The Casimir effect is a small attractive force between two plates in a vacuum caused by vacuum quantum fluctuations. It was predicted by Hendrik Casimir in 1948 and experimentally verified in 1958. The force is too small for current technologies but may be useful for micromechanical or nanomechanical devices in the future.
The Casimir effect refers to the tiny attractive force that appears between two discharged plates in a vacuum. This Casimir force is measurable only when the plates are extremely close together (different atomic diameters). This force was predicted in 1948 by Hendrik Casimir, a Dutch theoretical physicist. It was experimentally verified in 1958 by Marcus Spaarnay, still at Philips in Eindhoven while he was studying the properties of colloidal solutions. The recognized cause of the Casimir effect is vacuum quantum fluctuations (zero-point fluctuations) of the electromagnetic field between the plates.
The attractive force occurs because, as quantum theory indicates, even a so-called vacuum contains a multitude of virtual electromagnetic particles and antiparticles in a continuous state of fluctuation. This is known as vacuum energy. Since the space between the plates limits the possible wavelengths of virtual particle pairs, there are fewer virtual particles within the space between the plates than in the outer space. This means that the energy density between the plates is lower than the energy density of the surrounding space, creating a negative pressure that pulls the plates slightly together.
The closer the plates get, the lower the energy density of the vacuum. Only in 1997 was the exact magnitude of the Casimir force measured by Steve K. Lamoreaux of Los Alamos National Laboratory together with Umar Mohideen and Anushree Roy of UC Riverside. Since using two parallel plates would require low standards for precise alignment, a nearly perfect plate and sphere were used. Within a 5% margin of error, the intensity turned out to be just as predicted by quantum theory; defined as the zero-point energy of the Fourier modes of the electromagnetic field between the plates.
With certain materials and in certain configurations, the Casimir effect has been shown to be repulsive as well as attractive. It appears that the Casimir force is too small to be usefully applied to any of our current technologies, although knowledge of its existence may be essential for those designing micromechanical or nanomechanical robotic devices in the present and in the decades to come. One day it may be possible to exploit the Casimir effect for energy generation, although that day is a long way off and more efficient energy sources are likely to be discovered before this even becomes possible.
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