Does Measurement Measure Up?: How Numbers Reveal and Conceal the Truth

CHAPTER 10: HOW FUNNY IS THAT?: Knowledge Without Measurement?

CHAPTER 10 HOW FUNNY IS THAT? Knowledge Without Measurement? You can discover no measure, no weight, no form of calculation, to which you can refer your judgments in order to give them absolute certainty. In our art there exists no certainty except in our sensations. —Hippocrates (ca. 460–ca. 377 BC) A few honest men are better than numbers. —Oliver Cromwell (letter, 1643) The Measurement Cycle The December 26, 2004, earthquake and tsunami in the Indian Ocean was one of the greatest natural disasters in recorded history. Over 150,000 people were killed and more than half a million were injured. In the aftermath of this calamity, there has been much discussion of tsunami warning systems. The history of our attempts at the measurement of tsunamis in order to provide such warnings serves as a good example of what I believe we can D OES M EASUREMENT M EASURE U P ? 184 think of as the three stages in the ‘‘measurement cycle.’’ From a broad consideration of all the various measurement techniques described throughout this book, it seems to me that this measurement cycle is more or less repeated each time measurement finds its way into a new area—such as the measurement of tsunamis for the purposes of developing warning systems. This cycle consists of three stages of varying lengths of time: First there is the premeasurement era, which is characterized by ignorance, or at the very least by ‘‘meager and unsatisfactory knowledge.’’ Decision-making during this stage is governed not by reasoned analysis but rather, at best, by vague hunches and the powers of persuasion, or, at worst, by nothing at all. The period of meager and unsatisfactory knowledge that characterizes the first stage of the measurement cycle is followed by the second stage: the development of measurement—through inspiration, innovative research, trial and error, and so on. Finally, there is the third stage: the application of measurement, and its further development and refinement. Tsunamis are usually caused by underwater earthquakes, although they can have other causes, such as volcanoes, landslides, or meteor strikes. The earliest tsunami warning systems were developed in Hawaii in the 1920s. Prior to that, there was very little way to know when a tsunami might strike. Our ignorance was profound, but not complete. On earthquake-prone islands , such as in Japan, those who dwell near the shore have known for centuries to seek higher ground just after an earthquake has been felt. Experience taught that a tsunami might only be minutes away. However, tsunamis can strike coastlines even when the epicenter of an earthquake is so far away that its tremors are so small as to be imperceptible to humans. Following the Indian Ocean tsunami, some attention has been paid to the ‘‘sixth sense’’ that some animals seemed to have that warned them of this tsunami—it appears that relatively few land animals were killed by the tsunami. Do animals have internal seismographs more sensitive than we humans? We remain largely ignorant of whatever the animals may have been measuring internally that warned them of impending danger. The early tsunami warning systems relied solely on the detection of earthquakes, and not on the tsunamis themselves. Seismographs measure the magnitude of earthquakes by quantifying the magnitude of the seismic waves that travel though the Earth in the wake of an earthquake (or a huge explosion like a volcanic eruption). When an earthquake whose epicenter H OW F UNNY I S T HAT ? 185 is underwater is detected, warnings can be delivered quickly, because seismic waves travel through the ground 30 to 60 times faster than tsunami waves travel through water. Seismic wave speeds vary, but 8 kilometers per second (roughly 29,000 kilometers or 18,000 miles per hour) is a typical number. At that speed, a seismic wave would travel from New York to Los Angeles in about 10 minutes. Since tsunami waves only travel at 500–1,000 kilometers per hour (about 300–600 miles per hour) in open water, warning systems that rely on seismic waves generally allow enough time to warn affected populations. For example, a major earthquake off the coast of California could generate tsunamis traveling east that would hit California in minutes, but the waves traveling west would not arrive in Hawaii or Japan until hours later. The related, crucial issue of ensuring that people near the shore in affected areas actually receive the warnings...