Talk:Black hole/Archive 11

Black Hole therapy

There is a website called www.simplegravity.com/blackhole.html which suggests that matter cannot exist in a black hole and as a consequence there shouldn't be any gravity. It then goes on to explain why there is gravity and explains the life cycle and eventual demise of a black hole. Interesting and if not too off-the-wall should perhaps be included in the external reference section. —Preceding unsigned comment added by 188.220.117.212 (talk) 12:05, 4 November 2009 (UTC)

The website to which you refer doesn't seem to add any useful information. The information that it does add is mostly incorrect, not to mention non-notable. Dmitry Brant (talk) 19:46, 5 November 2009 (UTC)

Black hole formation

[e.g. a section of the main article The No hair theorem states that, once it settles down, a black hole has... but for the 'outside' obsever, it never settlles down!]

I think the article needs to clarify confusions such as this: for an observer outside the event horizon, the black hole takes infinite time to form [linked to the fact that the event horizon is teleological] -- so hawking radiation, computer simulations of colliding black holes, etc. - How do they mean anything physical to the observer outside the event horizon(s)? The article should clarify this, IMO... —Preceding unsigned comment added by 59.93.173.254 (talk) 12:51, 5 November 2009 (UTC)

  HI IM DOING A REPORT ON THIS BLAC HOLE!!!!!! =D  —Preceding unsigned comment added by 204.108.96.17 (talk) 16:43, 9 November 2009 (UTC) 

Grammatical point

Hi there - I wanted to make this change myself, but semi-protected status thwarted me as I haven't got around to registering an account yet.

The phrase "black body" in the introduction section should not be hyphenated. The phrase "black-body radiation" has a hyphen *only* because the words "black" and "body" form a compound adjective attaching to the word "radiation" in that context. In this introduction, though, "black body" is simply a compound noun and hyphenation is inappropriate. —Preceding unsigned comment added by 91.135.1.212 (talk) 17:57, 25 November 2009 (UTC)

Featured article drive

User:Cryptic C62 and I worked together on the featured article drive for gamma ray burst . We've agreed to turn our attention to black hole. My first observation is that the article is very bloated and needs to have excessively long and detailed sections replaced with summaries that link to daughter articles. Could the editors who've been working on this article summarize the current state of consensus with regard to shortening the article by converting it to Wikipedia:Summary style? Best regards, Jehochman ^Talk 17:29, 27 November 2009 (UTC)

I'm not a regular editor on this one, but Jehochmans's edits and changes look good to me; the net result so far is definitely an overall improvement in style and quality. In particular, changing the repetitive use of the phrase "settle down" was a job well done. I did tweak one replacement phrase, "steady state", to avoid possible confusion with Steady state or Steady State theory; but I'm not otherwise committed to any particular wording. Also, I strongly support the mass removal of unsourced, OR, and synth material. It's easy enough to replace specific items...if and when reliable sources are provided.

As of now, the article is at 94kb, which is still excessive in length, so I would support both further trimming (for style and clarity) as well as use of Wikipedia:Summary style which could significantly enhance readability. Doc Tropics 00:24, 28 November 2009 (UTC)

I've done quite a bit of editting to this article in the past. Many subsections are already brought into summary form. High on the things do for this article for me is a complete rewrite of the observation and the candidates section. The later should (IMHO) be trimmed down and integrated into the former. The former currently does not do a good job at giving an overview of the observational evidence for black holes. I've tried to gather some good material and draft a new version in one of my sandboxes. But I never got around to finishing it to a point that it could be added. It might be a good thing to look at for inspiration on how to improve that section. (it also has some good references not in the article.)

I completely approve of the removal of the intro section. I think it may be a good to look at some of the revision from before likebox started to edit in march 2009. He added a lot of unreferenced stuff. I don't have much time to help out. But if you are serious about trying to improve this article, I will definately try to help. TimothyRias (talk) 14:18, 30 November 2009 (UTC)

We do have to recognize that Likebox is an expert in this matter. Personally, I rather have a wiki article that violates OR and other core policies but contains correct and interesing information, than a dumbed down article that satisfies the core policies. Of course, if we want to make this article FA-class, then everything must be properly cited. But then, we can also ask Likebox to fix his stuff to make it appropriate for an FA-class article. If he does that in an unsatisfactory way, then we can always decide to remove his edits.

My opinion is for this article is that it should also mention how black holes appear in theoretical physics and what the issues in that field are in some detail. Count Iblis (talk) 16:28, 30 November 2009 (UTC)

I'm also an expert in the matter, and in the end likebox has some very funny ideas about what is mainstream and how to edit wikipedia. (TimothyRias (talk) 16:35, 30 November 2009 (UTC))

I agree that we can't take Likebox POV as gospel. I just looked at the stuff about unitarity, black hole evaporation, information paradox etc. etc. and I think that we need to trim down these sections. But it is better to do that on the basis of a list of priorities, instead of looking at what currently is cited. Because citations can always be added later. Sometimes you can have not so important stuff that is cited and some important stuff that is not. Also, we may need to add some stuff in these sections. E.g., the section about unitarity fails to make clear that if unitary is violated by black holes, then it will be violated in any process, even if it doesn't involve any black holes. This is one of the reasons why this is an important issue. Count Iblis (talk) 16:56, 30 November 2009 (UTC)

Agree. About unitarity/information loss, what we need here is a good two paragraph piece that highlights the main points on this in summary style and a main-link to the information loss article which should contain more of the technical details. Trimming down first, and then (re)adding what we really need may be a good way to achieve this though.TimothyRias (talk) 09:52, 1 December 2009 (UTC)

Jehochman, although I agree with trimming down some of the section, especially the unreferenced, your characterization of these as OR is both insulting to the people that wrote that, and a sign of complete ignorance on the matters on your part. You might want to be more careful in fling the term OR around. For example, this article should definitely at some point mention fuzzballs since they are this point probably the mostly likely candidate for a quantum description of a black hole, and it might be worth noting that these have neither a horizon nor a singularity. TimothyRias (talk) 09:02, 1 December 2009 (UTC)

I might be completely ignorant, but somehow I helped get gamma ray burst to a much better state than where this article presently is. Let's move beyond talking about the editors and focus on the fuzzballs. Which do you think are the two or three most important scholarly articles on that subject. Jehochman ^Talk 13:11, 1 December 2009 (UTC)

I don't see any relation between you first two remarks. (Note that my advice was to be a little more careful with calling stuff OR.) Anyway, with respect to fuzzballs arXiv:0810.4525 and arXiv:0804.0552 are quite extensive review articles on the matter from the proposal's main proponents. Although I think they should be mentioned in the article, a whole subsection seems like a bit much. TimothyRias (talk) 14:23, 1 December 2009 (UTC)

Can anyone argue against this evidence?

As far as I can see the evidence on this website is pretty conclusive. If anyone has a counter claim that they can support with observational or mathmatical evidence, please post. Otherwise it seems kind of silly to be talking about black holes at all. http://www.engr.newpaltz.edu/~biswast/ —Preceding unsigned comment added by 24.161.115.240 (talk) on 17:54, 27 November 2009

Well, when talking about we he calls myth #4 he is just plainly talking out of his ass, since it is quite is to prove rigorously that there are no timelike trajectories to go out of a black hole, end of story. (TimothyRias (talk) 18:16, 27 November 2009 (UTC))

More to the point, it's not us he needs to convince. It's the scientific community at large. Wikipedia's purpose is to describe the existing scientific consensus, not to attempt to change it. --Christopher Thomas (talk) 18:32, 27 November 2009 (UTC)

The article linked to above does not appear to have been published in a peer reviewed journal. Furthermore, chances seem good that it will never be published in anything but a comic book. Sorry, but no, this junior instructor has not changed the face of modern physics as we know it. Doc Tropics 19:02, 27 November 2009 (UTC)

Consensus is not Truth

This discussion has been closed. Please do not modify it.
The following discussion has been closed. Please do not modify it.
The last sentence of the opening section is: Such observations have resulted in the scientific consensus that, barring a breakdown in our understanding of nature, black holes exist in our universe. Such a sentence would indicate that the existence of black holes is a belief rather than a fact. The article should be more explicit. Have we actually discovered any black holes? WillMall (talk) —Preceding undated comment added 18:26, 1 December 2009 (UTC). WillMall (talk) 19:17, 1 December 2009 (UTC) There are no "beliefs" in science, just theories waiting to be proven or disproved. Here we have a theory which has (so far) accurately explained all data and never been contradicted by observable phenomena. It seems that discovering a black hole (in the physical context) would likely be a fatal experience, but they can indeed be deduced by observation. See Quasar for a good example. Doc Tropics 19:37, 1 December 2009 (UTC) We have a model of gravity that seems to work in the situations where we can measure it (including all observations of the universe). That model predicts black holes. Our observations of the universe have found matter falling into (and jetting away from the poles of) objects that seem to have the properties that black holes are predicted to have. So, we've discovered things that either are black holes, or that are objects very much like them. Whether that's what you meant by "discovered" is your call. --Christopher Thomas (talk) 04:02, 2 December 2009 (UTC) All you seem to be saying is that there is a great deal of evidence to support the theory of black holes and so far nothing has contradicted that theory. So you believe in the theory of black holes because that is the best possible explanation for the data so far collected. But it is still a Belief. (Contrast Beliefs with Facts, the two things are not the same.) Take a look at Scientific_consensus. That article completely supports what I am saying. e.g. # the theory of continental drift proposed by Alfred Wegener was soundly rejected by most geologists until indisputable evidence and an acceptable mechanism was presented after 50 years of rejection. So until we come up with some indisputable evidence for the existence of black holes it will remain a theory/belief. WillMall (talk) 17:44, 2 December 2009 (UTC) I hate to break this to you, but "believe in X because that is the best possible explanation for the data so far collected" applies for pretty much everything all of us consider true. It is logically impossible to prove something true by observation - there could always be a new observation that contradicts the old. You believe that if you drop a penny it will fall to the ground, and our model of gravity predicts that it will indeed do so, and all observations to date have been consistent with dropped objects falling. If it instead flew up into the sky, we'd have to alter the model. We can't say that it'd be impossible for it to do so - only that it would be inconsistent with everything we've observed so far. Do you understand what I'm getting at, here? --Christopher Thomas (talk) 18:06, 2 December 2009 (UTC) So how on earth can the comment above yours by Doc say that there are no beliefs in science? You are effectively saying that the entire body of science is a bunch of beliefs! Also, your statement that it is logically impossible to prove something true by observation needs to be proved and supported by an argument. But consider this: is it a belief or a fact that the Moon exists and that it orbits the Earth? Is the existence of the moon a belief or a fact? Let us not be naive here. Some facts are not contested. Of course things may change. The moon may stop orbiting the Earth. The moon may turn to dust. But for now at least we can accept the existence of the moon as a fact. So don’t try to demean me. The questions remains: is the existence of black holes a fact (like the existence of the moon is a fact) or is it simply a reasonable belief? WillMall (talk) 18:39, 2 December 2009 (UTC) User:Doc Tropics is using the word "belief" to mean something along the lines of "faith" - considering something to be true without substantial evidence distinguishing that interpretation from other possible interpretations. I'm not sure whether this is what you mean by "belief" or not; it seems that the two of you are using the word differently. His point was exactly the same as my point: that science attempts to take as little as possible on faith, instead using observations to distinguish between possible models of reality ("theories" isn't quite the right word for that; the word "theory" is misused quite a lot). What I'm trying to get you to understand is that there is no sharp dividing line between statements like "the moon probably exists" and "black holes probably exist". A more concrete example would be to consider an electron. Would you consider us to "know" that electrons exist? You can't see one with the naked eye, but saying that there's something called an "electron" with properties described by a certain mathematical model lets us describe a large set of observations in a useful way. Most scientists will give pretty much the answer I gave in my first response, when asked about black holes: either they exist, or something very similar exists; we have several approximate models of how they behave; we are looking for better mathematical descriptions of how they behave. --Christopher Thomas (talk) 18:57, 2 December 2009 (UTC) Yes, that's an excellent summary. Thanks, Doc Tropics 19:21, 2 December 2009 (UTC) Chris. Yes, we are using the word ‘belief’ in different ways. I am using the definition that comes from philosophy. A belief is any statement that is not conclusively supported by evidence and yet makes claims about reality. Conversely, a fact is a proposition about reality that is true and is conclusively proven. I see your point about degrees of difference. Where do we draw the line between fact and belief, and what counts as ‘conclusive evidence’? Ok fine. But surely ‘the moon exists’ is not up for dispute. On the other hand, ‘black holes exist’ does seem to be up for dispute. I actually think that you are hinting at an instrumentalist view of science, especially with your talk of ‘working models’ of reality. See Instrumentalism. I don’t really have any issue with that, but it is a far cry from presenting black holes as a feature of reality (see: Popper, Kuhn and Feyerabend). On the other hand, if you claim that black holes are a feature of reality (scientific realism) then you must hold distinctions between facts and beliefs. You can’t have it both ways. You can’t speak of working models and also talk of objective reality. If objective reality exists then we will have objective facts about that reality not ‘working models’ and not theoretical entities that help us ‘explain’ the observed phenomena. Do you see? You can be realist or instrumentalist, but you can't be both. Knowledge is made up of facts not beliefs. So putting aside Cartesian scepticism, brain-in-vat type thought experiments, metaphysical idealism, solipsism and other forms of methodological doubt, no serious scientist and no sensible person would say that the ‘moon probably exists’. They would say that ‘the moon does exist and it is a fact that the moon exists'. You are reluctant to accept a distinction between facts and beliefs. But in doing so you are coming very close to saying that there are NO facts in science. Do you really mean that? Are you seriously suggesting that there are no facts in science? Now, if facts do exist in science then you must distinguish between those propositions that are facts and those that are not. Surely that is the very job of science! lol. The moon exists is a fact. If black holes are merely the predictions of a testable theory, if they are nothing more than theoretical entities which even in principle cannot be verified but only indirectly inferred, then it is misleading to say, at this time, that their existence is a fact. The majority of scientists concur that black holes exist, but that does Not make it true. Do you see? WillMall (talk) 22:18, 2 December 2009 (UTC) I see what you're saying, but virtually nothing known to science fits your definition of "fact". The end result of your line of reasoning is to lump everything into the "belief" category regardless of amount of evidence or degree of certainty, which completely misrepresents science. Further, you seem to be overlooking the distinction between "black holes as described by model X exist" and "objects resembling black holes exist". Most scientists think there's enough evidence for the second statement but not for the first. Even with electrons, which you'd probably consider as factually existing, there's uncertainty in exactly how they behave or what they are. We just have a model that describes their behavior very well at low energies (below the electroweak scale). I believe that statements can be factual, but that we have no way to prove them so (only disprove). I think you'll find that most scientists hold this view (hence all of the weaselling about "X is likely to be true" and "X is unlikely to be true", rather than "X is true"). The models of reality that are considered scientific theories or scientific laws are those which _can_ be falsified by experiment and observation, but which large numbers of experiments and observations have so far failed to falsify. They are considered sufficiently likely to be true as to be treated as fact, but cannot be proven to be fact in the sense that you seem to be using. Does this give you a better idea of where I'm coming from? To put it another way, how would you propose to make statements of fact about celestial objects that are too far way to directly probe, or about particles that are too small to observe with human senses? We always have to rely on indirect measurements for that sort of thing, which requires assumptions about how the universe works. --Christopher Thomas (talk) 23:10, 2 December 2009 (UTC) The nature of science and of scientific knowledge is widely debated. Of course you are entitled to your own beliefs about science, but you are not in a position to speak for ‘most scientists’. Look up Falsifiability and Sokal. It is far from being the main view of science. Also, if your other statements are correct, then it simply means there are some aspects of the universe of which we will never have absolute certain knowledge. But so what? That’s not my fault :) WillMall (talk) 11:12, 3 December 2009 (UTC) No offense to the OP, but this page is for discussing improvements to the article, not for discussing the philosophy of science or the nature of knowledge. Did you have a specific suggestion for improving the article? Doc Tropics 15:48, 3 December 2009 (UTC) We are going round in circles. Take a look at my first comment. You will see my suggestions for improving the intro. Then take a look at your comment and you will see that you are the one that started the debate on the nature of science when you said, ‘‘There are no "beliefs" in science, just theories waiting to be proven or disproved.’’ That is your opinion about the nature of science and, by your own words, it has no place in this discussion page. WillMall (talk) 16:45, 3 December 2009 (UTC)

Observational evidence

As it is the observation (now observational evidence) and candidates section give an inadequate representation of the observational status of black holes. The sections currently read as some random random tidbits of evidence that have somehow reached the popular media without giving a general picture of the how and why of the bread and meat of the evidence available.

To try and alleviate this problem I've started adding/replacing some subsections with section I had been preparing in my sandbox. These are far from a finished product and will need some more work, but at least they give a better picture then the current/previous versions. These new sections also come with quite a few "citation needed" tags. These indicate statements that I know to be true from general knowledge of the field, but for which I have not yet found suitable references. (Anybody know a good recent review article on black hole observations, the one being referenced now is already ten years old.) They serve as an invitation to everybody to find suitable refs.

One of my goals with these revisions is to completely absorb the candidates section in the observation section. This should overal reduce the amount of redundant material. TimothyRias (talk) 10:57, 7 December 2009 (UTC)

???

How do we know that blackholes are there if we can see them?DellTG5 (talk) 23:06, 25 November 2009 (UTC)

We can see matter falling into them (per accretion disc), and not striking a surface (unlike the accretion discs around neutron stars or white dwarf stars). --Christopher Thomas (talk) 23:34, 25 November 2009 (UTC)

the article is not supporting black holes, in fact it properly uses "theory" and "hypothesis" quite often. However, we need a page describing to people what a black hole might be. The article should not be an argument of whether black holes exist, but I would support a section that mentioned alternate theories or information that debunks the theory. You'd have to find some articles that supported an alternate theory, though, and cite them.Akuvar (talk) 01:10, 14 December 2009 (UTC)

IMO, the "evidence" section needs an "alternatives" subsection(in fact I have one drafted in my sandbox). The problem is finding good sources. It is not hard to find articles and even review articles on some of these alternatives, but they usually have been written by the alternatives main proponents, making them not such a good source for the plausibility/acceptance of these alternatives, and whether they can be excluded based on current evidence. This makes it hard to select exactly which alternatives should be mentioned. Clearly, quark star and fuzzball need to mentioned, Q-star and gravastar are more questionable however. (There are for example articles claiming to debunk the later option.) TimothyRias (talk) 09:20, 14 December 2009 (UTC)

I visited your sandbox. I think it adds way too much, as it is written, to the length of the article, if added. I also think it reads too much as a personal explanation, like I was reading your thoughts in a book (there is probably some definition literature majors would call that) and not like reading an encyclopedia article. I suppose you could go back and fix that, but it is a lot of work. I suppose we could just have a heading and then list alternative theories with links to their wiki pages and no other explanations or rationalizations? Akuvar (talk) 03:09, 17 December 2009 (UTC)

Intro needs improvement

The intro needs to be NPOV. I have added a citation tag. WillMall (talk) 14:43, 4 December 2009 (UTC)

The intro definitely needs improvement. Per WP:LEDE, it should be up to four paragraphs long and summarize the entire article. At this point it does not do that. Jehochman ^Talk 15:14, 4 December 2009 (UTC)

Lead section is definitely better. User:TimothyRias has done some great work. WillMall (talk) 21:06, 16 December 2009 (UTC)

Assumptions about Black Holes

Some Muslim scholars believe that the Qur'an mentioned black holes in more accurate terminology. In Surah 81, it goes that Allah said: "So verily, I swear by the invisible celestial bodies that recede; those are the bodies that move swiftly and hide themselves, sweeping (anything towards themselves)". Translations of the terminology that came out in the verses referred to are variant, and most of them have been rendered based on a human (sometimes erroneous) understanding of the nebulous Arabic terms by some interpreters). The term assumedly used to refer to black holes in the Arabic text of the Qur'an is transliterated as "AlKhunnes", which means in Arabic 'any body that can never be seen'; it is from the verb "khanasa" meaning disappear - the devil being thus named "AlKhannas" or the Invisible. The other terms, 'moving' and 'hiding' in high speeds, and 'sweeping' whatsoever falls within their gravity, metaphorically like a broom. As often termed, the 'black hole' is not the accurate term; a hole usually denotes space or void or emptiness - vaccuum in scientific terminology, but these bodies, quite on the opposite, are not void; they are heavy masses of incredible weight. Furthermore, the description as black is not correct, either. These bodies are colourless, because they do not radiate any visible rays. The Qur'anic terms "the ever-hiding, the ever-invisible' and 'the sweeping brooms' can be more accurate terms as they precisely describe the nature and movement of these heavenly bodies in real fact; some cosmic physics scholars describe these bodies as sweepers because they sweep away any objects in the firmament. —Preceding unsigned comment added by Mohkheimer (talk • contribs) 07:41, 21 November 2009 (UTC)

I think your reference from the Qur'an is interesting. I think it it may find a place in the main article. I wouldn't want to make a heading of "black holes in literature" but it is certainly interesting along the "chariots of the gods" line, that an ancient text describes an "as of that time unknowable" cosmic feature. Your second point about the use of "black hole" and how accurate it is, and various descriptions for other names....well, people on wiki are going to search for black hole, as that is what they are commonly known as today. I want to point out that I support your introduction of the Qur'an description, but I am athiest and have no vested interest in promoting that or any other religious work.Akuvar (talk) 01:05, 14 December 2009 (UTC)

Any such addition would have to be supported a reliable source for this interpretation of that verse and some sort of evidence that this interpretation is somewhat notable. Normally, notability is not a requirement for inclusion in an article, but you can literally fill libraries with everything that has been written about black holes. Obviously, this article cannot reference everything, as such we need to stick to the most notable/main stream.

If there is sufficient evidence for notability, the best option might be to create an article Black holes in the Koran, which can be briefly reference from this article (probably either from the history section or from the see also section.)

Right, but there is no place for that topic to fit in under the current article. Unless you created a heading of "black holes in culture" or "black holes in literature" or something like that, and I don't support either of those because I don't think thee is enough relevant, notable information to go under such a heading. If the above user wants to include the Qur'an info, yes, citation and accuracy of translation, an then he will also need to find a suitable place to insert it into the existing article - but again, I'm at a loss at to where that would be. Let's see if he returns and makes a comment before I spend anymore time worrying about it! Akuvar (talk) 03:02, 17 December 2009 (UTC)

About, the name, well it is simply a name. Note that black holes are actually black according to the normal definition. (They absorb all radiation, and emit a black body spectrum.) TimothyRias (talk) 09:06, 14 December 2009 (UTC)

I'm going to also say that the original comment sounds like a point of view intended to attempt to "prove" a religion, in this case Islam. As the argument often goes, "this Quran/Bible/Talmud/etc predicted/described that and thus this religion is true". Obviously, such arguments are inherently biased - and often based on tenuous and subjective scriptural interpretations - and need a very very good source, not tied to the religion in any way, before appearing on Wikipedia. -RadicalOne---Contact Me 03:26, 17 December 2009 (UTC)

I agree with RadicalOne. Black holes are not mythological proofs to be used in religious debates. They are scientific predictions/description of an observed phenomenom. Quoting some religious book, no matter its origin, serves no purpose but confusing the reader, linking together science and religions where no such link is relevant. Paercebal (talk) 14:41, 27 December 2009 (UTC)

Escape velocity

I think this article needs to make it clear that it is NOT the fact that the escape velocity is superluminal that nothing can escape from a black hole. After all, escape velocity is only about the starting velocity at the surface of something. An astronaut climbing a ladder could easily "escape the Earth" without ever even getting close to the Earth's escape velocity.

Instead, the gravity of a black hole is such that there really is no way out. It curves space in such a way that there are no outward bound paths. Not even for someone walking or climbing out. Escape velocity is NOT the problem of being unable to get out of a black hole. Instead, the problem is that a black hole is "strong enough" to make all paths lead inward. It curves space inward.

I think that needs clarification in this article. 68.200.98.166 (talk) 20:07, 27 December 2009 (UTC)

T-Symmetry

This sentence needs to be removed: "That is if the position and velocity of every particle in the universe were measured, we could (disregarding chaos) work backwards to discover the history of the universe arbitrarily far in the past." This is a complete misunderstanding of the concept, and this conclusion is completely nonsense. The idea is that nature allows the time-reversed interactions. Nothing about the traceability of all interactions is claimed, sensibly so. Dr.P. —Preceding unsigned comment added by 165.201.140.155 (talk) on 18:07, 12 August 2009 (UTC)

Disclaimer in the Lead

You have to make it very clear in the Lead that black holes are still just a theory, so you have to give equal weight to that statement. All scientists agree that there is no firm proof. Circumstantial evidence does not prove anything and this must be made clear. The existence of black holes is just a THEORY. It cannot be presented as a fact. Thx. —Preceding unsigned comment added by 202.70.51.139 (talk) 00:16, 23 January 2010 (UTC)

I attempted to add the following statement to the lead: "Although the evidence for the existence of black holes is strong, it is largely circumstantial, and there is not yet any direct proof" with a reference to J. C. Wheeler's Cosmic Catastrophes. For those who are curious, here is a transcription of the passage I am referring to: "Black holes are so strange and so significant that the standard of proof must be exceedingly high. As we will see, the evidence is very strong, but still largely circumstantial." Two pages later, he writes the following: "Absolute proof escapes us, but the net of circumstantial evidence has grown ever tighter."

The edit was reverted, as I suspected it would be, with the following argument: "It is a fairly blanket statement to flat-out declare there is no direct proof - anywhere. Furthermore, this does not belong in this part of the article". I have two problems with this. The first is that it is not our job to determine which statements are too blanket-y to be included in an article. Our job is to report those statements made in reliable sources which reflect the consensus of the scientific community, which is what my proposed addition aimed to do. Although the theorists have shown that black holes can exist, and although there is a plethora of observations that can be explained by the presence of black holes, as far as I am aware there is not yet any proof that black holes do exist. Of course, I may be mistaken in this assumption; if anyone is aware of any recent breakthroughs that prove the existence of black holes, let's see it!

The second is that, regardless of whether or not black holes have been proven to exist, it is absolutely crucial to present this information in the lead. If there is not yet any proof, readers should not read through the article under the assumption that there is proof. On the contrary, if there is proof, the lead should make this clear as well. --Cryptic C62 · Talk 19:10, 16 January 2010 (UTC)

I don't know if they exist or not, so I stand with you. But we are talking about equal time here for a different theory that is probably not equal in standing. It is clear that the scientific community on a whole thinks that black holes exist, how strong is the opinion that they do not exist? I think the analogy of Darwinism to Intelligent Design is good here, the proponents of ID argue that both are theories and deserve equal time, why not present them both? And the answer is that one theory is extremely likely where the other, from a scientific view, is far from likely. So does the theory of black holes not existing deserve equal time here? Akuvar (talk) 21:16, 16 January 2010 (UTC)

Evolution is an interesting example. If you'll take a look at evolution, you'll see some of the minority opposing views in the section Social and cultural responses. This even has a daughter article, Objections to evolution. Also, I think in the case of black holes there isn't much opposition to the theory itself. I'm just trying to emphasize that, in the eyes of some authors, there isn't conclusive evidence of their existence yet. Some of this comes from the fact that some the observations can be explained by undetected neutron stars:

"Careful study of the Cygnus X-1 system, both the X-ray source and its companion massive star, shows that the companion has a mass of about 30 solar masses, and the X-ray source a mass of about 10 solar masses ... the reasonable conclusion seems to be that Cygnus X-1 is a black hole ... but all we really know for Cygnus X-1 is that a 10 solar mass "thing" is emitting X-rays. As an example, let us consider a way in which nature might be playing a trick on us. We know that truiple-star systems are present in the Galaxy ... Suppose that Cygnus X-1 consists of a neutron star of 1 solar mass orbiting an ordinary star of 9 solar masses, and that the pair of them are orbiting another ordinary star of 30 solar masses. If the 9-solar-mass star transfers mass to the neutron star causing the emission of X-rays, then we will have an X-ray source with total mass of 10 solar masses orbiting a 30-solar-mass star, just as the observations demand, yet there would be no black hole. This picture is unlikely, but not entirely impossible." Wheeler 2007, p. 210

The doubts as to the conclusiveness of the evidence also comes from the fact that the core collapse model (as well as various other models, I'd imagine) is not yet perfectly refined: "Unfortunately, understanding the mechanism which extracts the gravitational potential energy released as a massive star's core collapses down to a 10km neutron star has proven to be extremely difficult, requiring the implementation of a broad range of physics from neutrino interactions and transport to general relativity and to convection. Currently, no one has a model of the core-collapse of a massive star which contains all of this physics completely." Fryer 2001, p. 79

--Cryptic C62 · Talk 00:46, 17 January 2010 (UTC)

The issue of evidence for the existence of black holes is indeed subtle and filled with ifs and buts. The article can probably do a better a job elucidating these points. In the end it should give an accurate reflection on the current scientific consensus on this issue. The proper way to go about this is to first improve the "observational evidence" section, in which there is room for the subtleties of the arguments. Once that section has been fleshed out, and we have found a consensus with all the editors here, it will be much easier to summerize that section into a consize and accurate statement in the lead. Trying to added any statement directly into lead like Cryptic tried, as likely to be inaccurate and provoke edit wars with other editors that don't agree. Such a move is disruptive of the collaborative atmosphere here and generally a bad practice. TimothyRias (talk) 20:42, 17 January 2010 (UTC)

I see no reason to provide information on the actual existence of black holes in the lede, since they are theoretical constructs. There are very many different alternatives to black holes (see the footer template) The point/counterpoint should be in the meat of the article, or a criticism section. This is an article on black holes, so for the purpose of the article, they are what they are. 76.66.197.17 (talk) 06:10, 19 January 2010 (UTC)

Per Wikipedia:Lead, the lead should summarize all of the article's sections, which would include a criticism/alternatives section. --Cryptic C62 · Talk 16:23, 19 January 2010 (UTC)

That is folly, there are so many alternate explainations for black holes that it would explode the lead to exceed the size recommended in WP:LEAD. You do not need to say it, what you said, since all you need to state is that there are alternate explainations. 70.29.214.95 (talk) 06:05, 20 January 2010 (UTC)

Crossing the event horizon

I'm having a bit of trouble with the following paragraph from the Event horizon section:

"To a distant observer clocks near a black hole appear to tick more slowly than those further away from the black hole. Due to this effect (known as gravitational time dilation) the distant observer will see an object falling into a black hole slow down as it approaches the event horizon, taking an infinite time to reach it. At the same time all processes on this object slow down causing emitted light to appear redder and dimmer, an effect known as gravitational red shift. Eventually, the falling object becomes so dim that it can no longer be seen, at a point just before it reaches the event horizon."

Here's an alternative explanation which I find to be more intuitive, paraphrased/quoted from the Wheeler 2007:

"Consider a clock falling into a black hole. From the clock's perspective, it falls straight into the black hole, passes through the event horizon, and is then destroyed by gravity. From a distant observer's perspective, the clock runs more and more slowly as it approaches the black hole. The distant observer never sees the clock pass through the event horizon. The reason is that the photons being emitted by the clock take longer and longer to reach the observer as it comes closer to the black hole. The last photon emitted by the clock before crossing the event horizon takes a very long time to reach the observer; in principle, the observer can always see some photons from the clock, no matter how long they wait. Because of the increasing red shift and the delay between the arrival of the photons, the actual perception is that anything falling into the black hole turns black very rapidly."

Is this accurate? I tried coming up with a way to merge this explanation with the first one, but I'm afraid I don't really understand the concepts presented in the first one well enough. Any thoughts? --Cryptic C62 · Talk 00:04, 19 January 2010 (UTC)

Well, the paragraph you quote from this article does not really explain anything it simply states some of the effects that happen near the event horizon of a black hole. Wheeler's quote mostly does the same thing, although he leaves the impression of explaining. (Which mostly due to the difference in expected style for a work of popular science and an encyclopedia.) What I don't like about the quote form Wheeler is that it does not introduce what is meant by terms like "red shift", etc.

Cryptic, can you try to explain what it is that you have trouble with in the current paragraph? This might help in improve it further (maybe with some inspiration from Wheeler's quote).

Something else I did notice is that due to successive edits the explanation of what an in falling observer sees has disappeared from the article. We should try to remedy this as well.TimothyRias (talk) 09:48, 19 January 2010 (UTC)

Yes, I'll try to explain what I was having trouble with. When reading the two paragraphs, I realized that Wheeler's/my explanation of the photons taking longer to reach the observer as the object approached the event horizon was probably directly related to gravitational time dilation or gravitational redshifting. However, after glancing at both of these articles, I couldn't really figure out how they related. If, on the other hand, Wheeler's/my explanation does not directly relate to either of those two concepts, I am not sure how to merge the two explanations in a coherent manner. It is tempting to simply replace the current paragraph with the one I wrote and let the more scientific editors add in the relevant buzzwords later, but I'd rather discuss the matter first. Hope this helps. --Cryptic C62 · Talk 16:18, 19 January 2010 (UTC)

I'd prefer if you do not replace the current paragraph by your version since I have some gripes with some of the wording (for example "destroyed by gravity"). The photons taking longer to reach the outside observer is simply the time reverse statement of objects taking infinitely long to reach the horizon, both are a direct result of the gravitational time dilation approaching infinity near the horizon. Time running slower near the black hole means that everything including light moves slower too. Your/wheeler's explanation simply does not cover this time dilation aspect (well it basically drops it out of nowhere in the last line) and is very much fixed on a falling object, while the current paragraph is true for any object near the horizon. TimothyRias (talk) 16:42, 19 January 2010 (UTC)

Then I suppose we should work to tweak the current paragraph to make its meaning clearer. There is another section in the Wheeler book that explains in some depth how objects are destroyed, perhaps I can combine this with some information on the perspective of infalling observers to augment the current paragraph. --Cryptic C62 · Talk 23:10, 19 January 2010 (UTC)

Does your description of the slowing down of photons ("taking more time to reach the observer") imply that the velocity of light will be lower. Velocity of light only depends on the ambience, eg vacuum, air or water. In case of tge effect of gravitation on light, its spectre changes which is called "red shift", but the velocity (even the relative one) does not change. Is it right? Gantuya eng (talk) 04:13, 20 January 2010 (UTC)

In their own space, the photons will be going at the same speed. However, as space is extremely distorted in a gravity field of this intensity, it has more space to cross to cover the same "distance". Have you seen an image that showed space as a gridlined rubber sheet, with gravity forming a "dent"? The gravity "squeezes" space and thus the gridlines are closer when in proximity to the stellar remnant or singularity. Without images, it is nearly impossible to explain; please tell me if I have failed to convey the concept. -RadicalOne•^{Contact Me}•_{Chase My Tail} 04:25, 20 January 2010 (UTC)

OK, thanks. Gantuya eng (talk) 06:41, 20 January 2010 (UTC)

I've added a short paragraph on the perspective of an observer falling into the black hole. About the destruction of object by gravity, I suspect that Wheeler is talking about tidal forces. First thing to note is that this completely unrelated to the event horizon. The location where tidal forces become relevant is not in anyway related to the location of the event horizon. So, if we are to discuss it should be in a different section. There used to be a section on spaghettification, but it had major issues and was removed. I'm not really convinced that we should add something like that again. Tidal forces are a general issue for gravitating objects, and in the case of black holes it may very well be that quantum gravity kicks in before it becomes an issue. TimothyRias (talk) 09:22, 20 January 2010 (UTC)

Perhaps a bit about tidal forces / spaghettification (new favorite word) could be added to the Singularity section? I think that section should be expanded anyway; I suspect it will be the section which readers will jump to in an attempt to explore the 'weird' effects of gravity associated with a black hole. --Cryptic C62 · Talk 18:08, 20 January 2010 (UTC)

I've expanded that section a bit. Missing anything else? TimothyRias (talk) 16:11, 22 January 2010 (UTC)

Typo?

In section: Properties and structure:

where it says: "is lost as the field is evenly distributed alonE the event horizon" -> should be "along" maybe, not alone

Strange things happen near the event horizon. The usual laws of spelling as we know then start to break down. Jehochman ^Brrr 17:33, 26 January 2010 (UTC)

Mysterious paragraph

The following paragraph appears in the Galactic nuclei section of Black hole.

"From the orbital data they were able to infer that there was a spherical mass of 4.3 million solar masses contained within a radius of less than 0.002 lightyears. This is still more than 3000 times the Schwarzschild radius corresponding to that mass. This is consistent with the central object being a supermassive black hole."

This, if adequately referenced, is a very important claim! However, the only reference in that paragraph is Ref 78, the massive 16-year report by Gillessen et al. I obviously didn't read through all 1109 pages of the article, but I did make an earnest attempt to find the figures that appear in the paragraph. I couldn't find it. I admit the possibility that I was unable to find these exact numbers because the original figures were written in a different form (using scientific notation or different units), but if that's the case, then I would prefer to avoid making conversions and simply report what the article does. Even so, it seems to me that the Gillessen article is more focused on determining the masses of the relevant objects and the distances to them rather than determining the the radius of the black hole candidate.

So, any ideas? Can someone who is more familiar with the Gillessen article help us out? --Cryptic C62 · Talk 18:30, 1 February 2010 (UTC)

That article is only 35 pages long. It should not be too hard to find the values for the mass contained within the pericenter of s2 and the distance from the pericenter to the central object. Those are the numbers quoted here. All though the numbers appearing in that section are round to the nearest significant digit. TimothyRias (talk) 19:20, 1 February 2010 (UTC)

Ah yes, it is only 35 pages. I mistakenly assumed the original journal page numbering pertained to the individual article :P. Also, the Gillessen article does indeed specify the total mass of the central object—it even does so in the abstract. I cannot, however, find any discussion of the radius of the central object, nor the conclusion that it falls under the Schwarzschild radius. In fact, I found no instances of "Schwarzschild radius" within the entire article. I suspect that some of the figures quoted above may have instead come from the other articles cited within the Gillessen article. --Cryptic C62 · Talk 22:30, 1 February 2010 (UTC)

If you check the section on checking for an extendended mass component you will find that the article concludes that the 4.3 solar masses are contained within the radius of the pericenter of the S2 orbit, which is 0.58 mpc, which is the .002 ly cited in this article. As a matter of perspective I compared this to the schwarzschild radius of a 4.3 solar mass BH. This gives approximately the number 3000 cited. TimothyRias (talk) 06:57, 2 February 2010 (UTC)

I see it now (Section 6.3 if anyone else is curious). I suppose the conversion from parsecs to lightyears is alright, but I would be hesitant to include the 3000 figure or the conclusion that the central object is a MBH. Neither are included in the Gillessen article, and Section 6.3 in particular does not set out to prove/disprove the presence of an MBH. The problem now is that if this information were included in the paragraph, it would not be an accurate representation of the given source material. If, on the other hand, it is not included in the paragraph, then the paragraph no longer has a coherent purpose, although Sagittarius A* is tremendously important and should definitely be included here. My suggestion would be to keep Gillessen but to try to find alternative sources to back up the MBH claims. Thoughts? --Cryptic C62 · Talk 17:40, 4 February 2010 (UTC)

If I remember correctly, the Gillessen claims somewhere in its production that it gives the best available evidence that Sag A* contains a Supermassive BH. The comparison to the amount the amount of schwarzschild radii is a straight forward computation that adds a lot of context for a lay reader. Similar comparison can be found in many other articles that give restrictions on the size of a SMBH, the gillessen article probably omits only because it assumes readers to be familiar with the relevant scale. TimothyRias (talk) 21:46, 4 February 2010 (UTC)

Considering the size and complexity of the document in question, perhaps it would help our readers if we broke up the references into pages or sections. I highly doubt that anyone attempting to verify this material would want to sift through all 35 pages to find these figures. I suppose later tonight I can change the Gillessen ref to a Further Reading entry and then make each individual ref refer to a specific section. Do you happen to remember where he makes this claim? You are evidently more familiar with the article than I am. --Cryptic C62 · Talk 22:18, 4 February 2010 (UTC)

(outdent) As near as I can tell from skimming the paper, the authors are assuming a priori that most of the mass is in a central black hole, and are studying motions of nearby stars to see if the gravitational potential deviates from the one produced by that assumption (interpreted as looking for dark objects orbiting the "massive black hole" (MBH) object). Section 6.2.2 on page 1093 mentions testing the hypothesis that the radio source Sgr A* is indeed at the location of the black hole, but doesn't seem to be testing the assumption that a black hole is present. Testing the mass distribution around the hole is done in section 6.3 on pages 1094-1095, but uses very simple models (a uniform-density halo, a halo with a power-law radial density distribution, and a halo with a globular-cluster-like Plummer model distribution). In all cases, they're assuming a very large number of small halo objects, rather than a few big ones, and they're assuming uniform angular distribution (vs. being flattened into an accretion disk).

The most useful test they perform is the Plummer model test, which assumes a uniform-density core of objects and a halo that trails off outside the core. They cite a core radius of 0.015 parsecs from a previous paper by Mouawad et. al. (2005), and from that try to fit the Plummer model distribution to the measured orbit of the closest star to the hole (S2). They conclude that very little, if any, halo mass is between the closest and farthest points in this orbit (< 4% of the central mass at one sigma and < 6.6% of the mass at 99% confidence). The fitted values' error ranges overlap with the "none of the central mass" possibility. Difficulties are that 1) there's only one star close enough to try fitting, and 2) the closest approach had bad data, which they acknowledge and try to work around. More important to us would be the r = 0.015 pc number, which isn't addressed in this paper. For this paper, the relevant quote at the end of section 6.3, on page 1095, is "a single-point-mass potential is (still) the best description of the data", with the caveat that this mostly applies on scales on the order of the sizes of the orbits of the stars studied.

The possibility of a smaller (intermediate-mass) black hole orbiting the central one is discussed in section 7.2 on page 1098-1099, but not as rigorously (mostly they graph constraints found by other papers on this, combining the results) Their orbit fit for the S2 star excludes anything bigger than about 2% of the mass of the central hole.

Long story short, they make a convincing argument for mass being concentrated into a compact region considerably smaller than the innermost star's orbit without any extended halo to speak of, or any large companion components, but don't try to prove that it's a black hole. --Christopher Thomas (talk) 00:13, 5 February 2010 (UTC)

I agree, although they do think (as does most of the community) that this is the best evidence for the existence of an astrophysical MBH. (the article says so in the first paragraph). The first non-exotc, non-black hole scenario that would approach this density would be a cluster of millions of ~solar mass dark objects. It is well known that such clusters are not very stable, which rules them out. The thing simply is that people have not been able to come up with non-exotic alternatives that are as dense, dark and stable as this.

The problem with the Gillessen article is that it assume a familiarity withthe discussion surrounding the evidence for the existence of MBHs. They are only repeating the key calculations with their more accurate data.

I think that the current paragraph does a fairly good job of summarizing the conclusion that can be drawn from that article. Definitely, a lot better than the typical news media around the time of the release of that article. TimothyRias (talk) 12:12, 5 February 2010 (UTC)

I think we should be backtracking through the citation tree to find the first articles that explicitly drew the conclusion that the most reasonable assumption for type of object was a supermassive black hole, and cite other papers (like this one) as providing tighter constraints supporting that conclusion. That said, I'm supposed to be on sabbatical, so do as you see fit :). --Christopher Thomas (talk) 18:54, 5 February 2010 (UTC)

I concur with Chris's conclusion with the exception of this whole "sabbatical" notion :P. This weekend I'll dig through Gillessen's citations to try to find the paper that concludes that Sag A* contains a MBH. --Cryptic C62 · Talk 22:07, 5 February 2010 (UTC)

You're going to be going back more steps than that, I'm afraid. The hypothesis has been around for a while. I'd expect to find a series of papers proposing it (saying that observations are consistent with a massive object being present), but not ruling out other objects. Then you'll find papers putting tighter constraints on what's there, saying that a black hole is the most likely explanation. Most papers won't actually claim proof of a hole, because it's much easier to back up "probably a hole" than "certainly not anything other than a hole". The only paper that comes to mind that might do it would be the one from within the last decade where radio astronomers claimed to have imaged the inner edge of the accretion disk. Any other type of object would show impact light and other interesting things from that region, but Sag A* doesn't. --Christopher Thomas (talk) 22:25, 5 February 2010 (UTC)

What we really need is a good uptodate review article about astrophysical supermassive black holes. The most recent one I've found is the ten year old one (current ref 62). It is somewhat behind on recent developments. TimothyRias (talk) 19:57, 7 February 2010 (UTC)

Size Distribution Graph?

Intermediate-mass black holes appear to be much less common than stellar-size black holes and also rarer than galaxy-sized black holes. But how much rarer? It would be very useful to include a table, or preferably a graph, showing the number of black holes detected or predicted at each order of magnitude from the smallest detected hole size to the largest [ie across 9 orders of magnitude from 1.4 to 18 billion stellar masses] --Tediouspedant (talk) 13:31, 7 February 2010 (UTC)

It would be silly to create such a graph because black holes are still largely theoretical. --Cryptic C62 · Talk 17:04, 7 February 2010 (UTC)

On the contrary, we can certainly create a graph that lists compact objects of various mass ranges. Without major modifications to both general relativity and quantum mechanics, these would represent black holes or objects very much like them. If you insist on a caveat, call them "black hole candidates" rather than "black holes". The mass is something that can be directly measured, so there should be no problem with considering the data points in the graph factual. --Christopher Thomas (talk) 22:36, 7 February 2010 (UTC)

A good solution. The other problem: From where do we get our data set? Is there a database somewhere that lists black hole candidates and their masses? Anything other than that would be incomplete or WP:OR. --Cryptic C62 · Talk 23:25, 7 February 2010 (UTC)

Another issue I see is whether to plot the number of known candidates or the expected number of appearance. The first number would be terribly misleading since it very skewed by observational bias. There is also the issue of what counts as a candidate. The second would be more feasible as a graph. Expected frequencies of stellar mass black holes should be available from stellar evolution models, and a quick search on the archive shows quite some literature on the demography of supermassive black holes, but I think very little is known about the frequency of intermediate mass black holes. If they exist they could by quite a bit more frequent than the supermassive variety, but there are only vague ideas about how these form and thus about how many to expect.

To produce such a graph we basically would need a source that does this for us, since anything else would lead very much to WP:SYNTH territory. A quick look on the arxiv has produced little of promise but I'll keep my eyes open.TimothyRias (talk) 08:48, 8 February 2010 (UTC)

I agree that a plot of observed candidates would suffer from observation bias, but I'd also expect distributions based on models to be shown to be inaccurate as those models get revised (in particular, accretion models for IMBHs and SMBHs are still under active debate, last I heard). My best suggestion would be to put a dashed line indicating the expected distribution, with histogram bars for actual observations, and caveats about both sets of values in the caption/image description.

I don't have any useful suggestions about finding distribution data, as I don't follow the relevant literature. --Christopher Thomas (talk) 18:03, 8 February 2010 (UTC)

Citation needed

The article states "Roger Penrose proved that a singularity will form..."

Shouldn't such a fundamental statement be cited or is this so non-controversial that it can be stated as fact ? —Preceding unsigned comment added by 172.162.40.212 (talk) 23:39, 10 February 2010 (UTC)

It is widely accepted as fact (it's actually one of the more important results about black holes), but I agree that it should be cited. --Christopher Thomas (talk) 23:51, 10 February 2010 (UTC)

Maybe't it should also be stated that black holes can not combine inside the event horizon; since they are singularities they just orbit each other. —Preceding unsigned comment added by 172.164.76.224 (talk) 01:09, 11 February 2010 (UTC)

The same effect that causes matter to collapse to a singularity, would also force two singularities of a merging black hole to collapse into each other. Inside a certain radius (4/3 the Schwarzschild radius, if memory serves), moving tangentially pushes you inwards instead of outwards. Inside the horizon, _all_ timelike directions point inwards. --Christopher Thomas (talk) 03:52, 11 February 2010 (UTC)

Sidis' 1920 views on "black body" stars

Anyone know why William Sidis's 1920 views on "black body" stars (black holes) and "boundary surface" (event horizon) isn't in the history section:?

• The Animate and the Inanimate —Preceding unsigned comment added by 68.23.161.224 (talk) 08:49, 24 February 2010 (UTC)

As far as I can tell, it has had no impact (or real relation) to the developement of the theory of black holes.TimothyRias (talk) 09:38, 8 March 2010 (UTC)

Timothy, I appreciate your reply to the above query (even though I did not ask the question). This type of neutral reply gets the point across without causing unnecessary tension. Steve Quinn (formerly Ti-30X) (talk) 21:00, 8 March 2010 (UTC)

On Black Hole Formation alternate hypothesis.

This discussion has been closed. Please do not modify it.
The following discussion has been closed. Please do not modify it.
Seeing that nothing can travel faster than light, and the newtonian equation of gravity shows that inside of a shell of matter, the gravity is zero for the shell, and only defined by the inside matter of the shell, and under high gravity frame of reference time slows down, and the nature of Black Hole formation under finite energy forces, could it be that Black Holes do not form per-se, but rather Black Onions, where matter starting with a droplet of condensed time dilated state forms and that core grows in miliseconds to compresses all the additional time dilated shells of condensed time dilated mattter about it in similar state, into a long lived metastable state where all of the matter is in a condensed time dilated form against the upper regieme of relativistic forces, or does the matter fall straight past all resistant forces that form white dwarfs and neutron stars, quite certainly, including time dilation on said matter? Such a Black Onion would be a frozen object in time space, never collapsing into a singularity, but slowly radiating its particles starting with light, at the edge of the object with less than infinite relativistic effects due to the temporal near freeze of the collapse and bounce over extended spans of time? LoneRubberDragon (talk) 05:08, 28 February 2010 (UTC) It is a very technical equation set with nearly singular stiff equations, so it is slightly beyond me to answer, and I see little description of such a Black Onion description of the collapsed condensed relativistic state of such an unheard of entity description, based on that fact that matter and energy cannot accelerate matter and energy to the speed of light itself. Almost a chicken and egg problem given that singularity. LoneRubberDragon (talk) 05:08, 28 February 2010 (UTC) As I understand, a distant observer can never see something cross an event horizon. As stuff orbits closer, it redshifts dimmer and time dilates slower. Additionally, inside the ergosphere, frame dragging severely distorts the geometry of space as seen from an external frame of reference. Objects cannot travel a straight line into a rotative black hole (except perhaps at the poles). They get dragged around. Have you looked for sources that hypothesize black holes don't collapse, but rather the event horizon is like a bubble that inflates from the center, and all the mass remains in a shell just above? Have you looked at the gravastar hypothesis? Jehochman Brrr 05:25, 28 February 2010 (UTC) This part I understand well. However, is all of this presuming the existence of a Black Hole to begin with in a good, but potentially false, top-down analysis. An analysis that says, IF we start with mass M compressed to a singularity, THEN all that can be used to determine the Schwarzchild Radius, and other properties of this theoretical object, The Black Hole. However, IF one considers bottom-up the very formation from a star model, does the physics prove Black Hole formation, or does time dilation, entanglement relations, conservation of momentum on the macroscale compared to the time dilation factors that slow matter down and cause an equal and opposite negative gravity effect from entanglement backpropagation and consevation equivalencies, THEN does a Black Ontion form, instead, a highly energetic, but highly time dilated form of frozen superfluid, that slowly escapes out the surface, due to this, OR does the physics Still Show that all the matter will form a singularity. For, all of the equations involved, and factors of inter-frame relativistics to conservation properties and quantum fields of entanglement, and stiff equations, all lead to difficult numerical solutions en-masse, beyond my numerical simulation capabilities. But an extant paper, and not de-facto knowledge of standards and practices, leads me to wonder about this wayward case, that I have never seen an analysis of disproof, like Michaelsom Morley disproved quite smartly and expertly Luminiferous Aether, not knowing if it would be proven or disproven. I do understand the dogma, but not seeing this Black Onion analysis anywhere, leads me to still wonder, about unfinished business. LoneRubberDragon (talk) 03:30, 1 March 2010 (UTC) No a priori assumption of a black hole is required. For example, the collapse of a thin spherical shell of dust can easily be solved analytically in general relativity. Inside the shell spacetime is flat while outside the shell spacetime takes the Schwarzschild metric up to the radius of the sphere. The result is that the dust collapses into a singularity in a finite amount of time as measured by a comoving clock. The analysis can easily be extended to a set of concentric mass shells, with the same result. The analysis becomes much more difficult if you allow other interactions in the matter causing an outward pressure and if you drop the assumption that the initial mass distribution is not spherically symmetric. Nonetheless Hawking and Penrose proved in the 1970's (the Penrose–Hawking singularity theorems) that and mass distribution will collapse to a singularity provided it was dense enough at some point. For their proof they make only very mild assumptions about the nature of the collapsing matter, requiring only that it obeys certain energy conditions.TimothyRias (talk) 10:58, 8 March 2010 (UTC) Gravitational time dilation causes infalling matter to seem to stop from a distant observer's viewpoint, but from the viewpoint of infalling matter, nothing unusual occurs (it feels that it continues to free-fall inwards, passing the horizon in finite "proper time"). It can be thought of as an artifact resulting from the choice of coordinate system used. People did indeed use this interpretation of black holes in the past; they were called "frozen stars", because it seemed that all matter would come to a halt just above the Schwarzschild radius, using the original Schwarzschild description of black holes. Later, when other coordinate systems were applied, it turned out that this was just an artifact of the original coordinate system chosen by Schwarzschild. This is discussed at greater length at Schwarzschild metric. This is good stuff here. But it, too, assumes the top-down model of Black Hole's a priori existence. These models are quite clear, and true in their own frame of reference. But, as before, does the Formation from the initial droplet of superdense, super time dilated matter, surrounded in zero gravity (from newton shells of gravitating matter Surround It) and high collapse pressure state, along with released energies of degenerating matter, passing through electron degenerate white dwarf state, and then neutronic degenerate neutron star matter state, and all of the preceeding observations of effects conservation with time dilation between frames of reference holism and entanglements, produce a Black Onion state of matter that doesn't fall into a singularity, but collides with some energetic big bang like time dilated slowed metastate. And none of this denies that a supermassive Black Onion may exist at the center of the milky way, accreting new matter on it's surface into a similar, near black hole approximation state, and growing in mass, and reradiating itself with photons and neutrinos and such, over extended times, to reach some further state, perhaps Black Hole, or perhaps perfectly temporally frozen and asymptotically non-degenerate singular Hadron Star, or perhaps in Superunification, it all reradiates itself through Superunification chain reactions converted a continual portion of itself, into Black-Onion-escaping forms of radiation, sending all of itself back out to space ... eventually. Too many singular stiff equations for my Dragon Mind to grok completely, but that is what these Dragon Eyes see. LoneRubberDragon (talk) 03:30, 1 March 2010 (UTC) http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation (Newton Shells described, herein) LoneRubberDragon (talk) 03:30, 1 March 2010 (UTC) I will have to research this "Frozen Star" system you describe, to see if I can even penetrate their analysis, and see what they say. This is definitely not a commonly described term, because I have not heard it, from 1971 to 2010. Thank you for the lead on that neologism. I will see if the papers are fruitful on this subject. I do hate forgotten history of some improtance in physics understanding! That's why I still like the Michaelson-Morley experiment. Beautiful physics, even if it found a false. I just hope they are not propaganda articles, but really explain the whole deal down to the roots of equations without missing key physics effects that may have come up in recent years. Your description shows it is a nearly asymptotic system, with errors in original coordinates tipping effects. Could entanglement or other effects do the same backwards, with all effects still not being accounted for? It can still be an open question, if everything isn't known to the n'th degree (pardon the Masonic Reference). LoneRubberDragon (talk) 03:45, 1 March 2010 (UTC) Hehe, reminds me of the movie Dark Star. Great pulp movie from the 1970's, if you can understand it, like the movie Sunshine. These movies scare me as much as Quatermass and The Pit, for the eerieily subtle possible physics considerations of monoliths and entanglement and Colossus/Hal and such. LoneRubberDragon (talk) 03:46, 1 March 2010 (UTC) http://en.wikipedia.org/wiki/Dark_Star_(film) http://en.wikipedia.org/wiki/Sunshine_(2007_film) http://en.wikipedia.org/wiki/Quatermass_and_the_Pit Unfortunately, this Dark Star, is not a Hadron Star that I describe being just Below the limit of the speed of light escape, and asymptotically stuck on the time dilation in a near frozen state. LoneRubberDragon (talk) 03:54, 1 March 2010 (UTC) http://en.wikipedia.org/wiki/Dark_star Wiki (my CAPS bolding) [A dark star is a theoretical object compatible with Newtonian mechanics that, due to its large mass, has a surface escape velocity that EQUALS or EXCEEDS the speed of light. Whether light is affected by gravity under Newtonian mechanics is questionable but if it were, any light emitted at the surface of a dark star would be trapped by the star’s gravity rendering it dark, hence the name.] That's the very numerical problems involved with numerous colliding stiff asymptotic equation solutions. LoneRubberDragon (talk) 03:54, 1 March 2010 (UTC) http://en.wikipedia.org/wiki/Stiff_equation (Sorry, collided with another response (Jehoakim or something), try my talk.) LoneRubberDragon (talk) 03:59, 1 March 2010 (UTC) http://adsabs.harvard.edu/abs/1974IAUS...53..237C LoneRubberDragon (talk) 08:51, 8 March 2010 (UTC) http://articles.adsabs.harvard.edu/full/1974IAUS...53..237C LoneRubberDragon (talk) 08:51, 8 March 2010 (UTC) [secondary conversation on black hole hadron star indistinguishable models of the quantum object.] LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) A "Colossus Joke", that's looking up, Shimon! You have read me somewhere before in time space lines! LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) The reference to XYZT space, is because the baseband universe of mundane matter appears to follow XYZT on the main space of the universe, in your so-called cotangent space. There are small ripples in imaginary time related to quantum physics effects. Of course, in and only in special domains, the conventional notion of XYZ time may show a transformation into a so-called tangent space, as you colorfully or accurately convey, as I cannot yet determine the veracity of what you say, but remember what you have said from somewhere-someone-somewhen else before, perhaps even you. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) Like in the 1970's, people my age and some adult appearing humans, used to speak about black holes, physics, man, and God. As you may read in my delivered LoneRubberDragon.DOC, where I write on black hole formation. The traditional black hole so commonly defined, is a top-down model of a black hole, where a singularity or singularity ring with a geometric light escape velocity sphere or spheroid, is assumed to exist, a-priori, with all the theoretical physics characteristics belived to exist from physics, of that a-priori object, that quantum. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) But what do bottom-up models say about black hole formation? A perfectly round non-rotating star with perfect fusion completion collapse would crash through white dwarf electron degenerate state, neutron star nuclear degenerate state, and then what? Does it collapse into a perfect supersymmetry quantum state, where the star enters into a perfectly balanced hadron star quark degenerate state, akin to the big bang, with a time-dilated matter accreting sphere? Or is the mass-energy-space density against the time dilating sphere size ratio easily large enough to absorb the matter into a singularity from their perspective of infalling matter? LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) You comment about entanglement brings up a terrible question of this state of black hole versus hadron star, too. As the core of a theoretical straight to black hole model dictates, from our perspective, the infalling matter suddenly freezes in time-space on the event horizon, or even for the case of a hadron star, where the escape velocity is slightly less than light, by super symmetry arguments. This infalling matter becomes frozen in time, but newton's law dictates that for every action, there's an equal and opposite reaction. Well, in the core of a nuclear star, every particle has some measure of entanglement history stored in each particle. So, does every entangled atom in the time-dilated black hole, experience a blow back force, because the black hole sudden freeze in classical space, which is in a time dilated core of frozen infalling matter, and cannot express the equal and opposite reaction all of nature expects on the baseband XYZT coordinates of holistic systems? Or perhaps its time freezing state creates a temperature rise in the matter in the hadron star or black hole, commensurate with the time dilation field, in equal and opposite reaction, preventing in supersymmetry, the nature of a nearly frozen bounce in time, that looks like a black hole, but is merely a big bang spehere hadron star? LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) Another interesting property, of a giant hadron star, is that space around it, by definition, looses all sense of time, outside of the reference of the hadron star, since all matter has become absorbed, and the hadron star would experience an odd new state of matter, in supersymmetry, extremely time dilated, and compactly entangled with itself, with zero gravity at the center, and highest density, and mere big bang corraled nearly light escape velocity sphere, virtually indistinguishable from a black hole, a-priori. A place where the in and only in and the mundane matter space, for the most part, are unified. Of course, IF the density of matter is known to produce black holes easily, THEN that mucks up the whole idea, but I have never seen that specific calculation carried out clearly, yet. One commentor on Black Holes in wikipedia, once said that a "dark star" like a hadron star was looked at in 1920, but the calculations were on a hairy edge. Being on a hairy edge shows that the theory may still hold water, with entanglement, advanced analog-digital computers and such, can assist in looking at this so-called hairy edge problem, from the bottom up, as the universe produces such dark stars inferentially from the core of this galaxy, and so forth, evidences of either Black Holes or Hadron Stars. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) Imagine a giant gedanken, where all the matter of a galaxy, by completely artificial means of chaotic decision points, is made to coalesce onto a hadron star. Every new newton shell of matter doesn't contribute to the gravity inside of the shell, only pressure, as newton's shells show zero gravity integrals on their inside. In fact, the initial formation of a black hole, must address the newton's shells issue that at the center of the star, where the pressure is greatest and focus most pronounced of collapse, but also that it is in tensor shifted zero-gravity, of this same high density focus space, dilated from normal space, by the thousands of miles of star matter over its core. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) For a space like your described universe to exist, perhaps there is about 70,000,000,000 universes, all virtually identical, in interaction space, and all highly divergent on separation space, correlating with the 70 billion humans that have existed, both living now, and dead now. However, it flies utterly in the face of one God, outside and within one cosmic space of time and matter. But seeing the world His Lesson Plan Shows, it would explain God's finite bandwidth properties, being only One Being, where God's endless compromises, shatter the illusion, of His Own Integrity. One with infinite powers and continuity, in a One Body and Only One Body world that is created within Himself, of chaos and ill communication as His Master Plan, and The One God with a Broken Body of 70 billions souls, with threats of deaths and destructions terminating nearly all humans in their inner manipulation of a finite power. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) But to call it cotangent space normal and tangent space exception, is to say goodbye normally, in separations. Yes, frequency space is important and compact, but works hand in hand with temporal space of quantums like Laplace Transforms of impulses, toward even random number lists. This is the crux of issues on scatterings created when frequency space and temporal space collide. It is the core of wave and particle duality. It is where scales of the heirarchy of an infinite frequency spectrum cannot touch a delta, or where one DC frequency term can describe the entire list of DC offsets of the universe. It is the crux of reductionism and holism. Of cotangent-tangent space as a whole system. It is the possible flaw of Black Hole research only taking top-down holism assumptions, and not also considering the mirror image of bottom-up reductionist assumptions. And being a time dilated quantum the size of a Black Hole / Hadron Star, both may exist simultaneously at the infinity of a supersymmetry, and Indistinguishable Models of Quantum Physics, in the dark and time dilated form of this object astronomers confirm in implicated observations of black holes by the criteria of existence state beyond neutron star dynamics. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) To be more precise, I claim that freqeuncy spectrums, simply describe many natural systems of structure, as well as Laplacians for impulses, where the language shifts to a compact Laplacian system. And of course, synthetic signals make the most trouble, where neither wave, nor particle, but spirit of living word systems, like computers, and humans, and life, create signals of characters that are none of the above, but are of chaos systems of Lyanupov characteristics. A holy trinity between [wave system particle]. It is complex to describe, as you must obviously have noticed by now. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) But tell me more about this cotangent-tangent space concept. It reminds me of something, from a very long time ago, e.g. 1974, when I was three years old, learning about the prison planet earth cosmos as seen through this american dream of a finite bandwidth God made manifest through the hands of the children of men of the earth over the cosmos, in their pride of lies and finite bandwidth that no-one can deny. LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) "God's Endless Compromises, LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) shatter the illusion, LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) of His Integrity." - LoneRubberDragon LoneRubberDragon (talk) 09:00, 8 March 2010 (UTC) Wikipedia talk pages are for discussions related to improving articles, not for hypothesizing about the subject of an article. If you want to do that, please find a forum somewhere else on the internet. The header of this page has some suggestions. Of course, if there is something that you think is unclear about the current article, please, do ask about, but be concise and to the point. TimothyRias (talk) 09:37, 8 March 2010 (UTC) The formation method of Black Holes themselves are unclear in the article. All hypotheses need to be brought into the article of science. LoneRubberDragon (talk) 09:55, 8 March 2010 (UTC) Is a nuclear war, the only answer to save a NANO-UNIT of memory space, on this site? Are your defenses so close to the edge of criticality, that your system will fail, with a free and open discussion of the pertinent topics on this discussion page. I could zap the entire article, but I hold back, to observe the truth of all pertinent exquations of Black Hole formation, and associated topics, in a hypertext format. LoneRubberDragon (talk) 09:57, 8 March 2010 (UTC) If Timothy Rias, is God over the earth, then so be it, nuclear destruction of your planet, is desirable by humanity. LoneRubberDragon (talk) 09:59, 8 March 2010 (UTC) But you only serve to remind me of pedanitc first grade teachers, who make all dead according to the law, on pertinent data. Blagodurnost! LoneRubberDragon (talk) 09:59, 8 March 2010 (UTC) If improving articles on pertinent data, is hiding and dissembling data, then let us begin? Or should we? I consider your actions hostile on an international scale, and close to God Himself. But earth destruction is the game of man? Not collecting together data for the article, in a unified field of research? Too delicate a system, in my estimation, given your data of criticality of system memory constraints, to store such a small snip of text, Timothy Also-God Rias. LoneRubberDragon (talk) 10:01, 8 March 2010 (UTC) Did you, Timothy Is-God Rias, bring one link, or word, or paper, or discussion, to this very post, of some edification? Just asnwer that. I think you will find the answer is: nyet, Nyet, NYET! LoneRubberDragon (talk) Did I not post useful information for the improvement of "Complete Spatial Randomness", and "SuperResolution" articles on wikipedia? And this is a Discussion Page. If it isn't, what is it for, Your One Mystery Incompleteness Dogma, Only? LoneRubberDragon (talk) 10:21, 8 March 2010 (UTC) Discussion pages on wikipedia are for discussing improvements to an article (see WP:TALK), NOT for discussing the topic of the article in general. You're issues seem to be mainly with (your perception) of the state of Black hole research, not with how this article reflects that state. If you have problems with the actual content and think that it does not accurately reflect the available literature OR think that some of it is unclear. Then please say so and be precise about where you think the article can be improved. (I'm sure it can at many places.) But please leave your own theorizing out of it. Also, if you continue with personal attacks like here above, you are likely to be blocked or banned from wikipedia per WP:TALKNO. TimothyRias (talk) 11:22, 8 March 2010 (UTC) http://adsabs.harvard.edu/abs/1974IAUS...53..237C LoneRubberDragon (talk) 08:51, 8 March 2010 (UTC) http://articles.adsabs.harvard.edu/full/1974IAUS...53..237C LoneRubberDragon (talk) 08:51, 8 March 2010 (UTC) http://en.wikipedia.org/wiki/Gravastar LoneRubberDragon (talk) 09:52, 8 March 2010 (UTC)

Black hole and singularity

The section singularity descibes the center of a black hole as a point of infinite density. I don’t know much about general theory of relativity . But I think the concepts of black hole and singularity are quite different concepts. After all Pierre Simon Laplace knew nothing about general relativity and infinite densities ; but still he could postulate the black hole.

The Schwarzschild radius is ,

$r_{sc}={\frac {2\cdot G\cdot M}{c^{2}}}$

When the mass of a non rotating black hole is given in terms of its volume and the overall density it can be seen that there are two creterias for an object to be a black hole; the Schwarzschild radius and the critical density.

$\rho \cdot r_{sc}^{2}=C$

Here ρ is the critical density, r_sc is the Schwarzschild radius and C is a constant. (~1.6 10²⁶ SI units) . It is obvious from this relation that, for bigger objects, the critical density for being a black hole decreases. For solar mass the critical density can be as high as 1.85 * 10¹⁹ kg/m³ .But a spherical object with a radius of one light year becomes a black hole with a minute density of 1.8 mgr/m³ . For galactic dimensions the overall density approaches to near vacuum. I find it quite difficult to reconcile the idea of singularity to such low density super big black holes. Nedim Ardoğa (talk) 08:07, 9 March 2010 (UTC)

First note that Laplace's idea (or rather John Michell's idea) of a dark star is somewhat different from a black hole. For example, the dark star idea does not prohibit rocket aided escape, etc. It is somewhat of an (un)lucky coincidence that the radius of a dark star and the Schwarzschild radius coincide exactly, since this prompts people to think that the concepts are the same.

The average "density" of a black hole can indeed be quite low for very mass BHs, however the causal structure imposed by general relativity on the interior of the black hole makes the creation of a singularity inevitable. (This is the essence of the Hawking-Penrose singularity theorems) The formation of the singularity can take a while if the BH is big enough. For example, if you'd take a black hole of the Hubble radius (average density around 1 atomic mass per cubic meter) the actual collapse could take billions of years.

Note that the article does not define a black hole as a singularity, but merely notes that the description of BHs in general relativity necessarily contains a singularity. TimothyRias (talk) 09:12, 9 March 2010 (UTC)

Straw poll: talk page notice

As we've had a few recent extended off-topic threads about peoples' personal ideas about how black holes work, and as this has happend fairly frequently in the past, I floated the idea at WT:PHYS about putting a banner on this page along the lines of the one at the top of Talk:Big Bang. This would direct people towards suitable venues for proposing their own models, while making it clear that this talk page isn't the best venue.

Response at WT:PHYS was positive, so I'm opening a straw poll here to see if implementation should go forward. A draft copy of the Big Bang notice-blurb, tweaked for use with the black hole article, is at Talk:Black_hole/noticeblurb.

Suggestions for suitable forum links are appreciated; I'd like to be able to point users in useful directions, rather than just say "not here".

What are all of your thoughts on this? --Christopher Thomas (talk) 22:52, 10 March 2010 (UTC)

Votes/Comments

• Support addition of such a notice, as long as useful links to other venues are provided (I don't have any). --Christopher Thomas (talk) 22:52, 10 March 2010 (UTC)
• Support don't care what it says, we can tweak it later. --Michael C. Price ^talk 23:13, 10 March 2010 (UTC)
• Support It seems like a useful tool, which would allow the Wikiproject physics editors to have the best use of their valuable time and attention. I certainly don't see this as overkill. Steve Quinn (formerly Ti-30X) (talk) 00:23, 11 March 2010 (UTC)
• Support unpublished personal theories should not clog up the talk page, when there are so many published crank theories already that could better clog up the talk page. 70.29.210.242 (talk) 06:02, 11 March 2010 (UTC)
• Support/comment Such a banner would be useful. I should that there already is a "got a question? Don't ask here" banner at the top of the page. I like your formatting better though. (The old banner does have useful links you can salvage. TimothyRias (talk) 07:00, 11 March 2010 (UTC)

  I noticed the existing banner; I was going to keep it, with the new notice over it, much as with the ones at Talk:Big Bang. Good point re. links; my fallback option would be to tweak the proposed template to say "at any of the links below", but I was hoping for actual pointers towards alternative-physics forums where original material would be welcome, vs. Q&A forums where they'd meet more or less the same response as here. Harvesting the existing links is definitely an option, though! --Christopher Thomas (talk) 07:09, 11 March 2010 (UTC)

  Here is site where original material is welcome and allowed. It is a wiki. Wikinfo. "Wikinfo provides a platform for the meshing of encyclopedic material, original and creative work and public domain material to further education and information." "Wikinfo welcomes editors from Wikipedia and offers much more opportunity to edit freely. Original research and original ideas are welcome."

  Writing an article at Wikinfo is the same as writing an article for Wikipedia except OR and original ideas are acceptable content. The structure and software is either the same or very similar. ----Steve Quinn (formerly Ti-30X) (talk) 07:26, 11 March 2010 (UTC)

• Support - without comment. DVdm (talk) 07:44, 11 March 2010 (UTC)
• Support—I think it is a good idea. There are comparable notices on Talk:Earth about Mostly Harmless as well as the lack of coverage concerning young Earth creationism. It seems to cut down on the unhelpful noise a little. Likewise, some talk pages have notices about recurring themes. The Talk:Evolution page has a FAQ that includes past discussions.—RJH (talk) 17:48, 11 March 2010 (UTC)

Notice added. Links remain a question.

As the overwhelming consensus seems to be in favour of the notice, I added it (with "...at one of the forum links below" as placeholder-directions). If anyone knows where fringe/non-standard black hole theories are usually debated, by all means add a link. I've held off on listing WikiInfo, as that seemed on inspection to a) be fairly low-traffic, and b) be geared more towards non-verified descriptions of mainstream work than fringe work, but that impression could easily be mistaken (and of course I'm not the final arbiter of what goes into the template; I'm just one editor). I hope this is a useful starting point. --Christopher Thomas (talk) 08:15, 12 March 2010 (UTC)

The http://www.physicsforums.com/ site is fairly active. I've posted there before and received useful responses. There seems to be discussion of black holes under the astrophysics section, along with a few unconventional topic headings.—RJH (talk) 16:10, 16 March 2010 (UTC)