>>11224781>Would there be new stars forming, or would everything just collapse into a bunch of black holes?Much more dramatic than that.
The current density of the universe is 10^{-26} kg/m^3. That's including dark matter and dark energy and all that. The density of water is 10^3 kg/m^3. This completely changes how the universe works on a large scale.
Unless you also make the universe be expanding 10^15 times faster than it is today, adding that much density would make the universe curl up into a three dimensional sphere. If the Hubble parameter were the same as it is today, the radius of curvature of the universe would be about 10^15 times smaller than 14 billion light years. That's around the same order of magnitude as the distance between the earth and the sun.
