Why does Alduin have to eat the world each time? What's so bad about having the current Kalpa keep on running? And what's going to happen if we defeat him in Skyrim?
This is from the Yokudan Monomyth:
“Satak was First Serpent, the Snake who came Before, and all the worlds to come rested in the glimmer of its scales. But it was so big there was nothing but, and thus it was coiled around and around itself, and the worlds to come slid across each other but none had room to breathe or even be. And so the worlds called to something to save them, to let them out, but of course there was nothing outside the First Serpent, so aid had to come from inside it; this was Akel, the Hungry Stomach. Akel made itself known, and Satak could only think about what it was, and it was the best hunger, so it ate and ate. Soon there was enough room to live in the worlds and things began.”
Alduin/Aka(tosh)/Auri-EL is the time god. Perhaps the emphasis of the world eating is more about him eating the world in a temporal sense, he’s eating the time the world existed in so therefore the world itself is consumed. Alduin’s concern seems to be that the Kalpa could ‘run forever’. Maybe there is a finite amount of time that can occur. If Alduin didn’t eat the time of the previous Kalpa then maybe there wouldn’t be temporal ‘room to breathe or even be.’ Perhaps there would be a perpetual Dawn Era or something approaching absolute stasis.
He eats the world to be free. The Mundus is like a cage to him and he wants to eat it to be free of it. Unfortunately, Lorkhan just tricks him and the other Aedra into creating it all over again. It's a vicious cycle.
I’m not sure about this. Could it be that Alduin’s Kalpa turning is a part of the cage itself (his function within it) rather than his means to escape from it. In the Eating Birth of Dagon Alduin remembers the previous Kalpa feasts, how could he and the other aedra be tricked/persuaded/cajoled into taking in part in Lorkhan’s scheme repeatedly?
what's going to happen if we defeat him in Skyrim?
Well it seems from Alduin’s wall and Esbern’s narration that Alduin’s previous defeat simply delayed the world eating. Perhaps Time/Aka can’t be fully defeated, just postponed. It’s not clear how long for but if the Song of Return (500 companions of Ysgramor) is an account of history up to the point of Alduin’s previous visit then the fact that the song doesn’t seem to mention any event after the end of the Reman Empire implies that Alduin was defeated about 1200-1500 years before 5E200. This of course assumes (amongst other things) that the Dovahkiin will defeat Alduin in the same way as before.
I would guess that these are the Jills/Drakes/Dragons that we expect to meet in Skyrim.