Empty space can pull two plates together
The Casimir effect is an attractive force between two uncharged metal plates in a vacuum, caused by the way the plates change the quantum field between them.
Established2 min read
Quantum fields are not allowed to be perfectly still. A cavity between two mirrors permits only certain wavelengths. Outside, the spectrum is fuller. The imbalance is a pressure, tiny, pushing the plates together. Casimir calculated it in 1948. Lamoreaux measured it in 1997 between a plate and a sphere, at the piconewton scale, and the force sat on the predicted curve.
It is not airflow and not gravity and not stray charge, though all three try to fake it and the experiment has to be ruder than they are. The vacuum has structure. Put walls in it and the structure pushes back.
Caveats
- The force matters at micrometre gaps. It does not tow ships.
Sources
- 1Lamoreaux S. K.. Demonstration of the Casimir Force in the 0.6 to 6 μm Range. Physical Review Letters 78, 1997.