Casimir effect

A force born from the conditions of vacuum

Two neutral conductive surfaces, very close together, restrict the allowed modes of the electromagnetic field between them. The difference between the inner and outer modes produces a measurable force. This description using vacuum fluctuations coexists with another equivalent formulation based on interactions between charges and fields: the observed effect is real; the metaphor of particles appearing and disappearing should not be taken literally.

Why is time travel interesting?

In certain configurations, the energy between the plates is less than that of the reference vacuum. This negative effective density is the example that is usually invoked when talking about the exotic matter necessary for a traversable throat. However, going from a microscopic force between plates to a macroscopic distribution capable of bending space-time is an immense leap.

Quantum inequalities limit how long and in what region negative energy can be maintained. It is not enough to "add more plates": geometry, losses, stability and gravitational feedback are part of the problem.

What has been measured and what has not

• Casimir forces have been measured with high precision in microstructures.
• The effect is used in surface physics and nanotechnology.
• No macroscopic region of negative energy usable as gravitational fuel has been created.
• There is no experimental demonstration connecting the Casimir effect to a real wormhole.

The most fertile connection

Its conceptual value is in showing that classical energy conditions are not absolute in quantum field theory. This crack forces us to study whether the quantum gravity allows controlled exceptions or, on the contrary, protects causality.

Fuentes

APS Physics: exotic energy and throats · Physical Review D: Casimir energy in traversable models