Josephson was 22 years old when he did the work on quantum tunnelling that won him the Nobel Prize. He discovered that a supercurrent could tunnel through a thin barrier, predicting, according to physicist Andrew Whitaker, that "at a junction of two superconductors, a current will flow even if there is no drop in voltage; that when there is a voltage drop, the current should oscillate at a frequency related to the drop in voltage; and that there is a dependence on any magnetic field." This became known as the Josephson effect and the junction as a Josephson junction.