Showing papers in "Physics Today in 1972"
1,270 citations
TL;DR: The physicochemical basis of biological order is a puzzling problem that has occupied whole generations of biologists and physicists and has given rise, in the it, to passionate discussions.
Abstract: We have seen that the formation and maintenance of self‐organizing systems are compatible with the laws of physical chemistry. We must now confront this idea with the major problem of biology: How did biological systems arise?
365 citations
TL;DR: In high-energy physics, symmetry principles have been studied with an eye to circumventing two obstacles to the understanding of elementary particles: lack of precise knowledge about interparticle forces (with the exception of electromagnetism) and the mathematical intractability of any realistic models that propose to explain observed particle phenomena as mentioned in this paper.
Abstract: When symmetries are present the solution of almost any physical problem is simplified, because we can get at the properties of a system without completely solving all the equations that describe the system. In high‐energy physics, symmetry principles have been studied with an eye to circumventing two obstacles to the understanding of elementary particles: lack of precise knowledge about interparticle forces (with the exception of electromagnetism) and the mathematical intractability of any realistic models that propose to explain observed particle phenomena.
210 citations
150 citations
TL;DR: In this paper, the photon concept was formalized in the quantum theory of radiation, which has had unfailing success in explaining the interaction of electromagnetic radiation with matter, seemingly limited only by the ability of physicists to perform the indicated calculations.
Abstract: The idea of the photon has stirred the imaginations of physicists ever since 1905 when Einstein originally proposed the use of light quanta to explain the photoelectric effect. This concept is formalized in the quantum theory of radiation, which has had unfailing success in explaining the interaction of electromagnetic radiation with matter, seemingly limited only by the ability of physicists to perform the indicated calculations. Nevertheless, it has its conceptual problems—various infinities and frequent misinterpretations. Consequently an increasing number of workers are asking, “to what extent is the quantized field really necessary and useful?” In fact the experimental results of the photoelectric effect were explained by G. Wentzel in 1927 without the quantum theory of radiation. Similarly most electro‐optic phenomena such as stimulated emission,reaction of the emitted field on the emitting atom, resonance fluorescence, and so on, do not require the quantization of the field for their explanation. As we will see, these processes can all be quantitatively explained and physically understood in terms of the semiclassical theory of the matter–field interaction in which the electric field is treated classically while the atoms obey the laws of quantum mechanics. The quantized field is fundamentally required for accurate descriptions of certain processes involving fluctuations in the electromagnetic field: for example, spontaneous emission, the Lamb shift, the anomalous magnetic moment of the electron, and certain aspects of blackbody radiation. (The Compton effect also fits here, but see later under references 8b and c.) Here we will outline how the photon concept originated and developed, where it is not required and is often misused, and finally where it plays an essential role in the understanding of physical phenomena. In our discussion we will attempt to give a logically consistent definition of the word “photon”—a statement far more necessary than one might think, for so many contradictory uses exist of this elusive beast. In particular consider the original coining of the word by G. N. Lewis: “[because it appears to spend] only a minute fraction of its existence as a carrier of radiant energy, while the rest of the time it remains an important structural element within the atom…, I therefore take the liberty of proposing for this hypothetical new atom which is not light but plays an essential part in every process of radiation, the name photon!” (our exclamation point). Clearly the present usage of the word is very different. It has its logical foundation in the quantum theory of radiation. But the “fuzzy‐ball” picture of a photon often leads to unnecessary difficulties.
135 citations
114 citations
105 citations
TL;DR: The idea of using the sun as a source of energy has had a long history, but so far it has been a history of bright hope and dismal failure as discussed by the authors, but the early 1950's newspaper headlines were full of glowing predictions of what solar energy could do for mankind; the first International Conference on Applied Solar Energy had been held, and solar energy seemed ready to take its place, along with peaceful uses of atomic energy and with interplanetary exploration, on Vannevar Bush's "endless frontier of science".
Abstract: The idea of using the sun as a source of energy has had a long history, but so far it has been a history of bright hope and dismal failure. In the middle 1950's newspaper headlines were full of glowing predictions of what solar energy could do for mankind; the first International Conference on Applied Solar Energy had been held, and solar energy seemed ready to take its place, along with peaceful uses of atomic energy and with interplanetary exploration, on Vannevar Bush's “endless frontier of science.” And now in the 1970's nuclear power reactors and spaceflight are realities, yet solar energy, as recently as a year ago, was dismissed by a National Academy of Science–National Research Council committee as of no importance in our future—despite the admitted “energy crisis” looming ahead. Whatever happened to the grand predictions? Our search into the history of solar energy started with this question, because we were curious to know if 1970 technology might yield a different result.
TL;DR: In this article, the authors exploit the properties of elastic surface waves to perform very complex signal processing functions, identical to those carried out by conventional electromagnetic devices, and demonstrate that the energy in the elastic surface wave can readily be sensed anywhere along its path.
Abstract: Devices that exploit the properties of elastic surface waves can perform very complex signal‐processing functions, identical to those carried out by conventional electromagnetic devices. The great advantage to using surface waves instead of electromagnetic waves is the tremendous reduction in size of surface‐wave devices compared to their electromagnetic counterparts. This great reduction in size is the result of the great difference between the elastic and electromagnetic velocities. Surface waves propagate at velocities approximately 105 times slower than electromagnetic velocities; thus, at the same frequency, the elastic wavelength is 105 times shorter than the electromagnetic wavelength. A further advantage is that the energy in the elastic surface wave can readily be sensed anywhere along its path.
TL;DR: The challenges of generating and measuring such vacua will be described in the following articles of this issue of PHYSICS TODAY as discussed by the authors, which is devoted to recent developments in the study of surface phenomena, an area of science that has been both a beneficiary and contributor to advances in vacuum technology.
Abstract: The intrinsic interest in an empty box is limited, however difficult the task of evacuating it may be. It is the new vistas in science and technology opened by the ability routinely to produce ultra‐high vacua as a controlled environment that excite our interest. The challenges of generating and measuring such vacua will be described in the following articles of this issue of PHYSICS TODAY. We devote our discussion to recent developments in the study of surface phenomena, an area of science that has been both a beneficiary of and contributor to advances in vacuum technology.
TL;DR: In this article, a group of Nepalese men were discussing their views of nature and of man's relation to nature, and their discussion had ranged widely over the world of familiar phenomena from rice planting to cosmology, from rainbows to moon and planets.
Abstract: One evening not long ago I stood in the Nepalese town of Panga talking with a group of its citizens. For two hours or more I had been inquiring about their views of nature and of man's relation to nature, and our discussion had ranged widely over the world of familiar phenomena from rice planting to cosmology, from rainbows to moon and planets. Now as I was about to leave, we had stepped out into an enchantingly beautiful night. The houses across the square and the temple at its center were silhouetted against a brilliantly jewelled velvet black sky. Here and there a little mustard‐oil lamp offered a flickering challenge to the darkness, but there was no glare of street light or neon sign. Now and then a child's voice or the murmur of a conversation somewhere accentuated the quiet of the night, but there was no sound of vehicles or sirens or other machines of civilization, and we stood silent ourselves while enjoying the night. Just as I turned to leave, a bright “Echo” satellite appeared from behind the ...
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TL;DR: Cosmic numbers have intrigued modern cosmologists ever since puzzling coincidences were first noticed between some of the large dimensionless constants as mentioned in this paper, and they are possibly important to our understanding of the physical world.
Abstract: Cosmic numbers have intrigued modern cosmologists ever since puzzling coincidences were first noticed between some of the large dimensionless constants. Here I will try to show not only that these numbers are interesting, but also that they are possibly important to our understanding of the physical world. Have the coincidences always existed or is it merely fortuitous that they occur at the present stage of evolution of the universe?
TL;DR: In these days of emphasis on environmental problems, studies of clouds and precipitation take on an added importance as mentioned in this paper, and they cleanse the atmosphere of natural and manmade pollutants or process them for later removal.
Abstract: In these days of emphasis on environmental problems, studies of clouds and precipitation take on an added importance. Clouds and precipitation cleanse the atmosphere of natural and manmade pollutants or process them for later removal. Cloud radiative and dynamic properties control a good deal more than half of the solar energy available for keeping the atmosphere moving, and precipitation keeps the continents green (or white). Destructive storms are spawned mostly from cloud systems, but Man can modify his local environment to some extent now through the “seeding” of clouds, and possibly he will eventually be able to control severe storms and remove damaging pollutants.
TL;DR: In this article, the binding energies for all the orbitals of a molecule were used to describe the complete electronic structure of a molecular molecule by measuring binding energies of all the atoms in the molecule.
Abstract: Although electron energy spectra have been studied for years, only more recently has their usefulness in chemical‐structure problems been appreciated. Now we appear to have a new analytic method that can describe the complete electronic structure of a molecule by measuring binding energies for all the orbitals. Optical spectroscopy, in comparison, measures only the first ionization potentials, except for the very simplest molecules. And electron emission spectra, we shall see, are also useful in such applied work as protein structure analysis and investigations of environmental pollutants.
TL;DR: In 1972, the fortieth anniversary of the "annus mirabilis" of nuclear and particle physics was celebrated as discussed by the authors, which was a very special year in the history of the field.
Abstract: In 1972 we celebrate the fortieth anniversary of the “annus mirabilis” of nuclear and particle physics. Seen from the perspective of the present, the cluster of major conceptual and technical developments of 1932 mark that “marvelous” year as a very special one. It began with Harold Urey's announcement in January that he had discovered a heavy isotope of hydrogen, which he called “deuterium.” In February James Chadwick demonstrated the existence of a new nuclear constituent, the neutron. In April John Cockcroft and E. T. S. Walton achieved the first disintegration of nuclei by bombarding light elements with artificially accelerated protons. In August Carl Anderson's photographs of cosmic‐ray tracks revealed the existence of another new particle, the positively charged electron, soon to be called the “positron.” And later that summer Ernest Lawrence, Stanley Livingston and Milton White disintegrated nuclei with the cyclotron, an instrument that would generate almost 5‐million electron volts by the end of t...
TL;DR: A theoretical framework for testing theories of gravitation is considered in this article, where the authors separate theories into those that are viable and non-viable by sending each through a series of tests, i.e., completeness, self-consistency and agreement with Newtonian physics at lowest order.
Abstract: A theoretical framework for testing theories of gravitation is considered. This framework separates theories into those that are viable and those that are nonviable by sending each through a series of tests. Most of these tests compare the theory's predictions with the results of experiment, but one test judges each theory's completeness, self-consistency and agreement with Newtonian physics at lowest order. Only a few theories, including general relativity, are currently viable, that is, pass all five tests in the framework. Einstein's 1912 theory is also ruled out because it predicts only half the observed time-delay effect. Future tests proposed include improvements of old experiments and a number of new experiments.
TL;DR: In this paper, the theory of multilevel-lane-traffic flow is examined and the authors make a detailed prediction of the CHARACTER of the traffic flow in terms of DRIVER BEHAVIOR in DILUTE, NON-interacting, and a KINETIC EQUATION is derived to describe the space-time evolution of the VELOCITY DISTRIBUTION of cars.
Abstract: THE THEORY OF MULTIPLE-LANE TRAFFIC FLOW IS EXAMINED. A PREDICTION OF THE CHARACTER OF THE TRAFFIC FLOW IS MADE AT ARBITARY DENSITY IN TERMS OF DRIVER BEHAVIOR IN DILUTE, NONINTERACTING TRAFFIC, AND A KINETIC EQUATION IS DERIVED TO DESCRIBE THE SPACE-TIME EVOLUTION OF THE VELOCITY DISTRIBUTION OF CARS. THE ANALOGIES THAT EXIST BETWEEN STATISTICAL PHYSICS AND TRAFFIC HAVE BEEN EMPLOYED IN DEVELOPING A VIABLE THEORY. THE PROBLEM IS FORMULATED AND THE THEORY IS DEVELOPED TO A POINT WHERE THE MEETING OF THEORETICAL CONCEPTS WITH EXPERIMENTAL OBSERVATIONS WILL BE FRUITFUL. /AUTHOR/
Los Alamos National Laboratory1, Yale University2, University of Washington3, University of Wisconsin-Madison4, City University of New York5, University of Oregon6, University of Maryland, College Park7, University at Albany, SUNY8, University of Utah9, University of Amsterdam10, Lawrence Livermore National Laboratory11, University at Buffalo12