On The Expansion and Fate Of The Universe

The evolution of the universe from an initial dramatic event, the Big-Bang, is firmly established. Hubble's law [1] (HL) connects the velocity of galactic objects and their relative distance: v(r)=Hr, where H is the Hubble constant. In this work we suggest that HL is not valid at large distances because of total energy conservation. We propose that the velocity can be expanded in terms of their relative distance and produce a better fit to the available experimental data. Using a simple 'dust' universe model, we can easily calculate under which conditions an (unstable) equilibrium state can be reached and we can estimate the values of the matter present in the universe as well as the 'dark energy'. We do not need to invoke any 'dark energy', its role being played by the kinetic correction. The resulting picture is that the universe might reach an unstable equilibrium state whose fate will be decided by fluctuations: either collapse or expand forever

Bound Electron Screening Corrections to Reactions in Hydrogen Burning Processes

How important would be a precise assessment of the electron screening effect, on determining the bare astrophysical $S$-factor ($S_b(E)$) from experimental data? We compare the $S_b(E)$ obtained using different screening potentials, (1) in the adiabatic limit, (2) without screening corrections, and (3) larger than the adiabatic screening potential in the PP-chain reactions. We employ two kinds of fitting procedures: the first is by the conventional polynomial expression and the second includes explicitly the contribution of the nuclear interaction and based on a statistical model. Comparing bare $S$-factors that are obtained by using different screening potentials, all $S_b(E)$ are found to be in accord within the standard errors for most of reactions investigated, as long as the same fitting procedure is employed. $S_b(E)$ is, practically, insensitive to the magnitude of the screening potential.Comment: 13 pages, 5 figure

Chaos, Percolation and the Coronavirus Spread

The dynamics of the spreading of the COVID-19 virus has similar features to turbulent flow, chaotic maps, and other non-linear systems: a small seed grows exponentially and eventually saturates. Like in the percolation model, the virus is most dangerous if the probability of transmission (or the bond probability p in the percolation model) is high. This suggests a relation with the population density, ρs, which must be higher than a certain value (ρs > 1,000 persons/km2). A "seed' implanted in such populations grows vigorously and affects nearby places at distance x. Thus, the spreading is governed by the ratio ρ = ρs/x. Assuming a power law dependence τ of the number of positives to the virus N+ from ρ, we find τ = 0.55, 0.75, and 0.96 for South Korea, Italy, and China, respectively

Gamow peak approximation near strong resonances

We discuss the most effective energy range for charged particle induced reactions in a plasma environment at a given plasma temperature. The correspondence between the plasma temperature and the most effective energy should be modified from the one given by the Gamow peak energy, in the presence of a significant incident-energy dependence in the astrophysical S-factor as in the case of resonant reactions. The suggested modification of the effective energy range is important not only in thermonuclear reactions at high temperature in the stellar environment, e.g., in advanced burning stages of massive stars and in explosive stellar environment, as it has been already claimed, but also in the application of the nuclear reactions driven by ultra-intense laser pulse irradiations