Alternate reality

Alternate Realities, or parallel universes, are a concept that stems from Albert Einstein's theory of relativity. It is believed there are an infinite number of different realties, some more similar than others. Sometimes there are the same people, places, and objects, but with notable differences.

Summary
Stargate SG-1 has presented two major timeline theories over the run of the show: (1) alternate realities (also known as alternate universes or parallel universes) and (2) alternate timelines. Alternate realities are presented when various versions of SG-1 live in parallel universes, some almost identical; others, so extremely different so as to be unrecognizable. Alternate timelines are presented when it appears that the timeline in which "our" SG-1 exists is modified by a time traveling event.

Multiverse Theory
In a Multiverse, there exist a near-infinite number of universes, or realities, that are each created to reflect a different outcome to a decision. One could use the fork in the road as an analogy, where going in one direction defines the individual's current reality, whereas the roads not taken represent the alternate realities. These realities are progressing through time at the same rate as ours, but different paths are being taken, thus the term parallel universes is also used to describe them. Additional terms for "alternate realities" have included "alternate universes", "quantum universes", and "parallel worlds", and all have basically been used interchangeably, even though there are some differences in their definitions. But in the world of Stargate SG-1, these differences have not been expounded upon, and thus, the two more widely used terms "alternate reality" and "parallel universe" describe the same thing.

Some of these alternate realities have been created through the impact of a time traveling event (see Alternate Timelines), but most were the results of a decision so that all possible outcomes have their own realities. For example, one alternate reality included Daniel Jackson's turning down Catherine Langford's offer to translate the Stargate's coverstone instead of taking up the offer and solving the riddle of the Stargate. From that one event alone, several alternate realities were most likely created, carrying forward the idea that someone else opened the Stargate and went on the first mission, resulting in various realities where Ra was not defeated, and so on.

Entropic Cascade Failure
Traveling between alternate realities comes with some problems, the main one being Entropic Cascade Failure. This phenomenon results when two people representing the same person, such as two Samantha Carters, exist in the same reality at the same time, and is when the visiting person, the one out of his/her own reality, will start to suffer a physical breakdown at the cellular level due to temporal distortion. A traveler who has no living counterpart will not suffer from this breakdown.

Entropic Cascade Failure has been defined by Stargate SG-1 writer Joseph Mallozzi in this way: "The Multiverse theory of quantum physics posits the existence of endless alternate realities co-existing with our own. Some hold that the proximity of these realities is dependent upon the similarities between the various universes - i.e. the more similar the realities, the closer together/easier to access via an inter-universal bridge, while the more dissimilar, the further apart/more difficult to access. Some theorize that the temporal effects of entropic cascade failure are directly proportional to the proximity of the "universe of origin" from which a given element is introduced, ranging from dangerously high impact in distant, off-setting cases where the elements are more likely to be "out of sync" to negligible in closer, more attuned elements."

Based on this definition, the more "in sync" two realities are, perhaps having only a few differences in their "paths", the less the chance becomes that the traveler will suffer from these fatal effects. Entropic Cascade Failure was observed when the civilian Dr. Samantha Carter who worked at the SGA visited SG-1's reality, but not when several Carters who were in the Air Force and members of the SGC's SG-1 team visited.

Forming the Bridge
In order to travel to an alternate reality, one must form a link, called a "trans-universal bridge" or the more commonly used "inter-universal bridge", between the two realities. Various means of creating the bridge between realities have been discovered by the SGC.

SG-1 was introduced to the existence of alternate realities when they discovered the Quantum Mirror on P3R-233. This device appeared to be constructed of naquadah, the same material used to build the Stargates, and might have been the creation of the Ancients, but its actual origin was never determined. Using the hand-held remote control of the Quantum Mirror, an individual could "dial" an alternate reality, touch the mirror-like device, and be transported into that reality. As long as the link between the two realities was maintained, a traveler could go back and forth, but if the Mirror was turned off, the traveler would have to use a control device in their current reality to find the reality from which they had originally traveled. The method of determining the correct reality was purely by visual confirmation through the Mirror, as neither the Mirror nor its remote control seemed to record the placement of the originating reality or the last reality dialed.

Gen. George Hammond commanded that the Quantum Mirror in his reality be destroyed because he felt that there were some lines that were never meant to be crossed ; but other means of inter-universal travel were later discovered. If one were to direct a controlled energy blast within a wormhole traveling through a blackhole, one could actually open bridges among several alternate realities and another, making the wormhole's destination reality a point of confluence. This effect was reversed at the point of confluence with the use of an Asgard energy weapon discharged in the wormhole connected to the original point of origin's corresponding Stargate. Because the Stargate's wormhole was used to create the "inter-universal bridge," travel was only one-way, or uni-directional.

Another means of creating a uni-directional inter-universal bridge was developed by Dr. Rodney McKay and his sister, Jeanne Miller, to draw zero point energy from a parallel universe. A traveler could traverse this uni-directional bridge (from the reality from which the energy was being drawn) if he was beamed across with Asgard beaming technology while wearing an Ancient personal shield. This attempt to draw zero point energy into a containment field created universe-destroying exotic particles, and their research had to be abandoned. Similar research was done in an alternate reality by Maj. Samantha Carter and Doctor Bennett, but that research was destroyed in a power overload when they accidently tapped into SG-1's reality and drew Lt. Col. Samantha Carter into their reality while she was inside a contained field and out of phase. Maj. Carter and Dr. Bennett were totally annihilated in the explosion that resulted when Carter was drawn in. With the help of an alternate Dr. Rodney McKay, Carter was transported back to her own reality through another inter-universal bridge, but how her specific reality was determined as this bridge's destination was not revealed.

Within Stargate SG-1, several alternate realities and timelines have been glimpsed briefly throughout the series, providing an insight on how several alternate realities may have turned out.

SG1: "There But for the Grace of God"
Daniel Jackson is transported to a different reality via what is later called the Quantum Mirror.

Differences

 * The Stargate program's headquarters is known as the SGA.
 * Earth is currently under attack from the Goa'uld and is slowly being wiped out.
 * Daniel is not a part of the Stargate Program, his alternate self having turned down Catherine Langford's offer to work on the Stargate. He is also dead.
 * Teal'c is also not a part of the Program, and has remained the First Prime of Apophis and is currently leading the assault on Earth. Any chance of him turning was ended by the nuking of Chulak.
 * George Hammond is a colonel rather than a general.
 * Jack O'Neill is not a colonel, but rather a general and commanding officer of the SGA.
 * Samantha Carter has not joined the military and is a civilian scientist working for the SGA.
 * Jack O'Neill and Samantha Carter are engaged to be married.
 * Catherine Langford is still working as part of the SGA.

Question

 * What happened to the Kawalsky in this reality? He couldn't have died the same way as the Kawalsky from our reality because the alternate Kawalsky wouldn't have ever visited Chulak. Of course, Kawalsky may have never even been born in this reality.

SG1: "Point of View"
An alternate Samantha Carter and Charles Kawalsky come through the Quantum Mirror, fleeing Apophis's takeover of their Earth.

Differences

 * The Stargate program's headquarters is known as the SGA.
 * Charles Kawalsky is still alive and working for the SGA.
 * Samantha Carter did not join the military and works as a civilian scientist for the SGA.
 * Samantha Carter discovered how to open the Stargate rather than Daniel Jackson.
 * Samantha Carter and Jack O'Neill had been married for just over a year.
 * Teal'c is still the First Prime of Apophis and, apparently, is very loyal to his master.
 * The uniforms worn by Apophis' Jaffa are different.
 * Teal'c had a beard, as does Apophis. (This may be a nod to the Star Trek episode "Mirror, Mirror," where Spock's mirror counterpart had a beard.)
 * The symbols on the dialing computer are yellow instead of blue.
 * The people of this reality never met the Asgard, only coming into contact with them when Dr. Carter goes through the Stargate to ask for their help in freeing Earth from Apophis.

Other Realities Glimpsed in this Episode

 * At least two realties where the Quantum Mirror rests in an apparently undisturbed Cheyenne Mountain.
 * At least two realties where the Quantum Mirror rests in a Goa'uld-controlled Cheyenne Mountain.
 * At least two realties where the Quantum Mirror rests in Area 51. One of them is on a Goa'uld-controlled world.
 * One in which the Quantum Mirror rests in an apparently Earth-bound laboratory.
 * One in which the Quantum Mirror rests on the beach of an alien planet.
 * One, apparently identical to our reality, except for the fact Carter is still a Captain.

SG1: "Ripple Effect"
Several different realities are discovered and several teams of SG-1 come through the Stargate. Two realities is mostly seen on screen, where the command center is also called SGC, as in our reality. The "real" SG-1 team is distinguished as wearing "green" SGC uniforms throughout the episode.

Alternate Reality #1

 * Samantha Carter is married and has been on a honeymoon.
 * The Ori successfully planted a second beachhead in our galaxy.
 * During the second Ori incursion, at least two planetary systems, including Dakara, were destroyed.
 * The Prometheus has recently been lost in battle.
 * Earth does not have access to a functioning ZPM.
 * This team was distinguished by wearing "Black" SGC uniforms.
 * This team is desperate enough that it caused the problem with all of the alternate realities bleeding over into ours in order to steal the Prometheus and Atlantis' ZPM to protect their Earth with the weapons chair in Antartica. They fail and are sent home with nothing.

Alternate Reality #2

 * Samantha Carter is currently on maternity leave.
 * Both Janet Fraiser and Martouf are still alive; SG-1 consists of Martouf, Daniel Jackson and Cameron Mitchell. Fraiser is accompanying the mission, but wears an SGC patch.
 * General O'Neill is still Commander of the SGC.
 * Carter and Martouf had a romantic relationship, which led to Martouf joining the SGC and the two living together for a time. The relationship did not work out, however, and Carter is currently involved with someone else.
 * An Ori plague is ravaging Earth, with hundreds of thousands of people dying. As the team prepares to return, General Landry provides Fraiser with the antidote developed in our reality.
 * This team was distinguished by wearing "Camo-Desert" SGC uniforms.

Other Realities Glimpsed in the Episode
At least 17 different SG-1s were stranded at the SGC during this episode. After the arrival of the first, "black" SG-1, General Landry ordered that all further teams be instructed not to proceed through the gate, making exceptions only for those units that were under immediate fire and could not afford to shut down the gate and dial out again.
 * The second alternate SG-1 to arrive, distinguished by wearing "Tiger-Blue Camo" SGC uniforms, arrived from a firefight offworld. Its composition appears identical to the SG-1 of our reality, but its members are much more heavily armed than our universe's counterpart; notably, Teal'c is carrying a staff cannon. This team was still being examined (or examined again) in the SGC's infirmary after several other SG-1's had arrived.
 * Another SG-1 team, this one in green camo uniforms, can be seen in a side room as Teal'c, Daniel, and Landry passed by them. Mitchell and Carter were the only identifiable members of the team.
 * Another SG-1 team is seen exiting an elevator, consisting of Colonel Mitchell and three men who appear to be Jaffa.
 * Another SG-1 team, in "Haz-Mat Suits," passes by as the "real" Teal'c, Daniel, and Landry goes off-screen. This Colonel Mitchell turns to look after Landry, Daniel and Teal'c, then smiles and countinues walking down with his team.
 * Samantha Carter appeared to be a member of nearly every alternate SG-1. In the SGC's science lab, a room full of "Alternate-Carters" can be seen, some isolated and by themselves, others working together to help find a solution on the problem. The "real" Carter along with the "Black Carter" from the first SG-1 team who arrived, converses with Doctor Lee on finding a solution to return the alternate SG-1's back to their realities, just before the "Alternate" Martouf steps in.

Deleted Scenes

 * This episode was originally too long, so many scenes had to be edited and cut out for time. Joseph Mallozzi managed post the script sections of all cut scenes in his producer installment on Gateworld.

ATL: "McKay and Mrs. Miller"
An alternate version of Dr. Rodney McKay (known as "Rod") travels to our universe, seeking to shut down an experiment that might destroy his.

Differences
Since Rod's reality was never viewed directly, nearly everything we know about it is based on his description. No indication was given that Rod was lying, although our universe's Colonel Sheppard did state that he found him "creepy."
 * Both Earth and Atlantis have working Zero Point Modules.
 * Though Sheppard's team appears to have the same composition, the personalities of the team members are somewhat different: in Rod's words, Sheppard is an active member of Atlantis' Mensa chapter and something of a know-it-all that makes the McKay of our reality look humble, and Teyla is hard to talk to (though Ronon, apparently, is about the same). Rod himself is more easygoing and personal than our universe's McKay, and an honorary member of the Athosian council.
 * Jeanne Miller has three children; Rod, their godfather, carries photographs of them in his wallet.
 * The Ancient personal shield found in Atlantis has not yet exhausted its power source.

SG1: "The Road Not Taken"
In this reality, Anubis' attack on Earth forced the Stargate program into the public eye, and chaos ensued.

Differences

 * Hank Landry is President of the United States; his offices have been moved into Cheyenne Mountain for security purposes.
 * Major General George Hammond is commander of the SGC..
 * Major Evan Lorne is the leader of SG-1.
 * Doctor Daniel Jackson had recently been captured by the Ori forces.
 * Samantha Carter was never promoted to Lieutenant Colonel and, served on SG-1 until she was killed while trying to draw zero-point energy from alternate universes.
 * Rodney McKay apparently never went to work for the U.S. Air Force, instead making millions in the dot-com boom. He and Carter were divorced.
 * Teal'c left the SGC several years earlier.
 * Vala Mal Doran was imprisoned at a cell in Area 51.
 * Cameron Mitchell became a national hero after the battle with Anubis' forces over Antarctica, but was cut loose after he refused to support the harsh policies of the American government. He left the military and is currently wheelchair-bound and quite bitter.
 * Though Jack O'Neill is never mentioned, the sequence of events suggest that he may not have ever been removed from the Ancient stasis pod in Antarctica.
 * The Prometheus is still operational, and functions as Air Force One.
 * When the Stargate program became public as a result of Anubis' attack, panic and widespread riots forced the president to declare martial law. The United States' diplomatic relations were severely damaged as well; the Russian Federation took control of the Ancient outpost in Antarctica, though American forces managed to remove the Ancient control chair.
 * Widespread unrest led Congress to suspend the electoral process; the president is now re-elected by plebiscite, in which voters are given a simple yes or no choice as to whether he should remain in office.
 * Earth has managed to defeat an attack by an Ori mothership using the control chair, but its ZPM was nearly depleted in the process. The Ori subsequently sent at least five more ships to Earth, but our universe's Carter was able to use Merlin's phasing device to hide the planet from their attack.
 * The Alpha Site has been abandoned, and Earth has cut ties with offworld allies including the Jaffa.
 * Technology derived from the Stargate program is on display in normal planetary operations as well; American F-302s were used to bomb an alleged terrorist training camp in Ireland, and the U.S. Secret Service employs Goa'uld pain sticks and Zats.

SG1: "2010"
Ten years into the future, the Goa'uld have been defeated and the Stargate Program is public. Thanks to the Aschen, Earth is safe and humans are being given an anti-aging vaccine. But not all that glitters is gold.

Differences

 * The Stargate Program has become public knowledge.
 * The SGC is a museum; the Stargate is located in a large public complex not unlike an airport or train station.
 * Robert Kinsey is President of the United States.
 * Samantha Carter and Jack O'Neill are both retired from the United States Air Force.
 * Samantha Carter is married to Joe Faxon, the ambassador to the Aschen.
 * SG-1 is dismantled, with O'Neill estranged from his former teammates due to their difference in opinion on the Aschen's intentions.
 * General Hammond has been dead for several years; it is suspected by Janet Fraiser, Samantha Carter, Daniel Jackson, and Teal'c that he may have been murdered by the Aschen in order to preserve the secret behind the anti-aging vaccine.
 * The Aschen were met on their homeworld by SG-1 but have been attempting to take over the Earth through attrition
 * All of SG-1 is now dead. The only surviving member of the group that attempted to change the future is Dr. Janet Fraiser as she escaped through the Stargate to Chulak before the attempt began to alert Teal'c.

ATL: "Before I Sleep"
The Atlantis Expedition arrives in the Lost City to find its power supply failing, and are trapped undersea as the city floods.

Differences

 * All three Zero Point Modules that powered Atlantis had been running in tandem since the Ancients abandoned the city, and were all but depleted when the expedition team arrived.
 * The city's control systems failed to initialize, presumably for lack of power.
 * Colonel Marshall Sumner drowned along with several security teams searching the city before they could be recalled to the control room.
 * Atlantis' fail-safe mechanism took the form of emergency bulkheads that sought to close off vital sections of the city; unfortunately, these had the effect of trapping still more members of the expedition with water still rising.
 * Major John Sheppard and Doctors Weir and Zelenka are the only members of the expedition to escape the city, when Sheppard inadvertently activates a time-travel device inside one of the Puddle Jumpers.
 * The time machine takes them into orbit around Lantea during the siege by the Wraith; the jumper crashes and Sheppard and Zelenka are killed, but Weir is rescued by the Lanteans and lives out her days on Atlantis. These events are not part of an alternate timeline, as they in fact in the past of "our" timeline.

SG1: "Moebius, Parts 1" and "2"
Two alternate timelines result from this episode. First, Doctor Daniel Jackson discovers that Ra was in possession of a Zero Point Module during his reign on Earth, and General Jack O'Neill takes SG-1 back in time in order to retrieve it. Then, SG-1 is stranded in ancient Egypt, where it leads the rebellion and forces Ra to leave Earth, but inadvertently causes Ra to take the Stargate with him. As a result, the Stargate program never came into being.

Differences

 * Daniel Jackson teaches English as a second language.
 * Samantha Carter is not a member of the Air Force, and holds little of the confidence she is very well-known to have.
 * Jack O'Neill is retired from the Air Force and lives on a fishing boat.
 * Teal'c is still First Prime of Apophis, but still has his many doubts as to whether or not his master is a god.
 * George Hammond is a brigadier general and still commanding officer of the Cheyenne Mountain facility.
 * Charles Kawalsky is still alive, though he dies before he can escape Chulak with the rest of the team.
 * Rodney McKay is still working for the Air Force, and is involved with research on the Puddle Jumper. He is also apparently not allergic to citrus.
 * After O'Neill, Carter and Teal'c travel back once more to ancient Egypt, they manage to orchestrate the rebellion in such a way that the Stargate remains on Earth. The timeline as it existed before SG-1 went back in time to retrieve the ZPM had these differences from the one that existed after all this:
 * The rebellion in ancient Egypt happened somewhat later; though it's unclear what difference, if any, this made.
 * The fate of Ra's ZPM was unknown, but it's assumed that he took it with him when he left Earth.
 * Because of this, Earth would not have been able to send reinforcements to Atlantis, meaning the expedition team presumably would have followed through with its original plan to abandon and destroy the city.
 * There were no fish in General O'Neill's pond.

SG1: "Unending"
SG-1 is trapped aboard the Odyssey for 50-60 years in a time dilation field, as the teem seeks a means to prevent the ship's destruction by an Ori energy beam. During this period, Daniel Jackson and Vala Mal Doran became romantically involved, General Landry cultivated a garden in his quarters, and Samantha Carter learned to play the cello. Landry died of old age after about twenty years; all of SG-1 save Teal'c are killed when the Ori beam finally struck the ship. Teal'c used the energy to travel back in time and prevent the time dilation field from ever being established.


 * From Teal'c's perspective, all these events remain part of his past; but as far as everyone else in the universe is concerned, they belong to a timeline that has not and will not occur. For his part, Teal'c has declined to discuss any of these events with the rest of the team.

Note
With the exception of the events in "Moebius", all these "alternate timelines" in fact describe what would have happened if not for the intervention of an individual or individuals &mdash; SG-1 and Doctor Fraiser in "2010," Doctor Weir in "Before I Sleep," and Teal'c in "Unending" &mdash; from a future that, thanks to their intervention, no longer exists. (Since "Moebius" actually depicts two altered timelines, one of which is the "final" one, it could fall in this category as well.) In effect, then, it might be said that ours is the alternate timeline, as it is certainly an altered one.

Questions

 * Are the alternate versions of people different people entirely or what the same people would have been had their lives been different?
 * Can any one reality be considered "the real one" or the "Prime-Universe"?
 * Since it is now established that travel between alternate realities through the Stargate is now possible, would the SGC in the "real" reality start traveling through alternate realities as a form of exploration?