The value of the proton charge radius in itself is pretty much irrelevant, otherwise it wouldn't be so hard to measure. As scientists we want to know if our un

The value of the proton charge radius in itself is pretty much irrelevant, otherwise it wouldn't be so hard to measure. As scientists we want to know if our understanding of nature is correct. To test this, we measure the same quantity, for example the proton charge radius, in different ways. If the underlying theory is correct, the results should agree within the experimental uncertainties. Since 2010 there was a big disagreement between the proton charge radii measured by hydrogen spectroscopy and electron/proton scattering (which roughly agreed at the time), and a much more accurate measurement using muonic hydrogen spectroscopy. This has lead to a lot of excitement, since discrepancies could be a hint for new physics. Since then, more accurate hydrogen spectroscopy experiments have been performed and most agree with the muonic hydrogen value. This probably indicates that the discrepancy is due to underestimated error bars in the old measurements. In contrast to laser spectroscopy which gives relatively direct results, getting the charge radius out of electron scattering data is notoriously hard. Different groups have found different charge radii from the same data for a long time.