Multiple realities
(covers information from several alternate timelines)
An anti-tachyon pulse was a discharge of anti-tachyons that could be produced by a starship's main deflector.
In 2378, Captain Kathryn Janeway ordered the use of an anti-tachyon pulse to seal a temporal rift, which had been generated by Janeway's counterpart from the year 2404. (VOY: "Endgame")