You are watching: Which measurement is the most precise

In particular, in the case of the latter, we hosted off on defining this value till the two completing approaches because that measuring the kilogram agreed through each various other within the error border of their corresponding measurements.

Which leader me to wonder, what is the most precisely measured (not defined) worth that the scientific neighborhood has measured. I am thinking in state of loved one error (uncertainty / value). Before we characterized it, Plank"s constant was measured to a loved one error that $10^-9$. Have actually we measure anything with a reduced relative error?

Carrying the fame of being among the most exactly verified propositions in aramuseum.org, the ratio of the gravitational to inertial fixed was confirmed to be unity in ~ $1$ in $10^15$ through the microscope satellite in $2017$. The earlier finest precision to be $5 imes10^-14$, acquired by Baessler, et al. In $1999$.

References:

The magnetic minute of the electron has actually been measured to a couple of parts in $10^13$. (Source) This provides an exquisite check of quantum electrodynamics, and calculating the appropriate Feynman diagrams has been a Herculean initiative over decades.

Note that the much more precise tests cited in other answers are basically null results: no difference in between gravitational and also inertial mass; no difference in size of charge between proton and also electron; no mass of photon. For this reason I believe the magnetic moment of the electron is the most precise measurement the is non-null and also thus “interesting”.

A good candidate is the measure of the fine structure consistent $alpha$. This wiki write-up on precision tests of QED claims that:

The agreement found this way is to in ~ ten parts in a exchange rate ($10^−8$), based on the compare of the electron anomalous magnetic dipole moment and also the Rydberg consistent from atom recoil measurements...

There is also an upper bound on the mass of the photon, i beg your pardon is in the selection of $10^-27eV/c^2$ back that"s an top bound rather than a measurement since the expected value is $0$.

To prize the question from a different angle, LIGO has actually measured gravitational waves numerous times over the last few years. To execute so they have to observe a distortion in a 4km arm, in the order of $10^-18$m. In various other words, it has to detect a fractional imprecision in its length of ~$2.5 * 10^-23$. That"s nice accurate.

Another quantity that is famous is the frequency that the 21 centimeter line that Hydrogen hyperfine separating that has actually been measure to around 13 significant figures, 1420405751.7667±0.0009 Hz. Uneven the electron magnetic moment, discussed in one more answer, the QED calculation for hyperfine dividing is no as accurate. This calculation additionally depends top top other an essential constants, including electron/proton massive ratio and proton magnetic moment. Which space not well-known to indistinguishable precision.

The accuracy that the latest atomic clocks is a good candidate for the prize, with an accuracy of less than 1 component in 10^20. One example has been offered to check gravitational time dilation over a vertical elevation of a single millimeter, with even more precise confirmation possible with the latest atomic clocks.

**An atomic clock measure how general relativity warps time across a millimeter**

Aren"t clocks the most an accurate devices, relatively speaking? Their skepticism is 1 second in 33.7 exchange rate years, or far better than 10^-18.Refs:https://link.aps.org/doi/10.1103/PhysRevLett.123.033201https://en.wikipedia.org/wiki/Quantum_clock#Accuracy

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