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### Author Topic: Why is the fine structure constant the most fundamental constant?  (Read 2411 times)

#### DoctorBeaver

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##### Why is the fine structure constant the most fundamental constant?
« on: 01/03/2009 16:21:12 »
In an article I'm reading about measuring the fine structure constant it states:

Quote
As a dimensionless number, it is even more fundamental than other constants such as the strength of gravity, the speed of light or e itself.

Why is a dimensionless number more fundamental? (layman's terms if possible, please)
« Last Edit: 01/03/2009 16:23:42 by DoctorBeaver »

#### Vern

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##### Why is the fine structure constant the most fundamental constant?
« Reply #1 on: 01/03/2009 17:08:29 »
The fine structure constant, alpha, has no units of measure, so it is like a ratio. PI is another ratio of the diameter of a circle to its circumference. It is very much related to the charge amplitude of an electron.

Wikki has a good article on it.

Quote from: Wikki
The fine structure constant is the ratio between the velocity of the electron in the Bohr model of the atom and the speed of light. The square of alpha; is the ratio between the electron rest mass (511 keV) and the Hartree energy (27.2 eV = 2 Ry).
# In the theory of quantum electrodynamics, the fine-structure constant is the coupling constant for the strength of the interaction between electrons and photons. The theory does not predict its value; thus it must be determined experimentally. In fact, it is one of the 20-odd 'external' parameters in the Standard Model of particle physics.
« Last Edit: 01/03/2009 17:16:17 by Vern »

#### lightarrow

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##### Why is the fine structure constant the most fundamental constant?
« Reply #2 on: 01/03/2009 17:39:49 »
In an article I'm reading about measuring the fine structure constant it states:

Quote
As a dimensionless number, it is even more fundamental than other constants such as the strength of gravity, the speed of light or e itself.

Why is a dimensionless number more fundamental? (layman's terms if possible, please)
A dimensionless number is more fundamental because it doesn't depend on hour  specific choice of units: if you use the centimeter instead of the meter, for example, you get a different value of the dimensionful constant.

#### DoctorBeaver

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##### Why is the fine structure constant the most fundamental constant?
« Reply #3 on: 01/03/2009 18:18:33 »
Thank you for your replies. I understand now. It was mainly what "dimensionless" meant that I wanted clarified.

#### itisus

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##### Why is the fine structure constant the most fundamental constant?
« Reply #4 on: 03/03/2009 19:15:44 »
In an article I'm reading about measuring the fine structure constant it states:

Quote
As a dimensionless number, it is even more fundamental than other constants such as the strength of gravity, the speed of light or e itself.

Why is a dimensionless number more fundamental? (layman's terms if possible, please)
Dimensional units are subject to change in relativity, etc.  One constraint on hypotheses is that changes must be coordinated to keep alpha constant.  It's a good sanity check.

#### DoctorBeaver

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##### Why is the fine structure constant the most fundamental constant?
« Reply #5 on: 03/03/2009 21:07:23 »
Thank you, itisus.

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##### Why is the fine structure constant the most fundamental constant?
« Reply #5 on: 03/03/2009 21:07:23 »