Temporal Anisotropy . In a short video clip showing two billiard balls bouncing off each other, forward and backward in time are indistinguishable if one ignores friction and inelasticity. In a longer video of a billiards break, the future is the end in which the balls are no longer in a nicely ordered triangle. If causes can be attributed to effects as easily as effects can be attributed to causes, then causal laws do not distinguish past and future, and the future for an event is the direction of increasing disorder in the system. Traces and memories of the past are a localized increase in order at the expense of an increase in system-wide disorder. Due to statistical considerations, some systems can cycle between order and disorder. In such systems the direction locally considered to be future can vary over the timeline of the system.
Molded plastic light tubes are commonly used in the electronics industry to direct illumination from LEDs on a circuit board to indicator symbols or buttons. These light tubes typically take on a highly complex shape that uses either gentle curving bends as in an optic fiber or have sharp prismatic folds which reflect off the angled corners. Multiple light tubes are often molded from a single piece of plastic, permitting easy device assembly since the long thin light tubes are all part of a single rigid component that snaps into place.