physical constant


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physical constant

[′fiz·ə·kəl ′kän·stənt]
(physics)
A physical quantity which has a fixed and unchanging numerical value.
References in periodicals archive ?
It became the first of the basic units of the International System of Units, defined through a fundamental physical constant - the length of a light wave.
The authors found that experiments and careful measurements would yield a published value for this or that physical constant, complete with error bars.
Scientists unanimously voted for the new Planck's constant based metric and for those unaware, the Planck's constant is a physical constant that relates energy carried by a photon to its frequency.
Scientists meeting at the General Conference of Weights and Measures in Versailles voted on a proposal redefining the kilogram in terms of a physical constant called the Planck constant.
The electron and the proton are exceptionally stable quantum oscillators and therefore the proton-to-electron rest mass ratio can be understood as a fundamental physical constant.
No one knows why, but scientists say the kilogram's current definition--"a unit of mass equal to the mass of the international prototype of the kilogram"--no longer works; they're trying to develop one that's based on a physical constant rather than an object whose weight can change.
However, if the emergence of intelligent life requires a very precisely tuned value of the physical constant, which would otherwise be free to range over a very wide range of values with nearly equal probability, then [[sigma].sub.e.sup.2] << [[sigma].sub.[lambda].sup.2] and [[lambda].sub.obs] will be close to the value [[lambda].sub.e], implying that anthropic considerations will dominate the value of [lambda] that is selected.
This idea is termed the anthropic principle, and it applies to any situation in which the value of a physical constant or other fundamental quantity, if changed even a few percent, would preclude life.
These include a nearby supernova or other massive explosion (such as the collapse of an invisible black hole), or the sudden breakdown of a seemingly stable physical constant. Such dangers would rush upon us at the speed of light and destroy us at the instant we first became aware of them.
It turns out that if the strength of any force or the value of any physical constant were even slightly different, the universe would probably have evolved into something entirely unlike what we see today--and would not have led to the exquisite carbon chemistry that is key to the emergence of human life.
The value of the spacetime shear modulus [[bar.[mu]].sub.0] is not a known physical constant, neither is the value of the spacetime bulk modulus [[bar.[kappa]].sub.0].
As this is a physical constant (e), the amp will be directly measurable without reference to the attraction between two wires carrying a current in a watt balance.

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