'Exotic matter,' is a hypothetical form of matter that has both a negative energy density and a negative pressure - it is thus, an antigravity substance. All states of known matter have a positive energy density and pressure that are always less than the energy density in magnitude. A good example of energy density you may have heard of is in a stretched rubber band; when a rubber band is stretched, its energy density is about 100 trillion times greater than the pressure. If such matter could be created, it might help us to manage faster-than-light travel, or using it to grow wormholes big enough for human transportation back in time, as we saw in part titled 'time.'
Exotic matter is non-baryonic; and one form of exotic matter is called 'dark matter' - called dark matter, not because it is a darkly colored mass, but because scientists have no idea what it is. (Most) dark matter in the universe will be non-baryonic - and scientists are confident 20-25% of all matter in the universe is made up of the hypothetical and mysterious dark matter.
At the birth of our universe, 15 billion years ago, all that existed was a hot primordial soup of erratic particles. As the universe began to cool down, ordinary particles such as neutrons, protons and electrons started to join together to form stable atoms, forming all the elements we see today - which was predominantly helium and hydrogen atoms. The theory of element-making in the first few minutes of the universe was called, 'the big bang nucleosynthesis,' and is recorded in the 'standard model'. The theory was good in predicting hydrogen and helium to pervade our part of the universe. However, the theory, it turns out, relied rather sensitively on the amount of baryonic matter that the universe had available - and the big bang nucleosynthesis predicts the right ratio's for the produce of elements in our universe today - even if 15% of the critical mass of the universe was suffice in stopping cosmic expansion (big crunch).
Of course, it may turn out that our predictions are flawed. However, because the prevailing view that the standard model predicts at least more than 15% of all matter is made up of dark matter, we can be sure that most of all dark matter are not made up of baryons - and since we are not made up of dark matter, it must be another type of matter that accounts for the dark matter. We are made up of protons, neutrons, gluons, electrons, quarks ECT. - Just to mention a few. Some dark matter might be well-known. Some scientists think that the 'neutrino' particle is in the family of dark matter. Billions upon billions of neutrino's pass through our body every second, spurted out by the sun. For a while, scientists thought that the neutrino might not contain mass, and moved like a luxen particle; like a photon, and traveled at the speed of light. Yet, this hypothesis was proven to be wrong, as it was shown to have a small mass after all. Another hopeful candidate for non-baryonic dark matter goes by the acronym of 'WIMPS' - Weakly Interacting Massive Particles, that belong to a class of hypothetical heavy elements that hardly interact at all with common matter - hence the fact we have not discovered any as yet - heavy elements does not need to mean anything special - one heavy element we know of here on earth is iron but of a different class. Some think that the WIMPS do not exist - basing this on the evidence that we have never seen one of these hypothetical particles, like the 'axion'. German scientists are planning an experiment that is essentially designed to 'tease' out dark matter in the form of the exotic particles that can travel through hard physical substances, like a mountain - just like the Axion Particle.
Dr. Andres Ringwald of DESY laboratory hopes to use a magnetic field to transform a laser beam of photons into axion-like particles. He say's, 'the idea is to send a laser beam along a transverse magnetic field, a fraction of the laser photons will transform into the new particles and travel freely through a wall without being absorbed. Finally, another magnetic field located on the other side of the wall can transform back some of these particles into photons - apparently from nothing.' The discovery of exotic matter, if found through these experiments will extend the standard model of particle physics; some results that may even seem science-fiction-like, just as the good Dr. informs us, 'suppose that photon regeneration does work - you could set up an axion beam radio. Place the first part of the experiment somewhere to emit the beam and the second part far away, but in line with the first. You could then transport photons - and thus signals - over long distances through materials that normally absorb photons, such as rock and sea water.'
Scientists are sure these Wimps particles exist, and are in close rival of 'MACHOS' - Massive Compact Halo Objects. According to the theory of MACHOS, galaxies like our own are cocooned by exotic systems of dark matter haloes, which are populated by luminous objects, such as 'brown dwarfs', which is the remnant of a Red Giant. We can use specialized lenses, that can focus and bend light rays from a source behind the observable objects, like a shadow play. This is called 'microlensing,' and has had some success - some scientists think we might be able to detect the MACHOS using this technique - using the same technique, they have discovered the presence of planets previously not detected.
However, not enough MACHOS have been found to account for a fifth of all dark matter - however, as you can guess, because Macho's are made out of baryons, they will be restricted by the big bang nucleosynthesis predictions, since baryonic matter makes up a fraction of all the matter in the universe. This must mean, that our calculations say that MACHOS are ruled out for having the bigger slice of dark matter pie. Another way to catalogue dark matter is to say whether it is of the 'cold' or 'hot' varieties. Very light dark matter that moves a fraction shy of 'c' - the speed of light - is called hot dark matter. Cold dark matter is accounted for by WIMPS. There is, as scientists suspect, more cold dark matter than the hot varieties - just like we have more Bradyons than Luxens in our part of the universe.
We also know that, whatever dark matter is made out of, it will be a major gravitational producer in the universe. Thus, scientists suspect that the missing dark matter most probably helped in the formation of galaxies. In fact, there will be entire galaxies made up of dark matter. Most of these galaxies will look like our own - others like colorful clouds, set out in all their array, as if it where on a magicians darkened stage.