Simplicity

Relatively For Larger mass objects time passes slower meaning that the extremely small would be extremely hard to view for the extremely large due to time dilation (extremely fast) and for the extremely small it would be extremely hard to view things that are happening at the extremely large scale because of time dilation (happening to slow).. Mass displaces SpaceTime which forces SpaceTime to be compacted at the edges and when peering at that object from a distance we are peering through that compacted space-time which allows us to see it in the time relative to us but for that Mass object space time is actually expanding at a slower rate so in all actuality the compaction of spacetime is actually altering our perception of the reality for that object .

If time and space is relative then the expansion of space and how we perceive it is to. So there for when looking at a distant galaxy the expansion of space between all things could be happening at a faster or slower rate there for also changing our perspective of how gravity would behave in that said Galaxy and there for could account for what we believe to be dark matter but really is just the expansion of space and time between all particles at a different rate then our own