Beauty has physical structure on a couple levels. You can either talk about certain synapses lighting up (or whatever happens in the brain when someone experiences beauty) or you can talk about facial symmetry and 1.618.

Fun is an extremely vague notion, I'm not sure what it means or if it even has a consistent set of synaptic patterns (or whatever), but I think that's probably because people don't use the term consistently (or are confused, etc., as you say).

Spiciness is absolutely purely chemical.