[lukan]

"(Stock) market is, by definition, irrational"

I assume this is just your definition?

Is weather irrational, because you cannot calculate it?

Markets and weather are just too complex with too many unknowns to calculate it.

[CrimsonRain]

You're just being pedantic. To a sufficient advanced being (eg God), the whole universe is rational/calculable/etc. Are you the type who says "you're wrong! It's 9:01" when someone says it's 9?