Index charts are determined by big institutional trading companies. All of these companies trade continually and quickly, so if one sells a lot, the others quickly start to sell, and if one buys a lot, the others quickly start to buy. This sort of behavior, now even more pronounced with high-frequency algorithmically run trading, means the charts of the S&P500, Dow, and Nasdaq move together.
Index charts are determined by big institutional trading companies. All of these companies trade continually and quickly, so if one sells a lot, the others quickly start to sell, and if one buys a lot, the others quickly start to buy. This sort of behavior, now even more pronounced with high-frequency algorithmically run trading, means the charts of the S&P500, Dow, and Nasdaq move together.