A Testable Solution of the Cosmological Constant and Coincidence Problems

We present a new solution to the cosmological constant (CC) and coincidence problems in which the observed value of the CC, $\Lambda$, is linked to other observable properties of the universe. This is achieved by promoting the CC from a parameter which must to specified, to a field which can take many possible values. The observed value of Lambda ~ 1/(9.3 Gyrs)^2$(approximately 10^(-120) in Planck units) is determined by a new constraint equation which follows from the application of a causally restricted variation principle. When applied to our visible universe, the model makes a testable prediction for the dimensionless spatial curvature of Omega_k0 = -0.0056 s_b/0.5; where s_b ~ 1/2 is a QCD parameter. Requiring that a classical history exist, our model determines the probability of observing a given Lambda. The observed CC value, which we successfully predict, is typical within our model even before the effects of anthropic selection are included. When anthropic selection effects are accounted for, we find that the observed coincidence between t_Lambda = Lambda^(-1/2) and the age of the universe, t_U, is a typical occurrence in our model. In contrast to multiverse explanations of the CC problems, our solution is independent of the choice of a prior weighting of different$\Lambda$-values and does not rely on anthropic selection effects. Our model includes no unnatural small parameters and does not require the introduction of new dynamical scalar fields or modifications to general relativity, and it can be tested by astronomical observations in the near future.Comment: 31 pages, 4 figures; v2: version accepted by Phys. Rev.

Stability in Cosmology, from Einstein to Inflation

I investigate the role of stability in cosmology through two episodes from the recent history of cosmology: (1) Einstein’s static universe and Eddington’s demonstration of its instability, and (2) the flatness problem of the hot big bang model and its claimed solution by inflationary theory. These episodes illustrate differing reactions to instability in cosmological models, both positive ones and negative ones. To provide some context to these reactions, I also situate them in relation to perspectives on stability from dynamical systems theory and its epistemology. This reveals, for example, an insistence on stability as an extreme position in relation to the spectrum of physical systems which exhibit degrees of stability and fragility, one which has a pragmatic rationale, but not any deeper one

Stability in Cosmology, from Einstein to Inflation

I investigate the role of stability in cosmology through two episodes from the recent history of cosmology: (1) Einstein’s static universe and Eddington’s demonstration of its instability, and (2) the flatness problem of the hot big bang model and its claimed solution by inflationary theory. These episodes illustrate differing reactions to instability in cosmological models, both positive ones and negative ones. To provide some context to these reactions, I also situate them in relation to perspectives on stability from dynamical systems theory and its epistemology. This reveals, for example, an insistence on stability as an extreme position in relation to the spectrum of physical systems which exhibit degrees of stability and fragility, one which has a pragmatic rationale, but not any deeper one

Kinematics and Age of Syn-Intrusive Detachment Faulting in the Southern Alps: Evidence for Early Permian Crustal Extension and Implications for the Pangea A Versus B Controversy

Permian basin formation and magmatism in the Southern Alps of Italy have been interpreted as expressions of a WSW‐ENE‐trending, dextral megashear zone transforming Early Permian Pangea B into Late Permian Pangea A between ~285 and 265 Ma. In an alternative model, basin formation and magmatism resulted from N‐S crustal extension. To characterize Permian tectonics, we studied the Grassi Detachment Fault, a low‐angle extensional fault in the central Southern Alps. The footwall forms a metamorphic core complex affected by upward‐increasing, top‐to‐the‐southeast mylonitization. Two granitoid intrusions occur in the core complex, the synmylonitic Val Biandino Quartz Diorite and the postmylonitic Valle San Biagio Granite. U‐Pb zircon dating yielded crystallization ages of 289.1 ± 4.5 Ma for the former and 286.8 ± 4.9 Ma for the latter. Consequently, detachment‐related mylonitic shearing took place during the Early Permian and ended at ~288 Ma, but kinematically coherent brittle faulting continued. Considering 30° anticlockwise rotation of the Southern Alps since Early Permian, the extension direction of the Grassi Detachment Fault was originally ~N‐S. Even though a dextral continental wrench system has long been regarded as a viable model at regional scale, the local kinematic evidence is inconsistent with this and, rather, supports N‐S extensional tectonics. Based on a compilation of >200 U‐Pb zircon ages, we discuss the evolution and tectonic framework of Late Carboniferous to Permian magmatism in the Alps

A new methodology for determining thermal properties and modelling temperature development in hydrating concrete

A method is described for determining both the rate of heat generation and the time-dependent thermal properties of concrete so that the temperature development in a concrete section can be modelled. The method uses measured temperature data from concrete prisms and involves fitting data from the sample prisms of concrete to a simple theoretical heat-flow model. It is intended to facilitate on-site tests of concrete mixes; the resulting data can be used in computer models to predict the stresses that can lead to early thermal cracking in large pours. The method is tested by using the thermal properties obtained from the model to predict the temperature versus time profile at a number of locations in a large rectangular block of concrete and comparing these predictions with measured temperatures from the block.Not applicableRecord needs to include a link to the DOI version of article - http://dx.doi.org/10.1016/S0950-0618(02)00099-5. DG 08/07/10 ke.kpw21/7/1