Each new telescope looks farther out and reveals a mind boggling number of previously unknown distant galaxies.
Might the fact that we don't know how much visible matter is out there be the reason dark matter was theorized to account for "missing matter" our telescopes cannot yet see?
Dark matter has nothing to do with how far a telescope can see. Our own galaxy supposedly contains dark matter, as well as our local galaxy cluster. Its presumed existence is due to our inability to add up all the visible matter to equal the mass needed to keep ours and other galaxies orbiting at the rate they do. Orbital speed, you know, is a direct function of mass and distance. There is missing matter, and a lot of it—about 6 times what we can detect as stars or gas. Either that, or there is something wrong with out understanding of gravity over very large distances. It’s a mystery as of yet.