  We live in a four dimensional world. But the idea of unification of
fundamental interactions lead us to higher dimensional theories. Recently a new
theory with extra dimensions has emerged, where only gravity propagates in the
extra dimension and all other interactions are confined in only four
dimensions. This theory gives us many new hopes. In earlier theories
unification of strong, weak and the electromagnetic forces was possible at
around (10^{16}) GeV in a grand unified theory (GUT) and it could get unified
with gravity at around the Planck scale of (10^{19}) GeV. With this new idea it
is possible to bring down all unification scales within the reach of the next
generation accelerators, i.e., around $10^4$ GeV.
