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Unaccounted mass

  1. Dec 11, 2004 #1
    Einstien's theory states the mass of an object increases as it nears light speed. Much mass therefore must be gained in supernovae events, super massive black holes, ect. Why could not this be offered a possible explanation for the extra mass?
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  3. Dec 11, 2004 #2


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    Dark matter is a conclusion that flows primarily from the fact that in ordinary, sublight galaxies, thousands of examples of which exists, matter on the fringes of the galaxies is bound much more tightly to the core of the galaxy than the distribution of luminous matter in the galaxy and a simple GMm/r^2 theory of gravity would imply.

    Gravitational lensing data from light bent in the vicinity of galaxies likewise shows more bending of light than the luminous matter in the galaxies and Newtonian gravity would imply.

    In galaxies of low surface brightness, this discrepency is very high, in different kinds of galaxies, different discrepencies are visible.

    The weighted average discrepency from this data is huge, with the data implying that 80%-90% of mass in this low v envrionment is missing, and the disceprencies tend to be greater in lower v environments, rather than higher v environments. It therefore follows the any impact on mass from relativity is ruled out as a cause. The problem is either that there is substantial missing mass or that the non-relativistic case of Newtonian gravity is wrong.

    I personally am a strong proponent of the later approach (called MOND for Modified Newtonian Dynamics). The scientific community as a whole favors the dark matter resolution of this data, but respect that there is a difference of opinion on the issue which is respectable.
  4. Dec 11, 2004 #3


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    There are also galaxies whose rotational curves fit nicely to newtonian dynamics... i.e., no dark matter necessary. While this creates headaches for galaxy morphologists, it creates even more headaches for MOND.

    When you look at large scale effects, like galactic clusters, any local relativistic contributions are necessarily included. Remember too, the energy debt incurred to increase relativistic mass balances the books - an equivalency principle thing.
    Last edited: Dec 11, 2004
  5. Dec 11, 2004 #4
    Besides, the initial premise is incorrect. Mass don't increase as a consequence of velocity (According to the point of view of the greatest part of the physics community). What increases is its energy, according to the formula
    where va is the 4-velocity
    Last edited: Dec 11, 2004
  6. Dec 12, 2004 #5


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    Welcome to Physics Forums drew500!

    You may like to browse through the posts in the Special & General Relativity section of PF, it contains a lot of material discussing your post and amplifying considerably on meteor's (which hopefully sets you straight on what GR does, in fact, say).
  7. Dec 12, 2004 #6


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    I'd differ with you on the evidence there. There are large classes of galaxies where MOND predicts strictly newtonian dynamics. The principal gap in the evidence is in galactic clusters, where MOND and Newtonian dynamics make the same prediction, where there is a OOM discrepency in the direction one would hope (too little, rather than too much matter). MOND would propose bayronic dark matter in that context, CDM (Cold Dark MatteR) theories would predict modest amounts of CDM. But, CDM does a rather poor job, on its own, of predicting a priori how much CDM there will be in a particular system.
  8. Dec 20, 2004 #7
    hello drew500. I'm not sure what you mean.

    You mean due to the high speed at which the outer parts of the star move away from the supernova?
    If so, no. All the energy in this energy now in the form of velocity was in the star to begin with.

    you say it's an explaination for the 'extra mass'

    What extra mass?
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