Considering astrophysical evidence to the contrary as well as multiple simplifications(∆) underlying your argument, I'd say he was probably wrong.
∆) (Some of) the assumptions underlying your argument are the following:
Assumption 1: We're observers at infinity, observing time as given by the usual Schwarzschild/Kerr coordinate t (let's focus on Schwarzschild for simplicity). Yes, the argument in favor of this is that such observers observe Schwarzschild spacetime to be flat at infinity (which is more or less what we see) but there are certainly other[1] asymptotically flat foliations of Schwarzschild spacetime which don't have a coordinate singularity at the horizon and thus don't exhibit the behavior you describe. I have yet to see a convincing argument for why we, as observers, couldn't perceive any of these other foliations of Schwarzschild spacetime and for why we definitely wouldn't live to see someone else cross the event horizon. (I mean, the fact that this doesn't work in the usual Schwarzschild coordinates is really a consequence of their singular behavior at the horizon, so should be resolved by any smooth/non-singular choice of coordinates—of which there are infinitely many.)
Assumption 2: You're talking about a static black hole solution (or a simple spherical shell collapsing) while realistic scenarios of black hole formation are an entirely different beast.
Assumption 3: You cannot superpose / easily glue together solutions of Einstein's field equations. So I'd be at least careful making a statement about us, here on Earth, when it comes to a distant black hole.
> Considering astrophysical evidence to the contrary
There is none. The only things that has been observed are supermassive objects. No event horizon or black hole has been seen. Every observation so far is also consistent with Neutron stars.
In fact some observations attributed to black holes are actually more consistent with neutron stars because of the same time dilation issues. i.e. we observe the event occurring in finite time.
> I have yet to see a convincing argument for why we, as observers, couldn't perceive any of these other foliations of Schwarzschild spacetime
For the simple reason that we are not free falling into a black hole.
> I mean, the fact that this doesn't work in the usual Schwarzschild coordinates is really a consequence of their singular behavior at the horizon, so should be resolved by any smooth/non-singular choice of coordinates—of which there are infinitely many.
Forget mathematical coordinateness. Use the real world. In the real world you can not see a black hole form (or something fall into one) because time dilates to infinity.
The fact that there are solutions where it doesn't, hardly matters when none of those solutions are physical.
> You're talking about a static black hole solution while a black hole forming is an entirely different matter.
That's even worse. The matter falls inward so fast that every atom is massively time dilated (due to velocity) relative to the others, and it perceives them as taking infinite time to reach the center.
> So I'd be at least careful making a statement about us, here on Earth, when it comes to a distant black hole.
I said that because last time I raised this object people told me "But yah, there are solutions where you do see the black hole form", so I figured I'd preempt that by specifying a POV. It didn't help - you did the exact same thing, told me there are other solutions.
> Every observation so far is also consistent with Neutron stars.
This is not correct. Neutron stars have a maximum mass limit which is somewhere between 1.5 and 3 solar masses. Any compact object over that limit must be a black hole. The hole at the center of our galaxy, which is the subject of the article, is a million or so solar masses, way over the limit.
> some observations attributed to black holes are actually more consistent with neutron stars because of the same time dilation issues. i.e. we observe the event occurring in finite time.
This is not correct either. Events that happen outside the event horizons of black holes will also emit light signals that reach us in a finite time.
> The matter falls inward so fast that every atom is massively time dilated (due to velocity) relative to the others, and it perceives them as taking infinite time to reach the center.
This is not correct. You have a flawed understanding of time dilation. Relative to each other, the atoms in an object falling into a black hole are moving very slowly, and the time dilation they see each other to have due to relative motion is negligible.
> Neutron stars have a maximum mass limit which is somewhere between 1.5 and 3 solar masses.
Yes, but after that they can become Quark stars (if such things exist). We do not have enough knowledge of quark degeneracy pressure to be able to tell.
So we should not make assumption that they become physics-breaking black holes.
> Any compact object over that limit must be a black hole.
And how do you know the object is compact? Our telescopes do not have anywhere near sufficient resolution to distinguish that.
> Events that happen outside the event horizons of black holes will also emit light signals that reach us in a finite time.
OK, and what sort of events would that be? The only known signals are black hole mergers, which obviously can not be black hole mergers since such an event would take infinite time.
We could see blazars perhaps, but those are not necessarily caused by black holes.
> Relative to each other, the atoms in an object falling into a black hole are moving very slowly, and the time dilation they see each other to have due to relative motion is negligible.
You are forgetting the objects on the other side of the black hole. Or even at small angles. Your objection would only apply to object right next to each other, and such objects are obviously not forming black holes by themself.
They need all the mass nearby to make a black hole, but time dilation makes such mass unavailable.
> after that they can become Quark stars (if such things exist). We do not have enough knowledge of quark degeneracy pressure to be able to tell.The only known signals are black hole mergers
That doesn't matter. The derivation of the neutron star maximum mass actually doesn't require that the star is made of neutrons. Anything that responds to the strong interaction (including quark matter that for some reason is not bound into hadrons) will do. The key point is that physicists have modeled such objects using basically every possible equation of state for strongly interacting matter, and the maximum masses all lie in the range I gave (the reason for the range is that we don't know the precise equation of state, we only know it's somewhere within the range we've modeled). So even if quark stars exists, they will have a maximum mass somewhere in that range (which might not be precisely the same as the maximum mass for neutron star matter).
> how do you know the object is compact? Our telescopes do not have anywhere near sufficient resolution to distinguish that.
Sure they do. We know the object at the center of the galaxy is confined within a radius of less than about 10^13 meters; we know its mass is about 4 million solar masses. The only way to pack that much mass into that small a space without an object being there that would be easily visible to our telescopes is a black hole.
> what sort of events would that be?
X-rays and gamma rays emitted by hot matter falling into the hole. See, for example, the list of stellar mass black hole candidates here:
Not at all. See above. You really, really don't know much about black holes, do you?
> You are forgetting the objects on the other side of the black hole.
Huh? We were talking about a single object falling into a black hole. An object on the other side won't be able to see that object anyway; the hole will block its view.
> They need all the mass nearby to make a black hole, but time dilation makes such mass unavailable.
Incorrect. You are peddling misinformation here; you obviously do not have a good understanding of the actual physical model of black holes based on General Relativity.
> So even if quark stars exists, they will have a maximum mass somewhere in that range
You don't know that. If the quark degeneracy pressure is high it could support far more massive objects. After all simple heat is enough to support far more massive objects (large suns easily exceed that limit).
Why would you assume, without data, that there is no other degeneracy pressure that could support such pressures?
> within a radius of less than about 10^13 meters; we know its mass is about 4 million solar masses
> The only way to pack that much mass into that small a space without an object being there that would be easily visible to our telescopes is a black hole.
That is not true. A cold object would be invisible. If the area around it is empty of mass there would not be any jets to see either.
> X-rays and gamma rays emitted by hot matter falling into the hole.
How do you know it's a black hole and not a neutron star? The jets would look identical. You can not tell that there is an event horizon.
> An object on the other side won't be able to see that object anyway; the hole will block its view.
It would "see" it gravitationally.
> Incorrect.
You say that, yet you have not explained how I'm able to see anything fall toward the black hole. Anything heading toward a black hole would (from my POV) look like it was frozen in time.
This isn't something I've made up - all scientists agree about that part. No one has ever reconciled that with how the black hole is supposed to form in the first place.
"Light from the collapsing material takes longer and longer to reach the observer, with the light emitted just before the event horizon forms delayed an infinite amount of time. Thus the external observer never sees the formation of the event horizon; instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away." https://web.archive.org/web/20130526224126/http://www.imamu....
How much clearer than that can you get? And you should recognize the name of the author.
Join the black-hole deniers club and take that next step: Since we can never see any black holes form, black holes do not exist.
> No one has ever reconciled that with how the black hole is supposed to form in the first place.
Incorrect. The first scientific paper that showed how to reconcile these things was by Oppenheimer and Snyder, published in 1939. In the late 1950s through the 1970s, this subject was studied in detail in the idealized cases where exact analytical solutions exist. Since the 1980s, numerical simulations have confirmed that the key properties of those solutions remain in much more realistic cases. If you read some actual textbooks or peer-reviewed papers on GR, instead of pop science magazines and web forums, you would know all this.
Oh, wait--you did link to a peer-reviewed paper by Penrose. Have you looked at Fig. 2 of that paper and its accompanying text? It describes exactly the reconciliation that you claim doesn't exist (the model being described is basically the 1939 Oppenheimer-Snyder model in coordinates that make things easier to see than the ones O&S used).
> You don't know that. If the quark degeneracy pressure is high it could support far more massive objects.
Nope. Go read Shapiro and Teukolsky's textbook on compact states of matter. They go into excruciating mathematical detail to show that this is not true. It has to do with relativistic degeneracy, which is a general phenomenon that applies to any kind of compact state of matter.
> Why would you assume, without data, that there is no other degeneracy pressure that could support such pressures?
Because physicists have already figured out a general model that applies to all possible states of compact matter. See above.
> Run the numbers - that's about a factor of 1,000 too large to be a black hole.
You're missing the point. For a system of that mass, there is nothing else that could fit even inside a radius 1,000 times the Schwarzschild radius and remain stable for a significant period of time. For example, if there were a million stars (or neutron stars) of one solar mass each, they would not be in stable orbits; the whole system would collapse to a black hole. This has been studied in detail numerically and is part of why astronomers are highly confident that the object at the center of our galaxy is a black hole.
> A cold object would be invisible.
There would have to be on the order of a million cold objects, not just one, because of the maximum mass limit. See above.
> How do you know it's a black hole and not a neutron star?
All of the candidates I linked to are well over the maximum mass limit.
> It would "see" it gravitationally.
I'm not sure what you mean. If you mean, would an object on the other side of the hole detect the increase in mass when the first object fell in, yes, it would.
> Anything heading toward a black hole would (from my POV) look like it was frozen in time.
Not until it got very, very close to the hole. For example, in the case of the hole at the center of the galaxy, whose Schwarzschild radius is about 10 million kilometers, you could see an object fall to within well under a million kilometers of the horizon before the light emitted from it would be too redshifted to detect. (How close would depend on how low a frequency of EM radiation your detectors could detect; we can detect very low frequencies, which means my estimate above might be quite a bit larger than our actual current detection capability.)
> all scientists agree about that part
About the general fact of light from objects falling into a black hole being redshifted, yes. But I strongly doubt you have actually run the numbers to see how close an object has to get to the hole before the redshift becomes significant.
> Since we can never see any black holes form, black holes do not exist.
Faulty logic. Nor do any of the scientific sources you quote from make this claim. They know better.
From our perspective and according to the general consensus idea that the universe is of finite age and fully in accordance with all black hole models and general relativity, blacks holes cannot exist in our universe. That does not mean what we have observed is not interesting, It is, but we don't know what it is, though we know it is not the "black hole" of theory.
There are no circumstance under the prevailing theories for which any kind of "black hole" can come into existence anywhere in our universe. Black holes are wonderful "flights of fancy" just like the Stargate and the Ancients Hyperdrive and just like the Star Trek Warp Drive.
"Black Holes" require certain assumptions for their formation in the theoretical sense and since those assumptions are not found in our universe, all models of "black holes" have an automatic failure point. All discussions about "black holes" being real, ignore those discrepancies and assume that they can exist. If you fail to agree with the "reality" of "black hole" formation, you become persona non grata.
The problem with the "black hole reality" assumption is that we cut off entire streams of investigation into what the observed phenomena may be. We are stuck in a very little corner of the universe and we cannot see many things up close. Our model assumptions colour our understanding of what we see. There are many of our observations that are anomalous to the prevailing theories that are considered "correct". Yet, if you (as an observational or experimental scientist) raise questions in relation to the consensus models, you will be quickly put in your place.
It is quite interesting that for a supposedly advanced civilisation, much of our technology and scientific endeavour is ruled by dogma. This does not lead to the advancement of our understanding of the universe around us. Just as other people have said before me and as I have said before - "There are no silly or stupid questions".
Science is one useful tool we have for investigation of the universe around us. But the outcomes we find using it in our investigations of the universe around us are predicated on the basic assumptions we bring to the table in those investigations. It is one tool among many that we have and when people use it as the only tool that has meaning, they have moved it from being a useful tool to being a dogmatic tool. they have made science into a religion.
I have been occupied with other things and only now have the time to respond.
Every model of "black hole" has as a fundamental underpinning which is time dilation due to increasing gravity (by whatever definition of gravity you may use). At whichever "event horizon" you may choose (in discussions with physicists, they have claimed a minimum of three different event horizons), time at the event horizon as observed from the universe at large stops. The underpinnings of "black holes" requires an eternal universe, no "big bang", no finite age. Formation as we see stops and can never proceed in finite time. We live in a small isolated part of our galaxy and we are unable to observe clearly many sections of our own galaxy. We rely on proxies and a belief that these proxies are adequate to match to the models and theories that are considered to be correct by consensus.
If you think about "black hole" formation as described by the various models in use, there are a number of assumptions made that don't actually match what see in our observable universe or in any practical experiments we do.
I am no mathematician or theoretical physicist, but every source of mathematics that I have studied and am continuing to study makes it quite clear that our mathematics is approximate in its mapping to reality. There is nothing wrong with this technique, but it does mean that one has to take what results we get with a grain of salt when comparing to the actual universe around us.
I find that when any of the many mathematical models in use today is declared as "reality", then I see this as the peddling of misinformation. Mathematics can and does provide us with a tool that is useful in describing what we see around us. But it is limited and always has its failure points. It is interesting that I have had this discussion about disagreeing with the consensus view with someone (a physicist) who argue for it, yet they themselves hold a particular non-consensus view over other matters relating to cosmology and could not see the extended possibilities in looking at different potential models and theories.
The simple point is that the mathematical models and theories are possible maps of the territory and are not the actual territory itself. It doesn't matter how detailed that map appears to be, it is still missing a great deal of the detail of territory itself. When it is used to decry alternative models because they are different, without actually testing those models for any kind of veracity, then we have a problem.
The simple fact is, we actually have little understanding of the universe about us. When we find discrepancies or phenomena that don't match the current models, we should be big enough to allow people to investigate alternatives freely without treating them as pariahs and heretics. It may well be that those alternatives have no veracity, but then again, they may be the start of a new outlook and understanding of the universe about us.
It is an unfortunate fact of life that people who disagree with the consensus view will be treated badly. This is a function of what it is to be human.
> in discussions with physicists, they have claimed a minimum of three different event horizons
Huh? Where are you getting this from?
> time at the event horizon as observed from the universe at large stops.
Nope. The event horizon is a null surface--it is "made" of outgoing light rays. The concept of "time" does not apply to light rays.
> The underpinnings of "black holes" requires an eternal universe
No, they don't. An "eternal" black hole is an idealization, but a real black hole does not have to be exactly the same as the idealized model. I mentioned numerical simulations in another post down-thread; any realistic black hole cannot be exactly described by closed form equations, it needs to be simulated numerically. Numerical simulations make predictions that match what we see, and show how realistic black holes can form by gravitational collapse of stars and star systems.
> If you think about "black hole" formation as described by the various models in use, there are a number of assumptions made that don't actually match what see in our observable universe or in any practical experiments we do.
I don't know what assumptions you're talking about.
> When we find discrepancies or phenomena that don't match the current models
I don't know what discrepancies you're talking about as far as black holes are concerned.
> It is an unfortunate fact of life that people who disagree with the consensus view will be treated badly.
You can't effectively disagree with the consensus view if you don't understand it. You clearly don't understand the consensus view of black holes. I am simply trying to point out incorrect things you are saying about that view.
From the physicists themselves. Public discussions on their respective blogs.
>Nope. The event horizon is a null surface--it is "made" of outgoing light rays. The concept of "time" does not apply to light rays.
Are you then saying that all the physicists who say time stops here as viewed from outside are wrong?
> > The underpinnings of "black holes" requires an eternal universe
> No, they don't. An "eternal" black hole is an idealization, but a real black hole does not have to be exactly the same as the idealized model. I mentioned numerical simulations in another post down-thread; any realistic black hole cannot be exactly described by closed form equations, it needs to be simulated numerically. Numerical simulations make predictions that match what we see, and show how realistic black holes can form by gravitational collapse of stars and star systems.
The theoretical basis for "black holes" is an eternal universe with a single mass in it. There are many things that can be numerically simulated. However, one must be very careful what you are simulating and on what basis the simulation exists. The "black hole" is a solution from a specific model and that model does not match the real universe as we observe it.
I have no issue with there being large gravitational entities. i do however have an issue with the declarations that said entities are "black holes". We do not know what they are. You cannot in any way "prove" that they are "black holes", no matter what level of consensus you display. We observe by proxy, we are at this point unable to directly test what we see.
All one can say is that there is a model that is believed to be appropriate to explain the phenomena observed.
I'll put it this way by example. We observed an entity that we call and electron that has various observable attributes and we use a variety of models to describe theoretically that entity. Are those models correct. Well, no. They are what we use to try and predict further tests and outcomes that we expect to find. We get some approximate closeness and then move forward. At no point, are the models "fully correct" or "truth", there are still anomalies found between theory and experimentation.
When we forget that our models and theories are only approximations to reality and fall into the trap that they are reality itself, then we will become incapable of actually advancing our understanding.
> I don't know what assumptions you're talking about.
Single mass existing only, asymptotically flat universe are just two of the fundamental assuptions required.
> I don't know what discrepancies you're talking about as far as black holes are concerned.
We are not in a position to directly observe any such entity. The number of times that scientists have declared that we have now seen for the first time a "black hole" over the last how many decades. that alone says that each previous declaration has been a furphy.
> You can't effectively disagree with the consensus view if you don't understand it. You clearly don't understand the consensus view of black holes. I am simply trying to point out incorrect things you are saying about that view.
When simple questions are raised against the model and are not answered by those who lead the charge for the model and when their responses amount to "you don't understand the model, so go away", then you can quite rightly take the view that they themselves don't have a clue about what they are agreeing with. I have yet to see a clear exposition of why such entities such as "black holes" should exist in our universe and answer the various simple questions that arise in opposition.
If such an explanation was to be given in a logically clear manner, then yes, we could then put "black holes" back on the table.
I have been tied up myself and am only now able to respond.
> From the physicists themselves. Public discussions on their respective blogs.
Physicists will say all kinds of things in a popular forum. Do you have any references to textbooks or peer-reviewed paper?
Even on physicists' blogs, I have never seen any reference to three different event horizons, so if you have any specific ones you can point to, it would really help me to understand what you are talking about.
> Are you then saying that all the physicists who say time stops here as viewed from outside are wrong?
If any of them actually are saying that, yes, they're wrong. But I doubt you'll be able to find any textbooks or peer-reviewed papers that say that. I don't care what pop science sources say; they're not valid sources for learning the actual science.
> The theoretical basis for "black holes" is an eternal universe with a single mass in it.
No, it isn't. You are confusing an idealized model used for pedagogy with actual models used to make predictions about actual objects observed by astronomers.
> I have no issue with there being large gravitational entities. i do however have an issue with the declarations that said entities are "black holes".
If you want to be very careful, you could say that black holes are the only entities consistent with our current theories that these "large gravitational entities" could be. It is true that our current theories are incomplete, and it could be true that a more complete theory would tell us that these entities are not anything like our current model of black holes. But even if that happens, it won't be for any of the reasons you are giving.
> Single mass existing only, asymptotically flat universe are just two of the fundamental assuptions required.
Again, you are mistaking an idealized model used for pedagogy with the real models used to make predictions about real observations. The latter do not depend on any such assumptions for the universe as a whole. They only require that a suitable region of spacetime around the object being studied contains only that object (or objects--models of this sort are used to make predictions about multi-object systems such as binary pulsars, for example, as well as black holes) and becomes flat enough at its boundary for asymptotic flatness in the model to be a reasonable approximation. These conditions are certainly met by the objects and systems to which the real models in question are applied.
You cannot prove the results of decades of physics and mathematical debate wrong with a few paragraphs of emotional arguments about dogma or some cheap mockery of a TV show.
See my comments above. When it comes down to it, scientists of all ilks are people and are just as prone to every failing of people anywhere. I enjoy science fiction in its many forms, irrespective if it is based on consensus models or not.
But I do get somewhat concerned when freedom of investigation is curtailed due to those investigations not matching up to the consensus views. If someone wants to devote themselves to a particular field and do it logically and systematically designing experiments and theories based on their results, then why not let them without treating them as idiots, cranks and pariahs. It is their time and effort and if they can make a case for funding, then let them have the funding.
What is more important? Upholding the consensus view or increasing our understanding of the universe around us? Unless we test different models and theories, we have no idea whether or not our consensus models and theories are better or worse in giving us a practical basis for understanding the universe around us.
> Time dilation means it's impossible for them to form. (From the POV of me, here on earth.)
This is not correct. If a black hole forms, it forms regardless of anyone's "POV". All you can say from the "POV" of us on Earth is that we will never be able to see any light signals from at or below the hole's event horizon, since light signals can't escape from there.
Interesting you bring that up. "Black hole" formation is based on a similar idea. An inversion is used for sure. But the argument used is similar. How about that. I haven't considered that example as a logical means of ruling against "black holes".
What do you mean by an "event horizon"? If you're a physicist I would expect you to drill down to the math and assumptions and theorems, not just English, but as I'm not a physicist you don't need to humor me even if you are one. Still supposing you did, would what you mean jive with our best known physical theories? What sorts of implications[0] to the actual observable cosmos would there be which are comfortable and uncomfortable?
To a layman there's not much ambiguity. And so things a layman would recognize as describing a "black hole" were posited before general relativity existed, but if you modeled them mathematically you would be able to find contradictions with other established theory. Therefore it is important to know what a physicist like Einstein means, precisely, if they think a "black hole" doesn't exist. In the wiki link someone else provided (full of "citation needed"s) it's reasonable to infer that at least one component of a denial of the reality of black holes is that formation implies infinite energy, infinite energy cannot be, therefore formation cannot be. The belief of non-existence is then really belief in the faulty logical implication, not so much a layman "black hole".
In any case scientists now know many things that Einstein didn't about what the best theories say about objects both laymen and physicists might understand as "black holes" and "event horizons" as well as what the best observational evidence says about events in the cosmos -- some of that evidence being very recent (gravity waves). It's not very fruitful to cite Einstein authoritatively on any supposed dispute without taking into account modern knowledge.
[0] Tegmark's paper here https://arxiv.org/abs/astro-ph/0302131 is probably my favorite paper drilling home the idea that theories can predict unobservable entities. We don't seem to have problems with positing the continued existence of a spaceship that escapes our future light cone even though we'll never be able to interact with it again, but implications of other theories (especially around "parallel universes") seem to make people very uncomfortable.
Jeez man, I mean what one always means when saying event horizon in the context of black holes: the surface that separates causally disconnected inner region around very compact objects from the rest of the universe.
Now, the term "black hole" is admittedly from after Einstein died, but since he what he actually didn't believe was anything physical could be compact enough to have a size comparable to its Schwarzschild radius this is simply a difference in naming: clearly we are talking about the same sort of object.
The math does little difference to the discussion, but if you want it then I suggest you find a book like Wald or Shutz.
"On the Gravitational Field of a Mass Point according to Einstein’s Theory" by K. Schwarzschild, January 13th, 1916 (English translation)
Black holes are fiction. The whole mess started with people misunderstanding Schwarzschild's paper. Yes, there's a singularity in the math, but you can avoid it by changing the origin. This is one of those cases where conventional "science" has been gummed up by human foibles. (And the concept is so damned romantic and compelling. And that movie! It was like the opposite of "Jaws" for sharks.)
If you can't read the paper don't bother arguing with me. If you can, show me where the math says "black holes". I'm pretty sure it says "translate the origin and ignore the singularity".
Even if there is no actual singularity, those objects exist, once you get too close you can't get back out and that is true for light as well, so they are pretty much black. I think black hole is fitting name.
Confirmed black holes include Sagittarius A* and the GW150914 primary and secondary objects.
As for quasars, the source region is very compact, mere light minutes in some cases by the constraints from variability timescales. Further, the emission is from very many is obviously from a relativistically orbiting emitter (or otherwise explain the Iron alpha line profiles), so an accretion disk around a massive, very compact object: a black black hole.
Nice, ask for the definition of a event horizon in a paper from before it was defined and then use the absence as proof there are no event horizons in the universe (◔_◔)
