Zero Point Module

"It's kind of like a miniature universe in a bottle."

- Rodney McKay

A Zero Point Module, often abbreviated ZPM, is a power source, created by the Ancients, capable of supplying tremendous amounts of energy. It is one of the most formidable power sources known to exist, having been developed by the Ancients several million years ago during their original habitation of the Milky Way galaxy.

Overview
"It extracts vacuum energy from [an] artificial region of subspace-time until it reaches maximum entropy."

- Radek Zelenka Visually, a Zero Point Module resembles a large, translucent group of primarily orange-colored crystals approximately one foot in height with a roughly cylindrical shape. When activated, a ZPM emits a yellow glow from its center, with a small red circle at the top of illuminating once the device has been fully engaged. This illumination ceases once the ZPM has been disconnected from whatever it was powering or has become fully depleted.

The device itself serves as an enclosure for an artificially created pocket of subspace-time. Zero point energy is extracted from this pocket until it reaches maximum entropy, at which point the pocket collapses, leaving behind a useless shell.

Like many types of Ancient technology, Zero Point Modules are crystal-based. The crystals that compose the shell of the ZPM are similar in many ways to the crystals adapted by the Goa'uld and Tok'ra: red crystals contain the necessary programs to allow ZPMs to provide power to Ancient technology when a ZPM is interfaced with a conduit, while yellow crystals act as a buffer to prevent catastrophic overload. The crystals of a ZPM are virtually indestructible and can remain functional for hundreds of thousands of years. (MGM: "SGC Intelligence Briefing")

The life of a ZPM is directly proportional to the power demands placed on it. If not in use, a ZPM will maintain its power level indefinitely. However, even if exposed to constant strain, ZPMs will still supply power for thousands of years, depending on the degree of the strain; The power generated by three of them enabled Atlantis' shield to survive the pressure of several hundred feet of ocean for 10,000 years. A single ZPM, at nearly full power, could provide enough energy to resist constant bombardment by Wraith Hive ships for days before depleting.

History
"I couldn't believe my eyes: three ZPMs right in front of me."

- Elizabeth Weir

Ancient use
Zero Point Modules were created by the Ancients several million years ago during their original habitation of the Milky Way galaxy. Several outposts in the galaxy powered by ZPMs are known to have existed, including Taonas on Praclarush, the Antarctic outpost on Earth, and Atlantis. However, many other Ancient sites in the galaxy appear to be powered by other means, potentially indicating that the ZPM was developed relatively late in their time in the galaxy.

While most outposts required only a single ZPM to be fully powered, City-ships, including Atlantis, are designed to function at full power only when powered by a trio of Zero Point Modules simultaneously, though one ZPM is generally sufficient to activate most systems. ZPMs are among the only known power sources capable of effectively powering control chairs as well as the shield and stardrive of a city-ship. During the First siege of Atlantis, Atlantis was powered by three ZPMs, which ultimately proved capable of sustaining the city's shield meanwhile holding back several hundred feet of ocean for 10,000 years, until the city's discovery by the Atlantis expedition.

ZPMs dating back thousands of years may still be found on a number of worlds in the Pegasus and Milky Way galaxies; once colonized by the Ancients. However, they are quite rare, with many simply having been lost over the centuries. Following the departure of the Ancients from the Pegasus Galaxy, the only race capable of creating ZPMs were the replicators on Asuras.

Tau'ri use
The first ZPM encountered by the Tau'ri was on the planet of Proclarush where it had been powering a shield to protect an Ancient outpost. It was disconnected from the outpost's control chair and taken to power the Drone weapons of the Ancient outpost in Antarctica to defend Earth against Anubis' fleet (the original ZPM of the Antarctic outpost having already been depleted). It was later connected to the Stargate at the SGC to facilitate dialing the intergalactic address for Atlantis in the Pegasus Galaxy, which depleted it entirely. It was then used in a ruse against Ba'al.

Dr. Meredith Rodney McKay, Chief Science Officer of the Atlantis Expedition and a member of the First Atlantis Reconnaissance Team discovered a ZPM on M7G-677, where it was being used to power an Electromagnetic field generator protecting a series of villages on the planet from Wraith attack. McKay brought it to Atlantis in the hope of using it to power the city, but soon returned it after learning that it was much too depleted to be of any use to them.

The Goa'uld Camulus discovered a half-charged ZPM in an Ancient outpost. Unable to use it himself, he coated it with a volatile compound that would react explosively to an electrical charge. He led the Tau'ri to it in the hopes that they would destroy themselves. Despite Camulus' best efforts, the plan ultimately failed when Dr. Bill Lee discovered the compound by mistake when it became necessary to flood the base with Gamma rays. The estimated blast radius of the ZPM could have possibly encompassed the entire solar system, and at the very least would have completely destroyed Earth.

A ZPM, known to the locals as the Potentia, was left on Dagan by the Ancients, who entrusted the Quindosim to safeguard it for them. Repeated culling by the Wraith wiped out their membership and the location of the ZPM, but the new Brotherhood was able to locate it with the help of the Atlantis expedition. However because the expedition were not Ancients themselves the new Brotherhood refused to part with it, instead choosing to hide it in the continued belief that the Ancients would return and eventually reward them for their loyalty and dedication, unaware of the fact that the Ancients were long gone and as such, would never ever return to the Pegasus Galaxy.

SG-1 discovered a ZPM in Egypt that had previously belonged to the Goa'uld Supreme System Lord Ra, who was apparently unaware of its properties and used it as an object in religious rituals. They used a Time Jumper to travel back in time and steal it. After altering the timeline by mistake, they decided to plant it for future discovery where they knew it would remain safe.

After the alternate SG-1 corrected the timeline, this ZPM was later discovered and used to dial Atlantis and send reinforcements, to prepare for the coming Wraith attack, then installed on the Daedalus to increase its hyperdrive efficiency so it could arrive in time to be of use during the Battle of Atlantis. Upon arrival, the ZPM was used to power Atlantis' shield. Following a successful ruse to trick the Wraith into thinking the city was destroyed, the ZPM provided a steady power supply to Atlantis for nearly two more years. It was depleted to allow an alternate Rodney McKay to return to his own reality.

A depleted ZPM had been filed away in the Genii archives for hundreds of years. Realizing what it meant to Atlantis, Ladon Radim used it in his coup d'etat as part of a scheme to capture Lt. Colonel John Sheppard and a large strike team, which would be enough to bring Cowen out in the open. It was presumably destroyed in the nuclear explosion Ladon used to kill Cowen and his inner circle.

A ZPM was used to power the sublight engines of the Tria during its near-lightspeed journey from the Pegasus galaxy to the Milky Way. The effects of relativity meant that very little time had passed for the Ancients crewing the vessel. After being rescued by the Daedalus and returned to their city, the Ancients took control and asked expedition to leave, using the ZPM to power the city and dial Earth directly. After the Asurans attacked and subsequently occupied Atlantis, they installed at least two more ZPMs to power the stardrive. Sheppard's team was able to destroy the Asurans and acquire the ZPMs. Despite McKay's vehement protests, two were sent back to Earth: one to power the Antarctic outpost and another to power the Odyssey. The remaining ZPM was nearly depleted when the Asurans attacked Atlantis using a satellite weapon, eventually reaching critical levels and stranding Atlantis in space.

With their ZPM incapable of powering the Stardrive, the expedition raided Asuras for a replacement module. Upon successful completion of their mission, the ZPM was used to repower Stardrive, then the expedition finished their journey to M35-117, which served as Atlantis' new home. The ZPM then took on the role of powering Atlantis, with plenty of power levels left to suit their needs.

When the Wraith fought alongside the Tau'ri and Travelers in the Battle of Asuras, Todd managed to steal a cache of ZPMs from Asuras before the planet was destroyed. Three were used to power a Wraith cloning facility to bolster their numbers enough to defeat the Tau'ri and rival Wraith in the same manner they defeated the Ancients. These ZPMs were presumably destroyed with the rest of the facility when the Hive ship Atlantis had commandeered was driven into it. He also used an unknown number of ZPMs to power a Hive ship, enhancing every system to nigh-unbeatable levels. The empowered Hive's enhanced weapons could punch through the shields of a BC-304 in seconds, and its improved hull was virtually impervious to attack, easily withstanding the strikes from both plasma beam weapons and Drone weapons, both of which were easily capable of destroying a normal hive ship, and resilient enough make the intergalactic hyperspace journey to Earth. It was eventually destroyed by a nuclear weapon detonating inside of it, which presumably destroyed the ZPMs as well.

In addition to the ZPMs powering the Hive ship, Todd provided Atlantis with two additional ZPMs to power their Stardrive, having been convinced to by Sheppard as an act of spite against his treacherous underling who had stolen the Hive ship. Using the ZPMs, Atlantis was able to reach Earth through a combination of its hyperdrive and an experimental Wormhole drive. Ultimately, the city lacked the firepower to defeat the Hive, and in the attempt was forced into the atmosphere. Unable to regain orbit, the city landed in San Francisco, cloaked to ensure the continuing secrecy of the Stargate program.

Eventually it was decided to return Atlantis to Pegasus due to the efforts of General Jack O'Neill and Richard Woolsey forcing the IOA's hand. With three ZPMs powering the hyperdrive, Atlantis would be able to make the journey between Earth and Lantea in just nine days, but seven days into the journey, on the edge of the Pegasus Galaxy, one of the hyperdrive induction arrays malfunctioned from battle damage and began drawing massive amounts of power to widen the hyperspace corridor. Though dropping out of hyperspace fixed this, the damage was already done: the hyperdrive was damaged beyond the Tau'ri's ability to repair and the ZPMs were drained to twenty percent power. The crew managed to land Atlantis on a relatively close planet that was marginally habitable, but the process drained the ZPMs further down to nine percent.

Alternate realities

 * In an alternate reality, the Tau'ri never learned the location of Atlantis and the original ZPM retrieved from Proclarush was instead drained fending off an Ori attack of Earth. 
 * In an alternate timeline, the ZPMs powering Atlantis became depleted much more quickly after the Atlantis Expedition's arrival. As the city in this timeline also lacked a Failsafe mechanism, the city was destroyed by the ocean when the shield failed.