Entropy Of Matter Research Articles

Quantum effect on Kaluza-Klein cosmologies: High-temperature case.

The time evolution of a higher-dimensional universe with a topology of R\ifmmode\times\else\texttimes\fi{}${S}^{d}$\ifmmode\times\else\texttimes\fi{}${S}^{D}$ is discussed by using the effective action in a high-temperature limit. The universe, which starts at high temperature, always comes out of thermal equilibrium. Consequently, nonthermal quantum effects such as particle production become very important. The conversion from ``gravitational entropy'' to matter entropy through particle production might give the present large entropy.

Deuteron and entropy production and the nuclear liquid-gas phase transition

The entropy of hot matter produced in medium energy nuclear collisions is inferred from recent data on light fragment cross sections. A previously suggested model is used to fit the abundances of both the deuterons, and the deuteronlike pairings contained in higher mass clusters, with a single parameter. The model takes into account finite density effects in six-dimensional phase space. The entropy rises monotonically with energy, as expected, but remains rather high even at the lower energies. Surprisingly the measured entropy always lies above the theoretically expected value (about 3.3) at the critical point of the liquid-gas phase transition which, it is argued, depends only upon the gross features of the nuclear matter equation of state.

Entropy of hot matter produced in heavy ion collisions

We show that the observed excess of entropy in fireballs from heavy ion collisions near 1 GeV/nucleon (lab) can be explained by a modified pionic spectrum. Measurements of the dependence of entropy on excitation energy could show a transition from nucleonic to quark matter at higher excitation energies.

Role of surface integrals in the hamiltonian formulation of general relativity: Tullio Regge. Institute for Advanced Study, Princeton, New Jersey 08540 and Claudio Teitelboim. Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08540

We construct a generally-covariant formulation of non-equilibrium thermodynamics in General Relativity. We find covariant entropic forces arising from gradients of the entropy density, and a corresponding non-conservation of the energy momentum tensor in terms of these forces. We also provide a Hamiltonian formulation of General Relativity in the context of non-equilibrium phenomena and write the Raychaudhuri equations for a congruence of geodesics. We find that a fluid satisfying the strong energy condition could avoid collapse for a positive and sufficiently large entropic-force contribution. We then study the forces arising from the internal production of “bulk” entropy of hydrodynamical matter, as well as from the entropy gradients in the boundary terms of the action, like those associated with black hole horizons. Finally, we apply the covariant formulation of non-equilibrium thermodynamics to the expanding universe and obtain the modified Friedmann equations, with an extra term corresponding to an entropic force satisfying the second law of thermodynamics.

Particle creation by black holes

In the classical theory black holes can only absorb and not emit particles. However it is shown that quantum mechanical effects cause black holes to create and emit particles as if they were hot bodies with temperature $$\frac{{h\kappa }}{{2\pi k}} \approx 10^{ - 6} \left( {\frac{{M_ \odot }}{M}} \right){}^ \circ K$$ where κ is the surface gravity of the black hole. This thermal emission leads to a slow decrease in the mass of the black hole and to its eventual disappearance: any primordial black hole of mass less than about 1015 g would have evaporated by now. Although these quantum effects violate the classical law that the area of the event horizon of a black hole cannot decrease, there remains a Generalized Second Law:S+1/4A never decreases whereS is the entropy of matter outside black holes andA is the sum of the surface areas of the event horizons. This shows that gravitational collapse converts the baryons and leptons in the collapsing body into entropy. It is tempting to speculate that this might be the reason why the Universe contains so much entropy per baryon.

Entropy and Maxwell's demon: A simple demonstration of entropy and other important characteristics of matter and energy

Entropy and Maxwell's demon: A simple demonstration of entropy and other important characteristics of matter and energy