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black holes and singularities
Folks,
Before you all scream and kill this thread, please bear with me. I've found questions like this on this group, but no really satisfactory answers, so I'm going to try and phrase it right. Conventional wisdom says that at the centre of your average black hole, lies a singularity. Every book or article that I've read on this subject is adamant about this fact. So, my question would be, *why* the singularity. The presense of one isn't necesary to form a black hole, all you need is a body of sufficient density, e.g. if a sun shrinks beyond size x, it forms an event horizon. So, while the presense of a singularity neccessitates the presense of a blackhole, the converse isn't true. If that assertion is correct, that a singularity isn't neccessary, then why the assertion that they are always present? Doesn't Occam's Razor tell us that it's simply a super-dense object of finite, non-zero volume? Or does theory suggest that once a body reaches that sort of density, then it can't help but continue collapse to a point mass under its own gravity? Of course, that raises a whole host of quantum/classical conflicts, but those aside, what gives? cheers, a |
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black holes and singularities
"Abe" wrote in message
t... Folks, Before you all scream and kill this thread, please bear with me. I've found questions like this on this group, but no really satisfactory answers, so I'm going to try and phrase it right. Conventional wisdom says that at the centre of your average black hole, lies a singularity. Every book or article that I've read on this subject is adamant about this fact. So, my question would be, *why* the singularity. The presense of one isn't necesary to form a black hole, all you need is a body of sufficient density, e.g. if a sun shrinks beyond size x, it forms an event horizon. So, while the presense of a singularity neccessitates the presense of a blackhole, the converse isn't true. If that assertion is correct, that a singularity isn't neccessary, then why the assertion that they are always present? Doesn't Occam's Razor tell us that it's simply a super-dense object of finite, non-zero volume? Or does theory suggest that once a body reaches that sort of density, then it can't help but continue collapse to a point mass under its own gravity? Of course, that raises a whole host of quantum/classical conflicts, but those aside, what gives? The singularity is inevitable for two reasons. First, the collapse of the matter that formed the black hole exceeded the electron degeneracy pressure, the last thing that was preventing the density from growing without limit; there is nothing known, no known force, that can support the matter from total collapse past this point. Second, the equations show that all trajectories below the event horizon lead to the central singularity. Perhaps you've heard of the strange way that time and space seem to change roles inside a black hole? Well, similar to the way that for us out in normal space the future is always, inevitably ahead for us (there's no turning back!), the singularity lays ahead for every trajectory inside the BH. Space becomes like time below the event horizon, with the direction of the singularity being the direction of the "future". |
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black holes and singularities
On Sun, 14 Mar 2004 15:14:23 +0000, Abe wrote:
Conventional wisdom says that at the centre of your average black hole, lies a singularity. Every book or article that I've read on this subject is adamant about this fact. So, my question would be, *why* the singularity. The presense of one isn't necesary to form a black hole, all you need is a body of sufficient density, e.g. if a sun shrinks beyond size x, it forms an event horizon. So, while the presense of a singularity neccessitates the presense of a blackhole, the converse isn't true. If that assertion is correct, that a singularity isn't neccessary, then why the assertion that they are always present? Doesn't Occam's Razor tell us that it's simply a super-dense object of finite, non-zero volume? Or does theory suggest that once a body reaches that sort of density, then it can't help but continue collapse to a point mass under its own gravity? If you don't like a singularity - you can have a tangled ball of strings underneath the event horizon. See : http://www.sciencedaily.com/releases...0304073931.htm -- Gautam Majumdar Please send e-mails to |
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black holes and singularities
"Abe" schreef in bericht t... Folks, Before you all scream and kill this thread, please bear with me. I've found questions like this on this group, but no really satisfactory answers, so I'm going to try and phrase it right. Conventional wisdom says that at the centre of your average black hole, lies a singularity. Every book or article that I've read on this subject is adamant about this fact. Where did you read that ? Can you give me an url with a text which claims that. IMO singularities do not exist. A black hole is something that exists with has a certain radius 0 A singularity is a mathematical construct which you get when radius r goes to zero. In that case the force goes to infinity. So, my question would be, *why* the singularity. The presense of one isn't necesary to form a black hole, all you need is a body of sufficient density, e.g. if a sun shrinks beyond size x, it forms an event horizon. So, while the presense of a singularity neccessitates the presense of a blackhole, the converse isn't true. SNIP Nicolaas Vroom http://users.pandora.be/nicvroom/ |
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black holes and singularities
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black holes and singularities
In message , Nicolaas
Vroom writes "Abe" schreef in bericht et... Folks, Before you all scream and kill this thread, please bear with me. I've found questions like this on this group, but no really satisfactory answers, so I'm going to try and phrase it right. Conventional wisdom says that at the centre of your average black hole, lies a singularity. Every book or article that I've read on this subject is adamant about this fact. Where did you read that ? Can you give me an url with a text which claims that. IMO singularities do not exist. A black hole is something that exists with has a certain radius 0 A singularity is a mathematical construct which you get when radius r goes to zero. In that case the force goes to infinity. "According to general relativity, there must be a singularity of infinite density and space-time curvature within a black hole". A Brief History of Time p 88. -- Save the Hubble Space Telescope! Remove spam and invalid from address to reply. |
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black holes and singularities
"Abe" schreef in bericht t... In article , says... Conventional wisdom says that at the centre of your average black hole, lies a singularity. Every book or article that I've read on this subject is adamant about this fact. Where did you read that ? Can you give me an url with a text which claims that. Well, no, not offhand. However, I distinctly recall Thorne and Hawking mentioning this explicitly. Perhaps my memory is faulty, or my interpretation of what they said. May be this is the article we are looking for: http://home.comcast.net/~ernie1001/papers/blackhole.pdf The article claims at page 1 that there are 2 solutions and one avoids the singularity at r = 0. See also Conclusion at page 7. I did a search with google with "blackhole singularity" but I did not found anything of interest. This url mentions a singularity http://www.geocities.com/wasabidoh/BlackHole.html but does not explain what it is. Nicolaas Vroom http://user.pandora.be/nicvroom/ |
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black holes and singularities
"Abe" wrote in message
t... In article , says... The singularity is inevitable for two reasons. First, the collapse of the matter that formed the black hole exceeded the electron degeneracy pressure, the last thing that was preventing the density from growing without limit; there is nothing known, no known force, that can support the matter from total collapse past this point. Ah, OK. So, does this pressure limit occur at exactly the time at which the event horizon forms? This would depend upon the starting mass. For things like neutron stars, its the degeneracy pressure that keeps them from collapsing further; the electrons have already been squeezed together with protons to form neutrons, and the neutrons are pushed together (no electrostatic force to keep atom nuclei apart when they're all neutrons). It's actually possible to form an event horizon with enough perfectly normal matter. An observer, caught in the process, might not even realize that the event horizon had formed, yet any trajectory he might try to follow would end up taking him inevitably closer to the center of mass of the system. Likewise for everything else around him and below the event horizon. Eventually, the singularity would form when enough matter gets together in the center. Second, the equations show that all trajectories below the event horizon lead to the central singularity. Perhaps you've heard of the strange way that time and space seem to change roles inside a black hole? Well, similar to the way that for us out in normal space the future is always, inevitably ahead for us (there's no turning back!), the singularity lays ahead for every trajectory inside the BH. Space becomes like time below the event horizon, with the direction of the singularity being the direction of the "future". *brain melts* Are you saying that the _effects_ of the singularity are turned into the _causes_ of the singularity, due to this inversion? Not really. I'd have to think about what the implications are vis-a-vis causality. Let's just say that below the EH it's a one way trip to the center and in finite proper time. |
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