The BIG BAD BLACK HOLE

[csmyth3025]

As I understand it, the discovery of the CMB was a piece of direct evidence needed for the big bang theory to be widely accepted as "real". It was a sort of cosmic "smoking gun". Likewise, there's a lot of indirect evidence to suggest that black holes exist. Would we need to actually orbit a black hole candidate (at a distance) and make specific observations in order to prove that it is what we think it is?

If so, what sort of observations would we need to make in order to prove to a reasonable certainty that the candidate object possess an event horizon?

Chris

 

[yevaud]

People here have on occasion observed about various phenomena that what we "know" is merely a sort of placeholder, until further investigation clarifies matters. Dark Matter and Dark Energy being two such, since we aren't quite certain what either is yet.

That being said, there's precious little - to our limited understanding - that a Black Hole could be, except for a large mass compressed down to literal nothingness. Nothing else fits, nothing else is essentially mathematically workable. What we know is sufficient to describe it (even if things go wonky in describing events beneath the Event Horizon).

Also, there is the law of commonality. If we see one such Black Hole, then we know almost for a fact that it will be replicated countless times elsewhere, when the conditions allow - even if we haven't seen the rest yet.

So we actually know far more about Singularities than people might think. And we can be fairly certain what they are - even if we don't yet have a handle on the specifics.

 

[mental_avenger]

mental_avenger, sorry if it seems like I'm picking on you but I'm reading through the last few posts and I want to clear up a couple of misconceptions about how scientists approach problems like this.

Hey, no problem. After 10 years on this forum and over 15,000 posts, I understand that disagreement and debate are inevitable, and even desired in some cases.

Everything hinges on this idea - yeah, it's possible that X is the result of some phenomenon that we have no knowledge of. That is true for any scientific theory X ever. Including gravity, or our explanation for the sky being blue.

I agree, if you are differentiating between scientific theory and what is accepted as scientific fact.

I already explained what's wrong with this logic: the fact that other explanations may exist isn't an admission, it's something all scientists know. But when there's no known viable explanations, and the explanation we have works fine, then there's not much more to say on the matter.

Semantics. “Admission”, “validation”, “verification”, “concurrence”, whatever.

Um, yeah. In fact, the laws of physics have to be wrong, because the prediction of general relativity is that black holes form and we can't use our current theories to predict what happens once they do. So obviously something has to be off. Luckily a horde of very talented physicists are working on it.

Glad to hear it. It is possible that the “theory of everything” is a lot simpler than currently expected. I suspect that in the not too distant future, there will be a breakthrough that will shock everyone. I think that breakthrough is being significantly delayed by scientists going off on complex and exotic tangents.

Dude, it's not a theory if there are no details and no quantifiable predictions.

Sorry, my mistake. Hypothesis.

It's much, much harder to actually come up with a theory that has a basis in established physics and makes testable predictions. Because that requires math, and math is, like, hard.[/

True, advanced mathematics is extremely difficult for most people. However, we must keep in mind that mathematics can prove the existence of things that cannot exist, so we have to be careful about what we believe has been proven.

 

[csmyth3025]

Everything hinges on this idea - yeah, it's possible that X is the result of some phenomenon that we have no knowledge of. That is true for any scientific theory X ever. Including gravity, or our explanation for the sky being blue.

I agree, if you are differentiating between scientific theory and what is accepted as scientific fact.

This is an interesting concept. Can we put Classical (Newtonian) mechanics in the "scientific fact" category for non-reletavisic solutions? Does Special and General Relativity fall into the "scientific fact" or "scientific theory" category? Where does Quantum mechanics fit in? Where do we put the Standard Model of cosmology (especially in view of the fact that the model itself admits to having no inkling of what 96% of the mass/energy in the universe in made of)?

The reason I ask is that laymen such as myself have been taught that these theories (despite their limitations) are accepted as scientific fact. I think that anyone familiar with science knows that existing theories may be modified as new ideas and new information becomes available. This doesn't mean that the theories are wrong (within the limits of their applicability) but, like Newtonian mechanics, are incomplete in describing the full range of phenomena we observe.

Chris

 

[ramparts]

Well, my whole point was that there really is no difference between scientific theory and science fact. To whatever extent we draw a distinction between them, it's a matter of humans drawing an arbitrary line of certainty rather than a theory crossing some magic line to finally become "fact." I think mental_avenger does get this, as he referred to what is "accepted" as scientific fact rather than what "is" scientific fact*.

For a physicist, every scientific proposition - be it classical mechanics, quantum mechanics, or some highly speculative theory - has associated with it a rough probability of being right. For classical mechanics (within its domain of validity), that probability is probably p=1-10^N for some very large N (i.e., p=0.99999999....). I'd imagine for things like quantum and GR, most physicists would probably put the likelihood of at least the fundamentals of these theories being right as something higher than 0.99 as well (for example, I think given the rash of experimental evidence, there is less than a 1/100 chance that a theory like quantum mechanics is just completely wrong).

At what point does theory become fact? 0.9? 0.99? 0.99999? Really the answer is we can only call something proven fact when the probability of it being right is 1, but unfortunately we can never get to that point in physics. p=1 is solely the domain of math So we get to put an arbitrary dividing line, usually around 0.99 or something. But that's at our whims; there's no objective answer as to when a theory becomes fact.

Side note: the standard model of cosmology doesn't need to know what dark matter and dark energy are made of to be able to make predictions. We know how a cosmological constant works, and we know more or less how cold non-baryonic dark matter works. They're falsifiable, and ideas that have been borne out to a degree by experiment.

*Obviously scientific facts exist. Some things about the Universe are true, and some are false. Also, according to the Universe there are no theories, only facts. Theories are our attempts to approximate the facts of the Universe, and some of them are closer to the truth than others.

 

[csmyth3025]

Thanks Ramparts.
In view of mental_avenger's skepticism (I believe) about the real existence of black holes, how certain is the probability that there are objects that have collapsed within their Schwarzschild radius?

I realize that what lies within the event horizon is still a matter of much debate. General Relativity evokes no internal structure except for a central singuarity. There's a "fuzzball" model in string theory that avoids the singularity and leaves the event horizon as the surface of the compact (string) object within. It sounds to me like both models would look the same to an outside observer.

Chris

 

[ramparts]

Um, I'd put the probability at something like 0.99, but that's obviously a) very subjective/personal and b) very very fuzzy.

 

[BlackHoleAndromeda]

Notice that the article says “The only known object which can pack 4.1 million solar masses into a volume that small is a black hole.” The statement makes two important points. First, it admits (by omission) that there may be an explanation which is not known to us. Second, it makes the assumption that we actually know that “black holes” (as conventional wisdom describes them) exist...

What sort of observations would be needed to prove or disprove that hyperdense objects possess an event horizon? The Wikipedia article on black holes cites several lines of evidence suggesting that they exist. It can be found here:

http://en.wikipedia.org/wiki/Black_hole ... l_evidence

This same article also includes a short section on the possibility that they dont exist, as follows:

The evidence for stellar and supermassive black holes implies that in order for black holes not to form, general relativity must fail as a theory of gravity, perhaps due to the onset of quantum mechanical corrections. A much anticipated feature of a theory of quantum gravity is that it will not feature singularities or event horizons (and thus no black holes).[102] In recent years, much attention has been drawn by the fuzzball model in string theory. Based on calculations in specific situations in string theory, the proposal suggest that generically the individual states of a black hole solution do not have an event horizon or singularity (and can thus not really be considered to be a black hole), but that for a distant observer the statistical average of such states does appear just like an ordinary black hole in general relativity.[103]

Chris

Well everyone knows that Wikipedia is an unreliable source cause that information is always being edited.

 

[csmyth3025]

Notice that the article says “The only known object which can pack 4.1 million solar masses into a volume that small is a black hole.” The statement makes two important points. First, it admits (by omission) that there may be an explanation which is not known to us. Second, it makes the assumption that we actually know that “black holes” (as conventional wisdom describes them) exist...

What sort of observations would be needed to prove or disprove that hyperdense objects possess an event horizon?

Well everyone knows that Wikipedia is an unreliable source cause that information is always being edited.

Let's leave aside the question of the validity of Wikipedia articles in general for now. We can then turn to my original question: "What sort of observations would be needed to convincingly demonstrate that hyperdense objects possess an event horizon?"

Chris

 

[MeteorWayne]

Well everyone knows that Wikipedia is an unreliable source cause that information is always being edited.

Let's leave aside the question of the validity of Wikipedia articles in general for now.

We can then turn to my original question: "What sort of observations would be needed to convincingly demonstrate that hyperdense objects possess an event horizon?"

Chris

"Let's leave aside the question of the validity of Wikipedia articles in general for now. "


Yes, please let's do that. Any intelligent person realizes that Wiki is a good starting point, but that's all. Some articles are good, others may at times be not so good. The key is to look at the links at the bottom and read the actual sources of the information.

So let's get back to the original subject, OK?

 

[Couerl]

That being said, there's precious little - to our limited understanding - that a Black Hole could be, except for a large mass compressed down to literal nothingness. Nothing else fits, nothing else is essentially mathematically workable. What we know is sufficient to describe it (even if things go wonky in describing events beneath the Event Horizon)..

Now that you bring this up, "wonky describing events beneath the horizon" etc.. It seems to me that describing events would fall along similar lines to the initial moments of the universe where the 4 principle laws are again combined in to a single law. Or am I thinking incorrectly to assume that? Also, somewhere I read recently that due to Hawking radiation, black holes will eventually "glow" and then finally, once enough energy/mass has escaped they will "explode". Perhaps this happens after a trillion years, I don't know but, it is a different idea than the one I had previously understood where they simply fizzle out in to nothingness..

 

[robnissen]

Well, my whole point was that there really is no difference between scientific theory and science fact. To whatever extent we draw a distinction between them, it's a matter of humans drawing an arbitrary line of certainty rather than a theory crossing some magic line to finally become "fact." . . .

*Obviously scientific facts exist. Some things about the Universe are true, and some are false. Also, according to the Universe there are no theories, only facts. Theories are our attempts to approximate the facts of the Universe, and some of them are closer to the truth than others.

I agree with everything in your post, except maybe the footnote. In the quantum world (which is where we live), there are really no "facts" only probabilities. Now some probabilities are infinitely close to 1 (for example, in the next ten seconds, the earth, or if you prefer, the universe will not cease to exist due to random quantum fluctuations) but they are still not 1.000000....00000. A true scientific theory, as opposed to a laymen's version of a theory, is about as close to scientific fact as we can get. But since the probabilities are never 1, sometimes theories are proven wrong.

 

[yevaud]

That being said, there's precious little - to our limited understanding - that a Black Hole could be, except for a large mass compressed down to literal nothingness. Nothing else fits, nothing else is essentially mathematically workable. What we know is sufficient to describe it (even if things go wonky in describing events beneath the Event Horizon)..

Now that you bring this up, "wonky describing events beneath the horizon" etc.. It seems to me that describing events would fall along similar lines to the initial moments of the universe where the 4 principle laws are again combined in to a single law. Or am I thinking incorrectly to assume that?

Again, that's hard to say. Possibly.

Also, somewhere I read recently that due to Hawking radiation, black holes will eventually "glow" and then finally, once enough energy/mass has escaped they will "explode". Perhaps this happens after a trillion years, I don't know but, it is a different idea than the one I had previously understood where they simply fizzle out in to nothingness..

Either can (theoretically) occur, depending on the mass of the Singularity, and no doubt other considerations I'm not conversant in. But it is known that very small mass BH's will "evaporate" in a twinkling, while the supermassive Singularities may be prone to explosive events. Naturally this too is difficult to say with certainty, since we've never seen one do either. It's all only mathematics as yet (until observed or experimentally confirmed).

 

[neilsox]

Hardly anything can be proved beyond unreasonable doubt, so black hole event horizons may remain forever probable, but not certain. An extremely powerful, sturdy and shielded space craft can likely approach within 18 light minutes (assuming the event horizon radius is 17 light minutes) of the the center of a 4.1 million solar mass black hole. The black hole would (we think) look like Earth from low Earth orbit, except it would be black = no stars, and featureless, except for closer objects orbiting the black hole, the polar jets, and the accretion disk. We could likely measure the speed, direction, radiation levels and send other details to a more distant craft that had a better chance of escaping back to civilization. This data would increase the probability (or decrease the probability) of an event horizon. The gravity, and tide stress are moderate for 4.1 million solar mass black holes, just outside the event horizon. The Hawkins radiation would likely not be detectable even this close. Neil

 

[ramparts]

Well, my whole point was that there really is no difference between scientific theory and science fact. To whatever extent we draw a distinction between them, it's a matter of humans drawing an arbitrary line of certainty rather than a theory crossing some magic line to finally become "fact." . . .

*Obviously scientific facts exist. Some things about the Universe are true, and some are false. Also, according to the Universe there are no theories, only facts. Theories are our attempts to approximate the facts of the Universe, and some of them are closer to the truth than others.

I agree with everything in your post, except maybe the footnote. In the quantum world (which is where we live), there are really no "facts" only probabilities. Now some probabilities are infinitely close to 1 (for example, in the next ten seconds, the earth, or if you prefer, the universe will not cease to exist due to random quantum fluctuations) but they are still not 1.000000....00000. A true scientific theory, as opposed to a laymen's version of a theory, is about as close to scientific fact as we can get. But since the probabilities are never 1, sometimes theories are proven wrong.

The wave function still behaves deterministically. Quantum mechanics is a deterministic theory, just not in the sense we're used to. Anyway, that's a separate thread

 

[csmyth3025]

Regardless of the debate about what conditions might exist within the event horizon of a compact object, is there any reason to believe that any object with a surface gravity that equals or exceeds 300,000 km/sec^2 will not possess an event horizon and, by any observation we can make, have the attributes we describe as a "black hole"?

Chris

 

[Couerl]

Either can (theoretically) occur, depending on the mass of the Singularity, and no doubt other considerations I'm not conversant in. But it is known that very small mass BH's will "evaporate" in a twinkling, while the supermassive Singularities may be prone to explosive events. Naturally this too is difficult to say with certainty, since we've never seen one do either. It's all only mathematics as yet (until observed or experimentally confirmed).

Okay, that makes more sense. I don't know why I had it in my mind the way I did ("evaporate in to nothingness", I'll blame Hawking :lol: ), I suppose I'm not immune from assumption. I can see "micro" BH's "evaporating" as it were, but larger (true) one's, once they evaporate a given amount of mass/energy can no longer gravitationally bind to a singularity. They would eventually "glow" and then ultimately explode or at least "un-crunch" perhaps back to a Neutron star?. Let's say we have an abstract scenario where a BH formed say, 5 billion yrs ago with barely enough mass to form a singularity, a tipping point of an average moon's worth of mass for instance, maybe even less.. Wouldn't it be rational to assume that once enough mass/energy had "evaporated" that it would revert to a state where it was observable once again? Maybe explode is the wrong descriptor and un-crunch is at least closer to what I imagine happening.

 

[csmyth3025]

Either can (theoretically) occur, depending on the mass of the Singularity, and no doubt other considerations I'm not conversant in. But it is known that very small mass BH's will "evaporate" in a twinkling, while the supermassive Singularities may be prone to explosive events. Naturally this too is difficult to say with certainty, since we've never seen one do either. It's all only mathematics as yet (until observed or experimentally confirmed).

Okay, that makes more sense. I don't know why I had it in my mind the way I did ("evaporate in to nothingness", I'll blame Hawking :lol: ), I suppose I'm not immune from assumption. I can see "micro" BH's "evaporating" as it were, but larger (true) one's, once they evaporate a given amount of mass/energy can no longer gravitationally bind to a singularity. They would eventually "glow" and then ultimately explode or at least "un-crunch" perhaps back to a Neutron star?. Let's say we have an abstract scenario where a BH formed say, 5 billion yrs ago with barely enough mass to form a singularity, a tipping point of an average moon's worth of mass for instance, maybe even less.. Wouldn't it be rational to assume that once enough mass/energy had "evaporated" that it would revert to a state where it was observable once again? Maybe explode is the wrong descriptor and un-crunch is at least closer to what I imagine happening.

The Wikipedia article on Hawking Radiation can be found here:

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

It contains the following passage:

As an example, a black hole of one solar mass has a temperature of only 60 nanokelvin; in fact, such a black hole would absorb far more cosmic microwave background radiation than it emits. A black hole of 4.5 × 10^22 kg (about the mass of the Moon) would be in equilibrium at 2.7 kelvin, absorbing as much radiation as it emits. Yet smaller primordial black holes would emit more than they absorb, and thereby lose mass.

This description does not, of course, take into account any dust or gas that such black holes might accumulate.

Chris