The One-Way Speed of Light on Rotating Earth and the Definition of the Meter
The Onset of Chaotic Motion of a Spinning Particle around the Schwarzchild Black Hole
The operator product expansion for perturbative quantum field theory in curved spacetime
The optimal entropy bound and the self-energy of test objects in the vicinity of a black hole
The Ori-Soen time machine
The orientability of spacetime
The origin of black hole entropy
The Origin of Black Hole Entropy in String Theory
The origin of causal set structure in the quantum universe
The origin of spacetime topology and generalizations of quantum field theory
The Origin of Structures in Generalized Gravity
The origin of the area law of the entropy of a quantum field in a black hole
The origin of the difference between space and time
The Origin of the Electromagnetic Interaction in Einstein's Unified Field Theory with Sources
The Origin of the Entropy in the Universe
The Origin of the Radiation Reaction Force
The origin of the spacetime metric: Bell's `Lorentzian pedagogy' and its significance in general relativity
The Origin of Time Asymmetry
The origins of length contraction: I. The FitzGerald-Lorentz deformation hypothesis
The oscillating dark energy and cosmological Casimir effect