On Sat, Aug 9, 2014 at 9:18 AM, David Roberson <dlrober...@aol.com> wrote:
The wiki article seems to tie down the proton mass quite accurately, but it > may just be the accuracy of the calculation instead of actual measurements. > I would be interested in seeing actual mass measurements by real > instruments instead of super computer calculations. It is not too hard to > visualize that the measurement accuracy is questionable. How can I go > about finding those results? The wiki article gives the proton (rest) mass as being 938.272046(21) MeV/c^2 [1]. If this value is accurate, at that precision I believe we have +/- 1 0.21 eV to use for free energy speculation. As you allude to, there's the accuracy of the mass and the precision of the mass. The precision of the mass given above implies that the standard deviation of the measurements is very small (as small as the numbers in parentheses). The precision and the accuracy of the number are related. The accuracy is the fit with experiment, and it places a bound on the precision that can be specified. The number above is most likely not an ab initio calculation and is instead a summary of the experimental findings relating to the mass of the proton. Because there was no doubt some variability found in the proton mass, a more precise number (more decimal places out) could not be specified. All of this assumes the Wikipedia people are being appropriately diligent in this particular case. Eric [1] https://en.wikipedia.org/wiki/Proton
