In an alternate reality, or parallel universe, the events which happen may have a different outcome. This can be applied to many phenomena that occurrs on the Island.

In Fringe:

This information is from the first season finale of Fringe. If you have not seen this, and plan to, do not read the next paragraph.

The World Trade Center was never destroyed in an alternate reality in Fringe.

In Fringe, created by J. J. Abrams, alternate realities is a major subject. A portal to an alternate reality can be created in areas where the "fundamentals of nature" have been decayed. The Bermuda Triangle is an example of this, which shares similar properties to the Island in Lost. Olivia Dunham, the main character in Fringe, was told she could meet with William Bell, the founder of a multitriilion dollar company that specializes in advanced technology. The problem is, Bell is not in this reality, but in an alternate reality. Olivia is inside an elevator when there is a flash. The doors open, and she walks inside an office. On the desk is the May 12th 2009 edition of the New York Post. The main headline is "Obamas set to move into New White House" suggesting that the White House was destroyed. A side headline is "Former Pres. Kennedy to address UN", showing that JFK was never assassinated. Bell (played by Leonard Nimoy), appears, and introduces himself. Olivia looks outside the window to reveal that she is inside the South Tower of the World Trade Center.

Sayid shoots Ben, but Ben does not remember being shot.

Time Travel may not just involve travelling through time, but also travelling through alternate realities. Some of the survivors are in 1977, along with the Dharma Initiative. It is obvious that they were not in the Dharma Initiative in this reality, so they must be in an alternate reality. This would explain why Ben does not remember being shot by Sayid, or anyone else remembering any encounters from people in the past.

Jack believed, as Daniel Faraday suggested, that if they stop the Incident from ever happening, they will never crash on the Island. Flight 815 would of landed in Los Angeles, and the passengers would of continued living a normal life. Changing the past is not possible, since they could not stop themselves from crashing if they were not on the Island in the first place. However, in an alternate reality, where 1977 is the present, the Incident could be stopped. While the result of the detonation of the hydrogen bomb remains unknown, it is a possibility that the Incident could be prevented.

One major mystery in Lost is Christian Shephard appearing to be alive. While he died in Australia, he appears alive on the Island. Christian could be from an alternate reality which explains why he is alive. This can also explain the presence of other dead characters. Hurley can see into alternate realities, which explains why he can see "dead people". Richard is in a way, a constant, in which he can appear in any reality in any time.