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Veteran Member
Join Date: Apr 2001
Location: arse-end of the world
Posts: 2,305
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Interesting papers I've read over the past 12 months
Since popular science doesn't really do it for me anymore (unless it's very well written, e.g. Richard Dawkins, David Mermin) I tend to go straight to the source, i.e. scientific papers written by professional scientists. Review papers are especially nice because they often include the background information that I almost always lack. Anyway, here's some papers I've read (though not necessarily understood!) over the past 12 months and found utterly fascinating. Most of these papers can be found at the arXiv.org e-print archive web site. I hope they might provide some interesting reading for you. Abstracts are quoted here so you can quickly tell whether a paper is worth downloading.
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Quantum Mechanics as Quantum Information (and only a little more) by Christopher A. Fuchs (59 pages)
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In this paper, I try once again to cause some good-natured trouble. The issue remains, when will we ever stop burdening the taxpayer with conferences devoted to the quantum foundations? The suspicion is expressed that no end will be in sight until a means is found to reduce quantum theory to two or three statements of crisp physical (rather than abstract, axiomatic) significance. In this regard, no tool appears better calibrated for a direct assault than quantum information theory. Far from a strained application of the latest fad to a time-honored problem, this method holds promise precisely because a large part--but not all--of the structure of quantum theory has always concerned information. It is just that the physics community needs reminding.
This paper, though taking quant-ph/0106166 as its core, corrects one mistake and offers several observations beyond the previous version. In particular, I identify one element of quantum mechanics that I would not label a subjective term in the theory--it is the integer parameter D traditionally ascribed to a quantum system via its Hilbert-space dimension.
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Censorship and the Peer Review System by Karl Svozil (20 pages)
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In the best of all worlds, peer review amounts to benign censorship, saving trees, human efforts and money spent by attempts to cope with erroneous or badly written papers. In the worst case, peer review amounts to malign censorship, impede progress, and hence to a waste of human efforts and (mostly taxpayer's) money. It is argued that, in the way it is commonly executed by editorial boards and funding agencies, peer review does often more bad than good. Alternatives to peer review are briefly suggested and discussed.
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Laws, Symmetry, and Symmetry Breaking; Invariance, Conservation Principles, and Objectivity by John Earman (26 pages)
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Given its importance in modern physics, philosophers of science have paid surprisingly little attention to the subject of symmetries and invariances, and they have largely neglected the subtopic of symmetry breaking. I illustrate how the topic of laws and symmetries brings into fruitful interaction technical issues in physics and mathematics with both methodological issues in philosophy of science, such as the status of laws of physics, and metaphysical issues, such as the nature of objectivity.
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Is Mathematical Rigor Necessary In Physics? by Kevin Davey (25 pages)
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Many arguments found in the physics literature involve concepts that are not well-defined by the usual standards of mathematics. I argue that physicists are entitled to employ such concepts without rigorously defining them so long as they restrict the sorts of mathematical arguments in which these concepts are involved. Restrictions of this sort allow the physicist to ignore calculations involving these concepts that might lead to contradictory results. I argue that such restrictions need not be ad-hoc, but can sometimes be justified by considering some of the metaphysical issues surrounding the question of the applicability of mathematics to physical reality.
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The Cosmological Constant and Dark Energy by Jim Peebles and Bharat Ratra (55 pages)
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Physics invites the idea that space contains energy whose gravitational effect approximates that of Einstein's cosmological constant, Lambda; nowadays the concept is termed dark energy or quintessence. Physics also suggests the dark energy could be dynamical, allowing the arguably appealing picture that the dark energy density is evolving to its natural value, zero, and is small now because the expanding universe is old. This alleviates the classical problem of the curious energy scale of order a millielectronvolt associated with a constant Lambda. Dark energy may have been detected by recent advances in the cosmological tests. The tests establish a good scientific case for the context, in the relativistic Friedmann-Lemaitre model, including the gravitational inverse square law applied to the scales of cosmology. We have well-checked evidence that the mean mass density is not much more than one quarter of the critical Einstein-de Sitter value. The case for detection of dark energy is serious but not yet as convincing; we await more checks that may come out of work in progress. Planned observations might be capable of detecting evolution of the dark energy density; a positive result would be a considerable stimulus to attempts to understand the microphysics of dark energy. This review presents the basic physics and astronomy of the subject, reviews the history of ideas, assesses the state of the observational evidence, and comments on recent developments in the search for a fundamental theory.
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Cosmological Constant - The Weight of the Vacuum by T. Padmanabhan (112 pages)
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Recent cosmological observations suggest the existence of a positive cosmological constant $\Lambda$ with the magnitude $\Lambda(G\hbar/c^3) \approx 10^{-123}$. This review discusses several aspects of the cosmological constant both from the cosmological (sections 1-6) and field theoretical (sections 7-11) perspectives. The first section introduces the key issues related to cosmological constant and provides a brief historical overview. This is followed by a summary of the kinematics and dynamics of the standard Friedmann model of the universe paying special attention to features involving the cosmological constant. Section 3 reviews the observational evidence for cosmological constant, especially the supernova results, constraints from the age of the universe and a few others. Theoretical models (quintessence, tachyonic scalar field, ...) with evolving cosmological `constant' are described from different perspectives in the next section. Constraints on dark energy from structure formation and from CMBR anisotropies are discussed in the next two sections. The latter part of the review (sections 7-11) concentrates on more conceptual and fundamental aspects of the cosmological constant. Section 7 provides some alternative interpretations of the cosmological constant which could have a bearing on the possible solution to the problem. Several relaxation mechanisms have been suggested in the literature to reduce the cosmological constant to the currently observed value and some of these attempts are described in section 8. Next section gives a brief description of the geometrical structure of the de Sitter spacetime and the thermodynamics of the de Sitter universe is taken up in section 10. The last section deals with the role of string theory in the cosmological constant problem.
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The Cosmological Constant by Sean Carroll (50 pages)
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This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero) vacuum energy.
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How Did Globular Clusters Form? by Sidney van den Bergh (10 pages)
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It is suggested that there have been at least two physically distinct epochs of massive cluster formation. The first generation of globular clusters may have formed as halo gas was compressed by shocks driven inward by ionization fronts generated during cosmic reionization at z ~ 6. On the other hand a second generation of massive clusters might have been formed at later times by compression, and subsequent collapse, of giant molecular clouds. In some cases this compression may have been triggered by heating of the interstellar medium via collisions between gas-rich disk galaxies. It is also suggested that the present specific globular cluster frequency in galaxies was mainly determined by the peak rate of star creation, with elevated peak rates of star formation per unit area resulting in high present specific globular cluster frequencies.
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The Formation of Globular Cluster Systems by Patrick Cote (10 pages)
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I briefly review models for the formation of globular cluster systems, and summarize the observational properties (i.e., formation efficiencies, metallicity distributions, kinematics and ages) of the globular cluster systems of M87 and M49: two thoroughly studied elliptical galaxies. Many of the properties of the metal-poor clusters in these and other galaxies appear to be consistent with their formation in low-mass, proto-galactic fragments, as proposed by several different formation models. A number of outstanding questions concerning the formation of the metal-rich clusters in these galaxies are highlighted.
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Formation and Evolution of Disk Galaxies by Joseph Silk (14 pages)
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I review several of the current issues in the theory of disk galaxy formation. There is still much to be done, observationally and theoretically, before we can expect to approach an understanding of disk galaxies that is reliable enough to make robust predictions about the high redshift universe.
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100 Years of the Quantum by Max Tegmark and John Archibald Wheeler (9 pages)
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As quantum theory celebrates its 100th birthday, spectacular successes are mixed with outstanding puzzles and promises of new technologies. This article reviews both the successes of quantum theory and the ongoing debate about its consequences for issues ranging from quantum computation to consciousness, parallel universes and the nature of physical reality. We argue that modern experiments and the discovery of decoherence have have shifted prevailing quantum interpretations away from wave function collapse towards unitary physics, and discuss quantum processes in the framework of a tripartite subject-object-environment decomposition. We conclude with some speculations on the bigger picture and the search for a unified theory of quantum gravity.
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QCD and Natural Philosophy by Frank Wilczek (18 pages)
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QCD sheds considerable light on several of the most basic features of the natural world including the origin of mass, the feebleness of gravity, the extent to which the properties of matter can be determined conceptually, the possible utility of the anthropic principle, and the metatheoretic notions of effectiveness and computability. I discuss these applications here.
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Quantum Geometry and Gravity: Recent Advances by Abhay Ashtekar (24 pages)
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Over the last three years, a number of fundamental physical issues were addressed in loop quantum gravity. These include: A statistical mechanical derivation of the horizon entropy, encompassing astrophysically interesting black holes as well as cosmological horizons; a natural resolution of the big-bang singularity; the development of spin-foam models which provide background independent path integral formulations of quantum gravity and `finiteness proofs' of some of these models; and, the introduction of semi-classical techniques to make contact between the background independent, non-perturbative theory and the perturbative, low energy physics in Minkowski space. These developments spring from a detailed quantum theory of geometry that was systematically developed in the mid-nineties and have added a great deal of optimism and intellectual excitement to the field.
The goal of this article is to communicate these advances in general physical terms, accessible to researchers in all areas of gravitational physics represented in this conference.
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Measuring Spacetime: from Big Bang to Black Holes by Max Tegmark (11 pages)
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Nerd abstract: Observational constraints on spacetime are reviewed, focusing on how the underlying physics (dark matter, dark energy, gravity) can be tested rather than assumed.
Popular abstract: Space is not a boring static stage on which events unfold over time, but a dynamic entity with curvature, fluctuations and a rich life of its own which is a booming area of study. Spectacular new measurements of the cosmic microwave background, gravitational lensing, type Ia supernovae, large-scale structure, spectra of the Lyman alpha forest, stellar dynamics and x-ray binaries are probing the properties of spacetime over 22 orders of magnitude in scale. Current measurements are consistent with an infinite flat everlasting Universe containing about 30% cold dark matter, 65% dark energy and at least two distinct populations of black holes.
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The State of the Universe: Cosmological Parameters 2002 by Lawrence M. Krauss (20 pages)
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In the past decade, observational cosmology has had one of the most exciting periods in the past century. The precision with which we have been able to measure cosmological parameters has increased tremendously, while at the same time, we have been surprised beyond our wildest dreams by the results. I review here recent measurements of the expansion rate, geometry, age, matter content, and equation of state of the universe, and discuss the implications for our understanding of cosmology.
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An Exposition on Inflationary Cosmology by Gary Scott Watson (93 pages)
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This paper is intended to offer a pedagogical treatment of cosmological modeling and inflationary cosmology. In recent years, inflation has become accepted as a standard scenario making predictions that are testable by observations of the cosmic background. It is therefore manifest that anyone wishing to pursue the study of cosmology and large-scale structure should have this scenario at their disposal. The author hopes this paper will serve to `bridge the gap' between technical and popular accounts of the subject.
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01-07-2003, 01:41 AM
