OK sorry if this has been discussed before, and it likely has... But in Trek XI a separate timeline or alternate reality is created when the Narada destroys the Kelvin and then ofcourse subsequent events with the destruction of Vulcan. But it really starts with the Kelvin destroyed. So Spock Prime can't travel forward in time back to the late 24th century because he would be returning to a future from the universe he is in. Just like Doc and Marty in Back to the Future Part II. OK I get that, can't go back to the future. But what about all the previous time travel stories that Trek has done. Kirk and Spock traveling back in 1986 to pick up two whales and causing the disturbances they did, however minor...when they returned to the 23rd century shouldn't it have been a different universe then from when they arrived? The original timeline didn't have a group of weirdos foolin' around San Franciso looking for whales, and the original timeline didn't have that scientist/tour guide Gillian suddenly go missing without a trace. Same applies to all the other time travel stories, how was it that the characters returned to the "prime" universe after meddling around in the past? But poor Spock gets stuck in the past of an alternate universe.