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# Casimir Effect-Definition, Understanding, And Application

December 5, 2022
written by Qamar Zaman

The Casimir effect is related to quantum field theory.  It is a physical force which produces from the quantum fluctuation of the field. The Casimir effect acts on the macroscopic boundaries of a confined space.

## Casimir Effect

Hendrik Casimir a Dutch physicist predicted the effect of electromagnetic waves 70 years ago. The Casimir effect acts between two parallel closed uncharged conducting plates. It is a small attractive force that produces due to the fluctuation of the electromagnetic field.

The Casimir effect can be understood by imagining that the presence of macroscopic material interfaces (such as conducting metals and dielectrics) alters the vacuum expectation of the quadratically quantized electromagnetic field energy.

Because the value of this energy depends on the shape and position of the material, the Casimir effect appears as a force between these objects.

## Casimir Effect Measurements

Marcus Sparnaay performed one of the first experimental tests in 1958 in a sophisticated and challenging parallel plate experiment and obtained results that did not contradict Casimir’s theory but were subject to significant experimental error.

A more accurate measurement of the Casimir effect was made by Steve K. Lamoreaux of Los Alamos National Laboratory and Umar Mohideen and Anushree Roy of Riverside, California.

In practice, we measure the Casimir effect using a flat plate and another plate that is part of a large radius sphere, because using two parallel plates requires precise alignment to ensure they are parallel.

Finally, in 2001, a group at the University of Padua used microresonators to measure the Casimir force between parallel plates.

## Casimir Effect Understanding

Although the Casimir force seems completely counterintuitive, it’s actually quite well understood. In the old days of classical mechanics, the concept of a vacuum was simple. When you empty the container of all particles and drop the temperature to absolute zero, all that’s left is a vacuum.

However, the advent of quantum mechanics has completely changed our view of the vacuum. All fields—especially electromagnetic fields—show fluctuations. In other words, their current values ​​fluctuate around a constant average value at any point in time.

Even a perfect vacuum of absolute zero has fluctuation fields, so-called “vacuum fluctuations,” whose average energy is half that of a photon.

However, vacuum fluctuations are not an abstraction in the minds of physicists. They have observable consequences that can be seen directly in experiments at the microscopic scale.

For example, an atom in an excited state does not stay there indefinitely but returns to the ground state by spontaneously emitting a photon. This phenomenon is the result of vacuum fluctuations.

Imagine trying to hold a pencil vertically with your fingertips. It stays there when your hand is perfectly stable and nothing is affecting your balance. But the slightest perturbation will cause the pencil to drop to a more stable equilibrium position. Similarly, vacuum fluctuations cause excited atoms to drop to the ground state.

## Casimir Effect Application

It has been proposed that Casimir forces have applications in nanotechnology, especially in micro- and nano-electromechanical systems based on silicon integrated circuit technology and so-called Casimir oscillators.

The Casimir effect shows that the quantum field theory allows the energy density of some regions of space to be negative relative to the ordinary vacuum energy, and it is theoretically shown that the quantum field theory allows the energy of a given point to be arbitrarily negative.

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