Answer to the original question: Experimental evidence for the existence of giant black holes at galactic centers and for the existence of rather heavy holes from gravitational wave signals.

I am very happy with this sensible question. The famous drawing in Misner-Thorne-Wheeler of 1976, page 667, showing the infinitely slow disappearance of an in-falling astronaut, gives the correct answer.

Everyone believes that this were due to the slow return of light signals while "in reality" the in-fall is finished after two days (say) of proper time.

But if you invert time ("trampoline argument"), the astronaut returns after twice infinitely many days. This insight proves that nothing ever reaches the horizon of a black hole in finite outer universe time.

Hence there exist no finished black holes (only "almost finished" ones). I called them "almost black holes" 18 years ago.

November 26, 2016

Answer to the original question: Experimental evidence for the existence of giant black holes at galactic centers and for the existence of rather heavy holes from gravitational wave signals.

Dear Jürg!

In the centres of galaxies exist a very high aggregation of stars. I'm the opinion that you can misinterpret it as a black hole. Which detectors are used to detect the gravitational wave signals? The LIGO-experiment means to have observed gravitational waves. There are some doubts above.

The crux of the question is how matter can be compressed at the dimensions of black holes and what kind of matter would it be? Have we at least normal matter, dark matter and black hole matter?

Dear Otto!

I tend to your critical attitude. If anywhere a black hole exist, it would more and more matter and also radiation "suck in". The centres of galaxies would be sooner or later really "black" and at least the whole galaxy would disappear.

Dear Hans-G.:

I have to remind you of Birkhoff's theorem which says that the gravitational effects of contracted matter inside a given finite radius, and the same matter being non-contracted inside that same radius, are equal.

So almost black holes behave gravitationally speaking no differently than finished black holes, should the latter exist. 

Nevertheless if the universe is non-expanding (as follows from the return to the younger Einstein's global c), a recycling mechanism for black holes is needed. Dieter Fröhlich and I had the idea that in (almost) black hole mergers, always the smaller one would be recycled along the unstable manifold forming in between the two.

If so, the infinite cosmos would with half its mass consist of (almost) black holes.

November 28, 2016

Black holes were debated for several decades and finally accepted by a majority based on observations in agreement with predictions. First conclusion was in the Cygnus X1 system but astronomers are continually adding other systems. Eventually a majority is accepting the large black holes in centers of galaxies based on observed events of powerful extent in small space. Now the Quasars are thought to be powered by black holes because of much power in a small space, but they are far away and hard to observe. The debate continues but a majority is accepting the evidence.

@Jerry: The truth is not a question of majority. Bertrand Russel said: Auch wenn alle einer Meinung sind, können alle Unrecht haben.

@Otto: Jetzt warte ich darauf, dass Russells Ziatat downgevotet wird. Hier tobt sich anscheinend wieder ein strenggläubiger Theoretiker aus. Bin ich froh, dass Scheiterhaufen aus der Mode gekommen sind.

Dear Hans-G.: Russel's quote -- what exactly does it say? Thank you very much, Otto

Presumably, there is some matter outside but near the event horizon of most black holes. You may than argue that black holes do not exist. However, what may be really significant is that event horizons exist. There is little doubt that general relativity predicts the existence of event horizons and trapped surfaces.

Thank you, Jürg.

IF c-global is true (as I proved and no one challenges for  8 years), THEN there are no finished horizons and no interior solutions.

However, this fact also follows from the standard picture already. Look at the infinite infalling-plus-mirror-inverted return time to and fro the (for once assumed finished) horizon. I for this purpose refer to Figure 25.5 on page 667 of Misner-Thorne-Wheeler 1973 -- if you add the temporal mirror image on the right of the Figure. 

It is strange that such a simple thing could go overlooked ever since Oppenheimer and Snyder 1939.

It would be wonderful if you could disagree, since only in a sufficiently heated discussion does a long-overlooked truth have a chance to see the light of day.

Otto

Dear Otto!

I do not know Russells original wording but the meaning is clear. The truth respectively the reality is not depending on our opinion or on the opinion of the majority. I would remind of Alfred Wegener: The majority (including Einstein!) was the opinion that the continents would never shift.

Back to the topic: If any science invented first things/objects/structures to declare the reality and only then the science begins to search for those things/objects/structures than the evaluation of experiments/observations etc. is determined by the theory which required the inventions. This is a very doubtful way to reach knowledge. You can find currently in physics some of this distorted situations.

Hans

Question:

Do some of you question the formatIon of apparent horizons?

Remarks:

Imagine a spherical collapse of a huge gas cloud with a mass comparable to that of a typical  galaxy. When the extension of this gas cloud approaches its Schwarzschild radius, the average matter density is not larger than that of the air around you. We know since centuries enough about the physical properties of such matter to understand that further collapse is unavoidable. Euler could have explained this. What was then of course not yet possible was to follow the behaviour of a radial radiation bundle inside matter, but that there is some focusing at work is obvious from optics. There is absolutely no reason that trapped surfaces could never form in the further collapse, and that therefore an apparent horizon (that can, by the way, always  be determined locally) is impossible.-- The questions concerning event horizons are more subtil, but I leave it with this.

Otto,

After I looked more closely at the previous discussion, I would like to add that your point is certainly correct. Indeed, an astronomer will never really see a black hole, but only what was in the older Russian literature called a frozen star. In my many talks on black holes and all that I often stressed this, for instance in an invited talk at the 10th anniversary of the Einstein institute in Potsdam for a wide audience (that included the president of the Max Planck Society).

But this is all that we need for astrophysics. For instance, in numerical simulations of the LIGO-event one of the standard procedures is to excise the region inside the apparent horizon since no information can propagate from inside of the black hole to the outside. Non of the exterior spacetime can possibly be affected by the black hole interior, it is sufficient to simulate numerically only the exterior of black holes. This approach is referred to as black hole excisions. Mathematical, no boundary conditions are required at the excision surface, since the so-called characteristics are directed inward. (For detailed discussions of this I refer to the book on numerical relativity by T. Baumgarte and S. Shapiro (Cambridge University Press, especially chapter 13: "Binary black hole evolution").

Dear Norbert!

Thanks for your answers.

But my question is not answered: what kind of matter would exist in a "black hole"? Apart from some further contradictions in this theory. A black hole with a mass of the Planck mass ought have a extremely high density of matter. In comparison the nuclear matter would be a lightweight.

You can calculate mathematically formally the dimensions of any black hole depending on its mass. It leads inter alia to the Schwarzschild radius. But is the calculation relevant for reality? All theories about black holes demonstrate us an uncomfortable situation in modern physics: The "knowledge" is foundet often only on theories and mathematical models without observations and experimantal proofs.

My regards!

Hans

Dear Hans,

Your remaining question can not be answered and will not be answered within the framework of GR, because these regions are causally decoupled. Its a bit like with hell and heaven. We can speculate, but observational proofs are impossible. A radical positivist would say that these questions do not belong to physics proper; their study is only a fascinating mathematical game.

I do not really belong to this category, but tolerate this attitude. Since you speak german I add Einstein's reaction to Heisenberg's remark that physics should be based only on facts that are in principle observable. I quote Heisenberg: "Vom prinzipiellen Standpunkt ist es ganz falsch, eine Theorie nur auf beobachtbaren Grössen begründen zu wollen. Denn es ist ja  in Wirklichkeit genau umgekehrt. Erst die Theorie entscheidet darüber, was man beobachten kann." Viel später äusserte sich Pauli in einem Brief an Schrödinger ganz ähnlich.

Dear Norbert:

I am highly honored by your reply.

My point was a bit outlandish. I had shown that you can turn around (time reverse) an in-falling astronaut's trajectory on the horizon (or if you wish a tiny bit above it). And I had posed the apparently new question: When will she be back at the height of her outside waiting crew?

I presume, but am not sure that you will agree with me, that the answer reads: "twice infinitely many days" (or "almost twice infinitely many days," respectively). 

Now I am very apprehensive regarding what you will say instead.

There is a chance for a big friendship. Or a big disappointment on my part. But the truth always brings people closer together.

Take care,

Otto

Dear Norbert!

Your answer is very interesting. But with respect: Is this Heisenbergs quota or Einsteins reaction? (Paulis opinion anyway.)

I can understand now the sitiuation in physics. At least the theory has the primacy over the facts and also over the reality.

As I said above: The theories are determinig the evaluation of experiments, observations etc. The theoretical inventions dictate how we have to understand the reality. I am shocked!

I would remain that all exact sciences only then has made great advances and discoveries if they have leave the well-trodden paths. I think its time to do it once again.

My best regards!

Hans

Logically, theories of Physics can never be proven by experimental evidence, but only be falsified; (Karl Popper). However, theories that are correctly reproducing a great variety and a huge number of experimental data should be considered to be highly valuable as descriptions of Nature and as guides to designing new experiments; (see Norbert's quote of Einstein). General relativity has this quality. It has passed many experimental tests and has not been falsified by any experimental data, so far. It has made tantalizing predictions, such as the existence of gravitational waves, which apparently have now been discovered, (besides other predictions that have passed many observational tests, long ago). Without general relativity, nobody would have had the idea to search for gravitational waves! I therefore feel it is a pretty good idea to take seriously the prediction of General Relativity of essentially dark objects that are sources of very strong gravitational fields but do otherwise not emit interesting signals (besides some black-body radiation that is too weak to be observed). Such objects are commonly called "black holes". (Incidentally, the first speculation about the existence of black holes goes back to Laplace, long before the advent of general relativity. He argued that there might exist compact objects that are so heavy that light may not be able to climb all the way up their gravitational potential hill.) Evidence for the existence of black holes can, for example, be inferred from the shape of trajectories of shining stars that draw their orbits around regions in space from which a very strong gravitational pull emerges, but which are otherwise dark; (observations by Reinhard Genzel). -- What more should we desire? -- As natural scientists, we are well advised to be skeptics. But at some point we must overcome pure skepticism and negative thought and create interesting pictures of Nature! Historical evidence suggests that such pictures do not come about by overturning what our ancestors have discovered, but by building on their ideas and accomplishments and further developing and extending them.

Dear Jürg!

Thank you for your detailed answer. I agree that theories can be only falsified by experiments. But there is a unconsidered problem espacially in physics:

If the experiments, the observations etc. are evaluated under the assumption or premise that the theory has to be right what means that the evaluation is predetermined by the theory to be proved then you will never find a falsifying experiment. Alternative explanations for the experimental results are unconsidered completely. On this way you can establish every theory.

A classic example of the evaluation of an experiment by theoretical predictions is the so-called Savannah-River experiment. The experimenters Reines and Cowan and the most other scientists have not discussed alternative causes. The observed positron-events and neutron-events are also caused by stray neutrons. To say: „This is the prove of neutrinos and therefore the theory right“ is one of the far-reaching faulty assumptions of the 20.th century. (See the link below.)

If you look closely you will see that the most experiments are tailor-made to confirm the theoretical assumptions and not to falsify them. Furthermore a „presumption of validity“ does not apply for theories. A theory is an attempt to describe and declare the reality on a certain stage of knowledge. We can be sure that the knowledge proceeds and not stays on the level of current theories.

By the way: Was Popper he who has made a proof of the existence of god by the resources of logic?

My regards!

Hans

Research Theory and reality on the experiment of Reines/Cowan 1956

We all wait for Norbert.

Dear Hans,

From my many contacts with experimentalists, especially in elementary particle physics, I must say that what you claimed in your reaction to Juerg is not correct. Experimentalists are usually eager to discover facts that would be in contradiction to established theories. Nothing could be more important for them. Just an example:

When the Paul Scherrer Institute (PSI) had built up a machine with only medium energies, but with pion and muon beams that had the highest intensity in the world, certain groups began to search for rare decays that were forbidden in the standard picture. A famous case was the decay of a muon (then the only heavy brother of the electron) into an electron plus a photon. At some point the data seemed to contain a few of these events. I had then built up a theory group at the Institute and was therefore involved in the discussions, in particular whether the evidence was compelling. If real this would have been a sensation and of enormous significance for the new institute. Fortunately, the warnings and demands for more data and further analysis were followed, and ("unfortunately") the evidence for the mu-e-gamma-decay disappeared. But the group was not giving up and improved the bound for the decay rate considerably. As far as I know there are still efforts to go further.

This was just an example. I remember several experiments at the time when QED was tested, that were claimed to be in contradiction to the theory, and these were seriously discussed at important conferences. In connection with GR look at the story of the Pioneer Anomaly that was only settled a few years ago.

Dear Norbert!

Usually dictates the theory over the evaluation of experimenal facts. I remaind of the GALLEX-experiment. The theory has never predict a neutrino-oscillation. The shattering results led to the invention of the „neutrino oscillation“, indirectly foundet on an indirect proof as all proofs in neutrino-physics. A neutrino-oscillation or a neutrino was never directly observed!

Your answer contents some detailed informations. Can you tell me on which year the theory group was built? You said: „Experimentalists are usually eager to discover facts that would be in contradiction to established theories.“ This raises hope!

Unexpected particle decays are observed not only at the PSI. The Particle Data Group has the „disappeared“ mu-e-gamma-decay on its tables with a very low frequency.

μ− = (e−)* → e− + γ

This decay is espectable if you consider the muon as an exited electron as I wanted to formulate. Other facts lead also to this conclusion. The excited electrons/positrons (muons) can interact on this state to different particles with different numbers of electrons/positrons and different structures. This is in accordance with the results of electron-positron impacts (as PETRA).

Someone who has the imagination to describe the particle zoo by using uncertain quarks, gluons etc. should have also the imagination that the real particles electron and positron are sufficient for the description of all particles. The reason of the particle duality is foundet on this elementary duality and not on an assumed anti-characteristic. The particle duality is at least a structural antisymmetry. Some particles have not a antisymmetrical structure and therefore no anti-particle.

I consider the theories in physics as a distorted shadow of the reality.

My regards!

Hans

Dear Hans!

What you wrote about neutrino oscillations and the GALLEX-experiment is plain wrong. Proofs:

1.Bruno Pontegorvo suggested already in 1967 the possibility of neutrino oscillations (Sov. Phys. JETP, 26, 984 (1968)).

2. At the time when Kirsten in Heidelberg and Ray Davis were planning a Gallium experiment, and did not yet know where, I was at a Gentner Meeting in Engelberg and went with Davis at a free afternoon on the Titlis (altitude about 3300 m). We talked much about the Solar Neutrino Problem, and the possibility of neutrino oscillations. (At the meeting I had given a talk on neutrino astrophysics.)

On the top of the Titles I told Davis the in the middle of the recently finished road tunnel there existed already a small laboratory, which was installed because the two tracks from North and South had not exactly met. A group in Bern and Neuchatel was already searching for double beta-decays.

Davis was very interested, asked about the depth, the background radioactivity, etc. I invited him to give after the meeting a talk at PSI (then SIN). The possibility that a group at PSI, that collaborated with Mössbauer on neutrino oscillations at the nearby nuclear reactor, was seriously discussed, even ways to get the necessary amount of gallium through a Swiss firm in the Walls, ....

So, a Gallium experiment was planned, but not yet started, after the theoretical suggestion of neutrino oscillations. (The first results of the GALLEX collab. and the SAGE collab. were published in 1994, 1995.)

Hans, before you distribute claims that are plain wrong, you should first read some important sources. John Bahcall, among others, has repeatedly written on the history.

At this point I do not want to comment your further points, except for this: I did build up the theory group immediately after my return as a visiting professor at Duke University in 1967 (the year when Martin Luther and Robert Kennedy were shot, and Nixon was elected).

Now, only one (me) is still waiting for Norbert.

Otto,

Since you expect an answer: As for every mechanical motion in a stationary force field, one can reverse the orbit path. In your case, depending on the mass of the "frozen star", one has to use a very strong rocket to come back. Furthermore, even close to a neutron star the tidal forces acting on the rocket are so strong that no living  engineer would be able to construct one that would not be disrupted; no living being could survive if the return would not be initiated sufficiently early. All this is a nice exercise for students.

Dear Norbert:

Exactly right, it is a thought experiment. Is it in your sense if I ask you to follow me onto the treacherous ground of this gedankenexperiment?

Thank you very much, take care, Otto

Dear Norbert!

Apart from "neutrino oscillations": At first the scientists should have discussed all reasons of the inverted decay of 31-Ga-71 nuclei. This event happens independent of neutrinos. If a 31-Ga-71 nucleus reaces a certain inert energy it can decay to 32-Ge-71. You can be sure if you would have heating up the GaCl3-solution the observed decays would more often occure. The amount of "solar-neutrinos" would be maybe not enough to declare then the amount of decays.

If you study the table of nuclids you will find some nuclei which are showing such flip-flop-decays without "neutrinos".

My Regards!

Hans

What have recent entries to do with the original question?

Nothing, of course, but some wrong statements had to be corrected. 

In my Springer book on GR I wrote extensively about the evidence for black holes, in particular in Sect. 8.7 (of the 2013 edition) which has the title: "Evidence for Black Holes". I do not intend to repeat the content on a few lines.

I understand this completely! I very much appreciate your comments, Norbert!

I might quote a kind of summary contained in the cited Sect. 8.7:

"Most astrophysicists do not worry about possible remaining doubts. The evidence for (super-massive) black holes is now so overwhelming that we can pass the burden of proof against them to the hard-core skeptics."

Dear Norbert:

Am I a nuisance if I repeat my question?

With great respect, Otto