  The two major goals in fundamental physics are: 1) Unification of all forces
incorporating relativity and quantum theory, 2) Understanding the origin and
evolution of the Universe as well as explaining the smallness of the
cosmological constant.
  Several efforts have been made in the last few decades towards achieving
these goals with some successes and failures. The current best theory we have
for unification of all forces is Superstring/M Theory. However current evidence
suggests our Universe is flat and accelerating. A Universe with a positive
cosmological constant will have serious implications for string theory since
the S-Matrix cannot be well defined and Superstring/M Theory is only formulated
in flat Minkowski background. Holographic principle provides a way out as shown
by the AdS/CFT and dS/CFT correspondence, but it remains to be proved if it is
valid for our non-conformal, non-supersymmetric Universe. Aside from the issue
of defining M-Theory in a de Sitter background, why the cosmological constant
is so small remains puzzling and needs to be understood. The ``cosmological
constant problem'' has brought physics to a standstill towards any major
development and remains currently the most disturbing issue.
  Conventional big bang cosmology has not yet produced a satisfactory
explanation of the small value of the cosmological constant. An attempt by
SuperString/M Theory in this direction is given by the Ekpyrotic/Cyclic model.
  The aim of this review is not to introduce any new concepts not already
known, but give an overview of current state of affairs in high energy physics,
highlighting some successes and failures and making some few suggestions on
areas to focus to resolve some of these outstanding issues.
