Quote from HedgefundTrader2:
Yes its a scam. SPX is one of the most manipulated indexes in the world. Institutions traders / hedge funds/mutual funds/ various other sundry pin stripped ghouls on Wall street play it every day. That is why you see it stop on a dime and do not crash, cause no one would like to kill their golden goose and start working at the local car wash...
no actually SPX is not manipulated,
however, its constituent components are themselves subject to so many various strategies and automated trading engines that they themselves, most of the 500 component equities are unfairly manipulated.
given that the top 30 of the 500 stocks within the S&P500 show these irratic trading patterns, then when you combine them into one ETF, whether the SPX or other similar multiple component ETF's, then all those whipsaws are magnified to an extreme.
another factor is / are these automated systems don't all fire at the same time, whether using some quant software, auto submission or other electronic method, such that when the index moves it triggers additional actions which are delayed, almost predictably, to within and less than 1.4 minutes of the initial actions.
another factor is / are the index balancing actions of other participants that use, trade and represent themselves as major index equivalents, such that they too represent balancing orders that are triggered when the index, and its components move.
most of this discussion falls along the lines of basic quantitative execution theorum.
when you net, net, net out these significant influences, one draws the conclusions that you mentioned, however the reality is vastly more complicated.
what is very good is that these hybrid and double hybrid vehicles exist and attract all this fickle trading, neutral trading, hedge trading and balance fund trading instead of the actual underlying stocks and their equity options, as used to be the case before they were invented.