The FLASH communicator consists of an apparatus which can distinguish between plane unpolarized (PUP) and circularly unpolarized (CUP) light plus a simple EPR arrangement. FLASH exploits the peculiar properties of “measurements of the Third Kind.” One purpose of this article is to focus attention on the operation of idealized laser gain tubes at the one-photon limit.

Mandel and Pfleegor have shown the existence of interference effects produced by the superposition of two independent single-mode lasers even under conditions in which one photon is absorbed before the next is emitted by one or the other source. We propose here a modification of their experiment which would establish (if the interferences persist) the simultaneous existence of waves and particles (photons), a result which is assumed as basis by the stochastic interpretation of quantum mechanics.

The density matrix ρ describing a decaying system can be expressed in terms of correlations among observables belonging to the subsystems. Due to this structure and to the difficulties in measuring higher rank tensors of decay products for a single decay event, it is found that the mean value of ρ cannot be determined, in general, from measurements on the decay products. We also discuss the consequences of this conclusion as far as tests of quantum mechanics are concerned.

We illustrate a generalization of Bell's inequality which is not limited to spin-1/2 or photon systems and does not depend on model-dependent assumptions. We then construct a specific class of examples, in terms of the decaying state and the correlated observables to be measured on the decay products, for which this inequality is violated by quantum mechanics. Finally we discuss the basic and practical problems involved in the measurement of these correlations.

We show that a local theory conforming to the requirement of reducing to usual quantum mechanics for single-particle states and describing two-particle correlations in terms of mixtures violates the condition of perfect anticorrelation between spin components in the case of Bohm's version of EPR.

The basic theme of Popper's philosophy--that something can come from nothing--is related to the present situation in physical theory. Popper carries his investigation right to the center of current debate in quantum physics. He proposes an interpretation of physics--and indeed an entire cosmology--which is realist, conjectural, deductivist and objectivist, anti-positivist, and anti-instrumentalist. He stresses understanding, reminding us that our ignorance grows faster than our conjectural knowledge.

Este trabalho analisa idéias e atividades de Karl Popper referentes à controvérsia sobre interpretações e fundamentos da mecânica quântica. Atenção especial será dedicada às relações entre Popper e o físico italiano Franco Selleri, ao longo da década de 1980. A interpretação proposta por Popper para os enunciados probabilísticos como propensões, bem como seu ponto de vista realista, contribuíram para estabelecer uma ponte entre suas investigações filosóficas e a pesquisa física em mecânica quântica, ainda que sua idéia sobre as propensões tenha (...) tido uma pequena repercussão entre físicos, matemáticos e filósofos. Argumentaremos neste trabalho que a influência de Popper na física foi possível devido à legitimação, a partir de 1970, da controvérsia sobre os fundamentos da teoria quântica como uma genuína controvérsia científica com implicações filosóficas. Popper foi beneficiado por essa legitimação, mas ele também contribuiu para fazer aquela controvérsia chegar a um público mais amplo que aquele dos físicos envolvidos na própria controvérsia.I intend to present in this paper Karl Popper’s ideas and activities concerning the controversy about the interpretations and foundations of quantum mechanics. I will pay special attention to Popper’s relationship with the Italian physicist Franco Selleri, during the 1980s. Popper’s ideas of propensity and realism contributed to build a bridge between his philosophy and physical research in quantum mechanics, even if his idea of propensity has had a weak reception among physicists, mathematicians and philosophers. I will argue that Popper’s contributions to physics were possible due to the legitimization in the 1970s of the controversy about the foundations of quantum mechanics, a process which permitted a trading zone between physics and philosophy. Popper was benefited by that process, but he also contributed to give to that controversy a larger audience thanthat of the physicists involved in that controversy. (shrink)