[logicchains]

It's only an efficient market because of arbitrage. If the price of copper futures in Europe suddenly soars, the price of copper futures in America doesn't magically, spontaneously rise to meet it; somebody has to do the work. You don't need to be better at modelling, you just need to be faster, or have a way of getting information earlier.

[bdkoepke]

Not necessarily true; if you got a mark on copper futures in Europe then you would expect the best American copper futures bid/ask to change fast. Updating bid/ask doesn't require trading.

[infinite8s]

It requires active participants in the market.