Have aliens visited earth?

[TimM]

But how would they find us?

If complex life is common enough for highly advanced civilizations to be nearby, there would be many more planets with civilizations not as advanced, such as our own, also nearby. Many of these will be closer to them than we are.

If not, well, our own radio transmissions haven't gotten far enough from Earth yet to be received by anyone advanced enough to reach us. We've only been transmitting for less than a century, and 100 light years is not very far - 0.1% of the diameter of our galaxy.

Either way, finding us is like finding the proverbial a needle in a haystack. The only question is, are we one of many needles in a small haystack, or one of a few in a very big one.