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DanArmak comments on [LINK] The half-life of a fact - Less Wrong
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Comments (9)
This is a non sequitur. "Atomic weight" has to refer, implicitly or explicitly, to a particular isotope to be meaningful. The weight of an isotope is not going to change over time, and it's very unlikely that we're significantly wrong about the weight of an isotope.
ETA: comments below explain my confusion. Thanks.
I don't know the history of the discovery of isotopes. I wouldn't be surprised if atomic theory started with weights assigned by the most common isotopes, and further checking led to "Hey, what we thought was just one sort of atom for each element needs to be more sophisticated because we were almost cutting reality at the joints but not quite".
That's how it was. Atomic weights were known to be not in whole number ratios, although sometimes tantalisingly close to them, and a lot of effort went into determining them precisely. There was a certain amount of chagrin when scientists realised that these numbers had no fundamental significance, but were just the average weights of the distribution of the different isotopes.
In practice "atomic weight" commonly refers to the average weight of the most common isotope mix.
Although you are right, as a nitpicker I don't think non sequitur, i.e. "doesn't follow", is correct to use here.
Well, as it turned out, I was mostly wrong: "atomic weight" refers to the average weight of the most common isotope mix of the element (on Earth), and our data about the isotope distribution changes. I didn't remember that, but that's probably what that original quote meant.
You seem to be right about the non sequitur.