Uncertainty Principle

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The Uncertainty Principle is inherent in the properties of all wave-like systems, and that it arises in Quantum Mechanics simply due to the matter wave nature of all quantum objects. Thus, the uncertainty principle actually states a fundamental property of quantum systems, and is not a statement about the observational success of current technology. It must be emphasized that measurement does not mean only a process in which a physicist-observer takes part, but rather any interaction between classical and quantum objects regardless of any observer.This is not a statement about the inaccuracy of measurement instruments, nor a reflection on the quality of experimental methods; it arises from the wave properties inherent in the quantum mechanical description of nature. Even with perfect instruments and technique, the uncertainty is inherent in the nature of things.

In Quantum Mechanics, the Uncertainty Principle, also known as Heisenberg's uncertainty principle, the more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. This is a succinct statement of the "uncertainty relation" between the position and the momentum (mass times velocity) of a subatomic particle, such as an electron. This relation has profound implications for such fundamental notions as causality and the determination of the future behavior of an atomic particle. [1]

Heisenberg's uncertainty principle tells us that it is impossible to simultaneously measure the position and momentum of a particle with infinite precision. In our everyday lives we virtually never come up against this limit, hence why it seems peculiar. In this experiment a laser is shone through a narrow slit onto a screen. As the slit is made narrower, the spot on the screen also becomes narrower. But at a certain point, the spot starts becoming wider. This is because the photons of light have been so localized at the slit that their horizontal momentum must become less well defined in order to satisfy Heisenberg's uncertainty principle.

Essentially, the Heisenberg Uncertainty Principle is relative to the act of observation that collapses a wave potentiality that makes a situation, event or object become physical in ways that are not measurable. When we observe EMF wave-forms we change the physical environment and how that is expressed in tangible ways, yet the process of how it changes is uncertain.

Important steps on the way to understanding the uncertainty principle are wave-particle duality and the DeBroglie hypothesis.(Suggested by De Broglie in about 1923, the path to the wavelength expression for a particle is by analogy to the momentum of a photon.) As you proceed downward in size to atomic dimensions, it is no longer valid to consider a particle like a hard sphere, because the smaller the dimension, the more wave-like it becomes. It no longer makes sense to say that you have precisely determined both the position and momentum of such a particle. When you say that the electron acts as a wave, then the wave is the quantum mechanical wavefunction and it is therefore related to the probability of finding the electron at any point in space. A perfect sinewave for the electron wave spreads that probability throughout all of space, and the "position" of the electron is completely uncertain.

Observer Effect

In science, the term observer effect refers to changes that the act of observation will make on a phenomenon being observed. This is often the result of instruments that, by necessity, alter the state of what they measure in some manner. A commonplace example is checking the pressure in an automobile tire; this is difficult to do without letting out some of the air, thus changing the pressure. This effect can be observed in many domains of physics. The observer effect on a physical process can often be reduced to insignificance by using better instruments or observation techniques.Historically, the observer effect has been confused with the uncertainty principle.[2]

The Uncertainty Principle has been frequently confused with the observer effect, evidently even by its originator, Werner Heisenberg. The uncertainty principle in its standard form actually describes how precisely we may measure the position and momentum of a particle at the same time — if we increase the precision in measuring one quantity, we are forced to lose precision in measuring the other. An alternative version of the uncertainty principle, more in the spirit of an observer effect,fully accounts for the disturbance the observer has on a system and the error incurred, although this is not how the term "uncertainty principle" is most commonly used in practice.[3]

Double Slit Experiment

Photons or particles of matter (like an electron) produce a wave pattern when two slits are used

The modern double-slit experiment is a demonstration that light and matter can display characteristics of both classically defined waves and particles; moreover, it displays the fundamentally probabilistic nature of quantum mechanical phenomena. This experiment was performed originally by Thomas Young in 1801 (well before quantum mechanics) simply to demonstrate the wave theory of light and is sometimes referred to as Young's experiment. The experiment belongs to a general class of "double path" experiments, in which a wave is split into two separate waves that later combine into a single wave. Changes in the path lengths of both waves result in a phase shift, creating an interference pattern. In the basic version of this experiment, a coherent light source such as a laser beam illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate. The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen—a result that would not be expected if light consisted of classical particles. However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves), the interference pattern appearing via the varying density of these particle hits on the screen. Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave).

These results demonstrate the principle of wave–particle duality, which states that all matter exhibits both wave and particle properties: the particle is measured as a single pulse at a single position, while the wave describes the probability of absorbing the particle at a specific place of the detector.This phenomenon has been shown to occur with photons, electrons, atoms and even some molecules, including Buckyballs.

Other atomic-scale entities such as electrons are found to exhibit the same behavior when fired toward a double slit. Additionally, the detection of individual discrete impacts is observed to be inherently probabilistic, which is inexplicable using classical mechanics.The experiment can be done with entities much larger than electrons and photons, although it becomes more difficult as size increases. [4][5]


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