Wikipedia:Reference desk/Archives/Science/2016 March 17

= March 17 =

Ancient Greeks in Norway
Hello! Last night, I was reading Robert Graves' The Greek Myths, and on page 729, he explains the origins of the Laestrygonian myths. He says that amber merchants were warned against Norwegian Fjord dwellers, who had "barbarous habits". My question is how did the Greeks (the ancient ones) hear of them? Did they sail all that way, or did they hear of them from other peoples, or did they walk there? It seems like a very long and perilous journey to me!

By the way, I did not research this on Wikipedia at all, so the answer may be very obvious. Do not be too hard on me! Thanks, Megaraptor12345 (talk) 12:22, 17 March 2016 (UTC)


 * Much amber came from (and still comes from) the Baltic area - not specifically Norway. And there was certainly trade in amber ("electrum")  so yes - the trade appears to have been through modern Germany thence into northern Italy.  The peoples of the Baltic etc. were certainly aware of the Norse raiders - so  Graves is quite likely within reason here. Collect (talk) 12:31, 17 March 2016 (UTC)


 * So, you are saying the Greeks walked? And the Norse were around at that time?! I have only heard of them from the Middle Ages, so that is why I am asking. And another source says that the tale of the Aesir-Varnir War was a war between Asian invaders (Aesir), and the indigenous chieftains (Varnir), so did this happen before the Greeks came or after?Megaraptor12345 (talk) 12:46, 17 March 2016 (UTC)
 * The Greeks had extensive settlement on the north coast of the Black Sea. If you follow the Volga from there to its source, you end up only about 300 miles from the Baltic.  To reach a waterway that connects to the Baltic is a much shorter journey.  In other words, they might not have needed to walk very far. Looie496 (talk) 15:36, 17 March 2016 (UTC)
 * You may find this blog post (fairly well referenced to original peer reviewed papers). This article discusses the similarity in sheld construction as being an indication of cultural connections between Baltic Germany and Greece in the Ancient World as well, perhaps another connection between northern and southern Europe.  Here is another article about Baltic-Greek trade in Amber.  However, one should also be aware that the "Ancient Greeks were influenced by Scandinavians" thread is a favorite topic of the white power movement; so separating the wheat from the chaff in this topic can be difficult.  -- Jayron 32 14:34, 17 March 2016 (UTC)
 * Wow!! Thank you! That really helped! But something is nagging me; who precisely were these Fjord dwellers who Graves refers to? Were they raiders or simply a hostile tribe? Also, why were they considered "barbaric"? In the Odessey, they were cannibals, so is that the reason? Thanks again for the links, Megaraptor12345 (talk) 15:02, 17 March 2016 (UTC)
 * In Ancient Greek terms, 'barbarians' were simply people who spoke a non-Greek language because it supposedly sounded like meaningless "Bar-bar-bar" to them (but the Greeks sometimes also used it as an insult for other Greeks they were having a disagreement or war with).
 * The "Fjord dwellers" were presumably just whoever was living around the Baltic at that time – possibly ancestors of the later Norse, possibly not. They probably weren't cannibals, but it was easy and convenient to make up lurid stories and attach them to people in distant lands that the stories' audience would never meet. The term "cannibal" itself comes from a supposed tribe of "Caribs" in the Caribbean region, but the evidence for them actually being eaters of human flesh is not very strong.
 * Bear in mind that Robert Graves was writing some time ago – The Greek Myths was published in 1955, in part re-used material from The White Goddess published in 1948, and apparently relied mainly on a reference work published in 1844 – (so later research might have superseded him) and he was primarily a poet and fiction writer rather than a historian, and sometimes made historical assumptions because he thought they ought to have been true. (Long Story Short, don't trust all his historical interpretations.) {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 18:52, 17 March 2016 (UTC)
 * There also is Pytheas of Marseille (and his lost manuscript), describing many features of northern Europe, possibly including parts of Scandinavia. He quite probably reached the area around Trondheim. It's unlikely that he was the only Greek to explore the area.  --Stephan Schulz (talk) 14:53, 17 March 2016 (UTC)
 * There seems reasonable evidence, both from Pytheas and from archaeology, of Greek traders getting as far as Britain and Ireland - mainly to buy tin which was hard to come by and essential in the bronze age. Any further north is less certain: trade goods certainly reached Scandinavia, and amber went the other way, but they often passed through various middle men, and are not evidence of Greek traders travelling the whole way. Stories undoubtedly got transmitted in much the same way as the amber. As to why they were barbarians - to the Greeks a barbarian was simple someone who couldn't speak Greek (so sounded as if they made ba-ba-ba type sounds). It didn't carry the modern connotation of cruelty or uncivilized behaviour. 109.150.174.93 (talk) 18:46, 17 March 2016 (UTC)

What's an "anti-dark soliton"?
I'm no kind of physicist at all. Actually I'm trying to define antidark for Wiktionary. Any hints? Thanks. Equinox (talk) 21:49, 17 March 2016 (UTC)
 * In optics a soliton is a wave packet of energy that travels without getting dispersed or distorted. For this to happen the packet must be described by a set of partial differential equations where the effects of nonlinearity and dispersion cancel in the medium through which the wave travels. Some reported mathematical descriptions of solitons distinguish between "dark" and "antidark" solutions, relating (I believe) to their effects on a background continuous "bright" radiation. References:  . AllBestFaith (talk) 22:29, 17 March 2016 (UTC)

LIGO precision
The LIGO observatory uses interferometry to detect the movement of two mirrors placed 4 km apart. A laser is split, bounces off two mirrors, and recombines. But each reflection is the interaction of a photon of light in the laser with an electron in one of the atoms in the mirror. It seems to me that there is unavoidable quantum "noise" due to the electrons' movement within the atom. I know "movement" isn't really the right word when discussing quantum phenomena, but basically it seems to me that the position of the electrons, and thus the position of the reflecting surface, can't be determined with precision much less than the size of an atom. Yet LIGO claims to detect movement on the order of 10^-18 m, millions of times smaller than an atom. How does this work? CodeTalker (talk) 22:38, 17 March 2016 (UTC)
 * I don't think an electron actually "move" inside an atom, in a classical sense, such that it is closer to the "boundary" at one moment and further away at the next. The way I understand it (and I'm not physicist either) is there's a free flowing "cloud" of electrons free to move around in a metal. So when light hits the " boundary layer" an electron will essentially be "there" at the energy state to reflect it. Remember a wavelength of light is hundreds of times larger than an atom too, how does a sub 0.1 nm "atom" reflect a 500nm wave? at that point I think it's more about the energy states than the "position" of individual components.  Vespine (talk) 23:22, 17 March 2016 (UTC)


 * The magic of the LIGO is that it uses a Fabry Perot interferometer design, bouncing the laser many times between the mirrors. By bouncing the laser multiple times, the beam actually travels through an optical path length of 1120 kilometers.  "This bit of 'mirror magic' greatly increases LIGO's sensitivity and makes it capable of detecting changes in arm-length thousands of times smaller than a proton, while keeping the physical size of the interferometer manageable."
 * Nimur (talk) 00:54, 18 March 2016 (UTC)
 * In retrospect, I'm not certain that this actually addresses the OP's precise question, which is how anything smaller than an atomic radius can be measured, when the interaction itself seems to involve a photon/electron collision whose scale length is necessarily related to the "electron cloud size." I guess the best way to phrase this: no individual photon needs to have its phase (or its "position") measured so accurately; but the ensemble of lots and lots of coherent photons interacting with lots and lots of optically flat atoms can be precisely measured.  This is ensemble mechanics, and it's the only way we can make meaningful macroscopic sense out of millions of individual quantized interactions.
 * Maybe it's hard to believe that we can use such a simple method - averaging - to get a good signal from a noisy source - but this is actually a very normal phenomenon, and we can even find examples outside of atomic physics. For example, in image processing, we can use sample gain to pull pixels out of noise, even if the signal is smaller than the quantization noise.  We do this sort of thing all the time - there are lots of engineering applications where we average huge numbers of samples in order to pull a tiny tiny but coherent signal out of noise.  This is one of the miracles of digital signal processing: signals are coherent and noise is incoherent, so you can easily distinguish the two.  (The worst kind of noise is coherent noise!)
 * Nimur (talk) 02:25, 18 March 2016 (UTC)
 * The LIGO article says that it is only 280 trips, not very impressive really. I am suspicious that a part of it might be that the detector sits right on a node, so that light from two paths precisely cancels out, so that very dim light can be measured from a very bright laser.  But when I looked around I didn't see any explicit statement of that, and my idea seems to have a severe difficulty, which is - how do you tune the position of the detector down to a millionth of the size of an atom to begin with?  Oh, I dunno, I guess you bend something really stiff just a little bit under a field...?  Just speculation there, NOT an answer! Wnt (talk) 03:40, 18 March 2016 (UTC)
 * Two things, I don't see why you need to tune the position of the detector that finely. 2 out of phase but "in sync" lasers are "in sync" along their entire length, not just at the peaks or troughs. Second, I imagine the phase of the laser is probably something that you need to be able to control from the source, so they probably calibrate at the 'source' side, not necessarily the destination side. Vespine (talk) 04:56, 18 March 2016 (UTC)