Search results for "theoretical physics"

Is empty spacetime a physical thing?

2005

This article deals with empty spacetime and the question of its physical reality. By "empty spacetime" we mean a collection of bare spacetime points, the remains of ridding spacetime of all matter and fields. We ask whether these geometric objects--themselves intrinsic to the concept of field--might be observable through some physical test. By taking quantum-mechanical notions into account, we challenge the negative conclusion drawn from the diffeomorphism invariance postulate of general relativity, and we propose new foundational ideas regarding the possible observation--as well as conceptual overthrow--of this geometric ether.

Ernst Julius Öpik’s (1916) note on the theory of explosion cratering onthe Moon’s surface—The complex case of a long-overlooked benchmark paper

2014

High-velocity impact as a common phenomenon in planetary evolution was ignored until well into the twentieth century, mostly because of inadequate understanding of cratering processes. An eight-page note, published in Russian by the young Ernst Julius Opik, a great Estonian astronomer, was among the key selenological papers, but due to the language barrier, it was barely known and mostly incorrectly cited. This particular paper is here intended to serve as an explanatory supplement to an English translation of Opik's article, but also to document an early stage in our understanding of cratering. First, we outline the historical–biographical background of this benchmark paper, and second, a …

Fundamentals of Gravity, Elements of Potential Theory

2009

Looking for the imprints of nonlinear structures on the cosmic microwave background

1997

Abstract Many authors have estimated the anisotropies produced by one isolated cosmological non-linear inhomogeneity. This paper is an updated review about these estimates. The main methods used in order to deal with this problem are described. The limitations of these methods are analyzed. Results appear to be particularly interesting in the open non-linear case, in which a general treatment of the anisotropies produced by inhomogeneity distributions is very troublesome. The effects produced by very big structures such as the Great Attractor and the Bootes Void are studied in detail. Some generalities about the origin, detection and features of the Cosmic Microwave Background anisotropies …

Appendix: listing of programs mentioned in the text

2009

Engineering novel optical lattices.

2013

Optical lattices have developed into a widely used and highly recognized tool to study many-body quantum physics with special relevance for solid state type systems. One of the most prominent reasons for this success is the high degree of tunability in the experimental setups. While at the beginning quasi-static, cubic geometries were mainly explored, the focus of the field has now shifted toward new lattice topologies and the dynamical control of lattice structures. In this review we intend to give an overview of the progress recently achieved in this field on the experimental side. In addition, we discuss theoretical proposals exploiting specifically these novel lattice geometries.

Logarithmic Enumerative Geometry and Mirror Symmetry

2020

WIGNER TRANSFORM METHODS IN INCLUSIVE ELECTRON SCATTERING FROM NUCLEI

1984

A multiple scattering series for deep inelastic leptoninduced reactions is derived by using semiclassical Wigner transform methods. In contrast to the usual Glauber theory there is no limitation for the energy loss since a time-dependent formulation is used throughout. A simple parametrization of the generalized profile function yields a closed analytical expression for the longitudinal and transverse response function of p-shell nuclei. Comparison is made with the Saclay data for -'• C. I Introduction It is common knowledge that geometrical optics is valid if the wavelength of the scattering wave is small compared to the dimensions of the scatterer. Under these conditions the phase-space d…

Elementary theory and brief history

1991

In the history of the theory of deuteron photodisintegration one may distinguish roughly three periods: (i) the primitive period of the elementary theory using very simple wave functions and forces and considering lowest multipoles (E1, M1) only, (ii) the classical period still in the framework f conventional nuclear physics, but using realstic forces with correspondingly elaborate wave functions and considering also higher multipole transitions, (ii) the post-classic period with explicit treatment of subnuclear degrees of freedom like meson and isobar degrees of freedom and very recently quark-gluon degrees of freedom.

Is the Universe Fractal?

1999

One of the key issues in cosmology is the question of whether the universe is smooth or fractal at large dimensions. The answer has a bearing on the big bang model of the origin of the universe. MartA­nez discusses why recent analyses have come to opposing conclusions regarding this question and looks at how good a case can be made for large-scale smoothness of the universe.