In his inaugural lecture at Cambridge in 1980, the recently elected Lucasian professor of mathematics, Stephen Hawking, posed the question: "Is the end in sight for theoretical physics?" Outstanding physicists have fretted over this issue for more than a century. The claim that Lord Kelvin warned of the imminent death of physics at the British Association meeting in 1900 is much quoted even today, despite its being apocryphal.
Many physicists and science writers have contributed to a voluminous literature on the future of physics. Russell Stannard, a former head of physics at The Open University, has added to the corpus. As a former high-energy physicist and an accomplished author of books on relativity aimed at children, he is well placed to write a non-technical account of the present state and uncertain future of theoretical physics.
The continuing dilemma in the academy can be stated succinctly. An intractable puzzle is embedded in general relativity and quantum mechanics, the two revolutionary (and highly productive) ideas of the 20th century. The conundrum arises because relativity is a classical theory that is our best description of the Universe, whereas quantum theory applies in the subatomic world. As Stannard points out, both theories have withstood every test in their respected domains, and yet they are mutually incompatible. Despite the efforts of Albert Einstein, Paul Dirac, Arthur Eddington, Stephen Hawking and their students, there is no plausible theory of quantum gravity.
I can think of three reasons why we should worry about this. The academic field that studies the origin and early properties of the Universe is known as particle physics and cosmology, which means that two conflicting sets of ideas are being used to study the emergence of the hot Big Bang Universe from a singularity, a point with no volume at the centre. Second, in the standard model of particle physics there are 19 unknown parameters, the values of which can be found only by experiment in order for the theory to work. For a striking example of our lack of knowledge, consider the velocity of light: why does it have the value it has? Its value is now fixed exactly by the standard definition of the metre. Another troublesome loose end concerns the masses of elementary particles: how does mass arise?
The End of Discovery is a lucid tour of this unfinished business. Although there is no new knowledge in this account, the problems are presented clearly. No equations are used. Each problem is set out as a short question in the margin of the page, for example, "What is time?" So it is easy for the reader to keep track of the argument. The author makes a brave attempt to describe string theory, which has a large following but little in the way of prediction. So it is possible that physics has indeed hit the boundaries of the knowable.
I would have preferred a slightly deeper account of the philosophical issues connected with attempts to understand the nature of time, matter, consciousness, the anthropic principle, and the Universe. That quest began in antiquity.
Stannard does not address societal issues that could conceivably act as a showstopper. For example, does anyone seriously believe that society would be willing to fund a successor to the Large Hadron Collider, or would be capable of constructing safe, large-scale fusion reactors, or agree to send humans on long-duration space missions?
Fundamental physics and astronomy have already gone global, producing papers with hundreds of authors in dozens of countries. Big science is expensive science, and the payback is far in the future, if indeed an economic return exists at all.
The End of Discovery: Are We Approaching the Boundaries of the Knowable?
By Russell Stannard
Oxford University Press
Published 23 September 2010