Wikipedia:Reference desk/Archives/Science/2011 January 20

= January 20 =

Plant hardiness - temperature versus sunlight volume
It's about -20C outside these days, though my apartment (apart from near windows) is around 20 degrees at all times. I have a Creeping Charlie that was placed too close to a window and began to die. However, the ambient temperature was never at or below freezing.

This made me wonder about plant hardiness and why some plants cannot tolerate super-freezing temperatures. If a tropical plant like a banana tree was given ample, full-spectrum artificial light but kept at an ambient temperature of 5~10C, would it still die? If yes, why? There wouldn't be any cell damage from freezing... The Masked Booby (talk) 01:14, 20 January 2011 (UTC)


 * I don't know, but a conjecture is that different enzymes work best at different temperatures. Perhaps the plants that like warmth have enzymes that only function at those temperatures. Ariel. (talk) 06:16, 20 January 2011 (UTC)


 * Yes, it's basically the same reason why humans die if their body temperature is to far away from 37°C (without freezing). The physiology of most life forms is tuned (by evolution) to certain ranges of environmental and internal variables, and if you cross the thresholds, the processes in the cells don't work anymore as they should. That's the same principle for plants, animals and even single celled organisms (some bacteria that thrive in warm shallow sea water won't grow at all or even die in cold shallow sea water, for example). --TheMaster17 (talk) 10:33, 20 January 2011 (UTC)


 * This previous question covers some of the relevant points (I was posting as 131.111). Chilling can damage plants because it disrupts the cell membranes by making them solid, instead of fluid which then makes them leaky, allowing all the parts of cells to mix, whcih is not good news at all. A banana plant will certainly die at 5-10C because they have never evolved to cope with those temperatures. Ariel's point about enzymes is probably partially true, but the disrupting of cell membranes is more of an issue - unlike us, plants have to cope with a wide range of temperatures and so they have enzymes which function over wider ranges, or will have isozymes for different temperatures. As to how some plants survive super-freezing, it's pretty complicted! There are some details at Ecophysiology (unfortunately unreferenced, but I can vouch for its accuracy as I wrote it from lecture notes - I will try to reference it some day!) and combined these allow trees like larch in Siberia to survive liquid nitrogen, because the cells are placed in suspended animation. If you want a paper discussing this, this one might be a good start. SmartSE (talk) 15:43, 20 January 2011 (UTC)

Pregnancy and radiation-blocking smocks...
Here in China pregnant women wear smocks with a thin lead liner in the workplace. I can understand the need for such clothing if someone worked in an area with serious radiation potential, like an x-ray equipment factory or something. However, 99% of these women only ever sit in front of a computer doing routine tasks. I suspect this practice, like many medical habits in China, is based on no real proven science. Is there anything to gain from such clothing? I didn't see any indications in the Electromagnetic radiation and health article... The Masked Booby (talk) 01:17, 20 January 2011 (UTC)
 * Well, considering that lead doesn't even block EMF I don't know what they're trying to achieve. I would be much more worried about exposure to lead! Even if it is sealed, what if a section becomes exposed due to wear or tear? Lead rubs of extremely easily onto hands or clothes, even just touching it and then handling food or inadvertently touching your mouth sounds like a much higher risk then sitting in front of a computer or monitor. Vespine (talk) 03:35, 20 January 2011 (UTC)
 * I'd hesitate to concur -- while lead doesn't attenuate all forms of electromagnetic radiation well, it does do a great job for x-rays, for example. This may not relate to the circumstances posed in a positive fashion (it may reveal the ignorance of Chinese women and/or their husbands), but your blanket statement is certainly incorrect on the whole.  DRosenbach  ( Talk 05:02, 20 January 2011 (UTC)
 * EMF |= electromagnetic radiation. I didn't think computers and lcd monitors are significant sources of EMR, unless you have a wifi or bluetooth transmitter or something. It's hard to find reliable sources to look this up because of all the fear mongering but my guess is there would be small amounts of things like radio waves and stuff coming out of a normal computer, but there's certainly no ionizing EMR coming out of your computer. Vespine (talk) 05:24, 20 January 2011 (UTC)
 * It could have started with ladies worried about the X-Rays emitted from older model CRTs (Which, for all I know might still be in wide use in China.).  Once these sorts of things start they usually become divorced from their rational underpinnings pretty quickly, so it's not hard to imagine that some ladies would still wear them even if they never use anything that emits anything dangerous. APL (talk) 15:30, 20 January 2011 (UTC)
 * Yes, but you said, "lead doesn't even block EMF."  DRosenbach  ( Talk 16:09, 21 January 2011 (UTC)
 * I'm confused, why are you saying "but you said"? Yes I did say it, and? Is the confusion because a lot of the internet seem to use the terms EMF and EMR interchangeably? They are not the same thing. However both are blamed for adverse health effects by the alt med crowd. Vespine (talk) 00:42, 22 January 2011 (UTC)

Biology vs. the Cosmetics Industry
(My last question of the day...) My wife, like many women, spends a fair bit of money on facial cleansers and moisturizers, always used in conjunction. She also makes a big stink about my need to have empty pores on my face in order to be "clean". I am skeptical of this entire process. I've read Cleanser, Sweat gland, Acid mantle, and Sebaceous gland and have not been able to definitively confirm or refute my contention that: stripping oil from your face with cleansers and then applying moisturizer is equivalent to doing nothing at all and letting your skin regulate itself, it just costs loads more. But again, none of those articles directly say whether this is truly necessary or not. Can anyone shed some scientific light on this? The Masked Booby (talk) 01:28, 20 January 2011 (UTC)
 * We have a refdesk rule about medical diagnoses, do we need one about marital harmony? Ariel. (talk) 01:33, 20 January 2011 (UTC)
 * This is not a medical diagnosis request. This is a question about the biological/chemical function of the face and the utility of cosmetics. I am inherently distrustful of the cosmetics industry given their proven non-sense like conditioner making your hair "healthier" and would like to know if facial cleanser/moisturizers fall into the same sphere. I included the bit about my wife for color, not because I'm going to print out your replies and wave them in her face and say SEE! WIKIPEDIA SAID SO! The Masked Booby (talk) 01:38, 20 January 2011 (UTC)
 * Stuff in small print is usually for more light hearted (or off topic) comments. Ariel. (talk) 01:42, 20 January 2011 (UTC)
 * You aren't just stripping the oil off of your face, you are stripping all of the stuff that tends to get stuck to the oil, like dead skin cells, dirt, (for many women) makeup, etc. It may be quite difficult to remove, for example, dead skin cells from pores with just soap, while an astringent cleanser which dissolves the oil the skin cells are stuck to will make it much easier to get them out.  Bacteria like to feed on these dead skin cells; this can be a primary cause of acne.  The deal is, since you just removed all that oil, you need to replace it to prevent your skin from drying out, hence the moisturizer.  In summation, it isn't the skin oils per se that need removing, its all of the stuff that is in the oil.  -- Jayron  32  01:37, 20 January 2011 (UTC)
 * I guess the question is, Does that stuff really need removing? Where is the science behind it? (PS: Agree with comment about marital harmony.) HiLo48 (talk) 02:52, 20 January 2011 (UTC)
 * Which is a fair question. I'm more familiar with the argument against shampoo-conditioning, which is a somewhat similar arrangement: the hair is cleaned of oil (and the attached dirt) and then has a moisturizer (hair conditioner) added back on. Our article on that argument can be found at the humorously titled "no poo", though it's a pretty poor article. Western habits (and obviously Chinese ones as well) on cleanliness are hugely influenced by social expectations, to the point where the "necessity" of having to shower multiple times a day, for example, borders more on ritual purification than anything to do with an increase in health or other objective goal. As with anything else, moderation is probably the sensible option. Matt Deres (talk) 03:02, 20 January 2011 (UTC) Quick aside - I got a chuckle by reading that our article on cleanliness has been flagged for "cleanup" for seven months...
 * @HiLo48 for some people, probably not, but for others definately. I am a life-long sufferer of acne (I basically have the exact same skin problems at 34 that I had at 14); through years of trial and error I have found that some products work for me, and some do not, and I use those that do.  Clearly, for people who have acne, skincare can be tricky business.  It's one of those "if you don't have the problem, you just don't understand" sort of deals.  For people without acne problems, washing daily with the bar soap they use for the rest of their body works fine.  For others, however, it just doesn't cut it.  -- Jayron  32  03:35, 20 January 2011 (UTC)
 * I seem to remember discussing something similar about washing hair too, but can't find an archive link. If you're correct, it almost certainly has something to do with differences in skin flora. I found this which says "soap may reduce the normal skin flora, leading to an increased colonization of the skin with coagulase-negative staphylococci; this effect has been linked to the shift in skin pH caused by soaps. Lastly, it has been found that applying agents that specifically inhibit gram-positive cocci, such as antibacterial soap, generally increases gram-negative rods." and this paper tells a similar story. I think it's probably difficult to give you a definitive answer and as everyone else is ORing so will I - I think that cleansers + moisturisers change the balance of skin flora and that if you then stop using them, your skin condition detiorates because the equilibrium was being maintained by the products. For those of us who don't use such products (myself included) our skin flora is in equilibrium, and generally speaking we don't suffer from unhealthy skin. Carrying on, we obviously evolved in a world without soap, and our skin produces oils for a reason, I see no reason why you would need to replace this with something else. (Maybe you can experiment with your wife's face, only letting her clean + moisturise one side and come back with photos in a few months) Interestingly, I don't think anyone has done any metagenomic studies of skin flora, which would be a very interesting thing to do, when comparing you and your wife. SmartSE (talk) 16:12, 20 January 2011 (UTC)
 * What about situations where skin flora is "off" in the absense of products, but correctly balanced with them, before such products were used by the person? I had acne before I started using products... Your explanation isn't consistant in that skin problems exist in absense of even the existance of skin care products.  It would only make sense if skin problems didn't exist prior to people using skin care products.  However, that is demonstratably false.  -- Jayron  32  16:29, 20 January 2011 (UTC)
 * I don't think anyone is suggesting that corrective action is never a good thing - at least, that's not what I'm saying. If you've got a busted leg, wearing a cast is probably a good idea, but when it seems that virtually everyone is wearing one, I think it's justifiable to say "Look, there are negatives to wearing these things." Such comments aren't really directed at the people with broken legs, they're just reminders of the "If it ain't broke, don't fix it" adage. Matt Deres (talk) 19:50, 20 January 2011 (UTC)
 * Fair enough. I actually agree with you on that; many people use uneccessary or even harmful products under the misbegotten notion of retaining a "youthful appearence" whatever that means.  Much of the skincare industry hinges on the fact that people believe they can avoid looking their age by smearing some gunk or another on their face.  Sometimes, however, that gunk does actually help people with a real problem.  It's not the gunk, per se, that's the problem...-- Jayron  32  20:13, 20 January 2011 (UTC)
 * WP:OR Face wash products work well. They just include sticky substance which once applied to your face you must wash your face thoroughly with lot of water to remove it, and any other dirt/oil on your face, if any, also washes out along with the water :) - manya (talk) 04:10, 20 January 2011 (UTC)
 * Another great euphemism - moisturiser, which suggests something like morning dew or condensation on an ice-cold glass. Actually, it replaces what cleanser removes - oil. Would it be so popular if called "oiler" or "greaser", I wonder?→81.132.237.123 (talk) 12:57, 24 January 2011 (UTC)

Calcium oxide reaction
calcium oxide reaction with water —Preceding unsigned comment added by 125.99.5.139 (talk) 09:08, 20 January 2011 (UTC)
 * . DMacks (talk) 11:04, 20 January 2011 (UTC)

Is there anybody to reply me positively
1.Is a photon massless? If yes,then why does it has particle nature as a particle has a must property of mass and it also has momentum? If no,then why it cannot be proved?

2. Is a vacuum really vacuum or not? If yes,then why does there exist a dark energy as energy cannot be held without any medium? If no,then what does there exist?

3. Does a string really exist? If yes,then what is the matter the string made of? If no,then what is the cause of producing charge in an electron?

4. Do the photons carry the energy from one place to another? If yes,then why does the intensity of radiation decrease gradually and if an electro magnetic radiation is one kind of transverse wave,then the main property of this kind of radiation should be transfer of energy not the particle and it definitely needs a medium to traverse?

5.What is the situation before the Big Bang? Is it a cyclic process?

6. What is the way to transfer energy from one place to another? If it is vibration of different mode which produce different kind of energy,then is it possible to construct the T.O.E. equation?

(I think I have some definite reasons to explain those things stated above. But I need a definite person to explain these mathematically. 117.194.164.185 (talk) 14:35, 20 January 2011 (UTC)


 * You asked a lot of very hard questions, so it is impossible to answer them all here. You should look at the articles on Wikipedia and ask if you have specific questions.


 * 1. A photon has no rest mass, though it does have momentum. Who says that particles must have mass?  It's perfectly possible to conceive a massless particle.


 * 2. Vacuum and Vacuum energy explain this better than I could. The exact nature of a vacuum is complex - however it is quite well defined in quantum theory.  The idea that energy cannot be held without a medium is just a hypothesis and may not be true.


 * 3. String theory is still a matter of debate, and it's not clear if any version of it is true. Therefore nobody is certain what the strings are made of, or even if it makes sense to ask if they are made of anything (just as Einsteinian space-time is not made of anything, and electrons are, in standard models, made of electron without any internal structure).


 * 4. Photons do indeed carry energy. Intensity of radiation decreases with distance from the source because photons spread out as they travel and the further from the source you are, the fewer photons hit you (see inverse-square law).


 * 5. Nobody knows. See cyclic model.


 * 6. See energy transfer for a partial answer. --Colapeninsula (talk) 15:12, 20 January 2011 (UTC)


 * For 1, see also invariant mass ('rest mass') versus relativistic mass. Blame Einstein.  TenOfAllTrades(talk) 15:16, 20 January 2011 (UTC)


 * Almost identical to previous response, but I've written it now and don't want to discard it.
 * 1. If you mean "does a photon have zero rest mass ?" then the answer is yes, although the question is somewhat meaningless as a photon is never observed at rest. This does not prevent a photon being a particle.
 * 2. If you mean "is the vacuum empty" then the answer is no - any vacuum in our universe will contain the electromagnetic field, its quanta (photons), a large number of passing neutrinos and a "sea" of virtual particles.
 * 3. If you mean the strings in string theory then we don't know whether they really exist.
 * 4. Yes, photons carry energy. The intensity of radiation decreases with distance because the flux of photons per unit area decreases as the area over which the photons are spread increases. For large photon fluxes the intensity appears to follow a continuous curve; for small photon fluxes the continuous model breaks down and individual photons are observed. You can recover the continuous model by averaging the photon flux over a long enough period of time.
 * 5. We don't know what was before the Big Bang. We don't even know if this question makes any sense.
 * 6. In quantum field theory, you can think of energy as being carried by waves in quantum fields or by the momenta of particles associated with those fields. These are dual models - "reality" is both, not one or the other. A field does not need a medium. Gandalf61 (talk) 15:40, 20 January 2011 (UTC)


 * @OP: Regarding 3: What does "really exist" mean? String theory is a model just like many other models.  It is useful insofar as it matches observations, and has a useful predictive power.  Is an electron a little ball, a standing wave, a probability distribution?  It is all of these, depending on which model you use.  None of this is wrong, though some models better match observation, and some are more useful in certain applications.  Is light a wave or a particle?  Neither, it is just light, but we have wave-based models of light which are useful in some explanations (see diffraction, refraction, etc) and we have particle-based models of light useful in others (see photoelectric effect).  If you commit yourself to "The Truth" rather than "Consistent with observations" you miss the point of science.  It is perfectly fine and consistant to have multiple, accepted models of the same phenomenon, and each of these models is "real" insofar as any can be.  So, stop worrying about if strings "exist" or what they are "made of" and instead focus on what the model teaches us about how the universe works.  -- Jayron  32  16:00, 20 January 2011 (UTC)


 * It remains to be seen whether or not string theory is a useful model of reality capable of offering testable predictions. In this context, showing that string theory is capable of making new verifiable predictions is basically the same as showing that strings "really exist".  Dragons flight (talk) 16:28, 20 January 2011 (UTC)
 * That's kinda the point; though it would be better to say that "really exist" misses the boat in that it implies only a single "right" answer; after all if strings really exist, than other models which do not contain strings, really don't exist. Having a paradigm that searches for the One Right Answer completely misses the point of science.  Lets go back to the light example.  Does light really and truly exist as a particle or does it really and truly exist as a wave?  If you commit yourself to that mindset, you are left with three very unsatisfying results:
 * Light is only one or only the other (observationally inconsistent; light clearly behaves like a particle in some situations, and like a wave in others)
 * Light is both at the same time (logically inconsistent; a little ball and a mode of movement don't occupy the same class of nouns even. It's akin to claiming that something smells like the color red.  It has a poetic appeal, but it doesn't make any logical sense)
 * Light switches between the two modes, depending on the type of observation (seems better at first, but it begs the question about what light is doing when it isn't being watched.)
 * People have grappled with this concept for a very long time, the only satisfying result comes when you come to realize that there is a difference between reality and perception, and most importantly reality is not observable at all at the most fundemental level. All you can say is that your mind perceives an object or phenomena to be real, but you have no way to confirm that.  Look at your keyboard.  How can you confirm your keyboard exists, as an entity seperate from your internal, mind-created construct of what it is.  At some point, you need to accept that as true.  But that's still an unproven (and unprovable) proposition.  When we deal with scientific concepts which are only observable in the second or third order, where we are further removed from the observable properties of it, these sort of problems become manifest in the situation.  Back to light, rather than trying to decide what light "really" looks like, and "really is", change your paradigm to just accept that light is what it is, and is fundementally unconcievable apart from the models we make to describe it.  Accept that, while light exists and is consistent, our models being by definition imperfect representations, can never fully capture what it means to be light, and let yourself be OK with that.  Understand that the two competing and mutually exclusive models of light work in their own domains, are uncontradicted by other models, and so are as close to "real" as we can get, insofar as anything is "real".  On that level, string theory may be "real", but also be willing to accept other, competing, and apparently mutually exclusive models as equally "real" insofar as they contradict neither logic nor observations.  -- Jayron  32  16:48, 20 January 2011 (UTC)
 * ... and if you were claiming that electro-magnetic radiation "definitely needs a medium to traverse", then the claim is mistaken.   D b f i r s   21:43, 20 January 2011 (UTC)

Electron proton collision
What happens in general when an electron collides with a proton? My understanding is a neutron and a neutrino are produced, but where is a good reference for the dynamics prior to the moment of collision? Also, in particular, how does the electron's de Broglie wave shape change as it transitions from free to collided? 71.198.176.22 (talk) 21:10, 20 January 2011 (UTC)
 * In general, nothing happens when an electron collides with a proton. They pass clear through each other. Electrons in s orbitals have a (locally) maximal probability to be found right at the nucleus, and don't appear to suffer any wear and tear from that.
 * In order to something interesting to happen between an electron and a proton, either the electron must spontaneously break into a neutrino and a W- boson, and the W- must then hit the proton and convert it to a neutron, or the proton must turn into a neutron and a W+ which combines with the electron to form a neutrino. Both of these possibilities are energetically disfavored and so happen extremely seldomly, except if the proton really wants to be a neutron, in which case see electron capture.
 * De Broglie waves are not really a good model for describing particles that turn into other kinds of particles. You'll need a quantum field theory for that. –Henning Makholm (talk) 01:59, 21 January 2011 (UTC)
 * Actually, electron-proton collisions (and resulting inverse beta decay into a neutron) happen when a neutron star is formed. At densities such as those of a white dwarf, it is the electron degeneracy pressure (the statistically-favorable Pauli exclusion principle) that holds the dead star up from further gravitational collapse. But when the mass is great enough that this pressure is overcome, the electrons will literally collide with protons to form neutrons (and neutrinos), which is seen as neutron-degenerate matter (that last article has a more-complete explanation). SamuelRiv (talk) 03:18, 21 January 2011 (UTC)
 * Hm, yes. I didn't consider that case. However, I don't that it should actually be understood kinematically as the electrons being pushed into the protons by the pressure of the collapsing star. In the (slightly facetious) language I'm using above, it would not be a case of "the proton really wanting to be a neutron" (because the proton is in a high-energy shell within the nucleus), but "the electron really wanting to become a neutrino" (because the electron is in a high-energy state within the degenerate electron gas).
 * But I am now puzzled why the expression for Chandrasekhar's limit appears to be completely independent of the mass of a neutron (and in particular to the difference in mass between a neutron and a proton, which ought to be important for when electron capture becomes favorable) –Henning Makholm (talk) 08:57, 21 January 2011 (UTC)
 * The mass of the neutron is not important because the Chandrasekhar's limit simply states the maximum mass that can be held against gravitational collapse by electron degeneracy. The mass of the neutron plays no role except for the fact that they add mass to the star without increasing the number of electrons (assuming electrically neutral matter). Once the collapse happens, then the mass of the neutron becomes important in determining the fate of the star. In other words, the star doesn't collapse because the electrons join the protons into neutrons. The electrons join the protons into neutrons because the star collapses.

Research of Light-Dependent reactions as an energy source
Is anyone researching the Light-Dependent reactions as an alternate energy source? Albacore (talk) 21:13, 20 January 2011 (UTC)


 * How do you mean? -- Jayron  32  21:30, 20 January 2011 (UTC)
 * Are you referring to Photosynthesis? P. D. Cook  Talk to me! 21:46, 20 January 2011 (UTC)
 * If that's the case, the answer is "cut down the tree and burn it". Plants are already a very efficient way of storing energy from the sun; I'm not sure we can do it better in a laboratory outside of the plant than plants are already doing it on their own.  There are actually some pretty advanced ideas on how to use photosyntheis to generate energy for us, but they all involve letting plants do the actual hard bits.  Biofuel in general is all produced via photosynthesis, albeit indirectly.  There is also the use of Algae fuel produced in Photobioreactors.  There's some really interesting stuff being done in the field of Biological hydrogen production which uses photosynthesis by plants to produce hydrogen for use in fuel cells.  -- Jayron  32  21:53, 20 January 2011 (UTC)
 * Though plants are pretty efficient at photosynthesis, there are indeed people who are working on artificial light dependent chemical reactions: see Artificial photosynthesis. Buddy431 (talk) 22:56, 20 January 2011 (UTC)


 * A perfect opportunity to advertise our department: do you mean something like this? There should be a lot about the project in english, but couldn't find it just now... Albval (talk) 20:03, 22 January 2011 (UTC)