## Different Classes of Volumes

This webpage is part of www.mass-gravity.com

Volumes may be classified into five categories:

#### 1/ Closed volumes

This category of volumes is explained in the Mass Webpage.

#### 2/ Open volumes

This category of volumes is explained in the Mass Webpage.

#### 3/ Standard apparent volumes

This category of volumes is explained in the Mass Webpage.

#### 4/ Hermetic apparent volumes

These volumes are combinations of closed and open volumes but their global volume is hermetic regarding spacetime.
For example, a nucleus is made of nucleons (closed volumes), separated by empty space (open volume).
Whatever the name given to this empty space or to the various components inside it (gluons...), the
behaviour of this combination of volumes is that of a closed volume regarding spacetime.
Consequently, the whole volume of the nucleus, i.e. closed volumes of nucleons + empty open volume + various volumes
enclosed in the nucleus, deforms spacetime and gets mass since *spacetime curvature = mass (Einstein, GR)*.
This does not conflict with Quantum chromodynamic (QCD).

#### 5/ Special apparent volumes

These volumes are "special" because we do not know their behaviour regarding spacetime.
This is the case of _{6}He, _{8}He, _{14}Be...
For example, _{11}Li has a core with 3p6n and a halo of 2n.
Since we do not know exactly the structure of such nuclei or the penetration of spacetime inside them,
it is not possible to classify these volumes into a particular category.

To summarize, we must always bear in mind that the word "volume" without any qualification is meaningless. It is important to make the difference between:

- Volumes (undefined),
- Closed Volumes (with mass),
- Open Volumes (massless),
- Standard Apparent Volumes,
- Hermetic Apparent Volumes,
- Special Apparent Volumes.

Since these volumes have different behaviours regarding the curvature of spacetime, i.e. mass, they must be differentiated.

We can continue to use apparent volumes in traditional physics. The separation closed/open volumes, as described here, is only necessary to explain the curvature of spacetime and the origin of mass and gravitation, and in astrophysics to solve some enigmas such black holes or black matter.