Ranku said:Is there an equation of backreaction
Ranku said:It is being explored how the effect of inhomogenities in matter influence average cosmic evolution (Arxiv).
It is an advanced-level critique of a rival paper, so doesn’t go much into the basics of backreaction.PeterDonis said:What does the paper you referenced tell you?
Ranku said:It is an advanced-level critique of a rival paper
I’ve just come to know of the topic. So l’m looking for some basic information here.PeterDonis said:What does the rival paper say? Or other references? The paper says references 1-8 are general reviews of the topic of backreaction.
Ranku said:I’ve just come to know of the topic. So l’m looking for some basic information here.
All I say to you is ‘May Your Tribe Increase’.Klystron said:Back when adults routinely wore hats outdoors, STEM teachers and authors used an expression "First find a place to hang your hat." when studying new concepts. IOW begin with material that you understand.
While reading the cited paper and following this discussion thread, I found a "place to hang my hat" in reference number 21] Abbott E A 1884 Flatland: A Romance of Many Dimensions. Curious why the authors referenced this classic Victorian mathematical satire, I followed the Abbott reference back through this paper's critique of the prior Green and Wald (GW) papers.
The common thread among this critique and GW papers describes how scientists measure and understand the topology of their universe, specifically in 'Sphereland' with 3+1 dimensions discussed in section 2 of your PDF. This paper discusses difficulties in proving relevance of backreaction inhomogeneities in cosmological theory without offering a primer on backreaction as a concept.
Regardless of level of understanding, any relevant material is useful for improving understanding. Thanks for the reference link; it was informative.phyzguy said:@Ranku I don't know what level of understanding you have, but I found this paper to help me understand the concept. The simulation run here seems to support the claim that backreaction may be significant.
https://arxiv.org/abs/1607.08797
Backreaction refers to the effect of small-scale inhomogenities in matter on the overall evolution of the universe. In other words, it is the influence of local variations in matter and energy density on the large-scale behavior of the universe.
Backreaction challenges the traditional model of cosmic evolution, which assumes a homogeneous and isotropic universe on large scales. It suggests that these local variations in matter and energy density can have a significant impact on the overall behavior of the universe, leading to deviations from the predicted expansion and acceleration.
Inhomogenities in matter can take many forms, including variations in the distribution of galaxies, clusters of galaxies, and dark matter. They can also arise from fluctuations in the cosmic microwave background radiation and the presence of large voids in the universe.
Scientists use a variety of observational and theoretical methods to study backreaction. These include analyzing data from telescopes and satellites, running simulations on supercomputers, and developing mathematical models to describe the behavior of inhomogenities in matter.
Backreaction has the potential to significantly change our understanding of the universe and its evolution. It could provide new insights into the nature of dark energy and the structure of the universe on large scales. It may also challenge the validity of the cosmological principle, which assumes that the universe is homogeneous and isotropic on large scales.