119109018
Approaching the problem of time with a combined semiclassical-records-histories scheme
I approach the problem of time and other foundations of quantum (QM) cosmology using a combined histories, timeless and semiclassical approach. This approach is along the lines pursued by Halliwell. It involves the timeless probabilities for dynamical trajectories entering regions of configuration space, which are computed within the semiclassical regime. Moreover, the objects that Halliwell uses in this approach commute with the Hamiltonian constraint, H. This approach has not hitherto been considered for models that also possess nontrivial linear constraints, Lin. This paper carries this out for some concrete relational particle mechanics (RPMs). If there is also commutation with Lin—the Kuchař observables condition—the constructed objects are Dirac observables. Moreover, this paper shows that the problem of Kuchař observables is explicitly resolved for 1D and 2D RPMs. Then as a first route to Halliwell’s approach for nontrivial linear constraints that is also a construction of Dirac observables, I consider theories for which Kuchař observables are formally known, giving the relational triangle as an example. As a second route, I apply an indirect method that generalizes both group averaging and Barbour’s best matching. For conceptual clarity, my study involves the simpler case of Halliwell 2003 sharp-edged window function. I leave the elsewise-improved softened case of Halliwell 2009 for a subsequent paper II. Finally, I provide comments on Halliwell’s approach and how well it fares as regards the various facets of the problem of time and as an implementation of QM propositions.
17420273
Seminar on Records Theory
In quantum gravity, one seeks to combine quantum mechanics and general relativity. In attempting to do so, one comes across the `problem of time' impasse: the notion of time is conceptually different in each of these theories. In this seminar, I consider the timeless records approach toward resolving this. Records are localized, information-containing subconfigurations of a single instant. Records theory is the study of these and of how science (or history) is to be abstracted from correlations between them. I explain how to motivate this approach, provide a ground-level structure for it and discuss what kind of further tools are needed. For a more comprehensive account with many more references, see [1].
15861745
Does relationalism alone control geometrodynamics with sources
This paper concerns relational first principles from which the Dirac procedure exhaustively picks out the geometrodynamics corresponding to general relativity as one of a handful of consistent theories. This was accompanied by a number of results and conjectures about matter theories and general features of physics -- such as gauge theory, the universal light cone principle of special relativity and the equivalence principle -- being likewise picked out. I have previously shown that many of these matter results and conjectures are contingent on further unrelational simplicity assumptions. In this paper, I point out 1) that the exhaustive procedure in these cases with matter fields is slower than it was previously held to be. 2) While the example of equivalence principle violating matter theory that I previously showed how to accommodate on relational premises has a number of pathological features, in this paper I point out that there is another closely related equivalence principle violating theory that also follows from those premises and is less pathological. This example being known as an `Einstein--aether theory', it also serves for 3) illustrating limitations on the conjectured emergence of the universal light cone special relativity principle.
10694441
Strong-Coupled Relativity Without Relativity
GR can be interpreted as a theory of evolving 3-geometries. A recent such formulation, the 3-space approach of Barbour, Foster and Ó'Murchadha, also permits the construction of a limited number of other theories of evolving 3-geometries, including conformal gravity and strong gravity. In this paper, we use the 3-space approach to construct a 1-parameter family of theories which generalize strong gravity. The usual strong gravity is the strong-coupled limit of GR, which is appropriate near singularities and is one of very few regimes of GR which is amenable to quantization. Our new strong gravity theories are similar limits of scalar-tensor theories such as Brans–Dicke theory, and are likewise appropriate near singularities. They represent an extension of the regime amenable to quantization, which furthermore spans two qualitatively different types of inner product.We find that these strong gravity theories permit coupling only to ultralocal matter fields and that they prevent gauge theory. Thus in the classical picture, gauge theory breaks down (rather than undergoing unification) as one approaches the GR initial singularity.
17821899
Records Theory
In quantum gravity, one seeks to combine quantum mechanics and general relativity. In attempting to do so, one comes across the ‘problem of time’ impasse: the notion of time is conceptually different in each of these theories. In this paper, I consider the timeless records approach toward resolving this. Records are localized, information-containing subconfigurations of a single instant. Records theory is the study of these and of how science (or history) is to be abstracted from correlations between them. I critically evaluate motivations for this approach that have previously appeared in the literature. I provide a ground-level structure for records theory and discuss what kind of further tools are needed, illustrated with some toy models: ordinary mechanics, relatonal particle dynamics, detector models and inhomogeneous perturbations about homogeneous cosmology. PACS numbers 04.60-m, 04.60.Ds
119274399
Kerr–Newman black hole thermodynamical state space: blockwise coordinates
A coordinate system that blockwise-simplifies the Kerr–Newman black hole’s thermodynamical state space Ruppeiner metric geometry is constructed, with discussion of the limiting cases corresponding to simpler black holes. It is deduced that one of the three conformal Killing vectors of the Reissner–Nordström and Kerr cases (whose thermodynamical state space metrics are 2 by 2 and conformally flat) survives generalization to the Kerr–Newman case’s 3 by 3 thermodynamical state space metric.
119292607
Operator evolution via the similarity renormalization group: The deuteron
Similarity renormalization group (SRG)flow equations can be used to unitarily soften nuclear Hamiltonians by decoupling high-energy intermediate-state contributions to low-energy observables while maintaining the natural hierarchy of many-body forces. Analogous flow equations can be used to consistently evolve operators so that observables are unchanged if no approximations are made. The question in practice is whether the advantages of a softer Hamiltonian and less-correlated wave functions might be offset by complications in approximating and applying other operators. Here we examine the properties of SRG-evolved operators, focusing in this article on applications to the deuteron but leading toward methods for few-body systems. We find the advantageous features generally carry over to other operators with additional simplifications in some cases from factorization of the unitary transformation operator. DOI: 10.1103/PhysRevC.82.054001
124543914
The Production and Distribution of Natural Radiocarbon
120381541
Experimental study of pi- p ---> pi- n* at 8 and 16 gev/c
32865960
Recent advances in low level counting techniques.
Problems involving low level counting techniques are encountered in many diverse fields including biological and chemical tracer studies, archaeo­ logical and geological dating (I), investigations of natural and induced radio­ activities, and the study of fundamental particles. Such a host of methods and variations on methods have been reported that an exhaustive catalog would constitute little more than an annotated bibliography. We have, there­ fore, limited our attention to a few selected examples which seem to be of special interest because of their versatility or their extreme sensitivity. We prefer to organize our discussion around specific problems rather than around types of detectors since this permits a comparison of alternative methods and provides practical examples of various techniques in actual operation. Alpha counting is arbitrarily excluded. For a discussion of photographic methods (radioautographs) the reader is referred to Norris & Woodruff (2) and refer­ ences cited therein. We will discuss the methods developed for the measure­ ment of natural radiocarbon and tritium, cosmic ray produced Be7, and the K(O content of the human body. DOUble-beta decay experiments are consid­ ered since they seem to constitute one of the most difficult of the outstanding problems and because of their importance from the viewpoint of theoretical nuclear physics. Finally, an account is given of recent attempts to detect the neutrino, probably the most difficult low level counting problem of all and one which seems finally on the verge of successful solution. Principles.-The fundamental principles of low level counting are simple: maximize the number of detected events of the desired kind (signal) and minimize all others (background). The number of detected events is, of course, the product of sample size, over-all counting efficiency, and counting time. However, the striking importance of the net sample counting rate is not always fully appreciated. It can be shown (3) from elementary counting statistics, that if the sample rate is small compared with background (which is usually the case in a truly low level problem) and if counting statistics is the limiting source of error (also usually true), then the proper parameter for the comparison of counting methods is S2/B, the ratio of the square of the net sample rate to the background rate. (Any sample strength can be used in making the comparison so long as the same strength is used in testing all methods.) The method giving the maximum value of S2/B will yield the
122807269
Observation of increasing charged multiplicity as a function of transverse momentum in 28.5-GeV/c pp interactions