B What are the biggest misconceptions about black holes?

[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.