Inflation after Planck

Gratuitous Picture of Planck

There’s a paper on the arXiv by Debika Chowdhury et al with the title Inflation after Planck: Judgment Day and abstract:

Inflation is considered as the best theory of the early universe by a very large fraction of cosmologists. However, the validity of a scientific model is not decided by counting the number of its supporters and, therefore, this dominance cannot be taken as a proof of its correctness. Throughout its history, many criticisms have been put forward against inflation. The final publication of the Planck Cosmic Microwave Background data represents a benchmark time to study their relevance and to decide whether inflation really deserves its supremacy. In this paper, we categorize the criticisms against inflation, go through all of them in the light of what is now observationally known about the early universe, and try to infer and assess the scientific status of inflation. Although we find that important questions still remain open, we conclude that the inflationary paradigm is not in trouble but, on the contrary, has rather been strengthened by the Planck data.

You can download a PDF of the full paper here.

This is a pretty good introduction to live issues around the theory of cosmic inflation in the light of the results from the Planck mission. I’ll leave it to you to judge whether or not you agree with the concluding sentence of the abstract!



2 Responses to “Inflation after Planck”

  1. “I’ll leave it to you to judge whether or not you agree with the concluding sentence of the abstract!”

    It depends on what you mean. Does Planck provide data which make inflation less certain? No. Are the more fundamental issues still there? Yes. However, more data can’t dispel them, though it might make people think it is worth trying to find a solution to them, rather than rejecting inflation outright. For example, inflation claims to solve many fine-tuning problems. (Others and I have argued in many places that the flatness problem isn’t really a problem, but this doesn’t apply to the isotropy (horizon) problem, which appears to be a real problem but one which inflation could solve.) The question here is whether the cure is worse than the disease, for example if inflation itself requires fine-tuned conditions—perhaps even more fine-tuned than the fine-tuning problems it is trying to solve—then this is something which needs to be thought about.

  2. laboussoleestmonpays Says:

    This article looks to me more like a Solomonic judgement discussing with scrutiny and pedagogicaly the theoretical issues the inflation scenario has to cope with through the light of Planck mission data thorough analysis. The latter was a judgement day only for some specific models I think (see below for a possible stronger statement*).

    I feel happy the article reminds also “the inflationary scenario also provides a natural mechanism for generating primordial perturbations that subsequently act as seeds for the formation of large-scale
    structures. According to inflation, they are the unavoidable quantum fluctuations of the inflaton and gravitational fields, amplified by gravitational instability and stretched by the cosmic expansion.”

    A honorable russian cosmologist would add ( “Irrespective of the amplification mechanism of the initial quantum fluctuations, the theory of the quantum origin of structures in the
    Universe with all its nontrivial predictions is now reliably
    confirmed, and there are no viable alternatives*. We also note
    that besides black holes, cosmology is the only field where the
    nonperturbative Einstein theory is needed. Numerous cosmological data confirm that this theory is valid in a wide range from 10^-27 cm to 10^28 cm”

    Whatever the correct UV completion of the inflation theory “Allow me to express now, once and for all, my deep respect for the work of the [Planck Mission collaboration] and for [its] fight to wring significant facts from an inflexible Nature, who says so distinctly “No” and so indistinctly “Yes” to our theories.” as Hermman Weyl would conclude.

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