As we experience it, time flows in a single direction. This is what we think of as the arrow of time, which stretches from the big bang to the present, and off into the future.

But our experience of time doesn’t match with most physicists’ view of it, as a dimension rather than linear path. We muse on one phenomenon that is intrinsically linked to directional time: entropy, and explore the link between the second law of thermodynamics and time itself.

Entropy and the Arrow of Time from The Royal Institution’s 2016 advent calendar celebrating thermodynamics.

Next: Professor Brian Cox discusses the arrow of time and entropy near the Perito Moreno glacier and in the Namib Desert.

Also: A Briefer History of Time: How tech changes us in unexpected ways.