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A New Solution for the friedmann equations

International Journal of Astronomy and Astrophysics 2016年第1期6卷 122-134页

作者： Naser Mostaghel Department of Civil Engineering University of Toledo Toledo USA

Assuming a flat universe expanding under a constant pressure and combining the first and the second friedmann equations, a new equation, describing the evolution of the scale factor, is derived. The equation is a general kinematic equation. It includes all the ingredients composing the universe. An exact closed form solution for this equation is presented. The solution shows remarkable agreement with available observational data for redshifts from a low of z = 0.0152 to as high as z = 8.68. As such, this solution provides an alternative way of describing the expansion of space without involving the controversial dark energy.

关键词： Cosmological Constant Distances and Redshifts Expanding Universe friedmann equations

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A New Version of the Lambda-CDM Cosmological Model, with Extensions and New Calculations

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Journal of Modern Physics 2024年第2期15卷 193-238页

作者： Jan Helm Department of Electrical Engineering Technical University Berlin Berlin Germany

This article gives a state-of-the-art description of the cosmological Lambda-CDM model and in addition, presents extensions of the model with new calculations of background and CMB functions. Chapters 1-4 describe the background part of the model, i.e. the evolution of scale factor and density according to the friedmann equations, and its extension, which results in a correction of the Hubble parameter, in agreement with new measurements (Cepheids-SNIa and Red-Giants). Based on this improved background calculation presented in chapters 5-9 the perturbation part of the model, i.e. the evolution of perturbation and structure according to the perturbed Einstein equations and continuity-Euler equations, and the power spectrum of the cosmic microwave background (CMB) is calculated with a new own code.

关键词： Lambda-DCM friedmann equations CMB Metric Perturbation Hubble Parameter

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The Hubble Field vs Dark Energy

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Journal of Modern Physics 2016年第12期7卷 1607-1615页

作者： Juan Lartigue Department of Nuclear Chemistry Faculty of Chemistry National University of México México City México

The Hubble equation was considered valid enough to calculate the recession velocity of galaxies, until further observations showed that there would be an accelerated recession in the Hubble flow, necessarily tied to an accelerated expansion of the Universe. So, this paper postulates the existence of a Hubble field as a possible cause for such an accelerated expansion, with some conditions: it must be a scalar field whose intensity should be a constant in respect to distance and whose Poisson equation should not be zero nor a function of mass;such field could rather be a property of the space-time. The obvious expression for acceleration should be the derivative of the Hubble equation respect to time, which gives two opposed-signs terms whose substitution by the De-Sitter equation drives to a permanent negative acceleration, similarly to that obtained by the 2nd friedmann equation. Otherwise, the inclusion of the ? term in the gravitational Einstein equation has led to a two opposed-signs terms expression, resembled to a non-published Newton equation. The negative term expresses the gravitational attraction and the positive one expresses the accelerated expansion as a ? function, which usually is attributed to dark energy. In this paper it is shown that Λ is proportional to the squared Hubble parameter and that the uncertain dark energy may be substituted by the calculable Hubble field intensity to obtain an equation for the net Universe acceleration. equations for the Hubble parameter as functions of time and radius are also deduced. A relation is shown between the various assumed masses of the Universe and its critical radius. Additional Universe parameters are estimated such as the deceleration factor and a solution for the Poisson equation in the Hubble field. A brief comment t on high-standard candles is included.

关键词： Hubble Law Hubble Field Cosmological Constant friedmann equations

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