Wikipedia:Reference desk/Archives/Science/2021 December 29

= December 29 =

Questions on spacecraft in DLU
Hi all, retired editor here from the aughts but wanted to get some expert opinions on the starship in the ending credits of Don't Look Up (2021 film), since a myriad of futuristic sci-fi alternatives exist rather than just the relatively old technologies of cryogenics and nuclear engines it is obvious the filmmakers wanted it to use emerging technology and not sci-fi.


 * So what is that ship why that design and why move the capsules forward on release? Did every passenger get cryogenically frozen upon boarding the ship?  Could you with cutting edge or next year technology make a ship that one could survive on for years or decades and then get cryogenically frozen?


 * Then the question of the 22,000 some years, would the nuclear engine last that long, would life support for cryogenically frozen humans last that long (I know they said some did die in the movie)?


 * Finally the software and hardware, could next years AI or algos find another suitable planet and still work after 22,000+ years, would the ships "bones", electronics, mechanics, heck even the lights last 22,000 years if you had trillions to spend on it?

I majored in political science so economics, humanities, anthropology, philosophy, I can kind of guess at but I would love to talk to those in the know about the film staying true to emerging technologies that if you did have an unlimited budget could be possible now on those three areas. Thanks so much!2600:1702:690:F7A0:2D68:4556:F69C:4ED0 (talk) 04:46, 29 December 2021 (UTC)
 * Man knows how to dump man in liquid helium but man doth not know how to reanimate. Sagittarian Milky Way (talk) 05:40, 29 December 2021 (UTC)
 * Comas are also not like soap operas, learning how to keep someone alive and un-brain damaged for 200 lifetimes by next year is a tall order. Sagittarian Milky Way (talk) 05:51, 29 December 2021 (UTC)
 * Sagittarian great point on reanimation and also comatose, to be fair to the film I was reading too much into it, it seems not to be cryo but some sort of coma with spacetime aging (lightyears and such) on life support systems, even with it not being 100% would any life support system work for 22,000 years even considering the faster and farther you go the slower you age theory?2600:1702:690:F7A0:43F:4C14:1E71:D2FA (talk) 06:12, 29 December 2021 (UTC)
 * The Lorentz factor governs how much time speeds up from nearing lightspeed. It would take about a year of rockets (or other propulsion) that feel like just sitting in a chair (you could do 2g's but it'd feel like your clone is on you 24/7, this is probably bad) to get to the juicy Lorenz factors. But at as little as 10% lightspeed which is far below the juicy Lorenz factors all feasible spacecrafts would erode away or blow up from hitting things. A tiny rock would be like a nuclear bomb and interstellar dust which does exist could annoy your spaceship and make craters in it. The Space Shuttle was once hit by a paint fleck so small you could barely see and it made a crater in the window a tenth of an inch wide. It only hit at ~0.00003 times lightspeed, at 10% lightspeed it would have 3,333 squared or 1,000,000,000 percent more kinetic energy. If you had an invincible spaceship and a fuel cornucopia and magic drag cancellers the stars would do some cool, vaguely hyperspace jump-like visual transformations like you can start to see behind you (not exactly behind the motion axis) and stars become blue and eventually the cosmic microwave background radiation becomes red, then orange, yellow, white (entire windshield is white), blue, ultraviolet, sunburn ultraviolet, vacuum ultraviolet, extreme ultraviolet, X-rays, hard X-rays, gamma rays, hard gamma rays, hard-ass gamma rays, Oh-My-God Particles, photons with the energy of bombs, by the time the windshield reaches about 1 with dozens of zeroes degrees no one knows what would happen. Maybe each photon collapses into a black hole that spits another Big Bang and explodes in a titanic explosion of Hawking radiation? You could reach the edge of the observable universe in a half century this way but your spaceship would be destroyed long before it could get there. Stars would elongate but only as much as the Lorentz factor for length elongation, it'd take a lot of speed to stretch to long streaks like Star Wars. The James Webb Space Telescope starts observing in half year, with a mirror the size of a small apartment it is the first object able to see if foreign star systems have planet airs with oxygen lines it's infrared spectrum and thus likely photosynthesis. It would suck if you wake up at the planet and don't have enough resources for a planet B and find out it has only one species and that's oily low-calorie microbes that cause stomach cramp, diarrhea and taste like shit. Sagittarian Milky Way (talk) 07:59, 29 December 2021 (UTC)
 * High-energy cosmic rays will damage the electronics. You need, next to redundancy and robust components, an on-board repair facility. In view of the rapid advances in AI and robotic technology, this may be feasible in the near future. But I think it is asking too much of the screenplay writers of a satirical comedy to adhere to scientifically defensible extrapolations; a lack of blatant implausibility, allowing one to suspend disbelief, is good enough. A technological alternative might have been a generation ship, but that would work less well for the gruesome ending. --Lambiam 10:03, 29 December 2021 (UTC)
 * This source presents a dim view on the scientific credibility of the starship credit scene. --Lambiam 12:43, 29 December 2021 (UTC)
 * Very interesting links and observations, any others are welcomed as well, thank you all for the robust discussion.2600:1702:690:F7A0:B17B:900F:8E9B:75E8 (talk) 15:41, 29 December 2021 (UTC)

Effective nuclear charge (ENC)
Our article notes that the effective nuclear charge experienced by the outer electrons of an atom increases going down a main group of the periodic table. If ENC increases going down a main group why does ionization energy (IE) decrease? For example, consider the group 18 noble gases:

ENC     IE kJ/mol  Atomic radius (pm) He 1.688    2372.3     31 Ne 5.758    2080.7     38 Ar 6.764    1520.6     71 Kr 9.338    1350.8     88 Xe 12.425   1170.4    108

ENC goes up yet IE goes down, implying that the ENC experienced by the outer electrons is in fact reducing, rather than increasing? Weird.

I've added atomic radii for comparison since these seem to play a role. Whatever ENC is, it doesn't seem to be equivalent to the net attraction experienced by the outer electrons of an atom. Sandbh (talk) 05:44, 29 December 2021 (UTC)


 * The outer electrons are also subject to a repulsive force due to the other electrons. Inasmuch as the ionization energy depends on the electric force, it is the net force that counts. --Lambiam 09:30, 29 December 2021 (UTC)

Microwave electric motor
What's the part number of the electric motor which drives the turntable of the Toshiba Solo ML-EM45PIT(BS) microwave oven? 69.181.91.208 (talk) 07:10, 29 December 2021 (UTC)
 * Have you tried contacting the manufacturer? --←Baseball Bugs What's up, Doc? carrots→ 13:58, 29 December 2021 (UTC)
 * Contact page: Toshiba customer support. --Lambiam 15:13, 29 December 2021 (UTC)

corrosion potential of mercury in flowing seawater
What is the corrosion potential of mercury in flowing seawater? Horus1927 16:55, 29 December 2021 (UTC) — Preceding unsigned comment added by Horus1927 (talk • contribs)
 * Are you asking if mercury will corrode or oxidise in seawater? Graeme Bartlett (talk) 11:32, 30 December 2021 (UTC)
 * Perhaps this is about the electrode potential if mercury serves as the electrode and the electrolyte is seawater. Like Zn: −0.76V; Cu: +0.34V; Hg: +0.??V. The "flowing" makes the question unanswerable; the steady-state concentration of mercury ions is unknowable. --Lambiam 16:34, 30 December 2021 (UTC)
 * I'll bet it's to do with Brine_mining. Card Zero  (talk) 01:46, 31 December 2021 (UTC)

Physics of penny challenge
If you connect a phone charger halfway to a plug and touch the two exposed prongs with a US penny coin, would you get a massive electric shock? Or would you just generate a short cut and blow a fuse?

I won't ask my 10 year old daughter to try it. She's so small and I'm afraid she could get harmed.

Note: at first I was surprised that it was possible, having in my mind European 1 cent coins and plugs. But yes: 1 US penny coin has a diameter of 20 mm and the prongs are 13 mm apart. --Bumptump (talk) 17:27, 29 December 2021 (UTC)
 * Do not attempt the experiment that you propose. It is reckless with a severe risk of damage, injury or death by electric current passing through the body, see Electrocution. Philvoids (talk) 18:45, 29 December 2021 (UTC)


 * With the europlugs I typically encounter on phone chargers, touching the metal of the prongs with the plug halfway inserted is hard. But there are other plugs making this easier, especially on older types of outlets.
 * It depends a bit on how well you're insulated from the ground and whether you touch the phase or neutral first. If you first touch the phase, you get about 230V over you. Your resistance is probably low enough to get a current of more than 100mA, so that hurts, but is probably not lethal. The residual-current device (RCD) will then cut off the current to save you. The fuse won't blow.
 * If you first touch the neutral, maybe nothing happens before you touch the phase too. Maybe something does happen, as the neutral isn't always exactly neutral, so some current may flow, giving you a shock and tripping the RCD. Otherwise, connecting the coin to both prongs will cause a short circuit, which may, if the resistance between prong and coin is low enough, blow the fuse. But at the same time, the potential on the coin is somewhere between 0V and 230V, depending on the ratio of the resistances to the prongs, which can still give you a nasty shock and may trigger the RCD, even before the fuse has a chance to blow. I think you'll survive, but you can't be sure. I don't think it will be pleasant.
 * That's all assuming an RCD has been installed. They've been mandatory for decades. PiusImpavidus (talk) 19:35, 29 December 2021 (UTC)
 * With Europlugs and BS1363* it's not possible. The pins are shielded for part of their length so that no metal is exposed until after the contacts have parted from the socket.  *Very old BS1363 plugs may not have this feature, it has been mandatory since 1984. Martin of Sheffield (talk) 21:18, 29 December 2021 (UTC)
 * The clicky things? I've been in a young NYC apartment that only had partial clicky socket penetration (bathroom yes, under window no) and I've seen a completely ungrounded 1920s-looking thing in an old middle-class NYC house. There are plenty of non-crimey New York City apartments that still have fuses. Sagittarian Milky Way (talk) 21:39, 29 December 2021 (UTC)


 * Not sure what "clicky things" you are referring to. Europlugs are used in Europe, and BS stands for British Standard. Martin of Sheffield (talk) 23:02, 29 December 2021 (UTC)
 * These. Press until click to test and make socket stop working, do the same to the other button to swap which of the two is recessed and make the socket work again. Sagittarian Milky Way (talk) 23:58, 29 December 2021 (UTC)
 * That'a a GFCI in North America and an RCD (mentioned above) in some foreign countries. Now, what's "non-crimey"? --184.144.97.125 (talk) 01:25, 30 December 2021 (UTC)
 * I don't know much about American electrical systems. Where I live (NL, Europe), you usually find one or more RCDs on the distribution board, protecting every circuit in the house, not just those wall outlets that have their own RCD. In fact, I've never seen a wall outlet with its own RCD built-in, but if you want higher sensitivity on some wall outlets or a smaller-scale blackout when it trips, it makes sense. PiusImpavidus (talk) 10:52, 30 December 2021 (UTC)
 * In the UK they are also normally installed in the "fuseboard". However for older installations they can be incorporated into the socket outlet or even as a plug-in adapter.  In both the UK and the US (NECA 130-2010) three pin outlets are nowadays meant to be installed with the earthing (grounding) pin uppermost so that a foreign object falling onto a partially withdraw plug will hit the earth pin first. Martin of Sheffield (talk) 11:55, 30 December 2021 (UTC)
 * That must be why the ones installed the other way round look shocked and frightened. Card Zero  (talk) 19:02, 30 December 2021 (UTC)
 * But the 120V/20A and 240V/20A are winking at you. DMacks (talk) 03:49, 31 December 2021 (UTC)
 * I suppose the OP's question was inspired by this: --←Baseball Bugs What's up, Doc? carrots→ 21:55, 29 December 2021 (UTC)


 * It is absolutely stupid and potentially lethal. Since you have a daughter I suppose it isn't Darwinism in action, but it comes pretty close. Greglocock (talk) 23:33, 29 December 2021 (UTC)


 * Just to add that a number of fires have been started by this stupid social media "challenge".--Shantavira|feed me 11:57, 30 December 2021 (UTC)
 * I live in the U.S. About 60 years ago, I witnessed a rebellious child insert a two pronged fork into an electrical outlet. There was a loud noise, the kid fell backwards, there was smoke and charring, and droplets of molten metal. And angry parents. But no serious injury. Cullen328 (talk) 23:31, 30 December 2021 (UTC)
 * The good old days. --←Baseball Bugs What's up, Doc? carrots→ 00:06, 31 December 2021 (UTC)
 * I can confirm the loud noise. When I was 11 I came up with the "bright" idea to cut off an unneeded cord, bifurcate it, strip the ends, hold one sheath while stepping on the other (shoe-d) to keep the ends away from each other and myself, plug it in and bring the copper twines together. There was a pop of the thunder mechanism and blue plasma much hotter than the surface of the Sun (which I knew enough to look away from), but I held them far from the ends and killed arc ASAP so didn't melt metal or get molten plastic on me. I never did that again. I also poked a tool that lights up if dangerous current in each slot to find one of the billions of socket slots that I could insert an uninsulated fork in with bare hands. And inserted an uninsulated fork in with bare hand as deep as it would go (I didn't feel anything). Lucky the kid didn't squeeze the fork with the max force physiologically possible, as grabbing mains voltage often does that. Sagittarian Milky Way (talk) 03:39, 31 December 2021 (UTC)


 * If the penny somehow hit both prongs at the exact same instant, it would short the line.
 * If you managed to hit the live prong before the neutral prong, you would very likely get a nasty shock. This is very possible. In fact, if you've got thin fingers you can shock yourself that way without the penny.
 * There's no good way for the challenge to end. It's entirely a prank on anyone sucker enough to try it. Either you shock yourself, blow a fuse/breaker, or quite likely both. ApLundell (talk) 05:59, 5 January 2022 (UTC)

Blood oxygen readings on fitness bands
I've been wearing a Xiaomi fitness band for a few weeks. My mom has been wearing a Fitbit. After accurate readings at the start, both devices now give readings mostly in the low 90s. I've never had a bad reading at the doctors', so today while I asked a nurse for a reading. She got 98%; I had 94%. Clearly, the devices are not to be trusted. I've tried all sorts of things--sitting still, dark room, etc.--but it didn't matter. I just got a 96% after showering, but I don't think it helps consistently.

Is there any way such readings can be improved, or will I need to get a standalone pulse oximeter to get good readings? Thank you. 74.64.73.24 (talk) 23:52, 29 December 2021 (UTC)


 * Fitness wearables are generally unreliable. Companies that offer such products always display a disclaimer about they not being intended for medical purposes, even if their ads somehow imply they might be useful. In the case of Fitbit, they state: "for general wellness purposes only and should not be used or relied on for any medical purposes."
 * Their values are affected by your blood pressure, ambient light, how snug the device is to your wrist, and so on. They could show a normal value, even if the user notices difficulties breathing, and make you believe everything is fine.
 * Use a medically approved device and/or talk to a medical professional if you need reliable values.Bumptump (talk) 02:20, 30 December 2021 (UTC)


 * Pulse oximeters are known to be less accurate when used on people with darker skin than on people with pale skin. DuncanHill (talk) 04:04, 31 December 2021 (UTC)


 * That makes perfect sense as melanin is brown which is dark orange and orange is 1 ROYGBV color away from red finger oxygen lights. Sagittarian Milky Way (talk) 05:43, 31 December 2021 (UTC)


 * That kind of error overstates oxygenation levels. 74.64.73.24 (talk) 02:07, 6 January 2022 (UTC)