Near-thermal radiation in detectors, mirrors, and black holes: A stochastic approach

In analyzing the nature of thermal radiance experienced by an accelerated observer (Unruh effect), an eternal black hole (Hawking effect) and in certain types of cosmological expansion, one of us proposed a unifying viewpoint that these can be understood as arising from the vacuum fluctuations of the quantum field being subjected to an exponential scale transformation. This viewpoint, together with our recently developed stochastic theory of particle-field interaction understood as quantum open systems described by the influence functional formalism, can be used to address situations where the spacetime possesses an event horizon only asymptotically, or none at all. Examples studied here include detectors moving at uniform acceleration only asymptotically or for a finite time, a moving mirror, and a collapsing mass. We show that in such systems radiance indeed is observed, albeit not in a precise Planckian spectrum. The deviation therefrom is determined by a parameter which measures the departure from uniform acceleration or from exact exponential expansion. These results are expected to be useful for the investigation of non-equilibrium black hole thermodynamics and the linear response regime of backreaction problems in semiclassical gravity.Alpan Raval, B. L. Hu, Don Kok

Thermal Particle Creation in Cosmological Spacetimes: A Stochastic Approach

The stochastic method based on the influence functional formalism introduced in an earlier paper to treat particle creation in near-uniformly accelerated detectors and collapsing masses is applied here to treat thermal and near-thermal radiance in certain types of cosmological expansions. It is indicated how the appearance of thermal radiance in different cosmological spacetimes and in the two apparently distinct classes of black hole and cosmological spacetimes can be understood under a unifying conceptual and methodological framework.Comment: 17 pages, revtex (aps, eqsecnum), submitted to PRD, April 199

Entropy and Uncertainty of Squeezed Quantum Open Systems

We define the entropy S and uncertainty function of a squeezed system interacting with a thermal bath, and study how they change in time by following the evolution of the reduced density matrix in the influence functional formalism. As examples, we calculate the entropy of two exactly solvable squeezed systems: an inverted harmonic oscillator and a scalar field mode evolving in an inflationary universe. For the inverted oscillator with weak coupling to the bath, at both high and low temperatures, $S\to r$, where r is the squeeze parameter. In the de Sitter case, at high temperatures, $S\to (1-c)r$ where $c = \gamma_0/H$, $\gamma_0$ being the coupling to the bath and H the Hubble constant. These three cases confirm previous results based on more ad hoc prescriptions for calculating entropy. But at low temperatures, the de Sitter entropy $S\to (1/2-c)r$ is noticeably different. This result, obtained from a more rigorous approach, shows that factors usually ignored by the conventional approaches, i.e., the nature of the environment and the coupling strength betwen the system and the environment, are important.Comment: 36 pages, epsfig, 2 in-text figures include

Simultaneity and Precise Time in Rotation

I analyse the role of simultaneity in relativistic rotation by building incrementally on its role in simpler scenarios. Historically, rotation has been analysed in 1 + 1 dimensions; but my stance is that a 2 + 1 -dimensional treatment is necessary. This treatment requires a discussion of what constitutes a frame, how coordinate choices differ from frame choices, and how poor coordinates can be misleading. I determine how precisely we are able to define a meaningful time coordinate on a gravity-free rotating Earth, and discuss complications due to gravity on our real Earth. I end with a critique of several statements made in relativistic precision-timing literature, that I maintain contradict the tenets of relativity. Those statements tend to be made in the context of satellite-based navigation; but they are independent of that technology, and hence are not validated by its success. I suggest that if relativistic precision-timing adheres to such analyses, our civilian timing is likely to suffer in the near future as clocks become ever more precise

Decoherence, entropy and thermal radiance using influence functionals / Don Koks.

Bibliography: p. 121-124.vii, 124 p. ; 30 cm.Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1997

Explorations in Mathematical Physics: The Concepts Behind an Elegant Language

Have you ever wondered why the language of modern physics centres on geometry? Or how quantum operators and Dirac brackets work? What a convolution really is? What tensors are all about? Or what field theory and lagrangians are, and why gravity is described as curvature? This book takes you on a tour of the main ideas forming the language of modern mathematical physics. Here you will meet novel approaches to concepts such as determinants and geometry, wave function evolution, statistics, signal processing, and three-dimensional rotations. You'll see how the accelerated frames of special relativity tell us about gravity. On the journey, you'll discover how tensor notation relates to vector calculus, how differential geometry is built on intuitive concepts, and how variational calculus leads to field theory. You will meet quantum measurement theory, along with Green functions and the art of complex integration, and finally general relativity and cosmology. The book takes a fresh approach to tensor analysis built solely on the metric and vectors, with no need for one-forms. This gives a much more geometrical and intuitive insight into vector and tensor calculus, together with general relativity, than do traditional, more abstract methods. Don Koks is a physicist at the Defence Science and Technology Organisation in Adelaide, Australia. His doctorate in quantum cosmology was obtained from the Department of Physics and Mathematical Physics at Adelaide University. Prior work at the University of Auckland specialised in applied accelerator physics, along with pure and applied mathematics

The Uniformly Accelerated Frame as a Test Bed for Analysing the Gravitational Redshift

Ever since Eddington’s analysis of the gravitational redshift a century ago, and the arguments in the relativity community that it produced, fine details of the roles of proper time and coordinate time in the redshift remain somewhat obscure. We shed light on these roles by appealing to the physics of the uniformly accelerated frame, in which coordinate time and proper time are well defined and easy to understand; and because that frame exists in flat spacetime, special relativity is sufficient to analyse it. We conclude that Eddington’s analysis was indeed correct—as was the 1980 analysis of his detractors, Earman and Glymour, who (it turns out) were following a different route. We also use the uniformly accelerated frame to pronounce invalid Schild’s old argument for spacetime curvature, which has been reproduced by many authors as a pedagogical introduction to curved spacetime. More generally, because the uniformly accelerated frame simulates a gravitational field, it can play a strong role in discussions of proper and coordinate times in advanced relativity

Microstates, entropy and quanta: an introduction to statistical mechanics

Statistical mechanics: the bane of many a physics student. But when pared back to its underlying concepts and built from the ground up, the field takes on a charm of its own, and embraces a wide variety of physical phenomena. This book presents a straightforward introduction to the key concepts in statistical mechanics, following the popular style of the author's highly successful textbook "Explorations in Mathematical Physics". Offering a clear, conceptual approach to the subject matter, the book presents a treatment that is mathematically complete, while remaining very accessible to undergraduates. It commences by showcasing the counting of configurations, which leads to entropy, thermodynamics, and physical chemistry. The Boltzmann and Maxwell distributions then appear, with related topics of thermal conductivity and viscosity. Next come bosons via Einstein's and Debye's theories of heat capacity, and fermions via electrical conduction and low-temperature heat capacity of metals. The text ends with a derivation of blackbody radiation, and uses this to discuss the greenhouse effect, cosmology, and lasers. Suitable for use with core undergraduate courses in statistical mechanics and thermodynamics, this book concentrates on using solid mathematics, while avoiding cumbersome notation. All mathematical steps are included in the text and worked examples. About the Author Don Koks studied at the University of Auckland in the 1980s, where he obtained a Bachelor of Science in pure and applied mathematics and physics, and a Master of Science in applied accelerator physics. He was awarded a doctorate in quantum cosmology (quantum statistics and black hole theory) by Adelaide University. He works in Australian Defence, specialising in relativistic precision timing, orbital mechanics, spatial orientation concepts, and radar signal processing. Review of Explorations in Mathematical Physics by Don Koks “With enjoyable and sometimes surprising excursions along the way, the journey provides a fresh look at many familiar topics, as it takes us from basic linear mathematics to general relativity... look forward to having your geometric intuition nourished and expanded by the author’s intelligent commentaries.” Eugen Merzbacher, University of North Carolina