You wrote: ” So instead of the universe keep expanding due to the pushing property of dark matter lead to the heat death, once it decay, it’ll no longer have that property and act just like regular matter and pulling the universe together, maybe even back to the singularity.”
1. The idea of the whole universe emerging from a “Big Bang” is the current scientific THEORY. It is NOT proven.
2. Buddha taught a VERY DIFFERENT picture. In that, only clusters of stars are destroyed from time to time. Each star with a planetary system is a cakkavala. A cluster of 10,000 cakkavala is destroyed at a time. Then it “re-builds” over a long time.
– That is the process described in detail in the Agganna Sutta.
– See, “Buddhism and Evolution – Aggañña Sutta (DN 27)“