This demonstration shows how a distant observer’s now slices can sweep into your past or future. At first, you and a distant observer are not moving relative to one another and so, share the same now slices. Then, the distant observer starts to move either towards you (negative velocity) or away from you (positive velocity). Use the sliders to set the distance and velocity of the observer and see how the observer’s new now slice rotates into your past or future. Notice that even at low speeds, the very distant observer can sweep far into your past or future. The larger the speed and the larger the distance, the greater the effect.