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November 27

Mycoplasma vs mushrooms

Is there some connection between mycoplasma (a class of bacteria) and mycology (the study of mushrooms)? Or is the name resemblance coincidental, or what? The mycoplasma article didn't say anything about this. Thanks. 2601:644:8501:AAF0:0:0:0:6375 (talk) 04:36, 27 November 2023 (UTC)[reply]

You can look up Wiktionary wikt:mycoplasma says the word means "fungus shaped". wikt:mycology can be checked out too. Graeme Bartlett (talk) 07:04, 27 November 2023 (UTC)[reply]

Thanks! I didn't think of looking there. 2601:644:8501:AAF0:0:0:0:6375 (talk) 23:13, 27 November 2023 (UTC)[reply]

Ozone-like smell after carbon dioxide buildup

I used to cover myself entirely with a blanket (up to the head) while sleeping and noticed that after unbearable CO₂ buildup there and pulling the blanket down to breathe openly I sense ozone-like smell for a few seconds which rapidly disappears. Is it because of ground-level ozone, oxygen itself or something else? 212.180.235.46 (talk) 13:39, 27 November 2023 (UTC)[reply]

what on earth does ozone smell like im curious mushi^{( ? )} 14:52, 27 November 2023 (UTC)[reply]

See ozone, second paragraph. Or stick your nose near a photocopier. Bazza (talk) 14:55, 27 November 2023 (UTC)[reply]

One can readily generate small amounts of ozone from static discharges (see Static_electricity#Ozone_cracking) caused by blankets, especially nylon ones in a dry atmosphere. Mike Turnbull (talk) 17:13, 27 November 2023 (UTC)[reply]

It maybe just due to bad breath, when you breathe deeply, perhaps you get to smell it. Graeme Bartlett (talk) 10:24, 28 November 2023 (UTC)[reply]

I do not have a reference, but I have assumed it is temperature change. I get the same ozone-smell sensation when I walk out of a warm house into the cold outside, just for a few seconds. The change from breathing warm air to cold air appears to be the trigger more than anything else... at least for me. 12.116.29.106 (talk) 13:15, 28 November 2023 (UTC)[reply]

Thanks. Indeed, it appears to happen to me in cold weather rather than in warm weather. 212.180.235.46 (talk) 13:22, 28 November 2023 (UTC)[reply]

Interaction picture transformable into Heisenberg picture

Since matrices can basically be treated as a type of vector and vice versa, could the Heisenberg picture transformed into the Dirac Picture? 2A02:8071:60A0:92E0:9D32:9360:2436:9F78 (talk) 16:41, 27 November 2023 (UTC)[reply]

The Heisenberg picture can be transformed into the Schrödinger picture, and (in a non-relativistic setting) the latter can be transformed into the Dirac picture, so by taking the product of the two operators you should be able to skip the middle man. --Lambiam 09:44, 28 November 2023 (UTC)[reply]

November 28

Airplanes with 2 pilots.

Afaik airlines for same-country typically have 2 pilots, with none sitting in "the center." How do they split the work? Like 80/20, or 50/50? Is 1 more of an assistant pilot? I suspect now, the airline company can also control the plane, on some auto-pilot, like if there was a solo pilot who went to the bathroom, the airline company can control the plane via some remote auto-pilot? Thanks. 131.193.14.154 (talk) 20:46, 28 November 2023 (UTC).[reply]

From what I've learned by watching Mayday and general reading on the subject, it's typically 50/50 between the two pilots. The "pilot flying" is responsible for operating the controls and the "pilot not flying" is responsible for radio communications, consulting written reference material, and so on; and they each do each job about half the time, with the captain in overall command. As to the autopilot and related devices, they can do things like keep the plane flying straight and level, turn to a specific heading, climb to a specific altitude, and so on. But airliners cannot be controlled remotely. --142.112.220.31 (talk) 23:14, 28 November 2023 (UTC)[reply]

(edit conflict) One of the two pilots is the "pilot flying", which means they operate the flight controls of the aircraft (possibly those of the autopilot), while other tasks, such as contact with air traffic control, can be delegated to the second pilot. There is no fixed formula, but one of the pilots is the pilot in command, and they can make the decision who will be the pilot flying, taking all aspects into consideration. For more challenging parts of a flight, the more experienced pilot will often (but not necessarily) be in control. Another factor is that pilots need to reach a certain amount of flying hours to obtain or keep certain flying licenses. --Lambiam 23:20, 28 November 2023 (UTC)[reply]

That last sentence suggests that hours in the air as Pilot Not Flying do not count as 'flying hours' in maintaining currency for licenses, even though there are monitoring and communication responsibilities. Is this correct? And if so, what is the mechanism by which 'hours as PF' are distinguished from 'hours aloft'? -- Verbarson ^talk_edits 13:59, 29 November 2023 (UTC)[reply]

Some unmanned aerial vehicles can be controlled remotely by a human operator, but airline aircraft and other passenger aircraft are never controlled remotely. These aircraft can be flown by an auto-pilot but turning the auto-pilot ON and OFF, and setting the target parameters such as altitude and heading, is normally carried out by the pilot flying. Dolphin (t) 00:01, 29 November 2023 (UTC)[reply]

Company in-flight control would require installing a lot more equipment to get a grasp of the situation. Also, imagine someone hacking into the system and either holding the passengers for ransom or going 9/11. Clarityfiend (talk) 07:47, 29 November 2023 (UTC)[reply]

Remote Control Airlines has to be implemented very carefully to keep things safe and secure, but a limited way for ATC to send instructions to the flight management system (proceed past holding point X of your flight plan, execute standard terminal arrival Y, change altitude to the minimum published for this holding stack, execute instrument approach procedure Z with autoland) could have saved Helios Airways Flight 522. PiusImpavidus (talk) 18:57, 29 November 2023 (UTC)[reply]

There has to be a pilot in the cockpit at all times; if not flying, then at least to monitor the autopilot or take action when something unexpected happens. On flights with a single pilot, the pilot can't go to the bathroom. Flights with only a single pilot are normally short hops in small aircraft that don't even have a bathroom. PiusImpavidus (talk) 19:04, 29 November 2023 (UTC)[reply]

From what the 1st responder said, does not sound like 50/50 work to me. Can both pilots drive the plane from their spots, even though 1 at a time? 170.76.231.162 (talk) 19:08, 29 November 2023 (UTC).[reply]

Sure. It has to be possible for either one to take over without getting up. The 50/50 division is time spent as pilot flying vs. pilot not flying. "You fly from here to Boston and I'll fly coming back", that sort of thing. --142.112.220.31 (talk) 03:06, 30 November 2023 (UTC)[reply]

I recall seeing that for one of the Airbus models, the aircraft could be flown from either seat, but while taxiing the plane could only be controlled from the left seat. Jc3s5h (talk) 20:18, 29 November 2023 (UTC)[reply]

The Airbus flight controls are on side sticks, which can (somewhat unbelievably) be operated independently by both pilots while being mounted in such a way that one pilot cannot see what the other pilot is doing. This played a role in the fate of Air France Flight 447. This document, dated years before the crash, describes a fix that should have prevented the accident, but was apparently insufficient. --Lambiam 21:29, 29 November 2023 (UTC)[reply]

Jc3s5h: In transport category aircraft (large aircraft of the kind that are used by major airlines and freight carriers) it is universal as far as I know that only the pilot in the left seat has a tiller for steering the nosewheel. It isn't just Airbus. Consequently taxying is performed by the pilot in the left seat, but in flight the aircraft can be flown from either seat. When the pilot in the right seat is performing the take-off, the other pilot will use the nosewheel tiller to keep the aircraft on the center-line until the aircraft reaches about 60 knots when the rudder pedals become adequate for directional control. Dolphin (t) 12:26, 1 December 2023 (UTC)[reply]

See Pilot in command. --Preceding unsigned comment 01:56, 5 December 2023 (UTC)[reply]

November 30

Little experiment to determine whether it's worth having blinds/curtains open in the day in winter

I'm interested in whether the heat from the sun on cold, overcast days in northern England is worth having the blinds open for during the winter. I reckon it is but my mother reckons it isn't. My plan to determine this experimentally is to use an Arduino or similar to record the temperature on the windowsill every five minutes and store it on an SD card. I thought it could also be interesting to record the light intensity (I would probably measure that every 15-30 seconds and store an average alongside the temperature). My question is what should I use to measure the light intensity? I know that LEDs will generate a small voltage but I also have some photodiodes (if I can find them) or maybe just a CdS light-dependent resistor, assuming that it doesn't max out too easily. Or would something else entirely be much better? The heating would not be on for the duration of the experiment. --05:58, 30 November 2023 (UTC) 92.7.46.126 (talk) 05:58, 30 November 2023 (UTC)[reply]

The outcome will be dependent on the insulation value of the windows. Undoubtably direct sunlight coming in will contribute some heat (this is a commonplace observation I often make at my partially glazed front door), but this may or may not be negated by more heat radiating or conducting out (I will charitably assume no actual draughts). Any light-intensity measuring instruments you use need to be able to capture infrared as well as visible light – specifically photographic instruments may not. {The poster formerly known as 87.81.230.195} 51.194.245.32 (talk) 08:21, 30 November 2023 (UTC)[reply]

I'm pretty sure that on a typical Western European overcast winter day (I'm in the Netherlands), the thermal radiation from the clouds exceeds the sunlight by a comfortable margin, but the outgoing thermal radiation is even more. When sitting at a north facing window, clear days feel a lot colder than overcast days at the same temperature. Of course, good, modern windows are supposed to be fairly reflective in the infrared, but taking infrared into account may be useful. It will vary with the height (and therefore temperature) of the cloud base, but not by a huge amount. Semiconductor-based light sensors have some cut-off; above the wavelength corresponding to the band gap of the semiconductor they can't detect light.

FYI: I would take two rooms, one with the blinds/curtains open, the other closed, and record temperature during the day. Next day with identical weather, swap the roles of the rooms to compensate for differences in window size and room heat capacity. PiusImpavidus (talk) 10:16, 30 November 2023 (UTC)[reply]

To obtain data that can be properly used to draw a conclusion, the experiment should also be repeated on several days, preferably under varying weather conditions (outside temperature, precipitation, wind factor, sky coverage). There should be some effect; see also Greenhouse § Theory of operation. Before you engage in performing this non-trivial experiment, you should decide for which size of the effect you will consider it "worth" having the blinds/curtains open. --Lambiam 12:20, 30 November 2023 (UTC)[reply]

December 1

AC vs refrigerator

Hi. I was told by my HVAC installers that AC units need regular re-fills of refrigerants. I have followed their advice and have refilled my AC units regularly.

But then I realized that my refrigerator has never had a refill of refrigerants. Nor have I ever heard of any non-commercial user refill their refrigerator with new refrigerants. These three sources seem to confirm my understanding [1][2][3].

How come ACs need refills when refrigerators don't?

Are they not both closed systems? (Assuming no system damage or leaks) Liberté2 (talk) 03:46, 1 December 2023 (UTC)[reply]

According to this,[4] refrigerators can leak, and then you have to deal with adding more freon. And according to this,[5] air conditioners shouldn't need new freon unless - guess what - they leak! ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:36, 1 December 2023 (UTC)[reply]

Both are closed systems, but the piping in refrigerators is created in the factory under controlled conditions. The piping for AC is installed on site. Combine that with the larger size and length of piping and it becomes probable that the AC systems will leak more. Rmvandijk (talk) 09:18, 1 December 2023 (UTC)[reply]

Thanks. Is there some sort of comparison between the pipe lengths of the average home refrigerator, vs the pipe lengths of the average home AC unit?

Or maybe the total pipe surface area would be a better comparison? Liberté2 (talk) 09:58, 1 December 2023 (UTC)[reply]

More the number of joints made in the field and the circumference of those joints. Poor joints are the most likely place to get leaks. PiusImpavidus (talk) 11:10, 3 December 2023 (UTC)[reply]

Thank you.Liberté2 (talk) 21:08, 3 December 2023 (UTC)[reply]

Blueshift

Is there any theoretical limit, on the blueshifting effect (whether caused by gravitation or by the Doppler effect)?

i.e. a limit on how much a given object's color can be blueshifted.

I guess there is no such limit, but I want to be sure.

( I ignore the issue, of limits caused - if at all - by the Planck units, which is a controversial issue brought up by another user some days ago. As far as my question is concerned, I'm asking about a process, i.e. about changing the color).

HOTmag (talk) 09:58, 1 December 2023 (UTC)[reply]

The wavelength of a spectral line can be blueshifted to arbitrarily small (but always positive) values — or equivalently, the frequency to arbitrarily large values. This is not different to the redshifting effect(s). However, the usual quantification in terms of

z={\frac {\lambda _{\mathrm {obs} }-\lambda _{\mathrm {emit} }}{\lambda _{\mathrm {emit} }}}

is limited to values

z>-1

, but that's a numerical limit, not a physical one. --Wrongfilter (talk) 10:22, 1 December 2023 (UTC)[reply]

Thanks. So, I understand there's no theoretical limit on the very process of blueshifting, when it's caused by the Doppler effect. I guess the same is true for a blueshifting effect caused by gravitation, right? HOTmag (talk) 10:35, 1 December 2023 (UTC)[reply]

The largest increase in energy should be observed in a photon approaching a massive black hole. While gravitational time dilation will have the effect of decreasing its frequency, the blueshift can only be observed by an observer near the black hole. (Sending the photon back with a mirror makes it travel out of the gravitational well and get redshifted back to normal.) The observer undergoes the same time dilation, so (I think) this effect can be ignored. A limit on the mass of black holes (such as the mass of the observable universe) should then give a limit on the gravitational blueshift. --Lambiam 12:11, 1 December 2023 (UTC)[reply]

Here's a thought on this type of question and the types of answers that we are giving. What is meant by a "theoretical limit"? Purely within a theory, such as special or general relativity, there may not be a limit on, say gravitation or Doppler redshifts. In special relativity, there is no limit on the energy that a particle can have as we can always transform to an inertial system where the particle's energy is Lorentz boosted to any value you'd like. This is the type of answer that I tend to give, because I don't feel particularly at ease in the real world. There are however limits that are tied to the particular realisation of our universe, these are contingent limits. For instance, we do not expect to observe cosmic rays of arbitrarily high energy, even ignoring the GZK limit, because in our universe there are no processes that create particles of arbitrarily high energy and no relative velocities that would Lorentz boost to arbitrarily high energies. Lambiam's limit would be of the second type. Does that make sense? I'm not sure what you mean by "The observer undergoes the same time dilation" — observers always carry their proper time with them, which I would understand as "observers do not undergo time dilation". But maybe you meant something else. --Wrongfilter (talk) 12:46, 1 December 2023 (UTC)[reply]

From the point of view of an outside observer, clocks slow down near a black hole, and the frequency of incoming photons decreases accordingly. However, an outside observer cannot measure this frequency; this has to be an inside job. But the clocks of "inside" observers also slow down – still from the point of view of an outside observer. --Lambiam 07:58, 2 December 2023 (UTC)[reply]

There's no theoretical limit that I know of but there are practical limits as explained in Greisen–Zatsepin–Kuzmin limit and the higher the energy the less far they can go. I guess in the limit the source has to be enormous and the distance they can go gets very small . But that's in astronomical terms ;-) NadVolum (talk) 13:51, 2 December 2023 (UTC)[reply]

Longest earthquake?

I keep thinking of a question of the longest earthquake ever recorded, by duration. Can anyone answer what it is? Thank you. Brennan1234567890 (talk) 13:27, 1 December 2023 (UTC)[reply]

Multiple sources claim that the longest earthquake was 32 years. It was a "slow slip event" that occurred in Sumatra. The event was undetected by the people who lived through it. It ended with an 8.5 magnitude earthquake in 1861. 97.82.165.112 (talk) 15:36, 1 December 2023 (UTC)[reply]

Source:National Geographic (provided by 1861 Sumatra earthquake)-gadfium 19:54, 1 December 2023 (UTC)[reply]

The 2011 Tōhoku earthquake and tsunami is also thought to have been at the end of long slow slip event, in that case it lasted 9 years (see here, which also discusses such events in general). Mikenorton (talk) 17:15, 4 December 2023 (UTC)[reply]

If we ignore slow earthquakes, the longest quake was probably the one with the largest magnitude, the 1960 Valdivia earthquake, which lasted for about 10 minutes or the 2004 Indian Ocean earthquake, which was of similar duration. Mikenorton (talk) 17:15, 4 December 2023 (UTC)[reply]

December 2

Lucky charm in cockpit

Is there any way to bring a talisman into the cockpit of a fighter jet such that it does not become a hazard during a dogfight (keeping in mind that the plane and everything in it may be subjected to a force of up to 12 G's)? (I know that this is against regulations regardless, but this is for a work of fiction and is important for symbolic reasons, so I just want to know how much creative license I can take with this!) 2601:646:8080:FC40:DDBC:A58:C6C:6D97 (talk) 06:07, 2 December 2023 (UTC)[reply]

It depends on the nature of the object. If it is a relatively thin and light medaillon-shaped object that can be worn under the clothing, put in a back pocket or be stitched-on like a button, it shouldn't pose a problem. --Lambiam 07:47, 2 December 2023 (UTC)[reply]

See The adorable story of Scoff, the plushy ducky who flies in an F-15. Alansplodge (talk) 11:58, 2 December 2023 (UTC)[reply]

Also Cockpit photo exposes North Korean pilot using a ridiculous lace-trimmed ejection seat headrest cover (probably made by his wife). Alansplodge (talk) 12:02, 2 December 2023 (UTC)[reply]

And several more examples here: These stuffed animals have way more flight hours than you. Alansplodge (talk) 12:09, 2 December 2023 (UTC)[reply]

Carl Sagan and Stephen Hawking

Nowadays I see many videos about Carl Sagan in social media. In the past, all media used to cover Stephen Hawking as the most celebrated scientist.

I have seen they did not win any science Nobel Prize.

Why do they get more media coverage than Nobel Prize winning scientists and inventors? 2409:40E1:107C:3400:F11D:AA8C:2EA6:A965 (talk) 10:07, 2 December 2023 (UTC)[reply]

Both Sagan and Hawking have done a lot for the popularisation of science, Sagan notably through his TV series Cosmos, Hawking through his book A Brief History of Time. While both were eminent scientists, they lacked that one discovery that might have been deemed worthy of a Nobel prize — this doesn't make them any less important. Nobel prizes are awarded for particular discoveries, which are oftentimes somewhat too technical for the general public to appreciate, and so the laureates tend not to remain so much in the public eye except maybe for a brief moment after the announcement of the prize. --Wrongfilter (talk) 11:02, 2 December 2023 (UTC)[reply]

Didn't you think about the case of A. Einstein, who was both a Nobel laureate and a highly celebrated scientist (and still to some extent today)? When Einstein was alive and resided in US, there were moments when the media reporters couldn't stop from interviewing and asking him about "that theory" (the general relativity) =)). But ironically, A. Einstein was awarded the Nobel prize for his works on photoelectric effect instead of "that theory", which must be in some ways more prominent. 2402:800:63AD:9E45:652D:5A64:8F07:FE00 (talk) 14:14, 2 December 2023 (UTC)[reply]

The ability to educate or transmit knowledge effectively is not necessarily the same skill set as making groundbreaking discoveries. Science popularizers may also sometimes suffer from Tall poppy syndrome. Stephen J Gould discussed this very topic with regards to Sagan in one of his essays, though I don't recall which one. Matt Deres (talk) 00:33, 4 December 2023 (UTC)[reply]

December 3

Locating pre-clovis sites

How are pre-clovis sites located? For many of them traditional archaeological site locating techniques don't seemed to be used, and they are often in bizarre or random locations like the Topper site or Cactus Hill. The articles or other sources never seem to mention how they are located either. — THORNFIELD HALL^(Talk) 01:09, 3 December 2023 (UTC)[reply]

The article on the Topper site says it was a chert quarry. Such sites are easy to spot because people would "rough out" stone tools and cores to make the usable chert lighter and easier to pack out. There are typically tens of thousands of flakes and rejects lying all over the area. Abductive (reasoning) 09:13, 3 December 2023 (UTC)[reply]

The verb to locate has several meanings. It can mean "to place in a particular spot or position", but it can also mean "to find out where something is located". I assume you mean the latter. I am not sure what is bizarre about the locations of the sites you mention. The archaeological excavations for both sites initially identified them solely as Clovis sites. I do not know how the finder of the Topper site, David Topper,^[6] identified the site as a site for archaeological finds, but it was unrelated to any later pre-Clovis theories.^[7] The Cactus Hill site was being commercially mined for sand; an archaeological research group testing the site from time to time found Clovis artifacts, which led to an archaeological excavation.^[8] The hypothesis of a pre-Clovis layer only arose as a result of such excavations. --Lambiam 09:24, 3 December 2023 (UTC)[reply]

Reportedly, David Topper was a local forester who spotted stone tools on the ground there and alerted archaeologist Albert Goodyear.^[9] --Lambiam 10:19, 3 December 2023 (UTC)[reply]

I actually read that book, I must have forgotten that part. That's interesting he found them on the surface. There must have been a lot of erosion and they were younger (and above) the pre-clovis artifacts. — THORNFIELD HALL^(Talk) 10:23, 3 December 2023 (UTC)[reply]

Long story short: no-one says "Today I'm going to look for a new pre-Clovis site, where might one be?" Instead they say "Hey, this site I'm excavating seems to have a pre-Clovis layer!" or "Hey, the test results have come in for the site I excavated last year, and some of it dates to pre-Clovis!" {The poster formerly knoiwn as 87.81.230.195} 51.194.245.32 (talk) 09:38, 3 December 2023 (UTC)[reply]

Or, as happens so often with archaeological or paleontological finds, "someone was doing something ordinary and not at all related to scientific research and found something interesting". --User:Khajidha (talk) (contributions) 22:40, 3 December 2023 (UTC)[reply]

Much moe modern sites can be found by satellite but early sites like that just don't have any big man made structures. Possibly you could train an AI to recognize sites worth investigating - sites near a river that can be defended and have some resource like flints for example. Maybe where there used to be a river but it has wandered so it isn't overlain by too many later sites. So it may be possible to find them mre systematically in the fture. NadVolum (talk) 23:43, 3 December 2023 (UTC)[reply]

Huygens probe

Why was the Huygens (spacecraft) or something like it never repeated? To this day, it is the only landing in the outer solar system. Despite only working for minutes, it provided valuable data about a body that we know very little about. Meanwhile we send countless rovers to Mars? Even though there's still things left to do on Mars (like a sample return mission) tackling Titan again or Europa has steeper engineering challenges, but nonetheless would be a very rewarding feat. — THORNFIELD HALL^(Talk) 10:57, 3 December 2023 (UTC)[reply]

Several reasons, mostly coming down to "sending something to the outer solar system is hard."

Mars missions mostly rely on solar power. Some rovers use RTGs, but even those use a solar-powered communications relay. Near Saturn, an RTG is the only option and those RTGs are hard to get, as the supply of Pu-238 is limited. The Mars Curiosity rover has 4.8 kg of plutonium dioxide, Cassini used 28.3 kg because of its higher power requirements.
Mars rovers can make use of the existing fleet of orbiters as a communication relay. Every NASA or ESA orbiter send to Mars since around 2000 has that capability, including for each other's landers. Communicating directly from the surface to Earth is hard, as the antenna+transmitter would be either too heavy or power-hungry or too low bandwidth for science data (it can sometimes be used for engineering data, to troubleshoot the high bandwidth comms link). No orbiters exist near Saturn, so a Titan lander must go with its own comms relay, adding cost and mass.
Sending something to Saturn requires a bigger launcher or a smaller, less capable payload than sending something to Mars.
The low temperature and the communication difficulties make a Titan mission far riskier than a Mars mission. Managers, politicians and taxpayers don't want to see a complete failure, so risks are often avoided.
The return on investment happens far slower. For a Mars mission, you've several years of preparation, a few months flight time and a few years of science. For Saturn, add several years of flight time.

PiusImpavidus (talk) 12:08, 3 December 2023 (UTC)[reply]

Add to those the fact that you need the appropriate planetary alignments to be able to use gravity assists (Cassini–Huygens used four). Such multiple alignments arise at rare-ish intervals, you can't launch whenever you like, so the entire mission has to be designed, built and launched to an immovable deadline. For missions involving multi-national co-operation (and funding) this is not easy to achieve. {The poster formerly known as 87.81.230.195} 51.194.245.32 (talk) — Preceding undated comment added 16:58, 3 December 2023 (UTC)[reply]

Good point. Specifically, when heading for Saturn, you really want that gravity slingshot at Jupiter. There's a few-year window once every 20 years. PiusImpavidus (talk) 20:22, 3 December 2023 (UTC)[reply]

You haven't even discussed the actual landing yet. Going out there is difficult and expensive but it has been done several times and is sort of routine by now. Going down for a controlled soft landing is another step or two up from that. In the case of Huygens, the thick atmosphere of Titan helped getting the probe down for a soft landing so that it could be expected to survive for a few minutes. However, there was no telling where it would come down, and I'm not sure it is well known even now where it did come down. It should be noted that the main purpose of Huygens was to study the atmosphere during the descent phase, and the landing was a bit of an add-on. To make good scientific use of a lander good knowledge of the landing site is a prerequisite. Europa has only a thin atmosphere, making a soft landing harder than on Titan. Having said that, there is a proposal for a Europa Lander; not sure what the current status of that is. --Wrongfilter (talk) 21:04, 3 December 2023 (UTC)[reply]

While covering neither, but also involving a moon of Saturn there's also the Enceladus Orbilander proposal. The details in our article cover one of the issues mentioned by others above "The mission, with an estimated cost of $4.9 billion, could launch in the late 2030s on a Space Launch System or Falcon Heavy with a landing in the early 2050s." Nil Einne (talk) 11:56, 4 December 2023 (UTC)[reply]

December 4

Mothball smell

I recently purchased some insect specimens: they're mounted in wooden shadow boxes with clear plastic windows for viewing. There's a seal around the window as well. Inside each case is a tiny box containing some form of mothball to deter other critters from munching on them. The thing is, the smell is pretty overpowering. What can I do to reduce it from being a nuisance while still hopefully retaining the preservative effect? The boxes appear pretty well sealed already, but mothballs are pretty intense, so even the tiniest crack would leave me in the same boat. Right now I have them sitting out in my garage to gas out for a bit; are there any other suggestions? Matt Deres (talk) 00:25, 4 December 2023 (UTC)[reply]

NatSCA advises investigating methods other than PDB, Naphthalene, and Camphor, mentions cedar and lavender oils, but doesn't go as far as to recommend them.[10] fiveby(zero) 04:10, 4 December 2023 (UTC)[reply]

It may be that most of the smell is coming from residual traces on the outside of the boxes. Try leaving them, sitting so as to expose the undersides as well, exposed to a continual draught for a week, and see if it lessens. {The poster formerly known as 87.81.230.195} 51.194.245.32 (talk) 13:14, 4 December 2023 (UTC)[reply]

Colors: What's unique in our planet, that lets us see this photon as yellow, rather than redshifted or blueshifted as seen by another galaxy's inhabitants?

Let there be a photon in our universe, outside our planet.

The photon is independent, i.e. it's not emitted by any system.

Let's assume our planet's inhabitants see this photon as yellow (i.e. with the respective frequency), while another galaxy's inhabitants see this photon have another color - whether redshifted or blueshifted.

I wonder what unique physical attributes our planet has (e.g. velocity and likewise), that let us predict that we will see this photon as yellow (i.e. with the respective frequency), as opposed to the other galaxy which doesn't have these physical attributes.

Note our planet's physical attributes I'm looking for cannot rely on what the other galaxy's inhabitants see, because we only know they see the photon have another color without us knowing - what this different color is - and whether it's redshifted or blueshifted. HOTmag (talk) 10:52, 4 December 2023 (UTC)[reply]

What do you mean by "predict that we will see this photon yellow"? We cannot predict that. Also, if we see the photon then the other galaxy's inhabitants don't. Detecting a photon destroys it, or at least changes its properties (ignoring the question of the identity of photons). It is not at all clear what you're asking and what the ideas behind the question are. --Wrongfilter (talk) 11:50, 4 December 2023 (UTC)[reply]

Now you are using Quantum considerations: Measuring it destroys it. But I'm asking from a statistical point of view. Note that under your Quantum considerations, but without statistics, the Doppler effect would have no meaning, because it discusses a photon's frequency (i.e. a photon's color) measured by two different frames of reference. HOTmag (talk) 12:14, 4 December 2023 (UTC)[reply]

Didn't you just answer your own question? --OuroborosCobra (talk) 13:42, 4 December 2023 (UTC)[reply]

Where? HOTmag (talk) 13:51, 4 December 2023 (UTC)[reply]

Reference frames. --OuroborosCobra (talk) 15:46, 4 December 2023 (UTC)[reply]

Yes, by "our planet" I meant "our planet's reference frame". I asked, if you can point at any quantified attributes our planet's reference frame has, which let us predict we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants who have another reference frame. HOTmag (talk) 16:37, 4 December 2023 (UTC)[reply]

The fact that the observed wavelength in our reference frame is that of yellow, and the observed wavelength in another reference frame is a different wavelength. I don't really understand what type of quantifiable thing you are asking, not if you understand the color/wavelength relationship and what a reference frame is. --OuroborosCobra (talk) 17:10, 4 December 2023 (UTC)[reply]

Of course I understand well, the color/wavelength relationship, and what a reference frame is.

Actually, instead of asking about colors, I could ask the same question about wavelengths, so wherever I mentioned "yellow", you are allowed to replace it by its respective wavelength, and then you will see that my question still remains.

I will do the job for you: So, I'm only asking, if you can point at any quantified attributes our planet's reference frame has, which let us predict we will see this photon have the wavelength of yellow - rather than the wavelength of the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants who have another reference frame. HOTmag (talk) 17:40, 4 December 2023 (UTC)[reply]

A reference frame is a definition, it isn't anything that can have quantifiable attributes. It isn't a thing that physically exists. --OuroborosCobra (talk) 18:50, 4 December 2023 (UTC)[reply]

But the very relation between two different reference frames is defined, by the relative velocity between them. Do you see my point? On the one hand, the difference between reference frames is relative: if I see you approach me - then you see me approach you, and if I see you move away from me - then you see me move away from you; On the other hand, colors (as well as their respective wavelength) are objective: If you see it redder than how I see it (e.g. when I'm on the other galaxy), then I see it bluer (rather than redder) than how you see it.

Let me present my question from another viewpoint, because I don't want you to misinterpret me by "objective": so my question is, what makes you see the photon as yellow, rather than the other color (whether redshifted ot bluehsifted) - as seen by me when I'm on the other galaxy? Why don't our colors interchange, so that I will see the photon as yellow, and you will see it have the other color (whether redshifted ot bluehsifted)? HOTmag (talk) 19:28, 4 December 2023 (UTC)[reply]

We are in the same reference frame, at least as far as it is relevant to light coming from a common source towards both of us. The difference in location and velocity between you and me, no matter where you are on the planet, is incredibly minute in the scale we are discussing. Outside of that, you’ve answered your own question in how you have phrased it. That, or you are still not understanding what a reference frame is. —OuroborosCobra (talk) 19:59, 4 December 2023 (UTC)[reply]

What makes you suspect I don't understand what a reference frame is?

Contrary to what you ascribe to me (as your suspicion), I don't ascribe to you misunderstanding, but only (maybe) misinterpretation. Maybe you misinterpreted the words "other galaxy" I'd used from the very beginning. Actually, I'd written "other galaxy", just because the relative velocity between planets and stars in the same galaxy is usually very low with respect to the speed of light, while my question is about two totally different frames of reference - the relative velocity between each other being pretty close to the speed of light. This is what I've been asking about. I was sure you correctly interpreted my question - from the very beginning, but now I suspect you didn't.

Actually, when I posted my question, I didn't feel I had to indicate that the relative velocity between the frames of reference was close to the speed of light, because I was sure this was what everyone should have inferred, reading that my question was about - our planet's inhabitants seeing the photon as yellow - while the other galaxy's inhabitants see it have another color whether redshifted or blueshifted. I'd written "other galaxy", and "redshifted or blueshifted", just for this purpose: For my readers to realize that the relative velocity between both frames of reference was close to the speed of light. Naturally (i.e. disregarding electrons being the "observers" in a particle accelerator and the like), such a high relative velocity is only possible (naturally) if the question involves two different galaxies. I hope my question is clear to you now. HOTmag (talk) 20:58, 4 December 2023 (UTC)[reply]

Measured from what place and time on Earth? The yellow photon will be slightly redder/bluer due to relativistic velocity addition regardless of whether it's been recently emitted. Note that we are certainly using local instruments (and perhaps different models of these) to measure each. Modocc (talk) 13:03, 4 December 2023 (UTC)[reply]

As to your question in your first sentence: When we measure a galaxy we usually say we see it (e.g.) redder than what it really is. We don't ask "measured from what place and time on Earth", because the color is pretty similar from every place on earth and at any time on earth. So the same is true for the photon I'm asking about. My question is: Can you point at any quantified attributes our planet has, which let us predict we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 13:50, 4 December 2023 (UTC)[reply]

All the observable galaxies are in the same boat, so to speak, with respect to their inhabitants' measurements. We, as in our galaxy, are not special in that regard. Modocc (talk) 14:05, 4 December 2023 (UTC)[reply]

Of course. By "our planet" I meant "our galaxy". Can you point at any quantified attributes our galaxy has, which let us predict we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 14:11, 4 December 2023 (UTC)[reply]

Your question is premised on the assumption that the photon is not correlated with anything. Yes? Not with matter or even other photons. Then this question is like asking us to predict what the weather will be like tomorrow without sufficient data. Modocc (talk) 14:33, 4 December 2023 (UTC)[reply]

If I know, that your velocity is 2 units (of velocity), and that your mass is 3 units (of mass), I can "predict" your momentum is 6 units (of momentum).

Please fill in the blanks: If I know, that our galaxy's ________ is _ units (and so forth), then I can "predict" our galaxy's inhabitants will see the photon as yellow (with the respective frequency).

The question is, if you can fill in the blanks in the second sentence, just as I could fill in the blanks in the first sentence. If you think you can't fill in the blanks in the second sentence, then how can you explain that our galaxy's inhabitants see the photon have the yellow color (i.e. with the respective frequency) - rather than the other color (whether redshifted or blueshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 16:06, 4 December 2023 (UTC)[reply]

Now you seem to be asking me to try to kick this ball/sphere/galaxy within the usual paradigm of removing it from consideration with respect to the ground/graviton sea/field. Hmm. I'm not Charlie Brown. Modocc (talk) 16:58, 4 December 2023 (UTC)[reply]

Actually, my question was about whether we can point at any factors that make our galaxy's inhabitants see this photon as yellow, just as we can point at the meteorological factors (e.g. humidity and barometric pressure) that made the day of 1.1.1743 so rainy in LA, just as we can point at the physical factors (e.g. velocity and mass) that make this Chinese man's momentum so and so. I can't see how my question is related to kicking the ball you've mentioned. In my opinion, my question is more similar to the question about the rainy day and about the man's momentum. HOTmag (talk) 17:24, 4 December 2023 (UTC)[reply]

Classically, both the KE of mass and the color of light are always reference frame dependent. With both, the energy of an interaction between the photon and any galaxy is in fact relative. What other factors would you have in mind that would be sufficient?? Of course, classical Doppler is asymmetric (and not symmetric which is why it was mothballed), a paradox that my unpublished work resolves. Modocc (talk) 17:43, 4 December 2023 (UTC)[reply]

Your question: "What other factors would you have in mind that would be sufficient??", is pretty similar to mine: Is there any eqaution in your mind, that may let us predict, that our galaxy's reference frame will make us see this photon have a yellow color - rather than the other color seen by the other galaxy's inhabitants. Of course, you are allowed to replace the word "yellow" by its respective propery: whether frequency or wavelength or momentum or energy.

As for your comment about the classical Doppler effect: The same is true for the relativistic one. HOTmag (talk) 17:58, 4 December 2023 (UTC)[reply]

None. Modocc (talk) 18:26, 4 December 2023 (UTC)[reply]

I'm sad. HOTmag (talk) 18:33, 4 December 2023 (UTC)[reply]

I'm patient. Thanks. Modocc (talk) 19:00, 4 December 2023 (UTC)[reply]

We have the right reference frame to make the photon yellow.

In every reference frame, the photon has a direction and a wavelength (let's ignore polarisation and phase). No reference frame is any better than any other reference frame. Redshift and blueshift of this photon are only relative to a different reference frame. This yellow photon is blueshifted relative to the frame where it appears red and redshifted relative to the frame where it appears blue.

Multiple observers can't measure the same photon, but there's nothing stopping us from making multiple identical photons. Lasers do it all the time. PiusImpavidus (talk) 13:06, 4 December 2023 (UTC)[reply]

I agree to all of what you've written. Obvious, and yes: by "this photon" I mean one of those multiple identical photons. But still the fact is, that our planet's inhabitants see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants, so can you point at any quantified attributes our planet has, which let us predict we will this see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants? HOTmag (talk) 13:50, 4 December 2023 (UTC)[reply]

How would a photon (or a collection of them) not be emitted by something? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:14, 4 December 2023 (UTC)[reply]

Do you have any sources for your alluded claim, that every photon can't be idependent but rather must be emitted by a system? HOTmag (talk) 16:12, 4 December 2023 (UTC)[reply]

I'm not claiming anything. I'd just like to know what the basis of your premise is. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:25, 4 December 2023 (UTC)[reply]

See my response to NadVolum, below. HOTmag (talk) 18:30, 4 December 2023 (UTC)[reply]

If there is a monochromatic source of light somewhere in the cosmos that can be seen from the Earth and is found to have a wavelength of about 589 nm, it will appear yellow to us. There is no reason to think observers in other galaxies will find a different wavelength, unless they move with a very high velocity with respect to us. --Lambiam 15:28, 4 December 2023 (UTC)[reply]

Exactly. The other galaxy I'm talking about moves with a very high velocity with respect to us. Still, I'm looking for the attributes our glaxy has, that let us predict that we we will see this photon have the yellow color - rather than the other color (whether redshifted or bluseshifted) as seen by the other galaxy's inhabitants. HOTmag (talk) 16:10, 4 December 2023 (UTC)[reply]

Here's a direct answer to your question: There are no attributes our galaxy has that let us predict that we will see this photon have the yellow colour. Put differently: Your question makes no sense. --Wrongfilter (talk) 16:47, 4 December 2023 (UTC)[reply]

If so, then how can you explain the fact, that our galaxy's inhabitants see the photon have the yellow color (i.e. with the respective frequency) - rather than the other color (whether redshifted or blueshifted) as seen by the other galaxy's inhabitants? By the way, note that I have already responded to your previous comment: See above. HOTmag (talk) 16:55, 4 December 2023 (UTC)[reply]

The premise is flawed: "The photon is independent, i.e. it's not emitted by any system." Photons do not have any existence independent of their emitters and absorbers. As pointed out by Gilbert Newton Lewis when he invented the term "photon", the emitting and absorbing events are separated from each other by a spacetime interval of zero. From the photon's point of view, traveling at the speed of light, no time elapses from when it is emitted until when it is absorbed, and its wavelength is infinite. From the point of view of the emitter and absorber, the energy, momentum, and wavelength are related, but identical only if the two have no velocity between them in a reference frame. No photon can be "seen" by two different observers, but photons of the same energy from the emitter will have different energies by different aborbers moving at different velocities. The idea of a photon as a "particle" confuses this picture, suggesting that a photon might have an independent existence. It's better to think of the photon as a "process", exchanging a quantum of energy between the emitter and the absorber, though here the "quantum" concept again confuses the picture, since the emitter and absorber don't see the same size quantum in the exchange if they have a relative velocity. There are lots of other ways to look at this, too, but it's nothing special about our place in the universe, just about relative velocities. Dicklyon (talk) 16:15, 4 December 2023 (UTC)[reply]

If so, then could you please answer my question in my previous thread? You can answer it on my own talk page if you want to. HOTmag (talk) 16:30, 4 December 2023 (UTC)[reply]

Both this question and your last presupposes something that doesn't fit with ay current physical theory I know of. Pleas try reading Dicklyon's response above with a view to accepting your current beliefs make no sense in physics.The reference desk is not going to provide some fairytale to bolster your worldview. NadVolum (talk) 18:00, 4 December 2023 (UTC)[reply]

I had already read Dicklyon's answer thoroughly. His answer, which was totally different from the other answers given here (except for Baseball Bugs's hint alluded in his question), was actually the answer I had had in my mind before I posted this thread, but I was not sure if this was the correct answer, so I wanted to know if other users thought what I had thought, and that's why I posted this thread, emphasizing the assumption that the photon was independent. Eventually, DickLyon noticed this assumption (as Baseball Bugs did in his question). But if his answer (identical to what I'd had in my mind before I posted this thread) is really correct, then my previous thread becomes more actual. That's why I wanted him to respond to it, and I'm still waiting. (As I responded to him, he can respond back on my talk page, if he doesn't want to respond here to my previous thread). HOTmag (talk) 18:23, 4 December 2023 (UTC)[reply]

You got lots of reasonable answers, there is no cathecism of approved answers and you got ones appropriate to the level of understanding you showed. NadVolum (talk) 21:05, 4 December 2023 (UTC)[reply]

Some of the answers were wrong, while several answers referred to other questions I didn't ask. Other answers were reasonable but still inappropriate to me, because they were imperfect, i.e. the users who gave those imperfect answers ignored my request for further clarifications - me explaining exactly what was still missing in those imperfect answers. Anyway, I didn't want "reasonable" answers, but rather "the best answer". Meanwhile, the best answer I've received was the one I had had in my mind before I posted this thread, and this answer was actually the one you thought I hadn't read. HOTmag (talk) 21:38, 4 December 2023 (UTC)[reply]

A slight digression here: A single photon cannot be "seen as yellow", because it can activate only a single photorecptor, and our cone cells correspond roughly to red, green, and blue. --Trovatore (talk) 19:01, 4 December 2023 (UTC) [reply]

Agreed. HOTmag (talk) 19:32, 4 December 2023 (UTC)[reply]

The rods can respond to single photons okay, but no signal is sent to the brain unless about ten or more nearby rods register something within a short time - so normally about a hundred photons are required. And the cones are far less sensistive. NadVolum (talk) 20:57, 4 December 2023 (UTC)[reply]

There is so much light pollution where I am the sky is a dull red and one can walk around at night even without street lights. NadVolum (talk) 21:12, 4 December 2023 (UTC)[reply]

Phase diagrams of the noble gases

Does anyone know where I can find up-to-date phase diagrams of the noble gases with the high-pressure phases (e.g. metallisation of Xe)? Double sharp (talk) 13:00, 4 December 2023 (UTC)[reply]

Possible lead-ref: doi:10.1038/nchem.445 (from 2009). DMacks (talk) 14:22, 4 December 2023 (UTC)[reply]

As a failed chemist, I thought 'that has to be fairly complicated': yep: Diamond anvil cell. Nice. MinorProphet (talk) 15:46, 4 December 2023 (UTC)[reply]

Thanks! Looking through the cites at metallization pressure, it seems that experiments are available only for Xe (and that that's the only one that we can metallise with current technology, though Kr should be close). As it turns out (doi:10.1016/0375-9601(89)90503-3) metallisation happens because the outer d-subshells drop down in energy under pressure and become available for bonding: per calculations (and experiment for Xe), Ar, Kr, and Xe first turn from fcc to hcp (with some intermediate close-packed structure for Xe), then metallise. Neon is weird here as it doesn't have a 2d to drop down, so it should require much, much greater pressure (terapascals rather than gigapascals) because it needs to use 3d instead: it also seems to stay fcc all the way.

Helium is interesting. Per doi:10.1103/PhysRevLett.71.2272, solid ⁴He also goes through a fcc-hcp transition; it's just that at cryogenic temperatures fcc is bypassed altogether and hcp is the first solid phase. Apparently it stays hcp pretty much up to the terapascal pressure it takes to metallise (still seems lower than Ne, though).

I can't find anything (even theoretical) about radon. Not that I expected to, though. Presumably it would follow the trend from Ar onward. Double sharp (talk) 17:04, 4 December 2023 (UTC)[reply]

Blimey. My maths is even worse than my chemistry, but I suspect that the mere 150 Gpa to metallise Xe is approximately 15,295,000 tons/m². I imagine you would need something like this to achieve those sort of pressures. MinorProphet (talk) 19:33, 4 December 2023 (UTC)[reply]