Ses
Seos (pronounced /sɛs/) is a cosmos where magic comes through dreams, and shadows of dreams seem to impinge upon the waking world itself. Indeed, so prevalent is the influence of dreams that the cosmos itself takes its name from them: "Seos" originated as an acronym for the longer term "Sanduche E Os Sobindoys", which means "World of Dreams".
The usual adjective form to refer to things related or pertaining to Seos is "Seosi" (pronounced /ˈsɛsi/).
Physics
Everything in Seos is made up of fundamental components known as wavelets, microscopic waves traveling through a medium called ether. Each wavelet has a certain mass associated with it; the mass of an object is the sum of the masses of the component wavelets. However, in addition to a mass, each wavelet also has an orientation; the orientations of the wavelets of a particular object are usually, but not always, the same. The weight of an object is the vector sum of the weight vectors of each wavelet, a wavelet's "weight vector" being a vector with a magnitude equal to the wavelet's mass and a direction equal to the vector's orientation. When all the wavelets are aligned, the object's mass and weight are of equal magnitude, but otherwise the magnitude of the weight may be significantly less (never greater) than the mass—in the extreme case, if the wavelets' weight vectors all cancel each other out, a massive object may have zero weight.
Any object with a non-zero weight has an inherent tendency toward acceleration. This fact is responsible for the phenomenon known in Seosi as gravitation. The exact formula for an object's acceleration is [math]\displaystyle{ F = gw\cos{(2c(w\cdot v)/m} }[/math], where g and c are constants known as the gravitational constant and the velocity constant, either or both of which may be equal to unity, depending on the system of units in use.
A number of forces affect the interaction between wavelets (note that Seosi gravity is not usually considered a true force, though this is mostly a semantic matter). The two best known are the metric force and the directive force, the former regulating the distance between wavelets and the latter causing nearby wavelets to move as a unit. These two forces are jointly responsible for solid objects retaining their cohesion, rather than dissolving into a myriad of disconnected wavelets. More recent discoveries have established that the metric force and the radial force are not in fact separate forces at all, but orthogonal components of a force now called the sympathetic force, but this information has not become common knowledge on all Seosi worlds, and the two are still often treated as different forces. (And, in fact, it is often mathematically convenient to treat them as different forces even for those who know they are not.) The term "sympathetic force" was originally used for the directive force (and indeed still often is, on those worlds where its unified nature is unknown); this may lead to some ambiguity, but when necessary the directive force is frequently referred to as the "pure sympathetic force", as opposed to the "total sympathetic force" that includes the radial metric component.
Chemistry
The minuscule wavelets that make up all matter on Seos come in various discrete frequencies, known as s. Unlike the case of quarks in Xi, the term "color" here is not arbitrary, but corresponds to a real connection between the wavelets and visible (and invisible) colors; a body made purely of wavelets of a given color will appear to be that color to the eye, though in practice few objects are really composed solely of wavelets of a single color, and the resultant appearance produced by the interaction of wavelets of different colors is not always straightforward. Wavelets are held together by the sympathetic force into larger units called plemmyrides, which in turn join into macroscopic objects.
Magic
The preeminent form of magic in Seos is dream magic, which seems to be brought into Seos through the dreams of its denizens, from another cosmos some scholars call Goetogenia. Mages learn to manipulate their dream energy to produce all manner of effects, and certain formulae of various sorts allow magical effects to be sparked by other impetuses as well, a phenomenon called association. Common types of association include geasa, through which people gain powers by adhering to certain strictures, and the potential of names to hold power over what they refer to.
Legend has it, however, that dream magic was not always inherent in Seos—that it was brought into the cosmos, ages ago, by the person who would become the god Gomar the Ancient. Considerable evidence has recently come to light supporting these legends, in the form of the discovery of whole alternate versions of Seos where dream magic does not exist at all. In light of this, the term "Gomara" was coined to refer collectively to those alternate versions of Seos in which dream magic exists. To refer to those alternate Seoses in which magic does not exist, the name "Aramog" was first proposed in jest, but has since caught on and become the accepted term. A few alternate Seoses have also been discovered where magic of some sort exists, but not dream magic; these are not considered part of either Gomara or Aramog, but there is no standard name to refer to them.
In those versions of Seos where dream magic does not exist, neither do the pervasive dreamdisks which contribute to the perception of dreams as an important force in the cosmos. This means, ironically, that the cosmos takes its name from something which not only does not exist in all versions of it, but apparently did not originally exist in any version. This is explicable by the fact that the cosmos was, of course, named in Gomara before it was realized that dreams had not always played such a large part there; the people of Aramog had no knowledge of other cosmoi and therefore required no specific name for their own. Still, while arguably inappropriate, the name "Seos" seems likely to stick.
Planes
The best known plane of Seos, and the one to which humans seem to be native, is Charos, a vast plenum filled with varicolored mists. Floating in the mist are numerous worlddisks, enormous flat circles (or, rarely, other shapes), the faces of which are the home of most life on the plane. Charos is also known for the dreamdisks that frequently appear there in seemingly random places, and that apparently represent someone's dreams, though whether they are the dreams of someone elsewhere in Seos or in another cosmos entirely remains in dispute. These dreamdisks do not appear exclusively in Charos, but have been seen in other planes as well, but it is in Charos that they seem to be the most prevalent.