Google Search

A recent study (See paper here, Nature) finds that the level of searches by particular terms is highly correlated to overall portfolio returns, particularly when trading strategies are based on these terms. The idea is that the search terms are a predictor of trading behavior, whether bullish or bearish.

Efficient Markets?

Market efficiency comprises two aspects. First, markets respond quickly to new information. Secondly, and often overlooked, the market responds accurately to this information. The recent twitter hoax (See article here, USA Today) is just one example of the market responding quickly to new information. Whether it is accurate or not is where the debate rages.

Circuit Breakers

Following the "Flash Crash" in 2010, the SEC implemented new trading curbs. Following continued discussion, these curbs have been updated once again--for both individual stocks and the market as a whole. See this Bloomberg article and this NYSE summary.