For all we know they could already be here.
Perhaps so advanced that they could be visiting Earth as if it was some sort of zoo.
I don't expect anyone to believe, but my sources are close friends having experiences, and a sighting of my own.. Seemed like a ball of light, or some sort of probe, zipping and zigzagging all over the night sky.
Then there's mysteries like crop circles and ancient civilizations and their knowledge.
Yeah, mysteries. We have no idea yet what it could be.