Wikipedia:Reference desk/Archives/Science/2012 September 20

= September 20 =

Satellite imaged from a satellite - first?
Is this image (found in this BBC story) the first instance of one satellite photographing another, or is this sort of thing routine? Your Username 04:14, 20 September 2012 (UTC) — Preceding unsigned comment added by Hayttom (talk


 * It has been going on for a while in the military. Article on satellite to satellite imaging Zzubnik (talk) 11:35, 20 September 2012 (UTC)

No-cloning theorem
Is it possible to copy a qubit in a way that destroys the original (e.g. for transferring data from one quantum computer to another) to avoid violating the no-cloning theorem? --168.7.234.182 (talk) 05:16, 20 September 2012 (UTC)
 * Yes. -- BenRG (talk) 14:55, 20 September 2012 (UTC)
 * How? --168.7.235.89 (talk) 17:34, 20 September 2012 (UTC)
 * You do it in the same way you do anything else in your quantum computer, however that is. For example if you've implemented a controlled NOT gate with laser pulses or something, you can swap two qubits with three consecutive CNOT operations by the trick described in XOR swap algorithm. Quantum teleportation is another way of moving a qubit from one place to another which might actually be useful over large distances, assuming quantum computers ever become useful at all. You can also physically move the object storing your qubit from one place to another. -- BenRG (talk) 20:26, 20 September 2012 (UTC)

There should exist a unitary map U that acts on two qubits as:

U(a|0> + b|1>)|0> = |0>(a|0> + b|1>)

S, the qubit the unknown state is moved to is initialized to be |0>, and then after U acts, that qubit's state is what the first qubit's state was, while the first qubit is now in the state |0>. All you have to do is check that U is a unitary map. Count Iblis (talk) 18:06, 20 September 2012 (UTC)


 * Also, if the state is known to be in either |0> or |1> (or any other set of two prior specified orthogonal states) it's possible to copy the state without destroying the original state. This allows classical information to be copied. Count Iblis (talk) 15:34, 20 September 2012 (UTC)

I hate to collapse everyone's wave function here, but quantum computing is just a fantasy. Fortunately, reality is just down the hall and to the right... 66.87.126.54 (talk) 22:26, 20 September 2012 (UTC)

Plant exposure to vacuum
If a (food) plant is subjected to 40*10−11 Pa for 30 minutes or so before being returned to normal pressure 101 kPa. Would it die or not grow as usual anymore? how does seeds fare? Electron9 (talk) 05:49, 20 September 2012 (UTC)


 * The plant might be dehydrated, although 30 minutes might not be too bad. I suspect a seed would do better. StuRat (talk) 05:54, 20 September 2012 (UTC)


 * If it froze, the cell walls would burst, and it would die. Zzubnik (talk) 08:06, 20 September 2012 (UTC)
 * Freezing? Plasmic Physics (talk) 09:23, 20 September 2012 (UTC)
 * It won't freeze, as a vacuum doesn't conduct heat, and unless the vacuum box is in a freezer or some such, the plant won't lose enough heat via radiation to freeze, because once the plant and the walls of the box are at the same temperature, the box will radiate just as much heat back to the plant as the plant will to the box. Whoop whoop pull up Bitching Betty 10:03, 20 September 2012 (UTC)
 * That depends on how the vacuum is achieved. If the vacuum is achieved by pumping out the air after the plant has been placed in the container, then the temperature of the progressively thinned air will drop, in accordance with the kinetic theory of gasses.  If the vacuum is as good as 40 x 10-11 Pa, pumping was slow enough to allow some conduction, and the air mass before pumping was greater than the mass of the plant, it will certainly be frozen.  Wickwack120.145.206.111 (talk) 13:10, 20 September 2012 (UTC)


 * If it freezes, it will die for the reason ZZubnik gave. In any case, during pumping and venting, while not frozen, the moisture content of the plant will rupture the plant and then crush it, as there will be a pressure diferential between internal moisture and the container air.  Wickwack120.145.206.111 (talk) 13:16, 20 September 2012 (UTC)
 * No it won't. The plant structure will likely be able to withstand the vapor pressure of water, which is for example only 17.3 mmHg at 20°C. See also Vacuum: Effects on humans and animals, if animals recover from vacuum exposure up to 90 seconds, I'm sure some plants will be able to last much longer. Tardigrades can even survive days in vacuum. Ssscienccce (talk) 15:12, 20 September 2012 (UTC)


 * I award Ssscienccce a Ref Desk Point for being the first, and so far only, participant in this thread to even try to present a genuine reference of any kind – even to a Wikipedia article – in response to this question, rather than just guessing. TenOfAllTrades(talk) 16:23, 20 September 2012 (UTC)
 * In the published literature, there's Wheeler et al., who offer us "Plants survive rapid decompression: Implications for bioregenerative life support", Advances in Space Research 47(9):1600-7. The experimenters grew a variety of different food plants (wheat, lettuce, radish) and then pumped them down to as low a pressure as they could achieve with their rig (about 1.5 kPa, or about 11 mmHg) and kept them there for 30 minutes.  A week later, the plants were harvested; the authors found no difference between the plants exposed to decompression and control plants.
 * However, that study comes with a couple of howevers.  First, the decompression was not rapid&mdash;their pumping apparatus took five minutes to get down to 5 kPa, so if you're hoping to include the effects of 'explosive' decompression (oops, my space station split in half), you'll have to look elsewhere.  Much more significant, the minimum pressure achieved, 1.5 kPa, is comparable to the boiling pressure of room-temperature water.  (Water has a vapor pressure of 1.5 kPa at about 13&deg;C).  The authors believe that there was enough water in their plants and (particularly) in their hydroponic apparatus to maintain a low-pressure water-vapor atmosphere for the duration of their test, even under constant pumping.  This means that their plants avoided the worst effects of a really hard, dry vacuum&mdash;a high effective relative humidity cut down on the rate of water loss, and the low-but-perceptive ambient pressure prevented fast evaporative cooling of the plant tissues down to their freezing point (which would have caused the sort of damage Wickwack expected).  For the purposes of the study – the aerospace question of 'what happens to our greenhouse on Mars or in orbit if it gets a leak?' – the conditions were reasonable.  For answering the question of what happens to naked plants under a half hour of real, hard vacuum, the conditions were too gentle.  TenOfAllTrades(talk) 16:23, 20 September 2012 (UTC)


 * Is the level of vacuum quoted by the OP so low as to be practically unobtainable with vegetation in a practical vacuum chambr? In space the experiment would be easy, but in an earthly lab, a hard vacuum is not easy to obtain. In early lightbulb research it was fantastically difficult to get the extreme vacuum needed, perhaps one microPascal, since gases would be released from a filament or from the glass itself. The miniscule pressure would be maintained for a good while with continued pumping. The vegetation would be thoroughly desicated by the time a hard sustained vacuum was arrived at. The moisture and other gases from the seeds or vegetation would present a challenge in many earth-bound labs. Edison (talk) 18:53, 20 September 2012 (UTC)

The "rapid decompression: Implications for bioregenerative life support" rapport as suggested by User:TenOfAllTrades is on the right track. I saw the Outland (film) (1981) movie where a hitman inside a huge green house tries to kill marshal (Sean Connery) in a space suit outside. However it backfires as the windows crack and explode and suck him into space. The green house is built on the moon surface with a steel skeleton that holds transparent windows in between the grid mesh. The question then is if plants are somewhat recoverable? for continued food (and oxygen?) supply, or if it has to be eaten directly and any leftovers has to be discarded? I think LEO, Moon and Mars (or it's moons) surface are the most likely candidates. The scenario is likely a small piece of debris crack the windows causing explosive decompression, follow up patching and then recompression. Growing again takes time, and one better have stored spare supplies in the meantime. So quick recovery is essential. Electron9 (talk) 23:51, 20 September 2012 (UTC)

Some comments:
 * About the temperature drop: slow reduction of the pressure assuming an ideal gas (I know that's not totally correct) and reversible process (giving largest temperature drop), in a space with 20% plant volume, 80% gas, plant heat capacity being equivalent to half it's weight in water, starting at 20°C, iterating over 1% pressure drops (calculating the resulting drop in air temp and the end temp of the water + air in equilibrium) results in a total temperature drop of 0.668°C.
 * For 1% plant 99% gas volume the drop is about 16°C. Keep in mind that at atmospheric pressure water is almost 1000 times more dense than air, and it's heat capacity is four times that of air.


 * About plants bursting: Without air trapped inside the plant, it would only burst in vacuum if the vapor pressure was enough to rupture the cells. A pressure of 1.5 kPa seems insufficient for that, considering osmotic pressure cells deal with, cappilary forces etc.. A search for "mean turgor pressure" gave results from 0.18 to 0.44 MPa (1.8 to 4.4 bar), so at least some plant cells can withstand pressures 1000 times higher.
 * About the loss of water: this would depend mostly on the type of plant, the size and number of stomata, whether the palnt automatically closes them in vacuum... Ssscienccce (talk) 15:10, 21 September 2012 (UTC)


 * Sounds like time for an experiment.. ;) How would the reaction be to not being able to breathe CO2 for 30 minutes? Electron9 (talk) 00:52, 22 September 2012 (UTC)
 * CAM plants only collect co2 at night, transform it into malic acid and use it during the day. Plants don't need continuous co2 supply, they close the stomata when the roots signal a water shortage. Much would depend on the stomata mechanism, how it reacts to decreased pressure. Increased cell pressure opens them, maybe they open first and close when water loss decreases pressure. An experiment seems the only way to be sure, yes.
 * I notice I neglected the evaporative cooling in my previous comment. Free water inside the stomata could perhaps cool to freezing point and do some damage, but imo there won't be enough to freeze the cells.
 * I'm presuming plants well suited for such conditions. If others presume plants most vulnerable to vacuum, their assessment may well be accurate. Ssscienccce (talk) 08:15, 22 September 2012 (UTC)

volcanic activity
How has the scale and frequency of volcanic activity changed over geological time? Is there any evidence that the radioactive material in the earth's core is less active than in earlier geologial times? — Preceding unsigned comment added by Quantumt (talk • contribs) 08:28, 20 September 2012 (UTC)
 * See History of the Earth for a general overview. There's lots of links there to take you to more information.  See also Archean and Hadean for more details.  -- Jayron  32  11:22, 20 September 2012 (UTC)
 * See also Large igneous province for examples of periods of relatively intense volcanic activity in the past. Mikenorton (talk) 05:48, 21 September 2012 (UTC)

Large submarines rise because of their large sophisticated mechanisms, but how do small or midget submarines do this "rise and dive" activity in a much more simpler manner
It is certain that military submarines and other kinds can submerege and rise by filling their ballast tanks with either sea water or air so as to rise, but this mechanism is so complex and exlusive only to large sophistcated submarines, but how do miget submersibles or even the pre-modern ships of this kind like the Nautilus submarine rise or dive. In other words what is the basic, simple principle simple for this "rise-dive" activity for small submarines? Please provide links to illustrations or diagrams concerning the topic. — Preceding unsigned comment added by Rt56h3 (talk • contribs) 13:25, 20 September 2012 (UTC)


 * They did more or less what the ones do today: take on water (ballast) to sink, pump it out again to rise. For the Nautilus, the metal keel served as a ballast tank, and the pumps to remove the water for rising are visible on this diagram. Similarly on this diagram of the Turtle you can see the pumps and where the ballast would enter in, at the bottom, and go into a bilge tank. On this diagram of the American Diver, the ballast tank is the long little compartment at the bottom, and there is a little pump in front of the guy steering. It is not really a complex mechanism — let water in when you want to sink, pump it back out when you want to rise. The difficulty and complexity only comes when the volumes of water are huge, as they are with modern military submarines on account of their great sizes, but early submarines were terribly small, so required a lot less water to sink, and a lot less energy (e.g., enough to be delivered by a man operating a hand pump) to rise. For a more modern example, notice the numerous ballast tanks here for DSV Alvin. --Mr.98 (talk) 13:46, 20 September 2012 (UTC)


 * It's worth noting that submarines can also control their depth to some extent using their diving planes - as long as they have forward motion. AndyTheGrump (talk) 17:24, 20 September 2012 (UTC)
 * In "typical" submarines, centrifugal pumps are used for improved efficiency and pumping capacity. These have a limited head (pressure they can supply), therefore multi-stage pumps are used. At shallow depth, these are working in parallel for maximum capacity, at greater depth they work in series for maximum head. A centrifugal pump needs a primer pump to fill them first because they can't self-prime i.e. provide suction when there's air in them. Silent operation may require special pumps with lower capacity. Drain pumps are needed to remove leakage water. Contaminated water (containing machine oil and such) can reveal the position of the sub if pumped outside, so it must be stored in tanks. balancing the center of gravity requires moving water between several balast tanks. All these make it a complex system. A basic small sub only requires one pump capable of providing the pressure needed at maximum depth. In theory one simple positive displacement pump can do that; the head these provide is proportional to the force applied, unlike centrifugal pumps where the head is a function of the applied power. You can use levers or gears to drive a positive displacement pump with a smaller motor, that won't work with a centrifugal pump.
 * Pictures and descriptions of early submarines
 * More on the mechanisms used in submarines in general: Design Studies of German Submarines by the US Navy and Submarine trim and drain systems, part of a series of submarine training manuals. Thanks for the question, given me some new bookmarks! Ssscienccce (talk) 09:54, 21 September 2012 (UTC)
 * The Invention Of The Submarine Ssscienccce (talk) 06:23, 23 September 2012 (UTC)

Human height growth
I have read on some book that say that human growth according to height will stop at age 18 (female) and 20-21 (male).I'm wondering if this age (the age that human stop to grow) is fixed or it depends on the age where puberty comes?Let say if a male had an early puberty,will he have an earlier age where he will stop to grow (in height)?118.101.54.28 (talk) 14:54, 20 September 2012 (UTC)
 * It's a bit dense, but in the section Determinants of growth and height of our Human height article, it states that it is those ages are on average, if all else is normal (no growth-related diseases or conditions). That means it doesn't literally stop on your birthday of those ages. It also appears that puberty causes a growth spurt, but it doesn't say that it affects the timeline overall. Mingmingla (talk) 16:51, 20 September 2012 (UTC)

University Textbook Soapboxing
In looking stuff up in Neville's textbook Oral & Maxillofacial Pathology, 2nd Edition (2002) for the recent peer review on "meth mouth", I found it very odd to see the editors treat oral trauma from sexual practices in the way that they did. They begin the section with, "Although orogenital sexual practices are illegal in many jurisdictions, they are extremely common." There is even the following sentence: "Recurrences are possible with repetition of the inciting (exciting?) event."

To me, this seems very unprofessional. The section on lead poisoning mentions the legalities of lead solder in passing, but this just seems like the authors/editors are trying to make a statement. I would understand if this was published in the 1940s when society was more prudish, but 2002 seems a bit late for such comments. Does anyone else find this odd?  DRosenbach  ( Talk 17:35, 20 September 2012 (UTC)
 * When the book was published (2002) there were many states in the U.S. that still had sodomy laws on the books, most of which prohibited any form of non-genital intercourse. See Sodomy laws in the United States.  It wasn't until 2003 that the last 14 states (including the large states of Florida, Texas, and Michigan) had their laws overturned by the Supreme Court.  I'm not sure there was any widespread or serious enforcement of these laws in most cases, but the fact remains that the statement "orogenital sexual practices are illegal in many jurisdictions" is perfectly factual.  If one takes "many jursidictions" to mean in the entire world, then there are still many places where it is illegal.  The author is not passing a value judgement, merely stating a fact regarding the legality of the practice.  -- Jayron  32  17:50, 20 September 2012 (UTC)
 * I can up-pedantic you by pointing out that some of those states quite likely still have those laws "on the books" &mdash; they're just not enforceable after Lawrence v. Texas. --Trovatore (talk) 01:50, 21 September 2012 (UTC)
 * I find it hard to see what is unprofessional in what you have quoted. The "inciting event" means the event which led to the condition. Inciting does not mean exciting. --TammyMoet (talk) 18:04, 20 September 2012 (UTC)


 * But to be fair, "incite" is almost always used in connection with violence, hatred, rioting or other negative events. One doesn't incite joy or happiness.  --  ♬  Jack of Oz  ♬  [your turn]  21:15, 20 September 2012 (UTC)
 * One could argue that oral trauma is a negative event:) DMacks (talk) 21:24, 20 September 2012 (UTC)
 * In a medical context, the term "inciting event" is a neutral one. It just means, "the event that caused whatever we're talking about." E.g., here is a passage from a surgery book on colitis: "Patients are often elderly, debilitated patients in an intensive care unit with multiple medical problems in which the inciting event is difficult to determine. The onset may be insidious, not recognized, or attributed to medical morbidities. ... Onset of acute colonic ischemia is heralded by the sudden onset of cramping abdominal pain." An expert reading this doesn't dwell on the larger connotations of words like "inciting" (colitis is not a riot), "debilitated" (no negative that elderly people are often weakened), "morbidity" (just means disease), "insidious" (colitis is not being ascribed the agency to be treacherous), or "heralded" (no actual heralds need apply). This is just how doctors talk, and in this context these words have pretty precise technical definitions. --Mr.98 (talk) 12:31, 21 September 2012 (UTC)
 * Thank you for those insightful and educative comments. --  ♬  Jack of Oz  ♬  [your turn]  21:27, 22 September 2012 (UTC)


 * I'm with TammyMoet on this. This is just medical jargon. I don't see the value passing. This is how all medical texts generally read. The language is technical and dry, and the focus is on pathology. In a pathology guide, you aren't going to find little asides like, "but even though we're only talking about the medical problems associated with these practices, I should note that lots of people enjoy them, and they're OK by me." That's not the genre. It is not touchy-feely, it is not meant for popular consumption. It's not unprofessional, per se; it's the opposite: it's clinical. --Mr.98 (talk) 12:37, 21 September 2012 (UTC)

where is my question
where my question related to stress is. it is surprising because before i can give you clarification that how your answer is not satisfying me you have deleted. i dont want that you keep it in the list but at least give me chance and time to work upon it. — Preceding unsigned comment added by Drcsjain (talk • contribs) 17:50, 20 September 2012 (UTC)
 * It was removed. You can see it and the responses by clicking this link. The reason provided for its removal was "rmv discussion, non-question, not appropriate for the RD". In other words, you didn't ask a question that can be answered here.  Sean.hoyland  - talk 18:17, 20 September 2012 (UTC)


 * Well, why was the OP's question, and my answer, removed? What is an "rmv discusion?".  While the OP did not structure his question very well - he first implied he is an expert - it is still a valid question.  And somehow he worked the word religion into it, but it is not clear whether he meant religion as in a religious belief system or meant it to mean carefull thought. He in effect stated that he had been working on a topic, formulated a theory, and asked us if he is on the right track.  That is considerably better than many questions we get where there is no evidence the OP has made any effort to solve homework at all.  How is this question different to that of, for example, one submited by "Floda", Distribution of translational and rotational kinetic energy in a gas?  This was allowed, but it is the same style of question - the OP presented an understanding he had, but was unsure of, and asked for confirmation.  Wickwack124.182.2.57 (talk) 01:09, 21 September 2012 (UTC)


 * I don't know. You'll need to ask OsmanRF34. With a keen interest in legal issues and always eager to comply with rules, my cats are still awaiting the ruling on another question that was removed here.  Sean.hoyland  - talk 03:37, 21 September 2012 (UTC)

Slug reproduction
I watched a video made by David Attenborough saying sometimes when slugs exchange sperms their penis get stuck together so either both or one of their penis gets chewed off by the other slug and that slug carries on only as female from that point. Since it can not exchange sperm with other slugs anymore, can it still reproduce? How? How do sperms travel from the penis to the ovary anyway? Thanks! -- RexRowan 忍( Ninja signal ) 19:34, 20 September 2012 (UTC)
 * See Apophallation for a short description. If you search for that name outside of Wikipedia, you'll likely get more info.  -- Jayron  32  21:24, 20 September 2012 (UTC)

Live oak growth
Approximately how long would it take a live oak seedling to grow from a seedling to 20 feet (6.096 meters) tall? Bubba73 You talkin' to me? 20:54, 20 September 2012 (UTC)
 * Various sources say they grow at up to 3 feet per year when young, so somewhere around 10 years, given good conditions, seems about right. Looie496 (talk) 21:03, 20 September 2012 (UTC)

Women and pimples
Why do some people pop other people's pimples?

Why women like blowing up other people's pimples so much?--85.52.87.164 (talk) 23:05, 20 September 2012 (UTC)
 * Where's the source that says they do? HiLo48 (talk) 23:10, 20 September 2012 (UTC)


 * (EC) What are you talking about? Whoop whoop pull up Bitching Betty 23:12, 20 September 2012 (UTC)
 * The reference desk does not answer requests for opinions or predictions about future events. Do not start a debate; please seek an internet forum instead. μηδείς (talk) 23:27, 20 September 2012 (UTC)


 * Come on, that's not really assuming good faith, I think the above replies are unnecessarily terse. Maybe it is a common misconception, in which case the above are still not appropriate or helpful replies. However I suspect most people who have had a couple of girlfriends will testify to this. I have never felt an urge to squeeze someone's pimple myself and I know no other guy who has admitted it either, but my wife and most girlfriends I've had absolutely love it, it's almost like a Christmas present when I let my wife squeeze a pimple on my face, which isn't very common. As to why? Google women love popping zits and there's lots of discussion, but yeah, not much of it is refferenced. I don't think that makes it a completely invalid question.. I suspect it's just preening instinct.. Vespine (talk) 23:39, 20 September 2012 (UTC)
 * I have de-hatted the discussion. Please discuss further at WT:RD.  -- Jayron  32  23:43, 20 September 2012 (UTC)
 * The question as posted was quite offensive, assumes as fact a ridiculous claim, and invites debate. If there's an objective way to answer it it can be done as currently edited. μηδείς (talk) 00:46, 21 September 2012 (UTC)
 * I disagree that it is a ridicolous claim and I honestly don't see why you find it offensive.. Like I said, IF it is a misconception, it's a VERY common one, so I would put the burden of proof back on you and ask why you think it's a ridicolous claim? Vespine (talk) 00:57, 21 September 2012 (UTC)
 * If the question is offensive, ignore it. If it contains a ridiculous claim, correct it.  If it invites debate, don't start one, and instead point to reliable sources.  I mostly read here on the Ref desk, yet even I'm getting sick and tired of Medeis treating the Ref desks as his personal property and censoring all discussions he doesn't personally like.  --140.180.242.9 (talk) 01:06, 21 September 2012 (UTC)
 * Back to trying to answer the question in good faith: the concept is widespread enough, as noted by this google search that I would doubt that no scholar has ever studied it. It takes some practice and skill to use something like Google Scholar to tease out the correct search terms and come up with actual scholarly works on the topic.  For example, this book has a case study of a woman who gets sexual satisfaction from popping other's pimples.  this paper seems to discuss mutual grooming behavior in romantic couples in general; I can't find reference to pimples in the abstract, but it came up when I did a google scholar search that included the term.  -- Jayron  32  03:34, 21 September 2012 (UTC)
 * this book discusses social grooming in humans, and notes specifically about mutual pimple-popping behavior on page 73, where it states "Once the ice was broken, other students, both male and female [were] 'posessed by a strong urge' to carry out acts of social groom particularly squeezing out the pimples of a partner" (emphasis mine)  The whole section titled "Social grooming in Germany" starting on Page 73 discusses the behavior of popping other people's pimples in some detail.  It's a decent read on the topic.  -- Jayron  32  03:41, 21 September 2012 (UTC)

Comment removed, sorry this was intended for the talk page, not sure how I manged to double post it here. Vespine (talk) 05:04, 21 September 2012 (UTC)


 * Part of the beauty training I did was to pop pimples and apply antiseptic to them. I wouldn't say I enjoyed it, but I was told it was necessary in some circumstances while giving facials and applying make up. (I have to say I never quite understood it and I don't do facials any more.) --TammyMoet (talk) 10:01, 21 September 2012 (UTC)
 * Motherly instincts (grooming)?165.212.189.187 (talk) 12:47, 21 September 2012 (UTC)