An experiment in non-linear time conducted by Doctor Paul Manheim on Vandor IV, which opened a rift into another dimension and sent ripples of repeated moments across the sector.
In The Next Generation episode We'll Always Have Paris, the Enterprise-D and other ships experience brief loops in which a few seconds happen twice. A distress call leads to Vandor IV, a planetoid in a binary system where Doctor Paul Manheim has worked in isolation for years on the nature of time.
An accident has killed his team and left Manheim convulsing, his mind caught between two dimensions. His wife Jenice is unhurt. She is the woman Picard failed to meet in a Paris cafe twenty-two years earlier, when he chose his career over her.
The distortions, which come to be called the Manheim Effect, are worsening. Data, best able to cope with them, enters the laboratory, meets two time-shifted versions of himself and at the right instant drops antimatter into the rift to seal it. Manheim recovers and stays on with Jenice to continue his work.