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Fiery Phoenix
2014-Sep-24, 07:35 PM
So I saw this posted on another forum and wanted to share. Posted in courtesy of Phys.org.

I apologize profusely if this is the wrong section and/or if it has been shared before, but the article seems like it was only published mere hours ago.



"I'm still not over the shock," said Mersini-Houghton.


In 1974, Stephen Hawking used quantum mechanics to show that black holes emit radiation. Since then, scientists have detected fingerprints in the cosmos that are consistent with this radiation, identifying an ever-increasing list of the universe's black holes.

But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole.

Before a black hole can form, the dying star swells one last time and then explodes. A singularity never forms and neither does an event horizon. The take home message of her work is clear: there is no such thing as a black hole.


The paper, which was recently submitted to ArXiv, an online repository of physics papers that is not peer-reviewed, offers exact numerical solutions to this problem and was done in collaboration with Harald Peiffer, an expert on numerical relativity at the University of Toronto.


Experimental evidence may one day provide physical proof as to whether or not black holes exist in the universe. But for now, Mersini-Houghton says the mathematics are conclusive.

More... (http://phys.org/news/2014-09-black-holes.html)

While I don't believe it, it's interesting nonetheless. Also, I should emphasize this was not peer-reviewed, so probably best to take it with a grain of salt.

antoniseb
2014-Sep-24, 07:52 PM
This seems to be about stellar mass black holes, because M-H's work is about that star collapse process. We see objects in space that are co-orbiting small dark things with several solar masses, so clearly there are some things which act like black holes, even if this paper says that they cannot form, or if they form they cannot be long lived. I'm not sure what this paper implies about SMBHs.

Jerry
2014-Sep-24, 10:31 PM
That accretion rings 'rip apart and eject stellar mass' is a conclusion that is more consistent with a wide range of observations. Over cosmic time, black holes should continue to grow and the mass of the center eventually swallow-up the light emitting portions of the galaxy: Naked black holes. But we have as strong evidence against this the Tully-Fisher relationship: No matter how big the galactic center and black hole mass, there is a constant relationship between the rotational velocity - the mass; and the luminosity. It is as if the entire universe of galaxies is at the same point in their aging process, where the black hole mass is proportional to the mass of the younger, light emitting regions of the system.

On the other hand, if horizon events 'evaporate' away they entire mass of stars which enter the accretion ring; now you have a system that over-time will reach an equilibrium. This is consistent with the Tully-Fisher relationship; black hole physics are not.

If stars caught in accretion rings are ripped into fundamental elements; the jets of rather primal gas we observe at the poles of accretion rings and in blazers, quasars and AGN are much easier to understand. Yes, this does require 'new physics'; a distributed possible violation of basic thermoldynamics, but frankly, so does dark energy.

There is the distribution of metals; which does not seem to change with cosmic time nearly as much as it does within the mass gradient of galaxies and by galaxy type.

Finally there is the recent revelation that galaxies are axially distributed within clusters, and dwarf galaxies are axially radiant from more massive galaxies. If very large black holes eject matter axially, escape velocities could be reached; where-as disbursements in the plane of the galaxy would be more likely not to reach escape velocity from the mass of the galaxy as a whole. Over time, this would lead to the axial distribution that we are observing; with younger galaxy crops radiating axially from very large, old parent galaxies.

There are obviously missing pieces; but this is heading in a much more simple direction than existing models, which offer no explanation what so ever for these new families of observations.

Jens
2014-Sep-24, 11:04 PM
Regarding the issue of peer-review, my understanding is that in the physics community, it's fairly common to post a paper on arxiv and then get a sort of informal peer review before submitting it to a journal. It says she has an earlier paper on the subject that has been published in a good journal.

Reality Check
2014-Sep-25, 03:16 AM
That accretion rings 'rip apart and eject stellar mass' ....
Quite irrelevant to this thread, Jerry.

Jerry
2014-Sep-25, 03:27 AM
Experimental evidence may one day provide physical proof as to whether or not black holes exist in the universe. But for now, Mersini-Houghton says the mathematics are conclusive.

Read more at: http://phys.org/news/2014-09-black-holes.html#jCpThe mathematics are only as good as the theories behind them. Removal of the black hole has a lot of implications; and I don't see how they are addressing enthalpy and entropy issues. This is clearly not the last word; but it is pointing in a new direction.

Reality Check
2014-Sep-25, 03:27 AM
I come from a theoretical physics background and so would like this neat bit of theory to be correct :D.
But the evidence that stellar black holes exists is quite strong. IMO the most convincing evidence is the lack of Type I X-ray bursts (http://en.wikipedia.org/wiki/X-ray_burster) from matter piing up on a surface. This distinguishes the black hole candidates from hypothetical objects denser than neutron stars like quark stars (http://en.wikipedia.org/wiki/Quark_star).
See The Rates of Type I X-Ray Bursts from Transients Observed with RXTE: Evidence for Black Hole Event Horizons (http://adsabs.harvard.edu/abs/2006ApJ...646..407R); Remillard, et al., Astrophysical Journal 646(1): 407-419, July 2006.

KlausH
2014-Sep-25, 03:35 AM
Quite irrelevant to this thread, Jerry.

No.
I appreciate that Jerry is providing background information.

Reality Check
2014-Sep-25, 03:56 AM
No.
I appreciate that Jerry is providing background information.
It is irrelevant background information - the paper is not about accretion rings, SMBH, galaxies, the Tully-Fisher relationship, jets, etc.
Relevant background information could be a primer on the existing theory of how stellar back holes form from collapsing stars.

William
2014-Sep-30, 10:01 PM
The theoretical hairless black hole did not include a consideration of the quantum mechanics implications as matter is compressed and hence is not in compliance with quantum mechanics fundamental principals. A classic black hole is theoretically impossible.

Massive objects when they collapse arrested the collapse by generating a magnetic field that creates particle pairs. The object looks similar to a classical BH except it has a massive magnetic field and it evolves with time. There is a host of observational evidence and analysis results to support these assertions.

Have you heard of Magtars? Quasar emission spectrum also supports a MECO like solution. Quasar emission is primarily caused by synchrotron like radiation (non-thermal) from particles moving in very, very, massive magnetic field. The alternative theory to explain quasar emission is a classical BH with an accretion disk. There is however an extraordinary number of observed naked quasars, quasar spectrum with no host galaxy to supply gas for the accretion disk. There is also observational evidence that the quasar massive magnetic field is located in a region that is too close to the massive object for a accretion disc to survive.

This is a good example of why cosmological theoretical research makes no progress. Theories (toy models, what happens when a massive object collapses is a toy model, a simplified guess of what really happens) become written in stone people have spent their entire careers working with a particular toy model. To accept the possibility that the MECO theory is correct, is to accept the possibility that their life's work (or some of their profs) did not advance cosmology (actually held it back). 'Standard theory' should proceed and include two or three theories (toy models c/w (pros/cons) for what forms when a massive object collapses. The method of analyzing multiple possible solutions increase the likelihood of solving the problem.

P.S.
Cosmological theory work is analogous to watching a person lose a chess game over and over as they insist on playing the same first 10 moves. There is one correct physical solution to the cosmological puzzle. To find it the first 10 moves must be correct. A fundamental error in the first ten moves generates paradoxes and pointless work inventing new physics to try in vain to make the paradoxes go away. The method of formally considering alternative theories is how breakthroughs occur.

http://arxiv.org/abs/gr-qc/0603055


“Radiation Pressure Supported Stars in Einstein Gravity: Eternally Collapsing Objects” by Abhas Mitra

Even when we consider Newtonian stars, i.e., stars with surface gravitational redshift, z ≪ 1, it is well known that, theoretically, it is possible to have stars, supported against self-gravity, almost entirely by radiation pressure. However, such Newtonian stars must necessarily be supermassive(Hoyle and Fowler 1963; Fowler 1966;Weinberg 1972). We point out that this requirement for excessive large M in Newtonian case, is a consequence of the occurrence of low z ≪ 1. But if we remove such restrictions, and allow for possible occurrence of highly general relativistic regime, z ≫ 1, we show that, it is possible to have radiation pressure supported stars at arbitrary value of M. Since radiation pressure supported stars necessarily radiate at the Eddington limit, in Einstein gravity, they are never in strict hydrodynamical equilibrium. Further, it is believed that sufficiently massive or dense objects undergo continued gravitational collapse to the Black Hole stage characterized by z = ∞. Thus, late stages of Black Hole formation, by definition, will have, z ≫ 1, and hence would be examples of quasistable general relativistic radiation pressure supported stars (Mitra 2006). It is shown that the observed duration of such Eddington limited radiation pressure dominates states is t ≈ 5 × 108(1 + z) yr. Thus, t → ∞ as Black Hole formation (z → ∞) would take place. Consequently, such radiation pressure dominated extreme general relativistic stars become Eternally Collapsing Objects (ECOs) and the BH state is preceded by such an ECO phase. This result is also supported by our previous finding that trapped surfaces are not formed in gravitational collapse(Mitra1 2005) and the value of the integration constant in the vacuum Schwarzschild solution is zero(Mitra2 2005). Hence the supposed observed BHs are actually ECOs.

“Does SGR A* have an Intrinsic Magnetic Moment Instead of an Event Horizon?” by Stanley Robertson and Darryl Leiter

http://arxiv.org/abs/astro-ph/0603746v2



“Evidence for Intrinsic Magnetic Moments in Black Hole Candidates” by Stanley Robertson and Darryl Leiter

http://arxiv.org/abs/astro-ph/0102381v2



http://arxiv.org/pdf/astro-ph/0406163


Naked active galactic nuclei By M.Hawkins
...Such ‘naked’ AGN appear to be quite common, comprising roughly 10% of the sample of the emission line galaxies observed, the remainder being Seyfert 1 galaxies with broad permitted lines, or non-variable objects with Seyfert 2 type spectra, which are presumably normal Seyfert 2 galaxies or starburst galaxies.

There is much anecdotal evidence from surveys based on UVX selection for objects with featureless spectra for which there is no plausible classification. Such objects are typically ignored for lack of observational evidence as to their nature. The broad line region has been seen as a fundamental part of the structure of AGN, although the unified model explains its presence rather than providing a compelling argument for its existence. It is now clear that in a significant fraction of AGN the broad line region is not present. Although here has been much debate over the structure of the BLR, there seems little doubt that it involves an interaction between the central accretion disc and a surrounding star cluster (Williams et al. 1999). The idea is that gas from the cluster falls onto the accretion disc causing a complex and unstable high velocity flow pattern in which the inflowing material is eventually accreted onto the central black hole or ejected as bi-polar winds. This high velocity turbulent gas is ionised by radiation from the accretion disc, resulting in the broad line emission. Williams et al. (1999) make the case that given inflowing material, this picture is virtually inevitable. On this basis it would thus appear that for those AGN where broad emission lines are not present, the source of inflowing material has dried up. These naked AGN therefore would represent a period in the duty cycle intermediate between activity and dormancy. They would survive on the fuel reserves present in the accretion disc.

KlausH
2014-Sep-30, 10:20 PM
Cosmological theory work is analogous to watching a person lose a chess game over and over as they insist on playing the same first 10 moves.

I think that is an excellent analogy!
Sisyphus comes to mind as well.

Reality Check
2014-Oct-01, 12:26 AM
.... A classic black hole is theoretically impossible.
...nonsense snipped...

No, William: A classical black hole is theoretically inevitable :eek:. A massive object that collapses enough to form an event horizon is a black hole. Classically we know of no process that can stop this. The subject of this thread as an application of GR + QM that shows that collapsing stars explode rather than form a BH. The problem with this is that there is strong evidence that BHs exist.
Nonsense about magnetic fields/Magtars does not stop magically this.

Cosmological theories do not come from thin air - they are created to explain the universe as we see it and tested against new observations of the universe. They are irrelevant to this thread which is about black holes, not he universe as a whole.

Does Sgr A* Have an Intrinsic Magnetic Moment Instead of an Event Horizon? (http://arxiv.org/abs/astro-ph/0603746v2) is a 2008 pre-print (first uploaded in 2006!) that looks unpublished and has 1 citation in 6 years.
Evidence For Intrinsic Magnetic Moments in Black Hole Candidates (http://arxiv.org/abs/astro-ph/0102381v2) (2001)

This constitutes an observational test for the physical realization of event horizons and suggests that they may not be formed during the gravitational collapse of ordinary matter.
and when this observational test is performed:
On the Lack of Thermal Emission from the Quiescent Black Hole XTE J1118+480: Evidence for the Event Horizon (http://adsabs.harvard.edu/abs/2004ApJ...615..402M)

Naked active galactic nuclei By M.Hawkins (http://arxiv.org/abs/astro-ph/0406163) is not about AGN without a galaxy (the word galactic should be a clue!), William.

In this paper we report the discovery of a new class of AGN where the high velocity clouds are completely absent, although the nucleus is viewed directly, unobscured by the torus. These naked AGN have the spectral properties of Seyfert 2 galaxies, with
the exception that they have a strong variable continuum implying that we are seeing the active nucleus directly. This result is discussed in the context of current AGN models.

William
2014-Oct-01, 02:55 AM
From the abstract of this paper. “Some bright AGNs may genuinely lack a broad line region.” and “the temporal properties of the naked AGNs, are crucial to shed light on the central engine of these sources, which may be representative of a large class of AGNs.”



http://arxiv.org/pdf/astro-ph/0703269


A CHANDRA VIEW OF NAKED ACTIVE GALACTIC NUCLEI
However, long-term optical monitoring campaigns, carried out over more than two decades, show that the same sources are strongly variable, like type 1 (un-obscured) AGNs.Based on short Chandra observations, the sources appear to be fairly bright in the X-rays, with typical Seyfert 1s values for the photon index (approx. Tau approx.1.8) and without significant intrinsic absorption, supporting the conclusion that some bright AGNs may genuinely lack a broad line region. Future, broad-band studies as well as deeper X-ray observations, probing both the spectral and the temporal properties of the naked AGNs, are crucial to shed light on the central engine of these sources, which may be representative of a large class of AGNs.


Observations supporting the existence of an intrinsic magnetic moment inside the central compact object with in the Quasar Q0957+561 by Schild, Leiter, and Roberston.

http://arxiv.org/pdf/astro-ph/0505518



Since observations of the Schild-Vakulik structure within Q0957+561 imply that this quasar contains an observable intrinsic magnetic moment, this represents strong evidence that the quasar does not have an event horizon.

In the following sections we show that the two different lines of research discussed
above converge in a manner allowing the construction of a logical chain of observational and theoretical arguments which solves the mystery of the physical origin of the Schild-Vakulik structure observed within the quasar Q0957.

William
2014-Oct-01, 03:16 AM
There is a set of unresolved problems concerning quasars. For example quasar spectrum metalicity increases with redshift rather than decreases. Quasar's at the highest redshift have super solar metalicity. A key paradox concerning quasars is they do not exhibit time dilation. Other cosmically distant objects such a super nova exhibit time dilation.

This is a good summary paper that lists the unresolved issues and provides an explanation as to what the issue is as well as provides peer reviewed paper links to support the summary.

http://www.scirp.org/journal/PaperInformation.aspx?PaperID=5509

tusenfem
2014-Oct-01, 01:59 PM
Please keep on topic which is stellar mass black holes, and not quasars or smbh in the centre of a galaxy.

Amber Robot
2014-Oct-02, 04:22 PM
Considering that the basis of this person's conclusions is another as yet unproven theory (Hawking radiation), I think it is a bit premature to use words like "proves" and "shows".

Reality Check
2014-Oct-02, 10:27 PM
A theory that is "unproven" need not be invalid, Amber Robot. The theory for Hawking radiation is based on strong theories - QM and GR.
However it is highly unlikely that Hawking radiation will ever be directly measured since no detected BH is small enough to produce measurable Hawking radiation. There is the possibility that micro-BH were created in the Big Bang and still exist today to produce measurable Hawking radiation.

Here we have a paper that mathematically proves that stellar BH cannot exist. Thus it shows that stellar BH cannot exist. The questions is whether the paper is mathematically correct.

Amber Robot
2014-Oct-03, 04:56 PM
A theory that is "unproven" need not be invalid, Amber Robot. The theory for Hawking radiation is based on strong theories - QM and GR.
However it is highly unlikely that Hawking radiation will ever be directly measured since no detected BH is small enough to produce measurable Hawking radiation. There is the possibility that micro-BH were created in the Big Bang and still exist today to produce measurable Hawking radiation.

Here we have a paper that mathematically proves that stellar BH cannot exist. Thus it shows that stellar BH cannot exist. The questions is whether the paper is mathematically correct.

I didn't say that the theory of Hawking radiation was "invalid". Because the new work uses numerical modeling, it's not clear to me that it even proves anything mathematically.

Even if you believe the paper and you say that mathematically "stellar BH cannot exist", you'll have to try to explain all the physical evidence for stellar black holes.

The author says the following:

"Being forced to give up on either unitarity or causality is at the heart of the problem. But the quantum theory is violated if unitarity is broken. Einstein's theory is violated if causality is broken. Violations of the quantum theory imply Hawking radiation may not exist. Violations of Einstein's theory of gravity, on which the singularity theorem is based, imply black holes may not exist."

So, when faced with this dilemma and all the evidence for black holes and no evidence for Hawking radiation, what is one to think?

Buttercup
2014-Oct-03, 05:12 PM
I posted regarding this some months ago. It'd seemed "certain"(*) for decades that black holes do exist. Then all of a sudden: Nope, impossible.

That "threw" me...but then, I'm not a scientist. Wish they'd be more careful with sounding certain to begin with. :eh:

*admitted layperson lingo

Amber Robot
2014-Oct-03, 07:11 PM
I posted regarding this some months ago. It'd seemed "certain"(*) for decades that black holes do exist. Then all of a sudden: Nope, impossible.


I did not think that the theories of quantum gravity were so mainstream and accepted as to make these kinds of conclusions with such certainty.

Buttercup
2014-Oct-03, 07:20 PM
I did not think that the theories of quantum gravity were so mainstream and accepted as to make these kinds of conclusions with such certainty.

Well they sure SOUNDED like it was certain. :(

p.s.: Even very recently, a news item via Twitter about a black hole (allegedly a very large one).

Stated as though *fact.* These are science sources.

Amber Robot
2014-Oct-03, 08:50 PM
Well they sure SOUNDED like it was certain. :(

p.s.: Even very recently, a news item via Twitter about a black hole (allegedly a very large one).

Stated as though *fact.* These are science sources.

Yes, this is a major peeve of mine. I felt it was entirely inappropriate that this was presented as proven fact.

Someone is going to have a hard time explaining Cygnus X-1 and its ilk, if stellar black holes can't exist.

I prefer proof by observation over proof by theory.

Reality Check
2014-Oct-05, 10:59 PM
Even if you believe the paper and you say that mathematically "stellar BH cannot exist", you'll have to try to explain all the physical evidence for stellar black holes.

Which is exactly my point, Amber Robot.
However the techniques used in the pre-print does not matter unless someone shows that they were used incorrectly. As of now, the pre-print is correct in its conclusion that stellar black holes cannot theoretically form.

The author says the following:
"Being forced to give up on either unitarity or causality is at the heart of the problem. But the quantum theory is violated if unitarity is broken. Einstein's theory is violated if causality is broken. Violations of the quantum theory imply Hawking radiation may not exist. Violations of Einstein's theory of gravity, on which the singularity theorem is based, imply black holes may not exist. Thus black hole physics provides the best arena for understanding the friction between quantum and gravitational physics. In this light, an investigation of the evolution of the star's interior as it is approaching its singularity with the backreaction of the Hawking radiation produced by quantum effects, is of fundamental importance.
So faced with this statement that exploring the interaction between QM and GR in black holes is important, one is to think that it is important :eek:! Black hole physics is an obvious area where any quantum gravity theory can be tested.
N.B. this is not a pre-print about a quantum gravity theory.

Hlafordlaes
2014-Oct-06, 07:25 AM
I'd like to ask if what is being stated is that stellar mass BHs can indeed form classically but not without violating QM. Since we do observe BHs, what implications does this have? Are likely solutions probably related to a changed understanding of QM, or something else? How fruitful are the quandaries in this area of BHs in terms of suggesting any pointers toward, say, a GUT? Thx.

Grey
2014-Oct-06, 03:22 PM
It's probably worthwhile to note that there are already other physicists suggesting that Mersini-Houghton and Pfeiffer are mistaken. For example, look here (http://galileospendulum.org/2014/09/28/you-cant-get-rid-of-black-holes-that-easily/) or here (http://www.iflscience.com/physics/physicist-claims-have-proven-mathematically-black-holes-do-not-exist). I agree with Michael Francis:


But whether my thinking is right or wrong, the point is that we can — and should! — check the results before declaring black holes dead. When a new paper is strongly at odds with other calculations, the first response shouldn’t be to rush to press and shout about how everything has changed.Rather than worrying about all the implications of this result, and speculating on how it will affect everything we know about stellar evolution, and trying to figure out just what all those objects we observe that behave so much like black holes might be, we should wait a little while to see if their paper withstands peer review.

Amber Robot
2014-Oct-06, 05:33 PM
This is another good response: http://backreaction.blogspot.com/2014/09/black-holes-declared-non-existent-again.html

antoniseb
2014-Oct-06, 05:48 PM
This is another good response...
Response is great. The comments and replies are also quite helpful. Definitely worth the time to read if you care about the topic.

Ken G
2014-Oct-11, 02:31 AM
I'm afraid this all shows what happens when you have a field starving for data, that also involves equations that are famously hard to solve and you have almost no way to know if your calculation has made a hidden error somewhere. Experts don't agree, and each has their own proof that the other's view is wrong, but there's no data to decide if either is right. As far as I know, the main way astronomers "detect" black holes is still by saying "there's too much mass in too small a space to be anything else," so at least we can probably use that observation to rule out the claim that black holes evaporate by Hawking radiation before they even form. But what actually does form seems pretty unclear, and does it lose information, is there a "firewall", is there "chaos", is there exotic physics, and just what does go on behind an event horizon, seem like almost hopeless questions to resolve given the little data outside the event horizon, and the complete absence of data inside one. So in my opinion, the main error of that paper was claiming black holes can't exist, rather than saying "if we are right and black holes can't exist, you should expect to observe X," and let the astronomers then say "we don't observe X, we observe Y, and Y seems a whole lot more consistent with the presence of black holes than with their absence." But at least this serves to stress the importance of observing Y instead of X, which is exactly what observers need-- a reason to know why their observations matter, and what observation to do next.

Reality Check
2014-Oct-13, 12:09 AM
You have a good point, Ken G. One thing lacking from the paper seems to be a prediction of observable effects. Maybe it is obvious, e.g. a new type of supernova (a bigger version of a Type II supernova (http://en.wikipedia.org/wiki/Type_II_supernova)?). But then the question becomes of why we have not detected anything that looks like the phenomena described in the paper. Stellar BH should be forming frequently enough for us to have observed the phenomena.

However the main way that astronomers actually detect stellar black hole candidates is to look at X-ray binaries (http://en.wikipedia.org/wiki/Stellar_black_hole#X-ray_compact_binary_systems) where you have a normal star and a X-ray BH candidate. The orbit of the candidate tells you its mass. A mass of the candidate above the Chandrasekhar limit indicates a black hole. The lack of the properties of a neutron star such as " differential rotation, and can have a magnetic field and exhibit localized explosions" is further evidence that the candidate is not a neutron star.

Ken G
2014-Oct-13, 03:15 AM
However the main way that astronomers actually detect stellar black hole candidates is to look at X-ray binaries (http://en.wikipedia.org/wiki/Stellar_black_hole#X-ray_compact_binary_systems) where you have a normal star and a X-ray BH candidate. The orbit of the candidate tells you its mass. A mass of the candidate above the Chandrasekhar limit indicates a black hole.Yes that's what I mean, "the only way to have that much mass in such a small space is to have a black hole" (though note it has to be well above the Chandra limit-- just a little above is a neutron star). So it is essentially an argument from incredulity, we'd rather see specific evidence that a black hole is present.
The lack of the properties of a neutron star such as " differential rotation, and can have a magnetic field and exhibit localized explosions" is further evidence that the candidate is not a neutron star.Yes, that's important too, but it still makes black holes a kind of "if all else fails" kind of diagnosis. If Hawking radiation were ever observable and identifiable as such, that would be a different story. That's the irony here-- that paper says that the black hole evaporates before it can form, but that would in effect be an observable form of Hawking radiation, so they are in effect saying that the only way to see a black hole is to see one in the process of not forming! I don't even see how the conservation of energy would work out, usually you need a lot of mass to collapse to the event horizon to explain where the energy comes from for the rest of what you see (though that's hard to distinguish from the formation of a neutron star, but you can at least put limits on the mass of the resulting neutron star in the manner you suggest).

Grey
2014-Oct-13, 01:20 PM
Yes that's what I mean, "the only way to have that much mass in such a small space is to have a black hole" (though note it has to be well above the Chandra limit-- just a little above is a neutron star). So it is essentially an argument from incredulity, we'd rather see specific evidence that a black hole is present.
...
Yes, that's important too, but it still makes black holes a kind of "if all else fails" kind of diagnosis. If Hawking radiation were ever observable and identifiable as such, that would be a different story.I think it was true for a long time that black holes were pretty much a case of "we don't know what else could possibly be that massive but small; theory says it has to be a black hole". In my opinion, the thing that particularly changed that were some observations done a few years back, comparing some objects that we thought were neutron stars to objects that we thought were black holes (here (http://arxiv.org/abs/astro-ph/0509758)'s one of the examples that I know of; there have been other similar studies done). All the objects had companion stars close enough to be dumping material onto them, and to allow an accurate measurement of their masses from orbital characteristics. For the suspected neutron stars, we can observe bursts of x-rays at irregular intervals that are best explained as material impacting on the surface of the neutron star. However, for the black hole candidates, no similar bursts were ever observed.

So here we have an object that's massive and compact, somewhat similar to a neutron star, except that it behaves as if it has no surface that matter can fall onto. Now, sure, maybe there's some other kind of exotic object that we haven't imagined yet that could behave this way, but that fits the expected behavior of a black hole with its event horizon perfectly. Indeed, I'd argue that the event horizon is far more a defining characteristic of a black hole than Hawking radiation. Even if someone were to develop a full theory of quantum gravity and show that black holes shouldn't emit Hawking radiation after all, we wouldn't say that they had shown that black holes aren't possible, we'd just say that Hawking was wrong about how they behave.

With direct observations (well, the researchers in the paper above call it "indirect evidence", but I think they're just being typically cautious scientists; it really seems like pretty direct evidence to me) that there are objects that would fit our models of how black holes should behave, including having something that behaves like an event horizon rather than any kind of material surface, it very much seems to me that we've moved from black holes being "the only thing left" to having a pretty sound observational basis for them. As far as I'm concerned, Mersini-Houghton and Pfeiffer are welcome to explore other possibilities, but if they think that black holes can't form, we shouldn't take them too seriously unless they've got at least a plausible explanation that can account for these kinds of observations. An object that behaves like it has an event horizon rather than a physical surface trumps a theoretical argument that an event horizon can't form every time, unless your theory also includes an alternate explanation for the observation.

Jeff Root
2014-Oct-13, 07:51 PM
I'll attempt an executive summary:

The theory of stellar black hole formation shows that, due to
Hawking radiation, black holes cannot form in collapsing stars.
In the absence of solid evidence that stellar-mass black holes
exist -- which was the case just a very few years ago -- this
could imply that stellar-mass black holes might not exist. But
it always implies that the theory of stellar black hole formation
might either be incorrect or incomplete, whether or not black
holes actually exist.

Not having looked at the details, I wonder, for example,
whether the blockage of outgoing Hawking radiation by infalling
matter was adequately accounted for. That can't be easy to
model correctly.

-- Jeff, in Minneapolis

Grey
2014-Oct-13, 08:40 PM
I'll attempt an executive summary:

The theory of stellar black hole formation shows that, due to
Hawking radiation, black holes cannot form in collapsing stars.This is a more or less accurate summary of the paper, but I think it's important at this point to note that most of the other physicists who have weighed in on the matter (including William Unruh (http://en.wikipedia.org/wiki/W._G._Unruh), who probably knows a little bit about Hawking radiation) think that Mersini-Houghton and Pfeiffer are simply mistaken.

Of course, I think it almost goes without saying that there's much we don't yet understand about the formation of stellar black holes.

Ken G
2014-Oct-13, 11:41 PM
For the suspected neutron stars, we can observe bursts of x-rays at irregular intervals that are best explained as material impacting on the surface of the neutron star. However, for the black hole candidates, no similar bursts were ever observed.Yes, that is starting to rise to the level of direct evidence of the existence of an event horizon, but it still has some of the flavor of reasoning from incredulity-- "if there are no bursts, it's hard to imagine what could be going on but an event horizon". What if neutron stars undergo some kind of change in their equation of state at higher mass, such that they just don't yield those bursts? We can predict more easily when our current EOS approximations break down, than we can what takes their place. I'm not suggesting any physical argument, just saying I'd rather see more direct evidence that an EH is there.

Indeed, I'd argue that the event horizon is far more a defining characteristic of a black hole than Hawking radiation. Even if someone were to develop a full theory of quantum gravity and show that black holes shouldn't emit Hawking radiation after all, we wouldn't say that they had shown that black holes aren't possible, we'd just say that Hawking was wrong about how they behave.True enough, the event horizon always had a kind of ephemeral quality, so it's not surprising that its best diagnostic at present seems to be seeing nothing! It's just kind of the nature of the beast, though not an entirely satisfactory state of affairs. It's even worse if you want to understand what goes on inside the EH, like if there is a 2D singularity in there or something totally different. Some of our best theorists argue quite vehemently about what happens behind that veil, and predict the existence of some of the least testable kinds of macroscopic objects that any theory has ever suggested to my knowledge. The grander scale analog of string theory (indeed, string theory arguments are often in the mix). It disturbs me a little when we hold up black hole physics as some of the greatest physics that humans have accomplished, which in many ways it is, yet we see these problems with it under closer inspection.

As far as I'm concerned, Mersini-Houghton and Pfeiffer are welcome to explore other possibilities, but if they think that black holes can't form, we shouldn't take them too seriously unless they've got at least a plausible explanation that can account for these kinds of observations. Yes I agree, the whole problem is the debate should not be about what the theory says does or does not exist, it should be about what we should be looking for, or what we have already looked for and haven't seen. Theories are great for motivating and interpreting observations, but when they get used as replacements for observations, we are in danger of forgetting what we are doing here-- and since it gets an awful lot of press, it's not such a good thing for science as a whole.

Reality Check
2014-Oct-14, 01:24 AM
Yes, that is starting to rise to the level of direct evidence of the existence of an event horizon, but it still has some of the flavor of reasoning from incredulity

Not really, Ken G: Any body with the mass of the BH candidates and a surface will produce the x-ray bursts that we see from neutron stars. That is what hydrogen piling up onto a high gravity surface does - fuse, explode and produce x-rays. Stopping that will require some fundamental physics to be wrong.

Ken G
2014-Oct-14, 02:24 AM
Not really, Ken G: Any body with the mass of the BH candidates and a surface will produce the x-ray bursts that we see from neutron stars. That is what hydrogen piling up onto a high gravity surface does - fuse, explode and produce x-rays. Stopping that will require some fundamental physics to be wrong.And yet that is an argument from incredulity-- "I can't believe fundamental physics would be wrong in that extreme environment where we have no laboratory experiments." Perhaps we have a reason to be incredulous at times, but arguments from incredulity have a checkered history in science. Fundamental physics wouldn't really even need to be wrong, just incomplete. Remember we are talking about an environment that we don't even know the equation of state of the material that we expect to be there, let alone what we do not expect to be there. There is certainly no Earthbound laboratory that can do experiments in that environment, and most of the physics used is extrapolated from something else. We can say event horizons provide an effective interpretation of what we see, but we can't rule out that other observations may require a different explanation. It is already debated if event horizons are even possible (Hawking himself speaks of "apparent horizons", though the notion is controversial), given the physics we think we know, so what about physics we haven't thought of yet? A smoking gun of the presence of an event horizon would still be far better than the absence of what we expect from the only alternatives to event horizons that we can think of.

Reality Check
2014-Oct-14, 03:20 AM
And yet that is an argument from incredulity....
It is an argument from the body of knowledge that we have about the universe including the conditions in that extreme environment. We see the x-ray bursts from neutron stars. The only difference between the BH candidate + surface hypothesis is the increase in gravity. This cannot stop fusion according to our body of knowledge.
You have missed the point: X-ray bursts are not a consequence of the equation of state of a neutron star. They are the consequence of matter falling onto any body with a strong gravitational field. This is well established physics - squeeze hydrogen gas hard enough and it will fuse just as it does in the core of stars.
There is no problem in science with extrapolating known physics to other places in the universe with conditions that we cannot create here on Earth.

ETA: That post makes it look like you would never accept any evidence for event horizons :D. We can never see an event horizon directly since it emits nothing but Hawking radiation. The "direct" evidence for an event horizon will be things like the bending of light by a BH as predicted by GR close to an event horizon.

Ken G
2014-Oct-14, 03:52 AM
It is an argument from the body of knowledge that we have about the universe including the conditions in that extreme environment. We see the x-ray bursts from neutron stars. The only difference between the BH candidate + surface hypothesis is the increase in gravity. This cannot stop fusion according to our body of knowledge.Yet the increase in gravity can have a lot of important effects. The neutrons are more and more relativistic, so that's what ultimately leads to an event horizon, but some new physics could kick in as they go relativistic. Their equation of state could change. Then there's all the hubbub about event horizons, whether they are real or apparent, or whether there are fireballs just below them, or whether they can't form at all (not convincing, I grant you, but people are wondering). If Hawking is right, the spacetime gets so chaotic that you wouldn't expect a flash of X-rays to be able to emerge, perhaps, but it would also not be an idealized event horizon (though pretty close in practice). But maybe no singularity in there-- what do we need to say we have a black hole, or an event horizon?

You have missed the point: X-ray bursts are not a consequence of the equation of state of a neutron star. They are the consequence of matter falling onto any body with a strong gravitational field. This is well established physics - squeeze hydrogen gas hard enough and it will fuse just as it does in the core of stars.Well you certainly need something to squeeze it. I'm not suggesting a serious model, but what if the equation of state of highly relativistic neutrons created an interior that was extremely soft, and a crust that was thin and fragile, such that gas just fell right into it without compressing and fusing? It's idle speculation at this point, because there are no observations to require something other than an EH, that's the unique aspect of the problem-- we are looking for a model that does not produce a signal, and finding one, but that's not as good as predicting a signal and seeing it. It's pretty good evidence, certainly better than just saying the mass is too large to be something else, but ideally one is predicting something that is seen.

There is no problem in science with extrapolating known physics to other places in the universe with conditions that we cannot create here on Earth.That depends on what you mean by "no problem." We can do it, and we do do it, but we sometimes get it wrong. If we cannot create the conditions here on Earth, it is not always "known physics." We get surprised a lot! Cosmology is a good example, it currently includes phenomena that go well outside any known physics. If we just extrapolate what we already know, we don't understand inflation, dark matter, or dark energy, so if we couldn't observe the need for those things, we'd never dream them up. Or a much earlier example, when the ancient Greeks didn't see stellar parallax, they thought they had an excellent explanation for what they didn't see-- the Earth wasn't moving. It took the presence of other planets in our solar system to falsify that, had there been no other planets we would have gone on thinking that until we could finally detect parallax. When we did detect parallax, we finally had a way to predict what we did see, rather than why we didn't see anything, and the former was a more powerful model constraint.


ETA: That post makes it look like you would never accept any evidence for event horizons :D. We can never see an event horizon directly since it emits nothing but Hawking radiation. The "direct" evidence for an event horizon will be things like the bending of light by a BH as predicted by GR close to an event horizon.Yes, you answered your own question-- I'd accept as direct evidence the bending of light near an EH, or an observed effect of Hawking radiation-- all examples of something we could see that we can use the EH model to predict.

Grey
2014-Oct-14, 08:45 PM
Yes, that is starting to rise to the level of direct evidence of the existence of an event horizon, but it still has some of the flavor of reasoning from incredulity-- "if there are no bursts, it's hard to imagine what could be going on but an event horizon".I think that's an unfair characterization. It's not a situation of someone saying, "Hey, that's odd behavior, it must be an event horizon". Rather, a team of researchers, aware that we see x-ray bursts from material impacting the surface of neutron stars, realized that they could use that to test a specific prediction of general relativity and our models of stellar evolution (that black holes would form, and that they'll have event horizons). So they specifically seek out a set of good candidates, some of which are thought to be neutron stars while others should, according to theory, be black holes. Their hypothesis going in is that they shouldn't see those bursts from the black holes, since theory says they should have no surface. They get observation time for these objects, perform the analysis, and the data confirms their suspicions: no bursts from the objects that are thought to be black holes, but numerous bursts from the objects that fit the profile for neutron stars. That's not an argument from incredulity, that's a specific test of a theoretical prediction, with a result that corroborates that prediction.


What if neutron stars undergo some kind of change in their equation of state at higher mass, such that they just don't yield those bursts?It's always possible to come up with an alternate explanation for any observation. Using that logic, we could make statements like: "I don't think dark matter exists; there might be some kind of change in gravity at galactic scales" and call the dark matter model an argument from incredulity. But no, in that latter case, we say that it's up to the MOND proponent to show that a modified theory of gravity actually explains the data better than a model that includes dark matter. And if they can't do so, we say, "Hey, it's nice that you're considering alternatives; come back if you manage to make it work".

Similarly, if someone wants to propose massive neutron stars that somehow behave as though they have no physical surface as an alternate explanation, that's great. The first step would be to come up with a model of such a neutron star. It's not reasonable to dismiss corroborating evidence by claiming that there might be some alternate explanation without doing the work to show that the alternate explanation is at least plausible.


True enough, the event horizon always had a kind of ephemeral quality, so it's not surprising that its best diagnostic at present seems to be seeing nothing! It's just kind of the nature of the beast, though not an entirely satisfactory state of affairs.I don't think this will ever change for stellar black holes; it's not just a limitation "at present". Hawking radiation, assuming it exists, is likely to be much too faint to detect directly. So the only way to detect the presence of an event horizon is by noticing a lack of something that you'd otherwise expect to see there. Heck, even if we could zip over to a stellar black hole in a spaceship and point our cameras right at the thing, we'd see gravitational lensing around it showing us that there's a massive object there, and possibly a visible accretion disk, but the only sense in which we'd "see" the event horizon is by noticing there's a region from which we don't receive any light.

If we our models of black holes are at least reasonably close to accurate, we might be able to get some direct observations by creating a nano-sized one in a particle accelerator, and then watching it evaporate into Hawking radiation (or creating one and finding out that it doesn't evaporate; might be best to make sure that any we do create are moving faster than escape velocity, just in case ;)). But even then, if we were to try to probe the event horizon itself, we'd see it by its absence. It is indeed the nature of the beast, and we don't get to change that, even if we're not happy about it.


Yes I agree, the whole problem is the debate should not be about what the theory says does or does not exist, it should be about what we should be looking for, or what we have already looked for and haven't seen. Theories are great for motivating and interpreting observations, but when they get used as replacements for observations, we are in danger of forgetting what we are doing here-- and since it gets an awful lot of press, it's not such a good thing for science as a whole.My biggest concern is that when sensationalist papers like this come out, they have headlines that are like, "Researchers overturn everything we know about science! Previous scientists shown to be completely wrong about everything!" I think it contributes to a growing sentiment among the public that scientists don't really know what they're talking about, so if there's a result from science that might be inconvenient or that might clash with someone's worldview, it's easily dismissed since scientists always have it all wrong anyway.

Ken G
2014-Oct-15, 03:18 AM
I think that's an unfair characterization. It's not a situation of someone saying, "Hey, that's odd behavior, it must be an event horizon". Rather, a team of researchers, aware that we see x-ray bursts from material impacting the surface of neutron stars, realized that they could use that to test a specific prediction of general relativity and our models of stellar evolution (that black holes would form, and that they'll have event horizons). So they specifically seek out a set of good candidates, some of which are thought to be neutron stars while others should, according to theory, be black holes. Their hypothesis going in is that they shouldn't see those bursts from the black holes, since theory says they should have no surface. They get observation time for these objects, perform the analysis, and the data confirms their suspicions: no bursts from the objects that are thought to be black holes, but numerous bursts from the objects that fit the profile for neutron stars. That's not an argument from incredulity, that's a specific test of a theoretical prediction, with a result that corroborates that prediction.I see what you are saying, it is much better to predict a null result in advance, where other theories predict a non-null result, and then you go out and get a null result. But null results are still a bit tricky, because there are often multiple roads that lead there. I once heard a famous observer say that the best way to do a careful measurement is do to something that will give zero if the effect you are looking for is not present, like for example the search for magnetic monopoles. It's more conclusive to argue you have seen something when you should have seen nothing than that you saw nothing when you should have seen something. For example, consider ancient Greek astronomers, who predicted that, since the Earth was stationary, stars would not appear to deviate from their circular motions across the sky no matter how carefully we looked. They looked as carefully as they could, and sure enough, their prediction was correct-- they did not see any deviations from the circle, so the model was accepted. That was a kind of argument from incredulity too, because they knew perfectly well another explanation for not seeing any deviations would be if the stars were spectacularly far away, but that seemed difficult to believe. So they did not say "either the stars are incredibly far away, or the Earth is stationary", instead they announced "yes, the Earth is stationary." It is the exclusion of the other possibility that is the argument from incredulity, not the noticing that their theory had worked-- that's fine. In the current example, not seeing any X-ray bursts means we should say "either there is an event horizon, or there is not the kind of surface there that could stop and compress the gas, or there is something preventing the X-rays from escaping to be seen." We just report what we can conclude, with no incredulity attached. Note also that the latter statement leaves open the possibility that we could have things like "apparent" event horizons, which experts can argue should count or should not count as bona fide black holes. Note also that if we said "if there is a conventional event horizon there, we should see Hawking radiation, which should look like X," and if we then see X, we have a much stronger statement, because X is very specific prediction, it is not a prediction of a null result. (Though of course the normal interpretation of Hawking radiation is that it is the most spectacularly unobservable predicted effect in the history of science.)


It's always possible to come up with an alternate explanation for any observation. Using that logic, we could make statements like: "I don't think dark matter exists; there might be some kind of change in gravity at galactic scales" and call the dark matter model an argument from incredulity.Not quite, saying "I don't think dark matter could exist" is an argument from incredulity! There's never any harm in avoiding arguments from incredulity, you'll never make a scientific mistake by avoiding them.


But no, in that latter case, we say that it's up to the MOND proponent to show that a modified theory of gravity actually explains the data better than a model that includes dark matter. And if they can't do so, we say, "Hey, it's nice that you're considering alternatives; come back if you manage to make it work".Sure, just as the ancient Greeks might have said "if you can come up with a theory that says the Earth is moving but the stars are really really far away, knock yourself out, let us know how that comes out." But they didn't! Because a theory like that is actually really easy, it was just ruled out from the outset as being implausible. Similarly, it is relatively easy to come up with theories of exotic objects that don't have event horizons and don't show X-ray bursts, they just seem forced or implausible. And maybe they are, as forced or implausible as Lorentz and Poincare's theory that clocks really slow down and rulers really contract if they are not in the aether frame. But it is still important to science to recognize that these theories are not ruled out by observation, and theories like that have a way of coming back to haunt you in time-- just as did the idea that the stars are incredibly far away.


Similarly, if someone wants to propose massive neutron stars that somehow behave as though they have no physical surface as an alternate explanation, that's great. The first step would be to come up with a model of such a neutron star. Exactly, and I certainly haven't done that. But I doubt it's all that hard, if you have no incredulity to fight against. Indeed, if we didn't have general relativity, but we did have the observations of no X-ray bursts, that's probably just what we would be doing, and we'd probably succeed just fine, though the result would not have the far-reaching ramifications of general relativity and would not unify so many different things like GR does. But there is still active debate that GR goes outside its domain of applicability when you get to event horizons, and their concomitant information paradoxes that seem to conflict with quantum mechanics. Maybe what you get is something other than an event horizon, and doesn't have an information paradox, and doesn't produce X-ray bursts-- that was more or less Hawking's latest opinion.

Don't get me wrong, it is certainly true, and appropriate, that we favor the event horizon interpretation, just as the Greeks favored the stationary Earth, all I'm saying is that avoiding arguments from incredulity always keep the door open for ideas you might end up being glad you pursued. But no one will pursue those when incredulity rules the day, just as it took Copernicus to re-suggest something Aristarchus suggested almost 2000 years earlier, even though Copernicus had no new information to go on. 2000 years is an awful long time for incredulity to rule!

Of course, if a prediction made by the event horizon model that gives a non-null result is confirmed, like we see bending of light in a particular way that we predict is there only when an event horizon is there, or Hawking radiation or some such non-null result, then at some point it becomes foolish to keep trying to create other theories because you are just shooting in the dark whereas the other theory is making a specific prediction that tested out. But those darn null results are stickier, simply because there are a lot more ways to get them.


I don't think this will ever change for stellar black holes; it's not just a limitation "at present". Hawking radiation, assuming it exists, is likely to be much too faint to detect directly. Yes I agree, and this is a disappointing situation. Indeed, when I read about the latest flap about Hawking's "apparent horizons", I was a bit sad. There is no question that general relativity is one of the finest theories we've ever created, and uniting it with ideas like AdS/CFT correspondences and holographic principles as Hawking does is physical reasoning at the highest level that humanity has ever empowered itself to do. Yet his conclusions were scoffed at, almost laughed at really, since they weren't really fleshed out. That may be what he gets for not using greater rigor, but it is still true that other physicists are also using equally lofty analyses (with a lot more equations and in some cases more seeming rigor), yet still a bunch of other experts then scoff at those results (like the "fireball", or other models about what is going on inside the EH). Without non-null observations to predict, it's really not a very pleasing state of affairs-- it gives me a sinking feeling that some of our best minds are just spinning their wheels because they are working with insufficient information and it ultimately becomes what science is never supposed to be: a clash of opinions.


So the only way to detect the presence of an event horizon is by noticing a lack of something that you'd otherwise expect to see there. Heck, even if we could zip over to a stellar black hole in a spaceship and point our cameras right at the thing, we'd see gravitational lensing around it showing us that there's a massive object there, and possibly a visible accretion disk, but the only sense in which we'd "see" the event horizon is by noticing there's a region from which we don't receive any light.We could predict what it would look like in detail though, it's not just a null result because we'd have a run of intensity as a function of angle, say as some background object went behind it. It might be tough to get the equivalent of that from Earth, but that would be nice.


My biggest concern is that when sensationalist papers like this come out, they have headlines that are like, "Researchers overturn everything we know about science! Previous scientists shown to be completely wrong about everything!" I think it contributes to a growing sentiment among the public that scientists don't really know what they're talking about, so if there's a result from science that might be inconvenient or that might clash with someone's worldview, it's easily dismissed since scientists always have it all wrong anyway.Yes, I agree we live in a highly sensationalized world, and people are always trying to do the same to scientists. The scientists sometimes play along too, all we need now is a virtual reality show with black hole theorists or string theorists who are willing to pretend like their daily discoveries shock the world, in between catfights with their romantic rivals.

KlausH
2014-Oct-15, 07:22 AM
Sure, just as the ancient Greeks might have said "if you can come up with a theory that says the Earth is moving but the stars are really really far away, knock yourself out, let us know how that comes out." But they didn't! Because a theory like that is actually really easy, it was just ruled out from the outset as being implausible. Similarly, it is relatively easy to come up with theories of exotic objects that don't have event horizons and don't show X-ray bursts, they just seem forced or implausible. And maybe they are, as forced or implausible as Lorentz and Poincare's theory that clocks really slow down and rulers really contract if they are not in the aether frame. But it is still important to science to recognize that these theories are not ruled out by observation, and theories like that have a way of coming back to haunt you in time-- just as did the idea that the stars are incredibly far away.

...

Don't get me wrong, it is certainly true, and appropriate, that we favor the event horizon interpretation, just as the Greeks favored the stationary Earth, all I'm saying is that avoiding arguments from incredulity always keep the door open for ideas you might end up being glad you pursued. But no one will pursue those when incredulity rules the day, just as it took Copernicus to re-suggest something Aristarchus suggested almost 2000 years earlier, even though Copernicus had no new information to go on. 2000 years is an awful long time for incredulity to rule!


How refreshing it is to hear such words from somebody who (I assume) is a professional astronomer!
All we usually get in threads like this is mainstream arrogance decorated with a few misplaced smilies.

We know so little, especially in fields like astronomy where the objects of our interest are very far away and rather inaccessible.
And yet, there are always our little know-it-alls who pompously parade these threads, spitting down on anybody who dares to doubt!

Thanks, Ken, for speaking out what needs to be heard more often by certain mainstream enthusiasts.

Ken G
2014-Oct-15, 08:45 AM
Thanks for that support, though let us be clear that Grey and Reality Check were not saying anything pompous, I don't think you meant them. I interpret their remarks as ranging from being a little defensive of the conventional wisdom, to just being a candid summary of the current evidence. Maybe the conventional wisdom needs some defending, but maybe it also needs some challenging. I agree with you that we almost always think we know more than we do about the heavens (I have to laugh every time a see a headline "astronomers are shocked to discover...", we lost the right to be shocked by anything a very long time ago), so it's useful to bear in mind all those possible answers that were shelved because they just seemed too implausible. That's the best possible thing about astronomy! So the balanced stance is to recognize what is the currently favored view, but not elevate it to the level of a dogma. Grey and Reality Check were pointing out the reasons behind the currently favored view, and why there is solid evidence for it, and I was just keeping that crack in the door open because solid evidence is not quite the same as direct confirmation. Scientists are always caught between a rock and a hard place-- we want to know the truth, and we want to feel like our knowledge is indeed some form of truth, yet at the same time we need to maintain the skepticism that fuels scientific progress. It can be a difficult line to walk sometimes.

Reality Check
2014-Oct-15, 08:54 PM
Yet the increase in gravity can have a lot of important effects.
But it cannot stop fusion from happening at some point during the mass building up on the surface of not-a-neutron star. One more time: This has nothing to do with the equations of state of a neutron star, Ken G.
It is the relatively simple scenario of matter falling on a surface, piling up and being squeezed until it fuses.

Ken G: The laws of physics that we determine here on Earth are assumed to apply throughout the universe. This is one of the basic things that everyone should know about science. It is these that say that x-ray bursts that we observe on neutron stars will happen on any not-a-neutron star with a surface. The other bit of science is that what we observe about the universe also applies here on Earth (i.e. Earth is not a special place). Thus cosmological observations that lead to the expansion of the universe, dark matter, dark energy, inflation also apply locally (even if they have little or no effect).



Yes, you answered your own question-- I'd accept as direct evidence the bending of light near an EH, or an observed effect of Hawking radiation-- all examples of something we could see that we can use the EH model to predict.

No one would expect top see an "observed effect of Hawking radiation" for an existing BH.
But, Ken G, here is direct evidence for an EH from 2001: New Evidence for Black Holes (http://science.nasa.gov/science-news/science-at-nasa/2001/ast12jan_1/)
The first bit is an extension of the "X-ray bursts do not happen" observation - the overall energy expected from a neutron star is not seen for BH candidates.
The last bit though is a match to a prediction from the EH model you want:

Without an event horizon, the blob of gas would have brightened as it crashed onto the surface of the accreting body. One event had six decaying pulses; the other had seven pulses. The results are consistent with what astronomers would expect to see if matter were really falling into a black hole, Dolan said.

Reality Check
2014-Oct-15, 09:02 PM
How refreshing it is to hear such words from somebody who (I assume) is a professional astronomer!

KlausH: What made you assume that Ken G is a professional astronomer when you do not seem to assume that I, Grey or any other poster are also professional astronomers?

FYI: I am not a professional astronomer, just a person with an old, unused degree in solid state physics. However I can read the literature and see that the evidence for BH is very strong. The only thing missing is detection of an event horizon rather than the current non-detection of a surface.

KlausH
2014-Oct-15, 09:30 PM
KlausH: What made you assume that Ken G is a professional astronomer when you do not seem to assume that I, Grey or any other poster are also professional astronomers?
Your assumption is wrong.
I did assume that both you and Grey had at least a degree in astronomy or physics.
I don't doubt either of your qualification.
I do, however, very much doubt some of your conclusions.

What you'd consider "direct evidence" for an event horizon is just conjecture to me.
Some seem to take repeated assumptions in papers as facts if they are repeated often enough.
One corner stone of the scientific method is verification by experiments. And that element is missing in many cosmological theories and for obvious reasons.

Anyways, the reason I addressed Ken as a professional astronomer in my post is that - as a professional - his tone and assessments seem much more cautious and measured than the usual mainstream enthusiasts who may give lip service to the limits of our understanding but act as if it was all known and only somebody who doesn't have a degree could possibly doubt that.
Ken seems to be more keenly aware of the practical and principal limits of our knowledge than many other professionals.
Or at the very least he voices them more clearly and is not afraid of doing so.

I thought that deserved positive mentioning and hence my post.

Amber Robot
2014-Oct-15, 09:31 PM
I was until recently a professional astronomer, though that doesn't necessarily make me qualified to accurately answer any questions on this forum.

Ken G
2014-Oct-15, 09:41 PM
No one would expect top see an "observed effect of Hawking radiation" for an existing BH.Not for an existing one, but the paper that this thread is about claims you'd see something in the supernova, since Hawking radiation is supposed to prevent the formation of the black hole. I'm not saying I believe it, because I'm not sure they made any predictions about what would form instead.


But, Ken G, here is direct evidence for an EH from 2001: New Evidence for Black Holes (http://science.nasa.gov/science-news/science-at-nasa/2001/ast12jan_1/)
The first bit is an extension of the "X-ray bursts do not happen" observation - the overall energy expected from a neutron star is not seen for BH candidates.
The last bit though is a match to a prediction from the EH model you want:They are certainly interpreting watching those dimming blobs as direct evidence. However, as I said, Hawking's own recent paper would not interpret the dimming blobs as crossing a true event horizon, he might well interpret that same data as gas crossing a chaotic region of spacetime that would mask the presence of whatever is below it. Hawking called that an "apparent" event horizon, which would mean that in some formal sense, black holes would not form, but I'm not sure what he is saying would form instead. Perhaps the data should be checked for evidence of variability that might rule out a chaotic spacetime, or be evidence of it. That's the point-- if we rush to conclusions, we may overlook the need to look more closely and even if our conclusion is right, we may miss additional opportunities to bolster it with more careful analysis. It's not clear how important is the distinction between a "real" event horizon around a "real" black hole, and an "apparent" event horizon around an "apparent" black hole, but all the same-- either might be consistent with that observation. It's all a matter of keeping track of all the possibilities, and not marrying any until all the alternatives have been ruled out. If they simply say words to the effect of "we feel the most natural interpretation of this data is the presence of an event horizon, though we cannot rule out other spacetime features that mimic a true event horizon in some way", then they still get to report their conclusions, yet are being better scientists. The pop sci writers will still use the same headline, the scientists can still be conservative.

Reality Check
2014-Oct-15, 10:25 PM
What you'd consider "direct evidence" for an event horizon is just conjecture to me.

Sorry, KlausH, but that statement is just conjecture to me :D. The science is quite clear - if we see something that could be a neutron star but has no signs of a surface, e.g. no x-ray bursts, and is too massive for a neutron star according to the known laws of physics then it is very probably not a neutron star. The best candidate is a black hole.

Everything that we see in the universe cannot be replicated in a lab for "verification by experiments". We cannot even have a star in the lab, yet we kind of assume that they exist!
One corner stone of the scientific method is verification by experiments. Another corner stone of the scientific method is verification by repeated observations. Another corner stone of the scientific method is that the laws of physics that we discover locally are applicable globally (and that we continuously test this assumption). No corner stone of science should be ignored in preference for another.

KlausH
2014-Oct-15, 10:43 PM
Sorry, KlausH, but that statement is just conjecture to me :D. The science is quite clear - if we see something that could be a neutron star but has no signs of a surface, e.g. no x-ray bursts, and is too massive for a neutron star according to the known laws of physics then it is very probably not a neutron star. The best candidate is a black hole.

Yes, according to current models. I don't contest that.

But since all we actually and directly see is the absence of x-ray bursts what can we directly conclude? Only that there is a massive object and that it doesn't produce detectable x-rays.
Actually, even the conclusion that we are dealing with a massive object is not direct evidence. It is just how we make sense of the behavior of directly observable neighboring objects using current models. If neighboring stars show very fast and narrow orbits around a center then assuming a massive object as the center is our current best bet.

To hail this as "direct evidence" is just flat wrong. It is merely indirect evidence.
It is strong evidence given current models. I grant you that. But it is not direct evidence.

Reality Check
2014-Oct-15, 11:40 PM
But since all we actually and directly see is the absence of x-ray bursts what can we directly conclude? Only that there is a massive object and that it doesn't produce detectable x-rays.

Not quite right, KlausH: The keyword in x-ray bursts is bursts. The x-ray bursts that must be produced from any matter piling up on a surface in a strong gravitational field as seen from neutron stars.
Actually the evidence that we are dealing with a massive object is direct - the orbital mechanics establishing the masses of BH candidates has been around for centuries. Other than putting stars in gigantic scales, this is a direct measurement! The uncertainty in the measured masses (http://en.wikipedia.org/wiki/Stellar_black_hole#Candidates) are quite large for example, 4 ± 1 or 14 ± 4.0 solar masses.

I do not claim this as direct evidence - direct evidence of an event horizon is basically physically impossible since they do not emit any light except Hawking radiation. Any evidence of an EH is thus indirect. The problem that I have with x-ray bursts is that it is negative evidence, i.e. it is the lack of bursts excluding the candidates from being neutron stars. The most direct evidence will be indirect - the bending of light by an EH as predicted by GR.

Shaula
2014-Oct-16, 04:09 AM
To hail this as "direct evidence" is just flat wrong. It is merely indirect evidence.
It is strong evidence given current models. I grant you that. But it is not direct evidence.
Could you give some examples of things in fundamental physics we have direct evidence for? Just to understand your criteria a little better.

Ken G
2014-Oct-16, 01:53 PM
I'll describe the basic distinction I'm using, and I suspect the same for KlausH, in the form of an example. Of course any distinction that draws a line in the sand is to some degree artificial, but can be useful by way of emphasizing contrast.
Indirect evidence:
If you cannot see anything unless you turn on the lights, then it is night.
Direct evidence:
If you clearly see stars with your naked eye, and the Sun is not eclipsed, then it is night.

The difference is in predicting what you will see, and would have no reason to expect to see otherwise, versus predicting that you won't see something. Or there's the analogy I used above-- the Greeks predicted they would not see the stars appear to move over the course of a year, since the Earth was not moving. That was indirect evidence. Today we predict that our astrometrical satellites will see the stars move in tiny ellipses over the course of the year, due to the motion of the Earth. That's direct evidence. The idea being, if you predict something specific, and get it right, it's pretty strong evidence. If you predict seeing nothing, and get it right, there tend to me more ways that could come about than just your way of predicting it.

But let us also note that the key issue here is not so much what we will call direct or indirect evidence, because that is a slippery slope and sometimes direct evidence can be wrong and indirect evidence can be strong. What really matters is that we not mistake "evidence in favor of some model" for "reasons to close up our brains and say that the model expresses some true reality and there's no point in considering alternatives any more." It's a mistake to say "black holes can't exist" because some theoretical calculation that might be completely wrong was interpreted that way without making any testable predictions, but it's also a mistake to say "black holes must exist" just because we don't see X-ray bursts when gas falls in. All the same, we are all in agreement that the absence of x-ray bursts is an important and telling diagnostic that something important is going on there, and is certainly consistent with the presence of a traditional event horizon.

Grey
2014-Oct-16, 06:14 PM
Everyone's been busy since I last stopped by. :) I'm going to still respond to this slightly older message, if that's alright.


I see what you are saying, it is much better to predict a null result in advance, where other theories predict a non-null result, and then you go out and get a null result. But null results are still a bit tricky, because there are often multiple roads that lead there. I once heard a famous observer say that the best way to do a careful measurement is do to something that will give zero if the effect you are looking for is not present, like for example the search for magnetic monopoles. It's more conclusive to argue you have seen something when you should have seen nothing than that you saw nothing when you should have seen something.Perhaps, but sometimes you're limited by the nature of what you're studying. For example, if you want to test the equivalence principle, you can't do too much better than the Eöt-Wash (http://www.npl.washington.edu/eotwash/) experiments. If we're right about the equivalence principle, they'll just keep getting zero as the result, to better and better precision. Of course there's always a possibility that there's some discrepancy below the threshold of error, and there always will be. But that doesn't change the fact that their results provide good corroborative evidence that the equivalence principle holds. We can (and do, of course) also test other predictions from general relativity that have non-null results, but that doesn't mean that the experiments they're doing at Eöt-Wash don't have value (even if general relativity is shown to be flawed, it's possible that the principle of equivalence still holds), and it doesn't seem reasonable to call everything they do an argument from incredulity, and suggest that it can all be dismissed as indirect evidence.

Besides, having multiple roads that lead to some result isn't unique to results where you're measuring the absence of something you might otherwise expect. Even if you measure some nonzero value of something, there's still always the possibility that some other explanation is the correct one. That should always be considered a possibility in science, and isn't particularly unique to an experiment that gives a null result.


Not quite, saying "I don't think dark matter could exist" is an argument from incredulity! There's never any harm in avoiding arguments from incredulity, you'll never make a scientific mistake by avoiding them.Perhaps, but I'd argue that it is equally an argument from incredulity to say "I don't think black holes exist, therefore this behavior that's consistent with an event horizon must be some other exotic object (even though I don't have any plausible explanation of what that object might be)". I'm not saying that we shouldn't always remember that science is always provisional. But it's fascinating to me that an exotic object like a black hole has now become somehow so commonplace that if you say that we've got pretty good evidence that they exist and appear to behave at least in some important ways like we think they should, you get called "incredulous" for not assuming that there's instead some other kind of exotic object that behaves almost just like a black hole in the ways we've been able to check.


Similarly, it is relatively easy to come up with theories of exotic objects that don't have event horizons and don't show X-ray bursts, they just seem forced or implausible.To be pedantic, I haven't seen any such theories, even here on this thread. I've heard ideas or proposals of hypothetical exotic objects, but those aren't theories in the scientific sense. Until someone does the work to flesh them out and show that they're plausible, they aren't theories, except in the colloquial non-scientific sense. And sure, that doesn't mean there aren't other possible explanations, and we should keep an open mind about them. But that doesn't mean we can't say that these types of observations show strong support for general relativity's predictions.


Exactly, and I certainly haven't done that. But I doubt it's all that hard, if you have no incredulity to fight against.I disagree. It is very easy to say "maybe there's some other kind of exotic object that somehow behaves as if it has no surface". I think it's fairly difficult to come up with an actual model that would be consistent with all of the observations. That's not to say it can't be done, but most of the alternative models I've seen (for example, gravastars (http://en.wikipedia.org/wiki/Gravastar) or dark energy stars (http://en.wikipedia.org/wiki/Dark-energy_star)) still have something very much like an event horizon.


Of course, if a prediction made by the event horizon model that gives a non-null result is confirmed, like we see bending of light in a particular way that we predict is there only when an event horizon is there, or Hawking radiation or some such non-null result, then at some point it becomes foolish to keep trying to create other theories because you are just shooting in the dark whereas the other theory is making a specific prediction that tested out. But those darn null results are stickier, simply because there are a lot more ways to get them.I actually find it very surprising that you (and others) have commented that being able to see the gravitational lensing or observing Hawking radiation would be better evidence of a black hole than these observations that show no apparent surface. I think the latter is actually much better evidence that these objects are something like what we call black holes. Any object that's comparable in mass and size to a black hole should produce exactly the same gravitational lensing effects. Those effects don't actually depend on the event horizon in any way. So just observing gravitational lensing doesn't provide evidence that the candidate object isn't some other compact massive object (and we already know that from other observations). Similarly, Hawking radiation is just (very cold, for a stellar mass black hole) thermal radiation. There's nothing that would particularly distinguish it from thermal radiation from a non-black-hole source at a comparable temperature, except perhaps that it's more uniform. Of course, you'd have to come up with some reason that your hypothetical object is so cold, but maybe that's linked with your explanation of why it behaves like it has no surface. :) And as I've already pointed out, Hawking radiation isn't really an essential characteristic for a black hole. If it has an event horizon but emits no Hawking radiation, I think we'd consider it a black hole and that Hawking was wrong, rather than deciding that it's some other object and that "true" black holes don't exist. For that matter, I'd expect that an object with an "apparent horizon" would in most cases still be considered a black hole. It would probably depend on the details, but if your "black hole alternative" still prevents any material or radiation from escaping once it gets sufficiently close, well, that fits the basic definition of a black hole pretty well, even if you want to argue with other theorists about the semantics. I agree with your assessment that such arguments are pretty silly.

So for me, prior to this kind of research, we had objects that we knew were very massive and compact that we thought were probably black holes. But with observations steadily showing that those objects also specifically behave like they have no physical surface (here (http://arxiv.org/abs/astro-ph/9706112)'s another such paper, by the way, people were testing this somewhat longer ago than I had realized), as per the prediction from general relativity (and if you think about it, that really is a pretty unusual and specific prediction), I think that provides the best kind of corroborative evidence that we're likely to get. Is it perfect? Of course not. Could they be some other kind of compact exotic object? Of course, but the burden of demonstrating that an alternate model would work to explain those observations falls to the proponents of such a view. And as the links above show, there are physicists working on other possible models; it's not like alternative ideas are ruthlessly quashed.

mkline55
2014-Oct-16, 07:32 PM
So for me, prior to this kind of research, we had objects that we knew were very massive and compact that we thought were probably black holes. But with observations steadily showing that those objects also specifically behave like they have no physical surface (here (http://arxiv.org/abs/astro-ph/9706112)'s another such paper, by the way, people were testing this somewhat longer ago than I had realized), as per the prediction from general relativity (and if you think about it, that really is a pretty unusual and specific prediction), I think that provides the best kind of corroborative evidence that we're likely to get. Is it perfect? Of course not. Could they be some other kind of compact exotic object? Of course, but the burden of demonstrating that an alternate model would work to explain those observations falls to the proponents of such a view. And as the links above show, there are physicists working on other possible models; it's not like alternative ideas are ruthlessly quashed.

It sounds to me as though you and Ken G are in agreement on this. His point, if I have it right, is that many scientists argue from incredulity. They argue that because some evidence supports a particular widely-accepted theory, then there is no possibility that any aspect of that theory could be wrong, and until someone else produces a different perfect theory and proof with indisputable evidence, then they must be completely wrong to question any aspect of the current widely-held theory. Is the burden of proof on the one bringing the question? Yes, certainly. But any evidence supporting the current theory is given more credence than any equal evidence supporting an alternate explanation.

Grey
2014-Oct-16, 08:28 PM
His point, if I have it right, is that many scientists argue from incredulity. They argue that because some evidence supports a particular widely-accepted theory, then there is no possibility that any aspect of that theory could be wrong, and until someone else produces a different perfect theory and proof with indisputable evidence, then they must be completely wrong to question any aspect of the current widely-held theory.I think that is his main point. The thing is, I don't think that scientists really do that as often as he seems to think. If you take a look at the papers I've linked, they do explicitly leave open the possibility that there are other explanations. It's probably true that popular articles written for a lay audience sometimes make it seem like scientists are absolutely certain about everything. That was one of my complaints above, especially that they do this every time any new paper is published that seems to contradict some previously held idea, even if the new idea has yet to be corroborated. So those popular articles make it seem like scientists are absolutely certain about everything, and then they change their minds and are absolutely certain about something else, and then change their minds again and decide that they're absolutely certain about the first thing again (or something else entirely). Scientists generally are quick to admit that they aren't absolutely certain about much at all. And as for "no possibility that any aspect of that theory could be wrong", scientists are constantly updating and revising even the most well-accepted theories.

I do see scientists getting frustrated when a non-scientist comes along and says that all of modern cosmology (or quantum mechanics, or relativity) must be wrong, when they don't seem to really understand just what the details of the theory that they're criticizing are. If you're going to propose a replacement for dark matter, say, it seems like it should be obvious that you should be familiar with all of the lines of evidence that have forced us to take dark matter seriously in the first place.


Is the burden of proof on the one bringing the question? Yes, certainly. But any evidence supporting the current theory is given more credence than any equal evidence supporting an alternate explanation.I don't think it's that any specific piece of evidence is given more credence, although certainly if it seems to contradict established theories that will probably prompt a closer look. I do think that someone who isn't familiar with a given field may not understand just how much corroborating evidence there is for the mainstream theories; that's why they've become mainstream. When the folks doing the research at OPERA found results that looked like neutrinos were going faster than light, rather than saying "well, relativity must be wrong" right away, they asked the broader community to look at their results and see if anyone could see any problems (and they found some). So why did their experiment require more scrutiny than an experimental result consistent with relativity? Because it's not just competing with one other experiment. There have been literally thousands of results that all fit the predictions of relativity. It's certainly possible that there's something new and unexplained going on (and contrary to some folks' belief, all the physicists would be really excited if someone could document a violation of relativity), but it's more likely that the researchers simply made a mistake.

Amber Robot
2014-Oct-16, 08:32 PM
They argue that because some evidence supports a particular widely-accepted theory, then there is no possibility that any aspect of that theory could be wrong, and until someone else produces a different perfect theory and proof with indisputable evidence, then they must be completely wrong to question any aspect of the current widely-held theory.


Though some may have that attitude, I'd be surprised if most do. I think there is definitely a strong adherence to a well-tested, well-supported theory and a lot of skepticism of not well-fleshed-out alternative theories. An alternative theory would have to come in strong, i.e., with lots of mathematical underpinnings and quantitative predictions, to be competitive with existing theories, let alone usurp them.

KlausH
2014-Oct-16, 10:57 PM
But let us also note that the key issue here is not so much what we will call direct or indirect evidence, because that is a slippery slope and sometimes direct evidence can be wrong and indirect evidence can be strong.
I agree.
I hesitated to answer Shaula's question because it is indeed a slippery slope to enter a discussion about direct and indirect evidence, since it is fairly easy to construct cases where the distinction may not be clear at all.


What really matters is that we not mistake "evidence in favor of some model" for "reasons to close up our brains and say that the model expresses some true reality and there's no point in considering alternatives any more." It's a mistake to say "black holes can't exist" because some theoretical calculation that might be completely wrong was interpreted that way without making any testable predictions, but it's also a mistake to say "black holes must exist" just because we don't see X-ray bursts when gas falls in. All the same, we are all in agreement that the absence of x-ray bursts is an important and telling diagnostic that something important is going on there, and is certainly consistent with the presence of a traditional event horizon.
Yes, that is my main point.

Let's take the black hole at the center of our galaxy as an example.
I assume most here know the story.
Sagittarius A* was assumed to be a smbh. The analysis of the movement of several stars around that center can with current models only be explained with the assumption of a very massive and compact object at the center of their orbits.
That is very compelling evidence indeed.

But - it is indirect evidence.
All we can say for sure is this:
We can (directly) observe stars that orbit Sagittarius A* and their orbits are consistent with a very massive and small object at the center.

Does that prove that there is smbh at the center of our galaxy?
No, it doesn't. All it proves is that the movement of some stars is consistent with it.
But at the time everybody pretty much took it for granted (and I admit I was quite excited myself).
It was referred to in papers. It got repeated and repeated as if it was a proven fact.

And now this paper (OP) comes along and questions the very formation of stellar mass black holes, which in some models are assumed to be the seeds of super massive black holes.
It is clearly too early to fully accept the conclusions in the paper but it does cast quite a shadow of doubt on the accepted position.

However, we have direct evidence for the movement of some stars around Sagittarius A* and whatever model replaces the current one (if it comes to that) must be able to explain that observation.

I very much agree with Ken when he says

What really matters is that we not mistake "evidence in favor of some model" for "reasons to close up our brains and say that the model expresses some true reality and there's no point in considering alternatives any more."

Amber Robot
2014-Oct-16, 11:15 PM
Sagittarius A* was assumed to be a smbh. The analysis of the movement of several stars around that center can with current models only be explained with the assumption of a very massive and compact object at the center of their orbits.
That is very compelling evidence indeed.

But - it is indirect evidence.

What would you consider to be direct evidence?

KlausH
2014-Oct-16, 11:47 PM
What would you consider to be direct evidence?

A good question.
In some cases it is simply impossible to gather direct evidence.
In fact, that is true for many cosmological and astronomical phenomena.
For principal reasons we will never have direct evidence for the evolution of the cosmos, for inflation, the BB itself, for what happens behind the event horizon of a BH (if they indeed exist).

Is it possible to have direct evidence for a BH?
I don't know. I guess it would be pretty direct evidence if we could travel into the vicinity of one with a spaceship full of instruments such that we can directly observe the accretion disc and other phenomena.
But that's not going to happen anytime soon, if ever.

Jean Tate
2014-Oct-17, 12:36 AM
A good question.
In some cases it is simply impossible to gather direct evidence.
In fact, that is true for many cosmological and astronomical phenomena.
For principal reasons we will never have direct evidence for the evolution of the cosmos, for inflation, the BB itself, for what happens behind the event horizon of a BH (if they indeed exist).

Is it possible to have direct evidence for a BH?
I don't know. I guess it would be pretty direct evidence if we could travel into the vicinity of one with a spaceship full of instruments such that we can directly observe the accretion disc and other phenomena.
But that's not going to happen anytime soon, if ever.(my bold)

Isn't it true that there is no direct evidence for anything outside our solar system (just the detection of some photons)? And even for most things/objects inside it too?

I'm not sure you can come up with a convincing answer, one that avoids the "slippery slope", or at least addresses most of Ken G's point with what is, ultimately, an arbitrary choice.

More generally, if I understand most of what's in this thread, isn't it going over ground which the great Imre Lakatos covered, quite a few decades ago now?

Ken G
2014-Oct-17, 12:39 AM
Perhaps, but sometimes you're limited by the nature of what you're studying. For example, if you want to test the equivalence principle, you can't do too much better than the Eöt-Wash (http://www.npl.washington.edu/eotwash/) experiments. If we're right about the equivalence principle, they'll just keep getting zero as the result, to better and better precision.The question, though, is that experiment a test of the equivalence principle, or an effort to falsify it? I'm sure the experimenters would rather get a signal, they would win the Nobel prize! No signal there, no Nobel prize. Same for the search for the electron dipole moment. But that may be more of an issue of, you get the prize if you falsify the prevailing theory, not if you confirm it, it might not matter all that much if you get a null result or a non-null. I'm just saying that there are often more ways to get a null result, like if the electron has no dipole moment, or if it has a dipole moment but it is just way too small to observe. If you get a non-null result, you kill both those birds with the same stone, and now you are looking for a theory that gives the electron a dipole moment.

But we are still largely in agreement-- there is nothing fundamentally unimportant about a null result, and Michelson and Morely found. And the absence of X-ray bursts is a telling diagnostic of something. But I wonder if Hawking could take it as evidence for his chaotic spacetime idea-- and if he did, he might say to go and look for variability as that gas was "blinking out". That way, we take an observation and use it to open a door to discovery, rather than close it.

Perhaps, but I'd argue that it is equally an argument from incredulity to say "I don't think black holes exist, therefore this behavior that's consistent with an event horizon must be some other exotic object (even though I don't have any plausible explanation of what that object might be)". I agree completely, that would also be an argument from incredulity, and scientists should not do that. Basically, we should have learned by now never to be incredulous about anything. We have theories that can be interpreted as saying you can set up an identical experiment and get a totally different outcome, the universe has an origin in which all our physics breaks down, most of what the universe is made of is invisible, space has a bizarre tendency to just want to expand, and there may be a mind bogglingly huge number of other universes out there with different parameters than ours. How do scientists choose what to be incredulous about, given that state of affairs?
But it's fascinating to me that an exotic object like a black hole has now become somehow so commonplace that if you say that we've got pretty good evidence that they exist and appear to behave at least in some important ways like we think they should, you get called "incredulous" for not assuming that there's instead some other kind of exotic object that behaves almost just like a black hole in the ways we've been able to check.Actually I wouldn't call that statement an argument from incredulity, it wasn't the statement I was talking about.

And sure, that doesn't mean there aren't other possible explanations, and we should keep an open mind about them. But that doesn't mean we can't say that these types of observations show strong support for general relativity's predictions.I agree with both those statements-- neither is an argument from incredulity! The argument from incredulity here is "since we cannot imagine anything that would not have a hard surface other than a classical event horizon, we must have a black hole here." Saying "this observation can be understood if there is an event horizon there" is a very different statement, and much more scientifically strong. Imagine the church in Galileo's day saying "we can understand all the observations if the Earth is stationary" instead of "the Earth is known to be stationary." It would have saved so many problems, Galileo could just respond to the first statement, "until now", and that's that. But the latter statement leads to a trial. I'm not saying anyone here said black holes have to exist because we don't see X-ray bursts, we all agree it is significant that black holes explain that observation, I'm just distinguishing the argument-from-evidence that "black hole event horizons explain this observation, conventional objects in more traditional spacetimes do not," from the argument-from-incredulity that "it must be a black hole event horizon, because we have no theory for anything else that would do that." That was the mistake made by the ancient Greek astronomers, they should have looked for the other theory, even though they were incredulous about it. Who knows, maybe someone did follow up on Aristarchus' idea, but it was lost to history. Probably they didn't, it might have seemed like a long shot, and we all have to choose where we invest our time, and hindsight is 20-20.


I disagree. It is very easy to say "maybe there's some other kind of exotic object that somehow behaves as if it has no surface". I think it's fairly difficult to come up with an actual model that would be consistent with all of the observations. That's not to say it can't be done, but most of the alternative models I've seen (for example, gravastars (http://en.wikipedia.org/wiki/Gravastar) or dark energy stars (http://en.wikipedia.org/wiki/Dark-energy_star)) still have something very much like an event horizon.As would a chaotic "apparent horizon." That's fine, it can have something very like an event horizon-- and not be a black hole, at least in some formal sense. We never get there, if we just say "we have proven it is a black hole."


I actually find it very surprising that you (and others) have commented that being able to see the gravitational lensing or observing Hawking radiation would be better evidence of a black hole than these observations that show no apparent surface. I think the latter is actually much better evidence that these objects are something like what we call black holes.The difference is that lensing and Hawking radiation would make specific predictions, they could be used to characterize the details of the EH-like behavior. Such as, is it chaotic, or not?


Any object that's comparable in mass and size to a black hole should produce exactly the same gravitational lensing effects. Those effects don't actually depend on the event horizon in any way.They would if you see lensing from along the horizon, something that could be used to make a full spacetime map.

Similarly, Hawking radiation is just (very cold, for a stellar mass black hole) thermal radiation. There's nothing that would particularly distinguish it from thermal radiation from a non-black-hole source at a comparable temperature, except perhaps that it's more uniform.It would have to be some crazy version of it, like the one that prevents the black hole from forming. I am not at all convinced by that physics, but if it were true, it would presumably have observable effects.

And as the links above show, there are physicists working on other possible models; it's not like alternative ideas are ruthlessly quashed.That is reassuring! They are avoiding arguing from incredulity, in essence-- they are stoking their anti-incredulousness!

KlausH
2014-Oct-17, 04:52 AM
Isn't it true that there is no direct evidence for anything outside our solar system (just the detection of some photons)? And even for most things/objects inside it too?

I'm not sure you can come up with a convincing answer, one that avoids the "slippery slope"...

Well, you've just made it quite a bit more slippery, haven't you? :)

This is tricky business, but if I'd ventured a first attempt at a specification as to what constitutes "direct evidence" I'd say we gain direct evidence or data about an object if we have unencumbered access with instruments.

I am fully aware that this is far from satisfactory.

What constitutes "unencumbered"?
In astronomy you hardly ever have a direct line of sight. There are always some pesky gas or dust clouds in the way.
Fair enough, but I think it is fair to say that we have a pretty good understanding as to how those clouds affect the photons we are interested in.

Also, what makes an instrument? Do gravitational lenses count?

You can easily tear my definition apart, but if you stick with obvious examples I think you get at least the spirit of where I am coming from.

One thing is safe to say:
As far as cosmological evolution is concerned, evidence is always and necessarily indirect.

Jean Tate
2014-Oct-17, 08:42 AM
Well, you've just made it quite a bit more slippery, haven't you? :)

This is tricky business, but if I'd ventured a first attempt at a specification as to what constitutes "direct evidence" I'd say we gain direct evidence or data about an object if we have unencumbered access with instruments.

I am fully aware that this is far from satisfactory.

What constitutes "unencumbered"?
In astronomy you hardly ever have a direct line of sight. There are always some pesky gas or dust clouds in the way.
Fair enough, but I think it is fair to say that we have a pretty good understanding as to how those clouds affect the photons we are interested in.

Also, what makes an instrument? Do gravitational lenses count?

You can easily tear my definition apart, but if you stick with obvious examples I think you get at least the spirit of where I am coming from.

One thing is safe to say:
As far as cosmological evolution is concerned, evidence is always and necessarily indirect.(my bold)

Thanks for this; I think it's well worth the effort to try to think this through, and discuss it.

"Unencumbered" becomes quite problematic - and ultimately just as arbitrary - when you consider trying to understand what goes on 'inside' ... is the Sun powered by nuclear fusion (of hydrogen) in its core? Is the Earth's magnetic field generated by a core (or part of one) comprising a liquid form of iron? Are white dwarf stars almost entirely composed of a form of matter in which the electrons are in the form of a Fermi gas?

And even when you have "direct evidence or data about an object if we have unencumbered access with instruments", how can you interpret that direct evidence if you've never seen such a thing in your own laboratory?

For example, a great many astronomical objects have a strong emission line at (rest frame) ~500.7 nm. This is said to be caused by a particular electronic transition in a particular oxygen ion, yet no such line has ever been observed in any laboratory spectrum of oxygen (as far as I know). The reason for the high degree of confidence in associating the emission line with an [OIII] transition comes from the success of applying quantum theory to atoms (nuclei and their electrons): the theory says such a transition should happen (and, by 'the ergodic theory', or is it principle? *must* happen), but the conditions under which it will happen cannot be created in any laboratory.

Which leads to this comment about 'argument from incredulity' when applied to 'null observations': logically, there's no difference between spending time and effort doing Eot-Wash type experiments and doing spectroscopy on oxygen under various temperature/pressure/etc conditions; both are tests of well-established theories (assuming proper designs, etc), both expect null results.

Ken G
2014-Oct-17, 03:51 PM
Certainly any distinction will be somewhat artificial, but the purpose of making distinctions is to bring out some useful contrast. The useful contrast brought out by the difference between "direct" and "indirect" evidence has nothing to do with physical proximity, it has to do with what you might call "inferential proximity,' i.e. how many assumptions you need to invoke, and how much doubt those assumptions introduce, on your way to reaching your conclusion. So examples would be, if you step on a scale or measure your height, those are very direct measurements because there are no assumptions, that's just what we mean by weight and height. If you see light from space, and you have a well-tested theory that identifies it as a forbidden line of oxygen, that is less direct but still fairly direct, because the theory is well tested and it makes a fairly precise prediction that you will see that wavelength. That's also what I mean by a "non-null" prediction, it has a specific value that you would have no reason to expect without that theory. Indirect evidence, on the other hand, goes like "this is evidence of X as long as we assume Y," where Y is not a well-tested theory and already does involve some assumptions that might be incorrect. Now, of course this distinction can be difficult to enforce in all cases, because there can be debate as to how well tested is assumption Y, so we should tend to err on the side of caution and call the evidence indirect as long as there is a significant contingent of scientists who are not willing to make assumption Y, and see value in testing that assumption as well.

A classic example of the difference is the shape of channels on the surface of Mars, seen from orbit, that was indirect evidence for past flowing water. That would be considered indirect because other things than water can flow. So we landed on the surface and looked for rocks that only form under water, and that is regarded as direct evidence, not because we know with absolute 100% certainty that such rocks require water, but because we have enough confidence to feel that we are not testing whether those rocks form under water, we are testing whether or not they exist on Mars. The connection with "arguments from incredulity" is that when we regard evidence as direct, it means we feel we have sufficient cause to be incredulous of alternatives, but what I'm saying is, we should always leave that door open. The careful scientist should always say "the presence of these rocks is direct evidence of water, insofar as we feel safe assuming that such rocks only form under water." That allows it to be perfectly clear when reasoning from incredulity is involved, and leaves the door open for others to be skeptical that rocks like that might form some other way-- spurring research into rock formation and possibly leading to a big discovery that shatters our current understanding of the evidence for water on Mars. One never makes a mistake identifying one's assumptions.

Jean Tate
2014-Oct-18, 12:28 PM
Certainly any distinction will be somewhat artificial, but the purpose of making distinctions is to bring out some useful contrast. The useful contrast brought out by the difference between "direct" and "indirect" evidence has nothing to do with physical proximity, it has to do with what you might call "inferential proximity,' i.e. how many assumptions you need to invoke, and how much doubt those assumptions introduce, on your way to reaching your conclusion. So examples would be, if you step on a scale or measure your height, those are very direct measurements because there are no assumptions, that's just what we mean by weight and height. If you see light from space, and you have a well-tested theory that identifies it as a forbidden line of oxygen, that is less direct but still fairly direct, because the theory is well tested and it makes a fairly precise prediction that you will see that wavelength.

Certainly, these are useful distinctions to make. However, I think it's almost never so clean and clear; there is far more than just one path (i.e. semi-independent sets of assumptions, several different chains of inferences, and so on). In the case of the leading topic of this thread, several different ways you can get to a conclusion like 'stellar mass black holes exist'.


That's also what I mean by a "non-null" prediction, it has a specific value that you would have no reason to expect without that theory. Indirect evidence, on the other hand, goes like "this is evidence of X as long as we assume Y," where Y is not a well-tested theory and already does involve some assumptions that might be incorrect. Now, of course this distinction can be difficult to enforce in all cases, because there can be debate as to how well tested is assumption Y, so we should tend to err on the side of caution and call the evidence indirect as long as there is a significant contingent of scientists who are not willing to make assumption Y, and see value in testing that assumption as well.

Further, it is rarely the case that Y is essential, or unique, or even a 'pure theory'; how often, for example, is Y derived from a theory, by a method which is not necessarily rigorous (gravistars are a good example, I think).


A classic example of the difference is the shape of channels on the surface of Mars, seen from orbit, that was indirect evidence for past flowing water. That would be considered indirect because other things than water can flow. So we landed on the surface and looked for rocks that only form under water, and that is regarded as direct evidence, not because we know with absolute 100% certainty that such rocks require water, but because we have enough confidence to feel that we are not testing whether those rocks form under water, we are testing whether or not they exist on Mars.

And to bolster the point I'm making: the shape of 'remotely viewed' channels was nowhere near the only evidence (direct or indirect) for the past existence of flowing water on the surface of Mars.


The connection with "arguments from incredulity" is that when we regard evidence as direct, it means we feel we have sufficient cause to be incredulous of alternatives, but what I'm saying is, we should always leave that door open. [...]

If it's OK with those still participating in this thread, I'd like to take this as a starting point for something else, indirectly related to be sure :rolleyes:

Scientists are human, finite in number, and with seriously limited resources (instruments, computing power, time, etc).

Perhaps there's a cline? At one extreme are those often called cranks and crackpots, who are incredulous about this or that aspect of some of the best-tested/established theories of physics, who reject even versions of the Copernican principle which state that 'the laws of physics are universal' or 'we do not live in a special place'. True, few such people do anything much about their incredulity and rejection other than rail and rant; none (?) propose serious alternatives, conduct experiments, make observations, even write up their ideas in a coherent fashion. But, for them, the door to alternatives if firmly jammed open.

For most scientists, however, I think it's more to do with 'what is interesting?' or 'what can I investigate that will best test X?' Undoubtedly, for some, the chance to firmly add another digit or two to estimates of the value of the fine structure constant, or show that the electron is consistent with a point particle down to another order of magnitude in size, etc will always be alluring, no matter how well established QED is otherwise (though I doubt anyone has much interest in creating a lab experiment in which the [OIII]5007 line is observed!). For others, a quite different terra incognita beckons: what does the universe look like at radio frequencies of 1kHz? 1Hz? (both quite beyond today's capabilities to answer, directly; indirectly?); how do supermassive black holes launch jets (i.e. they waste no time wondering if supermassive black holes exist or not)?

Perhaps the most interesting areas to explore are the ones hardly any scientist is working on, areas open to today's citizen scientists, who have oceans of high quality data (free!), excellent tools (also free), and Maxwell-would-die-for computing power (not quite free) available to them pretty much instantly. There are plenty of examples, right here in the CosmoQuest Forum's threads ... dark matter as something other than 'essentially zero EM cross section mass' (from molecular hydrogen to some variant of MOND, with a dozen way stations in between), to take just one class of examples.

To close with a puzzle: with such a vast expanse of unexplored ocean, with so many fascinating things professional scientists are hardly likely to ever get around to, why is there essentially zero work being done by amateurs?

William
2014-Oct-18, 05:30 PM
http://www.sciencedaily.com/releases/2014/06/140604133818.htm

Surprisingly strong magnetic fields can match black holes' pull: Long-neglected magnetic fields have an unexpected presence
A new study of supermassive black holes at the centers of galaxies has found magnetic fields play an impressive role in the systems' dynamics. In fact, in dozens of black holes surveyed, the magnetic field strength matched the force produced by the black holes' powerful gravitational pull.

Tchekhovskoy says the new results mean theorists must re-evaluate their understanding of black-hole behavior. "The magnetic fields are strong enough to dramatically alter how gas falls into black holes and how gas produces outflows that we do observe, much stronger than what has usually been assumed," he says. "We need to go back and look at our models once again."

"This paper for the first time systematically measures the strength of magnetic fields near black holes," says Alexander Tchekhovskoy, the Berkeley Lab researcher who helped interpret the observational data within the context of existing computational models. "This is important because we had no idea, and now we have evidence from not just one, not just two, but from 76 black holes."

Previously, Tchekhovskoy, who is also a postdoctoral fellow at the University of California, Berkeley, had developed computational models of black holes that included magnetic fields. His models suggested a black hole could sustain a magnetic field that was as strong as its gravity, but there was not yet observational evidence to support this prediction. With the two forces balancing out, a cloud of gas caught on top of the magnetic field would be spared the pull of gravity and instead levitate in place.


This thread is an example of the ever popular arm chair theoretical cosmology. Completely removed from observations. If you were investigating an airplane crash you would not try to answer the problem without data. You would understand that is ridiculous, absurd. The data would be analyzed to determine the physical cause, to explain what happened. An airplane crash analysis would be expected to find and identify anomalies. To ask questions. To write a summary report that summarizes the data and analysis, that summarize alternative hypotheses with pro/cons. The analysis would be expected to be independent, to follow a process.

Billions upon billions of dollars have been spent to get multi-spectrum data on astronomical objects and there is now very, very good data (the very, very good new data has uncovered new anomalies and paradoxes hot off the press which are labeled as anomalies and paradoxes by the specialists).

It appears there is now sufficient observational data to solve the cosmological problem which should be an interesting time to discuss cosmology and to be a cosmologist. The problem (as to why this problem has not been solved let say five years ago or ten years ago) is not the data, it is the complete lack of process and understanding as to how to solve complex scientific problems.

I am a senior specialist. I have more than 20 years experience in leading and assisting teams of specialists to solve complex problems. We have successful solved every problem assigned. We have developed processes and systems to solve problems, we take courses to help understand why problems are not solved, to learn how to think out of the box, to understand how process helps to solve the problem. Rule number one which is used by ever private industry investigating team, develop theories after looking at the data. Rule 2 challenge every theory and assumption again and again, come up with alternative theories, relook at theories again and again. The breakthroughs which our teams found were almost always due to or connected to theory mistakes and misunderstandings. In private industry each and every paradox and anomaly is identified in the preliminary investigation report. In cosmology there is no preliminary summary report. This is no independent investigating analysis team. Independent investigating teams challenge theories and develop alternative explanations, if they do not they are not independent. In cosmology paradoxes are hidden under the rug and some have been known for at least 20 years. In private industry I would lose my job for hiding or ignoring anomalies. There is a physical explanation for everything that happens.

What happens physically to stop a massive object from collapsing and how the massive object evolves after the collapse is the most important unsolved problem in cosmology. There are roughly 30 different observational paradoxes and anomalies that are all related to the answer to this question. The standard hairless black hole with an accretion disc does not explain the quasar observations. That is a fact. No one has even bothered to list the piles of quasar observational anomalies and paradoxes.
It appears that the quasar anomalies and paradoxes are directly connected with the galaxy evolution and morphology paradoxes and anomalies, also related the large scale paradoxes (see thread large scale observations for a list of the paradoxes).

The hairless black hole cannot form in theory (the theoretical analysis ignored the process/step of getting to a event horizon). I find it astonishing that we know it is a fact that we cannot explain the solar magnetic cycle and yet we believe that we can know with certainty that a hairless black hole could even exist and with certainty exclude the possibility that the massive object that forms is an active object, not a hairless black hole.

Ken G
2014-Oct-18, 10:01 PM
Certainly, these are useful distinctions to make. However, I think it's almost never so clean and clear; there is far more than just one path (i.e. semi-independent sets of assumptions, several different chains of inferences, and so on).I agree, there can be more danger in enforcing contrasts if it forces a kind of "black vs. white" approach. One must see contrasts as nothing but a rational tool.
In the case of the leading topic of this thread, several different ways you can get to a conclusion like 'stellar mass black holes exist'.How science invokes the term "exist" is quite tricky. I'm fine with using that word, as long as it is provisional. It's awkward to attach the appropriate conditions onto everything we say in science, we'd like to say things like "matter is made of particles" or "there are electromagnetic fields in plasmas," that sort of thing. Of course we have to realize that all we mean by this is "our current description gains practical advantage by imagining these things are true, we recognize that a thousand years from now these statements might be regarded as misleading or even false." It is a judgement call when such provisos are required, or can be simply assumed. But to me, the statement "classical stellar-mass black holes exist" is a statement that requires missing provisos. I can't see going past "current observations are consistent with the existence of stellar-mass black holes", or even adding Grey's point that "this is rather significant, given how differently event horizons behave than just about everything else we've ever encountered." All of those are objectively true statements, no incredulity required. But to say "black holes exist", that is closing a door to discovery of all the other possible models that could agree with those observations. Two that come to mind are chaotic spactimes, a la Hawking's latest thinking, or torsional spacetimes, a la Einstein/Cartan theory, neither of which yield something quite the same as a classical black hole. Whether we'd still want to call those some kind of "effective" black holes, I don't know, that may depend on the purposes one has for the black hole moniker.


And to bolster the point I'm making: the shape of 'remotely viewed' channels was nowhere near the only evidence (direct or indirect) for the past existence of flowing water on the surface of Mars.I'm not aware of any direct evidence of it, prior to the landers. If you get enough indirect evidence, there's some kind of exchange rate between indirect and direct, but one has to watch out for systematic effects, like a single wrong assumption that underpins all the indirect evidence.


Perhaps there's a cline? At one extreme are those often called cranks and crackpots, who are incredulous about this or that aspect of some of the best-tested/established theories of physics, who reject even versions of the Copernican principle which state that 'the laws of physics are universal' or 'we do not live in a special place'.The defining characteristic of "cranks" is not that they are skeptical of that which is widely held, or else we'd have to call Copernicus a crank, or Lemaitre. A crank is someone who suggests some simple fix to what they are incredulous about, but their "fix" ruins a lot of other things, or makes no quantitative predictions in the first place. They are generally motivated by either an unwillingness, or an inability, to believe that some theory could provide a good description, which is a lot like being motivated by incredulity. Skepticism is much different from incredulity-- skepticism says "ah, but that evidence would also work for model Y, not just model X, even though Y is not as powerful or unified as X, or is just downright harder to believe." Incredulity say "no way X could be true, it just doesn't make sense to me." So incredulity can be invoked to argue against black holes (they are too weird), or to argue for them (it's too weird that anything else could behave like that). We live in a weird universe, nothing is too weird any more.


True, few such people do anything much about their incredulity and rejection other than rail and rant; none (?) propose serious alternatives, conduct experiments, make observations, even write up their ideas in a coherent fashion. But, for them, the door to alternatives if firmly jammed open.True, they are very willing to look for alternatives, but as you say, they are not motivated by skepticism, they are motivated by incredulity. The history of science is a story of the value of skepticism and the danger of incredulity!


For most scientists, however, I think it's more to do with 'what is interesting?' or 'what can I investigate that will best test X?' Undoubtedly, for some, the chance to firmly add another digit or two to estimates of the value of the fine structure constant, or show that the electron is consistent with a point particle down to another order of magnitude in size, etc will always be alluring, no matter how well established QED is otherwise (though I doubt anyone has much interest in creating a lab experiment in which the [OIII]5007 line is observed!).We all have to decide where to put our efforts, and what we can get funded to do. But it's good for science when there are "contrarians", as long as they are not "cranks." Just because QED uses a point electron is no reason not to look for a tiny dipole moment there, or a tiny mass to the photon, or even the O[III]5007 line. You just never know what you might find!

For others, a quite different terra incognita beckons: what does the universe look like at radio frequencies of 1kHz? 1Hz? (both quite beyond today's capabilities to answer, directly; indirectly?); how do supermassive black holes launch jets (i.e. they waste no time wondering if supermassive black holes exist or not)?Yes, it is natural to make "contingent" progress, which is progress that applies only insofar as the theory used is applicable. But here's the thing-- you can study how a jet gets launched, without marrying that it is a black hole that launches it. You can look for general properties of jets-- and you might even discover that having a black hole is not the key thing to get a jet. Or, you might discover that certain characteristic of a jet are different if there is a standard event horizon there, than if there is some other more exotic animal there-- maybe you'll discover that jets can carry information out of what you thought was a barrier to doing that, say if you use some modification to standard GR that allows a "hole" in the event horizon.


To close with a puzzle: with such a vast expanse of unexplored ocean, with so many fascinating things professional scientists are hardly likely to ever get around to, why is there essentially zero work being done by amateurs?
I think the problem is that it is hard to make progress if you don't have a fairly complete set of skills. It is a huge ocean, and we have lots of boats, if you will, but not lots of sailors. You're saying, why not try, no one drowns in this analogy. But it still might not be possible-- people without sophisticated sailing skills might not get very far. Still, perhaps there are some problems more conducive to what you are talking about, than the search for the theory of everything.

Jean Tate
2014-Oct-19, 12:38 PM
http://www.sciencedaily.com/releases/2014/06/140604133818.htm


Looks like an interesting paper, William, but it's behind a paywall for me. May I ask, do you have access to a 'free' version? I assume you read the paper (and didn't rely just on the various summaries/abstracts).


This thread is an example of the ever popular arm chair theoretical cosmology.

Hmm, that's not how I see it; rather, until I started to move it OT, it was focused on stellar mass black holes (or at least that's what this post (http://cosmoquest.org/forum/member.php?755-tusenfem) insists on). Such objects - theoretical or otherwise - are only vaguely related to cosmology (at least, as I understand it).


Completely removed from observations. If you were investigating an airplane crash you would not try to answer the problem without data. You would understand that is ridiculous, absurd. The data would be analyzed to determine the physical cause, to explain what happened. An airplane crash analysis would be expected to find and identify anomalies. To ask questions. To write a summary report that summarizes the data and analysis, that summarize alternative hypotheses with pro/cons. The analysis would be expected to be independent, to follow a process.

Billions upon billions of dollars have been spent to get multi-spectrum data on astronomical objects and there is now very, very good data (the very, very good new data has uncovered new anomalies and paradoxes hot off the press which are labeled as anomalies and paradoxes by the specialists).

It appears there is now sufficient observational data to solve the cosmological problem which should be an interesting time to discuss cosmology and to be a cosmologist. The problem (as to why this problem has not been solved let say five years ago or ten years ago) is not the data, it is the complete lack of process and understanding as to how to solve complex scientific problems.

And so it might be very interesting to have a discussion of the Zamaninasab+ (2014) paper, in a thread of its own (provided we can all get to read a copy of it). I, for one, am quite interested in reading how the authors analyzed the observational data (and which data, more to the point); AGNs are of great interest to me.




I am a senior specialist. I have more than 20 years experience in leading and assisting teams of specialists to solve complex problems. We have successful solved every problem assigned. We have developed processes and systems to solve problems, we take courses to help understand why problems are not solved, to learn how to think out of the box, to understand how process helps to solve the problem. Rule number one which is used by ever private industry investigating team, develop theories after looking at the data. Rule 2 challenge every theory and assumption again and again, come up with alternative theories, relook at theories again and again. The breakthroughs which our teams found were almost always due to or connected to theory mistakes and misunderstandings. In private industry each and every paradox and anomaly is identified in the preliminary investigation report. In cosmology there is no preliminary summary report. This is no independent investigating analysis team. Independent investigating teams challenge theories and develop alternative explanations, if they do not they are not independent. In cosmology paradoxes are hidden under the rug and some have been known for at least 20 years. In private industry I would lose my job for hiding or ignoring anomalies. There is a physical explanation for everything that happens.

What happens physically to stop a massive object from collapsing and how the massive object evolves after the collapse is the most important unsolved problem in cosmology. There are roughly 30 different observational paradoxes and anomalies that are all related to the answer to this question. The standard hairless black hole with an accretion disc does not explain the quasar observations. That is a fact. No one has even bothered to list the piles of quasar observational anomalies and paradoxes.
It appears that the quasar anomalies and paradoxes are directly connected with the galaxy evolution and morphology paradoxes and anomalies, also related the large scale paradoxes (see thread large scale observations for a list of the paradoxes).

The hairless black hole cannot form in theory (the theoretical analysis ignored the process/step of getting to a event horizon). I find it astonishing that we know it is a fact that we cannot explain the solar magnetic cycle and yet we believe that we can know with certainty that a hairless black hole could even exist and with certainty exclude the possibility that the massive object that forms is an active object, not a hairless black hole.

Why not start a new thread, on this topic, so we can discuss it?

Perhaps you could kick such a thread off with the published results of your own research?

William
2014-Oct-19, 05:10 PM
Looks like an interesting paper, William, but it's behind a paywall for me. May I ask, do you have access to a 'free' version? I assume you read the paper (and didn't rely just on the various summaries/abstracts).

Hmm, that's not how I see it; rather, until I started to move it OT, it was focused on stellar mass black holes (or at least that's what this post (http://cosmoquest.org/forum/member.php?755-tusenfem) insists on). Such objects - theoretical or otherwise - are only vaguely related to cosmology (at least, as I understand it).

And so it might be very interesting to have a discussion of the Zamaninasab+ (2014) paper, in a thread of its own (provided we can all get to read a copy of it). I, for one, am quite interested in reading how the authors analyzed the observational data (and which data, more to the point); AGNs are of great interest to me.


Why not start a new thread, on this topic, so we can discuss it?

Perhaps you could kick such a thread off with the published results of your own research?

I could not find a non pay wall version of the above paper as it was published in nature. There are however very, very good peer reviewed papers which are non pay wall protected or there are advance copies of the key papers concerning the piles and piles of anomalies and paradoxes.

I will start two new threads (one for quasar observations/paradoxes and the second for the disc galaxy observations/paradoxes), however, we need some structure and goals for the threads, at least for the key people who read the papers and can summarize and remember the logical constraints of the observations/problem and are capable of constructing, understanding, and comparing hypotheses.

As I said, I have been directly involved with and/or have led dozens of successful investigating teams. There is a structure and purpose to the analysis I have been involved with. The analysis starts with the process of preparing a summary of the key observations and the formation of a list of possible hypotheses which are parked. As the analysis progresses, one at a time the hypotheses are pulled out of the parking lot and discussed based on the logic of the observations, with the objective of logically narrowing the work down to less hypotheses and to understand the 'nature' of the problem. The hypothesis analysis is pro/con, what if analysis. As I said, we do not throw away hypotheses (they are always kept in the parking lot and we encouraged the creation of new hypotheses) and we again and again relooked at old hypotheses or look for a modified version, that could possible be correct. The structured analysis approach is often compared to a game, were the rules were developed to effectively solve complex holistic problems, to enable the discussion of incompatible hypotheses without fights. There is no name calling. There are no idiotic hypotheses. A summary that documents the analysis progress and initial findings is essential, as it forces us to write down the logical constraints of the observations and to formally record each and every paradox/anomaly. Finding and identifying paradoxes and anomalies requires a deeper understanding of the hypotheses/theories and the actual observations.

Analyzing and discussing peer reviewed papers is not effective, purposeful, and/or fun, if it is a fight and/or if it is not observationally and logically based.

There are now excellent, mature, observations and analysis which appear are sufficient to solve the cosmological problem. It is surprising how effective a structured analysis is, how much difference following a process makes, how much easier it is to solve a problem if the observations and logic of the problem is summarized.

Reality Check
2014-Oct-19, 09:40 PM
http://www.sciencedaily.com/releases/2014/06/140604133818.htm
..snipped a mostly irrelevant rant...

Nothing to do with this thread, William.

This thread is an example of the ever popular actual theoretical physics done by actual scientists, William. It is not cosmology - it is an application of GR + QM.
The paper that this thread is about is a theoretical way to "stop a massive object from collapsing" by showing that it explodes instead.
However physically we know of no way to stop a massive object from collapsing. How the massive object evolves after the collapse is a well known solved problem in astrophysics (if I recall right, Eddington was the first to model a collapsing star).

Jean Tate
2014-Oct-20, 05:51 PM
[...]
How science invokes the term "exist" is quite tricky. I'm fine with using that word, as long as it is provisional. It's awkward to attach the appropriate conditions onto everything we say in science, we'd like to say things like "matter is made of particles" or "there are electromagnetic fields in plasmas," that sort of thing. Of course we have to realize that all we mean by this is "our current description gains practical advantage by imagining these things are true, we recognize that a thousand years from now these statements might be regarded as misleading or even false." It is a judgement call when such provisos are required, or can be simply assumed.
This is a context/background that, for all practical purposes, can be assumed. Most of the time.

Of course, at what we - today - consider to be the frontiers (and some of physics, cosmology, etc is undoubtedly right there), the myriad caveats are important.


But to me, the statement "classical stellar-mass black holes exist" is a statement that requires missing provisos. I can't see going past "current observations are consistent with the existence of stellar-mass black holes", or even adding Grey's point that "this is rather significant, given how differently event horizons behave than just about everything else we've ever encountered." All of those are objectively true statements, no incredulity required. But to say "black holes exist", that is closing a door to discovery of all the other possible models that could agree with those observations.

Myself, I'm much more relaxed about this. For example, I am under no illusions whatsoever that my research into SDRAGNs has - at the most extreme - only most contrived connection with concerns central to the existence (or not) of black holes (per Einstein, anyway).


[...]

I'm not aware of any direct evidence of it, prior to the landers. If you get enough indirect evidence, there's some kind of exchange rate between indirect and direct, but one has to watch out for systematic effects, like a single wrong assumption that underpins all the indirect evidence.

Ah, systematic effects! The black holes (and more) of astronomers ...

Given how frequently, and how radically, failure to fully acknowledge systematic effects in observational astronomy has (eventually) caused major upsets, you'd think astronomers would be hyper-sensitive to them, wouldn't you? My personal experience - at the coalface, so to speak - suggests the reality is very different.


The defining characteristic of "cranks" is not that they are skeptical of that which is widely held, or else we'd have to call Copernicus a crank, or Lemaitre. A crank is someone who suggests some simple fix to what they are incredulous about, but their "fix" ruins a lot of other things, or makes no quantitative predictions in the first place. They are generally motivated by either an unwillingness, or an inability, to believe that some theory could provide a good description, which is a lot like being motivated by incredulity. Skepticism is much different from incredulity-- skepticism says "ah, but that evidence would also work for model Y, not just model X, even though Y is not as powerful or unified as X, or is just downright harder to believe." Incredulity say "no way X could be true, it just doesn't make sense to me." So incredulity can be invoked to argue against black holes (they are too weird), or to argue for them (it's too weird that anything else could behave like that). We live in a weird universe, nothing is too weird any more.

I think it's a bit more complex than that.

For example, from reading Tom Bridgman's excellent blog, or Stuart Robbins', you quickly learn that what you think an absolute minimum for consistency, rigor, etc is very different for other people. In other words, the words are the same, and should have the same meanings, but in fact there are nigh-on mutually incomprehensible languages being spoken. Oddly, the parasitical nature of these worldviews (if that's what they can be called) is completely invisible to the relevant cranks! :eek: (how does the computer on which they compose their screeds work? the internet they use to disseminate them? how does their GPS 'know' where they are? etc).


[...]
We all have to decide where to put our efforts, and what we can get funded to do. But it's good for science when there are "contrarians", as long as they are not "cranks." Just because QED uses a point electron is no reason not to look for a tiny dipole moment there, or a tiny mass to the photon, or even the O[III]5007 line. You just never know what you might find!

Well, if someone - professional or amateur - decided to dedicate resources to observing that line in a laboratory setting, I'd have to wonder whether they'd seriously considered the multitude of potential alternative uses of their time! :)


Yes, it is natural to make "contingent" progress, which is progress that applies only insofar as the theory used is applicable. But here's the thing-- you can study how a jet gets launched, without marrying that it is a black hole that launches it. You can look for general properties of jets-- and you might even discover that having a black hole is not the key thing to get a jet. Or, you might discover that certain characteristic of a jet are different if there is a standard event horizon there, than if there is some other more exotic animal there-- maybe you'll discover that jets can carry information out of what you thought was a barrier to doing that, say if you use some modification to standard GR that allows a "hole" in the event horizon.

All surely true.

However, when it comes to writing the introduction to your paper, you will need to genuflect towards SMBH, and having gotten it out of the way, spend happy words talking about your really cool observations, or simulations, or ... Let someone else, someone who is excited about these distinctions, take your results and run with them.


I think the problem is that it is hard to make progress if you don't have a fairly complete set of skills. It is a huge ocean, and we have lots of boats, if you will, but not lots of sailors. You're saying, why not try, no one drowns in this analogy. But it still might not be possible-- people without sophisticated sailing skills might not get very far. Still, perhaps there are some problems more conducive to what you are talking about, than the search for the theory of everything.

A topic I'm very interested in discussing further, and more deeply (I have the experience, inside dope, scars, etc). Suffice it to say that, ahem, 'selection effects' abound, not to mention myths, all-but-overt discrimination, pride, and much more.

If I throw a party (start a new thread), would you come?

Jean Tate
2014-Oct-20, 05:53 PM
[snip]

I will start two new threads (one for quasar observations/paradoxes and the second for the disc galaxy observations/paradoxes), [snip]
Am looking forward to it.

Ken G
2014-Oct-20, 09:23 PM
If I throw a party (start a new thread), would you come?Sure, I'm open to anything that explores the limits.

Jean Tate
2014-Oct-22, 01:17 PM
Sure, I'm open to anything that explores the limits.

Come one! Come all! Over in the Public Outreach (http://cosmoquest.org/forum/forumdisplay.php?88-Public-Outreach) section of the CosmoQuest forum, Why is there essentially zero work being done by Citizen Scientists (amateurs)? (http://cosmoquest.org/forum/showthread.php?153992-Why-is-there-essentially-zero-work-being-done-by-Citizen-Scientists-(amateurs))

Let the partying begin! :D