The Tahitians and New Guineans could see and touch the Europeans, and did...and got diseases from them. We see lights and funny images on radar which have, as Wolfgang notes, other possible explanations.. ...(yes, yes, and a few puzzling pictures)...

It's all worth investigating...etc, etc...but I sure wish those smart aliens would decide poor Bill & Wolfgang have been teased long enough *grin*...and park a BIG saucer right on the Mall in Wash DC!