The Casimir effect is a physical force affecting macro-size objects and arises from vacuum energy, which are quantized oscillations in the electromagnetic field permeating every microscopic crevice of the Universe that give that field a non-zero energy.

When two conductive flat plates of the same material are less than about 1000 nanometers apart (about twice the width of a common bacterium), they begin to form an electromagnetic cavity that excludes larger-wavelength components of vacuum energy. This reduces the energy between the plates, creating a pressure imbalance that pushes them together. This imbalance reaches a pressure of about one standard atmosphere when the plates are 10 nanometers apart (in the extreme-UV or the width of four human DNA strands) as a greater number of increasingly energetic virtual particle pairs with shorter wavelengths are excluded. Here, the gap permits only excitations with wavelengths no greater than green ones to pop into existence between them, excluding yellow, orange, red ones.

This image was created using Ashlar's Cobalt and final adjustments to color were made using Apple's Preview.