During the 100 years that astrophysics has been recognized as a separate discipline, there has been progress in interpreting observations of stars and galaxies using the principles of modern physics. Here we review some of the highlights, including the evolution of stars driven by nuclear reactions in their interiors, the emission of detectable neutrinos by the sun and by a supernova, the rapid and extremely regular rotation of neutron stars, and the accretion of matter onto black holes. A comparison of the observed Universe with the predictions of general relativity is also given.

Scanning tunneling microscopy appeared as a new method to deal with atoms, molecules, and nanometer-scale structures. It was the first of a growing family of local probes for imaging and measuring, which can serve at the same time as tools. Local probe methods have changed the way we perceive, think about, and treat atomic structures, and have brought about a new appreciation of mechanics. They play a central role for science and technology on the nanometer scale and will allow us to build systems of the same complexity as used by nature, which has built life on nanofunctionality.

The history of superconductivity is reviewed, beginning with its discovery in 1911. Various theoretical approaches are discussed and are compared with experiment.

Electric current flow, in transport theory, has usually been viewed as the response to an applied electric field. Alternatively, current flow can be viewed as a consequence of the injection of carriers at contacts and their probability of reaching the other end. This approach has proven to be particularly useful for the small samples made by modern microelectronic techniques. The approach, some of its results, and related issues are described, but without an attempt to cover all the active subtopics in this field.

Two-dimensional electron systems in a high magnetic field behave very strangely. They exhibit rational fractional quantum numbers and contain exactly fractionally charged particles. Electrons seem to absorb magnetic flux quanta, altering their statistics and consuming the magnetic field. They condense into a manifold of novel ground states of boson and fermion character. These fascinating properties are not characteristic of any individual electron but rather emerge from the highly correlated motion of many.

Instead of having to rely on gedanken (thought) experiments, it is possible to base this discussion of the foundations of quantum physics on actually performed experiments because of the enormous experimental progress in recent years. For reasons of space, the author discusses mainly experiments related to the Einstein-Podolsky-Rosen paradox and Bell’s theorem, that is, to quantum entanglement. Not only have such fundamental experiments realized many historic proposals, they also helped to sharpen our quantum intuition. This recently led to the development of a new field, quantum information, where quantum teleportation and quantum computation are some of the most fascinating topics. Finally the author ventures into a discussion of future prospects in experiment and theory.

Lasers have caused revolutionary changes in many fields of science and technology. A brief review is presented here of how lasers have provided access to measurements of short time intervals. Since 1960, six orders of magnitude, from ${10}^{-9}$ to ${10}^{-15}$ seconds, have been added to time-resolved observation of fast phenomena. New subfields of science, including femtochemistry and femtobiology, have been created. Some representative examples of transient Raman scattering and of impulsive and displacive excitations in molecules and crystals illustrate the usefulness of picosecond and femtosecond pulse techniques. In addition, the domain of power flux densities has been extended from ${10}^{12}$ to ${10}^{19}{\mathrm{w}\mathrm{a}\mathrm{t}\mathrm{t}\mathrm{s}/\mathrm{c}\mathrm{m}}^2$ by the use of short focused pulses. This has given experimental access to new phenomena, including ultrafast phase transitions in electronic structure, above-threshold ionization of atoms, and high-order harmonic generation and acceleration of relativistic electrons by light pulses.

After introducing some basic definitions, the article describes several optical interference experiments in which quantum effects appear. An analysis of these experiments leads to some new and improved measurement techniques and to a better understanding of the quantum state.

We summarize the history and discuss quantum subtleties of maser/laser physics from early days until the present.

Neutral atoms and ions can now be cooled, trapped, and precisely manipulated using laser beams and other electromagnetic fields. This has made it possible to control external degrees of freedom at the quantum level, thereby making possible a variety of interesting new physics.

In this paper the authors discuss recent advances and trends in laser spectroscopy and quantum optics. It is obvious that both are fields that experienced a tremendous development in the last twenty years. Therefore the survey must be incomplete, and only a few highlights are touched on.

This Section contains examples of important areas in atomic physics, including articles on cold atoms collisions, accelerator-based atomic collisions, fundamental-type atomic collisions, high-precision atomic theory and the few-body problem, and “exotic atoms.”

Nuclear physics is the branch of physics that deals with the properties and structure of matter on the hadronic level. This article states a current perspective of the field and of some of the issues that are now on its frontiers.

Black holes are among the most intriguing objects in modern physics. They power quasars and other active galactic nuclei and also provide key insights into quantum gravity. We review the observational evidence for black holes and briefly discuss some of their properties. We also describe some recent developments involving cosmic censorship and the statistical origin of black-hole entropy.

The cosmic microwave background radiation (CMBR) is widely interpreted as the thermal afterglow of a hot big bang. Measurements of the CMBR intensity as a function of frequency constrain the history of cosmic energetics. Measurements of the anisotropy in the CMBR temperature provide a snapshot of the distribution of fluctuations in the gravitational potential at the earliest stages of cosmic structure formation. The authors review the interpretation of the CMBR emphasizing the status of current observations and future observational prospects. Our knowledge of the CMBR will dramatically increase in the first decade of the twenty-first century.