Perhaps I just have a bias against parallel dimensions (as evidenced from my interpretation of Silent Hill's otherworld), but I want to take some time to clear up what might be a mis-conception in the conventional wisdom interpretation behind Dark Souls' multiplayer summoning mechanics. Dark Souls co-op is not necessarily based on parallel dimensions, as many players seem to assume. It might, in fact, be intended to be an abstraction of some kind of time travel. I've noticed that many players online already seem to refer to the multiplayer mechanic of these games in terms of time travel, but I've yet to see any wikis, lore videos, or blogs that seem to explain multiplayer as a time travel mechanic.

I want to preface this analysis by stating that I'm not asserting that the following explanation is the absolute, 100% correct interpretation of the mechanic. Individual players may disagree based on their own reading of the game, and I'm personally somewhat conflicted on the topic myself. I merely want to propose this as a possible alternative to the defacto "parallel worlds" interpretation. I'm going to point out in-game evidence that supports the idea that Dark Souls' multiplayer is based on time travel, but there is also in-game evidence and mechanical evidence that flat-out contradicts that interpretation. I will address those contradictions as well. So that being said, please keep an open mind, and enjoy the read!

The summoning mechanic

There are two games in the series that are not part of the Dark Souls franchise, and which have different in-game explanations and rules for the same multiplayer features (more or less). Those games are, of course, Demon's Souls and Bloodborne. Both have asynchronous multiplayer and summoning mechanics that work similarly to Dark Souls.

Demon's Souls summoning operates under the idea of summoning the spirit of a fellow adventurer who's soul is trapped in the Nexus. This is why you must be in soul form in order to be summoned. Bloodborne's beckoning operates [similarly] under the principle of manifesting hunters out of dreams (which seems to operate under a similar cyclical paradigm to Dark Souls, but I'm not 100% sure). In Dark Souls, you aren't necessarily summoning ghosts (as you do in Demon's Souls), since the undead in Dark Souls are more akin to zombies than ghosts. Also, characters in Dark Souls can leave summon signs whether they are hollowed (dead) or in human form (revived), which is a significant alteration from Demon's Souls. A lore reason for summoning is provided in Dark Souls:

Solaire explains to us how summoning works:
"We are amidst strange beings, in a strange land.
The flow of time itself is convoluted; with heroes centuries old phasing in and out.
The very fabric wavers, and relations shift and obscure.
There's no telling how much longer your world and mine will remain in contact.
But, use this, to summon one another as spirits, cross the gaps between worlds, and engage in jolly co-operation!"

Both Solaire's dialogue, and the White Sign Soapstone (along with other online play items) make references to other "worlds", which leads to many jumping to the conclusion that each player's game is a sort of parallel universe within the Dark Souls lore. However, this may not necessarily be correct. Both Solaire's dialogue and the soapstone also provide explanations for these worlds: "time is convoluted | distorted". This seems to be the explanation for what is meant by "worlds", and it seems that Solaire and the in-game descriptions may be using "time" and "world" interchangeably (could it be a translation / localization issue?). The phrasing in the white soapstone's description joins "the flow of time is distorted", and "the White Soapstone allows undead to assist one another", into a single, compound sentence, which definitely implies that the two phrases (and ideas) are linked.

"Online play item. Leave summon sign.

Be summoned to another world as a phantom through your sign, and defeat the area boss to acquire humanity.

In Lordran, the flow of time is distorted, and the White Sign Soapstone allows Undead to assist one another"

 

The dialogue of Saulden (the Crestfallen Warrior of Dark Souls II) is even more explicit...

Interstellar is a rare hard sci-fi movie.

There has been a sad dearth of hard science fiction movies in recent memory. While comic book and alien invasion movies and the like have been proliferating (and some of them have been very good), there haven't been as many movies that have been willing to take science fiction subject matter seriously. The only mainstream releases that I can think of off the top of my head are District Nine, Inception, and Gravity, neither of which really wowed me. District Nine was alright, but I felt that its racism allegory fell flat since the aliens themselves considered the majority of their species to be mindless automatons. Inception was a fun ride, but nowhere near as clever or complicated as people made it out to be. And Gravity wasn't really "science fiction"; more like just "space drama" disaster porn.

That leaves the indie movie Moon and the surprisingly good Rise of the Planet of the Apes and Dawn of the Planet of the Apes as the only really good examples of high-brow science fiction that I can think of - and maybe Edge of Tomorrow can count as "medium-brow".

That's why I've been very excited about Christopher Nolan's new movie, Interstellar. It had all the trappings of a modern-day 2001: A Space Odyssey, which (confusing psychedelic ending aside - read the book!) is one of the best hard science fiction movies ever made. Interstellar definitely lived up to this expectation, but it's a much gloomier and more depressing epic than Arthur Clark and Stanley Kubrick's masterpiece.

The space travel plot is, in fact, almost identical to 2001. A crew must travel in hypersleep in an experimental spacecraft to investigate an anomaly around Saturn (the original 2001 book placed the monolith in orbit around Saturn, but it was changed to Jupiter for the film). The sleeping crew is even overseen by intelligent robots. The rising action has conspiratorial undertones, and the climax dives deep into metaphysical fringe science.

Interstellar [LEFT] is very similar to Arthur Clark and Stanley Kubrick's 2001: a Space Odyssey [RIGHT]
in its detail-oriented depiction of space travel.

A lot of the science in the first half of the movie is solid, and it's actually integral to the narrative and drama between the characters. The second half takes a lot more creative license for the sake of plot. There are significant issues with relativity with regard to a black hole, metaphysical stuff about a "ghost", and some ham-fisted mumbo jumbo about the power of love transcending time and space. But despite some silly science, there's a very real possibility that audiences might leave the theater with a better understanding and appreciation of relativity.

So Interstellar definitely earns its comparisons to 2001...