Seven Brief Lessons on Physics

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1. 01

   Heat always flows from hot things to cold ones, never the other way, and this simple rule is what gives time its forward direction.

   Seven Brief Lessons on Physics · 2014

   Heat always flows from hot objects to cold ones, and this direction gives time its forward arrow.

   Pour warm milk into a cup of cold tea: they mix and reach the same temperature. That never happens in reverse on its own. Rovelli shows that this simple rule about heat, not some mysterious law, explains why the past differs from the future and why time seems to move forward.

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