  We study a simple model of an asset market with informed and non-informed
agents. In the absence of non-informed agents, the market becomes information
efficient when the number of traders with different private information is
large enough. Upon introducing non-informed agents, we find that the latter
contribute significantly to the trading activity if and only if the market is
(nearly) information efficient. This suggests that information efficiency might
be a necessary condition for bubble phenomena, induced by the behavior of
non-informed traders, or conversely that throwing some sands in the gears of
financial markets may curb the occurrence of bubbles.
