So this is just a proposal or idea on how to possibly deal with interactions between dimensions, and eventual problems that may, have, and will happen.
So the idea is the the Multiverse does exist, there are an infinity of universes (I call them universes and dimensions too, but maybe dimension would be more accurate when they start to become more conceptual), and each universe undergoing the change of time, split into parallel universes at each single change, one universe for each possibility.
Our universe follows some rules, like the constants, they never change, light will always travel the same distance during the same amount of time and in the same medium (like interstellar void). But what stops it from travelling another distance instead ? Well in the Multiverse there are an infinity of universes with every possible value for each possible constant (they can be truly anything that mathematics allow).
So because of this, finding one specific alternate universe is a terribly hard task, that only the cultures which are extremely advanced in the mathematics field would be able to achieve.
The travel between them is a whole other story that requires to solve even more complex mathematical problems. And any mistake could bring upon unspeakable doom that can't be imagined.
Because of this there were only a handful of encounters from other dimensions, the most part being from relatively close parallel universes. And from most of the visits to other universes, very few if any had any form of satisfying information coming back from the other dimensions. Due to the seemingly non-reciprocal aspect of the communication between dimensions, there is not much enthusiasm left for any further trial.
However then come the ethereal dimensions, the ethereal dimensions are a group of parallel universes (parralel to their own, not ours). Their inhabitants seem to have extremely advanced technology (their culture extremely old too, probably older than our own universe) and they managed to create relatively solid communications between their parallel universes. However recently (recently is a vague word, this could be only centuries just as it could be several millenias ago) they found an universe which features laws of physics relatively similar to their universes, similar enough to allow travel between them. But it is only a few years ago that they finally managed to get solid communications.
However their dimensions still feature major differences between ours, the most notable being a form of energy called Ethereal energy. However there is an oddity in which a relative to an Ethereal being can control said energy even without being in said dimension although the control over it is severely weakened.
However do keep in mind that in a single universe goes through the change of time, time is only a word describing change, that means that the future is not written, and that the past doesn't exist, it's only an everchanging now.
But because of the infinite nature of the Multiverse, every possibility exists, so somewhere in the unending amount of universes, you may find an universe that is just one second to the past of our own universe.
And also, universes that have spatial dimensions similar to ours also feature an infinite universe, they also don't need dark energy to be that way.