Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent every weekday. It’s an age-old tale: A knuckle-cracking lover and hater enter a room. Then, a loud pop cuts through the silence. That’s hurting your knuckles, says the hater. No, it’s not, says the lover. Turns out, science says the knuckle cracker is right. Just like the myth that crossing your eyes will make them stay that way, warnings from parents, grandparents, and Great Aunt Mildred that cracking causes harm to knuckles remains an urban legend, says Dr. John Fernandez, an orthopedic surgeon specializing in hands, wrists, and elbows at Rush University Medical Center in Chicago. Here’s the science that backs that up.  Why cracking your knuckles got a bad reputation Fernandez has a suspicion about where the myth about knuckle cracking dangers emerged. He suspects Great Aunt Mildred and other critics had social etiquette on the mind when they warned against the practice. “It’s rude to make noises in public,” Fernandez says.  Indeed, most people don’t relish hearing (and smelling) other biological …