Fun with black holes
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From: Edward Green on 21 May 2010 19:14 On May 21, 6:41 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > Edward Green wrote: > > On May 16, 11:58 pm, eric gisse <jowr.pi.nos...(a)gmail.com> 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. > > > The point is that the answer sounds like some kind of trick, whereas I > > am proposing that the object never "really" penetrates the horizon, > > for suitable values of "really". > > According to the object actually doing it, it does I find that debatable. Finite proper time either means it actually falls in, or actually freezes. > (which is the only answer > that matters). According to the external observer, it doesn't. This doesn't > need to be rehashed. > > > Unless, that is, as something I have > > read leads me to believe, the horizon eventually rises to meet the > > infalling mass. > > Uuuuuuhhhhhhh no. The horizon is a static fixture of the manifold. > > > Thereafter the black hole rings out like a bell until > > the perturbation to its horizon has been absorbed. > > No again. There is no analysis anywhere which supports this. It's in Thorne's popular book. I'll try to go back and find the page references. > > Black holes _can_ have hair > > No again. That would depend on an obvious interpretation of the truth value of the above statements, so that is not really a separate "no". Ah. Here we go. p. 417 "When matter falls into a black hole, the absolute horizon starts to grow ... before the matter reaches it ... " As for the idea that black holes can ring, p. 295 ff. "Not only can black holes spin, they can pulsate". Put these ideas together and you have some support for a black hole horizon rising to meet incoming matter, then pulsating away the resulting distortion as gravity waves. Two merging holes forming a new spinning hole are certainly thought to pulsate, so the concept exists. In this case it seems at least plausible that the membrane is going to ring whenever you drop something into it.
From: Edward Green on 21 May 2010 20:10 On May 21, 6:41 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > Edward Green wrote: <...> > > Thereafter the black hole rings out like a bell until > > the perturbation to its horizon has been absorbed. > > No again. There is no analysis anywhere which supports this. MTW p.886 "When matter falls down a black hole, it can excite the hole's external spacetime geometry into vibration. The vibrations are gradually converted into gravitational waves..."
From: eric gisse on 21 May 2010 21:21 Edward Green wrote: > On May 21, 6:41 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> Edward Green wrote: > > <...> > >> > Thereafter the black hole rings out like a bell until >> > the perturbation to its horizon has been absorbed. >> >> No again. There is no analysis anywhere which supports this. > > MTW p.886 > > "When matter falls down a black hole, it can excite the hole's > external spacetime geometry into vibration. The vibrations are > gradually converted into gravitational waves..." Which does not mean the horizon itself changes.
From: eric gisse on 21 May 2010 22:23 Edward Green wrote: > On May 21, 6:41 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> Edward Green wrote: >> > On May 16, 11:58 pm, eric gisse <jowr.pi.nos...(a)gmail.com> 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. >> >> > The point is that the answer sounds like some kind of trick, whereas I >> > am proposing that the object never "really" penetrates the horizon, >> > for suitable values of "really". >> >> According to the object actually doing it, it does > > I find that debatable. Finite proper time either means it actually > falls in, or actually freezes. It most certainly does not 'freeze'. Physics is local. Proper time is the only relevant quantity. What a far-away observer sees is irrelevant to the physics. > >> (which is the only answer >> that matters). According to the external observer, it doesn't. This >> doesn't need to be rehashed. >> >> > Unless, that is, as something I have >> > read leads me to believe, the horizon eventually rises to meet the >> > infalling mass. >> >> Uuuuuuhhhhhhh no. The horizon is a static fixture of the manifold. >> >> > Thereafter the black hole rings out like a bell until >> > the perturbation to its horizon has been absorbed. >> >> No again. There is no analysis anywhere which supports this. > > It's in Thorne's popular book. I'll try to go back and find the page > references. > >> > Black holes _can_ have hair >> >> No again. > > That would depend on an obvious interpretation of the truth value of > the above statements, so that is not really a separate "no". No. The no-hair theorems are explicit. > > Ah. Here we go. p. 417 > > "When matter falls into a black hole, the absolute horizon starts to > grow ... before the matter reaches it ... " Once the matter is redshifted into oblivion it is a part of the black hole as far as external observers are concerned. As for the horizon _growing_ before the matter reaches it, nonsense. The horizon will only grow in response to further input of mass-energy. > > As for the idea that black holes can ring, p. 295 ff. > > "Not only can black holes spin, they can pulsate". For what value of 'spin' or 'pulsate' ? The spin of a black hole is an imprint of angular momentum upon spacetime. There's nothing actually spinning. Plus black hole thermodynamics sorta nix the idea of the horizon 'pulsating'. > > Put these ideas together and you have some support for a black hole > horizon rising to meet incoming matter, then pulsating away the > resulting distortion as gravity waves. Riddle me this. How do you reconcile the mathematical certainty that a black hole's event horizon can not change in area with the notion of it pulsating? > Two merging holes forming a > new spinning hole are certainly thought to pulsate, so the concept > exists. Rapidly changing quadrupole moment of two merging black holes => "pulsating". > In this case it seems at least plausible that the membrane is > going to ring whenever you drop something into it. The event horizon is isn't a membrane. It is not a material surface. It is not 'there'. Nothing special happens when something passes through it, other than the certainty of never leaving the black hole.
From: eon on 22 May 2010 07:43
On May 19, 5:48 am, 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. well, why should light, in your GR, falls into a black hole light, as gravity, must be geometry as well > > > For that reason, black holes > > are absurd. > > No. What is absurd is your entire approach. > > Tom Roberts seems that Sue has a valid point here, and you dare not taking a position why are are they looking for gravity waves traveling at speed of light? good bye |