By the 1940s, it became clear that the value of the fine-structure constant deviates significantly from the precise value of 1/137, refuting Eddington's argument. With the development of quantum chemistry in the 20th century, however, a vast number of previously inexplicable dimensionless physical constants were successfully computed from theory.

The reason for this is that the choice of units is arbitrary, making the question of whether a constant is undergoing change an artefact of the choice (and definition) of the units. For example, in SI units, the speed of light was given a defined value in 1983.

Thus, it was meaningful to experimentally measure the speed of light in SI units prior to 1983, but it is not so now.

For the fine-structure constant, this upper bound is comparatively low, at roughly 10−17 per year (as of 2008). The gravitational constant is much more difficult to measure with precision, and conflicting measurements in the 2000s have inspired the controversial suggestions of a periodic variation of its value in a 2015 paper.

For the fine-structure constant, this upper bound is comparatively low, at roughly 10−17 per year (as of 2008). The gravitational constant is much more difficult to measure with precision, and conflicting measurements in the 2000s have inspired the controversial suggestions of a periodic variation of its value in a 2015 paper.

For the fine-structure constant, this upper bound is comparatively low, at roughly 10−17 per year (as of 2008). The gravitational constant is much more difficult to measure with precision, and conflicting measurements in the 2000s have inspired the controversial suggestions of a periodic variation of its value in a 2015 paper.

Similarly, with effect from May 2019, the Planck constant has a defined value, such that all SI base units are now defined in terms of fundamental physical constants.

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