Talk:Black hole/Archive 3

message: The article states:
"A black hole's gravity as described by the
Theory of Relativity causes a number of peculiar effects. An object approaching a simple causes a number of peculiar effects. An object approaching a simple Schwarzschild-type (non-rotating) black hole's centre will appear to distant observers as having an increasingly slow descent as the object approaches the event horizon. This is because photons emitted as the object approaches the horizon take an increasingly long time to escape from the pull of the black hole to allow the distant observer to gain information on the object's fate."
Sorry, but I still think the reason given ("This is because photons emitted as the object approaches the horizon take an increasingly long time to escape from the pull of the black hole to allow the distant observer to gain information on the object's fate.") is plain nonsense, as it gives the impression that "the pull of the black hole" pulls the photon back just as a bullet fired into the sky is pulled back by earth's gravity. The Infidel 17:39, 21 January 2006 (UTC)
replies: text: Actually (according to my physics teacher/guru) the time for the photon leaving from inside the event horizon slows down relative to the outside universe; thus instead it would take an eternity for the photon to get outside the event horizon, rather than it being pulled back. It simply comes to a virtual standstill. Not a real standstill, but slower than any actual speed. Think of the lowest non-negative non-zero speed, and it's even smaller. But it's not zero. --AK7 22:07, 22 January 2006 (UTC)
replies: text: Yea but the photon in question is outside the Schwarzschild radius. The Infidel 19:13, 23 January 2006 (UTC)

text: I'd reword it to something like "Because of the peculiar effects of Relativity, local space in the vicinity of the black hole is "stretched", constantly increasing the distance required to escape the gravitational field, thus photons take much longer to exit the closer they are created to the event horizon." Tzarius 22:21, 26 January 2006 (UTC)

text: I think it's correct the way it is. -- SCZenz 23:23, 26 January 2006 (UTC)

text: One might also mention that the emerging photons are red-shifted -lethe talk 00:59, 27 January 2006 (UTC)
replies: text: Infidel is probably right to complain, because it is grossly misleading to speak of "time slowing down" or such nonsense.  At least some of the above comments fail to distinguish between coordinate time and proper time, or between coordinate speeds and velocity measured in some frame at some event.  It is correct to speak of gravitational time dilation, but only if one describes the observers one has in mind (as ought to be clear from thinking about relative motion in flat spacetime, using a special relativistic analysis)!  And the geometric cause of the gravitational time dilation is easy to spot: the spacetime curvature causes the congruence of radially outgoing null geodesics to diverge.  (The very same spacetime curvature can cause other congruences of null geodesics to converge, of course, which is one reason why we need a tensor to define curvature in Lorentzian manifolds of dimensions exceeding two.)  I'd recommend Geroch, General Relativity from A to B to everyone who doesn't (literally) see what I mean.  Enjoy: it's a great book!---CH 04:56, 22 April 2006 (UTC)
thread_title:  Sorry, but 

message: Question:  If our galaxy has a black hole at its center, does time dilation from the perspective of someone outside the galaxy increase everywhere as the galaxy swirls closer to the event horizon and how does this impact our galaxy bound observations of the rest of the universe?- Dave
:Answer: Very very little.  From far outside, a black hole creates the same gravitation as any other object of the same mass.  (For example, if our sun were replaced by a black hole of the same mass, nothing would change except that it would be very dark.)  Time dialation and other effects of general relativity are very small except when there's very strong gravity, i.e. very near black holes. -- SCZenz 13:17, 27 January 2006 (UTC)
thread_title:  Dave's question 

message: It is a fact that the Schwarzschild radius of the mass the entire universe is assumed to have (incuding dark matter), is larger than the diameter of the universe. If the definition of a "black hole" is a mass inside its own Schwarzschild radius, then the universe is a black hole.
I have searched a little on this matter, starting with this Google search . Accordning to these articles this does not necessarily mean that the universe is a black hole, depending on the definition of "black hole". I have no astronomics education, just a reader of scientific magazines. Please write about this in Wikipedia. /BIL 20:11, 31 January 2006 (UTC)
thread_title:  Universe is a black hole? 

message: Recently this was added:
:According to Scientific American, a black hole can only be formed from a star less than 25 solar masses. If a star is greater than 25 solar masses, when it undergoes supernova it will become a neutron star.
Can someone provide a citation? Kaimiddleton 04:47, 25 February 2006 (UTC)
replies: text: I'm backing this out, both because we don't (yet) have a link to the SciAm article, and because I think it's backwards (larger stars have a substantial enough implosion to form black holes, while smaller don't, and ones above about 40 solar masses go hypernova, collapsing directly to a black hole). --Christopher Thomas 06:26, 25 February 2006 (UTC)
thread_title:  Scientific American - cite please 

message: The escape velocity has to do with the minimum speed at which an object has to be "thrown" away from the "surface" of a body to escape the gravity well. It only applies to objects that do not use their own power while trying to escape. Escape velocity is irrelevant when objects have their own propulsion. For instance, an astronaut climbing a very long ladder from Earth's surface can easily escape Earth's gravity well while his speed will always be much, much, much lower than Earth's escape velocity. Saying that nothing can escape BECAUSE of the high escape velocity is incorrect. By the same reasoning, the astronaut can never leave Earth's gravity well because his velocity is much less than Earth's escape velocity. However, the astronaut can "easily" climb that ladder and escape.
While it is correct that the escape velocity for a black hole is more than the speed of light, the ONLY reason that nothing can escape (not even a "very strong" astronaut on a "very strong" ladder) is that near a black hole, space bends back on itself. It is like a trapdoor. You can go in, but you can never come out because the space inside is bent in such a way that whichever direction you go, you will remain inside. The astronaut cannot keep climbing away from the singularity, because there IS no way away from it. It has nothing to do with not being able to generate enough speed or having enough power or surviving long enough. Even if you could travel FTL, could withstand the force of gravity, and lived long enough, you would not get out simply because no direction you can take is a direction out of it.
In short: What is mentioned at the beginning at the article as well as in the section "Event Horizon" is incorrect.
—Preceding unsigned comment added by Ben Jos (talk • contribs) 
Sorry, didn't mean to leave it unsigned. Ben Jos 05:20, 26 February 2006 (UTC)
replies: text: The short answer is that while you can apply this type of reasoning to situations where the escape velocity is much lower than C (and gravity is more or less Newtonian), things end up working differently when the effects of relativity become important. The Newtonian view of the problem ends up giving the right answer for not-entirely-right reasons. The short version of why you end up not being able to escape a black hole is that within the event horizon, all "time-like" directions point inward, making further progress into the hole (or away from a distant observer) as inevitable as (and equivalent to) moving forwards in time. The way you show this mathematically involves tracing the light-cones emitted from all points on some boundary surface and showing that this boundary contracts no matter what directions the light gets emitted in. More detailed descriptions, and other ways of looking at it, are given in many of the threads above, and in the archived talk page threads. --Christopher Thomas 08:18, 26 February 2006 (UTC)
replies: text: OK... maybe I should have said that spacetime is bent, instead of saying space is bent. I still think the argument made in the article is wrong. It says "escape velocity is c, nothing with mass can go at speed c, ergo nothing can escape". I think you are actually saying the same thing I am. That the reason nothing can escape is because there is no way out. Spacetime is bent, no directions point outward. I cannot climb out because there is no way out, not because I can't produce enough speed. Ben Jos 09:03, 26 February 2006 (UTC)
thread_title:  Escape velocity vs. nothing can escape 

message: The theory that a black hole can be explained as an object who steals time and matter, and sucks it in to nothingness is logically impossible.  You cannot create something from nothing, nor can you change something in to nothing.  You can only change things from one thing in to one other thing.  Thus a black hole in this theory is not possible.  Of course, we can never prove this theory to be true, which is another aspect of the evidence criteria, since nobody has ever seen a black hole, and indeed nobody ever will, since they supposedly steal light and thus as soon as you saw one you would be dead.  All that we have seen are phenomena which we cannot explain.  A black hole, in the concept of something which steals time and matter is not the only explanation, and indeed there are a dozen or more other theories to explain what really happens.  Whilst this particular theory is pushed a lot in non-scientific communities, and has been popularised in the media, within the scientific community other theories are well and truly discussed, and as I understand it this is not the most popular theory.  The use of "Occam's Razor" to ignore other far more logical and likely explanations is nonsensical and biased, and it should not be used in this way.  All of the explanations for what a black hole is or might be should be given equal credit, and it should be made very clear that this is a theory.  
The most logical explanation for what is happening is, of course, that things are not destroyed, that they just change shape, or else are moved elsewhere.  Since things seem to disappear, therefore it is most likely that the "black hole" is not a portal to nothingness but rather a portal to somewhere else (see white hole).  Where this other place is is another matter entirely, but the balloon theory for the universe has been used to explain that it could very easily be a portal from one part of the cosmos to another.  This concept is used almost exclusively in Science Fiction genre with examples like Star Trek using some version of a wormhole to move quickly from different parts of space.  So why is this concept not even mentioned in the article?  Even Albert Einstein thought that white hole theory was a more logical explanation for the theory of black holes, and indeed if I am not mistaken he was the person who postulated that theory.
There are other explanations of equal validity, however, such as the changing shape concept.  Just because we cannot see what they change in to does not mean that they disappear.  It could be that they just become very black and actually exist in some other form.  
Treating this as a fact, however, is a very wrong thing to do.  It is a theory, not a fact.  It is a theory that is taught in schools, but it is not widely accepted in the scientific community.  There are many paradoxes over many elements of this theory that make it a logic impossibility.  To accept it, we must make a leap of faith, and presume that the laws of physics no longer apply.  But if the laws of physics do not apply for Black Holes, then how can they apply elsewhere?  If this exception is true, then the only logical conclusion is that we are misunderstanding the laws and must rewrite them.  
But of course before we do this, we must get over the concept that we can have something that is then turned in to nothing.  Logical impossibility.  Cannot be true.  This theory is nonsense.  It is an explanation that is only accepted because it has been discussed in more detail than the other more believable theories.  And the main reason why it has been discussed is because of the "magical" element of it.  Because it could change the laws of physics.  Because it could mean so many exciting things.  But often the more mundane explanation is the answer.  The more mundane white hole theory with or without balloon theory is far more obvious and makes a lot more sense than the black hole nothingness theory.  Why must we be always accepting things that take such a stretch of the imagination to believe?  This is what Occam's Razor was all about.  It was to stop this kind of nonsense theory from being given credibility.  Its nice for kids, but for serious scholars they should rely on something a bit more believable. User:Zordrac 20:31, 27 February 2006 (UTC)
replies: text: Black holes are objects predicted by general relativity; they're not a theory on their own.  And General Relativity passes every test we've put it to with flying colors, so we tend to think of its predictions as credible.  We've seen objects in the cosmos we're pretty sure are black holes.   That being said, we've never tested any details, and certainly nobody knows what exactly happens at the center.  But physicists take black holes very seriously; in order to compare them to another theory you'd have to say what the alternate theory is trying to explain, which you're really not doing.  Can you clarify your quesetions, please? -- SCZenz 20:47, 27 February 2006 (UTC)
replies: text: Black holes do not turn "something" into "nothing".  When a black hole absorbs light, the mass of the black hole increases.  So the mass of the light is still around, it hasn't disappeared.  Now, if that light were carrying a signal, some information, then a classical black hole would erase that information.  Therefore, classical black holes violate your "something into nothing" rule; they keep the mass-energy, but lose the information (this is known as the black hole information paradox.  Physicists find turning "something into nothing" just as objectionable as you do).  It's a good thing that real black holes are not classical, and quantum mechanics governs the universe: when you model black holes with quantum mechanics taken into account, then even the information stays.  Real world black holes do not turn "something into nothing" (where here, real world means the universe according to string theory.  Snicker).  Hope that helps you get to sleep at night, finally knowing that black holes don't turn something into nothing. -lethe talk [ +] 21:06, 27 February 2006 (UTC)
replies: text: Watch out, guys!  IP address 203.122.209.179 is apparently geolocated in Gosford, New South Wales, AU and registered to Internode Systems Pty Ltd, which is headquartered in Adelaide, AU.  This anon is in fact a suspected sock of User:Zordrac, who is in turn a confessed sock of User:Internodeuser.  The latter two users have apparently been blocked for vandalism and violating WP:NPA. ---CH 05:22, 22 April 2006 (UTC)
thread_title:  A logical impossibility 

message: I am starting an effort to trim this topic a bit. -MegaHasher 20:55, 1 March 2006 (UTC)
replies: text: You might want to stick a  template on it while you edit, as it seems to be edited fairly frequently. Also, please be very careful to fact-check changes made, to avoid removal of correct information. There are plenty of lurkers on the talk page who will be happy to address any concerns you want to raise about the present content. --Christopher Thomas 21:30, 1 March 2006 (UTC)
thread_title: Topic trimming

message: In the formation section, second paragraph, the last sentence reads: "This is because there is a limit to the strength of materials due to the fact that the speed of sound, related to the materials stiffness, cannot be greater than the speed of light."
I was unable to verify if this sentence is correct or if it is the result of vandalism. Enrique Vargas 16:01, 13 March 2006 (UTC)
thread_title:  Vandalism in "Formation"?