ULTRA doesn't know how to access the other realms yet.  They're only just starting to set up sensors over Tokyo that can detect the supernatural.<br/><br/>Specific individuals can, though, if they have the Dimension powers, and certainly other beings can pass through to Earth if they have the magical know-how.<br/><br/><hr/><br/>One thing I should probably note is that for the most part, scientists in ULTRA don't automatically eschew magic.  There's at least a few trying to study magic well enough to become wizards but they tend to go about it in very scientific ways.  Magical energy can be studied the same way electricity can.  Thus the sensors.