Because gravity is a gauge theory with a noncompact gauge group-since the group of diffeomorphisms, which is the gauge group, is noncompact. It isn't known how to quantize gauge theories with noncompact gauge group, in general; more precisely, it isn't known what the quantum theory, whose classical theory is a gauge theory with noncompact gauge group, can be. The gauge theories that describe the other known interactions have as symmetry groups compact groups.

Out of this very technical detail of Stam,

Gravity applies to astronomical distances, and the quantum

To atomic distances.

Then ask yourself what would be the gain of

Unifying both, or how you could even imagine such thing.

Till you answer yourself that, no hope.

It depends upon the accuracy needed. Newton's gravity is good enough for our planetary exploits. For phenomena like the precession of the planet Mercury Einstein's gravity is needed. On Earth and the other planets there are surface areas where gravity is a little bit stronger or weaker because of matter densities below. We use Geology to analyze this on Earth.

Einstein has 10 partial differential equations for gravity that rarely can make exact calculations, but estimates can be used to come to close approximations that sometimes can be otherwise tested including by Newtonian gravity and observable movements. Getting the correct information into the equation can also sometimes be a formidable task.

@ Author of the question

The gravitation has been shown to be a n electromagnetic force, be sure, without any doubt without any doubt whatsoever. Read my published papers available on ResearchGate in my profile.

If you assume General Relativity as the best theoretical description of gravitational available presently( like I myself), it is impossible to quantize gravitation, simply because, according to this theoretical framework, gravitation IS NOT A FORCE! See, for example, the introduction at the text book( a very good one, indeed) by Nightingale and Foster, A Short Course on General Relativity

Dear All,

It's interesting that many people don't dare to simply think. Nature reveals everything about itself if we look at it properly. Instead, what we do is we foreground our subjective imagination, which is like sand for an ostrich to stick its head in.

Here is a theory that, in order to resolve the provability of the graviton, had to resort to metaphysics because current theoretical physics lacks an adequate conceptual background.

Article The existence of the graviton can be proven physically and m...

(Pg.2 )

I've known for about few days that the article has a slight philosophical flaw: because our Universe is a Multiverse. In this framework, the A Priory Entity is not compatible with the Entire Universe. Only on the elementary level seems good.

For days ago I already got the binary unity, which is the elementary a priori entity that we cannot demonstrate instrumentally with anything.

And solved with it a natural phenomenon which actually does not have such a simple explanation.

There will not be an article about it, but a video will be made about it on the Geo-intuition YouTube channel to reach ordinary people.

Regards,

Laszlo

Quantizing gravity is difficult because, unlike other forces, gravity is not considered a force acting on spacetime; instead, it is a manifestation of the curvature of spacetime itself, making it challenging to reconcile the quantum mechanical concept of particles with the continuous nature of spacetime curvature described in general relativity; this leads to mathematical inconsistencies and problems with renormalization when attempting to quantize it.

The thread question

“Why is it difficult to quantize gravity?

- really is questionable, really correct question would be as “Why is it impossible to quantize gravity provided that the GR is true??

The scientific answer is:

- that happens because, first of all, that in QM the “kinematical” space coordinates X,Y,Z are in purely kinematical empty flat space, that fundamentally hasn’t any dynamical properties, so are also the corresponding operators, while the “dynamical" operators, first of all momentum operators, are derivatives by the space coordinates proportional to ∂/∂X,YZ,

- while in the GR spacetime points’ X,Y,Z have both – kinematical and dynamical properties.

So innumerous attempts “to quantize GR” correspondingly logically inevitably resulted only in some speculative theories.

Though in this case there is a specific difficulty - though Gravity fundamentally is nothing else than some fundamental Nature force – as that the other known [and so well “quantized”] Weak, Electric and Nuclear/Strong Forces are, and

= while, as that rigorously scientifically rationally shown in the Shevchenko-Tokarevsky’s Planck scale informational physical model, two main papers are

https://www.researchgate.net/publication/354418793_The_Informational_Conception_and_the_Base_of_Physics, [in this paper section 2.9 “Mediation of the forces in complex systems” can be passed since this is more comprehensively given in section 6.“Mediation of the fundamental forces in complex systems” in other paper below] , and

https://www.researchgate.net/publication/383127718_The_Informational_Physical_Model_and_Fundamental_Problems_in_Physics

- the Mater’s spacetime is fundamentally absolute and fundamentally by

No means can be impacted by/impact on anything in Matter,

- Gravity is extremely weak Force, and so really seems in Matte at all, and for humans for sure, it is impossible to make/observe some QM gravitationally coupled system, say, some ” gravitational atom” with distant energy levels, etc. If that would be real, rather probably now in physics there would not be the GR theory.

Nonetheless quantum nature of Gravity rather probably can be observed in proposed yet in 2007 on Earth interferometer experiment with photons , more see

https://www.researchgate.net/publication/215526868_The_informational_model_-_possible_tests at least the section 2.1.2. “Monochromatic photon beam distortion”

More about what is Gravity [and Electric and Nuclear Forces also, though] Force see the section 6 above, series of SS posts in

https://www.researchgate.net/post/NO47What_is_Force_a_Field_Where_is_the_Force_Field_How_does_it_appear_Is_the_Force_Field_a_Regulating_Effect_of_the_Energy-Momentum_Field

contain SS comments that clarify some points in this case.

Cheers

This issue is analyzed in this paper with respect to the electromagnetic nature of the elementary particles of which all masses are made:

Article Our Electromagnetic Universe (Expanded republication PI)

Foundations of a theory of gravity with a constraint and its canonical quantization

https://doi.org/10.1007/s10701-021-00521-1

The scientific answer to the thread question see in SS post on page 1.

Besides here - an example how Gravity quantum nature reveals itself in cosmology see short paper “The Informational Physical Model: Detection of Dark Matter Particles”

https://www.researchgate.net/publication/388922029_The_informational_physical_model_detection_of_dark_matter_particles

Cheers

Quantizing gravity is difficult because General Relativity (GR) is a classical, geometric theory, while Quantum Mechanics (QM) relies on probabilistic wavefunctions. Unlike other forces, gravity is tied to spacetime itself, making it non-renormalizable at high energies—leading to infinite, uncontrollable divergences in calculations. Additionally, the lack of direct experimental data at quantum gravity scales further complicates the development of a consistent theory. Sincerely IJAZ

Have you ever sensed something quantized

About gravity? No? Its not needed!

The quantum nature of Gravity is rather well sensed in the problem of detection of dark matter particles – see SS post above;

- and becomes be really critical problem at description of what happens in exotic physically, but quite non-exotic in Matter “black holes” – not, of course in the GR holes in the spacetime; what are the BH really see section “Cosmology” in https://www.researchgate.net/publication/383127718_The_Informational_Physical_Model_and_Fundamental_Problems_in_Physics.

Though even yet in neutron stars Gravity possibly is tangible, and by some ways forms partially the stars structure.

Cheers

Maybe the effective quantum theory of gravity below the Planck scale is possible (see e.g. arXiv:2403.09487), while the quantum gravity at the Planck scale is still unclear.

The scientific answer to the thread question see in SS post on page 1; some comments in some specific cases see in SS posts on this page.

Recent SS posts in https://www.researchgate.net/post/Why_arent_scientists_trying_to_come_up_with_alternative_theories_of_Gravity_as_a_universal_manifestation_beyond_Einsteins_General_Relativity/12

https://www.researchgate.net/post/Can_it_be_argued_that_GR_must_be_only_an_interim_theory_of_gravity , page 1, and

- the updated version V2 of the preprint “The informational physical model: detection of dark matter particles” in https://www.researchgate.net/publication/388922029_The_informational_physical_model_detection_of_dark_matter_particles ,

- are relevant to this thread question.

Cheers

Lets wait till we get some hard empirical data.

Not mumbo jumble speculation.

Solve the problem of gravitational divergence and complete the theory of quantum gravity! and I'd like you to read it.

While major frameworks like Effective Field Theory (EFT) and String Theory address the challenges of quantum gravity through parametrization or new fundamental entities, this paper introduces a new framework, Sphere Theory, built upon the single physical principle of gravitational self-energy. This framework provides a physical UV completion for the perturbative approach to quantum gravity. We assert that its synthesis with EFT, the most successful of these models, constitutes a complete, predictive, and testable theory of quantum gravity. Our analysis is built upon the principle that the effective source of gravity is not the free state mass (M_fr), but the equivalent mass (M_eq), which includes its own gravitational self-energy. This principle leads to the conclusion that the equivalent mass (M_eq) vanishes at a critical scale R_gs ∝ G_N/M_fr/c^2, which in turn defines an effective running gravitational coupling G(k) that is driven to zero, providing a self-renormalization mechanism that suppresses divergences at their source. This unified mechanism provides coherent, physically-grounded solutions to several foundational problems:

1) Resolves the singularity problem via a repulsive force that emerges at a macroscopic, not quantum, scale (Section 2, 3, 4.5).

2) Solves the non-renormalizability of gravity, as exemplified by the 2-loop divergence of Goroff and Sagnotti, by demonstrating that the interaction is dynamically turned off at a critical scale (Section 4.6.3).

3) Resolves the unitarity crisis in high-energy graviton scattering by showing that the scattering amplitude naturally vanishes as the physical source of the interaction is quenched (Section 4.9).

4) Provides the physical origin of the UV cutoff for quantum field theories, demonstrating that the gravitational self-energy of force mediators (e.g., photons, gravitons) dynamically suppresses their propagation at the Planck scale (Section 4.7~ 4.9).

5) Resolves the divergence and the Landau pole problem in QED, transforming it into a potentially fundamental theory by providing a physical cutoff mechanism rooted in the gravitational self-energy of the photon (Section 4.8).

6) Provides a UV completion for EFT. It resolves divergence problems arising in (1)the gravitational potential between two masses and (2)the bending of light. This approach also renders the infinite tower of unknown EFT coefficients (c_i) unnecessary and makes a novel, falsifiable prediction of a "quantum-dominant regime” (Section 5).

7) Offers a unified explanation for major cosmological puzzles by providing (1)a mechanism for cosmic inflation, (2)a model for the universe's accelerated expansion}, and (3)a predicted upward revision of the neutron star mass limit} (TOV limit) (Section 9).

8) Finally, it culminates in a declaration that the synthesis of EFT and Sphere Theory constitutes a self-consistent and testable framework for quantum gravity, providing a consistent description from the lowest to the highest energy scales (Section 10).

Since the paper is long, I have written a summary. Please read the article in the following link for the summary.

https://www.reddit.com/r/NegativeMassPhysics/comments/1lox9li/sphere_theory_beyond_string_theory_completing/

Preprint Sphere Theory: Completing Quantum Gravity through Gravitatio...

Dear Hyoyoung Choi ,

Excuse me for the only shortly remark:

At first glance, your theory is clearly baseless, as it relies on a physical reality that cannot be directly verified. This violates a fundamental principle of classical Chinese philosophy, which states:

Direct experience is worth more than what we see, and what we see is worth a hundred times more than what we hear.

Regards,

Laszlo

Dear László Attila Horváth

Your entire claim is bullshit.

The mass defect due to binding energy is a proven fact in particle physics and astrophysics. Also, Sphere Theory is based on equivalent mass. Thus, the theory is grounded in clear physical realities. In other words, Sphere Theory is not based on physical phenomena at the Planck scale but on mass defect and equivalent mass. Therefore, your criticism is not valid.

Sphere Theory offers testable predictions near the Planck scale, though we have not yet reached the technological capability to test at this level. (Section 5)

Predicting something that is currently technologically unverifiable does not make it baseless, as such a your claim is not logically sound. Predictions are made by leveraging other physically verified phenomena. Moreover, just because something is currently technologically unverifiable does not mean it is not a valid subject for scientific research. There are countless examples in science where phenomena, initially unverifiable due to technological limitations, later became testable as technology advanced.

It’s laughable that you’re using some random saying you picked up somewhere as the foundation of your argument.(This "violates" a fundamental principle of classical Chinese philosophy 百聞不如一見. 百見不如一行 )

Existing quantum gravity models reside in domains that are technically challenging to verify. However, Sphere Theory is different.

Sphere Theory applies across scales, from the Planck scale to cosmological scales, enabling verification through cosmological phenomena as well.

The core of the Sphere Theory, R_gs, is proportional to mass or energy.

R_gs ∝GM/c^2

Its critical radius R_gs, is not a fixed constant but a dynamic variable proportional to mass (R_gs ∝ GM/c^2). This inherent scalability means the theory's core principle applies from the quantum fluctuations at the Planck scale to the observable universe.

If the radius of the mass distribution, R_m, is smaller than R_gs, the system enters a negative mass state, resulting in the presence of anti-gravity. Consequently, the mass distribution undergoes accelerated expansion.

Applying this to the observable universe, since the R_m of the observable universe is smaller than the R_gs created by its mass and energy, it exists in a negative mass state, leading to accelerated expansion. (Section 7.2.2~ 2) The origin of cosmic acceleration from gravitational self-energy)

Observable universe R_m=46.5BLY

Observable universe R_gs=275.7BLY

Accelerating expansion : R_m