Perhaps there is no expansion, at least not due to a big bang which never happened. About 20 years ago, Halton Arp and John Bahcall published a debate in The Redshift Controversy, presenting both sides of the argument.
Big bang was all made up.
( z1 make-up :ARG1 ( z2 bang :mod ( z3 big ) ) :mod ( z4 all ) )