Introduction to Modern Physics

Introduction to Modern Physics#

This electronic book is an adaptation and expansion by Don Smith of a printed text on the theory of Special Relativity written by Prof. Rex Adelberger before he passed. Rex also developed an inquiry-driven pedagogy of teaching the basic ideas of the Standard Model of particle physics by guiding students through the major discoveries of the twentieth century, letting the students realize at each step that their previous knowledge could not explain the “new” data he was sharing with them. They therefore had to keep revising what they thought they knew about the world and its contents. I struggled for years with the paradox of how to capture this discovery process in a book without just giving the reader the answers.

By casting the book in this electronic format, it is possible to make it far more interactive than a paper text could ever hope to be. The interactive web interface allows me to show data to the reader and encourage them to engage with it before clicking a button or moving the mouse to check their answers. I have created animated and interactive graphical representations of concepts that were only static images in the original text. Most of these interactive graphs have been produced using the VPython library on the WebVPython web site. As with all VPython visualizations, you can zoom, pan, and rotate the animation however you like, using the tools of your particular device’s interface (be it a smartphone, tablet, or trackpad). Interactive elements such as buttons and sliders are explained in the caption for each such figure. Most static graphs are created by Python code embedded in the book, rather than imported as images created by separate analysis software. This is a benefit because they are actual calculations, not simply illustrations.

This book, therefore, consists of two parts. The first “volume” represents a walk through a simplified version of twentieth century particle physics. No previous physics knowledge is assumed, and the math used consists primarily of algebra, with a very little calculus. The relationship of exponentials and logarithms is important for the material on radioactive decay and halflife.

Note

This book will consist of two parts. The second part, an introduction to relativity theory, is basically done. I am currently working on the first part, and introduction to particle physics, but that part is not yet included in this online version of the book.

The second volume, an explanation of Einstein’s theory of Relativity, is aimed at an audience of students that have completed at least a year of introductory Physics and are comfortable with the mathematics of calculus as well as vector and matrix manipulation. I will assume the reader is familiar with the relationships between displacement, velocity, acceleration, momentum, and force, as defined in classical Physics, as well as the classical properties of electric and magnetic fields. The Pythagorean Theorem is ubiquitous, although the reader will see that it works a little differently when time is incorporated as a fourth dimension.

There have been many books written on Relativity Theory since Albert Einstein first proposed it in 1905. You could go right to the source and read [Einstein, 1961]. However, my hope is that this synthesis of different ways of explaining the concepts and presenting the ideas with the interactive visualizations will help the reader become proficient with the tools and concepts more easily.

Acknowledgements:

I would like to thank colleagues A. Titus and J. Heafner for reading early drafts and giving feedback. Thanks to my students in 2023 and 2024 for their careful reading: they spotted typos and let me know which sections were not as clear as they could be. Of course this book could not exist without the leadership and mentorship of Prof. Rexford Adelberger, and I owe him a great debt. Thank you to his family for their support in my taking on this project. Thank you most of all to Kembra Howdeshell, who put up with my disappearing into the computer to add just another section before dinner.

The Theory of Relativity

References