In a sense, this book is the result of those questions. I know that any city is multifaceted, that it can be seen in many ways.... My goal in writing this book is to provide yet another way to see the city -- to examine it through the eyes of science and technology.

I hold to the scientist's standard conceit that important changes -- fundamental changes -- in the way cities function depend on the development of new insights into the functioning of nature and the technologies that follow from them. ... Social constraints may have profound effects on cities in the short term, but in the long run the changes that matter most are driven by science and technology.

The desire to put up a tall building may depend on social and economic factors, but the ability to do so depends on the science and technology available to the builders. The kinds of cities we build depend on our understanding of the natural world -- what we call science -- and on our ability to turn that understanding to our own ends -- what we call technology.

There are advantages -- bonuses, if you will -- to looking at cities through the eyes of science. If you can see the history of the technological threads that have been woven together to make cities what they are, then you already have come a long way toward seeing where they are going. ... technology sets the limits on what cities can be, defines the general directions in which they will grow. In the language of the engineer, technology defines the "envelop" inside of which cities can develop.

I want you to see modern cities, then, as products of a series of discoveries about the physical universe. In particular, I will look at three of these discoveries, each of which has irreversibly altered the kinds of cities we live in, and will continue to shape the cities of the future.

1. The Ability to Manipulate Atoms
2. The Ability to Unlock Stored Energy
3. The Ability to Store and Transmit Information Electrically

To start our tour of cities, I'll talk about the city as a natural ecosystem and discuss what this means in terms of limits to urban growth. After this introduction, I'll turn to the three scientific threads listed above, talking about physical structures, energy and transportation, and communications.

What I want to do in this book is to suggest another point of view -- another way to look at cities -- that can add another dimension to this understanding. This other point of view is that of the natural scientist, who sees the various parts of cities as examples of the laws of nature in operation, and the whole as a system that can be described in much the same way as other systems in nature.

The city, in fact, can be thought of as a natural system on at least three different levels, each of which can give us insight into what a city is. At the most obvious level, although we don't normally think in these terms, a city is an ecosystem, much as a salt marsh or a forest is. A city operates in pretty much the same way as any other ecosystem, with its own particular collection of flora and fauna. This way of looking at cities has recently received the ultimate academic accolade -- the creation of a subfield of science, called urban ecology, devoted to understanding it.

At a somewhat deeper level, a natural ecosystem like a forest is a powerful metaphor to aid in understanding how cities work. Both systems grow and evolve, and both require a larger environment to supply them with materials and to act as a receptacle for waste. Both require energy from outside sources to keep them functioning, and both have a life cycle -- birth, maturity, and death.

Finally, our cities are like every other natural system in that, at bottom, they operate according to a few well- defined laws of nature -- laws that are knowable and, indeed, largely known.