This article is a celebration of the centenary of Schwarzschild’s presentations of his external and internal solutions describing spacetime outside and inside an incompressible, spherically symmetric body. I ...

The Levi-Civita Bertotti Robinson (LBR) spacetime is investigated in various coordinate systems. By means of a general formalism for constructing coordinates in conformally flat spacetimes, coordinate transformations ...

Alexander Friedmann, Carl Wilhelm Wirtz, Vesto Slipher, Knut E. Lundmark, Willem de Sitter, Georges H. Lemaître, and Edwin Hubble all contributed to the discovery of the expansion of the universe. If only two persons are ...

In this paper we study the evolution of spatially homogeneous and anisotropic Bianchi type-I Universe models with the cosmological constant, Λ, and filled with nonlinearviscous fluid. The dynamical equations for these ...

The concept of negative temperatures has occasionally been used in connection with quantum systems. A recent example of this sort is reported in the paper of S. Braun et al. [Science 339, 52 (2013)], where an attractively ...

The effect of gravity upon changes of the entropy of a gravity-dominated system is discussed. In a universe dominated by vacuum energy, gravity is repulsive, and there is accelerated expansion. Furthermore, inhomogeneities ...

The twin paradox is intimately related to the principle of relativity. Two twins A and B meet, travel away from each other and meet again. From the point of view of A, B is the traveller. Thus, A predicts B to be younger ...

The question whether rotational motion is relative according to the general theory of relativity is discussed. Einstein’s ambivalence concerning this question is pointed out. In the present article I defend Einstein’s way ...

The theory of electrodynamics of radiating charges is reviewed with special emphasis on the role of the Schott energy for the conservation of energy for a charge and its electromagnetic field. It is made clear that the ...

John Nash has proposed a new theory of gravity. We define a Nash-tensor equal to the curvaturetensorappearingintheNashfieldequationsforemptyspace,andcalculateitscomponents for two cases: 1. A static, spherically symmetric ...