  How the energy conservation law is obeyed by the universe during its
evolution is an important but not yet unanimously resolved question. Does the
universe have a constant mass during its evolution or has its mass been
increasing with its radius? Here, we evaluate the two contending propositions
within the context of the Friedmann equations and the standard big bang theory.
We find that though both propositions appeal to the Friedmann equations for
validity, an increasing mass with increasing radius is more in harmony with the
thermal history of the big bang model. In addition, temperature and flatness
problems that plague the constant mass proposal are mitigated by the increasing
mass with radius proposal. We conclude that the universe has been increasing in
mass and radius in obedience to the energy conservation law.
