Before revision: Brownian motion has been a pillar of statistical physics for more than a century, and recent high-frequency trading data have shed new light on microstructure of Brownian motion in financial markets. Though evidences of trend-following behaviour of traders were indirectly shown in such trading data, the microscopic model has not been established so far by direct observation of trajectories for individual traders .
After revision: A microscopic model is established for financial Brownian motion from the direct observation of trajectories for individual traders .