Exploring The Discrepancies Between General Relativity And Scalar-Tensor-Vector Gravity Theory

General Relativity is, currently, the best theory to explain gravitational phenomena. Published by Albert Einstein in 1915, the theory found agreement with known astronomical observations, and it stated novel predictions that have been confirmed with great accuracy. Such predictions are actually groundbreaking: the bending of light, the existence of gravitational waves, black holes (yet to be directly confirmed), among others. The genius of Einstein cannot be overstated.

However, the theory is not perfect. On philosophical grounds, none mathematical representation of reality is perfect. But also physically, General Relativity fails to explain galaxy rotation curves, galactic bending of light, and cosmological data. Such discrepancies between the theory and reality can be solved if we assume the existence of the so-called dark matter. Most physics seem to rely on this hypothesis, but it has a serious drawback: although huge efforts, dark matter has not been directly detected.

In this context, it is at least reasonable to think of other ways to solve the problem. If we are not willing to assume the existence of dark matter, then we are forced to modify the laws by which gravity works, i.e. to look for a new theory of gravitation. This is a long enterprise that may be traced back to 1983, with the work of Mordehai Migrom and his MOND theory. Since then, several modified gravity theories have been proposed, and several have stayed behind.

One of the latest is Scalar-Tensor-Vector Gravity (STVG) theory, also referred as Modified Gravity (MOG). Published by John Moffat in 2005, the weak field limit of this theory predicts an enhanced gravitational attraction on the boundaries of galaxies, where phenomena related to dark matter use to happen and agrees with General Relativity inward. The behavior of this weak field limit served, for instance, to correctly describe galaxy rotation curves, galactic light bending, and the Bullet Cluster phenomena, without requiring the existence of dark matter.

The transition of a standard to enhanced gravitational attraction comes from the interplay between tensor, vector and scalar physical fields. However, this mechanism seems to work solely where gravity is weak. Close to black holes or other compact objects like neutron stars, the gravitational field is very strong and Moffat’s mechanism to retrieve General Relativity breaks.

Then, General Relativity and STVG also differ at the strong gravity regime. Such physical systems are key to compare both theories, and our work focuses on them: we found, for instance, that the proposed vector field leads to bigger and heavier neutron stars than General Relativity. On the other hand, the vector field would play a crucial role in the formation, collimation, and rotation of astrophysical jets, ejected by active galactic nuclei. Further, accretion disks around STVG black holes turn to be colder and underluminous than in the case of GR.

While we keep exploring the discrepancies between both theories, we anxiously expect the outcomes of strong gravity observations, headed by gravitational waves and the Event Horizon Telescope. They will have the last saying in this discussion.

These findings are described in the article entitled Effects of Scalar-Tensor-Vector Gravity on relativistic jets, published in the journal Astrophysics and Space Science. This work was led by Federico G. Lopez Armengol from the Instituto Argentino de Radioastronomía.

About The Author

Federico G. Lopez Armengol

I am on my fourth year of PhD on relativistic astrophysics, under the supervision of Prof. Dr. Gustavo E. Romero, at Instituto Argentino de Radioastronomía (IAR). My research goals involve testing General Relativity in the strong field regime. To that end, I am mainly involved with Numerical Relativity. I am also interested on Pulsar Timing Arrays, Modified Gravity theories, and foundational issues of space-time theories.

Comments (4)

  1. I would like to ask that you consider the following alternative gravity theory as regards dark matter. At the bottom of the page given in the link, there is also a discussion of gravitational lensing and how this theory deals with it.

    I think that at a certain galactic distance, gravity reverses and the galaxies begin pushing against each other. This would do away with cosmological expansion, dark matter, and dark energy. This is a claim that can be easily tested:
    A revised gravity equation looks like this (I have made an adjustment compared to my last version):

    F = (1.047 X 10^-17) m1m2 [-cos(Θ)] / r^2 where tan Θ = r / (1.419 X 10^22)

    By playing with the constants, this equation can be fitted and tested against the data of galactic motion. It means that at a certain distance, gravity will reverse and the galaxies will be pushing against each other. This pressure against each other does away with the need for dark matter or dark energy in cosmology.

    So the equation can be tested against current data to see if it fits. This equation also predicts that galaxies near the edge of the universe will be deformed — concave with the concavity pointing towards the center of the universe.

    This equation also predicts the existence of isolated galaxies that are far away from other galaxies, that would behave normally without the need to posit dark matter. An example of this type of galaxy is NGC1052–DF2 . Talked about in this article:

    https://www.nature.com/articles/nature25767?error=cookies_not_supported&code=fba64fb5-e843-4739-9f46-fedecc97e940

    So what I am asking is very precise, very narrow, very testable: Someone please test this equation to see if slight adjustment of the constants will account for galactic motion or not. If it does, then proceed to the rest of the theory.

    If it cannot, then the theory can be dismissed. Either way, I would like to know — but I would not be convinced with a simple “absurd!” or dismissal unless it has been tested out.

    If it is true that the motion of galaxies can be modeled in this way, I would ask that you take a look at the explanation in this theory:

    https://www.reddit.com/r/MyTheoryIs/comments/87pcgq/what_dark_matter_is/

  2. If space is mostly empty, wouldn’t it be easier to measure the emptiness to come up with a substantive equation of what something is?

    I always found that when trying to show what something is, it often helps to show them what, the thing you’re tying trying to teach, isn’t.

    Even in school, the teacher only seems to notice us when we don’t come to class.

  3. As Einstein’s relativity has been disproved theoretically (https://www.eurekalert.org/pub_releases/2016-03/ngpi-tst030116.php ), the speed of light becomes isotropic only in the reference frame moving with its medium i.e. aether which seems a compressible viscous fluid filling up the entire visible part of the universe.

    With the confirmation of the existence of aether and Newton’s mechanics, all so called unsolved problems seem easily explainable:

    1. The extra gravitation binding the stars in any galaxy is provided by the mass of aether;
    2. The accelerating expansion of the universe is the result of the high pressure of aether which pushes all galaxies away from each other, just like an exploding bomb in which its explosive high pressure gas pushes fragments away from each other in acceleration in its initial stage;
    3. Light bending and so-called “gravitational lensing” are actually the results of non-uniform distribution of the density and velocity of aether around massive celestial objects;
    4. Since aether is everywhere and participates in all physical processes, quantum mechanics is also a wrong theory as it does not take into consideration the effects of aether in all its studies physical processes;
    5. The wave of the wave-particle duality is actually the wave of aether, not misteric wave of probability which is a mathematical concept, not a physical existence;
    6. The phenomenon that the speed of light becomes slower in a heavier medium is caused by the higher density of aether in the medium;
    7. The speed of light is not the speed limit in the universe, which can be easily broken in a denser medium as shown by Cherenkov radiation; the reason that particles can’t break the speed of light in vacuum is because the particles are accelerated by electromagnetic forces which themselves are delivered at the speed of light;
    8. All electromagnetic phenomena are not governed by Maxwell’s equations, but by the equations of fluid mechanics for aether.

  4. Dark Matter is a problem in understanding how gravity works!

    The fundamental laws of atomic gravity are a good place to start. The 3 rules are so simple that high school students easily understand the principles confirming the simplicity by which nature works.

    The laws of atomic gravity interconnect the sciences and can be applied to any area of research or study providing a perfect platform for innovation.

    Seeking a mathematically adept wizard or group :::)

    The three principles of atomic gravity which define how the force of gravity works in quantum atoms are defined both visually and in mathematical relationships and yet the equation eludes the brilliance behind the physics. A mathematical mind is needed to claim the elusive equation of everything?

    Can this be you?

    If you are searching for a path to innovation within your field of study or research or perhaps you are just a mathematical brainiac then feel free to begin by exploring the google docs below.

    Principles of Atomic Gravity

    https://docs.google.com/document/d/e/2PACX-1vRTa9BoY64I0KsYrM1y7aRMONd7OrFm5RGIgPGA7PolB8hIXjF66azQOTu2yHWpl3uzw614aX6Ks-9q/pub

    Zero ‘G’ flight at the Atomic Scale

    https://docs.google.com/document/d/e/2PACX-1vRhOSAFyKb9r0kMaEGbLm-skalqF7UAXaqKQDq_RcJCWDAmOQCkbUvIIwih5DALMnqa6p7DzmQxAbzI/pub

    If I have seen further it is by standing on the shoulders of giants.
    — Sir Isaac Newton

    Nature did not deem it her business to make the discovery of her laws easy for us.
    — Albert Einstein

    Principles of atomic gravity are a North American innovation.

    If too busy to investigate the principles no worries floundering will turn to submersion as main stream beliefs slide down under. 🙂

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