  Satyendra Nath Bose's attempt to describe the quantum statistical aspects of
light consistently in terms of particles, and Einstein's generalisation, lead
to the concept of Bosons as a class of quanta obeying `Bose-Einstein
statistics'. Their identity as a class came in sharp contrast when the Pauli
exclusion principle and the Dirac equation revealed the other class called
Fermions, obeying `Fermi-Dirac statistics'. Spin, and spin alone, is the
determining factor of the multiparticle behaviour of fundamental quanta. This
is the basis of the Spin-Statistics Connection. While it is known that the
overall theoretical picture is consistent, the physical reason for the
connection is unknown. Further, the class difference is sensitive only to the
total spin in a quantum aggregate, as spectacularly seen in superconductivity
and superfluidity, and in the Bose-Einstein condensation of neutral atomic gas.
Can we grasp the true reason behind the difference in the collective behaviour
of Bosons and Fermions? An explorer's journey demanding logical and physical
consistency of what we already know takes us to the hidden factors in the
relation between spin and the statistics of quanta. The surprising answer is in
the domain of gravity, that too, on a cosmic scale.
