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This is a continuation of Cosmological constant of standard model of cosmology and observational data asked in 2012. In 2016, Prof S. Sarkar, Nielsen and Guffanti published an article(see: https://arxiv.org/abs/1506.01354) where they have performed maximum likelihood estimation on Joint Lightcurve Analysis (JLA) catalogue for 740 Type Ia supernovae and only found a marginal evidence ($<3\sigma$) for " widely accepted claim that the expansion of universe is presently accelerating". However, this work was faced with criticism from D. Rubin and B. Hayden (https://arxiv.org/abs/1610.08972). The controversy persisted even after that (see the web discussion: https://4gravitons.com/2016/11/11/a-response-from-nielsen-guffanti-and-sarkar/) and eventually these discussions boil down to a debate over what kind of statistical method should be deemed appropriate for cosmological observations.

So, what is the current status of this controversy over positive $\Lambda$? Do we really have enough evidence for existence of positive $\Lambda$ ? S. Sarkar and co. claims that interpretation of evidences from other sources like baryon acoustic oscillations and CMB are very model dependent, where it is sort of already assumed that our universe is homogeneous and isotropic. Does it mean that we have sufficient evidence and should seriously look for a better model for cosmology?

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The majority of cosmologists believe that the LCDM model is the best available. It's successful at accounting for many observations.

It's healthy for cosmology that alternatives like Sarkar's are discussed - but if he wants his model to be accepted he has to convince enough cosmologists of its benefits - and that hasn't happened yet.

Some would say that the LCDM model has various philosophical difficulties and unexplained phenomena such as dark energy and inflation. There is also the Hubble tension at the moment .

So yes, we have should seriously look for a better model for cosmology. The same as we should look for better models in all areas of science.

In physics a theory is never 'proved right' it can only be 'proved wrong' (by experiment) and cosmology is no exception.

If the LCDM model continues to survive experimental tests it'll continue to be accepted. If there is enough evidence against it, presumably it'll fall out of favour (or a new generation will not find it convincing enough) and it'll become unpopular.

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  • $\begingroup$ Thank you. Does inhomogeneous cosmological models provide any better solutions than the current LCDM model? $\endgroup$
    – KP99
    Jul 5, 2021 at 9:16
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    $\begingroup$ There are some that model our region as being in a gigantic 'void' and they are able to account for differences in the $H_0$ measurements, they say that local measurements for $H_0$ would be higher if we are in a void, than distant measurements. But there is other data to account for, supernovae that appear to show an accelerating universe, measurements of the matter density, that show approx $\Omega_m -= 0.3$ and LCDM accounts well for the details of the spectrum of the CMBR. It's complicated so it's good if all models are considered. Good news is the amount of good data nowadays... $\endgroup$ Jul 5, 2021 at 10:07
  • $\begingroup$ @JohnHunter Just to add to what you said, my impression was also that the "void" models also require us to be very close to the center of the void, so there is a fine tuning problem. $\endgroup$
    – Andrew
    Jul 6, 2021 at 21:02

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