The Fourth Way cosmology is based on a scale of seven worlds or cosmoses. The scale of densities of the Ra and Cassiopaea materials is related to this but the emphasis in the classification is different.
It is often said that the universe is a great cosmos or macrocosmos and that man is a small cosmos or microcosmos. The hermetic maxim as above, so below for instance can be understood to refer to this. The idea is quite abstract and does not produce practical conclusions in this form. The Fourth Way exposition is broader and more detailed and may to a degree be at least circumstantially glimpsed in nature.
Both In Search of the Miraculous and specially Mouravieff's Gnosis series discuss cosmoses in detail, hence we will only summarize the main points here and attempt to relate these to the idea of densities and dimensions.
From In Search of the Miraculous:
"The first cosmos is the Protocosmos--the first cosmos. "The second cosmos is the Ayocosmos, the holy cosmos, or the Megalocosmos, the 'great cosmos.' "The third cosmos is the Macrocosmos--the 'large cosmos.' "The fourth cosmos is the Deuterocosmos--the 'second cosmos.' "The fifth cosmos is the Mesocosmos--the 'middle cosmos.' ' "The sixth cosmos is the Tritocosmos--the 'third cosmos. ' "The seventh cosmos is the Microcosmos--the 'small cosmos.' "The Protocosmos is the Absolute in the ray of creation, or world 1. The Ayocosmos is world 3 ('all worlds' in the ray of creation). The Macro-cosmos is our starry world or the Milky Way (world 6 in the ray of creation). The Deuterocosmos is the sun, the solar system (world 12). The Mesocosmos is 'all planets' (world 24), or the earth as the representative of the planetary world. The Tritocosmos is man. The Microcosmos is the 'atom.'
The relationship between each cosmos and the next higher cosmos is like the relationship of 0 to infinity. One way to interpret this is to say that different cosmoses have a different number of dimensions. The relationship of a plane to a 3 dimensional space is an example. The plane has 0 volume and the space is formed by an infinity of parallel planes, so to speak.
A cosmos cannot be understood by itself. It must be seen in relation to the next higher and next lower cosmos. A 'miracle' is a manifestation that accords to the laws of a higher cosmos than the cosmos where it is observed. It seems supernatural only because the laws which govern it are not known or understandable in the cosmos where it occurs. Cosmoses should be seen in triads, together with the immediately higher and lower. What is the center of one triad will be the lower end of another and the higher end of yet another, thus cosmoses overlap and interpenetrate.
Ouspensky and Mouravieff say, somewhat confusingly, that cosmoses are each three dimensional in their own right. Still, each higher cosmos adds a dimension. We may understand this to mean that the analog of three dimensionality of a cosmos is formed by the dimensions added by itself and its lower and higher neighbors. Still, even this concept is problematical since from the human perspective all processes in space, whether molecular or galactic, thus a full five cosmoses apart, take place in the same three dimensions of space. Too much literal interpretation loses the point.
Time is different in each cosmos. The lower the cosmos, the shorter the timespans. The life of bacteria is about a day, the life of man around 30000 days. The lives of planets and stars are correspondingly longer. Some authors such as Rodney Collin attempt applying constant scale factors to relations between cosmoses but these are at best approximate and little can be deduced from this, aside the fact that processes at different scales take different amounts of time. These comparisons give some impression of a cosmic pattern but the analogies are not exact and it is not possible to directly extrapolate from one scale to the other. According to esoteric science, the laws of 3 and of 7 apply at all scales but the form and locus of occurrence is not identical.
The cosmoses or worlds of the Ray of Creation are subject to varying numbers of laws. The lower the cosmos, the more deterministic and mechanical or less conscious and alive it is. Each level has all the laws of all levels above it plus three new laws of its own. The laws are similar in concept but even within one law, the manifestation may be different and specific to the cosmos where it takes effect.
Here too we will be misled by taking the descriptions too literally. Seen from the viewpoint of terrestrial science, a planet is not necessarily more conscious or alive than a human. We may think that what is seen as a planet is a cross section of a being that extends into dimensions not discernable to human perception, thus one cannot say anything of the planetary entity's aliveness or consciousness. Even this is however too literal. It is most likely incorrect to associate the terms of planet, sun and galaxy as used in the schema of worlds and cosmoses to the astronomical definitions of these things.
We may see cosmoses in relation to the table of hydrogens. A higher hydrogen holds a higher 'density of or 'vivifyingness'vibrations' or is 'closer to the source of creation.' The scale of hydrogens as presented by Ouspensky and Mouravieff spans elements of multiple cosmoses. Beings of different cosmoses would be constituted of different hydrogens and feed on hydrogens of a lower level and produce hydrogens serving yet a higher level. Each entity can be defined by its place on a food chain. The higher the entity is, the more vivifying its 'food' is, or the more 'density of vibrations' or 'intelligence' it involves.
For example, humans eat H768. As evidenced by the cattle mutilation phenomenon and other circumstancial evidence, the fourth density aliens eat blood (H192) and endocrine secretions (H96) at least when interacting with third density. The 'food for the moon' or the 'vibrations required of humanity by nature' consist of H24 and H12, that is intense emotion or sexual energy. We may thus see the human form as a stage in a food chain feeding denizens of a higher cosmos.
Man, according to his degree of development, may participate in different cosmoses. The formation of the astral body in man 5 will allow contemplation of a higher world. The formation of the mental body or real I in man 6-7 opens yet more possibilities of perception. In Gnosis, these are associated to the mesocosmos (which we tentatively identify with planetary world or fourth density) and the deuterocosmos, solar world or sixth density. In the Fourth Way system , composing a body of hydrogens belonging to a specific world allows interaction with it, eventually making one a natural inhabitant of said world. Hence one may use the hydrogens secreted by experiencing shocks for one's own edification instead of shedding these to 'feed the moon.'
Beings composed of different hydrogens have their natural residence in different cosmoses and have correspondingly different levels of intelligence and capacity of perception, also as concerns the concept of time and dimensions of space. This corresponds roughly to the scale of densities of Ra and Cassiopaea. While the concept of world on the Ray of Creation or cosmos emphasizes the constituent matter and laws applying to the level, the Cassiopaean concept of density emphasizes the characteristics of consciousness and lessons that apply to each level. Both scales measure a qualitative degree of distance from a single source of all creation. Both scales feature different types of living entities at different levels of such a ladder. The diagram of everything living in In Search of the Miraculous also alludes to this topic.