Spherical space in the Newtonian limit: The cosmological constant

We compute the cosmological constant of a spherical space in the limit of weak gravity. To this end, we use a duality developed by the present authors in a previous work. This duality allows one to treat the Newtonian cosmological fluid as the probability fluid of a single particle in nonrelativistic quantum mechanics. We apply this duality to the case when the spacetime manifold on which this quantum mechanics is defined is given by [Formula: see text]. Here, [Formula: see text] stands for the time axis and [Formula: see text] is a 3-dimensional sphere endowed with the standard round metric. A quantum operator [Formula: see text] satisfying all the requirements of a cosmological constant is identified, and the matrix representing [Formula: see text] within the Hilbert space [Formula: see text] of quantum states is obtained. Numerical values for the expectation value of the operator [Formula: see text] in certain quantum states are obtained, which are in good agreement with the experimentally measured cosmological constant.

Theory of machine learning based on nonrelativistic quantum mechanics

The goal of this paper is the presentation of the elementary procedures that normally are done in nonrelativistic Quantum Mechanics in terms of the principles of Machine Learning. In essence, this paper discusses Mitchell’s criteria, whose block fundamental dictates that the universal evolution of any system is composed by three fundamental steps: (i) Task, (ii) Performance and (iii) Experience. In this paper, the quantum mechanics formalism reflected on the usage of evolution operator and Green’s function are assumed to be part of mechanisms that are inherently engaged to the Machine Learning philosophy. The action for measuring observables through experiments and the intrinsic apparition of statistical or systematic errors are discussed in terms of “quantum learning”.

Wave Function Realism in a Relativistic Setting

This chapter considers and responds to criticism that wave function realism is only plausible as an approach to the interpretation of nonrelativistic quantum mechanics and not relativistic quantum theories and quantum field theories. This critique gains traction as wave function realism has until now been formulated and defended solely within the context of idealized, nonrelativistic quantum mechanics. The chapter considers five such arguments and responds to each. An important lesson is that wave function realists should only adopt the wave-function-in-configuration-space picture as part of an interpretation of an idealized nonrelativistic quantum mechanics. More generally, the space the wave function inhabits will vary as the quantum theory the wave function realist is developing an interpretation of varies. The chapter develops a sketch of what wave function realism looks like in one relativistic context. It then discusses the issue of the interpretation of quantum theories in the limit of physical theorizing.

The Phase Space Model of Nonrelativistic Quantum Mechanics

We focus on several questions arising during the modelling of quantum systems on a phase space. First, we discuss the choice of phase space and its structure. We include an interesting case of discrete phase space. Then, we introduce the respective algebras of functions containing quantum observables. We also consider the possibility of performing strict calculations and indicate cases where only formal considerations can be performed. We analyse alternative realisations of strict and formal calculi, which are determined by different kernels. Finally, two classes of Wigner functions as representations of states are investigated.

The cosmological constant of emergent spacetime in the Newtonian approximation

We present a simple quantum-mechanical estimate of the cosmological constant of a Newtonian Universe. We first mimic the dynamics of a Newtonian spacetime by means of a nonrelativistic quantum mechanics for the matter contents of the Universe (baryonic and dark) within a fixed (i.e. nondynamical) Euclidean spacetime. Then we identify an operator that plays, on the matter states, a role analogous to that played by the cosmological constant. Finally, we prove that there exists a quantum state for the matter fields, in which the above-mentioned operator has an expectation value equal to the cosmological constant of the given Newtonian Universe.

Time in quantum theory, the Wheeler–DeWitt equation and the Born–Oppenheimer approximation

We compare two different approaches to the treatment of the Wheeler–DeWitt (WDW) equation and the introduction of time in quantum cosmology. One approach is based on the gauge-fixing procedure in theories with first-class constraints and the construction of the corresponding Hilbert space of quantum states. The other approach uses the Born–Oppenheimer (BO) method, based on the existence of two energy scales in the model under consideration. We apply both to a very simple cosmological model, including a massless scalar field filling a flat Friedmann universe, and observe that they give similar predictions. We also discuss the problem of time in nonrelativistic quantum mechanics and some questions concerning the correspondence between classical and quantum theories.

Dirac Equation in the Presence of Hartmann and Ring-Shaped Oscillator Potentials

The importance of the energy spectrum of bound states and their restrictions in quantum mechanics due to the different methods have been used for calculating and determining the limit of them. Comparison of Schrödinger-like equation obtained by Dirac equation with the nonrelativistic solvable models is the most efficient method. By this technique, the exact relativistic solutions of Dirac equation for Hartmann and Ring-Shaped Oscillator Potentials are accessible, when the scalar potential is equal to the vector potential. Using solvable nonrelativistic quantum mechanics systems as a basic model and considering the physical conditions provide the changes in the restrictions of relativistic parameters based on the nonrelativistic definitions of parameters.