How can a blackhole crush matter into infinite density?

[Syntho-sis]

I don't believe it's possible. I read it in the 'Scientific American Desk Reference' where it talks about black holes. Can somebody please explain this?

[iNow]

AFAIK, blackholes do NOT crush matter into infinitely dense bits, but instead rips apart matter into infinitely small pieces. This is due to the tidal effects. The gravitational pull on the part of the object (or particle) which is closer to the blackhole center is stronger than the gravitational pull on the other side of the object (the part farther away from the blackhole center), and hence the object gets spaghettified. It's pulled and stretched until it rips, then the pieces which result from the rip get pulled and stretched until they also rip... and this process continues until there's simply nothing left to rip.

[insane_alien]

well, the only force that repulses the particles is electromagnetic in nature. and as the particles can only exhert a repulsive force inwards as space is so warped that all paths lead to the center, it is reasonable to assume that the particles are confined to a very small area. it is probably wrong to think of it as infinite density as it will occupy a plank volume at the very least.

[Klaynos]

We don't really know what happens at the centre of a black hole, yet. GR tells us that it should be an infinitely dense point.

[Spyman]

Singularity

 

At the center of a black hole lies the singularity, where matter is crushed to infinite density, the pull of gravity is infinitely strong, and spacetime has infinite curvature. This means that a black hole's mass becomes entirely compressed into a region with zero volume. This zero-volume, infinitely dense region at the center of a black hole is called a gravitational singularity.

 

The singularity of a non-rotating black hole has zero length, width, and height; a rotating black hole is smeared out to form a ring shape lying in the plane of rotation. The ring still has no thickness and hence no volume.

 

The appearance of singularities in general relativity is commonly perceived as signaling the breakdown of the theory. This breakdown, however, is expected; it occurs in a situation where quantum mechanical effects should describe these actions due to the extremely high density and therefore particle interactions. To date it has not been possible to combine quantum and gravitational effects into a single theory. It is generally expected that a theory of quantum gravity will feature black holes without singularities

http://en.wikipedia.org/wiki/Black_hole#Singularity

[Syntho-sis]

At the center of a black hole lies the singularity, where matter is crushed to infinite density, the pull of gravity is infinitely strong, and spacetime has infinite curvature. This means that a black hole's mass becomes entirely compressed into a region with zero volume. This zero-volume, infinitely dense region at the center of a black hole is called a gravitational singularity.

 

^That's pretty much what my book said. Wouldn't an infinite pull of gravity require and infinite mass on which to exert force?

 

 

How would we know matter exists in infinite density at a singularity though? Maybe it's just an extremely high value?

 

I mean think about it. What's the maximum density matter can have anyway? What the crap does 'infinite density' even mean on a subatomic level? Are the particles entirely close or do they almost meld within one another?

[Sisyphus]

^That's pretty much what my book said. Wouldn't an infinite pull of gravity require and infinite mass on which to exert force?

 

No. The pull of gravity is inversely proportional to the square of the distance from the center of mass. In a black hole, all of the mass is theoretically in a single, dimensionless point, meaning you can get arbirtrarily close to the center, meaning the pull of gravity as you approach diverges to infinity.

 

For example, a black hole of 1 Earth mass would have 1g of gravity at 1 Earth-radius distance, 4g at 1/2 Earth's radius, 16g at 1/4, 1000000g at 1/1000, etc.

 

How would we know matter exists in infinite density at a singularity though? Maybe it's just an extremely high value?

 

Maybe it is. However, the point is that there exists no known force that would prevent it from collapsing to infinite density, i.e. into a zero-volume, dimensionless point. Once you reach a certain threshold, (the Schwarzschild radius), the force of gravity is strong enough to overcome all other forces that would prevent its collapse. And as it collapses further, the force of gravity only gets stronger.

 

I mean think about it. What's the maximum density matter can have anyway? What the crap does 'infinite density' even mean on a subatomic level? Are the particles entirely close or do they almost meld within one another?

 

We don't know of anything that would limit density. As far as we know, all of the mass occupies the same mathematical point. AFAIK the most fundamental particles don't have any inherent volume in themselves (I may be wrong about that), they just occupy space because of the forces that repel them apart and bind them together.

[ajb]

In the context of a classical theory, like general relativity infinite densities are encountered. They are usually understood as a sign that general relativity are not complete. This is not really unexpected as quantum theory is not taken into account.

 

Questions like maximum density before black hole formation are not very well understood, maybe apart form the spherically symmetric case.

 

Anyway, it is expected that quantum effects will smear out any infinities encountered in classical gravity. Thus, I doubt any body thinks that infinite densities and curvature singularities are a reality.

[Mr Skeptic]

I don't believe it's possible. I read it in the 'Scientific American Desk Reference' where it talks about black holes. Can somebody please explain this?

 

Well almost everyone agrees with you. The singularity is a prediction of general relativity, due to the fact that no known force can at that point counteract the force of gravity. However, in practice it doesn't matter since we can't get any closer to a black hole than the event horizon and still be able to report back. These supposed points of infinite density are always confined to a sphere of finite volume and density that we can't in any way examine the insides of.

 

Many people take the predicted singularity at the center of a black hole as a failing of general relativity, but then again there's no way to look and see.

[ajb]

Many people take the predicted singularity at the center of a black hole as a failing of general relativity, but then again there's no way to look and see.

 

Mathematically, describing singularities is quite involved. The generic definition is that a Lorentzian manifold is singular if it is geodesically incomplete. (Forget about energy conditions, non CTC's etc for the moment) That is that affine parameter cannot be extended to infinity.

 

Physically this is not very satisfactory. Simply put, (timelike) geodesics are the paths of particles in free-fall and being singular means we cannot just "sit there and watch the particle for ever". In some sense it "falls off the manifold".

 

General relativity does not rule out singular Lorentzian manifolds as solutions. In fact it seems that most physically reasonable Lorentzian manifolds are singular. So they seem part of the theory. Thus, we conclude that general relativity cannot be complete.

 

Like I said, this does not really come as a surprise.

Edited November 19, 2009 by ajb

[Syntho-sis]

Well almost everyone agrees with you. The singularity is a prediction of general relativity, due to the fact that no known force can at that point counteract the force of gravity. However, in practice it doesn't matter since we can't get any closer to a black hole than the event horizon and still be able to report back. These supposed points of infinite density are always confined to a sphere of finite volume and density that we can't in any way examine the insides of.

 

Many people take the predicted singularity at the center of a black hole as a failing of general relativity, but then again there's no way to look and see.

 

Is it possible that there's some unknown force we haven't discovered yet? I'd bet money that elementary particles do some veryyy strange (Not behaving normally) things within a black hole. They are so mysterious and fascinating at the same time.

 

I just realized something. Since photons are massless (at rest), how is it that they can have density? By definition since there is no mass, there should not be any volume which means density cannot exist if a photon is confined to an infinitely dense point. huh?

 

But then, on acceleration a photon has mass- because of gravity. Is this a constant value or is it proportional to the force exerted by gravity on it?

 

How does gravity even affect it in the first place, if there is no mass for it to act on when it is accelerating?

[insane_alien]

Energy and mass are different facets of the same thing.

 

and taking a photon at rest is an invalid frame.

[Mr Skeptic]

Is it possible that there's some unknown force we haven't discovered yet? I'd bet money that elementary particles do some veryyy strange (Not behaving normally) things within a black hole. They are so mysterious and fascinating at the same time.

 

Bet as much as you like. We can't ever look inside black holes.

 

I just realized something. Since photons are massless (at rest), how is it that they can have density? By definition since there is no mass, there should not be any volume which means density cannot exist if a photon is confined to an infinitely dense point. huh?

 

 

But then, on acceleration a photon has mass- because of gravity. Is this a constant value or is it proportional to the force exerted by gravity on it?

 

How does gravity even affect it in the first place, if there is no mass for it to act on when it is accelerating?

 

Photons have zero rest mass, but are never actually at rest, instead always traveling at c. They have non-zero relativistic mass, all in the form of kinetic energy.

[Syntho-sis]

Photons have zero rest mass, but are never actually at rest, instead always traveling at c. They have non-zero relativistic mass, all in the form of kinetic energy.

 

I read some thing where this guy used E=mc^2 to convert sunlight to pounds or something. Like the sunlight to hit Earth in 100,000 years equaled so many pounds. I thought that was kinda strange. For one thing the photons even converted to pounds would need to remain at c in order to have mass? If they were at rest, then they wouldn't have mass..

 

I have another question though. You say photons have a non-zero relativistic mass, which I'm guessing means that they have a mass that exists relative to something which would probably be the speed of light, correct?

 

Is there really anything there though? I mean if photons are considered massless, what causes the forces to act upon them? You say acceleration induces gravity, but in order for something to accelerate it must have mass! It's a bit confusing.

 

Or if you say its just small packets of energy, well then you would have matter and thus mass and thus volume and density.

 

So maybe photons are just kinetic energy? Like insane_alien said. Caused by the acceleration of the photons.

 

So it seems to me that:

 

Photons exists to move, and move to exist?

 

I'm done ranting. Is that the correct assumption?

[Sisyphus]

I read some thing where this guy used E=mc^2 to convert sunlight to pounds or something. Like the sunlight to hit Earth in 100,000 years equaled so many pounds. I thought that was kinda strange. For one thing the photons even converted to pounds would need to remain at c in order to have mass? If they were at rest, then they wouldn't have mass..

 

Photons have energy. The E=MC^2 equation gives the equivalence between energy and mass. So any type of energy can also be expressed in terms of mass.

 

I have another question though. You say photons have a non-zero relativistic mass, which I'm guessing means that they have a mass that exists relative to something which would probably be the speed of light, correct?

 

They have momentum proportional to their frequency, and this is in turn dependent on frame of reference. i.e. moving towards a lightsource will blue-shift the incoming photons, and so they will have more energy. (They will still have a velocity of C relative to you, though.)

 

Is there really anything there though? I mean if photons are considered massless, what causes the forces to act upon them? You say acceleration induces gravity, but in order for something to accelerate it must have mass! It's a bit confusing.

 

Light follows geodesics, which basically means "straight lines" accounting for the curvature of space. Mass curves space, and so a beam of light passing by a mass will appear to "bend" as viewed from an outside observer. It never turns, though, or accelerates in any other way. It only travels at C in a straight line.

 

Black holes bend space so much that any straight line inside a certain radius will just lead elsewhere within that radius. There is literally no way out.

 

Or if you say its just small packets of energy, well then you would have matter and thus mass and thus volume and density.

 

So maybe photons are just kinetic energy? Like insane_alien said. Caused by the acceleration of the photons.

 

So it seems to me that:

 

Photons exists to move, and move to exist?

 

I'm done ranting. Is that the correct assumption?

 

I don't know what the rest of this means.

[Thikr]

Correct me if I'm wrong but as of yet, we do not even know for sure if Electrons (and other sub-atomics) even have a "volume" per se. As far as I know (from internet sources), they are singular points, possibly infinitely small, emitting a repulsive radiation (negative electromagnetic for electrons.) In this sense, the force of gravity at or near a singularity, could simply compress the energy waves emitted by the electrons (effectively compressing the electron itself.) If applicable at all to other subatomic particles, a singularity could in theory, compress matter at a quantum level to arbitrarily small spaces. First post on the forum by the way, hi all!

[J.C.MacSwell]

 

I'm done ranting. Is that the correct assumption?

 

Well. You did click submit reply.

[ajb]

Correct me if I'm wrong but as of yet, we do not even know for sure if Electrons (and other sub-atomics) even have a "volume" per se. As far as I know (from internet sources), they are singular points, possibly infinitely small, emitting a repulsive radiation (negative electromagnetic for electrons.)

 

Well the notion of a size of a particle is more involved than you might think. A classical particle is taken to be point-like. However, it does have an effective size due to its interaction with force fields.

 

The size is all to do with how other particles scatter of it. Have a look at the Wikipedia article on cross-section.

[DrP]

I was going to post this as an idea in speculations, but I think it is relavent here. I might have seen a discussion similar to it in the past, which got ripped apart, but anyhow, this is what I have been thinking recently in relation to infinite mass at a point and have been meaning to ask about it again in speculations.

 

At absolute zero there is no energy left in a system and things stop vibrating. You get something really weird happening where electrons can actually break all of their exclusion laws and actually occupy the same energy levels as each other. This means, I assume, they can occupy the same space. This is called a Bose-Einsten condensate.

 

My speculation is that at the other end of the scale with infinite presure, temperature, mass and presumably gravity, at the centre things are SO tightly crushed and compact that there is no longer any room for vibrations to take place (if light cannont escape or move out - nor can matter, even down to the level that the can be no vibraction as this would mean matter moving away from the centre during half of the oscilation). If this is the case then this is similar to the situation at 0K where there is no energy or vibration and everything colapses into the B-E condensate. Maybe at infinite pressue, K, and gravity matter ends up collapsing into the same volume in a similar way to the how it collapses into this B-E condensate so that not only do we now have electrons in the same energy levels, but all matter in the volume co-existing within the same volume, which would be impossible under any other conditions other than infinite density.

 

I would like to call this 'state' of matter "The DrP condensate" if no-one has any objections. I'll do the maths later on..... Obviously matter with infinite energy is alot different to electrons with zero energy, but I reckon that all the mass is broken to it's smallest particles and even busted into pure energy inside the black hole, thus allowing (at the infinite density inside the singularity) ALL of the individual quantised bits to occupy the same wave function / energy level (because there is no more vibration and they fall into the Bose-Einstein or the DrP condensate). Thus any extra mass or energy that gets sucked in past the event horison will be stripped to base sub attomic particles and then further broken to pure energy and then crushed into the same wavefunction as the rest of it as one super massive, but infinitely small point - the singularity.

 

Any thoughts?? Is this pure crap or resonable speculation. Obviously I am joking about calling this the DrP condensate - but I think this superposition of matter could be possible under the right conditions - such as in a black hole.

[ajb]

At absolute zero there is no energy left in a system and things stop vibrating. You get something really weird happening where electrons can actually break all of their exclusion laws and actually occupy the same energy levels as each other. This means, I assume, they can occupy the same space. This is called a Bose-Einsten condensate.

 

At absolute zero the vibration of the molecules/atoms etc. is minimal, but not zero. Quantum mechanics means we cannot have absolutely no vibration. It is a fact that the ground state of a quantum mechanical harmonic oscillator is non-zero.

 

I think by "fermions breaking the exclusion principle" you are referring to Cooper pairs.

 

Cooper in 1956 showed that due to a tiny attractive forces between electrons in a metal at low temperature electrons form pairs. The energy of which is lower than the Fermi energy. (maybe why you said no vibration?)

 

These bound pairs behave as a bosonic pseudo-particle. Thus they can be in the same state and condense into the ground state. This is an important mechanism in supercondustors.

 

You must note however, that we have pseudo-particle bound pairs and not fundamental particles. The bosonic nature is a collective phenomena within a metal.

[DrP]

^ What the crap does 'infinite density' even mean on a subatomic level? Are the particles entirely close or do they almost meld within one another?

 

This is what I'm talking about exactly - I'm suggesting a total collapse such that the wavefunctions of the smallest sub-attomic particles actually superimpose on each other, much the same as electrons do in a Bose-Einstein condensate. (pure speculation though).

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Merged post follows:

Consecutive posts merged

At absolute ..within a metal.

 

Thanks - I know it's not the same, I'm just saying that under extreame conditions some laws get broken. Something happens in a black hole that we can't explain and I rekon we might end up discovering some kind of situation where matter gets super imposed or space gets folded in or something else we don't know about yet. It's just recently I've been thinking about it all occupying the same space by collapsing into the same wavefunction - similar only to the B-E condensate as far as I know.

Edited December 8, 2009 by DrP
Consecutive posts merged.