Does an event horizon ever exist?

[Dale]

My last example shows that crossing the event horizon does not occur until after an infinite time has elapsed in a static coordinate system, in a physically measurable sense. The light path and the mirror are all outside the event horizon and the light path is symmetrical in time. I cannot see any way this could be ambiguous.

This means that even though there appears to be a time at which something can fall through the event horizon from the falling point of view, the event at which the event horizon is reached, in a standard coordinate system as seen by a static observer, is infinitely into the future, in a physically measurable sense (in that we can at least measure that any event before that point can be arbitrarily far into the future). That means that BEFORE the falling object can do whatever GR says it does after crossing the event horizon, it first remains above the event horizon for an infinite time into the future.

As far as I can see, this matches up with my original model of a "stasis box", in that something falling towards the horizon effectively ends up slowed down to zero relative to our universe. What happens AFTER an infinite time doesn't seem like meaningful physics to me.

Your logic applies equally well to a uniformly acclerating observer in flat spacetime. For such an observer the same radar coordinates that you use here leads to an event horizon in flat spacetime (Rindler horizon). So, by your logic, what happens after an infinite amount of Rindler time isn't meaningful physics either. And since a Rindler horizon can be anywhere then no physics is meaningful since any physics is after some Rindler horizon.

This highlights a problem that you have with assigning some sort of existential importance to radar coordinates. They are known to be observer-dependent not merely in terms of the exact coordinates given to specific events, but also which portions of spacetime they cover. If it isn't physically meaningful to speak of something which is not covered by some observer's radar coordinates then who determines which observer's coordinates are right? How does that observer become so privileged that his or her radar coordinates determines what is meaningful and what is not?

 

[Mordred]

I often post this link on Blackhole accretion disk as questions such as ths often arise. I found this article useful as its a good collection of formulas etc on accretion disk/jets as well as some of its maths involving event horizons. There is also a section covering a possible manner of determining if a BH candidate has a solid core (neutron star) or classic singularity by measuring its jets in a specific manner.

http://arxiv.org/abs/1104.5499

its a lengthy 91 technical pages I'm still studying it myself as its so broad in scope that study is taking a while.

I should also note the article is continually updated since I first came across it I've seen 4 updates on it

 

[ZVdP]

Now I think you're overstating the case.
As far as I can see, this matches up with my original model of a "stasis box", in that something falling towards the horizon effectively ends up slowed down to zero relative to our universe. What happens AFTER an infinite time doesn't seem like meaningful physics to me.

There is a significant difference between your box and someone falling into a black hole. If an observer in the box were to look outside, he would see the rest of the universe age at an ever increasing rate as his time approaches 1 (and see the infinite future of the rest of the universe).

An observer in free fall towards a black hole doesn't see that. He won't be able to see all future events happening in the universe. He will see the universe age a limited amount of time before he hits the singularity.
A distant observer can for example send light pulses to someone falling towards a black hole. The falling observer can send a response back when he receives the signal. For the distant observer the responses will take longer and longer to arrive, but there exists a time on his watch after which he never receives a response at all when he sends a pulse towards the black hole.

 

[Passionflower]

An observer in free fall towards a black hole doesn't see that. He won't be able to see all future events happening in the universe. He will see the universe age a limited amount of time before he hits the singularity.

Do you agree that most (or perhaps all) black holes rotate?
Do you agree that what you write is not true for rotating black holes?

 

[PeterDonis]

I'm sorry, but I don't agree that the fact that the maths continues means that something "actually happens" which according to any static coordinate system occurs after an infinite time.

But the whole point is that GR does not make predictions based on coordinates; it makes predictions based on invariants. GR predicts that something does "actually happen" when an object falls through a BH horizon. You are basically saying you don't agree that this case is within GR's domain of validity: but classically, there is no good reason to make such a claim. Classically, the rule is that GR makes predictions based on proper time along worldlines, not coordinate time (whether it's in the Schwarzschild chart or any other chart). You are basically claiming you can arbitrarily change that rule for no good reason at the event horizon.

If you want to say that the classical rule is correct, but that what "actually happens" is not governed by classical GR but by some quantum gravity theory, that's a different discussion. But you appear to be talking about the classical prediction.

I think I'm correct in saying (after doing a quick integral to check) that even light takes an infinite time to pass the event horizon in static coordinates.

Infinite coordinate time, yes. So what?

If so, a conveniently placed static mirror could reflect the light beam back from any point arbitrarily close to the event horizon, and we could unambiguously assign a time to that reflection event in static coordinates by assuming it to occur at the half-way point of the symmetrical round trip, as usual for clock synchronization. There is no theoretical limit on how far in the future the round trip could be set to complete.

Yes. Again, so what?

This seems to make it very clear that the time at which the light actually crosses the event horizon is after an infinite time in our universe, as defined in a normal physically measurable way.

This is fine, as long as you recognize that there can be a whole region of spacetime "after an infinite time in our universe". You are implicitly assuming that this can't be the case, but that assumption is not valid. At least, it's not valid unless you are also willing to claim that you can arbitrarily change the rules by which GR assigns physical interpretations to the math, for no good reason, at the event horizon. (The only difference with a light beam is that you can't use proper time as an affine parameter; but you can still assign an affine parameter along an ingoing null geodesic and show that it has a finite value at the horizon, indicating that the geodesic must continue further.)

[Edit: Another way of seeing this is to note that, as DaleSpam pointed out, your argument proves too much: it proves that the region behind a Rindler horizon in Minkowski spacetime "can't exist", because it is "after an infinite time" according to Rindler observers. I doubt you are willing to defend that claim.]

 

[Mordred]

As its related another favourite article I have in my database lol this one has been posted by otheres a few times but it covers a falling observer toward the EH

http://www-e.uni-magdeburg.de/mertens/teaching/seminar/themen/touching_ghosts.pdf

 

[photonkid]

I am not sure why this question wasn't answered but just as a link:
http://en.wikipedia.org/wiki/Sagittarius_A*

yeah, I had seen that but I hadn't read much of it ... but now I have.

It says - a 2008 study ... <quote> delivered "what is now considered to be the best empirical evidence that super-massive black holes do really exist. The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt." </>

So if it's a black hole it must have an event horizon.

The article then says <quote> While, strictly speaking, there are other mass configurations that would explain the measured mass and size, such an arrangement would collapse into a single supermassive black hole on a timescale much shorter than the life of the Milky Way. </>

But, if time slows down inside the event horizon and "almost stops" relative to the vast majority of the universe, how could a black hole ever form?

The guy who solved Einsteins equations for rotating black holes (Roy Kerr) plays at my local bridge club and I *think* he told me that an event horizon doesn't exist because it takes an infinite amount of time to form.

 

[Passionflower]

The guy who solved Einsteins equations for rotating black holes (Roy Kerr) plays at my local bridge club and I *think* he told me that an event horizon doesn't exist because it takes an infinite amount of time to form.

Which is not a problem provided spacetime is open if it is closed it can never completely form.

I am often flabbergasted by the 'stiff upper lip' double standard attitude. When it comes to the Schwarzschild solution an observer passing the event horizon is A-OK 'because the math shows it', but when we start talking about a Kerr solution and an observer goes into the ergosphere or beyond it is suddenly 'obviously' no longer physical.

 

[Mordred]

Which is not a problem provided spacetime is open if it is closed it can never completely form.

What ?you lost me on that one.

 

[Passionflower]

What ?you lost me on that one.

You might want to read:
http://arxiv.org/abs/gr-qc/0003082

 

[photonkid]

Which is not a problem provided spacetime is open if it is closed it can never completely form.

I am often flabbergasted by the 'stiff upper lip' double standard attitude. When it comes to the Schwarzschild solution an observer passing the event horizon is A-OK 'because the math shows it', but when we start talking about a Kerr solution and an observer goes into the ergosphere or beyond it is suddenly 'obviously' no longer physical.

When Roy Kerr told me an event horizon doesn't exist, he also immediately said "we don't know what happens inside a black hole". I was taken by surprise and may have misheard what he said - but he did say that there is a black hole at the center of the milky way. Hence I'm trying to find out what a black hole is. Is it just a large concentration of mass - or does it have special observable properties other than what a "large concentration of mass" would have.

 

[photonkid]

yeah, I had seen that but I hadn't read much of it ... but now I have.

It says - a 2008 study ... <quote> delivered "what is now considered to be the best empirical evidence that super-massive black holes do really exist. The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt." </>

And now that I look at the "talk page" for the Wikipedia article,
http://en.wikipedia.org/wiki/Talk:Sagittarius_A*#There_is_no_evidence_to_support_that_it_.22must_be_a_black_hole_beyond_any_reasonable_doubt.22
someone says

<quote> There is no evidence proving that it is a black hole. There is only evidence that it is a supermassive object somewhere nearby but it's size is not known. </>

And someone else on the talk page says this
<quote> Small, dense, with lensing does not require the conclusion that it is a singularity. The point being there may be additional states of matter beyond neutron/quark densities but less than the infinities of a singularity. </>

I think it's strange that most articles on black holes never mention that the idea of a singularity is just a theory and that what actually happens when mass collapses into itself is completely unknown.

 

[PeterDonis]

You might want to read:
http://arxiv.org/abs/gr-qc/0003082

Ah, Tipler and his Omega Point spacetime. He wrote a whole book called The Physics of Immortality based on it. I've always like John Walker's review:

http://www.fourmilab.ch/documents/tipler.html

which includes the priceless quote: "[W]e're twiddling the Higgs field to make the whole bloody universe collapse asymmetrically, with the whole universe becoming a delay line memory."

(Note: as far as I can tell, the Omega Point spacetime is a valid solution to the EFE, mathematically speaking; it just has some pretty unusual physical implications.)

 

[PeterDonis]

And now that I look at the "talk page" for the Wikipedia article

Once again, I would not consider Wikipedia, particularly a talk page, to be a good source of information for something like this.

there may be additional states of matter beyond neutron/quark densities but less than the infinities of a singularity.

AFAIK this is a sort of "Hail Mary pass" speculation by people who don't want to accept the straightforward implications of classical GR regarding the formation of event horizons.

Basically the problem is this: to have a stable static equilibrium "end state" of matter that will resist gravitational collapse indefinitely, it needs to be stable at zero temperature, because otherwise it will radiate away energy and become more tightly bound. (Yes, technically it only needs to be stable at the temperature of the CMBR, but that's effectively zero temperature for this problem.) Also it needs to be made of fermions, because at zero temperature the only possible source of pressure is fermion degeneracy pressure (the Pauli exclusion principle)*. And it needs to be made of particles that don't decay into other particles, because otherwise they will, giving off energy and making the system more tightly bound.

[* - Edit: Technically the strong nuclear force is believed to become repulsive at short distances, so it does provide some pressure in neutron stars. AFAIK this only happens if quarks are involved; an object made solely of gluons, like a glueball, would not, AFAIK, exhibit this behavior. In any case, what I say below about the maximum mass limit applies even if a short-range repulsive interaction provides some pressure in addition to fermion degeneracy.]

The list of known particles out of which you can make a stable object that meets the above criteria is very short: electrons, up quarks, and down quarks. Electrons make white dwarfs; up and down quarks make neutron stars. And we know that both of those types of objects have a maximum mass limit; for white dwarfs it's 1.4 solar masses, for neutron stars it's around 1.5 to 3 solar masses (AFAIK, I haven't seen a recent estimate). Furthermore, the theoretical reasons why these objects have a maximum mass limit (basically because there is a relativistic limit to the ratio of pressure to density) would seem to be applicable to *any* object made out of fermions that meets the above criteria; so even if we discover some other stable fermions, stable objects made out of them should have a maximum mass limit as well.

I think it's strange that most articles on black holes never mention that the idea of a singularity is just a theory and that what actually happens when mass collapses into itself is completely unknown.

They don't say this because it isn't true. Classically we *do* know what actually happens when mass collapses into itself. We don't know the full effects of quantum corrections, as I said before, but we still know quite a lot, so to say that it's "just a theory" and what actually happens is "completely unknown" is a serious misstatement.

 

[Mordred]

I read that article, it was interesting so I will probably examine again in more detail.

I just come across this paper on Kerr Schild geometry, they make some interesting claims in it.
http://arxiv.org/abs/1212.5595

It goes into BHs with no event horizon I'm still reading it but as its related thought I would post it.

 

[photonkid]

Classically we *do* know what actually happens when mass collapses into itself.

If we did know what actually happens, you wouldn't qualify with "classically". Roy Kerr told me we don't know what happens inside a "black hole" (whatever he meant by "black hole") and I believe him.

 

[PeterDonis]

If we did know what actually happens, you wouldn't qualify with "classically".

If we knew nothing at all about what actually happens, I wouldn't have made the statement even with the qualification.

Roy Kerr told me we don't know what happens inside a "black hole" (whatever he meant by "black hole")

Exactly: "whatever he meant". Do you know what he meant? Do you think he meant that horizons don't form? Or do you think he meant that we can't see what happens inside horizons (by definition), so we can't have direct knowledge of what happens there? I think he meant the latter.

 

[Nugatory]

Roy Kerr told me we don't know what happens inside a "black hole" (whatever he meant by "black hole") and I believe him.

That's a different and much more reasonable claim than the claim that infalling objects don't cross the event horizon within a finite amount of proper time.

We really don't know what happens on the far side of the event horizon predicted by the Schwarzschild solution. We do know what GR predicts, and we have no particular reason to doubt those predictions except in the immediate vicinity of the central singularity; but we don't know that those predictions are correct.

 

[PeterDonis]

When it comes to the Schwarzschild solution an observer passing the event horizon is A-OK 'because the math shows it', but when we start talking about a Kerr solution and an observer goes into the ergosphere or beyond it is suddenly 'obviously' no longer physical.

The two cases are different because what the math shows is different. In the Schwarzschild solution, the math shows a horizon forming; that's all. In the case of the Kerr interior, the math shows closed timelike curves forming inside the inner horizon. (I have never seen a reputable physicist claim that the ergosphere, which is outside the outer horizon, is "obviously no longer physical"; indeed, a good portion of writing about the ergosphere specifically discusses how to use it to extract energy from a rotating black hole. The only claims I've seen about a portion of the Kerr spacetime being "unphysical" refer to the region inside the inner horizon where CTCs are predicted.)

It's worth noting, also, that physicists' beliefs about what happens in gravitational collapse are not just based on the limited number of exact solutions we know, since obviously those have a high degree of symmetry and a realistic collapse would not. A realistic model of a collapse should be stable against small perturbations, and none of the highly symmetric exact solutions are AFAIK. The only exact solution for a collapse that I'm aware of that is stable against small perturbations is the BKL model, which seems to be the current "best guess" at an exact solution for the region far inside the horizon in a realistic collapse.

Also, numerical simulations have been done of a lot of non-symmetric collapse scenarios, and AFAIK all of them show horizons forming. I don't know if any of the simulations of rotating collapses have shown any regions corresponding to the Kerr interior, but I suspect not since the Kerr interior is not stable against small perturbations.

 

[photonkid]

If we knew nothing at all about what actually happens, I wouldn't have made the statement even with the qualification.

But if physicists are still debating whether event horizons actually exist, how can you say we know what actually happens?

Exactly: "whatever he meant". Do you know what he meant? Do you think he meant that horizons don't form? Or do you think he meant that we can't see what happens inside horizons (by definition), so we can't have direct knowledge of what happens there? I think he meant the latter.

I will ask him after I do some more reading.

I'm not a physicist and it's hard for me to grasp these arguments about "proper time" continuing for an object falling into a black hole. How could mass that falls past the event horizon ever make it to the singularity in "our time"?

If the mass of the Earth became a black hole, it would have an event horizon radius of 1 cm or something. So photons coming from the sun should reach the center of the black hole real fast (in our time). If it was possible to measure it, would we see the photon slowing down inside the event horizon?

Does light slow down in "our time" when it "goes past" a large mass?

 

[Passionflower]

The only claims I've seen about a portion of the Kerr spacetime being "unphysical" refer to the region inside the inner horizon where CTCs are predicted.)

I just love to have a pair of batteries with negative energy, then I can finally get my anti-gravity rockets to work.

By the way I really do not see the big deal about CTC's, so the state of an object keeps rotating: "rock, paper, scissors", rendezvous-ing allover again, so what?

 

[photonkid]

I just love to have a pair of batteries with negative energy, then I can finally get my anti-gravity rockets to work.

http://www.stuff.co.nz/the-press/christchurch-life/8372542/Bright-sparks-and-black-holes

<quote> He says there is this little idea he has about negative particles that would have repulsive gravity. If he can refine the mathematical detail, he might just alarm his hosts with a presentation when he collects his Einstein Medal in May. </>

 

[pervect]

And now that I look at the "talk page" for the Wikipedia article,

The Wiki isn't a terribly reliable source. The talk page is probably slightly less reliable than the wiki.

I think it's strange that most articles on black holes never mention that the idea of a singularity is just a theory and that what actually happens when mass collapses into itself is completely unknown.

This is a bit of a non-sequitur. The central singularity is not the event horizon.

I don't really agree with the remarks made about the singularity either but that seems like a topic for a different thread.

Sticking to the topic of the event horizon and not getting sidetracked:

The event horizon is both predicted by GR, and confirmed well by experiment. One recent paper:

http://arxiv.org/abs/0903.1105

Black hole event horizons, causally separating the external universe from compact regions of spacetime, are one of the most exotic predictions of General Relativity (GR). Until recently, their compact size has prevented efforts to study them directly. Here we show that recent millimeter and infrared observations of Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, all but requires the existence of a horizon. Specifically, we show that these observations limit the luminosity of any putative visible compact emitting region to below 0.4% of Sgr A*'s accretion luminosity. Equivalently, this requires the efficiency of converting the gravitational binding energy liberated during accretion into radiation and kinetic outflows to be greater than 99.6%, considerably larger than those implicated in Sgr A*, and therefore inconsistent with the existence of such a visible region. Finally, since we are able to frame this argument entirely in terms of observable quantities, our results apply to all geometric theories of gravity that admit stationary solutions, including the commonly discussed f(R) class of theories.

The short version of this is that our black hole candidate is -- black. If it were any sort of object with an observable surface, we'd expect to see radiative emissions from said surface due to infalling matter. For instance, we can easily detect the surface of a neutron star if matter is falling on it.

The primary astrophysical importance of a horizon is
that the gravitational binding energy liberated by ma-
terial as it accretes can be advected into the black hole
without any further observational consequence. This is
very different from accretion onto other compact objects,
e.g., neutron stars, in which this liberated energy ulti-
mately must be emitted by the stellar surface.

There may still be a few small experimental loopholes, but the bulk of the evidence very storngly suggests that event horizons are very real, and that Sag. A has an event horizon.

Event horizons are also firm theoretical predictions of SR.

The fact that one can reach the event horizon in a finite proper time is another firm theoretical prediction of GR.

 

[PeterDonis]

But if physicists are still debating whether event horizons actually exist, how can you say we know what actually happens?

I didn't say we know what actually happens, period. I said we know a lot more than nothing. We know that classically a horizon is predicted to form. We know that quantum effects, if they are going to prevent the horizon from forming, would have to be large: just small changes in the classical behavior won't do it. And we know that, for black holes of astronomical size, the spacetime curvature at the horizon is small compared to the expected scale of quantum gravity (which would be a radius of curvature comparable to the Planck length); it's hard to see how quantum corrections could be large in such a regime.

As I understand it, arguments like these are why the current mainstream view is that horizons form. (AFAIK arguments like Susskind's for why this does not violate quantum unitarity are also mainstream, but that's really a separate question since it has to do with how quantum corrections affect the singularity as well as the horizon.)

Btw, it's important to distinguish two things: whether or not a horizon forms, and whether or not a singularity forms (meaning a singularity at r = 0, the "center" of the black hole). All the stuff I said above (and in earlier posts) was about whether or not a horizon forms. But even if a horizon forms (because quantum corrections are too small to prevent it for a black hole of astronomical size), we still expect quantum corrections to the classical behavior to be large as the singularity is approached, because the classical prediction is that spacetime curvature increases without bound in that regime, so at some point it will certainly reach the Planck regime.

I'm not a physicist and it's hard for me to grasp these arguments about "proper time" continuing for an object falling into a black hole. How could mass that falls past the event horizon ever make it to the singularity in "our time"?

The classical prediction is made using the same sort of math that predicts a finite proper time to fall to the horizon. However, the use of the term "our time" is not correct. The coordinates that are "natural" to an observer far away from the black hole, which are where the concept of "our time" comes from, simply do not cover the region of spacetime inside the horizon. Many people get hung up over this because they simply can't conceive how that can be; but once again, the math is unambiguous, and it is not controversial at all.

If it was possible to measure it, would we see the photon slowing down inside the event horizon?

This question doesn't really have a meaningful answer, because there's no way to define what "slowing down" means inside the horizon. Outside the horizon, there is a set of "hovering" observers that stay at the same altitude above the horizon, and these observers can be used as a reference to define what "time slowing down" means (observers closer to the horizon have clocks that "run slow" compared to observers higher up). Inside the horizon, there are no such observers, so there's no way to construct a reference for "time" that works the way the reference system outside the horizon does.

(This lack of "hovering" observers inside the horizon is related to the fact I noted above, that the natural time coordinate in the exterior region does not cover the interior region.)

Does light slow down in "our time" when it "goes past" a large mass?

If you mean light that stays outside the horizon (including the case where the mass doesn't have a horizon, like an ordinary planet or star), then yes (where "slow down" means relative to the time reference I described above, that only works outside the horizon). This is called the Shapiro time delay, and it has been measured:

http://en.wikipedia.org/wiki/Shapiro_delay

 

[photonkid]

The Wiki isn't a terribly reliable source. The talk page is probably slightly less reliable than the wiki.

So is there any detail on this page that you dispute and if so, why don't you correct it? It seems to me that the people contributing to the article are mainstream physicists and considering the unpleasantness and number of kooks on the usenet relativity forum, it's just as well.

The short version of this is that our black hole candidate is -- black. If it were any sort of object with an observable surface, we'd expect to see radiative emissions from said surface due to infalling matter. For instance, we can easily detect the surface of a neutron star if matter is falling on it.

But does time slow down close to the neutron star as it does close to the "almost" event horizon of an almost black hole.

The fact that one can reach the event horizon in a finite proper time is another firm theoretical prediction of GR.

You mean in the falling object's frame of reference? Can the falling object reach the singularity? The closer you get to the singularity, the slower time goes?

 

[photonkid]

As I understand it, arguments like these are why the current mainstream view is that horizons form. (AFAIK arguments like Susskind's for why this does not violate quantum unitarity are also mainstream, but that's really a separate question since it has to do with how quantum corrections affect the singularity as well as the horizon.)

Btw, it's important to distinguish two things: whether or not a horizon forms, and whether or not a singularity forms (meaning a singularity at r = 0, the "center" of the black hole). All the stuff I said above (and in earlier posts) was about whether or not a horizon forms. But even if a horizon forms (because quantum corrections are too small to prevent it for a black hole of astronomical size), we still expect quantum corrections to the classical behavior to be large as the singularity is approached, because the classical prediction is that spacetime curvature increases without bound in that regime, so at some point it will certainly reach the Planck regime.

ok, so this page
http://en.wikipedia.org/wiki/Black_hole#Singularity
says <quote> there exist attempts to formulate such a theory of quantum gravity. It is generally expected that such a theory will not feature any singularities. </>
Do you know if this is a correct statement?

Many people get hung up over this because they simply can't conceive how that can be; but once again, the math is unambiguous, and it is not controversial at all.

(This lack of "hovering" observers inside the horizon is related to the fact I noted above, that the natural time coordinate in the exterior region does not cover the interior region.)

ok, I haven't managed to understand special relativity yet so I'm not likely to understand this in the near future.

If you mean light that stays outside the horizon (including the case where the mass doesn't have a horizon, like an ordinary planet or star), then yes (where "slow down" means relative to the time reference I described above, that only works outside the horizon). This is called the Shapiro time delay, and it has been measured:

http://en.wikipedia.org/wiki/Shapiro_delay

Yes, that's what I meant. Thanks.

 

[photonkid]

If you DO like my suggested definition, hopefully I have already answered your question, and you just neeed to read it and think it over a bit.

Well for your information, your answer comes across as arrogant and convoluted. Nobody else in this thread saw any need to debate what "exists" means.

Also, note that although the subject was "does an event horizon ever exist", in the content I said
<quote> Is it true that the event horizon never comes into existence - or at least, if time slows down like general relativity suggests, would an event horizon and a singularity never come into existence? </>

If you wanted me to take your answer seriously you should have said
"mainstream physicists believe that event horizons actually do exist because..."

"mainstream physicists do/ do-not believe that singularities exist because..."

since it turns out that the answer is quite complicated evidenced by the fact that people in this thread are debating what happens to time near an event horizon.

 

[PeterDonis]

<quote> there exist attempts to formulate such a theory of quantum gravity. It is generally expected that such a theory will not feature any singularities. </>
Do you know if this is a correct statement?

AFAIK it is, yes. I note that there is a statement later on on that Wiki page, in the "Alternatives" section, to the effect that a quantum gravity will not feature any event horizons either. I wasn't aware that that was a mainstream view (as I've said in this thread), but the footnote there references a review article in Annalen der Physik that I haven't read. I'll take a look at it.

 

[Nugatory]

But does time slow down close to the neutron star as it does close to the "almost" event horizon of an almost black hole.

Yes. Also close to the surface of the earth, although there the effect is much smaller because the gravitational field of the Earth is much weaker than that of a neutron star. It's been measured on Earth.

 

[Nugatory]

So is there any detail on this page that you dispute and if so, why don't you correct it?

Editing some wikipedia pages is a thankless and Sisyphean task.
Answering questions here is merely thankless.