Neutron Star to Black Hole

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

  1. tashja Registered Senior Member

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    I'm pretty sure they would disagree with that statement (in bold). ''In general relativity, all forms of energy create gravity, not only mass.* (for example, photons, which contain no mass, but gravitate). But I could always ask.

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    * Sean Carroll
     
    Last edited: Feb 14, 2015
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  3. tashja Registered Senior Member

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    OK, I asked Prof. Rovelli. Here's what he said:

     
    Last edited: Feb 14, 2015
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  5. wellwisher Banned Banned

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    If we converted this energy to mass, would the mass equvilnet gravitate more?

    The idea of space-time havibg mass seems to be a relative illusion. The reason is if we use SR and create a local space-time contraction, due to velocity approaching C, such as in accelerators, does extra mass appear? If space-time can create mass, does most of the particles in accelerators stem from this mass induction and therefore are not part of the original particles?

    Einstein would call this relativistic mass which he never said gravitated via GR, but because it has an energy equivalent may change into other particles as it steps down, which were never part of the original rest particle.
     
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  7. OnlyMe Valued Senior Member

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    Tashja, were those responses directly to my comment? If not, could you link to the full statements for both. I am pretty sure both Moore and Rovelli would agree that gravity propagates at c.., and that the equations that describe a gravitational field require a non zero mass. (I will address Rovelli's comment to this in another post.)

    I don't read Prof Moore's statement as contradicting my intent. I don't read him as saying that the field exists in the abscence of a gravitational mass, only that the field itself carries angular momentum.

    Prof Rovelli seems to start out describing a gravitational field originating with a gravitational mass.., and then as I interpert it, how the propagating field, which he describes as gravitational waves, may interact with other fields or even objects. I believe the idea that gravitational fields, interact and affect the local gravitational field dynamics is pretty straight forward. The detail in his example is way too advanced for most lay discussions. But, I would say or admit that as two gravitational fields interact they do affect the way each propagates..., IOW the associated curvature of spacetime becomes far more complex than in an isolated system. Which can be argued affects not only objects moving through or within the field but how two fields propagate in proximity to oneanother.
     
  8. OnlyMe Valued Senior Member

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    Out of context the above is an overly bold statement. There is no definition of exactly what is meant by, all forms of energy. Do you believe that Carroll includes, all potential and kinetic energies?.., which might imply.., that the kinetic energy, associated with a small mass with a relativistic velocity, increases the gravitational mass of that same object.., which could then imply that gravitational and inertial mass.., are not equivalent... And returns to an old debate about the the relationship between relativistic mass and gravitation.

    Carrol's statement seems either out of context or intended as theoretical.

    While still largely theoretical the following quote does connect the gravitational contribution of energy to an object and mass.

    In Einstein's theory, there is a greater variety of gravitational sources. ... However, it holds true in general relativity as well: all kinds of energy contribute equally to an object's gravity - not only the mass of the body's constituent elementary particles, but also, to give some examples, its thermal energy and the energy of any electromagnetic radiation trapped inside that body.

    Does energy apart from any energy trapped inside a massive object, have an effect of a gravitational field? I would say yes, but that is not the same as saying that, that same energy creates its own gravitational field.

    Discussions on forums like this always teeter on the edge of practical experience or what can be observed.., what a lay person thinks of as reality.., and the implications of purely theoretical interpretations...
     
  9. OnlyMe Valued Senior Member

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    Prof. Rovelli's comments seem clearly theoretical. Read his first sentence carefully and then put it in the context of his further statements in that first paragraph. While both Bondi mass and ADM mass have implications that extend to real world gravitational fields, they originate in vacuum field flat spacetimes, where there is no mass other than a single gravitating mass, or even any competing gravitational fields.

    His last paragraph where he begins with, For instance, there may be a universe where spacetime is flat, obviously is not talking about the universe we live in.

    Most of those posting and reading these discussions are lay persons and very often the line between theoretical solutions to EFE and what we observe to be consistent with the predictions of GR, are not clearly understood. Of those posting recently Bruce may be the exception, he does understand the theory, though he and I often bump heads on the practical or conceptual implications...

    When dealing solely within the context of theory the professor's comments can be true, but if in the context that my comment was made, his response is true, there would be no need for dark matter. From a lay perspective the implication is that a gravitational field can create itself, or that once created it will exist forever, even in the abscence of any mass. I believe the issue has been raised in the past.., but remember this is a lay discussion.., and it is very easy to confuse a theoretical interpretation and what has been observed. So if those responses were to my comment, please ask the professor's where we can find any gravitational field, other than as associated with dark matter, that does not involve a central mass (which might even cosmologically, be a gas cloud).

    Yes, GR can describe a gravitational field distant from any originating gravitational mass and how it may interact dynamically with other fields, that does not mean that it is describing a gravitational field that is self generating, or that energy in the abscence of mass has ever been observed to result in a gravitational field.
     
  10. paddoboy Valued Senior Member

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    Professor's Rovelli and Moore's replies from memory [which tashja may correct if I'm wrong] were in reply to my claim a while back that gravity makes gravity, due to the property of nonlinearity. I had some opposition to that from Q-reeus.
    A gravitational field without mass/energy is in my opinion a "thought experiment"

    I also see the definition of an "Eternal BH" as relevant and again a thought/theoretical exercise and defined in the following......
    "A massless black hole which is a stable topological structure held together by the nonlinearity of its gravitational field."
    http://scienceworld.wolfram.com/physics/EternalBlackHole.html


    Again, as I have said earlier, although all replies have been helpful and appreciated, none of those experts have been privileged to the whole discussion and some of the more outrageous claims that have been made, which in my opinion, reveals an agenda by the poster that is questioning the main concept of this debate.
     
    Last edited: Feb 14, 2015
  11. tashja Registered Senior Member

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    Hi wellwisher,

    I'm sorry I can't answer your questions. I'm learning myself. Perhaps a more knowledgeable member can answer them.
     
  12. tashja Registered Senior Member

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    OnlyMe, I will try to get you some answers. Here's another reply:

     
  13. OnlyMe Valued Senior Member

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    Tashja, my formal exposure to GR was long in the past and while in a literal sense Prof Baez is correct there is no mass term. However, the momentum and energy Terms are dependent to a significant extent on the presence of mass. Following the link Prof Baez provided in the first section you will find the following, (edit: this is not from the first section if you count the Introduction and Preliminaries, it is from the 3rd section Einstein's Equation.)
    This equation says that positive energy density and positive pressure curve spacetime in a way that makes a
    freely falling ball of point particles tend to shrink. Since E = mc^2 and we are working in units where c = 1, ordinary mass density counts as a form of energy density. Thus a massive object will make a swarm of freely falling particles at rest around it start to shrink. In short: gravity attracts.

    While a mass term is not used directly, GR is a geometric description of how two (or more) massive objects interact gravitationally. At least that was it initial purpose... And yes the field equations can be used to describe the curvature at a distantance from a massive object, becoming essential flat at infinity.

    I agree that many if not most of the problems encountered at the event horizon and almost certainly the singularity will be resolved by a successful quantum theory of gravitation.., which I do not believe will overturn GR other than perhaps in its conceptual interpretation. But though I try, I am not qualified to do more than speculate about what little I can understand of any of the theoretical work being done on QG.

    All along I think the issues being raised have been complicated by differences in conceptual approaches and even perhaps for at least one poster a hidden agenda other than science.

    There could be a good cross discipline discussion here but I am not clear headed enough at present.

    It would be nice if you could get those responding to better differentiate what of their comments remains theoretical interpretation and what has been observed to be an accurate description of reality. (Like I said I am not clear headed right now so I hope that did not come out badly.)
     
    Last edited: Feb 15, 2015
  14. river Valued Senior Member

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    Within GR you maybe correct

    But to theories that are beyond GR .....GR is questioned and challenged and rightly so
     
  15. river Valued Senior Member

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    Einstein himself considered the freedom to QUESTION was important mindset for science

    How would you disagree ?
     
  16. OnlyMe Valued Senior Member

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    River, I don't believe there is anything wrong with GR, other than conceptual interpretation.
     
  17. river Valued Senior Member

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    GR is based on gravity , gravity alone explains the Universe

    I disagree
     
  18. paddoboy Valued Senior Member

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    That's OK, as I have told you previously. All you need is evidence to support your now defunct pet Plasma/Electric hypothesis.
    And of course the vast majority totally disagree with you, and perhaps you need to ask yourself why.
     
  19. paddoboy Valued Senior Member

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    Professor Baez's reply seems rather paradoxical from where I am.....
    Take this for instance.....
    "it's possible for the matter to fall into the singularity and completely disappear, leaving nothing but vacuum, with spacetime curved to form a black hole".
    Obviously these people are busy, and the above highlight, although maybe pedantic, does give the wrong impression.
    Matter to fall into the singularity?

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    Firstly, the singularity only exists because of the failure of our models at the Planck/Quantum level, secondly it's that which creates the singularity as the mass collapses beyond the parameters of our theory, and thirdly, most do not believe that the classical point singularity does exist.
    As a I said these busy people are not privileged to have followed this debate and are not aware of the whys, where fors and what other erroneous claims have been made.
     
  20. river Valued Senior Member

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    the vast majority are not Einstein's
     
  21. tashja Registered Senior Member

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    No more paradoxical than what Prof. Thorne says in this video. Notice how he speaks of the singularity as if it's an actual, physical object. And on 1:51 he goes on to say that ''... a black hole is an object that is made not from matter, but from warped space and warped time.'' '' .. there is no matter in that black hole. It's not a very dense object made of very dense matter. There is no matter at all..''

    See for yourself

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  22. paddoboy Valued Senior Member

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    "We tried to keep the math down to a bare minimum, except at the end. The gravitational field equations say how certain aspects of spacetime curvature at a point are determined by the flows of energy and momentum through that point. But even if these flows are zero - as in a vacuum - spacetime can be curved there".

    This part of Professor Baez's reply can be explained by the quality of spacetime/gravity that I have raised before...."nonlinearity" and which seems supported by the Eternal BH definition at....
    "A massless black hole which is a stable topological structure held together by the nonlinearity of its gravitational field."
    http://scienceworld.wolfram.com/physics/EternalBlackHole.html

    But again, I see these just as "thought experiments" in a similar vane to the naked singularity argument.
    I don't believe they exist in reality.
     
  23. river Valued Senior Member

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    how can a massless anything , have a topological structure ?
     

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