Fun with black holes
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From: eric gisse on 18 May 2010 00:53 Greg Neill wrote: > eric gisse wrote: >> Edward Green wrote: >> >> [...] >> >> What's the point of this? You are rehashing a well known point that >> observers outside a black hole's event horizon do not see the transit of > an >> object through the event horizon in finite observer time. >> >> It doesn't matter how you rephrase the question, the answer is always > going >> to be the same. > > How about a vaiation involving the observed gravitational > field? Since gravitation is a manifestation of the > curvature of space it doesn't have any problem "escaping" > from a balck hole -- after all, black holes certainly > present a strong gravitational influence outside of their > event horizons. > > Suppose there's an observer situated a goodly distance from > a black hole with a sensitive gravitational compass (like a > small mass on a string that will point in the direction of > the net gravitational force, only one as sensitive as can > be made by the Gedankenwerks manufacturers). > > Using this apparatus the observer monitors the straight-line > appoach and infall of a significantly massive body towards > the black hole. He's watching the infall in profile, so the > motion is perpendicular to his line of sight. During the > infall, his "compass" points in a direction that is essentially > the center of mass of the infalling body and black hole. > > The question that arrises is, at what point in time, if any, > with the observed center of mass coincide with the center > of the black hole? That is, when will the external observer > conclude that the infalling mass has met its fate at the > singularity? I'll answer a slightly different question because it has already been answered for me, then explain how the two relate. MTW Page 864 (Box 32.2 A: Density perturbations) discusses a _similar_ problem of a perturbation on the surface of a collapsing star. The question there is whether the star creates a 'lumpy' event horizon (nee non-spherical gravitational field). According to MTW, the logic is that the 'information' about the lump is contained in backscattered long wavelength gravitational waves which get trapped within/around the black hole. They are long because the closer the object is to the black hole, the more redshifted the waves are by the time they reach the observer. The waves are contained by backscatter against the gravitational field. Now an observer sitting out yonder that is sensitive to only the gravitational field [already know the answer for gravitational waves] will observe a quadrupole (and higher, but irrelevant) perturbation upon the region of the black hole which will all fade out as the object approaches the event horizon for the same reasons as above. As for how long, it is a small number that exponentially decreases as a function of the mass of the black hole. Exponentially is the correct word, as well.
From: Tom Roberts on 18 May 2010 23:48 Sue... wrote: > Objects that can't radiate light, also can't > radiate gravity. Not in GR, which is the best generally-accepted theory of such things. > For that reason, black holes > are absurd. No. What is absurd is your entire approach. Tom Roberts
From: Tom Roberts on 19 May 2010 00:36 Greg Neill wrote: > Suppose there's an observer situated a goodly distance from > a black hole with a sensitive gravitational compass (like a > small mass on a string that will point in the direction of > the net gravitational force, only one as sensitive as can > be made by the Gedankenwerks manufacturers). > > Using this apparatus the observer monitors the straight-line > appoach and infall of a significantly massive body towards > the black hole. He's watching the infall in profile, so the > motion is perpendicular to his line of sight. During the > infall, his "compass" points in a direction that is essentially > the center of mass of the infalling body and black hole. [My context is GR.] Let me assume no other massive objects exist, that the black hole is Schwarzschild, that the object is pointlike, and it falls straight in. Then the "gravitational compass" points in a fixed direction, as the c-o-m does not move (conservation of momentum, which applies because of the asymptotically flat manifold). Note that the "gravitational compass" is insensitive to the passage of the gravitational waves generated by the infall. At least I think all that is true. The caveat is that conservation of momentum only applies APPROXIMATELY here, but I think the approximation is extremely good and better than required. All that I say here is an educated guess based on knowledge of the properties of black holes and the structure of GR, not the result of any rigorous computation. > The question that arrises is, at what point in time, if any, > with the observed center of mass coincide with the center > of the black hole? Using the distant observer's time and observations at her location: As the object is observed to approach the horizon, the asymmetry of the horizon + object will quickly get redshifted to unobservability. That asymmetry is related to the observed difference between the center of the black hole and the c-o-m. > That is, when will the external observer > conclude that the infalling mass has met its fate at the > singularity? That is a COMPLETELY different question. An unanswerable one. The relaxing of the horizon to a sphere has nothing to do with the infalling object intersecting the singularity. Indeed they occur at different locations in the manifold, and the horizon is not causally connected to any point inside the horizon (including all points near the singularity). Indeed there is no point in the entire manifold that is causally connected to the limit point of the object's trajectory intersecting the singularity. The distant observer cannot observe the infalling object cross the horizon (much less intersecting the singularity inside) -- the relevant data get redshifted to unobservability. Tom Roberts
From: BURT on 19 May 2010 01:04 On May 18, 8:48 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > Sue... wrote: > > Objects that can't radiate light, also can't > > radiate gravity. > > Not in GR, which is the best generally-accepted theory of such things. > > > For that reason, black holes > > are absurd. > > No. What is absurd is your entire approach. > > Tom Roberts Black holes violate energy laws. Light can be blue shifted or red shifted from infinite energy to zero. These predictions spell nonsense prediction. There are no black holes. Mitch Raemsch
From: Sue... on 19 May 2010 01:14
On May 18, 11:48 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > Sue... wrote: ============== > > Objects that can't radiate light, also can't > > radiate gravity. ============== > Not in GR, which is the best generally-accepted theory of such things. > > > For that reason, black holes > > are absurd. > > No. What is absurd is your entire approach. You are arguing for the acceptance of mathematical absurdity if it is "generally accepted". This is not surprising for such a dedicated defender of the absurdities of Lorentz ether theory as yourself. :-( Also there is reason to question your lame assertion: "Not in GR". The dual electromagnetic field tensor http://farside.ph.utexas.edu/teaching/em/lectures/node122.html Induced gravity and gauge interactions revisited http://arxiv.org/abs/0809.4203 It is Newton's gravity that violates electromagnetic principles, not so much Einstein's as you assert without support. In any case, known flaws make a poor argument to accept absurd interpretations. http://www.physics.ucla.edu/~cwp/articles/noether.asg/noether.html Sue... > > Tom Roberts |