If beings from the astral realm lack a physical form, then how can they exist?

Assuming that the astral realm and metaphysical shit are real of course. I know physicists have theoretically proven that extra dimensions and alternate realities can in fact exist. But I don't get how an unseen, spiritual realm can have entities living in them if they don't have any form or shape. Or do they have it but it's just beyond our comprehension and/or perception?