Search within the article for 'Casimir effect': https://en.m.wikipedia.org/wiki/Virtual_particle https://en.m.wikipedia.org/wiki/Virtual_particle It is not the

Search within the article for 'Casimir effect': https://en.m.wikipedia.org/wiki/Virtual_particle https://en.m.wikipedia.org/wiki/Virtual_particle It is not the most-useful/calculable way to think about it, but it is an evocative way to motivate the idea of fluctuations of quantum fields.