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Because zero point energy is the lowest possible energy a system can have, this energy cannot be removed from the system. A related term is Zero-point Field , which is the lowest energy state of a Field , i.e. its Ground State , which is non-zero.1 Despite the definition, the concept of zero-point energy, and the hint of a possibility of extracting "free energy" from the vacuum, has attracted the attention of amateur inventors. Numerous Perpetual Motion and other Pseudoscientific devices, often called Free Energy Device s, exploiting the idea, have been proposed. As a result of this activity, and its intriguing theoretical explanation, it has taken on a life of its own in popular culture, appearing in Science Fiction books, games and movies. HISTORY In 1900, Max Planck derived the formula for the energy of a single "energy radiator", i.e. a vibrating atomic unit, as: : :''Here, is Planck's Constant , is the Frequency , ''k'' is Boltzmann's Constant , and ''T'' is the Temperature .'' In 1913, using this formula as a basis, Albert Einstein and Otto Stern published a paper of great significance in which they suggested for the first time the existence of a residual energy that all oscillators have at absolute zero. They called this "residual energy" and then ''Nullpunktsenergie'' (in German), which later became translated as ''zero-point energy''. They carried out an analysis of the specific heat of hydrogen gas at low temperature, and concluded that the data are best represented if the vibrational energy is taken to have the form:2 : Thus, according to this expression, even at Absolute Zero the energy of an atomic system has the value ½''hν''. Introduction to Zero-Point Energy - Calphysics Institute FOUNDATIONAL PHYSICS In Classical Physics , the energy of a system is relative, and is defined only in relation to some given state (often called reference state). Typically, one might associate a motionless system with zero energy, although doing so is purely arbitrary. In Quantum Physics , it is natural to associate the energy with the Expectation Value of a certain Operator , the Hamiltonian of the system. For almost all quantum-mechanical systems, the lowest possible expectation value that this operator can obtain is not zero; this lowest possible value is called the zero-point energy. (Caveat: If we add an arbitrary constant to the Hamiltonian, we get another theory which is physically equivalent to the previous Hamiltonian. Because of this, only relative energy is observable, not the absolute energy. This does not change the fact that the minimum momentum is nonzero, however.) The origin of a minimal energy that isn't zero can be intuitively understood in terms of the of a moving particle is proportional to the square of its velocity, it cannot be zero either. This example, however, is not applicable to a free particle - the kinetic energy of which can be zero. VARIETIES OF ZERO-POINT ENERGY The idea of zero-point energy occurs in a number of situations, and it is important to distinguish these, and note that there are many closely related concepts. In ordinary quantum mechanics, the zero-point energy is the energy associated with the Ground State of the system. The most famous such example is the energy associated with the ground state of the Quantum Harmonic Oscillator . More precisely, the zero-point energy is the Expectation Value of the Hamiltonian of the system. In quantum field theory, the fabric of space is visualized as consisting of Fields , with the field at every point in space and time being a quantized Simple Harmonic Oscillator , with neighboring oscillators interacting. In this case, one has a contribution of from every point in space, resulting in a technically infinite zero-point energy. The zero-point energy is again the expectation value of the Hamiltonian; here, however, the phrase Vacuum Expectation Value is more commonly used, and the energy is called the Vacuum Energy . In quantum Perturbation Theory , it is sometimes said that the contribution of One-loop and multi-loop Feynman Diagram s to Elementary Particle Propagator s are the contribution of Vacuum Fluctuation s or the zero-point energy to the particle Mass es. EXPERIMENTAL EVIDENCE The simplest experimental evidence for the existence of zero-point energy in quantum field theory is the Casimir Effect . This effect was proposed in 1948 by Dutch Physicist Hendrik B. G. Casimir , who considered the quantized Electromagnetic Field between a pair of grounded, neutral metal plates. A small force can be measured between the plates, which is directly ascribable to a change of the zero-point energy of the electromagnetic field between the plates. Although the Casimir effect at first proved hard to measure, because its effects can be seen only at very small distances, the effect is taking on increasing importance in Nanotechnology . Not only is the Casimir effect easily and accurately measured in specially designed nanoscale devices, but it increasingly needs to be taken into account in the design and manufacturing processes of small devices. It can exert significant forces and stress on nanoscale devices, causing them to bend, twist, stick and break. Other experimental evidence includes Spontaneous Emission s of light ( Photon s) by Atom s and nuclei, observed Lamb Shift of positions of Energy Level s of atoms, anomalous value of electron's Gyromagnetic Ratio , etc. GRAVITATION AND COSMOLOGY In Cosmology , the zero-point energy offers an intriguing possibility for explaining the speculative positive values of the proposed Cosmological Constant . In brief, if the energy is "really there", then it should exert a Gravitational Force . In General Relativity , Mass and energy are equivalent; either produces a gravitational field. One obvious difficulty with this association is that the zero-point energy of the vacuum is absurdly large. Naively, it is infinite, but one must argue that new physics takes over at the Planck Scale , and so its growth is cut off at that point. Even so, what remains is so large that it would visibly bend space, and thus, there seems to be a contradiction. There is no easy way out, and reconciling the seemingly huge zero-point energy of space with the observed zero or small cosmological constant has become one of the important problems in theoretical physics, and has become a criterion by which to judge a candidate Theory Of Everything . USE IN PROPULSION AND LEVITATION Another area of research in the field of zero point energy is how it could be used for propulsion. NASA and British Aerospace both have programs running to this end though practical technology is still a long way off. For any success in this area, it would have to be possible to create repulsive effects in the quantum vacuum, which according to theory should be possible and experiments to produce and measure these effects are planned for the future. Professor Ulf Leonhardt and Dr Thomas Philbin , from the University Of St Andrews in Scotland , have worked out a way of reversing this pheneomenon, known as the Casimir Force , so that it repels instead of attracts. Their discovery could ultimately lead to frictionless micro-machines with moving parts that Levitate . Telegraph article ''Physicists have 'solved' mystery of levitation'' published July 8, 2007 See also physicsworld and st-andrews.ac.uk . Rueda, Haisch and Puthoff345 have proposed that an accelerated massive object interacts with the zero point field to produce an ''electromagnetic drag force'' which gives rise to the phenomenon of Inertia ; see Stochastic Electrodynamics . "FREE ENERGY" DEVICES The Casimir Effect has established zero point energy as an uncontroversial and Scientifically Accepted phenomenon. However, the term ''zero point energy'' has also become associated with a highly controversial area of human endeavor — the design and invention of so-called " Free Energy " devices, similar to Perpetual Motion machines in the past, and with a similar level of success. Related patents |
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