Wikipedia:Reference desk/Archives/Science/2016 January 6

= January 6 =

Homocysteine elevated
Recommendations for reducing levels of homocysteine
 * Presuming that you mean in humans, is what you're looking for covered in the Hyperhomocysteinemia article? Cannolis (talk) 02:17, 6 January 2016 (UTC)
 * Isn't that medical advice? It is impossible to know if a person is taking enough nutrients without a homocysteine blood test. So, go ask a doctor if you need on. --Denidi (talk) 16:41, 6 January 2016 (UTC)
 * It's not medical advice when you're giving a general indication, rather than prescribing to a specific patient. But in any case, the article above already says so much we'll be hard pressed to think of more (and if we do, we really ought to add it there and just ping here after we do) Wnt (talk) 20:35, 6 January 2016 (UTC)

Destroyer
Hello! Mr. Zoot Cig Bunner (talk) 20:15, 6 January 2016 (UTC)
 * 1) What is the difference between an 'atomic' bomb and a 'hydrogen' bomb? What does each do? - simplistically.
 * 2) What is more powerful from the two enquoted above, or is it a 'molecular' destroyer?


 * See atomic bomb, then fission bomb and thermonuclear bomb (a hydrogen fusion bomb being the most common type). The latter is far more powerful, but uses the former to trigger it.  A fission bomb is where atoms split apart, releasing energy, and a fusion bomb is where atoms fuse together, releasing energy.  It might seem confusing that atoms can release energy either when splitting or joining, but, in general, larger radioactive atoms (like some isotopes of uranium and plutonium) release energy by splitting, while smaller atoms (like isotopes of hydrogen) release energy when fusing.


 * Not quite sure what you mean by a "molecular destroyer", but any molecule near a nuclear explosion will be destroyed, although no significant additional energy is typically released in that process (with a possible exception for fires that spread). You also might be interested in the theoretical antimatter bomb, which would be on the order of 10 thousands times more powerful yet. StuRat (talk) 20:19, 6 January 2016 (UTC)


 * Oh, great Stu, you and your gee dee antimatter bomb advocacy. Next you'll have the Romulans destroying Vulcan. μηδείς (talk) 21:06, 6 January 2016 (UTC)


 * Lol. -- Mr. Zoot Cig Bunner (talk) 18:32, 7 January 2016 (UTC)


 * In the Star Trek universe, I would have expected wider use of antimatter bombs, since they used matter/antimatter reactors to power their star ships. Specifically, a warp-capable torpedo could drop out of warp on the target and detonate immediately, with enough power to destroy a planet.  But star ships within sight of each other, firing volleys back and forth, seems more exciting, so that's what we got. StuRat (talk) 21:14, 6 January 2016 (UTC)


 * Standard 24th century photon torpedoes carry 1.5 kg each of matter and antimatter (hydrogen specifically), giving on the order of 64 megaton yield. Do some maths and see what's needed to actually destroy a planet..... 82.8.32.177 (talk) 22:42, 6 January 2016 (UTC)


 * Well, it shouldn't be a problem to carry 1000x as much, maybe a million times as much. By comparison, a B-52 carried 31,500 kg in bombs, some 20 thousand times as much. StuRat (talk) 22:54, 6 January 2016 (UTC)


 * A B-52 load of mixed matter/antimatter would have a yield of 2.84x1021 J. The Chixalub impact is estimated at 1x1024 J. Still would barely make a dent. 82.8.32.177 (talk) 23:02, 6 January 2016 (UTC)


 * Then try a million times as much. What was the weight of the Enterprise supposed to be ?  Try that much. StuRat (talk) 23:11, 6 January 2016 (UTC)


 * What do you mean by "destroy" a planet? There used to be (perhaps still is?) a Usenet group called alt.destroy.the.earth, whose FAQ explained that the group was for people who didn't "want the Earth to be there anymore".  Just destroying civilization, or human life, or all life, well, that wasn't taking the matter seriously.
 * The gravitational binding energy of the Earth, according to that article, is around 2&times;1032 J, which works out to something like 1015 kg of antimatter, a trillion metric tons. I don't know what the towing capacity of Enterprise was supposed to be, but I doubt it's that bit. --Trovatore (talk) 23:05, 9 January 2016 (UTC)


 * Destroying all life on the planet will be quite sufficient. StuRat (talk) 00:02, 10 January 2016 (UTC)


 * I've seen in two movies, 1) a movie called Machete (film) where it was like a normal gun/pistol like, and 2) can't recall the movie name but a group of little kids command a group of 'space ship' vessels, one containing a 70-72 billion dollar worth of a gun (molecule destroyer), what they use to destroy a planet filled with 'a kind' of a specie. Yes they destroyed the whole planet with one laser lookalike shot.


 * Thanks btw Stu.
 * Mr. Zoot Cig Bunner (talk) 18:56, 7 January 2016 (UTC)


 * Briefly - there are two ways to get energy out of atoms - you can persuade a big atom to break apart ("fission")- or you can persuade some small ones to join together - tossing out a fraction of their mass as energy as they do so (fusion).


 * A bomb made with heavy elements like uranium or plutonium (a "fission bomb") are the simplest to make because those heavy atoms are so big and bloated that they are already trying to fall apart (hence the fact that they are radioactive). Just put together a big enough pile of the stuff (and do it quickly enough) and you have a nuclear weapon.   But there is a snag - once you put more than about 10kg of plutonium in one place, it's going to go explode all by itself - this is called "the critical mass".  To make a bomb, you take a couple of chunks, each weighing less than 10kg and throw them together (possibly using conventional explosives to do it fast enough) to make something weighing more than 10kg.  But you can't make a bomb twice that big using that trick because if you take two 10kg chunks - each one is going to explode before you want them to.  So if you need something much bigger than a Hiroshima-sized bomb - you need more, smaller pieces - and getting them all to slam precisely together at exactly the same moment becomes increasingly difficult as the size of intended explosion gets bigger.  You have to slam the pieces together quickly or they'll get crazily hot and either melt or set off a half-hearted "fizzle" before you get it all together in one place to make a decent sized bang.  Thats why they use conventional explosives to push the heavy plutonium/uranium together.  It's tricky to get this right so the bomb doesn't "fizzle" - which has been a problem for several of the recent efforts in N.Korea and elsewhere.  The bigger the bomb, the harder it gets.


 * With a hydrogen bomb, the idea is to force the teeny-tiny hydrogen atoms together so hard that they fuse together to form helium and produce a shit-load of energy in the process. Hydrogen by itself is extremely easy to handle - you can put an awful lot of it in a small place - and it won't explode or anything (well, so long as there isn't oxygen around).  The trick is to force it all together tightly enough (and quickly enough) to unlock all of that energy.  To do that, the usual trick is to use a regular fission bomb as a trigger.   So now, a conventional explosion forces together a couple of chunks of plutonium or uranium - that explodes as a fission bomb - which compresses the hydrogen sufficiently to cause it to fuse into helium and make a much MUCH bigger bang.  This is tricky because this all has to happen before either the conventional explosion or the resulting fission bomb explosion destroys the whole machine.


 * So hydrogen bombs are clearly harder than plutonium/uranium bombs to make - but the size of explosion you get from them is also vastly larger.


 * SteveBaker (talk) 20:06, 7 January 2016 (UTC)
 * That's a good starting point as an explanation, but it's incomplete enough on its own that I think it's actually kind of misleading. In most thermonuclear weapons, while certainly hydrogen fusion provides a significant part of the yield, I don't think it's the majority of it.  The bigger contribution of the fusion component is that it generates massive neutron flux, which in turn causes fission in the uranium shell surrounding the bomb.  Still, your explanation is right in principle; you can't make that much uranium fission all at once by ordinary means, but you can if you throw fusion into the equation. --Trovatore (talk) 03:51, 8 January 2016 (UTC)


 * Yeah - I was trying to keep things simple (our OP asked for a 'simplistic' answer). There is an additional category of weapon which works more exactly as I described - where the fusion reaction is deliberately NOT used to trigger a secondary fission event - and that is a neutron bomb.  These weapons are hydrogen bombs with thin casings and they are engineered to produce a huge neutron flux and not produce such a large explosion.  The idea is to kill people over a larger radius - but without doing so much damage to buildings and other infrastructure.  The US invented them as a means to prevent large soviet conventional armies from taking over an area by killing their personnel without destroying other infrastructure.  Adding a heavy uranium casing produces a bigger explosion from that secondary fission event.  The lighter casing allows these neutron-bomb weapons to be fired from conventional artillery.
 * SteveBaker (talk) 14:29, 8 January 2016 (UTC)

Good to know that there is more than what I stated... Thanks guys. -- Mr. Zoot Cig Bunner (talk) 18:47, 9 January 2016 (UTC)

How tall could an artificial mountains be?
Using just known materials, how high could we pile them (formed like a mountain)? Would that be a less expensive, less risky possibility to go to space? That is, a pile built century after century reaching more than 50 miles high.--Scicurious (talk) 21:23, 6 January 2016 (UTC)


 * No. The current highest mountains give you an idea for what the limit is.  All sorts of things happen to cause that limit.  The ground underneath compresses, there is erosion from the top down, there are landslides, etc.  And realize that it doesn't just take twice the effort to build a mountain twice as high.  It would also be twice the diameter, which means 8 times the volume and mass (not counting compression), and the materials have to be lifted higher, so require more time and energy per block.  So, you could well be looking at 16 times the effort to make a mountain twice as high.  And the current tallest mountains at 5.5 miles high are nowhere near into space, so you would need to double the height (and increase the effort by 16), many times to get there.


 * A better approach might be to create a launch tube in an existing mountain, so the ship will leave the top at high speed, not having used any of the onboard fuel yet. StuRat (talk) 21:31, 6 January 2016 (UTC)


 * Consider Olympus Mons, a mountain the size of France and about three times the height of Mt Everest. Consider how much effort it would take to "build" a mountain of that size and then consider it's still just a "wart" on the surface of mars, you would need a mountain 4 times the height to get to space. Vespine (talk) 21:38, 6 January 2016 (UTC)


 * And it's only as large as it is due to Mars' reduced surface gravity (0.376 g, or about 3/8ths as much as Earth). StuRat (talk) 21:41, 6 January 2016 (UTC)


 * The cone building limit is approximately:
 * $${\sigma_c \over \rho g}$$
 * where $$\sigma_c$$ is the limit of compressional stress, $$\rho$$ is the density of the material, and g is the surface gravity. For granite (limit ~200 MPa, density ~3 g/cm3), this works out to about 7 km, which is also about the prominence of the highest mountains.  Most materials with better stress limits are also denser so it isn't easy to find materials that can be piled higher.  I'm not really sure if any easily available material would allow one to reach 100 km or other extreme height.  Dragons flight (talk) 22:05, 6 January 2016 (UTC)


 * People have seriously thought along the lines of "building a stairway to heaven", though you wouldn't do it by building a mountain. A space elevator is a commonly-discussed idea; see non-rocket spacelaunch for others. --71.119.131.184 (talk) 22:40, 6 January 2016 (UTC)


 * Something that will work against any attempt to build such a mountain is isostasy - the lithosphere will be warped downwards under the load - that's why mountains have roots. On a very short timescale this may not matter too much, but over millennia it will become important. Mikenorton (talk) 22:53, 6 January 2016 (UTC)


 * What does that mean, “mountains have roots”? —Tamfang (talk) 04:39, 7 January 2016 (UTC)
 * Mike Norton is referring to the geology underneath large mountains. In order to "float" heavy rocks on top of liquid rocks, the mountains need to buoyantly displace some of that material, or else they would sink.  Mountains abide by the same physical laws as everything else; we often just don't notice, because these processes occur very slowly (...rock is a lot denser and more viscous than, say, water).
 * Things get very complicated, because different parts of the crust and mantle have different geochemistry (and thus, different densities); and in some places, mountain uplift is a dynamic and unstable process (like in the Sierra Nevada Mountains, which will probably start sinking once they lose some of that upward momentum from their convective bobbing). They've been having their first upward bounce for a few hundred million years, so it might be a while before they sink.
 * In other words, when you see a mountain, you're only seeing the "tip of the 'berg."
 * Nimur (talk) 16:36, 7 January 2016 (UTC)
 * Thanks Nimur - see also Continental_crust. One of the counterintuitive results is that large mountains have large negative bouguer gravity anomalies (gravity field that has been corrected for topography), first noticed near the Peruvian Andes by Pierre Bouguer in the 18th century. Mikenorton (talk) 17:35, 7 January 2016 (UTC)
 * Nitpick: the mantle isn't liquid (as the article says); this is a common misconception. It's solid but plastic (in the original sense of the word, not the common modern meaning of "a man-made hydrocarbon material"). This distinction is important for understanding its properties. You are of course correct about the overall issues of buoyancy and displacement. --71.119.131.184 (talk) 07:16, 9 January 2016 (UTC)


 * Also, another thing worth discussing: even if we could magically create a mountain that reaches into space, if you want to stick things into orbit from the mountain's peak you still have to impart a bunch of energy to them. Objects wouldn't "float" into orbit if you released them from the peak; Earth's gravity is still pulling down on them. "There's no gravity in space" is a very common misconception, but it's obviously wrong (what keeps the Moon in orbit around the Earth?). To stay in orbit around Earth, you need to be moving really fast. You're weightless in orbit because you're in freefall; your orbital motion cancels out the gravitational pull of whatever you're orbiting. (Suggested resources for understanding this more: Newton's cannonball,, ) For a rocket used for an orbital launch, most of its fuel is used to impart sideways motion, not to make it go up. Proposals for non-rocket spacelaunch often revolve around a way to impart energy to the payload from an external source, instead of using fuel carried as part of the payload. This avoids "the tyranny of the rocket equation". --71.119.131.184 (talk) 00:08, 7 January 2016 (UTC)
 * Unless, of course, you could build a mountain that reached up to geostationary orbit...but that's so utterly out of the question as to not be worth considering. However, that is precisely the plan for the space elevator.  What's interesting about that altitude is that after that point, the higher you build, the LIGHTER the structure becomes - which is why the space elevator doesn't need to be a tower - it's a cable that's kept in tension by nothing more than the fact that it's very long. SteveBaker (talk) 19:39, 7 January 2016 (UTC)
 * What about a "mountain" consisting of a pyramid or cone shaped framework, made of light but strong materials, rather than it being solid? ←Baseball Bugs What's up, Doc? carrots→ 12:37, 7 January 2016 (UTC)


 * Using that idea... reduce weight by reducing materials. Make the bottom of the pyramid smaller and smaller and the sides steeper and steeper. Eventually, you would have a long cord - a space elevator. 209.149.114.138 (talk) 16:11, 7 January 2016 (UTC)
 * Bingo! ←Baseball Bugs What's up, Doc? carrots→ 16:34, 7 January 2016 (UTC)


 * A lattice might remove most of the weight, but it also removes most of the strength. As it turns out these factors tend to more or less offset each other so that the limiting height of an open lattice construction tends to not be very different than building a solid construction of the same material.  Dragons flight (talk) 16:52, 7 January 2016 (UTC)

Rules restricting use of centi, deci, deca, hecto SI prefixes.
I heared that SI has special rules restricting the use of centi, deci, deca, hecto SI prefixes, namely that unlike the other prefixes, these prefixes are recommended only for certain particular units of measure, and possibly for certain uses of those units. Where can I find a description of these rules? I'd prefer a description easily accessible on the internet. &#x2013; b_jonas 21:47, 6 January 2016 (UTC)


 * Not sure where to list them, but they are mostly going to be "only use them where it is currently customary", like cm. StuRat (talk)
 * Maybe, but if I am wrong and such rules aren't available, I'd like at least a description of the customary use of those prefixes. The difficulty here is that the use of prefixes in everyday topics differs by location, and the use in professional contexts may differ by area of expertise.  In particular, decagrams are commonly used in informal speech in Hungary to measure food items, such as meat products or cheese when bought in amounts smaller than 0.5 kg, but in some other countries it isn't used for such a purpose.  Similarly, deciliters and centiliters are used in everyday speech about liquids.  &#x2013; b_jonas 10:25, 7 January 2016 (UTC)
 * I can't find any rule suggesting their usage should be restricted on the BIPM site. See e.g. . I did find  (and other sites replicating the same thing) which say
 * "The prefix hecto- to centi- are not 'preferred prefix' but referred to as 'other prefix' by SI .... Le Système International d'Unités (SI) name the prefix giga and nano, milliard and milliardth respectivly. The wording shown here was approved by the General Conference on Weights and Measures and has been adopted in practice."
 * But I can't find this or any reference to preferred prefix or other prefix anywhere on the BIPM site. So either it isn't on the site in English in searchable format (bearing in mind the official language is I believe French and it's possible some of the older stuff is still in images that may not be OCRed or may not be properly OCRed), my search is screwing up and there is something somewhere, or the wording above is confusing and the "preferred prefix part isn't coming from the BIPM or the CGPM. (The wording is also confusing because it doesn't discuss deca etc.) It's possible the wording used to be there, but was removed at some stage and I'm having trouble finding the resolutions where this happened. You're correct their usage is uncommon in many areas of work and units, with some variance from country to country. (The bit you mentioned is partly mentioned in our articles like Deca- and litre. Actually the later article mentions the bit about their usage being discouraged, but it's unsourced.) National standards and other bodies and style guidelines may also have their own rules rejecting or discouraging the use of these prefixes. E.g.      & Metric prefix (the part about building codes). I also came across this interesting perspective  with claims of centimetre causing problems in adoption. Nil Einne (talk) 13:28, 7 January 2016 (UTC) Edit: Probably should have incluided  which appears to be the resolution where the prefixes were adopted. You'll also see linked on that page this PDF  which is the report/proceedings, in French of course, of the 11th conference where that resolution was adopted (page 87) if anyone wants to investigate further for any discussion of preferred prefixes (or whateve). That page also mentions the 1958 CIPM, I think this is the whole report in French, if anyone is interested in finding if there is any mentioned of preferred prefixes there instead. Nil Einne (talk) 14:30, 7 January 2016 (UTC)
 * I'd like to mention that it's hard to get usage info about how spread these prefixes are because they're used in speech more frequently than in writing. This is not surprising: in speech, 25 decagrams or 35 decagrams is easier to say and understand than 250 grams or 350 grams, but in writing, 250 g or 350 g or 0.250 kg or 0.350 kg are easier to read than 25 dag or 35 dag or 25 dkg or 35 dkg.  This is why people ask for 25 decagrams of cheese in the shop, but then the electronic weight scale prints a label with "0.250 kg" or something similar on that cheese.  This applies to me as well: I often use decagrams and centimeters in speech, but rarely in writing.  &#x2013; b_jonas 16:08, 7 January 2016 (UTC)
 * Don't confuse the metric system with the SI system. The metric system is the full set of prefixes.  The SI system is a subset of the metric system based around 7 base measurements for the seven defined measurements: length, mass, time, temperature, amount, current, and luminosity.  Since all other measurements can always be a derivation of those seven basic measurements, you define units for those seven base units, and let the rest fall out; i.e. volume is length cubed, electric charge is current multiplied by time, energy is mass multiplied by distance squared and divided by time squared, and so on.  The SI system only uses 7 units as their standards, and all except 1 are "base units", with no prefixes.  The only SI unit with a prefix is the kilogram.  There's an alternate system called the CGS system, which only uses centimeters as a prefixed unit, the rest are the base units.  So, I think you're confusing the terms here.  There's two different systems, one of which is a subset of the other:
 * The metric system, which is the full set of all possible measurements you can make, along with the full set of power of ten prefixes (hecto, giga, pico, whatever)
 * The SI system only uses the seven base units (meter, kilogram, second, kelvin, mole, ampere, candela). All other units must be some combination of those base units, known as the SI derived unit.
 * Other units are valid metric units, but not SI units. The centimeter is not an SI unit, the meter is.  In volume, the SI unit of volume is the cubic meter (m3), the liter is not an SI unit, because it is not a mathematical combination of the other units (it's a cubic decimeter, but decimeter is not an SI unit).  Similarly we have two common metric units of pressure: The pascal and the bar.  The pascal is in the SI system, because it can be reduced to SI base units, 1 pascal = 1 kg/(m*s2).  The bar is not, because it cannot be simplified to only SI base units (it's 100 megagrams/(m*s2)  I hope that clarifies things.  -- Jayron 32 21:15, 7 January 2016 (UTC)
 * Mostly this is a matter of semantics, but while it's true that the SI base units don't have prefixes except for the kilogram, I would suggest the prefixes are part of SI and not just part of the metric system. They are mentioned in our International System of Units article. And our Metric prefix article mentions SI prefixes. And for good reason, the prefixes are mentioned under the SI brochure published by the BIPM as SI prefixes. And the resolution which originally adopted/defined "the system founded on the six base units above is called the "Système International d'Unités"" ("le système fondé sur les six unités de base ci-dessus est désigné sous le nom de « Système international d'unités") or "international abbreviation of the name of the system is SI" ("l'abréviation internationale du nom de ce Système est : SI") said "names of multiples and submultiples of the units are formed by means of the following prefixes" ("les noms des multiples et sous-multiples des unités sont formés au moyen des préfixes suivants") and then went on to define/name the earliest prefixes . (See above for more links including the conference proceedings etc.) Nil Einne (talk) 10:11, 8 January 2016 (UTC)

The SI standard is available freely in PDF here. (This is the US edition, but that only means it uses American spellings and adds a few notes regarding recommended practice in the US. The content is the same as other editions.)  There is nothing in it to the effect that any prefixes are more preferred than any others. As indicated above, there may be national or other standards that make such recommendations, but if so, they are not part of the SI. --76.69.45.64 (talk) 02:32, 8 January 2016 (UTC)
 * Thank you for all the answers. Your answers agree that only national standards, not the SI, that give explicit rules for these prefixes.  &#x2013; b_jonas 08:05, 11 January 2016 (UTC)

What's the smallest or shortest building that'd be measurably weaker if it didn't follow Earth's curve?
Inspired by the mountain question, I wonder the above. The Boeing factory is about 100 meters tall and a half mile square, did they build the walls "not parallel" because of the curvature of the Earth? Did they have to mathematically alter the shape of the roof of the Aalsmeer Flower Building for its vast square kilometer size? How long would a catenary arch on a spherical planet have to be for it to be measurably weaker than the best shape for a globe? Does this shape have a name, too? Sagittarian Milky Way (talk) 22:54, 6 January 2016 (UTC)


 * Not sure if you really have to alter your plans in building construction to account for the curvature of the Earth. That is, there is a certain amount of tolerance in every joint, and that may well add up to more than enough to counter the effect.  For example, the I-beams at the top would be slightly farther apart than at the bottom, but that spread would just be in the location of the rivets.  Each vertical beam is likely made to be "normal to the Earth" using a plumb-bob, rather than "parallel to the rest". StuRat (talk) 23:17, 6 January 2016 (UTC)

And one more: How heavy could a structure on strong, geologically stable bedrock in a tectonically dead place be before you start affecting the crust? What would happen if you exceeded the pounds per square inch level of whatever the strong, stable bedrock is made out of without screwing with the crust? Sagittarian Milky Way (talk) 23:10, 6 January 2016 (UTC)
 * Read geotechnical engineering to get an idea of what is involved. Graeme Bartlett (talk) 07:23, 7 January 2016 (UTC)


 * I don't know about buildings, but suspension bridges are built with towers that are vertical but are further apart at the top than at the bottom due to the curvature of the earth. For example, the Humber bridge has 155m (510ft) towers that differ by 34mm (1.3 inches) and the Verrazano-Narrows Bridge has 693ft (211 m) towers that differ by 1 and 5/8ths inches (41 mm). Widneymanor (talk) 11:14, 7 January 2016 (UTC)
 * Modern boreholes, for example the ones used in deep petroleum extraction, are an engineering marvel: drilling a hole through "solid rock" becomes a complex engineering challenge when the length-scales imply that the rock is not very solid! For example, drilling in salt is plagued by the fact that salt "flows" like a glassy liquidy mush (among its other fun behaviors).  You won't see that effect in table salt - but if you were to try and cut a straight line through a few miles of mostly sodium-chloride, you'd see that your straight line starts to squish in all sorts of interesting ways as the overburden changes.
 * Along the same lines, petroleum and gas extraction are often accused of creating induced seismicity. This is not because the buildings on top are too heavy: it's because drilling wells and extracting fluids reduces pore pressure over a large volume.  That effect can cause subsidence and even earthquakes.
 * Nimur (talk) 16:05, 7 January 2016 (UTC)
 * Nice find about the bridges, Widneymanor! I once heard the Colossus of Prora was the first building to include the curvature of the earth in its plans, but a quick Google search for "Erdkrümmung Prora" didn't yield any results. &mdash; Sebastian 17:10, 7 January 2016 (UTC)


 * Does it really matter from an engineering point of view? What you can about in engineering is not if your walls are parallel, but if they distribute the load correctly, and deal with stresses correctly.  If you are using standard simple engineering tools, things like plumb lines to detect true "down", then you're designing your stresses to be aligned with the earth's gravitational field, and not as perfect 90 degree angles anyways.  I'm not an engineer, but it seems if you're making measurements based on physically checking against the earth's gravitational field (i.e. geodesy) then it comes out right in the end, even if it doesn't come out parallel.  -- Jayron 32 20:56, 7 January 2016 (UTC)
 * Then how wide or tall would a building have to be for it to be detectibly unparallel (either with engineering-grade instruments or the best tool known to man (a gravity wave detector?))? How wide or tall would a hypothetical parallel building have to be to be measurably weaker than a real one of otherwise equal quality? Sagittarian Milky Way (talk) 21:27, 7 January 2016 (UTC)


 * The problem with this question is that you use the word "measurably" - so this is more a question of how sensitive our measurements can be than about the orientation of walls to the local vertical. How would we measure whether a building was "weaker" than it "should be" with any kind of precision?  We don't generally measure the strength of buildings anyway - mostly we know the engineering parameters of the construction techniques used and we make sure there is ample safety margin.  There are sometimes small-scale tests done in wind tunnels or on shaker tables (to simulate earthquakes) - but that's entirely impractical for any building large enough for the curvature of the earth to remotely matter.


 * So, no - the building won't be "measurably" weaker.  We might ask whether it would theoretically be weaker - but that's a very different matter.


 * As others have said - builders routinely use plumb-bobs and spirit levels to get things straight and square - and those tools naturally ensure that walls are 'vertical' relative to the local gravitational direction (which might not be in the exact direction you'd predict from earth curvature anyway. Changes in underlying rock densities, nearby chasms or mountains - all of these things might result in the two side walls of a building not being perfectly parallel.  The degree of difference between the width of a tall building at top and bottom is going to be a matter of inches at most.  If you ever watch people on a building site measuring stuff - they are using long tape measures that are blowing in the wind, sagging in the middle, twisted and so forth - their errors are going to be much higher than errors due to the curvature of the earth.  So these kinds of differences due to the earths curvature are probably comparable in scale to the normal construction errors.  Architects must allow for reasonable measurement tolerances when they design the building - so it's really not meaningful to ask whether the building is weaker...it might easily be stronger - depending on small details of the design.


 * Because the building construction is continually checked with plumb-bobs and spirit levels - there isn't going to be any induced weakness - the walls will be vertical and the floors still horizontal, not by design - but by virtue of the instruments used to construct it. All that would likely result would be that the top floor of a very tall building would be slightly larger in area than the bottom floor in a building that's designed to be perfectly cuboid...but even that difference will likely be hidden by the fact that the load-bearing structures on the lower floors have to be built stronger to carry the weight of the upper floors.


 * For a very wide building - which would technically need a slightly curved roof and floors - the same kind of thing applies. As the roof and floors are constructed, small errors in the sizes of support columns and such will be checked using a spirit level - and the floors and roofs will naturally curve because of that.


 * You might argue that a building that has prefabricated steel beams or something might need special attention - but steel expands and contracts with temperature - and the building has to be designed with compensations for that - and that is likely to be more than sufficient to take care of any earth-curvature differences.


 * SteveBaker (talk) 14:12, 8 January 2016 (UTC)

Aversion to IQ tests
I noticed that I have a certain aversion to IQ tests so that I can't complete them and know my IQ. Out of 40-60 questions that an IQ test seems to contain I can't go beyond approximately 5th question (and certainly not beyond 10th). After first initial tests, as they get more complicated, I'm like "f*ck it" and quit, as I can't force myself to think further. Do some other people have the same issue or was it mentioned somehow before? Thanks.--93.174.25.12 (talk) 23:44, 6 January 2016 (UTC)
 * Certainly people with test anxiety have difficulty taking tests, but because of reference desk policy (see the top of the page) we cannot diagnosis any particular reason or reasons why you have had difficulty taking an IQ test. Hellmari (talk) 00:12, 7 January 2016 (UTC)
 * I agree with the above. What could possibly be relevant here is if there WAS any specific codified considerations for people who have trouble completing the "standard" test, but that almost certainly would not be part of any "online" IQ test which the vast majority of are not "official" in any way. You'd probably need input from someone who actually works with "official" tests whether they have special rules for people with attention disorders and such things, maybe they allow more time, or allow short breaks between every 5 questions (that's just speculation). It would seem to me that while this might not be "common" surely it would have to be common enough. Vespine (talk) 00:22, 7 January 2016 (UTC)


 * You need to figure out a way to make answering questions "fun" for you. I'd venture a guess that a large percentage of ref desk regulars enjoy taking such tests. ←Baseball Bugs What's up, Doc? carrots→ 01:37, 7 January 2016 (UTC)


 * Intelligence quotient is usually measured by a standardized test. Omitting answers - for any reason, including boredom - contributes to the correct scoring of the test.  IQ absolutely corresponds to your ability to focus; and whether this makes you happy or not, if you can't focus, you probably have a lower IQ than somebody of otherwise equal capability who can focus well.  The standardized test format test is designed to include that dimension in its scoring.
 * If you are taking a test like the SAT, where omitted answers are unscored, you can obtain a base-level score even if you omit every question after the first few. But: you probably will not like the score you get: you can't expect to turn in a blank test card and receive a high score.  (If you're interested in a discussion about treating SAT score as a correlate of IQ, or as a general intelligence test, it came up on this desk in October 2015).
 * Some researchers term this effect "mismeasurement" - for example, from our article on Attention-Deficit Hyperactivity Disorder, I found this 2008 article. But, for all these researchers calling this "mismeasurement," there are many more psychometrics research publications calling it "correct measurement."  If you can't perform well on an IQ test, your IQ Is lower than somebody who can.  This is the operational definition of IQ; it's why we can use IQ to measure the effects of, say, hypoxia on aviators, or sleep-deprivation on students, or the effects of trauma on soldiers, and so on.  There are all sorts of confounding factors that affect focus.  Here is a wonderful piece of quantitative psychometric research: Effects of Hypoxia... (1997), in which test subjects performed the MATB test battery with different oxygen levels.  Amazingly, being a smoker has an incredible negative effect on your ability to focus - perhaps stronger than the effect of hypoxic hypoxia!  These effects adversely impact test scores on standardized tests.  So, why should any effects caused by your personality or behavior get a free exemption?
 * As I always like to remark when this topic comes up: not all psychologists believe that psychometrics is a relevant approach. This means that some psychologists discount the importance of standardized testing.
 * Also: almost any internet-based free "test" is not an IQ test. Internet-based tests are usually very poor quality - they use invalid testing methods, and often use poor quality questions and methodology.  Do not treat "free web-based tests" as IQ tests.  They are not the same at all.
 * Nimur (talk) 15:16, 7 January 2016 (UTC)


 * In this case the IQ test is doing what it should do. IQ tests were developed to help predict how well a person would do in a structured school environment. Those with a higher IQ would do better and go further in education. Those with a lower IQ would do worse. In your case, you admit that you fail at structured exams, which are a requirement for nearly all structured education systems. So, you would do poorly in a structured education system and, per the IQ test result, you should receive extra resources to help you with your education. In my opinion, the notion that high IQ equates to high intelligence has made this a difficult subject to discuss. High IQ simply means that you have a tendency to better in a structured education system. If you begin with that understanding, then having difficulty taking the IQ exam should make perfect sense to you. 209.149.114.138 (talk) 16:03, 7 January 2016 (UTC)


 * I agree - the definition of "IQ" is "Your score on an IQ test" and if you don't score as well - then your score is your score regardless of the reason why.


 * The problem here is that our society has conflated "IQ" with actual intelligence - or "worth" to society - or some other damned thing - and that's just stupid. An IQ score measures your ability to do an IQ test - and nothing more.  So, if you can't cope with the test and end up with a lower score than you think you're worth - then...well...you DO have a lower IQ.  The problem is not that you wound up with a lower score than you hoped - the problem is that you (and others) tend to misinterpret the number as having some kind of importance to them.


 * That said, there are studies that show that people who do better at IQ tests (and hence get a higher IQ score) are statistically able to earn more money than someone who is less good at doing IQ tests - and to that degree, the IQ score does predict how well people do in the world. However, it's only a statistical relationship...it's not always the case that high IQ people earn a fortune or that people who earn a lot of money have a higher IQ.  For a particular individual, you can't say "This person earns a lot of money because they have high IQ"...it could be for any of a million other reasons.


 * What we don't know is whether people with a lesser IQ score have a shorter attention span (and so get sick of doing the increasingly painful questions) - or whether it's because they simply don't have the intellectual capability to solve the harder puzzles - or whether their brains are better at intuitive reasoning rather than logical reasoning - or they were sick on the day they took the test. You can somewhat check that for yourself by taking a test and doing (say) only every third question.  If you get further through the test before starting to fail - then your problem is really attention span - but if you still don't get very far because the puzzles start to get too hard - then perhaps you are less able at logic/reasoning challenges.


 * The real world is much more complicated than can be tested that easily - and certainly more multi-dimensional than could possibly be expressed in a single number. My IQ score is pretty good (probably because I actually enjoy doing the puzzles in IQ tests rather than being in some way "superior").  BUT just about anyone can beat me at playing chess - which is commonly considered to be a game that requires a lot of intelligence and which appears (at first sight) to depend on the same kinds of logical thinking as IQ tests.  If we used "CQ" (chess-quotient - I just made that up) rather than "IQ" as our standard metric of how smart people are, I'd be in the 70's rather than the 170's...but I'd still be the exact same person - and who is to say that IQ is more or less valuable than CQ?


 * So in the end - don't sweat it. Your IQ score doesn't matter a damn - and anyone who says otherwise is wrong. SteveBaker (talk) 17:55, 7 January 2016 (UTC)
 * Chess is a unique game: a very small number of early game permutations exist, and by rote memorization of those openings, a player can develop a very strong advantage in the middle and late game. What this means (to me, anyway) is that the game of chess has a very strong bias towards individuals who have played a lot of chess, rather than to individuals who are very good at logical thinking.  This is one reason why chess rating is not correlated strongly with other things, like IQ.  Rote memorization of a specialized skill - one that can be improved by practice - is actually something that is typically excluded from definitions of the general intelligence factor.
 * A handful of chess enthusiasts have put forward one relation or another to compare chess skill and g: for example, Levitt's equation, by one chess author, converts from Elo rate to IQ; but it's not a scientific result - it's just one guy's opinion, and he's not a psychology expert; nor are his ideas peer-reviewed by other psychology experts. Besides, we've already discussed some of the flaws of the Elo rating scheme: it is not a standardized test.  At best, its analogous to "grading on a curve," and in that respect, chess rating does have some similarity to IQ normalization; but it's also a very unstable metric that depends heavily on who else is playing, and in what order they're playing their games.
 * Nimur (talk) 19:52, 7 January 2016 (UTC)
 * Well, yes - but don't you think that an IQ test is also "a unique game"...and it's been found that practicing helps you do better (but not by much). The question is: "What do you mean by 'intelligence'" - and then "To what purpose do you intend to put the number once you've measured it?" - neither of which are very well defined at this point. SteveBaker (talk) 22:02, 7 January 2016 (UTC)


 * Based on your description I suspect you're talking about free online "IQ tests". A lot of them give most people a high score in the hope that they'll pay for a paper certificate showing their score. Real IQ tests are proctored and cost money, and the questions may not be very similar to the questions in fake online tests. -- BenRG (talk) 00:18, 9 January 2016 (UTC)