It appears that the MBTA forgot to pay the electric bill! For at least part of the morning commute, the lights were out at Arlington and Copley (I also heard rumors of Hynes and Boylston going dark as well). A series of underground fires in Downtown Boston forced the power to be shut off for a few hours. Inspectors, CSA's, and other MBTA personnel stood guard with flashlights. Waiting passengers were told to board whatever train came into the station and change at another stop.
Here are some photos I snapped: