B What are the biggest misconceptions about black holes?

[PAllen]

Another misconception: An in-falling person will not experience anything abnormal at the exact moment she is crossing the event horizon. Truth: It is a popular hypothesis, but not a fact (and continues to be challenged as in firewall etc).

In fact, any statement on what happens at or within the horizon is only a hypothesis (as of now?).

It removes confusion to talk in terms of what model of BH you are using. That nothing unusual happens at horizon crossing is mathematical fact of the classical GR black holes. Firewalls are a feature of a semi-classical treatment of quantum gravity, under commonly held assumptions (there treatments in this realm, with less accepted assumptions that don't involve firewalls; such eminent physicists as Juan Maldacena think the firewall hypothesis will ultimately be rejected). There is no full, consistent treatment in quantum gravity because there is no complete theory. Apart from all this, you are clearly correct that we don't, and may never, have a way to verify this feature of real world BH. The best we can do is choose to believe the predictions of a complete QG theory that is verified elsewhere (whenever that is achieved).

 

[write4u]

If I may be permitted a set of analogies.
In context of a *multiverse*, perhaps BHs are the *eggs* of new *baby galaxies*, or *tunnels* to new *baby universes*, invisible to us?

 

[pinball1970]

Sorry I joined the party late - a comment about colour and black holes

wavelengths in the vis spectrum are colour not beyond, you would not refer to microwaves as colour

 

[rootone]

If I may be permitted a set of analogies.
In context of a *multiverse*, perhaps BHs are the *eggs* of new *baby galaxies*, or *tunnels* to new *baby universes*, invisible to us?

What is the evidence for this?, as far as I know there is none.
On that basis, one might equally well argue that black holes are portals to the holy kingdom of the flying spaghetti monster.

 

[guhan]

It removes confusion to talk in terms of what model of BH you are using. That nothing unusual happens at horizon crossing is mathematical fact of the classical GR black holes.

I don't think one can apply a theory beyond its domains of validity and call it factual. It would have been ok before the limitations of classical theory came up, by virtue of it being an 'unknown unknown' problem, but not anymore since it is a 'known unknown'.

On firewalls etc, sure they are hotly debated, with eminent names on either side, and I don't have the expertise to pick a side on this. Mentioned it merely to exemplify my case.

 

[PAllen]

I don't think one can apply a theory beyond its domains of validity and call it factual. It would have been ok before the limitations of classical theory came up, by virtue of it being an 'unknown unknown' problem, but not anymore since it is a 'known unknown'.

On firewalls etc, sure they are hotly debated, with eminent names on either side, and I don't have the expertise to pick a side on this. Mentioned it merely to exemplify my case.

Please note: I said mathematical fact. There is no ambiguity or need for qualification in this statement. At present, no one knows what the bounds of validity of classical GR are. In particular, whether it is fully applicable to high precision at the horizon of a large BH is itself subject to dispute. However, what the math of classical GR predicts is not disputed at all.

 

[guhan]

Please note: I said mathematical fact. There is no ambiguity or need for qualification in this statement. At present, no one knows what the bounds of validity of classical GR are. In particular, whether it is fully applicable to high precision at the horizon of a large BH is itself subject to dispute. However, what the math of classical GR predicts is not disputed at all.

I am sure neither of us is keen on prolonging this over pedantics! :) I believe the definition of 'mathematics of a theory' also includes those statements on no-go domains, where we know** that the physics is unknown or not established. It is absolutely ok if you believe otherwise.

**as you said, the region at (and within) the horizon is known to be an unsolved domain

 

[PAllen]

I am sure neither of us is keen on prolonging this over pedantics! :) I believe the definition of 'mathematics of a theory' also includes those statements on no-go domains, where we know** that the physics is unknown or not established. It is absolutely ok if you believe otherwise.

**as you said, the region at (and within) the horizon is known to be an unsolved domain

It is only unknown per theories other than GR. For example, Newtonian mechanics domain of applicability is not determined by Newtonian mechanics, it is determined by SR/GR. One regularly speaks of predictions of Newtonian mechanics that are wrong in that they reach into where SR//GR is required. However, they are still predictions of Newtonian mechanics, and are mathematical facts of Newtonian mechanics taken as a theory. For example, I've never heard anyone dispute the statement that "Newtonian mechanics states that the momentum of a ball of mass m, moving at twice the speed of light, is 2mc".
With what GR says about the horizon, the situation is not even quite like this. We know that the above statement is outside the domain of validity of Newtonian mechanics (based on our knowledge of other well established theories). Statements GR (as a self contained theory) makes about the horizon are NOT known to be outside its domain of applicability. Instead, it is an open question, which is very different status from known to be superseded by a different theory in this domain.

 

[votingmachine]

Since there is a debate here about the event horizon, I have a question. Is the event horizon an important boundary, or just the distance beyond which nothing from the surface can be seen?

That is vague and I will walk thru the question. The black hole cannot emit light that can escape. There is an event horizon, where if you parked our spaceship just outside it, you would not see the thing in the center, no matter how bright a flashlight you shone at it. But what about a thing not far inside that event horizon. Say you shot a bottle rocket at the black hole and it goes 100 feet and blows up ... do you see that?

I hope that is not too vague a question about what the event horizon is. And if it is answered in another thread ... just point that direction.

 

[PAllen]

No, you would not see the bottle rocket blow up. However, if you shine a flashlight at it, the bottle rocket would be hit by the light (inside the horizon), and would reflect it, but this reflected light would not progress toward the horizon. Instead, it would simply 'fall' much slower than the bottle rocket.

Per other debate: this is all per classical GR. If the firewall hypothesis is true, the description would be completely different.

 

[write4u]

What is the evidence for this?, as far as I know there is none.
On that basis, one might equally well argue that black holes are portals to the holy kingdom of the flying spaghetti monster.

I don't know how you came to that conclusion.
In a multiverse each universe would be invisible to the other, but each universe, for it to contiue as a universe (Hawking), it would have to have mathematical properties and chemical reactions, similar to our universe. Nothing divine or *ridiculous* in my statement.

I do admit, it was a purely speculative statement, but then the concept of a multiverse is speculative to begin with, yet it is discussed by serious cosmologists. I was speaking in that context. I am an atheist, I like spaghetti on my plate with lots of sauce.

If we live in a multiverse, when and how do they form ?

 

[phinds]

I don't know how you came to that conclusion.

I think he came to that conclusion because your speculation does not comport with physics as we know it. The "black hole as an egg for a new universe" just doesn't work. His point was, and I agree with it, that your speculation was nonsensical.

 

[write4u]

I think he came to that conclusion because your speculation does not comport with physics as we know it. The "black hole as an egg for a new universe" just doesn't work. His point was, and I agree with it, that your speculation was nonsensical.

I used the egg as a metaphor. In context the singularity from which this universe originated can be metaphorically described as an *universal egg*.

And as far as I know the center of a BH is a singularity (a metaphorical egg) and maybe...could be the singularity from which a new universe expands. We would not know about this because we cannot observe what goes on inside the separated spacetime of a BH.

We know what goes in and we what occasionally *leaks*out, but do we know much more than that?

 

[phinds]

I used the egg as a metaphor. In context the singularity from which this universe originated can be metaphorically described as an *universal egg*.

And as far as I know the center of a BH is a singularity (a metaphorical egg) and maybe...could be the singularity from which a new universe expands. We would not know about this because we cannot observe what goes on inside the spacetime of a BH.

But the universal egg cannot be, as you stated it to be, a black hole, so I still think what you said makes no sense.

 

[write4u]

But the universal egg cannot be, as you stated it to be, a black hole, so I still think what you said makes no sense.

Where did I state that?

Assuming a multiverse, should all that have happened all at once with the inflation of *our* universe? Or are new universe being created constantly? If so, where would the energy come from? Hyper massive BH contain a lot of potential energy, no?.

 

[phinds]

Where did I state that?

You said it here. Do you not even understand what you said?

If I may be permitted a set of analogies.
In context of a *multiverse*, perhaps BHs are the *eggs* of new *baby galaxies*, or *tunnels* to new *baby universes*, invisible to us?

In what way does this not specifically say that "perhaps BH's are eggs" ?

Assuming a multiverse, should all that have happened all at once with the inflation of *our* universe? Or are new universe being created constantly? If so, where would the energy come from? Hyper massive BH contain a lot of potential energy.

Individual BH's are utterly trivial compared to the universe.

 

[write4u]

You said it here. Do you not even understand what you said?
In what way does this not specifically say that "perhaps BH's are eggs" ?

You don't seem to understand the implication of a metaphorical egg, which expands, first inside the shell, then breaking out of the shell and creating a whole new *system*, which has no resemblance to an egg anymore. Let's also not forget the phenomenon of metamorphosis

Individual BH's are utterly trivial compared to the universe.

Of course it would seem that way to us., We can only see the *entrance* of a BH. Beyond that what do we know what goes on inside ? I can visualize an type of universal hour-glass configuration with mass/energy constantly trickling (tunneling) from our universe through the "relatively" small BH into the singularity (the metaphorical egg), but eventually expanding into a new separate universe, invisible to us.

Question: in a multiverse are all universes the same size as our universe?

Instead of calling it nonsense, why don't you explain why this could NOT be so according to what we know from our science of BH. To me that would be useful.

If you recall, I qualified my probing metaphor as pure speculation. What happens when a BH singularity reaches a physical and gravitational limit? Do they blow up, do they evaporate? Into what? Back ito our own universe? What are the limits of BH and what happens when those limits are reached.. Does anyone know and wish to share?

I am merely posing hypothetical questions, but as yet have not seen a coherent answer.

 

[Droidriven]

[HIDE]You don't seem to understand the implication of a metaphorical egg, which expands, first inside the shell, then breaking out of the shell and creating a whole new *system*, which has no resemblance to an egg anymore. Let's also not forget the phenomenon of metamorphosis Of course it would seem that way to us., We can only see the *entrance* of a BH. Beyond that what do we know what goes on inside ? I can visualize an type of universal hour-glass configuration with mass/energy constantly trickling (tunneling) from our universe through the "relatively" small BH into the singularity (the metaphorical egg), but eventually expanding into a new separate universe, invisible to us.

Question: in a multiverse are all universes the same size as our universe?

Instead of calling it nonsense, why don't you explain why this could NOT be so according to what we know from our science of BH. To me that would be useful.

If you recall, I qualified my probing metaphor as pure speculation. What happens when a BH singularity reaches a physical and gravitational limit? Do they blow up, do they evaporate? Into what? Back ito our own universe? What are the limits of BH and what happens when those limits are reached.. Does anyone know and wish to share?

I am merely posing hypothetical questions, but as yet have not seen a coherent answer.[/HIDE]

Even after several warnings about posting things in the direction of your personal theories, you are still posting on the same subject. I think you are pushing your limits, my friend.

 

[PAllen]

You said it here. Do you not even understand what you said?

In what way does this not specifically say that "perhaps BH's are eggs" ?

Individual BH's are utterly trivial compared to the universe.

Note that Lee Smolin pushed a model of black holes seeding new universes, extracting testable predictions from this model. If I recall correctly, this model is close to being ruled out by observation.

 

[write4u]

Even after several warnings about posting things in the direction of your personal theories, you are still posting on the same subject. I think you are pushing your limits, my friend.

In context of the OP question, you could have also said. "W4U, this is one of the *Misconceptions* about Black Holes" , instead of a veiled threat implied in your of "pushing my limits". Moreover, those previous warnings were about my posting of "disallowed links" to lectures of qualified physicists, to wit, Renate Loll's proposition of CDT (causal dynamical triangulation) and not about my "personal theories".

Causal dynamical triangulation (abbreviated as CDT) invented by Renate Loll, Jan Ambjørn and https://en.wikipedia.org/w/index.php?title=Jerzy_Jurkiewicz&action=edit&redlink=1 , and popularized by Fotini Markopoulou and Lee Smolin, is an approach to quantum gravity that like loop quantum gravity is background independent.

https://en.wikipedia.org/wiki/Causal_dynamical_triangulation

If you are a theoretical scientist, you seem possesses a very narrow and limited viewpoint. Give me a break will you. I am here because I am interested in science, but if you keep threatening me because I use *informal* language (English is my second language), I'll just leave and won't waste any more of your valuable time having to give me warnings. In fact, I won't waste my valuable time anymore on this forum. You have just managed to lose a member. Be well all. Bye, bye...

Physics Forums - The Fusion of Science and Community ?

Oh, and please stop inviting me back. After leaving once before, I am not going to subject myself to try once more and then being "warned" on semantics.. At 76, I don't need that anymore in my life.

Note that Lee Smolin pushed a model of black holes seeding new universes, extracting testable predictions from this model. If I recall correctly, this model is close to being ruled out by observation.

Thank you Sir, for that reply. Now I have something to research. Seems my thought processes (right or wrong) are along the lines of Lee Smolin.

p.s. I wonder how many warnings he would get if posting his hypotheses on this forum without revealing his name and qualifications.

 

[guhan]

That is vague and I will walk thru the question. The black hole cannot emit light that can escape. There is an event horizon, where if you parked our spaceship just outside it, you would not see the thing in the center, no matter how bright a flashlight you shone at it. But what about a thing not far inside that event horizon. Say you shot a bottle rocket at the black hole and it goes 100 feet and blows up ... do you see that?

We can say for sure that you won't see any stuff inside the horizon from your position just outside of it - so no, you won't see any thing inside, even if it is glowing brightly, however close that thing is from the horizon.

In fact, you won't even be able to live long enough to watch your bottle rocket cross the horizon when you launch it form your position outside - you will only watch it asymptotically fade as it appears to approach the horizon forever.

And from known limitations of current physics including GR (cf. my discussion earlier here), we don't know what happens to that rocket (as observed by someone in rocket's local frame) as it crosses the horizon.

 

[Droidriven]

In context of the OP question, you could have also said. "W4U, this is one of the *Misconceptions* about Black Holes" , instead of a veiled threat implied in your of "pushing my limits". Moreover, those previous warnings were about my posting of "disallowed links" to lectures of qualified physicists, to wit, Renate Loll's proposition of CDT (causal dynamical triangulation) and not about my "personal theories". https://en.wikipedia.org/wiki/Causal_dynamical_triangulation

If you are a theoretical scientist, you seem possesses a very narrow and limited viewpoint. Give me a break will you. I am here because I am interested in science, but if you keep threatening me because I use *informal* language (English is my second language), I'll just leave and won't waste any more of your valuable time having to give me warnings. In fact, I won't waste my valuable time anymore on this forum. You have just managed to lose a member. Be well all. Bye, bye...

Physics Forums - The Fusion of Science and Community ?

Oh, and please stop inviting me back. After leaving once before, I am not going to subject myself to try once more and then being "warned" on semantics.. At 76, I don't need that anymore in my life.Thank you Sir, for that reply. Now I have something to research. Seems my thought processes (right or wrong) are along the lines of Lee Smolin.

p.s. I wonder how many warnings he would get if posting his hypotheses on this forum without revealing his name and qualifications.

I was mentioning the fact that personal theories are not accepted in this forum but your posts are still about your original theory that you were asked to discontinue your persistence in.

 

[guhan]

It is only unknown per theories other than GR. For example, Newtonian mechanics domain of applicability is not determined by Newtonian mechanics, it is determined by SR/GR. One regularly speaks of predictions of Newtonian mechanics that are wrong in that they reach into where SR//GR is required. However, they are still predictions of Newtonian mechanics, and are mathematical facts of Newtonian mechanics taken as a theory. For example, I've never heard anyone dispute the statement that "Newtonian mechanics states that the momentum of a ball of mass m, moving at twice the speed of light, is 2mc".
With what GR says about the horizon, the situation is not even quite like this. We know that the above statement is outside the domain of validity of Newtonian mechanics (based on our knowledge of other well established theories). Statements GR (as a self contained theory) makes about the horizon are NOT known to be outside its domain of applicability. Instead, it is an open question, which is very different status from known to be superseded by a different theory in this domain.

Yup, I get it - that is your belief. And per my belief, when I refer to Newtonian mechanics I am also referring to the boundaries of its validity. As for GR, Iike we agreed, its status at event horizon is known to be unknown. So per my belief, when I refer to GR I am also referring to these boundaries.

With that said, I am going to end my discussion on this. I sincerely hope you don't get offended if I don't reply to you on this in future :)

 

[Herald Swegart]

The single Largest misconception about black holes is, that we know a lot about black holes.

 

[nikkkom]

Obviously we can see the surrounding galaxy, but in the center of this galaxy resides a Black Sphere which is invisible to us because it cannot emit radiation from inside its event horizon.

Things which do not emit radiation are not "invisible". Black cat does not emit radiation which your unaided eyes can see. Do you call black cats "invisible cats"?

 

[write4u]

write4u said: ↑
Obviously we can see the surrounding galaxy, but in the center of this galaxy resides a Black Sphere which is invisible to us because it cannot emit radiation from inside its gravitational event horizon.

Things which do not emit radiation are not "invisible". Black cat does not emit radiation which your unaided eyes can see. Do you call black cats "invisible cats"?

If you placed the black cat in a totally black room, it would be invisible to you.
But it would still radiate infrared and could be observed that way.

But I recently read that BH actually do emit bursts of (Hawking) radiation, which apparently relieves the *internal pressure" and prevents the BH from reaching a *limit* and when all the matter in the vicinity has been consumed, the radiation may actually aid in the evaporation of a BH back into our spacetime.

Apparently, Hawking radiation has found a way to defy gravity altogether. Taking your example of the black cat in a dark room, we may not be able to see it, but if it meows, we could *hear* it, revealing its presence, even though we cannot *see* it.
Now I'll be suspended for sure :

 

[nikkkom]

If you placed the black cat in a totally black room, it would be invisible to you.

But we still don't call the cat "invisible". The famous "The Invisible Man" sci-fi novel by H. G. Wells was not about a black human, it was about a transparent human, with refractive index of ~1.

 

[write4u]

But we still don't call the cat "invisible". The famous "The Invisible Man" sci-fi novel by H. G. Wells was not about a black human, it was about a transparent human, with refractive index of ~1.

Who is talking about sci-fi movies? I am not.

Simple Definition of invisible: impossible to see : not visible.
http://www.merriam-webster.com/dictionary/invisible

I like to keep it basic, simple. The rest is just semantics.