<article_title>Black_hole</article_title>
<edit_user>Headbomb</edit_user>
<edit_time>Thursday, March 17, 2011 3:42:44 PM CET</edit_time>
<edit_comment>clean up using [[Project:AWB|AWB]]</edit_comment>
<edit_text>|doi=10.1103/PhysRevD.74.084004
<strong><strike> |id={{arxiv|gr-qc|0609055}}
</strike></strong><strong> |arxiv=gr-qc/0609055
</strong>}}&lt;/ref&gt; This would put the creation of black holes firmly out of reach of any high energy process occurring on or near the Earth. Certain developments in quantum gravity however suggest that the Planck mass could be much lower: some braneworld scenarios for example put it much lower, maybe even as low as &lt;ref&gt;{{Cite journal |last=Arkani–Hamed |first=N.</edit_text>
<turn_user>RJHall<turn_user>
<turn_time>Wednesday, March 16, 2011 7:20:38 PM CET</turn_time>
<turn_topicname>Random observations</turn_topicname>
<turn_topictext>Here are some random observations in the nature of a partial review. Hopefully these may be of some small use to the primary editors of this article.&amp;RJH (talk) "...although its black hole nature..." I think the meaning of this statement needs to be explained for the reader because it is vague. I agree, this phrasing is not optimal. It is meant to convey the fact that although, the Schwarzschild solution was found the in 1916, it took until 1958 for someone to give this the physical interpretation of what we now call a black hole, as is detailed in the history section. If you have an idea for a better phrasing, please have a go.TR 10:08, 17 March 2011 (UTC) Perhaps "...although the physical details of this model were not fully understood for another four decades."?&amp;RJH (talk)I've tweaked the sentence a bit. Is that better?TR 09:01, 30 March 2011 (UTC) Sorry, the new wording kind of has the same issue.RJH (talk) Would it help if "black hole" in the offending sentence would be replaced "region of space from which nothing can escape"?TR 08:19, 4 April 2011 (UTC)
Regarding the sentence: "This is different from other field theories like electromagnetism, which does not have any friction or resistivity at the microscopic level, because they are time-reversible." This sentence jumps between the use of plural and singular, leaving some ambiguity. Is the macroscopic-level sub-sentence talking about the theories or electromagnetism? If the latter, why does the end of the sentence jump back to plural?Should have been plural. TR 10:08, 17 March 2011 (UTC)
Why does the article need a section on the "Photon sphere"? It seems to add little value.It is an interesting feature of black holes (although it is not restricted to black holes). More importantly it has a very direct effect on the appearance of a black hole. The black disk shown in the simulated view of BH in the lead, actually is the photon sphere, not the horizon. (Because any light ray passing through the photon sphere is captured by the BH.) Maybe this could be made more clear? Anyway, I don't see much harm in having the section.TR 10:08, 17 March 2011 (UTC)
Per the "Formation and evolution" section, it is possible that supermassive black holes formed directly from direct gas inflow without the need for one or more seed black holes.http://www.nature.com/nature/journal/v466/n7310/full/nature09294.html Does this need to be mentioned?Probably, not yet sure where though.TR 10:08, 17 March 2011 (UTC)
I think the entire section "Observational evidence" could be substantially tightened up by eliminating tangential information and compacting the summaries.Did you have anything specific in mind? Giving it a quickly look, I don't see many point that could be significantly tightened without loss of relevant information, except may be the galactic nuclei subsection.TR 10:08, 17 March 2011 (UTC) I'm not clear (from the wording) that GRBs provide "observational evidence" of black holes as such. They do provide evidence of collisions or gravitational collapse, which could result in a black hole. Hence, this part seems to belong in the "Formation and evolution" section.&amp;RJH (talk)I think the article could do without the section GRBs altogether. It is more a subject for the GRB article than this one. Here it doesn't really add anything.TR 09:01, 30 March 2011 (UTC)
In the "Galactic nuclei" section, I think it should more strongly suggest that the SMBH are responsible for the AGN. Otherwise, the activity wouldn't necessarily provide observational evidence.&amp;RJH (talk)I'll have a go at sharpening the wording later.TR 09:01, 30 March 2011 (UTC)
The "Alternatives" section doesn't seem to discuss observational evidence. Possibly it should be moved to the Open questions section?&amp;RJH (talk)The "Alternatives" section discusses alternative explanations for the presented observation evidence, which is why it is in that section. It does two things, on one hand it shows why current evidence is not completely conclusive. On the other hand it shows which physical principles/assumptions you would need to give up in order for the current evidence not to prove that black holes exist.TR 09:01, 30 March 2011 (UTC)
The article is inconsistent about the use of "a black hole" vs. "the black hole". If it is talking about, say, "the black hole event horizon", then I think "the" makes sense. Otherwise, as there are many black holes, most of the time it should probably say "a black hole" or "the black holes".I'll have a look.TR 10:08, 17 March 2011 (UTC)
"...it is best to free fall the rest of the way." Why is it "best"? Quicker death?Best to maximize the time it takes to hit the singularity. Not sure why there is a source of confusion, considering the first half of that sentence.TR 10:08, 17 March 2011 (UTC) "They can prolong the experience by accelerating away to slow their descent, but only up to a point; after attaining a certain ideal velocity, it is best to free fall the rest of the way." As I read it, this is saying that, below the ideal velocity (which remains undefined), constant acceleration away from the singularity shortens the duration until the observer reaches the singularity (in the observer's reference frame, presumably). At first glance this seems counter-intuitive; is this another relativity-based paradox?&amp;RJH (talk)This is indeed paradoxical. It is related to the fact that a timelike geodesic is a path that maximizes the proper time between two events, i.e. free falling clocks tick faster than other clocks. This leads to a common statement that, to prolong once stay in a black hole before hitting the singularity, one should just free fall all the way. There is a subtlety, however. The singularity is not one point in space time, it is a line of points, and it matters at which point on the line you hit the singularity. For an observer entering the black hole at a certain time there is an optimal (from the perspective of maximizing life expectancy) point to hit the singularity. To maximize your lifetime you should follow a timelike geodesic (free fall) to this point. (If think this coincides with entering the black hole at zero radial velocity.) Observers entering the black hole at any other velocity should try to change their velocity to get closer to the ideal one as fast as possible. The longer they wait the further away from the ideal trajectory they will end up (with a different ideal final velocity.) The ideal velocity therefore depends on the initial velocity a ship has as it enters the BH and the maximum thrust it can produce. (Which why it is not really possible to mention what the ideal velocity is.As you can see this a somewhat lengthy explanation, which is why it isn't in the article. A reader interested in the details can look up the reference, which is fairly readable.TR 09:01, 30 March 2011 (UTC)
Thank you.&amp;RJH (talk) 19:20, 16 March 2011 (UTC) No, thank you for taking the time.TR 10:08, 17 March 2011 (UTC)</turn_topictext>
<turn_text> "...although its black hole nature..." I think the meaning of this statement needs to be explained for the reader because it is vague.</turn_text>