  Quasiparticles and collective effects may have seemed exotic when first
proposed in the 1930s, but their status has blossomed with their confirmation
by todays sophisticated experiment techniques. Evidence has accumulated about
the interactions of, say, magnons and rotons and with each other and also other
quasiparticles. We briefly review the conjectures of their existence necessary
to provide quantitative agreement with experiment which in the early period was
their only reason for being. Phase transitions in the Anderson model, the Kondo
effect, roton roton interactions, and highly correlated systems such as
helium4, the Quantum Hall Effect, and BEC condensates are discussed. Some
insulator and superconductor theories seem to suggest collective interactions
of several quasiparticles may be necessary to explain the behavior. We conclude
with brief discussions of the possibility of using the parameter to detect
quantum critical points and some background on bound states emerging from the
continuum. Finally, we present a summary and conclusions and also discuss
possible future directions.
