The term

physical constant expresses the notion of a

physical quantity
subject to experimental measurement which is independent of the time or
location of the experiment. The constancy (immutability) of any
"physical constant" is thus subject to experimental verification.

Paul Dirac in 1937

speculated that physical constants such as the

gravitational constant or the

fine-structure constant might be subject to change over time in proportion of the

Age of the Universe.

[1] Experiments conducted since then have put upper bounds on their time-independence. This concerns the

fine structure constant, the

gravitational constant and the

proton-to-electron mass ratio specifically, for all of which there are ongoing efforts to improve tests on their time-dependence.

The laws of physics are structured in such a way that everything
hinges on a handful of universal constants. These are specific numbers
that have been measured to a high degree of precision and are key to the
operation of the universe. When doing calculations in physics, these
constants show up all over the formulae. One of these numbers is ‘π’
(or ‘pi’ in english). If you divide the circumference of a circle by
its diameter, the answer will always be exactly ‘pi’ (or approximately
3.141592654…..), regardless of the size of the circle. Another is ‘e’,
the charge on an electron. All electrons have a charge of
0.000000000000000000160 Coulombs (or 1.60E-19, in scientific notation).
Yet another value is ‘c’, the speed of light in a vacuum (299792458
meters per second). These values have all been measured, calculated and
confirmed thousands of times by physicists all over the world. We know
their values and according to the principal of universality, we know
them to be eternal and unchanging. But what if we’re wrong about this?One
of these constants, α (alpha), is called the Fine-Structure Constant.
Unlike those mentioned so far, it is a derived constant which means
that it’s not a single measured attribute but a combination of other
constants. If you take the square of the charge on an electron (e)
divided by the speed of light (c) and planck’s constant (h), and then
multiply the whole lot by 2π, you find that all those units cancel out
and the answer is a pure ratio of α = 1/137.036. This rather arbitrary
seeming number turns out to be pretty fundamental to the inner workings
of the universe. It governs the force between electrically charged
particles, including between an atom’s electrons and protons. If this
value were different by as little as 4%, the universe would be a very
different place. Nuclear fusion as we know it would not work, so stars
would not burn. Without stars, there would be nothing to convert
primeval hydrogen and helium into heavier elements like carbon or
oxygen. And without carbon and oxygen, we could not exist. The
Fine-Structure Constant is important.

Physicists have pondered whether the fine-structure constant is in fact
constant, or whether its value differs by location and over time. A
varying

*α* has been proposed as a way of solving problems in

cosmology and

astrophysics.

[12][13][14][15]String theory and other proposals for going beyond the

Standard Model of particle physics have led to theoretical interest in whether the accepted

physical constants (not just

*α*) actually vary.