In Part Four of this book I describe how quantum mechanics provides an understanding of the quantum nature of the atom, of chemistry, and of the physics of materials, the intellectual elements from which wonderful modern inventions have been created. Many of these are described in Part Five.

But before we turn to these more practical aspects of the theory, I want to give you a sense of other exciting aspects of our world, what we know of the smallest things that existed from the beginning of time to the present day, and of the galaxies, and of the overall structure of the universe of which they are a part. This is a world of relativity and the quantum—a fascinating world.

In explaining this world, it is useful to use analogies, both to provide insight and to connect the parts of what is presented. I am assuming the role of your tour guide in a time-travel visit of our universe. I have already been to many of the fascinating places that we will visit, often as a visitor in other tours. I have usually been escorted by local guides (authors, through their books). Sometimes these are people of authority, but often they are people skilled at providing me the information from authoritative sources in a way that I can more easily understand. (Some of these writers may be thought of in analogy to the guides at galleries or architectural wonders, or the docents who may lead us through museums.)

As your overall tour guide, I have selected those topics that I have found to be particularly interesting, and I have arranged your tour in a way that logically sequences and connects them within an overall journey that takes us backwards from the present to the beginnings of time. Some of the places at which we will stop (topics that we will cover) are included in the title of Chapter 9. I have chosen a good set of guides for us on each topic, and, because these guides often have somewhat different interpretations of their subject matter, they may emphasize one thing or another.

While most of what will be described is based on hard evidence and well tested and proven theory, in some cases what the local guides and drivers present may be conjecture or even opinion. In these places, I will point this out and qualify what is presented. And I will, in most cases, introduce you to the guides and drivers (by referring you to my sources) so that you may explore further with them directly. Because we make brief stops in the various topic areas, and because they are many and by my design flow one to the next, I have not chosen to break their descriptions into separate chapters. Rather, all topics are included in this single Chapter 9, which comprises all of Part Three.

While this chapter is nominally structured as a tour of specific topics, the topics are tied together to leave you with an understanding of two pillars of modern physics that describe our world: the big bang model, which traces the evolution of our universe; and quantum mechanics, which applies generally in what is called the Standard Model and describes the fundamental particles that either transmit the forces of nature or (for some of them) lie within the atomic building blocks that make up everything that we see around us.

I welcome you now to a trip of great discovery and beauty, with concepts and observations that may challenge your view of the world around and within us.