If the big bang was so dense then how come it wasn’t a black hole?
Think of it as a black hole backwards. At the moment of the big bang there was, what we now know as, the cosmological constant–dark energy which drives the expansion or inflation of the universe. Without this force there would be no expansion. Understanding this question will help us understand how the universe will end. We have three options for a physical eschatological scenario to occur. 1) Gravity will overcome the expanding force and the universe will collapse back in on itself creating an intense heat death. 3) If the force keeps expanding forever then there will be a thermodynamic equilibrium and there will be a maximal stretching and a cold death. 3) Or, there will be a big rip in which the force expands so fast that it continually rips the whole universe apart.