Ordinarily, to measure an object we must interact with it in some way. Whether it’s by a prod or a poke, an echo of sound waves, or a shower of light, it’s near impossible to look without touching.

In the world of quantum physics, there are some exceptions to this rule.

Researchers from Aalto University in Finland propose a way to ‘see’ a microwave pulse without the absorption and re-emission of any light waves. It’s an example of a special interaction-free measurement, where something is observed without being rattled by a mediating particle.