New valuation of ΛCDM Cosmology by 41 authors....

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Discussion Overview

The discussion revolves around the valuation and implications of the ΛCDM cosmological model, particularly focusing on its perceived problems and the nature of the cosmological constant (\Lambda). Participants explore theoretical perspectives, critiques, and alternative viewpoints regarding the model's validity and the mysteries surrounding \Lambda.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants recommend reading a paper titled "Beyond ΛCDM" which humorously critiques the model, suggesting that it is difficult to move beyond ΛCDM due to significant obstacles.
  • Another participant suggests balancing the discussion by reading a paper on the cosmological constant problem, implying that the mystery surrounding \Lambda may need reevaluation.
  • One participant agrees with Bianchi and Rovelli that \Lambda is simply a constant in Einstein's equations and is not a problem for classical physics, although it poses challenges for quantum physics.
  • Concerns are raised about the lack of a strong argument from particle physics for a non-zero \Lambda, with some suggesting that it is easier to argue for \Lambda = 0 than for its observed small value.
  • A participant references a previous discussion regarding differing reactions to non-zero \Lambda, indicating that opinions on the matter have not significantly changed since a 2010 article.
  • Another point raised questions whether the small matter-antimatter asymmetry in the universe could be related to \Lambda.

Areas of Agreement / Disagreement

Participants express differing views on the implications and interpretations of \Lambda within the context of cosmology. There is no consensus on the nature of the cosmological constant or the validity of the arguments surrounding it.

Contextual Notes

Participants note that the arguments from particle physics regarding \Lambda = 0 are not robust, and there are unresolved questions about the relationship between quantum field theory and gravity in the context of a non-zero cosmological constant.

grauitate
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P.Bull, Y. Akrami, et al. "Beyond ΛCDM: Problems, solutions, and the road ahead" 77 pages + 517 references
arXiv:1512.05356
Written not without humour: e.g. pg. 67:
"As Tom Shanks once said, there are only two things wrong with ΛCDM: Λ and CDM."
" ΛCDM is like Hotel California: it is very hard to leave, and most, if not all, efforts to do so have ended with some insurmountable obstacle."
I'd like to recommend this paper for reading between the years for some discussions in 2016.
 
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For balance, I'd suggest reading this paper along with it:
http://arxiv.org/pdf/1002.3966v3.pdf
maybe "the cosmological constant problem" as a "great mystery" needs a little debunking : ^)
 
I agree with Bianchi and Rovelli that as far as cosmology per GR is concerned, there is no mystery surrounding [itex]\Lambda[/itex], it's simply a constant per Einstein's equations to be measured. We don't have a better theory for cosmology per classical (non-quantum) physics than GR, so they say simply that [itex]\Lambda[/itex] is not a problem for the best classical physics. But, they do acknowledge that it's a problem for whatever quantum physics underwrites GR. They write:

Third, we do not yet fully understand interacting quan-
tum field theory, its renormalization and its interaction
with gravity when spacetime is not Minkowski (that is, in
our real universe). But these QFT difficulties have little
bearing on the existence of a non vanishing cosmological
constant in low-energy physics, because it is a mistake
to identify the cosmological constant with the vacuum
energy density.

This is what bothers those who are bothered by non-zero [itex]\Lambda[/itex]. Particle physics gives us an argument for [itex]\Lambda = 0[/itex], but nothing for the value currently measured. While that's not a problem for "low-energy physics," it's certainly a problem/mystery for quantum physics.
 
RUTA said:
Particle physics gives us an argument for [itex]\Lambda = 0[/itex]

Where?
 
A point along the lines of those by Bianchi and Rovelli in http://arxiv.org/abs/1002.3966 might be - why is the matter anti matter assymmetry of the universe so tiny [1 ppb]. Could lamba be somehow related?
 

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