Wikipedia:Reference desk/Archives/Science/2009 February 19

= February 19 =

xkcd science reference
I was looking through some old xkcd comics (I was bored, and you know, there's worse ways to spend your internet-time), and came upon this this comic that contains a science reference I've never heard of. It talks about some hypothesized supermassive object outside the visible universe that's pulling a bunch of galaxies towards it.

I've never heard of this. Can anyone enlighten me to what Mr. Munroe is talking about? 90.234.71.57 (talk) 00:32, 19 February 2009 (UTC)
 * The title of the comic suggests that our article dark flow may be relevant, and indeed it is. Algebraist 00:40, 19 February 2009 (UTC)


 * Ahh, silly me! Should've seen that :) Thanks! 90.234.71.57 (talk) 00:43, 19 February 2009 (UTC)
 * Hmm, aside from my disappointment at seeing an xkcd I've already read and enjoyed, my first thought was actually the Great Attractor. Are "Great Attractor" and "dark flow" about the same thing? Franamax (talk) 00:56, 19 February 2009 (UTC)
 * No, not at all. As the article explains, the Great Attractor is well within the visible universe. Algebraist 01:00, 19 February 2009 (UTC)
 * When reading XKCD, it's frequently necessary to read the popup that appears when you hover the mouse over the cartoon. SteveBaker (talk) 02:10, 19 February 2009 (UTC)
 * Yes, but I doubt the Pioneer anomaly is due to the force of my love would have helped much in this instance.... --Trovatore (talk) 02:15, 19 February 2009 (UTC)
 * Well, it points towards some of the odder theories that have been used to explain the anomalous behavior of the Pioneer probes - which includes stuff like 'dark flow'. SteveBaker (talk) 03:34, 19 February 2009 (UTC)
 * Oh-mi-god. Like reahl-ii! - Now I have to review every single xkcd to see the tooltips! Never tried that before. :)
 * And what is the deal with the Pioneer satellites (beyond the fact that they are still working)? Should I frame that as a separate question thread? I just know that things aren't working out as expected beyond the heliopause... Franamax (talk) 03:44, 19 February 2009 (UTC)
 * This is an encyclopedia, you know: pioneer anomaly. Algebraist 03:47, 19 February 2009 (UTC)
 * FYI, they aren't still working. At least, they aren't communicating with Earth any more. You may be thinking of the Voyager probes. --Tango (talk) 13:42, 19 February 2009 (UTC)


 * Did you check the forum? — DanielLC 17:45, 19 February 2009 (UTC)

Boyle's Law
What is an everyday situation that involves Boyle's Law? I had thought of tire pressure but that doesn't work. Thanks! Reywas92 Talk 02:22, 19 February 2009 (UTC)


 * How about an inflatable arm chair? When you sit on it (increasing the pressure) it sinks down (decreasing the volume) and goes back again when you stand up. (You can replace the arm chair with a lilo, an inflatable mattress, or any other non-elastic inflatable thing - elastic things, like balloons, work a little differently.) --Tango (talk) 02:34, 19 February 2009 (UTC)


 * For that matter, the same applies to car tires when the car is lifted off the ground for maintenance. When the car's on the ground and its weight is on the tires (increasing the pressure), the bottom of each tire flattens (reducing the volume of the air inside).  Also in the realm of tires, consider a bicycle pump: the manual air pump you might use for inflating bicycle tires.  Each time you stroke you handle in, you reduce the volume inside and this raises the pressure.  --Anonymous, 04:31, February 19, 2009.


 * Compare how a completely sealed pouch of airline peanuts looks when you're aloft vs after landing. DMacks (talk) 02:39, 19 February 2009 (UTC)
 * I suppose resisting the temptation to actually eat the peanuts in flight is a bit easier these days :(  hydnjo talk 02:54, 19 February 2009 (UTC)


 * Thanks! Anything that goes the other way? Increase the volume to decrease the pressure, or decrease the volume to increase the pressure. Reywas92 Talk  02:42, 19 February 2009 (UTC)
 * Compression stroke of internal combustion engines. DMacks (talk) 02:46, 19 February 2009 (UTC)


 * Not exactly everyday but... a syringe without a needle is usually available from a veterinary office to administer liquid meds to your pet. Fill part way with room temperature water, seal the opening with your thumb, withdraw the plunger and watch the water boil at room temperature due to the decreased pressure resulting from the increased volume. -hydnjo talk 03:48, 19 February 2009 (UTC)

—Preceding unsigned comment added by TungstenCarbide (talk • contribs) 04:02, 19 February 2009 (UTC)

Eyes wide shut?
Nothing tempers feelings of being smart like fielding questions from an inquisitive child. This evening, my daughter asked me what keeps your eyes shut while you sleep. My first thought was that having the lids shut was the neutral position, but that's not so; when I relax my facial muscles, my lids go to half mast and dead people don't close their eyes either. Googling around gives answers to some related topics, but generally miss the mark. So, what's the deal? Are certain muscles kept taught during the sleeping hours (excepting the usual flutters, etc.) Don't the muscles become fatigued? Matt Deres (talk) 04:34, 19 February 2009 (UTC)


 * I've taken care of quite a few critically-ill patients, some of whom required deep sedation and neuromuscular blockade. Uniformly, those people need ointment and often mechanical closure (tape is often used) to prevent exposure keratitis (I am amazed that WP has no actual content on exposure keratitis).  Of course, my experience is just OR, so here's a quote from an article on exposure keratitis in the intensive care unit:


 * "Eyelid closure is an active process that requires contraction of orbicularis oculi and inhibition of levator palpebrae superioris"


 * Thus, it is an active process. There are plenty of important things we do in our sleep.  If we did not keep our eyes closed, we would be at significantly greater risk of blindness.  Certainly, some people have their eyes partly open during sleep; this is mitigated somewhat by of upward rotation of the globe during sleep. HTH  --Scray (talk) 05:51, 19 February 2009 (UTC)


 * ...and some people have their eyes completely open during sleep, or at least sometimes during sleep. Anecdote time: my father, for one. My parents are divorced, and my brother and I used to spend every other weekend at my dad's place. When I was really young -- pre-school age, I guess -- we all slept in the same bed, and I remember several times when I woke up in the middle of the night to find him staring at me, or the ceiling, or something else, depending on what position his head happened to be in. It spooked the crap out of me, because there was no recognition, no movement, no comprehension in his eyes; they were just completely empty. No wonder, 'cause he was asleep -- it's not as if he was in the driver's seat at the time. When I got used to it, it was just funny, but those first few times, it was really creepy and, well, alien. It just wasn't something that jibed with my experience of how humans interact, at all. -- Captain Disdain (talk) 07:02, 19 February 2009 (UTC)


 * I'd say it takes a muscle contraction to either open or close the eye lids, but they will normally stay at their current position, otherwise. Note that the eye lids of the dead stay however they are left.  It's quite possible for muscles to contract during sleep, though, as heart beats and breathing both require this. StuRat (talk) 14:01, 19 February 2009 (UTC)


 * As I said above, neuromuscular blockade leaves the eyes open. I provided a quote from a reliable source above, stating that it is an active process.  Rigor mortis can leave the eyes open or closed, but that's an active process (involving muscle contraction), hence the "rigor" part in the name.  The OP asked whether keeping the eyes closed during sleep requires muscle contraction, and the answer is yes.  --Scray (talk) 00:13, 20 February 2009 (UTC)


 * When I read that quote, that "Eyelid closure is an active process...", it sounds like they refer to closing the eyes, not keeping them closed. If your interpretation was correct, all dead people would have their eyes open until rigor mortis sets in, right ?  This doesn't seem to be the case. StuRat (talk) 04:45, 20 February 2009 (UTC)


 * Fully opening the eyes is an active process. Closing them is active (and was the OP's question).  Midpoint seems to be the neutral position, and that's where I've seen the eyes of people under pharmacologic paralysis.  In people who have just died peacefully, I've seen the eyes closed and slightly open - but I have not made a study of the time course, or changes in this.  --Scray (talk) 05:54, 20 February 2009 (UTC)


 * The original question was "what keeps your eyes shut while you sleep" not "what causes your eyes to shut initially". The fact that any dead people keep their eyes fully closed before rigor mortis implies that no muscle contraction is required to maintain this state. StuRat (talk) 13:36, 20 February 2009 (UTC)


 * As for dead people, their eyes tended to be open. It was common in olden times to place coins on the eyes to keep them closed. Embalmers now use cement to keep the eyelids closed. . Edison (talk) 05:16, 21 February 2009 (UTC)

Weight Scales
Hey, everyone. I have a question refering to the weight scales that you use to measure lightweight things. I only recall the act of figuring out the weight: first, you must calibrate it; then, you have to move the dials, and it would either even out, get heavier, or get lighter. I have completely forgot the name of this weight measurer! Help, and thanks.--Miss Hollister (talk) 06:32, 19 February 2009 (UTC)


 * We have an article on Weighing scales which has lots of different pictures of different types and models of scales. Do any of these help you?  --Jayron32. talk . contribs  06:35, 19 February 2009 (UTC)
 * The description ("calibrate via dial, add the weight to be measured, adjust to cancel it out") sounds like a torsion balance (which is actually a type of spring scale not a "balance"). Useful for measuring very small forces, and not listed on the Weighing scales page. DMacks (talk) 06:51, 19 February 2009 (UTC)

Aristotelian perfect heavens and Galileo
I've repeatedly read that Galileo used his telescope to prove that the Moon was not a uniform, unblemished body, shattering the Aristotelian view of perfect crystal spheres. But the lunar maria are quite visible with the unaided eye -- how could a view of perfect unblemished moon be held? Or is this one of those common but incorrect beliefs like 'Columbus proved the earth was round to Queen Isabella'?

Also, I've repeatedly heard that there are no European records of the Crab Nebula supernova, but there were in other cultures: this is supposedly attributed to the Church's influence, but in the 1050s much of Europe (especially the Scandinavian parts), while maybe Christian, definitely weren't dogmatic. Could it simply be that the records didn't survive? 128.194.250.39 (talk) 07:06, 19 February 2009 (UTC)


 * Galileo/Moon - The point was not the dark maria, which anyone can see, but the mountains. In any event, the person who banished the notion of crystal spheres wasn't Galileo, but Johannes Kepler.
 * Crab Nebula - From what we can tell, nobody in Europe noticed Sn1054. In the middle of the Dark Ages, astronomy was not a major concern. One would have to be quite familiar with the night sky to know that one particular star hadn't been there last week. Altogether, in order for us to have records, four things would have to have happened: (1) someone noticed the star, (2) they reognized that it had not been there before, (3) they made a record of it. and (4) the record survived. All four are low probability. So while the problem might be point 4, more likely it's 1, 2, or 3. +
 * &mdash; B00P (talk) 08:27, 19 February 2009 (UTC)


 * Oh, OK. I had heard it was too bright to miss (as bright as the full Moon), but if that's not the case, then definitely. 128.194.250.39 (talk) 08:38, 19 February 2009 (UTC)


 * SN 1054 says it was bright enough to see during the day for about 23 days, but I don't know if it was as bright as the full moon. Bear in mind it would still have been a lot smaller then the moon. It's also suggested it may have been referred to in Irish monastic annals. Edit: Sorry I didn't look at the article properly. The peak magnitude has been estimated as -6 which while brighter then Venus and an ISS flare, is no where near as bright as the moon and isn't even as bright as an Iridium flare. Nil Einne (talk) 10:48, 19 February 2009 (UTC)


 * OK, that makes a lot more sense. It would still have been noticeable, but it wouldn't have been as likely to have been recorded and remembered. (I'm still rather surprised it wasn't taken as some sort of omen, though, as comets were.) 165.91.80.170 (talk) 19:42, 19 February 2009 (UTC)


 * I would think a more likely explanation for why it wasn't noticed in Europe was bad weather when the event occurred. Perhaps they had rain/clouds/overcast skies on those days, while there were clear skies elsewhere. StuRat (talk) 13:56, 19 February 2009 (UTC)


 * All over Europe, for three weeks? Algebraist 13:58, 19 February 2009 (UTC)


 * Doesn't it ever get cloudy in Europe for 3 weeks at a time ? StuRat (talk) 21:31, 19 February 2009 (UTC)
 * Over the whole of the continent? I doubt it. --Tango (talk) 23:31, 19 February 2009 (UTC)


 * The supernova was apparently recorded in early July 1054. It would have been relatively close to the Sun in the sky hence not so easy to observe during the day due to Sun glare and mostly below the horizon during the night, pretty low on the horizon in the late hours / early morning (along with a sunrise) at European latitudes. In other words, it was probably not as easy to spot as its alleged brightness would have you think. At latitudes closer to the tropic the supernova would have been somewhat higher on the horizon in the late hours of the night, so maybe a little easier to spot (which may or may not explain why the Chinese recorded it and not Europeans).
 * I would not dismiss weather out of hands either, I expect the supernova wasn't a magnitude -6 throughout the whole of July, a few days of clouds *might* just have hidden it from sight when it was most obvious, though I'm just guessing here.
 * Anyhow, it would have appeared in the sky as a bright Venus, which would not have been particularly shocking to anyone but someone keeping track of the planets and preferably awake late in the night. Equendil Talk 03:07, 20 February 2009 (UTC)

Grooves (archaeology)
The article on grooves said that the initial theory about grooves found carved into rock was that they were used for sharpening swords, but this has been disputed because (among other reasons) some of them are the wrong shape for sharpening swords.

Leaving aside the other reasons, if someone carved a groove for sharpening a sword hundreds or thousands of years ago, wouldn't the shape have been widened or altered by weathering in the present day, thus making it unsuitable? Or does weathering not work quickly enough? --86.159.223.93 (talk) 08:17, 19 February 2009 (UTC)


 * The article says that many of the grooves are in limestone, it's difficult to see how you could use such a relatively soft material (made of calcite, hardness=3) to sharpen a sword, even a bronze one. As to the weathering, some modification of the grooves in the limestone would be expected over periods of thousands of years, but probably not for the other rock types. Mikenorton (talk) 13:46, 19 February 2009 (UTC)


 * I had the same thoughts. Why wouldn't they use a harder mineral for sharpening swords ?  Note that weak acids can also dissolve limestone, such as acid rain after a volcanic eruption. StuRat (talk) 13:47, 19 February 2009 (UTC)
 * Our article doesn't say, but have they ruled out food preparation or processing fibers for ropes or clothing? 76.97.245.5 (talk) 22:20, 19 February 2009 (UTC)

Apple juice
If I make apple juice at home, what can I add to it to prevent oxidation - at least for some hours? Mr.K. (talk) 13:22, 19 February 2009 (UTC)


 * Lemon juice might work, but would of course also change the flavor.  Why do you need to prevent oxidation ?  It will just cause the juice to turn darker brown, like cider, right ?  What's wrong with that ? StuRat (talk) 13:40, 19 February 2009 (UTC)


 * Perhaps ascorbic acid (aka. Vitamin C)? I'm pretty sure it helps prevent oxidation on split fruits, so I suppose it'd work in apple juice as well. Adding too much will no doubt make it taste (more) sour, though. -- Aeluwas (talk) 14:54, 19 February 2009 (UTC)


 * Cover it up so that no air can get to the surface, or as little as possible. (Cling film is good.) Put the container in a cool dark place until ready to drink. (Pantry or fridge is good.) BrainyBabe (talk) 15:01, 19 February 2009 (UTC)


 * BTW searching for "oxidation" leads to Redox, which sounds like a brand of sneakers or band or punks, take your choice. Or a literary term. Or a Landseer painting. I digress....  The article has nothing on oxidation in food preparation, which is a lacuna, though it does have a section for biology. BrainyBabe (talk) 15:05, 19 February 2009 (UTC)


 * I know cut apples oxidize, but I did not know that apple juice did. The strategy seems simple though, keep it cold and keep it from being sloshed around.  A layer of lemon juice on the top would help as mentioned above.  Just remember for oxidation, you need oxygen.  So, keeping it from moving keeps oxygen from diffusing any more than necessary into the liquid.  Keeping it cold lowers the ambient energy and thus makes chemical reactions, in general, less likely.  So, fridge + plastic on top (as already said) sounds like the answer to me.--Mrdeath5493 (talk) 18:50, 19 February 2009 (UTC)
 * A layer of lemon juice? Does lemon juice float on apple juice? They're both mostly water, surely they just mix... A layer of oil on top would certainly work, but you may not want to drink the apple juice afterwards...--Tango (talk) 23:36, 19 February 2009 (UTC)


 * here is a random recipe for making homemade apple juice from teh iterrwebz. I used this google search to find it.  Oxidation isn't a big deal here.  Oxidation makes whole apples mushy and brown, which some people find unpalatble, but it isn't harmful in any way.  Considering that if you are making homemade apple juice, you are masserating and mushing up the apples anyways, all the oxidation that is going to happen will have already happened by the time you get to bottling the juice.  The juice is perfectly safe from further oxidation at that point, though some ascorbic acid or citric acid, as mentioned above, may have a mild preservative effect, extending the shelf-life of the homemade apple juice.  --Jayron32. talk . contribs  02:35, 20 February 2009 (UTC)

Coffee and brain
How does coffee affect our brain? Is it like a soft cocaine, that inhibits the serotonin re uptake or is it like an amphetamine that makes us release serotonin? —Preceding unsigned comment added by Mr.K. (talk • contribs) 13:24, 19 February 2009


 * Does our caffeine article explain this ? StuRat (talk) 13:39, 19 February 2009 (UTC)


 * (ec) Our article on caffeine has a pretty extensive section on pharmacology and its mechanism of action. You should be able to get a good start there; let us know if you're stuck on anything.  TenOfAllTrades(talk) 13:42, 19 February 2009 (UTC)


 * Wow, wikipedia's english article on caffeine is pretty extensive. It does leave one thing kind of vague, why does consumption of this substance result in arousal?  I would first consider the reticular activating system.  This is an area of the brain that serves to maintain consciousness.  It does this by diffusely stimulating the brain.  The neuronal pathways coming from this area go to all parts of the brain.  While you are awake there is constant excitatory stimulation traveling from the RAS to the rest of the brain.  More excitatory stimulation leads to nerve communication being easier to establish which leads to more nerve activity.  The more nerve activity there is, the less likely it is you can ignore it (your surroundings, your thoughts, noises, etc.) and go to sleep.  As an analogy I would say that the RAS is like a volume knob to all sensory input.  If you ever undergo anesthesia for a surgical operation, the drugs they give you basically mute the RAS, thus you go unconscious. Anyway...


 * So, what does that have to do with caffeine? Caffeine has a "disinhibitory" effect which means it subdues a system that normally is inhibitory or works in a way that opposes the RAS.  The result is an essentially diffuse excitation and thus increased awareness/wakefulness.  The brain is so complicated we still can't fully explain how it works.  What I understand about it is that it contains a complex system of excitatory processes balanced against inhibitory processes.  No matter if you increase an excitatory process or subdue an inhibitory process, the end result is the same....more excitation>more awareness>more going on inside your head.  --Mrdeath5493 (talk) 18:37, 19 February 2009 (UTC)
 * Firstly, if you are assuming that the "serotonin increasing" property of cocaine and amphetamine is responsible for the stimulant effect, then you are mistaken. That is caused by a release (or reuptake inhibition in the case of cocaine) of noradrenaline (see: fight-or-flight). Secondly, as mentioned earlier, the mechanism of action section of the caffeine article pretty much explains it: Caffeine is an antagonist at adenosine receptors. --Mark PEA (talk) 19:26, 20 February 2009 (UTC)

Time travel survival
Imagine you were to travel back in time to, say, the Permian, and you had to stay and live there for a year. You know you're traveling back 275 million years ago but you don't know on which part of the Earth you're going to appear, only that you'll appear on dry land.

If you were only allowed to bring five (5) modern objects with you, what would be the best choice? I thought about the following:


 * 1) Water purifier (drinking water is essential for life)
 * 2) Storm-proof lighter (fire keeps you warm and helps you cook)
 * 3) Swiss knife (comes handy in many situations)
 * 4) Net (for catching food)
 * 5) A medical kit (for treating injuries and diseases)

Am I forgetting any important objects? --83.45.155.43 (talk) 15:50, 19 February 2009 (UTC)


 * Don't worry about a water purifier - you can boil water to make it safe to drink. A Swiss Army knife probably isn't particularly useful, I'd prefer a simpler, lighter, more reliable knife. For a lighter I would probably go with flint and striker or similar - the simpler the better. You can make a net fairly easily from plants, snare wire would probably be a better tool to bring. If you're allowed a whole first aid kid as one object, then are you allowed a whole survival tin? If so, that has pretty much everything you need. A survival tin, a first aid kit and a decent knife - if you have all of those, you stand a good chance of surviving wherever and whenever you get dumped. --Tango (talk) 16:03, 19 February 2009 (UTC)


 * This is no different than "If you were stranded in xxxxx what would you need to survive?" There are thousands of survival books and now we have plenty of survival TV shows.  Just read the books or watch the shows and decide what you think you will need. --  k a i n a w &trade; 16:21, 19 February 2009 (UTC)


 * There are many interesting and (potentially) unanswerables here.  What would the human digestive and immune systems feel about the biology of the Permian?  Do you have to worry about purifying water or getting infections at all - none of the bacteria/viruses of the time has ever encountered a modern human immune system.  Is there actually ANYTHING you can eat there?  Perhaps there are trace elements or vitamins that you need that are simply not present in animals or plants in the Permian?  I don't think there were any grasses or flowers in the permian (I could be wrong about that) - so no grains in your diet.  Getting dietary fibre could be hard.  If you tried to live on meat alone, you'd pretty soon get in trouble.  I agree that a swiss army knife is probably better than a simple knife - but I'd want a customised one...I see no point in taking a philips screwdriver, a USB thumbdrive or a corkscrew to the Permian - but the magnifying glass, tweezers and such could be invaluable.   Your lighter will run out of fuel - so you'll want something more like a steel rasp that you can strike rocks against to make sparks.  I'd want to take something like a cooking pot - so I can actually boil water (you didn't take anything to boil it in!) and make soup from whatever critters I catch, melt snow for drinking water in the winter. Most of the land in the permian was one gigantic desert - so if you're going to be dropped on land at random - you're going to die for sure!  The CO2 content in the air (around 1000ppm) is at the upper limit of what is recommended for outdoor air quality - you're going to stand a good chance of suffering from headaches and nausea.  If you make your home in a cave or someplace else with limited airflow - you could get into deep trouble. SteveBaker (talk) 16:31, 19 February 2009 (UTC)


 * There's a hard decision to make, between providing for immediate-needs vs. long-term needs. This largely depends on personal preference and estimation of the environment you will encounter.  Often, the most critical items of the first few days turn out to be consumable and non-permanent (things like the very first meal, first blanket/clothing, toilet paper).  Without those items, you will find life very uncomfortable and possibly even be unable to pursue longer-term solutions (for example, will you really be able to weave yourself a blanket out of ... Permian insect silk... if you die of hypothermia after the first two nights?)  On the other hand, there is a strong inclination to only bring things you know you cannot re-build in any reasonable amount of time (like a nice forged-steel knife or ground-glass optical magnifier or some aspirin), with the hope of getting multiple uses out of each of those sorts of items.  How often will you need a magnifier (rarely, for starting fires and so forth)?  But when you DO need it, it will not be remotely possible to build one on short notice.  As I mentioned, a blanket is probably easy enough to make, but you are going to want that on day 1 (environmentally dependent, of course).  Steve brings up some very interesting points about Permian Earth, which will be an awfully foreign place (from the perspective of molecular biology).  Nimur (talk) 18:13, 19 February 2009 (UTC)
 * I would have thought the human immune system encountering a virus it had never met before would be a bigger problem for the immune system than vice versa.
 * Anyway, I'll take as my 5 items: the machine that brought me there, the manual that explains how to use it to go back, a canister of time machine fuel or whatever it needs to go back, and in the event that I'll have time to kill while it recharges or whatever, a ham sandwich and a porn mag.
 * Don't tell me "you can't take the time machine, it's not modern, it's futuristic". In order to take me back it has to be in the same point in time as me. So regardless of where or when it came from, at the point I have to go in it, it's modern. --86.159.223.93 (talk) 18:13, 19 February 2009 (UTC)
 * Sadly, the rules say you have to stay there for a year. By then you'll definitely be reduced to reading the porn mag "for the articles" - assuming you didn't already need it to start a fire.  You don't need the time machine - the you-in-your-future can pop back with a spare machine in a year from now - assuming you survive that long! ;-) 18:19, 19 February 2009 (UTC)
 * You have to pick yourself up once the year is up? That's an impressive paradox! It can be done consistently, though - took me a few attempts, but I got there! --Tango (talk) 18:42, 19 February 2009 (UTC)
 * You picked yourself up from the Permian? Nimur (talk) 18:48, 19 February 2009 (UTC)
 * Oh sure! For time travellers, it's the only way to go.  Firstly, you can be sure the future-you will know exactly where permian-you will be on the pickup day - secondly, they know to come early if you're about to be eaten by a rampaging...erm...therocephalian (OK - I had to look that one up...but I'm pretty sure they rampage!) - fourthly, if for some reason you don't survive for the entire year, your family can avoid wasting the outragious cost of a time trip to fetch you.  Of course if you screwed up and somehow accidentally changed the future...not so good. SteveBaker (talk) 18:50, 19 February 2009 (UTC)


 * I'm thinking you need better shelter to survive for a year.
 * Sturdy 1-person tent
 * A sleeping bag that keeps you alive in -20F temps
 * Bow and arrows (they'd be reusable)
 * Camouflage that you can wear for a year
 * Some sort of pot/pan/utensil set


 * And before you leave, I would learn how Bear Grylls makes fire.--Mrdeath5493 (talk) 19:12, 19 February 2009 (UTC)
 * I thought the Permian was much hotter than nowadays, so shouldn't it be warm enough to keep you from freezing to death? And, regarding the high carbon dioxide content of the atmosphere, couldn't it be solved by not exercising too hard, and therefore taking full advantage of what little oxygen you've got? --83.56.184.105 (talk) 20:06, 19 February 2009 (UTC)


 * I'd say:

-a good survival knife -A pack full of food and water for the first few days -A good sleeping bag -Some means of making fire -A very sturdy pot with a well-fitting lid, both for cooking and for storing water


 * Water will be a problem, but finding it (which I can't think of anything to bring that would help with that), not purifying it. I *severely* doubt any Permian waterborne disease could affect humans -- this was before any mammals.
 * 275 mya is a little colder than modern Earth, so some nighttime shelter would be necessary. It's unlikely to be cold enough during the day to need a parka or anything -- ordinary
 * One big advantage is that this is before 275 million years of evolutionary arms race, so Permian animals would probably seem slow and stupid to us. (Most Permian creatures are sprawlers, so though they may be fairly fast over short distances, they could easily be run down and killed with a hefty rock. The same would allow me to escape predators, even if any of them recognized me as food -- humans often look scarily large to other animals because of our height. Permian animal meat should still be edible -- humans can eat reptiles as well as mammals, so there's no reason to think Permian reptiles or protomammals would be inedible.
 * Hmm, assuming my assumptions about diseases not affecting humans are correct, then a non-desert location in the Permian might be easier to survive in than almost any modern wilderness...
 * I think Permian diseases could affect humans - bacteria and viruses evolve to suit their host by making sure they don't kill the host too soon and they can effectively get passed on to new hosts. Permian diseases would probably not be able to pass from human to human (but you're alone, so that's irrelevant), but I expect they could still kill you - probably quite quickly. Compare this with Avian flu - a human can catch it and it can be pretty nasty, but it can't pass from human to human. Birds are probably about as different from us genetically as Permian animals, so it's a good comparison. --Tango (talk) 21:55, 19 February 2009 (UTC)
 * Given the high carbon dioxide et al, wouldn't you become a sprawler too? And would that affect fire for cooking that thing you killed with a rock? Julia Rossi (talk) 22:34, 19 February 2009 (UTC)
 * I'm not sure about you, but the fire would be fine. Fire just depends on oxygen levels, which I think were actually very slightly higher then (making it easier to light, I guess). --Tango (talk) 23:30, 19 February 2009 (UTC)
 * I'm pretty sure there were no grasses or flowers in the Permian: if I remember correctly, flowers didn't exist until the late Jurassic and grasses not until the Cenzoic. Maybe eat some ginkgo, perhaps? You might have to watch out for the large reptile/proto-mammals. ~ A H  1 (TCU) 23:34, 19 February 2009 (UTC)
 * Flowering plant indicates early Cretaceous. Poaceae says there is some doubt about when grass evolved, but it looks like late Cretaceous at the earliest. So certainly no grasses of flowers in the Permian. Ginkgo biloba suggests there would be some edible plants about, though. --Tango (talk) 00:36, 20 February 2009 (UTC)


 * This is exactly the kind of thing that makes me doubtful of your survival chances. You can't survive by only eating meat. (See, for example, Rabbit starvation).  There are no grasses - and hence no grains and there are no flowers.  So most - if not all - of the plant-based foods we're used to finding won't be there at all.  Most of the plants are things like ferns which don't make up a part of our normal diet.  Without plants, you won't get enough fiber and roughage - and that's going to be pretty bad on a timescale of months to a year.  Lack of vitamin C in your diet would also make you likely to suffer from Scurvy...you can find vitamin C in oysters - but who knows what Permian shellfish have?  I think it would be pretty tough to find enough of the right kinds of foods to keep you alive.  Everything you'd experiment with is a potential poisonous plant.  There are all sorts of complicated field guides you can get for modern day earth to tell you what's safe and what isn't...but in the Permian?  All bets are off.  The only things we really know about plants from that time are fossils - and you can't tell whether something is poisonous from a fossil! SteveBaker (talk) 01:48, 20 February 2009 (UTC)


 * Re: fiber. In Two Years before the Mast, Richard Henry Dana remarks about the exclusive diet of beef aboard ship (with explicit reference to Dr Graham's diet) and the lack of any detrimental effects. Of course, the cows did eat grass.  Saintrain (talk) 00:59, 21 February 2009 (UTC)


 * Did nobody think of taking a laptop and a copy of Wikipedia on CD? In case you haven't heard about Wikipedia, click on the links <- Rfwoolf (talk) 03:41, 20 February 2009 (UTC)
 * A very big CD! You would need to narrow down which articles are likely to be useful if you want to get it down to a reasonable size. And how do you intend to power your laptop? I think printing the articles off would be better. --Tango (talk) 10:38, 20 February 2009 (UTC)
 * You can actually buy (or download for free and burn) Wikipedia on CD-ROM. The trouble is that you can't fit it all on one CD.  There are several Wikipedia projects who are trying to pick a suitable subset for CD and/or DVD.  I did download the CD version a year or two ago and it's very sad.  Almost all of the cross-links are gone - and only the most significant articles are there.  Also all of the photos are stored only at their thumbnail size. SteveBaker (talk) 04:34, 21 February 2009 (UTC)


 * A solar panel perhaps? Personally, I'd bring Jessica Alba, but that's just me.  She can light my fire! A Quest For Knowledge (talk) 14:28, 20 February 2009 (UTC)
 * Maybe an extra person could bring five extra things for the list. You'd have to know your ferns and maybe have a video chip implant in your head because when you get back and tell us, we'll need proof. :) Julia Rossi (talk) 22:25, 20 February 2009 (UTC)

Object 1:Swiss Army knife (largest and most complete version). 2:Firemaking kit. 3:Sleeping bag. 4:tent. 5:Messkit(small pot, skillet, cup, fork & spoon). In addition, you'd better know how to hunt and fish with equipment you can make from sticks and flint tools you make yourself, and you'd better know how to make clothes etc from hides and fiber. If a 6th object is possible, bring the Rae Dawn Chong character from "Quest for Fire (film)." Or just substitute her for items 1 through 5. Edison (talk) 05:30, 21 February 2009 (UTC)
 * I have a very large and complete penknife, it's mostly screwdrivers. A screwdriver is completely useless when you are a few hundred million years before the invention of the screw. I really think a simple, good quality knife would be better. --Tango (talk) 13:53, 21 February 2009 (UTC)
 * A Swiss-type knife might have tools other than screwdrivers, wire strippers and other items useless in the ancient past. I have seen other brands with a knife and fork. I have seen them with an excellent saw, extremely helpful in woodworking. They also may have an awl/needle, highly useful for sewing sinews through hides. The scissors would also be useful for making garments or shoes out of hides The tweezers are helpful for getting splinters out, and don't discount the toothpick as a comfort item. Extra knife blades are useful when you break one. If you can afford to time-travel, you can afford to create a custom Swissknife with sewing awl, 2 knife blades, saw, pliers, drill, tweezers, compass, and solar charged LED light. Count the assembly as one item., Whatever is not explicitly forbidden by the rules is permissible. Edison (talk) 01:37, 22 February 2009 (UTC)
 * If you're allowed a custom made Swiss Army knife, you're allowed the survival tin I mentioned above. My survival tin contains a spare knife, a sewing kit, a wire saw, a compass, a candle, some water proof matches, flint and striker, water purification tablets (that expired Sept 05... I should replace those!), a whistle (not particularly useful when on your own, I guess), fishing gear, some snare wire, safety pins and a mini survival guide. Admittedly, no tweezers, you'll have to dig the splinter out with one of the safety pins. --Tango (talk) 02:05, 22 February 2009 (UTC)


 * Let's assume you don't end up in the desert. If you end up in an area with cycads you can leech and process those make flour.  Unfortunately some of the animals you hunt may have eaten the toxins and have become unsafe for human consumption.  Since cyanobacteria are generally considered to be very early representatives of the group it would be too much to hope that the Cycads did not yet contain the toxin back then.  Cycads would also be useful because their palm fronds can be made in to lots of things.  {{Ginko]] nuts can be eaten.  To the poster who'd like to produce hides and use sticks.  Very few if any plants in that period produced usable wood AFAIK.  Most were soft, gnarled and stringy.  Producing hides from reptiles is a difficult process that requires specialized vats and chemicals.  One of the most common sources for tanning materials in earlier times were oaks and similar trees.  They weren't available in the era our traveler is headed for.  So you'd have to make do with processing plant fibers.  Flint might also not yet be available in a usable form.  A saw wouldn't do a good job cutting stringy plants.  I'd take a machete, a whetstone, a first aid foil blanket |66%3A2|65%3A12|39%3A1|240%3A1318 (We don't have a page??), a cooking pot, a water desalination device and a halberd, pike (weapon) or lance.  You'd have to learn how to make fire using friction and make a hammock in a hurry, otherwise you might want to take those.  Douse yourself in tons of bug repellent before you go and hope it'll work on cockroaches.  Be very sure you have the means to return to the present should the need arise.  If one of the local pathogens or critters turns out to be lethal there's not that much you can do about it.  The good news is that they found that the human genome contains sections that used to belong to bacteria once.  Bon voyage. 76.97.245.5 (talk) 07:48, 22 February 2009 (UTC)
 * Yes there is, in wikipedia it's "Space blanket". Maybe the whistle helps if there are mosquitoes, see Ferroequinology, train whistle. Julia Rossi (talk) 22:05, 22 February 2009 (UTC)
 * What is the water desalination device for? They had fresh water rivers in the Permian, surely? --Tango (talk) 00:27, 23 February 2009 (UTC)
 * Assuming you could find a salt water source, this device might provide a source of salt (could be very useful). Not sure if such devices actually produce the salt in a useful form, though.  --Scray (talk) 00:35, 23 February 2009 (UTC)
 * You could just drink the salt water, though. (You would generally want to dilute it with fresh water first, although I'm not sure what the salinity of Permian oceans was.) --Tango (talk) 00:44, 23 February 2009 (UTC)
 * Sorry - I should have been more explicit. A renewable supply of dry salt could be valuable.  --Scray (talk) 02:46, 23 February 2009 (UTC)
 * What for? And if you just want the salt you can get it the same way people have got salt for millennia - just collect some sea water and let it evaporate. --Tango (talk) 12:04, 23 February 2009 (UTC)
 * A very big box of vitamin pills? --131.188.3.21 (talk) 23:35, 22 February 2009 (UTC)

Basics
what is the best easy going reference which discuss the basic concepts about physics...thanks alot.


 * Physics for Scientists and Engineers (~$150 US) doesn't cut corners. It is considered "basic" at the college-level.  What is your approximate grade level or mathematical background?  That will help decide the right book or resource for you.  Nimur (talk) 18:33, 19 February 2009 (UTC)


 * IMHO, you cannot beat The Feynman Lectures on Physics. There are three large books - he teaches at a basic level but he doesn't start with boring topics like most physics books do.  There aren't many basic books written by Nobel prize winners - this is a good one!  SteveBaker (talk) 18:43, 19 February 2009 (UTC)
 * I've found that the conceptual richness of Feynman's basic physics takes precedence over fundamental, basic quantitative skills. As such, they are a great review for a well-versed expert in the field; and a great conceptual overview for somebody who is just dabbling; but they're a terrible way to start learning with intent to solve quantitative physics problems.  Nimur (talk) 18:47, 19 February 2009 (UTC)
 * I agree to a point. I don't think I'd necessarily recommend Feynman to someone who wanted to learn equations and such - but to our OP who wants an easy-going 'concept' book - these get my vote. SteveBaker (talk) 01:10, 20 February 2009 (UTC)

How can i get this books for free ,pdf if possiblThe Feynman Lectures on Physicsthanks ....


 * Coincidentally, I have Feynmann on PDF, but I don't think Gmail can handle such large attachments ~70MB total. Someguy1221 (talk) 20:57, 19 February 2009 (UTC)
 * Not to mention how illegal that would be. SteveBaker (talk) 01:10, 20 February 2009 (UTC)

will ... evry one has the right to learn, knowledge is as important as food , and you can't blame the theif for stealing food ,can you ,knowledge is right for evry one even for the poor  , i can't afford it ... so what ...??
 * People who write and publish books for a living have the right to feed their families and put roofs over their children's head just as much as you do. Stealing the works of their effort is as much crime against them as is stealing any other object.  Spend the money, buy the book.  this link shows copies availible used for as little as $34.00.  Likewise, you are likely within reasonable distance of a lending library where you can get books for free.  If your local library does not carry the book, you can probably get it via interlibrary loan.  --Jayron32. talk . contribs  02:28, 20 February 2009 (UTC)


 * It's ILLEGAL - period. If you can't afford to buy a copy - you can check out a copy for free from your local public library.  There is no justification for infringing copyrights. SteveBaker (talk) 02:29, 20 February 2009 (UTC)


 * Actually the 'period' shouldn't be there. There are countries without criminal penalties for copyright violations particularly when we are talking about for personal use. (For example, according to Spanish copyright law it is only a crime if there is an intent to make profit and if I understand it's the same in Israel.) The copyright holder could usually still sue for infringement but saying something is illegal usually implies it is in violation of criminal law. Also there are countries which don't recognise American copyright (and for which the US doesn't recognise their copyright), therefore the book would likely not be copyrighted in those countries so you couldn't even sue for infringement. The OP's IP looks up to Jordan and Jordan is party to WIPO and according to Jordanian copyright law it is illegal in Jordan and it sounds like this is even in personal use case, but that doesn't change the fact it's misleading to claim it's always illegal. As for the comments on libraries, do either of you know what Jordanian libraries are like? While there are public libraries in Jordan, i have no idea what they're like, I'm doubtful either of you do either. Nor is it likely we know that there is one where the OP lives... (Coming from Malaysia I know that libraries are not always that ubiqutious nor that well stocked in developing countries.) Note that even if public libraries exist, they may not be free so unless the OP is already a member, buying a copy of the book if that's all he/she wants may or may not be cheaper. IMHO there's a very good chance even if they exist, they don't carry the book. Getting it via interloan may or may not be possible but could take a long while and add to the cost. I'm not of course going to help the OP get a copyright violating copy of the book but this doesn't mean it's fair to the OP to presume to know what the OP can or cannot do without considering his/her local circumstances or to provide misleading information like claiming it's illegal period when in reality the situation is often far more complicated then that. Nil Einne (talk) 10:45, 20 February 2009 (UTC)
 * That's a strange definition of "illegal". Civil law is still law. It may not be a criminal offence, but it's still illegal if it is against civil law. --Tango (talk) 12:28, 20 February 2009 (UTC)
 * However our very own wiktionary:illegal says "Contrary to or forbidden by law, especially criminal law". The Law Encylopaedia says "Laws written by Congress and state legislators that make certain behavior illegal and punishable by fines or imprisonment. In contrast, civil laws are never punishable by imprisonment" and a different Law Encylopaedia says  says "The power to make certain conduct illegal is granted to Congress by virtue of the Necessary and Proper Clause of the Constitution (art. I, § 8, cl. 18). Congress has the power to define and punish crimes whenever it is necessary and proper to do so, in order to accomplish and safeguard the goals of government and of society in general. Congress has wide discretion in classifying crimes as felonies or misdemeanors, and it may revise the classification of crimes" ... "Municipalities may make designated behavior illegal insofar as the power to do so has been delegated to them by the state legislature". From some attorney on a forum  "Laws written by Congress and state legislators that make certain behavior illegal and punishable by fines and/or imprisonment. Whereas, civil laws are not punishable by imprisonment. In order to be found guilty of a criminal law, the prosecution must show that the defendant intended to act as he did; in civil law, you may sometimes be responsible for your actions even though you did not intend the consequences. For example, civil law makes you financially responsible for a car accident you caused but didn't intend. " The NZ Ministry of Justice offers  this distinction between civil law and criminal law "Civil cases uphold the rights of individuals" and "Criminal cases are designed to maintain law and order and protect society". I also wonder how many people would agree it's illegal to violate a contract and how many people ask 'why isn't it illegal to X' even if X would actually be a violation of civil law. It also gets more complicated when you think of complex examples. In many countries a partner may sue for spousal support under various circumstances. Does that mean it's illegal to leave your partner? I suspect few would agree with that. Is it only illegal to leave your partner without paying spousal support? If so wouldn't that imply it's only illegal to violate copyright if you don't pay the copyright holders costs that are ordered by a court? What about if the copyright holder doesn't sue you? Have you done something 'illegal'? How does this compare to if your partner doesn't sue for spousal support even though they would be entilted to do so? Similar examples for child support or even violating a contract which I mentioned earlier. I was perhaps a little extreme in my comments earlier, since clearly some people do think at least some violations of civil law as illegal (I considered using defamation/libel/slander which in many countries doesn't or no longer has a criminal element but found a few people arguing it was illegal so didn't use that example) however the idea that violations of civil law are best not described as illegal is clearly something quite a few people hold and there are a variety of complexities which demonstrate why it's far from clear cut how you decide whether something is illegal when it involves civil law. Nil Einne (talk) 10:16, 31 May 2010 (UTC)


 * Lets not get off topic here, please. If the OP needs a free copy of any information, your local library would be your best bet. Livewireo (talk) 20:38, 20 February 2009 (UTC)
 * If the OP wants free free information, then Physics is the place to start. As much as I am a zealot of Free Information, I recommended a book which is copyrighted and expensive (neither free nor free) because the quality of the content is so very high.  I'm sure that is the same reason Steve Baker recommended the Feynman lectures.  If the purveyor can not afford expensive resources, and does not want to be bound by legal restrictions on copyrighted materials (philosophical arguments notwithstanding), there is fortunately an excellent alternative right here.  Nimur (talk) 23:18, 20 February 2009 (UTC)
 * It's perfectly legal in Colombia where I used to live. They have a "for educational purposes" fair use clause. Don't be so US centric. —Preceding unsigned comment added by 144.82.194.103 (talk • contribs) 22:51, 23 February 2009
 * That's not a U.S.-centric view, it's international copyright law, which according to this is respected by the Colombian government. If that's the case, then taking entire copyrighted books without paying for them is no more legal in Colombia than it is in the U.S.  Do you have a reliable source to the contrary?  --Scray (talk) 05:28, 24 February 2009 (UTC)

Linear Variable Differential Transformer
In LVDT when we draw the graph between displacement & output voltage the graph does not start with zero & the graph is not completly linear. Why?
 * Nimur (talk) 18:43, 19 February 2009 (UTC)
 * While we don't normally answer homework questions, we can point you in the right direction. The three places where you are MOST likely to find the answer, in order, are:
 * In your lecture notes that you wrote in your notebook the day that your teacher told you the answer to this question.
 * In your textbook that your teacher gave you at the beginning of class, probably in the chapter which closely matches the lecture note that you have.
 * In our article on Linear variable differential transformer. Good luck!  --Jayron32. talk . contribs  02:24, 20 February 2009 (UTC)

Squirting Orgasm
How do a give a woman a squirting orgasm? —Preceding unsigned comment added by 24.128.170.126 (talk • contribs) 20:39, 19 February 2009
 * Buy her a squid. Hang on. Thought you meant organism! Aw shucks. —Preceding unsigned comment added by 222.152.165.220 (talk • contribs)
 * I don't believe there is a guaranteed method. There isn't even agreement on whether it is possible at all. See Female ejaculation. --Tango (talk) 20:51, 19 February 2009 (UTC)
 * Tango, your first answer was fantastic! Thanks for the laugh.  --Scray (talk) 03:17, 20 February 2009 (UTC)
 * Wasn't me - that's an unsigned comment. --Tango (talk) 19:10, 20 February 2009 (UTC)
 * Turn off the spam filters on your email account and you'll find PLENTY of people who will be happy to offer help. Make sure you reply to thank them all.  :-) SteveBaker (talk) 01:03, 20 February 2009 (UTC)
 * WARNING nsfw, it's basically porn, have fun: redtube.com / 15878. I don't think this is scientific or anything though.. 74.14.48.202 (talk) 02:07, 20 February 2009 (UTC)

I get this question a lot.Cuddlyable3 (talk) 14:50, 21 February 2009 (UTC)

Blue supergiant
Is blue supergiant a main sequence star? Does it eventually swells up and become a orange hypergiant/supergiant? Does orange dwarf swells up and become a orange giant, actually what's a blue dwarf?--216.100.95.90 (talk) 21:03, 19 February 2009 (UTC)


 * See blue supergiant and supergiant - they aren't main sequence stars. I've neverhttp://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&action=edit&section=59 heard of "orange" stars, do you mean red? Stars can change between red and blue supergiants, sometimes multiple times - they usually die in a supernova eventually. Red dwarfs are theorised to just slowly collapse into white dwarfs, although they live so long that hasn't happened yet so we can't really tell. I've never heard of a blue dwarf. --Tango (talk) 21:21, 19 February 2009 (UTC)
 * Plenty of stars are orange. class K stars are yellow-orange, while class M stars are red-orange. The terms 'orange dwarf' and 'orange giant' are not standard, though, but red giants are in fact generally orange. Algebraist 21:40, 19 February 2009 (UTC)
 * Yes, I've heard of orange stars, but not "orange" stars - I was referring to "orange" as a name, rather than just an adjective, by putting quotes around it. With hindsight, this was not at all clear! --Tango (talk) 21:49, 19 February 2009 (UTC)
 * I would expect a blue supergiant to become a red supergiant, but there have been examples of blue supergiants directly going supernova. A red dwarf would survive for possibly 50 billion years, then fade into a black dwarf. There are white dwarfs, but I don't think I've heard of "blue dwarfs". ~ A H  1 (TCU) 23:31, 19 February 2009 (UTC)
 * Oh, those were use–mention quotes. I assumed they were quote quotes. This language needs more punctuation symbols. Algebraist 02:23, 20 February 2009 (UTC)

Does shaking bus indicate particular type of drive train?
Recently I was on an older charter bus whose rear end shaked up and down so violently that several of my friends in the last two rows were unable to type text messages on their cellphones. The front end did not shake. I was told the reason for this was that the bus was designed for an evenly distributed weight of passengers, but that most of the passengers were in the front half. Does this indicate that the bus had a particular type of drive train, and would a different type of drive train have eliminated the problem? Neon Merlin  22:00, 19 February 2009 (UTC)


 * Did it shake badly only when it was stationary?  Only when it was moving?   Both?  Did the vibration change with the speed of the bus?  SteveBaker (talk) 01:01, 20 February 2009 (UTC)


 * Only when moving. I don't think the speed made much difference (although the speed changed so rarely that I'd have to have had measurement instruments recording to know for sure). Neon  Merlin  04:01, 20 February 2009 (UTC)


 * All I can think of that matches the description is a rear-wheel drive bus with front engine which has most of the weight on the front axle. If most of the passengers also rode up front, the rear wheels might tend to bounce off the ground going over bumps.  This could happen with front-wheel drive, too, but wouldn't be as noticeable because you wouldn't have the drive wheels alternating between engaging and spinning.  If we ignore what you were told, then one or more unbalanced rear wheels could also be the cause, or perhaps the rear suspension is shot. StuRat (talk) 04:32, 20 February 2009 (UTC)


 * Yep - that would be my diagnosis too - something amiss with the rear shock absorbers would make it do that. The shocks should damp out low frequency vibrations and stop them from building up like that.  I rather doubt the weight of the passengers counts for much though.  A standard US schoolbus weighs about 13 metric tonnes...about the same as 180 'typical' adults.  SteveBaker (talk) 02:45, 21 February 2009 (UTC)