100% scientific explanation of Mass, Gravity and Curvature of Spacetime
 
Problem to solve
Let's consider a flat spacetime (a). The insertion of an object will curve this spacetime (b).
We see that it is the VOLUME of the object, not its MASS, that deforms spacetime. This is a logical observation ...but since 1919, experiments show the contrary.
Indeed, Einstein demonstrated that spacetime is curved by masses, not by volumes. This assertion, which is verified by   experimentation, is totally irrational since, to date, no one can explain how a mass can curve spacetime. So, the question is:
 
ï¿½ by volumes? (logical, consistent...)
     ï¿½ or by masses? (irrational, but proven)
 
Solution to this problem
Spacetime isn't curved by VOLUMES, or by MASS as we think, but by a special type of volumes: "Volumes with mass". This kind of volumes satisfies both general relativity   (curvature by MASS) and common sense (curvature by VOLUMES), as the previous fig. b shows.
Volumes with/without mass
a/ Let's drop an empty sphere in metal in a container filled with water. It is the volume    of the sphere - not its mass - that produces the displacement of water. The latter exerts a pressure   on the surface of the sphere.
b/ If we make holes in the sphere, water will go inside and the pressure will disappear.
Thus, two identical volumes may have different behaviors: in one case we have a pressure (a), and in the other   not (b).
In spacetime, on Earth and everywhere in the universe, we also have these two types of volumes:
(a) Closed volumes (volumes with mass),     such as elementary particles. Their internal spacetime "pushes" the surrounding spacetime to make room.     Thus, "closed volumes" produce a convex curvature of spacetime. Since the latter has properties of elasticity     (Einstein), it exerts a pressure on the surface of these volumes. As a result, a "mass effect" appears, i.e.     an effect having all the characteristics of mass. The mass component [M] can be extracted from the pressure     [M/LTï¿½] by simple mathematical operations (see the mathematical demonstration section). This conducts     to a 4D expression of the mass: m = f(x,y,z,t).
(b) Open Volumes (massless volumes): It is just a vacuum, but     sometimes found in various forms such as the volume of orbitals or the space between atoms. These volumes     exist but they are "porous" regarding spacetime. More exactly, they are subject to variations of spacetime     but they don't curve spacetime themselves. Therefore, open volumes are massless since no curvature means no mass (Einstein).
So, replacing "Mass" by "Closed volumes" doesn't change anything but allows us to solve three enigmas:
It gives a rational explanation of the curvature of spacetime,
It explains with great simplicity the mass origin, which is a consequence of the pressure of spacetime     on closed volumes,
And also gives the 4D mass expression m = f(x,y,z,t). See the mathematics section.
The following example shows the relation between mass and volumes.
Apparent Volumes
Objects we use daily are apparent volumes defined as:
 
Apparent volume = Σ Closed volumes + Σ Open volumes
 
These volumes, mainly atoms, are a combination of:
Closed volumes (protons, neutrons,     electrons). These volumes deform spacetime and, as explained, have a mass, more precisely a "mass effect".
Open Volumes (volumes of orbitals, space between atoms...).     These volumes are transparent regarding spacetime since they don't curve it. They are massless.
The proportion of closed/open volumes (i.e. mass/massless volumes) varies from one atom to another, from one   molecule to another, from one object to another...  This is why we feel that mass and volume are two different   quantities. This is an illusion. In reality,
It is the proportion of closed/open volumes
in each atom that varies from one object to
another, which gives us the feeling that mass
and volume are two different quantities.
Note 3 (for physicists)
Conclusions about mass
The 4D expression of the mass effect means that the entire universe can be described with only 4D expressions,   as Einstein thought his whole life. We don't need extra-dimensions such as 5D, 6D, 7D...nD, or extra fields such   as the Higgs Field.
We must always have in mind that the word "Volume" without any precision doesn't mean anything, at least to   understand the curvature of spacetime, mass, and gravity. It is important to clarify our definition of volume.   Are we talking about:
Closed volumes?...
 
What is Gravity?
If we replace the closed volume of precedent figures by two or more closed volumes, the pressure exerted by spacetime on   these volumes tends to bring them closer to each other. The result is equivalent to that of an attraction. For example, a pressure   on one side of a sheet of paper is equivalent to an attraction on the other side. In both cases, the sheet is curved.
Finally, mass and gravity are nothing but the consequence of the pressure of spacetime on closed volumes. In both cases,   we are faced with the same phenomenon, as the figure shows.
 
Gravity is not an attractive force between
masses, but a pressure force exerted by
spacetime on closed volumes that tends
to bring them closer to each other.
 
Current Theory vs. Proposed Theory
Mass and gravity explained in 4 steps