And they let there be light

Andrew Briggs on how physics feeds technology and vice versa.

Newton's laws of motion and gravitation, the laws of thermodynamics, geometrical and wave optics and acoustics, Maxwell's equations, the kinetic theory of gases, the periodic table of the elements, radio and telephones, the existence of the electron - all these were well-established in physics at the start of the 20th century, when the number of scientific papers published annually was still less than 2,000.

Still to come were relativity, quantum physics, the structure of the atom and the nucleus, atomic energy and bombs, string theory, radio astronomy, atmospheric physics and geophysics, transistors and lasers, superconductivity, the Josephson and quantum Hall effects, seeing atoms and molecules with electron microscopes, dislocations, the theory of condensed matter, and most of what we now recognise as materials science. More Things in Heaven and Earth: A Celebration of Physics in the Millennium is a reprint in book form of a special issue of Reviews of Modern Physics, compiled and published to mark the centenary of the American Physical Society. The book's appropriate title comes, of course, from Shakespeare's Hamlet . When Horatio describes a phenomenon as "wondrous strange", Hamlet replies, "Therefore as a stranger give it welcome. There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."

It was the discovery of the electron in 1897 by J. J. Thompson working in Cambridge University that proved to be the overture to the discoveries in physics of the following hundred years. Cambridge, where many of these key advances would be made, was then behind other universities in Britain and Germany in teaching experimental physics. For all the personal distinction of Maxwell and Rayleigh, the research they led at the Cavendish Laboratory "was largely on standards of electrical measurement - thorough and highly important at the time, but safe rather than exciting", wrote Brian Pippard of his predecessors in the Cavendish chair. But then, Pippard continued, "JJ turned from natural philosophy , mathematical analysis supplemented by measurement, to experimental physics , the investigation of phenomena only tenuously related to accepted laws, when he began to study the passage of electricity through rarefied gases."

The aim of this collection of writings was not to achieve encyclopaedic coverage of the achievements of physics this century, which had already been shown in the magnificent three-volume Twentieth Century Physics , published jointly by the Institute of Physics and the American Institute of Physics in 1995. Rather, it was to collect personal and informal vignettes from a range of writers, all of them distinguished, including 15 Nobel laureates. The topics are divided into sections: "Historic Perspectives - Personal Essays on Historic Developments", "Particle Physics and Related Topics", "Astrophysics", "Nuclear Physics", "Atomic, Molecular, and Optical Physics", "Condensed Matter Physics", "Statistical Physics and Fluids", "Plasma Physics", "Chemical Physics and Biological Physics", "Computational Physics" and "Applications of Physics to Other Areas".

Since the contributions are so personal, they can be read in almost any order. I confess I went straight for the article by Abraham Pais, simply because I have enjoyed his previous books Subtle is the Lord and Niels Bohr's Times so much, and I was not disappointed by his account of theoretical particle physics.

I then moved to Walter Kohn's admirable essay on condensed-matter physics. The development of the theory of materials in this century is a truly remarkable story. Neville Mott and Rudolf Peierls were among the first to see that quantum mechanics would help to explain the electronic and optical properties of solids. I remember once hearing Mott talk about how, as a student, he found himself wondering what it was that determined whether or not a crystalline solid was transparent, and how, much later, he pondered the same question about amorphous solids. Even before the middle of the century William Hume-Rothery insisted, with almost prophetic insight, that metallurgy would be left behind as a science if it did not take quantum mechanics on board. During the last three decades of this century it has become possible to make accurate calculations of the structure of materials by directly solving the Schrodinger equation from first principles. This is done using the local-density approximation to density functional theory, for which the key starting point is the Kohn-Sham self-consistent equations.

Although the existence of the electron had been established by the turn of the century, the existence of molecules had not been. In 1905, the year in which he published his seminal paper on relativity (a paper with 11 sections, one acknowledgement, and no references), Einstein developed no fewer than five different methods for calculating Avogadro's number. The over-determination of this quantity from phenomena as apparently unrelated as radioactivity, Brownian motion, and the blue colour of the sky, clinched the argument for believing in molecules long before they could be seen with a microscope. We have come a long way since then. Gerd Binnig and Heinrich Rohrer, who were awarded the Nobel prize for the invention of the scanning tunneling microscope (STM), describe scanning-probe techniques in a chapter entitled "In touch with atoms". They include spectacular pictures, including a quantum corral for electrons built with 48 iron atoms on copper. This confinement of the electrons then enables the STM to image the standing-wave pattern of the electrons' wave function,in a way that brings the five-finger exercises of undergraduate quantum mechanics to life. The STM is used both to manipulate individual atoms with sub-nanometre precision, and then to image electronic states via the tunneling current that flows across the forbidden energy gap between the sample and the ultrasharp tip of the microscope. Binnig and Rohrer also illustrate how biology and physics can converge, with the first atomic force microscopy (AFM) images of the pores in the cytoplasmic surface of the cell envelope of Deinoccus radiodurans . The envelope is a molecular sieve; the pores are the channels of this sieve, and they exhibit two conformations whose dynamic changes can be viewed in real time by AFM, which instead of detecting the tunneling current between sample and tip actually allows the tip to touch the sample and detects the atomic force between them. One can see individual molecules by both STM and AFM, and hence molecular bonding sites on surfaces and the behaviour of the molecules can be observed directly.

The interplay between physics as science and physics as technology is never far away. The chapter on laser physics by Willis Lamb, Wolfgang Schleich, Marlan Scully, and Charles Townes is subtitled "Quantum controversy in action". The section headings alone are enough to make you want to read on: "The idea on the park bench", "Why not earlier?", "Why lasers will not work", "Lasers without inversion". "When God said 'let there be light'", they explain, "he surely must have meant perfectly coherent light, that is a perfect oscillator. But how to create such a perfect oscillator? Start from a source of dc energy for an oscillator; then by some trick, change the dc into ac: the result is a self-sustained oscillator." If only it had been that simple. It is well known that people once asked if the laser would ever have any use; certainly its most prevalent current uses, such as in domestic CD players, played no part in the seminal developments of laser physics.

Probably the same is true of much semiconductor physics. The quantum Hall effect and the fractional quantum Hall effect would never have been discovered without the wizardry of scientists like Art Gossard and their ability to grow tailor-made designer semiconductor materials, as he describes in a chapter with Horst Stormer and Daniel Tsui. That in turn would not have been possible without the dramatic advances in vacuum technology that occurred in this century. And yet one sometimes hears physicists talking as though developments in molecular beam epitaxy happened solely in order to make better samples for research in low-dimensional solids, and engineers talking as though progress in the physics of low-dimensional solids was driven solely by the need to grow better quantum structures. May there not be mutual benefits between pure science and technology?

As the punchline of the whole book, the editor has chosen for the final chapter one by William Brinkman and David Lang on "Physics and the communications industry". It complements a delightful chapter on the invention of the transistor, by Michael Riordan, Lillian Hoddeson, and Conyers Herring, and includes a history of developments in Bell Laboratories and AT&T. They conclude: "in all four major eras of physics - electromagnetism, the electron, quantum mechanics, and quantum optics - the fundamental discoveries were applied by the communications industry within 15-20 years ... The communications industry's practice of employing the best physicists to do both basic and applied research resulted in the successes noted in this review ... The current leaders of the communications industry continue in this tradition."

Who is this book for? Anyone who is not a graduate in physics or a related subject may find something to enjoy, but much of it will certainly be hard going for them. To explain the advanced concepts of 20th-century physics to non-specialists in a way that maximises their appreciation of the developments requires an extremely gifted communicator; most of the contributors are to be commended for having a very good try. What is missing? Maxwell would have spotted it straight away. In a century in which a physicist, Joseph Rotblat, was awarded the 1995 Nobel prize for peace, this book has no discussion of the ethical or philosophical issues raised by physics, nor of the contributions of the physics community to the wider society and vice versa. Fair enough, provided this omission is openly recognised and the reader appreciates that key questions have been consciously avoided. For as Maxwell, a committed Christian, wrote: "There are many things in heaven and earth which by the selection of our scientific method have been excluded from our philosophy."

Andrew Briggs is professor of materials, University of Oxford.