It's all psychology and perception, Wall Street wants main street to stay long and keep buying. These big swings are contract roll over from the June contract to the September. For the next week expect similar price action.
Go turn on the TV put it on a business channel, you will hear..."AT THE HIGH OF THE SESSION"
or...."MARKET HAS RECOVERED FROM EARLIER LOSSES AND IT NOW TRADING HIGHER"
Keeps people feeling good, keeps them from selling. Thats all it is, plain and simple.
You really need to stop referring to "they" on here. It makes you seem like a conspiracy theory nut like S2007S. By "they", are you referring to people who choose to own companies ? And of course, that would have to be new owners, not the masses of mutual funds and insiders who own the same companies already.
Tell me something, what did "they" do today that supposedly prevented prices from dropping ? What is so interesting about an essentially flat year on equity markets ?
So expect more positive Greek spin overnight, America will wake up to another agreement and by lunch time we will be at the highs of the session AGAIN!