Physics in Perspective最新文献

The fiftieth anniversary year of Brookhaven National Laboratory was momentous, but for reasons other than celebrating its scientific accomplishments. Legacy environmental contamination, community unrest, politics, and internal Department of Energy issues dominated the year. It was the early days of perhaps the most turbulent time in the lab’s history. The consequences resulted in significant changes at the lab, but in addition they brought a change to contracts to manage the Department of Energy laboratories.

This is the second in a three-part article describing the development of the Thomas Jefferson National Accelerator Facility’s experimental program, from the first dreams of incisive electromagnetic probes into the structure of the nucleus through the era in which equipment was designed and constructed and a program crafted so that the long-desired experiments could begin. These developments unfolded against the backdrop of the rise of the more bureaucratic New Big Science and the intellectual tumult that grew from increasing understanding and interest in quark-level physics. Part 2, presented here, focuses on the period from 1986 to 1990. During this period of revolutionary change, laboratory personnel, potential users, and DOE officials labored to proceed from the 1986 laboratory design report, which included detailed accelerator plans and very preliminary experimental equipment sketches, to an approved 1990 experimental equipment conceptual design report, which provided designs complete enough for the onset of experimental equipment construction.

In the early 1960s, a PhD student in physics, Costas Papaliolios, designed a simple—and playful—system of Polaroid polarizer filters with a specific goal in mind: explaining the core principles behind Julian Schwinger’s quantum mechanical measurement algebra, developed at Harvard in the late 1940s and based on the Stern-Gerlach experiment confirming the quantization of electron spin. Papaliolios dubbed his invention “quantum toys.” This article looks at the origins and function of this amusing pedagogical device, which landed half a century later in the Collection of Historical Scientific Instruments at Harvard University. Rendering the abstract tangible was one of Papaliolios’s demonstration tactics in reforming basic teaching of quantum mechanics. This article contends that Papaliolios’s motivation in creating the quantum toys came from a renowned endeavor aimed, inter alia, at reforming high-school physics training in the United States: Harvard Project Physics. The pedagogical study of these quantum toys, finally, compels us to revisit the central role playful discovery performs in pedagogy, at all levels of training and in all fields of knowledge.

The carbon cycle, or Bethe-Weizs?cker cycle, plays an important role in astrophysics as one of the most important energy sources for quiescent and explosive hydrogen burning in stars. This paper presents the intellectual and historical background of the idea of the correlation between stellar energy production and the synthesis of the chemical elements in stars on the example of this cycle. In particular, it addresses the contributions of Carl Friedrich von Weizs?cker and Hans Bethe, who provided the first predictions of the carbon cycle. Further, the experimental verification of the predicted process as it developed over the following decades is discussed, as well as the extension of the initial carbon cycle to the carbon-nitrogen-oxygen (CNO) multi-cycles and the hot CNO cycles. This development emerged from the detailed experimental studies of the associated nuclear reactions over more than seven decades. Finally, the impact of the experimental and theoretical results on our present understanding of hydrogen burning in different stellar environments is presented, as well as the impact on our understanding of the chemical evolution of our universe.

In 2016 the LIGO-Virgo collaboration announced “the first direct detection of gravitational waves.” This was to distinguish their result from the indirect observation of Russell Hulse, Joel Weisberg, and Joseph Taylor, which used the decrease in the period of a binary pulsar to “establish, with a high degree of confidence the existence of gravitational radiation as predicted by general relativity.” This raises several interesting questions. One might ask how one can distinguish between direct and indirect observation and whether that distinction is exemplified in the practice of science. One might also ask whether a direct observation has more epistemic weight than an indirect observation. In this essay, I briefly discuss several episodes from the history of modern physics in an attempt to answer those questions. These episodes include Galileo and falling bodies, the discovery of the neutrino, the Higgs boson, and gravitational radiation.

This article chronicles the most recent history of the Deutsches Elektronen-Synchrotron (DESY) located in Hamburg, Germany, with particular emphasis on how this national laboratory founded for accelerator-based particle physics shifted its research program toward multi-disciplinary photon science. Synchrotron radiation became DESY’s central experimental research program through a series of changes in its organizational, scientific, and infrastructural setup and the science policy context. Furthermore, the turn toward photon science is part of a broader transformation in the late twentieth century in which nuclear and particle physics, once the dominating fields in national and international science budgets, gave way to increasing investment in the materials sciences and life sciences. Synchrotron radiation research took a lead position on the experimental side of these growing fields and became a new form of big science, generously funded by governments and with user communities expanding across both academia and industry.