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What Scientists Really Do

What Scientists Really Do by Priyamvada Natarajan The New York Review of Books


Kahan’s research does not address the degree to which people understand the scientific method—not whether they know what protons or logarithms are, but whether they have an adequate sense of what a scientific theory is, how evidence for it is collected and evaluated, how uncertainty (which is inevitable) is measured, and how one theory can displace another, either by offering a more economical, elegant, honed, and general explanation of phenomena or, in the rare event, by clearly falsifying it. The L’Aquila case shows that many people expect science to provide 100 percent certainty, while the North Carolina case reveals the possibility that any uncertainty can be used to render a theory either false or just as good as any other theory.

In a word, the general public has trouble understanding the provisionality of science. Provisionality refers to the state of knowledge at a given time. Newton’s laws of gravity, which we all learn in school, were once thought to be complete and comprehensive. Now we know that while those laws offer an accurate understanding of how fast an apple falls from a tree or how friction helps us take a curve in the road, they are inadequate to describe the motion of subatomic particles or the flight of satellites in space. For these we needed Einstein’s new conceptions.

Take, for example, the Global Positioning System (GPS) that many of us use when driving. GPS is based on a fleet of twenty-four satellites orbiting the earth, each equipped with a precise atomic clock on board. A GPS receiver on an iPhone detects radio signals from any of the satellites overhead, and computes the user’s position within one meter or less. As predicted by Einstein’s theory of special relativity, the satellite clocks circling at 14,000 kilometers per hour tick more slowly than clocks on earth, losing about seven microseconds per day. However, since the clocks are 20,000 kilometers above the earth’s surface, and since, according to Einstein’s general relativity theory, gravity curves space and time, a clock orbiting at this height should tick slightly faster. The combination of these two effects results in a net speeding up so the time on a GPS satellite clock is faster than one on earth by about thirty-eight microseconds per day. To achieve navigational accuracy this speeding up predicted by Einstein must be compensated for.

Einstein’s theories did not refute Newton’s; they simply absorbed them into a more comprehensive theory of gravity and motion. Newton’s theory has its place and it offers an adequate and accurate description, albeit in a limited sphere. As Einstein himself once put it, “The most beautiful fate of a physical theory is to point the way to the establishment of a more inclusive theory, in which it lives as a limiting case.” It is this continuously evolving nature of knowledge that makes science always provisional.

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"Provisionality refers to the state of knowledge at a given time."

What a cool concept.

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