Explanation, Uncertainty, and Levels of Organization
Let me try to clarify something pertaining to issues of explanations and levels of organization, that will have bothered some readers. A few pages back, I suggested that, like many people, you might harbor reservations about the notion of falli- bilism; that, despite intellectually going along with it, you might not completely buy into the notion that you can't be 100% certain of anything in science.
Now, let's acknowledge that, on the face of it, fallibilism seems nonsensical. We must know some scientific facts with absolute certainty, mustn't we? Can there be any doubt, for example, that the earth goes around the sun? How can we square such blatantly obvious truths like this with the dictum that science can't achieve certain truth?The reason is that the provisional truth of scientific statements, their explanatory adequacy for a given problem, is bound up in the concept of levels of organization of nature. At one level, represented by artists' graphic illustrations of the solar system, the earth does go around the sun in a smooth, elliptical orbit. From a much larger cosmological perspective, this is not exactly what happens. Both earth and sun revolve around the center of mass of the solar system (technically, the “barycenter”), and the location of the center of mass is constantly changing as the planets orbit the sun. Zoom out farther, and you'll see that the solar system moves through the Milky Way galaxy; the Milky Way moves within the local cluster of galaxies; the local cluster moves within the universe; and the universe expands. In summary, it is convenient, and true enough for most purposes, to think of the earth as traveling in an elliptical orbit on a flat plane around the sun in spite of the fact that a complete explanation of its motion is way more elaborate than that.
A homey allegory borrowed from Richard Feynman teaches a similar lesson in a different way.33 Suppose, he says, you are told that your dear old Aunt Minnie is suddenly laid up in the hospital because “she slipped on some ice and fell and broke her hip.” At first this strikes you as a perfectly satisfactory answer, and normally you'd head to the store for a sympathy card.
But suppose that this time you want a thorough explanation, and you ask why she slipped on the ice. You are told that her stepping on the ice caused a thin layer of liquid water to form on the surface, the water reduced the friction between her boot and the solid ice, and the reduced friction caused her to slip. This seems odd; when you step on a wood floor, the wood does not liquefy, so you ask about the situation with the ice; after all, if you are really going to understand why the poor old soul is in the hospital, you need to know that! At this point, the answers become increasingly tricky.34 Water expands when it freezes, and scientists used to think that the slipperiness came about when the pressure and friction caused by, say, somebody's boot heel, melted a bit of ice. However, explanations based solely on melting predict that if no melting could occur, ice would not be slippery, and so you ask about that and learn that at temperatures near absolute zero, where ice can't melt, it is still slippery. And nobody knows exactly why. '1 he present thinking is that, at the surface of a sheet of ice, water molecules never truly freeze in place because, at the surface, which is essentially two-dimensional, there are fewer stabilizing atomic bonds among the molecules than there are around the molecules in the threedimensional depths of the ice. The interactions between the weakly bound surface molecules and the deeper lying ones mean that the surface of ice is always in a quasi- liquid state that accounts for its slipperiness. 'lhe apparently simple question about why Aunt Minnie is in the hospital takes us to levels of nature where we don't have complete answers. All the same, it would be idiotic to say that, because we don't understand ice at its most basic physical levels, we don't know why she is in the hospital. We do. She slipped on the ice!'lhe moral of the story is that uncertainty, the concept of fallibilism, is related to the level of organization of nature, or its complexity, that you're interested in.
An adequate explanation depends on what you need to know, the level of complexity of the system you are working with, and the kind of question you are asking. An explanation may only suffice at a particular level. This is why we can feel sure of some things and, at the same time, accept that all of our scientific knowledge is uncertain.Science has different standards for different purposes. For basic (i.e., “pure”) research, nothing short of perfect knowledge will do. So pure research keeps striving with no end in sight. For applied research and technology, it's another matter entirely; for applied purposes, we have to take action based on the best information we have. We know enough about ice and elderly people to put down sand or salt on ice on a sidewalk without knowing everything there is to know about ice. We understand enough about physics and the movements of planets to launch a space probe and put it into orbit around Jupiter 5 years later35 without having a ToE.
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