Causality and classical interference and diffraction phenomena

Bayyarapu Prasada Rao

Ángel S. Sanz, F. Borondo, Salvador Miret-Artés

Diffraction and interference of matter waves are key phenomena in quantum mechanics. Here we present some results on particle diffraction in a wide variety of situations, ranging from simple slit experiments to more complicated cases such as atom scattering by corrugated metal surfaces and metal surfaces with simple and isolated adsorbates. The principal novelty of our study is the use of the so-called Bohmian formalism of quantum trajectories. These trajectories are able to satisfactorily reproduce the main features of the experimental results and, more importantly, they provide a causal intuitive interpretation of the underlying dynamics. In particular, we will focus our attention on: (a) a revision of the concepts of near and far field in undulatory optics; (b) the transition to the classical limit, where it is found that although the quantum and classical diffraction patterns tend to be quite similar, some quantum features are maintained even when the quantum potential goes to zero; and (c) a qualitative description of the scattering of atoms by metal surfaces in the presence of a single adsorbate.

Chandrasekhar Roychoudhuri

The interpretation of the detection of very slow rate of photo counts in interference and diffraction experiments have given rise to the prevailing interpretation that photons interfere by themselves and they are indivisible, albeit non-local. The purpose of this paper is to inspire the development of alternate models for the photons by underscoring that, in reality, light does not interfere with light. The effects of superposition, registered as interference fringes, can become manifest only when a suitable detector can respond simultaneously to all the superposed light beams separately arriving from all the paths (or, slits). It should be a strictly causal process. In fact, different detectors with different quantum properties, report different results while exposed to the same superposed fields. Interference and diffraction effects are always observed as fringes through the processes of re-distribution and/or re-direction of the measured energy of the superimposed fields. Accordingly, we present a number of experiments, actual and conceptual, which highlight the contradictions built into the notion of non-locality in interference. A closer examination of these experiments can guide us to develop a conceptually congruent and causal model for both the evolution of photons and the interference (diffraction) effects by adapting to the classical diffraction theory. This theory has been correctly predicting the characteristics of light whether it is star light propagating through the inter galactic space, or nano tip generated light propagating through complex nano photonic waveguides.

Antoine Labeyrie, S. G. Lipson, Peter Nisenson

Arkady Plotnitsky

The argument of this article is grounded in the irreducible interference of observational instruments in our interactions with nature in quantum physics and, thus, in the constitution of quantum phenomena versus classical physics, where this interference can, in principle, be disregarded. The irreducible character of this interference was seen by N. Bohr as the principal distinction between classical and quantum physics and grounded his interpretation of quantum phenomena and quantum theory. Bohr saw complementarity as a generalization of the classical ideal of causality, which defined classical physics and relativity. While intimated by Bohr, the relationships among observational technology, complementarity, causality and the arrow of events (a new concept that replaces the arrow of time commonly used in this context) were not addressed by him either. The article introduces another new concept, that of quantum causality, as a form of probabilistic causality. The argument of the article is based on a particular interpretation of quantum phenomena and quantum theory, defined by the concept of 'reality without realism (RWR)'. This interpretation follows Bohr's interpretation but contains certain additional features, in particular the Dirac postulate. The article also considers quantum-like (Q-L) theories (based in the mathematics of QM) from the perspective it develops. This article is part of the theme issue 'Thermodynamics 2.0: Bridging the natural and social sciences (Part 2)'.

Samantha Strong