"Black holes"

Originally posted by flexmore
Hawking radiation has never been seen, and is not predicted by all theories ... stuff being sucked in has been seen to radiate before it crosses the line.

Hawking radiation is a well based explanation why micro Black Holes are not stable. If no Hawking radiation, then the Earth wouldn't survive pretty long...

Originally posted by FabianFnas
I don't believe in an infinitly small object with infinitly densed energy at the center of a BlackHole.
I believe that there is something about these objects that we don't yet fully understand.

But my point was that physicists do not claim that an infinitely dense object is at the centre of a Black hole. As far as I know, that concept is an invention of this thread and has nothing to do with science.
A black hole has a finite mass and a finite / non zero radius. Its density is its mass in proportion to its volume which is finite.

Originally posted by twhitehead
But my point was that physicists do not claim that an infinitely dense object is at the centre of a Black hole. As far as I know, that concept is an invention of this thread and has nothing to do with science.
A black hole has a finite mass and a finite / non zero radius. Its density is its mass in proportion to its volume which is finite.

We agree fully (I think).

The concept is however not an invention only in this thread. I have read it in several textbooks (popular ones), that inside black holes, and in the very beginning of universe (at BigBang, t=0), there are/were pointlike singularities with r=0 and dencity=inf. I have even heard physics teachers with this misconception.

And as I see it, this is a solution when you extrapolate down to t=0 or r=0 without taking other known or unknown properties into account.

Originally posted by FabianFnas
We agree fully (I think).

The concept is however not an invention only in this thread. I have read it in several textbooks (popular ones), that inside black holes, and in the very beginning of universe (at BigBang, t=0), there are/were pointlike singularities with r=0 and dencity=inf. I have even heard physics teachers with this misconception.

And a ...[text shortened]... ou extrapolate down to t=0 or r=0 without taking other known or unknown properties into account.

I would agree that for the Big bang, one could theoretically extrapolate down to t=0, r=0. However, I know of no theory that includes black holes with ether zero radius or infinite density. It appears that some people are confusing the Big bang with black holes. They are not the same thing at all.

Originally posted by Tera
At the event horizon there are the same spontaneous creation of particles and antiparticles as in the remainder of space. But once in a while these antiparticles and particles happen to pass the way so that the antiparticles move inside the black hole and the particles of course move the opposite direction. Thus in effect the black hole is "radiating" a certain ...[text shortened]... , I don't know much about that but it struck me as funny. Don't mess with thermodynamics :p

You can't calculate this unless you know for a fact that the black hole isn't growing by means of grabbing more mass from the surrounding space.

Originally posted by Wheely
You can't calculate this unless you know for a fact that the black hole isn't growing by means of grabbing more mass from the surrounding space.

Yes of course, my situation described in my last post is probably hypothetical. And the time i gave last post also was something i read which has to do as described with the size of course.

But the concept of infinity and black holes seems to have been discarded by this thread. I don't really agree, the event horizon of a black hole is just a line in space mostly, and once your inside you can't get out. However the mass that is inside the black hole would still gravitate towards the center, if it wasn't by some chance circling the rim at the speed of light. So the mass density at the center of a black hole would still be very very high.

Does it have to have a "center" at one point? Well we know that if it didn't then the spread out mass would attract and so on. Basically yes we can assume this.

How small is this "point" then? Well we know that what keeps the masses we can observe intact are the electromagnetic forces between the atoms. If the gravitational force would surpass this force then the atoms would not hold stable (their unions at least) and as such the matter would probably collapse as well.

Then the 50 000 euro question. What the darn is at the center? How high is average density taken at really low scales? - Maybe density is hard to calculate since high gravity gives high distortions of spacetime.

Center of a black hole. Pure hell, or pure pleasure?

I think that a lot of the confusion in this thread -- and in the world -- is that the terms "black hole" and "singularity" are sometimes used interchangeably. If one takes the totality of the accretion of mass into a body so dense that light no longer can escape but "information" in the form of "Hawking radiation" can escape... along with jets of energy shooting millions of light years in hellishly powerful magnetic/quantum "jets" and an "event horizon" of tormented matter/energy in the vicinity of this "black hole", then -- that is one of the beasts. This beasty we can call the "black hole".

So then what is the "singularity" which -- in the vernacular -- "lies at the center" (whatever that is without benefit of dimensionality or time) -- of the "black hole"? It is this singularity that leads physicists to say that once inside the event horizon, the only two knowns are mass and spin, if one assumes that the singularity is the only true force that matters any more inside that "thing".

The singularity is that place where time ceases to exist and there is a blending of the "definitely massive" with the quantum realm (though that is a poor word) of "smallness". Everything "outside" of singularity can be measured with mathematical surety. Everything "within" the quantum realm "disappears" from mathematical surety. If we measure it, it ceases to exist. If we observe it, we have measured it. The thing about a singularity is that we never need worry about "observing" it, as we would be naught but disassembled bits of atoms once we fell past the line of no return of the "Black Hole" wherein the Singularity ... What? Can we say "Is"? I can't. Neither can anyone with any certainty. It's that "time" thing. And that "quantum" thing. And that "quantum-time" thing. For at the singularity, time is “not”.

Originally posted by StarValleyWy
I think that a lot of the confusion in this thread -- and in the world -- is that the terms "black hole" and "singularity" are sometimes used interchangeably. If one takes the totality of the accretion of mass into a body so dense that light no longer can escape but "information" in the form of "Hawking radiation" can escape... along with jets of energ ...[text shortened]... e" thing. For at the singularity, time is “not”.

Back holes also have charge, not just mass and spin.

I think one of the things that are misleading in this thread is the discussion of the event horizon. The event horizon is not a thing. It is the boundary at which space-time is bent so far that there is no longer a route out again. This last bit is the important bit. Although it has since been found that photons are, indeed, subject to gravitational forces, it was never the gravity that was supposed to keep light from leaving a black hole. It was the fact that there isn´t actually a path in three dimensions that the light could come from.

Originally posted by Wheely
Back holes also have charge, not just mass and spin.

I think one of the things that are misleading in this thread is the discussion of the event horizon. The event horizon is not a thing. It is the boundary at which space-time is bent so far that there is no longer a route out again. This last bit is the important bit. Although it has since been found ...[text shortened]... as the fact that there isn´t actually a path in three dimensions that the light could come from.

Well said. I missed mentioning the Charge and the basic typing of black holes. Your last sentence is what I was trying to say with my use of the phrase "whatever that is without benefit of dimensionality or time"... there literally isn't a time/space continuum that works like the one we are used to.

Originally posted by Tera
But the concept of infinity and black holes seems to have been discarded by this thread. I don't really agree, the event horizon of a black hole is just a line in space mostly, and once your inside you can't get out. However the mass that is inside the black hole would still gravitate towards the center, if it wasn't by some chance circling the rim at the speed ...[text shortened]... s high distortions of spacetime.

Center of a black hole. Pure hell, or pure pleasure?

I believe that there are objects known as Neutron stars which have a density similar to that of the nucleus of the atom. Thus electromagnetic forces have already been over come, without becoming a black hole.

What I do not know is whether or not a black hole can exist in which the gravitational forces do not exceed the forces keeping nuclear elements apart (protons/neutrons). I don't see why not.

I see no reason to believe that the physics going on inside a black hole is significantly different from outside, and suspect that many phenomena are possible in both scenarios.

Originally posted by twhitehead
I believe that there are objects known as Neutron stars which have a density similar to that of the nucleus of the atom. Thus electromagnetic forces have already been over come, without becoming a black hole.

What I do not know is whether or not a black hole can exist in which the gravitational forces do not exceed the forces keeping nuclear elements a ...[text shortened]... icantly different from outside, and suspect that many phenomena are possible in both scenarios.

Is that the one where the core is kind of sustained cause of the fact that it's still burning, and when the fuel run out it will collapse instead of supernova? That sounds maybe plausible. I didn't really think about that they have surpassed the electromagnetic force "barrier" though, hmm... Cool :p

Can that happen without a shriveled space time?

What stops the matter then from collapsing to a singular point? And if nothing then we are back to the question about the center of a black hole being "infinitely dense". Though we can agree that term is flawed for this subject, since you can't measure volume of space in such curled dimensions.

Originally posted by Tera
Is that the one where the core is kind of sustained cause of the fact that it's still burning, and when the fuel run out it will collapse instead of supernova? That sounds maybe plausible. I didn't really think about that they have surpassed the electromagnetic force "barrier" though, hmm... Cool :p

Can that happen without a shriveled space time?

What sto ...[text shortened]... awed for this subject, since you can't measure volume of space in such curled dimensions.

There is no complete theory about the center of black holes and there won´t be until some can comes up with a clever idea to combine relativity and quantum theory.

Originally posted by Wheely
There is no complete theory about the center of black holes and there won´t be until some can comes up with a clever idea to combine relativity and quantum theory.

I think the physics of center of Black Holes are for ever unexplainable with the aid of relativity and quantum theory.
I think we need a new theory for that. Quantum gravity (Lee Smolin) is a promising candidate for such a theory.

Originally posted by nihilismor
I have began to study these. They are very interesting. The idea of a "point" having that much influence is fascinating.

I've been in a black hole. And believe me, it wasn't pleasant.
I don't know who the hell's writing Lonely Planet these days, but take this little bit of advice from me: If you ever go to Calcutta (they even changed the name to Kolkota to lure in unexpecting Lonely Planet readers), make sure you've got a galaxy's worth of toilet paper with you. Or a Tardis full of imodium.

Originally posted by Wheely
There is no complete theory about the center of black holes and there won´t be until some can comes up with a clever idea to combine relativity and quantum theory.

As far as I can tell (and believe me, that's not very far at all), gravity is the problem surrounding black holes... excuse the pun.

If matter is that heavy it's sucking everything in, including light, then that means a black hole will get bigger and bigger at an ever increasing rate... infinately. Meaning that we'd all have been sucked in by now.

With a little bit of luck, again as far as I've been reading, we've all got a chance for a short vacation in Geneva at the end of July though... so it's not all bad news (CERN).