Ghost in the machine

The first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three tracks emanate on the right of the photograph.

Neutrino's are everywhere, passing through us by the trillions every second. They are truly ghosts in the machine. They are the only particle connecting to the weak force and gravity, hence their unique ability of being in the world but not of it.

A neutrino (/njuːˈtriːnoʊ/ new-TREE-noh; denoted by the Greek letter ν) is an elementary particle that interacts via the weak interaction and gravity.[2][3] The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The rest mass of the neutrino is much smaller than that of the other known elementary particles (excluding massless particles).[4] The weak force has a very short range, the gravitational interaction is extremely weak due to the very small mass of the neutrino, and neutrinos do not participate in the electromagnetic interaction or the strong interaction.[5] Consequently, neutrinos typically pass through normal matter unimpeded and with no detectable effect.

As per Gemini, 

They are the only particles that exclusively feel the macro fabric of spacetime (Gravity)
and the discrete quantum decay of the atomic world (the weak force).

Standard Model of Particle Physics. The diagram shows the elementary particles of the Standard Model (the Higgs boson, the three generations of quarks and leptons, and the gauge bosons), including their names, masses, spins, charges, chiralities, and interactions with the strong, weak and electromagnetic forces. It also depicts the crucial role of the Higgs boson in electroweak symmetry breaking, and shows how the properties of the various particles differ in the (high-energy) symmetric phase (top) and the (low-energy) broken-symmetry phase (bottom).

Perhaps a way to achieve unification of the four forces may be possible by looking closely at the relationship of the neutrino to gravity and the weak force as the Standard Model doesn't include the one entity keeping all of reality together 24/7. It's worth a shot, right? :)