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.

/pdf/the-confrontation-between-general-relativity-and-experiment-5dqdube5p9.pdf

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.

/pdf/ferroelectric-thin-films-review-of-materials-properties-and-rc7umdkxk5.pdf

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

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

New developments in the Casimir effect

We have used an atomic force microscope to make precision measurements of the Casimir force between a metallized sphere of diameter 196 \ensuremath{\mu}m and flat plate. The force was measured for plate-sphere surface separations from 0.1 to 0.9 \ensuremath{\mu}m. The experimental results are consistent with present theoretical calculations including the finite conductivity, roughness, and temperature corrections. The root mean square average deviation of 1.6 pN between theory and experiment corresponds to a $1%$ deviation at the smallest separation.

https://arxiv.org/pdf/physics/9805038.pdf

Precision Measurement of the Casimir Force from 0.1 to 0.9 μ m

1. Introduction I: PHYSICAL AND MATHEMATICAL FOUNDATIONS OF THE CASIMIR EFFECT FOR IDEAL BOUNDARIES 2. Simple models of the Casimir effect 3. Field quantization and vacuum energy in the presence of boundaries 4. Regularization and renormalization of the vacuum energy 5. The Casimir effect at nonzero temperature 6. Approximate and numerical approaches to the Casimir effect 7. The Casimir effect for two ideal metal planes 8. The Casimir effect in rectangular boxes 9. Single spherical and cylindrical boundaries 10. The Casimir force between objects of arbitrary shape 11. Spaces with non-Euclidean topology II: THE CASIMIR FORCE BETWEEN REAL BODIES 12. The Lifshitz theory of van der Waals and Casimir forces between plane dielectrics 13. The Casimir interaction between plates made of real metals at zero temperature 14. The Casimir interaction between real metals at nonzero temperature 15. The Casimir interaction between metal and dielectric 16. The Lifshitz theory of atom-wall interaction 17. The Casimir force between rough and corrugated surfaces III: MEASUREMENTS OF THE CASIMIR FORCE AND THEIR APPLICATIONS IN BOTH FUNDAMENTAL PHYSICS AND NANOTECHNOLOGY 18. General requirements for Casimir force measurements 19. Measurements of the Casimir force between equals 20. Measurements of the Casimir force with semiconductors 21. Measurements of the Casimir force in configurations with corrugated surfaces 22. Measurement of the Casimir-Polder force 23. Applications of the Casimir force in nanotechnology 24. Constraints on hypothetical interactions from the Casimir effect 25. Conclusions and outlook

Advances in the Casimir Effect

The physical origin of the Casimir force is connected with the existence of zero-point and thermal fluctuations. The Casimir effect is very general and finds applications in various fields of physics. This review is limited to the rapid progress at the intersection of experiment and theory that has been achieved in the last few years. It includes a critical assessment of the proposed approaches to the resolution of the puzzles arising in the applications of the Lifshitz theory of the van der Waals and Casimir forces to real materials. All the primary experiments on the measurement of the Casimir force between macroscopic bodies and the Casimir-Polder force between an atom and a wall that have been performed in the last decade are reviewed, including the theory needed for their interpretation. The methodology for the comparison between experiment and theory in the force-distance measurements is presented. The experimental and theoretical results described here provide a deeper understanding of the phenomenon of dispersion forces in real materials and offer guidance for the application of the Lifshitz theory to the interpretation of the measurement results.

The Casimir force between real materials: Experiment and theory

A precision measurement of the Casimir force using metallic gold surfaces is reported. The force is measured between a large gold-coated sphere and flat plate using an atomic force microscope. The use of gold surfaces removes some theoretical uncertainties in the interpretation of the measurement. The forces are also measured at smaller surface separations. The complete dielectric spectrum of the metal is used in the comparison of theory to the experiment. The average statistical precision remains at the same 1% of the forces measured at the closest separation. These results should lead to the development of stronger constraints on hypothetical forces.

Umar Mohideen

Papers

New developments in the Casimir effect

Precision Measurement of the Casimir Force from 0.1 to 0.9 μ m

Advances in the Casimir Effect

The Casimir force between real materials: Experiment and theory

Precision measurement of the Casimir force using gold surfaces