This recent thread: https://www.physicsforums.com/showthread.php?t=386121" leads me to the following thought experiment: Your spaceship flies by another spaceship which appears to be highly electrically charged. From measurement of E and B fields on board your craft, you conclude that either you or the other craft is accelerating. Without referencing any other physics besides Maxwell, can you tell which craft is accelerating? That is, you do not use any Newtonian or Einsteinian or galactic far field acceleration measurements. Only EM field measurements.