Entropy, Cosmic Inflation and the Theory of Relativity: In Honour of Prof. Øyvind Grøn

Dear Colleagues,

It is our pleasure to invite you to contribute to a Universe topical collection titled "Entropy, Cosmic Inflation and the Theory of Relativity: In Honour of Prof. Øyvind Grøn".

The aim is to gather a collection of contributions that relate to the scientific works of Øyvind Grøn. His doctoral thesis was titled “Repulsive gravitation”.

Early works of Grøn were concerned with the asynchronous formulation of relativistic kinematics and dynamics. Then, he wrote several articles on the relativistically rotating disk and proceeded with several works concerned with inertial dragging.

Together with professor Erik Eriksen, he subsequently worked out a series of papers on electromagnetic radiation and the principle of equivalence.

At the same time, Øyvind Grøn and Harald Soleng produced several articles together about different topics, for example the Einstein–Cartan theory.

Then, in a series of papers with Steinar Johannesen, conformally flat spacetimes were studied, and they showed that the Levi-Civita-Bertotti-Robinson solution of Einstein’s field equations represents spacetime outside a charged spherical domain wall.

Grøn also studied Kaluza-Klein theory, and together with Matthew T. Aadne, the Nash gravitational theory. Furthermore, together with Johannesen, Bræck and Ivar Farup, he studied rotating universe models.

Observational consequences of different inflationary models were recently reviewed by Grøn. He has earlier written about viscous inflationary universe models together with professor Iver Brevik.

Grøn also showed how an anisotropic universe isotropizes due to the presence of Lorentz invariant vacuum energy, for which he introduced the acronym LIVE. 

Another topic studied by Grøn and co-workers—Sigbjørn Hervik, Håvard Alnes, Morad Amarzguioui and Øystein Elgarøy—was gravitational entropy.

Together with Simen Bræck, Grøn introduced the concept “river of space”, and with Bræck and Ivar Farup, the concept “causal cosmic mass”. Grøn has also written several papers on the twin paradox—one together with Simen Bræck.

Prof. Dr. Sigbjørn Hervik
Guest Editor

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• the asynchronous formulation of relativity
• the ehrenfest paradox and physics in rotating reference frames
• the twin paradox
• electrodynamics of radiating charges
• effects of repulsive gravitation such as isotropization of anisotropic universe models
• conformally flat spacetimes
• rotating universe models
• gravitation and entropy
• the inflationary era
• inertial dragging
• Kaluza-Klein theory