  In both stars and in the early universe, the production of deuterium is the
first step on the way to producing heavier nuclei. If the strong force were
slightly weaker, deuterium would not be stable, and many authors have noted
that nuclesynthesis would be compromised so that helium production could not
proceed through standard reaction chains. Motivated by the possibility that
other regions of space-time could have different values for the fundamental
constants, this paper considers stellar evolution in universes without stable
deuterium and argues that such universes can remain habitable. Even in
universes with no stellar nucleosynthesis, stars can form and will generate
energy through gravitational contraction. We show that such stars can be
sufficiently luminous and long-lived to support life. Stars with initial masses
that exceed the Chandrasekhar mass cannot be supported by degeneracy pressure
and explode at the end of their contraction phase. The resulting explosive
nucleosynthesis can provide the universe with some heavy elements. We also
explore the possibility that helium can be produced in stellar cores through a
triple-nucleon reaction (roughly analogous to the triple-alpha reaction). Next
we show that with even trace amounts of heavy elements --- produced through the
triple-nucleon process or by explosive nucleosynthesis --- the CNO cycle can
operate and allow stars to function. Finally, we consider Big Bang
Nucleosynthesis without stable deuterium and find that only trace amounts of
helium are produced, with even smaller abundances of other nuclei. With stars
evolving through gravitational contraction, explosive nucleosynthesis, the
triple-nucleon reaction, and the CNO cycle, universes with no stable deuterium
are thus potentially habitable, contrary to many previous claims.
