Does Anyone Know What Makes the Stock Market Go Up and Down Anymore?

In this day and age of computerized trading programs and algorithms, how do we even know what makes the stock market go up or down anymore? All of the computerized programs are different and we are never sure what exactly triggers a sell or a buy (or a hold, for that matter). When the human element is taken out of trading, it's hard to say what triggers a rise or a fall. Do you agree?

Suggestion:

Not necessarily. For instance the computerized programs at least used by financial firms are highly technical and a layman w/ no economic knowledge can't use it. In fact the human element is exactly the reason why it's hard to see what causes stock to go up and down.

1. Herding Behavior
2. Fads

These are caused by the human element. B/c not all ppl trading stocks are rational investors, if a majority of stock traders trade b/c of fads (remember Tulips and the Dotcom) and the rest follow b/c of herding behavior, then a stock may go up even though the company isn't really making any money. However, a rational investor will at least attempt to ignore the fad and analyze w/ computer tools to see if the company can make profits or not.

However, note that even if everyone in the stock market are rational investors. There is still random elements b/c of expectations. No one can tell the future precisely and accurately. Who knows one day a disaster could strike Silicon valley thus lowering the value of every stock in IT?