Quantum

In quantum mechanics, said Bohr, there is no way of knowing what light ‘really is’. The only question worth asking is: Does the light ‘behave’ like a particle or a wave? The answer is that sometimes it behaves like a particle and at others like a wave, depending upon the choice of experiment.

Since particle and wave were complementary but mutually exclusive facets of one underlying phenomenon, in no actual or imaginary experiment could both be revealed.

For him there simply is no electron with a well-defined position or a well-defined momentum in the absence of an experiment to measure its position or momentum. A measurement of an electron’s position creates an electron-with-a-position, while a measurement of its momentum creates an electron-with-a-momentum.

In reality the very opposite happens. It is the theory which decides what we can observe.

In the days that followed he had time to think about ‘Bohr’s remark that part of infinity seems to lie within the grasp of those who look across the sea’.