# Black Hole Entropy

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### Black Holes, Entropy, And Information

This implies black holes have an entropy. Page 6. For a solar mass black hole, the temperature is very low (T ~ 10-7 K) so it is astrophysically negligible. But ... [ReadMore..]

### Extremal Limits And Black Hole Entropy

Taking the extremal limit of a non-extremal Reissner-Nordström black hole (by externally varying the mass or charge), the region between the inner and outer event horizons experiences an interesting fate -- while this region is absent in the extremal case, it does not disappear in the extremal limit but rather approaches a patch of $AdS_2\times S^2$. In other words, the approach to extremality is not continuous, as the non-extremal Reissner-Nordström solution splits into two spacetimes at extremality: an extremal black hole and a disconnected $AdS$ space. We suggest that the unusual nature of this limit may help in understanding the entropy of extremal black holes. Jan 8, 2009 ... ... non-extremal Reissner-Nordström black hole (by externally varying the ... may help in understanding the entropy of extremal black holes. [ReadMore..]

### Black Hole Entropy From Quantum Geometry

Quantum Geometry (the modern Loop Quantum Gravity using graphs and spin-networks instead of the loops) provides microscopic degrees of freedom that account for the black-hole entropy. However, the procedure for state counting used in the literature contains an error and the number of the relevant horizon states is underestimated. In our paper a correct method of counting is presented. Our results lead to a revision of the literature of the subject. It turns out that the contribution of spins greater then 1/2 to the entropy is not negligible. Hence, the value of the Barbero-Immirzi parameter involved in the spectra of all the geometric and physical operators in this theory is different than previously derived. Also, the conjectured relation between Quantum Geometry and the black hole quasi-normal modes should be understood again. ... Quantum Gravity using graphs and spin-networks instead of the loops) provides microscopic degrees of freedom that account for the black-hole entropy. [ReadMore..]

### Black Hole Paradoxes Reveal A Link Between Energy And Entropy ...

What happens to a black hole as it decays? Investigating the possibilities has led researchers in recent years to major clues about quantum gravity. Jun 7, 2020 ... Almost 50 years ago, the late physicists Jacob Bekenstein and Stephen Hawking independently discovered that a black hole's entropy is directly ... [ReadMore..]

### On The Nature Of Black Hole Entropy: AIP Conference Proceedings ...

I argue that black hole entropy counts only those states of a black hole that can influence the outside, and attempt (with only partial success) to defend this claim against various objections, all... Mar 27, 2008 ... I argue that black hole entropy counts only those states of a black hole that can influence the outside, and attempt (with only partial ... [ReadMore..]

### A Microscopic Account Of Black Hole Entropy - Physics

String theory provides a microscopic description of the entropy of certain theoretical black holes—an important step toward understanding black hole thermodynamics. May 18, 2020 ... In the 1970's, theorists determined that black holes have entropy [1], a remarkable finding that points at analogies between these spacetime ... [ReadMore..]

### On Black Hole Entropy

Two techniques for computing black hole entropy in generally covariant gravity theories including arbitrary higher derivative interactions are studied. The techniques are Wald's Noether charge approach introduced recently, and a field redefinition method developed in this paper. Wald's results are extended by establishing that his local geometric expression for the black hole entropy gives the same result when evaluated on an arbitrary cross-section of a Killing horizon (rather than just the bifurcation surface). Further, we show that his expression for the entropy is not affected by ambiguities which arise in the Noether construction. Using the Noether charge expression, the entropy is evaluated explicitly for black holes in a wide class of generally covariant theories. Further, it is shown that the Killing horizon and surface gravity of a stationary black hole metric are invariant under field redefinitions of the metric of the form $\bar{g}_{ab}\equiv g_{ab} + Δ_{ab}$, where $Δ_{ab}$ is a tensor field con Two techniques for computing black hole entropy in generally covariant gravity theories including arbitrary higher derivative interactions are studied. The ... [ReadMore..]

### Do We Understand Black Hole Entropy?

I review various proposals for the nature of black hole entropy and for the mechanism behind the operation of the generalized second law. I stress the merits of entanglement entropy {\tenit qua\/} black hole entropy, and point out that, from an operational viewpoint, entanglement entropy is perfectly finite. Problems with this identification such as the multispecies problem and the trivialization of the information puzzle are mentioned. This last leads me to associate black hole entropy rather with the multiplicity of density operators which describe a black hole according to exterior observers. I relate this identification to Sorkin's proof of the generalized second law. I discuss in some depth Frolov and Page's proof of the same law, finding it relevant only for scattering of microsystems by a black hole. Assuming that the law is generally valid I make evident the existence of the universal bound on entropy regardless of issues of acceleration buoyancy, and discuss the question of why macroscopic objects ca I stress the merits of entanglement entropy {\tenit qua\/} black hole entropy, and point out that, from an operational viewpoint, entanglement entropy is ... [ReadMore..]

### Black Hole Entropy In Loop Quantum Gravity

We calculate the black hole entropy in Loop Quantum Gravity as a function of the horizon area and provide the exact formula for the leading and sub-leading terms. By comparison with the Bekenstein-Hawking formula we uniquely fix the value of the 'quantum of area' in the theory. Jul 14, 2004 ... We calculate the black hole entropy in Loop Quantum Gravity as a function of the horizon area and provide the exact formula for the leading and ... [ReadMore..]

The pages related to black hole entropy are also listed below:

### Black Hole Thermodynamics - Wikipedia

In physics, black hole thermodynamics is the area of study that seeks to reconcile the laws of ... [ReadMore..]

### On Black Hole Entropy

Two techniques for computing black hole entropy in generally covariant gravity theories including arbitrary higher derivative interactions are studied. The techniques are Wald's Noether charge approach introduced recently, and a field redefinition method developed in this paper. Wald's results are extended by establishing that his local geometric expression for the black hole entropy gives the same result when evaluated on an arbitrary cross section of a Killing horizon (rather than just the bifurcation surface). Further, we show that his expression for the entropy is not affected by ambiguities which arise in the Noether construction. Using the Noether charge expression, the entropy is evaluated explicitly for black holes in a wide class of generally covariant theories. For a Lagrangian of the functional form L\ifmmode \tilde{}\else \~{}\fi{}=L\ifmmode \tilde{}\else \~{}\fi{}(${\mathrm{\ensuremath{\psi}}}_{\mathit{m}}$, ${\mathrm{\ensuremath{\nabla}}}_{\mathit{a}}$${\mathrm{\ensuremath{\psi}}}_{\mathit{m}}$, Jun 15, 1994 ... Two techniques for computing black hole entropy in generally covariant gravity theories including arbitrary higher derivative interactions ... [ReadMore..]