Time-variation of fundamental constants

The term <a href="/facts/Physical_constant/uI2QvAHw">physical constant</a> expresses the notion of a <a href="/facts/Physical_quantity/S8pWBEpK">physical quantity</a> 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.
<a href="/facts/Paul_Dirac/6bt5yRdk">Paul Dirac</a> in 1937 <a href="/facts/Dirac_large_numbers_hypothesis/7uKcM0Hb">speculated</a> that physical constants such as the <a href="/facts/Gravitational_constant/GdQ8tcBD">gravitational constant</a> or the <a href="/facts/Fine-structure_constant/zyzpmTJV">fine-structure constant</a> might be subject to change over time in proportion of the <a href="/facts/Age_of_the_universe/BaByputq">age of the universe</a>.
Experiments conducted since then have put upper bounds on their time-dependence. This concerns the fine-structure constant, the gravitational constant and the <a href="/facts/Proton-to-electron_mass_ratio/mnAK3JXX">proton-to-electron mass ratio</a> specifically, for all of which there are ongoing efforts to improve tests on their time-dependence.
The immutability of these fundamental constants is an important cornerstone of the laws of physics as currently known; the postulate of the time-independence of physical laws is tied to that of the <a href="/facts/Conservation_of_energy/12CdN4Ik">conservation of energy</a> (<a href="/facts/Noether%27s_theorem/VFjqrEvz">Noether's theorem</a>), so that the discovery of any variation would imply the discovery of a previously unknown law of force.
In a more <a href="/facts/Philosophy_of_science/aonsfhTY">philosophical</a> context, the conclusion that these quantities are constant raises the question of why they have the specific value they do in what appears to be a "<a href="/facts/Fine-tuned_universe/y8SaFx8R">fine-tuned universe</a>", while their being variable would mean that their known values are merely an accident of the <a href="/facts/Cosmic_time/yl6n1wqe">current time</a> at which we happen to measure them.

Time-variation of fundamental constants open-in-new

Time-variation of fundamental constants