This review explores the relationship between physics and communications over the past 125 years. The authors find that four eras of major change in communications technology can be traced to the corresponding major discoveries of physics that directly influenced the communications industry. The four areas of physics that define these periods are electromagnetism, the electron, quantum mechanics, and quantum optics.

Laser technology during the 20th century is reviewed emphasizing the laser’s evolution from science to technology and subsequent contributions of laser technology to science. As the century draws to a close, lasers are making strong contributions to communications, materials processing, data storage, image recording, medicine, and defense. Examples from these areas demonstrate the stunning impact of laser light on our society. Laser advances are helping to generate new science as illustrated by several examples in physics and biology. Free-electron lasers used for materials processing and laser accelerators are described as developing laser technologies for the next century.

Throughout history there has been a close relation between physics and the military. In this article the author concentrates on the connection between physics and U.S. national security. In particular he discusses applications of physics to photo reconnaissance from space, antiballistic missile systems, nuclear testing, and scientific advising. The author also touches briefly on ethical aspects of the relation between science and the military.

In the 1990s, experiments in tokamak magnetic fusion devices have finally approached “breakeven”—power out equal to power in—at fusion power levels exceeding 10 MW, and great progress has also been made with inertial-confinement fusion laser experiments. Based on these results, the requirements to achieve ignition and high-energy gain are now fairly clear for both approaches. This article focuses on developments in modern plasma physics that led to these achievements and outlines the historical development of the field. Topics include the stability of magnetic fields, field reconnection and the magnetic dynamo, turbulent heat transport, and plasma absorption of intense beams of light. The article concludes with a brief discussion of future research directions.

Medical imaging is the principal method for noninvasively obtaining anatomic and physiologic information about the human body. Imaging has experienced a quantum leap in technology and clinical applications over the past 25 years. This leap includes x-ray computed tomography (CT); emission computed tomography (SPECT and PET); magnetic-resonance imaging (MRI) and spectroscopy (MRS), including functional MRI (fMRI), and the networking of images in digital networks (PACS and IMACS). Even traditional projection x-ray imaging is undergoing a major change with the advent of digital x-ray image receptors. Images are important not only to the detection and diagnosis of disease and injury, but also to the design, delivery, and monitoring of treatment. The evolution of medical imaging is the product of physicists working in collaboration with engineers and physicians. Further advances are limited only by the creativity and imagination of these individuals.

Physics and biology have interacted for at least two centuries. In the twentieth century, this interaction has become very strong and the overlap between the two fields has expanded enormously. In the present contribution, the authors sketch where physics has influenced biology and where investigations on biological systems have led to new physical insights.

Vignettes of three frontier areas illustrate the eclectic scope of modern chemical physics. (1) Radioastronomy has revealed a profusion of organic molecules in interstellar clouds, now attributed to sequences of exoergic, bimolecular ion-molecule reactions proceeding far from thermodynamic equilibrium. The organic profusion occurs because ${\mathrm{He}}^{+}$ ions react far more readily with CO than with the much more abundant ${\mathrm{H}}_2$ molecules. (2) Molecular clusters, generated by supersonic expansions, have become a favorite medium for study of reactions and spectra. Exemplary episodes are the discovery of carbon-60 and kindred fullerene molecules and the observation of sharp rotational spectra of guest molecules in superfluid helium clusters. (3) New means to control molecular trajectories are being developed. These include spatial orientation or alignment by field-induced hybridization of rotational states, corralling (or trapping) molecules after collisional or mechanical quenching of translational kinetic energy, and laser control of photochemical reaction pathways.

Two phenomena that illustrate the collisionless nature of high temperature plasmas are Landau damping (or, more generally, the resonant wave-particle interaction) and collisionless shock waves. The first half of this paper traces Landau’s idea through the years as it is tested experimentally, extended nonlinearly, and applied. The second half traces the progress in understanding collisionless shocks in space and astrophysical plasmas.

Remarkable and varied pattern-forming phenomena occur in fluids and in phase transformations. The authors describe and compare some of these phenomena, offer reflections on their similarities and differences, and consider possibilities for the future development of this field.

The swirling motion of fluids that occurs irregularly in space and time is called turbulence. However, this randomness, apparent from a casual observation, is not without some order. Turbulent flows are as abundant in nature as life itself, and are pervasive in technology. They are a paradigm for spatially extended nonlinear dissipative systems in which many length scales are excited simultaneously and coupled strongly. The phenomenon has been studied extensively in engineering and in diverse fields such as astrophysics, oceanography, and meteorology. A few aspects of turbulence research in this century are briefly reviewed, and a partial assessment is made of the present directions.

Granular matter describes large collections of small grains, under conditions in which the Brownian motion of the grains is negligible (sizes d>1 micrometer). The grains can exhibit solidlike behavior and fluidlike behavior, but the description of these states is still controversial. The present discussion is restricted to static problems, for which the main approach is to describe properly the initial state of each volume element, when it was deposited from a fluid flow.

The distinctive behavior of polyatomic structures such as colloidal particles, surfactant micelles, and polymer molecules in a liquid are reviewed. The qualitative differences between these forms of “soft matter” and small-molecule solids and liquids arise from their weak connectivity and entropic interactions. These effects produce spatial organization within one polyatomic structure and cooperative organization amongst many such structures. Such self-organization may arise in thermal equilibrium, from an irreversible growth process, or from flow. Conversely, the structures alter the transmission of forces in new ways. Potential benefits from the understanding of soft matter for electronic materials, for chemistry, and for biology are mentioned.

This brief overview is designed to introduce some of the advances that have occurred in our understanding of phase transitions and critical phenomena. The presentation is organized around three simple questions: (i) What are the basic phenomena under consideration? (ii) Why do we care? (iii) What do we actually do? To answer the third question, the author shall briefly review scaling, universality, and renormalization, three of the many important themes which have served to provide the framework of much of our current understanding of critical phenomena. The style is that of a colloquium, not that of a mini-review article.

I give a highly selective overview of the way statistical mechanics explains the microscopic origins of the time-asymmetric evolution of macroscopic systems towards equilibrium and of first-order phase transitions in equilibrium. These phenomena are emergent collective properties not discernible in the behavior of individual atoms. They are given precise and elegant mathematical formulations when the ratio between macroscopic and microscopic scales becomes very large.

Extraordinary advances in materials physics have occurred over the last century. These advances have influenced almost every aspect of human endeavor. In this note, the authors sketch some of these exciting developments in structural, polymeric, and electronic materials.