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October 8

Transgender children and suicide

It seems that transgender identity has risen sharply among minors in recent years. It has been argued by many that this huge increase is a result of the notion that this many trans people have always existed but they simply were not comfortable coming out as trans in the past. Transgender advocates and many medical professionals have also argued that if transgender children do not receive gender affirming care such as surgeries, hormone therapy, and puberty blocker, they will end up committing suicide. However, gender affirming care is relatively new meaning there were million of unaffirmed trans kids for decades and centuries before this. Is there any evidence that there was an epidemic of suicide across the world due to lack of affirmation? StellarHalo (talk) 02:46, 8 October 2022 (UTC)

You can take a look at this report: https://williamsinstitute.law.ucla.edu/wp-content/uploads/Suicidality-Transgender-Sep-2019.pdf "Suicide Thoughts and Attempts Among Transgender Adults" but this is not about children. 19.9% rate of attempted suicide per year, but this will be in those that have identified as trans. The report has far more detail on things that affect that rate. Graeme Bartlett (talk) 06:27, 8 October 2022 (UTC)

Nit: 19.9% is of the subset who are in "poor general health", which does not seem to mean "lack of affirmation". The overall rate reported in that study is "only" 7.3% in the year. The "Unique Risk Factors" summary starting on page 2 indeed does have lots of good breakdowns of it. DMacks (talk) 19:49, 8 October 2022 (UTC)

This increase of course also coincides with a huge rise in anti-trans bigotry in politics in many countries. Yes, correlation does not imply causation, but it's not going to help. Fgf10 (talk) 08:45, 9 October 2022 (UTC)

Berries

Would like help in identifying the species of these berries. I want to pick them, but make sure they are not poisonous. 212.180.235.46 (talk) 11:35, 8 October 2022 (UTC)

It looks like a Pyracantha of some sort: The pulp [of the berries] is safe for human consumption, but it is insipid, and the seeds are mildly poisonous... AndrewWTaylor (talk) 17:28, 8 October 2022 (UTC)

I would like to suggest those berries may be Sea buckthorn. Superficially similar to pyracantha but sea buckthorn have greyer leaves. Information about its edibility is in the link. Richard Avery (talk) 14:34, 11 October 2022 (UTC)

And of course, we're not telling you it's OK to eat them. EEng 20:08, 14 October 2022 (UTC)

Detecting alien spaceships

Some days ago I had a discussion with someone. He said that he once saw an alien spaceship in the sky, and I rejected the notion: I have no idea what was the thing he saw, but if an alien spaceship came all the way to Earth, enter into planetary atmosphere, made a passing-by fly and then fly away, it would have been detected and seen by all the satellites out there. And the usual "the military concealed it all" excuses would not work, we are talking about satellites from many countries, and some of them belonging to the private sector. Even without a proper first contact, it would be the event of the century, all the world would be talking about it and there's just no way to stop something like that.

But then I thought: am I right? do satellites work that way, would they detect a spaceship out there? There are space telescopes, but are they on the look for something unexpected, or stay focused on whatever they are studying right now? Considering that a spaceship would be a tiny object (compared with other celestial bodies) and not following a known orbit, how far away would we be able to detect it? Cambalachero (talk) 15:50, 8 October 2022 (UTC)

Considering that there are approximately 9,000 items larger than a softball orbiting the Earth, all of which are tracked and monitored by the Department of Defense,[1] it seems unlikely that an "alien spaceship" could sneak by. Of course, in the realm of science fiction, sneaky sentient aliens (or time travelers, alternate universe jumpers, etc.) could use any of a variety of methods to troll your friend. 136.56.52.157 (talk) 17:03, 8 October 2022 (UTC)

Or cloaking devices, momentarily disabled when the aliens spot someone who seems like a good target for such trolling. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:16, 8 October 2022 (UTC)

(edit conflict)One should also consider that just because an observer cannot identify something witnessed in the sky, it is not necessarily an "alien spacecraft". I personally had a fairly close encounter with 3 UFOs that flew directly over me in the desert near Yuma, AZ. Although they were "unidentified" (by me) and were "objects" that were "flying", I did not assume they were alien spacecrafts. A year or so later when the F-117 was publicly disclosed, they became identifiable to me. 136.56.52.157 (talk) 17:03, 8 October 2022 (UTC)

They were not sufficiently stealthy? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:28, 8 October 2022 (UTC)

I have a pair of organic orbital photon sensor arrays that were able to detect them. 136.56.52.157 (talk) 17:50, 8 October 2022 (UTC)

Remember the sticker at the back of each Nighthawk: "If you can read this sign, we wasted US$ 111 million of taxpayer money." ;-) --Stephan Schulz (talk) 00:13, 11 October 2022 (UTC)

Satellites don't scan for UFOs. There are telescopes scanning for asteroids that could hit earth and a big alien spaceship would be picked up by those if it was close enough, but only if it passed through their field of view. Those telescopes only scan the entire sky once every few days. Military radar systems designed to detect strategic nuclear missiles would also detect alien spaceships close to earth, but only cover some parts of the world. Only when it flies in the lower atmosphere it would be picked up by ordinary military radar systems, except when it flies over some remote ocean or Antarctica – and even if detected, only one country's military would know about it. Earth observing radar satellites would detect it if the UFO flies beneath them, but they too only scan the entire earth once a week or so – and would automatically flag it as an aeroplane. Radars tracking orbital debris don't keep the full sky in view permanently; they target the known objects to refine their orbits once every few weeks and occasionally scan for new objects in such a a way that anything orbiting Earth should have passed through their beam. Remember: every sensitive detector has a small field of view. I'm quite sure an alien ship could sneak through if they wanted and carefully planned to avoid such radar beams. PiusImpavidus (talk) 20:24, 8 October 2022 (UTC)

The 900 yard wide asteroid Hermes was discovered 2 to 3 million miles out in 1937 when it was way too dim for the naked eye. Maybe even cats couldn't see it? It was getting 11 miles closer every second and finally reached closest approach 2 days later (still billions of feet above sea level though at least some cats could now see it). Sagittarian Milky Way (talk) 22:54, 8 October 2022 (UTC)

The number of times the planet Venus is mistaken for an unidentified flying object would surprise you. Reports of a strange light in the sky are sometimes traced back to the full moon. 2A00:23D0:6D1:2301:9D6B:19E5:3932:5A51 (talk) 12:49, 9 October 2022 (UTC)

Years ago, my father, who was the secretary of the local astronomy club, got a phone call from the police station in a different city. Apparently the police had been unable to contact the public observatory there after being called by many people who had seen something strange in the sky: two bright dots very close together. Had two planets collided? An alien ship? It turned out to be a conjunction of Jupiter and Venus. PiusImpavidus (talk) 09:13, 10 October 2022 (UTC)

• Detection of intelligent extraterrestrial life is something that try to do, the SETI Institute is one of the more famous organizations that perform and fund this kind of research, but see also Search for extraterrestrial intelligence for more information. If we were to detect an alien civilization capable of interstellar flight, it's going to be one of those studies that does so, not some yahoo in New Mexico probably blitzed on peyote and cheap beer... --Jayron32 18:20, 11 October 2022 (UTC)

self-unscrewing screws

I have a desk at home made partially from glass. They probably stopped making such. My desk is probably 25 years old. There is a glass surface on the top and a metal surface below where you can reasonably place your keyboard and the mouse. The metal surface can telescopically be moved back and forth. It is a computer desk.

Recently while I was working and needed to finish a letter quickly, the metal surface collapsed on to my knees. It turned out this surface rests on a metal rod, and the rod is attached to a metal leg with a screw. I found this screw on the floor. The screw had been sitting there probably for 20 years. Why did it come out? Over the years it unscrewed itself for a tiny angle counterclockwise. And finally my desk dropped. I could describe many similar episodes with other screws and with other mechanisms or constructions. And why do the screws always unscrew themselves, never tighten themselves up? And why does the screw is given this push which is circular although I don't see anywhere rotating parts in my desk? AboutFace 22 (talk) 21:28, 8 October 2022 (UTC)

When the screw was originally screwed in, force was applied, compressing the wood around the screw to make place for the screw. The compressed wood is pushing back. Almost all force is orthogonal to the axis of the screw, but a tiny amount has a net component pushing the screw out. In a world without friction the screw would come out immediately, but the tiny force pushing the screw out cannot overcome the (static) friction. However, occasionally some other force, like when the desk is moved or bumped into, for a brief moment of time exceeds the friction. This causes a microscopic rotation of the screw with a bias towards getting it out. I suppose that 20 years of such microscopic rotations can add up to a very macroscopic one.  --Lambiam 21:57, 8 October 2022 (UTC)

The desk joint is described as all-metal, not metal-into-wood. Presumably the leg is more like a nut (pre-formed threads) than your description as a wood-screw. Bolted joint is our main article. It has a ton of technical engineering and math detail. DMacks (talk) 05:45, 9 October 2022 (UTC)

Why does vibration loosen screws?. Alansplodge (talk) 11:33, 9 October 2022 (UTC)

I have a metal chair. The legs are kept from splaying out (and depositing me on the floor) by two horizontal bars which screw into the legs at either end. Once the screws have loosened a little the legs will splay out a bit. Any tightening vibration will not tighten them because it would have to overcome the weight of the structure acting to move the legs outwards. Any loosening vibration is aided by this and eventually the screws would disengage. However, before this happens a wobbling of the chair warns me to retighten the screws. All this could be avoided by having the screws protrude beyond the channel in the leg which they screw into and placing a nut on the exposed end, but then you would have the problem of hands coming into contact with sharp pieces of metal. 2A00:23D0:6D1:2301:9D6B:19E5:3932:5A51 (talk) 12:46, 9 October 2022 (UTC)

The general problem of loosening bolts and nuts can be obviated by the use of Thread-locking fluid. {The poster formerly known as 87.81.230.195} 90.193.128.129 (talk) 16:01, 9 October 2022 (UTC)

• Screws fall out all the time. The world is an imperfect place... --Jayron32 18:22, 11 October 2022 (UTC)

October 9

Recent hunter's moon

Today Polish media announced a reddish hunter's moon with peak visibility across Poland on 9 October at 22:54 local time and other sources confirm the date. The visibility was clear, without clouds, and when I looked out at that time the full moon appeared ordinary with its pale yellow color and size. What went wrong? Brandmeister^talk 22:50, 9 October 2022 (UTC)

22.54 would be far too late see an orange hunter's moon. You would need to observe it shortly after sunset. Shantavira|^{feed me} 08:32, 10 October 2022 (UTC)

A red moon can appear during a lunar eclipse, which can only happen at full moon, but didn't happen at this full moon, or when the moon is very low in the sky. 22:54 local time was the exact moment of full moon, but that's not so important. It takes about 12 hours to clearly see the difference between a full moon and an almost full moon. To see a red moon, you'd have to look right after moonrise, the exact moment of which depends on your location. At full moon, moonrise is at about the same time as sunset.

There was nothing really special about this full moon. All full moons (except those with an eclipse) look about the same, the only difference being the position in the sky. The place in the sky where you can see the full moon is about the same as where you can see the sun half a year later. The variation in size is too small to notice with the unaided eye.

It happens quite often that the media tell about some special full moon that is in fact not really special. PiusImpavidus (talk) 08:56, 10 October 2022 (UTC)

It's been happening a lot more recently, dunno why. Farmers' Almanac and other such things have always listed the various names for the various moons, but for whatever reason they've become more popular to talk about in "gosh wow" media. Likewise "supermoons". --jpgordon^{𝄢𝄆𝄐𝄇} 20:52, 10 October 2022 (UTC)

I agree, this modern fad for calling all full moons by some bizarre name which purports to come from some ancient tribal origins is absurd and misleading. I suggest the September full moon should be called the "Strictly Come Dancing Moon" because it occurs when that programme commences its season on the television. Yes, absurd isn't it, but no more absurd the the "Strawberry Moon" Richard Avery (talk) 14:24, 11 October 2022 (UTC)

I have noticed the same tendency on social media posts by people with a superficial interest in astronomy. They will trumpet very minor and repetitive fluctuations in moon phases or planetary alignments as a very big deal without any genuine evidence, and without presenting proper context, and applying dramatic names derived from folklore or pop culture to utterly routine astronomical events. Cullen328 (talk) 05:43, 11 October 2022 (UTC)

Our article supermoon introduces the word "micromoon." That's a new one on me, and there's no indication of what the name means. As to publicising the names of the lunar months, this may be related to some of them having been named ahead of the introduction of a common Easter date. The month in which Orthodox Easter falls (which currently begins at earliest on 17 March and at latest on 14 April) is Miri, while the third month before that (the twelfth and last of the year) is Paul. As the tropical year contains more than twelve lunar months, every second or third year Paul is followed by Paul II. - 2A00:23D0:511:4601:5CDB:1C06:42BD:A049 11:01, 11 October 2022 (UTC)

In general I agree with the foregoing, the press love a "gee whiz" story. However in the case of the harvest moon there appears to be a bit more to it than that. The OED has the earliest recorded use of harvest moon in 1709 "Seventy Harvest-Moons Fill'd his wide Granaries with Autumnal Joy", so hardly a "modern fad". The connection between the harvest moon and granaries is not co-incidental, when trying to get in the last of the corn an early, bright moon allowed a pre-industrial agrarian world to continue working. You can't easily harvest by candles or torches and flames are a seriously bad idea in a field full of flamable grain. Martin of Sheffield (talk) 14:46, 11 October 2022 (UTC)

Of course the names aren't a "modern fad" -- making a fuss about them every month is the modern fad. --jpgordon^{𝄢𝄆𝄐𝄇} 14:55, 11 October 2022 (UTC)

There was a trend in social media a few years ago when people would post something like "This year, October 13 falls on a Friday, making it the most evil day of the most evil month, an occurrence that only happens once every 856 years" or some bullshit like that. Even 5 seconds of thinking reveals that there's a Friday October 13th on average about every 7ish years or so, so most people will experience several in their lifetime, not once every millenium. But people post things on Facebook because they think they might be interesting, not because they might be true. It's the same with these moons. Even the most unusual "moons" like blood moons or blue moons or "supermoons" happen every few years at the outside. Even lunar eclipses happen about twice per year, so even accounting for the fact that they are only visible on part of the earth each time, most people will see one every few years or so. --Jayron32 18:14, 11 October 2022 (UTC)

The version I've seen is "This year there are 5 Thursdays in October, something that only occurs once every 856 years". That such rank stupidity will be instantly believed and breathlessly re-shared is a terribly sad indictment on everyone involved. -- Jack of Oz ^{[pleasantries]} 21:25, 11 October 2022 (UTC)

Discussed at Wikipedia:Reference desk/Archives/Mathematics/2015 February 17#Is it an anomaly that the month of February 2015 contains four occurrences of each day of the week? (February 10). 88.111.188.163 (talk) 17:08, 12 October 2022 (UTC)

800 years (ones the oldest millennial could remember if they die at 85 in bold):

5 Thursdays in October: 1585, 1586, 1587, 1591, 1592, 1596, 1597, 1598, 1602, 1603, 1608, 1609, 1613, 1614, 1615, 1619, 1620, 1624, 1625, 1626, 1630, 1631, 1636, 1637, 1641, 1642, 1643, 1647, 1648, 1652, 1653, 1654, 1658, 1659, 1664, 1665, 1669, 1670, 1671, 1675, 1676, 1680, 1681, 1682, 1686, 1687, 1692, 1693, 1697, 1698, 1699, 1704, 1705, 1709, 1710, 1711, 1715, 1716, 1720, 1721, 1722, 1726, 1727, 1732, 1733, 1737, 1738, 1739, 1743, 1744, 1748, 1749, 1750, 1754, 1755, 1760, 1761, 1765, 1766, 1767, 1771, 1772, 1776, 1777, 1778, 1782, 1783, 1788, 1789, 1793, 1794, 1795, 1799, 1800, 1801, 1805, 1806, 1807, 1811, 1812, 1816, 1817, 1818, 1822, 1823, 1828, 1829, 1833, 1834, 1835, 1839, 1840, 1844, 1845, 1846, 1850, 1851, 1856, 1857, 1861, 1862, 1863, 1867, 1868, 1872, 1873, 1874, 1878, 1879, 1884, 1885, 1889, 1890, 1891, 1895, 1896, 1901, 1902, 1903, 1907, 1908, 1912, 1913, 1914, 1918, 1919, 1924, 1925, 1929, 1930, 1931, 1935, 1936, 1940, 1941, 1942, 1946, 1947, 1952, 1953, 1957, 1958, 1959, 1963, 1964, 1968, 1969, 1970, 1974, 1975, 1980, 1981, 1985, 1986, 1987, 1991, 1992, 1996, 1997, 1998, 2002, 2003, 2008, 2009, 2013, 2014, 2015, 2019, 2020, 2024, 2025, 2026, 2030, 2031, 2036, 2037, 2041, 2042, 2043, 2047, 2048, 2052, 2053, 2054, 2058, 2059, 2064, 2065, 2069, 2070, 2071, 2075, 2076, 2080, 2081, 2082, 2086, 2087, 2092, 2093, 2097, 2098, 2099, 2104, 2105, 2109, 2110, 2111, 2115, 2116, 2120, 2121, 2122, 2126, 2127, 2132, 2133, 2137, 2138, 2139, 2143, 2144, 2148, 2149, 2150, 2154, 2155, 2160, 2161, 2165, 2166, 2167, 2171, 2172, 2176, 2177, 2178, 2182, 2183, 2188, 2189, 2193, 2194, 2195, 2199, 2200, 2201, 2205, 2206, 2207, 2211, 2212, 2216, 2217, 2218, 2222, 2223, 2228, 2229, 2233, 2234, 2235, 2239, 2240, 2244, 2245, 2246, 2250, 2251, 2256, 2257, 2261, 2262, 2263, 2267, 2268, 2272, 2273, 2274, 2278, 2279, 2284, 2285, 2289, 2290, 2291, 2295, 2296, 2301, 2302, 2303, 2307, 2308, 2312, 2313, 2314, 2318, 2319, 2324, 2325, 2329, 2330, 2331, 2335, 2336, 2340, 2341, 2342, 2346, 2347, 2352, 2353, 2357, 2358, 2359, 2363, 2364, 2368, 2369, 2370, 2374, 2375, 2380, 2381

5 Thursdays in February: 1596, 1624, 1652, 1680, 1720, 1748, 1776, 1816, 1844, 1872, 1912, 1940, 1968, 1996, 2024, 2052, 2080, 2120, 2148, 2176, 2216, 2244, 2272, 2312, 2340, 2368

Decade starting on Sunday: 1640, 1690, 1730, 1860, 1950, 2040, 2090, 2130, 2260, 2350

Latest possible Easter: 1666, 1734, 1886, 1943, 2038, 2190, 2258, 2326

Non-leap Olympic years: 1700, 1800, 1900, 2100, 2200, 2300

Earliest possible Easter: 1598, 1693, 1761, 1818, 2285, 2353

Leap centuries: 1600, 2000

Millenniums on Friday night or Saturday night: 2000. Once per 2,000 years.

Halloween blood moons (50 hours of Halloween worldwide): None. Next 2441 AD only time zones UTC+12 to 14.

That are also blue and hunters: All of them, it's guaranteed.

That your hometown can see on its actual Halloween night (dusk to midnight): About once per 4,000 years if clouds block half of these, a bit commoner where it's fall instead of spring.

That are also supermoons: >10 millenniums.

A total solar eclipse at the roof of your birthplace on your birthday: 260,000 years if clouds block half the events.

The chance of being born during a total solar eclipse: 2 minutes per 360 years. After accounting for clouds and non-emergency C-sections being delayed to see could be 1 per 200,000,000 births.

Century starting on Sunday: NEVER!!!!!!!

Even with 8 chances per cycle (1600, 1601, 1700, 1701, 1800, 1801, 1900 and 1901) Sunday is never used. No other weekday misses all 8 (Julian centuries starting Sunday: 400, 601, 1100, 1301, 1800) Sagittarian Milky Way (talk) 00:10, 13 October 2022 (UTC)

Point made, but with a couple of errors. Decades start on 1641 ... 2351; centuries start on 1601 ... 2001 and millennia on 2001 etc. Martin of Sheffield (talk) 08:09, 13 October 2022 (UTC)

The 165th decade starts 1641 but everyone uses 1640s instead. The 21st century and 3rd millennium are not the 2000s yet 2000 was a bigger party. Thanks a lot backwards Romans. India was probably already using the modern number system (didn't reach modern shape yet) by the Roman heyday which determined which backwards numerals the inventor of AD would use in 525 AD. There was one last chance to make at least the Anglosphere's millennium 2000 in the 74th decade as Bede popularized AD, he can fix it but alas Europe would continue using Roman numerals for general purposes for centuries more. Tacking on a year 0 to AD (but not BC as BC is a much newer invention) would also have the added benefits of being able to add 32.0 to 2022.0 if wondering how many years ago October 13th, 32 BC was, and bringing the birth of Jesus a little closer to December 25, 1 BC. As Jesus was born about 4-8 BC and in the summer. Sagittarian Milky Way (talk) 20:32, 13 October 2022 (UTC)

Why should every other decade suffer because decade 0 was defective, missing a year zero? Oh wait, we argued this to the ground around Y2K (or Y2K+1). --jpgordon^{𝄢𝄆𝄐𝄇} 21:22, 13 October 2022 (UTC)

An odd couple of posts IMHO. Year numbers are not completed years like ages (but then again, consider that a 40 year old man in in his 41st year), but the year in which the event occurs. Something that occurred 6 months after the arbitrary start of AD was in the first year of AD, so June 1 AD. Something that happened 12 months previously was in the first year BC, so June 1 BC. Year 0 is a mathematician's erroneous dream, it is not a number line nor yet a missing year or a "defective decade". It simply cannot logically ever have existed, just as both Dionysius Exiguus and Bede wrote. Martin of Sheffield (talk) 21:45, 13 October 2022 (UTC)

B1950.0, J2000.0, 1900.0 1875.0, December 31.5 GMT, 2011.5 (on some star and "planet path this year" maps in paper books, the meridians move less than 0.014 degrees per year yet they still change the half year every year). Damn straight it should be extendable to a number line. If their numbers were like 3888.9 instead of MMMDCCCLXXXVIIIS····· (and 11/12ths) then year zero would probably exist. And maybe Jesus would rise Monday morning? (Saturday, Sunday, Monday — 3 days). In some American cities I think the addresses are the exact number of feet of latitude or longitude from something yet the streets can still have traditional names like 10th or Oak. So North 1st Street might be 1,000 feet north of Main and 1001W East 1st Avenue can't exist cause the center of the property would have to be 1 foot north of the center of 1st Street but a cop could write the body was at about N1001 E940. Or something like that. Two intersecting number lines far more precise than 1 block from just a street grid, now that's advanced! Sagittarian Milky Way (talk) 01:12, 14 October 2022 (UTC)

October 10

Why not travel to Mars in a straight line?

My understanding is that when we send a space craft to Mars, the ship goes into an orbit around the Sun like this and the ship's orbit eventually intersects with Mars' orbit. Why not go in a straight line from Earth to Mars? That would certainly be the shortest distance. I'm guessing that takes more energy? Pealarther (talk) 21:57, 10 October 2022 (UTC)

Going in a proper straight line would take very much energy indeed. And you would need to aim very carefully not to miss. But more generally, for any plausible spacecraft, such an approach does not work. Remember that you don't only have to match position, you also need to match speed. In other words, both when departing Earth and when arriving at Mars you must necessarily have the same position and the same speed as the corresponding planet. Usually, the most efficient way to do that is a Hohman transfer orbit. --Stephan Schulz (talk) 00:19, 11 October 2022 (UTC)

Yes, the path shown uses the least energy. Bubba73 ^{You talkin' to me?} 05:44, 11 October 2022 (UTC)

Hello, Pealarther. Start by reading Orbital mechanics several times until you understand it. Then read the references in that article until you understand them. Then you will understand the answer to your question. Cullen328 (talk) 05:49, 11 October 2022 (UTC)

See also Interplanetary Transport Network.  --Lambiam 06:09, 11 October 2022 (UTC)

• The ideal path to Mars is the one that follows a geodesic, which is (in some sense) a "straight" path through curved spacetime, which has been curved through gravity (see General relativity for how this works). The analogy of a geodesic in terms we can visualize is a great circle path on a globe. The most efficient path between two points on earth is along a great circle. This path is not straight and curves when viewed in three dimensions, but in a sense it is straight along the 2D curved manifold that forms the surface of a sphere. In the same way, the most efficient path between two points in 4D spacetime is a geodesic. If you want to think about it in non-GR terms (i.e. not thinking about curved spacetime), then the most efficient path to Mars (the one that uses the least fuel) is the one where you spend the least amount of energy fighting against the gravity. Since the earth, the sun, and other planets all exert gravitational forces on your spacecraft, fuel spent fighting against those forces unnecessarily is wasted fuel. The greatest effect is going to be that of the sun; since the spacecraft leaving the Earth already has the earth's momentum, it's going to want to continue to orbit the sun in an ellipse under the sun's gravity. The most efficient path to Mars is one that doesn't fight against that tendency, and so will be a curved path. --Jayron32 12:29, 11 October 2022 (UTC)

Photon duration

Today we know how to generate photons individually or a few units. So a photon is emitted at a time t1 and from a time t2 it is considered to have left (like a car with a front and a rear), if so, does its length correspond to its wave length ?

In this Nature article they used "pulse of light", so a pulse have a Start time t1 and end time t2, right ? Malypaet (talk) 22:06, 10 October 2022 (UTC)

References

A photon exhibits wave–particle duality. Viewed as a wave, it has no definite extension in space, and viewed as a particle, it has no definite wavelength. The wavelength of a photon is directly proportional to the inverse of the magnitude of its momentum. Position and momentum are complementary variables. So, by the uncertainty principle, the more precisely we determine the wavelength, the less we know about its position.  --Lambiam 05:54, 11 October 2022 (UTC)

The photon either has left, or it has not. There's no time when it's in the process of leaving. PiusImpavidus (talk) 09:11, 11 October 2022 (UTC)

This is like saying, either Schrödinger's cat has died, or it has not. Welcome to the world of quantum weirdness.  --Lambiam 15:04, 11 October 2022 (UTC)

When you take a measurement, the photon has either left or not. Otherwise, it can be in a superposition of having left and not having left (in which case the photon hasn't been created), but the photon is never in the state of leaving, which is the state OP implied. Schrödingers cat however can be dying, in addition to being dead and alive at the same time. PiusImpavidus (talk) 15:13, 12 October 2022 (UTC)

Photons, insofar as they are particles, are point particles. As such, they have no dimensions, and take no time leaving. They don't have sides or edges as such. --Jayron32 12:21, 11 October 2022 (UTC)

Viewed as wave packets, however, photons do have a spatial extension.  --Lambiam 14:56, 11 October 2022 (UTC)

(edit conflict)Kinda-sorta-in-a-way-but-probably-not-really-depending-on-how-you-think-of-it. The wave in this sense is a probability distribution of some property of the particle in question (its wave function), and while "location" (Δx in one dimension) is one of those properties, the "wave packet" in this case is a complex function, and while it is common to treat the "real part" of this function as something like "location", eh? It's really that the wave packet represents the uncertainty in the location of the photon itself; when you do any measurement of the photon, either at emission or absorption, it acts as a point particle. It doesn't have any dimensions when you measure it, so it doesn't take any "time" to absorb or emit; it doesn't behave as though it has a front or back edge. --Jayron32 16:25, 11 October 2022 (UTC)

(post EC comment) Or what Nemur said below, which is much better than my comment. --Jayron32 16:25, 11 October 2022 (UTC)

Or, to resolve the condundrum, (if we're being really rigorous), we have to stomp on the notion and shout loudly in to the abyss: "photons don't work like that!" And then we can rest easy knowing that we don't really know...

Really, the issue comes down to a semantic problem; an issue of trying to use natural English language to describe something for which natural English language is a poor representation.

The original post used an interesting word-choice - it asked about when a photon had left. What exactly does that mean? What exactly does it mean for a photon to "leave"?

If we can use some physics-ese to define precisely what "leaving" means for a photon, we can probably answer with scientific rigor. Has a photon "departed" or "left" from some well-defined point in space only when the expectation value for the electric field falls below some threshold? If this is what "departure" means for a photon, we can answer precisely - albeit, couched in a statistical, predictive sort of manner - by solving for some quantum-mechanical wave equation, or something. The details of this boring equation, I leave to the physicists, who already know how to solve it (it's trivial!)

In my experience, most of the conundrums of quantum mechanics stem from trying to force a vague, plain-language description onto the system. In large, every-day macroscopic systems, the vagueness is not quite so apparent - but when we try to translate plain language descriptions onto the microscopic scales that we care about for most of the text-book problems of quantum mechanics, those ambiguous, plain-language words make for ill posed problems. This is why many physicists quip: "shut up and calculate."

Now, to first order, that sounds like we're being dismissive about a sophisticated question; we're saying "stop asking that!" And that's not a very nice or educational thing to do. But... there's nuance, here. So let's rephrase "shut-up-and-calculate" into something that is both more polite, and more aligned to what we're trying to say: "The words you're using, in the English language, are not a good way to describe photons. We'd rather teach you to use a different language - mathematics - and then we will politely ask you to phrase your question using this language - because this language will be better at expressing questions and answers relating to the way photons really behave."

And that's why if we pull out any of our books-about-photons - I mean, take your pick! I've got a shelf full of them, if you'd like to read them! - as soon as they get into the nitty-gritty details about photon behavior, they jump out of English and codeswitch into physics-ese mathematical language. We don't talk about "when photon has left." Rather, we reference Equation 26.3 in Section 12, and in order to understand it, you need to have learned how to read it in its native language.

Fundamentally, this is not so different from any other academic pursuit. We can teach an introductory class on Roman history in English, but an advanced study of the topic invariably requires learning at least a little Latin. To English, certain things, well, do not translate, well.

Nimur (talk) 16:14, 11 October 2022 (UTC)

I did mention some books, for further reading -

The Griffiths' series -

• Introduction to Electrodynamics
• Introduction to Quantum Mechanics (book)

Jackson's famous book -

• Introduction to Electrodynamics

...

Of course, As I've said many times before, in many years of responding on the reference desk - don't underestimate this stuff.

I quote myself, here:

Normally, people read this book after they have completed a full four or five years of prior full-time preparation as full-time undergraduate physics students, because many very smart people find this mathematical content to be just at the limit of their mental capacity for comprehension after four or five years of full-time preparation. If you are not presently writing and solving wave equations for electrodynamics in conventional cases, you probably are not going to have great success writing and solving wave equations for nontrivial relativistic cases; and if you plan to understand general relativity without solving any equations, you're not going to get very far.

So - and I really don't want to be dismissive - the answer is, it ain't easy to answer questions about quantum mechanical behaviors of photons - not correctly and concisely, at least. Very smart people typically spend years trying to understand the complexity.

Nimur (talk) 16:30, 11 October 2022 (UTC)

A radar which emits a pulse of an electromagnetic beam of a certain energy for one microsecond between a time t1 and t2 is very real and trivial. Either we have n waves (E=hv) at // and there we know the beginning and the temporal end of each wave (t1 and t2), or we have a flux of n photons (E=hv) at // and there they must each be framed within an interval < t2 - t1? Sorry, but a point is in the realm of math, not physics. This impulse, when it encounters an obstacle, comes back to us at a time t3, it reacts like classical mechanics, simple ballistics. There's a very old cartoon from the beginning of computing where engineers disassemble a huge computer looking for a fault, next to them is a cleaning lady leaning on her broom and showing them the plug unplugged: "Is that what you're looking for?" Malypaet (talk) 20:41, 11 October 2022 (UTC)

But you asked about a single photon, not a pulse. A photon has no size and cannot be known precisely in location and momentum simultaneously. Also it might not even exist if you don't look at it, according to this year's Nobel prize winners (or something like that) Rmhermen (talk) 04:59, 12 October 2022 (UTC)

Exactly! The reformulated question posed an "either/or" scenario - and Lambian already described earlier (by bringing a cat into the mix) that this kind of "binary" yes/no certainty is at least inapt.

Even if we restrict to macroscopic systems, simply determining whether we did receive a signal devolves into a game of statistics and probability and confidence.

Every real signal has noise. Every signal! This is a stronger statement than it might initially appear. Noise isn't some mere annoyance that we can will into oblivion. It's not even some "practical detail" that we can usefully ignore in theoretical physics. We cannot construct a perfect (frictionless, while we're at it!) machine in our lab that observes signals with zero noise - not even in a purely theoretical construction. Some noise is an annoyance of unrefined engineering; we can hire better designers or purchase better parts to take this noise out of our machine (real or theoretical). But... other noise is inherent to the physics, and we may not ignore it!

At the most fundamental level - the regime of quantum mechanics - we have quantization noise - the inherent uncertainty involved in correctly counting a small integer number of physical events. If the number of events is "either zero or one," the best we can say is that we "either did or did not observe one single event, with some level of confidence."

How can we boost our confidence? We can re-take the measurement - but you see, that would literally entail observing a second time, for which the event either did or did not occur! If the first event had uncertainty and never even arrived, the second experiment might be the the first observance of the single event; or it might be a second repeated observance of two identical events, or maybe we failed to observe either, or maybe we saw the event only on one of two tries (first, or second attempt?...) and so ... this is noise. It cannot be avoided. As I said, even if we define "photon present" as equal to some measured level of electric field ... how do you know that electric field came from your photon and not from my other thermal photon that I (a notoriously troublesome nearby emitter of white noise) fired toward your detector at exactly the instant to interfere with your finely-crafted imported artisinal photon detector?

And this bizarreness - this "quantum weirdness" - as Lambian said, and as Rmhermen said, is really important stuff. Great minds have spent a lot of cycles stewing on it. As Rmhermen also said - this has something to do with some prestigious development in modern physics.

What we can do here is point our readers toward resources, and maybe inspire them to be enthusiastic about the miraculous complexity of even the most simple small particle of our universe.

We cannot, however, completely, correctly, concisely explain "the photon." It is too mysterious an animal to describe in a few words.

Nimur (talk) 15:37, 12 October 2022 (UTC)

The radar pulse is a group of photons and is a very concrete example contradicting the answers given to me. And for the photon that doesn't exist if you don't look at it, that's science fiction. So for a blind person, the moon does not exist? And yet it exists, regardless of whether we can see it or not. It is the same for a photon in a radar pulse, we are sure that it travels in this pulse. Here we know its speed, its wavelength and its position at least somewhere in the pulse. Malypaet (talk) 21:29, 12 October 2022 (UTC)

What Rmhermen said. If you change your question midpost than the answer will of course change too. One photon is a point particle and has no dimensions, and takes no time to interact with what is absorbing it. A group of photons has a spatial component, and does take an amount of time to interact with what is absorbing them. --Jayron32 10:50, 12 October 2022 (UTC)

The easiest way to simplify the description of one complicated thing is to add lots more of them!

Yeah, we treat individual photons differently than we treat groups of photons, ... but I'm already feeling that the original question has become less coherent as it progresses forward along its light cone...

Nimur (talk) 15:50, 12 October 2022 (UTC)

Less coherent? Do you frequently make such apt puns? --Jayron32 11:34, 13 October 2022 (UTC)

October 11

Unidentified fruit

Mystery fruit...

Cross-section if that helps.

Can anybody help identify this fruit on a shrub found at Abbey Gardens in Bury St Edmunds (East of England) today? Fruits are about 2 cm across and slghtly downy, a bit like peach fuzz. A taste test was not unpleasant but inconclusive and I'm still alive at the time of writing. Alansplodge (talk) 16:35, 11 October 2022 (UTC)

Quince? Bazza (talk) 16:39, 11 October 2022 (UTC)

Ah yes, you may be right. I was thinking that it was far too small to be a quince, but I see that some flowering cultivars - like this one - have smaller fruits. Dissecting the sample I brought home matches the illustration in our article and it is indeed "fragant". Alansplodge (talk) 16:53, 11 October 2022 (UTC)

• So it may be useful if you happen to be at risk of scurvy (see 2nd paragraph at link). --174.95.81.219 (talk) 07:24, 12 October 2022 (UTC)

  Also it was allegedly what the serpent used to tempt Eve in the Garden of Eden, at least according to a movie I saw once. Does anyone know what movie? I think it had Rosie Perez appearing on Jeopardy, with Alex Trebeck appearing as himself, and she answered that question. --Trovatore (talk) 16:23, 12 October 2022 (UTC)

  Found my own answer -- appears to be White Men Can't Jump. --Trovatore (talk) 16:36, 12 October 2022 (UTC)

You might also consider one of the Chaenomeles. DuncanHill (talk) 17:00, 11 October 2022 (UTC)

Oh, I see you have linked to one of them. The Flowering Quinces are not cultivars of the Quince, they are a different genus. DuncanHill (talk) 17:03, 11 October 2022 (UTC)

We have Quince#Cultivars which are of the same tribe, but Pseudocydonia and Chaenomeles are not, despite all are being known as "quince" in English. I can't see an exact match so far, but won't be losing any sleep if we can't pin down an exact species. Alansplodge (talk) 17:18, 11 October 2022 (UTC)

• It looks to me like some kind of citrus cultivar rather than a quince. There are hundreds of different citrus fruits (maybe thousands) and while commercial varieties available in western supermarkets account for only a few (lemon, persian lime, key lime, meyer lemon, grapefruit, mandarin, navel orange, tangerine, maybe pomelo and kumquat) there are many more varieties than most people are familiar with. Maybe a citron or a papeda of some type. --Jayron32 18:40, 11 October 2022 (UTC)

  Citruses rarely survive the winter, unless brought indoors, in Britain. The leaves are smooth-edged too, which is un-citrus-like. DuncanHill (talk) 18:46, 11 October 2022 (UTC)

The stem and leaves are very citrus-like. It is definitely Citrus trifoliata. Thriley (talk) 18:51, 11 October 2022 (UTC)

• Looks like Citrus trifoliata, a hardy citrus common in England. Thriley (talk) 18:43, 11 October 2022 (UTC)

Sounds plausible. I have added a cross-section - it does look a bit citrus-like inside and has the "fuzzy texture" mentioned in our article. Alansplodge (talk) 21:38, 11 October 2022 (UTC)

Thank you for the photo. You can see the Juice vesicles found in citrus fruit. Thriley (talk) 21:52, 11 October 2022 (UTC)

I am persuaded. Many thanks. Alansplodge (talk) 12:38, 12 October 2022 (UTC)

Resolved

Energy delivered by a machine gun

I read this online: "kinetic energy of a bullet = k kinetic energy of n bullets = nk According to the law of conservation of energy, the kinetic energy of the bullets must be equal to the work done by a machine gun per second".

So can I write that the energy "E" delivered by a machine gun with a firing frequency "f", "F" = "f" without time, is : "E = kF" ? — Preceding unsigned comment added by Malypaet (talk • contribs) 21:07, 11 October 2022 (UTC)

No, you can't. The addition "per second" makes no sense in the "online" statement. Conservation of energy means "kinetic energy = work". When time is brought into this, you talk about power. --Wrongfilter (talk) 08:07, 12 October 2022 (UTC)

So if I reformulate, I can only consider the kinetic energy of the group of bullets over one second "E=kF", (even if they were emitted in sequence at different times). But for the machine gun I have to consider its power "P=kf"? On the other hand, for a target (a regid ball with a mass a thousand times greater for example) which receives this energy over one second, it is indeed energy, isn't it? Malypaet (talk) 08:47, 12 October 2022 (UTC)

What does "F" stands for? Is it a dimensionless quantity? You ask several questions of the nature of "which is better/more correct?". The answer depends on what you are seeking to achieve, which is not entirely clear. In either case, depending on what is given and what is wanted or needed, one can consider either energy or power, or both.  --Lambiam 09:32, 12 October 2022 (UTC)

Compared to earlier questions, this time our OP has asked a surprisingly easy question: "can I write...?"

Yes! You can write this! It's free country, (I think! I'm not sure what country you're in, but it sounds like it has an alarming amount of machine-gunnery, which causes me to wonder about the relative merits of "freedom" in so-called free countries)... but let's assume (with, perhaps, some loss of generality) that it is a free country. You can write this mathematical expression!

Does it help you to write this expression?

Do you find it therapeutic? Does it help you to understand photons, or machine guns? Does it help you to communicate your insight with others who study photons (or machine guns)? Does it help you design a better photon, or a better machine (gun? ... Please don't - we've got plenty of fine-enough of those machines already!)

Really, though, I read a lot of philosophy into the question. For what purpose do you express these ideas? For a practical one? If so ... the science reference desk is not a place to participate in practical design and engineering of machines (or guns).

Is it for a thought experiment of some kind? If so ... we can point you to better thought experiments, constructed by smart, well-respected authors. (I did link several introductory texts, above!)

Is it some form of artistic expression? If so, I commend it... I think! I applaud artistic expression, even if I don't particularly subscribe to its aesthetic. In this case, I interpret it as some kind of reactionary postmodernism extolling the absurdity of technological progress and the self-destructive nature of the human. But, ... the science reference desk might not be the place for it. Besides, as they say, viewers impose their own meaning on to art, so... let's not fall victim to pro-institutionalist interpretations. This is a free country encyclopedia where anyone may contribute. "Can I write...?" Yes! But Why?

In seriousness, our OP can write any equation they want - some equations are useful, some writings serve to encapsulate useful content, and the rest we call art, I think. Art, in all its forms, including open-form prose on public internet websites. Art, an abstraction that can provide a medium to reflect complex ideas and stimulate the minds of the viewer... easier to make and yet harder to define than science...

Nimur (talk) 16:16, 12 October 2022 (UTC)

October 12

Metal object on the top of styrofoam balls

A metal object on the top of a box of styrofoam balls (the kind used for filling a package) would not necessarily sink to the bottom (unless some shaking is applied). I imagine that that's because the friction between styrofoam balls, that locks them in place. Is this intuition right? And could you put some object on the top of a liquid with lower density in a similar way (without it sinking)? Bumptump (talk) 20:08, 12 October 2022 (UTC)

Water certainly has a high surface tension that allows you to float heavier objects carefully on it. Rmhermen (talk) 00:45, 13 October 2022 (UTC)

But could we say that, for example, a needle floating in water it's the same physical phenomenon as in the styrofoam balls case above? Bumptump (talk) 01:00, 13 October 2022 (UTC)

No, it is a different phenomenon; it has some superficial similarities, but (perhaps obviously!) solid materials differ from liquid materials (and perhaps non-obviously!) this manifests in profound ways when we study the complicated dynamics of such systems.

The behavior of a group of solid spheres in profoundly different from the behavior of liquid molecules - and despite the appeal of using analogy to model liquid molecules as "very very small" solid spheres, that's just not quite right.

We have an article on granular materials, which are an actively studied area of applied condensed matter physics.

Nimur (talk) 03:10, 13 October 2022 (UTC)

Part of the reason why the metal object stays on top of the styrofoam balls is friction. The other part is that the metal object can only move down when the styrofoam balls move up. The geometry may be such that the styrofoam balls must initially rise much faster than the metal object sinks, so we get a local minimum in the potential with the metal object still on top.

As you correctly observe, with a bit of shaking, the metal object will sink. In water, there's always shaking: Brownian motion. If we stop Brownian motion by freezing the water, the metal object can stay on top again. PiusImpavidus (talk) 09:42, 13 October 2022 (UTC)

Surface tension is sufficient if the object is small enough; things like paper clips and small needles and the like can be floated on water if one is careful to not submerge them under the surface. --Jayron32 11:02, 13 October 2022 (UTC)

Ships with no atmosphere

If Earth's atmosphere disappeared suddenly, would steel ships continue floating in water? (The role of air isn't addressed in Buoyancy.) On one hand, I think "no", because the vacuum would have essentially no mass, and I think the air filling the ship helps to make the whole thing lighter in relation to the water, and the ship's slight buoyancy in air makes it weigh less than it would in a vacuum. On the other hand, I think "yes", because the water would weigh much more than the vacuum, and the weight of ship + vacuum would still be less than the weight of the water that fills the same volume. 175.39.61.121 (talk) 21:00, 12 October 2022 (UTC)

The whole thing would be moot, water can not stay in liquid state in the vacuum. It will either freeze or become vapor. Cambalachero (talk) 21:24, 12 October 2022 (UTC)

While it's technically true that you can't have liquid water in equilibrium at zero pressure, the triple point pressure of fresh water is only about 612 Pa, less than a hundredth of an atmosphere, and it goes down as you add salt. I conclude that, if all the air suddenly vanished, the oceans would start to boil, but not very fast. There would be plenty of time to observe a ship floating. --Trovatore (talk) 06:44, 13 October 2022 (UTC)

I think any potential observer would have more important things to worry about than watching ships float.... --User:Khajidha (talk) (contributions) 17:25, 13 October 2022 (UTC)

"air filling the ship helps to make the whole thing lighter": Why would that be? I believe if you created a vacuum in a dome above water and put an empty ship inside (completely empty, without air) its walls would crumble with the water pressure outside. It was not designed for that. Empirical data would be needed to determine if this is right. Bumptump (talk) 22:05, 12 October 2022 (UTC)

OK, but the answer is that yes they would float. It isn't the air that makes them float it is the absence of heavy stuff. Greglocock (talk) 22:17, 12 October 2022 (UTC)

A vacuum tube floats in water. So, an object with as much of a vacuum as we can create on earth still floats. This is not about having a vacuum inside the ship. 97.82.165.112 (talk) 00:51, 13 October 2022 (UTC)

Actually, the air inside a ship has weight, so it makes the ship heavier. When the air is pumped out of an airtight-sealed floating container, it rises ever so slightly.  --Lambiam 05:27, 13 October 2022 (UTC)

The answer may be more complicated than it looks at the first glance. Air actually adds to buoyancy – the above-water parts of a ship experience buoyancy force (upwards) from air in which they are immersed. On the other hand, air also exerts pressure downwards on parts, whose lower surface is under water (mostly the bottom of the hull). So, if the whole ship is made of materials heavier than air, then disappearing of air will make the ship's draft to grow, the hull will sit deeper in water. However, if you mount a helium or hydrogen tanks (baloons) in it, they will be adding net buoyancy in air and net weight in vacuum. I can't estimate in my head what size the balloon should be compared to the hull itself to reduce the ship's draft on atmosphere removal. Let's imagine a normal floating toy balloon with a small weight attached to it. You can choose the weight small so that it floats just by touching the water surface. If you remove air, the balloon would fall and the weight would immerse in water. However, you cant make such 'ship' to sink this way: if the balloon's buoyancy force in air is (almost) enough to fly with the weight, it obviously will prevent the weight from sinking in water. --CiaPan (talk) 06:58, 13 October 2022 (UTC)

It can go either way. The structure of the ship above the waterline (excluding air-filled spaces) experiences buoyancy from the air, which will disappear in a vacuum. In the air-filled spaces below the waterline, air provides less bouyancy than vacuum. If the volume of the ship above the waterline is less than the volume of air below the waterline, the ship will rise when put in a vacuum. In a fully metal ship this is always the case, or it wouldn't float. If however the ship is loaded with something less dense than water (like oil), the ship may sink a little.

If the vacuum is high enough, the top few decimetres of water will be boiling, until it freezes. The vapour bubbles lower the density of the water, which can cause the ship to sink a bit, but not much. PiusImpavidus (talk) 10:27, 13 October 2022 (UTC)

• If we want to spherical cow this and ignore all of the complicating factors of the oceans boiling away and all the rest, of course the ships float. They float better, because air is matter and matter has mass. A ship filled with air is heavier than a ship filled with nothing. The ship filled with nothing will thus displace a smaller volume of water than a ship filled with air will. It will thus float higher in the water. --Jayron32 11:00, 13 October 2022 (UTC)

  Just to run this into the ground, that argument applies only to the part of the air in the ship that's below the waterline. The weight of the air above the waterline is cancelled by the buoyancy due to the air outside the ship. --Trovatore (talk) 16:41, 13 October 2022 (UTC)

  That's true, but because the ship is less buoyant in air than it is in water, there will always be (in air) a volume inside the ship which has air below the waterline. If we replace that space with vacuum, it weighs less. That means the volume of the steel+void now has a lower mass than a similar volume of water than did the volume of steel+air, and as such, will displace less water. Thus, the ship floats higher in the water, QED. --Jayron32 12:21, 14 October 2022 (UTC)

October 13

Planck relation and time

The kinetic energy of an asteroid is independent of time and energy in general, otherwise we speak of power in Watts. In Planck's relation the radiant energy depends on a frequency which is temporal. How is it possible ? — Preceding unsigned comment added by Malypaet (talk • contribs) 08:40, 13 October 2022 (UTC)

Sorry, what? Radiant energy is a function of temperature. See blackbody radiation. It is unrelated to kinetic energy. The first is about the motion of individual atoms and molecules, the second is about the motion of the entire object. Also, it's vague and unclear what you mean by "depends on". Dimensional analysis will also tell you that all measurements of energy have time embedded in their units; a joule is a kilogram meter squared per second squared (kg m² s^-2), or if you want to think in terms of unitless measure, energy is mass times distance squared divided by time squared. So your first statement is nonsensical; time is embedded in the measurement of energy. A watt, by the way, is a kilogram meter squared per second cubed, or power is mass times distance squared divided by time cubed. --Jayron32 10:54, 13 October 2022 (UTC)

Sorry, but 1 W is equal to 1 kg m² s⁻³.  --Lambiam 12:42, 13 October 2022 (UTC)

So corrected. --Jayron32 12:08, 14 October 2022 (UTC)

Effectively radiation energie (not radiant) and when you have "E=hv" you don't agree that "E" depends on "v" ? Malypaet (talk) 21:46, 13 October 2022 (UTC)

That's the energy of one photon. Your question is still unclear, which is why it is hard for people to respond meaningfully. Can you please explain again, using more details and in different words, what you are trying to understand? --Jayron32 12:17, 14 October 2022 (UTC)

Perhaps you meant asteroids are not losing or gaining energy with time. That is true for KE + PE (potential energy), but not KE alone due to differences in orbital speeds. In fact, since Compton's experiments 99 years ago scientists have known that radiated photons are particles that carry energy that gain or lose energy during collisions with matter. Photons also have an EM quantum wave nature that interacts with matter so as to impart or acquire their characteristic frequencies such as with Doppler effects. Modocc (talk) 21:32, 13 October 2022 (UTC)

If we compare with a bullets flow from a machine gun with firing frequency "f" (I'm peaceful, it's just a thought experiment), so that we can write the kinetic energy equation for a group of bullets "Ec=k 1/2mv2 f" this group must have been emitted over 1s with the constant "k=1s". In this case we can also write "h=k 1/2mv2" and "v=f", we then find "Ec=hv". There it is coherent for me as it would also be if we replaced the bullets by the peaks of an elementary wave, whereas for the Planck relation I cannot manage to find coherence with the frequency. Malypaet (talk) 22:25, 13 October 2022 (UTC)

If a pulse of light (possibly a single photon) has a certain energy E_p, then n such pulses have, together, the energy nE_p. If these pulses are fired with a frequency f, then there are fs pulses per second, giving a power of fE_p. This holds equally if we fire bullets instead of light pulses. The only difference is in the energy E_p. The photon energy of a single photon equals hν, whereas the kinetic energy of a single bullet equals ½mv². There is no relation between the frequency f of firing, and the frequency ν of the photon.  --Lambiam 06:16, 14 October 2022 (UTC)

Per Lambiam, and to clarify: The vibration of a light wave is unrelated to how often a photon hits a target. While both could be described as a "frequency", they are completely different and unrelated things. --Jayron32 12:13, 14 October 2022 (UTC)

October 14

Human surrogacy of animals

Basic idea: if you implanted a fertilised animal egg into a human womb, could it grow and be birthed (whether naturally or via cesarean). I think something similar was done with dogs and wolves, which are obviously closely related. My guess would be that you couldn't do it with say a human and a cat because of differing hormones, blood chemistry, etc. -mattbuck (Talk) 15:18, 14 October 2022 (UTC)

Dogs and wolves are not merely "closely related", they are different varieties of the same species. Dogs were domesticated from wolves, and can readily interbreed with them; the distinction between dogs and wolves is largely linguistic, with dogs being "wolves who we bred and trained to not eat our babies". All that being said, WHAAOE, see Interspecific pregnancy. That should help direct you to your answers. --Jayron32 15:46, 14 October 2022 (UTC)

That is the best description I have ever read about the domestication of the dog. I may have to steal it. --User:Khajidha (talk) (contributions) 18:06, 14 October 2022 (UTC)

Thanks. The wit there was inspired by CGP Grey's video on animal domestication. See Why Zebras are Terrible Horses. If my quote gave you a chuckle, CGP Grey's video will have you rofling your waffles. --Jayron32 18:18, 14 October 2022 (UTC)

mushy cough drops

I bought a bag of cough drops earlier this year. They are basically hard candies with menthol or something like that added. Since then there has been a heat wave here in CA (temperature reached maybe 33C on some days) though I don't know if that relates to the current situation: the cough drops are now somewhat mushy, like hardened chewing gun, underneath the outer layer but above the center. They are still usable but it is a bit annoying.

Any idea what has happened? Can they be fixed, such as by putting the bag in the freezer for a while? Current indoor temperature is reasonably cool. The cough drops are individually wrapped and idk if moisture could have gotten into them. The outer bag is not sealed. Maybe I should have put them into a sealed container. Thanks. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 19:57, 14 October 2022 (UTC)

ObPersonal: in my experience (over three decades, in the UK) this always happens to such cough drops if left long enough, even in a fairly stable environment. 'Long enough' might be a few months on an open shelf or similar in a hot summer, or a few years inside a more enclosed cupboard. I don't think the softening (and eventual leakage) materially effects the cough drops' effectiveness, but it does make them considerably more difficult to use. Freezing them might help with the latter (if you don't mind spitting out bits of wrapping paper).

In this recent Covid-enforced regime, with limited social contact and (until recently) mask-wearing in the proximity of others, I haven't had a cold or cough for nearly 3 years, so all my stored cough drops have deteriorated in this way. {The poster formerly known as 87.81.230.195} 90.195.172.49 (talk) 20:50, 14 October 2022 (UTC)

Hard candy mentions that it's harder if amorphous and softer if crystalline. That sounds similar to what can happen to liquid honey over time. You might try heating them up, rather than freezing them, and then letting the result set again, although that will give you a single bar of something like cough toffee, unless you get fancy and create a lot of little molds somehow.  Card Zero  (talk) 00:26, 15 October 2022 (UTC)

Thanks both. Hmm hard=amorphous soft=crystalline is the opposite of what I would have guessed. I will try heating them still in the wrapper. I hope the wax in the wrapper doesn't melt all over. I'll try with one or two of them first. Might use hot water, or a heat gun, or microwave. I wonder why they crystallized to start with. I see the bag they came in is the resealable type, but I haven't been sealing it because I figure that's to carry the bag around without spilling them, and this bag is sitting in one place. But, I may try sealing it, or making a point of keeping the next bag sealed. This is unfortunately a pretty large bag that will last a while, but it is ok. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 05:53, 15 October 2022 (UTC)

Decline in insect populations

Could it be caused by microplastics? Rich (talk) 22:13, 14 October 2022 (UTC)

Microplastic Polystyrene Ingestion Promotes the Susceptibility of Honeybee to Viral Infection, Deng et al (2021) thinks it might be, at least in honeybees. It's the first paper listed here (NB: it's a pdf that will want to download, which I have, but I haven't read it in full yet). There are other relevant papers in the list (not surprisingly) – have a browse!

You will have seen that the Wikipedia article Decline in insect populations doesn't mention microplastics (yet). {The poster formerly known as 87.81.230.195} 90.195.172.49 (talk) 03:16, 15 October 2022 (UTC)