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 ...

But the second law of thermodynamics is different, and shows us an arrow of time. If you see a system heading towards disorder, you can bet your bottom dollar that it is going forward in time. You ...