Sounds like a newbie question but still:
Let's take ASX:IVV, an ETF that tracks S&P 500. The ETF itself is traded within ASX trading hours, and the price is obviously determined by those who buy and sell. On the other hand, stocks that compose S&P 500 are traded within the U.S. trading hours, and the index value is derived from the prices of those stocks. How can possibly the two be in sync? What am I missing?