It is shown that a violation of signal locality and unitarity occur in a particular merger of quantum mechanics and general relativity.

The current status of wave particle duality using single photon sources is briefly reviewed

An experiment is suggested that is capable of distinguishing between the de Broglie-Bohm theory and standard quantum mechanics.

It is shown that conventional de Broglie-Bohm quantum theory is incompatible with the standard quantum theory of a system unless the former is ergodic.

Unlike the previous theoretical results based on standard quantum mechanics that established the nearly elliptical shapes for the centre-of-mass motion in Rydberg atoms using numerical simulations, we show analytically that the Bohmian trajectories in Rydberg atoms are nearly elliptical.

A unified classical theory of gravity and electromagnetism with a torsion vector $\Gamma_{i} \neq 0$, proposed by S N Bose in 1952, is introduced. In this theory, the torsion vector acts as a magnetic current and it is shown that (i) the electromagnetism is invariant under continuous Heaviside–Larmor transformations and (ii) the electric and magnetic charges are topologically quantised, satisfying the Dirac quantisation condition, without implying any Dirac string provided $\Gamma_{i}$ is curl-less.

The nature of the Lüders projection and its relationship with the von Neumann projection are clarified. It is shown that Lüders-like transformations can be obtained by local unitary transformations on single and productstates, but not entangled states. Several examples are given to illustrate this. The distinction between the two projections is further clarified by the analyses of the measurement process on both entangled and single-particle systems. A possible experimental test of the Lüders postulate for non-degenerate systems is also proposed.