Yeah, we're getting ever closer to the era in which: - you step out to home depot to buy a $20 hammer - when you get there "The Flash" (of dc comics fame) fig

Yeah, we're getting ever closer to the era in which: - you step out to home depot to buy a $20 hammer - when you get there "The Flash" (of dc comics fame) figures out you're looking to buy a hammer and buys all the $20 hammers - he leaves a post-it note saying "if you want a hammer meet me in aisle 7" - you get there and he offers to sell you a $20 hammer for $21 - either you buy it or you don't; once you've made your decision he returns either (N-1) or (N) hammers back to the store (30 day return policy and all that) - if you head over to lowe's instead well he is "The Flash" Not an exact metaphor for "flash trading" (as sketched it's riskless) but it's imho a relevant thought experiment. At the individual level the winners and losers are pretty obvious. At the systemic level it's unclear any actual efficiency is gained; differentiating between actual "efficiency gains" and "red queen" scenarios is tricky.