For future reference, here’s the nineties-tastic webpage NIST maintains to list the current best values for fundamental physical constants, called the “CODATA Internationally recommended values”. CODATA is the Committee on Data for Science and Technology and maintains a spectacularly uninteresting brochure of a website which frankly makes the NIST page seem attractive. The empirically-derived CODATA values all come with uncertainty information attached, which you can read more about here. As a further note, the ‘e’ used in the plain-text values means '10^', so 1e5 means 10[sup]5[/sup] (10^5, 100000) and 1.5e-3 is 1.510[sup]-3[/sup] (1.5*10^-3, 0.0015).
A stopwatch? Luxury! I can never find my caesium 133 atom when I need to experimentally derive the second.
We don’t know if it’s the master that’s changing mass or the copies.
Amperes and coulombs being taken as the base units, you can derive 1 second = 1 coulomb/ampere, and calibrate your stopwatch accordingly.
This has been empirically observed to be approximately = 1 zombie/fortnight[sup]2[/sup]
I thought amperes were defined by the total amount of current flowing through a conductor, and volts were the force of the current itself, i.e., the measurement of the electrical potential difference between two points that current is flowing between.
Clearly I am ignorant. LOL
That’s true, but it’s unlikely. Given some random variation, a collection of samples should have error on the order of 1/sqrt(N), where N is the number of samples, as compared to just one sample. Even if the copies are a bit less accurate than the original, as a collection they should be more accurate. No guarantees, of course, but pretty likely.
But since they’re all stored separately, can you single out the original and say THIS has changed relative to the lot? You could also say copy #3 has changed relative to the remainder.
Yes–at least in a statistical sense. If you have 10 samples and one is lighter than the rest, you can never be sure that the 9 didn’t increase in mass instead of the one decreasing. It’s just a lot less likely.
My understanding is that when the current standard was created, 40 identical platinum-iridium cylinders were created, and one was designated the primary. In some sense this means that the primary can’t vary in mass, since it is the very definition of the kilogram, but obviously this is silly. At any rate, these 40 cylinders have diverged in mass over time for a variety of reasons, only some of them known. They tend to gain mass over time, until they are cleaned, and the mass after cleaning has tended to decrease–likely due to scratches/abrasion/etc. from handling.
What a quaint embarrassment. As an American, I am ashamed that we put definitively state-of-the-art content above trendy web site design, and resort to plain text that any old troglodyte can access.
I see another problem: the definition of the amp presupposes you know what a kilogram is.
You should take more care where you put it down, then. Did you remember to store it in a cool, dry place? :dubious:
Meanwhile, let’s not forget that the unit referenced in the OP is subject to seasonal variations. I’m sure everyone’s heard of the Christmas Ampere.
“A lot less likely” presupposes that the variation of the kilogram prototypes is random. If there is a systematic variation, it depends on the nature of that variation. Suppose there were atmospheric contamination that migrates into the cylinder, and so can’t be cleaned off, and no other causes of variation. Then all the kilogram prototypes are gaining mass, and the one that is lighter than the rest will be the most accurate.
Yes, because it has been proven that it is impossible to have both content and web design that is accessible to people with handicaps. It simply cannot happen.