"This means that the birth time of the electron that flies away is not known in principle. You could say that the electron itself doesn't know when it left the atom," says Burgdörfer. "It is in a quantum-physical superposition of different states. It has left the atom at both an earlier and a later point in time."

Which point in time it 'really' was cannot be answered—the 'actual' answer to this question simply does not exist in quantum physics. But the answer is quantum-physically linked to the—also undetermined—state of the electron remaining with the atom. If the remaining electron is in a state of higher energy, then the electron that flew away was more likely to have been torn out at an early point in time; if the remaining electron is in a state of lower energy, then the 'birth time' of the free electron that flew away was likely later—on average around 232 attoseconds.