Wikipedia:Reference desk/Archives/Science/2014 January 16

= January 16 =

science behind makara jyothi
There lies a big mystery behind the makara jyothi(a light glown on the day of makara sankranti near the sabarimala hills,kerala,India).There is no proper scientific reason given yet.Most of the people believe it as a divine light and many criticise it as an 'artificial light created to cheat people'.Please solve the mystery and help the wikipedia users.Kindly use the following links to know more about it. http://sinosh.wordpress.com/2008/08/26/makarajyothy/ http://www.spiderkerala.net/resources/4618-Divinity-Makarajyothi-questioned-Is.aspx http://ayyappadevotionalsongs.blog.com/2010/12/01/the-science-behind-makara-jyothi-in-sabarimala/ Makara_Jyothi — Preceding unsigned comment added by Kathir kishan (talk • contribs) 12:57, 16 January 2014 (UTC)


 * I see no mystery. As stated in the article (and ignoring the blog sites you linked to, where anyone can write anything) Makara Jyothi is a star.--Shantavira|feed me 13:33, 16 January 2014 (UTC)


 * Indeed. According to our article on the star Sirius (technically, it's a binary star): "The star is referred as Makarajyoti in Malayalam and has religious significance to the pilgrim center Sabarimala." - which makes sense because Sirius is the brightest star in the sky (after the sun, of course).  This star has many names in many cultures - and many of them give it religious significance and time ceremonies to it's rising and setting at particular days of the year.  So there is really no mystery to resolve here.  A complicating factor for people writing about this ceremony is that there is an entirely different ceremony carried out a few miles away called Makaravilakku which also entails worshipping Sirius - as well as lighting massive fires to celebrate various aspects of the star.  These might very well be visible over the horizon in the hilly countryside of that part of the world and might add to the whole mystical aspects of it all.  SteveBaker (talk) 14:24, 16 January 2014 (UTC)

Books like "Summa Technologiae"
Dear Gentlemen.

I am looking for more books like "Summa Technologiae" from Stanislaw Lem. Literature that deals with the possible far future and the technologies of such eras.--92.105.189.138 (talk) 14:52, 16 January 2014 (UTC)


 * Depends on how far is "far". The Diamond Age is a fun book set in the next ~80 years or so, and has a lot of interesting stuff about how nano technology interacts with society. Also a good adventure. If you want much farther future, one classic is Isaac Asimov's Foundation_(novel), as well as its sequels. --But really, In my opinion, most of the best Science fiction isn't really about the specifics of technology, it's about human nature and societies. For example, the classic A_Canticle_for_Liebowitz covers thousands of years, but has very little to say about specific technology. SemanticMantis (talk) 15:02, 16 January 2014 (UTC)


 * Diamond Age is a great choice - although it focusses entirely on nanotech. I'd like to recommend another book by the same author: Anathem - which describes a world where technology causes horrific boom/bust cycles and the future is largely held by a group of geek/monks who largely eschew technology and who (in a sense) hold the world together by virtue of nothing more than clear thinking and dedication....and it's also a great story!   It's rather hard to come up with books where future technology is actually a good thing rather than causing problems.  SteveBaker (talk) 15:19, 16 January 2014 (UTC)
 * From your description, Anathem sounds exactly like Star Wars!165.212.189.187 (talk) 15:31, 16 January 2014 (UTC)
 * Really? Well, the books couldn't be more different.  The monks of Anathem are pacifists and work passively and quietly in the background to make change.  I don't think the Jedi of StarWars are much like monks and the rest of the universe seems to be at a more or less static technological level rather than going through boom/bust cycles.  The monks of Anathem are reclusive in the extreme - with some sects cutting themselves off from the outside world (and even other monks) for 1000 years at a time.   Anyway - trust me, Anathem and StarWars are about as opposite as any two SciFi universes that I could imagine! SteveBaker (talk) 15:40, 16 January 2014 (UTC)


 * Jedi don't use guns, and do alot of "behind the scenes" social work. "Reclusive in the extreme"; You mean like Yoda?165.212.189.187 (talk) 19:22, 16 January 2014 (UTC)
 * Death Star: boom->BUST!165.212.189.187 (talk) 19:25, 16 January 2014 (UTC)


 * For an example of where technology turns out to be a very good thing, see Asimov's short story The_Evitable_Conflict. He was a rather optimistic guy :) We don't have a list of techno utopian novels, but there are some leads in Technological_utopianism. In contrast, there are tons of entries at List_of_dystopian_literature, many of which are broadly science fiction, and discuss technology to some extent. SemanticMantis (talk) 15:45, 16 January 2014 (UTC)
 * Technology has reached an "interesting" level in Iain Banks Culture series. His writing is also more literary than most of the classical hard-core SF writers, so it might be a better match for Lem's books than, say, Asimov or (shudder) David Weber. The Player of Games is often recommended as an entry to the series, and is excellent. --Stephan Schulz (talk) 07:43, 17 January 2014 (UTC)

Extrapolation of energy components and the end of scarcity


1. How reliable are the dotted line projections on this graph?

2. What is the proper way to extrapolate the sum total of the components of the graph?

3. What is the proper way to extrapolate the individual components of the graph?

4. When renewables overtake fossil fuels, does that mean the NAIRU can be reduced? Tim AFS (talk) 15:17, 16 January 2014 (UTC)


 * How reliable are the dotted line projections on this graph? - they are highly susceptible to political change. If the major politicians of the world truly understood the global climate change problem - then oil, coal and gas ought to start to head downwards - but if they continue to ignore the problem then at least natural gas consumption will increase.  The solar power increase is a technology-driven thing, and that's somewhat unknowable.  Nuclear power is a matter of public opinion more than science - and one event like Fukushima is enough to set back development for another decade until it fades from public memory.
 * What is the proper way to extrapolate the sum total of the components of the graph? - just plot a new graph that is the sum of the others with an extrapolation curve that is the sum of the other extrapolation curves.
 * What is the proper way to extrapolate the individual components of the graph?  - In the absence of any new knowledge of the future (eg some new technology that's due to come on-stream at some particular date), there are standard mathematical techniques as outlined in extrapolation. But in fields like this, it's common for people who are expert in the field to point out those kinds of things that will alter the mathematical expectation in some way.   For example, we think we have a fair idea about how much oil there is left in the ground and what the cost and difficulty that extracting it would entail - and that might cause the graph to dip downwards in the future, even though the demand for the stuff might continue unabated.
 * When renewables overtake fossil fuels, does that mean the NAIRU can be reduced? - that's a tough call. I don't have a good answer for you. But  beware though - the vertical axis is a logarithmic one - it tends to make renewables look much more important than they really are and it strongly emphasizes change where there may not be much - and de-emphasizes drastic changes by turning exponential growth into a more gentle curve.  This graph makes it look like hydro and nuclear are a huge chunk of the total energy supply - when in reality there is ten times less hydro power than there is oil - and thirty times less than all fossil fuels put together!  Wind contributes only about 1% as much as oil and 0.3% as much as all fossil fuels combined!
 * SteveBaker (talk) 15:28, 16 January 2014 (UTC)
 * This is admittedly un-sourced speculation, but I don't really see how the projection for solar is remotely plausible. There are some pretty serious technical challenges with increasing the efficiency of solar cells, I don't really see how the sum total of energy produced by solar power could be expected to increase linearly without relying on a (as of yet non-existant) major technological breakthrough.  It seems as though this chart conflates two issues, especially relevant to the solar example: 1) increased efficiency of solar cells and 2) increased coverage/usage of solar cells.  Even if you get 100% coverage, you're still going to hit a ceiling unless you also develop better photovoltaics. (+)H3N-Protein\Chemist-CO2(-) 17:15, 16 January 2014 (UTC)
 * Oh - it's *FAR* worse than that. The vertical axis is on a log scale - so they are predicting exponential growth at an insane rate.   I don't pretend to know whether those graphs are correct - and that's not really what we're being asked here. SteveBaker (talk) 20:00, 16 January 2014 (UTC)
 * The historical exponential rates depicted are not insane, and while there are always good reasons that no growth lasts forever, the potential for moving out into the Solar System has convinced me that the projections individually and collectively are sane and accurate enough for my purposes, which is depicting the changes in these production levels. Tim AFS (talk) 01:55, 18 January 2014 (UTC)
 * There is no technical reason that one can't grow solar power 100-fold solely by deploying 100-fold more capacity even without improvements in efficiency. As of 2010, you could increase US solar power 300-fold just by putting solar panels on every rooftop.  That's not even considering that there is enough sun in the desert of the American southwest to meet all of the world's electricity demand.  Now putting a solar panel on every roof or blanketing the desert wouldn't be cost-effective right now, but it doesn't actually require more efficient solar cells, just cheaper ones.  Solar PV has a long history of falling prices, and with the recent expansion of Chinese production, that trend has actually accelerated.  A solar module today costs only about 25% of what it cost five years ago, which is fueling a lot of growth, and if prices continue to fall then projecting solar as a significant component of the global energy mix might not be unreasonable.  Dragons flight (talk) 18:22, 16 January 2014 (UTC)
 * The problem is that you can only collect energy from solar panels during daylight - and perhaps only usefully collect in summer at some latitudes. In order to make practical use of all of that energy, you need a means to store it efficiently - and that does not yet exist on anything like the scale required here.  But in any case, that same argument could be applied to wind, tidal, hydroelectric, geothermal and nuclear - yet those graphs are not anywhere close to that crazily steep.  SteveBaker (talk) 20:00, 16 January 2014 (UTC)
 * Thank you so much! Please see Sustainability and, , and . Tim AFS (talk) 22:48, 16 January 2014 (UTC)
 * I should have also mentioned that solar and wind are much less expensive than hydroelectric and nuclear, and the former are falling while the latter rise in cost. Tim AFS (talk) 01:58, 18 January 2014 (UTC)
 * How much would it cost to subsidize renewables overtaking fossil in half the time, compared to flood and crop insurance costs? Tim AFS (talk) 22:48, 16 January 2014 (UTC)
 * It is a hard thing to estimate, but one can look at the difference between solar / wind costs and coal / gas costs. Based on current costs, replacing fossil fuels over the next 30 years would add roughly a $100 billion / yr to the cost of electricity.  The hope is that as renewables continue to scale up, the added cost will come down.  Global insured losses due to natural disasters (all types) average $20 - 50 billion / yr (though some years can top $100 billion).  At present, it is probably cheaper to insure losses than to fund the wholesale conversion to renewables, though that probably won't always be the case.  Dragons flight (talk) 22:13, 17 January 2014 (UTC)
 * Thank you! Does that include government flood insurance plans and self-insurance costs? Please let me ask the same question a different way: What proportion of the world's $650 billion per year of fossil subsidies should be moved to renewables in order to minimize total energy, flood mitigation, and food spending? I am convinced that the answer is on the order of 85% because raising the cost of transportation fuel raises the cost of food, but only in a very small proportion. Tim AFS (talk) 01:55, 18 January 2014 (UTC)


 * Was this graphic created by a bot? The "Author" is listed as a redlink user:AI.Graphic, here . LogLinScale.svg, while linear growth looks logarithmic.]]Anyway, I looked at the source and found this 45 page pdf, and this interactive charting tool . There doesn't seem to be a similar chart in the pdf, nor can I get the tool to display the info broken down that way. The tool does show an exponential increase in all renewable sources over the time period 1967-2012. I did a few spot checks against the tabular data in the pdf, and it looks ok so far.


 * What I can't find anywhere in either document is projections, let alone exponential extrapolation. Naively, (without getting into geopolitics, etc), I'd say use of exponential extrapolation here is unwarranted, unless further justification is provided (which would constitute WP:OR, unless you find other WP:RS that specifically talk about extrapolating this stuff). Linear extrapolation would be much more conservative, but the graph is probably most informative without any projections at all. As it stands, it runs the risk of misrepresenting the source data. On summary, I think the best course of action is to keep only historical data on this plot, and use other sources for projections (there are indeed hundreds of such sources, but that's a different can of worms.) SemanticMantis (talk) 21:19, 16 January 2014 (UTC)
 * I do not know who created the graph. Tim AFS (talk) 22:50, 16 January 2014 (UTC)
 * Sorry, I thought you might know since it has so few links, and two are from you. I found that an IP editor claimed authorship here, but it would probably be difficult to track them down, if they are only associated with a redlink user and an IP. Anyway, I stand by my claim that the projections in the graph are generally unreliable, and should not be included in an article unless further justification and references are given. SemanticMantis (talk) 23:16, 16 January 2014 (UTC)
 * Well, in nature most growth is exponential unless it hits a snag. Much the same is true in economics - notice how we are always talk about GDP growths in percent - a constant 2% growth results in an exponential curve. More realistically, most of these "exponential curves" are probably the lower half of a logistic curve, but it's generally hard to find out where in the curve we are. In the diagram, solar, geothermal and wind seem to match exponential curves very well for the last few years (the solid parts of the curve). So yes, the exponential growths will stop (after all, the sun puts out only 3.846×1026 W, so that's a hard upper limit on the maximum solar and wind can provide). But it is very hard to say where the exponential growths will stop. --Stephan Schulz (talk) 12:26, 17 January 2014 (UTC)

Animal mating
During copulation, is there a biological mechanism that helps guide the semen to the appropriate external orifice of the female without entering the WRONG orifice (namely, the anus)? 140.254.227.253 (talk) 18:06, 16 January 2014 (UTC)
 * I'm talking about mammals here. It doesn't have to be specifically humans, since I've observed dogs and cats engage in copulatory acts, and apparently, the male dog's penis somehow finds its way to the correct orifice. 140.254.227.253 (talk) 18:10, 16 January 2014 (UTC)


 * I will answer for non-human mammals. There is not one single mechanism, but rather a suite of physical adaptations and evolutionary processes at play. In simplest terms, any individuals that don't successfully copulate cannot pass on their genes and traits to the next generation, so at a first approximation, we could say that a large percentage of unsuccessful copulation is maladaptive, and such individuals will tend to die out/go extinct (there are some caveats here). Have a look at Animal_sexual_behaviour, Reproductive_system and mate choice for the general background. It's a bit unhelpful, but for most mammals, successful copulation by delivering semen to a vagina is simply instinct, as well as a path of least resistance. We do have an article Homosexual_behavior_in_animals, but note that many of those examples don't involve penis-in-anus copulation. SemanticMantis (talk) 19:00, 16 January 2014 (UTC)
 * For the caveats, there are ways that non-reproductive animals can pass on their genes and traits. In particular all ant species and many bee species have sterile workers, that still can contribute to evolution and natural selection. This evolution of sterility was confusing even to Darwin (Eusociality), but it can be explained through haplodiploidy and kin selection, but that's a bit off-topic to your question. SemanticMantis (talk) 19:00, 16 January 2014 (UTC)
 * That makes sense. Instinctive behaviors are much more easier to explain in nonhumans than humans. I merely asked this question out of curiosity, based on the sex positions article. One might wonder how oral sex and anal sex evolved, when those are not procreative acts. One might also wonder how a male and female can engage in vaginal sex in so many different sex positions, or whether there is a quick-and-easy, intuitive, instinctive way of impregnation. 140.254.227.55 (talk) 21:28, 16 January 2014 (UTC)
 * The simple (but again not that informative) explanation for oral and anal sex in humans is "because humans are creative, there is no big cost, and some people enjoy those sex acts" -- But the big thing to realize is that, though sex is the sole method of reproduction in mammals, it can also serve other purposes as well, e.g. pair bonding. I recommend "Why is Sex Fun? The Evolution of Human Sexuality" by Jared Diamond, google books here . I haven't read it yet, but the author is generally highly regarded, and the table of contents indicates that it discusses many of your questions. SemanticMantis (talk) 22:01, 16 January 2014 (UTC)
 * Cool. I've heard of Jared Diamond before on PBS, wherein he talks about Germs, Guns, and Steel. 140.254.227.55 (talk) 22:15, 16 January 2014 (UTC)
 * By the way, is human sexual foreplay required in successful copulation (that is, erection), or is that only for intimacy? 140.254.227.55 (talk) 21:55, 16 January 2014 (UTC)


 * No it isn't necessary but according to this it may improve the chances of conception. If you watch other primates copulating they don't usually bother with foreplay at all. Richerman    (talk) 22:13, 16 January 2014 (UTC)

Marking of university exams
How are university exams in the UK marked compared to school GCSE and A-Level exams where examiners simply follow a mark scheme? I.e. Witnout a mark scheme, how are the allocation of marks decided? Clover345 (talk) 18:46, 16 January 2014 (UTC)
 * British universities use a system of internal moderation followed by assessment by External examiners. The systems used are overseen by The Quality Assurance Agency for Higher Education (QAA) who ensure the procedures used are fair and equitable. See:  Richerman    (talk) 22:55, 16 January 2014 (UTC)

Microwaveable meal storage
How long can a microwaveable ready meal be safely stored in a fridge after it has been opened but not microwaved? 82.40.46.182 (talk) 19:11, 16 January 2014 (UTC)
 * It would certainly depend on whether you mean *opening the box* or *removing the plastic screen-cover*, the environmental conditions in the kitchen or cooking area, the type of preserved food, and the label on the food package that sets the approximate due date. 140.254.227.55 (talk) 21:03, 16 January 2014 (UTC)
 * The plastic screen cover opened and stored in a fridge. 82.40.46.182 (talk) 23:47, 16 January 2014 (UTC)

Delaying heat-death by pausing stars?
Is it conceivable that a star could be stopped and later restarted in the year 3000? --78.148.110.69 (talk) 22:39, 16 January 2014 (UTC)


 * "We don't answer requests for opinions, predictions or debate". AndyTheGrump (talk) 22:40, 16 January 2014 (UTC)


 * If you mean conceivable using human technology, the answer is most definitely no. Human technology cannot even control a terrestrial weather system or tsunami, which involve the movement of a tiny fraction of Earth's mass, which in turn is 1/300,000 the Sun's mass.  --Bowlhover (talk) 23:59, 16 January 2014 (UTC)


 * There are many reasons why this is impossible - but one of the more serious is that stars are immensely heavy - to the point that they would collapse into a tiny dense core (a neutron star - or even a black hole). What prevents that from happening is the radiation pressure of all of the light coming from the star.  So if you could somehow prevent it from consuming fuel by nuclear fusion, it would immediately collapse under it's own weight.  SteveBaker (talk) 03:19, 17 January 2014 (UTC)

Thanks guys. Especially you, Grump. <3 78.148.110.69 (talk) 21:57, 17 January 2014 (UTC)


 * Of course we will be able to turn stars on and off. After all, reality is only a projection of the "real" universe, so once we are able to pull back the curtain, anything will be possible. I'm only half kidding. The more we find out about how the universe works, the stranger it becomes. It might be that we have it all wrong and one day some wise guy will show us that if you just look at the world sideways ... — Preceding unsigned comment added by 50.43.12.61 (talk) 07:16, 20 January 2014 (UTC)