Neutron Star to Black Hole

Discussion in 'Astronomy, Exobiology, & Cosmology' started by RajeshTrivedi, Jan 12, 2015.

  1. OnlyMe Valued Senior Member

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    You are right Tashja, this was a clear and straight forward description.

    In fact I believe that the way przyk approached the question, emphasizes the conceptual divide I have been trying to point out.

    If you approach GR as a mathematician, solutions emerge that predict a variety of things. Some seem to be supported by observation and others remain closer to mathematical science fictions.., at least at present. Which does not mean there is no value, in attempting to understand those results which seem to be mathematical science fictions. After all black holes once fell into that catagory.

    Over the last 8 to 10 years I have been trying to get a grasp on gravitation and inertia, from the context of QM. Some of the things that emerge from solutions to EFE seem to me to represent road blocks to any successful quantum theory of gravity. The singularity is one and the way spacetime is believed to behave at the event horizon is another, though the singularity is by far the more extreme problem, because it represents, in essence a sink hole where the mass required for a QTG to be successful, just disappears.

    Yes, I favor przyk's 1st variant as more likely representing reality. But I reject the mathematical conclusion that the collapsing mass just disappears, in a singularity. My referencing a singularity as essentially a point mass is really a statement that the mass cannot just disappear! And I believe I have said more than once that you cannot actually characterize a singularity as having any physical charateristics, including mass.

    To the issue of mass being the source of the gravitational field even in GR, My assertion that mass is involved is supported not only by the vast majority of what we observe, in that at the centers of all gravitational fields we can observe with any certainty, the exists a planet, star, even a galaxy or some other massive object. The exception being black holes where we cannot observe anything inside the event horizon. However, the following portions of przyk's comments, support the existence of a central mass even in the case of black holes.

    In that first section he points out that,
    Tμν is a quantity called the "stress-energy tensor", whose components include local energy density (including but not limited to mass) and momentum.

    If you remove mass from consideratation, what else is there that physically contributes to local energy density? If you remove contributions by mass/matter from the equations, what other than perhaps photons is there to consider as energy? And the momentum associated with a photon is not even certain other than as it interacts with an atom.

    And then later when he describes the first of his two variants he adds,
    1) Black holes formed by gravitational collapse of matter (e.g. a star that collapsed into a black hole). In this case you can simply imagine you're feeling the gravitational field produced by the collapsing matter at some point in the past just before it passed through the event horizon, which is only reaching you now.

    As I said, I favor this 1st variant, and contend that if a black hole originates with the colapse of a massive onject, while that mass may retreat beyond an event horizon where it is no longer observable, it does not seem reasonable to assume that it disappears in a singularity.

    As far the existence of mathematical singularities are concerned, I agree with Prof Wiltshire, from one of Tashja's earlier posts, but where he was speaking specifically about the Kerr ring singularity, I would include all mathematical singularities.

    Without this last assertion, it would seem to me that there can be no possibility of developing a quantum theory of graviation.
     
    Last edited: Feb 15, 2015
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  3. QuarkHead Remedial Math Student Valued Senior Member

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    Hmmm....

    tashja, I know you mean well and that others here appreciate your efforts to contact practicing professionals. Personally I think these efforts are misplaced. Because.......

    1. This is a discussion forum. In an ideal world (which of course does not exist) following a disagreement a disputant will admit "you are right after all, I was wrong" In the unlikely event that this occurs, it can only be done on the forum

    2. Calling in outside sources of "authority" who are unwilling to engage in the discussion is just that - an appeal to authority. And if these "authorities" are unwilling to engage in discussion, they cannot be engaged with, and you may as well quote web sites or the Wiki.

    If this is an unpopular view, then so be it
     
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  5. paddoboy Valued Senior Member

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    This is what I have been inferring from day one.
    Although I'm not against "appeals to authority" per se, not being able to engage in the discussions puts them somewhat behind the eight ball.
    Still useful though and need not be dismissed outright.
    And of course the quoting of WIKI and reputable web sites, are also naturally helpful.
     
    Last edited: Feb 15, 2015
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  7. tashja Registered Senior Member

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    OnlyMe, see this reply by Prof. Krauss:

     
  8. paddoboy Valued Senior Member

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    Can't argue with that.

    Please Register or Log in to view the hidden image!

    E=Mc2
     
  9. tashja Registered Senior Member

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    The questions is: to what mass is that equation referring to? Is it the Komar, the Bondi, or the ADM??
     
  10. paddoboy Valued Senior Member

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    Not sure if it matters.
    http://en.wikipedia.org/wiki/Mass_in_general_relativity
    The concept of mass in general relativity (GR) is more complex than the concept of mass in special relativity. In fact, general relativity does not offer a single definition of the term mass, but offers several different definitions that are applicable under different circumstances. Under some circumstances, the mass of a system in general relativity may not even be defined.
     
  11. OnlyMe Valued Senior Member

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    Tashja, przyk's explanation was far better. Prof. Krause' one liner is of no value at all unless he defines exactly what energy is, in the same context.

    As I said earlier in a literal sense it is true there is no mass term, that does not mean that mass is not involved in creating a gravitational field. It only means that the filed itself, which is what the equations describe, is not composed of mass. To pull a Farsight.., think of it as the same, as the difference between describing a magnet and a magnetic field. The magnetic field is not composed of matter, but the magnet is. No matter/mass no magnetic field..., and no matter/mass and there is no gravitational field....., you can point to in reality.

    Prof. Krauss' answer, emphasizes the divide between most lay oriented discussions and a literal translation of the math... Most lay discussions don't really become disconnected from the reality we observe and experience in the world. As a few of your responders have mentioned, theoretically a gravitational field can be described without any mass/matter.., the question is can any of those presenting those descriptions, point to any gravitational field that is not associated with a center of mass?... Without assuming there is some unseen matter or dark matter, to explain the field they point to?
     
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  12. OnlyMe Valued Senior Member

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    Some years ago I listen to a series of explanations of that equation by about a dozen well known physicists. There was a lot of variety in their answers.

    But the best answer for this discussion I think is, the m in E = mc2, referrs to rest mass.
     
  13. OnlyMe Valued Senior Member

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    3,914
    My first response to the above was along the lines of looking at the question and equations in the same context that przyk's responce addressed the question. Specifically within the context of the general theory of relativity, and nothing more.

    However, if I jump into speculation involving the concept of a quantum theory of gravity.., and I emphasize the speculation, gravity itself could become a kinetic interaction between energy and mass/matter.., but you are then still left with the burden of providing a more specific definition of what is meant by the terms/words energy and matter.
     
  14. paddoboy Valued Senior Member

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    Bingo and well said. This is what I have been saying for a few posts. Along with "eternal BHs" and "naked singularities" the insinuations of massless BHs and similar, are highly theoretical concepts and thought experiments to some extent, that do not really infer reality.
     

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