Posted on behalf of Andrea Taroni
Physics, along with jurisprudence, is principally known for its laws. And physical laws are amazing: they can predict almost anything, from the effects of gravity to why the Sun shines. Explaining them is surprisingly hard, however. Anybody first encountering them in the classroom, typically as mathematical formulae applied to abstract problems, can attest to that. The result is countless hours spent by teachers, educators and popularisers of science devising ways to make physics (and its laws) ‘more interesting’.
Richard Feynman’s The Character of Physical Law – published in 1965 and now newly reissued by MIT with a foreword by Frank Wilczek – stands out as an early example of a successful attempt towards this end. The book is based on a series of lectures the iconic physicist had delivered the previous year at Cornell University. But it’s a layered work, and clearly shows Feynman also drawing from another set of lectures, delivered at the California Institute of Technology from 1961 and 1963. Those would go on to become his most famous work: The Feynman Lectures in Physics (reviewed here).
However, whereas The Feynman Lectures were an attempt to reinvigorate the pedagogical approach to ‘freshman’ physics, The Character of Physical Law is, in Wilczek’s words, far more than an exposition of facts and ideas. It is also a character study of Feynman himself.
By physical law, Feynman is quick to explain that he means “the rhythm and pattern of phenomena of nature which is not apparent to the eye, but only to the eye of analysis”. In other words, the very phenomena we uncover through painstaking empirical observation, and tend to ultimately write down as mathematical equations. But the topic of the lectures is broader still. They focus on the characteristics common to all the laws: “that is another level, if you will, a higher generality over the laws themselves”.
The big picture
What is really striking about The Character of Physical Law is Feynman’s ease in covering broad areas of physics — for instance, the law of gravitation, the relationship between physics and mathematics, the role of symmetry in physical laws. But crucially, he is equally adept at discussing the history of these topics and their relevance to everyday life, and lucidly articulating the reasons why one might be curious about them. It is this combination of skills that allows him to avoid excessive abstraction and philosophising, a common pitfall when looking at the big picture of things.
For instance, Feynman kicks off by discussing the law of gravitation. In plain words, this describes how a particle is attracted to every other particle through a force directly proportional to the product of their masses, and inversely proportional to their distance. Though acknowledging that it is a discovery of the Enlightenment, he argues that by “describing its history and methods, the character of its discovery, its quality”, he recontextualises it for the present.
In the space of a few pages, the reader learns the way mathematician and astronomer Johannes Kepler established how the planets orbit around the sun. And they are provided with a clear description of the Newtonian mechanics that explain what makes them go around — including, of course, a brief explanation that, eventually, even Newton’s laws are found wanting and Einstein’s relativity takes over. At the next level of generality, Feynman also considers other instances in which inverse-square laws appear in nature — for example, to describe the interaction between electrical charges. The reader is invited to think deeper as each layer of description is peeled away, while at the same time keeping in mind the common threads that bind them together. Yet Feynman isn’t afraid to admit when even the boundaries of his knowledge are reached: “instead of having the ability to tell you what the law of physics is, I have to talk about the things that are in common to the various laws; we do not understand the connection between them”.
This approach certainly demonstrates an unusual depth of physics understanding. It also reveals Feynman’s humanity. Feynman was of course famously charming and charismatic — and, arguably, flawed, perhaps propagating the myth of his stage persona a little too enthusiastically. But ultimately he was, in my view, a man driven by a playful, down-to-earth spirit of curiosity, not the dry and abstract reasoning of a detached academic.
Rules of the game
As Wilczek notes in the foreword, a lot has happened in physics since 1965; yet The Character of Physical Law holds up extremely well today. My favourite chapter is the one on symmetry in physics. Feynman starts off by noting that symmetry appears to fascinate the human mind, if only for aesthetic reasons. But he chooses to emphasise the symmetry within the laws of physics themselves. Certain laws can be symmetric with respect to time and space, for example, but not necessarily under changes of scale. The implications of these symmetries are more obvious in some cases than others. But the key point is that by focusing on these underlying rules of the game, one gains an appreciation for the character of the physical laws they apply to.
To underline that, he masterfully explicates the far-reaching implications of charge-parity violation in the weak nuclear force. In his own words, “it is as if 99.99% of nature is indistinguishable right from left, but that there is one little piece which is completely different”. This ultimately explains the preponderance of right-handed molecules, such as proteins, that play a central role in the biochemistry of life. Feynman’s genius as a communicator lies in his ability to explain this connection in a manner that is accessible, fascinating and accurate in equal part.
Ultimately, I wouldn’t go quite as far as Wilczek by describing The Character of the Physical Law as the single best introduction to modern physics. Somehow, I suspect there is a reason why the more incremental approach espoused in The Feynman Lectures in Physics has gained traction with a wider readership over the years. But for the interested reader looking for more, this book offers enlightenment to those exploring its facets.
Andrea Taroni is chief editor of Nature Physics. He tweets at @TaroniAndrea.
For Nature’s full coverage of science in culture, visit www.nature.com/news/booksandarts.