Chaos energy

Chaos energy, also known as Emerald forces, is an unstable, yet powerful energy that each Chaos Emerald generates by turning thoughts into power in the games and Sonic X, or by drawing it from the Chaos Force in the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics. This energy can be used for super transformation, to perform Chaos Control and various other abilities, or as a power source for machines. This power can be controlled by the Master Emerald, if requested or commanded by its guardian.

The Chaos Emeralds, including the Master Emerald, have been used before to charge Super States or Eggman's weapons of destruction on many occasions (e.g. Sonic the Hedgehog 3, where Dr. Robotnik steals the Master Emerald to charge the Death Egg). The energy from the Master Emerald is mostly used to keep Angel Island floating in the air.

As the Chaos Emeralds are perpetual power sources, they can be used to power various machines or technology. Like batteries, the emeralds have positive and negative polarity. The positive energy is primarily used by Sonic and his friends to transform into their Super States while the negative energy is used by villains for their powers and transformations.

Sonic Adventure
In Sonic Adventure, the original guardian of the Master Emerald is revealed to be Chaos, who also protected the Chao that lived in peace at the altar.

According to Tikal, the prayer that her grandmother taught her tells about the nature of chaos energy:

"The servers are the seven Chaos. Chaos is power, power is enriched by the heart. The controller serves to unify the chaos."

In the "?" story, Chaos absorbs the negative energy of the Chaos Emeralds generated from his heart being full of rage and sadness to become Perfect Chaos. After the Emeralds are recharged by everyone's combined hearts, Sonic uses their positive energy to transform into Super Sonic.

Sonic Adventure 2
In Sonic Adventure 2, Shadow the Hedgehog was awakened by the power of a Chaos Emerald and demonstrates harnessing the power of Chaos Emeralds for such powers like Chaos Control, and later stocking the Eclipse Cannon with the Emeralds for another doomsday plot.

Shadow shows that chaos energy can be harnessed for means other than a super transformation such as Chaos-based attacks like Chaos Control and Chaos Spear, and in later games for Chaos Blast.

Sonic Unleashed
In Sonic Unleashed, Doctor Eggman managed to trap Super Sonic in his Chaos Energy Cannon that drained him of chaos energy and robbed him of the Chaos Emeralds. The machine then reversed the polarity of the Chaos Emeralds, forcing them to generate a negative chaos energy blast that provoked Dark Gaia to awaken millions of years earlier than intended, while draining the Chaos Emeralds of all their energy. Sonic's intense exposure to the chaos energy drain also attracted Dark Gaia's power, which traveled a long distance from earth to space and through the space station to allow some of Dark Gaia's energy to escape to Sonic, which caused his transformation.

Throughout the game, Sonic had to restore the Chaos Emerald's power using the Gaia Temples. At the end of the temple, a stand rises up. If the de-powered Emerald is placed in it, its power is restored, and the Chaos Emerald in turn restores that piece of the world.

Sonic Chronicles: The Dark Brotherhood
In Sonic Chronicles: The Dark Brotherhood, chaos energy is the source for the Blue Cyclone and helps Imperator Ix achieve his Super State. It was also used to power the Kron factory and to forcibly control the entire Voxai race.

Sonic the Comic
In the continuity of UK's Sonic the Comic, chaos energy (also known as Chaos Emerald Radiation) was created by the alien Drakon Empire as an incredibly powerful, yet highly unstable, power source. In their search for vessels for this power, they discovered the Emeralds from the sacred mine of the Echidnas on Mobius, and created the seven Chaos Emeralds - six to contain the power and a seventh, the Grey Emerald, to control the others. A fierce war was fought between the Drakons and the Echidnas over these Emeralds and the power they contained, which the Echidnas eventually won (although with heavy losses).

When brought together outside of certain stabilizing conditions (such as extreme cold, the presence of Golden Rings, or in the temple of Floating Island), the Chaos Emeralds would produce energy in the form of radiation, building to a chain reaction. In some circumstances, this would cause a spatial warp that teleported the Emeralds into the other-dimensional Special Zone.

Chaos Energy in this continuity was shown to be capable of the following feats:
 * Absorbing nearly all of the evil from planet Mobius, while in the Retro-Orbital Chaos Compressor;
 * Transforming the kindly Doctor Ovi Kintobor into Doctor Ivo Robotnik;
 * Turning Sonic into the demonic Super Sonic;
 * Powering a massive energy weapon on the Floating Island, capable of destroying the Death Egg;
 * Powering an impenetrable forcefield around the whole of the Floating Island, apparently indefinitely;
 * Granting Doctor Robotnik godlike omnipotence; and
 * Transforming a Drakon prosecutor into the terrifying monster Chaos.

Archie Comics
In the Sonic the Hedgehog and its spin-offs published by Archie Comics, Chaos energy originally came from the Chaos Force, the all-encompassing force of the universe. Objects like the Chaos Emeralds and certain individuals possessed a natural link to the Chaos Force, allowing them to harness Chaos energy. After the Super Genesis Wave, Chaos energy originates from the Chaos Emeralds, though there is no explanation for how certain individuals can upon Chaos energy without the emeralds.

Trivia

 * When the energy of the Chaos Emeralds are absent, they will become colorless (black or gray). Emotions can restore the Chaos Emeralds (positive emotions create positive power, while negative ones create negative power), as well as the seven Gaia Temples.
 * In the Archie Comics, chaos energy was present but was instead referred to as the Chaos Force.