Metallic Hydrogen

Metallic hydrogen is a state of hydrogen which results when it is sufficiently compressed and undergoes a phase transition; it is an example of degenerate matter. Solid metallic hydrogen is predicted to consist of a crystal lattice of hydrogen nuclei (namely, protons), with a spacing which is significantly smaller than the Bohr radius. Indeed, the spacing is more comparable with the de Broglie wavelength of the electron. The electrons are unbound and behave like the conduction electrons in a metal. In liquid metallic hydrogen, protons do not have lattice ordering; rather, it is a liquid system of protons and electrons.

Liquid metallic hydrogen

Helium-4 is a liquid at normal pressure and temperatures near absolute zero, a consequence of its high zero-point energy (ZPE). The ZPE of protons in a dense state is also high, and a decline in the ordering energy (relative to the ZPE) is expected at high pressures. Arguments have been advanced by Neil Ashcroft and others that there is a melting point maximum in compressed hydrogen, but also that there may be a range of densities (at pressures around 400 GPa) where hydrogen may be a liquid metal, even at low temperatures.

Astrophysics

Metallic hydrogen is thought to be present in large amounts in the gravitationally compressed interiors of Jupiter, Saturn, and some of the newly discovered extrasolar planets. Because previous predictions of the nature of those interiors had taken for granted metallization at a higher pressure than the one at which we now know it to happen, those predictions must now be adjusted. The new data indicate much more metallic hydrogen must exist inside Jupiter than previously thought, that it comes closer to the surface, and that therefore, Jupiter's tremendous magnetic field, the strongest of any planet in the solar system is, in turn, produced closer to the surface.

General Relativity (A. Einstein - 1915)

General Relativity Wikipedia
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General relativity (GR) (aka general theory of relativity (GTR)) is the geometrical theory of gravitation published by Albert Einstein in 1915/16.It unifies special relativity, Newton's law of universal gravitation, and the insight that gravitational acceleration can be described by the curvature of space and time. General relativity further calls for the curvature of space-time to be produced by the mass-energy and momentum content of the matter in space-time. General relativity is distinguished from other metric theories of gravitation by its use of the Einstein field equations to relate space-time content and space-time curvature.

General relativity is currently the most successful gravitational theory, being almost universally accepted and well-supported by observations. The first success of general relativity was in explaining the anomalous perihelion precession of Mercury. Then in 1919, Sir Arthur Eddington announced that observations of stars near the eclipsed Sun confirmed general relativity's prediction that massive objects bend light. Since then, many other observations and experiments have confirmed many of the predictions of general relativity, including gravitational time dilation, the gravitational redshift of light, signal delay, and gravitational radiation. In addition, numerous observations are interpreted as confirming one of general relativity's most mysterious and exotic predictions, the existence of black holes.



In spite of its overwhelming success, there is discomfort with general relativity in the scientific community due to its being incompatible with quantum mechanics and the reachable singularities of black holes (at which the mathematics of general relativity breaks down). Because of this, numerous other theories have been proposed as alternatives to general relativity. An early and still-popular class of modifications is Brans-Dicke theory, which, although not solving the problems of singularities and quantum gravity, appeared to have observational support in the 1960s. However, those observations have since been refuted and modern measurements indicate that any Brans-Dicke type of deviation from general relativity must be very small if it exists at all.