Horizon problem

Abstract: Observations indicate that the universe is effectively flat, but they do not rule out a closed universe. The role of positive curvature is negligible at late times, but can be crucial in the early universe. In particular, positive curvature allows for cosmologies that originate as Einstein static universes, and then inflate and later reheat to a hot big bang era. These cosmologies have no singularity, no "beginning of time", and no horizon problem. If the initial radius is chosen to be above the Planck scale, then they also have no quantum gravity era, and are described by classical general relativity throughout their history.

Abstract: We develop a conceptual model of the career horizon problem of CEOs approaching retirement and discuss its implications on firm risk taking, specifically in engagement in international acquisitions. Based on prospect theory and agency theory, we emphasize the legacy conservation and wealth preservation concerns of CEOs and investigate how their holdings of in-the-money unexercised options and firm equity accentuate or mitigate the career horizon problem. The model is tested in the context of international acquisitions with a sample of 293 U.S. firms over a five-year period (1995–1999). We find that a longer CEO career horizon is associated with a higher likelihood of international acquisitions. We also find that CEOs nearing retirement with high levels of in-the-money unexercised options and equity holdings are less likely to engage in international acquisitions than CEOs with low levels of in-the-money options and equity holdings. The study raises important considerations about the implications of CEOs' equity and in-the-money option holdings on firm risk taking at various stages of their career horizon. Copyright © 2008 John Wiley & Sons, Ltd.

Abstract: Context. The horizon problem in the standard model of cosmology (ΛDCM) arises from the observed uniformity of the cosmic microwave background radiation, which has the same temperature everywhere (except for tiny, stochastic fluctuations), even in regions on opposite sides of the sky, which appear to lie outside of each other’s causal horizon. Since no physical process propagating at or below lightspeed could have brought them into thermal equilibrium, it appears that the universe in its infancy required highly improbable initial conditions. Aims. In this paper, we demonstrate that the horizon problem only emerges for a subset of Friedmann-Robertson-Walker (FRW) cosmologies, such as ΛCDM, that include an early phase of rapid deceleration.Methods. The origin of the problem is examined by considering photon propagation through a FRW spacetime at a more fundamental level than has been attempted before.Results. We show that the horizon problem is nonexistent for the recently introduced R h = ct universe, obviating the principal motivation for the inclusion of inflation. We demonstrate through direct calculation that, in this cosmology, even opposite sides of the cosmos have remained causally connected to us – and to each other – from the very first moments in the universe’s expansion. Therefore, within the context of the R h = ct universe, the hypothesized inflationary epoch from t = 10-35 s to 10-32 s was not needed to fix this particular “problem”, though it may still provide benefits to cosmology for other reasons.

Abstract: Cosmological inflation gives a natural answer for a variety of cosmological questions, including the horizon problem, the flatness problem, and others. However, inflation yields new questions relating to the flatness of the inflaton potential. Recent studies of `little' fields, a special class of pseudo-Goldstone bosons, have shown it is possible to protect the mass of a field while still yielding order-one interactions with other fields. In this paper, we will show that `little inflatons' are natural candidates for the slow-roll field of hybrid inflation models. We consider both supersymmetric and non-supersymmetric models, and give a simple examples based on approximate Abelian symmetries which solve the inflaton flatness problem of supergravity. We also present hybrid models in which components of gauge fields in higher dimensions play the role of the inflaton. Protected by higher-dimensional gauge symmetry, they, too, naturally have large couplings while suppressed mass terms. We summarize the implications of the new WMAP data on such models.