Is 4D less or more dense than 3D?

[Infinite]

Well if 4th density is defined as "Astral World"...
As such 4th density body is defined as "Astral Body".. or "Astral Presence".

Then tadaaa..... you all already have it all along!
Although some of the human might not be aware of it.
No need to wait for some alien to do some things or event in the future like harvest or things like that.
By the way I also don't understand what this 'harvest' really is... are we some kind of a crop?

I see the fourth density as a kind of astral universe, but not the same as our astral plane. Just as the subtle bodies that we have seem to me analogous to the bodies that we will use at higher densities, but they are not exactly the same thing. The fourth density body would be a vehicle superior to the astral body of a third density entity. Therefore, both the microcosm and the macrocosm have the rays of all densities in potential.

In certain esoteric traditions it's said that for ascension it's necessary that man build a body called "solar astral body". I suppose that is the fourth density body. The term "solar" refers to the fact that the astral body that every 3D entity naturally has is classified as "lunar". It's an inferior body, which cannot be expressed in the superior astral plane.

About the Harvest, simply speaking is a metaphysical process in which an entity can goes from one density to another. Ra explains that it's about walking on steps of light until the entity stops at the frequency most comfortable for it. This frequency can also be of the third density or of the fourth (using the Harvest for 4D as an example).

This Harvest can occur in two ways: entities that reach the eighth level of the third density, which is the level of intelligent infinity, are able to harvest themselves, whether they are STO or STS entities. We can call this "self-harvesting". The second way is through a process that takes place at the end of a 25,000-year cycle. In this process, the gateway to intelligent infinity opens and entities that have a minimum fourth density vibration (51% STO or 95% STS) are able to go to fourth density. At least in terms of the third density, this need to reach the level of intelligent infinity seems to me due to the octave nature of the densities. To reach the eighth level of an octave is to reach the first level of the next. This process has been called "quantum leap".