# 2006

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### The publication of the journal has ceased

We regret that we have to stop the edition of the Online Journal "Physics and Philosophy", due to lack of personal assistance, lack of financial support and problems to find referees.

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Item Light Quanta(2007-04-19T19:51:48Z) Klaus, HentschelI will begin by identifying 12 layers of meaning of the concept of light quanta as it is understood today. The main part of this contribution will then discuss some of the earlier layers. I will also briefly discuss the extreme skepticism with which the concept of light quanta was received between 1905 and 1922 and close with a thesis on what makes Einstein's thinking so exceptional.Item String Theory - From Physics to Metaphysics(2007-03-16T21:54:30Z) Hedrich, ReinerCurrently, 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, the sequence of metamorphosis it ran through, and the ever more increasing number of involved physicists, until now, it did not make any empirically testable predictions. Because there are no empirical data incompatible with the quantum field theoretical standard model of elementary particle physics and with general relativity, the only motivations for string theory rest in the mutual incompatibility of the standard model and of general relativity as well as in the metaphysics of the unification program of physics, aimed at a final unified theory of all interactions including gravity. But actually, 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.Item The Phase of a Bose-Einstein Condensate(2006-11-30T14:32:27Z) DÃ¼rr, StephanIf two Bose-Einstein condensates are prepared independently and then overlapped, a spatial interference pattern is observed. This prompts the question what determines the phase of the fringe pattern, and whether a condensate has a well-defined value of the phase. This problem has been studied in the literature in detail. The objective of this article is, to present an introduction to the subject and to summarize the discussion for a wider audience.Item What You Always Wanted to Know about Bohmian Mechanics but Were Afraid to Ask(2006-11-30T14:26:28Z) Passon, OliverBohmian mechanics is an alternative interpretation of quantum mechanics. We outline the main characteristics of its non-relativistic formulation. Most notably it does provide a simple solution to the infamous measurement problem of quantum mechanics. Presumably the most common objection against Bohmian mechanics is based on its non-locality and its apparent conflict with relativity and quantum field theory. However, several models for a quantum field theoretical generalization do exist. We give a non-technical account of some of these models.Item Detection of High-Energy Particles(2006-11-08T20:40:23Z) Lohse, ThomasIn spite of quantum field theoretical and philosophical problems to define the concept of elementary particles and to understand their localizability, particles become intuitively apparent by the traces they leave in particle detectors. Today, experimental particle physicists have reached a high degree of perfection in measuring and visualizing particles up to highest energies using a variety of high technology detection devices and sophisticated, powerful particle accelerators. The paper reviews the basic detection techniques and puts the microscopic quantum field theoretical processes of interest into perspective with the measurements performed at macroscopic scales. It is shown that particle detectors and accelerators are highly classical devices which localize particles without significantly affecting the tails of their wave functions. It is discussed which properties of particles can be measured and how these measurements relate to the dynamics of elementary particles at microscopic length scales.Item Einstein's Objections against Quantum Mechanics(2006-10-12T18:57:33Z) Mittelstaedt, PeterAfter the discovery of quantum mechanics by Heisenberg and SchrÃ¶dinger in 1925, Einstein raised again and again objections to this theory. Obviously, he had the impression that (a) quantum mechanics does not adequately grasp reality, that it is (b) based on probabilistic laws of nature and that it is (c) for this reason incomplete. Einstein must have obtained this impression from many presentations of quantum mechanics in the first decade after its discovery. -- However, technical refutations of Einstein's objections were not possible when these arguments were put forward, since the necessary formal tools were not yet available at this time. Instead, the advocates of quantum mechanics tried to disprove Einstein merely by intuitive and less rigorous arguments. -- In the light of current physics we find that the objections (a) and (b) are irrelevant since, in accordance with Einstein's intentions, quantum mechanics does refer to reality and is not based on probabilistic laws. Only the incompleteness argument is incorrect. However, for technical reasons a convincing refutation of this objection only became possible thirty years after its formulation and ten years after Einstein's death.