Where is most "gravity", inside or out?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by nebel, Feb 29, 2016.

  1. nebel Valued Senior Member

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    so, given the size of the singularity BH, is it save to say that all the gravity is on the outside, infinitely in time and space until Hawking radiation takes it's toll?
     
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  3. DaveC426913 Valued Senior Member

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    No.
     
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  5. nebel Valued Senior Member

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    so there is more gravity inside a black hole than the outside? whereas there is zero gravity at every other center?
     
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  7. nebel Valued Senior Member

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    Can you double check that? Does not relativistic speed lead to the opposite? a slowing of the movement through time? at c time becomes zero? at least as observer? and
    since the OP is about the extend of gravity on the outside, If the matter disappears from spacetime, there is no more effective inside, and the gravitational effect must be all on the outside, and with the inverse square law remaining effective, to infinity.
     
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  8. nebel Valued Senior Member

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  9. nebel Valued Senior Member

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    Akademe Foundation, Research in Quantum Relativity, QCD, & Field Theory (In " Quora ")

    "--The gravity is in an enfolding surface tension--"


    Tracing the singularity from the beginning, in an " even " molecular cloud, all particles there would be in a balanced gravitational condition, but a lesser density with distance would start a squeezing by gravity from the outside, the area of lesser density. This warping of spacetime would propagate at the speed of light, and matter would be pushed by that pressure into the center, where gravity would always be zero, be balanced.
    Would the arrival of a singularity condition change that ? . The compression of matter leaves behind the gravitational field, long before the arrival of the EH or the singularity condition,
    gravity is a surface tension.
    There is much more gravity on the outside than any inside. orbital velocities show that, dark matter or not.
     
  10. Write4U Valued Senior Member

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    I understand the concept of zero gravity at the very center of a massive star, but the pressure exerted from the surrounding mass still will collapse the center into its smallest possible size.

    Zero gravity would exist anywhere there is no matter, ergo no attractive force or compressive pressure.

    Seems a little contradictory....

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  11. DaveC426913 Valued Senior Member

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    It is not zero gravity.

    The term is gravitational potential.

    There is a very high gravitational potential at the centre of a star, and as such, one would experience time dilation discrepancies due to GR with remote reference points.
    It just happens that, at that point, the force exerted by gravity from the surrounding mass balances out to net zero. IOW, you are not pulled in any particular direction (including inward).
     
  12. DaveC426913 Valued Senior Member

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    An external observer would see the mass slowing to a stop (and dimming out of existence) as they approach the event horizon.

    But the infalling mass itself experiences no such effect - in fact, nothing special happens as they cross the EH. But the singularity is only a few dozen to a few thousand km away, and they will traverse that in a very short time at their speed.

    The matter does not disappear from spacetime. It is there, and can be measured. The gravity of the black hole is the gravity of the mass at its centre.
     
  13. Write4U Valued Senior Member

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    Not trying to be argumentative, but does potential not precede actuality/ i.e. zero gravitational potential = zero gravity ?
     
  14. nebel Valued Senior Member

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    but it can not be in the center, because the center has no size. Mass might be infinitely compressed in the zero size singularity, but the resulting gravity is on the outside, in spacetime. has been there since day one.
     
  15. nebel Valued Senior Member

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    gravity is an acceleration. The only acceleration at the precise center of the mass is zero, around it, it is acceleration back to that central zero condition.
    An gravity meter would read zero in the center of any cavity, because the gravity acceleration is outside of the shell. shall we look at the shell theorem again?
    True: gravity of the mass at the centre, not gravity at the centre.
     
    Last edited: Sep 13, 2018 at 11:37 AM
  16. DaveC426913 Valued Senior Member

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    Potential has many meanings. The point is that even if you experience no net gravity (i.e. no pull in any direction), you are still in a gravitational well, and thus subject to GR time dilation.

    Hm. I may actually have it backwards. It may be that the g-potential at the centre of a star is zero. (Potential energy is what one gains when one climbs a hill. You can use that energy gain to fall back down.) So, at the centre of a star, you cannot extract useful work from falling further - it's potential energy is zero.

    However, that is not the same as being at infinity. You are subject to GR.
     
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  17. DaveC426913 Valued Senior Member

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    Not true.

    Compressed beyond our current models does not mean compressed to infinity. That's what singularity means: it means our models break down.

    The phrase "gravity is on the outside" is sloppy - which is why I am avoiding it.

    You experience gravitational forces anytime you are outside the singularity.
    You will experience it at 1 million km, you will experience outside the event horizon, you will experience it inside the event horizon, you will experience it all the way down to the singularity, where you will stop experiencing anything altogether.
     
  18. nebel Valued Senior Member

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    This being the amateur section, unprofessional terms will have to do.
    Outside could mean for example to the right of the origin diagram peak of gravity measured, at R. so,
    since Black holes were not discussed in the OP, where would peak gravity occur in a black hole?
    Best candidate: just outside the singularity, and from there to go to zero inside, at an infinitely small point at half a Planck length? beyond the breakdown? Anyway it has to go to zero to climb up on he other side to Max. and
    Yes you are right, the gravity outside the sequestered BH mass will be felt as far as the square over distance formula reaches.
     
    Last edited: Sep 13, 2018 at 8:57 PM
  19. nebel Valued Senior Member

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    So, if I picture this right, there is this additional matter falling from all direction into the singularity. Like in any entity, as in origins's diagram, acceleration becomes zero at the centre, but, the velocity is bad enough as it is, with having reached maximum acceleration= maximum gravity somewhere at the border outside the singularity.
    It seems CERN is recreating the centre of a singularity when particles collide at near "c" coming from opposite directions.
    All acceleration happening on the "outside." --rambling aside,
    If you underestimate the inside needed velocities, commensurate with an overestimated gravity, because of ignoring the near zero effective gravity there, you are bound to over - estimate the required escape velocities on the outside.
     
  20. Write4U Valued Senior Member

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    Oh ty, very nice analogy....

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    I do have a question; with "from opposite directions" to mean "from all opposite directions" ?

    If so, the term opposite directions may itself be a little misleading as it is true from a flat spacetime perspective, however in reality, a black hole in spacetime forms a vortex point where all infalling matter converges at an angle and not on a "head-on" collision course.

    a) Is that what makes it possible for a black hole singularity to form in the first place?

    b) How deep can a black hole vortex go before spacetime and matter begin to form a singularity?
     
    Last edited: Sep 16, 2018 at 12:00 AM
  21. DaveC426913 Valued Senior Member

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    Incorrect. We don't know.


    Might be. We don't know.

    Outside of what? The singularity? The event horizon?

    You are partially correct. Let me 'splain.

    Every particle of mass floating around the universe makes its own tiny dent in spacetime. As a particle approaches the event horizon of a black hole, it visibly starts to redshift, and from an external observer's point of view starts to experience strong time dilation. An external observer will never see any particle actually fall past the event horizon, they will simply get slower and slower and dimmer and dimmer - only disappearing when there are too few photons to reach us.

    Likewise, that dent in spacetime gets closer and closer to the EH, but never seems to reach it. The black hole absorbs it and becomes just a slightly deeper dent in spacetime. That is how the mass is able to affect the universe around it - despite the fact that the mass itself must have fallen into the singularity.

    So, the effect of mass on the curvature of spacetime does remain, though its cause has long since fallen out of our reach.
     
  22. DaveC426913 Valued Senior Member

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    Stop right there.

    The definition of singularity is that our models stop working. You cannot apply known laws of physics beyond this point.
    We are certain other laws heretofore unknown will manifest, but there's no point in idly speculating - and there's definitely no point in attempting to project our current physics into that realm.
     
  23. DaveC426913 Valued Senior Member

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    Who says?

    If you aim a particle at the dead centre of a black hole, why would it deviate?
     

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