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Uncertainty principle of Heisenberg, 1927. The uncertainty principle , also known as Heisenberg's indeterminacy principle , is a fundamental concept in quantum mechanics . It states that there is a limit to the precision with which certain pairs of physical properties, such as position and momentum , can be simultaneously known.
The uncertainty principle states the uncertainty in energy and time can be related by [4] , where 1 / 2 ħ ≈ 5.272 86 × 10 −35 J⋅s. This means that pairs of virtual particles with energy Δ E {\displaystyle \Delta E} and lifetime shorter than Δ t {\displaystyle \Delta t} are continually created and annihilated in empty space.
For every non-zero commutator of two operators, there exists an "uncertainty principle", which in our present example may be expressed in the form: / In this ill-defined notation, Δ x {\displaystyle \Delta x} and Δ p {\displaystyle \Delta p} denote "uncertainty" in the simultaneous specification of x {\displaystyle x} and p {\displaystyle p} .
Although the thought experiment was formulated as an introduction to Heisenberg's uncertainty principle, one of the pillars of modern physics, it attacks the very premises under which it was constructed, thereby contributing to the development of an area of physics—namely, quantum mechanics—that redefined the terms under which the original thought experiment was conceived.
Δp x is uncertainty in measured value of momentum, Δt is duration of measurement, v x is velocity of particle before measurement, v′ x is velocity of particle after measurement, ħ is the reduced Planck constant. The measured momentum of the electron is then related to v x, whereas its momentum after the measurement is related to v′ x ...
The uncertainty principle requires every quantum mechanical system to have a fluctuating zero-point energy greater than the minimum of its classical potential well. This results in motion even at absolute zero. For example, liquid helium does not freeze under atmospheric pressure regardless of temperature due to its zero-point energy.
This principle of uncertainty holds for many other pairs of observables as well. For example, the energy does not commute with the position either, so it is impossible to precisely determine the position and energy of an electron in an atom.
An example of a source of this uncertainty would be the drag in an experiment designed to measure the acceleration of gravity near the earth's surface. The commonly used gravitational acceleration of 9.8 m/s² ignores the effects of air resistance, but the air resistance for the object could be measured and incorporated into the experiment to ...