When was it theorized that universe was still expanding?
The concept of the expanding universe was first expressed by Hubble in the 1920's In 1998 observations were made that shows that the rate of expanding is increasing.
Hubbles observations of a red shift in the universe shocked the scientific community. The observations of the red shift led to the theory of an expanding universe and to the theory of the Big Bang.
Before Hubble's observations the scientific community almost universally believed in a steady state of the universe. The Steady State Theory stated that the Universe had always existed in the observed present state. The Steady State was compatible with the Enlightenment philosophy of material realism. The Material Realism philosophy was that Matter was eternal and self existent.
After Hubble the consensus scientific theory became the alternating or Rubber Ball Universe. The idea was a Big Bang would alternate with a Big Crush that would bring the universe back together. The alternating universe theory allowed for the idea that the material universe was eternal.
In 1998 observations of an increasing rate of expansion of the universe went against the hypothesis based on the alternating universe that the rate of expansion should be slowing down. The idea that the universe is eternal and self existent is now contradicted by the empirical evidence of Hubble's red shift and the increasing rate of expansion.