Wikipedia:Reference desk/Archives/Science/2023 June 5

= June 5 =

Do vaccines have any efficacy once someone is in the throes of a viral sickness?
I am no doctor or scientist, but I thought I had a pretty strong understanding of how vaccines work.

(Spoiler alert for a popular show).

I was just watching the series Utopia (the American 2020 remake; not the 2013 British version). At a plot point, they have a character who is supposedly a virologist (no less), who has come prepared with a vaccine for a specific flu. Another character is in the throes of the virus, and this virologist is begged by the father of the sick character to save his daughter by testing the vaccine on her (as if a vaccine is some type of a magic bullet antiviral). My understanding is that this would have no effect whatsoever; that this is obvious and basic if you know how vaccines work; that this is the heart-rending misunderstanding I read about of some people in hospitals during the pandemic— dying from the infection who had refused the vaccine, who now finally wanted it, and had to be told “it’s too late”; “that’s not how vaccines work”, and yet I am utterly baffled. How could they have a show that has virology and viruses and vaccines at its very heart and not understand this basic stuff and perpetuate this misunderstanding—especially now. But then I thought am I wrong in some way about this? 108.41.147.194 (talk) 04:54, 5 June 2023 (UTC)


 * Haven't seen it, but TV can be pretty bad when it comes to medical stuff and plain not doing the research, or not caring about errors as long as it makes good drama. How many times have you seen a medical drama (who you'd think would likely have doctors working as technical consultants) where the patient's heart stops and the doctor is like "defibrillator now!", or a pneumothorax is treated by stabbing the patient, ice-pick style in the chest with a syringe, followed by a loud hiss of air and then the person waking up and being pretty much fine straight after? I used to watch House and I remember a website back in the day that was dedicated to pointing out all the medical inaccuracies/straight up nonsense in the show. There was a lot. Iloveparrots (talk) 06:05, 5 June 2023 (UTC)
 * You are not wrong. A vaccine works by coaxing the immune system to produce antibodies against a potential pathogen, so it can be nipped in the bud on infection by the primed immune system. Administering it to an infected patient whose immune system is already in a total state of war makes no sense; it is like installing a fire alarm system in a building that is on fire. --Lambiam 09:57, 5 June 2023 (UTC)
 * Injecting a vaccine is not always too late even after someone has caught an infection. The most well-known example for this is the rabies vaccine.  Although the vaccine is routinely given to pet dogs, it is not deployed at large scale to humans, probably because it has too severe side effects.  However, when a human gets bitten by a wild animal or an unvaccinated dog (in areas where rabies is endemic), it is suspected that they may have got rabies, so doctors give them the rabies vaccine as a precaution.  The vaccine still works even when the wild variant of the virus is in the human.   – b_jonas 14:33, 5 June 2023 (UTC)
 * Rabies is an exception because the infection develops very slowly as the virus propagates along the nerves into the brain. The infection is also almost invisible to the immune system. By the way the modern rabies vaccines does not have any series side effects. They are not given at large scale to humans because it is generally considered unnecessary. Ruslik_ Zero 20:35, 5 June 2023 (UTC)
 * And, rather famously, once the rabies symptoms begin (i.e. the patient is visibly sick), it's essentially a lost cause and the vaccine is useless. Matt Deres (talk) 16:51, 6 June 2023 (UTC)
 * Two encouraging stories: . 2A00:23C3:FB81:A501:24FC:4B46:8DAC:E612 (talk) 12:53, 10 June 2023 (UTC)
 * Thank you for those links. A fascinating, thought provoking and hopeful report. Martin of Sheffield (talk) 15:59, 10 June 2023 (UTC)
 * Another case (though relating to a bacterium rather than a virus) of potentially effective post-exposure vaccination is the tetanus vaccine. It provokes immunity to the toxin rather than to the bacterium itself, and it takes some time for the infection to produce the toxin.  That said, I think I recall some study saying that the effect of the vaccine may not really be prompt enough, and that people with serious potential tetanus infection should actually get immunoglobins rather than just the vaccine.  Maybe someone can dig that up, or maybe it's even in the link I gave. --Trovatore (talk) 04:17, 12 June 2023 (UTC)
 * Ah, here it is. I should emphasize that even this is relating to the tetanus vaccine booster in previously vaccinated individuals.  I expect the unvaccinated will pretty much always need immunoglobins rather than the vaccine. --Trovatore (talk) 04:52, 12 June 2023 (UTC)

Any symbol for heights below sea level?
The article Height above mean sea level mentions several variants for heights above sea, like AMSL, MAMSL, MSL, MASL for '(meters) (above) ( medium mean) sea level.' The existing variety suggests none of them is commonly accepted. Anyway, it clearly documents the fact some commonly understood acronyms exist.

On the other hand, however, the term Below sea level redirects to List of places on land with elevations below sea level, which does not use any symbol for the notion and just gives negative heights everywhere. The article on the Dead Sea uses a negative number for 'Surface elevation' in the infobox and positive numbers with a plain text explanation 'below sea level' troughout the text. The only exception is the 'Max. depth' in the infobox, where BSL is used to distinguish the depth relative to the whole-world's sea level from the depth within the Dead Sea itself.

There is a BSL dab page in Wikipedia, but this doesn't mention 'below sea level' at all.

So, here my question comes: is there any abbreviation or other symbol used in English written texts to denote heights in depresions? --CiaPan (talk) 09:32, 5 June 2023 (UTC)
 * See Sea_level last paragraph: "In the rare case that a location is below sea level, the elevation AMSL is negative", so probably not. Martin of Sheffield (talk) 09:43, 5 June 2023 (UTC)
 * The abbreviation "BMSL" is used in our article on the Sotra Bridge. There are sporadic other uses of this abbreviation. --Lambiam 10:07, 5 June 2023 (UTC)
 * There's ATD which stands for Above Tunnel Datum. This saves tunnellers below sea level having to calculate using negative heights. Shantavira|feed me 18:23, 5 June 2023 (UTC)
 * Of course if you really want to be confused, see a nautical chart. Depth are positive numbers below chart datum (usually lowest astronomical tide) and drying heights are negative numbers above! Martin of Sheffield (talk) 18:49, 5 June 2023 (UTC)
 * To make things even more complicated, while drying heights are negative (usually indicated by an underscore rather than a minus) and measured relative to Chart Datum, altitudes of hills etc are shows as positive heights relative to high tide. Iapetus (talk) 09:24, 7 June 2023 (UTC)
 * Very true. In a channel you may well have a depth below LAT printed next to a bridge clearance above HAT.  A further wind-up for the metric purist: heights and depths are in metres, distances in nautical miles and cables. :-) Martin of Sheffield (talk) 10:16, 7 June 2023 (UTC)

Cosmological Redshift
True or false - this breaks the Law of the Conservation of Energy? A photon losing freq is a photon losing energy so where does it go?

What does Relativity (no aether) have to say about this?

An aether explains this easily - it is the aether doing the expanding. Byron Forbes (talk) 12:12, 5 June 2023 (UTC)


 * The photons are being measured in a different reference frame to where they started, you might as well ask why a a car going the same way on the road has lost so much energy and one going in the opposite direction has gained so much. If two cars have a crash it'll show they really have lost or gained energy relative to each other. NadVolum (talk) 13:12, 5 June 2023 (UTC)
 * Are you saying that if I stay in 1 single reference frame that a photon will not lose freq?
 * AFAIK, for any given FOR the photon's speed will remain the same and its freq will decrease! Byron Forbes (talk) 14:46, 5 June 2023 (UTC)
 * When a photon impacts an idealized Black body the photon energy is absorbed as heat and momentum is imparted to the body. If the black body is the energy sensor of an Optical spectrometer, the spectrometer has been calibrated to convert the received energy to a spectral frequency. If the photon source and spectrometer are in relative motion apart, the received energy is lessened, perceived as a Red shift. A different spectrometer moving differently might detect increased, unchanged or lessened energy with different consequent colour shifts that essentially occur only in the act of observation and not in the earlier emission of the photon. Astronomers may apply a K correction to recover the source frequency (colour) of a red-shifted astronomical object. While the energy perceived in the detecting of a photon can be changed by relative motion of source and viewer, there is always conservation of energy and momentum as a whole in the detection process. The Pound–Rebka experiment was a test of general relativity's predictions about photons' energy change when rising or descending through a gravitational potential, see Gravitational redshift. Aether theories have fallen out of use in modern physics. Philvoids (talk) 14:52, 5 June 2023 (UTC)
 * I must assume that went over my head because I fail to see how you answered the question. Do you have an answer for what a cosmologically red-shifted photon loses energy to? Byron Forbes (talk) 15:02, 5 June 2023 (UTC)
 * It doesn't lose the energy to anything. NadVolum's answer above is correct, and applies to cosmological, Doppler and gravitational redshifts: They all come about because the observer or measuring device is in a different frame of reference than the emitter; they are distinguished by which reference frames are involved. This is rather more abstract than the mechanistic view of a photon "losing energy" through some process; but that is what the theory of relativity is about. It is easiest to visualise this with the Doppler effect, where emitter and observer move at different speeds. Energy is "relative" in the way that velocity is: what velocity you measure for a person sitting in a car depends on whether you're standing at the side of a road or whether you're sitting in the car next to them. Similarly for cosmological redshift: the energy you measure for a given photon (say an Hα photon from a star-forming region, for example's sake) depends on whether you're in the same galaxy as this star-forming region or whether you're in a galaxy a billion lightyears away (and further along in cosmic history). Conservation of energy does not enter here because it's not the right setting to apply it (CoE is always applied in the same frame of reference and locally, i.e. at some point). Having said that, it is possible to write down conservation of energy in the form of the first law of thermodynamics for some volume of the universe containing a certain number of photons from the cosmic background radiation: the decrease of the internal energy in this volume (due to cosmological redshift) is then balance through pV work connected to the expansion of that volume. This approach is not a correct relativistic approach but it does lead to the same result, the Friedmann equation for the expanding universe. --Wrongfilter (talk) 15:59, 5 June 2023 (UTC)
 * If you rename pound-rebka experiment "Apparent Weight of the photon" by "real weight of the photon", so you don't have blue/red-shift but classical gravity effect in their experiment and then cosmological red-shift is entirely doppler effect, then you don't speak energy but power of the photon flow energy that stay the same from the emission to the reception . Malypaet (talk) 16:57, 5 June 2023 (UTC)
 * What? --Wrongfilter (talk) 16:59, 5 June 2023 (UTC)
 * To put it simply, "energy" is relative to the reference frame in which it is being measured. If someone throws a 1 kg ball at you at 10 m/s, you measure it to have a kinetic energy of $$\frac{1}{2}mv^2 = \frac{1}{2}(1 kg)(10 m/s)^2 = 0.05 J$$. If you are in a train moving away from the thrower at 2 m/s, you will measure the energy of the same ball as $$\frac{1}{2}(1 kg)(8 m/s)^2 = 0.032 J$$. Energy is conserved in one reference frame, but it's not necessarily the same in different reference frames. CodeTalker (talk) 19:17, 5 June 2023 (UTC)
 * But you are all missing the point - this takes place for any given reference frame.
 * In relativity, c is always c, so in any given reference frame the only thing that changes for a photon is its frequency when we are talking CRS.
 * It seems you all need to sit back and properly understand CRS and what it actually says! You are all confusing it with normal Doppler and in relativity that's not what it is.
 * In fact, even normal Doppler doesn't work in Relativity but that's a whole other conversation. Byron Forbes (talk) 01:17, 6 June 2023 (UTC)
 * We are not confusing cosmological and Doppler redshifts. As I wrote above: "they are distinguished by which reference frames are involved." We are using the Doppler situation as an analogy because it's closest to everyday experience and therefore easiest to describe. In a curved spacetime, as used to describe the expanding universe, each point has its own reference frame (the local tangent space or Lorentz frame) and transformation between any two points (e.g. emitter and observer of a light signal) leads to a redshift. --Wrongfilter (talk) 06:09, 6 June 2023 (UTC)
 * This is the greatest non explanation of all time.
 * Again, the fact is, put yourself in any FOR you like and look at this photon and it loses energy IN THAT FOR! And this is exactly the distinction between CRS and normal Doppler situations.
 * Again, this is a blatant, 100% violation of CoE! Byron Forbes (talk) 09:14, 6 June 2023 (UTC)
 * Please explain what you mean by a frame of reference. In the way it's understood in general relativity there is no global frame of reference in a curved spacetime, only local ones. It then makes no sense to say "it loses energy in that FOR". But I have the impression that you've made up your mind already and that your original post is not a question but a mission. --Wrongfilter (talk) 09:49, 6 June 2023 (UTC)
 * A photon only has a particular energy relative to a given frame of reference. If a photon is sent from A to B and B is moving away relative to A then each wave will take longer to reach B than it took to leave A so its frequency will be lower. The observed frequency measures the energy in the frame of reference it is measured in. So the energy of the photon is lower according to B than to A. Conservation of energy applies to the whole system, not to the individual bits measured in difference reference frames and added up. NadVolum (talk) 09:56, 6 June 2023 (UTC)
 * Well ok then, so if CoE applies to the "whole system", then where did the energy go?
 * This whole thing is just laughable - I have one person who cant even work out what a FOR is and another who talks as though the photon in question isn't the "whole system".
 * I am impressed by you dedication to your religion! :) Byron Forbes (talk) 22:03, 6 June 2023 (UTC)
 * THere is no real difference between the doppler and cosmological red shifts. The thing that is strange in cosmology is that matter moves faster than the speed of light compared to other matter if it is far enough away from it so there is a horizon beyond which we can't see. This does mean things become difficult for checking conservation of energy and a lot of other things as 'the system' becomes rather ill defined, but there is no problem for straightforward things like light coming from distant galaxies. NadVolum (talk) 10:26, 6 June 2023 (UTC)
 * It is well worth to make a difference between Doppler and cosmological redshifts. The Doppler effect is a local effect that arises due to emitter and observer moving at relative velocity at the same point (or nearly so) in spacetime; this velocity is limited by the speed of light. The cosmological redshift arises because observer and emitter are at different cosmic time, and the redshift only depends on the scale factor ("size") of the universe at these two times. Strictly speaking there is no velocity involved at all (hence no speed limit – it's actually not strange at all); one can speak about an increase in distance, but that distance would have to be measured at a particular time, so that's very different from the light emission/observation scenario that we are discussing here. There are a lot of good cosmology books that discuss these issues, although I'm always struggling to point to one that has everything in a nice manner. Peacock's "Cosmological Physics" has a section that discusses misconceptions about the expansion of the universe and cosmological redshift. --Wrongfilter (talk) 11:06, 6 June 2023 (UTC)
 * Look, I'm no supporter of Relativity, but there is no need to have distant planets travelling at c and beyond resulting in them being non visible - the fact is, distant light is red shifted to such a degree that it's undetectable! Byron Forbes (talk) 22:08, 6 June 2023 (UTC)
 * I apologise to the OP that my answer disappointed his inquisitorial probing "True or false...?" but not for the 8 Wikipedia articles that I referenced, each of which is pertinent. His abbreviation "CRS photon" for "cosmologically red-shifted photon" is unusual and it must not obscure these clarifications:


 * A photon is a quantum of electromagnetic energy. It has no rest mass. In a vacuum it travels at constant velocity. Its frequency (and colour if within the visible range of frequencies) and energy, related by Planck's constant, are established when the photon is emitted and they never change.
 * A view of photons as mass particles that shift in colour and energy the further they travel is an incorrect view. There are no intrinsically red-shifted or blue-shifted photons en route through space. Whether those photons now en route will be perceived with any frequency shift depends entirely on who happens to detect them, noting that star gazing is no longer exclusive to Earth bound telescope users.
 * No aether theory "explains this easily" and these days only pandering to outdated ballistic notions about light particles motivates clinging to such theory. Quite brutally speaking, Hermann Weyl wrote in 1922 summarizing the results of Michelson, Rayleigh and others that the aether had "betaken itself to the land of the shades in a final effort to elude the inquisitive search of the physicist". Philvoids (talk) 16:51, 6 June 2023 (UTC)
 * This is well so nice in the original German, "Es wäre also die Aufgabe der Äthermechanik, nicht nur die Maxwellschen Gesetze zu erklären, sondern auch diese merkwürdige Wirkung auf die Materie, die so erfolgt, als hätte der Äther sich ein für allemal vorgenommen: Ihr verflixten Physiker, mich sollt ihr nicht kriegen!" In my translation: "So it would be the task of aether mechanics to explain not only Maxwell's laws, but also this strange effect on matter, which occurs as if the aether had decided once and for all: You cursed physicists, you shall not catch me!". Nothing in the original corresponds to the translator's "land of the shades", and "verflixt", a minced form of "verflucht", is quite a bit stronger than "inquisitive".  --Lambiam 18:03, 6 June 2023 (UTC)
 * Lambiam's translation looks more authentic than the "...land of the shades.." version that was inserted by XOR'easter. Philvoids (talk) 19:37, 6 June 2023 (UTC)
 * That insertion is a verbatim rendering of a sentence in the English translation of the book, which came out in 1922. The translator, Australian physicist Henry Brose, then doing a D. Phil. in Oxford, not only cut Weyl's sentence in two but apparently flinched at translating Weyl's powerful prose more literally. --Lambiam 12:07, 7 June 2023 (UTC)


 * So name me one thing that utterly dismisses aether for you? Byron Forbes (talk) 22:29, 6 June 2023 (UTC)
 * Hate to disappoint you, but an aether theory does explain CRS with ease.
 * The aether is expanding, thus the photon speeds up and gains KE. It simultaneously loses freq in a manner that conserves energy as will be observed in any given FOR!
 * This is exactly the same as red shifting with sound waves - it works via the energy being able to travel at different speeds to different observers!
 * Relativity is not merely broken for CRS, it is broken with all applications of Doppler. If you want clarification, just ask me. Byron Forbes (talk) 22:15, 6 June 2023 (UTC)
 * No, thank you. --Lambiam 13:02, 7 June 2023 (UTC)
 * It would seem the conclusion to this conversation is that there is indeed no such thing as an inertial FOR anywhere in the universe, because not only can we never eliminate gravity, but every point in the universe is accelerating away from all others as well!
 * What a strange universe we live in! :)
 * And there was I, just the other day, thinking space doesn't bend, stretch or contract for anyone! Byron Forbes (talk) 16:36, 7 June 2023 (UTC)
 * No aether theory "explains this easily" and these days only pandering to outdated ballistic notions about light particles motivates clinging to such theory.
 * I would just like to clarify here that when I mentioned particles, I was not talking about photons, I was talking about the particles of the aether that a photon (packet of energy) travels through. Same as what air particles are to a phonon. Byron Forbes (talk) 16:41, 7 June 2023 (UTC)

What does sunlight/UV do to fruit juices?
I will take a generic answer, and a specific answer. For specific answer, consider this:

Sunlight, for UV-A ad UV-B range. That's 400-315 nm and 315-280 nm. That is strong enough to break the C-C bond, which requires at the most <343 nm (UV-A range), as well as C-O. But not enough to break C=C bonds. Vitamin C has C-C as well as C-O bonds. But if sunlight did break such a bond, aren't the bonds able to quickly reform back? It's not like sunlight can substitute something... Not likely any replacement reactions...? Thanks. 170.76.231.162 (talk) 20:58, 5 June 2023 (UTC)


 * Not sure if this counts but I put your question into ChatGPT and I found the answer was decent. PalauanLibertarian🗣️ 23:43, 5 June 2023 (UTC)

Answer

 * When fruit juices are exposed to sunlight, particularly to ultraviolet (UV) radiation in the UV-A and UV-B range, several photochemical reactions can occur. These reactions can lead to various changes in the composition and properties of the juice. Here's a breakdown of the potential effects of sunlight/UV on fruit juices:
 * 1. Vitamin C (ascorbic acid): UV radiation can cause the degradation of vitamin C in fruit juices. Vitamin C contains both C-C and C-O bonds, and UV light can break these bonds, leading to the decomposition of vitamin C. The extent of degradation depends on factors such as the concentration of vitamin C in the juice, the intensity and duration of UV exposure, and the presence of other protective compounds or antioxidants in the juice.
 * 2. Flavor and color changes: Sunlight can also cause changes in the flavor and color of fruit juices. UV radiation can induce the breakdown of various organic compounds present in the juice, leading to the formation of new compounds and the degradation of existing ones. These reactions can alter the taste, aroma, and color of the juice, resulting in a decrease in quality.
 * 3. Formation of off-flavors: In some cases, UV radiation can trigger the formation of off-flavors in fruit juices. This can occur through reactions between UV-generated free radicals and the components of the juice. These off-flavors may be described as "sunlight-induced" or "sunstruck" flavors and are generally considered undesirable.
 * 4. Nutrient loss: Besides vitamin C, other nutrients present in fruit juices, such as certain vitamins, antioxidants, and phytochemicals, can be affected by UV radiation. The extent of nutrient loss depends on the specific compounds and their susceptibility to UV-induced degradation.
 * Regarding your question about the reformation of broken bonds, it is true that chemical bonds can reform after being broken. However, the reformation of bonds typically requires specific conditions and catalysts. Sunlight alone is not sufficient to facilitate the immediate reformation of bonds that have been broken by UV radiation. The restoration of broken bonds in fruit juices would require additional factors and time, which may not occur under normal storage conditions.
 * It's worth noting that the packaging of fruit juices can provide some protection against UV radiation. Many juice containers are designed to block or reduce UV light transmission, which helps to minimize the potential adverse effects of sunlight exposure. PalauanLibertarian🗣️ 23:43, 5 June 2023 (UTC)

Perplexity.AI

 * FWIW, an answer from Perplexity.AI/| copilot has some more details regarding the chemistry involved (with references):


 * --136.54.99.98 (talk) 03:51, 6 June 2023 (UTC)

Chemical compounds that can fluoresce, but not phosphoresce, and phosphoresce but not fluoresce?
What are examples of those? As well as compounds that can do both, is there a pattern? For inorganic, as well as simple organics. I know for organics, for /most/ cases you can find a molecule that will only fluoresce, and another that only phosphoresce, then connect them together via an alkyl chain, then now that new compound can do both, so for organic examples am looking at simpler 1s. Also, I'm making this question for room-temperature ranges. I'm aware that the colder the temperature, the probability for phosphorescence increases. Thanks. 170.76.231.162 (talk) 21:11, 5 June 2023 (UTC).
 * Our fluorescence and phosphorescence articles talk about the chemical details that lead to each of these two phenomena. As a starting-point, a main difference is the timescale of the re-emission, and a main cause of that difference is whether an intersystem crossing occurs from the excited state. DMacks (talk) 21:21, 5 June 2023 (UTC)