  We report, for the first time, some experimental observations regarding a new
type of long range interaction between rigid particles that prevails when they
are suspended in an soft elastic gel. A denser particle submerges itself to a
considerable depth inside the gel and becomes buoyant by balancing its weight
against the elastic force exerted by the surrounding medium. By virtue of a
large elastic-capillary length, the surface of the gel wraps around the
particle and closes to create a line singularity connecting the particle to the
free surface of the gel. Substantial amount of tensile strain is thus developed
in the gel network parallel to the free surface that penetrates to a
significant depth inside the gel. The field of this tensile strain is rather
long range owing to a large correlation length and strong enough to pull two
submerged particles into contact. The particles move towards each other with an
effective force following an inverse linear distance law. When more monomers or
dimers of the particles are released inside the gel, they orient rather freely
inside the capsules they are in, and attract each other to form close packed
clusters. Eventually, these clusters themselves interact and coalesce. This is
an emergent phenomenon in which the gravity, the capillarity and the elasticity
work in tandem to create a long range interaction. We also present the results
of a related experiment, in which a particle suspended inside a thickness
graded gel moves accompanied by the continuous folding and the relaxation of
the surface of the gel.
