Alternate reality

Alternate Realities stem from Albert Einstein's theory of relativity. It's 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.

Appearances
Within Stargate SG-1, there have been five notable different realities.

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 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.
 * 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.
 * 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 not retired, but 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 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 the 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 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: "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 is public knowledge and the SGC is a museum.
 * 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 the Ambassador to the Aschen, Joe Faxon.
 * 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 and 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.

Note
This reality was, at first, the reality SG-1 was heading for, but thanks to the actions of SG-1 of the future, this future has now been averted.

SG1: "Moebius, Parts 1" and "2"
The Stargate was never discovered at Giza, due to it being taken away from Earth when Ra fled, thousands of years before.

Differences

 * Daniel Jackson is a teacher of languages.
 * 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 as an astrophysicist.

Note
This reality was caused by SG-1's actions in the time of Ancient Egypt and their efforts to obtain a ZPM.

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.

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.

Alternate reality #2

 * Samantha Carter is at this time on maternity leave.
 * Both Janet Fraiser and Martouf are still alive.
 * SG-1 consists of Janet Fraiser, Martouf, Daniel Jackson and Cameron Mitchell.
 * Jack O'Neill is still Commander of the SGC.
 * An Ori plague is rendering Earth, with 100,000s of people dying.
 * With help from our reality, they gather the intel they need to be able to stop this plague from spreading any further.

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?"