Fine tuning

Paper: Inflation doesn’t solve fine-tuning puzzles

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From Physical Review D:

We investigate the initial conditions of inflation in a Bianchi I universe that is homogeneous but not isotropic. We use the Eisenhart lift to describe such a theory geometrically as geodesics on a field-space manifold. We construct the phase-space manifold of the theory by considering the tangent bundle of the field space and equipping it with a natural metric. We find that the total volume of this manifold is finite for a wide class of inflationary models. We therefore take the initial conditions to be uniformly distributed over it in accordance with Laplace’s principle of indifference. This results in a normalizable, reparametrization invariant measure on the set of initial conditions of inflation in a Bianchi I universe. We find that this measure favors an initial state in which the inflaton field is at or near its minimum, with a mild preference for some initial anisotropy. Since inflation requires an initial field value with a large displacement from its minimum, we therefore conclude that the theory of inflation requires finely tuned initial conditions.

Kieran Finn, Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom

Note: “Since inflation requires an initial field value with a large displacement from its minimum, we therefore conclude that the theory of inflation requires finely tuned initial conditions.”

“Thus, under this measure, initial conditions that lead to significant inflation are indeed finely tuned.”

“It is therefore far from clear that inflation truly solves the fine-tuning puzzles that it was designed for.”

Paper. (paywall)

A number of popular science writers will not like this. They love to talk about a universe accidentally barfing itself into existence.

4 Replies to “Paper: Inflation doesn’t solve fine-tuning puzzles

  1. 1
    PavelU says:

    The fine tuning puzzle is resolved by the multiverses.

  2. 2
    EugeneS says:

    PavelU

    You must be joking.

  3. 3
    Latemarch says:

    This is one of those fake papers generated by computer…..isn’t it?

  4. 4
    Fasteddious says:

    I did not think Inflation was hypothesized to solve the fine tuning “problem”. Rather, Inflation was invented to solve the flatness and uniformity problem, wherein the known Universe is homogeneous and isotropic in space, despite the fact that one side has never been in contact with or even “seen” the opposite side. By smoothing everything out in a hyper expansion, the inflation hypothesis could supposedly account for those attributes of the Universe as we observe it. Of course, Inflation has numerous problems of its own, including additional fine tuning.
    Instead, it was the multiverse that was imagined to “solve” the fine tuning “problem”, in that we happen to be the one in a gazillion universes spewed out by some hyper-universe (with its own fine tuning) where the physical constants and initial conditions are suitable for the development of complex life. How those constants and conditions are assigned is left rather vague.
    In one version of the multiverse, it is the same inflation that burps out the gazillions of universes somehow. Of course there is zero hard evidence for either inflation or the multiverse, but that does not stop people from playing mathematical and cosmological games with each other.

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