Apple's stock fell 12 percent today, its worst tumble in four years. Nobody knows if this is the beginning of the end, or a lull between two glorious chapters of market dominance.

What we do know is that Apple lost an eighth of its market cap today, or $52 billion in stock value. That's more than the market cap of some very big, very famous companies (h/t Rebecca Jarvis for the first comparisons) ...

Big picture: This says as much about the monstrous size of Apple (which just "disappointed" with $54 billion in revenue last quarter) as it does about the size of today's sell off.