In the latest Star Trek movie, manipulation of the timeline causes a whole new series of events to occur. This has lead to many to speculate whether the Star Trek universe we all came to know would continue to exist.
As the handy chart from
Star Trek Online shows, the new timeline splits off from the standard timeline and both alternative realities continue to exist, in fact the alternate timeline needs the events in the standard timeline to have
occurred, otherwise the alternate timeline could never have been bought into
existence. So both
timelines are valid.

Of course this is not the first time alternative universes have been seen in Star Trek.
The Original Series episode "Mirror, Mirror" introduces us to the idea of a Mirror Universe, which runs
parallel to the Standard Universe. Virtually everything in the Standard Universe is duplicated in the Mirror Universe, however the Mirror Universe counterparts are opposite in nature and so are
morally corrupt. In the Enterprise episode "In A Mirror, Darkly" we see how this alternative universe came about. Instead of welcoming the
Vulcans when they make first contact, the Humans kill them and seize control of their ship. Thus, the Terran Empire is born and becomes a conquering force instead of a society based on peace and exploration.
We saw how in "Yesterday's Enterprise" (a Next Generation episode) altering the events of the past has
repercussions in the future. When a previous
starship Enterprise ( the Enterprise C) emerges from 22 years in the past, Federation history is distorted, and an alternate timeline is produced. Instead of living in peaceful
coexistence, the Federation and Klingon Empire are at war. The Enterprise C left a focal point in history, and needed to return to its point of origin to restore history. The alternate timeline that had been created was still valid, as it allowed Tasha
Yar to exist, and thus go back in time with the Enterprise C, which played a role in the events surrounding the Klingon civil war.
In the Voyager series finale "Endgame" we see
Admiral Janeway alter history to get the crew of Voyager home. In the
Admirals timeline it takes Voyager 23 years to travel back to Earth, but by manipulating the timeline, Voyagers' journey back to Earth only takes 7 years. Using technology from the future, the
Admiral also deals a
crippling blow to the Borg Collective, and so a new timeline is created. Again both
timelines would exist
simultaneously as the technology used to defeat the Borg and travel back in time came from
Admirals alternative timeline.
It may all sound like science fiction
mumbo jumbo, but it does
illustrate the principle of quantum theory, which is a valid scientific
hypothesis. Like ripples in a pond, the
further away you get from an event which causes an alternative quantum reality to form, the more divergence you are likely to see. It just means that in the
mulitiverse, all possibilities exist.