Wikipedia:Reference desk/Archives/Science/2010 July 30

= July 30 =

in a cell culture medium, pH 7.4, will hydrogen peroxide oxidise colloidal gold?
I incubated a549 cells in 200 micromolar H2O2 for 90 minutes, washed the cells with fresh media and then observed them under DIC. (The cells had already been incubated in the presence of colloidal gold prior to incubation with H2O2.) The results were rather spectacular: an insane amount of intercellular bridges and connections (on all sorts of levels, criss-crossing everywhere) could be found, compared to situations without hydrogen peroxide. Oh was I happy!

But then 40-60 minutes into the experiment, my cells started dying from the bottom of the slide upwards. It was strange -- normally apoptosis is a stochastic event and is a rather random process that increases in chance as time goes by, but here it was like there was an invisible wave of apoptotic death slowly creeping up the slide. Is it nutrient exhaustion? I am sure I sealed the slide with nail polish to prevent evaporation.

A few papers I found said that H2O2 at 200 micromolar shouldn't decrease the viability of a549 cells too much...but they used 24h assays. Maybe in the time frame of a few hours, the H2O2 kills a lot of cells only to have the really mitogenic ones produce lots of viable ones?

Or maybe they are not apoptotic at all? The normal "apoptosis bubbles" were hard to see -- the entire cytoplasm changes viscosity almost -- it becomes very viscous and the cell's "insides" appear to slow down and look very different. Maybe it's the actin polymerising? I wonder if it's because the hydrogen peroxide is oxidising the colloidal gold, producing lots of Au(III) oxide and at the same time, decreasing the pH since Au(III) seems like a strong Lewis acid. John Riemann Soong (talk) 00:06, 30 July 2010 (UTC)


 * I thought that Au2O3 was insoluble, so the Lewis acidity was "locked away". --Chemicalinterest (talk) 11:58, 30 July 2010 (UTC)


 * Mmm, I didn't see any precipitate, but then again this is colloidal gold, not bulk gold, so Au(I) and Au(III) atoms would remain attached to Au(0) on the nanorod. I believe the sulfide thioether linkages popular for functionalising colloidal gold with are made by having the functionalised thiol precursor bind to the residual Au(I) sites (on an otherwise Au(0) rod) that weren't reduced in the initial manufacture of these nanorods. (Someone correct me if I'm wrong). John Riemann Soong (talk) 13:58, 30 July 2010 (UTC)


 * Oh it just hit me. According to the thioether article, they can be oxidised to sulfoxides and sulfones. I do pipette most of the old media (containing the nanorods) before I add the H2O2 but maybe I should do a few buffer rinses first? H2O2 won't react with membrane-bound gold rods inside endosomes in cells, right? Are sulfides bound to Au(I) more reactive or less reactive? Do they become more or less nucleophilic -- I mean, the Au(I) should sap some of the sulfide's nucleophilicity, right? (The linkage looks like: (rod)=Au(I)-S-(short alkyl/polyether chain)-COO-. John Riemann Soong (talk) 14:20, 30 July 2010 (UTC)

Also, why is the standard half-cell reaction potential for Au(III) + 3e- ---> Au(0) less than the reaction potential given for Au(I) + e- ---> Au(0)? (The latter has a higher potential than the two electron reduction of hydrogen peroxide in the presence of H+). I'm trying to figure out how favourable gold oxidation by hydrogen peroxide is, and I only spent a third of a semester on electrochemistry. John Riemann Soong (talk) 14:28, 30 July 2010 (UTC)


 * If bromine can oxidize gold to gold(III) bromide, then H2O2 should be easier. Also the colloidal property means it has much more surface area. --Chemicalinterest (talk) 15:12, 30 July 2010 (UTC)


 * Yeah but for the noble metals, halide compounds are more stable than oxide compounds. I think? Also from gold(III) chloride: "Reaction with reducing agents such as hydrogen peroxide or Fe2+ causes elemental gold to be precipitated from solution." Hydrogen peroxide is a reducing agent??? (My main issue is oxidation of the sulfur linkage -- if the sulfide is attached to an Au(I) atom, will hydrogen peroxide break the Au(I)-S bond, leaving free Au(I) and sulfonic acid? John Riemann Soong (talk) 16:41, 30 July 2010 (UTC)


 * A common example of H2O2 as a reducing agent is its reaction with NaClO, where it reduces Cl+ to Cl-, itself oxidized to O2. --Chemicalinterest (talk) 19:43, 30 July 2010 (UTC)

Stress Energy Tensor
I don't completely understand this. Why is this used instead of mass in General Relativity? What's the difference? ScienceApe (talk) 00:23, 30 July 2010 (UTC)


 * Because energy and mass both exert gravitational force; in Newtonian physics, mass is used in gravity calculations. The stress energy tensor (hint: read that article) takes energy and momentum into account; remember that according to General Relativity, gravity is a pseudoforce caused by curvature of spacetime.  In most layperson explanations of GR gravity, it is explained that large masses curve spacetime, and that gravity is really just objects moving staight (as objects do), but doing so in curved spacetime.  However, it turns out that mass is not the value which describes the curvature of spacetime, the stress energy tensor is the relevent value.  -- Jayron  32  00:38, 30 July 2010 (UTC)


 * Momentum as well will curve space-time? So if we take an a 1kg object, it will curve space-time more if it's moving at 99% the speed of light? ScienceApe (talk) 01:16, 30 July 2010 (UTC)
 * Well, yes, but not because of momentum, per se, but because it has more energy, via KE = 1/2 mv2. Well, not exactly, but via the GR equivalent at relativistic speeds near the speed of light.  Objects moving at a higher velocity have more energy, and thus curve spacetime more than than those which are stationary.  Velocity affects energy, and energy is mass. -- Jayron  32  01:26, 30 July 2010 (UTC)
 * How does momentum bend space-time? ScienceApe (talk) 01:32, 30 July 2010 (UTC)
 * How? By inducing a noether current that must be counterbalanced in order to conserve mass/energy/momentum flux.  Consequently, some other "thing" needs to either move or change velocity, or else the flux conservation is violated.  But Newton tells us that things don't just start "moving" for no reason - we have inertia!  A body at rest remains at rest!  So, if we want to remain at rest, and also change our momentum, we need to start warping space so that maintaining a constant position yields a change of momentum - ergo, gravitation.  The exact geometry of the warping is nontrivial - and requires solutions of the general relativistic equations - but in the simplest case, we see elliptical planetary orbits, - planets that are tracing out an  vector path, when in fact all good sense tells us that they should be inertially stationary.  Nimur (talk) 04:32, 30 July 2010 (UTC)
 * In a bit more details on why the tensor includes momentum; its because there are three fundemental conserved quantities in any physical interaction between bodies: energy, mass, and momentum. This is true even in classical physics.  So, when two objects interact, even classically, momentum must be conserved.  Even under the Newtonian definition of gravity, as two objects interact with each other gravitationally, their total momentum must remain constant throughout the interaction.  Think of it this way.  If you are a chunk of space rock flying by the earth; as the earth slows you down by "pulling" on you via gravity, the earth itself must speed up by the exact same amount.
 * In GR physics, its FAR more complex, and requires some pretty advanced mathematics. However, the law of conservation of momentum still cannot be violated.  So, any calculation of gravity must take momentum into account.  The stress energy tensor itself is described by a matrix of values.  It isn't a single number like "mass".  It is a tensor, which is a multi-dimensional quantity.  If you know what a vector is, you can think of a tensor as a vector on steroids.  Where as a vector quantity has two values (origin and direction), a tensor can have dozens of values, which are manipulated via matricies.  The stress energy tensor uses four "types" of values (though there are multiple groups of values for some of the types).  There is the "energy density", the "momentum density", the "energy flux" and the "momentum flux".  Basically, in order to correctly calculate the effect of gravity within a system, say a simple two-particle system, you need to know a) the mass-energy of each object (energy density) at your initial conditions b) the momentum of each object initially (momentum density) c) the mass-energy changes experienced by each object as they interact (or curve spacetime, whatever your perspective) (energy flux) d) momentum changes experienced by each object as they interact.  Now, it is even more complex because each location in the matrix isn't a simple number like "three", but rather a complex polynomial which describes, say, the energy density of the entire system in three dimensions (that is, how much mass-energy is at every point in space in our system).   This is of course a gross oversimplification, since you actually have to do the math to get the implications here.  I can't do the math myself, really, but this is how I understand it as a layperson.  Perhaps someone with a better physics background could fix my errors or explain it better.  -- Jayron  32  01:44, 30 July 2010 (UTC)
 * And just as an addendum, you may want to read Stress-energy-momentum pseudotensor, which is the actual value used in GR. The stress-energy tensor has other uses, but it is not strictly applicable to GR apparently.  Again, I lack the math to understand exactly why, but I do read english, and that's what the article seems to say.  -- Jayron  32  02:00, 30 July 2010 (UTC)
 * Another way to rephrase Jayron's explanation: the stress energy tensor allows a physicist to describe the gravitational interaction of a body in the form of a matrix that describes all the relevant concepts - energy, momentum, position, and so on, in generalized coordinates. The way that the body behaves depends on the mathematical laws that are expressed as degrees of freedom of the system dynamic.  In a simple case, like a ball rolling down a hill, the only relevant degrees of freedom are position (x,y,z); and the respective derivatives with respect to time (velocity in x, y, z).  These parameters are constrained by Newton's laws of motion - a set of empirically derived relationships between position, velocity, and acceleration due to gravity.  General relativity allows the physicist to consider these relationships in a more general way, (hence "general"); part and partial to this generalization is that the position, velocity, and acceleration must be described only in a relative way, and not with respect to any fixed frame.  Now, there are lots of relativistic theories, including some that are classical and consistent with Newton's laws - Galilean relativity, for example.  But if you make the theory extremely generalized, you can no longer make the relationships simple: "F = m a" is not a general description of a gravitating system, because Force due to Gravity is a sort of "imagined" quantity that Newton invented.  (Sure, it mathematically explains the rate and distance at which the moon circles the earth, but it doesn't do a very good job at explaining why the moon keeps magically changing direction instead of flying off in a straight line).  So, general relativity seeks to eliminate that unnecessary invention by reformulating the relationships between the free parameters (position, velocity, mass, energy, and so on).  The only sensible way to reformulate those relationships and still describe the kind of behavior we observe is to write out a stress energy tensor in a generalized coordinate space.  The result is a description of gravity without any "spooky action at a distance" - in fact, the solution to the general relativistic equations that describe a planetary system yield accurate predictions about orbits; and do not rely on any weird spurious "force" of gravity.  Gravitation is instead a property of the system - it is a description of the way the masses influence each other.  Nimur (talk) 04:12, 30 July 2010 (UTC)

Piper nigrum and alcohol
So I was making steak au poivre the other day, and once the steaks were seared and removed from the pan, the recipe called for cognac to be added to the still-hot pan and the vapors ignited. Quite the impressive show resulted---the flames themselves were only about a foot tall, but the plume of hot air was at least six feet tall. I don't really want to recreate that indoors, but I don't really want to have to find an outside area free of flammables before I can make the dish. I'm wondering if I can skip the flashy vapor-igniting and just cook the alcohol off, though I'm concerned that without that step that some of the harshness of the cognac will remain. I certainly don't want to skip the alcohol both for its deglazing and solvent usefulness. Thanks for the help!72.219.136.28 (talk) 06:37, 30 July 2010 (UTC)
 * You should be okay to simply cook out the alcohol, if you make some changes. Igniting the flames like that serves two purposes: first, it is theatre (i.e. simply a show); second, it serves to remove the alcohol quickly. Depending on what else you plan on adding to the dish, you may want to significantly reduce the temperature to avoid burning something during the longer cook time. Incidentally, the alcohol never cooks "out" completely. Well, never is a long time, but you catch my point; don't try to just cook out (or flambé out!) alcohol for someone who is intolerant or something. Matt Deres (talk) 13:58, 30 July 2010 (UTC)


 * My wife (who is French and therefore "correct-by-definition" about all culinary matters) says that you're probably using WAY too much cognac. To cook a couple of steaks "au-poivre", she'd first cook the steaks in cracked soft/green peppercorns with a simdgeon of butter and ground black pepper until they are essentially "done".  Then she'd use just one tablespoon of cognac for two steaks - it's a strong flavor and you don't want to overpower the cream and make it bitter.  The flames are generally rather unimpressive, particularly because alcohol flames are almost invisible.  It's hard to get the cognac to ignite in the pan - so she lights it in the spoon and gently pours it onto the steaks while it's still burning.  Don't pour straight from the bottle into the pan!  She douses the pale blue flames very quickly by pouring on the cream - then turns off the heat and allows maybe 10 more seconds in the pan to get the cream hot and mixed in with the cognac, pepper and meat juices - and then serves it straight to the table.  But you do need to burn off the alcohol - it has to be added towards the end so that the flavors in the cognac don't get destroyed by the cooking - and you don't want to overcook everything else while you wait for the alcohol to simply evaporate off.  If you are getting a gigantic and colorful fire - then you may have set the fat from the steaks on fire - and that's "A Very Bad Thing" for both safety and flavor.  Since you're going to be serving the sauce from the pan - and you don't want a lot of ikky beef fat in it - if there is a lot of fat in the pan - then remove most of it before adding the cognac.  She suggests not cooking more than a couple of steaks in a pan - if you need to cook more then two or three steaks then use a second pan so that you can control everything more closely in that busy half minute at the end of cooking.  Also, avoid leaving the steaks too rare with this recipe because the blood in the cream doesn't look appetizing - so limit yourself to medium-rare.  The plates you serve onto need to be really hot.  She uses a sprig of parsley to decorate (and, I suspect, to meet the "7 ingredients rule" of French cooking that I've deduced from watching her cook!)  Because the timing of all of this is so important, she tends to serve vegetables that can stand being a little over-cooked - asparagus is generally her choice - because then she can give full attention to the steaks without having to panic about not over-doing the veg. SteveBaker (talk) 14:32, 30 July 2010 (UTC)

Very helpful advice! I think in the future I'll probably just "cook it out" to use the term instead of the big old show. Mr. Baker, you have a good point about the color of the flame---it was orange, and even though I poured off the excess fat, there was likely still some in the pan. There was 1/3 cup cognac (I used brandy, but anyways) in the recipe, so I think I agree on the sentiment of using too much of it. Not that I really tasted it at all...anyways, thanks so much!72.219.136.28 (talk) 21:13, 30 July 2010 (UTC)


 * An orange flame definitely indicates that something OTHER than the alcohol was causing the fire. Alcohol flames are notoriously hard to see...and when you can see them, they are pale blue.  I think you had a fat fire - possibly exacerbated by the cognac.  When a liquid flash-boils because it's hitting fat that's higher than the liquid's boiling point then it causes an 'aerosol' effect that sprays a fine mist of hot oil into the air.  If there is a source of ignition (and you handily provided one when you tried to set light to the cognac) - then you have a fat fire, which can be almost explosive.  Perhaps you need to turn down the heat and let things cool off a little before you add the alcohol? SteveBaker (talk) 06:06, 31 July 2010 (UTC)


 * And if you're cooking on a gas range, please make sure you turn it OFF before you start adding combustibles like alcohol! Matt Deres (talk) 14:50, 31 July 2010 (UTC)

Quantum Mechanics Problem
I'm working through a quantum mechanics book and have encountered a problem with one of the exercises and I need a little help. The problem defines a phase flipping operator in d dimensions to be a unitary operator with eigen values +1 or -1. Then, it wants me to show what happens if we take the whole collection of such operators relative a specific shared basis of eigen vectors and average their effect on a a density operator. However, by linearity, this should be the same as applying the average of the unitary operators to the density operator, but since there will be as many +1's as -1's for any eigen |k>; the overall operator appears to average to 0. This does not seem to be the answer the book wants since it says that it should preserve the populations of the density operator, but wipe out its coherencies. Thus, I suspect I am missing something really simple or the book is wrong, can anybody point me to which one of these is the case; if the former, can I have a small hint as to what I am missing. Thank you:) 66.202.66.78 (talk) 09:29, 30 July 2010 (UTC)

Nevermind, being half asleep, it somehow seemed reasonable to average the unitary's, get 0, then apply them; obiviously that does not follow from linearity. Instead, I should obtain that only the diagonal of the density matrix remains:) 66.202.66.78 (talk) 09:39, 30 July 2010 (UTC)

practical consequences of existence
philosophically, existance in an open question. what are the practical consequences of whether I exist? Does it really mean anything for me if in the end it is proved/discovered that I don't? —Preceding unsigned comment added by 92.224.207.77 (talk) 10:14, 30 July 2010 (UTC)

http://plato.stanford.edu/entries/existence/ --Zomzom12 (talk) 13:14, 30 July 2010 (UTC)


 * Philosophers are a waste of quarks. What is the definition of the word "exist"?  Sadly, it's not a very well defined concept.  Wiktionary says "to be; have existence; have being or reality".  So what is "reality"?  Well, again, Wiktionary comes to the rescue with:


 * The state of being actual or real.
 * The reality of the crash scene on TV dawned upon him only when he saw the victim was no actor but his friend
 * A real entity, event or other fact
 * The ultimate reality of life is it ends in death
 * The entirety of all that is real.
 * An individual observer's own subjective perception of that which is real.
 * If we discount circular definitions of reality as "that which is real", then we're left with only the last (and still somewhat shakey) definition - and since your own subjective perception of reality is that you exist - it is completely impossible for someone to prove to you that you don't exist. It might be possible to prove to me that you don't exist (Maybe you're an AI program designed to test reference desk response times!) - but that cannot ever (by the very definitions of the words) prove to you that you don't exist.  Since it can't be proved - the question of what that might mean for you is entirely moot.


 * Philosophers love to argue about this circular definition of what words in English mean - but, as I said, they are a waste of quarks and we may safely ignore everything they say.
 * SteveBaker (talk) 14:04, 30 July 2010 (UTC)

Wow, you are very dismissive of philosophy... Ironically, you yourself are engaging in philosophical argumentation above. Best regards. Zomzom12 (talk) 15:29, 30 July 2010 (UTC)
 * Ah - but I'm not pretending that anything terribly deep is going to come out of this. I'm merely pointing out that it can only be a matter of linguistics.  If these words mean X then Y is true because that's how the words are defined.  This is only a discussion about the meaning of words.  If I were to define the word "existance" as "Having an account on eBay" - then the conclusions of the debate would be wildly different.  Rational debate can only be undertaken when everyone agrees on the definition of the words being used because these are (mathematically speaking) a part of the axioms of the theory you're trying to prove.  The big philosophy debate on the nature of existance isn't anything to do with producing some deep understanding of the universe or the human condition - it's just a matter of defining a tricky word. SteveBaker (talk) 05:58, 31 July 2010 (UTC)


 * Cue the cartoon showing why engineers aren't invited to philosophers' parties. Comet Tuttle (talk) 17:09, 30 July 2010 (UTC)
 * He was engaging in philosophical argument in order to demonstrate how pointless it is. Philosophy was replaced centuries ago by science, but there are still a small number of philosophers that keep going for no gain whatsoever (well, they get paid, so I suppose that is a gain for them). --Tango (talk) 17:32, 30 July 2010 (UTC)
 * If you don't exist, how could you have asked this question? Looie496 (talk) 17:13, 30 July 2010 (UTC)


 * I think that the subject you are talking about is ontology. Ontology may have some ethical consequences.  For example, imagine a nearly-perfect computer simulation of a universe with some humans in it.  Does their "ontological inferiority" mean that they don't really exist, or do ethical obligations extend to them?  Paul (Stansifer) 17:24, 30 July 2010 (UTC)
 * That doesn't mean we need philosophers to debate it endlessly, we would just need to make a decision. It's no different from decisions that politicians make every day (assigning value to different people's lives) and we don't rely on philosophers for those decisions. --Tango (talk) 17:32, 30 July 2010 (UTC)
 * There is no word "existance" though it sounds a bit like the British punk band Exitstance. Wikipedia has an article about the metaphysical concept Existence.


 * Existence is apparent only in terms of interactions with an Observer. Thus a table does not exist to a blind man until he bumps into it. The OP did not exist (as OP here) to us until we observed his/her question. Some practical consequences of the OP existing are that we pay him/her attention and he/she pays us attention. If we discovered that the OP does not exist, which could happen if someone found that the question was posted not by a person but by a random sentence generating machine, it would mean our interactions would change. I might conclude I have better things to do than talk to a machine. The machine wouldn't notice anything except that its battery would eventually run down and probably not be replaced. Cuddlyable3 (talk) 18:36, 30 July 2010 (UTC)


 * But that example isn't really true. The table does exist for the blind man because it exerts a slight gravitational pull on him - it deflects and absorbs sound waves and thereby alters the acoustics of the room - it also alters the behavior of other people who live in the house - if there is a table, they might eat in that room, and if not then they wouldn't.  That too would have subtle ramifications for the blind man, and that change affects him even if he isn't actively aware that the table is there.  There is a measurable difference on him because the table is there.  So you can't say that it doesn't exist for him.


 * Because every atom in the observable universe eventually affects every other one (to an admittedly small degree) everything 'out there' interacts with us as observers. Since there are no totally unobserved things, you can't say that anything in the universe doesn't exist for us using a clear black-and-white definition.  To make this point about the table not existing for the blind man until he bumps into it, you have to set an arbitrary threshold for how much it's allowed to influence him without it "existing for him".  Maybe objects that produce less than 0.0000000001 g's of gravity and reflect electromagnetic radiation at us at less than lumen, etc, etc can be said to "not exist" for us...but that's an exceedingly unsatisfying answer.  Nobody is ever going to agree on such an arbitary threshold for "existence". SteveBaker (talk) 05:58, 31 July 2010 (UTC)


 * Philosophers don't debate it endlessly; they mostly talk about other things. Computer scientists don't talk about ones and zeroes forever, and historians do stuff other than memorize dates.  (However, I now wish I'd taken that philosophy class on nothingness in college, since it turns out that there are a lot of different varieties of nothingness, absence, and the void in computer science.)  And politicians might benefit from paying attention to what the philosophers have to say!  Well, at least humanity might benefit.   Paul (Stansifer) 18:57, 30 July 2010 (UTC)
 * Endlessly does not mean constantly. The debate on the nature of existence hasn't ended, has it? --Tango (talk) 20:45, 30 July 2010 (UTC)
 * They don't ever seem come to any widely agreed conclusions - so there is no end to their discussions. SteveBaker (talk) 05:58, 31 July 2010 (UTC)
 * All that money I spent on a philosophy course and what have I learned about? Nothing! Cuddlyable3 (talk) 21:01, 30 July 2010 (UTC)
 * Take a look at existentialism, consciousness, reflexive self-consciousness, homunculus argument, qualia, and metaphysical solipsism. And...sigh. Metaphilosophy. ~ A H  1 (TCU) 00:37, 2 August 2010 (UTC)

Misinterpretation of UN population report?
Has the media and the public completely misinterpreted the findings of the UN report "World Population in 2300" (http://www.un.org/esa/population/publications/longrange2/longrange2.htm)?

Here are some quotes:

"Fears that the human race may drive itself to extinction through over-population are challenged by new United Nations figures suggesting an eventual equilibrium as people in poorer countries come to understand the need for smaller families. " http://www.guardian.co.uk/world/2004/nov/06/population.brianwhitaker

"The world's population will stabilize in 300 years to about nine billion people, with an average life expectancy of 95 years, the United Nations predicts." http://www.cbc.ca/world/story/2004/11/05/population_041105.html

All the Report says is that "According to the medium scenario, world population rises from 6.1 billion persons in 2000 to a maximum of 9.2 billion persons in 2075 and declines thereafter to reach 8.3 billion in 2175. The return to replacement level fertility coupled with increasing longevity in the medium scenario produces a steadily increasing population after 2175 that reaches 9 billion by 2300. If the effects of increasing longevity are counterbalanced by fertility, population size remains constant at 8.3 billion from 2175 to 2300 as in the zero-growth scenario (figure 1)."

Does this mean that this medium scenario is the most likely?

Thanks for your help!

Zomzom12 (talk) 12:37, 30 July 2010 (UTC)


 * I don't see that implication anywhere in the report. SteveBaker (talk) 13:51, 30 July 2010 (UTC)
 * Thank you for the input. Zomzom12 (talk) 15:30, 30 July 2010 (UTC)
 * Predicting something 300 years in the future is pretty much impossible. I can't imagine why they would even try. The biggest flaw is usually that they extrapolate existing trends without accounting for changes (not that they could). Another common error is mistaking Exponential growth for Logistic growth. Ariel. (talk) 21:32, 30 July 2010 (UTC)
 * A world population near nine billion sometime this century and again in 300 years does not imply the population stablizes at that level in 300 years. See also our articles Malthusian catastrophe and population growth. ~ A H  1 (TCU) 00:28, 2 August 2010 (UTC)

canteloupe
how can you tell when a canteloupe from the garden is ready to be picked?--Horseluv10 13:02, 30 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)

http://www.youtube.com/watch?v=11-XzxukFoM --Zomzom12 (talk) 13:11, 30 July 2010 (UTC)


 * To summarise that video (since Horseluv has previously implied they are confined to a Whitelist that only allows Wikipedia).
 * The cantaloupe will get paler until it isn't green anymore, but rather a more buff-like colour. This will presumably vary between varieties.
 * The cantaloupe will start to smell of melon.
 * The melon will start to separate from the stem, so they no longer look like the stem and melon are all one piece.
 * You will be able to separate the cantaloupe from the stem with very gentle pulling/pushing. If you have to pull properly, or cut the melon off the stem, it isn't ripe.
 * Anyway, that's what the video says, while showing you so that it's clearer. 86.164.66.83 (talk) 14:52, 30 July 2010 (UTC)
 * As a onetime seller of the melons, I agree that color change is one sign of a canteloupe being ripe, but the smell of ripe melon is the best indication. Unlike watermelons, the sound when it is thumped does not become deep and dull. Edison (talk) 23:18, 30 July 2010 (UTC)
 * thanks for the info from the video. i couldnt get onto it. im blocked.--Horseluv10 01:10, 31 July 2010 (UTC) —Preceding unsigned comment added by Horseluv10 (talk • contribs)
 * The video is a great guide for growers to decide when to pick. Smell is the best guide for a consumer to decide which canteloupe to buy, since you can't tell, in the store, what the vine looked like. Edison (talk) 04:14, 31 July 2010 (UTC)

Atomic theory
Atomic theory tells us that valence electrons in an atom are the particles that are mostly involved in many phyisical or chemical activities of substances. In lasers, electrons move from one energy level to another and thereby releasing coherent and monochromatic photons. During chemical reactions,valence electrons move from one atom to another and thereby changing the properties of the substances involved.Duruing charging,substances lose or gain electrons.DOES AN ELECTRON MOVE AWAY FROM ITS MOTHER ATOM WITHOUT ITS MOTHER ATOM COMING TO CONTACT WITH AN ATOM THAT THE ELECTRON IS INTENDING TO GO TO.JUST AN ELECTRON(ALONE) MOVING AWAY FROM ITS MOTHERATOM,POSSIBLY IN A VACUUM. —Preceding unsigned comment added by Mlondo (talk • contribs) 14:37, 30 July 2010 (UTC)


 * I have added a header separating this question from the one above. 86.164.66.83 (talk) 14:43, 30 July 2010 (UTC)


 * I think that the electrons separate in a plasma. --Chemicalinterest (talk) 14:58, 30 July 2010 (UTC)


 * Are you talking about chemical reactions, electrons moving in metals, or lasers? John Riemann Soong (talk) 15:01, 30 July 2010 (UTC)


 * The OP was asking whether there is an instance that an electron moves away from the mother atom without an ionic bond occurring. I responded by saying that I think in a plasma the electrons are stripped from the mother atom and sort of float around it. --Chemicalinterest (talk) 15:18, 30 July 2010 (UTC)
 * The OP describes well what happens in a metal conductor. Atomic nucleii rest in fixed positions while electrons can drift in the intervening space. An electric current occurs when electrons move from orbiting one nucleus to orbiting a neighbouring nucleus. Cuddlyable3 (talk) 16:15, 30 July 2010 (UTC)
 * It does happen in a metal to and is the basis of electrical conductivity; this moving away of electrons from mother atoms without a redox reaction going on. An exception would be electrical conductivity in ionic solutions . --Chemicalinterest (talk) 12:26, 31 July 2010 (UTC)
 * The OP describes a standard gas-phase ionization reaction: see ionization energy for more details. Physchim62 (talk) 14:57, 31 July 2010 (UTC)
 * Maybe in cases of positron radiation where the β+ particle comes into close contact with an atomic electron? ~ A H  1 (TCU) 00:10, 2 August 2010 (UTC)

water
Ages ago I saw someone with a glass of water and a weird device with two metal prongs which they put into the water. Then the water started to go grey. I asked them what the fuck they were doing and they said it was putting silver into the water and then they'd drink it for health benefits. What the hell were they doing? —Preceding unsigned comment added by Fdge45y4uwuetj (talk • contribs) 15:01, 30 July 2010
 * I think it was an electrolytic apparatus. --Chemicalinterest (talk) 15:03, 30 July 2010 (UTC)
 * What makes you think it was anything other than putting silver into their drinking water? While unconventional, this is not really that weird considering the other weird stuff people consume in the name of health.  I would suspect the 'device' was some sort of soluble rod that allowed for easy introduction of silver into the water. --144.191.148.3 (talk) 15:05, 30 July 2010 (UTC)
 * Here it mentions electrolytically dissolved silver. --Chemicalinterest (talk) 15:09, 30 July 2010 (UTC)


 * It may well have been exactly what they said. Silver sometimes used as a quack medical cure-all, (Presumably because of its weak antiseptic abilities.) See : Colloidal_silver
 * Fun Fact : Overuse of silver 'supplements' can turn your skin blue. See : Argyria
 * APL (talk) 15:38, 30 July 2010 (UTC)
 * Fun idea: Argyria turns skin blue where it is exposed to light. Could sitting in front of a slide projector eventually produce a skin tattoo of a photograph? Cuddlyable3 (talk) 16:00, 30 July 2010 (UTC)
 * What happens when the sun shines on your tattoo? You would need a "fixer" to lock the color in so additional light will not make the whole area blue. --Chemicalinterest (talk) 19:59, 31 July 2010 (UTC)
 * Seems "safer" to do it topically in a small area...obviously "do not try this", but paint on a solution of some silver salt, expose self, wash off. Essentially make yourself into a photographic plate. DMacks (talk) 19:41, 30 July 2010 (UTC)
 * Lest you think I'm just proposing bad ideas, the idea of using a slide projector to trigger photochemical reactions that produce an image of what was projected is actually pretty cool! One neat application is 10.1021/ed800170t. DMacks (talk) 19:46, 30 July 2010 (UTC)
 * After reading your first two sentences and before reaching your third sentence, I was sure they were using one of those portable, unsafe, electric gadgets that you can put in a mug of water to boil it. You plug it into household AC, and it boils the water super-quick.  Of course, if you drop the gadget and the two prongs touch your skin, you're then plugged into household AC yourself.  Comet Tuttle (talk) 16:57, 30 July 2010 (UTC)
 * I don't think those "water heaters" have live AC current. If it was just two electrodes, then it would fizzle the water furiously, creating a highly flammable oxyhydrogen mixture. --Chemicalinterest (talk) 21:04, 30 July 2010 (UTC)
 * I have a humidifier that works like that. It's simply two electrodes directly connect to power, and in the instructions they say to add a little salt to the water. Ariel. (talk) 21:27, 30 July 2010 (UTC)

Silver is antibacterial, so it makes sense that they would want it. --138.110.25.31 (talk) 19:37, 30 July 2010 (UTC)


 * Well, it doesn't "make sense", because silver doesn't kill billions of bacteria on contact in the way that antibiotic ointment does. Comet Tuttle (talk) 20:09, 30 July 2010 (UTC)
 * Read medical uses of silver. Even the WHO adds silver ions to drinking water. --138.110.25.31 (talk) 20:12, 30 July 2010 (UTC)


 * Ok 138.110.25.31! Let's read that article!
 * "At present, there are no evidence-based medical uses for ingested colloidal silver. There are no clinical studies in humans demonstrating effectiveness, and a few reports of toxicity. The U.S. National Center for Complementary and Alternative Medicine has issued an advisory indicating that the marketing claims made about colloidal silver are scientifically unsupported, and that the silver content of marketed supplements varies widely and that colloidal silver products can have serious side-effects to the consumer, including 'argyria,... neurologic problems (such as seizures), kidney damage, stomach distress, headaches, fatigue, and skin irritation. Colloidal silver may interfere with the body's absorption of some drugs, such as penacillamine, quinolones, tetracyclines, and thyroxine.'"
 * Any questions? WHO does not use it for medicinal purposes.  They do sometimes use it to disinfect contaminated water in third-world countries, but in western countries with good public water systems that doesn't apply at all. APL (talk) 00:24, 31 July 2010 (UTC)

Isn't silver poisonous? Count Iblis (talk) 23:06, 30 July 2010 (UTC)
 * Yes. It is.  Alternative medicine fads are often dangerous. APL (talk) 00:24, 31 July 2010 (UTC)


 * No; silver is not poisonous. It is an unreactive element. Silver compounds are poisonous. Yeah I know --Chemicalinterest (talk) 00:53, 31 July 2010 (UTC)
 * Elemental silver can cause a number of health problems. The bit I quoted above mentions some of them, the articles mention more. (Besides, if it's so 'unreactive', how's it killing all that bacteria in third world water supplies?)
 * Please don't post things that you thought up off the top of your head. Especially when the actual facts are so close at hand. APL (talk) 19:29, 31 July 2010 (UTC)

Silver kills bacteria and is therefore useful as a disinfectant/antiseptic. --138.110.206.101 (talk) 01:25, 31 July 2010 (UTC)
 * Perhaps, a bit anyway. But you don't drink disinfectants! APL (talk) 03:40, 31 July 2010 (UTC)

Silver nanoparticles can be poisonous due to the presence of residual Ag+. John Riemann Soong (talk) 03:15, 31 July 2010 (UTC)


 * One additional word of caution about colloidal silver and gold is that when it changes your skin color, it does so permenantly. There is no cure and it doesn't fade or dissipate over the remainder of your life.  Since there is zero evidence of beneficial effects of putting the stuff into your body - you'd definitely have to be crazy to take the stuff.  The antibiotic effects of silver outside of the body are really rather mild - not even a fraction as good as modern antibiotics. SteveBaker (talk) 05:13, 31 July 2010 (UTC)
 * But don't you want your cells to be all bright and sparkly like these a549 cells? John Riemann Soong (talk) 05:44, 31 July 2010 (UTC)
 * My opinion is that the disinfectant in colloidal silver is too weak to be of any use in vivo. --Chemicalinterest (talk) 11:02, 31 July 2010 (UTC)
 * ChemInt, I don't mean to be rude, but no one cares what your opinion is. Not in the slightest. APL (talk) 19:29, 31 July 2010 (UTC)
 * I don't care. But since I don't know (haven't read the studies), I can only have an opinion. --Chemicalinterest (talk) 19:57, 31 July 2010 (UTC)
 * I did read a few studies while trying to mediate a wiki-dispute once, and my slightly-informed opinion matches the mainstream view - colloidal silver is utter crap and relies on confusing people with studies that examined ionic silver. Franamax (talk) 21:16, 31 July 2010 (UTC)
 * Then why would you imagine you needed to answer? I have an opinion on lots of things I haven't got evidence or sources for, but I'm not going to offer it when there are plenty of people offering more informed views. If those people do not present themselves, the second best option is to inform myself so that I can give an actually informed answer with sources. Giving an uninformed opinion is absolutely the last-ditch option when I can't find any information and nobody else has offered anything good and the question has been up for days. And even then, it has to be an opinion that might lead them to greater understanding of the topic, swathed in acknowledged limits. 86.164.66.83 (talk) 01:25, 1 August 2010 (UTC)
 * Except in burn treatment where for instance "Silver sulphadiazine continues to be the antimicrobial agent most often used in burn care facilities" and silver ions counteract problems with bacterial resistance. Note this is not colloidal silver. Entire sheets of metallic silver used to be used for burn treatment too, and I think there may even still be active research on this. Franamax (talk) 21:12, 31 July 2010 (UTC)

Flossing
I am writing a work of historical fiction surrounding the invention of flossing. The novel begins when the protagonist notices that on some days her teeth are very tight and it's impossible to get the floss between them without breaking it (the floss), while on other days it just glides through with no problems. She sets out to discover whether it's possible/normal for the teeth to cycle through this kind of tightening and relaxation and what it's called. Anyone know? Thanks. --Sean 16:59, 30 July 2010 (UTC)
 * You ask a good question. It's an evidence-based assertion that occlusion, or the manner in which teeth of the upper arch meet with the teeth of the lower arch, changes ever so slightly throughout the day.  Normal physiology dictates that hard tissue join not directly to other hard tissue but rather via ligaments.  Teeth are no exception, and they are attached to the alveolar bone via fibers of the periodontal ligament.  As such, there is some physiologic mobility to healthy teeth (contrast this to dental implants which, when properly osseointegrated into the jaw bone, fuses directly to bone and exhibits no mobility.  So, to respond to your question directly, I cannot say that I've heard of any research on that front, but it's certainly biologically plausible for contact between teeth to shift enough for a layman to detect with a floss test -- I question if the magnitude of change would be enough to tear the floss one day and allow it to pass though, as you described it, a nearly open contact.  Moreover, I have a pamphlet that describes the invention of floss, and if you email me and give me a few days, I'll scan it and send that to you.  DRosenbach  ( Talk 20:23, 30 July 2010 (UTC)
 * Thanks so much for the thorough answer. I'd never even considered that teeth were held in by ligaments, though that makes sense, of course.  Don't bother with the scan, but thanks; I've got enough to go on about the variable tightness issue from here. DRosenbach, I've thoroughly enjoy your dental-themed contributions to these desks over the last year or so.  Cheers! --Sean 21:25, 30 July 2010 (UTC)


 * (non EC-flagged EC) Whew. I can't think of anything that would cause that particular cycle, though hopefully our resident dentist can come up with something. I hope you don't mind me saying this, but that seems like a really bizarre way to start... anything. Seriously - the central problem of the story is why floss sometimes gets stuck? Good luck with the publishers, my friend. :-) Matt Deres (talk) 20:26, 30 July 2010 (UTC)
 * Oh, I assure you it will be a ripping yarn as we watch our intrepid flosser invent all manner of ludicrous backstories as she outwits the various bureaucratic regimes that stand in the way of her idle wonderings, even when she agrees with those regimes in principle! --Sean 21:25, 30 July 2010 (UTC)
 * Yeah, when you're heroine is busy being subtle, make sure she doesn't push her luck by gloating in the presence of people who played along with her. That wouldn't make her a terribly sympathetic protagonist. 86.164.66.83 (talk) 23:37, 30 July 2010 (UTC)
 * ... I was actually wondering if this was just an elaborate ploy to circumvent our medical advice policy. "So I was writing a work of historical fiction where my protagonist's foot looks like this.  Do you think it's infected?"  Does dental advice fall under the desk medical guidelines?  Nimur (talk) 23:55, 30 July 2010 (UTC)
 * It does, but I think this is one of those cases when we can AGF Nil Einne (talk) 11:03, 1 August 2010 (UTC)
 * Floccinaucinihilipilification? ~ A H  1 (TCU) 00:05, 2 August 2010 (UTC)

paradoxical redox reactions
Oxidising and reducing power should be a transitive property, right? According to the article hydrogen peroxide: "In acidic solution, H2O2 is one of the most powerful oxidizers known—stronger than chlorine, chlorine dioxide, and potassium permanganate."

Why then does hydrogen peroxide reduce potassium permanganate in acidic solution? Hydrogen peroxide would appear to be less reactive in alkaline solution (what with it being deprotonated and all) yet it would oxidise in alkaline solution? How can an oxidising agent A be a more powerful oxidiser than an oxidising agent B at say, pH 1.5 and yet get oxidised by agent B? John Riemann Soong (talk) 17:00, 30 July 2010 (UTC)
 * (That section is missing info, however this doesn't affect the answer)
 * Kinetics is the key here when considering products - since the reaction of H2O2 >>> 2H+ + O2 + 2e- is doable by permanganate there is nothing to stop it happening .. in this case it is the faster reaction. So that is what happens.
 * In fact since it is more thermodynamically favourable: half cell emf of above reaction ~0.2V giving an overall potential of 1.8V (cf the overall potential for the H2O2 + MnO2 > MnO4- + H2O reaction is about 0.2V) it can be expected (but not certainly) to be the faster reaction anyway. (Sf5xeplus (talk) 20:09, 30 July 2010 (UTC)
 * Additionally there isn't actually anything the permanganate could be oxidised to. Sf5xeplus (talk) 20:20, 30 July 2010 (UTC)
 * It might not be stronger than KMnO4 in acidic solution though. Reduction for MnO4-- is +0.59 in basic solution but +1.70 +1.51 (the article states reduction to Mn++) in acidic solution. H2O2 is +1.78 in acidic solution. As reducing agent its oxidation potential is -0.70. --Chemicalinterest (talk) 00:49, 31 July 2010 (UTC)
 * The curve of increase in oxidizing power as a result of pH may not be the same for both chemicals. So in an extremely acidic solution (all H+), H2O2 might be stronger, while in a more weakly acidic solution MnO4 might be stronger. Just an idea. --Chemicalinterest (talk) 00:51, 31 July 2010 (UTC)


 * Also bear in mind that one of the possible reduction products for permanganate, Manganese dioxide, is a catalyst for the (non-redox) decomposition of hydrogen peroxide.77.86.5.67 (talk) 12:05, 31 July 2010 (UTC)
 * 77, it is a redox reaction; specifically, it is disproportionation of 2 O22- into O20 and 2 O2-. --Chemicalinterest (talk) 12:22, 31 July 2010 (UTC)

Wisteria
I have grown a number of seed-containing pods. What should I do with them? Kittybrewster  &#9742;  18:39, 30 July 2010 (UTC)


 * Kill them. Wisteria is a highly invasive and troublesome plant.  If you decide to put it in your yard, you will have to prune it daily.  Even then, it will likely spread underground and take over not only your yard, but all yards around you.  A lady three houses down planted Wisteria in her yard two years ago.  Now, the entire neighborhood has an impossible Wisteria infestation that is not only problematic, but also causing property damage as Wisteria is a strong plant that can take down fences, trees, and crack the foundations under houses. --  k a i n a w &trade; 19:40, 30 July 2010 (UTC)
 * It is hardly kudzu. Kittybrewster  &#9742;  20:25, 30 July 2010 (UTC)
 * Out of curiosity, has anybody gotten the neighbor to pay for the damage? Comet Tuttle (talk) 20:07, 30 July 2010 (UTC)
 * Rylands v Fletcher? Kittybrewster  &#9742;  20:25, 30 July 2010 (UTC)
 * Wisteria in the UK is a beautiful slowish growing climber that rarely causes damage if planted in the right place. I have seen several that have been growing close to houses for decades with no obvious dammage. It is not invasive in the sense that it propagates in an uncontrollable way. I'd plant those seeds in the autumn in a gritty loam and see what happens. I have doubts that much will but just imagine - your very own wisterias. Good luck. Richard Avery (talk) 22:02, 30 July 2010 (UTC)
 * From what I recall reading, even in the UK they cause damage to brickwork, and they do not support their own weight so have to be supported. On the other hand there is an attractive wisteria growing up the side of a building in one of the Inns Of Court in central London. 92.29.119.4 (talk) 22:31, 30 July 2010 (UTC)
 * We (UK) have some wisteria growing that supports itself, but we do have to prune it back every year to stop it getting too heavy for itself, and too intrusive. 86.164.66.83 (talk) 23:35, 30 July 2010 (UTC)


 * Here (in the southeast US), Wisteria grows so fast that you can literally watch it grow. Every weekend, I have to trim back foot long vines such that no Wisteria can be seen.  It all grows back in just a week - over an inch a day. --  k a i n a w &trade; 17:19, 31 July 2010 (UTC)

veneer core plywood
what is veneer core plywood —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 19:19, 30 July 2010 (UTC)
 * You can find an explanation of the different types of plywood here. Looie496 (talk) 19:24, 30 July 2010 (UTC)

Strange patterns in the water
There is a lake on the University of Nottingham's Jubilee Campus (it's the north one if you want to look on Google Earth) and it has several what I assume are oxygenating bubble jets which cause the water to bubble. When it rains, there is always a disc visible around these jets where the water is a different colour (see picture). Can anyone explain why this would be the case? I'd have thought it might be the jets adding some sort of chemical, but the effect is too clear-cut than diffusion would suggest. I have uploaded a sunny picture for comparison. -mattbuck (Talk) 19:21, 30 July 2010 (UTC)
 * Heh, I live in Nottingham and spend a bit of time at that campus. How strange. Can't answer your question though, sorry! Regards, --— Cyclonenim | Chat 20:07, 30 July 2010 (UTC)


 * Possibly a convection cell - oxygenated water forced up by the pumps spreads out a specified distance and then rolls under. that would imply a density difference of some sort, however (either the oxygenated water is colder than the surrounding water or the oxygenation process changes water density).  You can see the pattern in the sunny picture as well, if you look closely - it's just more muted.  -- Ludwigs 2  20:14, 30 July 2010 (UTC)


 * Could be a visible effect from the submerged heat-exchangers in the lake. Nanonic (talk) 20:36, 30 July 2010 (UTC)


 * Is there something under the disk meaning the water is shallower there? --Tango (talk) 20:47, 30 July 2010 (UTC)
 * I honestly have no idea. All I know is there are a lot of big koi living in there, and that it leaks because they need to keep topping it up every week. -mattbuck (Talk) 22:10, 30 July 2010 (UTC)


 * If it's not artificial, it could be some form of natural spring. ~ A H  1 (TCU) 23:55, 1 August 2010 (UTC)


 * Upwellings can cause a texture on the water surface that give it another colour. This is seen on a larger scale in Langmuir circulation. EverGreg (talk) 07:39, 2 August 2010 (UTC)

Irrational fear
The other day me and a couple of friends were sitting and talking on a park bench pretty late, and the conversation came up about fear and how we all seem pretty susceptible to fear even when we know it's very, very illogical. For example, if you sit and look out into the distance in the dark, you can imagine things there that really quite obviously aren't, and the presence of fear can remain. Is there a term to describe irrational fear, other than just that? Also, is there a term describing when you see something that isn't there (not a mirage, I think you get the point)?

Cheers! Regards, --— Cyclonenim | Chat 20:05, 30 July 2010 (UTC)


 * Phobia, and hallucination? Looie496 (talk) 20:14, 30 July 2010 (UTC)
 * Not really what I was looking for. 'Phobia' doesn't quite fit as it's not an inherent fear that's there all the time, it's only there when you're really focusing on what you're actually thinking about! Hallucinations don't normally come across as hallucinations, do they? I mean, people having hallucinations usually think what they're seeing is real. I don't. Regards, --— Cyclonenim | Chat 20:31, 30 July 2010 (UTC)
 * It sounds a bit like paranoia. --Tango (talk) 20:48, 30 July 2010 (UTC)


 * For phobia I take your point. For hallucination I don't think you have the word down correctly -- it doesn't imply believing that the thing is real. Looie496 (talk) 20:54, 30 July 2010 (UTC)


 * Fear of the dark seems to cover this. It is a normal phenomenon, as distinguished from the pathological fear of darkness, nyctophobia.  Not great articles, but maybe that's a start? --- Medical geneticist (talk) 20:58, 30 July 2010 (UTC)
 * Thanks, that does pretty much cover it. What about the phenomenon of actually seeing things that aren't there? I take Looie's point above with respect but it still doesn't occur to me as an hallucination. This only really happens in the dark and it's basically if you stare at some space in the distance your mind wrongly decides that, say, a post by a tree is actually a person. Maybe I'm just overthinking this and it is a form of hallucination, I don't know. Regards, --— Cyclonenim | Chat 22:43, 30 July 2010 (UTC)
 * Imagination is not just for kids. It's easy to imagine things, and if you are good at it you can even (for a while) believe it. Imagine is often used as a negative word, but it doesn't have to be. Ariel. (talk) 23:25, 30 July 2010 (UTC)
 * Fear, anger, sadness and love are always irrational emotions but may be based on good cause. Hallucinations may be chemical and don't have to induce fear. Eg seeing a bunch of horses galloping past your right field of vision in your dining room. Kittybrewster   &#9742;  02:11, 31 July 2010 (UTC)
 * Also see fear of ghosts and boogeyman. ~ A H  1 (TCU) 23:54, 1 August 2010 (UTC)

Name this climbing plant?
What is this please? http://img201.imagevenue.com/img.php?image=27784_climbingplant_122_47lo.jpg Thanks 92.29.119.4 (talk) 22:28, 30 July 2010 (UTC)
 * My guess: Virginia creeper Parthenocissus quinquefolia --Digrpat (talk) 01:48, 31 July 2010 (UTC)

Looks like it. Thanks. 92.15.12.218 (talk) 13:41, 31 July 2010 (UTC)

Silent cars?
Will it ever be possible to have silent cars, and hence no traffic noise? Or is the current noise-level of modern cars as quiet as we can get? I assume most of the noise comes from the tyres and road surface rather than engine noise. Thanks 92.29.119.4 (talk) 22:55, 30 July 2010 (UTC)


 * While not directly answering your question, I'll direct you to Electric vehicle warning sounds, and ask you to keep in mind that the majority of modern cars are still operating with standard internal combustion engines. -- LarryMac  | Talk  23:00, 30 July 2010 (UTC)


 * Personal experience, but it's relevant. When the first Prius cars came out I was at an art festival in the Blue Ridge mountains and whilst walking through a parking lot had the very disturbing experience of a Prius appearing out-of-nowhere into my peripheral vision and then passing me as I walked along. Now - the Prius obviously had been driving through the parking lot at a safe speed and simply passed me as any other car would, but because of its engine design, the only thing I heard was the light sound of tires on gravel. Had it been blacktop, I'd not have heard a thing. That's pretty silent!
 * Assuming in some alternate reality everyone switches to electric or quiet hybrid cars, though, you're still going to have horns and the occasional need to use them. So if you include horns and aftermarket stereos in your "traffic noise" category, then the answer is clearly "no" regardless of engine noise levels... 61.189.63.171 (talk) 23:35, 30 July 2010 (UTC)
 * Maybe silent cars of the future will need radar-operated horns to honk and automatic brakes to operate when some doofus or blind person steps out in the street without looking both ways. Edison (talk) 04:12, 31 July 2010 (UTC)


 * Actually, at high speed on a freeway the dominant sounds are tire and wind noise. Engine noise is there, but it's nearly drowned out by the tire noise. An all-electric car with normal tires is nearly as loud as any other car on the freeway. If cars start using the tweel instead of inflatable tires, they'll be even louder (my company tested this for a military application; the rubber spokes flexing and snapping taught taut as the wheel turned generated a lot of noise). ~Amatulić (talk) 05:47, 31 July 2010 (UTC)
 * You mean taut. 92.15.12.218 (talk) 13:23, 31 July 2010 (UTC)
 * Yes. Thanks. ~Amatulić (talk) 06:02, 1 August 2010 (UTC)
 * Perhaps for the safety of pedestrians, electric cars should be fitted with external loudspeakers playing recorded or simulated internal combustion engine sounds in synchronisation with their speed and acceleration :-) . 87.81.230.195 (talk) 12:02, 31 July 2010 (UTC)
 * Or else Good Humor truck jingles, just to confuse all the kids. DMacks (talk) 15:16, 31 July 2010 (UTC)
 * Need I point out a lot of this is already somewhat discussed in the link LarryMac, the first respondent, provided? Incidentally I don't think people tend to cross on highways, looking first or not Nil Einne (talk) 19:34, 31 July 2010 (UTC)
 * ZENN vehicles (zero emission, no noise) are said to produce no "noise", but it's difficult for any car to be completely silent unless it integrates some kind of external sound absorption mechanism. ~ A H  1 (TCU) 23:50, 1 August 2010 (UTC)