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Gravity of Dark Matter - matters?

  1. Jan 12, 2014 #1
    Simple logical observation dictates that our sun (for example) would gravitationally attract Dark Matter to the sun's center of gravity because DM is "gravitationally attractive". What is the value of the gravitational component of dark matter between the center of gravity of the sun and earth? Whatever the Dark Matter component is it would require a slight modification of Newtons laws. This would be evidenced by additional "acceleration toward the sun" or gravity as a probe exits the solar system and experienced more gravitational attraction the Newton laws would predict. This is a prediction that can't be tested at this time, as far as I know, but it seems predictable. Is there a reference to this? Also DM would fall into black holes undetected but would have effect on Black Holes but what that effect be? Dark Matter is gravitationally attractive but not reactive to to matter or energy or the weak force. Two experiments so far show no evidence WIPS
    Last edited: Jan 12, 2014
  2. jcsd
  3. Jan 12, 2014 #2
    Did not finish statement (iPad slip). Do not know how to delete right now. Pardon my slip :-)
  4. Jan 12, 2014 #3


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    Dark matter rarely interacts with other matter, so it does not accumulate in stellar cores. It just yo-yo's back and forth through massive objects. It tends to spend most of its time in halo's surrounding massive objects. In the case of black holes, things are a little different. Dark matter that enters the event horizon will not escape, however, very little dark matter actually falls into black holes. Only those DM particles on a bullseye trajectory can be captured. Unlike normal matter, it cannot form an accretion disc and be eaten at leisure. It cannot shed kinetic energy via collisions or friction with other particles, so, a miss is as good as a mile and the DM particle continues on its merry way - its path is bent, but, not broken.
  5. Feb 4, 2014 #4
    Dark matter and normal matter both share gravity as a feature. Right?
    Therefore both dark matter and normal matter follow the grvitational curvature of the space they occupy. Dark mater and normal do not interact with each other but both are effected by gravity. Therefore it is logically constant to conclude dark matter and normal matter are attracted by the sun's gravity. What is wrong with that logic given the assumption that standard accepted science gives us - dark matter has gravity.

    Dark matter does not interact with normal matter but they both obey the law of gravity. Accretion disk and GammaRay burst of black holes are features of electromagnetism therefore do not effect dark matters task of following the local gravity field. With nothing in the way of dark matter - logically speaking more dark matter than normal matter would cross the event horizon.

    We can have different perspectives but we can not have different facts or escape logic. The facts I refer to follow scientific standards and logic is logic so please explain your logic and facts.
  6. Feb 4, 2014 #5


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    You are clearly not understanding. Dark matter IS attracted to the solar core, but so what? It doesn't STAY there. You need to re-read Chronos' post.
  7. Feb 4, 2014 #6


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    We can calculate about how much dark matter there is in the solar neighborhood and how it affects the gravity of the sun. The density of dark matter in the solar neighborhood is believed to be about 1GeV/cm^3. If it is a uniform density then there is about 1E15 g of dark matter interior to the Earth's orbit. The sun's mass is 2E33 g, so the dark matter is completely negligible. As others have said, there is no effect to cause the dark matter to clump up anywhere in the neighborhood of the sun - it just falls in and passes right through the sun.
  8. Feb 6, 2014 #7
    Apologies for chiming in, but just to get it straight, dark matter only lives by the law(s) of gravity?
  9. Feb 6, 2014 #8


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    I don't know what that means. Dark matter is an unknown particle or particles (probably ... we don't even know that for sure) and certainly obeys all of the laws of physics. It only interacts with other matter ("normal" matter AND itself) gravitationally. It might, or might not, interact very weakly in other ways, like, for example, neutrinos.
  10. Feb 6, 2014 #9
    So whatever dark matter is, it doesn't 'see' the bosons, just the curvatures of GR?
  11. Feb 6, 2014 #10


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    Dark matter hardly ever interacts anything, meaning it hardly ever participates in annihilations or other events that leave physical evidence of its existence - save that it has a gravitational influence on ordinary matter. This is only detected on large scales, like galaxies. We do not know if it has the same gravitational influence, or susceptibility, as 'normal' matter. We assume it consists of particles, like 'normal' matter', but, that is only a guess. We have not yet clearly detected any such constituent particles, although efforts have been underway for decades. Observational evidence indicates it behaves like some sort of fluid that collects in giant, diffuse clouds that serve as gravity wells for large scale structure formation. Scientists have mapped the apparent distribution of dark matter around galaxies and clusters of galaxes in what is called the cosmic web. We do not detect high concentrations of dark matter, like invisible stars or galaxies, hence, we deduce it is 'collisionless' - meaning it does not shed kinetic energy via friction, or 'clump' with other particles - including those of its own kind. It's like a very, very slowly dissipating, immiscible liquid drifting through space forming gigantic, tenuous filaments.
  12. Feb 6, 2014 #11
    Thank you for your description of dark matter. I saw that there was evidence or assumptions addressing my concerns.

    From your description it looks to me: Hypothetically; dark matter would need to create gravity 90 degrees out of phase with normal gravity. That way normal matter gravity pushes dark matter away from the center of gravity of normal matter. As normal matter gravity becomes asymptotic to zero then dark matter gravity falls in line with normal matter gravity thus increasing the gravity between stars. Stars and black holes would clear out dark matter from their gravitation field. All the other dark matter features seem to addressed - hypothetically
  13. Feb 6, 2014 #12


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    Huh?? It sounds like you've missed the point completely. Dark matter behaves just like ordinary matter with respect to gravity, both in the way it creates a gravitational field and in the way it responds to a gravitational field. What is different is that it doesn't respond to other forces, especially electromagnetic forces and the strong nuclear force. This explains why it follows different trajectories than ordinary matter.
  14. Feb 6, 2014 #13


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    Read slowly, clayjay, and suspend your disbelief. You are drawing unsupported conclusions.
  15. Feb 8, 2014 #14
    Wouldn't it be fair to say that it is Dark Gravity because we can't call it matter because we don't know it is, or is that just semantics?
  16. Feb 9, 2014 #15


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    I would say it is semantics. Dark matter has the same gravitational properties as regular matter, but, hardly ever interacts electromagnetically. The same is basically true of neutrinos, which are the most abundant particles in the universe.
  17. Feb 9, 2014 #16
    Neutrinos is a classic example mentioned by Chronos. It is also a weakly interactive particle.

    here is a quote from Griffiths "Introductory to Elementary particles"

    "By 1950, then, there was compelling theoretical evidence for the existence of neutrinos, but there was still no direct experimental verification. A skeptic might have argued that the neutrino was nothing but a bookkeeping device-a purely hypothetical particle whose only function was to rescue the conservation laws. It left no tracks, it didn't decay; in fact, no one had ever seen a neutrino do anything. The reason for this is that neutrinos interact extraordinarily weakly"

    Neutrinos and dark matter both carry similar weakly interactive characteristics, both are affected by gravity.

    Neutrinos are so weakly interactive that it can penetrate a 1000 light years of lead without an interaction.

    Neutrinos were later proved to exist by experimentation at the Savannah river nuclear power station by Cowan and Reines in the later 50's ( Cowan-Reines reaction) and also by the( Davis reaction). The lepton rules were described in the 1953's by Konopinski and Mahrnoud ( Rules which describe which reactions will work and which that don't)

    This allowed identification of whether they detecting neutrinos or anti-neutrinos etc.

    the dark acronym used in dark matter isn't due to it being so much missing mass or a placeholder. We know without very little doubt that the mass is there.

    the problem is we have very little understanding of what that mass is made up of. This is due to not having any observed interactions other than gravity. We have not acheived sufficient energy scales in nuclear reactors or particle colliders is one possible reason. This would imply that it is a very heavy particle. Its low interaction implies that it's net charge is neutral, as well as being a possible spin zero particle.

    The properties we do know of dark matter due to being so weakly interactive but at the same time not able to be a neutrino type (again due to its properties). Does not fall into any standard particle member or group. The organization and indeed the groups they fall into are determined by its appropriate reaction rules.

    google such examples as the Eightfold-Wayin which includes the baryon octet, meson octet and baryon-decuplet.

    Understanding of the above was further increased by understanding what flavor interactions can occur (quarks and gluons) described by the baryon de-cuplet and meson nonet.

    dark matter doesn't fall into any of these tables I mentioned.

    that should give you some idea of the complexity of problems due to dark matter to be resolved without providing an entire course of particle physics. Hope that helps

    the above can be found in


    his coverage of the history of discovery of elementary particles is a good read. As well as his teachings

    edit: also keep in mind the above tables named, represent earlier developments and understanding of today's standard model
    Last edited: Feb 9, 2014
  18. Feb 9, 2014 #17
    Einstein's relativity theory in its simplest terms created a function or field equation the relates the geometry function of space to the mass geometry in space. Dark gravity is not a science, it is speculation without relationship to current standard scientific thinking. There is some scientific proof of dark matter attributed to antimatter collision
    Savvas Koushiappas, an assistant professor in the department of physics at Brown University, and graduate student Alex Geringer-Sameth found that dark matter particles must have a mass greater than 40 giga-electron volts (GeV) — approximately 42 times the mass of a proton.
    A neutron of ordinary matter decays to a proton + electron is about 35 seconds and 'poof' you have a hydrogen atom. Perhaps dark matter is a stable dark neutron 42 times the mass of ordenary neutron. It seems dark matter has no electron shell or weak force expression.

    To me it is not semantics because dark matter & dark gravity define different things differently and I think that matters; semantically speaking.
  19. Feb 9, 2014 #18
    lol neutrons interact with the electromagnetic. You showed one such interaction. Dark matter is not known to have any electromagnetic interactions so cannot be a heavier form of neutron. PS a neutron is a neutron with set properties there is no heavy or light neutron or any heavy or light version of any particle. One particle of a type always have the same properties as any other sample, otherwise it is a different particle. (though it can have different energy levels)

    neutron also has a 1/2 spin and interacts with strong, weak, electromagnetic as well as gravity.
    Last edited: Feb 9, 2014
  20. Feb 9, 2014 #19


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    We don't know what dark matter is at this time. As such, anything put forward as an explanation here on the forums is just unsupported speculation, which is against PF rules.
  21. Feb 9, 2014 #20
    I understand that this a forum for teaching and learning standard academic explanations. Perhaps the tradition of “thought experiments” is to close to speculation for members to differentiate which is which through my composition. Einstein commonly used “thought experiments” as a way of explaining his theory but I am no Einstein. I never intended to speculate just to simulate thinking patterns. I am just attempting to have a discussion about the subject. I am here to cogitate, not here to speculate.

    I welcome your instruction.
  22. Feb 9, 2014 #21
    What we have here is a failure to communicate. You are right in everything you said. Perhaps I should have said dark matter particle instead of metaphorically referring to a dark matter neutron. I thought the my message was funny from your perspective. I will accept my faulty composition for the miscommunication.

    What are the defining characteristics of a dark matter particle?
    No experimental evidence that indicates presence of the electromagnetic or weak force by dark matter.
    That dark matter does not communicate / react with ordinary or dark matter except gravitationally.
    Dark matter does not clump to form objects made of itself.

    Mordred, may I ask what would be on your list?

    I respect the effort you put in here. Glad you do it. I didn't intend to miscommunicate.
  23. Feb 9, 2014 #22
    Dark matter is well described as most likely a weakly interactive massive particle with no known interactions with any forces other than gravity and possibly the weak force, with possibly other interactions no stronger than the weak force. As they are massive it will be slow moving
    ( non- relativistic). Hence cold dark matter. Dark matter may interact with the Higg's and they may or may not interact with other WIMP's, on those we still do not know. Another possibility is axioms and MACHO'S however the latter two are unlikely compared to WIMP's

    We do know that it does not interact with the electromagnetic, and as they do not influence atomic nuclei, we know it does not interact with the strong force.

    edit: this is an older article however has some useful data on dark matter


    try to keep in mind some of what it says may or may not be valid today
    Last edited: Feb 9, 2014
  24. Feb 17, 2014 #23
    I came across a better way to define dark matter and its problems associated with the known particles of the standard model. Thought I would post it.

    there are 4 known forces see chart below for their strength and theory of interactions


    Weak...................10-13........................ Flavordynamics......W and Z

    DM has no interactions with the electromagnetic, therefore it has no charge, it isn't known to interact with the strong force so it has no color(color interactions). If its found to interact with other weakly interactive particles such as the neutrino then it has a flavor interaction.(electroweak). we already know its influenced by gravity so is subject to geometrodynamic interactions. I included the relative strengths of each force.
    Last edited: Feb 17, 2014
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