When I look at the market indeces (S&P500, dow, nasdaq)....on any given day, they look like a carbon copy of one another. They go up and down with the same relative amount throughout the entire day. Probably a newbie question....but why is that? What is driving that? When I buy or sell a stock, I'm not buying or selling across all three indeces...so trying to wrap my head around what or who is making this happen? Is it 100% institutional investors that have major positions across the board, and they are making buys and sells across the board at the same time? Is it some computer driven modeling that is on autopilot? Any thoughts?