There is nothing wrong in particular with the idea of fine tuning. This
does not logically imply a fine tuner. If there is a fine tuner, then it is
reasonable to say there is fine tuning. However, the converse or modus
tolens does not hold; fine tuning does not logically imply a fine tuner.
Therefore, fine tuning is a necessary condition of a fine tuner, but not
sufficient.
I started reading this, but it is clearly not something I am going to
finish over early morning coffee. Yet the article so far covers in layman's
terms stuff I am well acquainted with. The multiverse is often cited as a
way around this. A vast plurality of cosmologies is a way to argue how the
particular observable cosmos is fine tuned. It is similar to the argument
with planets; given a large number of them it is not surprising that a few
are such that life may emerge. Of course with this multiverse I suspect
that many of these are not real cosmologies.
The cosmological constant for all putative cosmologies in the string
landscape, based on D-brane theory with gauge fluxes through branes wrapped
on Calabi-Yau spaces, have cosmological constants Λ much larger than that
for the observable universe. The Hubble constant H = (a'/a), a the scale
factor and a' = da/dt, also equals H = √(Λc^2/3) is numerically H =
72km/sec-Mpc and 68km/sec-Mpc, where these two come from galaxy data and
CMB data. This corresponds to a cosmological constant Λ ≃ 10^{-52}m^{-2}.
Most putative cosmologies have much larger values, and many orders of
magnitude larger. Such a de Sitter or FLRW spacetime would expand so
rapidly that nothing could form. In fact many have Λ ≃ 10^{66}m/s^2 with
the upper bound Λ ≃ 10^{70}m/s^2. The difference between this and what we
observe is the 122 order of magnitude issue.
The observed cosmological constant is a manifestation of the quantum vacuum
energy density, or in particular that vacuum energy density that plays a
role in gravitation. This vacuum energy ρ defines the cosmological constant
Λ = 8πGρ/3c^3 and for the observable universe this is quite small, far
smaller than the 123 order of magnitude larger figure a naïve summation of
QFT modes would suggest. However, there is a difference between the high
energy vacuum, or called false vacuum, and the low energy physical vacuum.
A quantum tunneling from the false to physical vacuum results in a gap of
mass-energy density in every volume of space, and this generates matter and
radiation. The sort of skewed Ginsburg-Landau potential involved is seen in
the figure below.
[image: quartic asymmetric potential.png]
There is a linear term in fields that skews this, and this I think is some
manifestation of renormalization theory, where the large majority of these
are analogous to virtual particles that give a mass-renormalization of
cosmologies. This would I think sweep the vast majority of these out of
ontological existence or classicality. I do not know if this is complete so
there is the reduction of the multiverse to a single universe, or whether
this is a reduction of the multiverse to a much smaller set.
It has to be noted that the tuning for flat, spherical or hyperbolic
geometry or topology of a spatial surface is not that hard to understand.
The Hamiltonian for the Friedman-Lemaitre-Robertson-Walker (FLRW) spacetime
is
ℋ = ½(a’/a)^2 - 4πGρ/3c^2 + k/a^2,
so that the Hamiltonian constraint Nℋ = 0 in ADM general relativity means
it is not hard to see this is zero. The energy density is ρ = ρ_vac +
ρ_energy for the vacuum and mass-energy in the spacetime. The additional
term k/a^2 gives flat, spherical and hyperbolic space for k = 0, k = 1 and
k = -1. If k = 0 then the vacuum energy density is constant. This is in
various ways more reasonable.
In this renormalization possibility somehow the observable universe may
have emerged. In ways not entirely clear this may have selected the world
we observe. So there are open questions. Maybe even the role of conscious
observers in the universe play some Wheeler delayed choice experiment in
measuring the early universe to select for the observed universe.
LC
On Wednesday, October 14, 2020 at 9:38:40 PM UTC-5 Jason wrote:
> I just finished an article on all the science behind fine-tuning, and how
> the evidence suggests an infinite, and possibly complete reality. I thought
> others on this list might appreciate it:
> https://alwaysasking.com/was-the-universe-made-for-life/
>
> I welcome any discussion, feedback, or corrections.
>
> Jason
>
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