Timeline for Why is the mole/"amount of substance" a dimensional quantity?
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| Apr 6, 2015 at 22:38 | comment | added | jvtrudel | And why my answer failed to address the point? "Nor am I asking about why it's chosen as a base quantity and not a derived quantity. I get that any particular choice of bases is more or less arbitrary. I don't understand why it's a dimensional quantity at all. " Its clearly because the nature is discrete and it was my point. Whatever you trust in Perrin or in the Queen ;-) (inside joke if you catch it) | |
| Apr 6, 2015 at 22:34 | comment | added | jvtrudel | What does OP mean? | |
| Apr 6, 2015 at 22:31 | comment | added | Emilio Pisanty | It is now 106 years since Perrin conclusively demonstrated the discrete nature of matter. Single ions can be loaded, imaged, and manipulated in ion traps; single molecules can be imaged and manipulated in condensed phases. There's really no excuse for claiming the discrete nature of matter to be an "approximation". In any case, this answer fails to address the points raised by the OP. | |
| Apr 6, 2015 at 22:04 | comment | added | jvtrudel | It appears that (at least in a certain approximation) the world is composed of individual particules and, yes, in many cases we need to count them one by one. It is especially true in chemistry were you consider atoms bounding and breaking. Stoichiometry - or the relatives "amount of substance" between reactives - is of prior importance. But even in (ab initio) quantum mechanics you need to postulate the number of atoms and electrons... you don't get them from first principle. In high energy physics, you may extract particules from vacuum but you need many moles of photon in a small volume! | |
| Apr 6, 2015 at 21:45 | comment | added | Emilio Pisanty | To rephrase your points: (1) you will not extract the same energy with 1 atom or $10^{23}$, (2) at fixed pressure and temperature the number of atoms will determine the volume of the gas, and (3) if a pond evaporates you must take into account the number of molecules in it. In no way do these processes describe anything that could not (at least in principle) be described by counting things. | |
| Apr 6, 2015 at 21:37 | history | answered | jvtrudel | CC BY-SA 3.0 |