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.

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Particle Creation by Black Holes

The 2016 APS Medal for Excellence in Physics was given to Edward Witten. This contribution was invited in conjunction with this award. These original notes contain concise explanations of some key results in the axiomatic and algebraic approaches to quantum field theory, which are relevant to quantum entanglement. They serve to put the connection between quantum field theory and quantum information theory on a precise and rigorous footing.

APS Medal for Exceptional Achievement in Research: Invited article on entanglement properties of quantum field theory*

Preliminaries.- Modular Hilbert algebras.- Generalized Hilbert algebras.- The commutation theorem for modular Hilbert algebras.- Self-adjoint subalgebras of generalized Hilbert algebras.- The spectral algebra.- The modular operator ?.- The resolvent of the modular operator ?.- The one-parameter automorphisms defined by the modular operator ?.- Formulation of the modular Hilbert algebra.- Tensor product and direct sum of modular Hilbert algebras.- The standard representation of von Neumann algebras.- The modular automorphism group and the Kubo-Martin-Schwinger boundary condition.- Semi-finiteness and the modular automorphism group.

Tomita's theory of modular Hilbert algebras and its applications

Algebraic quantum field theory provides a general, mathematically precise description of the structure of quantum field theories, and then draws out consequences of this structure by means of various mathematical tools -- the theory of operator algebras, category theory, etc.. Given the rigor and generality of AQFT, it is a particularly apt tool for studying the foundations of QFT. This paper is a survey of AQFT, with an orientation towards foundational topics. In addition to covering the basics of the theory, we discuss issues related to nonlocality, the particle concept, the field concept, and inequivalent representations. We also provide a detailed account of the analysis of superselection rules by Doplicher, Haag, and Roberts (DHR); and we give an alternative proof of Doplicher and Robert's reconstruction of fields and gauge group from the category of physical representations of the observable algebra. The latter is based on unpublished ideas due to J. E. Roberts and the abstract duality theorem for symmetric tensor *-categories, a self-contained proof of which is given in the appendix.

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Algebraic Quantum Field Theory

Entanglement entropy for the n-sphere

In the book of Haag [Local Quantum Physics (Springer Verlag, Berlin, 1992)] about local quantum field theory the main results are obtained by the older methods of C * - and W * -algebra theory. A great advance, especially in the theory of W * -algebras, is due to Tomita’s discovery of the theory of modular Hilbert algebras [Quasi-standard von Neumann algebras, Preprint (1967)]. Because of the abstract nature of the underlying concepts, this theory became (except for some sporadic results) a technique for quantum field theory only in the beginning of the nineties. In this review the results obtained up to this point will be collected and some problems for the future will be discussed at the end. In the first section the technical tools will be presented. Then in the second section two concepts, the half-sided translations and the half-sided modular inclusions, will be explained. These concepts have revolutionized the handling of quantum field theory. Examples for which the modular groups are explicitly known are presented in the third section. One of the important results of the new theory is the proof of the PCT theorem in the theory of local observables. Questions connected with the proof are discussed in Sec. IV. Section V deals with the structure of local algebras and with questions connected with symmetry groups. In Sec. VI a theory of tensor product decompositions will be presented. In the last section problems that are closely connected with the modular theory and that should be treated in the future will be discussed.

H. J. Borchers

Papers

On revolutionizing quantum field theory with Tomita’s modular theory