  Recent observations on Type-Ia supernovae and low density measurement of
matter (including dark matter) suggest that the present day universe consists
mainly of repulsive-gravity type exotic-matter with negative-pressure often
referred as dark-energy. But the mystery is about the nature of dark-energy and
its puzzling questions such as why, how, where & when about the dark- energy
are intriguing. In the present paper the author attempts to answer these
questions while making an effort to reveal the genesis of dark-energy, and
suggests that the cosmological nuclear-binding-energy liberated during
primordial nucleo-synthesis remains trapped for long time and then is released
free which manifests itself as dark-energy in the universe. It is also
explained why for dark energy the parameter w = -2/3. Noting that w=+1for stiff
matter and w=+1/3 for radiation; w = - 2/3 is for dark energy, because -1 is
due to deficiency of stiff-nuclear-matter and that this binding energy is
ultimately released as radiation contributing +1/3, making w = -1 + 1/3 = -2/3.
This thus almost solves the dark-energy mystery of negative-pressure &
repulsive-gravity. It is concluded that dark-energy is a consequence of
released-free nuclear-energy of cosmos. The proposed theory makes several
estimates / predictions, which agree reasonably well with the astrophysical
constraints & observations.
