Since I'm a Grade-A nerd, that's not going to be nearly as sexy as it sounds.
Between comic booky discussions of Bubble Worlds and Retcon, I've been asked to clarify my thought, so I'm going to propose visual aids to better define the terms I use. And I think it'll make new points on top of the old ones as well. Let's just take things one step at a time.
Before we even get into bubbles and whatnot, let me pay once again my debt to the Absorbascon's dynastic model. Scipio is especially interested in "dynastic centerpieces" (iconic figures like Superman, Batman et al. that can support their own series) and defines certain roles surrounding that centerpiece (the girlfriend, the loyal pet, the arch enemy, etc.). When all the pieces are in place, you have the makings of a true icon with a rich, memorable world around itself.
I'm throwing the net a little wider: Every character and concept surrounding a particular character is part of its "dynastic model", whether there's a defined role for them or not. Here's an example:Each character is a character's dynasty may also have his or her own dynasty, which probably has many of the same elements as the more iconic centerpiece. Note also the inclusion of the character's "contextualizing city", another Absorbasconcept, as an element of the character's dynasty. Now imagine these dynasties floating through what I'll call a Continuity Bottle:
This is the DC Universe, which I'm using as an example in all but a few places because it's got all the features I'm looking to discuss. Imagine all characters moving through this continuity fluid like molecules, brushing against one another and combining in varied ways. Usually, a character moves with and interacts only with its own dynasty, but any element can be shared by another "dynastic molecule" (a crossover, a guest-star, a lent villain, etc.) even to the point of losing that element to another dynasty over time (the Kingpin moving from Spider-Man to Daredevil for example). Let's not forget the particular problem of superhero teams:
Teams have their own dynastic model after all, HQs and vehicles and supporting cast and villains that are not usually shared with the member characters. Or a team might have members that aren't usually out on their own, so would usually remain with the team dynasty (the Legion of Super-Heroes for example). A team like the pictured JLA would have many large "receptor sites" to allow combination with lots of character that have their own large dynasties. As can be seen from this model, nothing is ever at the true "center" of a molecule, they're all on the "outside" to allow combination with other elements. In a shared universe, no man is an island.
Enter Bubble Worlds. As defined earlier, sometimes a character's world (read: its dynastic model) is expanded through both time and space in an effort to make its series at once a stand-alone world with its own particular rules within the shared universe, and at the same time add something to the sum of that universe. The dynastic model bubbles outward and/or backward. Let's put the recent Lantern Corps development into the bottle:
While the model shows a colored bubble around the dynastic model, this is just a graphic representation. In actuality, there is no difference between the fluid inside and outside the bubble, it's all the same continuity. However, it does mean that Green Lantern's dynasty has gotten less dependent on other character's dynasties, or possibly, that many more characters can now interact with his dynasty. The membrane is entirely porous. Over in Marvel's continuity bottle, Iron Fist's dynasty has bubbled backward in time as well, creating precursor Iron Fists. I mention this only to show that in a continuity bottle, all continuity is represented, not just the "present", but the past as well.
There's something else in the bottle though: Partitions. This is an attempt to explain the Vertigo problem whereby, mostly because of editorial fiat, some characters are trapped. They may have originated in the DCU proper, but having been used to tell "mature readers" stories (mostly horror and fantasy), they cannot be used in traditional G-to-PG-13 continuity.
Here the membrane is only semi-porous. Very often, characters go in, but don't easily come out. This is accepted as a different area of the same continuity, and characters don't often interact with characters outside their Partition though it happens from time to time, and certainly, some characters make the conscious move to that "other place". Vertigo isn't the only Partition in the DCU either. The Wildstorm universe might have been a totally different bottle, but with Captain Atom moving there and now Wildstorm taking its place in the multiverse, there's no question that it is behind a Partition. As are all the imaginary stories, possible futures, and Elseworlds:
With Partitions, you can see the fluid really is different, because there is a different continuity at work, and yet it's a continuity that exists side by side with the present one. Characters could conceivably move through the Partition and find themselves in the other, simultaneous continuity because it's all part of the same shared MULTIverse. Even Vertigo has its own rules that make normal continuity loopy. Can the world of superheroes be reconciled with the more mystical yet down to earth nature of many Vertigo titles?
Which brings us to Retroactive Continuity. My contention has been that a shared universe is continuously being retconned. World history and fashion change too fast for the character's age, personalities and looks are being amended with every creator change, and so on. So think of continuity fluid as if it were fermenting, always changing (usually subtly) to keep pace with the time scale, creative license and editorial direction. You need a less subtle Crisis? You'll need to shake the bottle.
Here's our bottle after one or more shake-ups. Past continuity isn't gone, so long as we remember it. Before the bottle was shaken, past continuity was partitioned off behind thick Continuity Walls. The new continuity is based on the old, but that's oversimplifying the interaction between continuities, isn't it? Upon shake-up, many elements are destroyed, others rearranged, partitions are busted up (such as other companies' properties poured into the bottle), leaving intact the bare bones of any given character's dynastic model. The stronger the bonds, the more likely these elements are to remain attached. That's why we'll never see a Superman without a Lois Lane, yet a villain like the Kryptonite Man might not make it. But isn't it strange that years after the reboot, a dropped element will show up again, say Red Kryptonite. How can that be? Let's look at that Continuity Wall more closely:
What appears here is Continuity Funnels, straws leading from the undercontinuities and sporadically feeding current continuity. When the old element hits the new fluid, it finds a way to adapt and transforms into a revamped version of the old element, sometimes as a wink and a homage, sometimes as a full blown element. During a shake-up, any number of old continuity elements might slip out of the funnels and reinfect the new continuity. Obviously, funnels to outside continuity are part of an Elseworld's genesis.
Funnels might also be how characters can travel from one bottle to another:
In these cases, a Partition somewhere inside or at the edge of the funnel is invariably created so that characters crossing over into another shared universe are not allowed to remember it. Whether it's DC. vs. Marvel or Batman/Spawn, none of it happened in any continuity but its own. Leakage between bottles is probably also responsible for homage/parody characters, like the Extremists looking like Marvel villains, or the Squadron Supreme being based on the Justice League.
Well, I hope that explains a few things. If not, I'm taking questions. It's also still an incomplete picture as I plan to add a few things to the model in the weeks to come.