Knocking on Heaven's Door Read Online Free PDF

and accessible scales. But technology combined with theory allows us to establish the nature of matter over a vast stretch of lengths.
    Known scientific theories apply over this huge range—spanning distances as small as the tiny objects explored by the Large Hadron Collider (LHC) up to the enormous length scales of galaxies and the cosmos. And for each possible size of objects or distance between them, different aspects of the laws of physics can become relevant. Physicists have to cope with the abundance of information that applies over this enormous span. Although the most basic laws of physics that apply to tiny lengths are ultimately responsible for those that are relevant to larger scales, they are not necessarily the most efficient means of making a calculation. When the extra substructure or underpinnings are irrelevant to a sufficiently precise answer, we want a more practical way to calculate and efficiently apply simpler rules.
    One of the most important features of physics is that it tells us how to identify the range of scales relevant to any measurement or prediction—according to the precision we have at our disposal—and then calculate accordingly. The beauty of this way of looking at the world is that we can focus on the scales that are relevant to whatever we are interested in, identify the elements that operate at those scales, and discover and apply the rules that govern how these components relate. Scientists average over or even ignore (sometimes unwittingly) physical processes that occur on immeasurably small scales when formulating theories or setting up calculations. We select relevant facts and suppress details when we can get away with it and focus on the most useful scales. Doing so is the only way to cope with an impossibly dense set of information.
    When appropriate, it makes sense to ignore minutiae in order to focus on the topic of interest and not to obscure it with inessential details. A recent lecture by the Harvard psychology professor Stephen Kosslyn reminded me how scientists—and everyone else—prefer to keep track of information. In a cognitive science experiment that he performed on the audience, he asked us all to keep track of line segments he presented on a screen one after the other. Each of the segments could go “north” or “southeast,” and so on, and together they formed a zigzagging line. (See Figure 2.) We were asked to close our eyes and say what we had seen. We noticed that even though our brains allow us to keep track of only a few individual segments at a time, we could remember longer sequences by grouping them into repeatable shapes. By thinking on the scale of the shape rather than the individual line segment, we could keep the figure in our heads.

    [ FIGURE 2 ] You might choose as your component the individual line segment or a larger unit, such as the group of six segments that appears twice.
    For almost anything you see, hear, taste, smell, or touch, you have a choice between examining details by looking very closely or examining the “big picture” with its other priorities. Whether staring at a painting, tasting wine, reading philosophy, or planning your next trip, you automatically parcel your thoughts into the categories of interest—be they sizes or flavor categories, ideas, or distances—and the categories that you don’t find relevant at the time.
    The utility of focusing on the pertinent questions and ignoring structures too small to be relevant applies in many contexts. Think about what you do when you use MapQuest or Google maps or look at the small screen on your iPhone. If you were traveling from far away, you would first get some rough idea where your destination is. Subsequently, when you have the big picture, you would zoom into a map with more resolution. You don’t need the additional detailed information in your first pass. You just want to have some sense of location. But as you begin to map out the details of your journey—as