Our current models of the universe with the way gravity works require "dark matter" which nobody has actually seen, or measured, or otherwise discovered.

Now, I give them credit to a point. They "discovered" planets by the influence of their gravity on nearby planet's orbits around the sun in the past, only later to find them with telescopes. But that was, admittedly, smaller in scope than trying to find a missing substance that makes the current model of the universe work.

My current theory is that our laws of physics, which we believe are universal, are in fact local or regional to our little area of the galaxy or cluster of galaxies at the most.