Knocking on Heaven's Door Read Online Free PDF Page B

your resolution becomes finer in seeking out the exact street you will need—you will care about the details on the finer scale that were inessential to your first exploration.
    Of course, the degree of precision you want or need determines the scale you choose. I have friends who don’t pay much attention to hotel location when visiting New York City. For them, the gradations in character of the city’s blocks is irrelevant. But for anyone who knows New York, those details matter. It’s not enough to know you are staying downtown. New Yorkers care if they are above or below Houston Street, or east or west of Washington Square Park, or even whether they are two or five blocks away.
    Although the precise choice of scale might differ among individuals, no one would display a map of the United States in order to find a restaurant. The necessary details won’t be resolvable on a computer screen displaying such an overly large scale. On the other hand, you don’t need the details of a floor plan just to know that the restaurant is there in the first place. For any question you ask, you choose the relevant scale. (See Figure 3 for another example.)
    The Eiffel Tower

    [ FIGURE 3 ] Different information becomes more obvious when viewed at different scales.
    In a similar manner, we categorize by size in physics so we can focus on the questions of interest. Our tabletop looks solid—and for many purposes we can treat it as such—but in reality it is made up of atoms and molecules that collectively act like the hard impenetrable surface we encounter at the scales we experience in our daily lives. Those atoms aren’t indivisible, either. They are composed of nuclei and electrons. And the nuclei are made of protons and neutrons that are in turn bound states of more fundamental objects called quarks. Yet we don’t need to know about quarks to understand the electromagnetic and chemical properties of atoms and elements (the field of science known as atomic physics). People studied atomic physics for years before there was even a clue about the substructure beneath. And when biologists study a cell, they don’t need to know about quarks inside the proton either.
    I remember feeling a tad betrayed when my high school teacher, after devoting months to Newton’s Laws, told the class those laws were wrong. But my teacher was not quite right in his statement. Newton’s laws of motion work at the distances and speeds that were observable in his time. Newton thought about physical laws that applied, given the accuracy with which he (or anyone else in his era) could make measurements. He didn’t need the details of general relativity to make successful predictions about what could be measured then. And neither do we when we make the sorts of predictions relevant to large bodies at relatively low speeds and densities that Newton’s Laws apply to. When physicists or engineers today study planetary orbits, they also don’t need to know the detailed composition of the Sun. The laws that govern the behavior of quarks don’t noticeably affect the predictions relevant to celestial bodies either.
    Understanding the most basic components is rarely the most efficient way to understand the interactions at larger scales, where tiny substructure generally plays very little role. We would be hard pressed to make progress in atomic physics by studying the even tinier quarks. It is only when we need to know more detailed properties of nuclei that the quark substructure becomes relevant. In the absence of unfathomable precision, we can safely do chemistry and molecular biology while ignoring any internal substructure in a nucleus. Elizabeth Streb’s dance movements won’t change no matter what happens at the quantum gravity scale. Choreography relies only on classical physical laws.
    Everyone, including physicists, is happy to use a simpler description when the details are beyond our resolution. Physicists formalize this intuition and organize