Tuesday, January 05, 2010

A Survey of the Observational Evidence for Dark Matter

Dark Matter: The evidence from astronomy, astrophysics and cosmology
Dark matter has been introduced to explain many independent gravitational effects at different astronomical scales, in galaxies, groups of galaxies, clusters, superclusters and even across the full horizon. This review describes the accumulated astronomical, astrophysical, and cosmological evidence for dark matter. It is written at a non-specialist level and intended for an audience with little or only partial knowledge of astrophysics or cosmology.

Ultra Dense Deuterium?

There is recent experiment evidence of ultra-dense deuterium from Sweden. "Ultra-dense deuterium would be by far the most dense material ever produced by man - one cubic centimetre would have a mass of 140 kilograms" - Wikipedia.
See also the preprint Ultradense Deuterium.
An attempt is made to explain the recently reported occurrence of ultradense deuterium as an isothermal transition of Rydberg matter into a high density phase by quantum mechanical exchange forces. It is conjectured that the transition is made possible by the formation of vortices in a Cooper pair electron fluid, separating the electrons from the deuterons, with the deuterons undergoing Bose-Einstein condensation in the core of the vortices. If such a state of deuterium should exist at the reported density of about 100,000 g/cm3, it would greatly facility the ignition of a thermonuclear detonation wave in pure deuterium, by placing the deuterium in a thin disc, to be ignited by a pulsed ultrafast laser or particle beam of modest energy.

When does a pair of Fermions act like a Boson?

Entanglement and Composite Bosons
Under what circumstances can a pair of fermions be treated as an elementary boson? Many authors have done detailed studies of this question, as it applies, for example, to atomic Bose-Einstein condensates, excitons, and Cooper pairs in superconductors. In a 2005 paper, C. K. Law presented evidence that the question can be answered in general in terms of entanglement: two fermions can be treated as an elementary boson if they are sufficiently entangled. Consider, for example, a single hydrogen atom in a harmonic trap. Within the atom, the proton and electron are strongly entangled with respect to their position variables; for example, wherever the proton might be found—it could be anywhere in the trap—the electron is sure to be nearby. Law suggests that this entanglement is the essential property underlying the (approximate) bosonic behavior of the composite particle, allowing, for example, a collection of many hydrogen atoms to form a Bose-Einstein condensate.