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Author Topic: What is the fine structure constant?  (Read 4381 times)

Offline stevewillie

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What is the fine structure constant?
« on: 08/09/2008 20:32:53 »
I know the Sommerfield fine structure constant is an important fundamental physical constant and its value is about 1/137. What exactly is it? It's straightforward to grasp the meaning of constants like the speed of light, the masses of protons, electrons, etc. But what is a dimensionless 1/137? There seems to be some mysticism associated with this number based on a Google search.
« Last Edit: 09/09/2008 00:22:36 by stevewillie »


 

Offline stevewillie

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What is the fine structure constant?
« Reply #1 on: 11/09/2008 19:16:55 »
This is supposed to be a physics forum. So why can't anyone tell me about the fine structure constant? Over sixty views, but no answers. 1/137th of what? a rhubarb pie?
 
« Last Edit: 11/09/2008 19:21:06 by stevewillie »
 

Offline Evie

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What is the fine structure constant?
« Reply #2 on: 11/09/2008 19:44:22 »
Easy there, fella... ;)

Quote
The fine-structure constant is a unitless numerical constant - whose value is approximately equal to: 1/137. If fact the exact value of the fine-structure constant is: 0.007297351 +/- 0.000000006. Accepted symbol for the fine-structure constant is Greek alpha.

http://www.physlink.com/education/askexperts/ae33.cfm
« Last Edit: 11/09/2008 19:45:59 by Evie »
 

Offline stevewillie

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What is the fine structure constant?
« Reply #3 on: 12/09/2008 00:46:58 »
Evie,

Thanks for the link. I was unable to find a good explanation suitable to my non-physicist brain before this. I've read some pretty good threads here, but, if I seem testy, it's because so much energy goes into nonsense and silliness while legitimate questions are ignored, even in this 'hard' science forum. There's a place for silliness and I've posted on a few silly threads. But there's a chat room and other forums here for that. There ought to be some place where good questions get good answers and more interesting threads are developed. Thanks again.

Stevewillie
s
« Last Edit: 12/09/2008 00:53:18 by stevewillie »
 

Offline RD

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What is the fine structure constant?
« Reply #4 on: 12/09/2008 02:45:13 »
Quote
the fine structure constant, fondly known as alpha (α).
It is related to the speed of light by the equation α = e2 (2ℎcε 0)-1
where:-
 e is the charge of an electron,
 ℎ is the Planck constant,
 c is the speed of light, and
ε0 is the permittivity of free space.
http://scienceandreason.blogspot.com/2008/08/proton-electron-mass-ratio.html
 

Offline Evie

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What is the fine structure constant?
« Reply #5 on: 12/09/2008 14:27:38 »
No problem! I understand how you feel, since I have had to shake my head at an unusually high number of posts on here lately. One thing to be said for the "silly" posts, though: it keeps me reevaluating things I may have come to take for granted and accept as absolute truth.
 

Offline stevewillie

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What is the fine structure constant?
« Reply #6 on: 12/09/2008 20:45:23 »
RD and Evie,

Some off-the-wall posts attacking established theories are better than others, but I don't think we going to find any new Einsteins here. As for the formula, it seems alpha can be expressed in SI units (is this my loopy idea?) You can see for yourselves the SI units associated with right side of the equation:

electric charge: coulombs (C)
c: meters/sec (MS^-1)
h: joule seconds (JS)
abs permittivity:farads/meter (FM^-1)
Source: Documenta Geigy
 
So we have alpha expressed in terms of SI units: C^2SM/JSMF = C^2/JF


     
« Last Edit: 12/09/2008 20:58:02 by stevewillie »
 

Offline lightarrow

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What is the fine structure constant?
« Reply #7 on: 12/09/2008 21:22:07 »
RD and Evie,

Some off-the-wall posts attacking established theories are better than others, but I don't think we going to find any new Einsteins here. As for the formula, it seems alpha can be expressed in SI units (is this my loopy idea?) You can see for yourselves the SI units associated with right side of the equation:

electric charge: coulombs (C)
c: meters/sec (MS^-1)
h: joule seconds (JS)
abs permittivity:farads/meter (FM^-1)
Source: Documenta Geigy
 
So we have alpha expressed in terms of SI units: C^2SM/JSMF = C^2/JF     
The constant has different expressions in different units, but it's dimensionless.

α = (1/4πε0)e2/hc   in SI

α = e2/hc   in cgs

α represent the absolute strenght of the coupling between electric charges and electromagnetic field; absolute in the sense that being dimensionless it doesn't depend on your choice of units. Exactly for this reason is a very important number, more important than e, h, c. It is really a number that comes from nature itself and not on us humans (as other dimensionful constants like e, h, c or others).

One of the greatest mysteries of physics is why nature chose that value for that constant. Where does it come from?

Note that the number α, linking electromagnetism (e and c) with quantum mechanics (h) seems to suggest that there should be a deeper connection (than what we presently know) from the two theories.
« Last Edit: 12/09/2008 21:26:53 by lightarrow »
 

Offline stevewillie

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What is the fine structure constant?
« Reply #8 on: 12/09/2008 21:38:51 »
RD and Evie,

Some off-the-wall posts attacking established theories are better than others, but I don't think we going to find any new Einsteins here. As for the formula, it seems alpha can be expressed in SI units (is this my loopy idea?) You can see for yourselves the SI units associated with right side of the equation:

electric charge: coulombs (C)
c: meters/sec (MS^-1)
h: joule seconds (JS)
abs permittivity:farads/meter (FM^-1)
Source: Documenta Geigy
 
So we have alpha expressed in terms of SI units: C^2SM/JSMF = C^2/JF     
The constant has different expressions in different units, but it's dimensionless.

α = (1/4πε0)e2/hc   in SI

α = e2/hc   in cgs

α represent the absolute strenght of the coupling between electric charges and electromagnetic field; absolute in the sense that being dimensionless it doesn't depend on your choice of units. Exactly for this reason is a very important number, more important than e, h, c. It is really a number that comes from nature itself and not on us humans (as other dimensional constants like e, h, c or others).

One of the greatest mysteries of physics is why nature chose that value for that constant. Where does it come from?

Note that the number α, linking electromagnetism (e and c) with quantum mechanics (h) seems to suggest that there should be a deeper connection (than what we presently know) from the two theories.

Of course you're correct. If you reduce these SI units to coherent fundamental dimensions (L,M,T,I,U) everything should cancel out. I was too lazy to actually do the math. If everything didn't cancel out, I'd be sure I'd made a mistake would have do it all again (and again and ...).

Alpha is mysterious and that's why I like it. I was displeased with the lack of response until I became the squeaky wheel. (Note I distinguish between "mysterious" which is what science probes, and "mystical" which is non-scientific).
« Last Edit: 13/09/2008 00:40:50 by stevewillie »
 

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What is the fine structure constant?
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