Is There a Dark Matter or Planet Vulcan?

In 1876, Arbaid Laverrier said there was a planet between the sun and Mercury. They searched for Vulcan but never found it. It actually turned out like our theory of gravity needed to be updated. Einstein told us that massive objects like the sun actually bend space around it. And his explanation solved the problem and explained why Mercury's orbit was where it was. So we really needed a reconceptualization of gravity.