Wikipedia:Reference desk/Archives/Science/2020 June 2

= June 2 =

Partners
Which articles deal with how humans select romantic partners? Benjamin (talk) 01:12, 2 June 2020 (UTC)
 * If you google "wikipedia mate selection", several articles come up, and you could review them. ←Baseball Bugs What's up, Doc? carrots→ 01:22, 2 June 2020 (UTC)


 * Which one in particular? To be clear, I'm asking romantic partners, not sexual reproduction or evolution. Benjamin (talk) 02:46, 2 June 2020 (UTC)
 * Reference desk/Humanities might be better equipped to answer. --OuroborosCobra (talk) 02:55, 2 June 2020 (UTC)


 * (Closed & moved to prevent duplicate discussions) 107.15.157.44 (talk) 05:13, 2 June 2020 (UTC)

List of all 21 Indian cities to run out of groundwater
There are many reports that 21 Indian cities will run out of groundwater in future. But everywhere I could read only Delhi, Mumbai, Chennai, Bengaluru, Hyderabad. I couldn't find the full list of 21 cities. https://www.aljazeera.com/news/2019/06/india-running-water-fast-190620085139572.html — Preceding unsigned comment added by സൂര്യചന്ദ്രൻ ഗ്രഹം (talk • contribs) 04:19, 2 June 2020 (UTC)
 * That article and the NDTV one it cites are dated 20 June 2019, and both cite a report by NITI Aayog. I cannot find a reoport on their website on this topic from that approximate time, and the two "Composite Water Management Index" reports I found from any timeframe do not appear to list 21 cities. DMacks (talk) 04:36, 2 June 2020 (UTC)
 * Here is the report:  (I haven't read it) -- As cited here: —107.15.157.44 (talk) 09:56, 2 June 2020 (UTC)
 * Question: are there any places anywhere in the world that actually have run out of groundwater as opposed to predictions that they are going to run out of groundwater? I don't mean "the old well ran dry but a new, deeper well is supplying groundwater", nor do I mean places that never had any groundwater. I searched and found plenty of places that are depleting their groundwater supplies faster than nature is replenishing them, but I could not find any examples of places that actually ran out of groundwater. I am sure that such places exist. --Guy Macon (talk) 15:25, 2 June 2020 (UTC)
 * It may depend on your definition of "run out", but the Australian town of Stanthorpe, Queensland is now fully dependent on water being carted in from outside because it has "run out" of its own. -- Jack of Oz   [pleasantries]  23:25, 2 June 2020 (UTC)
 * I searched for reliable sources (as soon as I saw that Daily Mail Link I refused to look at it -- to high a chance that they got most of the story right but added a few lies to make it better clickbait.)
 * From what I can gather from the other side of the globe, Stanthorpe ran out of water but not groundwater. They were getting water from Storm King Dam, and now they are having to cart water in trucks from Connolly Dam and dump it in Storm King Dam just to keep enough in the bottom so they send it to the town using existing pipes. And they are a couple of years away from emptying Connolly Dam.
 * The same source says "When the above-ground dams run out of water, the council will have to switch to using bores, which are already under pressure from agricultural and commercial use" (I am assuming the a Bore is what we in California call a well).
 * Another Australian source says that "Currently the shire is in discussions with the Queensland Government about getting access to the Dalrymple and Cunningham alluvium, underground water sources near Allora north of Stanthorpe." I couldn't find any sources that discuss how much groundwater is in those groundwater sources.
 * The Guardian has a related story which sort of implies not much water available underground, but they didn't give any actual numbers.
 * I just hope that I won't do a search a few years from now and see a bunch of "we told you we were going to run out of groundwater and now we have!" stories from around the globe.
 * Question: when talks about "standpipes" and " Avdata key holders" what are they talking about? Is that a Standpipe (street)? --Guy Macon (talk) 01:29, 3 June 2020 (UTC)
 * Probably holders of one of these [//avdata.com.au/controlling-access/], maybe one specific for the area, not sure [//avdata.com.au/water-and-waste]. Nil Einne (talk) 09:14, 3 June 2020 (UTC)

E = hf
Does $$E = hf$$ apply to all waves, including longitudinal waves like sound, or is it just used to describe electromagnetic waves? -- Puzzledvegetable Is it teatime already?  20:17, 2 June 2020 (UTC) + edit-- Puzzledvegetable  Is it teatime already?  22:58, 2 June 2020 (UTC)
 * You probably meant electromagnetic waves. Ruslik_ Zero 20:26, 2 June 2020 (UTC)
 * Yes, yes I did. Thank you. -- Puzzledvegetable Is it teatime already?  22:58, 2 June 2020 (UTC)
 * From Photon energy: Photon energy is the energy carried by a single photon... the photon energy equation can be simplified to $$E = hf$$. Sound waves are not made out of photons. --Guy Macon (talk) 21:18, 2 June 2020 (UTC)
 * No, but in some sense they are "made out of" phonons, and from that article it appears to me that the energy associated with a phonon is indeed hf. --Trovatore (talk) 23:09, 2 June 2020 (UTC)
 * Not really. Only in solids and a few oddball liquids do phonons even make sense; the phenomenon is nonseniscal in gaseous phases with free movement of particles, such that the movement of a mechanical vibration can be modeled perfectly in a non-quantum way.  Phonons really only make sense when there are highly-constrained single-frequency vibrations happening accross chemical bonds, which being composed of electrons, require some quantum explanation.  For sound waves moving through air, there's no quantumness to be had.  It's entirely a classical phenomenon.  -- Jayron 32 05:35, 3 June 2020 (UTC)
 * Hmm. I am less than entirely persuaded that phonons don't make sense in gases.  They might not usually be the most useful description, but that's a separate thing.  But I concede it's not really my field.
 * Just the same, even if you're correct that they don't make sense in gases, the solid-state version is still an example of E=hf being meaningful outside the domain of electromagnetic waves. --Trovatore (talk) 17:50, 5 June 2020 (UTC)


 * No, it really only applies to quantum phenomenon. E=hf applies to electromagnetic waves because there is no medium in any real sense, what is vibrating is simply the electromagnetic field, which is just a series of numbers (well, messy numbers, specifically a 4x4 matrix known as the Electromagnetic tensor, but it's still just a complicated number) assigned to points in space, and not a material in any meaningful sense.  The energy carried by that vibration in the field is just a function of the frequency of that vibration.  It's a simple calculation because it is functionally just a single kind of energy, kinetic energy of the field itself.  The energy carried by a sound wave is a fantastically more complicated matter, as it involves the actual motion of actual matter, and matter is WAY messier than a field.  Consider that the specific matter itself matters, including which atoms there are, and how they are organized and how they interact with each other and since we now have actual interactions between pieces of matter, now we have to introduce a new term, potential energy and wow does it become a mess.  Sound energy has an equation for you to use, but you have a LOT more variables to plug in, because matter is so much more complex than a field.  EM fields, by comparison, even with their messy tensor mathematics, are conceptually much easier to reduce to a simple equation, E=hf.  The phonon thing described above is a real phenomenon, but it really only manifests itself in some very specific situations; it's an important tool in all sorts of first-principles modeling of important phenomena, but basic sound like "I yell and you hear me" isn't one of them.  -- Jayron 32 05:51, 3 June 2020 (UTC)


 * The equation E = h f applies to all phenomena that exhibit oscillations at a fixed frequency. It is more precisely written as E = (n+1/2) h f, n is the number of quanta, or it refers to the nth excited state of the system and the 1/2 h f for n = 0 is the ground state energy, also called the vacuum energy. The energy contained in a single mode of sound waves, electric circuits like LC circuits are all given by this equation. For example in any electric circuit at room temperature is subject to Johnson–Nyquist noise which is due to the thermal motion of electrons in the circuit. Suppose that you cool the electric circuit to low temperatures to eliminate the noise. The E = n h f law will then become visible in the form of the Planck distribution of the frequency components of the noise. High frequency components of the noise are then cut off. You can then ask of the noise will become zero at absolute zero. The answer is no, because the formula is not actually E = n h f, but E = (n + 1/2) h f and at temperatures so low that the electronic degrees of freedom are all in the ground state, you still have noise due to quantum fluctuations that are present in the ground state. Count Iblis (talk) 13:34, 4 June 2020 (UTC)
 * That is true, but it is only strictly true for a portion of the energy of the wave. The problem with mechanical waves, like sound, is that the energy of those waves is dependent on all sorts of messy interactions throughout the medium the wave is traveling in.  The reason why we most associate that equation with things like photons is that light has no medium, so its energy is completely described by that equation.  A "phonon" in this context, as described above, is basically a way to conceive of the E = hf portion of a mechanical wave energy in crystalline media.  It isn't very useful when trying to calculate the total energy of sound, however.  -- Jayron 32 15:34, 4 June 2020 (UTC)