 In Figure 1 the planes represent the hypersurfaces of simultaneity. In relation to frame \(S\) the tachyon source is at rest, and a tachyon is emitted at event \(A\), with a superluminal but finite velocity. The absorption of the tachyon, event \(B\), will accordingly occur later than \(A\) in relation to the observer in \(S\), and the arrow of trajectory is for that reason pointing into the future above the hypersurface passing through \(A\) and standing perpendicular to the world-line of the source. But neither with respect to the frame \(S^*\) nor \(S^{**}\) is the tachyon source at rest and the hypersurfaces are therefore tilted in relation to the arrow of trajectory. An observer in \(S^*\) observes the tachyon to have infinite speed, and therefore the hypersurface is tilted so much that it coincides with the arrow. The observer in \(S^{**}\) is moving so fast with respect to the tachyon source that the hypersurface becomes titled so much that the arrow points into the past below the hypersurface.