I originally was going to leave this as a reply to this Fringe Review of season four episode 19 of Fringe, but I got rather longwinded and ran out of room, so instead I decided to put it here. If you haven’t seen the episode in question, the following may include spoilers. If you have seen the episode in question, the following may still not make any sense to you. I’m not even sure if it makes sense to me.

Spoiler warning blah blah blah you have been warned ok here we go.

If spacetime travel is quantum dimensional, that’d mean there’s a near infinite number of alternate timelines to choose from. I take this from one of the more fantastical interpretations of quantum physics, which has of course not been proven but other explanations make even less sense, or don’t allow time travel at all.

First off, according to Hawking and many other bright minds nowadays, space and time are technically not separate entities. We perceive them separately but they work in conjunction with one another in such a way where you can’t really separate them. Say for example you want to go back in time to your own tenth birthday party. You can’t just go back in time without also moving in space, because tho you don’t feel it right now, the Earth is spinning, revolving around the sun, which is revolving around the center of the galaxy, which is also moving, and so forth. So to go back in time you not only have to turn back the clock, but mathematically calculate where the Earth was in relation to the rest of the universe at the time you want to go back. Like I said, while space & time are perceived as separate, they’re so intertwined as to be practically the same thing.

But quantum physics entertains the notion of The Many Worlds Theory. This means that since the initial big bang, EVERY time a sub atomic particle could go either this way or that, both possibilities happened simultaneously in different spacetimes. This means in the first few seconds of existence, it wasn’t one reality that popped into existence, but billions. As alternate possibilities exponentially came to fruition, we had a multiverse of alternate realities. Any given moment of time, like say the moment you’re reading these words, more alternate realities are achieving fruition than there are grains of sand on all the beaches of the Earth. Every minute. Throughout the course of spacetime.

If the Observers “destroyed” their present, they could go back to any alternate past they wished. They could scatter themselves through a near infinite number of possible pasts. In fact, going back in time would technically change that time, creating an entirely new reality without erasing the one visited. Then if they could somehow communicate back to their original present, they could invite fellow Observers to visit where/when they were, after of course observing and determining it was suitable for their kind.

So traveling back to A past would be considered by The Observers as not unlike going on safari. How we might perceive snorkeling or doing missionary work in a third world country. The reality would be very real; an adventure, and at the same time the consequences of one’s actions would not necessarily affect directly your own home. Or at the very least, they can’t do any more damage to their past than the Observers apparently already have done to their present.

So, conquest of any one of these alternate pasts would not necessarily affect their own abandoned present, at least not directly. One could dramatically change A past without adversely affecting their already destroyed present. The alternative explanation, where there’s only one linear timeline, has already been dismissed by the storytelling of Fringe. There’s two alternate worlds that we know of. That was established. Furthermore, the Observers have spoken in the past of multiple futures. September told Peter he saw all of them and in all of them the unavoidable thing is that Olivia has to eventually die.

So we can assume there’s more than two. And if we go that far, it’s less of a stretch than one might think, of assuming there’s a near infinite number of alternate Fringe universes.