Very roughly put, my limited understanding is that dark matter is postulated because of effects seen in the geometry of space similar to those created by matter. Is it necessarily true that there is some form of matter causing that spacial distortion? Couldn't it be postulated that there are spacial distortions caused by some unknown phenomena, perhaps a nature of the fabric of the universe we don't understand? (interaction with a parallel universe for a far-fetched example). I'm not trying to promote any pet theory (far from it), just trying to understand a little better. I ask this because the public presentation of this idea seems entirely focused on some form of matter permeating space as opposed to understanding a distortion permeating space that might be caused by some form of matter. Expecting to find some new form of matter seems like wishful thinking (but an easy place to start looking). Am I way off base?