On what basis would you assume that it is impossible for aliens from other dimensions or beings from other planets to visit us? Are other dimensions impossible? How do you know? Are aliens on other planets impossible? How do you know? Is faster than light speed impossible? How do you know? Is it impossible that aliens might have developed a means of interplanetary or intergalactic travel which we don't know anything about yet? How do you know?

What do you base your certainty of a stated impossibility upon? Seems to me that it stands on a platform of conventional assumptions and nothing else whatsoever. Every society stands on a platform of conventional assumptions. Just look back through history. Those assumptions have, again and again, been proven wrong through new discoveries...yet each succeeding generation pats itself on the back in the certainty that it now KNOWS THE SCORE! Ha! Ha! The vanity of man, I call it.