Physics welcomes the idea that space contains energy whose gravitational effect approximates that of Einstein's cosmological constant, \ensuremath{\Lambda}; today the concept is termed dark energy or quintessence. Physics also suggests that dark energy could be dynamical, allowing for the arguably appealing picture of an evolving dark-energy density approaching its natural value, zero, and small now because the expanding universe is old. This would alleviate the classical problem of the curious energy scale of a millielectron volt associated with a constant \ensuremath{\Lambda}. Dark energy may have been detected by recent cosmological tests. These tests make a good scientific case for the context, in the relativistic Friedmann-Lema\^{\i}tre model, in which the gravitational inverse-square law is 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 not yet as convincing but still serious; we await more data, which may be derived from work in progress. Planned observations may detect the evolution of the dark-energy density; a positive result would be a considerable stimulus for attempts at understanding 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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The Cosmological Constant and Dark Energy

The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

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The Confrontation Between General Relativity and Experiment

Superstring theoryをめぐって(放談室)

An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems' applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems' applications, and permittivity and loss in ferroelectric films-important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. (c) 2006 American Institute of Physics.

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Ferroelectric thin films: Review of materials, properties, and applications

http://cds.cern.ch/record/503806/files/0106045.pdf

New developments in the Casimir effect

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Comment on "Spectroscopic Signatures of Novel Oxygen-Defect Complexes in Stoichiometrically Controlled CdSe'' Chen et al. Reply SO PHYSICALComment on "Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry"

In the current work we present the complete results for the measurement of normal Casimir force between a shallow and smooth sinusoidally corrugated gold coated sphere and a plate at various angles between the corrugations using an atomic force microscope. All measured data were compared with the theoretical approach using the proximity force approximation and theory based on derivative expansion. In both cases real material properties of the surfaces and nonzero temperature were taken into account. Special attention is paid to the description of electrostatic interactions between corrugated surfaces at different angles between corrugations and samples preparation and characterization. The measured forces are found to be in good agreement with the theory including correlation effects of geometry and material properties and deviate significantly from the predictions of the proximity force approximation approach. This provides the quantitative confirmation for the observation of diffraction-type effects that are disregarded within the PFA approach. The obtained results open new opportunities for control of the Casimir effect in micromechanical systems.

Experimental and theoretical investigation of the angular dependence of the Casimir force between sinusoidally corrugated surfaces

Experimental methods and procedures required for precision measurements of the Casimir force are presented. In particular, the best practices for obtaining stable cantilevers, calibration of the cantilever, correction of thermal and mechanical drift, measuring the contact separation, sphere radius and the roughness are discussed.

Experimental procedures for precision measurements of the Casimir force with an Atomic Force Microscope

Based on the Lifshitz theory we show that the illumination of one (Si) plate in the three-layer systems Au–ethanol–Si, Si–ethanol–Si and α-Al2O3–ethanol–Si with laser pulses can change the Casimir attraction to Casimir repulsion and vice versa. The proposed effect opens novel opportunities in nanotechnology to actuate the periodic movement in electro- and optomechanical micromachines based entirely on the zero-point oscillations of the quantum vacuum without the action of mechanical springs.

https://iopscience.iop.org/article/10.1088/1751-8113/40/34/F03/pdf

Umar Mohideen

Papers

Comment on "Spectroscopic Signatures of Novel Oxygen-Defect Complexes in Stoichiometrically Controlled CdSe'' Chen et al. Reply SO PHYSICALComment on "Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry"

Experimental and theoretical investigation of the angular dependence of the Casimir force between sinusoidally corrugated surfaces

Experimental procedures for precision measurements of the Casimir force with an Atomic Force Microscope

Pulsating Casimir force

Comparative energy measurements in single molecule interactions.