Thursday, January 26, 2023

Deur Takes On The Hubble Tension

Deur's analysis of the self-interaction of gravitational fields addresses the Hubble tension.
One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g., the Type IA supernova, tend to yield larger values than measurements from quantities originating at high-redshift, e.g., fits of cosmic microwave background radiation. It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements. 
Here we explore whether the self-interaction of gravitational fields in General Relativity, which are traditionally neglected when studying the evolution of the universe, can explain the tension. We find that with field self-interaction accounted for, both low- and high-redshift data are simultaneously well-fitted, thereby showing that gravitational self-interaction could explain the Hubble tension. Crucially, this is achieved without introducing additional parameters.
Corey Sargent, Alexandre Deur, Balsa Terzic, "Hubble Tension and Gravitational Self-Interaction" arXiv:2301.10861 (January 25, 2023).

@mitchell_porter at the Physics Forums discusses the analysis restates the argument made in the paper in summary form:
Gravitational self-interaction causes tighter binding of localized massive systems. This also leads to depletion of the gravitational field at large distances. The magnitude of gravitational depletion changes over the course of cosmic time, in a way depending on the number and type of gravitationally bound systems that have formed.

The Hubble tension can be resolved because the early universe was relatively homogeneous, so there was no gravitational depletion at high redshift; but once structure formation began, so did gravitational depletion.

A specific depletion function is proposed (equation 2, based on a 2017 paper . . .), depending on the rate and frequency of galactic mergers (parameters b and A in equation 2). The value of these parameters is inferred by fitting the depletion function to various cosmological data.

Indeed, the paper argues that the Hubble tension actually allows for a more precise determination of those parameters than Deur's previous papers that made the analysis, also allowing his previous work involving a depletion function to be more tightly fit. 

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