# Tag Info

1

As pointed out by Umaxo, a universe containing four forces would be a pretty boring place because it would contain no particles. When you add in the particles we know about, you have to insert their masses, charges and spins into the Standard Model and doing so adds in a list of physical constants whose values we measure through experiment but which are not ...

0

The answer depends on the exact definition of the set of fundamental constants, as well as on the choice of base units of a given system of units. A look at the NIST page Fundamental Physical Constants --- Complete Listing shows that they list too many fundamental constants to allow assignment of a unit value to each of them, within the International ...

5

You can use "natural units" to set some of the fundamental constants (usually $\hbar$, $c$, Coulomb's constant) equal to one, but this fixes the values of other constants as values other than one. For example, by setting $\hbar$, $c$ and $k_e$ equal to one, you can find the elementary charge, $e$, in terms of the fine structure constant, $\alpha$. \alpha=...

13

There are many, many instruments which are calibrated using the old definition of the kilogramme - the International Prototype Kilogramme (IPK) made of a platinum-iridium alloy. So one kilogramme measured using the new definition had to be as close as possible to one kilogramme using old definition so as not to have to recalibrate all instruments which ...

9

It is an updated experimental value that matches measurements by Kibble balances and by counting atoms in silicon spheres to determine Avogadro’s number. The 2010 measurement was presumably consistent with only one metrological approach. The new exact value is consistent with both. See this NIST page, which says The Kibble balance and Avogadro project ...

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