As others already mentioned above, there are arbs trading on both side. As soon as these bots detect a "huge order" on one side, they will place corresponding order to match it on the other end. This happens until both sides are back in equilibrium.Okay, "algos" sure. But you've got different sets of people trading each. Not everybody who buys in and out of QQQ is also in the futures market. You might get some huge order in the one that ain't equally placed in the other. So how the hell do they stay so synced?
But you need to understand that QQQ and NQ are merely shadowing the underlying index: NDX. NDX is also made up of 100 stocks. So you not only have arbs configured for NQ and QQQ. They will also be tied to those 100 stocks as well.
