Frank Close, "The Quantum Universe" (2005)

The quantum Universe
FRANK CLOSE
Nature 434, 438 - 439 (24 March 2005)

Frank Close is at the Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP,
UK.

Science and Ultimate Reality: Quantum Theory, Cosmology and Complexity
edited by John D. Barrow, Paul C. W. Davies & Charles L. Harper, Jr
Cambridge University Press: 2004. 742 pp. $60, Ł40

In the centenary year of Einstein's seminal contributions to human culture, Science and Ultimate Reality celebrates the 90th birthday of John Wheeler, who took two of Einstein's ideas and created new branches of science. The physics of the twentieth century was built on the twin pillars of Einstein's general theory of relativity and quantum mechanics. The former describes the macroscopic Universe of space-time and gravitation, and the latter is a theory of matter and radiation at subatomic dimensions. These two different theories seem to be incompatible, but Wheeler insisted that, at some level, quantum effects must have a meaningful impact on gravitational physics. And because Einstein's theory intimately links gravitational physics with geometry, the net result must be some sort of quantum space-time dynamics. It was using this reasoning that Wheeler predicted in 1957 the existence of space-time foam, one of many of his ideas that survive to this day.

Wheeler is popularly known for having coined the phrase 'black hole', and professionally for his wide range of profound contributions in physics, ranging from the very large to the smallest scales of size. Gravitation was reborn, with Wheeler's influence, as a mainstream branch of science, leading to the explosive growth in astrophysics and cosmology that we see today. At the other extreme of scale, he developed the theory of nuclear rotation, with Edward Teller, and the fundamentals of electrodynamics, with Richard Feynman. And it was Wheeler's seminal question that led to the perception of the positron as an electron travelling backwards in time.

His 90th birthday was celebrated with a symposium attended by a metaphorical galaxy of scientific stars, and this book records the event. Do not be put off by its length: at over 700 pages this is still only about ten pages per year of active research, and this is one of those rare volumes where quantity is matched by quality.

With such a variety of contributions * ranging from quantum reality (by Freeman Dyson and others), big questions in cosmology (including articles by Andreas Albrecht, John D. Barrow and Andrei Linde), higher dimensions (Lisa Randall) and the emergence of life (George Ellis) * how can a review do justice to them all? Perhaps I should focus on the man himself, aptly summarized in a readable and insightful opening chapter by Paul Davies.

Wheeler's gift has been in asking questions that are, in the modern parlance, 'outside the box'. While most of us rack our brains trying to determine and understand the implications of nature's laws, Wheeler wondered whether the very concept of physical laws might be an emergent property. Could law-like behaviour emerge stepwise from the ferment of the Big Bang, instead of being mysteriously and immutably imprinted on the Universe at the instant of its birth? As Davies says: "Wheeler was breaking a 400 year old scientific tradition of regarding Nature as subject to eternal laws."

As students we learn quantum mechanics, and as professionals we apply it with varying levels of unease as to what it actually means, but Wheeler had a singular attitude. He insistently asked: "How come the quantum?" Why is the world quantum mechanical? What would happen if we made small changes to quantum mechanics? The preface asks the same sort of questions as Wheeler: "Could it be that quantum mechanics is the simplest mechanics consistent with the existence of conscious beings?" Or does it "optimise the information processing power of the universe"? These are profound questions, as yet unanswered but extensively and profoundly discussed, and some sense of the debate can be found in this book.

Wheeler was the inspiration behind the most extreme connection of all: that quantum mechanics, a theory of subatomic dimensions, can be applied to cosmology, the largest system of all. In response to Einstein's question "Did God have any choice in the nature of his creation?", Wheeler has suggested that there are no truly fixed fundamental laws of physics at all. He was a remarkable man and this is a remarkable volume.