I’ve read that most comoglocial fluids can be modelled as perfect fluids. And that most perfect fluids obey ##p=w/rho##. I’m wondering (had a look around and can’t seem to find) two things: i) whenever ##p=w/rho## is obeyed does this always give the 3 descriptions of the universe – 2 open universes expanding at different rates and one closed universe ii) examples of cosmological fluids which do not obey ##p=w/rho##? And do these fluids still lead to the same 3 fates of the universe. Does any perfect fluid lead to these 3 universes? Thanks in advance. I'm new to this and my question is motivated by taking the single case of a couple of fluids, with different w values, which do obey the above equation of state and looking at friedmann equations and finding that it leads to the 3 desriptions of the universe. I'm now wondering how well this generalises - to finidng the same 3 universe fates.