Wikipedia:Reference desk/Archives/Science/2023 October 24

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October 24

Herbivore and carnivore

We are asked to eat balanced diet, but they eat only raw plant leaves and digest while others hunt them and eat their meat.

So the first group get all protein, minerals, fibre, calcium from leaves only and second group also don't face constipation eating only raw meat.

Right now due to urban life human beings might have become weaker, but is it possible that prehistoric humans could digest raw meat and leaves without cooking?

I am sure humans learned cooking and before that they ate everything raw. Nasterfilly (talk) 07:29, 24 October 2023 (UTC)

There's actually quite a lot of evidence of what our ancestors ate. In particular, they ate, in enormous quantities for tens of thousands of years, oysters. And we still eat them raw. See Pleistocene human diet. Abductive (reasoning) 07:55, 24 October 2023 (UTC)

The article Pleistocene human diet makes no mention of oysters.  --Lambiam 10:28, 24 October 2023 (UTC)

It says seafood. The article should mention the huge shell middens in Africa and Spain. Abductive (reasoning) 18:14, 24 October 2023 (UTC)

Maybe not in Nebraska though? Martin of Sheffield (talk) 09:06, 24 October 2023 (UTC)

It seems unlikely that there was human occupation of Nebraska before the invention of cooking, however loosely one interprets "human". {The poster formerly known as 87.81.230.195} 46.65.231.103 (talk) 09:10, 24 October 2023 (UTC)

Well use Chad then. The point is that "what our ancestors ate ... oysters" assumes a coastal population. Unless you are going to postulate significant Pleistocene trans-continental trade routes then any population more than a few day's journey from the sea would not have a significant proportion of seafood. Martin of Sheffield (talk) 09:19, 24 October 2023 (UTC)

I believe that is what's postulated; that most humans were coastal. The incredible availability of oysters once you have figured out that you can pop them out of the sand with a stick (a method not available to any animal except the oystercatchers), you have these 20+ meter high, kilometers-long shell middens appear in the geological record. Sea level change has submerged many of these, but those that remain are impressive. Abductive (reasoning) 18:22, 24 October 2023 (UTC)

See Etheria elliptica for oysters in Chad 2A01:E0A:D60:3500:6F61:27D8:6496:B242 (talk) 13:54, 26 October 2023 (UTC)

Modern humans routinely eat raw leaves – see Salad. Eating uncooked meat (including mammalian meat) is culturally more restricted, and is somewhat less favoured because of the increased possibility of disease transmission that cooking mostly eliminates, but see raw meat.

Different species have very different anatomies and metabolisms, including those aspects of both relating to digestion. It is pointless to compare obligate herbivores and obligate carnivores to omnivores such as humans in an attempt to deduce what is healthy for the latter. {The poster formerly known as 87.81.230.195} 46.65.231.103 (talk) 09:02, 24 October 2023 (UTC)

Many herbivores do not, or not only, eat plant leaves, but also whole plants or other parts of plants (stems, roots, tubers, seeds, nuts, berries, fruits). Some of this is also routinely consumed raw by modern humans (e.g. carrots, pumpkin seeds, almonds, tomatoes, apples).  --Lambiam 10:42, 24 October 2023 (UTC)

The most photons an electron can receive?

A week ago I askd the other way around. The most photons an electron can absorb. But I'm stuck on receiving. When an electron receives a photon, it goes up 1 shell? Big elements don't tend to have more than 7 shells, so it can only absorb up to 7 photons? Then what about the hydrogen atom?

When you shine light to an object like a solid, what happens to when photons strike the nucleus? Do majority photons miss the electrons and hit the nucleus? Thanks. 170.76.231.162 (talk) 16:30, 24 October 2023 (UTC).

I don't know this subject at all, but I'm reasonably sure the electron will fly off pretty easily and leave behind an ion. Can a photon hit a loose electron? Abductive (reasoning) 18:17, 24 October 2023 (UTC)

That is only true if the photon energy is above the work function of the material it is interacting with (see photoelectric effect), or the ionization energy if we aren't talking about solid surfaces. This is usually a fairly high amount of energy, which is good, or we would all immediately die if we turn on a lamp. Generally speaking, you need at least ultra-violet energy to start kicking off electrons, and possibly deep-UV or X-rays, especially if we are talking about core electrons as opposed to valence electrons. Again, this is why ultra-violet light is a bit dangerous; it's going to start doing things like ionizing some of the DNA in your cells, or ionizing other molecules around them into free radicals that then interact with your DNA, creating mutations that could lead to cancer. Below these energies, such as visible light (in most cases) and down, the photon will either not interact with the atom and its electrons at all, or only interact with them if the photon energy is resonant with an allowed transition of the electrons in the atom's electron cloud. As for hitting a lose electron... well, in photon/electron interactions, whether in an atomic electron cloud or a free electron, its probably better to picture these as waves interacting rather than particles interacting. An electron in an atom's cloud, for example, is a standing wave, and the electron field of the photon wave can, if resonant with an allowed transition, interact with that standing wave. The same can probably also happen with a free electron, since it is still also a wave. --OuroborosCobra (talk) 18:55, 24 October 2023 (UTC)

The interaction between a photon and a free electron is Compton scattering. For bound electrons, it is in most cases one photon that is absorbed, but there is also Two-photon absorption. The absorption of three or more photons at once is not disallowed but very unlikely. --Wrongfilter (talk) 19:03, 24 October 2023 (UTC)

That's kind of true, but only if we are talking about two-photons interacting with an electron at the same time/simultaneously. You can have non-simultaneous or sequential interactions, so long as an additional photon interacts with the electron that has already been interacted with before it returns to the ground state. Since these absorptions and relaxations are not instantaneous processes, that's absolutely possible. That's one of the ways we have Balmer series absorptions in hydrogen, for example. You can absorb a photon resonant with 1s -> 2p, and then absorb a second photon for 2p -> 4d (part of the Balmer series), but that won't happen at the same time as the first absorption; it must be subsequent, and before enough time has passed for relaxation. Of course, you can also have this with electrons being thermally excited to higher states and then interacting with a photon, but there's no reason it has to be initially thermal rather than from the electric field. --OuroborosCobra (talk) 19:30, 24 October 2023 (UTC)

Yes, and now what? You are describing multiple absorption events (and as there are in principle infinitely many excited states in an atom, it can in principle absorb arbitrarily many photons that way before ionisation), I referred to a single event involving two or more photons. And who knows what OP was asking about? --Wrongfilter (talk) 19:45, 24 October 2023 (UTC)

Exactly, who knows what they are asking about? I wouldn't assume they are asking about simultaneous absorption events anymore than their previous question was predicated on simultaneous emissions. --OuroborosCobra (talk) 21:15, 24 October 2023 (UTC)

When thinking about photons and electrons interacting, you are better off thinking of them as waves and fields interacting rather than particles. A photon isn't likely to "miss" an electron, rather, the electric field of that photon may or may not be resonant with an allowed transition to interact with the electron, or rather, the electric field interacting with the standing wave that is the electron. So, for example, a photon of the proper energy can interact with an electron around a hydrogen atom and give it enough energy to get to a state more than one shell higher than than the ground state. So, that ground state 1s electron standing wave can't interact with an electric field at the frequency (energy of the photon) equal to the energy difference between a 1s standing wave and a 2s standing wave because the change in the azimuthal quantum number must be +/- 1, and from 1s to 2s that would be a change of 0. To think of it visually, the interaction requires the electric field to be able to add a "node" to the electron standing wave, but just one additional node. So, you could have a 1s -> 2p, but nothing says that a high enough frequency in the electric field (high enough energy electron) can't be resonant with an excitation of 1s -> 3p, or 1s -> 4p, for example. However, you won't have a 1s -> 3d, since that would be a change of 2 azimuthal quantum numbers, or more than one "node" in the standing wave. There's a really great animation describing this and showing how you can only add one "node" at a time, and must add one node for that interaction to take place from Boston University, can find it here. As the video shows, if that photon energy isn't such that the frequency of the electric field is resonant with an allowed transition, then nothing will happen and the photon won't interact with the atom. I guess that could be described as "missing," but it isn't so much that the photon "missed" the electron so much as they saw each other, and nothing happened. I really love this video, since it also shows you visually why photon absorption isn't an "instantaneous" process! It is possible for the electric field from a second photon to also interact with the same electron, you could have a 1s -> 3p, and if another photon electric field is around before the electron returns to the ground state and is resonant with an allowed transition, it could then interact and transition from 3p -> 4d, or something like that. You can see this also at Hydrogen spectral series. So, an electron can absorb tons of photons, though those interactions need to be allowed transitions, and they can't necessarily all happen at the same time, since those absorptions are not instantaneous. As for really high energy photons, see photoelectric effect and ionization energy. Basically if that frequency of the electric field oscillation from the photon is really high, and we are generally talking ultra-violet or x-rays, then it might be enough to actually strip the electron off of the atom, ionizing it. Think of that animation I linked you to, but imagine that oscillation being really really fast, to the point that instead of just forming one more "lobe," it pushed the standing wave off of the atom altogether. That can happen. As for interactions with the nucleus, ultimately, protons and neutrons are themselves waves as well, so yes, they can interact with the electric field oscillating from a photon, but it is also going to be subject to proper selection rules and correct resonant frequencies. Someone else will have to answer in more detail on that, I'm not an expert on interactions of light with protons and neutrons. Lastly, lower energy/lower frequency photons can also interact in other ways, such as if they match the energy of a vibration or rotation of a molecule. See molecular spectroscopy, infrared spectroscopy, microwave spectroscopy, molecular vibration, and molecular rotation for more information on these. --OuroborosCobra (talk) 19:23, 24 October 2023 (UTC)

I'm a bit uneasy about the statement that the standing wave is the electron. The wave function describes the state of the electron (or perhaps more accurately the atom) and is used to derive probabilities, e.g. where the electron is and probabilities to transition from one state to another, but the wave function is not the electron itself. --Wrongfilter (talk) 19:47, 24 October 2023 (UTC)

As far as I understand, that's ultimately an axiomatic, philosophical distinction, see positivism and other related discourse surrounding the Copenhagen model and its competitors. Remsense聊 20:22, 24 October 2023 (UTC)

The wave isn't the electron, rather, the electron is a standing wave, when within an AO or MO. Researchers at IBM and and the University of Liverpool have even made high resolution images of various molecular orbitals, especially HOMOs and LUMOs conjugated π systems using scanning tunneling microscopy, so there appears to be something much more physical to these standing waves than them being just the mathematical descriptions (wavefunction) useful for deriving probabilities and properties. --OuroborosCobra (talk) 21:47, 24 October 2023 (UTC)

Well, naturally the "standing waves" (as you insist on calling them) translate into something that is physically measurable, otherwise they would be useless. In this case it is time-integrated charge distributions, which are proportional to the probability density for the location of the electron(s), which in turn is the absolute square of the wave function, $|\Psi (\mathbf {x} )|^{2}$. (Note that I'm not making any statement on what the electron is (that would be futile), at best on what it is not).--Wrongfilter (talk) 09:14, 25 October 2023 (UTC)

I do not know what your issue is with my calling them "standing waves." At least within physical chemistry, that is pretty standard terminology and the correct term for them. Indeed, even our articles on atomic orbital and molecular orbitals call them standing waves. I mean, in terms of the physical description given to the mathematical model, even if you want to just consider it a "model" as opposed to something more physical or "real" (I kind of hate using the word "real" here since it could be confused with the mathematical concept of real numbers and imaginary numbers, which is problematic linguistically when wavefunctions are complex), the model of these orbitals describe them as standing waves. --OuroborosCobra (talk) 13:39, 26 October 2023 (UTC)

I guess I want to see sines and cosines when talking about waves. You get these in non-stationary situations (a propagating particle), and some stationary situations like the one-dimensional potential wells. In the hydrogen atom, the eigenfunctions (solutions to the stationary Schrödinger equation) are spherical harmonics and Legendre polynomials. While these are "wave functions", they do not necessarily have to be "waves" in my mind. Maybe that's just me. I think I prefer abstract state vectors (i.e. $|\psi \rangle$) anyway... --Wrongfilter (talk) 14:03, 26 October 2023 (UTC)

I mean, in a spherical coordinate systems, there are sines in the mathematical descriptions and our article on spherical harmonics has sines and cosines as well. It's fine to just think of them as $|\psi \rangle$ but also important to think about what that actually is describing. Most of the time, when working with wave functions, we don't have to think that hard about it, but we shouldn't forget it. --OuroborosCobra (talk) 14:38, 26 October 2023 (UTC)

The wave function is a mathematically model of a physical phenomenon. As such the epistemological situation is not essentially different from that of mathematical models of physical phenomena in general. For some reason, quantum weirdness makes people ponder whether the physical phenomenon (the wave) itself is "real" or a mirage of some deeper reality. Lacking an operationalizable definition of "real", this ontological question is as meaningless as the question whether reality itself is real. (It is nevertheless conceivable that one day quantum theory will be superseded by another theory in which the "weirdness" emerges from more basic assumptions.)  --Lambiam 08:20, 25 October 2023 (UTC)

Now that's where I might object! I'd say the particular scrawling of the Schrödinger equation and the pondering of what is real, really? are equally meaningless. Meaning, I'm enthralled. — Remsense聊 08:23, 25 October 2023 (UTC)

I asked a physics professor yesterday who said the vast majority of light hits the valence electrons, and rarely hit the nucleus, i.e. light hitting a table. Does anyone know what %? Is it like 99%? And the remaining .9% could be the non-valence electrons, or the nucleus? It also depends on the light. UV will hit higher % of nucleus than say IR light, is there a formula to calculate this? 170.76.231.162 (talk) 16:45, 27 October 2023 (UTC).

According to our article Pair production, a photon near an atomic nucleus can be converted into an electron–positron pair (γ → e⁻ + e⁺), and this is the dominant mode of photon interaction with matter for photons with high photon energy (MeV scale and higher). At lower energies, the photoelectric effect will be larger. I don't know any formulas, but the sizes of these effects will depend on the energy of the photons and the chemical composition and physical state of the matter. Next to being absorbed, photons may be scattered by interaction with matter (Brillouin scattering, coherent backscattering, Compton scattering, Delbrück scattering, Rayleigh scattering, Raman scattering).  --Lambiam 12:16, 30 October 2023 (UTC)