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In Physics , the zero-point energy is the lowest possible Energy that a Quantum Mechanical Physical System may possess; it is the energy of the Ground State of the system. All quantum mechanical systems have a zero point energy. The term arises commonly in reference to the ground state of the Quantum Harmonic Oscillator . In Quantum Field Theory , it is a synonym for the Vacuum Energy , an amount of energy associated with the Vacuum of empty space. In Cosmology , the vacuum energy is taken to be the origin of the Cosmological Constant . Experimentally, the zero-point energy of the vacuum leads directly to the Casimir Effect , and is directly observable in Nanoscale Device s. Because zero point energy is the lowest possible energy a system can have, then this energy can not be removed out of the system. 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 , and aerospace giant BAE Systems . INTRODUCTION In Classical Physics , the energy of a system is relative, and is defined only in relation to some given state. Typically, one might associate a motionless system with zero energy, although doing so is purely arbitrary. There is no absolute way to state the energy of a classical system. 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. The origin of a minimal energy that isn't zero can be intuitively understood in terms of the of the particle. Thus, we deduce that the kinetic energy of the particle cannot be zero without violating the uncertainty principle, and so have a simple, intuitive picture of the zero-point energy: it is the vibration of a trapped particle, a vibration that cannot be removed. 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; although 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 on nanoscale devices, causing them to bend, twist and stick. 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 . A uniformly accelerating observer will observe zero-point energy of the electromagnetic field as a thermal bath of real Photon s, in an effect known as the Unruh Effect . Rueda and Haisch ( 1994 , 1998a , 1998b ) have proposed that the zero-point fields can have a drag on an accelerated observer, the drag being interpreted as the inertial mass of the accelerated object, and thus explaining the origin of mass. This approach also sheds light on Einstein's Principle of Equivalence ( Rueda and Haisch 2005 ). Numerous published papers on this topic are archived at the Calphysics website. HISTORY The concept of zero-point energy originated with Max Planck in 1911. The average energy of a harmonic oscillator in Thermal Equilibrium with its surroundings is: : Here, is Planck's Constant , is the Natural Frequency , ''k'' is Boltzmann's Constant , and ''T'' is the Temperature . At the same time Albert Einstein , L. Hopf ( 1910 ) and Otto Stern ( 1913 ) were also studying the properties of zero-point energy. Shortly thereafter Walther Nernst ( 1916 ) proposed that empty space was filled with zero-point Electromagnetic Radiation . Then in 1925 the existence of zero-point energy was shown to be “required by Quantum Mechanics , as a direct consequence of Heisenberg's Uncertainty Principle ” (Sciama 1991 ). FREE ENERGY DEVICES The Casimir Effect has established zero point energy as an uncontroversial and Scientifically Accepted phenomenon. However, due to a lack of public education in quantum mechanics, the term ''zero point energy'' has also become associated with a highly controversial area of human endeavour - the design and invention of so-called Free Energy Device s, similar to Perpetual Motion machines in the past. These devices purport to "tap" the zero-point field and somehow "extract energy" from it, thus providing an "inexhaustible", cheap, and non-polluting energy source. Controversy arises when such devices are promoted without scientifically acceptable proof that they tap the energy sources claimed. Promoters of a device demonstrate no understanding of how the device might do so; they demonstrate misunderstanding of widely accepted scientific facts and methods, in development or communication of a theory concerning a device; they make no attempt to exclude simpler explanations for the claimed performance of a device. Any of these behaviours are liable to taint the reputations of those involved with such devices, and qualified researchers are therefore likely to be reluctant to make any attempt to verify or even seriously dismiss such a device until its promoters demonstrate enough competence to be taken seriously. CULTURAL REFERENCES The claims made on behalf of free energy devices have earned them a spot in cultural folklore. Zero-point energy has also attracted the interest of independent researchers outside of mainstream research entities, such as the late Eugene Mallove , and figures into discussions on radio programs such as Coast To Coast AM . In fiction, zero-point energy is often used as Technobabble , usually to explain powerful sources of energy or devices that can lift heavy objects. Examples of such uses include the following: from computer game '' Half-Life 2 ''.]]
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