Alternate timeline

Alternate Timelines are an alteration or change in the current timeline, causing an alternate reality to form in the universe. An alteration in a timeline is usually caused by altering the past through Time Travel, which manipulates, shapes, and forms the current present and future. This results in a different outcome, and gives birth to a new alternate reality or universe.

It is possible to restore a timeline to its original state by returning to the past and correcting the damage from there, thus restoring the timeline to its original state.

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 since 2004; it is suspected by Samantha Carter,Janet Fraiser, 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, this is in fact the original timeline.

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 are 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. This changes the "real" reality that exists from these episodes, onward. The timeline after SG-1 went back in time to retrieve the ZPM had these differences from the one that existed prior to these episodes:
 * The rebellion in ancient Egypt happened somewhat earlier; though it's unclear what difference, if any, this made.
 * The "original" fate of Ra's ZPM was unknown, but it's assumed that he took it with him when he left Earth. In the new timeline, it was buried with the camera, preventing any need to go back in time in the first place.
 * Because of the ZPM, Earth was able to send reinforcements to Atlantis. In the original timeline the expedition team presumably would have followed through with its original plan to abandon and destroy the city.
 * There were fish in General O'Neill's pond. At the beginning of the episodes, and in the videotape, O'Neill admits that there are no fish in his pond, and in all episodes prior to these, when shown fishing, no one has any success.
 * The fishing scene in Threads didn't happen until the end of Moebius.

SG1: "Unending"
SG-1 is trapped aboard the Odyssey for 50-60 years in a time dilation field, as the team 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.

ATL: "The Last Man"
Sheppard travels 48,000 years into the future to find a timeline where Michael rules the galaxy and all of his friends but McKay were killed in the war that followed. This timeline was changed when Sheppard traveled back in time, rescued Teyla and destroyed Michael's crusier and army over M2S-445 and was prevented forever when Michael was later killed by Teyla.

Differences

 * Sheppard is trapped in the future and presumably dies there without ever being able to return home.
 * Michael is presumably still alive and has taken over everything.
 * Teyla was killed by Michael after her baby was born and he was taken and used to perfect Michael's Hybrids.
 * Ronon and Todd died fighting against Michael's Hybrids together.
 * The next 304 is named the Phoenix (in the new timeline its renamed the General Hammond in honor of General Hammond who died of a heart attack.)
 * The Phoenix is destroyed in the Battle of the Phoenix and Carter is killed in the destruction.
 * An unknown amount of humans die as a result of the Hoffan drug.
 * Michael destroys the Wraith, exterminates the weak of the galaxy's human populations and turns the strong into more of his Hybrids.
 * After Carter's death, Richard Woolsey orders all support pulled out of helping other worlds and focus on protecting Atlantis leaving at least one ship in orbit at all times. This causes Keller and McKay to quit.

Stargate: Continuum
Ba'al travels back to 1939 and sends the ship carrying the Stargate to America to the North Pole and heads out into the galaxy to create his own empire. Mitchell doesn't exisit and Carter is dead here and the Stargates were never found. Carter, Mitchell and Daniel end up here due to being in transit in the Stargate at the time of the changes and are thus protected from them. Daniel loses his leg to frostbite and the team are not allowed to travel through the Stargate and set things right and are forced to lead normal lives for a year. The gate in the Antarctic is found, but is not figured out how to use. Meanwhile the Russians find and take the Gate from the North Pole. Ba'al launches an attack with Teal'c as his First Prime and Vala (as Qetesh) as his queen. He now commands all of the System Lords and with their combined forces, comes after Earth believing to be unaware of the Goa'uld as he doesn't know SG-1 is there. He attempts to present an air of benevolence to the President by calling him on the phone and setting up a time to meet face to face, but is killed by Qetesh before he can finish. He also has the Gate in Antartica and the weapons platform destroyed under Qetesh's forcing before his death leaving Earth with no real defences. Qetesh plans to use the time travel device to gain power herself but is thwarted by Daniel, Teal'c, Carter, Mitchell and two other Jaffa who get to the planet before she does through the Gate that the Russians have and use the time travel device to set things right, but as Teal'c dies, he kills her with a grenade. The timeline is erased when Mitchell, in 1939, sets an ambush and kills Ba'al and his soldiers before they can change time.

Note
With the exception of the events in "Moebius", all these "alternate timelines" are in fact timelines lacking the intervention of a given individual or individuals &mdash; SG-1 and Doctor Fraiser in "2010," Doctor Weir in "Before I Sleep," and Teal'c in "Unending" &mdash; all originating from futures that their interventions have negated. (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 the primary timeline is the "alternate" timeline, as it is the result of repeated historical interventions.