Universe, Volume 4, Issue 7

A key challenge for many quantum gravity approaches is to construct states that describe smooth geometries on large scales. Here we define a family of $(2+1)$-dimensional quantum gravity states which arise from curvature excitations concentrated at poi...

We discuss a possible scale of gravitational origin at around 10 MeV, or ${10}^{-12}$ cm, which arises in the MacDowell–Mansouri formalism of gravity due to the topological Gauss–Bonnet term in the action, as pointed out by Bjorken several years ago. A leng...

Einstein’s theory of general relativity was proposed over 100 years ago and has successfully passed a large number of observational tests in the weak field regime. However, the strong field regime is largely unexplored, and there are many modif...

The Universe Editorial Office would like to report errors in the published paper [1].[...]

We study a new class of inflation model parametrized by the Hubble radius, such that $aH\propto \exp {(-\alpha \phi )}^n$. These potentials are plateau-like, and reduce to the power-law potentials in the simplest case $n=2$. We investigate the range of mo...

The present work is a brief review of the development of dynamical black holes from the geometric point view. Furthermore, in this context, universal thermodynamics in the FLRW model has been analyzed using the notion of the Kodama vector. Finally, s...

We perform an experimental test where we directly observe light-induced electron transitions with a macroscopic spatial discontinuity. The effect is related to the fundamental indivisibility of macroscopic orbit-like quantum states reminiscent of so-...

We consider the action of exact plane gravitational waves, or pp-waves, on free particles. The analysis is carried out by investigating the variations of the geodesic trajectories of the particles, before and after the passage of the wave. The initia...