The search for quantum gravity begins with adopting an intrinsic geometry in which Einstein’s field equations are interpreted as describing curved world lines in flat space-time. By adopting this interpretation, one can start embarking on an alternative path to quantum gravity since QFT is a theory built on flat space-time and has curved lines that appear as a sum over histories in the Feynman interpretation of QFT. Moreover the Ricci curvature tensor in GR is the average of the possible paths a test particle can take in a gravitational field. That is, given two vector fields
and
,
This statistical view which is analogous to thermal diffusion provides an intuitive glimpse in which Hamilton’s Ricci Flow
[
21] plays an important role in the formulation of quantum gravity. In the subsequent section, we introduce the Ricci Flow and its basic properties which will play a pivotal role in the formulation of a self-consistent model of QG.
2.1. Hamilton’s Ricci Flow
In 1982 Richard Hamilton introduced the concept of Ricci flow [
22]. In a Riemannian manifold
, the Ricci Flow is partial differential equation that evolves the metric tensor
where denotes the Ricci curvature of the metric . The time evolution of the metric under the Ricci flow spreads the curvature evenly through space. It should be noted that the
Ricci Flow also includes a quadratic reaction term which will be included later in the work.
In compact Einstein manifolds the Ricci Flow is expressed as follows:
where
is the Einstein tensor,
the speed of light and
the Hubble radius. Compact Einstein manifolds have the form
In GR with the cosmological constant
, the compact Einstein manifold assumes the form
Therefore, vacuum solutions of Einstein’s field equations are compact Einstein manifolds with proportional to the cosmological constant. The above equation describes a Ricci soliton of De Sitter topology and is divergenceless. That is where , is the Einstein constant and is the dark energy density. Here we have a packet of localized vacuum energy in the form of a Ricci soliton in which the energy
conservation holds. In other words, the Ricci soliton is a self-gravitating gravitational field.
2.2. Space-time Quantization
In the Nexus Paradigm of quantum gravity, we begin the quantization process by considering a large but finite patch of Minkowski space equipped with a non-degenerate symmetric bilinear form on the tangent space. We adopt a local coordinate system to avoid the need of an origin as well as point like events which are the sources of divergences in QFT. The local coordinate system makes the Minkowski space a displacement vector space. The inner product is therefore
Upon multiplying the right side we note that to get all the cross terms such as
to vanish we must assume
The above conditions generate a Clifford Algebra which implies that the coefficients
must be matrices, specifically the Dirac gamma matrices. These matrices are square roots of the Minkowski metric
Thus the displacement vectors
reside in Clifford space
implying an intrinsic quantized spin and can be perceived as Dirac 4-vector matrices analogous to the Pauli vector matrices. They
are also quantized wave packets of space-time and can be expressed as Fourier integrals as follows
Where
Here
is the Hubble radius,
=
are Bloch energy eigenstate
functions in which the four wave vectors assume the following quantized values
We set a high energy cut off limit at
the Planck 4-length since no measurement can be obtained below this length
without the creation of a black hole and the low energy cut off limit being the
Hubble 4-radius since no information can be obtained beyond the cosmic horizon.
The
states arise from the ratio of Hubble
four radius to the Planck four length.The Bloch functions in each eigenstate of
space-time generate an infinite Bravais four lattice.
The
conjugate momentum for the displacement vectors is
Where
is the four momentum of the ground
state
The wave packet is essentially a particle of
four-space and can be envisioned as enveloping a spherically symmetric lump of
energy from the quantum vacuum. This vacuum energy can be in any form of the
fields described by the Standard Model of particle physics.
We seek to find the relationship
between these wave packets of spacetime and the Ricci soltions of Eqn.(4).
First we determine the norm squared of the four momentum of the
-th state wave packet . We compute
this norm by multiplying the inner product of Eqn. (10) by the square of the
reduced Planck constant
where
is the Hubble constant. We
then express Eqn.(12) in terms of the cosmological constant,
as
From Eqn. (13), the wave packet can be considered
as a compact Einstein manifold or a trivial Ricci soliton of positive Ricci
curvature expressed in the form
Clearly Eqn. (14) depicts a
self-gravitating Ricci soliton and as explained in Refs: [
23,
24,
25,
26] this is DM which is a
localized packet of vacuum energy
in the
-th quantum state. Thus DM is a Ricci
soliton and should exhibit the following soliton characteristics
It is a localized lump of (vacuum) energy
It preserves its form while growing or diminishing in size
It preserves its speed and form after collision with another soliton
The lowest quantum state from
Eqn.(10) occurs when
suggesting that for Eqn.(14) to
become Ricci flat in this state, a Ricci soliton in the ground state must be
removed from the right side yielding Einstein’s vacuum field equations in the
quantized spacetime as
The above equation depicts a decay
mechanism in which a high energy graviton emits a ground state graviton to
assume a low energy quantum state. The force exerted by the emission process
can be computed via the Uncertainty Principle. We consider the ground state
graviton as having a temporal interval
equal to the Hubble time and a
spatial interval
equal to the Hubble radius
This implies that the mass of the
ground state graviton is
which in 3D space is
and the graviton induced
acceleration is
. Thus a spherical volume of space
containing a dark energy mass
within a radius
will always generate a constant
outward acceleration of
. This acceleration was first
empirically observed by Milgrom from data on galaxy rotation curves [
27]. As noted by Milgrom,
non-Newtonian dynamics begins to manifest at this critical acceleration. This
critical acceleration therefore marks a transition from the classical to the
quantum gravity regime.
If the graviton field is perturbed by
the presence of baryonic matter then Eqn. (15) becomes
From Ref.
[
23]
the solution to Eqn. (14) is
computed as
The above metric equation describes
curved worldlines in flat spacetime and has no singularities nor divergencies.
At high energies which are characterized by microcosmic scale wavelengths of
the graviton and high values of
, the worldline is rectilinear and
the local coordinates are highly compact or localized. This aspect also reveals
asymptotic freedom in quantum gravity since for high values of
, gravity (world line curvature) vanishes
asymptotically. Thus at high energies, graviton-graviton interactions are
non-existent due to the absence of curvature. The worldline begin to deviate
substantially from a rectilinear trajectory at low energies where the uncertainties
in its location are large and the associated graviton wavelengths are at
macrocosmic scales. In the ground state of spacetime
we notice that the metric signature
of Eqn. (18) becomes negative and that the worldline is rectilinear.
If we compare the quantized metric of
Eqn. (18) with the Schwarzschild metric we notice that
This yields a relationship between
the quantum state of space-time and the amount of baryonic matter embedded
within it as follows
Equation (20) shows a family of concentric black
hole like spherical surfaces of radii
with corresponding orbital speeds
. The innermost stable circular orbit occurs at
or at half the Schwarzschild radius implying that
in the Nexus Paradigm the event horizon is half the size predicted in GR. The
square term on the left makes it imperative that the mass term on the right
remains positive regardless of the positive or negative vibrational modes of
space-time explicit in Eqn.(10). This resonates well with the positive mass
theorems [
28,
29]. However, the argument
presented here is more direct and is a consequence of the quantization of the
gravitational field.
Evidently, the Ricci soliton arising from Eqn.(20)
has an anti-De Sitter topology and to differentiate it from a Ricci soliton of
De Sitter topology we label its quantum state as
. We can now replace the stress –momentum tensor in
Eqn.(17) and express the equation as
Here are the complete Einstein’s
field equations expressed in purely geometric terms as a compact Einstein
manifold. For any quantum state
in which a Ricci soliton has constant
curvature , energy is conserved. The right side is a symetric tensor expressing
the quantum/energy state of spacetime. The left side is a form of a laplacian
that averages the paths taken by a test particle in a gravitational field of
quantum state
.
The linearized Eqn.(21) is solved by
expressing it as another Ricci soliton in the
-th quantum state yielding the
equation
The above equation has a solution
Here
where the terms on right represent
the baryonic mass, the DM mass and the DE mass enclosed inside a sphere of
radius
. This yields a metric equation of
the form
where
and
The above metric equation leads to
the following equation for gravity
The dynamics become non-Newtonian when
Substituting for
in Eqn. (26) yields
This is the Baryonic Tully – Fisher relation.
Condition (26) reduces Eqn. (25) to
From which we obtain the following equations of
galactic and cosmic evolution