Black holes

[xXTheOneRavenXx]

Space could also be expanding because it's being pulled apart as opposed to being pushed apart.

But wouldn't we see a decrease in density then? What if with the universal expansion matter is evenly distributed into the newly formed "space" as it expands? Here in our solar system, solar winds transport particles far away from our sun distributing them throughout. What if a similar process fills in the gap as it forms? A negative pressure in the newly formed space would "draw in" these particles, etc...

 

[DrRocket]

lol, I like that explanation. It is true that dark energy may be the driving force of the expansion, and who knows may be a property of space... then I agree we have no idea if space is expanding or stretching. If space-time is one as in GR, then if space is expanding then would not time?

Space could also be expanding because it's being pulled apart as opposed to being pushed apart.

Are you suggesting that there is "someplace else" from which such a state of stress might be imposed? Just where might that be ?

 

[DrRocket]

No, I agree. It is a very difficult subject. Doesn't the Hubble Constant proven space itself expands? It certainly proves the recession rate. 70 km/s per megaparsec is still quite fast if you ask me. Looking at the properties of space itself, can I ask your opinion of whether virtual particles are considered a property of space or not?

You are asking a good but very subtle question.

Virtual particles are a part of the description of physics via quantum field theories. They are an intrinsic part of space in that setting. So yes, they are a property of space. But quantum field theories do not include gravitation and therefore are not models that can tell us much about the expansion of space-time.

The expansion of the universe is described within the model provided by general relativity. General relativity is not a quantum theory. So virtual particles are not an inherent part of space under that model. That does not mean that they simply do not exist, but rather that the physics of general relativity is not adequate to describe them.

To provide a truly satisfactory answer to your question would require a valid unfied theory that would iinclude all of known forces --- the electroweak force, the strong force, and gravity. Such a theory, which goes under the name "theory of everything" does not yet exist.

 

[xXTheOneRavenXx]

I do remember reading about the attempts to come up with The Theory of Everything.

You are asking a good but very subtle question.

Virtual particles are a part of the description of physics via quantum field theories. They are an intrinsic part of space in that setting. So yes, they are a property of space. But quantum field theories do not include gravitation and therefore are not models that can tell us much about the expansion of space-time.

Could space itself exist without gravity? or at least in some area's such as the massive voids discovered. If so then wouldn't that lead one to believe that virtual particles were developed beyond the reach of the influence of gravity? If this is the case, and they were distributed throughout the universe after their development, then in my opinion a possibility arises that equal distribution throughout the universe down to the particle (regardless of mass) level may exist. Am I completely out to left field on this one? Or is it a possibility?

To my understanding mass exists within space and creates a gravitational field based on it's properties. Without the mass, there can be no gravitational field. So in a void of mass area of space concept, are we not left with quantum field theories as the only way to calculate such properties within this area?

 

[DrRocket]

I do remember reading about the attempts to come up with The Theory of Everything.

You are asking a good but very subtle question.

Virtual particles are a part of the description of physics via quantum field theories. They are an intrinsic part of space in that setting. So yes, they are a property of space. But quantum field theories do not include gravitation and therefore are not models that can tell us much about the expansion of space-time.

Could space itself exist without gravity? or at least in some area's such as the massive voids discovered. If so then wouldn't that lead one to believe that virtual particles were developed beyond the reach of the influence of gravity? If this is the case, and they were distributed throughout the universe after their development, then in my opinion a possibility arises that equal distribution throughout the universe down to the particle (regardless of mass) level may exist. Am I completely out to left field on this one? Or is it a possibility?

To my understanding mass exists within space and creates a gravitational field based on it's properties. Without the mass, there can be no gravitational field. So in a void of mass area of space concept, are we not left with quantum field theories as the only way to calculate such properties within this area?

I don't know how one would even begin to answer your question. There is no place in the unverse that is out of reach of gravity. There is no place that is outside of space, rather by the definition of space. There is no quantum theory that includes gravity and it is quantum field theories that are the source of the prediction of virtual particles.

Even regions that appear to have no mass do have a little. And they are also within the gravitational fields created by the mass that does exist everywhere.

So the bottom line is that the available theories cannot address your question, and there is no place in the universe that is completely devoid of matter and outside of all gravitational influence.

 

[xXTheOneRavenXx]

I guess what I was trying to say is that in these voids you would still find gravity fields, however I am thinking along the lines that during the expansion these voids were quite a bit smaller. These smaller area's may of course been quit influenced at the time by the surrounding masses. As they grew larger with expansion the gravity fields also grew thinner, and detecting a gravity field presence is still found, but on a much smaller scale then an area of space that continues to house masses. In this area of lower gravity field may be where quantum field theories and GR have to come to some equal ground to explain virtual particles. Does that make any more sense? I was thinking that in such a region there may be pockets now present that may not be entirely influenced by gravity where these particles formed. Of course I cannot completely explain it. It was just a "spur of the moment" thought.

 

[DrRocket]

I guess what I was trying to say is that in these voids you would still find gravity fields, however I am thinking along the lines that during the expansion these voids were quite a bit smaller. These smaller area's may of course been quit influenced at the time by the surrounding masses. As they grew larger with expansion the gravity fields also grew thinner, and detecting a gravity field presence is still found, but on a much smaller scale then an area of space that continues to house masses. In this area of lower gravity field may be where quantum field theories and GR have to come to some equal ground to explain virtual particles. Does that make any more sense? I was thinking that in such a region there may be pockets now present that may not be entirely influenced by gravity where these particles formed. Of course I cannot completely explain it. It was just a "spur of the moment" thought.

No, general relatibity and quantum field theories do not have to come to any sort of mutual ground to explain virtual particles in the quantum vacuum. Quantum electrodynamics does that all lby itself. There is really no big problem with the description of virtual particles via quantum field theories under almost all circumstances. Not all but almost all (see the last paragraph).

The only issue is that quantum field theories don't include any gravitational effects. They just aren't up to it. But gravittional effects for problems in which QED is typically applied, including the prediction of the nature of the vacuum and virtual particles, are not important.

You only really need to find a theory that includes both quantum effects and general relativity for situations in which both are important -- the interior of black holes and the extremely early universe which was both tiny and very dense following the big bang. The other reason is less pragmatic but equally important and that is to have a set of physical laws that are mathematically consistent.

 

[xXTheOneRavenXx]

Okay, I understand. I was up for 17hrs, then I had about 1 hr sleep the other night, and then was awake for 18hrs. the head was kind of topsy-turvy, lol.

 

[dragon04]

Are you suggesting that there is "someplace else" from which such a state of stress might be imposed? Just where might that be ?

I can think of several "places" in an 11-dimensional Universe, no? Interaction between discrete branes maybe? Obviously a layman here and not a trained astrophysicist or theoretical mathematician. Just speculating. Feel free to edify me though. It's why I come here.

 

[DrRocket]

Are you suggesting that there is "someplace else" from which such a state of stress might be imposed? Just where might that be ?

I can think of several "places" in an 11-dimensional Universe, no? Interaction between discrete branes maybe? Obviously a layman here and not a trained astrophysicist or theoretical mathematician. Just speculating. Feel free to edify me though. It's why I come here.

It doesn't matter how many dimensions there might be, they would still be within the universe.

There has been, I think, some speculative research done by Brian Greene suggesting that one might be able formulate a string theory so that the additional hypothesized dimensions somehow result in the repulsive force that is currently called dark energy. But that is very speculative, and the result is still something akin to a state of internal compression being relieved, as opposed to an externally applied state of tension.

Dimensions are not separate little niches into which things can be placed. If they exist, they are connected to the dimensions that we perceive just as width and depth are connected to length. The idea behind the extra dimensions that have been hypothesized is that they are compacted and of very small scale. The standard example is a garden hose, which you perceive as a tube close up, but which looks like a line from far away. You have to remenber that these are dimensions of a manifold and not of some Euclidean space., so then can be hidden by simply having a small scale.

Another analogy that might be useful is to think about the usual balloon example for the manifold of space-time. In that analogy it is only the surface that is allowed. But now suppose that the balloon is very large, and that you are considering not only the surface as a locally Euclidean plane, but also the depth of the skin material. It is very thin, and at any large scale appears to be just a planar surface. But at a smaller scale it does have some thickness, just not a thickness that you would notice unless you looked at it with some magnification. So it is a 3-manifold at that scale but a 2-manifold at ordinary scales. The third dimension is "compactified".

 

[dragon04]

Another analogy that might be useful is to think about the usual balloon example for the manifold of space-time. In that analogy it is only the surface that is allowed. But now suppose that the balloon is very large, and that you are considering not only the surface as a locally Euclidean plane, but also the depth of the skin material. It is very thin, and at any large scale appears to be just a planar surface. But at a smaller scale it does have some thickness, just not a thickness that you would notice unless you looked at it with some magnification. So it is a 3-manifold at that scale but a 2-manifold at ordinary scales. The third dimension is "compactified".

Bear with me here. Using the balloon analogy, let's assume that our balloon gets sealed, but with "some" air molecules trapped inside it. Or more accurately, a quantity of air molecules equal to the ambient air pressure outside the balloon.

There are to ways to "inflate" that balloon. One, we can ADD air to it, thus increasing the "internal pressure" relative to the ambient air pressure outside the balloon, OR, we can expose the balloon to a vacuum. In either case, the balloon "inflates".

Granted, in a vacuum, the balloon will only inflate to a level that describes the interaction between hard vacuum and the tendency for trapped air molecules to travel to that vacuum inside the vessel (balloon). IOW, for every air molecule, the balloon will inflate to some predictable degree.

The balloon itself is doing nothing. The "outside force" of hard vacuum is pulling trapped air molecules towards it based on both volume of trapped air and the elasticity of the balloon. Now. We live on the balloon. See what I'm getting at?

We know that Gravity is an extraordinarily weak "force" compared to the other forces. If we try to unify those forces, then gravitational attraction may have to come from some dimension "outside" our 4 dimensional space-time. That is, unless you don't feel that Gravity has to be normalized with respect to the other Forces. In that case, one can conceive a Universe being "pulled apart" as opposed to being "pushed apart".

I don't have the math or lingo to explain it better than that.

 

[DrRocket]

Bear with me here. Using the balloon analogy, let's assume that our balloon gets sealed, but with "some" air molecules trapped inside it. Or more accurately, a quantity of air molecules equal to the ambient air pressure outside the balloon.

There are to ways to "inflate" that balloon. One, we can ADD air to it, thus increasing the "internal pressure" relative to the ambient air pressure outside the balloon, OR, we can expose the balloon to a vacuum. In either case, the balloon "inflates".

Granted, in a vacuum, the balloon will only inflate to a level that describes the interaction between hard vacuum and the tendency for trapped air molecules to travel to that vacuum inside the vessel (balloon). IOW, for every air molecule, the balloon will inflate to some predictable degree.

The balloon itself is doing nothing. The "outside force" of hard vacuum is pulling trapped air molecules towards it based on both volume of trapped air and the elasticity of the balloon. Now. We live on the balloon. See what I'm getting at?

We know that Gravity is an extraordinarily weak "force" compared to the other forces. If we try to unify those forces, then gravitational attraction may have to come from some dimension "outside" our 4 dimensional space-time. That is, unless you don't feel that Gravity has to be normalized with respect to the other Forces. In that case, one can conceive a Universe being "pulled apart" as opposed to being "pushed apart".

I don't have the math or lingo to explain it better than that.

You are carrying the analogy too far. I was using the balloon analogy in order to illustrate the concept of a manifold and of "compactified dimensions". Those are purely mathematical notions.

The balloon analogy is useful for illustrating the notion of a manifold, and for certain kinematics notions, for instance noting that all points move directly away from one another no matter the perspective or which point you choose to represent the observer. It is completely worthless in terms of representing the actual mechanisms involved in the expansion of the universe.

You need to be careful with the statement that gravity is an incredible weak force compared to the other forces. It is simply not true, despite the fact that it an often repeated statement. What is true is that if you look at the force of electric repulsion between two electrons, that force absolutely dwarfs gravity, and both forces follow inverse square laws. A similar comment applies to the repulsion between two protons, though the ratio is quite different because the mass of a proton is so much larger than the mass of an electron. It also applies to a proton-electron pair. But the gravitational force between two neutrons is hugely greater than the electrostatic force, since the neutron is neutrally charged. If you consider the strong force, then the situation is still different. The strong force increases with distance, sort of like stretching a rubber band, hence decreases as things get closer together. But at VERY small distances (small enough that what I am describing is rather speculative and not really known) the strong force should be very weak, while the gravitational forces increase with decreasing distance and therefore could be stronger than the strong force.

More importantly, the gravitational force is always attractive and depends solely on mass, charge being irrelevant. So for bodies that have significant mass and are charge-neutral at large scales, gravity is MUCH stronger than the electric force. That is why you don't go flying off into space. On the other hand, electric repulsion at a small scale keeps you from falling into the earth (there are some quantum mechanical effects here related to the uncertainty principle as well).

The problem with unifying gravity with the other forces does not seem to be the need for unseen dimensions. It is a problem with the inability, thus far, to formulate a quantum theory that does not result in infinities that cannot be handled through the process of renormalization. That in turn seem to stem from problems with the proposed particle called a graviton that would carry the gravitational force. The graviton should have the property of being able to interact with itself, and that results in a theory that is not renormalizable, hence a theory that predicts nothing but meaningless infinities. An awful lot of really good physicists have broken their pick on that problem -- there is a book, the Feynman Lectures on Gravitation tht basically shows Feynman's failed attempt. Feynman was as good with quantum field theories as anyone, and his failure ought to convince anyone of the high degree of difficulty associated with the problem of quantum gravity.

 

[altonhare]

This is slightly off topic, but I was wondering about GL. Specifically how much the bending of light is affected by mass density. If I have the mass m in the volume V versus m in the volume 100*V, how significantly does this affect the bending? Does it strictly affect the magnitude of the arc or would this change in density also affect focusing and other aspects?

I'm wondering primarily because I've read that there are different contributions to the lensing, one of which is "purely geometric". In this case it sounds like the size of the object, i.e. the volume, affects the lensing even if the mass (and the field) remain the same. With respect to this thread, is there a qualitative shift in lensing effect when we go from "normal" mass density to singular mass densities?

 

[xXTheOneRavenXx]

I can't answer that myself altonhare, someone else may be able to though. However I do have my own question. We look at BH's as being ever dense, meaning infinite density. I was wondering if the gamma rays we see given off when a BH "feeds" is in fact just converting the matter it draws in into gamma or X-Ray. The BH would only consume a percentage of the material for it's own expansion, but for the most part the ergosphere would act as a deflector. The matter enters orbit around the BH, as it's condensed it's also super heated. During this process the matter is broken down into particles. Once it reaches the ergosphere, the particles are deflected towards the poles via intense magnetic fields. This process would account for at least a large portion of the density. What do you think?

 

[MeteorWayne]

ergosphere?

 

[DrRocket]

I can't answer that myself altonhare, someone else may be able to though. However I do have my own question. We look at BH's as being ever dense, meaning infinite density. I was wondering if the gamma rays we see given off when a BH "feeds" is in fact just converting the matter it draws in into gamma or X-Ray. The BH would only consume a percentage of the material for it's own expansion, but for the most part the ergosphere would act as a deflector. The matter enters orbit around the BH, as it's condensed it's also super heated. During this process the matter is broken down into particles. Once it reaches the ergosphere, the particles are deflected towards the poles via intense magnetic fields. This process would account for at least a large portion of the density. What do you think?

ergosphere : http://en.wikipedia.org/wiki/Ergosphere Note that this applies only to a black hole with spin, which in itself is interesting.

I think there is a chicken and egg problem. You started iwth a phenomena associated with a black hole, proposed some mechanism for compacting matter as as result (I don't see the mechanism) and then proposed that the mechanisn might explain the necessary high density. But you need the high density to have a black hole in the first place.

 

[xXTheOneRavenXx]

I think the high density to form the black hole still comes from the collapsed star. We just see different processes going on. First we have a standard size black hole (i.e those that exist outside galactic centers), and those super-massive black holes. I understand the ergosphere may somehow be generated due to a spinning action of a black hole. I wonder if a spin may be caused due to the initial collapse process. If we have a fast rotating star that collapses, we could see this association being passed on to the black hole. However if the star's spin is much slower, perhaps during the collapse the material ceases to rotate. It's like the collapsing material creates enough drag to stop the rotation. I think what we could see is both types in existence. It could also be an evolutionary process whereas the black hole would be formed with a similar rotation as did the star to which formed it. Since this spin would exist in the beginning stages, thus so would the ergosphere. As the black hole matures it's rotation could be slowed as it takes on material. The rgosphere shrinks allowing more material to be consumed by the black hole at this point. Could explain the black holes that seem "dormant".

 

[DrRocket]

I think the high density to form the black hole still comes from the collapsed star. We just see different processes going on. First we have a standard size black hole (i.e those that exist outside galactic centers), and those super-massive black holes. I understand the ergosphere may somehow be generated due to a spinning action of a black hole. I wonder if a spin may be caused due to the initial collapse process. If we have a fast rotating star that collapses, we could see this association being passed on to the black hole. However if the star's spin is much slower, perhaps during the collapse the material ceases to rotate. It's like the collapsing material creates enough drag to stop the rotation. I think what we could see is both types in existence. It could also be an evolutionary process whereas the black hole would be formed with a similar rotation as did the star to which formed it. Since this spin would exist in the beginning stages, thus so would the ergosphere. As the black hole matures it's rotation could be slowed as it takes on material. The rgosphere shrinks allowing more material to be consumed by the black hole at this point. Could explain the black holes that seem "dormant".

Black hole or no black hole, you still have conservation of angular momentum. The angular momentum of a black hole is the angular momentum of the material that was involved in the formation and anything else that entered it. That angular momentum is not and cannot be changed by any internal process. There is a process for interaction with the rest of the universe (see the link that I posted) suggested by Penrose that could eventually reduce the angular momentum of the black hole -- which appears as angular momentum elsewhere.

 

[xXTheOneRavenXx]

meh, it was just a suttle guess