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Black Holes

smarek

New Blood
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Jun 13, 2007
Messages
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I am here because I would like to discuss some of the ideas of mainstream physics which are unsettling to me. It is good to finally find place full of skeptics which can objectively criticize topics without bias, personal or otherwise. Just to set it straight, I am not a professional physicist, but I have a huge interest in the field. So hopefully, you guys will be able to clear up either misconceptions I have, or explain whatever concept in terms such that I will be able to accept it for myself.

My first discussion will be about black holes. As far as I see it, they are nothing more than an over-extension of general relativity. While effects of the so-called black holes have been observed, no direct evidence has confirmed their existence. Not only have they been mathematically contrived, but hawking himself dropped his claim that no information can escape from a black hole, an idea which is purely theoretical and lacks any truth other than in the minds of physicists.

Cutting to the chase, my question is this. What direct evidence has confirmed the existence of black holes, such that the definition can be accepted for truth? To be perfectly clear, I am not doubting the presence of "something", because "something" is clearly causing a huge gravitational pull at the center of galaxies. What is in question is how the assumption can be made that an object whose presence depends on mathematics alone to exist could possibly be proposed as galactic nuclei.

The effects observed such as radiation emissions, gravitational lensing, and accretion disks are in no way direct conclusive proof of the existence of a black hole.

Any thoughts?
 
A fun question (with an answer!). I'll leave the explainations to people better qualified than I, and there are many of them here, but I'd direct you to www.badastronomy.com. The Bad Astronomer frequents this site as well, but you might fall to his attention faster that way.
 
(First a disclaimer: I'm no expert, just a skeptical layman)

I think that black holes are pretty well accepted by scientists.
You do accept general relativity? If so, why not black holes?
The evidence may not be "conclusive proof," but I believe that it is consistent with the theory of black holes.
If your objection is that it seems too wierd to be real, then you would probably also object to quantum mechanics. The universe is said to be "queerer than we can suppose."
 
My criteria

I accept anything that can be both experimentally confirmed and have sound theory to back it up. General Relativity ushered a huge paradigm shift in the field of physics, and Einstein's logic is laudable. However, he made the revelations during a time when little was known about modern cosmology (i.e. accelerating galaxies, great attractor, etc), and even the strong and weak forces had not been discovered yet. Generalizing the theory only allowed for more error, which is exactly what the theory produced when a strong gravitational pull was applied. A singularity is a mathematical feature, and I find it disturbing that anyone could accept such a thing as reality.

It is also important to remember that a theory is only a model, and it becomes difficult to gauge the completeness or validity other than direct experimental confirmation. In this stead, it can easily be understood that a theory which mathematically shows that a singularity exists means nothing in terms of reality. This indicates that it is the theory itself which needs tweaking.

The point is that much of black holes acceptance as far as I am aware, is based only on mathematics and hasn't been conclusively confirmed. Anyone able to refute this fact would be very much applauded should they be able to come forward and do so.
 
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One thing to keep in mind is that the existance of black holes was predicted before the mass at the center of galaxies were estimated.

Such mass estimations coupled with a lack of a visible source for such mass is a confirmation of the theory of black holes.
 
I'll believe it when I "see" it

rockoon said:
One thing to keep in mind is that the existance of black holes was predicted before the mass at the center of galaxies were estimated.

Such mass estimations coupled with a lack of a visible source for such mass is a confirmation of the theory of black holes.
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Your example is neither exhaustive nor conclusive. Once again, it is not in question whether or not something exists which exhibits the effects commonly attributed to black holes. However, what's to say that extended mathematics of a theory conceived almost a century before modern cosmology adequately describes observations today?

As many skeptics say, I'll believe it when I "see" it.
 
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I think you may have it a bit backwards there, Smarek. Physics predicted that black holes should exist IF the current understanding of quantum mechanics was accurate. We then sought for evidence of the phenomena which had previously been undetected (black holes). Astronomers have since found objects with the characteristics predicted. The prediction preceeded the evidence, thus stengthening the case for the accuracy of quantum physics.

If one doubts the existence of black holes before any evidence is found, fine, maybe the theory breaks down at a certain point (like some of Newton's work). However, after strong evidence is found and verified many times over, now the onus is on you to postulate something else which could have the same characteristics, yet NOT be a black hole.

(Fun side note: Hawkins and Kip Thorne had a bet involving a subscription to Playboy regarding whether or not black holes existed. The bet has been settled)
 
Puppycow said:
The universe is said to be "queerer than we can suppose."
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[TongueInCheek] Well, there you go. Science is all just a part of the nefarious Gay Agenda! [/TongueInCheek] :p

smarek said:
A singularity is a mathematical feature, and I find it disturbing that anyone could accept such a thing as reality.
(snip)
It is also important to remember that a theory is only a model, and is by no means complete. In this stead, a theory which mathematically shows that a singularity exists means nothing in terms of reality.
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Even under ordinary conditions, where we use classical (Newtonian) physics we treat all of the mass of an object as if it is concentrated in a single point, the center of mass. This is a mathematical singularity. Are you saying that Newtonian physics means nothing in terms of reality?

When black holes were first called singularities, it was because it was believed that nothing could be discovered about a black hole except its mass and the location of its center of mass. Because of this, it was believed that they would behave even more like single point objects than most objects.

Later developments in the theory showed that certain effects can escape a black hole. Some of these effects have been observed in reality.

smarek said:
The point is, that much of black holes acceptance as far as I am aware, is based only on mathematics and hasn't been conclusively confirmed. Anyone able to refute this fact would be very much applauded should they be able to come forward and do so.
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http://www.badastronomy.com/bitesize/jetplane.html
 
However, what's to say that extended mathematics of a theory conceived almost a century before modern cosmology adequately describes observations today?
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A vast body of direct experimental verification, that's what. Like GPS, which wouldn't work if Relativity were incorrect.

Black holes are a fairly direct consequence of the constant speed of light in a vacuum. Accumulate sufficient mass in a small enough volume and its escape velocity will exceed the speed of light. That's all a black hole is.

The surface gravity of an object is proportional to its mass and inversely proportional to the square of its radius. Since mass is proportional to volume, the surface gravity is directly proportional to the radius of a body (of fixed density).

Escape velocity is a little more complicated; it's proportional to the radius times the square root of the average density of the object. A small dense object has a lower escape velocity than a less dense object with the same surface gravity.

What all this means that you don't need to postulate any form of exotic matter: pile up enough dirt in one place and you have a black hole.
 
smarek said:
Cutting to the chase, my question is this. What direct evidence has confirmed the existence of black holes, such that the definition can be accepted for truth? To be perfectly clear, I am not doubting the presence of "something", because "something" is clearly causing a huge gravitational pull at the center of galaxies. What is in question is how the assumption can be made that an object whose presence depends on mathematics alone to exist could possibly be proposed as .....
Click to expand...

In his letters, Newton speculated about the possibility of objects with such a g force that all mass moved inward to a point. This isn't exactly new thought. Schwartzchild came up with an extension to the idea, the Schwartzchild radius, then he got knocked off in the trenches in WW1.

The math is real; the physical observations are secondary. Math has a different set of rules than the 3D world; for example it can work with N dimensional space quite nicely.
 
smarek said:
My first discussion will be about black holes. As far as I see it, they are nothing more than an over-extension of general relativity.
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Yes there is room for some degree of skepticism but not really to the degree you seem to be thinking.


smarek said:
While effects of the so-called black holes have been observed, no direct evidence has confirmed their existence. Not only have they been mathematically contrived, but hawking himself dropped his claim that no information can escape from a black hole, an idea which is purely theoretical and lacks any truth other than in the minds of physicists.
Click to expand...
Yes the tools may be a mathematically contrivance but the mathematics was not built on purely mathematical assumptions. The math is just a way to codify the physical insights so that the same rules that apply to planetary orbits and falling apples can be applied to far more complex situations. It is actually possible to calculate the perihelion of Mercury on just the principles of GR and high school algebra without the mathematics used in GR. Information loss is more than just a problem for black holes. It would also be very destructive to conservation laws in general. This would basically doom ALL physics as we know it right down to the rules of driving a car.


smarek said:
Cutting to the chase, my question is this. What direct evidence has confirmed the existence of black holes, such that the definition can be accepted for truth? To be perfectly clear, I am not doubting the presence of "something", because "something" is clearly causing a huge gravitational pull at the center of galaxies. What is in question is how the assumption can be made that an object whose presence depends on mathematics alone to exist could possibly be proposed as galactic nuclei.
Click to expand...
I'm with you in that a black hole may not be exactly what we are describing with the math at present. However you conceded a huge gravitational fields not otherwise emitting electromagnetic radiation. This is the most basic definition of a black hole. Again it is not based solely on mathematics but on the physical principles that have been codified by the mathematics. Add to this that the basic definition of black hole you conceded exist was predicted long before it was observed and you have good evidence. Add to this that gravitational lensing, radiation profiles just outside the event horizon, accretion disks, etc. were all predicted before they were found and the evidence just keeps getting stronger. We have even watched whole stars get swallowed.


smarek said:
The effects observed such as radiation emissions, gravitational lensing, and accretion disks are in no way direct conclusive proof of the existence of a black hole.
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Perhaps technically true but the fact they they were all predicted then found is very powerful evidence. It does pretty much prove that something that fits the basic definition of a black hole exist, i.e. a gravitation potential with no internal electromagnetic emissions.
 
Thanks

I appreciate all of your critical responses. The main thing that I wanted to establish (mainly for myself), is that that black holes may not be exactly what the mathematics says they are (thanks my_wan), and that the aforementioned effects do exist in some form. It is the form which is the cause of the argument.

rockoon said:
This is how it works:

predictions -> confirmations

Also, you need to learn about Occam.
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I am familiar with Occam's razor, but fail to see the relevance?

Jalbietz said:
If one doubts the existence of black holes before any evidence is found, fine, maybe the theory breaks down at a certain point (like some of Newton's work). However, after strong evidence is found and verified many times over, now the onus is on you to postulate something else which could have the same characteristics, yet NOT be a black hole.
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I will leave that to the theoretical physicists at this point, as I am hardly qualified to make such statements.

Gwyn ap Nudd said:
Even under ordinary conditions, where we use classical (Newtonian) physics we treat all of the mass of an object as if it is concentrated in a single point, the center of mass. This is a mathematical singularity. Are you saying that Newtonian physics means nothing in terms of reality?
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What I am saying is that the mathematics we have is a model, and that a singularity is encompassed only within that model. Mathematics can predict natural tendencies, but have yet to be aligned in such a way that anyone can conclude that the mathematics describes the said system perfectly (i.e. Newtonian physics work very well, but only within special conditions).

mhaze said:
The math is real; the physical observations are secondary. Math has a different set of rules than the 3D world; for example it can work with N dimensional space quite nicely.
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I definitely agree with you here. It is important to note this distinction between the behavior of nature and the realm of mathematics.

my_wan said:
I'm with you in that a black hole may not be exactly what we are describing with the math at present. However you conceded a huge gravitational fields not otherwise emitting electromagnetic radiation. This is the most basic definition of a black hole. Again it is not based solely on mathematics but on the physical principles that have been codified by the mathematics.
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My mistake. Once again I am not qualified in this field, I'm only asking questions.

my_wan said:
Add to this that the basic definition of black hole you conceded exist was predicted long before it was observed and you have good evidence. Add to this that gravitational lensing, radiation profiles just outside the event horizon, accretion disks, etc. were all predicted before they were found and the evidence just keeps getting stronger. We have even watched whole stars get swallowed.
Click to expand...

my_wan said:
... Perhaps technically true but the fact they they were all predicted then found is very powerful evidence. It does pretty much prove that something that fits the basic definition of a black hole exist, i.e. a gravitation potential with no internal electromagnetic emissions.
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On this I can certainly agree. The effects are there, what is needed is an accurate mathematical description.
 
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Cambridge has a brief page on this.

Basically, there are two kinds of evidence: invisible influence on visible matter, and distortion of light path around a point in space with no visible origin.
 
smarek said:
I am familiar with Occam's razor, but fail to see the relevance?
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On the one hand we have a perfectly simple theory which explains many things and which also predicts black holes, and have later found evidence to suggest that black holes do exist.

On the other hand we have someone who does not want to believe that black holes exist.

If black holes do not exist, what sort of alternatives support the evidence?

Are these alternatives as simple as sticking to a well tested theory that predicts black holes?
 
You might find it helpful to differentiate between singularities and black holes.

A black hole is a region of space within which there is enough mass to make the escape velocity at a particular distance from the center of that mass greater than the speed of light. The distance at which this becomes true is called the "event horizon," and even if Hawking's hypothesis regarding entropy is untrue, we still aren't ever going to find out much more about what's going on inside than that there is mass in there.

We have, at least, confirmation that such regions exist; we can measure the mass by measuring the curvature of orbits outside it. There are other predictions of what will happen to matter that enters such a region; we can look for the effects predicted, and we find them, and in just such areas.

Whether singularities exist inside the event horizons of black holes is a different matter entirely. I'd have to say that the proof of that is pretty much non-existent; if you follow the equations of GR down inside a black hole, they say it has to, but GR does not include quantum gravity, and long before you get to the state of singularity, quantum gravity has to take over, if it exists. Most physicists think quantum gravity will eventually be shown to exist, so it's pretty clear that any statements about singularities inside black holes are speculative at best, and not really very well accepted in physics.

Last but not least, that event horizon again. Even if we discover a consistent theory of quantum gravity, although it will tell us something about what's happening inside the event horizon, we won't ever be able to check. As a result, I prefer to talk about event horizons, since they're all we'll ever see. If your question is, "Do we have evidence of the existence of event horizons," the answer is, yes, we have evidence, but it is not yet compelling evidence. If your question is, "Do we have evidence of the existence of singularities," the answer is, no, and I think it will remain that way.
 
smarek said:
I definitely agree with you here. It is important to note this distinction between the behavior of nature and the realm of mathematics.
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I would be very careful with this assumption to. Mathematics is exactly what you put into it. Nothing more or less. If the physical principles the math is based on is complete and correct then math is complete and correct so far as it is solvable. This remains true no matter what branch of math you translate it to. The existence or nonexistence of a singularity is really more an ontological question. Ontology can share a symmetry with math. That is that two seemingly mutually exclusive ontologies can accurately describe the same physical system without contradiction. Einsteins recognition of this and the removal of ontology from the physics is largely what motivates much anti Relativity sentiment.

As a side note I'm of the opinion that some classes of solutions to GR is not properly constrained. Separate issue though than singularities or the claim that GR is wrong.
 
I've been thinking about this, and have a caveat to my statements about singularities.

If quantum gravity exists, it will probably modify relativity physics enough to avoid a real singularity, but quantum gravity will have to work at such short distances that the size of the "object" or region that would form around the center of mass of a black hole might well be so small that its manifestation would be indistinguishable except on a very fine level from a singularity. Physicists would then probably be justified in referring to this object/region as a "singularity," despite the fact that it is not a true relativistic singularity.

So keep that in mind.
 
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