  The recent research on the connection between gravity and thermodynamics
suggests that gravity could be an emergent phenomenon. Following this,
Padmanabhan proposed a novel idea that the expansion of the universe can be
interpreted as equivalent to the emergence of space with the progress of cosmic
time. In this approach, the expansion of the universe is described by what is
known as the law of emergence, which states that the expansion of the universe
is driven by the difference between the number of bulk and surface degrees of
freedom in a region bounded by the Hubble radius. This principle correctly
reproduces the standard evolution of a Friedmann universe. We establish the
connection of the law of emergence, which is conceptually different from the
conventional paradigm to describe cosmology, with other well-established
results in thermodynamics. It has been shown that the law of emergence can be
derived from the unified first law of thermodynamics, which can then be
considered as the backbone of the law. However, the law of emergence is rich in
structure than implied by the First law thermodynamics alone. It further
explains the evolution of the universe towards a state of maximum horizon
entropy. Following this, it can be considered that the first law of
thermodynamics, along with the additional constraints imposed by the
maximisation of the horizon entropy, can together lead to the law of emergence.
In the present article, we first make a brief review of Padmanabhan's proposal
and then studies its connection with the thermodynamics of the horizon in the
context of Einstein's, Gauss-Bonnet, and more general Lovelock gravity
theories.
