Wikipedia:Reference desk/Archives/Science/2014 November 18

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November 18

Why is Western Europe poorer than USA?

Question moved to the Humanities desk from the Science desk. -- Ariel. (talk) 06:44, 18 November 2014 (UTC)

Is it? According to List_of_countries_by_GDP_(nominal)_per_capita#List_of_countries_and_dependencies the US has the 9th highest GDP per capita of all the world's countries. 6 of those higher than the US are European. Two of those, Norway and Luxembourg’s are twice that of the US. The European Union as a whole, is half that of the US, and it would be ranked 26th in the world, if it was a country. The EU now contains several Middle-European countries that were former Soviet states, and as a result they are bringing the EU's GDP/capita down. The EU is spending its structural fund to help those countries improve. CS Miller (talk) 10:26, 18 November 2014 (UTC)

Visual illusion: red and blue text on black background

When you have both (saturated) red and blue text set against a black background, the red text will seem closer to you and the blue text, as if the text of the two colors were on different planes. What is a scientific explanation for this? --108.36.90.122 (talk) 01:53, 18 November 2014 (UTC)

I can't find our article on it, but found mention of it here Forced perspective: A monocular cue easily taken advantage of by painters is the trend for the color of objects in the distance to be shifted more towards the blue end of the spectrum, while closer objects' colors are shifted toward the red end of the spectrum. A painter can give the illusion of distance by adding blue or red tinting to the color of the object he is painting. Vespine (talk) 02:55, 18 November 2014 (UTC)

I have heard that the eye focuses red and blue at different distances due to refractive index varying with frequency of light, so the lens has to adjust between the two colours. Graeme Bartlett (talk) 11:02, 18 November 2014 (UTC)

Nothing to add except my thanks for asking a question and getting an answer to something that long ago (i.e. pre-Wikipedia) puzzled me: at the time I couldn't find any answer or even a mention of the phenomenon. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:25, 18 November 2014 (UTC)

• Our article is at Chromostereopsis. It's all about differential refraction, and is based on real physical phenomena in a addition to human perception. (I found it by googling /red blue depth perception/, and also added a wikilink to Forced perspective at the end of Vespine's quote) SemanticMantis (talk) 15:52, 18 November 2014 (UTC)

Is Quantum entanglement necessary?

The universe appears very fine tuned, with only a few exceptions. But what about Quantum entanglement? If quantum entanglement did not occur would there be any noticeable macro differences in the universe? Are there any processes that require it, or are at least affected by it? Or does is it only noticeable in human experiments (I'm sure it occurs naturally, but does it change anything)? Ariel. (talk) 06:50, 18 November 2014 (UTC)

Entangled states arise frequently as a consequence of the indistinguishability of fundamental particles, including in every atom with more than one electron. The resulting exchange interactions have important implications for electron structure and by extension chemistry. In such an example, it is not so much the entangled properties that are important, but rather that an entangled state can exist at all. I can't really think of any examples where the typical notion of entangled states, i.e. that composite object AB is such that measuring A instantly determines the state of B, has naturally occurring macroscopic consequences. It certainly matters for the pursuit of quantum computing and quantum cryptography, but the spooky action at a distance aspects of entangled states may not have a large natural role. However, the fact that fundamental particles routinely form entangled states (and that such states may have different energies than separable states) certainly does have consequences for chemistry and other aspects of physics, so the existence of entangled states definitely matters. Dragons flight (talk) 07:27, 18 November 2014 (UTC)

Quantum computing definitely needs entanglement, but quantum cryptography doesn't. At least, BB84 doesn't. -- BenRG (talk) 04:31, 19 November 2014 (UTC)

From a non-physical perspective, I think the answer must depend on how you are thinking of logical necessity and how you think of possible worlds. Also it's good to remember that the fine tuning of the universe is still widely debated, as is discussed with refs in our article. SemanticMantis (talk) 16:01, 18 November 2014 (UTC)

What I'm wondering is if Quantum entanglement did not occur, could there be a universe with stars and life. And it seems there could be. Ariel. (talk) 20:59, 18 November 2014 (UTC)

Note that without entanglement, you won't get an effectively classical world at the macro-scale. The reason why you can't do quantum computing with your PC essentially boils down to the fact that as soon as a superposition of a bit in a "0" or "1" state would arise, environmental degrees of freedom would quickly interact with that and the superposition would vey rapidly become entangled with many degrees of freedom from the environment.

Now, no entanglement at all means that there cannot be any interactions between particles. So, the universe could not support complex structures. Count Iblis (talk) 22:04, 18 November 2014 (UTC)

Complex structures such as protons. :-)

The question seems to contain an implicit assumption that a universe without quantum entanglement would be simpler. I don't think that's true at all. Quantum mechanics is mathematically simple. A replacement that allowed for nuclear fusion but not for entanglement at longer ranges would surely be much more complicated, if it's possible at all. -- BenRG (talk) 04:31, 19 November 2014 (UTC)

It sounds like what you (plural you) are saying is that to make a composite particle like a proton, the constituents entangle their states? And that also happens when two particles interact? Am I understanding that correctly? If so, then how were atoms (which are composite) explained classically? (i.e. is there an alternative way to explain it without entanglement.) Ariel. (talk) 07:32, 19 November 2014 (UTC)

I would conjecture that there is no philosophical reason why there couldn't be a non-quantum universe having classical versions of gravitation and electromagnetism, and some sort of nuclear force that holds atoms together, that would be macroscopically similar to our universe, but wouldn't be our universe. I disagree that entanglement is the only way to postulate interactions between particles. It is the way that interaction between particles happens in this universe. The classical non-quantum universe could behave macroscopically almost the same as this universe. That is my opinion, and it is worth what you paid for it. Robert McClenon (talk) 03:20, 20 November 2014 (UTC)

Cohesion of soils

Which part of the shear strength equation describes the fact that some soils have more weakness planes? Is it C, the cohesion value? 194.66.246.28 (talk) 10:42, 18 November 2014 (UTC)

It might be. What equation are you looking at? Also, not all models of soil strength will be fully three dimensional and correctly capture all forces in all planes. Here is a nice online book on the topic [1], linked from our article on soil mechanics. SemanticMantis (talk) 19:19, 18 November 2014 (UTC)

Powerful optical resonance in the optical fiber cables

Did it possible, that the optical fiber of the fiber optic cable is able to had the high-frequency superconductivity of electric current of high powerful voltage, if the optical reflectivity and optical refraction in this optical fiber cable will be not had the light spectrum?--Alex Sazonov (talk) 11:44, 18 November 2014 (UTC)

No, optic fibres are not conductors of electricity let alone super conductors. If you try to put a high voltage across the glass in the fibre, you may get an electrical break down with a spark, and the fibre will be damaged, and not so transparent. If your light becomes too strong down the fibre you will heat it up and melt it. Graeme Bartlett (talk) 11:49, 18 November 2014 (UTC)

Did the presence a spectrum in the light wave had hamper to the passage of light wave through the optical barrier (optical medium)?--Alex Sazonov (talk) 12:51, 18 November 2014 (UTC)

The "presence of a spectrum" implies that the light is white or at least polychromatic. This would "hamper" the signal because different colours (= different wavelengths) of light would propagate at slightly different speeds through non-vacuum media like the glass of a fibre-optic cable – this is why it's possible to produce a spread-out spectrum with, for example, a prism – which would cause the signal to spread out and degrade.

For this reason, the light used in fibre-optic cables (where used for communications rather than decoration) is laser light, which is monochromatic and therefore does not have a spectrum. Different wavelengths/colours can be used in the same cable (though its diameter might be optimal for one in particular), and different signals can in principle be sent simultaneously by using multiple wavelengths, one per signal, though this is not yet current practice in everyday communications cables.

Addendum: regarding your initial electrical query – some fibre-optic cables are called hybrid cables, and these do include an electrical conductor in addition to the light-conducting glass fibres. The electricity is used for controlling things like the motors that tilt the aerial that the light signal is going to. The electrical element, however is perfectly ordinary, ambient temperature metal (usually copper), neither superconducting nor carrying "high powerful" voltages. The electricity does not go through the optical fibres.

Disclosure: I work for a company that repairs/replaces co-axial and fibre-optic cables (amongst other things) in mobile (cell) phone aerial installations, and while technically unqualified myself (I do costing work) I have just checked all this with my office's fibre maven. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:11, 18 November 2014 (UTC)

The light spectrum is the idea (concept) of optical or magnetic (electromagnetic)?--Alex Sazonov (talk) 13:56, 18 November 2014 (UTC)

Spectrum can be derived using either concepts. Using electromagnetic theory you can calculate in the frequency domain or using normal physical units using time. A Fourier transform converts between the two forms. Optics precedes electromagnetics. You may also be interested in non-linear optics. Graeme Bartlett (talk) 23:05, 18 November 2014 (UTC)

To 212.95.237.92: You're mistaken when you say that it's not yet current practice to use multiple wavelengths to carry multiple signals over optical fiber. This is wavelength-division multiplexing, which is very common in long-haul telecommunications. A single optical fiber can carry over 100 separate channels this way.--Srleffler (talk) 06:27, 19 November 2014 (UTC)

Fair enough. The cables my Company work on are generally between ground and antenna, usually less than 100m, and the separate sites communicate with each other via microwave dishes: we don't deal with long-haul cables. My error in not delving into the references further. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:00, 19 November 2014 (UTC)

Verizon FiOS is three wavelengths (TV, downstream data, upstream data) on a single fiber from a central office to each customer. DMacks (talk) 05:00, 21 November 2014 (UTC)

What is a ductless gland

Ductless gland is a redirect to gland. That article's Endocrine glands section says that they are ductless. Are ductless and endocrine just different names for the same thing? 65.210.65.16 (talk) 15:42, 18 November 2014 (UTC)

Yes, the word "endocrine" implies ductless.[2] ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:38, 18 November 2014 (UTC)

Just in case you want to know why they are called ductless literally, it is because they excrete hormones directly into the blood, lke insulin or adrenaline, as opposed to things like the kidney or sweat glands that ultimately excrete into other organs (the bladder) or externally. μηδείς (talk) 01:40, 19 November 2014 (UTC)

Is melamine specially expensive (and/or difficult to produce)?

I find it amazing how much a whiteboard (dry erase) costs. Isn't there an alternative plastic for this? --Senteni (talk) 20:09, 18 November 2014 (UTC)

It's cheap enough that it is used criminally as an adulterant to fool tests of protein content in things like baby formula. μηδείς (talk) 20:28, 18 November 2014 (UTC)

Looks like melamine can be had for $850-920/metric ton [3]. I'm sure you can find it even cheaper with a bit of search. This is in the same ballpark as other polymeric materials PVC, HDPE, but I don't know if any of these would work well as a substrate for whiteboards. Mihaister (talk) 21:33, 18 November 2014 (UTC)

But you aren't just buying melamine - it's a white powder. You're buying a sheet of wood of some kinds with a layer of polished melamine bonded to it.

I have to dispute your claim that it's expensive though:

On Home Depot's web site they have:

• This [4] 4'x8' sheet of 3/4" MDF for $36.32
• And this [5] identical size and thickness sheets with Melamine coating for $36.56.

So the Melamine coating is 3 cents per square foot...actually, I think it's coated on both sides...so 1.5 cents per square foot. SteveBaker (talk) 03:01, 19 November 2014 (UTC)

Don't whiteboards normally have a steel core, rather than wood? CS Miller (talk) 13:58, 19 November 2014 (UTC)

Some do, some (most?) don't. I think the main point is that the cost of melamine is not the thing that makes some whiteboards expensive. As Steve points out, the raw materials are not that expensive. It's a value added thing to add a frame and a tray for markers. While individuals may DIY, that is rather uncommon in institutional settings. My WP:OR indicates that as "business" or "educational" supplies, prices of this sort of thing can get very inflated and still sell, because the largest lot of purchases are from institutional budgets, not personal budgets. SemanticMantis (talk) 15:18, 19 November 2014 (UTC)

Whiteboards should also be treated as if they are semi-disposable, since somebody will eventually use permanent marker on them accidentally, or leave dry erase marker on them long enough to become permanent. I've also seen them delaminate (form bubbles). I think the frame should be permanent, and have a sheet on it that can be periodically replaced. StuRat (talk) 15:29, 19 November 2014 (UTC)

I was just about to say the same thing, Stu. Melamine doesn't stand up well to regular wear. The best whiteboards are enamelled steel. I've used cheap melamine board as whiteboard, and it seems to last about as long as the more expensive versions, which is not very long in constant use. Dbfirs 20:32, 20 November 2014 (UTC)