. With higher precision, as-yet-unseen deviations representing new physical effects might appear that were impossible to see with previous less precise measurements. If so, these deviations would give us important insights into new physical phenomena. If not, we would trust that Einstein’s theory was even more accurate than had been demonstrated before. We would know we can confidently apply it over a greater regime of energy and distances and with a higher degree of accuracy. If you were sending a man to the Moon, on the other hand, you would want to understand physical laws sufficiently well that you aim your rocket correctly, but you wouldn