As the story goes, in 1666 Isaac Newton watched an apple fall from a tree, and it was this simple action that gave him the inspiration to develop the theory and the mathematics that was first published in 1687 in Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) where he laid out the foundations of classical mechanics. These new laws meant that for the first time people could track the progress of the planets across the night sky, and Halley used the laws laid down by Newton to predict the elliptical path of the celestial object to predict the return of Comet, an event that he was never to see, but it carries his name to this day. They were used to predict the presence of a new planet, Neptune, the first to be discovered using these principles.
Variations in the path of Mercury, lead astronomers to search in vain for another planet amongst the inner planets, a subject covered very well in The Hunt for Vulcan by Thomas Levenson, but this was to show the limitations of Newton’s laws.
These limitations were not addressed until a chap called Einstein who was unhappy with the anomalies that the current theory threw up. It took eight years for him to demonstrate that the concept of gravity as everyone understood it was better described mathematically as the curvature of space-time. The ten equations in his general theory of relativity can be distilled down into this elegant equation:
From this, all sorts of things can be deduced and predicted and it is only recently that one of those predictions was finally detected; gravitational waves. This final part of the books ventures into the strange, surreal and occasionally baffling world of string theory. The physicists working on this are trying to reconcile special relativity and quantum theory to one theory of everything and the current consensus is that the present theories, along with years of understanding will have to be totally re-written.
Gravity is a habit that is hard to shake off ― Terry Pratchett
Chown has given us a well written and thankfully, given that this is a physics book, a comprehensible text on the history and the most recent developments in research into gravity.
He goes some way to answering the big questions; what is space? What is time? How did it start, but I can’t help but have the feeling that the next breakthrough in this field will make Einstein’s theory as irrelevant as he made Newton’s work at the turn of the 20th Century.