In 2009, Erik Verlinde argued that gravity is an entropic force. This created a big stir—and it helped him win about $6,500,000 in prize money and grants! But what the heck is an ‘entropic force’, anyway?
Entropic forces are nothing unusual: you’ve felt one if you’ve ever stretched a rubber band. Why does a rubber band pull back when you stretch it? You might think it’s because a stretched rubber band has more energy than an unstretched one. That would indeed be a fine explanation for a metal spring. But rubber doesn’t work that way. Instead, a stretched rubber band mainly has less entropy than an unstretched one—and this too can cause a force.
You see, molecules of rubber are like long chains. When unstretched, these chains can curl up in lots of random wiggly ways. ‘Lots of random ways’ means lots of entropy. But when you stretch…
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