Wikipedia:Reference desk/Archives/Science/2020 September 14

= September 14 =

Effects of Gravitational Waves
The gravitational wave sources detected by LIGO and other experiments are so far away that the amplitude of the waves are tiny by the time they reach earth. The article section Gravitational_wave gives a description of how it would affect some particles on a plane, but I'm interested to know what the practical effects of a wave would be on material close to an intense source. Would it distort materials so much it destroys them? Would it injure organisms? Or does a ripple in the spacetime curvature not really affect things too much? If a tertiary system existed consisting of two black holes and a third massive object, could the merger of the two black holes have some substantial effect on the third object? Say the third object was a star, could the distortion affect the rate of fusion in the star's core, or trigger a gravitational collapse of the star, or anything like that? Handschuh-talk to me 01:13, 14 September 2020 (UTC)


 * Not an answer, but Scott Manley recently put up a video, 'Impossible' Black Hole Created by Largest Gravitational Wave Event [YouTube, 10:51], about GW190521, the gravitational wave signal detected on 21 May 2019 of what appears to have been the merger of two black holes of 85 and 66 solar masses, resulting in a single black hole of 142 solar masses, where the "remaining 9 solar masses were radiated as energy in the form of gravitational waves"! -- ToE 01:45, 14 September 2020 (UTC)


 * Yes, it was reading about the 9 solar masses of energy radiated out into the universe that go me thinking of what kind of effect it might have on something/someone close to the source, and also, the coinciding light flash (for which astronomers have already proposed an alternative explanation) got me thinking about how the GW might affect nearby stars. Handschuh-talk to me 02:26, 14 September 2020 (UTC)


 * Also not a full answer, but the frequency of the first gravitational wave ever observed went up to 250 Hz. That means a wavelength of more than 1000 km. The effect on a much smaller body being sloshed around in a wave of an extreme amplitude is much less violent than that of waves with ripples commensurate with the size of the body. Warning. This does not mean it is safe to observe a black hole merger from up close. Always keep a safe distance. --Lambiam 07:45, 14 September 2020 (UTC)


 * If you take the observed strain and use that it decays inversely proportional to the distance fro the source, then you find that at a distance of 1 AU from the source, the strain would have been just about detectable by our seismometers. Count Iblis (talk) 11:28, 16 September 2020 (UTC)
 * That interesting...so at a very short cosmological distance the effects are hardly earth shattering. Where did you get the observed strain from? It doesn't seem to be in the GW190521 article. Handschuh-talk to me 23:39, 16 September 2020 (UTC)
 * I used the strain sensitivity of $$10^{-23}/\sqrt{\text{Hz}}$$ of LIGO, the observed strain is then an order of magnitude larger, you can then multiply this by the distance to the source divided by the distance of some hypothetical planet close to the source to obtain the strain at that planet. Count Iblis (talk) 22:46, 17 September 2020 (UTC)
 * You might be able to get some idea by how much vibration can an organism stand. Since the frequency is high enough to be audible, the effect is probably similar to the human body being stretched in a rack but much faster. You could probably take a strain of 1% without disrupting the soft tissues, but that may be sufficient to break a bone. Graeme Bartlett (talk) 11:46, 20 September 2020 (UTC)

Marsh and swamp
In Polunin and Walters A Guide to Vegetation of Britain and Europe there is a different definition of marsh and swamp from Wikipedia (i.e. a marsh is a wetland dominated by grassland and swamp a forested wetland): a marsh is an area where at least in summer the water level is below the soil surface, whereas a swamp is permanently saturated with water. Could this distinction be defined with other words than marsh and swamp?--Carnby (talk) 16:02, 14 September 2020 (UTC)
 * I'm going to go on a bit of a side rant here; I have long suspected that scientists create word distinctions among synonyms that didn't used to exist, but try to make them so, and sometimes different groups of scientists will create different distinctions than each other because they never got together and got their story straight. The English Language has a surprising variety of words for (well anything, but in this case...) areas of non-quite-land-not-quite-water, and I'm not sure the distinction between those words as you note existed as long as the different words themselves.  I suspect such word difference were initially geographic rather than in quality or character, so that people from one area called such land a "swamp" or a "bog" or a "marsh" or a "bayou" or a "mire" or a "fen" or a... whatever.  People just named the wetland by their local name, and later the distinctions between such things as whether it had trees or grasses or whatnot was imposed by people trying to make sense of the system.  The problem you note, where two different supposedly expert sources have two mutually exclusive and entirely non-compatible systems for drawing such distinctions, is a symptom of that history.  In the means of actually providing sources to my side-rant, consider the etymology of various terms, swamp, marsh, fen, bog, they all have, in their origins going back to the 1500s or earlier, the same basic meaning, that being "wet spongy ground".  That being said, by 1775, the distinction between swamp and marsh was drawn, as noted in the link I provided for swamp, "[B]y swamps then in general is to be understood any low grounds subject to inundations, distinguished from marshes, in having a large growth of timber, and much underwood, canes, reeds, wythes, vines, briers, and such like, so matted together, that they are in a great measure impenetrable to man or beast .... [Bernard Romans, "A Concise History of East and West Florida," 1775]"  So take that what you will.  -- Jayron 32 11:38, 15 September 2020 (UTC)
 * To complicate things even more, which I assume everyone is begging for, it appears plausible (at least to me) that different branches of physical geography that study wetlands from different angles (e.g. ecology versus hydrology) use different classifications. Some fields (e.g. limnology) were developed originally by non-English scientists, and there may not be a clear correspondence beteen the French and German terms and the English ones. For the variety of types of wetlands, just look at Category:Wetlands – good luck developing an unambiguous classification for these. I noticed that Moorland is not in that category and not mentioned in the wetlands article, although some moors definitely are and many (most?) that are not started out that way, as mires. --Lambiam 16:02, 15 September 2020 (UTC)
 * " I have long suspected that scientists create word distinctions among synonyms that didn't used to exist" I think we can safely say that suspicion is more than justified. Speed and velocity being a typical example (and even acceleration or it's latin root probably had a similar meaning, lacking the technical distinction we now impose upon it). Handschuh-talk to me 23:47, 16 September 2020 (UTC)
 * Similarly "Mass" and "Weight". -- Jayron 32 15:02, 17 September 2020 (UTC)
 * The existing English word mass was repurposed to translate Newton's repurposing of the Latin massa for a concept that did not yet exist; the same happened for acceleration and inertia. Obviously, these terms did not have the technical physics meanings they have today before someone introduced the concepts they name. If these terms had synonyms (inertia = sloth), the technical sense was not simultaneously imparted on the synonyms. The earlier, everyday meaning of mass(a) was "lump (of dough)". --Lambiam 20:38, 17 September 2020 (UTC)
 * Yeah, but there's a few bad teaching practices that try to explain that "weight" only refers to gravitational mass while "mass" only refers to inertial mass, that's basically bullshit because we've known the two concepts are the same thing due to the equivalence principle. Even during the time of Newton there was suspicion they were because any measurement of one resulted in an equivalent measure of the other, but such conjectures were not proven until about 100 years ago.  There's some other texts and things that try to say that weight is only referring to gravitational force (i.e. Newtons) while mass is "mass" (i.e. kilograms), but I don't know any actual physicists that make such distinctions and legitimately say things like "Such and such weights X Newtons".  If one means force, they say force.  If one means weight, the use kilograms just fine.  -- Jayron 32 13:03, 18 September 2020 (UTC)
 * I'd like to add "morass" to the discussion. HiLo48 (talk) 04:30, 17 September 2020 (UTC)
 * as in "I've been eating a lot during this quarantine and I have morass than I used to.-- Jayron 32 07:35, 17 September 2020 (UTC)
 * Let's not get bogged down in trivia. ←Baseball Bugs What's up, Doc? carrots→ 08:36, 17 September 2020 (UTC)