This has caused some to suspect that the Abyss may lie outside the multiverse, which of course is contradictory and ontological; however, this theory would imply that the multiverse exists somewhere within the Abyss. I do not pretend to understand the ramifications of such a statement.
Understanding time is critical to understand the vast majority of the multiverse. Time is the zeroth dimension, and orders (and reorders) the multiverse. It is different from all of the other 665 dimensions that form the multiverse, in that it is the baseline for the ordering of the different universes of the material planes.
For clarification, the Planes of Orc — the material planes — comprise the majority of the multiverse and are its heart, assuming something that is technically infinite can be the majority of something super-infinite. The material planes are bound by, and ordered by, Time. The Outer Planes, as reflections of the material planes, are thus affected by time as well; however, the very powerful magineers (gods) living there are more than capable of distorting their own reflected worlds. I must cut this discussion short, because, while quite interesting, it comes perilously close to discussing one of the touchiest issues between the accords of the gods and demons, the Rules of Temporal Manipulation. Allowing that the RTM are a very political issue, I shall not discuss them further in this article.
As stated previously, the æthereal realms, being tied to their material planes, are temporally synchronized with them. The Astral Plane is loosely coupled in time with the material planes, and because of this loose coupling, there can be some very unusual circumstances. For example, two different incarnations of the same individual from different closely aligned timelines can actually meet with impunity in the Astral Plane.
The Elemental Planes are assumed to be relatively immune to, or unaffected by time. Since there is no life there, at least as far as anyone can determine, there is no clear way to measure or detect time in the Elemental Planes.
The Abyss clearly has time — is ordered by time — but as stated, there is only one timeline for the Abyss; there are no alternate Abysses. At least, not so far as anyone can determine. Similarly, the Abyss has no æthereal plane; we suspect this is related to the fact that spirit forms (animabodies) can exist here without being dissipated.
The time invariance can create some paradoxes when mortals come to the Abyss, as in theory, it should collapse a mortal’s timelines to a single instance; yet upon their return to their material planes do their timelines merge back to their original state? This is not clear to our researchers due to the fact that we cannot directly measure our own alternate timelines. We can only examine alternate timelines that are highly distinct from our own.
There is some speculation that this is how some “deceased” individuals in a particular material plane/timeline manage to return from “hell.” The idea is that an alternate, non-deceased version of them travels to the Abyss and then returns to their timeline. A glitch in their re-merge could cause the previously deceased timeline version to return to their original timeline, once more alive after having been in the Abyss.
In any event, back to time.
Most material planes of existence have a single primary timeline. This timeline may temporarily bifurcate when individuals make different actions in the same circumstance; however, if these differences (such as what one ate for breakfast) are minor and make no major impact on the timeline, they are quickly collapsed back to the main timeline.
However, there are times when a confluence of events is so extreme that the timeline will bifurcate more severely, and there may be multiple independent timelines for years, centuries or millennia before they collapse and merge back; and if the course of events compounds, the multiple timelines may end up being completely different planes of existence.
It is possible to travel purely in time, or nearly purely. To travel in time, one must also travel in space, unless one wants to end up in “outer space” (whatever that is in one’s universe) due to one’s planet moving. Thus, true time travel, except for very short jumps, is quite tricky, complex and energy-intensive.
This is one reason it is not done that often, other than by inexperienced individuals. Given that temporal bifurcations generally collapse back to the main timeline, there is little point in traveling back in time, unless one is planning to stomp on a large number of butterflies and thus force a permanent bifurcation of one’s material plane.