Wikipedia:Reference desk/Archives/Science/2012 January 23

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January 23

Difference in airplane fuel needs going to/from equator

We all know it takes more energy to walk from the center of a merry go round to the edge than vice versa because, well, however I explain it some pedant will correct me because I haven't taken a physics class in a few years. But imagine this: when you are at 20 degrees latitude, you are closer to the Earth's axis of rotation than you are when you're at the equator. In case 1, you take off from an airport at longitude X, latitude 20 degrees North (for instance), and fly due south to longitude X, right on the equator, and you note how much fuel you used. Then you take the exact same plane with the exact same conditions as far as the weather and your plane's weight (say, a 747), efficiency, etc. and fly back to your starting point. Given the energy content of jet fuel, would the difference in fuel used due to the difference in energy needed to get further away from the Earth's axis of rotation compared to the energy needed to get closer to it be, in terms of jet fuel, a few grams, a few kilograms, or what? If it's significant, airlines must have already thought of this and fueled the jets differently whether they're going from Rio to New York or from New York to Rio, for instance. 69.243.220.115 (talk) 00:12, 23 January 2012 (UTC)

Think that the moment of air from the poles to the equator (and the coriaceous effect) would mess up the calculations. On top of that, one should not fly due north/south because of the earth's rotation of about a thousand miles per hour and to ignore that, it would also mess up one's sums... one would have to fly at an angle to get a truer figure. Gravity at the poles is also less and the troposphere gets lower, thus the aircraft would require less fuel to stay in the air as it goes north, which is another factor to consider. Sorry, if I'm not answering your question.--Aspro (talk) 00:36, 23 January 2012 (UTC)

The OP has asked a very sound question. The fuel required when traveling towards the poles is less than when traveling towards the equator. I imagine that for a wide-body passenger jet on the Rio-New York City route, the difference would amount to several hundreds of kilograms (liters) of fuel. At the latitude of Rio de Janeiro the Earth's rotational speed is about 1545 km.hr^-1 whereas at New York City it is only about 1265 km.hr^-1. The extra fuel in going from NYC to Rio can be thought of as the fuel consumed in the time to accelerate the aircraft's ground speed from 1265 to 1545 km.hr^-1 while the aircraft's true airspeed is equal to its cruising speed.

Routine operations by airlines rely on standard tables to determine the amount of fuel to be carried at the time of take-off, and it includes a significant amount as a safety factor (often as high as 15%), so flight crews don't concern themselves with this effect. However, when an engine or aircraft manufacturer is carrying out fuel consumption tests, particularly tests to determine what guarantees of specific fuel consumption to offer, or to determine whether compensation must be paid to a customer, it is desirable to determine exactly where all the fuel went during a flight. When analysing these tests, the engine or aircraft manufacturer will calculate the amount of fuel to be allocated to the change in latitude from take-off to landing. Dolphin (t) 01:40, 23 January 2012 (UTC)

I take issue with the OP's assertion that, "it takes more energy to walk from the center of a merry go round to the edge than vice versa". Shouldn't the centrifugal force (a fictitious force, but a very real one in that rotating reference frame) aid the child walking from the center to the edge (after all, it is the total angular momentum of the system which is conserved (irrelevant for a powered merry go round)), and might not the same thing apply to the plane? -- ToE 04:09, 23 January 2012 (UTC)

Where the OP referred to more energy I assumed he meant the force discussed at Coriolis effect#Ballistic missiles and satellites. Dolphin (t) 04:25, 23 January 2012 (UTC)

Imagine a child wearing roller skates standing midway in on a carousel which has radial handrails. She will roll outward without any exertion on her part. Yes, she has more kinetic energy farther out, but she gains this energy as the carousel does work on her via the handrail. In the rotating reference frame, it is the centripetal centrifugal force which is accelerating her outwards, while it is the Coriolis force which is pressing her against the handrail, generating a normal force from the rail which checks her circumferential motion. In the non-rotating reference frame, this force of the handrail accelerates her tangentially, increasing her kinetic energy.

Prompted by the OP's mention of a merry go round, I first thought that it would take less energy to fly south along a meridian in the northern hemisphere, but that only works in a spherical world. Our geoid, roughly an oblate spheroid, is an equipotential surface which cancels out the effect of the centripetal centrifugal force. (See equatorial bulge.) If we measured altitude from the center of the earth instead of the surface of the geoid, then it would be easier flying at a constant elevation south, but the equatorial sea-level landing field would be at a higher altitude than the boreal sea-level departure field, canceling things out. It is as if the floor of the carousel is cup-shaped or banked.

The centripetal centrifugal force may be dispensed with, but we still have to take the Coriolis force into account. This ${\boldsymbol {F}}_{C}=-2\,m\,{\boldsymbol {\Omega \times v}}$ is perpendicular to the flight path and will be of the same magnitude when traveling in either direction. Thus the plane will have to correct by turning a very slight bit left of course to maintain track on the meridian, but this inefficiency will be experienced when traveling both north and south. So assuming still air, the simplest form of the OP's "exact same conditions", the northbound and southbound flights will require pretty much the same fuel. The Coriolis effect is greater at higher latitudes -- at the start of the southbound flight when the plane is heavier and the end of the northbound flight when the plane is lighter -- and this may have an effect on the fuel consumption, suggesting that the southbound flight may consume a bit more fuel than the northbound one. In real life the plane will not experience still air, and fuel consumption will be heavily affected by the winds along the flight path. See prevailing winds.

"tldr;" version: Centripetal centrifugal force isn't an issue due to the equipotential surface of the geoid. The Coriolis acceleration is perpendicular to the longitudinal flight path and will be of the same magnitude for northbound and southbound flights. This might not cancel out as the effect is greater at higher latitudes, when the southbound (northern hemisphere) flight is carrying more fuel, but the overriding issue in the real world will be the prevailing winds. -- ToE 20:30, 26 January 2012 (UTC) Warning: This Wikipedian is not licensed to practice physics.

ToE has written In the rotating reference frame, it is the centripetal force which is accelerating her outwards. It is unclear what he means by this. Centripetal means center-seeking, and a centripetal force always acts towards the center of rotation. It is never true to say that a centripetal force is responsible for the acceleration of a body away from the center of rotation.

It is often observed that a body fails to follow a circular path, and flies off at a tangent instead. In this situation, the acceleration of the body is due to the absence of a centripetal force. Some authors describe this situation by using the idea of the fictitious force called the centrifugal force. Dolphin (t) 21:26, 26 January 2012 (UTC)

Yikes! Yes, everywhere I wrote "centripetal force" in the long post, it should have been "centrifugal force". (The use of "centrifugal force" in my shorter pose several days ago was correct.) And yes, it is important to point out that centrifugal force and the Coriolis force are fictitious forces, but they are useful constructs employed in a rotating reference frame. (My impression is that secondary school physics stresses their fictitious nature, freshman college physics might hint at their uses but continues to emphasize non-accelerating reference frames, and university level classical mechanics exploits them, doing extensive work in rotating and otherwise accelerating reference frames.) The first two paragraphs of my long post were intended to dispense with the OP's "it takes more energy to walk from the center of a merry go round to the edge than vice versa", which, as I interpret it, is contrary to fact, but irrelevant to the question. -- ToE 02:12, 27 January 2012 (UTC)

ToE has also written that the magnitude of the Coriolis force is:

${\boldsymbol {F}}_{C}=-2\,m\,{\boldsymbol {\Omega \times v}}$

This formula is satisfactory for a carousel, but the Earth is a sphere and this formula can be misleading if the cross product is not handled properly. The cross product can be avoided if the Coriolis acceleration is expressed as 2 times omega times the rate of change of radius:

$a_{c}=-2\Omega {\tfrac {dr}{dt}}$

and so the Coriolis force is:

$F_{c}=-2m\Omega {\tfrac {dr}{dt}}$

In the case of the Earth, the rate of change of radius ${\tfrac {dr}{dt}}$ is not the same as the point's speed ${\boldsymbol {v}}$ on the surface of the Earth. The radius is not the radius of the Earth. It is the radius of rotation and that is the perpendicular distance from the point on the Earth's surface to the Earth's axis of rotation. At the equator the radius of rotation is equal to the Earth's radius, but at the poles it is zero. At any intermediate latitude the radius of rotation is equal to the Earth's radius times the cosine of the latitude. Dolphin (t) 21:43, 26 January 2012 (UTC)

I never called the vector F_c a magnitude, but instead spoke of its magnitude and direction. Perhaps its just as easy to give the scalar values, but the point of the cross product was to make clear that the Coriolis force was always perpendicular to the flight path, and was of the same magnitude for a given latitude, whether flying northbound or southbound (the difference between the two is v being reversed). I understand your restatement to arrive at the same conclusion, indicating that the only difference between the northbound and southbound flights are when the stronger Coriolis effects of the higher latitudes are experienced -- early in the southbound flight when the plane is heavier, or late in the northbound flight when the plane is lighter. Even that difference would lost with electric aircraft. (Nod to recent topic.)

The point is that the different rotation speeds of the earth at the different latitudes does not meant that the plane needs to use more energy to speed up to the faster equatorial rotation speed than it does to slow down to the slower boreal rotation speed. -- ToE 12:05, 27 January 2012 (UTC)

Thanks for your latest explanation. I have spent quite a bit of time trying to find a reason why thrust or drag (or specific air range) might be less for the aircraft flying towards the pole than for the aircraft at the same latitude flying towards the equator. I haven't been able to find such a reason so I must concede that whether flying north or south, the specific air range is the same. Perhaps the information I received from a competent organisation was that the Coriolis effect causes an additional element of fuel consumption for an aircraft flying north or south but not for one flying east or west. Thanks for a fascinating discussion. I learned a lot. Dolphin (t) 11:51, 29 January 2012 (UTC)

How "wrong" is string theory

I read the article, and I saw that the main issue seems to be it's testability, but I see many people (well honestly, on youtube, not scientific community!) that hold strong views about it and say it's somehow like religion, which I think is a dubious comparison.To what extent is it unacceptable?--Irrational number (talk) 00:27, 23 January 2012 (UTC)

XKCD explained the problem with string theory very well. Some people have used "string theory" as a term to describe some semi-religious pseudoscientific ideas they had. This does not necessarily discredit string theory itself of course. Von Restorff (talk) 00:48, 23 January 2012 (UTC)

I would not say its unacceptable, as it is just like any other of many other theories. The math is great when applied to attempts to answer certain questions. What I personal don't like about it is that it doesn’t scale up to the observable (dare I say it) real world. Way toooo complicated. --Aspro (talk) 00:49, 23 January 2012 (UTC)

Good one Restorff. As they say: a picture is worth a thousand words.--Aspro (talk) 00:59, 23 January 2012 (UTC)

The serious critics (e.g. Peter Woit, Lee Smolin) are unhappy because basically all theorists and especially young theorists are spending their time on it, and we are spending a lot of money researching it, when it isn't clear that it actually does resolve the problems in the previous theories or even explain the stuff that is already known. It's an issue with putting all of the scientific eggs in one apparently untestable basket. The quote in the Woit article sums it up well. It's about the fact that the scientific community is more or less pursuing this as its only option, even though there is not much evidence for it and it is not entirely clear even what it is. As for what is acceptable, it depends on who you ask. Smart people disagree on the matter. --Mr.98 (talk) 01:06, 23 January 2012 (UTC)

That was not very kind. Some of my best friends are fizzy-cysts. Yet, then again... maybe I should I ask for some of my tax dollars back? Oh, and I like your last quip - smart people disagree on the matter - does that apply to the dark stuff too ;-)--Aspro (talk) 01:22, 23 January 2012 (UTC)

Will you please hit the preview button before you post? Your mistake with the <small> shrank my own new section below. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:43, 23 January 2012 (UTC)

I did! However, how is the preview feature to alert me to anything you are to post after? As nothing had yet appeared below my post to see. As they say: Wikipedia is not a crystal ball.--Aspro (talk) 20:19, 23 January 2012 (UTC)

But what other baskets are there where we can put our eggs, 98? Not criticising, just very interested.--Lgriot (talk) 08:55, 23 January 2012 (UTC)

Heck if I know! I'm not a physicist. :-) But presumably there are clever enough theorists out there to think of non-string theory solutions to the various conundrums that vex physicists. --Mr.98 (talk) 19:15, 23 January 2012 (UTC)

To Lgriot: supersymmetry is also fashionable, but may or may not be testable, because the particles it predicts might appear only on energies much higher than what we will get in our latest and greatest particle collder LHC. – b_jonas 10:37, 23 January 2012 (UTC)

How large facility would one need to test supersymmetry theories?, assuming a "huge" budget ;) Electron9 (talk) 17:21, 26 January 2012 (UTC)

Smolin's alternative basket is loop quantum gravity. Woit seems to just focus on poking holes in the string theory basket. Gandalf61 (talk) 11:12, 23 January 2012 (UTC)

Woit does not like supersymmetry much more than he likes string theory. It is only slightly more testable than string theory: its predictions are of a kind "if the world is nice and it lacks fine-tuning, then we should be seeing new supersymmetric particles right around the corner" (in fact, we should have seen some of them in the LHC by now), "but, if we run LHC for three years and we don't find any, that's okay too." And supersymmetry has been the only game in town even longer than string theory. The last time when theoretical physicists made a fundamental prediction that was testable and subsequently proved correct was in the early 1970's. Right around that time, physicists got really excited about supersymmetry, then they built supersymmetry into supergravity, then supergravity became string theory, and, along the way, things were getting increasingly mathematical and abstract. Now that we have LHC, it's starting to look like maybe supersymmetry is not such a great theory after all, and that is a huge problem because we may have just spent 40 years chasing mathematical ghosts.

Loop quantum gravity is the most popular alternative basket. If you want to go straight for quantum gravity, there are a few closely related baskets, for example, Causal dynamical triangulation, which is one of a wider class of spin foam models. Some might question whether it is not too ambitious to go directly for quantum gravity - maybe we don't understand some important aspects of low-energy physics yet. Maybe non-supersymmetric GUTs such as Georgi–Glashow model weren't completely beaten to death.

But the most general problem, as per Woit, Smolin & co, is that the institution of academic science has become highly conformist, and that prevents "alternative baskets" even from being discovered. Younger scientists have no academic freedom because they have to work on what their advisers tell them to do. (I recall reading that, in biological sciences, mean age at first grant, which is basically the age when the scientist gets to work seriously on what he wants for the first time, is around 43. In physics, it's similar.) And, after you spent 15 years studying string theory under various advisers and amassing a portfolio of cited articles, are you going to drop everything you've achieved and go off working on some radical new idea? Probably not.

So we get some rather paradoxical outcomes, like when one of the most cited out-of-the-box "alternative basket" theories in recent years gets published by a 60-year-old physicist, because he is old and he does not have anything to prove any more and so he can work on whatever we wants. (Not that there's anything wrong with people his age publishing papers, but, traditionally, revolutionary science used to be done by people in their twenties. Isaac Newton began working on calculus at 23. James Maxwell derived his equations at 29. Albert Einstein was 26 when he came up with Special Relativity. Paul Dirac derived Dirac's equation at 26 and wrote a classic textbook on quantum mechanics at 28.) --Itinerant1 (talk) 13:49, 23 January 2012 (UTC)

I hadn’t thought of it in exactly that way Itinerant1 but your comments parallel my opinions very closely. I too, think that the current theorists will stay moribund with their esoteric math, until the next Newton or Einstein to comes alone and say's It is really like this... and it can be tested by observing the real world. Hopefully, s/he will also be a WP editor.--Aspro (talk) 20:08, 23 January 2012 (UTC)

It's hard for the next Einstein to come along. The number of highly intelligent individuals capable of doing this work is not much larger than it was in 1905, many of them avoid physics altogether, many others get sucked into the academic morass. And, worse, what if he comes along and no one notices? Arxiv averages 250 articles/month in hep-th, 350 articles in hep-ph, and 150 articles/month in gr-qc. Can he get lost there? --Itinerant1 (talk) 22:38, 23 January 2012 (UTC)

It's a general misconception that physicists achieve their best work during their twenties: [1]. Interesting related blog: [2] IRWolfie- (talk) 21:03, 23 January 2012 (UTC)

In the second link, the distribution is skewed by experimentalists and managerial types. For example, the four oldest physicists in the chart are Planck (42), Faraday (40), Oppenheimer (40) and Doppler (39). Planck and Doppler are outliers, Faraday was an experimentalist, and Oppenheimer got on the list because he was recruited as a leader of the Manhattan Project (he was already an accomplished scientist at 38). Van der Waals is a curious case. They put him as doing his best work at 35. This is because van der Waals was from a poor family, he had a very bumpy road to graduate education, and 35 was the age when he defended his doctoral thesis. --Itinerant1 (talk) 22:38, 23 January 2012 (UTC)

Most of Oppenheimer's best work as a theorist was in his 20s. His best work as a teacher was in his 30s. His best work as an administrator was in his 40s. His best work as a grumpy martyr was in his 50s. --Mr.98 (talk) 23:04, 23 January 2012 (UTC)

I don't agree with Itinerant1 that "conformism" is the problem. The problem is that there has been no meaningful experimental guidance for the last 30+ years. Even the smartest people in the world are not smart enough to figure this stuff out without help. They never have been. Ancient natural philosophy went nowhere until people started doing quantitative experiments. The reason for the interest in string theory is that it offers, or once seemed to offer, the hope of having few enough adjustable parameters to perhaps be tractable. Based on what we know about low-energy physics, the fact that these theories have only a few adjustable parameters is something of a fluke. There was every reason to expect quantum gravity to have infinitely many adjustable parameters, but string theory avoided that catastrophe. You can always say "but what if the real theory isn't simple?", but that's not really the issue. If the real theory is complicated then we will never find it. It's a version of searching under the lamp-post, except that we have no idea where the keys are, and they might be under the lamp-post for all we know.

Loop quantum gravity has been just as unsuccessful as string theory, and in contrast to string theory, there was never any reason to believe that it might be tractable in the first place. It is only mentioned by people like Woit for lack of anything better to offer as an alternative. I say that with no particular love for string theory, or dislike of LQG, but that's the reality of the situation. It's a very sad situation for anyone who cares about the future of particle physics. Unless the LHC finds something interesting—and a Standard Model Higgs boson is not interesting—we may already have reached the end of progress in theoretical particle physics, though we won't know it for a few decades. -- BenRG (talk) 08:20, 24 January 2012 (UTC)

It could certainly be both factors at once. Conformism could be overcome if there were meaningful guidance coming from experimentalists, and areas of inquiry could be more widely spread if not for the system of collective academic reinforcement.

And just to clarify, the view that "conformism" is a major problem is not so much my own view (although I don't like the way academia work either) as Woit's (that's what we were discussing, right?) (see here, and, for a longer discourse, see his book Not Even Wrong, starting at about the page 230), and Smolin's (here and in the book The trouble with physics, starting at page 261). --Itinerant1 (talk) 09:41, 24 January 2012 (UTC)

I'm reminded of the teacher who was confronted with an incomprehensible essay from a student: "It's not right. And, what's worse, it's not even wrong.". Similarly, if string theory doesn't make any claims which can be tested, it's simply irrelevant. We can come up with an infinite number of theories which can't be tested (and judging from all the equally untestable variants of string theory, they are well on their way). StuRat (talk) 21:10, 23 January 2012 (UTC)

Not even wrong actually derives from Wolfgang Pauli, and had been previously appropriated with regards to string theory by the aforementioned Peter Woit. Anyway, the testability question is a big one that physicists disagree on, and philosophers aren't totally sure of it themselves. The physicists claim that someday they'll probably find a way to test aspects of the theory, and they argue that its internal coherency can make up for this obvious deficit in the meantime. I dunno. I'm not confident in throwing all eggs in an untestable basket, but I also agree that insisting on testability inflexibly is not always a sensible approach. --Mr.98 (talk) 23:07, 23 January 2012 (UTC)

Thanks, I hope you don't think me so unprincipled as to purposely exclude Pauli. :-) StuRat (talk) 05:31, 24 January 2012 (UTC)

• Given that positivism is out of fashion, I'm going to apply methodological anarchism from the History and Philosophy of Science. String theory is "right" while it is funded. Fifelfoo (talk) 09:47, 24 January 2012 (UTC)

A nice way to think about science historically! But a poor way to run a budget. --Mr.98 (talk) 13:18, 24 January 2012 (UTC)

I feel hugely disappointed by reading above comments :'(--Irrational number (talk) 15:09, 24 January 2012 (UTC)

If you are curious about methodological anarchism, its prime proponent was Paul Feyerabend. A very smart guy! With a great sense of humor! A very persuasive way to talk about the historical development of science! I am a big fan! But I wouldn't put him in charge of the National Science Foundation. Point in fact, he was not even allowed to give letter grades as a professor, because he would give people A's for not attending his course. Fun guy, very Berkeley, but yeah, perhaps not the guy you'd want in charge of very much actual responsibility. --Mr.98 (talk) 20:59, 24 January 2012 (UTC)

BHeF₃

Shouldn't boron trifluoride, a strong Lewis acid, be able to form an adduct with any atom or molecule with at least one lone pair of electrons—which should also, at least in theory,make it able to form such adducts as S(F[BF₃]₃)₆, H₂O(BF₃)₂, BF₃He, and BF₃Ne? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:40, 23 January 2012 (UTC)

Well, I think you would struggle to find any professional chemist who thought Ne and He had a lone pair. SF₆ is too sterically crowded to fit 18 BF₃ molecules around it, and, again, whilst the fluorine atoms do each have 3 unused pairs of electrons around them, they're hardly lone pairs. You need to consider the difference between a lone pair and a pair of electrons. As for H₂O(BF₃)₂... it might exist, but under ordinary conditions would hydrolyse. The BF₃ is so Lewis acidic it would effectively suck the electrons from the OH bond and you'd get HF and B(OH)F₂, which would itself hydrolyse until you got B(OH)₃ or something similar. This is why BF₃ is moisture sensitive. Chris (talk) 09:22, 23 January 2012 (UTC)

BF₃ indeed does hydrolyze easily. Our boron trifluoride article has a reference for the equilibrium-reaction of it with water. The chemically sane analog is to use an ether instead of water: BF₃·OEt₂ and BF₃·SMe₂ are common lab chemicals. With one BF₃ unit on the oxygen, the oxygen atom has a +1 formal charge. Doesn't seem easy to have that highly positive center act as a Lewis base and react with another BF₃ unit (giving the oxygen a +2 formal charge). DMacks (talk) 17:02, 23 January 2012 (UTC)

The way to make Helium form chemical bonds is to remove one electron to make it resemble a hydrogen atom but with a charge. Then you can get helium hydride molecular ion, something of which I would imagine WWPU being a fan. Somewhere on this reference desk before someone calculated the energy to get a mole of protons or electrons into one liter of space. Can anyone find that? Graeme Bartlett (talk) 11:58, 23 January 2012 (UTC)

Exploding ions

Since a chunk of ions would instantly explode if the force containing it were removed, could chunks of pure ions be used as explosives? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:30, 23 January 2012 (UTC)

How are you proposing to make these 'chunks of pure ions' in the first place? AndyTheGrump (talk) 03:34, 23 January 2012 (UTC)

By getting a humongous number of ions and squishing them into the space they would occupy were they so many neutral atoms (using Herculean force, of course). Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:40, 23 January 2012 (UTC)

And after you've 'squashed' them, presumably you'll put them into some sort of container. What are you proposing to make it out of? Given the massive forces involved,it is going to be rather massively-built. Wouldn't it be simpler to just replace your six-tonne container for half a gramme of ionic solid (or whatever) with six tonnes of HE? I'm sure you could make a bomb of sorts by setting off a stick of dynamite inside a sufficiently-strong pressure vessel, and then dropping it on your enemy - though you'd need to construct it carefully to ensure that the pressure generated by the explosion wasn't quite enough to rupture it, and the impact with the ground would. A lot of effort for very little real effect... AndyTheGrump (talk) 04:50, 23 January 2012 (UTC)

Or you use H⁺ ions and squeeze them together until the strong nuclear force contains them for you. You might need a few neutrons for leavening. I wonder if you can get them out again... --Stephan Schulz (talk) 08:22, 23 January 2012 (UTC)

That sounds like it ought to work, yet I've never heard of ²₂He. Wnt (talk) 01:33, 27 January 2012 (UTC)

Coulomb explosion. Count Iblis (talk) 22:27, 23 January 2012 (UTC)

Why build up instead of down?

Is there any reason in highly populated urban areas (or any where else for that matter) we tend to build up (high-rises, sky scrapers, etc) rather than down? It seems the latter would have more benifits than the former, for instance: stability (an existing base, i.e. the ground to build aroundthrough), temperature control, plumbing (in that liquid naturally flows down, rather than having to be pumped up into high-rises), lesser visual impact (no ugly buildings marring the natural landscape), energy conservation, and overall square footage potential (in that, I imagine we can dig down a lot deeper than we can build up). Are there any cities/communities that are already doing this to a large extent? I am aware of existing subground houses and basement levels...I mean in more of a wide scale, modern development. (And please excuse all the parantheticals :) Quinn ^CLOUDY 04:04, 23 January 2012 (UTC)

I am thinking it would be more expensive to build down. I don't think people would like going far underground. The absence of most natural light would present a serious sacrifice in exchange for many of the benefits such as temperature control. But I have to admit that these are all guesses. Bus stop (talk) 04:11, 23 January 2012 (UTC)

Yes, I considered the cons before asking this question, and the absence (or difficulty of providing) natural light in underground dwellings was the first that came to mind. But most high-rises are office-type buildings, and are notorious for their florescent jungles and lack of natural light, unless you have a corner office. Of course, living quarters, like an apartment complex, generally come with at least one window looking outside, so that is definitely a consideration. Quinn ^CLOUDY 04:22, 23 January 2012 (UTC)

Plumbing goes both ways. We have to get rid of the waste. HiLo48 (talk) 04:14, 23 January 2012 (UTC)

I am not one normally to respond back answers given, b/c I appreciate the consideration given to my question, but I would just point out that, yes, the waste has to go down...but it goes down anyway. Why not a bit farther? Perhaps existing infrastructure is not condusive to deep-dwellings, in that they may exceed below the level of the existing sewer systems, and would have to be pumped back up regardless? Interesting point you make, thanks. Quinn ^CLOUDY 04:26, 23 January 2012 (UTC)

http://www.disinfo.com/2011/12/mexico-citys-65-story-inverted-skyscraper/ Greglocock (talk) 04:29, 23 January 2012 (UTC)

Ah, a very interesting article, and mentions the subject of fresh air, which is something I hadn't considered. Not sure about the plan for multiple "garden levels" to help produce it though. It seems like that would suddenly create a much more expensive maintenance cost to be be pratical, and if you had a deadbeat landlord, you might find yourself in a Total Recall situation. Maybe some sort of thermal heat-exchange process would be a better way to go. Quinn ^CLOUDY 04:39, 23 January 2012 (UTC)

Cost, technical difficulty and an absence of a market. Excavation is expensive, and few people want to live underground. Everybody would prefer to have a window, and the big boss gets a corner office. It's far more expensive to make a big hole in the ground and build or fit out a building in the hole than it is to enclose pre-existing space above ground, and it's remarkably hard and expensive to waterproof and dehumidity underground space. Geological considerations make structural design complicated (think of the trouble that Alpine tunnels have had), whereas bearing near the surface is usually easily accomplished and well understood. Undergroudn structures also have unique safety issues with respect to evacuation (it's easier to escape down than up) and require extreme measures to control smoke in the event of fire. As noted above, ventilation is a major concern. Acroterion (talk) 04:42, 23 January 2012 (UTC)

While only quite a small town, Coober Pedy, South Australia is a modern example of such a place, regularly featured in Australian travel programs, etc as a novel oddity. --jjron (talk) 11:38, 23 January 2012 (UTC)

Note that there are a few factors which may affect the likelihood of large-scale underground construction in the future:

1) Lighting: Improvements in lighting, such as compact fluorescents and LEDs, allow us to light an underground area far more efficiently, and generate less heat, than incandescent lights, and aren't as annoying as traditional fluorescent lighting.

2) TVs: Cheap large-screen TVs would also allow us to simulate window scenes, so it seems like we're someplace other than in a dungeon.

3) War: If a major war seems likely, all surface structures are highly vulnerable, especially if nuclear weapons are used. This could rapidly change all new construction to underground. The Pentagon, for example, has many floors underground, to reduce it's vulnerability somewhat. StuRat (talk) 17:30, 23 January 2012 (UTC)

I don't know that it would be more stable in an earthquake. Modern buildings can sway to a certain extent and I seem to recall some having gigantic shock absorbers, but you could hardly do that with a hole in the ground. See earthquake engineering. Plus there's the possibility of cave-ins. Clarityfiend (talk) 21:21, 23 January 2012 (UTC)

Earthquake risks should be reduced underground. The problem above ground is that the building is attached at one end, and vibrations at the bottom near the resonant frequency result in greatly magnified vibration near the top of the building. As for cave-ins, using a construction method with a series of reinforced concrete tubes, of the type currently used for water and sewage, would make that very unlikely. Only where the fault actually passes through the structure would it be likely to fail. StuRat (talk) 23:04, 23 January 2012 (UTC)

D'oh. Obviously I don't know engineering from a cavity in the terra firma. Clarityfiend (talk) 02:02, 24 January 2012 (UTC)

Actually, a properly designed above-ground structure can use its height to negate earthquake motion, either by design for an appropriate resonant frequency that mitigates most earthquake motion, or base isolation, or a tuned mass damper. None of those options are available underground, where the shear effect of the quake can't be mitigated, unless you build a free-standing structure in a much larger cavity - and then what's the point? Underground utilities are extremely vulnerable to earthquake unless they're flexible cable or tubing. A structural liner capable of withstanding rockfalls, soil liquefaction or crushing, yet sufficiently flexible to not fail itself, would be an additional cost burden. It's easier to design against falling down or sideways (which are predictable forces, or which can be defined within certain bounds) than against crushing or impact. My main point is that space above ground is already there. Space underground has to be made, and isn't especially desirable once done. Acroterion (talk) 03:26, 24 January 2012 (UTC)

Underground utilities fail because they extend for miles along the ground, and thus are quite likely to cross fault lines. Buildings, whether above ground or below, should be placed so that they don't cross a fault, because movement at a fault line through the center of a building would damage it no matter how it was constructed. You also mentioned a risk of impact below ground. I don't understand that, what's going to strike an underground building ? All of those tuning options you mentioned are to overcome the problem of vibrating a tall building from the bottom, so are completely unnecessary if you don't have that type of structure. Creating a gap around an underground building would just subject it to many of the problems of above-ground construction.

Also, does soil liquefaction create any additional pressure on the structure ? I suppose if it was resting on such soil alone, then it would become unstable, but the same is true for an above ground structure, like the infamous Leaning Tower of Pisa. StuRat (talk) 05:14, 24 January 2012 (UTC)

Underground structures undergo shear stress from earthquake motion that isn't confined to the fault line (the P-wave is compression, and can usually be neglected, the S-wave is a shearing motion that does the real damage). A tall underground structure would suffer from variations on the same problems as surface buildings do, since it may suffer distortion at different levels or sections as the shock waves pass through the earth. Unless it's decoupled from the surrounding earth, the forces would be directly transmitted to the underground structure. Above-ground structures have the freedom to move independently of the earth below, if correctly engineered. A structure locked into the earth has to do whatever the soil or rock makes it do. See Cheyenne Mountain for an example of an underground structure that's specifically designed to deal with this problem: it's a series of buildings in a large underground space, mounted on springs, in order to withstand the shock waves from a close detonation, which would produce many of the same effects. If you've created a gap, now you have a building structure and envelope to build, costing about the same as a surface structure, in a hole you had to excavate at great expense.

An example of utility disruption: the San Andreas Fault is offshore as it passes San Francisco (it comes ashore at Daly City), so no structures or underground utilities in the city sat astride the fault. The water system was destroyed. The main disaster in the 1906 San Francisco Earthquake was uncontrollable fire (though exaggerated for insurance purposes since direct earthquake damage wasn't covered, and by over-enthusiastic use of dynamite). Acroterion (talk) 06:14, 24 January 2012 (UTC)

To deal with soil liquefaction, you'd essentially be building a submarine, since the soil would be just that, a liquid, and you'd need a pressure hull of appropriate strength for the depth, assuming the structure stays at the place it started (if it stayed in one piece it would probably start to head up to the surface - a well-known problem with empty underground storage tanks in wet soil that haven't been strapped to a big flat chunk of concrete). However, I doubt a large habitable structure would be attempted in potentially liquifiable soil (as opposed to a transportation structure like a subway, which always seems to end up under the harbor) because of the effort needed to keep it dry under normal circumstances. Acroterion (talk) 06:09, 24 January 2012 (UTC)

An underground building is already likely to be below the water table, or at least to be surrounded by water after it rains, so would need to be engineered to be water-proof. Would soil liquefaction make the problem any worse ? As for the San Andreas, that fault, as well as others, has many sister faults which run parallel to the main fault, some of which no doubt intersect utility lines and were activated in 1906. I envision underground structures as being a series of small rigid chambers (perhaps spherical on the outside), connected by flexible passageways (perhaps cylindrical on the outside). They would be spaced out adequately so that the chambers would only need to support their own weight, not the weight of others above them (their weight would be redirected to the surrounding rock). So, when you free the structure from the stress of supporting all the floors above them and from wind loading, you gain a lot of excess strength for things like quakes. I would expect the force of the quake to be felt inside, but this is also true of above-ground buildings. While they can tune an above-ground building to resist a specific quake, if a quake occurs that is different than the one they predicted, the tuning may well fail. StuRat (talk) 18:02, 24 January 2012 (UTC)

Spherical seems like too much trouble: a vertical cylinder or a network of horizontal tunnels would be easier. Submerged spheres would be hard to ventilate unless designed like submarines (which tend to be expensive). Apart from sub-aqueous tunnels, few underground structures are designed as true pressure vessels: they generally assume some (sometimes significant) measure of seepage, which is allowed to drain to a sump and pumped away. In above-ground structural design, wind loads take a back seat to earthquake loads in all but the most benign geology (i.e., everywhere but Florida), so there's no savings from an absence of wind loads. I don't know how you would support the internal floor structures economically under your scheme: normal floor spans are on the order of 8 to 10m between vertical supports: greater spans increase cost exponentially, so any underground structure would have to support its own weight in the same manner as an above-ground structure. I doubt that under practically any circumstances that the lowest level of an an underground structure would be deeper than 100m from the surface in any case, unless built into the side of a mountain with direct access on a level grade. Acroterion (talk) 00:40, 25 January 2012 (UTC)

Modular spherical nodes could be built using geodesic dome techniques. Just hollow out a chamber slightly larger in the rock, build the sphere, then fill in around it, perhaps with gravel to allow for drainage. StuRat (talk) 02:46, 25 January 2012 (UTC)

One other point is that building down is harder to fit into a pre-existing city than building up. The only physical obstructions to building up are ancient lights and, if you're going really high, perhaps the flight plan of the city's airport. Building down, on the other hand, you'll hit sewers, water mains, gas mains, electrical wiring, communications wires, underground railways, steam tunnels, subterranean rivers, air-raid shelters, access tunnels and whatever else the city buried under that site in times past. Some of these would pose especially big headaches. For instance, you could probably get away with just tucking the phone lines through your walls, but a railway tunnel is for all intents and purposes unroutable - trains need gentle curves, so redirecting the line takes a lot of space and a lot of digging. I guess you could route a railway or a service tunnel through your building, but no-one's going to want to live or work in the floors immediately surrounding it. Smurrayinchester 01:02, 24 January 2012 (UTC)

Generally the economic incentive to build downward would be in a major city where land is dear, which generally results in subway systems and underground car parks in major cities. Those cities are also where the economic disincentives, in the form of underground utilities and transportation systems, are the greatest. An example of a city where there's already a lot of already-excavated moderately dry, stable underground space is Paris, which is underlain by huge networks of stone and gypsum quarries (as in plaster of Paris), some of them big enough to require viaducts for the Metro within the spaces. Yet these spaces are almost entirely unused, at least by the living. Acroterion (talk) 14:31, 24 January 2012 (UTC)

Making a hole in the ground to put your building into is massively more expensive than making a similar sized hole in the air. Roger (talk) 16:35, 24 January 2012 (UTC)

But you don't need to make the exterior attractive, and hire window washers, etc., to keep it attractive. StuRat (talk) 18:20, 24 January 2012 (UTC)

I am imagining a Syfy executive commissioning the next second-rate disaster movie The Burrowing Inferno. Sussexonian (talk) 20:42, 24 January 2012 (UTC)

Another problem is demolitions when a building becomes obsolete. It's far easier to use gravity to bring down a building than to shore up the walls of the existing hole while you carry out the old building piece by piece. Renovations are likewise an issue: you can add extra floors, or expand new wings of a building aboveground without too much issue. Trying to dig further down or outwards is a problem. 21:31, 24 January 2012 (UTC)

I would expect that only valuable items would be removed, and the rest just left in place, if there was ever an actual need to abandon an underground building. But, above-ground buildings are demolished because they are in danger of collapsing, or an eyesore, neither of which apply below ground. One other reason to demolish an above ground building is to build a new, bigger, better one in it's place, but underground buildings don't need to be torn down to add on.

I disagree about it being easy to add extra floors to an above-ground building. This is rarely feasible, as the lower floors wouldn't have the structural strength to support more floors, without cutting into the margin of safety. The only scenario I can see where floors could easily be added on later is if the construction was halted and resumed later. StuRat (talk) 23:13, 24 January 2012 (UTC)

Pressure at the bottom of Mariana Trench

The pressure at the bottom of the Mariana Trench in more than 1,000 atmospheres; can somebody explain to me how great that is using examples that I can understand? Some books say the human body gets crushed like a pancake, but that's too obvious. Also, are there any mundane objects that can survive such pressure? --Sp33dyphil ©^hat_ontributions 07:18, 23 January 2012 (UTC)

Depends on how you define "mundane", as there are actually creatures living in Challenger Deep, as incredible as that seems. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:57, 23 January 2012 (UTC)

I ain't no expert, but looking at Atmosphere (unit) and Atmospheric pressure, I gather that one atmosphere is about 1 kilogram per square centimeter. We have a lot of square centimeters on us, so that's a lot of kilograms, but apparently we've adjusted, just as the creatures in Challenger Deep have. So 1,000 atmospheres would be 1,000 kilograms per square centimeter, or a so-called metric ton. Definitely enough to squash a human. Submersibles like the Alvin and the Trieste are made of materials engineered to stand up to such pressures. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:11, 23 January 2012 (UTC)

Humans are mostly water, so its uncertain how much they would be "squashed" by pressure that is equal on all sides. Certainly, all the airspaces in the body would collapse. --Stephan Schulz (talk) 10:16, 23 January 2012 (UTC)

Interesting point, and perhaps it explains how soft-bodied creatures are able to survive at those depths. Presumably, they lack lungs or any other significant body "hollows". ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:36, 23 January 2012 (UTC)

I remember years ago seeing a pair of hollow metal (iron?) cubes used to demonstrate deep sea pressure. (I can't seem to find any images of such a thing on google though.) They were, I think, maybe a foot on each side, with walls about an inch thick. One of the cubes had been subjected to pressure of several hundred atmospheres, and its walls had caved in pretty deep, almost touching in the middle. I may remember the details inaccurately, but it was an impressive sight to a young person, and that's the image that still comes to my mind when thinking about great pressures: thick metal walls caving in. On the other hand, 1,000 atmospheres is within an order of magnitude from the pressure inside commonly used gas containers. The pressure inside a firearm cartridge can reach something like 50,000 PSI or 3,000 atmospheres, and at such pressures living organisms really begin to get "squashed": proteins denaturing, cell walls breaking. This kind of high pressure treatment can be used to preserve food without heating it.--Rallette (talk) 13:27, 23 January 2012 (UTC)

Losing compression at just 90m deep with a broken non-return valve is enough for a deep-sea diver in an old-style suit to be crushed into his helmet... and the Mariana Trench is at least 10.91 kilometres deep! Von Restorff (talk) 15:39, 23 January 2012 (UTC)

(Per Bugs, simplified.) Take a ton of iron, and support it on a base one square centimeter in area. The pressure it exerts on its base is similar to the pressure in the Marianas Trench. Looie496 (talk) 22:07, 23 January 2012 (UTC)

Just to put these things in perspective - about the most mundane thing I can think of is an empty beer can. Plenty of those are discarded overboard by people at sea. When empty cans fill with water they sink. I'm confident there would be at least a few thousand at the bottom of the Mariana Trench. If a can is completely filled with water by the time it sinks it would sit on the sea floor completely unaffected by the pressure and would just quietly corrode away. However, if there is a little air still inside, the can would deform as it sank until the pressure was high enough to force all the air into solution. Dolphin (t) 22:18, 23 January 2012 (UTC)

Deep-sea pressure effects on styrofoam, gummi-bears, and sadly, atmospheric-pressure equipment vessels: [3] DMacks (talk) 22:29, 23 January 2012 (UTC)

How much egg white do I have?

There are large eggs and small eggs. Egg yolks are usually about the same size. Large eggs have more egg white. I was told that older hens tend to lay larger eggs.

Now, let's get 11 very small fertilized chicken eggs and remove 0%, 10%, 20%, ... 100% of egg white from them respectively using advanced lab techniques. We put the eggs in an incubator. What will happen to the eggs? How many of them will hatch properly?

How does an egg know how much egg white it has? -- Toytoy (talk) 13:16, 23 January 2012 (UTC)

The egg white is about two-thirds of the total egg's weight out of its shell, with nearly 92% of that weight coming from water. The remaining weight of the egg white comes from protein, trace minerals, fatty material, vitamins, and glucose

— Egg white, S.G.^(GH) _ping! 15:14, 23 January 2012 (UTC)

"How does an egg know how much egg white it has?" The egg white is food and protection for the embryo. The embryo will know how much egg white it has if it runs out of food before it is time to hatch. There are probably ranges of acceptable amounts of egg white. The largest chicken eggs have probably been artificially bred to that size for human consumption and are probably larger than is necessary for the embryo to utilize, especially under laboratory conditions (in which protection of the embryo is less of an issue). --Mr.98 (talk) 19:13, 23 January 2012 (UTC)

That's probably true. When I've had duck eggs or quail eggs from normal ducks or quails that haven't been bred for anything in particular, the yolks seem unusually large in proportion to the whites, compared to store-bought chicken eggs. ~Amatulić (talk) 22:47, 24 January 2012 (UTC)

Coilguns and railguns

Some questions about coilguns and railguns:

(1) Coilguns vs. railguns: which of the two faces more challenging technical/engineering difficulties to be surmounted before...

(1b) ...they can be practical military weapons?

(1b) ...they can attain a high (comparable to that of, say, assault rifles) rate of fire?

(2) Would it be easier to construct practical coilguns and railguns with small bullet-sized projectiles or with large artillery-sized projectiles? My thinking is that small projectiles are more practical, as that would both reduce the energy required to accelerate the projectile (enabling the use of a smaller power supply) and minimize the resulting recoil; is this correct?

—SeekingAnswers (reply) 19:12, 23 January 2012 (UTC)

The main issues with railguns seem to be (1) wear on the rails (2) power supply. For a small portable unit, power supply is a major problem; explosives (as in a conventional bullet or shell) have a high energy density compared to the batteries that would be needed in a handgun but a low energy density compared to the fuels you might use in a warship's power plant (uranium or even fuel oil). Since serious prototypes have been built on warships, probably large size projectiles are more likely.

Power supply also relates to fire rates: typically existing models work by charging capacitors and then releasing the energy in a burst, rather than continuously feeding in the required power; but aside from having a bigger power source there's no easy solution to speeding up fire rates. These issues apply to both coil and rail guns.

As the article railgun says, another technical problem is the need for strong, heat-resistant rails that aren't damaged by arcing - this affects rate of fire, since it would heat up further with every firing.

Small projectiles would be easier in some ways, but the question is whether they would be useful in comparison to conventional small-arms fire. Coil and rail-guns have the advantage of being able to control their projectiles' speed and acceleration better than explosives, so they may be more suitable for delicate payloads like aircraft, rockets, drones, etc, than for slamming bolts of raw metal into the target. --Colapeninsula (talk) 10:46, 24 January 2012 (UTC)

Thanks for your detailed response, but it doesn't really address my question, which isn't so much "what are the technological difficulties?" as it is "which of the two faces greater technological difficulties?" —SeekingAnswers (reply) 21:25, 24 January 2012 (UTC)

Hard to answer your questions, but I'll tell you everything I know. The US Navy is working on a railgun that can be mounted on a naval warship and has the destructive power of a cruise missile and exceptional range while each projectile only costs a tiny fraction of a cruise missile. The main obstacle is of course the ablation of the rails and getting enough power to the railgun. The rail ablation problem could possibly be solved by using plasma rails. The rails don't have to be metal, they can be anything that's conductive, including plasma. There's no indication that the Navy is investigating this method though, probably due to technological hurdles involved. The power supply is the other issue. Because of this, railguns are more practical for large warships that have a reactor rather than small arms.

I should point out that railguns can potentially fire anything that is conductive. This includes conductive liquids and even plasma. There's some thought experiments that involve using a series of railguns aimed at a central point to initiate fusion. For tanks, it seems that Electrothermal-chemical technology might be more practical for the near future. I'm not entirely sure what it even is though, the article is a little ambiguous on even explaining the topic.

For small arms I heard coilguns are more feasible than railguns, but I'm not entirely sure why. Keep in mind, coilguns can only fire ferrous materials. ScienceApe (talk) 15:45, 24 January 2012 (UTC)

Why do animals use the thyroid hormone?

People who suffer from hypothyroidism do well using hormone replacement therapy. Why then does the body use the thyroid hormone to regulate the metabolism if you can just as well maintain the concentration of the hormone in the blood at some fixed level? Count Iblis (talk) 22:46, 23 January 2012 (UTC)

I don't follow your question. In a normal, healthy person with a proper diet (particularly with the proper amount of iodine in it), they would maintain the concentration of thyroid hormones in the blood at some fixed level. When something goes wrong, like the thyroid being removed due to thyroid cancer, that's when replacement hormones, natural or synthetic, must be taken. StuRat (talk) 22:55, 23 January 2012 (UTC)

Why then have animals evolved to regulate the metabolism using the thyroid hormone if the metabolism can be set at the same level anyway? It's not like insuline whose level will fluctuate strongly to regulate glucose levels. In the case of the thyroid hormone, no non-trivial regulation of anything seems to be going on. Count Iblis (talk) 23:07, 23 January 2012 (UTC)

Just because people can do okay with a fixed hormone level does not mean that a fixed level is optimal. This is not an area of expertise for me, but a quick scan of Google Scholar indicates that there are a variety of things that normally regulate thyrotropin secretion, which in turn regulates thyroid hormone levels. In particular, an exposure to cold causes a brief upregulation of thyroid hormone, which has the effect of increasing heat production. Looie496 (talk) 01:22, 24 January 2012 (UTC)

I concur with StuRat's confusion. You seem to be asking, "why do people need to regulate their thyroid horomone, if they can just regulate their thyroid horomone?" It has a tautological feel to it. Please feel free to elaborate if this isn't what you are saying. --Mr.98 (talk) 03:30, 24 January 2012 (UTC)

Well, *I* understood the question. He was asking why a hormone is needed to regulate the amount of thyroid activity, if the thyroid works perfectly well at a constant level of activity -- why couldn't the thyroid just be set to the correct level in the first place? Looie496 (talk) 03:48, 24 January 2012 (UTC)

Even if a constant level of activity works fine, some regulatory action may be needed to set the activity to that level and to keep it there. Dauto (talk) 03:57, 24 January 2012 (UTC)

Humans can get by with a constant level of thyroid hormone (chosen by a doctor). In the wild the thyroid hormone plays a role in adjusting the metabolic rate with nutrition, temperature and developmental status. Hope this answers your query.Staticd (talk) 05:57, 24 January 2012 (UTC)

Like most other bodily chemicals, a range of the hormone is "normal," not a fixed level. Staticd has the right of it: variable levels are needed depending on the conditions one is found in. — The Hand That Feeds You:^Bite 21:42, 24 January 2012 (UTC)

Understand that thyroid hormone has an ancient and important role in amphibian metamorphosis (and indeed, as the article mentions, even in fish). In humans, we don't see this metamorphosis because it occurs during embryonic development, during the formation of the stratum granulosum (the outer layer our skin forms to toughen and waterproof it against the air). Nonetheless, thyroid hormone still varies during this stage of development in the same way, and more or less for the same reason. Also, thyroid hormone controls heat production by brown fat as part of the normal homeostasis; thus adaptive T3 production helps in response to cold conditions.^[4][5] Wnt (talk) 03:17, 26 January 2012 (UTC)

Thanks! Count Iblis (talk) 23:57, 26 January 2012 (UTC)