Supersymmetry is a theory (commonly found in some forms of string theory) that says that when the universe was made, there was also the same number of theoretical "superparticles" created. If this theory is true, it would at least double the number of particles in the universe. Supersymmetry may create more than one copy, since there are many dimensions (some string theories predict up to 11). Many scientists believe in supersymmetry because it solves many inconsistencies in the Standard Model of physics.
Overview of Supersymmetry [change]
A superparticle is the supersymmetric copy of its counterpart (that is, regular matter). A superparticle also has a slightly different spin than its counterpart, by 1/2. Many scientists believe that in the Big Bang, superparticles were created for an almost immeasurably short amount of time (a ten trillionth of a ten trillionth of a nanosecond) before they effectively froze into space (this is their way of saying we don't really know where they went). Note that these "copies" of what we would call normal matter may or may not be identical copies (except for the fact that it will always have a half of a spin difference), depending on the correctness of "unbroken supersymmetry," which simply states that supersymmetric particles are copies of matter with a 1/2 spin difference.
If some of the principles of supersymmetry are correct, then it may be possible to recreate these superparticles with particle accelerators. This attempt could prove or disprove the ideas of supersymmetry.
Dark matter Theory [change]
In outer space, scientists have seen areas of matter that are completely dark. This is not normal, as all known matter reflects light–or absorbs it and reflects it in a different color. Light is a form of electromagnetism (see photon). Some scientists suspect that this means that the matter that is not giving off light may not even interact with electromagnetism. This would explain why they don't emit light, but not why no light would pass through them, as they simply don't interact with electromagnetism.
Many people wonder what "dark matter" is, and scientists do not really have an answer for them. However, a simple answer for this is that dark matter is matter that does not emit light. From now on, the above-mentioned matter will now be referred to as dark matter.
Existence of Dark matter [change]
Around the mid 1930's, scientists predicted the existence of dark matter for various reasons. For example, the spin of galaxies was nothing like how the visible matter would suggest it should. Also, some scientists noticed gravity fields from something that was not visible. They labeled it "dark matter." Many scientists accept that dark matter exists, but not all accept the connection between dark matter and supersymmetry.
Lack of Interaction With Electromagnetism [change]
Strong Force [change]
Matter as we know it is held together by strong force (aka nuclear force). Strong force holds the protons and neutrons together in an atom, and is thought to be a result of the lighter mesons for the interaction between protons. Protons (and neutrons) themselves are made of quarks, which are in turn thought to be held together by gluons. As a result of all of this, an atom nucleus is formed.
Strong force is necessary for an atom nucleus to hold together because apart from the fact that the protons wouldn't stick together, protons actually repel each other because of their electromagnetic charge. (The same statement applies to quarks, but it is due to both charge and chromodynamic forces which are governed by W and Z bosons).
Electromagnetic Force [change]
However, if a superparticle does not interact with electromagnetism, strong force would not be so necessary because the super-protons do not repel each other. However, this lack of interaction with electromagnetism would not allow electrons to orbit an atom nucleus. This poses many new questions about superparticles, as electrons are the reason that you cannot push your hand through a wall without the wall breaking; electrons are negatively charged and repel each other. In addition, electrons are fermions, which basically means that two electrons can't exist in the same place at the same time. Since no electrons would orbit the nucleus, it would be much easier to push two superparticle nuclei together.
It is difficult to imagine how a superparticle could exist if it was only held together by strong force. This is one of the many problems with the supersymmetry theory.