live in a midrange of energy as well as size. A living organism
must have enough energy to drive it, but not enough to destroy it.
Nuclear fission and fusion reactions are useless to a living cell
because they create so much energy that the molecules and arrangements
of molecules that the cell needs to function would be completely
shattered. The main problem today in commercial adaptation of controlled
nuclear fusion as an energy source is that we know of no material
that can withstand the temperatures developed by fusion, and that
can be used to make a container for the reaction. For stars this
problem is solved by simple physical separation in space.
Living chemical systems tap a milder energy source, the energy involved
in the making and breaking of chemical bonds between atoms, rather
than the energy involved in altering atomic nuclei. Such chemical
reactions have nothing to do with nuclear forces, but involve only
the shifting about of electrons outside the nucleus. Energies involved
in covalent bonds are typically one ten-millionth the energies of
nuclear reactions, yet these relatively weak interatomic bonds are
strong enough to tie atoms together, and to build structures of
a complexity unmatched at the stellar or nuclear levels. When we
turn our backs on the harsh conditions of stellar interiors and
nuclear reactions, we enter the world of the molecule. Large and
complex molecules are not common in our universe, but they are essential
for the occurrence of life.