How does expansion of the universe differ from other theories about the universe?
The theory of the increasing expansion of the universe differs in that it postulates a non eternal universe.
Most theories of the universe are based on the philosophy of material realism. The idea that the material universe is in the words of Carl Sagan " all that there is was or ever will be" These theories postulate an eternal material universe.
The theory ( based on the best current empirical evidence) of an ever expanding universe concludes that this universe we live in will come to an end and will not restart. This postulates that the material universe that can be observed is not eternal nor self existent. It is not in the word of Carl Sagan" all that there is was or ever will be".
The theory of an ever expanding universe contradicts the prevailing philosophy of material realism.