return to [3.17 Visible space]

Figure 3. The line segment QO is perpendicular to the wall’s surface. The observer at Q sees that the light traveling from O to Q does not move across distance-time parallel to the wall’s surface. However, the observer sees that the light going from P to Q does cross PO distance-time parallel to the wall’s surface. Consequently, at the distance of PO, P is separated from O relative to the observer.