Talk:Event horizon

message: "Roberts radius" is mentioned at the beginning of the first section. But it links to no article and a quick search on Google returns no results about such radius. Perhaps that's a mistake? That there's no "roberts" radius? If there is, at least a small explanation in the text might be very interessant. Rsreston (talk) 11:54, 12 May 2009 (UTC)
replies: text: Well spotted. This should obviously be "Schwarzschild radius". This got edited into "Roberts radius" on 19th April. Suspect hidden vandalism. Have restored it. JocK (talk) 01:06, 13 May 2009 (UTC)
thread_title: Roberts radius

message: Some please rewrite this sentence to make it more clear: "While this seems to allow an infalling observer to relay information from objects outside their perceived horizon but inside the distant observer's perceived horizon, in practice the horizon recedes by an amount small enough that by the time the infalling observer receives any signal from farther into the hole, they've already crossed what the distant observer perceived to be the horizon, and this reception event (and any retransmission) can't be seen by the distant observer." What is this "any signal from farther into the hole" phrase referring to? This sentence concludes the whole last paragraph but it may be too contracted.  —Preceding unsigned comment added by 209.77.137.57 (talk) 17:47, 6 October 2008 (UTC)
thread_title: Clarification Required

message: Please, someone rewrite this section. It is highly contradictory and just muddled with unclarity. I was looking this up for an assignment and I could not for the life of me figure out if being near an event horizon would tear me apart, since it was so unclear.
72.219.14.103 (talk) 00:26, 4 April 2008 (UTC)
replies: text: I just came across this article, and the entire second half of the "Interacting with an event horizon" section appears to need to be removed or rewritten. I'm no physicist, but I don't even think it's correct at all. FFLaguna (talk) 02:33, 11 May 2008 (UTC)
replies: text: pretty sure that entire section is wrong, it literally makes no sense at all. wtf?76.87.249.4 (talk) 00:31, 2 October 2008 (UTC)
thread_title: Rewrite request: "Interacting with an event horizon" section (April 2008)

message: The rewritten version of the article has been swapped in under the main title, and can now be edited. For easy reference, the old version of the article is here.
The main thing missing in the new version is a list of references and external links. Unfortunately, none of the old article's external links looked suitable (one Geocities page, one page that talked about black holes exclusively, and one tutorial that mostly talked about things other than event horizons). Useful references would be appreciated.--Christopher Thomas 00:07, 3 July 2006 (UTC)
replies: text: Perhaps you could mention that a black hole, to an fixed external observer, looks like a "frozen star", so you can't see the event horizon at all.  --Michael C. Price talk 17:15, 6 July 2006 (UTC)
replies: text: I'll add this after thinking about where best to put it. It isn't just black holes that have this effect. Light emitted from events near any event horizon can take arbitrarily long to reach the observer with respect to whom the horizon is defined. --Christopher Thomas 19:22, 6 July 2006 (UTC)

text: A rod held at rest relative to a distant observer is not in a "grazing orbit". Completely different type of path. Inifinite _tidal_ forces were never claimed, and I pointed this out to you in my first reply. There are plenty of GR-types in WikiProject Physics, and I'm sure some of them will take a look at the article to assess your concerns eventually (I've already made them aware of your previous message). --Christopher Thomas 15:36, 6 July 2006 (UTC)
replies: text: Dear anon user, please consider creating a login for yourself, and becoming active in the edit process. What you say sounds correct, although I did not see the offensive text you refer to in the article after a quick skim. The article is a bit muddled in places. WP could use competent, knowledgable writers who have both a formal education in the field, and have good english writing skills. There are articles here that are meant to be broadly accessible, and free of jargon, such as this one, and far more technical articles too, such as those in :Category:Riemannian geometry. Visit Wikipedia:WikiProject Physics and the far larger and more active Wikipedia:WikiProject Mathematics to get a taste of what goes on here. linas 14:55, 7 July 2006 (UTC)
replies: text: Are you sure that the anon's statements sound correct? The "total force is not infinite" one in particular seems wrong, for reasons covered in both of my responses. The part he was objecting to was the "interacting with an event horizon" section. I'd appreciate it if you could take a detailed look at that. --Christopher Thomas 16:20, 7 July 2006 (UTC)

text: This seems to be a question of terminology, then, as "unbounded and arbitrarily large" is exactly the definition of "tends towards (positive) infinity" that I've been hearing. I'm satisfied with the content of your rewrite to the relevant section. --Christopher Thomas 22:16, 10 July 2006 (UTC)
thread_title: First draft rewrite complete

message: There's one more entertaining way to try to intuit the physics behind the above discussion. Suppose one drops a fishing line with hook down towards the black hole, with the hook crossing the Schwarzschild radius. Now one gives the line tug, attempting to slow the fall of the whole thing. As the line slows, the event horizon for much of the line appears to recede off to the distance. As the hook is on the other side of the event horizon, the receding horizon ends up stretching the line. As the line is stretched longer and longer, its perhaps not surprising that it eventually breaks. By pulling the line hard enough to stop the fall, the event horizon recedes to infinity, and the fishing line would need to get stretched to infinity, clearly an impossibility. 
This picture is doubly nice because it provides intuition about the microscopic mechanism of breaking: the fishing line breaks because each of the atoms in the fishing line get pulled apart from one-another, as the distances between them increase as the line is slowed down. The unbounded stress that the fishing line feels is now not at all mysterious: the atoms are simply moving away from each other. It would perhaps be entertaining to try to understand quantum mechanics based on this insight, as it is simple, direct, and mechanical. The simplest model must surely be solvable: ask what the 1-D harmonic oscillator does if the one and only spatial dimension is slowly stretched. I'm guessing that a system in the ground state evolves continuously into a superposition of excited states, and thus must decay by a cascade of photons. That is, a slow stretching can be viewed as a perturbation (solvable via perturbation theory) that mixes the ground state with the excited states. Thus, a ground-state oscillator, when stretched, is no longer in the ground state. Perhaps this is also a simple and direct way of understanding Unruh radiation? Perhaps this an entirely equivalent formulation to Unruh radiation? Anyone care to work the problem and post the results somewhere? Interesting ... linas 04:58, 10 July 2006 (UTC)
replies: text: I can forsee one possible objection to the above description which is with phrase "with the hook crossing the Schwarzschild radius" in that the free-falling hook never crosses the horizon w.r.t. the external observer -- unless perhaps you include the increase in Schwarzschild radius associated with the inclusion of the extra mass.  --Michael C. Price talk 06:36, 10 July 2006 (UTC)
replies: text: Well, yes, but no. In the frame of reference of the falling hook, it most definitely crosses the schw. rad. The external observer may not be able to use a telescope to observe the hook crossing the schw. rad. but if the external observer has an IQ, she can certainly compute the position of every atom in the line in any reference frame desired. linas 04:11, 31 July 2006 (UTC)
replies: text: The stretching (as a source of the Unruh radiation) doesn't require the hook to cross the event horizon, hence there is no need to invoke this to explain the observations of the external observer (their IQ is not relevant).  --Michael C. Price talk 07:18, 31 July 2006 (UTC)
thread_title: Fishing line redux, and quantum mechanics

message: I changed "distance" --> "comoving distance" above the formula to be a little more precise.  There are a number of various "distances" cosmologically, and this is the one defined by the integral. Wesino 11:08, 24 November 2006 (UTC)
thread_title:  Event horizon of observable universe 

message: "A black hole is surrounded by an event horizon, for example. This means that an outside observer cannot be affected by anything inside the black hole."
Surely the gravitational field created by the singularity of the black hole affects outside observers? and is this singularity not within the event horizon?
:I was just going to bring up that sentence myself. The mass of the black hole beyond the event horizon surely can affect objects outside of it. I'm going to remove the sentence for now, I'll assume it was added without considering gravitational causation. Richard001 06:37, 1 January 2007 (UTC)
thread_title:  Slightly unclear sentance 

message: I'm having trouble with this phrase
:"Light emitted from inside the horizon can never reach the observer, and anything that passes through the horizon from the observer's side is never seen again."
If a photon has enough energy, why can't it climb out of the potential well?  As far as I know, there is no limit to the redshift a photon undergoes.  Wouldn't a photon trying to exit a black hole just be severely red-shifted on its way out?  —Preceding unsigned comment added by MaizeAndBlue86 (talk • contribs) 16:38, 25 February 2008 (UTC)
replies: text: The above is not correct.  Photons are not trapped at the black hole singularity, but at the horizon, where the curvature is perfectly well behaved.  One way to think about the trapping is that the red-shift factor at the horizon is infinite, so photons lose all of their energy in trying to escape.  Note that event horizons need not be associated with singularities at all: The De Sitter cosmologies have event horizons but no singularities, to choose one example.PhysPhD (talk) 17:15, 8 June 2008 (UTC)
thread_title:  Light can never escape? 

message: :Quantum electrodynamics states that photons can take all possible paths between two points. It also states that they can travel slightly faster :than (or slower than) the speed of light. It was theorized that a photon traveling from point A to point B near the event horizon of a black hole :could take an indirect path (described by Feynman's quantum electrodynamics) which skips into and out of the event horizon while traveling slightly :above the speed of light. This would enable that particle to 'skip' into the event horizon and come back out again due to the fact that the event :horizon is the barrier beyond which particles and photons would have to travel above the speed of light to escape. (theorized by A.J.B)
I removed this section again.  Quantum electrodynamics assumes a Minkowski background and hence arguments based on QED should not be applied to describe physics in highly curved regions such as the vicinity of a black hole.  
This technical point aside, WP:V and WP:NOR also seem to be an issue here. SwordSmurf (talk) 16:39, 8 June 2008 (UTC)
thread_title: Particles avoiding the event horizon

message: Does anyone have a fix on when the term "event horizon" was first used? I've been going through some older (pre-1980) literature, and I'm seeing all sorts of other names. I haven't looked through Thorne & Wheeler or Ellis & Hawking. Warrickball (talk) 14:52, 22 May 2009 (UTC)
thread_title:  Origin of the Term 

message: I believe the formula for lambda/lambda0 is incorrect.  Shouldn't it be 
lambda/lambda0 = sqrt( 1 - [2GM/c^2r]  ), where the square brackets represent missing parens?
I think this is the standard Schwarzschild time dilation factor.
From the page in question:
\frac{\lambda}{\lambda}_o=\sqrt\frac{1-2GM}{c^2r}.\ 
71.218.150.115 (talk) 21:02, 11 November 2009 (UTC)
replies: text: You're right, I've fixed it. (Though, frankly, that whole section isn't well written.) -- Dr Greg  talk  21:29, 11 November 2009 (UTC)
thread_title:  "The effect of the event horizon on light" error? 

message: There is the following text in the article:
The definition of "event horizon" given by Hawking & Ellis,[1] Misner, Thorne & Wheeler,[2] and Wald[3] differs from the one presented here. Their definition rules out the cosmological and particle horizons presented below (as well as the apparent horizon). However, modern usage has brought those ideas under the umbrella of the term "event horizon".[4] To make the distinction clearer, some authors refer to their more specific notion of a horizon as an "absolute horizon".
I have major concerns with just about every sentence there, so I'll go through each concern:
The definition of "event horizon" given by Hawking & Ellis,[1] Misner, Thorne & Wheeler,[2] and Wald[3] differs from the one presented here. Their definition rules out the cosmological and particle horizons presented below (as well as the apparent horizon).
Ignoring the definition of an "Event Horizon" as given by all three of the major texts that define it seems a bit of Original Research to me.  Where has this new definition come from?  Or did an editor simply make it up?  It is suggested that the standard definition rules out cosmological and particle horizons.  That could not be further from the truth.  The confusion seems to be that the editors of this article at some point decided that *all* horizons are event horizons.  Which takes me to the next sentence.
However, modern usage has brought those ideas under the umbrella of the term "event horizon".[4]
I was curious about this, as the umbrella term seems to more generally be "horizon."  "Event horizon" is a well defined technical term with a technical definition.  However, to be thorough, I looked up the reference that is claimed to show how "event horizon" has become an umbrella term.  The only quote that I could find regarding this actually states quite the opposite to what is attributed to it: "A particle horizon is not at all the same thing as an event horizon..." (page 86 of reference 4).  Thus it seems that some editor at some point made up this fact about "event horizon" being an umbrella term and then falsely attributed it to a reference that says exactly the opposite.
Since the need for a new, different, un-sourced, wikipedia-only definition of an event horizon is predicated on event horizon being an umbrella term and thus needing to be consistent with the definition of a particle horizon, or any other horizon, it seems that the article is in need of a major re-write.  One that takes sourced definitions for things and does not assert facts that are untrue, sourced to texts that actually say the opposite.
To make the distinction clearer, some authors refer to their more specific notion of a horizon as an "absolute horizon."
This really needs to be sourced.  The term "absolute horizon" is not found at the gr-qc archive (arXiv.org) upon a search of all abstracts.  A google search for the term brings up wikipedia, and a webpage from illinois.edu about the difference between apparent and absolute horizons (where the author uses absolute and event horizons interchangingly).  The fact that the terms is not found at all on the archive is quite damning (pretty much all work about event horizons gets put on arxiv.org).
68.48.203.77 (talk) 21:04, 6 February 2010 (UTC)
replies: text: In case anybody's interested, Roger Penrose has provided two neat (though small) illustrations, with accompanying text,  in "The Road To Reality", Jonathan Cape, 2004, Fig 27.18, page 726 that I think provide neat, clear and concise definitions of particle and event horizons in a generalised universe, and  also explain their causes and the situations in which they occur.  --Dendropithecus (talk) 02:16, 29 April 2010 (UTC)
replies: text: The concerns seem legit, I removed the entire paragraph.  However, I am not an active expert in such matters. linas (talk) 20:46, 13 November 2010 (UTC)
thread_title:  Event Horizon: technical term or generic? 

message: Ok.  The game "the white chamber" from developer Studio Trophis is *clearly* influence from this film.  Now, that by itself doesn't warrant it to be on here, I understand that.  However, there is a *direct* reference to the film.  The line "Where we're going, we won't need eyes to see" is spoken by Weir near the end of the film, and that exact quote is included in the game (in written form).  In fact it has the whole "eyeless" theme that is present in "7 Days A Stranger," which seems to be an acceptable reference.  Now, another user is contesting its inclusion, what are some other people's thoughts? Eridani (talk) 18:46, 2 July 2010 (UTC)
replies: text: Huh? linas (talk) 20:39, 13 November 2010 (UTC)
thread_title:  Additional Reference 

message: Event horizons are not strange and rare animals.  We pass through them continuously as our clocks tick along.
The future and past light cones for a space-time event also define event horizons, as does the 3-d "hyperplane" of an inertial observers t=0 "the universe right now" or any other null or space-like hypersurface.  The event horizon of a black hole is special as a stationary event horizon, and the event horizon of an accelerating observer is a real event horizon which is non-stationary to inertial observers but apparently stationary to the constantly accelerating observer's non inertial frame.  I think the article should emphasize this point but I don't off hand see how to say so in a simple way.  I'll think on it and post an edit if I think up a simple easy to understand exposition.  (and of course suggest anyone else try.)  I think this point is important for the typical reader of this article.
Regards, James Baugh (talk) 22:42, 21 February 2012 (UTC)
thread_title:  Stationary vs general event horizons... 

message: According to Sixty Symbols, kindly see , You would be "Terminated" the moment You pass the event horizon. But, at the moment, it might be considered as "Original research". If one could use the term "Research" for something where experimental evidence is a bit scarce...  — Preceding unsigned comment added by 83.249.147.54 (talk) 20:12, 21 July 2012 (UTC)
thread_title:  Just a short note 

message: At the beginning it says as follows:
"any object approaching the horizon from the observer's side appears to slow down and never quite pass through the horizon"
So, I want to ask those questions:
Think that there are two observers.
"Statinory observer" (SO) is at a stationary point away from the black hole. She is not moving but looking towards the black hole.
"Falling observer" (FO) is moving towards (falling into) the black hole. She is going to the black hole. SO is observing FO go through the black hole.
1. Approaching the Horizon
1.1. While FO approaches to the horizon, does the time acclerete for her?
1.2. While FO approaches to the horizon, what does she see while looking through the black hole?
1.3. While FO approaches to the horizon, what does she see if she looks back at SO?
1.4. While FO approaches to the horizon, what does shee see while looking towards the black hole? Will she see just a black circle (sphere, the central body/region of the hole)?
1.5. While FO approaches to the horizon, does she see the "black region" smalling down or does that black thing stay same size?
1.6. While FO approaches to the horizon, does she look slowing down according to the SO?
1.7. While FO approaches to the horizon, does she look "hanged at tome point" according to the SO?
1.8. Does SO observe many objects hanged (suspended, frozen, not moving) around the horizon?
2. Passing the Horizon
2.1. Can FO ever "touch" the horizon spehere/horizon line?
2.2. At the horizon, what does FO see while looking through the black hole? A black circle/sphere? Other objects falling through a black circle, other objects stopped at some distance from the black circle?
2.2.1. At the horizon, If FO ever sees other objects which are beyond the horizon abd falling thorugh the center, does she see they are falling or suspended/not moving?
2.2.2. At the horizon, IF FO ever sees other objects, does she see they disapper or explode/crush after some point?
2.3. At the horizon, what does FO see if she looks back at SO?
2.4. Just while passing the horizon, what does FO experience (if she still survives)?
2.4.1. Does she feel an "impact", a "hit"?
2.4.2. Does she explode/atomize just after passing the horizon?
3. After passing the Horizon (FO is still moving through the center)
3.1. After passing the horizon, can objects still stay intact (no explosion :)?
3.2. After passing the horizon, does the time acclerete for FO?
3.3. After passing the horizon, what does FO see while looking through the central region of the black hole?
3.3.1. Does FO see she is "in" a black region and there is nothing else besides blackness?
3.3.2. Does FO see a black central spherical region? Does she observe a distance from the center?
3.3.2.1. IF FOs see a "black region" does she see it is smalling down as she approaches or does that black thing stay same size?
3.3.3. Does FO ever see other objects which is closer to the center than her?
3.3.3.1. If FO sees closer objects, does she see they ar moving or hanging/not moving at some point between herself and the central region?
3.3.3.2. If FO sees closer "moving" objects, does she see they disappear/explode/crush at some point(at the center of the hole or smthg)?
3.4. After passing the horizon, what does FO see if she looks back at SO?
I'm sorry for many questions. But I'm just the reader and the current article bugged me. I felt I needed to know. These are the questions that the article should address if it aims at delivering information about interacting with the horizon.
I hope someone can fill it.--85.104.54.249 (talk) 06:46, 30 November 2012 (UTC)
thread_title:  Interacting with the horizon - some questions 

message: What is the difference between Inner and Outer event horizon? There is no mention of it in the article... It is mentioned briefly here: Penrose diagram, Malament–Hogarth spacetime and Ring singularity  — Preceding unsigned comment added by 213.151.44.210 (talk) 20:11, 27 February 2013 (UTC)
thread_title:  Inner event horizon vs Outer event horizon 

message: Proposed Minor Change
Stated currently in the article:
Light emitted from beyond the event horizon can never reach the outside observer.
Proposed change which I believe improves clarity 
Light emitted from within the event horizon can never reach the outside observer.
Bio watcher (talk) 19:49, 16 May 2014 (UTC)
replies: text: I'm not a scientist, and I only read the article a while ago. If the event horizon is an area for which there is an inside and and outside, then "from within" makes sense. If the event horizon is a border or line with a "this side" and "the other side", then "from beyond" makes more sense. Just judging from the use of the word "horizon", the second one would seem to make more sense. But I don't know.  and , what do you think? CorinneSD (talk) 20:51, 16 May 2014 (UTC)
replies: text: Altho I visualize an event horizon as a spherical shell around say a black hole - and within would be appropriate for from within the sphere. But, then within sounds like within the horizon itself perhaps - rather than within the sphere or region contained by the horizon. If that makes sense, then from beyond seems more reasonable. But, must the horizon be spherical? Another but ... i've no expertise here - you would need to ask an astrophysicist - or find a WP:RS. Vsmith (talk) 00:51, 17 May 2014 (UTC)
replies: text: I was asked to comment on this via a message on my talk page. Disclaimer: I'm an astronomer, but not an expert on relativity or black holes. For the event horizon around a black hole, within makes perfect sense and would be clearer, as the horizon is a closed boundary which we as observers are outside. However, for other types of event horizon (e.g. the cosmological horizon mentioned in the article) it would actually be the other way around, because we as observers are already within the horizon. A simple solution which would work in both cases would be to say 'Light emitted from the other side of the event horizon can never reach the outside observer', where outside has been deleted for the same reasons. I hope that's helpful. Modest Genius talk 01:57, 22 May 2014 (UTC)
replies: text: Again, I'm not a scientist, but that solution sounds fine to me. CorinneSD (talk) 15:09, 22 May 2014 (UTC)
thread_title:  Minor Change for Clarity 

message: is an account with no other history than the addition of these two papers  to Cosmological horizon, Particle horizon and this article back in December.
The papers are fine, I am sure, but the manner of their discussion is moronic. The papers study the question of the evolution of cosmological horizons over time in an accelerated universe. They are not suitable as a "nice and simple example of event horizon" to be given at the outset of the article. 
The discussion belongs under cosmological horizon, and there should be place in a special section about the time evolution of such horizons (now under a section called "future horizons").
Clearly, the way to do this is first explaining what a horizon is, then discuss its evolution under an expanding universe, and only then introduce the question of accelerated expansion. 
--dab (𒁳) 11:00, 2 June 2014 (UTC)
thread_title: Margalef-Bentabol papers

message: An event horizon only exists if an object is smaller than its Schwarzchild radius. Schwarzchild showed that a point mass can mathematically contain light but that doesn’t mean a point mass or singularity exists in reality. A star smaller than about twice its Schwarzchild radius would also contain light and makes more sense than a star smaller than its Schwarzchild radius. I'm suggesting there is no such thing as an event horizon (defined as an object smaller than the Schwarzchild radius). Ultimately what is in a black hole will probably be determined by comparing observations of accreting stellar size black holes with accreting neutron stars: Accretion and radiation stop at the surface of a neutron star. If there's a star larger than the Schwarzchild radius in a black hole, accretion and radiation will also stop at the surface. If there's a singularity or something smaller than the Schwarzchild radius, radiation will cease at the Schwarzchild radius. Something might be learned in only a few years by observing the large black hole in the Milky Way's center. Time will tell. 72.69.11.171 (talk) 14:11, 18 February 2015 (UTC)
thread_title:  Everybody could be barking up the wrong tree 

message: On the picture on the right up the equation for radius should be: R=2*G*M/(c*c).  — Preceding unsigned comment added by 130.117.142.50 (talk) 19:52, 8 March 2015 (UTC)
thread_title:  Article error. 

message: According to the equations it takes infinite time for matter to cross the event horizon.
This means that the collapse of the star stops directly before the horizon can be formed. 
I mean it is so simple if you just follow the equations and compare the times.
Formation takes infinite time, but Hawking radiation wastes energy in finite time :D 
Conseqeuntly, black holes are just extreme red shifted stars on the border to possess a real event horizon and they will not radiate hawking radiation.
My theory would also exclude all the silly theories about worm holes and singularities, which violate physics. 
Best, Daniel  — Preceding unsigned comment added by 109.193.96.59 (talk) 13:21, 29 March 2015 (UTC)
thread_title:  No event horizon and singularity possible in the universe 

message: The last paragraph of this section seems entirely wrong, but I'm having trouble finding any sources for or against that are reliable.  Most statements like those in the first sentence are off-the-cuff remarks by physicists in interviews, and not from actual papers.  My "problem" with these statements is that once anything has crossed the horizon, it's not simply that it can never escape again, but that no signal inside the horizon can travel away from the singularity.
This means statements like "Observers crossing a black hole event horizon can calculate the moment they have crossed it, but will not actually see or feel anything special happen at that moment." are false, or at least very misleading.  A person crossing the horizon feet first would surely "feel" that they can no longer feel their feet, for example, as no signal from their feet could ever reach their brain.  Once entirely inside the horizon, no signal from any part of your body could reach any other part that is more distant.  This applies as much to electrical signals in the nervous system as it does to light from your feet (you could not see them) and even to blood trying to pump back up from your feet.  — Preceding unsigned comment added by 69.161.127.120 (talk) 21:25, 5 June 2015 (UTC)
replies: text: It's still possible for signals to travel "outward" relative to your body, i.e. from foot to head. Your body is travelling very rapidly "inward", faster than the signal, so the overall direction of the signal is still "inward" relative to the horizon. -- Dr Greg  talk  00:49, 8 June 2015 (UTC)
thread_title:  Interacting with an event horizon (2015) 

message: if black holes exist only for a finite time from a perspective of an outside observer and eventually completely evaporate away emitting Hawking radiation, passing through the event horizon is impossible as it would take infinite amount of outside observer's time to do so, meanwhile the lifetime of a black hole would be finite.  — Preceding unsigned comment added by 188.167.67.127 (talk) 13:47, 27 August 2015 (UTC)
thread_title:  Hawking radiation 

message: I think there is contradiction
Article about black hole:
"it is impossible to determine the location of the event horizon from local observation"
Article about event horizon:
"Observers crossing a black hole event horizon can calculate the moment they have crossed it, but will not actually see or feel anything special happen at that moment"  — Preceding unsigned comment added by 78.56.153.73 (talk) 17:23, 2 August 2016 (UTC)
replies: text: No contradiction. "Local observation" means "what you actually see or feel happening at that moment". The calculation isn't a "local observation". -- Dr Greg  talk  18:42, 2 August 2016 (UTC)
thread_title:  Possible Contradiction

message: The collapse (wavefunctional particlization) is one accepable solution of the wavefunction. If you mix these two notions you create crap physics like most of the main article.
:: in the two slit experiment we know that if we open the detector after the time the "lightspeed front of potential collapse" passes the two slits, but before the final screen, then we destroy the interference pattern. This occurs because the wavefunction is the formalism of accepted solutions, not the solution which travel at luminal speeds. The wavefunction might change instantaneously!
:::: The visible horizon isn't a wavefunctional absolute truth, thus it cannot be fundamental!
 — Preceding unsigned comment added by 2A02:587:4105:1800:4C57:1430:31C8:E49C (talk) 22:38, 29 August 2016 (UTC)
thread_title:  classic mistake: mixing the lightspeed front of particle collapse potentiality with the wavefunctional formalism (wavefunction) 

message: Overall I think the way this article remains now is actually very good. Although there may be some subsections that can use more information at some point this article is very well written. I am no astrophysicist myself but I will likely be actively tweaking this article as I see fit. With some added information this could be an ever better article. AjBongiorno (talk) 16:40, 7 November 2016 (UTC)
thread_title:  Well written article 

message: Due to the time dilation, no object can really move across the event horizon in any finite time, so there is no way ever to pass the event horizon.
Besides, there is no way to know what is inside the event horizon, so any statement made about inside the event horizon can’t be falsified, and is therefore not part of science. A claim stating that inside the event horizon our laws of physics also apply doesn’t differ much from one stating inside the event horizon lives a God.
So please some in the future remove the sections that describes the picture inside or of crossing, or at least leave a note there to notify any reader that the description is merely some imagination based on certain assumptions (that will never be verified).  — Preceding unsigned comment added by ExistAX (talk • contribs) 08:38, 25 June 2018 (UTC)
thread_title:  No passing ever 

message: The earliest original notions of event horizon (EH) are based on escape velocity of light, meaning that a photon originating from EH could escape, while a photon originating inside EH could cross EH but would return back. 
Later more strict definition of EH was used, as a boundary from where no information could escape outside at all, or as a  "past causal boundary of future null infinity". The strict definition caused information and firewall paradoxes, therefore Hawking suggested in his writing ”Information Preservation and Weather Forecasting for Black Holes” that apparent horizons should be used instead to avoid those paradoxes.
Event horizons can, in principle, arise and evolve in exactly fat regions of spacetime, not having any black hole inside, if a hollow spherically symmetric thin shell of matter collapsing in a vacuum spacetime. The exterior of the shell is a portion of Schwarzschild space and the interior of the hollow shell is exactly fat Minkowski space. Bob Geroch has pointed out that if all the stars in the Milky Way gradually aggregate towards the galactic center while keeping their proportionate distances from each other, they will all fall within their joint Schwarzschild radius long before they are forced to collide. 
As a compaction, contradictions with respect to the strict definition of event horizon:
* assimilates event horizon to apparent horizon as a photon stopping surface - still those can be very separate 
* a surface that emits no photons is totally black, and it could actually be seen by slowly infalling observer. The original, escape velocity boundary of light, would not, because it is not any physical surface, and photons from inside could cross it momentary 
* information and firewall paradoxes
* implies the proposition that spacetime itself could not transmit any information - still gravitation anomalies and waves are measured with greatest interest
Still, the original EH would be the boundary where infaller would seem to froze and get infinitely red, as seen by distant observer. EH would be purely mathematical, not physical as apparent horizon is.
So, I think that the article is conservatively based only on EH, uncertainly regarding of horizons should be presented clearly. -Yoxxa (talk) 07:51, 25 April 2019 (UTC)
thread_title:   Alternative horizons 

message: Because the intro is quite Black Hole weighted, I'd suppose the all BH related text to be moved to 'Event horizon of a black hole' section, different kind of event horizons introduced and the basic properties of all event horizons shortly presented. So what would you think if new imtro would be shorly:
:"In astrophysics, an event horizon is thougth to be a boundary beyond which events cannot affect an observer on the opposite side of it. The notion was originally based to escape speed of light from massive object's gravity predicted already in 1700s, but event horizon is also related to the field of view of moving objects and expanding universe. 
:Any object approaching the horizon from the observer's side appears to slow down and its image becoming more and more redshifted as time elapses. This means that the wavelength of the light emitted from the object is getting longer as the object moves away from the observer.[2 ].  Event horizon caused by gravity does not stop gravity waves, so events causing gravity waves can affect observer on the opposite side of such event horizon, but a event horizon caused by speed affects gravity waves too."
I am not native English speaker, so proofreading and fine tuning is welcomed. Or, in a fact, there would be so much to rewrite, because section "Interacting with an event horizon" seems to contain mostly facts about black hole's event horizon, so maybe too much to do... 
Yoxxa (talk) 08:26, 16 August 2019 (UTC)
thread_title:  Restructuring needeed? 

message: There is a move discussion in progress on Wikipedia talk:Disambiguation which affects this page. Please participate on that page and not in this talk page section. Thank you.  —RMCD bot 20:01, 9 October 2019 (UTC)
thread_title:  Move discussion in progress 

message: It's correct, that future cone of free fall object (FFO) is narrows and tilts to event horizon, but what happen with past cone?
In really this can define causal connections between FFO and universe and trajectory of FFO too, that is: is possible to reach and cross event horizon or not?
If past light cone of FFO tilts away from event horizon in an extreme way (we would intuitively expect this), then it also allows (from distant observers frame only?) time like cause events for FFO, even from complete universe - asymptotically...
In other words: FFO may witness total history of complete universe under approach to even horizon of an black hole, while black hole evaporates (Hawking radiation) and event horizon disappears with it...  — Preceding unsigned comment added by 80.98.183.105 (talk) 17:29, 23 November 2021 (UTC)
thread_title:  light cones distortions under approaching event horizon of black hole