Cosmologist Pedro Ferreira has a new book about to come out, entitled The Perfect Theory. The author accurately describes the book as a “biography of general relativity”, and it’s quite a good one, of the short and breezy variety (as opposed to the detailed and exhaustive sort).
The theory’s parentage (Einstein), conception and birth are covered, in particular the way in which mathematics played a crucial role, with Einstein getting important help on this from his friend Marcel Grossman, as well as David Hilbert, who found the right dynamical equations at the same time. This material goes by fairly quickly though compared to many other sources for this history, in order to get to the main topic: the life story of the theory so far, nearly 100 years on. After the birth of the theory, it soon started to get wide acceptance, with Eddington helping to provide both the experimental confirmation in 1919 of the theory’s distinctive prediction about deflection of light by the sun, as well as ensuing publicity.
Some implications of GR were found immediately (e.g. the Schwarzschild solution in 1916), and the 1920s saw early work on applying the theory to cosmology (de Sitter, Friedmann, Lemaitre). By 1929 Hubble’s observations of an expanding universe had shown the way forward in this area. Ferreira goes on to follow several different strands of how the theory has developed. These include: black holes (Oppenheimer, Wheeler, singularity theorems from Penrose, Hawking, the information paradox), cosmology (Hoyle and steady state models, the CMB, Peebles and the now standard model, with dark matter and dark energy), relation to quantum theory (DeWitt, supergravity), gravitational waves (Weber, LIGO, proposals like LISA), and quite a few others. A wealth of different topics and interesting pieces of the history of the subject are covered, although none in great detail. The emphasis is on this history, along with the present state and prospects of the subject, with not much attempt to try and explain the intricacies of the physics (which would take a much longer book).
On the hot-button issues of string theory and the multiverse, Ferreira does a good job of giving an even-handed description of the arguments. For instance, he counsels reader to pay attention to George Ellis as well as multiverse proponents.
For more about the book, there’s a very good review by Graham Farmelo here. Oddly though, just like with his excellent biography of Dirac, which ended with a weird attempt to claim Dirac as a string theorist, here Farmelo ends by trying to enlist Ferreira and GR in the cause of string theory:
50 years later, the mathematical aesthetic of relativity has been enhanced by the beautiful demonstrations of its veracity that Ferreira describes. These would probably have made Born ponder why he and his peers did not spend more time developing a deeper appreciation of the theory soon after Einstein first presented it. Maybe there’s a lesson here for some of today’s string-theory sceptics?
I’ve never seen anyone else try and claim that the history of GR is analogous to the history of string theory. As Ferreira’s book explains, unlike string theory, GR is a classic example of a testable scientific theory, coming with one impressive post-diction (precession of the perihelion of Mercury) and followed up by an impressive test of a distinctive prediction (bending of light at the 1919 eclipse). As for mathematical aesthetics, GR uses beautiful mathematics (Riemannian geometry) and its dynamics is determined by the simplest possible Lagrangian density (the scalar curvature and nothing else). Whatever the equations of string theory might be, they remain unknown. Rather than a lesson for string theory sceptics, this book provides some good lessons about what a successful fundamental theory looks like, ones that string theory proponents would be well-advised to ponder.
“The Perfect Theory” is a good title for the book, with GR remaining our best example of a beautiful, powerful fundamental physical theory, based on the deepest mathematical ideas, with almost no free parameters. Ferreira does a great job of leading readers through the story so far of this amazing theory.