The laws of physics are symmetric under time-reversal transformations, and yet we only ever perceive time's arrow as running in one particular (forward) direction. The reason why is not yet known.

The length of this polyline is dynamic such that it is 0.0325% shorter than the distance that it spans. In the case of horizontal and vertical directions it will be 0.0325% shorter than the cell width ...

Time's Arrow Within Glass Appears To Go In Both Directions, ... But the second law of thermodynamics is different, and shows us an arrow of time. ... or at least looks the same in both directions.