I am trying to wrap my head around this with textbook knowledge. Index futures trade outside the regular hours of stocks. During Asian hours, ES trades but U.S stock exchange is closed. During these non-US hours, index arbitrage cannot be done. ES price can diverge a lot from the underlying stocks value during the non-US hours because arbitrage is not present to keep the values in step. So, during the opening hour when the stock exchange opens, wouldn't there be chaos during panicky time? Say, ES trade >3% down. When the stock exchange opens, wouldn't this cause an avalanche of sell orders of the underlying stocks? Why are index futures such as ES allowed to trade outside normal stock trading hours given the absence of index arbitrage?