One of the key ideas Edo followed was the idea that -

Nature tends to draw things together. 

• Clouds form in spite of gas laws that state they should diffuse.
• Galaxies exist when it appears they have insufficient mass to stick together.
• Rain drops form into droplets.
• Cells create their own little world.
• Crystals in rocks like granite, come together.

Given this observation Edo concluded the same is most likely true for atoms - there is a central pulling force that holds the nucleus together.  

This really isn't much different than the conventional theory about the atom.  Conventional belief is that a mysterious Strong force holds the atom together.  We don't know what the force is, we can't measure it, it has really odd properties compared to other forces, but it must exist.

This idea of a central pulling force was essential in Edo figuring out that the protons in the nucleus must be densely packed.  They have to be nestled down into each other very tightly.  They cannot be loosely stacked on top of each other like they are in a cube.  

For example it is known to Science that there are no stable elements with 5 or 8 nucleons.  Why is this?  When you apply a central drawing force it becomes apparent that both of these shapes break.  The protons are no longer densely packed - this means that some of the faces between the protons are no longer equilateral triangles.  The idea that all faces of the atom must be equilateral triangles is a key concept in SAM and governs how the atom grows.