And here is the crux: some scientists have suggested that the fine structure constant might not be constant, but could vary over time and space. In 1999, a team of astronomers using a telescope in Hawaii reported that measurements of light absorbed by very distant galaxy-like objects in space called quasars – which are so far away that we see them today as they looked billions of years ago – suggest that the value of the fine-structure constant was once slightly different from what it is today.
That claim was controversial, and still unproven. But if true, it must mean that at least one of the three fundamental constants that constitute it must vary.
Location, location, location
Kentosh and Mohageg fixed on h, and specifically on whether h depends on where (not when) you measure it. If h changes from place to place, so do the frequencies, and thus the “ticking rate”, of atomic clocks. And any dependence of h on location would translate as a tiny timing discrepancy between different GPS clocks.
So, what did they discover? Well, if there is any difference in h it would have to be really tiny. After careful analysis of the data from seven highly stable GPS satellites, Kentosh and Mohageg conclude that h is identical at different locations to an accuracy of seven parts in a thousand. In other words, if h were a one-metre measuring stick, two sticks in different places anywhere in the world do not differ by more than seven millimetres.
Spotting this variation of less than 1% in measuring sticks might be easy, spotting this in an exceedingly tiny number like Planck’s constant, which is 0.000000000000000000000000000000000662606957 joule seconds, demands the type of extreme accuracy of measurement that is most likely beyond the capabilities of our most accurate atomic clocks. At this point, however, we can feel reassured that there is no reason to suspect that this particular aspect of physics shifts between, say, London and Beijing – or indeed, between our galaxy and the next one.