Dear John, Eckard, and Steve
A photon is a particle elementary of the Nature. The Photon is the lightest/smallest particle type, which every thing (whole universe matter) is made of. And the Light is its effect (gravitational force interaction).
Terminology confusion;
The term "Atom" which we still use, had meaning of the Natures fundamental particle as the word origin was 'indivisible" and latter became divisible for several time and still seems to be
The term of "elementary particles", is still in a situation of undetermined stage, which may give bit confusing meanings.
I have been facing problem with terms, and realized that, we should be always aware with the change of term, time to time and its usage in different fields (even the native one).
What I means is that from the beginning (just after Big Bang moment) there was only extremely large number free photons (elementary particles) latter they clustered into bigger spheres due to gravitational force, and these resulted bigger spheres clustered also into bigger spheres and .... The phenomenon of the Gravitational force at this chain of clusters seems now to be scalar. In other words photons Gravitational force (influence) is what we know as Light and it is the smallest scale of the G force, and its also a mirror image the effect that a photon may have
There is something like "kissing spheres" at initial moment of each spherical clustering. One may also think that this spherical Lattice-like may be two forms, namely "Body Centered" (BC) and "Face Centered" (FC) due the quantity of sphere kissing initial moment. Note that some numerical characteristics here such us Odd and Even numbers of spheres, Charged and Neutral because of number of clustered photons.
The elementary particle is that which responses the elementary charge and that is the photon. Since Light is (Gravitational) wave the photons/particle can interact by influencing. In general the overall particles interactions in both statically and dynamically creates complex systems
I think the best way to get a good insight is to ask; What combinations/sequence are possible if one throw large number spherical and homogeneous balls that have attracting force at empty free space?.
Eckard
the attachment is some previous question I have tried. I think there is something relevant to your question think your question under the title "charge and the Nature of Gravity" If not, we will take a closer look and descuss.
best wishes
BashirAttachment #1: 1_Bashir_Quantum_Mech_and_Relativity_Theory.pdf