
#37
Jan909, 05:10 PM

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#38
Jan909, 06:21 PM

PF Gold
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Maybe this metaphor can help get a very rough and partial image: if you can only measure your shadow, then when the sun approaches noon exactly above you, the shadow will approach zero length, while at sunset it will become longer and longer, until going ideally to infinity. This does not mean your height is infinite, but just that it has been projected in some way onto different coordinates. 



#39
Jan1009, 01:03 AM

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#40
Jan1009, 01:46 AM

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GR may not be complete, but, nobody has proven it wrong. That hits my hot button. Show me the math before prophetizing.




#41
Jan1009, 02:13 AM

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#42
Jan1009, 04:58 AM

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#43
Jan1009, 05:48 AM

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To put it another way, even with this fundamental energy scale sitting in the theory, if there was no reason to believe that the energy density could ever get high enough to contest this energy scale we might well think that the theory could potentially be absolutely correct. And, of course, there are the incompatibilities with quantum mechanics to consider. 



#44
Jan1009, 05:49 AM

P: 4,513

I don't know what you all are talking about, but the horizon can't be crossed in finite time in the refererence frame of the exterior universe. So is it crossed, or is the question a nonsequiter?
Are we talking physics here, or UFOs? 



#45
Jan1009, 05:52 AM

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I think that the definitive answer to how this works in reality may potentially require an understanding of quantum gravity, which we don't yet have. 



#46
Jan1009, 10:27 AM

PF Gold
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#47
Jan1009, 10:56 AM

P: 604

These lecture notes by Kim Griest might be of interest
http://physics.ucsd.edu/students/cou...161.8feb07.pdf In all cases, [itex]r_s=2Gm/c^2[/itex] '..Suppose we take the case where someone starts from rest at ∞ and falls into the hole.. as viewed from far away the person’s time slows down and then stops as it enters the Schwarzschild radius. The calculation is done starting from radial and time equations: [itex]dr/d\tau=\pm\sqrt{2Gm/r}=\pm\sqrt{r_s/r}[/itex], and [itex]dt/d\tau=\left(1r_s/r\right)^{1}[/itex], where we used conserved energy E=m which is valid starting at rest from infinity. Dividing these equation we find the relation between r and t, that is the speed as seen from from away: [tex]v_{far\ away}=\frac{dr}{dt}=\left(1\frac{r_s}{r}\right)\sqrt{\frac{r_s}{r}}[/tex] We see again that as r→r_{s}, v→0. The far away observer never sees the person fall in..' The following is based on [itex]dr_{shell}=dr\left(1r_s/r\right)^{1/2}[/itex] and [itex]dt_{shell}=dt\left(1r_s/r\right)^{1/2}[/itex] '..We can also find the speed measured in the shell frame: [tex]v_{shell}=\frac{dr_{shell}}{dt_{shell}}=\left(1\frac{r_s}{r}\right)^{1}\frac{dr}{dt}[/tex] For the person falling in from far away, we put in the result for dr/dt above to find: [tex]v_{shell}=\frac{dr_{shell}}{dt_{shell}}=\sqrt{\frac{r_s}{r}}[/tex] This gives the result that to a shell observer, sitting at r=r_{s}, the falling objects goes by at v_{shell}=1, the speed of light! Isn’t it strange that the same object doing the same thing can be moving at 0 speed or c from different vantage points..' Steve 



#48
Jan1009, 11:59 AM

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Now, I'm not certain on this. The idea just occurred to me in reading this thread, and I haven't heard any GR experts' take on it. But it seems to make sense to me. Perhaps I'll send an email to my old GR professor... 



#49
Jan1009, 12:38 PM

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#50
Jan1009, 04:10 PM

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#51
Jan1009, 05:17 PM

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#52
Jan1009, 05:57 PM

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#53
Jan1009, 06:13 PM

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In addition to this, a central singularity is often invoked, but not proven nor motivated. 



#54
Jan1009, 06:36 PM

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If my suspicion were valid for a massive object that perturbs the event horizon, then this would indicate that a black hole might be thought of as a region of space where lots of matter is colliding, but that it's gotten so incredibly dense that time dilation has slowed the collision to an absurdly slow pace as far as outside observers are concerned. 


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