Lost!

[bewitched]

Originally Posted by Pirate Bill

The fork in the timeline occurred in 1977 when the bomb went off. Not in the air. Everybody's lives took a different turn way before flight 815 didn't crash.

Originally Posted by innerSpaceman

I missed Pirate Bill's excellent point that the timeline diverged in 1977 when the bomb/incident happened. That's a satisfactory explanation for why the sideways world is so different from what it "was" or rather would have been.

Originally Posted by sleepyjeff

It's actually possible that the timeline diverged way back in the 1950's....since Locke, Sawyer, Juliet, Dan, Charlotte and Miles all visited the Island in that decade.....after 815 crashed.

I think it's impossible to say when/how/if the sideways timeline diverged from the known timeline(s). So far, we only know for sure that Ben and his father were on the island; the Losties don't seem to actually remember being on the island and may never have been (at least in their sideways life). Personally, I think it probably did diverge at some point but I'm not discarding the possibility of it being a parallel timeline (as opposed to a divergent one).