[DoctorBeaver (OP)]

In an article I'm reading about measuring the fine structure constant it states:

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)

[Vern]

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.

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.

[lightarrow]

In an article I'm reading about measuring the fine structure constant it states:

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 (OP)]

Thank you for your replies. I understand now. It was mainly what "dimensionless" meant that I wanted clarified.

[itisus]

In an article I'm reading about measuring the fine structure constant it states:

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 (OP)]

Thank you, itisus.