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There are lots of different numbers that you can use quantum mechanics to predict. It turns out that the size of the proton is both harder to predict and harder
by db48x 5y ago
There are lots of different numbers that you can use quantum mechanics to predict. It turns out that the size of the proton is both harder to predict and harder to measure than many of those other numbers.
Meanwhile we can measure the fine structure constant to 12 decimal places (https://en.wikipedia.org/wiki/Electromagnetic_coupling_constant#History_of_measurements https://en.wikipedia.org/wiki/Electromagnetic_coupling_const...) and that measurement is in very close accord with the predictions of quantum mechanics.
- dnautics 5y agoI thought the fine structure constant was primitive: there is no theory arguing what it's value should be.
- fsh 5y agoThe fine structure constant can be measured in two different ways. One is to measure the g-factor of the electron in a Penning trap. This can be related to the fine structure constant using quantum electrodynamics (QED). The other is to measure the recoil that an atom receives when it absorbs a photon in an atom interferometer. By combining the result with another well known constant, the fine structure constant can be calculated. The results of both methods agree to 12 digits, which shows that the QED calculations of the electron g-factor are correct on that level.