Stiff Matter in the Universe | Chapter 3 | Physical Science: New Insights and Developments Vol. 1

The main objective of this article is to introduce a novel mathematical expression for the comoving volume element in a flat universe that includes a cosmological constant, cold matter, and stiff matter and utilised this to derive constraints on the amount of stiff matter in the universe based on the Planck measurements of the Hubble parameter. These constraints are then examined to assess whether stiff matter could potentially resolve the Hubble tension. The findings show that the difference between the Hubble constant in a universe with stiff matter and the ΛCDM−universe is positive. Hence, the Hubble constant is larger with stiff matter than without. This goes in the right direction since the point of departure for this calculation is the value of the Hubble constant as determined by the Planck measurements, and this value is lower than the late universe measurements. The findings also indicate that the Planck measurements impose an upper limit on the current value of the density parameter of stiff matter, ΩS0 < 5 · 10−23, which is insufficient to resolve the Hubble tension.

 

 

Author (s) Details

Øyvind G. Grøn
Faculty of Technology, College of Applied Sciences, Art and Design, Oslo and Akershus University, NO-0130 Oslo, Norway.

 

 

Please see the book here:- https://doi.org/10.9734/bpi/psniad/v1/5185

Can Anisotropic Cosmic Expansion or Stiff Matter Solve the Hubble Tension? | Chapter 5 | Current Research Progress in Physical Science Vol. 8

I deduce a new form of an exact anisotropic solution of Einstein’s field equations which was originally found and presented in a different way by Saunders (1969) in 1969. This form of the solution shows in an explicit way how it generalizes the isotropic ΛCDM universe model to a corresponding model with anisotropic expansion – an AΛCDM model. It is used here to investigate whether anisotropy of the cosmic expansion can resolve the Hubble tension, which is a long-standing problem in cosmology. The conclusion is that cosmic anisotropy, even in a general Bianchi type I framework, cannot solve the Hubble tension. Due to its mathematical similarity to the AΛCDM model, a universe model with stiff matter, a SΛCDM model, is also discussed in this chapter, and it is shown that observational restrictions on the amount of stiff matter in the universe, mean that there is too little stiff matter to solve the Hubble tension.

 

Author (s) Details

 

Øyvind G. Grøn
Faculty of Technology, Art and Design, College of Applied Sciences, Oslo and Akershus University, St. Olavs Plass, P.O. Box 4, NO-0130 Oslo, Norway.

 

Please see the book here:- https://doi.org/10.9734/bpi/crpps/v8/4477