Page "Complementarity (physics)" Paragraph 16

Various neutron interferometry experiments demonstrate the subtlety of the notions of duality and complementarity.

By passing through the interferometer, the neutron appears to act as a wave.

Yet upon passage, the neutron is subject to gravitation.

As the neutron interferometer is rotated through Earth's gravitational field a phase change between the two arms of the interferometer can be observed, accompanied by a change in the constructive and destructive interference of the neutron waves on exit from the interferometer.

Some interpretations claim that understanding the interference effect requires one to concede that a single neutron takes both paths through the interferometer at the same time ; a single neutron would " be in two places at once ", as it were.

Since the two paths through a neutron interferometer can be as far as to apart, the effect is hardly microscopic.

This is similar to traditional double-slit and mirror interferometer experiments where the slits ( or mirrors ) can be arbitrarily far apart.

So, in interference and diffraction experiments, neutrons behave the same way as photons ( or electrons ) of corresponding wavelength.