Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dark matter and MOND

  1. May 7, 2004 #1
    Space is filled with gravitons moving in every direction.
    These gravitons push masses together and cause "attraction".
    When gravitons approach a spiral galaxy parallel to its plane,
    they get pushed together and concentrated by the magnetic field lines of the galaxy.
    As they double their distance from the edge of the galaxy, the
    gravitons double their density and double the force they exert on a star.
    This allows stars to have higher velocities than we would
    expect them to have at a given distance from the centre of
    the galaxy and is in keeping with how gravity varies according to
    modified newtonian dynamics.
     
  2. jcsd
  3. May 11, 2004 #2

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    How would this work in clusters?

    Would you then expect that spiral galaxy gravitational lenses will produce quite different magnifications depending upon the angle (wrt the plane)?

    Presumably (spiral) galaxy collisions will be anything but isotropic (outcome strongly depends upon 'angle of incidence', once rotational effects of matter in the plane are taken into account).
     
  4. May 12, 2004 #3
    How would this work in clusters?


    The gravity particles ( they need a small electric charge to interact with the magnetic field so I'll stop calling them gravitons) get denser for all angles of approach to the plane apart from 90 degrees - directly above and below it- where the force the magnetic field exerts on them will be zero ( force = qvB).It is known that there are magnetic fields surrounding clusters but because the galaxies have such different
    orientations in each cluster, we would expect gravitational lensing to be differnet for each assuming the same object is being lensed.


    Would you then expect that spiral galaxy gravitational lenses will produce quite different magnifications depending upon the angle (wrt the plane)?

    I'm going to check hubble's images out for this.

    Presumably (spiral) galaxy collisions will be anything but isotropic (outcome strongly depends upon 'angle of incidence', once rotational effects of matter in the plane are taken into account).

    I think this would depend on how the magnetic field of the galaxies changed as they collided.

    The Earth and Sun 's magnetic fields are much stronger than the milky way's field and we don't notice the effects they have on gravity particles.However, the Aharanov-Bohn effect which is supposedly due to vector potential and not force, could be due to the strong magnetic field of a solenoid concentrating gravitons and shifting the
    phase of the electron interference pattern.The density of gravitons would have to be increased ten times by the solenoid's field to shift electrons
    10^ -6 metres which is what is observed.Using force = qvB ( force is proportional to magnetic field and therefore acceleration under Newton's law) and the fact that the solenoid used in AB effect is about 10^6 times stronger than the Earth's gravitational field,we would expect the Earth's magnetic field to cause gravity to increase on the Earth's surface by :
    increase in gravity strength for AB effect / solenoid magnetic field / earth's magnetic field strength

    = 10 / 1 / 10^ -6 = 10^ -5
     
    Last edited: May 12, 2004
  5. May 12, 2004 #4

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    We know a few things for sure about gravitons: they have zero electric charge, they have very little energy and real gravitons are only produced in any significant quantity by very rare astrophysical events due to the static nature of most graviational fields.
     
  6. May 12, 2004 #5
    We know a few things for sure about gravitons: they have zero electric charge,

    If gravitons move together as pairs of opposite charge they have zero electric charge.
    The magnetic field of a galaxy would push the pairs together and increase the density of gravitons and therefore the force of gravity.
     
  7. May 12, 2004 #6

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    No, the way that gravity works requires that gravitons have zero charge full stop.
     
  8. May 12, 2004 #7
    Gravitons must be spin 2 regardless of the theory that contains them.
    It is not beyond the realms of possibility that two spin 1 particles
    with opposite electric charge constitute a graviton.However to make the graviton massless one of those particles must have negative mass.Negative mass, I postulate ,carries momentum in the opposite direction to normal mass and so, some
    half-gravitons of the same charge will move towards each other in a magnetic field and increase the force of gravity by increasing the density of force carriers.
     
  9. May 12, 2004 #8

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    No, gravity must be carried by a chargeless massles spin 2 particle not a a charged spin 1 particle. A charged spin 1 particle cannot reproduce gravity as we see it.
     
  10. May 12, 2004 #9
    No, gravity must be carried by a chargeless massles spin 2 particle not a a charged spin 1 particle. A charged spin 1 particle cannot reproduce gravity as we see it.

    The above is true if the gravitational force carrier moves at the speed of light or less.
    But I reckon it moves way faster than that - something has to account in a causal way for epr paradoxes.
     
  11. May 12, 2004 #10

    jcsd

    User Avatar
    Science Advisor
    Gold Member

    The above is true only if gravity travels at the speed of light (it would not be massless if it traveled at less than the speed of light)

    Gravity can't account for the EPR paradox as it plays no role in it. Nothing has to be accounted for in the EPR paradox (which i why it is nom longfger considered a paradox) as there is a fully-understood and consistent explanation.

    The speed of gravity hasn't been measured satifactorily but to have any other speed than c sends GR pout of the window and to have a superluminal speed sends SR out the window too.
     
  12. May 12, 2004 #11
    The speed of gravity hasn't been measured satifactorily but to have any other speed than c sends GR pout of the window and to have a superluminal speed sends SR out the window too.

    SR isn't sent out of the window and nor is GR. The force carrier moving faster than light does not exist in space-time.It travels in space and time just like particles did in the good old days! And it reacts to magnetic fields in space and time.There is an asymmetry - the force carrier can only move in space and time but all other particles in the universe exist in space-time.The epr explanation stops people thinking about superluminal speeds which can explain a lot.
     
    Last edited: May 12, 2004
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Dark matter and MOND
  1. Dark matter? (Replies: 18)

  2. Dark matter (Replies: 5)

  3. Dark matter black hole (Replies: 19)

Loading...