One thing that became clear in the last section is that there is not one simple, pat answer to the question ``what is physics?''. Among other things, we attempted to draw a picture of physics as we experience it through the news. This perspective matters because it shapes how we think of the subject when we approach it for the first time, having only those perceptions behind us. It is also appropriate, because the simple statement of what physics ``is'' (our science to understand nature) somehow fails to represent the degree, or range, of importance that the subject has attained. We also tried, from a perspective ``looking forward'', to explain what changes in the way we live physics has already made possible, and what further paradigms it offers.

Now it is time to start ``taking physics apart'', to see it as its users see it, working with it every day. This will reveal (slowly) the structures that are responsible for the many qualities of importance that lie behind the simple, dry definition.

Before delving into the ineffables, we recognize what the concrete part, Physics, is. Simply put, it is the largest, most explicit and most correct set of statements about what nature does, that man has ever attained. Physics does not include hard-and-fast rules about everything, but it does provide them for an immense range of natural phenomena. It describes atoms, and all of the rules for how they can combine, which then fix the whole structure of chemistry. At a finer level, it describes all of the sub-particles that make up atoms (for atoms are not, as it turns out, really `indivisible'). A particular ``slice'' through this description, that includes a certain set of the sub-particles and describes them at a certain level, is the ``theory of fundamental processes'' we mentioned in the last section. We will see, at many points in later chapters, that this theory is almost certainly not ``ultimate''. However, it is a slice through Physics in the way one can take a slice through the foundation of a building. If one is careful to slice completely through the foundation, one is assured that everything else in the building rests somewhere on top of it. That slice through the foundation may itself rest on other things, which can be pursued separately. Meanwhile, it defines a self-contained description that gives meaning to what the ``base'' of the building is.

Physics contains a description of gravity, that includes the motions of all the things that fall or sit on the earth, the motions of all the planets and stars, their galaxies and clusters of galaxies. It appears that this description is even capable of including the whole ``fabric'' of the universe itself, predicting how it evolves, and saying some things about how it ``began''. This same theory tells us about the local ``structure'' of space and time, and how these two relate, which turns out to be non-trivial.

Physics contains many useful, different ways to describe simple things, like single objects that fly, spin, collide, break apart or join together. However, it also contains very powerful descriptions of large collections of things, like whole roomfuls of air (or stars full of the dissociated pieces of atoms), liquids made of huge numbers of molecules, etc. These descriptions encompass phenomena like sound and temperature, electrical conductivity of metals, how magnets are possible, and so forth. Such properties are special because they are properties of the collection itself, even though they are not properties of any of the atoms or molecules of which it is comprised. Such rules were the first steps in Physics toward also handling complexity.

In short, the knowledge of Physics is the largest and most useful tool we have for taking the occurences of nature, of a vast variety, and making them amenable to man's mind. The obvious question then becomes, how is this knowledge expressed? How is it organized that we can possibly remember enough of it to make use of it, or take it forward. In other words, how does it overcome the library problem? Also, with so many things described, how do we keep it from being riddled with mistakes? Certainly, one of the things we are aware of, when we think of physics, is that there are many things that Physicists do not know, but compared to other areas of thought, there is remarkably little that they get wrong. This is why all the machines work as well as they do.

The question of how the knowledge is expressed is intrinsically a question of how it relates to the user. To say that there are rules for making predictions is not enough to describe how they should be used. It turns out that the other questions, of how it is arranged, so as to be useful, or how it can grow so rapidly and still be kept correct, are closely tied together with the question of what ``confidence'' means in physics, and how this relates to the individual.

The first step in answering all of these comes from the recognition that the language of physics is a language of tools. In some circumstances, one might refer to it as a language of ``directions'', like directions for how to get somewhere. This is to be contrasted with the language of canons. It almost seems silly to mention such a point, except that it is increadibly influential and important. Whether we think of Physics as tool or as canon determines whether our relation to it will be active or passive. There are two very explicit places where this difference of approach is pivotal. To ``hear'' physics in ``the right way'', one needs to have in mind some paradigm of either tool or direction. It can make the difference between understanding everything and understanding nothing.

It is apparent immediately, that we hear directions differently than we hear established wisdom. Wisdom is something handed down, complete before it came to us, set as a canon by an authority beyond our reach. Moreover, a canon will usually go on existing, serving whatever purpose it serves, no matter how we receive it. Quite the contrary, we presumably hear directions only because we have asked for them, and we have done that because we wanted something from the answer. If they do not get us where we want to go, they will have accomplished nothing. They were created for us, according to how we asked, and the ones given to us will be gone after we have used them. Each new set of directions takes a slightly different form, but in the most important way, all correct directions to the same place say the same thing.

Most of all, we know right away whether we have understood the directions we have been given, because we expect to use them to act. If we are not sure of a clear, precise action, we are very aware that somewhere we have not understood. Hopefully, we ask again. The very important point here is that whatever criteria we automatically apply when we hear directions, we tend not to apply at all when we hear a canon. It is ``correct from antiquity'', or at the very least immutable, regardless of what we think of it. Did we understand or not? How can one judge? Does it make a difference?

This is the difference between whether one expects to hear something as a direction or as a canon. The difference is not contained in the statement itself, but in the attitude of the listener. Yet it is hardly subtle. We know frustration, and we know where it first occured, when we are given directions we do not understand. The frustration is the feeling that protects us from wasting the effort entirely. Even more, because we know there is a place we want to go, we expect that it should be possible to give concrete, understandable directions for how to get there, so we keep asking until we get them. Properly heard, the entire language of physics is a language of directions. Every piece of it is constructed to make some action possible. Usually that action is just a correct prediction of what will happen next. To understand physics, we must apply all of our criteria for directions. We must assume from the start that there are ways to tell whether something makes sense or not, just as there are ways to tell whether directions are clear. Either we know what to do next, or we do not. We may have taken a wrong meaning, but if we did, we will find out when we act according to it. We will take a wrong turn, and because we know where we want to go, we will know if we do not get there. We will have to work through many of the real statements of modern physics before it becomes clear how literally true this metaphor is. Meanwhile, expecting it, we can adopt the right orientation from the start.

(This discussion is intended to pre-empt the single biggest problem that usually afflicts descriptions of physics. The listener becomes lost without ever realizing it, because there were no criteria in the first place that told what it was to understand. Eventually, the words just wash over inconsequentially, because like other canons, even the expectation of a hard-and-fast understanding is no longer part of the exchange. The words themselves are implicitly being assumed to serve a different purpose.)

The metaphor of directions mostly applies to the posture of the listener. The metaphor of tools relates more to the structure of the statements themselves. The essence of a canon is its constrained-ness, its rigidity. The authority (of office, historical respect, or whatever) that makes it unchangeable is what protects its content. A language that describes tools is completely different. It is at the same time incomparably more strict, and completely flexible. The language of tools is more strict, because the language of a canon is, at some level, arbitrary. Its form is fixed, but could presumably have been anything different instead, since it could have been fixed a different way. The instructions for using a tool, however, must be consistent with the nature of the tool itself. If they conflict with it, the outcome they predict from using the tool will not be what actually happens. At the same time, though, a tool does not have to be used to do only one job, or used in only one way. Anything that it does presumably defines a use for the tool, and there is indefinite freedom of invention and variation in describing what it can do.

Similarly, the statements of physics do not have to be made only one way. In fact, one of the greatest strengths of physics is that it includes many completely different kinds of rules that describe the same part of nature. The user can decide which rule is most convenient to use, or invent a new one. At the same time, the rules describing nature are constrained by the same kind of strictness as the instructions for using tools. If a rule ever predicts something that doesn't happen, it is wrong. Period.

The entire second chapter is devoted to more careful explanation of these aspects of the language of physics, and our expectations as we use it. For now, enough has been said to suggest that language in itself is an important topic, that needs to be addressed before we try to use it to discuss anything else. It is also enough of a starting point that we can explore some of the consequences of using a language this way.

First we note what we gain from using physics-as-direction rather than physics-as-canon, and from the strictness of physics-as-tool. One difference is that the authority of a canon comes from somebody else. Therefore, if we need that authority do do something, we must have help from someone else before we can act. This relates to the library problem. The statements of physics are rules ``do such-and-such, to make such-and-such happen''. We want to take the right action, to create the desired effect. Any action we take consumes resources, though, or makes something happen, so we don't want to make mistakes. Therefore the authority we want from physics is an assurance that its rules are correct. This is the same kind authority that we expect from libraries, when we look something up rather than trust what we remember or already know. We need this authority before we are willing to act. When we think of physics as tool, right from the start, we appeal to our own experiences to validate what we hear. The fact that the knowledge is arranged to make the maximal use of our experiences is what makes it possible to treat the statements of physics as we treat directions. (Again, we will come back to how this is done in a moment.) With each new thing we hear, we imagine taking some action, and we expect it to make sense, because we expect to find tools in our own experience that are similar enough to be relevant.

Using knowledge this way buys us freedom to act. It is only possible because our sense of what can be trusted draws from our own experiences with nature. That is why we can appeal to it without always having to look something up, or rely on someone else to tell us. Our discussion of dimensional analysis in chapter three will give the first real demonstration of how efficient this process can be. The arrangement of physics is as powerful as it is, because in so many instances the appeal to experiences with familiar tools is the easiest source of confidence there is. More remarkable than that, just by living and experiencing the natural world, we already have a large reservior of such experience, once we learn to recognize and use it.

The escape from the library problem is also the key to the high integrity of the knowledge of physics, and to how fast it can grow. As we have said, people have always wanted to understand nature, and when they trust something, they would like it to be right. Those desires are only useful, though, if people have a way to test what is right themselves, and to do something to change things that are not. When knowledge is so arranged, as it is in physics, that each person's individual, repeatable experiences with nature can be used to test new claims, every person's desire for good answers can feed a similarly cosmopolitan useful effort to produce them. It happens that checking old results in Physics is usually easier than trying to discover new ones. As a result, much of any physicist's time is spent checking and re-checking old results against each new experience, to see if they remain trustworthy. This process can happen because of the strictness of physics-as-tool, but it does happen only as long as we hear, and think with the active scrutiny applied to physics-as-direction. The fact that the knowledge base has the integrity it does is our clue to how well this has been accomplished.

As a sidenote, this relation is also the one that accomplishes the separation of confidence in ideas from the authority of groups or histories. Because physics benefits us only when we use it, our first concern is making sure that the things we think we understand are correct. That makes active, harsh and persistent criticism of all established ideas one of the most important tasks of this co-operative society. The ideas that can convert their harshest critics to believers, because they are supported by experience, are the ones to be trusted most.

This very way of arranging knowledge and using experience is the special thing that people learned, for the first time, 300 years ago. One can find isolated, insightful and correct observations about nature scattered back through recorded history. However, the newfound ability to empower as many inventors and watchdogs as there were consumers, was what suddenly enabled physics to change the way the world lives in a few generations. It happens that Newton established the paradigm, and created one of the first examples, with his laws for gravity and the motions of the planets. The arrangement of physics has become more powerful since then, though, so we will treat it as it applies today.


Thu Aug 31 12:01:42 CDT 1995