Category: Uncategorized

COMMON IRREVERSIBILITY. “There are a number of similarities between black-hole physics and thermodynamics. Most striking is the similarity in the behaviors of black-hole area and of entropy: Both quantities tend to increase irreversibly. In this paper we make this similarity the basis of a thermodynamic approach to black-hole physics. https://lnkd.in/d_-_tga View in LinkedIn

BLACK HOLES AND ENTROPY is the theme for the next section of posts. The introductory posts are from Jacob Bekenstein’s prescient Princeton PhD thesis in 1972. https://lnkd.in/d_-_tga View in LinkedIn

Barcelona has some of the most exquisite old stucco work of any city, done by an army of highly skilled artesans, but the skill has almost entirely vanished and few know how to do this today. View in LinkedIn

THE CHRONOGEOMETRY OF REALITY. “In short, the effect has been for matter to now play second fiddle to space and time. As these field theories, both classical and quantum, are presented to us, their basic objects seem to be just spacetime points. All else—matter, fields, and even the metrical structure of spacetime, the ‘chronogeometry’ of the world—are represented as mathematical structures defined on these points; in particular, as just emphasised, physical quantities for matter and fields are represented by structures defined point by point.” https://lnkd.in/dMm_YkR View in LinkedIn

TRANSMOGRIFICATION. “Furthermore, this assimilation of matter to the concept of a field continued with quantum theory. Even elementary quantum theory has a formulation (wave mechanics) which can be thought of as a field theory. And this picture deepens with the advent of quantum field theory: here physical quantities describing matter are again represented by a field; albeit in a transmogrified form in which an operator (rather than a simple real number) is associated with each space, or space-time, point.” https://lnkd.in/dMm_YkR View in LinkedIn

TIME IN QUANTUM GRAVITY. “On the other hand, the problem of time is about ‘finding’ a time in quantum gravity theories: and so not, in the first instance, about finding some kind of classical limit of, or classical approximation to, such theories.” https://lnkd.in/dMm_YkR View in LinkedIn

FIELD LANGUAGE. “Thus, with the rise of classical field theory, culminating in general relativity, the field gradually became endowed with properties previously thought peculiar to matter. Thus the electromagnetic field was discovered to possess mechanical properties like momentum and angular momentum, and (after the advent of special relativity) mass-energy. The ‘action-at-a-distance’ of Newtonian gravity readily admits a translation into the language of fields; and, of course, the theory of general relativity was couched in such language from the outset.” https://lnkd.in/dMm_YkR View in LinkedIn

THE EMERGENCE OF TIME. “The problem of time vs. the emergence of time. Perhaps the most obvious difference is that the problem of time is mostly about time rather than space; while as we said in Section 1, we intend ‘the emergence of time’ to also cover the emergence of spacetime, and so space. At a technical level, the tendency not to dwell on a ‘problem of space’ stems from the fact that, as noted above, in constrained quantization, the momen- tum constraint —which, from a spacetime perspective, shuffles spacetime points within a given 3-dimensional spacelike slice—is much easier to deal with, conceptually and technically, than the Hamiltonian constraint, which is related, at least classically, to diffeomorphisms that map points from one spacelike slice to another.” https://lnkd.in/dMm_YkR View in LinkedIn

MATTER AS A FIELD. “Some of the most distinctive characteristics of matter, at least as idealized by the mechanical philosophy of the seventeenth century—such as impenetrability and continuity— turn out to be only apparent; and others, such as massiveness, turn out to be shared with invisible fields that extend in ‘empty space’ arbitrarily far from their sources. Further, matter itself has come to be treated as a field, and this involves being represented mathematically by an assignment of a mathematical object—at its simplest: an item like a real number, or a vector, or a matrix—to each point of space or spacetime.” https://lnkd.in/dMm_YkR View in LinkedIn

PREQUANTUM TIME. “Rather, one has to confront the extremely difficult problem of solving a collection of very non-linear, coupled (elliptic) partial-differential equations. So far, this has proved intractable. This, then, is the first form of the problem of time: the problem of finding a time ‘before quantisation’.” https://lnkd.in/dMm_YkR View in LinkedIn