According to quantum theory, the 'void' or empty space in which atoms move is not really empty but filled with quantum particles that constantly appear into and disappear from our observable universe. This leads to a large intrinsic energy density of the 'void', known as zero-point energy, and to a force, called Casimir force, acting between objects strictly as a result of the quantum properties of the so-called 'void'. The effect was predicted more than 50 years ago but it was measured for the first time in 1997 by Steve K. Lamoreaux and by Umar Mohideen, just three years before Casimir's death (aged 91). Chris Binns, Professor of Nanoscience at the University of Leicester explained: "According to quantum field theory every particle is an excitation (a wave) of an underlying field (for example the electromagnetic field) in the void and it is only the energy of the wave itself that we can detectâ€. "A useful analogy is to consider our observable universe as a mass of waves on top of an ocean, whose depth is immaterial. Our senses and all our instruments can only directly detect the waves so it seems that trying to probe whatever lies beneath, the void itself, is hopeless. Not quite so. There are subtle effects of the zero-point energy that do lead to detectable phenomena in our observable universeâ€. "An example is a force, predicted in 1948 by the Dutch physicist, Hendrik Casimir that arises from the zero - point energy. If you place two mirrors facing each other in empty space they produce a disturbance in the quantum fluctuations that results in a pressure pushing the mirrors together." Casimir realized that only those electromagnetic waves whose wavelengths fit a whole number of times into the gap between the two plates should be counted when calculating the vacuum energy. As the gap between the plates is narrowed, fewer waves can contribute to the vacuum energy and so the energy density between the plates falls below the energy density of the surrounding space. The result is a tiny force trying to pull the plates together – a force that has been measured and thus provides proof of the existence of the quantum vacuum. "Detecting the Casimir force, however, is not easy as it only becomes significant if the mirrors approach to within less that 1 micrometer (about a fiftieth the width of a human hair). Producing sufficiently parallel surfaces to the precision required has had to wait for the emergence of the tools of nanotechnology to make accurate measurements of the force." But now recent investment by the University of Leicester in the Virtual Microscopy Centre and the Nanoscale Interfaces Centre has put the University in a key position to take a lead in Casimir force measurements in novel geometries. The research team carrying out this work has received a grant of 800,000€ from the European framework 6 NEST (New and Emerging Science and Technology) program to lead a consortium from three countries (UK, France and Sweden). The program, entitled Nanocase, will use the ultra-high vacuum Atomic Force Microscope installed in the Physics and Astronomy Department to make very high precision Casimir force measurements in non-simple cavities and assess the utility of the force in providing a method for contactless transmission in nano-machines. "The research will help to overcome a fundamental problem of all nano-machines, that is, machines whose individual components are the size of molecules, which is that at this size everything is 'sticky' and any components that come into contact stick together," said Binns. "If a method can be found to transmit force across a small gap without contact, then it may be possible to construct nano-machines that work freely without gumming up. Such machines are the stuff of science fiction at present and a long way off but possible uses include the ability to rebuild damaged human cells at the molecular level. In a sense the actual value of the zero-point energy is not important because everything we know about is on top of it." The new instrumentation at the University of Leicester will enable researchers to extend measurements to yet more complex shapes and, for the first time, to search for a way to reverse the Casimir force. This would be a ground-breaking discovery as the Casimir force is a fundamental property of the void and reversing it is akin to reversing gravity. Technologically this would only have relevance at very small distances but it would revolutionize the design of micro- and nano-machines.
I've often thought that The Casimir effect could also play a role in accurate force measurements between the nanometre and micrometre scales. Newton's inverse-square law of gravitation has been tested many times at macroscopic distances by observing the motion of planets. But no-one has so far managed to verify the law at micron length scales with any great precision. Such tests are important because many theoretical models that attempt to unify the four fundamental forces of nature predict the existence of previously undiscovered forces that would act at such scales. Any deviation between experiment and theory could hint at the existence of new forces. But all is not lost even if both values agree: the measurements would then put new limits on existing theories. Jens Gundlach and colleagues at Washington, for example, have used a torsion pendulum to determine the gravitational force between two test masses separated by distances from 10 mm down to 220 µm. Their measurements confirmed that Newtonian gravitation operates in this regime but that the Casimir force dominates at shorter distances. Meanwhile Joshua Long, John Price and colleagues at the University of Colorado - together with Ephraim Fischbach and co-workers from Purdue University - are trying to eliminate the Casimir effect altogether from sub-millimetre tests of gravitation by carefully selecting the materials used in the experiment. This article only gives a flavour of the many experimental and theoretical studies of the Casimir effect. There are many other exciting developments as well. Many groups are, for example, looking at what would happen if the interaction between two mirrors is mediated not by an electromagnetic field - which is made up of massless bosons - but by fields made of massive fermions, such as quarks or neutrinos. Other research teams, meanwhile, are studying the Casimir effect with different topologies, such as Möbius strips and doughnut-shaped objects. But despite the intensive efforts of researchers in the field, many unsolved problems about the Casimir effect remain. In particular the seemingly innocent question of the Casimir force within a single hollow sphere is still a matter of lively debate. People are not even sure if the force is attractive or repulsive. Hendrik Casimir himself thought about this problem as early as 1953 while looking for a stable model for the electron. Half a century on, the mysteries of the Casimir force are likely to keep us entertained for many years to come.
But Crazy Rob, Some background information may be useful, before describing the experiment. Quantum electrodynamics (the part of quantum theory dealing with electromagnetic phenomena) predicts that empty space isn't really empty, so that there is no such thing as a perfect vacuum. Even in a vacuum, and even at a temperature of absolute zero, all kinds of particles pop in and out of existence as a consequence of the famous Uncertainty Principle of quantum mechanics. These particles pop into existence (in particle-antiparticle pairs), hang around for a little while, but must then must disappear again. How long they can hang around depends on how heavy the particles are -- the heavier the particles, the faster they must disappear, but even light particles can hang around for very short periods of time. These particles are called virtual particles, because they normally can't be directly detected - you might say they almost don't exist. The only time you normally notice virtual particles is by observing their interactions with normal particles during the short time that they do hang around. As a consequence of the existence of these virtual particles, there is an energy density associated with the vacuum (remember, matter is energy, and vice-versa).
All data can be extrapulated from Black Holes (No, Dennis Rodman won't be of any help). One would expect spacetime to have a foamlike structure on the Planck scale with a very high topology. If spacetime is simply connected (which is assumed in this paper), the nontrivial homology occurs in dimension two, and spacetime can be regarded as being essentially the topological sum of S2×S2 and K3 bubbles. Comparison with the instantons for pair creation of black holes shows that the S2×S2 bubbles can be interpreted as closed loops of virtual black holes. It is shown that scattering in such topological fluctuations leads to loss of quantum coherence, or in other words, to a superscattering matrix S/ that does not factorize into an S matrix and its adjoint. This loss of quantum coherence is very small at low energies for everything except scalar fields, leading to the prediction that we may never observe the Higgs particle. Another possible observational consequence may be that the θ angle of QCD is zero without having to invoke the problematical existence of a light axion. The picture of virtual black holes given here also suggests that macroscopic black holes will evaporate down to the Planck size and then disappear in the sea of virtual black holes.
Excellent points, Jason. Indeed, "Higgs" seems to be the only reality, and the rest only the expressions of Higgs.
You are finally coming around young grasshopper. The Higgs particle is of critical importance in particle theories and is directly related to the concept of particle mass and therefore to all masses.