The Casimir effect isn't what you think it is

Recently I saw a post on twitter claiming that AI could be powered with quantum vacuum energy. The post was accompanied by a figure from a paper published in Nature. Unfortunately for the poster, but fortunately for science, the paper had nothing to do with extracting energy from the vacuum. Rather, it was a description of an experimental realization of a transistor that uses the Casimir effect to mediate and amplify energy transfer across a new kind of transistor.

The Casimir effect is a quantum effect where if you have two metal plates very close together in a vacuum a force will appear pulling them together. This force has been measured and is a real phenomenon.

The Heisenberg uncertainty principle says that the energy of the vacuum is non-zero. We can also calculate that quantum harmonic oscillators, basically quantum versions of springs, have a non-zero ground state. This means that, unlike a real spring, which at rest will have zero energy, a quantum spring always has fluctuations. It is always bouncing.

From this physicists will often explain that the Casimir effect occurs because the metal plates exclude virtual particles of wavelengths larger than the distance between the plates. Because there are more virtual particles outside the plates than inside, they produce pressure on the plates pushing them together.

Traditional zero-point energy explanation of the Casimir effect. Emok. Wikimedia Commons. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

As with Stephen Hawking’s bad explanation of Hawking radiation in A Brief History of Time using illustrations of virtual particles, this explanation is also false. (Sadly, the paper on the Casimir effect I consulted for this article, which was otherwise very sound, repeated Hawking’s falsehood!)