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March 14[edit]

How can a same electron situated at multiple places?[edit]

According to Louis de Broglie, Electron travel around neutron in wave form so that it can't lose energy and fall into lower orbit. Which means Neil Bohr atom model was proved wrong. But How can a same electron situated at multiple places? Best example: Hydrogen wave function. Rizosome (talk) 06:48, 14 March 2021 (UTC)[reply]

I think you are mis-understanding "travel around" based on your experiences with macroscopic physical objects. At the scale of an electron in an atom, you have to contend with wave–particle duality. It doesn't have any single exact location and motion of a simple object, but only a general "probability region". DMacks (talk) 07:29, 14 March 2021 (UTC)[reply]

See also Uncertainty principle and Matter wave. --Lambiam 07:37, 14 March 2021 (UTC)[reply]

Rizosome, you seem to be misunderstanding the purpose of a scientific model. All such models are, ultimately "wrong" because no model can completely replicate the thing itself. Models are, instead, useful to a lesser or greater degree in given circumstances. The Bohr model was and is useful at a certain level of analysis, just as Newtonian mechanics are still useful, even though Einsteinian relativity gives answers closer to reality in certain circumstances.

The Apollo Moon landing flights were calculated purely according to Newtonian and not Einsteinian mechanics, for example, because with the velocities and masses involved, the difference between the answers given by both are indistinguishable (and the maths of the former are much simpler).

A factor that causes a good deal of confusion is that in school (and elsewhere), children (and adults embarking on an entirely new area of study) are often considered to be unable to understand the most recent scientific models because they involve advanced mathematics and sometimes unfamiliar, seemingly nonsensical phenomena not readily experienced in the 'everyday' world. They are therefore first taught simpler models, often those developed historically that were once the cutting edge of scientific theory but have long since been superceded. This is necessary to prepare them for more advanced models later in their academic careers, if they get that far. This approach is sometimes called "Lies to children", which sounds worse than it actually is. {The poster formerly known as 87.81.230.195} 2.221.80.5 (talk) 09:21, 14 March 2021 (UTC)[reply]

2.221.80.5 All such models are, ultimately "wrong" because no model can completely replicate the thing itself.

What is the meaning of this bold part of your sentence? Rizosome (talk) 12:00, 14 March 2021 (UTC)[reply]

A description of a real-world system can never faithfully capture all aspects of the system. In the words of Korzybski, "a map is not the territory it represents". Images are also never a 100% accurate representation, not even the Mars 2020 images. --Lambiam 13:29, 14 March 2021 (UTC)[reply]

We have an all models are wrong article:) DMacks (talk) 13:48, 14 March 2021 (UTC)[reply]

Lambiam So which atomic model came close to reality then?

All models, when they were conceived, were at that time the best effort to model physical reality. Better instrumentation allowed for experiments that observed discrepancies, leading to a next, better model – better in the sense of being a more accurate description of experimental results. At the moment, the model used for the electron cloud is that of atomic orbitals, which may be called Schrödinger's model inasmuch as they are solutions to the Schrödinger equation. It conforms, within experimental error, with observations – the main problem being, actually, the intractable calculations needed to make precise predictions. The nuclear structure is less understood. The nuclear shell model works well, but needs to be supplemented by field theories for the nucleon–nucleon interaction. This has been measured experimentally, but we don't yet have a good mathematical model. --Lambiam 13:47, 15 March 2021 (UTC)[reply]

Remember, the goal of physics is to explain how a system of things will change over time. Physics is ultimately the study of mathematically describing change. The simplest (and thus most taught) method of doing physics is the Newtonian system, which is based on a couple of basic axioms:

Objects have a well-defined location the exist in at any one time
Objects have a well-defined path they take through space

So, if you know the location of all of your objects, and you know the paths they are taking, you can make predictions about how a system of objects will change over time, you track their paths, you follow some simple rules for governing what happens when the objects collide.

Now, I want you to imagine a physical system where our two basic axioms don't apply: Where objects do not have a well-defined location and where objects do not take a well-defined path through space. You still need to come up with some way to make predictions about how that system will change over time; but you simply can't use Newtonian mechanics to do so, because things like "Object A bumps into Object B, and flies off in a new direction" don't make any sense in such a system: How do things bump when we don't even know where they are or how they are moving? That's the problem quantum mechanics solves for the atom: things like electrons are not smaller analogues of macroscopic objects. They are not little balls. They don't have well defined sizes or locations and they don't travel through space on well defined paths. But we still need a way to predict what they are going to do given some set of initial conditions and some perturbation to their environment, just like we can predict how two rolling balls will collide in a Newtonian sense, quantum mechanics gives us a way to predict how things on the atomic and subatomic level will behave. Insofar as they give us fantastically accurate predictions for the behaviors of these particles, it is a useful model. Insofar as the predictions it makes, and even the objects it is working on, don't have any analogue on the size scales you and I operate on, it can be confusing, but that's an us problem, not an atom problem. Atoms, near as we can tell, behave like quantum mechanics tells us they behave. --Jayron 32 17:02, 15 March 2021 (UTC)[reply]

An example of the problems of telling "lies to children" from primary school: the music teacher (Miss Adams) told us that "a crotchet is one beat". Crotchet says "often musicians will say that a crotchet is one beat, but this is not correct, as the beat is indicated by the time signature of the music; a quarter note may or not be the beat." When she gave the correct definition the following term the class didn't believe her - she said she had lied to keep things simple but the class wasn't convinced until she produced the textbook definition in Rudiments of music. 95.149.135.227 (talk) 16:58, 15 March 2021 (UTC)[reply]

Yeah, but the issue there is (and actually, it is true in physics too, but more obliquely) is that even the concept of what a "beat" is, it is just something for the convenience of the player and the conventions invented to represent it are just an arbitrary (though useful) system we just made up to efficiently communicate music. There isn't even one best way to use that system. Is Jesu, Joy of Man's Desiring in 3/4 with triplets or is it in 9/8? Am I counting three beats per measure and three subdivisions per beat, or am I counting 9 beats per measure? Do I go "one-and-a-two-and-a-three-and-a" along with my metronome, or do I go "one-two-three-four-five-six-seven-eight-nine" when I count that? The answer is: whichever way makes it easier for the musician to play it. None is "more correct", in the sense that "the Universe has deemed that it should be such!", instead, it is only what is useful, and some of useful is only "what somebody already arbitrarily decided so we're kinda stuck with it". Heck even physics turned out that way; the sign convention electric charge turned out to probably be a bad choice, but it was already burned into convention, so we're stuck with it. --Jayron 32 17:12, 15 March 2021 (UTC)[reply]

Sidney Coleman explains it quite well in this lecture to students with a different backgrounds. Count Iblis (talk) 18:51, 15 March 2021 (UTC)[reply]

It's not set in stone. For example, from the very beginning longitudes west of Greenwich had positive sign and longitudes east of Greenwich had negative sign, examples Auburn, North Carolina +79°, Auburn, New South Wales -151°. Recently that was reversed, so that Auburn, NC is now -79°, and Auburn NSW is +151°. 95.149.135.227 (talk) 11:53, 16 March 2021 (UTC)[reply]

Alcohol cleaning power[edit]

I've noticed that my alcohol-based antimicrobial spray is also remarkably good at cleaning various surfaces. Almost any dirt falls off easily, from that on smartphone screen to earwax when I sprayed my mp3 earbuds. Do such alcohol-based solutions have something in their chemistry that removes dirt quite easily? 212.180.235.46 (talk) 10:42, 14 March 2021 (UTC)[reply]

Isopropyl alcohol, which is probably what you are using, is well able to dissolve fats and oils which are the main marks on your mobile screen and earwax has a high fat content which will be easily dissolved by isopropyl alcohol. Richard Avery (talk) 13:00, 14 March 2021 (UTC)[reply]

Ethanol is also widely used in cleaning preparations and that article explains why. Cheap versions include methylated spirits. One aspect is that excess solvent evaporates, so you wouldn't want the solvent mixture to contain high-boiling components that would leave smears. Mike Turnbull (talk) 14:24, 14 March 2021 (UTC)[reply]

First illustration of a dinosaur?[edit]

Is there a particular dinosaur illustration thought to be the first depiction of how any dinosaur appeared while alive? I know that the first known illustration of a dinosaur bone is this (although the concept of a dinosaur was not understood at the time). Zagalejo (talk) 19:55, 14 March 2021 (UTC)[reply]

Benjamin Waterhouse Hawkins created the models for the Crystal Palace Dinosaurs, with guidance from Richard Owen, which were unveiled in 1854. An older illustration of large reptiles (not dinosaurs) is Duria Antiquior (an older Dorset), which depicted life in ancient Dorset based on fossils collected by Mary Anning, drawn by Henry De La Beche in 1830. Mikenorton (talk) 21:23, 14 March 2021 (UTC)[reply]

I don't think I've ever seen Duria Antiquior before. Very cool! Zagalejo (talk) 04:15, 15 March 2021 (UTC)[reply]

An earlier illustration of a prehistoric reptile is a sketch by French naturalist Jean Hermann, a restoration of what is thought to be a Pterodactylus antiquus fossil. --Lambiam 13:22, 15 March 2021 (UTC)[reply]

Interesting! Zagalejo (talk) 18:09, 15 March 2021 (UTC)[reply]

If you're interested in early interpretations of fossils, I highly recommend The First Fossil Hunters: Paleontology in Greek and Roman Times). Matt Deres (talk) 18:14, 15 March 2021 (UTC)[reply]

Thanks, I'll check that out! Zagalejo (talk) 02:58, 16 March 2021 (UTC)[reply]

Poking around Commons, I came across The country of the Iguanodon, which is pretty cool. It's from 1837. Zagalejo (talk) 02:58, 16 March 2021 (UTC)[reply]