“Information is physical,” Melvin Vopson tells me. “The fact that information is physical goes back to much older studies. What I did in 2019, I asked myself a question: If a bit of information is physical, and you can detect that energy associated with the bit of information when you erase it, what happens to that energy when the information is at rest, at equilibrium, stored? Where is that energy going? And the only conclusion I could come up with is that that energy condenses into a small mass.”