Cosmological Constant from the Emergent Gravity Perspective
  Observations indicate that our universe is characterized by a late-time
accelerating phase, possibly driven by a cosmological constant $\Lambda$, with
the dimensionless parameter $\Lambda L_P^2 \simeq 10^{-122}$, where $L_P = (G
\hbar /c^3)^{1/2}$ is the Planck length. In this review, we describe how the
emergent gravity paradigm provides a new insight and a possible solution to the
cosmological constant problem. After reviewing the necessary background
material, we identify the necessary and sufficient conditions for solving the
cosmological constant problem. We show that these conditions are naturally
satisfied in the emergent gravity paradigm in which (i) the field equations of
gravity are invariant under the addition of a constant to the matter Lagrangian
and (ii) the cosmological constant appears as an integration constant in the
solution. The numerical value of this integration constant can be related to
another dimensionless number (called CosMIn) that counts the number of modes
inside a Hubble volume that cross the Hubble radius during the radiation and
the matter dominated epochs of the universe. The emergent gravity paradigm
suggests that CosMIn has the numerical value $4 \pi$, which, in turn, leads to
the correct, observed value of the cosmological constant. Further, the emergent
gravity paradigm provides an alternative perspective on cosmology and
interprets the expansion of the universe itself as a quest towards holographic
equipartition. We discuss the implications of this novel and alternate
description of cosmology.
