Timeline for Is Bohr's postulate really necessary from classical perspective?
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11 events
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| May 28, 2020 at 12:47 | comment | added | hagebutte | I assume you refer to specific rigorous calculations and resulting numbers with the energy argument? Because,… I mean … of course, you do need energy to change a charge distribution (classical), and also: you do need energy to change a charge-probability distribution (QM)?! In both cases there are some distributions that have the same energy and in both cases there are some distributions with different energy where you have to work to change the distribution. | |
| May 28, 2020 at 12:35 | comment | added | hagebutte | Yes, Millikan (experiment) pre-dates QM (theory), that doesn’t imply charge quantization is a classical thing. My question revolves around the Classical Perspective (headline). Classical ED but also old QM give no deeper insight to (not even speaking of derivation of) charge quantization (besides the changing of interpretation of the involved distribution). Or in other words “Charges are quantized” is (imo) a awesome historical postulate to go from classicalED to QM: from charge distribution to charge-probability distribution. | |
| May 28, 2020 at 12:02 | comment | added | hagebutte | Answer to your 2nd comment: An electric field alone would not stretch anything. Classically you would need a quite hefty field gradient (like that of light ;)) to do this. But besides that, of course you are right. And also: your thought experiment happens all the time: The headache is solved by changing the interpretation of the distribution associated with the electron from “charge” to “(charge)probability”. I wouldn’t complain if THIS would be the content of a postulate. But that’s not the content of the postulate in question. | |
| May 28, 2020 at 11:21 | comment | added | probably_someone | @hagebutte Also, it takes energy in order to change the shape of a charge distribution. Suppose we ionize one of your atoms. This means that the charge distribution corresponding to your electron must go from the spinning ring that's consistent with the atom, to the spherically-symmetric, tiny distribution consistent with scattering experiments. Either a) the electron needs some extra energy to change shape during ionization, so you will predict the wrong ionization energy, or b) the electron is at a larger radius than the pointlike model, so you will predict the wrong atomic radius. | |
| May 28, 2020 at 11:09 | comment | added | probably_someone | @hagebutte Ok, great, so with your definition of the electron, what specifically is preventing Millikan from seeing fractional electron charges on his droplets? The atomizer violently separates different parts of the oil to create droplets, so it stands to reason that you might, for example, trap half an electron on one droplet while the other half is on another droplet, giving each droplet a charge of $e/2$. But we never see that; we only see droplet charges that are integer multiples of $e$. | |
| May 28, 2020 at 11:05 | comment | added | hagebutte | "So is your claim that the electron can change its shape depending [...] " I would rephrase that to: classically, the electron is (or: "is associated with" in case "is" might be too strong) a charge distribution. And, yes, of course, classical charge distributions are allowed to change. Why shouldnt they? | |
| May 28, 2020 at 11:02 | comment | added | probably_someone | @hagebutte And, if the electron can change its shape in response to electric fields, then what's preventing us from applying a strong electric field to "stretch out" the electron, then trapping some of its charge distribution on the other side of a barrier? This idea breaks quantization of charge, as far as I can tell; and the fact that the electron cannot be subdivided is a fact that predates quantum mechanics, which came in large part from the results of the Millikan oil drop experiment. | |
| May 28, 2020 at 10:59 | comment | added | probably_someone | @hagebutte So is your claim that the electron can change its shape depending on whether it's free or bound? It seems like this has to be the case if we simultaneously want to explain the existence of atoms and low-energy electron scattering observations (the classical explanations of the latter rely on the electron having a pointlike charge distribution). | |
| May 28, 2020 at 10:37 | comment | added | hagebutte | Of course, your calculations are perfectly correct, thats not the point. The point is, that this doesn't indicate that a postulate is necessary, it only indicates, that the electron distribution is not a dirac but a different classical charge distribution could do the job (one with J=const) | |
| May 28, 2020 at 10:31 | comment | added | hagebutte | "A classical electron is a point charge" you lost me already there. As indicated in the first post, the electron as a charge distribution (however it might be shaped: a point, a hard or soft sphere or something else) is a classical picture. Classical electrodynamics, covers any kind of charge distributions. Claiming, that only when an e- is associated with very specific distributions (like tophat-sphere or dirac point) it is called classical and otherwise not, is somewhat a postulate in itself and I don't understand why one would do this restriction, nor what evidence supports this claim | |
| May 28, 2020 at 10:14 | history | answered | probably_someone | CC BY-SA 4.0 |