Quantum Gravity: Has Spacetime Quantum Properties?

The incompatibility between GR and QM is generally seen as a sufficient motivation for the development of a theory of Quantum Gravity. If - so a typical argumentation - QM gives a universally valid basis for the description of all natural systems, then the gravitational field should have quantum properties. Together with the arguments against semi-classical theories of gravity, this leads to a strategy which takes a quantization of GR as the natural avenue to Quantum Gravity. And a quantization of the gravitational field would in some sense correspond to a quantization of geometry. Spacetime would have quantum properties. But, this strategy will only be successful, if gravity is a fundamental interaction. - What, if gravity is instead an intrinsically classical phenomenon? Then, if QM is nevertheless fundamentally valid, gravity can not be a fundamental interaction. An intrinsically classical gravity in a quantum world would have to be an emergent, induced or residual, macroscopic effect, caused by other interactions. The gravitational field (as well as spacetime) would not have any quantum properties. A quantization of GR would lead to artifacts without any relation to nature. The serious problems of all approaches to Quantum Gravity that start from a direct quantization of GR or try to capture the quantum properties of gravity in form of a 'graviton' dynamics - together with the, meanwhile, rich spectrum of approaches to an emergent gravity and/or spacetime - make this latter option more and more interesting for the development of a theory of Quantum Gravity. The most advanced emergent gravity (and spacetime) scenarios are of an information-theoretical, quantum-computational type.Comment: 31 page

String Theory - Nomological Unification and the Epicycles of the Quantum Field Theory Paradigm

String Theory is the result of the conjunction of three conceptually independent elements: (i) the metaphysical idea of a nomological unity of the forces, (ii) the model-theoretical paradigm of Quantum Field Theory, and (iii) the conflict resulting from classical gravity in a quantum world. String Theory is sometimes assumed to solve this conflict: by means of an application of the model-theoretical apparatus of (perturbative) Quantum Field Theory. But, String Theory does not really solve the conflict. Rather it exemplifies the inadequacy of this model-theoretical apparatus in the context of Quantum Gravity: After several decades of development it still exists only in an essentially perturbative formulation (with minor non-perturbative extensions and vague ideas with regard to a possible non-perturbative formulation). And, due to its quantum field theoretical heritage, it is conceptually incompatible with central implications of General Relativity, especially those resulting from the general relativistic relation between gravity and spacetime. All known formulations of String Theory are background-dependent. On the other hand, it was not even possible to reproduce the Standard Model. Instead, String Theory led to a multitude of internal problems - and to the plethora of low-energy scenarios with different nomologies and symmetries, known as the String Landscape. All attempts to find a dynamically motivated selection principle remained without success, leaving String Theory without any predictive power. The nomological unification of the fundamental forces is only achieved in a purely formal way within the model-theoretical paradigm of Quantum Field Theory - by means of physically unmotivated epicycles like higher dimensionality, Calabi-Yau spaces, branes, etc.Comment: 23 page

String Theory - From Physics to Metaphysics

Currently, string theory represents the only advanced approach to a unification of all interactions, including gravity. In spite of the more than thirty years of its existence it did not make any empirically testable predictions. And it is completely unknown which physically interpretable principles could form the basis of string theory. At the moment, "string theory" is no theory at all, but rather a labyrinthic structure of mathematical procedures and intuitions which get their justification from the fact that they, at least formally, reproduce general relativity and the standard model of elementary particle physics as low energy approximations. However, there are now strong indications that string theory does not only reproduce the dynamics and symmetries of our standard model, but a plethora of different scenarios with different low energy nomologies and symmetries. String theory seems to describe not only our world, but an immense landscape of possible worlds. So far, all attempts to find a selection principle which could be motivated intratheoretically remained without success. So, recently the idea that the low energy nomology of our world, and therefore also the observable phenomenology, could be the result of an anthropic selection from a vast arena of nomologically different scenarios entered string theory. Although multiverse scenarios and anthropic selection are not only motivated by string theory, but lead also to a possible explanation for the fine tuning of the universe, they are concepts which transcend the framework defined by the epistemological and methodological rules which conventionally form the basis of physics as an empirical science.Comment: 30 pages, submitted to "Physics and Philosophy" (Online-Journal

Communications satellite technology

Communications satellite technology - echo, relay, and syncom project

Las Bases Materiales de Nuestras Capacidades Epistemicas. Ensayo de Una Revision Sintetica de la Epistemologia

Tras el fracaso del fundamentalismo epistemológico (que es el fracaso de los ideales de la fundamentación, de la certeza y de la justificación rigurosa de nuestro conocimiento) existen motivos suficientes para una transición de la epistemología pura y analítica a un procedimiento sintético, que integra componentes empírico-científicos en el contexto de la epistemología descriptiva. De una relevancia específica para la cuestión de la realización de nuestros conocimientos son por ejemplo los resultados recientes de las neurociencias. El artículo presenta los primeros resultados de una "neuro-epistemología" constituida con la integración de elementos procedentes de las neurociencias en los problemas de la epistemología.After the breakdown of epistemological fundamentalism (i.e. the ideals of fundamentation, of certainty and of a definitive justification for our knowledge) we have sufficient causes to change the traditional pure and analytic epistemology for a synthetic procedure, which integrates components from the empirical sciences into the context of descriptive epistemology. Of specific relevance for the question of the neurosciences. The article presents the first results of a "neuro-epistemology", hich forms by the integration of elements from the neurosciences into the consideration of the problems of epistemology

A Paper at the ECE Symposium on Application of Economic-Mathematical Models in the Energy Sector, Alma-Ata September 1973

The energy sector of each country is a part of the national economic subsystems which directly and to a considerable degree has an influence on the growth rate of the national economy and the increase of national income. Therefore it is a permanent objective to always provide a rational basis for the provision of society with demand-determined supply of energy sources. A tool for the proper achievement of this goal is the application of mathematical-economic models for optimization of the energy sector with consideration of national economic constraints. It is in the interest of society to include the largest possible system in the optimization models. According to the current condition of our understanding, that type of objective can be achieved only with mathematical-economic system models which consider all essential economic, technological, technical, parameters, and to a limited degree also political-economic influences

Preliminary Overview of Institutional Structures and Models: Information Systems for Energy/Environmental Planning and Management in GDR, Rhone-Alpes, and Wisconsin

This paper is one of a series describing a multidisciplinary IIASA research program on Integrated Energy System Modelling and Policy Analysis. The initial phase of this research program is focused on the energy systems of three regions: the State of Wisconsin in the U.S.A.; the German Democratic Republic; and the Rhone-Alpes Region in France. The primary purposes of the study are at least three-fold: (1) To identify existing patterns of regional energy use and supply at appropriate levels of disaggregation. (2) To compare alternative methodologies for regional energy forecasting, planning, and policy development. (3) To use the ,above methodologies to examine alternate energy policy strategies for each of the regions, to explore their implications from various perspectives using sets of indicators related to environmental impacts, energy use efficiency, etc., and to evaluate the adequacy of the alternative methodologies as policy tools. Out of these above three items should evolve improved methodologies for energy systems research and policy analysis. The comparative method, intersecting the different disciplines and nations which would be involved in this project, should serve as a powerful tool to the mutual benefit of the participating nations as well as to other countries facing similar energy problems. It could also serve as a prototype for similar studies on other resources such as materials, water, air, i.e. as a vehicle for development of an approach for improved resource management

Sucrose- and H+-Dependent Charge Movements Associated with the Gating of Sucrose Transporter ZmSUT1

Background: In contrast to man the majority of higher plants use sucrose as mobile carbohydrate. Accordingly protondriven sucrose transporters are crucial for cell-to-cell and long-distance distribution within the plant body. Generally very negative plant membrane potentials and the ability to accumulate sucrose quantities of more than 1 M document that plants must have evolved transporters with unique structural and functional features. Methodology/Principal Findings: To unravel the functional properties of one specific high capacity plasma membrane sucrose transporter in detail, we expressed the sucrose/H+ co-transporter from maize ZmSUT1 in Xenopus oocytes. Application of sucrose in an acidic pH environment elicited inward proton currents. Interestingly the sucrose-dependent H+ transport was associated with a decrease in membrane capacitance (Cm). In addition to sucrose Cm was modulated by the membrane potential and external protons. In order to explore the molecular mechanism underlying these Cm changes, presteady-state currents (Ipre) of ZmSUT1 transport were analyzed. Decay of Ipre could be best fitted by double exponentials. When plotted against the voltage the charge Q, associated to Ipre, was dependent on sucrose and protons. The mathematical derivative of the charge Q versus voltage was well in line with the observed Cm changes. Based on these parameters a turnover rate of 500 molecules sucrose/s was calculated. In contrast to gating currents of voltage dependentpotassium channels the analysis of ZmSUT1-derived presteady-state currents in the absence of sucrose (I =Q/t) was sufficient to predict ZmSUT1 transport-associated currents. Conclusions: Taken together our results indicate that in the absence of sucrose, ‘trapped’ protons move back and forth between an outer and an inner site within the transmembrane domains of ZmSUT1. This movement of protons in the electric field of the membrane gives rise to the presteady-state currents and in turn to Cm changes. Upon application of external sucrose, protons can pass the membrane turning presteady-state into transport currents