For example, we saw how scattered spinning hydrogen nuclei in our body can be lined up to generate a coherent MRI signal from the quantum property of spin—but only by applying a very strong magnetic field provided by a big, powerful magnet, and only for as long as that magnetic force is maintained: as soon as the magnetic field is switched off, the particles become randomly aligned again by all the molecular jostling, and the quantum signal becomes scattered and undetectable.
