Wikipedia:Reference desk/Archives/Science/2015 June 4

= June 4 =

The psychological aspect of spoilers and spoiler warnings
Have there ever been studies as to why people care about spoilers? As in, the practice of people avoiding plot details and/or people's enjoyment of media being affected by knowledge of said plot details: have there ever been studies of it from a psychological perspective? I'm aware there was that one study which concluded that people would actually enjoy a work more if "spoiled", but that study was to see if people's enjoyment of media would be affected by prior knowledge of plot details: it did not answer the question on why people care about spoilers in the first place. I'm aware I've asked similar questions to this before on the Entertainment and Humanities reference desks, but this time I'm seeking answers from a scientific/psychological perspective. Narutolovehinata5 tccsdnew 08:41, 4 June 2015 (UTC)
 * I'm at work and can't check for a link at the moment, but Cracked.com had a listicle that discussed the properties of "spoilage", though I don't recall if they touched on your specific question. Their material typically contains links for further reading, so searching their back catalog might get you something. Matt Deres (talk) 17:42, 4 June 2015 (UTC)
 * The question is addressing an aesthetic question as if it were one of epidemiology. The logic is quite simple. "A plot is a purposeful progression of logically connected events leading to the resolution of a climax."  If that's true, knowing the resolution before the climax and prolog ruins the progression and weakens the emotional impact of an unexpected or doubtful resolution. Very good dramas have many more aspects than just whodunnit, so may be worth seeing repeatedly.  But having the plot spoiled the first time is aesthetically offensive. μηδείς (talk) 23:02, 5 June 2015 (UTC)
 * I know this has come up here before, because I've cited this Peanuts cartoon in the past. It explains the situation perfectly. ←Baseball Bugs What's up, Doc? carrots→ 06:23, 6 June 2015 (UTC)

What are "Plasma tubes"?
Per this source and a new BLP about her, Australian astrophysicist Cleo Loi has apparently confirmed the existence of "plasma tubes inside the Earth's magnetosphere and extending into the plasmasphere."

These have, apparently, been theorized about for decades. I tried various searches but can't find out much about them, I'm thinking that "plasma tube" may not be the correct terminology. I also tried "Plasma duct", and "Plasma conduit" without much success. Searching Google for "flux tube" +magnetosphere gave possibly more relevant results. The published article uses the term "cylindrical density structures (ducts)".

• Can anyone fill me in on this phenomena and it's significance? 220  of  Borg 17:11, 4 June 2015 (UTC)


 * "Ducts" are theorized regions where electron density is not at equilibrium with the electron density elsewhere in the ionosphere (at the same altitude and latitude, or more precisely, at the same L shell). Such a duct, if it exists, would change the parameters of electromagnetic wave propagation, possibly enabling better signal or even amplification of signal.  Robert Helliwell was one of the original theorizers of this effect.  Along with many other researchers, Helliwell based his ideas on experimental observations of radio signals that traveled through the magnetosphere, including the famous experiment at Siple Station, Antarctica.  Such long-wave, long-distance propagation of radio signals causes radio energy to travel to very high (orbital!) altitudes, and allows scientists to probe the near-Earth space environment without the hassle of launching a rocket.
 * HAM radio enthusiasts are familiar with electron count in the ionosphere: total electron content and electron density are some of the most important parameters that govern the effectiveness of the skywave propagation effect. NOAA's Space Weather Prediction Center publishes TEC data, and as you can see, the resolution of the data is quite coarse.  If a duct existed, it would be a small, magnetic-field aligned region where these properties were different from equilibrium.
 * If you're really interested in this topic, you can buy Helliwell's book, Whistlers and Related Ionospheric Phenomena (1965), on several online retail websites. You can also find the idea of plasmospheric ducts cited in a wide variety of atmospheric/ionospheric research and radio science literature.
 * Nimur (talk) 17:47, 4 June 2015 (UTC)
 * So it's related in some way to Atmospheric ducting in radio communications as I suspected? And the correct term is Plasmospheric ducts? 220  of  Borg 00:19, 5 June 2015 (UTC)
 * Or is it more related to Tropospheric ducting? (Answers self: probably not, too low in the atmosphere.) 220  of  Borg 00:27, 5 June 2015 (UTC)
 * Those low atmosphere effects are distinct phenomena. We can surely find some similarities by analogy, but the governing physics is quite different, mostly because the atmospheric pressure is so different as such different altitudes.  At very high altitudes, we call the atmosphere the ionosphere: this is the region where non-negligible percentage of the gas molecules have ionized due to solar radiation.  At these altitudes, the small fraction of atoms and molecules that have ionized actually dominate the behavior of the bulk medium, because the air is too sparse to reach thermal equilibrium by way of ordinary gas dynamics.  Physicists who study this region of Earth are always looking for changes and deviations from equilibrium; a duct would be one such special-case.  Nimur (talk) 14:50, 5 June 2015 (UTC)

Age of Ultron's proposed extintion event
In the film Avengers: Age of Ultron the villain manages to rip a whole city off the ground (including, of course, the ground below the city) and take it to the sky, expecting to raise it beyond the atmosphere and then let it fall back to Earth, causing a mass extintion event, similar to the extintion of dinosaurs. The heroes manage to evacuate all the people and blow up the city, so that only small pieces fell to the ground.

Ignoring the part where the city floats to the sky, is the other part scientifically accurate? Is an object of that size and falling at terminal velocity from that distance enough to cause an extintion event? And what about the ending? Being so close to the ground, does it make a difference if it is a huge monolithic rock or a huge number of smaller rocks, but with the same combined size and all falling at terminal velocity anyway? Cambalachero (talk) 18:45, 4 June 2015 (UTC)


 * It was the Chicxulub_impactor that heavily contributed to dinosaur extinction. Our article says it was about 6 miles/10 km in diameter. Related info at Cretaceous–Paleogene_extinction_event and Chicxulub_crater. As for the movie - as I recall, the hunk of Earth/city seemed smaller than that to me. As for the bigger/smaller pieces, it absolutely matters. Think - would you rather be under a 1 ton rock falling from 1 mile up, or 1 ton of sand? The sand will tend to disperse and not hurt you as much. SemanticMantis (talk) 19:11, 4 June 2015 (UTC)


 * Far more critical than mass is velocity, and "terminal velocity" is wildly low. Kinetic energy is proportional to mass but to the square of velocity. Further, interplanetary impactors are traveling at least 11 km/s and potentially much faster. "Terminal velocity" as it's commonly used with respect to atmospheric drag doesn't matter; the impactor is through the atmosphere and on the ground before substantial deceleration can occur (at least for the big ones). So take 11 km/s for a minute: the city in Ultron was, give or take, less than 11 km above sea level (Everest is less than 9 km up; civilians in the movie were commenting on air pressure but operating without external oxygen; that's maybe-barely possible at Everest's peak but not much above). So if the city needs to impact at around 11 km/s, and it's less than 11 km up, impact would have happened within two seconds of the engines reversing thrust. Did that happen? No. So the speed just wasn't there, even if the mass was roughly in the ballpark. And by "just wasn't there", the speed wasn't even remotely close. As depicted, the city was falling at ~1 km/s, tops, and that's generous. But at that speed, it's only got 1% of the KE of a true impactor (far less if you start looking at the median speed for an impactor). A better estimate would be orders of magnitude lower still. So, several hydrogen bombs? Sure. Extinction? Not remotely. &mdash; Lomn 20:45, 4 June 2015 (UTC)


 * (edit conflict) Giant impactors like asteroids have more potential energy than simple height above the ground. These impactors do not begin falling from low Earth orbit at zero velocity.  Instead, they can enter Earth's atmosphere with much greater kinetic energy, because they came from some other orbit.  If you are an amateur radio astronomer, perhaps you have already built your own meteor RADAR receiver, so you are already familiar with the doppler shifts of meteors that commonly hit Earth: the common value you'll see in standard homework problems is around 50 kilometers per second.  By the time the meteor gets to the ground, it's also gained a little bit more gravitational potential energy; but it also loses energy to aerothermal heating, ablation, and other non-ideal effects that are harder to quantify.  The point is, giant impactors from space have more energy than an equally-massive rock dead dropped from orbit.
 * Nimur (talk) 20:48, 4 June 2015 (UTC)


 * g is around 9.8 m/s2 and only drops a little at 11 km. The distance s of a free fall for time t with no air resistance is s = ½gt2, so the time of a free fall from height s is t = sqrt(2s/g). Assuming 11 km we get t = sqrt(2×11000m/(9.8 m/s2) = 47.4s. The impact speed would only be 47.4s × 9.8 m/s2 = 464 m/s. Air resistance would decrease it a little but I guess the ground of the city would have to be so shallow it couldn't hold together in order for terminal velocity to be reached. An asteroid impact at 20 km/s would have (20000/464)2 = 1858 times as much kinetic energy for the same mass. PrimeHunter (talk) 13:11, 5 June 2015 (UTC)


 * Were the city to fall from that height into the deep ocean it would probably cause devastating world-wide tsunamis. That wouldn't match the archeologically known extinction events, but it would be quite dramatic. Simple sea-level mountain collapses from Hawaii and the Canary islands are believed to have caused megatsunamis with 40 foot waves coming ashore across the Pacific and Atlantic, respectively. μηδείς (talk) 22:56, 5 June 2015 (UTC)

Former North African fauna on Roman mosaics
A referenced sentence in Climate of Ancient Rome which I once added says "Numerous Roman mosaics from North African sites depict fauna now found only in tropical Africa". Is there any such image in the internet (or perhaps one can upload it)? My knowledge is somewhat limited in this regard, so I couldn't pick any google result. Brandmeistertalk  20:27, 4 June 2015 (UTC)


 * On the website of the Tunisian Ministry for Culture, there is a page about the Sousse Archaeological Museum. Among the photographs available is a Carthage-era mosaic of a tiger drawn chariot, a cherub riding a lion, and a leopard.  (To be clear, the museum webpage is a bit terse and does not formally specify whether this is a Roman or a Carthaginian mosaic, or attributable to some other culture; but if you're willing to accept a less reputable source, this is a mosaic of the Cortege of Dionysus, which would be Roman artwork).  Certainly you will be able to find many other resources.
 * I also came across the Winter 2011 issue of Expedition (available online). This is the magazine of the University of Pennsylvania's Archaeology and Anthropology museum).  This issue is entitled Animals in Antiquity and seems worth a read.  There's a whole chapter on bulls in Egypt, although I didn't spot any obvious tropical fauna.
 * Another website I found that is full of mosaics is Siti Archeologici Africani (in Italian), the website of an independent Italian archaeological and religious historical society. The page on Curubis has a mosaic that includes bears; on the page for Vaga, there are some other curious mosaiced animals that I can't identify.
 * Nimur (talk) 21:18, 4 June 2015 (UTC)
 * Thanks for leopards, found the Magerius Mosaic, reportedly Tunisian. Brandmeistertalk  22:18, 4 June 2015 (UTC)
 * A tiger, in Africa? -- Jayron 32 00:17, 5 June 2015 (UTC)
 * Fair point. To address it non-humorously, it was doubtless obtained through trading links with Eurasia or India, like the Hindu statue excavated from Pompeii (or Herculaneum) shown in a recently repeated BBC programme narrated by Mary Beard. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 12:42, 5 June 2015 (UTC)
 * So far as I know the Romans were famous for importing exotic beasts as a demonstration of their power, alliances, and trading opportunities, and last but not least because they made such a spectacular show of killing captives. It should be clear that artists' mosaics are thus very poor evidence for former climate, though I'd have a bit more trust for the artwork of the Nubians mentioned in Sahara.  The Neolithic Subpluvial article describes evidence from ancient garbage dumps, such as antelope bones, which is much more convincing. Wnt (talk) 13:17, 5 June 2015 (UTC)
 * Surely, Wnt, you don't mean to imply that historical artwork of a thing is distinct from solid evidence that a thing existed! That sort of logic would discredit the ancient astronaut hypothesis and many world religions!  Nimur (talk) 14:52, 5 June 2015 (UTC)
 * Agree with User:Wnt - see Wild Animals at the Colosseum which lists chimpanzees and giraffes among the exhibits, which were generally killed in various unpleasant ways for the entertainment of the crowd. Alansplodge (talk) 17:14, 5 June 2015 (UTC)
 * Yep, I've modified the related sentence in the Roman climate article accordingly, but won't object its removal. Other sources I've read imply that leopards, for example, disappeared from North Africa due to overhunting. Brandmeistertalk  21:34, 5 June 2015 (UTC)
 * The Wild Animals at the Colosseum list includes jaguars - which sheds some doubt on its reliability, unless it's drawing on hitherto unknown evidence of Roman visits to South America.  Ghmyrtle (talk) 21:43, 5 June 2015 (UTC)
 * Presumably its presence is due to the fact that people often confuse jaguars and leopards. μηδείς (talk) 02:57, 6 June 2015 (UTC)
 * User:Ghmyrtle, there is evidence of Roman visits to South America, depending on how much credence one gives to it. See Pre-Columbian trans-oceanic contact theories.  --   Jack of Oz   [pleasantries]  07:37, 8 June 2015 (UTC)


 * Many famous historians have written about ancient Roman art and have theorized about whether such art was descriptive of climate. The source referenced, already noted above, is a worthwhile read.
 * Even if we do not believe a historical item as factual today, if historians did believe it at some time in the past, our encyclopedia should make note of the detail. This is historiography: historical fact, as written by historical historians, as opposed to historical fact as determined by modern scientific theory and method.
 * To parrot the source linked, we do not need professional standing as an archaeologist, or as a climatologist, to make an editorial collection of important theories proposed by archaeologists and climatologists. Even if these theories have been discredited, many of them are noteworthy because they provide context for the study of ancient history.
 * As far as the factuality of a "tropical" climate in North Africa in the early Roman era, most scientists and historians today seem to think that is false. There exist many more parsimonious explanations for the appearance of these animals on Roman artwork.
 * Nimur (talk) 01:41, 6 June 2015 (UTC)

The Roman era is a couple thousand years too late but Green Sahara (formally, the African Humid Period) was a real thing. Although the exact timing and extent is uncertain, the generally accepted explanation is that the African Humid Period came about because cyclical changes in Earth's orbital geometry allowed the African monsoon to extend farther north than at present. The WP article is not very good, but for a better overview you can see this article. Short Brigade Harvester Boris (talk) 15:51, 6 June 2015 (UTC)
 * Well, desertification was still ongoing in Roman times, and indeed is still ongoing today. Even if the climate were no longer shifting, the stored aquifer water for oases would still be steadily used up, even before the Great Man-Made River.  Wnt (talk) 23:15, 6 June 2015 (UTC)