Dark side

A dark side of something is a side of that something where, by definition, it is dark. A dark side is created by blocking all the light that would be going to the desired side with another side. However, this also produces a light side. Therefore, if you wish to create a dark side, the area that will become the light side should be the area that you care about the least, unless you intend to use the dark side for an evil purpose, such as cutting off a the light to a side so that all plants die and people can no longer tan so that everyone is sickeningly pale and you blend in with the crowd, or you want to destroy the potential of solar power because you own and manage an oil company.
A dark side is characterized by its power, or rather its lack of power. A dark side, ironically, finds itself at its most powerful when a power plant stops providing power for its corresponding light side. Even though constantly asked by various evil overlords to do so, Luke Skywalker could never see the true power of the dark side. Actually, he could never even see the dark side itself, because the dark side was too dark for him to see. Maybe you, with the aid of night-vision devices, will be more successful.
==Science==
As everyone knows, light is made of particles called photons that travel in waves. When a photon makes contact with matter capable of reflecting certain wavelengths of light, the photon is reflected off at the angle of incidence, as described by the Law of Reflection. The Law of Reflection states that the direction of incoming light (the incident ray), and the direction of outgoing light reflected (the reflected ray) make the same angle with respect to the surface normal, thus the angle of incidence equals the angle of reflection (\theta _i = \theta _r in the figure), and that the incident, normal, and reflected directions are coplanar. This was first discovered the by the Greco-Egyptian mathematician Hero of Alexandria.
This essentially means that sides of objects in the paths of photons reflect the photons, and in so doing deprive other sides, and even other objects entirely, of light: giving rise to dark sides. As you have probably already hypothesized, sides in the path of light rays are the meanest of sides. How do you think it is that they got into the path of light; by asking nicely? No, those sides pushed, shoved, and clawed their way there, and they won't give up their spots without a fight.
===Creating a dark side===
To create a dark side, one must know how to manipulate natural light so that it cannot penetrate the would-be dark side. The direction of reflection can be calculated directly, without first determining the orientation of the plane of incidence. 
Given an incident direction \mathbf{\hat{d}}_\mathrm{i} and the surface normal direction \mathbf{\hat{d}}_\mathrm{n}, the specularly reflected direction \mathbf{\hat{d}}_\mathrm{s} (all unit vectors) can be calculated as:
:\mathbf{\hat{d}}_\mathrm{s} = 2 \left(\mathbf{\hat{d}}_\mathrm{n} \cdot \mathbf{\hat{d}}_\mathrm{i}\right) \mathbf{\hat{d}}_\mathrm{n} - \mathbf{\hat{d}}_\mathrm{i},
where \mathbf{\hat{d}}_\mathrm{n} \cdot \mathbf{\hat{d}}_\mathrm{i} is a scalar obtained with the dot product.
Assuming these Euclidean vectors are represented in column form, the equation can be equivalently expressed as a matrix-vector multiplication:
:\mathbf{\hat{d}}_\mathrm{s} = \mathbf{R} \; \mathbf{\hat{d}}_\mathrm{i},
where \mathbf{R} is the so-called Householder transformation matrix, defined as:
:\mathbf{R} = 2 \mathbf{\hat{d}}_\mathrm{n} \mathbf{\hat{d}}_\mathrm{n}^\mathrm{T} - \mathbf{I};
\mathrm{T} denotes transposition and \mathbf{I} is the identity matrix.
Everybody obviously understands what that means, so there will be no further explanation of this given.
==Religious significance==
The Sith religion is centered around The Force, which the Sith unwillingly share with the Jedi. Both the Sith and the Jedi use the term "Midi-Chlorians" as a metaphor for their source of power. Contrary to popular belief, Midi-Chlorians are not microscopic organisms. For Sith, Midi-Chlorians are dark sides, while for Jedi, Midi-Chlorians are photons (particles of light). Because of this difference, the Sith base their belief system around only dark sides, while the Jedi base belief system around only photons. Because of this, the Sith are called "The Dark Side of the Force" or simply "The Dark Side". The Sith use dark sides like black holes to capture particles that they then use to enhance their powers. Some of these particles are gravitons, which the Sith use to "Force Jump" and do other acrobatic maneuvers that the average person could not do; and electrons, which the Sith use to create "Force Lightning." Jedi, on the other hand, use photon energy to manipulate gravity by creating gravity bubbles that they can use to do their bidding.
==Appearances in fiction==
*2001: A Space Odyssey by Arthur C. Clarke; film directed by Stanley Kubrick - Part of the story takes place on the Moon, which has a dark side
*"The Raven" by Edgar Allen Poe - takes place at night, which is actually the dark side of the Earth
*Moby Dick by Herman Melville - explores the dark side of obsession
*Star Wars directed by Jerry Mucus (?) (possibly Steven Spielberg) - an obscure sci-fi film that met no success at all. This film allegedly has Sith and the dark side in it, but the film is so unknown that finding a copy is practically impossible, so no one can be sure.
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