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I've recently learned that there is an official Kilogram (IPK) kept in Paris which is used to calibrate, directly or indirectly, all weight measurement tools. I've also learned that each time the IPK is measured, there is a good chance the measurement is a little different by a few micrograms. Statistically speaking, this is a chance error being observed in the measurement.

Now for my question, if you take out any human component, is the reason for the chance error in the measurements due to the probabilities at the quantum level? Can quantum probabilities observed while weighing micrograms?

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For one, because of the way we currently define the kilogram, this is wrong:

each time the IPK is measured, there is a good chance the measurement is a little different by a few micrograms.

The kilogram, by definition, is the mass of the IPK. You cannot measure its mass and get anything other than one kilogram.

What you can do is make a copy, keep it in identical conditions, and then measure both objects. We've been doing that for a while, with a bunch of different copies, and the copies differ from each other by a few tens of micrograms.

Image source

Now, to be clear: these variations in mass have nothing to do with quantum physics. Instead, they are caused by things like

  • diffusion of atmospheric contaminants into the metallic lattice,
  • oxidation of the surface layer of the metal, or
  • loss of microscopic amounts of metal when the piece is polished.

None of them have anything to do with quantum physics.


And if you're thinking "that variability sounds pretty bad", then yes, the world of metrology agrees with you. There are plans in place to replace the artifact-based definition of the kilogram, which should come into force on May 2019.

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