Alternate timeline

An alternate timeline is a tangential space-time continuum, typically created upon the alteration of one or more events in the 'past'. Alternate timelines are frequently the result of unintentional temporal interference.

Classification

Closed timelines

Closed timelines occur when an alternate timeline is created, then eliminated through the actions of "external" agents. Typically, the participants within these timelines are unaware of any change, either upon the creation of the alternate timeline, or once the timeline reverts to its "true" form, unless shielded from those changes by temporally-sensitive materials (for example, chronitons and temporal shields). Since this is the case, most incidents of closed timelines go unreported, except by the Department of Temporal Investigations. Such timelines usually involve a cyclic aspect (action in the original timeline altering the past/future, creating an alternate timeline, an object/person unaffected by the temporal change traveling to/already present in the past/future to ensure the original timeline is re-established). Often in the case of alternate timelines, they are erased by actions by the people within them, such as when USS Voyager destroyed the Krenim weapon ship and erased it from history, or when the crew of Enterprise sacrificed themselves and the ship in an alternate future in order to destroy parasites in the present Captain Archer's brain in the hopes that he'd be able to save the future, erasing that timeline.

Examples of alternate timelines

• In 2344, the USS Enterprise, NCC-1701-C--C responded to a distress call from a Klingon outpost on Narendra III, which was under attack by Romulan forces. In the "real" timeline the Enterprise saved the outpost and strengthened relations between the Federation and the Klingons. However, during the battle with the Romulans a Temporal rift opened and the Enterprise, badly damaged and disoriented, traveled to 2366, in the presence of its successor, the USS Enterprise, NCC-1701-D--D . Because the Enterprise-C was not there to save the outpost it was destroyed and the Klingons declared war on the Federation. For the next 22 years, the two powers engaged in a bitter war that cost 40 billion lives and left the Federation on the brink of defeat. In this timeline, Tasha Yar was still alive and serving as tactical officer aboard the Enterprise-D in 2366.
  
  Guinan began to feel the change in time as "not right". She advised Captain Picard of the changes and eventually convinced him to send the Enterprise-C back through the rift. Yar discovered through Guinan that she died in the other timeline and felt that she could help aboard the Enterprise-C rather than where she felt she didn't belong. The Klingons attacked the two ships as the Enterprise-C flew toward the rift, while the Enterprise-D defended her. The Enterprise-D was likely destroyed by the Klingons, but the Enterprise-C made it through the rift and restored the timeline, erasing the war from history.
  
  However, during the battle with the Romulans, the Enterprise-C was forced to surrender and prisoners, including the alternate Yar, were taken. Yar had a child with a Romulan and was later executed. The child, Sela, became a commander in the Romulan military and encountered the Enterprise-D several times.

It can be presumed that Worf was fighting with the Klingons elsewhere in this timeline, or that he did not survive the Romulan attack on Khitomer, or because of the war between the Federation and the Klingons the Romulans didn't attack Khitomer and Worf is living in the Klingon Empire, or because of the war he wasn't accepted to Star Fleet Academy.

• Sometime before 2174, the Krenim temporal scientist Annorax built a temporal weapon that caused incursions in the timeline. He used this weapon against the enemies of the Krenim Imperium and erased them from the timeline. The first species he eliminated restored the Imperium to great power. The second species he eliminated caused a once cured disease to ravage much of the Imperium. His attempt to correct this mistake accidentally erased his wife from history. In an obsession, he led the crew of his weapon-ship for two hundred years, trying to restore the Imperium to power and restore his wife. No matter how much of the Imperium was restored, his wife never came back. These multiple eliminations caused paradox after paradox in the timeline, eliminating dozens of species.
  
  In 2374, the USS Voyager attempted to cross Krenim space, unaware of the constant changes in the timeline. A Krenim ship intercepted them and attempted to destroy them, but the ship was no match for Voyager and fled. The crew then met with the Zahl, who had claimed Krenim territory for their own and make peaceful contact. Annorax meanwhile took his weapon to the Zahl homeworld and eliminated the species. The Zahl ambassador and the two Zahl ships nearby disappeared, the crew had no memory of encountering them. The small Krenim ship they encountered was suddenly much larger, and powerful.
  
  For the next several months, Voyager was attacked again and again by Krenim ships. unable to defend against their chroniton torpedos, Voyager sustained heavy damage and many of the crew died. Eventually Seven of Nine discovered an intact and armed torpedo in Voyagers hull. She scanned the torpedo and formulated a defense against the weaponry, but in the process she disobeyed orders and Tuvok was rendered blind. This led to the creation of temporal shields. Voyager finally had a defense against the Krenim ships and continued through their territory. Nearby, Annorax eliminated yet another species, but Voyagers shielding protected them from the change and threw Annorax's calculations off, reducing the Imperium to a small region of space.
  
  Annorax intercepted Voyager, kidnapped Tom Paris and Chakotay and attempted to erase Voyager. Voyager escaped and sustained heavy damage, forcing Captain Kathryn Janeway to order the crew to abandon ship. The senior staff continued to man Voyager and hid the ship in a nebula to make what few repairs they could. Meanwhile, Chakotay and Paris were held hostage as "artifacts" from lost times aboard the weapon. Annorax began to influence Chakotay while Paris still wanted to escape. Finally, they managed to contact Voyager and a plan was formulated. Voyager made allies with two alien species and led a small fleet to intercept the weapon. Chakotay and Paris managed to lower the weapon's shields and render it vulnerable to conventional weapons. After the fleet is crippled and Voyager nearly destroyed, Janeway crashed the ship into the weapon. With the weapon destroyed, the entire timeline was restored and the paradoxes ceased. In the "real" timeline, Voyager approached Krenim space and was advised to avoid it due to territory disputes. They altered course and never encounter the Krenim again.
  
  Annorax found himself on his home colony, with his wife, unaware of the chaos in time he had, and never had, created.

• In 2372, the Bajoran Wormhole was about to undergo an subspace inversion. On board the USS Defiant, NX-74205 , Captain Benjamin Sisko and his son Jake Sisko attempted to observe this phenomenon. When the wormhole began to invert, it caused a problem in Engineering and Ben went to look into it. Jake followed him, even though he was told to stay behind. The warp core suddenly went critical. Benjamin stopped it, but then the core released a discharge and struck both Ben and Jake. Ben disappeared and was presumed dead.
  
  Days later, Jake suddenly saw his father in a flash of light. He consulted Jadzia Dax and she found no anomalous traits. Jake dismissed it as a dream and moved on.
  
  With the death of Benjamin, the Bajorans felt that the Prophets had abandoned them and formed a defense pact with the Cardassians. The Klingons became angry as this happened and threatened war. The civilian population left Deep Space 9, but Jake stayed behind. Nog left and joined Star Fleet. Months later, he found his father in a hallway on the station. Jake took him to the infirmary and it was discovered that Ben was trapped in a temporal inversion, suddenly he would appear in normal space and then fall into subspace, unaware of the time that passed. Before they could help him, Benjamin went back into subspace.
  
  The situation with the Klingons became more dangerous and Star Fleet turned over DS9 to them. Jake left and moved to Louisiana, where he married a Bajoran woman named Korena and became a writer. Years later, the Klingons began to allow Federation ships through the wormhole again. One night, Ben appeared again and learned of the changes that had occurred. He disappeared right after he told Jake how proud of him he was. Jake became obsessed with getting his father back, to the point where Korena left him. Fifty years had gone by since Ben disappeared and the wormhole was about to invert again. Nog had become a captain and resurrected the Defiant from mothballs. With most of the crew, Jake went to the wormhole. As it inverted he was pulled into subspace and he saw his father again. Ben was horrified to find that Jake had lost his wife just to get him back and urged him to return to his life. Jake returned to normal space without his father.
  
  Years later, a woman named Melanie visited Jake and told him she was a fan of his written works. Jake told her the story of his father. The next day, Ben returned once again and was pleased to see that Jake has begun to write again. Jake explained that he discovered that he himself was what kept drawing Ben back from subspace. If Jake died while Ben was in subspace, he would be lost. But Jake discovered that if he died when Ben was in normal space, he would return to the moment of the inversion. Jake poisoned himself and died while his father was in normal space. Ben witnessed the death of his son, and suddenly found himself back on the Defiant and leaped at Jake, knocking him out of the way from the energy discharge, and preventing his disappearance into subspace.