system
Given the following post, respond as if you're commenting on Reddit:
human
What causes the Casimir effect?
gpt
In a vacuum, there are constant energy fluctuations resulting in the formation and annihilation of short-lived virtual particles, including photons. These fluctuations are always present, and in a normal vacuum, the forces from these fluctuations counteract each other. When two surfaces are brought very close together, the possible modes for the vacuum energy to couple to are confined by the plates. If the plates are, for example, 500 nm apart, only photons with wavelengths which fit within 500 a whole number of times (250, 100, 50, etc.) are allowed states for the vacuum to couple to. Since the position of the plates suppresses the formation of virtual photons in between, and the creation is not suppressed outside of the plates, there will be a force pushing the plates together.