1. Introduction
General Relativity, a form of spacetime
geometrization, is derived by utilizing two fundamental conditions: the
equivalence of inertial and gravitational masses, and the principle of least
action [
1]. On the other hand, it is also true
that the equivalence of inertial and gravitational masses corresponds to
imposing the covariance of the classical equations of motion in curved
spacetime. In this sense the general Relativity can be conceptualized as
classical spacetime geometrization consequent to the minimum action principle.
If, instead of the covariance of the classical motion equation, we assume the
covariance of quantum mechanical motion equations for the mass distributions
we obtain the spacetime geometry consequent to the
presence of quantum bodies.
This can be achieved by utilizing the Madelung
hydrodynamic representation of quantum mechanics [
2,
3,
4]
that transforms the quantum equations (such as the Schrodinger or the
Klein-Gordon or the Dirac ones) as a function of the field
in a system of two equations as a function of the
real variables: and .
This transformation for the Klein-Gordon equation
(KGE)
leads to [
5] the
motion equation
coupled to the conservation equation
that gives rise to a classical-like description
where the mass density
owing the hydrodynamic impulse
is subject to the additional non-local quantum
potential interaction
conceptualizing (3) in the form
If in the non-relativistic limit where (2) reduces
to the Schrodinger equation, Eq. (3) reduces to the classical equation of
motion [
4]. In the quantum case, analogously
to the general relativity procedure, by imposing the covariance of (3) in
curved spacetime we can utilize the minimum action principle to obtain the
geometry of spacetime subject to the quantum physics.
As shown in ref. [
5,
6]
minimum action condition
in the quantum hydrodynamic representation can be expressed
as
where
is the quantum hydrodynamic Lagrangian density
given in ref. [
2].
Furthermore, by comprehending the contribution coming from the spacetime
curvature,
the overall minimum condition
defines the quantum gravity equation (QGE) [
5,
6]
where
in (10) is explicitly derived as a function of the
quantum hydrodynamic Lagrangian density
in ref. [
5].
For the particular case of interest, of the
macroscopically stable state (stationary energy eigenstates [
7]),
reads
Therefore, as shown in ref. [
5], in the macroscopic weak gravity limit (10) acquires the form
where the energy tensor density
reads
where
is the metric tensor, where
and where
Furthermore, by defining
and
the wavefunction of the particle and antiparticle. respectively, it follows that
and
Moreover, by utilizing, in the low curvature limit (Newtonian gravity), the KGE expression
(15) reads
It is interesting to note the quantum nature of Eqs. (13,17) in the presence of not-null off-diagonal terms, as pointed out by the non-commutative field theory [
8].
Given the physical description of antimatter provided by quantum mechanics, the gravity equation (10) naturally incorporates it into gravitational theory. Consequently, performing the (non-relativistic) weak gravity limit of (10) yields the Newtonian forces for both matter and antimatter.
To derive the macroscopic Newtonian gravity of matter and antimatter, it is necessary to disregard the quantum contributions performing the limit
from which we have [
5]
and
Moreover, we have to impose the conditions for the establishing of low energy non-relativistic limit [
7]
leading to the identity
that introduce into (17) leads to
where is the velocity field.
Therefore, from (23) the weak gravity limit of QGE reads
leading to the trace identity
Thus, in the particles reference system where
2. The Antimatter Newtonian Field
Given the Newtonian gravitational potential
, as a function of the component
of the metric tensor [
9]
whose trace, at zero order, reads
it follows that
Therefore, given that
and, thence,
it follows that the antiparticle mass density is equal to that of the particle mass density and the Newtonian gravity of antimatter is equal to that of matter.
3. Newtonian Gravity at Short Distance Between Two Quantum Bodies
The results (29-32) are valid as far as the wave function localization produces a mass distribution that is satisfactory well described for distance much larger than the quantum mass density distribution of particles respect the scale of the problem (for instance by the Dirac’s delta typical of the classical macroscopic approach). On very short distance, when the physical length of the problem is of order of the quantum body mass distribution, the gravitational interaction is influenced by the effective form of the quantum mass density distribution .
Here we consider the case of quantum bodies (sufficiently large) to be described by continuous fields. Furthermore, the gravity interaction is derived by assuming the particle densities are very much lighter than the Planck mass in a cube of Planck length side, so that (at zero order of approximation) the spacetime can be assumed Minkowskian. Then, the gravitational force is derived by the first order curvature produced by such mass distributions.
Therefore, we are in the position to derive the gravitational potential of a particles as deriving by the curvature induced by its mass distributions
through the gravity equation
Here, for sake of completeness, we also re-consider the contribution that can come from the quantum pressure term
where the cosmological-like term
, given in ref. [
5], reduces to a small constant in quasi-Minkowskian spacetime approximation [
10]. Therefore, Equation (33) for the non-relativistic case, where
, leads to
Furthermore, by using the identity
it follows that
leading to the gravitational potential
where, we can recognize the classical and quantum parts that read, respectively,
It is worth noting that the quantum contribution (39) becomes larger smaller the particle mass
leading to the asymptotic expression for infinitesimal mass
From (40) it is important to highlight that, to prevent gravitational energies from diverging, the mass of particles cannot decrease continuously to zero but must be quantized with minimum values. This implies the existence of elementary particles with discrete mass values and the necessity of quantizing their fields, pointing to a gravitational constraint that drives field quantization. Furthermore, this hypothesis supports the notion that only fields require quantization, while gravity itself, as defined by the left side of gravitational equation (10), becomes indirectly a quantum operator through the equivalence to the quantized fields on the right side of (10) [
11].
4. Discussion
Quantizing particle masses to avoid gravitational divergences is a compelling topic in theoretical physics, with ongoing research exploring its implications. Some nonlinear field theories propose that gravity could play a pivotal role in the formation of elementary particles, suggesting the existence of regular solitonic solutions that can be interpreted as particles with discrete masses [
12].The stability and discreteness of masses might be a consequence of intrinsic gravitational constraints.
Despite this, quantum gravity remains a non-renormalizable theory, meaning that it cannot fully eliminate divergences to yield finite results, in contrast to renormalizable frameworks like the Standard Model. The Higgs field, while providing mass to elementary particles such as quarks, electrons, neutrinos, and the W and Z bosons, has no direct connection to the gravitational field.
However, certain models suggest that quantum effects in gravity might influence the discretization of black hole masses, implying the existence of a minimum mass required for their formation [
13].
The quantum contribution of the gravitational field, arising from quantum potential energy, is characterized by a term
inversely proportional to the particle mass that is also present into the quantum potential expression in (5) that, for weak Newtonian gravity, takes the form:
This term diverges as the particle mass approaches zero. However, it can remain constant if we increase the delocalization of the particle state, thereby reducing the spatial density term
. Moreover, since particle delocalization can extend up to the maximum elemental spacetime cell, corresponding to the lowest possible gravitational curvature and tied to a minimum critical value of the cosmological constant [
14], below this critical value, the presence of a smaller mass density would cause spacetime to collapse into a polymeric-like, non-metric state.
Thus, in physical spacetime, particles with vanishing rest mass are not permissible, while the presence of discrete mass particle in spacetime stabilizes it in the metric physical state.
If elementary particles with continuously decreasing mass were possible, the universe's outer regions could become infinite, making possible additional large discrete spacetime cells at will (with practically null mass inside). Conversely, if only particles with finite mass, resulting in cells of minimum curvature, can exist, the external horizon of the universe could assume a finite extension. Beyond this horizon, the void spacetime would collapse into a polymeric phase lacking metric structure.
Similar principles are observed in black hole physics, where a critical density is linked to horizon formation. Analogously, the critical cosmological constant value, connected to mass discretization, might define a boundary separating the metric spacetime from its non-metric counterpart.
5. Conclusion
By employing the quantum spacetime geometrization, which describes gravity in spacetime with quantum bodies, the weak gravity limit of the Newtonian potential for antimatter is theoretically demonstrated to be identical to that of matter, even when the mass and energy of antimatter assume negative values. The theory also reveals additional weak gravity contributions that arise directly from the quantum nature of spacetime, exhibiting dependence on the quantum mass density distributions. .
The quantum contribution to gravity, stemming from the energy of the quantum potential, reveals that a continuous spectrum of mass in elementary particles approaching zero would lead to a diverging gravitational potential energy, thereby justifying the fields quantization and enforcing a discrete spectrum of elementary particle masses. The emergence of discrete masses driven by gravitational principles has profound implications for the nature of our universe. It aligns with the concept of a fundamentally quantized reality, where discreteness is an intrinsic and necessary property, shaping time, space, matter, their origins, their extent, and their ultimate end.
Funding
This research received no external funding.
Data Availability Statement
The original contributions presented in this study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author(s).
Conflicts of Interest
The author declares no conflicts of interest.
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