Dark Matter, What is it?

I have a question for all you science gurus. As I understand it, concerning the big bang theory, for a short period of time both matter and antimatter existed at the same time. Therefore, my question is, could dark matter be the result of incomplete combustion between matter and antimatter, for example formation of great quantities of neutrons?

Also, would antimatter have the quality of antigravity, if normal matter has an attractive force, I.E. matter attracts matter, otherwise known as gravity, would antimatter repel? In other words would an anti hydrogen atom repel another anti hydrogen atom? If so could this explain the uniformity of the cosmic microwave background radiation? In other words the antimatter dispersed itself somewhat evenly before becoming annihilated. Is this possible?

Perhaps you folks have a deeper insight into the subject. I’m just curious.

Thanks,

----Cesar

I'm not an expert but I can answer some of this.

When matter and anti-matter meet, there is a fantastic explosion. There is no "incomplete combustion". Either they annihilate one another or they never meet.

No one knows what Dark Matter is. To be perfectly honest, no one knows if it even exists, and there are more than a couple physicists with serious doubts. But if it exists, it seems to be matter that is affected by gravity, but not by electromagnetism. In other words, it can tug on you, but you can't see it.

Anti-matter reacts with gravity the same way normal matter does (we think). It is electromagnetism that it eschews. Anti-matter does not repel itself.

The only matter I know that can’t be seen would be matter below the 400-nanometer spectrum. I’m not sure if hydrogen is below 400 nanometers but I know atomic particles are.

If the universe was indeed born violently, visually then, it is conceivable that after the big bang a significant quantity of particles below the 400-nanometer range could have been dispersed to the point where they cannot interact with each other to form matter above the 400-nanometer spectrum. The outside residue if you will. Over time the distance of these particles below the 400-nanometer range would be increasing like concentric circles. Is this plausible?


----CS

I have a hard time with the current conceptualizations of Dark Matter. If one supports the theory of a constantly expanding Universe, then one must in consequence, support the Big Bang theory. The stone thrown into the pond, if you will. If the Big Bang theory is correct, then we are witnessing the ever-widening ripples in the pond. Physicists and Astrophysicists are at odds over the concept of Dark Matter, whether or not it exists and if it does indeed exist, what is its composition? The physicists' concept of MACHOS and the Astrophysicists' concept of WIMPS are diametrically opposed. Both sides, however, are in agreement on one point, that Dark Matter must exist, as the Universe would not have coalesced without it. The massive force of the Big Bang would have expelled matter, presumably including Dark Matter, in all directions at phenomenal velocity. A natural conclusion for one to draw would be that the tempering effect of Dark Matter somehow prevented the visible matter from being scattered too quickly, a tempering effect that is also moderating the rate of expansion of the Universe. As of this moment in time, the composition of Dark Matter is a mystery. But like the electron, the existence of Dark Matter cannot in the strictest sense be positively defined. Yet the effects of both can be identified, which may satisfy the quantum physicists in the crowd, but no one else. If Dark Matter is composed of sub-atomic or non-baryonic particles, as WIMPS advocates believe, then the instruments able to discern such infinitesimally small bits of matter do not yet exist. Nor does a mathematical model exist that can reasonably prove the existence of these particles. Consequently, the jury is still out on this theory.

On the other hand, it is hard to lend credence to the evidence offered up by supporters of the MACHOS theory. If Dark Matter can be described as a consequence of the existence of massive yet invisible forces such as Black Holes, would it not be reasonable to assume that the presence of such a force would be in some way discernible?

All the above is contingent on the Big Bang being a certainty. Whether or not the Universe will expand into infinity, whether it will expand to a point and then contract, or whether it will expand to a point and remain static will probably remain a baffling conundrum for theorists for the foreseeable future. It gives me some solace to think of the Universe as a big bowl of Jell-O, with lots of fruit bits thrown in. The Dark Matter being the Jell-O, the visible Universe being the fruit bits.

You wrote:

“If Dark Matter can be described as a consequence of the existence of massive yet invisible forces such as Black Holes, would it not be reasonable to assume that the presence of such a force would be in some way discernible?”

The presents of a force would not necessarily be discernible. Predicated on the above statement, I believe we are entering the area of relativity, in a manner of speaking. The presence of a force would be discernible if and only if it precipitated a contrasting effect to a point of reference. So in essence, how would you measure the effect of the black hole in the center of our galaxy? Our point of reference is inebriated by the presence of the black hole within the center of our galaxy. To put simply we are (the black hole and us) in the same frame of reference (same space).

Additionally, the presence of a force would not be discernible if it acted upon all frames of reference equally, (through out the entire universe) due to the fact that there would be no contrast in the measure of the force. Alas, we are now trapped within a self-referential paradox. I should stop here before this becomes a philosophical thesis.

Needless to say this is a subject of endless fascination with me and perhaps one-day technology will offer deeper insight. However, I did enjoy reading your post.

It's not a function of size. It is simply a matter of not interacting with photons. We don't know that Dark Matter exists, but if it does, it has a gravitational effect but not a photo effect. The molecules could be a kilometer across and twenty feet away and we still wouldn't see them.

There are alternate explanations for what has been observed. Many people think we simply don't understand gravity as well as we thought. Modified Newtonian Dynamics (MOND) is one such theory.

This is not true. There are other possible ways to get the universe expanding without a Big Bang beginning. For instance, Heim Theory predicts three different kinds of gravity, one of which is a repulsive gravity that correlates with Quintessence. Heim Theory does not have room for a Big Bang, but it does achieve an expanding universe through one of its forces of gravity.

This is not to say that Heim Theory is correct, and of course the expanding universe and Big Bang Theory normally go hand in hand, but one can have the former without the latter.

This evokes a question for me. How small can a black hole be?

I assume that the answer has something to do with the amount of mass required to produce a zwarschild radius larger than the volume of the matter contained in it, but I don't know what that would be.

I assume that a clump of neutrons can coagulate into a very small volume, and by doing so become a black hole at a relatively low threshold of mass, but I've never read anything about the minumum mass/volume possible for the formation of a black hole.

I don't believe there is any lower limit on black hole size.

No, any collection of matter has a Schwarzschild Radius that corresponds to its mass. If you compress that matter to the point where its volume fits within its Schwarzschild Radius, it will become a black hole. Under normal conditions, this kind of compression is all but impossible, but when you are dealing with extreme gravitational potential or extreme velocities, this becomes possible.

Neutrons can't "coagulate" into a black hole. In a supercollider, it might be possible to slam two particles into each other, thereby compressing them beyond their aforementioned radii and creating a very small and short-lived black hole. If you want to find out why small black holes don't live very long, look up Hawking Radiation.

This depends on what you mean by a black hole. The actual "hole" itself, according to current theories, has no size. It is matter condensed to a point. If you mean the event horizon beyond which light cannot escape...

... I don't know.

I was under the assumption, according to Hawking's explanation of a Black Hole that, although the centre is indeed a singularity, the Black Hole itself(or the diameter of the Event Horizon) can be of varying dimensions. An interesting simulation on how two Black Holes in close proximity will eventually combine, in the process emitting energy equivalent to 10 billion suns, is available on skyandtelescope.com/skytel. A fascinating by-product of this merging is the emission of gravity waves strong enough to dislodge proximate planets from their orbits.

This post has been edited by THE Golfer on Jan 5 2010, 04:40 AM

im diverting a bit from the subject, and i'm not a science buff but i was wondering about one of the aspects of dark matter. I heard on a documentary that dark matter could pass through solids. if thats true, how can the concept of suction work? imagine a person sucking on a plastic bottle; the plastic would bend inwards as a result of the lack of gas inside the bottle. But if something could go through the plastic, wouldn't it allow for the pressure inside the bottle to remain constant, and thus never cause this?

If it passes through ordinary matter, it doesn't push against it, and so doesn't create pressure.