baudrunner's space: Happenings in the space between atoms
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Tuesday, January 22, 2008

Happenings in the space between atoms

"Nature abhors a vacuum." -- so said Aristotle. While his statement actually referred to the workings of the lever-operated water pump it also holds true for the realm of quantum physics in the form of the Casimir force. This is the force which is described as that which is responsible for holding atoms together and refers to the fluctuations of the energy fields in the empty space between objects. It is not an electromagnetic force or a gravity force and is measurably effected only at extremes of proximity.

In the nano-technology industry, where operations involving microelectromechanical systems often encounter friction due to the Casimir effect, the ideal scenario would see this attracting force changed to a repelling force. This would result in zero energy losses due to friction during the normal functioning of nano-scale devices (such practical devices already exist, such as the lab on a chip). Well, Professor Ulf Leonhardt and Dr Thomas Philbin, from the University of St Andrews in Scotland, claim to be able to do just that. The direction that their research is taking them might very well ultimately lead to the true levitation of large objects although admittedly that idea is pretty far-fetched at present.

Converting the attracting effect of the Casimir force into a repelling one involves placing a specially constructed lens fabricated from a meta material between the objects. Meta materials are concerned with structural design properties rather than composition. They have been physically demonstrated to offer invisibility to micro wavelength radiation (that research will ultimately lead to real cloaking devices functional at visible wavelengths).

If we scaled an atom's nucleus to the size of a golf ball then the outermost electron orbital would be about 12 kilometres away. One might question that since there is seemingly much more empty space between subatomic particles than there is space occupied by those particles then why don't objects fall apart? How can any object be solid?

Atoms cannot mesh because of the strong inter atomic forces which bind the electrons to the oppositely charged protons inside the nucleus. Known subatomic particles have their properties well defined and they exhibit characteristics which allow physicists to identify them. Insomuch as all matter is made up of energy the energy of which these particles are made have definite limits in their normal state and they exhibit properties which confine those characteristics and which make them identifiable and to some extent predictable, notwithstanding Heisenberg's uncertainty principle. In a sense, we are describing a law of quantum mechanics: that particles can only respond -- and correspond -- to discrete values of energies.

The space between particles also contains fluctuating energies but those energies possess no discrete boundaries which might confine them and potentially define a particle nature. These energies are said to occur as virtual particles which randomly pop into and out of the vacuum of the space giving the vacuum an average zero point energy. Another law of quantum mechanics, analogous to Heisenberg's uncertainty principle which forbids knowing the position and momentum of a particle, forbids knowing both the energy and time of the electromagnetic wave properties of a particle and therefore the absolute value of a system cannot be defined as zero. A vacuum can therefore not exist as a still and inactive void but is a quantum state of matter and energy fields.

In the presence of two flat surfaces brought very close together the fluctuating virtual particles exert a greater pressure outside the plates than between them, therefore causing them to be attracted to one another. This observed phenomenon is known as the Casimir effect, and was predicted by Hendrik B. G. Casimir in 1948.

The idea that the Casimir force could come under the control of the two Scottish physicists poses an interesting premise -- that there is a tendency toward order in this Universe and that this tendency is demonstrated even by randomly occurring energy fluctuations in what we used to call the vacuum of space. The Scottish researchers propose that a "perfect lens" made of a meta material with a negative index of refraction could reverse the Casimir effect. A negative index of refraction means that light refracts in the opposite direction than is normally observed passing through a conventional denser medium. Such materials have already been fabricated. Light is just EM radiation in the visible part of the optical spectrum. Our perfect lens would need to be precisely tuned to the parameters of the virtual reality of space. Quite a noble feat.

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