Q: Is there an equation that determines whether a question gets answered on ask a mathematician/physicist?

Mathematician: Yes, but neither the Physicist nor I know it, and its shortest representation in standard mathematical notation is much too long to ever be written down. More precisely, there are an infinite number of such equations. These equations “exist” in the same sense that an equation describing the current position of every hair on your head exists. But these equations do not exist in the same sense that Chicago exists.