Steven S

Actually, this is not possible. If you start boxing in a particle like a quark into a smaller and smaller space the momentum of the particle will increase and thus so will the kinetic energy.
This will provide an intrinsic pressure against
gravity plus since quarks are fermions and thus have an antisymmetric wavefunction there will be a degenerate pressure acting against gravity also.
So your idea is already unphysical since we can't regard quarks as marbles. Now, I can't answer your remaining questions since I don't know enough particle and nuclear physics to say when gravity will break the degeneracy pressure. However, I will be attending a mini-seminar in a couple of weeks on the subject of quark stars so maybe that will shed some light on this problem.

Steven S

Bill

I would say that the exact internal structure of a black hole is a matter of considerable debate (and speculation) among scientists. As others have noted, the idea of "infinite density" is repulsive to most scientists (as is the idea of any actual infinity).

I personally side with those who would assert that a new theory of physics at the smallest scales is necessary before we can hope to understand how best to MODEL reality. The model, of course, need not actually represent the full and complete state of reality for it to be useful. At this point, a more useful model need only unify relativity and quantum mechanics to be useful. No such model is widely accepted at this point in time, although many scientists believe that string theory holds out the most promise for EVENTUALLY evolving into the aforementioned useful model.

The event horizon is the gravitational "can't get back out again" point. There need not be any actual particles of matter at the event horizon. However, there certainly are at least some particles of matter there because we can measure the phenomena of external matter passing through the event horizon, interacting with the matter which is there, and then emitting detectable energy (which is how we have verified the actual existence of black holes, which are otherwise invisible to observation).

Kenetic energy in particle physics is a function of (among other possible things) the heat level of the matter. Heat excites greater kinetic energy in particles, and the absence of heat causes the particles to assume a rest state (at least, with respect to other particles at the same "absolute zero" energy level). Since one of the measures of temperature is the kinetic energy level of the particles, this raises the rather interesting paradox that if the particles within the interior of the black hole are not actually moving with kinetic energy, then the temperature of the interior of the black hole might well be said to be at absolute zero. As has been noted above, the amount by which gravitational force can suppress kinetic energy levels in particles is a matter of some debate.

As we learn more about physics at both the largest and smallest scales accessible to our instruments, we keep discovering new things, some of which are inconsistant with present theories and which thus must force an evolution in the underlying theories. My best guess is that it is way too early to be able to give an unequivocal answer to the sorts of questions you pose about the interior of black holes.

== Bill

Answerer

Sorry Hans, is me again. Well, field particles and leptons are definately smaller than quarks if they are being compared. Furthermore physicists are not very certain that quarks aren't made of smaller particles yet. So, with this lack of knowledge, i don't think that they could tell you what the quarks will break down or decays into inside a black hole.

Friar Bellows

At some point, doesn't pressure actually contribute to gravity? Doesn't the stress-energy tensor (the source of gravity according to GR) contain a pressure term (in addition to the familiar energy density term)? So maybe rather than counteracting gravity, in highly degenerate stars (like neutron stars) the pressure can become so great that it can be considered partly responsible for the subsequent collapse of the star into a black hole? Maybe a quark star, despite being much denser than a neutron star near the stability limit, has a smaller degeneracy pressure (no idea how that's calculated, but probably need to use QCD!) and so it remains stable? Maybe rotation can affect things, too?

I'm clueless, just asking naive questions.

[ April 19, 2002: Message edited by: Friar Bellows ]</p>

Hans

Steven S

Wouldn't the kinetic energy eventually be radiated away?

That quarks can't be regarded as marbles may be the crux of my misunderstanding.

I understand density as the amount of mass in a given volume. The more mass per volume the higher the density. We say a neutron is of a particular density. But can a neutron be crushed to a yet smaller volume? Are the quarks that compose a neutron in virtual contact so that to force a neutron into a smaller volume would require that the quarks themselves be reduced in volume instead of any space between quarks being reduced?

And I'm running into a paradox following this line of thinking. It seems to require that for infinite density to exist would require infinitely dense subatomic particles of which all matter is composed but seperated by subatomic forces. But infinitely dense particles (be it quarks or something even smaller) would need one of two properties: A) Occupy zero space. or B) Have infinite mass. "A" is confusing in the least and "B" is obviously wrong. Zero space that has mass?

So what the heck is a quark??

liquid

A quark is a particle that forms protons and neutrons (in groups of threes). They come in six varieties - up, down, bottom, top, strange and charm, IIRC. These varieties are called flavours. In fact, if memory serves, I think they are named after a line of shakespeare or some other piece of literature which goes something like:

"Three quarks for Mr. ......" - or is it quarts? Anyway, physicists seem to like odd names.

They have charges in thirds, lke 1/3, and that's about as much as I can remember!

Hans

A black hole having a mass of one million solar masses will produce an event horizon of a predictable radius. We'll say radius equals X.

My question is will a hypothetical one million solar mass ball of quarks have a radius that is equal to, greater than, or less than X?

Do quarks have a three dimensional radius that the above question could be calculated? Assuming you could put a big pile of quarks together without them reacting with each other. And/or do the even smaller particles (field particles and leptons) as Answerer mentioned have a 3 dimensional radius?

Bill

Well, you've just grasped the essence of string theory. The whole business rides on the idea that so-called "point particles" can't really exist. There must be a "smallest thing," and it cannot be a "point particle" that occupies zero space and yet has mass. Once again, the idea that the interior of the black hole has "infinite density" must obviously be wrong, in spite of any acceptance of that idea in the field of cosmology.

== Bill

fando

I wonder why people are uncomfortable with the idea of a singularity in spacetime. I don't think that the possibility has ever been ruled out, and probably will never be. It seems astounding to me that people would proclaim that singularities are obviously impossible without any basis for their claim. To know for sure would imply a very deep knowledge that is beyond the scope of modern physics, and possibly any physics we can discover!

The idea that spacetime cannot have a singularity is a conjecture. The motivation is probably due to the unpleasant consequences that discontinuities in our "reality" will have. Specifically, a discontinuity in spacetime implies that the universe isn't closed and self-consistent. To explore the physics of such a universe, we would need an exo-physics that deals with the beyond, for lack of a better term. Does the matter in a singularity fall off our universe? If so, why do we still experience the curvature in spacetime caused by the pressence of the mass? We don't have the heuristic tools or experimental know-how to learn of such things, so we're better off finding an alternative explanation that would keep the universe closed and self-consistent.

To reiterate, it isn't obvious that singularities are impossible. We merely don't like the direction that embracing such a possibility will lead us.

Bill

It also is not obvious that either flying, fire-breathing, dragons are impossible; nor is it really obvious that an invisible pink unicorn is impossible.

But believing in either of those mythical beasts is clearly contra-indicated by the true nature of reality. So too is the belief in singularities, as point particles with infinite density. Singularities are quite ludicrous to contemplate as actually existing in reality.

=====

Among the ludicrous results of an infinitely dense point particle would be the absurd result of infinite mass. So far, we have not discovered any astronomical body that has infinite mass. And, if we did discover such a thing, would not the next conclusion be that it had an infinite amount of gravitational attraction towards all matter contained within our universe? And with those conclusions in place, should we not be rusing towards that point of infinite density at the speed of light, again along with all of the other matter in space?

But, exactly the opposite effect is taking place. We are instead rusing AWAY from all other matter in our universe. So, we can turn the above logic around: 1) there is no infinite source of gravitational attraction; 2) there is no infinite mass located at some point in space; and 3) there is no actual singularity.

I'm afraid that the evidence clearly points to the fact that actual singularities do not exist. So, upon what basis can you conceivably claim that their actual existence is even POSSIBLE?

== Bill