I hesitated quite a bit when I picked up Peter Bergmann’s bookThe Riddle of Gravitation — From Newton to Einstein to Today’s Theories for the following reasons:
Firstly, the book was published in 1968, so I suspected its views might be outdated.
Secondly, I had never heard of Professor Bergmann before (hardly the professor’s fault!).
Thirdly, the reviews on Goodreads.com were mediocre.
However, after reading a few random passages, my impression changed, and I decided to purchase it.
The book is quite good for reasons I will articulate below. Regarding the intended audience, the reader is expected to understand at least the fundamentals of the special and general theories of relativity and some quantum mechanics. Although the book is of the popular science genre with hardly any maths inside, its physics is serious and thorough.
The Riddle of Gravitation explains the physics of gravitation and the theories that describe it. This is the principal aim of Dr Bergmann as far as this book goes. It begins by surveying Newton’s theory of gravity and the three laws of dynamics, moving on to the Special Theory of Relativity and finally covering the General Theory of Relativity, both in theory and in terms of experiments at that day.
Although the theoretical physics discussions in the book were fascinating, the observation and experimentation physics is quite outdated. However, it must be pointed out that this book was written before the discovery of black holes and while the Cosmic Background Radiation observations and cosmological modes were still in their infancy.
3. Structure of The Riddle of Gravitation
The book is divided into three parts:
Newtonian Physics and Special Relativity. The chapters in this part of the book discuss Newtonian concepts of gravitation, such as inertial frames, planetary orbits, mass, energy, momentum, and the conservation laws of these quantities. Then it briefly touches on Maxwell’s theory of electromagnetism, the constancy of the speed of light in a vacuum, and how special relativity resolves the apparent paradox between Newton and Galileo’s laws and the latter.
General Relativity. The chapters in this part of The Riddle of Gravitation focus on the principal tenets of General Relativity, i.e. the stress-energy tensor, the curvature of spacetime, and Einstein’s field theory of gravitation. It also discusses the Schwarzschild solution to Einstein’s field equation and its implications on massive bodies and the motion of particles, as well as the event horizon.
Recent Developments. Given that the book was published more than 55 years ago, what was recent back then has become classical or outdated today. For example, I found the discussion on the steady state theory of cosmology quite superfluous. However, this part covered other fascinating topics like gravitational collapse, quantum gravity, and the nature of space and time.
Some examples of what sets Dr Bergmann’s book The Riddle of Gravitation apart from other titles in the genre.
The book has zero fluff. No anecdotes, laborious metaphors, or personal accounts. This meant a new idea, concept, or insight in every chapter, section, and paragraph.
Conciseness. The book’s chapters span a few pages at best, in which the author aims to explain a single complex idea in as few words as possible. This conciseness meant the reader was expected to be familiar with the fundamentals of Newtonian physics, the special and general theories of relativity, and have at least a high-school level of understanding of mathematics.
Only physics. The entire book discusses hardcore physics only. The math is scarce and, aside from the appendices, almost inexistent. There is only a brief history of gravitational theories and no mention of the philosophical implications of the new physics.
The book succinctly articulates the following concepts with compelling insights on how the greatest minds in physics discovered the new theories of gravity:
Kepler’s equal areas law and how it led Newton to discover gravity’s attractive pull between planets.
The universality of the speed of light in unaccelerated inertial frames and how Einstein derived the laws of special relativity as a result.
Minkowski’s spacetime, spacetime transformations, and the curvature of spacetime.
Mass, energy, momentum, and their conservation laws.
The principles of equivalence of inertial and gravitational mass, and the rest vs relativistic mass.
Curved spacetime, geodesics, and event horizons
The stress-energy, Ricci, Weyl, and Einstein tensors. Although not in great detail, the insights are nevertheless fascinating.
Free fall, the principle of General Covariance, and Einstein’s field equations
5. Originality of Content in The Riddle of Gravitation
The book presents a fresh perspective on the theory of gravitation. It is midway between popular sciencebooks written for the layman (Other Worlds by Paul Davies, A Brief History of Time by Stephen Hawking, or The Elegant Universe by Brian Greene) and textbooks incomprehensible for non-physics graduates.
The Riddle of Gravitation presents complex ideas with plenty of insight and rigour. The author achieved this without mathematics by focusing on a single but powerful idea in every chapter.
6. Themes
Theory of gravitation
Newtonian physics
Laws of dynamics
Kepler’s laws of planetary motion
Maxwell’s theory of electromagnetism
Inertial frames
The relativity of motion
The Special Theory of Relativity
The General Theory of Relativity
The equivalence principles
Relativistic vs rest mass
Gravitational collapse
Einstein’s field equations
Geodesics and the motion of massless particles
Mass, energy, and momentum conservation
Cosmology
7. Biography
Peter Gabriel Bergmann (24 March 1915 – 19 October 2002) was born in Germany and studied at the University of Prague, where he got his PhD in 1936. He subsequently migrated to the US and worked as a theoretical physicist. He is best known for his work with Albert Einstein on a unified field theory encompassing all physical interactions. Bergmann established one of the first research centres devoted to studying the general theory of relativity to reconcile it with quantum theory.
He authored a classic textbook, Introduction to the Theory of Relativity, in addition to The Riddle of Gravitation, and coauthored Albert Einstein: His Influence on Physics, Philosophy and Politics.
