Multiple realities
(covers information from several alternate timelines)
USS Enterprise-D firing inverse tachyon pulse into anomaly

An anti-time eruption

An anti-time eruption, otherwise know as multi-phasic temporal inversion, is a multiphasic temporal convergence in the spacetime continuum caused by a breakdown in the subspace barrier separating time and anti-time.

In an alternate timeline, such an eruption was discovered in the Devron system, taking the form of a highly-focused temporal energy source whose energy output was approximately the same as ten G-type stars. Due to anti-time's opposite nature relative to normal time, the eruption traveled backwards in time, growing larger as it did so. Exposure to the temporal energy emitted by the eruption caused the crew of the Enterprise to experience temporal reversion, a phenomenon whereby the crew's cellular structures began to coalesce, reverting to earlier stages of development. This manifested itself by causing old scars to heal, the DNA in Commander La Forge's optic nerves to regenerate, and the death of Nurse Alyssa Ogawa's unborn child, due to the reversion of the embryo's fetal tissue.

Captain Picard, who was shifting through time between three different time periods due to the influence of Q, ordered an inverse tachyon pulse initiated in all three time periods to penetrate the subspace barrier and examine the interior of the eruption. Picard learned from Q that, approximately 3.5 billion years previously, the eruption would disrupt the formation of life on Earth, eliminating humanity from the timeline unless Picard found a way to stop the eruption from traveling back through time. It was eventually discovered that the convergence of the tachyon pulses in the three different time periods caused the anomaly in the first place. By taking each time period's Enterprise into the center of the eruption and initiating a static warp shell, they were able to create an artificial subspace barrier to separate time and anti-time. Although this action led to the destruction of all three Enterprises, it successfully collapsed the anomaly and negated the timelines in which these events occurred. (TNG: "All Good Things...")