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Light inside a black hole?
David, Jan, Jan didn't say anything about the speed of a body causing an increase in its mass. He just said that little masses falling onto a large mass make the large mass larger. And he didn't describe masses falling into an existing black hole. He was trying to describe how a black hole forms: JP image for a moment matter falling into a body. JP As its mass increases, the escape speed from it will JP increase. At some point the escape speed will be JP greater then C, so light cannot escape, we no longer JP see any EM waves coming from it, we call it a black JP hole (is this correct?). George gave a more accurate description. Jan was wrong in suggesting that matter builds up until the escape speed at the surface is greater than c. Instead, the body collapses long before the escape speed is anywhere close to c. The collapse starts at the center, which suddenly increases the density. The event horizon forms inside the body. It grows larger as the body becomes smaller and denser. The event horizon quickly grows larger than the collapsing body. DAS Just because the light announcing the body's position DAS is trapped near the horizon, doesn't mean the body is. DAS This light is special. Most light from the body's DAS passage will have preceeded it into the BH. That's an excellent description. I was almost ready to argue about whether things actually fall into black holes, but I agree completely with what you said here. If we could watch something free-fall into a black hole, we would see it quickly redshift to invisibility at our event horizon. -- Jeff, in Minneapolis |
#22
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Light inside a black hole?
"Jan Panteltje" wrote in message ... ... George, thank you for the explanation. For a real description of the collapse process, have a look at Andrew Hamilton's excellent pages: http://casa.colorado.edu/~ajsh/collapse.html Maybe one day they will figure out some way to know what happens in the BH. The idea is that merging QM and GR may give some answers but also predict some subtle effects in other areas that might be testable. Maybe one of those big particle accelerators will make a tiny BH, and deduce something from that. Even for the smallest BH, the singularity would be far inside the EH and inaccessible to observation. In theory spinning up a BH to expose the singularity might work. Bear in mind that, if Hawking Radiation exists, the BH will evaporate with quite a bang unless it is large enough for its temperature to be at a maintainable level. http://casa.colorado.edu/~ajsh/hawk.html#evaporation A BH with a mass of 10^11 kg has a temperature of 10^12K so you need one much more massive if it is to be stable. A large BH gives of 1000 tonnes energy in the last second of evaporation while the Hiroshima bomb converted 0.6g so you don't want that going off in the lab. The question of how you prevent a BH of that mass falling through the lab floor is also not simple. For much smaller holes, the energy would only be the mass it contains but the lifetime will be correspondingly shorter. George |
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Light inside a black hole?
"dlzc" wrote in message ups.com... Dear Jeff Root: Jeff Root wrote: David, You "plonked" me long ago, so I don't know if you'll see this. Time to clear out some entries then. My understanding of a black hole event horizon is that its location depends on the location and motion of the observer. Agreed. Just like a horizon moves away from you as you move towards it. David, that is one reason why I have doubts about the physicality of the transposition of space and time coordinates. The other is that I suspect any real BH must have a non-zero angular momentum and in the Kerr solution the coordinates revert before the singularity. George |
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Light inside a black hole?
Dear George Dishman:
"George Dishman" wrote in message ... "dlzc" wrote in message ups.com... Dear Jeff Root: Jeff Root wrote: .... My understanding of a black hole event horizon is that its location depends on the location and motion of the observer. Agreed. Just like a horizon moves away from you as you move towards it. David, that is one reason why I have doubts about the physicality of the transposition of space and time coordinates. George, the physicality of length contraction and time dilation in SR can never be answered. I don't expect this to be any simpler. The other is that I suspect any real BH must have a non-zero angular momentum and in the Kerr solution the coordinates revert before the singularity. You are on pretty solid ground there. Seems there was a post here just a couple of days ago that pulsars got their spin not from conservation of angular momentum (with "pre-formation momentum"), but from shedding their outer layers... if BHs were formed in some sort of "shock wave" in dense matter... David A. Smith |
#25
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Light inside a black hole?
Dear Jan Panteltje:
"Jan Panteltje" wrote in message ... On a sunny day (5 Jan 2007 07:45:35 -0800) it happened "dlzc" wrote in . com: Dear Jan Panteltje: Jan Panteltje wrote: On a sunny day (Fri, 5 Jan 2007 09:31:03 -0500) it happened "Greg Neill" wrote in : "Jan Panteltje" wrote in message ... If you move to the centre of a black hole, where gravitational forces sort of cancel, can light and normal matter exist in some area there? Gravitational forces don't cancel because the mass of a black hole (except for the infalling matter from its "feeding") is located at a singlularity at the center. But why? image for a moment matter falling into a body. As its mass increases, The mass of infalling matter does not increase. I was trying to say that the mass of the body increaes. I finally got it. There is no black hole yet. The body you are speaking of is at some threshold. It accumulates more mass. Then you started talking about what happens next. I need to practice "reading for comprehension". Sorry. David A. Smith |
#26
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Light inside a black hole?
N:dlzc D:aol T:com (dlzc) wrote: "George Dishman" wrote in message ... "dlzc" wrote in message ups.com... Dear Jeff Root: Jeff Root wrote: ... My understanding of a black hole event horizon is that its location depends on the location and motion of the observer. Agreed. Just like a horizon moves away from you as you move towards it. David, that is one reason why I have doubts about the physicality of the transposition of space and time coordinates. George, the physicality of length contraction and time dilation in SR can never be answered. In what way David? There is obviously the question of whether the geometry is "truly" Riemann or it is an emergent property but I don't see any problem with the "physicality" of it other than the usual semantic problem that some people include geometric effects in "physical" while other draw a distinction. I don't expect this to be any simpler. I don't think the physics of BHs is "simple" in any way, and it is certainly a lot harder than SR, but that doesn't mean that the answer isn't know by people somewhat marter than I. The other is that I suspect any real BH must have a non-zero angular momentum and in the Kerr solution the coordinates revert before the singularity. You are on pretty solid ground there. Seems there was a post here just a couple of days ago that pulsars got their spin not from conservation of angular momentum (with "pre-formation momentum"), but from shedding their outer layers... if BHs were formed in some sort of "shock wave" in dense matter... Regardless of their formation, suppose you had that most elusive of objects, a non-rotating BH, say 1km in radius. Then one atom falls into it but on an approach trajectory that would miss the exact centre by just 1mm if projected as a straight line from the path a light year away. Once the atom merges with the hole, the hole has a non-zero angular momentum. I think the Schwarzschild solution must be seen as purely hypothetical. Even the electrical charge would have a noise component (thermal ?) as positive and negative ions fall in at random times even though the mean (DC) might stay close to zero. George |
#27
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Light inside a black hole?
Dear George Dishman:
George Dishman wrote: N:dlzc D:aol T:com (dlzc) wrote: "George Dishman" wrote in message ... "dlzc" wrote in message ups.com... Dear Jeff Root: Jeff Root wrote: ... My understanding of a black hole event horizon is that its location depends on the location and motion of the observer. Agreed. Just like a horizon moves away from you as you move towards it. David, that is one reason why I have doubts about the physicality of the transposition of space and time coordinates. George, the physicality of length contraction and time dilation in SR can never be answered. In what way David? There is obviously the question of whether the geometry is "truly" Riemann or it is an emergent property but I don't see any problem with the "physicality" of it other than the usual semantic problem that some people include geometric effects in "physical" while other draw a distinction. I was referring to the ongoing (eternal) struggle between relativists and "Lorentz aetherists". Nature does not allow instantaneous signalling, so the Lorentz aether cannot yield to measurement. "Does the moving rod really contract, or is it an artifact of measurement?" It thought that was germaine to the question of "physicality" I don't expect this to be any simpler. I don't think the physics of BHs is "simple" in any way, and it is certainly a lot harder than SR, but that doesn't mean that the answer isn't know by people somewhat marter than I. I wouldn't put a lot of money on anyone having the one-and-only answer. Just one that is consistent with their knowledge and beliefs. The other is that I suspect any real BH must have a non-zero angular momentum and in the Kerr solution the coordinates revert before the singularity. You are on pretty solid ground there. Seems there was a post here just a couple of days ago that pulsars got their spin not from conservation of angular momentum (with "pre-formation momentum"), but from shedding their outer layers... if BHs were formed in some sort of "shock wave" in dense matter... Regardless of their formation, suppose you had that most elusive of objects, a non-rotating BH, say 1km in radius. Then one atom falls into it but on an approach trajectory that would miss the exact centre by just 1mm if projected as a straight line from the path a light year away. Once the atom merges with the hole, the hole has a non-zero angular momentum. I think the Schwarzschild solution must be seen as purely hypothetical. Even the electrical charge would have a noise component (thermal ?) as positive and negative ions fall in at random times even though the mean (DC) might stay close to zero. Agreed. David A. Smith |
#28
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Light inside a black hole?
dlzc wrote: George Dishman wrote: N:dlzc D:aol T:com (dlzc) wrote: .... George, the physicality of length contraction and time dilation in SR can never be answered. In what way David? ... I was referring to the ongoing (eternal) struggle between relativists and "Lorentz aetherists". Ah, it was your inclusion of ".. in SR .." that threw me. .. Nature does not allow instantaneous signalling, so the Lorentz aether cannot yield to measurement. Perhaps, though the discovery of aether particles in the next generation of accelerator would change that. "Does the moving rod really contract, or is it an artifact of measurement?" It thought that was germaine to the question of "physicality" Between the philosophies yes, but within SR we know the mechanism and it is just a question of how we classify the effect. I don't think the physics of BHs is "simple" in any way, and it is certainly a lot harder than SR, but that doesn't mean that the answer isn't known by people somewhat smarter than I. I wouldn't put a lot of money on anyone having the one-and-only answer. I think GR gives just a single answer. Whether that correctly models nature is a different question but around the EH of a large BH, the indications are that is is a good fit. Quantum effects become significant at much smaller radii. George |
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