Can someone explain Heisenberg's uncertainty principles in physics?  .?
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It is a principle that can be either experimentaly shown or derived from quantum mechanical equations (shrodinger, dirac...) \nIt states that if you try to measure the value of a particles position and momentum you will always have an uncertanity of (&#92;hbar)/2 where &#92;hbar is basicly a h that is crossed like a "t".  It is planks constat divide by 2 (&#92;pi)\nso its around 10^(-34) Js\n\nthe principle it self says &#92;sigma_x &#92;sigma_p >= &#92;hbar /2\nwhere &#92;sigma_x is the standard deviation of x\n\nso if you take a bunch of identical systems and measure a particals possition and momentum you will not get exactly repeating results.  \n\n\nAlso notice that if you prepare the system such that the possition is exactly known the momentum can be any thing and vice versa.  \n\nBut that is the simple explination
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zero-point energy \nIn a quantum mechanical system such as the particle in a box or the quantum harmonic oscillator, the lowest possible energy is called the zero-point energy. According to classical physics, the kinetic energy of a particle in a box or the kinetic energy of the harmonic oscillator may be zero if the velocity is zero. Quantum mechanics with its uncertainty principle implies that if the velocity is measured with certainty to be exactly zero, the uncertainty of the position must be infinite. This either violates the condition that the particle remain in the box, or it brings a new potential energy in the case of the harmonic oscillator. To avoid this paradox, quantum mechanics dictates that the minimal velocity is never equal to zero, and hence the minimal energy is never equal to zero.\n\n\nA few formulae\nA particle in a box is defined by the potential energy\n\nV(x) = 0 for  \nwhich is defined to be infinite for . The wave function with the minimal energy eigenvalue is then\n\nψ(x) = Csin(πx / l) \nwhere C is an important normalization constant. The (zero-point) energy of this wave function is pure kinetic and equal to\n\n \nwhich is non-zero. Similarly, the zero-point energy of the quantum harmonic oscillator with the frequency ω is equal to\n\n \nBoth of these simplest cases have a useful generalization to the case of quantum field theory. Quantum field theory - such as Quantum Electrodynamics - may be regarded as a collection of infinitely many harmonic oscillators, and quantum mechanics therefore predicts a nonzero vacuum energy. Although the absolute value of the vacuum energy is partly a matter of convention, the difference between the vacuum energy of various configurations has a physical meaning.\n\n\nExistence\nDoes electromagnetic zero-point energy exist, and if so, are there any practical applications and does it have any connection with dark energy? The theoretical basis for electromagnetic zero-point energy is clear. According to Sciama (1991):\n\n"Even in its ground state, a quantum system possesses fluctuations and an associated zero-point energy, since otherwise the uncertainty principle would be violated. In particular the vacuum state of a quantum field has these properties. For example, the electric and magnetic fields in the electromagnetic vacuum are fluctuating quantities." \nThe Casimir effect is an example of a one-loop effect in quantum electrodynamics that can be simply explained by the zero-point energy.\n\n\nHistory\nThe concept of zero-point energy originated with Max Planck in 1911. The average energy of a harmonic oscillator in this hypothesis is (where h is Planck's constant and ν is frequency):\n\n \nAt the same time Einstein and Hopf (1910) and Einstein and Stern (1913) were also studying the properties of zero-point energy. Shortly thereafter 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). As any textbook on quantum optics will show (e.g. Loudon 1983), the way to quantize the electromagnetic field is to associate each mode of the field with a harmonic oscillator with the result that the minimum energy per mode of the electromagnetic quantum vacuum is hν / 2 .\n\n\nProblems and answers\nZero-point energy shares a problem with the Dirac sea: both are potentially infinite. In the case of zero-point energy, there are reasons for believing that a cutoff does exist in the zero-point spectrum corresponding to the Planck scale. Even this results in an enormous amount of zero-point energy whose existence is assumed to be negated (in spite of the unmistakable mandate of the Heisenberg uncertainty principle) by the claim that the mass equivalent of the energy should gravitate, resulting in an absurdly large cosmological constant, contrary to o
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yeah, the guy was right, it's position and momentum, not energy and momentum. \n\nSee, if everything is a wave, it has a frequency spectrum associated with it (look up Fourier analysis). If something has one specific frequency only, then you can measure the frequency perfectly; the frequency gets you the wavelength, the wavelength gets you the momentum. But by definition, a wave at a single pure frequency extends to infinity in both directions, so you have no information about position. \n\nOn the other hand, if the wave looks like a single peak, you can calculate the position very nicely, but the frequency makeup (Fourier analysis) of a single peak contains an infinite number of frequencies, therefore an infinite number of momenta. \n\nFrom frequency /Fourier analysis, it's sort of obvious that the tighter you get the frequency/momentum, the wider the position spreads, and vice versa. No way you can specify a single frequency at a single point. (you can kind of see this intuitively; imagine a little chunk of a waveform, like just the tip of one peak; you can see the position precisely, but it's hard to estimate the frequency).
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Einstein didn't like the quantum impossibility to make exact predictions or the probabilistic reality that Quantum Mechanics postulates. He considered it an incomplete theory, he thought that quantum uncertainties where the result of incomplete knowledge and not a characteristic of the Universe. The EPR paradox is one of the aspects in which Relativity and Quantum Mechanics appear to contradict each other. There is a kind of particles that are called entangled particles in which a change in a characteristic in one of them immediately results in a change in the other. This apparently goes against Quantum Mechanics because it would be a way to lift Heisenberg's Uncertainty Principle (we could measure the position of one of the particles and the momentum of the other). On the other hand, the existence of entangled particles means that there must be some way by which such particles trade information between them, because each of them knows what the other one is doing (and they know it instantly, which means they exchange information at infinite speed!) And this kind of "subatomic telepathy" was not something Einstein liked, since Relativity states that the speed of light is the maximum speed allowed in the Universe. Mysteries...
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This is one of the questions that led to the quantum theory.  Heisenberg proposed that there is an inherent uncertainty in certain attributes of a particle: if you know its momentum precisely, you can say nothing about its position, and vice versa.  The product of the uncertainties in position and momentum cannot be less than a certain number called Planck's constant.  So, if the electron were to be eaten by the proton, both its position and momentum would become known to high precision, and that would be a violation of Heisenberg.  There is, however, an interesting exception in which what you posit actually occurs: it is a form of radioactive decay called k-electron capture, in which an atomic nucleus eats an inner electron, and the remaining electrons cascade downward to fill the hole, emitting characteristic x-rays in the process.  This can happen only under special circumstances, and involves a significant amount of energy.
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the classical def of the momentum is indeed p=mv, however, for  massless particles, this def no long applies, for the photon for instance, the momentum is given by\np=h/lambda, where h is the planck constant and lambda, the wave length\nIn that case, energy is given by E=hv, v bieng the frequency of the photon (v=c/lambda)
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To detect something, you have to observe that something has interacted with it.  In Heisenberg's Uncertainty Principle, that "something" is a photon.  As a spinoff of the quantized nature of reality at that small level, you can measure THIS with precision, only by losing precision on THAT: the commonest pairing is change in energy times duration, dE and dt.  In this case, dt*dE has to be on the order of Planck's Constant--this being the classical statement of Heisenberg's Uncertainty Principle.\n\nIf I may offer a simplistic example...  With a photograph, you can only record things on the image that are at least the size of the "grain" of the dye on the film.  Smaller things will disappear, or their color will be blurred in with things near by.  (In CT/MRI technology, we say that the volume element averages anything in it with all else in it)  The grain size limits your ability to see the small stuff, and if you can detect it (by a bit of fancy guesswork in color distortions of nearby 'grains') you're going to be left with increased doubt about its actual color.\n\nThe Heisenberg's Uncertainty Principle is a lot more complex than that--it's a very sloppy analogy!--but I hope that it helps.
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Probably not.  There are several problems\n\n1) because of the Heizenberg(sp?) uncertainty principle to learn of the exact direction of an atom one would change it's original direction.\n\n2) even if we could know a priori all that information it would require a simulation machine the size of the universe to calculate everything exactly.\n\n3)  I think there are still events of randomness at the atomic level that cannot be predicted.
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http://www.physics.gatech.edu/advancedlab/labs/frankhertz/\n\nhttp://www.physics.sfsu.edu/~rrogers/Phys%20321/5_Frank.htm\n\nhttp://www.physics.ucla.edu/demoweb/demomanual/modern_physics/quantum_mechanics_and_atomic_physics/frank_hertz_experiment.html
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Heisenbergs uncertainty principle states we cannot tell where any electron is at any given moment.
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(1) there is no problem with the concept\n\n(2) the concept refers not to "a wave of particle". But to the fact that the wave IS the particle, and the particle IS the wave.  More precisely, the particle (in our everyday definition, i.e. a small bit of matter) does not really exist at a precise point in space, but it is to be found in a given region, and the probability of finding it there is proportional to the absolute value of its "wave function"\n\nyou seem to view this as little bits of matter / light undulating on top of a wave - that's wrong.\n\n\nhistorically, what happened is that various experiments seemed to suggest that SOMETIMES it seemed that you had a wave, and other times, a particle.\n\nThe most famous one is the double slot experiment.  Incoming light will go through the two slots, and lights re-emitted after having gone through each slot will interfere with each other, and on a screen you will observe an interference pattern, i.e. a series of bright and dark bands.\n\nso then someone suggested to use light of such low intensity so that you'd literally emit one photon at a time.  Hoping to not get any interference picture - since each photon could not interfere with anything.\n\nbut what happened was that the photons would arrive at various points on the screen, and little by little, their accumulation would reconstruct the interference picture\n\nthis is what caused people problems - until they invested quantum physics, which deals perfectly with this.
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Quantum Theory, also quantum mechanics, in physics, a theory based on using the concept of the quantum unit to describe the dynamic properties of subatomic particles and the interactions of matter and radiation. The foundation was laid by the German physicist Max Planck, who postulated in 1900 that energy can be emitted or absorbed by matter only in small, discrete units called quanta. Also fundamental to the development of quantum mechanics was the uncertainty principle, formulated by the German physicist Werner Heisenberg in 1927, which states that the position and momentum of a subatomic particle cannot be specified simultaneously.
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Looks like only one person got the right idea so far so I will try to underscore that.\n\nEveryone who says that it is possible to have NOTHING inside a box if you have a total vacuum has ignored quantum theory which has proven to reflect reality extremely well.\n\nThe uncertainty principle allows energy to be borrowed from the vacuum for a very short time.  The vacuum is seething with pairs of "virtual" particle+antiparticle pairs that are created with this borrowed energy.  They pop into existence and then annihilate with each other extremely quickly.\n\nSo no, as far as anybody knows we have strong reason to believe that it is impossible to have absolutely nothing inside a box because something is always popping up everywhere in space.  Maybe if you had a very small box and very big luck luck it would be empty just for the tiniest period of time.
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To understand why an electron doesn't crash into the nucleus of an atom you first have to understand Heisenberg's uncertainty principle:  That it is impossible to know with absolute certainty both the location and momentum of a particle.  Any attempt to observe the location of the particle will change its momentum and vice versa.  This is the principle concept of quantum physics.  Like Einstein's description of light, this defies all logic in Newtonian physics, but it has been repeatedly proven nonetheless.  For now, just accept it.\n\nAn electron must stay a certain distance (or multiple of a certain distance) from the nucleus because it if it were within that distance we would know its location in relation to the nucleus with such certainty that its momentum would become extremely large, causing it to fly away from the nucleus.  Therefore any time we observe an atom it MUST be located a minimum distance from the nucleus which is always a multiple of Planck's constant h [6.626068x10^-34 (m^2)kg/s].
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The lowest possible energy in a quantum mechanical system is called the zero point energy. \n\nThe difference between classical and quantum mechanical system can be seen very easily from zero point energy stand point.\n\nFor a classical system, the minimum energy for a system may be zero if the velocity of the particles contained in the system is zero.\n\nBut for a quantum mechanical system, the minimum energy of the particles can not be zero. Because, from uncertainty principle, if the velocity (hence Momentun)is measured with certainty to be exactly zero, the uncertainty of the position must be infinite. Which means the particle is not confined within the system anymore.
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I think the author of the article linked to in your referenced web page (it's the link below) explains it well. One of the many  fundamental constants, the Fine Structure Constant, may have changed very slightly -- or it may not have. The data acquired so far is not conclusive, especially as decided by the scientific establishment, which generally demands pretty overwhelming proof of such a radical idea. And as the author says, confirming evidence must be obtained not merely from more iterations of the same experiment, but from totally different kinds of experiment, and he adds that precision in these other experiment types is not yet high enough to be useful as a proof.
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A good website on quantum mechanics: http://en.wikipedia.org/wiki/Quantum_mechanics\n\nAlso, if you are intrigued by the cosmological theory of the universe, The Life of the Cosmos by Lee Smolin is an excellent read.