Humphreys' book is _Starlight and Time_ (Master Books, 1994). I
commend him for trying to develop a YE model with real physics instead
of just handwaving. I haven't done a detailed analysis, but note the
On p.124, "At some point the black hole had to become a white
hole. I propose that God did this on day two by increasing the
cosmological "constant" [lambda] to a large positive value, beginning a
rapid, infaltionary expansion of space. He marked off a large volume
within the ball wherein material would be allowed to pull apart into
fragments and clusters as it expanded, but He required the "waters
below" and the "waters above" to stay coherently together ..."
The we're told on p.126 that God reduced the cosmological
constant to a small or vanishing value on day 6, and perhaps increased
it again for the flood.
I.e., supernatural interventions are apparently required, since
no mechanism for the changes in lambda are suggested. There are
cosmological models in which an effective cosmological "constant" is
actually a variable, but such changes would be significant only in the
consitions of the extremely early universe at densities much exceeding
that of nuclear matter.
The supernatural element in Humphreys' model may appeal to some,
but in an attempt to present a consistent scientific picture, it reminds
me vividly of the well-known "Then a miracle occurs" cartoon".