The theory of quantum mechanics has transformed daily life since being proposed a century ago, yet how it works remains a mystery—and physicists are deeply divided about what is actually going on, a survey in the journal Nature said Wednesday.

“Shut up and calculate!” is a famous quote in quantum physics that illustrates the frustration of scientists struggling to unravel one of the world’s great paradoxes.

For the last century, equations based on quantum mechanics have consistently and accurately described the behavior of extremely small objects.