Aliens

I do believe in the possibility of intelligent life elsewhere in the universe -- possibly even our own galaxy. However, there are so many possibilities for what other life may be like, from being silicone-based rather than carbon-based (and therefore be completely incompatible with our ideas of biochemistry), to having developed on a planet in its star's habitable zone, but on a planet significantly different in mass than the Earth, which would have a considerable effect on how life develops.

To be a bit on topic for the board, I also think -- besides evolutionary differences -- that there would be some similarities, at least in principle, and some other societies may have long decoded how the 'powers of the mind' work to such an extent that what we still consider magic, they consider mundane. It would so very easily explain some tales that people have about connecting with extraterrestrial life via telepathy or astral projection. Then again, it could also still just be UPG.

They don't want to be seen. For all you know they could be spirit like entities and you just can't see them.

I'd say they must be real
Somewhere far in space
Crowley actually met and spoke to a being and drew it that looked very much like todays Grey aliens.