Fine-structure constant

Sep 5, 2009 11:43 AM

The fine structure constant determines the STRENGTH OF the electromagnetic interaction:  alpha.

It is dimensionless.   It is about 1/137.  (from Feynman quote at bottom)   -  the amplitude for

a real electron to emit or absorb a real photon.

or see pysical interpretations: the second item there:

<ul>

<li>The ratio of two energies: (i) the energy needed to overcome the electrostatic repulsion between two electrons when the distance between them is reduced from infinity to some finite d, and (ii) the energy of a single <a href="/wiki/Photon" title="Photon">photon</a> of wavelength λ = 2πd (see <a href="/wiki/Planck_relation" class="mw-redirect" title="Planck relation">Planck relation</a>):</li>

</ul>

So, its a ratio of two energies: of 1) the electrostatic interaction of 2 electrons and 2) the energy of a photon (? given

off by one to the other ?).

Feynman:  all good theoretical physicists put this number up on their wall and worry about it.) Immediately you would like to know where this number for a coupling comes from: is it related to pi or perhaps to the base of natural logarithms? Nobody knows. It's one of the greatest damn mysteries of physics: a magic number that comes to us with no understanding by man.

and here from  everything2.net

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<td>(<a href="/user/Gorgonzola/writeups/Fine+structure+constant" onmouseup="document.cookie='lastnode_id=1233343; ; path=/'; 1;">thing</a>) by <a href="/user/Gorgonzola" onmouseup="document.cookie='lastnode_id=1233343; ; path=/'; 1;">Gorgonzola</a></td>

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A <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/dimensionless+numbers" title="dimensionless numbers" class="populated">dimensionless number</a>, α = <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/e" title="e" class="populated">e</a>2/4<a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/pi" title="pi" class="populated">π</a><a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/permittivity+of+free+space" title="permittivity of free space" class="populated">ε0</a><a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/Planck%2527s+Constant" title="Planck's Constant" class="populated">h</a><a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/speed+of+light" title="speed of light" class="populated">c</a> = 1/137.03599

This number determines the strength of the <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/electromagnetic+force" title="electromagnetic force" class="populated">electromagnetic force</a>. More accurately, it governs how strongly a <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/charged+particle" title="charged particle" class="populated">charged particle</a> will interact with that force (i.e. absorb or emit <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/photon" title="photon" class="populated">photon</a>s).

This is one of the primary physical constants that determines <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/the+nature+of+the+Universe" title="the nature of the Universe" class="populated">the nature of the Universe</a>. If it were a different value, electrons wouldn't orbit <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/atomic+nuclei" title="atomic nuclei" class="populated">atomic nuclei</a> in quite the same way, if at all.

If it were larger, you wouldn't be able to tell the difference between <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/matter" title="matter" class="populated">matter</a> and <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/radiation" title="radiation" class="populated">radiation</a>.

If it were smaller, particles might as well ignore the <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/electromagnetic+interaction" title="electromagnetic interaction" class="populated">electromagnetic interaction</a>.

The fine-structure constant, α is the ratio of the <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/quantum" title="quantum" class="populated">quantum</a> unit of <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/electromagnetic" title="electromagnetic" class="populated">electromagnetic</a> force to the <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/electron" title="electron" class="populated">electron</a>-based quantum unit of <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/inertial" title="inertial" class="populated">inertial</a> force.

It plays a key part in <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/Quantum+Electrodynamics" title="Quantum Electrodynamics" class="populated">Quantum Electrodynamics</a> theory in which the electromagnetic force is transmitted by <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/photon" title="photon" class="populated">photons</a>. In that theory the <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/g-factor" title="g-factor" class="populated">g-factor</a>, or <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/magnetic+moment" title="magnetic moment" class="populated">magnetic moment</a>, of an electron is modified by a series of terms involving the fine-structure constant.

The fine-structure constant is so called because it is related to the <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/fine-structure" title="fine-structure" class="populated">fine-structure</a> apparent in <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/atomic" title="atomic" class="populated">atomic</a> <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/spectrum" title="spectrum" class="populated">spectra</a>. These <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/spectral+line" title="spectral line" class="populated">spectral lines</a> are due to the transitions of electrons between available <a onmouseup="document.cookie='lastnode_id=0; ; path=/'; 1;" href="/title/energy+level" title="energy level" class="populated">energy levels</a>.

Fine-structure constant

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