Since 12w22, smelting yields experience orbs.
Stone, when mined with a normal pickaxe (without silk touch enchantment), yields cobblestone.
Smelting cobblestone yields stone and some experience orbs (according to the wiki it's 0.1 xp).
So if one keep smelting cobblestone to stone, then mine the stone to get cobblestone, then keep this going, could it be an efficient way for gaining experience orbs?
Don't ask me to try before seeing definite answers
because I afraid it would take a lot of time.
I don't want anybody to try to waste their own time and give me an empirical answer. I expect seeing some sort of calculation which probably involves probability, and also taking account of something that I may have missed.