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``Constants of Nature'' and cosmological parameters may in fact be variables related to some slowly-varying fields. In models of eternal inflation, such fields will take different values in different parts of the universe. Here I show how…

High Energy Physics - Theory · Physics 2009-10-31 Alexander Vilenkin

The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations. Arguments are commonly presented to the…

Cosmology and Nongalactic Astrophysics · Physics 2013-05-07 Eugenio Bianchi , Carlo Rovelli

As a compelling pattern for the holographic principle, our covariant entropy bound conjecture is proposed for more general dynamical horizons. Then we apply our conjecture to $\Lambda$CDM cosmological models, where we find it imposes a…

General Relativity and Quantum Cosmology · Physics 2009-03-20 Song He , Hongbao Zhang

Astronomical observations have shown that the expansion of the universe is at present accelerating, in a way consistent with the presence of a positive cosmological constant. This is a major puzzle, because we do not understand: why the…

Astrophysics · Physics 2007-05-23 Jordi Miralda-Escude

After a short history of the $\Lambda$-term it is explained why the (effective) cosmological constant is expected to obtain contributions from short-distance physics, corresponding to an energy at least as large as the Fermi scale. The…

Astrophysics · Physics 2007-05-23 Norbert Straumann

In the context of models where the dark energy density $\rD$ is a random variable, anthropic selection effects may explain both the "old" cosmological constant problem and the "time coincidence". We argue that this type of solution to both…

Astrophysics · Physics 2009-11-07 J. Garriga , A. Vilenkin

The idea that the vacuum energy density $\rho_{\Lambda}$ could be time dependent is a most reasonable one in the expanding Universe; in fact, much more reasonable than just a rigid cosmological constant for the entire cosmic history. Being…

General Relativity and Quantum Cosmology · Physics 2015-07-08 Harald Fritzsch , Joan Sola

It is possible that there may be differences in the fundamental physical parameters from one side of the observed universe to the other. I show that the cosmological constant is likely to be the most sensitive of the physical parameters to…

High Energy Physics - Phenomenology · Physics 2009-11-07 John F. Donoghue

An artificial scale of observable cosmological constant is dynamically related to its natural bare value due to an installation of relevant coherent state for the inflationary field in a finite volume of early Universe, because of…

General Relativity and Quantum Cosmology · Physics 2014-01-15 V. V. Kiselev

If the parameters defining the physics of our universe departed from their present values, the observed rich structure and complexity would not be supported. This article considers whether similar fine-tuning of parameters applies to…

Popular Physics · Physics 2020-08-26 Jeffrey M. Shainline

In a quest to explain the small value of the today's cosmological constant, following the approach introduced in [1], we show that the theoretical value of cosmological constant is consistent with its observational value. In more detail, we…

General Relativity and Quantum Cosmology · Physics 2015-10-08 T. Rostami , S. Jalalzadeh

We revisit our 2013 claim [arXiv:1303.7476] that the Universe is the result of a conspiratorial plot, and find that it cannot be trusted, because even the belief in this conspiracy likely results from a conspiracy. On the basis of…

Popular Physics · Physics 2020-04-23 Jörg P. Rachen , Ute G. Gahlings

It has recently been proposed [M. P. Hertzberg and A. Loeb, arXiv:2302.09090] that the observed value of the cosmological constant can be related to the physical parameters of the Standard Model. In the present compact note we point out…

General Relativity and Quantum Cosmology · Physics 2023-02-23 Shahar Hod

Probably not, because there are lots of manifestly unanthropic ways of producing entropy. We demonstrate that the Causal Entropic Principle (CEP), as a replacement for the anthropic principle to explain the properties of the observed…

High Energy Physics - Theory · Physics 2008-12-05 Irit Maor , Thomas W. Kephart , Lawrence M. Krauss , Y. Jack Ng , Glenn D. Starkman

Physical cosmology tries to understand the Universe at large with its origin and evolution. Observational and experimental situations in cosmology do not allow us to proceed purely based on the empirical means. We examine in which sense our…

History and Philosophy of Physics · Physics 2017-01-18 Jai-chan Hwang

We provide a consistency relation between cosmological observables in general relativity with the cosmological constant. Breaking of this relation at any redshift would imply the breakdown of the hypothesis of the cosmological constant as…

Astrophysics · Physics 2009-06-23 Takeshi Chiba , Takashi Nakamura

The causal entropic principle aims to predict the unexpectedly small value of the cosmological constant Lambda using a weighting by entropy increase on causal diamonds. The original work assumed a purely isotropic and homogeneous cosmology.…

General Relativity and Quantum Cosmology · Physics 2012-01-20 Daniel Phillips , Andreas Albrecht

We explicitly calculate the value of the cosmological constant, based on the recently developed theory connecting entropic gravity with quantum-events, induced by transactions, called transactional gravity. We suggest a novel interpretation…

General Relativity and Quantum Cosmology · Physics 2024-07-31 Andreas Schlatter

The peculiar value of $\theta$ is a challenge to the notion of an anthropic landscape. We briefly review the possibility that a suitable axion might arise from an anthropic requirement of dark matter. We then consider an alternative…

High Energy Physics - Theory · Physics 2018-07-04 Michael Dine , Laurel Stephenson Haskins , Lorenzo Ubaldi , Di Xu

In the framework of a model of minimal of dilatonic gravity (MDG) with cosmological potential we consider: the relations of MDG with nonlinear gravity and string theory; natural cosmological units, defined by cosmological constant; the…

General Relativity and Quantum Cosmology · Physics 2007-05-23 P. Fiziev
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