The Casimir effect

Key words: casimir effect, quantum mechanics, physics, non conservation energy, plate, vacuum energy, zero point energy.

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The Casimir effect manifests itself in the form of a very weak attractive force between two parallel metallic plates immersed in a resonant cavity (hermetically sealed metal box) in the absence of an electromagnetic field.

According to the classical theory of electromagnetism and classical mechanics, the two plates should remain motionless since there reigns in the cavity an absolute void of any field. To be able to move, the metal plates need energy that they can not draw anywhere.

The Casimir effect is a pure result of quantum field theory. It was imagined and calculated by the Dutch physicist Hendrick Casimir in 1948.

According to quantum field theory, the electromagnetic field (and this is also applicable to all quantum fields) has different energy states. The lowest energy state - the ground state - corresponds to the absence of quanta of energy (photons in the case of the electromagnetic field) or in other words, vacuum. The first "excited" state is the state with a quantum of energy or a photon. The second excited state is the two-photon state, and so on.

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However, the representation given by the quantum field theory of vacuum is at least paradoxical. This void is in fact full of energy that is not "materialized" in the form of particles. However, over short periods, this energy can materialize in particles or quanta whose life is very short. They are called virtual particles. Although qualified as virtual, the effects of these quanta (photons in our case) are real.

In the cavity, virtual quanta (virtual photons) will spontaneously "emerge" from the void. The wavelength spectrum of these photons is continuous but because the cavity is closed, most of the frequencies will be destructive and eventually only a few particular frequencies (called resonance modes) will remain in the cavity. This is the classic phenomenon of resonance in a resonant cavity. The resonance modes are characterized by the fact that the wavelength of the mode is an entire submultiple of the distance that separates the faces of the cavity. The number of authorized modes is therefore proportional to the distance that separates the faces of the cavity.

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In the configuration which interests us, resonances are established between the faces of the cavity and the plates and between the plates themselves. If the distance between the plates is less than their distance from the faces of the cavity, then there will be more resonance modes between the faces of the cavity and the plates, than between the plates themselves. The radiation pressure exerted on the "internal" faces of the plates is therefore less than that which applies to their "external" faces. This results in a very weak force that brings the plates closer to each other.

Although predicted since 1948, this effect was only observed experimentally for the first time in 1997.

To be rigorous, it would be necessary to involve the quanta of all existing quantum fields. But these fields require a lot of energy to materialize from the void which translates into a low probability of materialization of the associated quanta compared to the electromagnetic field. Therefore, their contribution to the Casimir effect is very largely negligible.

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The Casimir effect shows thatwith vacuum, it is possible to generate motion. In this it constitutes a major violation of the classical principle of conservation of energy and can measure how quantum physics can be confusing!

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