What is the Dark Matter Problem, and can WIMPS or MACHOS solve it INTRODUCTION The concept of Dark Matter is a difficult one to wrap your brain around. Because it cannot be seen directly, scientists must indirectly infer its presence based on the movements of astronomical objects, i.e. stellar, galactic, and galaxy cluster/supercluster observations. If we measure the velocities of these objects in a specific region, there must also be some large quantity of mass that enables gravity to prevent the objects from dispersing throughout space. When these calculations are done on a large scale, we find that there is much more inferred mass than can be accounted for by luminous objects. Therefore, we infer the existence of dark matter. Furthermore, dark matter holds significance concerning the evolution of the universe and the structures within it. Flat, Open, and Closed Universal Shapes 
Dark matter Not dark matter 
According to Einstein's theory of general relativity, the universe must take shape to one of three possible types: flat, open, or closed. Once all matter and energy in the universe can be accounted for, the evolution of the expansion of the universe can be determined. This process begins with the understanding and evaluation of two categories of dark matter candidates: non-baryonic (WIMPS) and baryonic (MACHOS).
Dark Matter rings detected by Hubble THE DARK MATTER PROBLEM The concept of dark matter has yet to be fully explained by scientists. Dark matter is a hypothetical matter that is believed to exist in our universe. In fact, it is believed to account for about 90% of all matter. It cannot be seen directly but its existence is show by the gravitational effects on the matter that is visible. It is believed that dark matter is much more massive than all visible matter in the universe. Dark matter, though undetectable to the human eye, is an important player in galaxy formation. Oddly, such an important piece in understanding how the universe works, there is still very little known so little about it. Images from space reveal its affects on galaxies and stars. Dark matter explains why disk stars in most spiral galaxies move at constant speeds around their galactic cores-a constant speed requires extra gravitational pull and therefore suggests the presence of dark matter Two dark matter candidates have been proposed: baryonic dark matter and nonbaryonic dark matter. Baryonic dark matter, consisting of protons and neutrons, can only account for a portion of the dark matter in the universe. Accordingly, another solution arises. Nonbaryonic dark matter refers to the type of substance containing no atoms and does not interact with electromagnetic forces, such as black holes, axions, and supersymmetric particles. This type has been broken down into three separate groups, hot, warm, and cold dark matter. Hot dark matter consists of particles that travel at unrelativistic velocities. Warm dark matter consists of nonbaryonic particles that move relativistically in regard to velocity. Cold dark matter consists of nonbaryonic particles that move non-relativistically in regard to velocity. As of now, one type of hot dark matter is known, the neutrino. Neutrinos have a very small mass and do not interact with electromagnetic forces (which explains why it cannot be seen). This alone, however, isn’t enough to explain the mysteries of dark matter.
The problem with all of this dark matter theorizing is that scientists simply aren’t sure exactly how to prove it and find out its composition. Studying dark matter is a great challenge for cosmologists and astronomers. Attempting to study something that cannot be directly seen is difficult, but new methods of detection are advancing each day.
WIMPS Some Physicists have a smaller solution to the “missing mass problem”. They theorize that 90% - 99% of the mass missing is due to the existence of tiny particles of matter that don’t interact with known matter in any known way. These nonbaryonic particles, called WIMPs (Weakly Interactive Massive Particles), cannot interact with matter in ways that are detectible by modern science . As the theory is currently constructed, these WIMPs behave similarly to a particle known as a neutrino, in that they have no electrical charge and can pass through matter itself. This dark matter cannot be made entirely of neutrinos however, because neutrinos would not account for the huge amounts of mass undetectable by scientists. These WIMPs would have to be significantly more massive than neutrinos. The probability for the existence of such particles is high, and even proponents of the MACHOs theory admit that they probably exist. Some physicists even go as far to suggest that WIMPs are the dark matter that started galactic formation.
The detection of these particles is something that is being pursued currently. Despite the probability of such a particle existing, the fact that they rarely or never interact with ordinary matter makes them almost impossible to detect. However, experiments are being constructed hoping to observe a WIMP interacting with ordinary matter. Attempts to detect WIMPs are being made. One experiment involved freezing a crystal to almost absolute zero in the hopes that any interaction that WIMP would have with regular matter would register in the form of heat. Other projects include placing WIMP detectors far underground in Antarctica to use the ice sheet as a detector itself. As recent as 2008, as team called Dama claims to have detected these dark matter particles using a detector more than a mile underneath the Gran Sasso mountain in Italy.
MACHOS
MACHOs, which stands for Massive Compact Halo Objects, are large bodies that are commonly found in the halos of galaxies. They are heavy objects that are one possibility for the missing dark matter in the universe. These objects are very hard to detect because they cannot be seen; however, there is a technique that will allow for the discovery of these objects.
MACHOs can be detected by Albert Einstein’s theory of General Relativity. This theory, proven by Arthur Eddington in 1919, says that gravity will warp the fabric of space and the more gravity an object has, the more it can warp space. General Relativity can be applied to MACHOs by using distant stars. When a MACHO passes a star, the gravity of the MACHO bends space around the star so when the light from the star travels through the warped space, it becomes magnified. The star undergoes gravitational lensing when the MACHO passes in front of it and this makes the star appear to grow and move. This then allows astronomers to weigh the MACHO.
CONCLUSION
So what have we learned? Like many of the mysteries we face in the Universe, there can be no single, resolute solution that accounts for the problem surrounding dark matter- not yet anyway. For now, all we can do is speculate. While both WIMPS and MACHOS each present compelling arguments, it is more likely that the two are not independent of one another- that, to provide a truly more "whole" solution requires the understanding and consideration of each theory. Still, there is more to be learned about the mysterious dark matter that is, without doubt, an omnipresent force in our universe.
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Sources:
“MACHOS”. BBC. Science & Nature: Space <http://www.bbc.co.uk/science/space/deepspace/darkmatter/ machos.shtml> Miller, Chris. "Cosmic Hide and Seek: the Search for Missing Mass." Eclipse.1995. 7 Dec. 2008 <http://www.eclipse.net~cmmiller/ DM/>. Science Beat: Berkley Lab. 2 Mar. 2000. 7 Dec. 2008 <http://www.lbl.gov/Science-Articles/Archive/dark-matter- CDMS.html>. White, Martin. Dark Matter. 6 December 2008. <http://astro.berkeley.edu/ ~mwhite/ darkmatter/dm.html> Yarris, Lynn. "Findings by Lab Collaboration Contradict Dark Matter Claim."
