Research into the area of quantum gravity suggests that time flows like rotating fluid within our galaxy, theoretically making time travel possible by allowing a traveler to journey backward and forward through streams of time at will, given a sufficient power source.
An Ancient spacecraft containing a time travel device that was recovered from Maybourne's planet was brought back to Area 51 for study. Both devices require the presence of the Ancient gene for activation, a gene which O'Neill possesses, but SG-1 had agreed not to use the device for time travel because of the danger of adversely affecting the timeline. However, they reconsidered the idea of time travel after the discovery among Catherine Langford's possessions of a reproduction of an ancient Egyptian wall painting that suggested the presence of a zero point module on Earth during the reign of Ra. Neither historical evidence nor satellite sweeps indicated that the ZPM had remained on Earth, making travel to the past the best means of obtaining the device. Because a working ZPM would be able to power Earth's defenses as well as to power the stargate to reach Atlantis in the Pegasus galaxy, the mission was deemed to be worth the risk of altering history.
According to historical records, Ra's reign on Earth ended approximately 5000 years ago when the ancient Egyptians rebelled and buried the stargate. Targeting that time period with his mind, O'Neill was able to fly the Ancient spacecraft and successfully activate the Ancient time travel device, sending SG-1 instantly back in time to Egypt in the year 3000 BC. Their intention was to gain access to the Temple of Ra, locate and steal the ZPM, and use the ship to immediately return to the present day with minimal contact and minimal impact on history, although Daniel had brought along a video camera in order to take advantage of the unique opportunity to record history and to prove that the great pyramids predate the fourth dynasty. The spacecraft was left in the desert, concealed by the cloaking device, and the team joined two of the locals, Katep and his brother Salatis, for a pilgrimage to the temple where they came face to face with Ra. The plan to steal the ZPM from the treasure room at the temple worked flawlessly, however they returned to the desert to find that a sandstorm during the night had partially covered the invisible spacecraft, drawing the attention of Ra's Jaffa. Confronting the Jaffa could alter the future immeasurably, and the team was forced to remain in the past, hoping that when the human slaves would eventually rise up and force Ra to abandon Earth, they would be able to retrieve their ship. By doing so, they allowed themselves to be drawn into a spiral of historical events that would play out exactly the way they were meant to.
A month before the mission through time began, a team of archaeologists from the University of Chicago had uncovered an ancient Egyptian tomb of the first dynasty near Giza, and their discovery provided SG-1 with an opportunity to communicate with their future selves even if they were unsuccessful in returning to their own time. In the tomb they buried the ZPM as well as their video camera with which they had recorded a message explaining the details of their mission and the future world they had left behind, should the future need to be changed. The video recording described the discovery of the stargate in 1928 and the creation of Stargate Command, as well as necessary information about the dialing system, gate addresses, points of origin, the Ancient spacecraft and time travel device, and the significance of the Ancient gene, all tools that would be required if history had inadvertently been changed and had to be set right. The tape also described the members of SG-1 and the nature of their mission to ancient Egypt, and included details of the future as they knew it including the recent fall of communism, the presidency of Henry Hayes, and the absence of fish in O'Neill's pond. The tape failed to mention, however, the cloaking device on the Ancient spacecraft, and just as Daniel had begun to explain the significance of the ZPM, the camera batteries expired.
Despite Carter's insistence that they must not affect the timeline, ultimately O'Neill and Teal'c couldn't stand the idea of living out the rest of their lives under Ra's rule without taking action, and so they made the decision to become involved in the rebellion that they knew would overthrow Ra. With Katep, they planned an uprising and began gathering forces, but they were exposed by those still loyal to Ra, and before the plan could be carried out, O'Neill, Carter, and Teal'c were captured and executed. O'Neill had been the only one capable of flying the Ancient spacecraft, and following his death, the ship remained buried in the desert, and Daniel remained trapped in the past. Daniel and Katep began again to slowly build up an underground movement, and eventually, in 2995 BC, they led the uprising against Ra. The rebellion was successful, Earth was freed, and Ra abandoned the planet, however he took the stargate with him.
Realizing that history would be drastically changed, Daniel carved a stone tablet with a message in hieroglyphics using an obscure Egyptian dialect. The tablet told the date of the rebellion and the location of the second stargate in Antarctica, and Daniel buried it in Giza where the stargate should have been, hoping that it would be discovered in the future. Indeed, the rebellion set into motion an alternate timeline in which Dr. Langford excavated the area at Giza where the stargate should have been in 1934, and had found only Daniel's tablet which no one had been able to translate. Without a stargate, there had been no Stargate Command, and the facility deep within Cheyenne Mountain was used by the Air Force as the USAF Research Institute. Robert Kinsey was president of the United States, and Henry Hayes was his Secretary of the Interior. Brigadier General George Hammond commanded the USAF Research Institute at Cheyenne Mountain, where Dr. Rodney McKay was one of the leading research scientists. Colonel Jack O'Neill, who had served on many covert missions, including Peru, Sierra Leone, and Uganda, with Major Charles Kawalsky, had retired from the Air Force and made a living chartering his boat, named "Homer," for tours, fishing, and parties. Major Paul Davis and Major Samuels remained with the Air Force, however Dr. Samantha Carter had never joined the military and worked instead at the Department of Aerospace Research Headquarters in Washington DC, where she applied her PhD in astrophysics to checking other people's reports for factual errors or omissions, forced to endure the plagiarism of her own work, including her theory on spin wave technology and the effects of antigravity on electromagnetism, by her superior, Dr. Hirschfield. Dr. Daniel Jackson, a gifted linguist with a PhD in Egyptology, had applied his background in archaeology to put forth the possibility that the Egyptian pyramids were landing pads for alien spacecraft, a theory which failed to gain acceptance among his colleagues, and which left him to earn a living by teaching English as a second language to immigrants.
When the team of archaeologists from the University of Chicago uncovered the ancient Egyptian tomb of the first dynasty at Giza, they discovered the ZPM and the video camera, as well as the Ancient spacecraft and time travel device which were found during an excavation of the same area. The artifacts were brought to the USAF Research Institute for study, and after reviewing the tape, the Air Force summoned O'Neill, Carter, and Daniel to Cheyenne Mountain. Although O'Neill refused the summons, Carter and Daniel were briefed on the contents of the videotape, and Daniel was offered the tablet of hieroglyphics to translate in the hope of finding a way to correct history. According to the tablet, the ancient Egyptians rebelled against Ra in 2995 BC, and Ra abandoned Earth in a great flying ship, taking the stargate with him, however, a second Earth stargate existed in "the land of cold to the south," which Daniel interpreted as Antarctica. Meanwhile, Dr. McKay, an arrogant man with a fondness for Carter and no apparent allergy to lemon chicken, had overseen the research into the alien spacecraft. Realizing that only Jack O'Neill or someone with the Ancient gene could operate the technology, the scientists were unable to activate the ship, and attempts to enter dialing sequences into the console seemed to have no effect. However, when Carter cross-referenced the dialing attempts of the scientists with seismic activity in Antarctica, the epicenter pointed to a location approximately 50 miles outside of McMurdo, and the beta stargate was recovered and installed at Cheyenne Mountain.
Hammond prepared to send a mission through the stargate to Chulak to find Teal'c, and Major Kawalsky was assigned to assemble the team for the mission, which did not include Carter or Daniel because of their lack of military experience. Both Hammond and Kawalsky knew that only the strong mutual respect between O'Neill and Kawalsky would convince O'Neill to come out of retirement and join the mission, and it was O'Neill's instincts that convinced Hammond to include Carter and Daniel on the team. O'Neill demonstrated his ability to activate the alien technology, and a seven-man team consisting of O'Neill, Kawalsky, Carter, Daniel, Bosworth, Mansfield, and Donner, departed in the ship, through the gate to Chulak. Their mission was recon only, and time travel was forbidden, but shortly after their arrival they were captured by a Jaffa patrol and imprisoned.
In prison on Chulak the team encountered Teal'c, who treated their words of false gods as blasphemy and brought Daniel before Apophis. Determined to learn of the Tauri, Apophis tortured Daniel with a ribbon device, and when he would not give in, had him implanted with a Goa'uld symbiote to learn all he knew of Earth. Meanwhile, Teal'c's true beliefs led him to request to see the videotape the team had brought, and upon seeing an alternate version of himself telling of his son and a free Jaffa nation, he agreed to help the prisoners escape. Teal'c joined the team and warned that Daniel had been implanted as a Goa'uld spy and that Apophis had launched a fleet of ships to attack Earth. The Goa'uld within Daniel killed Bosworth before being killed himself by O'Neill and Kawalsky, and in an ambush by Apophis's Jaffa, Kawalsky, Mansfield, and Donner were also killed. Only O'Neill, Carter, and Teal'c survived to make their escape in the spacecraft. Pursued by death gliders and unaware of the cloaking device, the team had no choice but to use the time travel device to escape capture and to attempt to prevent the attack on Earth. Accessing the ship with his mind, O'Neill brought the team back in time 5000 years and escaped through Chulak's stargate to ancient Egypt.
The year was 2995 BC, and there in ancient Egypt O'Neill, Carter, and Teal'c from the alternate timeline met Daniel from the original team, who explained the fate of his teammates and the preparations that he and Katep were making to bring about the rebellion. Now realizing that the rebellion would alter history because Ra would take the stargate, the team developed a new plan to distract Ra's forces from the gate so that it could be cabled to the cloaked spacecraft and flown to safety. Following the rebellion, the gate would be buried, but Carter insisted that in order to limit any further changes to history, they must destroy the ship and live out the rest of their lives in Egypt.
Just as history was meant to be, O'Neill, Daniel, Carter, and Teal'c, led the rebellion against Ra that freed Earth from the Goa'uld, and the stargate was buried in Giza where it would be found 5000 years later. When the archaeological team from the University of Chicago uncovered the Egyptian tomb at Giza, they discovered the ZPM and the videotape left behind by SG-1. The artifacts were returned to the SGC for study two weeks before the original mission through time had begun. This time, however, the SGC had acquired a functioning ZPM, and the facts on the tape coincided with the current timeline. A mission into the past was unnecessary, and SG-1 instead enjoyed some vacation time at O'Neill's Minnesota cabin with a pond full of fish. Close enough.
Cross Reference: Ancient Spacecraft, Ancient Time Travel Device, Apophis, Beta Stargate, Bosworth, Samantha Carter, Chulak, Crandall, Paul Davis, Egypt, Egyptian, George Hammond, Dr. Hirschfield, Homer, Daniel Jackson, Katep, Charles Kawalsky, Catherine Langford, Airman Mansfield, Rodney McKay, Jack O'Neill, Ra, Colonel Samuels, SGC, Stargate, Teal'c, Time Travel, Zero Point Module
Episode Reference: Moebius