Am I wrong to assume that Theravada takes the cosmology to be merely symbolical or allegorical?The picture of the world presented in Buddhist cosmological descriptions cannot be taken as a literal description of the shape of the universe. It is inconsistent, and cannot be made consistent, with astronomical data that were already known in ancient India. However, it is not intended to be a description of how ordinary humans perceive their world; rather, it is the universe as seen through the divyacakṣus (Pāli: dibbacakkhu), the "divine eye" by which a Buddha or an arhat who has cultivated this faculty can perceive all of the other worlds and the beings arising (being born) and passing away (dying) within them, and can tell from what state they have been reborn and into what state they will be reborn. The cosmology has also been interpreted in a symbolical or allegorical sense (see Ten spiritual realms).
Anyway, Wikipedia says that, but then there are actual stories I've heard of monks' meditation being disturbed by gandhabbas (I believe the commentary says this?) and of people actually seeing devas... And the various miraculous stories of the suttas, Classical Theravadins take this literally, yes?
I'm not so sure what to make of cosmology based strictly on the suttas, because the suttas have so many stories of such things which are apparently literal, yet despite this, certain other stories seem to poke fun at these things.
In the Juñha Sutta, Sariputta, whose wisdom is said to be second only to the Buddha himself, is meditating and a yakkha hits him on the head. Moggallana sees this and asks Sariputta how he is feeling, and Sariputta mentions only a slight headache. Was this a joke by Sariputta or was he actually totally unaware of the Yakkha's presence?
Another sutta I remember (though I'm lacking a reference at the moment -- but it's well-known, so should be easy to find.. Mahaparinibbana Sutta, maybe?), the Buddha remarks to one of his followers that they need to step out of the way, because there are many gods who trying to see him and they're blocking his view.
Some have also remarked that the Agganna Sutta, the most elaborate sutta on the creation of the world, was a satirical parody of metaphysical speculation but the joke was lost on later commentators. Could this be true?
But in any case, if the cosmology is not literal... and it is not merely metaphorical... and it is the way a Buddha sees with his divine perception, how would this relate to mundane experience? As an example, how might a kalpa relate to the physical expansion and contraction of a universe, during the Big Bang and the theoretical Big Crunch? As another specific question, if devas can choose to take physical form or not, then what is their locality and nature when they are not in physical form?