Black holes have piqued much curiosity. But thus far they have been important only in “remote” subjects like astrophysics and quantum gravity. We show that the situation can be improved. By a judicious application of black hole physics, one can obtain new results in “everyday physics.” For example, black holes yield a quantum universal upper bound on the entropy-to-energy ratio for ordinary thermodynamical systems which was unknown earlier. It can be checked, albeit with much labor, by ordinary statistical methods. Black holes set a limitation on the number of species of elementary particles-quarks, leptons, neutrinos-which may exist. And black holes lead to a fundamental limitation on the rate at which information can be transferred for given message energy by any communication system.