Gravity from Heat: How Entropy Rewrites the Equations of the Universe
The event horizon of a black hole behaves like a thermostat: it has a temperature and an entropy. In 1995, physicist Ted Jacobson showed that if you apply the ordinary rule of heat transfer to this thermostat, Einstein's equations of gravity follow from it on their own. Heat, temperature and a measure of disorder on the boundary of an accessible region of space: that, it turns out, is what attraction is made of.