Saturday, October 12, 2019

Physics for Astronomers: The Works of Steven Weinberg

The telescope is a wonderful instrument, but if you do not know what you are looking at, you have not gained much. The stars are pretty at any magnification. 

[This article originally appeared in the October 2019 issue of Sidereal Times of the Austin Astronomical Society.] 

Understanding the views requires learning astrophysics; and that is hard work. Think of it like basketball. One of my physics professors was answering homework questions at the blackboard. “I don’t understand number 3. …. How do you do number 5?... What equation do you use for number 1?...” He was going along and then he stopped. “You people would go out in the backyard and shoot hoops for 45 minutes and not make a single shot and still say you had a good time. How long did you spend on number 4? How many ways did you try to solve it?” It was a valid argument. On the other hand, you could have Michael Jordan or LeBron James come to your backyard and be your coach, but the honest fact is that you will not ever be good enough to play in the NBA. Still, you can improve your skills and your appreciation of the masters and their game. And so, too, with astrophysics, if you want to “show good game” (whether or not you turn professional), let the greats be your coaches. 

This past July, our guest speaker was Nobel laureate Steven Weinberg. His topic was “Gravitational Wave Astronomy.” Dr. Weinberg delivered a layman’s overview of the development of the field and its current state. Having done my homework before the lecture, I was impressed by his clear, concise, and cogent explanations. So, I went to the UT libraries and checked out four of his books.

They had nine copies of Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity (John Wiley & Sons, Inc. 1972). Two are missing. One is in the Life Sciences Library Hall of Noble Words. One is at Perry-CastaƱeda Library. The rest are in the Kuehne Physics Mathematics Astronomy Library. The great body of mathematical discussions are beyond my skill level – like having to play guard against LeBron James: the moves are easy to explain, but doing them is a workout. However, Weinberg’s narratives are understandable and compelling. He takes the reader where no one has gone before. He has his own framework for presentation, different from the traditional teachings.

Weinberg maintains that Einstein’s preference for Riemann geometry and our respect for Einstein have limited the ways that we choose to approach these problems. Instead, Weinberg begins with the equivalence of gravity and inertia. That, he says, allows us to understand quantum events in ways that the geometric approach cannot.  

Over the course of 633 pages, Gravitation and Cosmology ties the historical development with the modern discoveries. The histories of the theory of gravity, non-Euclidean geometry, and the principle of relativity open the book. Part One closes with a detailed examination of the special theory of relativity from Lorentz transformations through the discovery of antiparticles. 

Part Two covers the General Theory of Relativity with a treatment of the equivalence principle that is so important to Weinberg’s framework. He also provides mere outlines of mathematics including tensor analysis, covariant differentiation, and div-grad-curl. These are only to make the text complete. Other books are better at explaining the subjects. And, just to note, Einstein went back to the books to learn tensors; and it is recorded elsewhere that Einstein’s wife at least checked his math if she did not actually do his homework for him. 

Part Three explains General Relativity, including Post-Newtonian Mechanics and Post-Newtonian Hydrodynamics. (The physics of moving water allows us to approach the problems involving huge bodies of discrete particles.) Part Three Section 10 Chapter 8 addresses the Quantum Theory of Gravitation which was the topic of Dr. Weinberg’s lecture to us on July 12. In the book, it is marked with asterisk meaning that you can skip it. Back then, it was just theory. Gravitation waves were predicted by relativity and quantum mechanics, but would not be detected for another thirty years.
Weinberg by David Levine for NYRB.
This drawing appeared in
"Nature’s Biggest Secret,"
October 21, 1993.
Framed prints are for sale from
The New York Review of Books.

The last third of the book, Part Five, is dedicated to Cosmology. The greater mass of that consists of the so-called “Standard Model” what we in the backyard call the Big Bang Theory. Weinberg takes you from “the first three minutes” to the synthesis of helium and to the formation of galaxies. The book closes with considerations of other models. 

Dr. Steven Weinberg is tireless in taking physics to the public. He summarized the Standard Model in The First Three Minutes: A Modern View of the Origin of the Universe (Basic Books, 1977). If you go to the website of The New York Review of Books and put his name in the search box you will find that he is quite popular. (Use quotes and the full name “Steven Weinberg” to narrow the results.) He wrote seven major essays for them, six on physics, one on politics.

Weinberg is quite outspoken on social issues, especially as they impact science. Among his other books is Facing Up: Science and Its Cultural Adversaries (Harvard University Press, 2001). He does defend against religion and creationism, but most of the book is a defense of science against post-modernism. To Weinberg, the philosophy of science is worth studying, and defending it matters. 

Weinberg’s The Discovery of Subatomic Particles (Scientific American Library, 1983) creates a bridge between a physics textbook and a popularization. His narrative history from the Greeks through the electron of the 19th century and up to the hadron of our day is easy to read. In the text, he presents the standard equations as verbal statements. “Electric force on a body = Electric charge of the body on which the force acts X Electric field.” However, the Appendix delivers all of the equations in their standard forms. In the Appendix, Weinberg starts with Newton’s Second Law and ends with particle collisions. 

You can find pithy sayings by Dr. Weinberg in Wikiquote. Most of them are about subatomic physics. Interesting as they are to ponder, they will not make good bumperstickers. 

Five hundred years before Galileo the Persian astronomer Abd al-Rahman al-Sufi (known in the Latin West as Azophi) catalogued the Andromeda Galaxy. He knew that it was a cloud among the fixed stars but did not know what it was. By the time Edwin Hubble settled the question in 1925, astronomers had been informed by Newtonian mechanics, Maxwell’s Equations, Planck’s quanta, and Einstein’s General Relativity. Physics is hard work. The pay-off is understanding what you are looking at—and why the looking is important. Dr. Steven Weinberg explains it all. 


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