Fun with black holes
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From: Tom Roberts on 15 May 2010 22:13 Edward Green wrote: > [ensemble of rocket probes] > This strongly suggests to me that the probes never > cross the event horizon, A more sensible conclusion is that we don't know when the last one will return. This, of course, says NOTHING AT ALL about whether any has fallen in or not. And, of course, those programmed to turn around inside the horizon will never return. Indeed, by timing the return of each probe, and using the value of r at which it fired its rockets to return, you can determine where the horizon is located. As I have said before, the distant observer cannot know if an infalling object falls through the horizon or not. This, too, says NOTHING AT ALL about whether it actually falls in -- it is a statement about what that observer CAN OBSERVE. When a friend goes around the corner of a building, you can no longer observe her. You cannot tell if she goes into the building through a door around the corner, or not. Just because you cannot OBSERVE something does not mean it does not happen. The horizon of a black hole is a much greater impediment to observation than the walls of a building, but the principle is the same. As Tom Clancy has emphasized in a rather different context: "Don't know means DON'T KNOW." The distant observer does not know if a probe fell through the horizon; inferring that it did not do so is COMPLETELY UNWARRANTED. Especially when a straightforward analysis shows that it does. Tom Roberts
From: BURT on 16 May 2010 04:23 On May 15, 7:13 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > Edward Green wrote: > > [ensemble of rocket probes] > > This strongly suggests to me that the probes never > > cross the event horizon, > > A more sensible conclusion is that we don't know when the last one will return. > This, of course, says NOTHING AT ALL about whether any has fallen in or not. > > And, of course, those programmed to turn around inside > the horizon will never return. Indeed, by timing the return > of each probe, and using the value of r at which it fired > its rockets to return, you can determine where the horizon > is located. > > As I have said before, the distant observer cannot know if an infalling object > falls through the horizon or not. This, too, says NOTHING AT ALL about whether > it actually falls in -- it is a statement about what that observer CAN OBSERVE. > > When a friend goes around the corner of a building, you can > no longer observe her. You cannot tell if she goes into the > building through a door around the corner, or not. Just > because you cannot OBSERVE something does not mean it does > not happen. The horizon of a black hole is a much greater > impediment to observation than the walls of a building, but > the principle is the same. > > As Tom Clancy has emphasized in a rather different context: "Don't know means > DON'T KNOW." The distant observer does not know if a probe fell through the > horizon; inferring that it did not do so is COMPLETELY UNWARRANTED. Especially > when a straightforward analysis shows that it does. > > Tom Roberts Light has no escape speed as matter does. Mitch Raemsch
From: Edward Green on 16 May 2010 19:42 On May 15, 10:13 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > Edward Green wrote: > > [ensemble of rocket probes] > > This strongly suggests to me that the probes never > > cross the event horizon, > > A more sensible conclusion is that we don't know when the last one will return. > This, of course, says NOTHING AT ALL about whether any has fallen in or not. > > And, of course, those programmed to turn around inside > the horizon will never return. Indeed, by timing the return > of each probe, and using the value of r at which it fired > its rockets to return, you can determine where the horizon > is located. > > As I have said before, the distant observer cannot know if an infalling object > falls through the horizon or not. This, too, says NOTHING AT ALL about whether > it actually falls in -- it is a statement about what that observer CAN OBSERVE. > > When a friend goes around the corner of a building, you can > no longer observe her. You cannot tell if she goes into the > building through a door around the corner, or not. Just > because you cannot OBSERVE something does not mean it does > not happen. The horizon of a black hole is a much greater > impediment to observation than the walls of a building, but > the principle is the same. > > As Tom Clancy has emphasized in a rather different context: "Don't know means > DON'T KNOW." The distant observer does not know if a probe fell through the > horizon; inferring that it did not do so is COMPLETELY UNWARRANTED. Especially > when a straightforward analysis shows that it does. Fair enough. Let me propose a slight refinement of the gedanken though. (1) Let the ensemble of probes be infinite in number (I really intended this, but didn't specify it). (2) Let 10% of them be programed to never fire their rockets. (3) Let the remaining 90% be programmed to fire their rockets in one impulsive burst at the point of lowest descent, bringing them back to their radius of release at a standstill (as you proposed to interpret my original gedanken). (4) Let the 90% be programmed in distribution so that there is an infinite sequence of firings converging in r coordinate on r_Schwarzschild. (5) We agree, that the sequence of return times T will go to infinity. (6) By symmetry, it seems reasonable to say that when a probe returns at time T (taking the drop time to be zero) that it had reached its point of lowest descent at time T/2 (?) (7) Since this sequence of times T/2 also goes to infinity we can evidently always say that the surviving population of probes has yet to reach the event horizon. (?) This would seem to be the suspect assumption. It would be natural in Newtonian gravitation. Perhaps it is insupportable here. Note however that if this is my error, I did not reason that "We don't know" and therefore "It didn't happen". We _do_ know (or at least we would if assumption (6) is correct) that the surviving flotilla of probes has yet to fall in at a sequence of times T/2, which goes to infinity. (??) It is interesting to compare this assumption with Daryl McCullough's objection involving the Rindler Horizon. There, in a non- accelerated reference frame, the assumption of symmetry breaks down completely. It takes the probes much longer to claw their way back to the mother ship than it does to fall near the horizon.
From: Sue... on 16 May 2010 20:47 On May 12, 5:50 pm, Edward Green <spamspamsp...(a)netzero.com> wrote: > Consider an ordinary Schwarzschild black hole: Objects that can't radiate light, also can't radiate gravity. For that reason, black holes are absurd. Consider your notion, considered. http://en.wikipedia.org/wiki/Induced_gravity Sue...
From: eric gisse on 16 May 2010 23:58
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. |