For an interesting take on the subject read up on Martin Armstrong. He's was the Chairman for Princeton Economics who developed a computerized formula to predict cycles. The CIA wanted his brain and his model but he refused and eventually got brought up on BS charges. He's predicted most events including 9-11, the RE market crash and many others since he's been in jail. Oddly enough today 3-19 (give or take a week) G20? is the date picked when a rather large cycle turns.
'It's Just Time"
http://www.contrahour.com/ItsJustTim...nArmstrong.pdf
This is his latest
http://www.contrahour.com/MartinArms...alism12708.pdf