Because they have mass and are therefore sensitive to gravity, because they are neutral and therefore insensitive to electromagnetic forces, and because they are small, neutrons are ideal tools for investigating the quantum effects of gravity.

ILL scientists have shown that neutrons falling in a gravitational field do not drop like a stone but descend in distinct "quantum leaps", in the same way that a moving film strip will appear to be continuous even though it is actually a series of separate images.

V. Nezvizhevsky, ILL brochure "Neutrons and the Universe", p.14.