You can change the future, but you can't change the past by JackBauer

I'd like to share my view with you on the Flash-sideways and the reason we are seeing them.

Remember what Faraday and Miles said back in season five about the rules of timetravel? Them being back in 1977 does NOT mean they can't die there, because they would excist in 2007. In fact, in their own life's timeline it is their present, whatever year it may be around them!

The whole discussion about WHH/ALT (They can/cannot change things) has suddenly become irrelevant. Since we're seeing the flash-sideways, I think we can all agree that BOTH happend! Here's my scenario:

Losties from 2007 travelled back in time to 1977. They want to chance the outcome of events, that to THEM already happened, but to the timeline did NOT happen yet..

So what will happen if they create a 'plothole' in history by detonating the bomb? Time would course-correct the timetravellers' presence back to where they belong, which is on the island in 2007 where they left off!

That is why we see them on the exact same location they were at in 1977 (around the Swan's location). So basically, to them, time around them moved back to the present but their place was unchanged!

Like I just said, the events the losties wanted to prevent already happened to the them and you can't change the past, because whatever happened in the past (their past), happened and therefore can not be changed!

Now the other side of the story. Since the Jugghead detonation took place in 1977 and none of the things that had to be prevented happened yet at that time, it WAS possible to change the outcome, because you CAN change the future!

So why are we seeing flight Oceanic 815 again, but not crashing this time? Because this is the NEW future of the new created timeline caused by the 1977 detonation! Probably the bomb created a hole in the ground causing the entire island to sink and everyone on the island at that time: Dharma, Others, Jacob/Blacky (?) to die!

But chronologically, it is 2004 again just like the original flight 815 that did crash. So in time, the new timeline is happening at the exact same time as the original one. Based on the season premiere I'd say both timelines seem to be doomed and in order to create a happy ending, a fusion of these two might need to happen.

Summarized: You CAN change the future, but you CAN'T change the past.