Wikipedia:Reference desk/Archives/Science/2012 August 2

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August 2

No electricity for you!

According to a news article discussing the recent massive blackouts in India, [1], 1/3 of India's 1,200,000,000 never have access to a supply of grid electricity at all, under the best of circumstances, even for part of each day. It's hard to imagine viewing a house for sale in the US or the UK and hearing that there is no electric line close enough to supply it with electricity. How long ago were electric lines extended to more than 2/3 of the population of the US, the UK, France, and Germany ? Was it 100 years ago, 50 years ago, or what? Do the nonelectric 400 million Indians use Kerosene lamps, candles, or what, once the sun goes down? Edison (talk) 01:13, 2 August 2012 (UTC)

This is one of my favorite graphs. The US hit the 2/3 mark a little over 80 years ago, and we hit the 100% mark about 50 years ago. This graph is by households, and I can't rule out that that the average number of household members might be different for wired and unwired homes. Someguy1221 (talk) 01:27, 2 August 2012 (UTC)

A substantial number of that 1/3 don't even have houses. They live in camps, train stations, or wherever they can find a bit of shelter. Looie496 (talk) 01:41, 2 August 2012 (UTC)

But aren't the train stations electrified? 203.27.72.5 (talk) 02:51, 2 August 2012 (UTC)

I suspect in the more rural areas they may not be, and even if they are the lights etc are likely turned off when no train is expected. Nil Einne (talk) 05:22, 2 August 2012 (UTC)

How many homeless in India? Literally no shelter, not even a public shelter, a derelict automobile, or an improvised shack? Sleeping on the ground, in the open? In some countries many people live in hovels, but tap into electric lines and steal current. The key thing would be having mains run somewhere near the house/shack. Edison (talk) 03:03, 2 August 2012 (UTC)

Theft of electricity is a common problem in India (our article appears to be solely on the situation in India), but I think much more among those who already have or could have electricity [2] [3] [4] [5] [6]. For those in situations you mention, they are unlikely to be able to convince corrupt officials to turn a blind eye, plus if someone's shack in the middle of no where has electricity it's a bit of a dead giveaway. Not to mention they may not have the skills or tools to do it, or the equipement to do anything useful with the eletricity. (And if they did have the tools and skill, they'd probably be better of just stealing the wire to sell provided they can avoid vigilantes [7] [8].) Nil Einne (talk) 06:08, 2 August 2012 (UTC)

Agree with Someguy. In the US, the 2/3 mark was reached by about 1927, and electrification was essentially universal by 1952. Can't say about India, but the house I grew up in in Pennsylvania was not electrified until 1972 because of a combination of remoteness and local political bickering (whereas my grandparents' home in the nearby city was electrified from when it was built in 1920). Lighting and refrigeration were powered by propane gas, supplemented with kerosene lamps, with candles for dinner. The level of comfort, though, far exceeded that that you will find in rural India, even in those areas that are electrified. Clotheswashing was probably the only chore that was significantly more time consuming than in a contemporary electrified household. So comparing when the US and India reached the 2/3 mark is like comparing apples and oranges. It does not mean the levels of comfort and convenience were comparable at that point. Dominus Vobisdu (talk) 02:00, 2 August 2012 (UTC)

Another factor you need to take into account is home generation. In Australia, large amounts of the population outside of metropolitan areas of the large cities were not covered by grid electricity until the 1960's. But what people had was gasoline or kerosene - powered home and/or farm generators. So they had all modern electric lihting and appliances, it's just that they were powered from their own generators and not from a power station. In many small rural communities in those days, often a local business such as a gas-station would provide electricity to nearby houses and other buildings in the village centre. I imagine a similar thing happened in rural USA and many other countries with a significant dispersed largely farming based population. And some people had gasoline powered washing machines. Wickwack120.145.176.119 (talk) 03:08, 2 August 2012 (UTC)

I think kerosene lamps are the most popular source of lighting besides electricity in Indai by far [9] [10] [11] [12] [13] [14] [15] for households. (Despite what [16] may lead one to think, propane doesn't seem to be a significantly lighting source.) From the last two results, the percentage of households without lighting is fairly small although given the population of India, still around 1.1-1.2 million households depending on which source you use (not sure what percentage of the population this is). BTW, with reference to some of the answers above, according to the census data at least, the number of houseless households (according to the definition they use) is relatively small, although given the population of India still affecting close to 2 million people as of the 2001 census [17]. I expect the number is an underestimate (the PDF mentions it may be an overestimate but also mentions how they only visited certain areas and how they may have difficulties getting cooperation). Perhaps more importantly, just because you have access to kerosene lighting doesn't mean you use it regularly. In fact some of the other sources also note that just because you are nominally connected to the electric grid doesn't mean you have a reliable or even particularly usable supply, even discounting things like the recent blackouts. Nil Einne (talk) 05:58, 2 August 2012 (UTC)

In the UK, nearly all houses were connected to the "National Grid" by the 1960s. The nearest mains electricity to where I live was five miles away until 1961. A few houses had their own generators, but most of us used paraffin or bottled gas for lighting. One house near where I live was not connected until about ten years ago, and there are still just a few isolated properties in the UK without a connection to the "grid", but they are rare. Dbfirs 07:10, 2 August 2012 (UTC)

It's a technical quibble, mostly, but the national grid and mains electricity aren't the same thing. "Mains" just means you get electricity from a shared community power supply; "national grid" means there's a high-voltage connection between that community power and the UK's overall generating capacity. In the islands of Scotland, plenty of people have mains electricity but aren't on the grid - e.g. people on Orkney are on both, but on Shetland the power grid is isolated from the national grid. Eigg only recently got mains electricity (meaning householders didn't have to generate their own) but still isn't on the grid. -- Finlay McWalterჷTalk 00:26, 3 August 2012 (UTC)

Thanks for the correction. I'd forgotten about some of the Scottish islands. I think all the English and Welsh islands are connected to the National Grid, or at least the ones with significant population. Dbfirs 07:59, 3 August 2012 (UTC)

Why Does the Annual Mortality Rate Rapidly Increase Between Ages 113 and 114?

A 113-year old person has about a 50% chance of surviving to age 114 on his/her 113th birthday, but a 114-year old person has about a 30% chance of surviving to age 115 on his/her 114th birthday. How come? Futurist110 (talk) 02:46, 2 August 2012 (UTC)

I want to point out that the annual mortality rate stays roughly constant at ages 110-113, yet rapidly increases for ages 114 and 115. Look at the Gerontology Research Group's supercentenarian tables and you'll see what I mean. Futurist110 (talk) 02:49, 2 August 2012 (UTC)

From [18]:

Human mortality after age 110 is at at a constant level of λ = 0.7. This implies an annual probability of death of q_x = 0.5. This result confirms the previous analysis by Robine et al. (2005). Correspondingly, life expectancy after age 110 is about 1.4 years. Beyond the age of 114, data become too sparse to allow us to make reliable statements. (emphasis added)

There just aren't enough people who live to 114 in order to get good statistics on their mortality rate. Dragons flight (talk) 03:23, 2 August 2012 (UTC)

We had a similar question a couple months ago. You may be interested in some of the answers to it. Evanh2008 ^{(talk|contribs)} 03:26, 2 August 2012 (UTC)

When researching my answer for that question, I came across a wide variety of sources that gave wildly different estimates for the death-rate-vs-age curve. I recall once finding, although I can't remember where, a review that compared different methods of calculating that curve. Based on which source you went by, you could make the curve come out as a positive, negative, flat, or some exotic non-monotonic function, and the values themselves varied significantly, but all probably in the vicinity of 70% at those ages. The numbers of data points to go on at those ages is really just too small for good statistics, if you want to incorporate years worth of mortality data, you have to keep in mind that the lifespan average is a moving target, complicating things significantly. You can only trust a lifespan histogram for a cohort that is 100% dead. Someguy1221 (talk) 04:58, 2 August 2012 (UTC)

Mortality rates (or at least the ones that I'm using) are all for dead people only. And for the record, it's interesting that as the 115+ year old people ever sample got larger over the last 10 years, the mortality rate at age 114 and 115 actually increased a lot, from about 50-55% in 2000 to about 70% right now. Futurist110 (talk) 05:58, 2 August 2012 (UTC)

There are enormous numbers of different mortality tables created by different people for different purposes based on different populations and datasets. To talk about the mortality rate is meaningless. Please link to the mortality table you are talking about. Normally, mortality tables are pretty much just guesses after around age 90. They use real data until there isn't enough to draw meaningful conclusions (which, depending on your dataset and methodology will be somewhere between about 90 and 110 - definitely well before 113), and then you just pick an arbitrary age as the maximum possible lifespan and pick some smooth curve to get you up to 100% by then. You shouldn't take any mortality figures too seriously after about age 90. They are based on too little data. --Tango (talk) 17:41, 2 August 2012 (UTC)

http://www.grg.org/Adams/B2.HTM - Here is the table that I was talking about. The mortality rates are very easy to calculate from it. Futurist110 (talk) 19:48, 2 August 2012 (UTC)

That's not a useful data set for this kind of work. It is collated from various sources with no way of knowing it if is complete or unbiased. It spans more than 20 years, during which time mortality rates have changed enormously. It spans multiple countries, which have widely varying mortality rates. It is also far too small. Your 30% figure is, with 95% confidence, assuming a simple binomial model, anywhere between 21% and 37%. Your 50% is actually anywhere between 33% and 61%. So, you see, they could actually be exactly the same and it would still be consistent with your data. Your dataset is too small to give enough make the confidence intervals small enough that they don't overlap. That means you can't draw any conclusions. --Tango (talk) 01:14, 3 August 2012 (UTC)

Ah, the miracle of the confidence interval. --TheMaster17 (talk) 08:54, 3 August 2012 (UTC)

Actually, I think that all or almost all of these cases with the exception of the Japanese ones have been verified by the Gerontology Research Group and its correspondents. As for Japan, their koseki system is very efficient, and thus the GRG does not usually consider it necessary to double-check Japanese cases. Thus, we know for a fact that all or almost all of these cases are accurate and reliable. As for what you said about confidence intervals, that is very interesting. Let me look more into that. Futurist110 (talk) 22:00, 3 August 2012 (UTC)

Earthing

What is the simple way to check whether the earth wire of a house electrical circuit is properly grounded? Thank you.175.157.5.252 (talk) 03:17, 2 August 2012 (UTC)

Call a competent electrician and ask them to check it out. Nil Einne (talk) 05:20, 2 August 2012 (UTC)

I tried looking this up online, only to deduce that doing it properly is not simple at all. Someguy1221 (talk) 05:26, 2 August 2012 (UTC)

The OP geolocates to Sri Lanka. I'm not at all certain, but Sri Lanka should be a country that uses the Multiple Earth Neutral System (MEN), or a close variant. In this system, the house earthing system has two main parts: An earth stake buried in the soil, and a connection to the street distribution nuetral wire. The house earth stake is of prescribed length, and it is generally sufficent to make a visual inspection. If the stake has no significant corrosion, and the wire connected to it is sound and the method of connection is sound (ie a pip clamp in good condition), then assuming the original installer did the right thing, that's all that's realy needed. The earth stake at each house does not ON ITS OWN do much - the system relies on all earth stakes at each premises fed from the street distribution having all their earth stakes connected in parallel by the power company's nuetral wire. All the earth stakes in parallel provide a low impedance to sink fualt currents even though an indiviual eartb stake caould not do so. If the neutral connection from the power company's strett wires to the house nuetral is deffective, then the house will have no power. If you know how to use a multimeter, check between your nuetral bar (in meter box) or the nuetral or earth pin of any wall outlet and the earth stake, on the earth stake below where the wire connectes to it. Check first for voltage - there should be well under a volt. If there is no voltage, then check resistance - it should be less than one ohm. These checks do not 100% guarantee everything is fine - beyond that you need a trained electrician. However they cover alll common deficiencies in an MEN system in a reasonably built up area. If you live in a new, undeveloped area or are isolated in a remote location, there's a bit more to it. Kiet121.215.2.150 (talk) 05:55, 2 August 2012 (UTC)

Determining that you have a ground is relatively simple, but determining that it's a proper ground is not. For example, you might currently only have a ground because a puddle of water is making the connection, which obviously isn't a proper ground, as you will no longer be grounded once that puddle disappears. StuRat (talk) 08:27, 2 August 2012 (UTC)

With the MEN system, that isn't generally a factor. A visual inspection, and grasping the stake and attempting to wriggle it is sufficient, assuming the installation was done in accordance with standards, as the electrical resistance to the "great body of earth" of an individual earth stake is unimportant. If an earth stake is so badly corroded that a puddle makes any significant difference, you'll almost always notice it on inspection. The most common defect is the wire is broken or the wire is no longer connected to the earth stake due to accidental damage or a defective clamp - all of which is easily spotted on visual inpection. In unusual situations such as remote area single-wire-earth-return feeds, there's more to it, but I did include a disclaimer. Keit120.145.189.101 (talk) 10:28, 2 August 2012 (UTC)

The suggestion to "wiggle the stake" is utter nonsense except to note that the wire is not connected to the ground rod. Such a practice could result in you holding a wire broken off by the action from the ground rod, with lethal high voltage on it, flowing through your body to ground. A utility I worked for would drive ground rods at transformer sites in 5 foot or so incremental lengths, with each stake screwed into the previously driven one. I would use a "ground megger" to measure the resistance of the new ground to several remote grounds. Sometimes it required 30 feet of ground rod to get to a required low impedance in soil underlaid by sand. A puddle at the surface would have scant effect on the portion 10 or more feet down, Several rods might be driven several meters apart and connected in parallel by large cables. One approach was to drive multiple grounds and use solution of a system of equations to determine ground impedance. Another approach was to use a remote ground. as a reference.Requirements might be less severe at a residence. Local codes will specify how low the impedance must be.and how many amperes of fault current the ground rod or system must sink without melting, possible thousands of amps for some time until fuses or breakers operate. In some US locations, codes might allow a clamped connection to a cold water pipe connected to a municipal water system by sturdy metal pipe, with a suitable jumper bypassing the water meter. It is not a job for the uninformed novice. Electrical shock hazard or structural fire might be the punishment for a mistake. The local ground has as one job the prevention of dangerous high voltage on all the conductors in a building if the transformer has a fault and primary voltage arcs to the low voltage secondary. Edison (talk) 05:14, 3 August 2012 (UTC)

Actually, Edison, it is YOU that wrote utter nonsense. Let's go thru this carefully: Firstly, the OP specifically asked about a HOUSE installation - not a substation, not a power station, not even a street transformer - just a house. My answer above is valid for a house, and is not intended for substations etc. Secondly, he geolocates to Sri Lanka. If he was in UK, Australia, Germany, etc, my answer would have been "go find a qualified electrician." But in Sri Lanka, he could be well off and in a quality city dwelling, or he could be in more third world conditions, and he may need to be both more interested and more resourceful. An lastly, and most importantly:-

I'll say this one more time, in capitals, so read it carefully: IN THE MEN SYSTEM (which these days is most of the World. USA may be different) INDIVIDUAL DWELLING EARTH STAKES INDIVIDUALLY DO NOT DO MUCH. THE SYSTEM OPERATION AND SAFETY COMES FROM A MULTITUDE OF SUCH EARTHS CONNECTED IN PARALLEL by the supply authority's neutral wire. You can (though it is illegal) cut any ONE of them without making any noticable difference. You are NOT at risk of shock if you disloge the wire from the electrode, any more than you would be if you disloged it accidentally, as I have done with a lawnmower. Electrical saftey standards must cover this sort of situation - in fact any system that allowed safety to be compromised by a single point of failure is just not on. You are however, generally expected by the terms of the supply contact you have with the electricity supplier to put any damged or corroded wire and/or elctrode right promptly - otherwise you could end up with most of the earths in the area damaged, and then there would be a problem. Household earths are not normally specified by performance, they are specified in terms of a mandatory stake/electrode length (typically 1.5 meters). A typical house earth may well be several hundred ohms resistance. If there is an appliance fault, the bulk of the fault current DOES NOT go to earth via your own earth stake. It returns to the transformer via the supply authority's nuetral wire, with only small amounts of current entering and leaving earth via individual stakes on the way.

It is thus perfectly ok to check the validity of the clamp that connects the wire to the eath stake by attempting to wriggle it. If it moves it's not up to scratch and needs fixing. It is possible that the buried part of a stake has corroded away. But if you grasp it and try to move it, and you can't then it's fine (resistance is not what makes it legal - only its depth). If you can feel it move at the top , then it needs fixing. Visual inspection and "wriggle" testing is what an electrican will do. An earth megger and similar instruments is not what the OP will have, and it has no relavence, as the requirement is a buried depth, not a specified resistance.

Keit60.230.203.89 (talk) 12:44, 3 August 2012 (UTC)

If you are testing grounds relative to other grounds, how is it determined that the first ground is working? Someguy1221 (talk) 07:54, 3 August 2012 (UTC)

This has absolutely NO relavence to teh OP's question, however: Special instruments are available, for which the internal operation is a bit complex to explain here, at least without diagrams and assuming a sound knowlege of meshed electrical circuit mathematics. Essentially, what they do is use selected earth stakes chosen as potential reference access points, and force a current though the earth stake under test, monitored by a sensing coil clamp around the electrode or its' connecting wire. The instruments do an internal calculation to find the resistance to "great body of earth" of the electrode under test. As long as the resistance of the reference electrodes is less than a certain amount, the resistance of reference electrodes does not affect the result. Earth electrodes near each other and near to other structures (eg metal pipes) share current paths through the soil to the great body of earth - this is manifested in what electrical engineers call "common resistance" - a resistance common to nearby stakes/electodes and added to the unique "component" resistance each electrode. In other words, 2 nearby electrodes form what is equivalent to "Y"-shaped circuit to great body of earth. I hope this is clear, as the subject is actually of some complexity, and the accurate measurement of earth systems is actually something that requires specialist knowlege of engineers. Whole textbooks have been written on this subject alone.

I point out that the words "ground" and "grounded" is USA terminology, but has spread around do to the wide availability of US textbooks and magazines. This is unfortunate, as the meaning of these words depends on context, and can be a source of confusion. The correct terminology for most of the English-speaking world is earth, meaning the great body of earth, earthed, meaning effectively connected to the great body of earth, earth stake or earth electrode, meaning the means of connecting to the great body of earth. Keit120.145.181.139 (talk) 11:15, 3 August 2012 (UTC)

Supplementary question from editor Edison moved to a new question Explain electricity consumer earthing by Keit. I moved it because an answer requires coverage of several related topics and would most likely not help the OP for this question. The OP is of course free to read the new question and its' answer(s). Keit60.230.207.82 (talk) 04:01, 5 August 2012 (UTC)

spina bifida case

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203.27.72.5 (talk) 08:16, 2 August 2012 (UTC)

Big Bang of nothing

Was the initial condition of the Universe an infinitely tiny bit of totally empty space? Since the initial mass of the Universe would be zero, dividing zero mass by zero volume does not give a singularity.

Then cosmic inflation hits and this empty space is blown up at vast speeds. This is all fine and dandy until a virtual meson pops up. This virtual meson is then torn apart before it can pop out. In order to avoid two bare quarks, each of the quarks gets paired up with another quark, giving a universe of two mesons. Each of these two mesons is then torn up, giving four mesons. Then eight, then sixteen, etc.

Exponential meson production continues until the Universe has enough mass/energy to reach a flat state and this stops inflation. The mesons then decay through the weak force, which applies its bias towards matter over antimatter. Would the result fit the observed Universe? Hcobb (talk) 13:14, 2 August 2012 (UTC)

I'm not an expert cosmologist, but as far as I understand the current theory, the standard models of the big bang start at infinite (or at least very high) densities, not at density zero. Energy already existed during cosmic inflation and was "stretched flat" by it - this explains the largely flat, isotropic and homogeneous appearance of the cosmos. If matter/energy was created during inflation, there is no good reason for this flatness. --Stephan Schulz (talk) 13:25, 2 August 2012 (UTC)

For most of the inflationary epoch, the universe is almost empty except for the scalar field (the inflaton), which is similar to the modern-day dark energy and the Higgs field—it has mass/energy but it's not matter in the conventional sense. Eventually the inflaton field decays, and that's the origin of all of the matter in the present-day universe. Any ordinary matter from before inflation is diluted to the point of irrelevancy. There is interest in looking for magnetic monopoles as relics of the pre-inflationary universe, but there's no theoretical reason to suppose there's even one of them in the present-day observable universe. -- BenRG (talk) 19:45, 2 August 2012 (UTC)

One outstanding question in cosmology is whether the early universe was isotropic and homogeneous. For example, consider reading this section, anisotropy in the observed cosmic microwave background. To the best of my understanding, the universe we see today appears very isotropic and inhomogeneous: it is still unknown if today's universe evolved from a similar isotropic, inhomogeneous initial condition. Nimur (talk) 15:10, 2 August 2012 (UTC)

If you mean the universe of 13.7 billion years ago, there's no question that it was extremely isotropic and homogeneous. The present-day universe is still very much so at large scales (~1 billion light years), but it's neither homogeneous nor isotropic at smaller scales. This is a result of magnification of slight inhomogeneities in the early universe by ordinary gravitational attraction. This process is well understood (though not by me). If you mean the universe before inflation, nobody has any idea. According to the inflationary model, the observed fluctuations in the CMB come from quantum fluctuations during inflation. They have nothing to do with the pre-inflationary universe. -- BenRG (talk) 19:45, 2 August 2012 (UTC)

Stephen Hawking insists that there was nothing prior to the big bang.

If our big bang article is correct, the concensous among scientists currently is to asume that the universe started of as a singularity with very very very high tempretures and pressure. The whole thing is very very complicated (I haven't been able to digest it completely yet) and coupled with the fact that the article provides a lot of info on this I feel that I don't need to repeat all of it here.Aliafroz1901 (talk) 16:10, 2 August 2012 (UTC)

Singularities are maths way of telling you you've made a mistake. I'm not sure any scientists actually think the universe had infinite density at time t=0 - what would that even mean? The singularity just tells us that it doesn't make sense to extrapolate all the way back to t=0 like that. Our understanding of physics starts a tiny fraction of a second after the "Big Bang", at which point the density was extremely high, but finite - we don't know what actually happened before that. It may well be that nothing interesting happened at t=0, it's just the time you happen to get to if you incorrectly extrapolate back. --Tango (talk) 17:51, 2 August 2012 (UTC)

Given the evidence,[19] it's safe to say that it all happened in the Big Inning. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:21, 3 August 2012 (UTC)

The inflaton field does not need to decay. Just mix with virtual particles and Quantum chromodynamics will suck the energy out of the inflation field into a uniform meson soup. It's Hawking radiation on steroids because as soon as any mesons are created they'll exponentially multiply like rabbits. No new physics is needed, just an empty tiny bit of space suffering from a Negative Space Wedgie. Hcobb (talk) 00:37, 3 August 2012 (UTC)

Tango I never said that the universe had infinit pressure, what I said was that it may have had extremely great pressure. And you are correct We don't know what was there at T=0, I know that and I was not presenting unchalengeable facts, only presenting the sciontific concensous on the matter.Aliafroz1901 (talk) 10:46, 3 August 2012 (UTC)

... and, of course, in some models, there never was a time t = 0, as Tango implied above. Dbfirs 11:22, 3 August 2012 (UTC)

"and, of course, in some models, there never was a time t = 0" some models doesn't mene all thereies, and If the above linked big bang article is correct the big bang only tooke a few seconds to complete so most thereies would include a time T=0. — Preceding unsigned comment added by Aliafroz1901 (talk • contribs) 16:32, 3 August 2012 (UTC)

... It all depends on what you think time is! Using conventional modern "time", the earliest we know about is the Planck epoch. Dbfirs 06:13, 4 August 2012 (UTC)

How do antibodies kill antigens/pathogens?

How do antibodies kill antigens and pathogens? Does the antibody kill the pathogen/antigen directly, or does immune cells kill the marked pathogen/antigen, or both, and if the antibodies kill the pathogen/antigen directly, how does that work? — Preceding unsigned comment added by 187.126.186.208 (talk) 14:10, 2 August 2012 (UTC)

See the Wikipedia article titled Antibody which explains all of that, and a lot more. --Jayron32 16:17, 2 August 2012 (UTC)

I found the following in the above article

"An antibody (Ab), also known as an immunoglobulin (Ig), is a large Y-shaped protein produced by B-cells that is used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, called an antigen. Each tip of the "Y" of an antibody contains a paratope (a structure analogous to a lock) that is specific for one particular epitope (similarly analogous to a key) on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly (for example, by blocking a part of a microbe that is essential for its invasion and survival). The production of antibodies is the main function of the humoral immune system.

Antibodies are produced by a type of white blood cell called a plasma cell. Antibodies can occur in two physical forms, a soluble form that is secreted from the cell, and a membrane-bound form that is attached to the surface of a B cell and is referred to as the B cell receptor (BCR). The BCR is only found on the surface of B cells and facilitates the activation of these cells and their subsequent differentiation into either antibody factories called plasma cells, or memory B cells that will survive in the body and remember that same antigen so the B cells can respond faster upon future exposure. In most cases, interaction of the B cell with a T helper cell is necessary to produce full activation of the B cell and, therefore, antibody generation following antigen binding. Soluble antibodies are released into the blood and tissue fluids, as well as many secretions to continue to survey for invading microorganisms."

So the answer to your first questionn seemes to be that both antibodies and immune cells kill antigens. and for the second it semes to be that antibodies kill pathogens via several methods with one of them being blocking an issential part of a microbe.Aliafroz1901 (talk) 16:49, 2 August 2012 (UTC)

Weight increments on a digital scale

I have always been curious and puzzled by this. Can someone please explain this to me? I have consistently noticed that digital weight machines (for weighing the human body) always seem to present the person's weight in increments of 0.2 pounds. So, the person weighing himself might get results of, say, 170.0 or 170.2 or 170.4 pounds, and so forth. But, the scale will never list weights such as 170.1 or 170.3 or 170.5 pounds. Why is this? I assume it has something to do with accuracy, precision, and rounding, etc. But, still, can't the machine (scale) "round" to the 0.1 pound increment, just as easily as its programmers selecting to round it to the 0.2 pound increment? This befuddles me. Any input? Again, I am referring to digital scales that measure the human body (e.g., a person trying to lose weight). I am not referring to the smaller types of scales that might measure fruit or food (in ounces or grams) or such. Thank you! Joseph A. Spadaro (talk) 16:51, 2 August 2012 (UTC)

A digital scale typically has an electronic sensor that converts weight to a voltage. This analog voltage is then converted in an analog to digital convertor (ADC) to a digital number. The ADC outputs a number with a fixed step size, each step representing a voltage difference of, in this case, 0.2 pounds. The ADC has a fixed and limited number of output values, so the scale cannot detect changes smaller than the step size of the ADC. To display these changes, the scale would need a more sensitive, more expensive ADC. It is also possible that manufacturers prefer to use the same ADC in scales that use pounds as they use in metric scales, which have often a step size of 0.1 kg, which is roughly 0.2 pounds. - Lindert (talk) 17:13, 2 August 2012 (UTC)

I've noticed that digital scales also have programming to make it look like you weigh exactly the same thing unless there's some large difference. This keeps it from giving a slightly different weight if you step off and right back on, and thus makes it seem more precise than it really is. I'm surprised they don't randomly sometimes add 0.1 to the weight (and then remember that), to make them look more accurate as well. (Heck, they could evenly randomly add several digits, to really make it look accurate, but that would cost more in display digits.) StuRat (talk) 17:43, 2 August 2012 (UTC)

Never confuse resolution with accuracy. Most digital scales for body weight are designed to weigh to a maximum weight of 130 kg or 300 Lb, with a display resolution of of 0.2 kg or 0.2 Lb. That's a resolution of 0.2/130 => 0.15% (in metric mode) or 0.2/300 => 0.07% (USA mode). The accuracy won't be anywhere near as good as that - 2% accuracy would be a good achievement with standard electronic circuitry. So while the display can resolve to within 0.1 kg or 0.1 Lb in terms of available digits, when weighing a 100 kg (220 Lb) man, you can only trust it to within 2 kg (4.4 Lb).

So why do they display to within 0.2 and not 0.1? ADC's (as mentioned by Lindert above) are made in standard resolutions: 8-bit, 10-bit, 12-bit, 16-bit, and 24-bit. The more bits, the greater the cost. If a scales manufactuer chooses to buy 8-bit ADC's, and decides to set the maximum weight at 300 Lb, the resolution will be 300/2⁸ = 1.17 Lb. That's good enough weighing a 300 Lb man (it exceeds the system accuracy) , but what if Mother wants to weigh her 20 Lb child? The resolution is then 1/20 ~ 5% - not too good. So, most manufacturers wil choose a 10-bit ADC. Then the resolution will be 300 /2¹⁰ = 0.3 Lb. Most electronic engineers, though, know a simple circuit trick to get another bit of resolution without the expense of a 12-bit ADC. So the system resolution is 11 bits i.e., 0.15Lb. Since to display this will require the cost of an extra digit, a quick bit of programming of the internal micro-computer will round it to 0.2. This can also save a few cents on the cost of a transistor etc to drive the display to resolve to 0.1.

The reason for the disply stability mentioned by StuRat is an issue with digital readouts well known to electronic engineers known as "Least significant bit uncertainty". In digital systems fed by an analog (ie continously variable) inputs such as force measuring strain gauges, small random variation in the input value and noise in electronic circuitry can, if the measured vaule is close to toggling the last digit, cause the last digit to rapidly flip between two adjacent values. Electronic engineers are used to this, but it can make non-technical people think the device is faulty or not trustworthy. So what we do is add hysteresis - the weight must increase at least twice the display resolution before the display is updated. Most bathroom scales wait until the weight is stable for a few seconds before settling on a value though.

Keit121.215.24.203 (talk) 23:58, 2 August 2012 (UTC)

I think they go beyond that, though. They don't want anyone to weigh themself twice in a row and get a different reading the second time, so require quite a large change from last time before they will register a change. Ironically, this improves the apparent precision while actually reducing the accuracy. You can trick it into giving you a real 2nd reading by adding a known weight, like 10 lbs, and then subtracting that. StuRat (talk) 04:16, 3 August 2012 (UTC)

That could add more error than you think it's eliminating unless you've ensured that your 10lb weight is exactly 10lbs. I highly doubt it is common practice for digital scale designers to include hysteresis, as consumer goods' sales are unaffected by small differences in post-purchase observed quality, perceived or otherwise. It is possible to see instrumentation report an identical voltage several measurements in a row, and there may even be some hysteresis effected by the circuitry, but to suggest it is intentional is unsubstantiated. BigNate37_(T) 05:27, 3 August 2012 (UTC)

It's definitely the case on my scale. I can eat a big meal, without using the bathroom, and it still reports the same weight as before. They don't want people returning the scales when they see how imprecise they are. With this system, they likely fool the people until after the return period ends. StuRat (talk) 05:32, 3 August 2012 (UTC)

Have you tried weighing yourself, and then reweighing yourself holding some weight that's say something like 5 pounds just to see if the scales still report the same thing? You could also weigh yourself repeatedly and each time increase the weight you're holding until you should be reading quite a substantial amount more. I, for one, doubt that any scales are designed in that way. 101.172.127.247 (talk) 08:13, 3 August 2012 (UTC)

What StuRat is describing is a symptom of possible mechanical binding, or a possible fault in the electronics. As a professional electronics engineer I am very familiar with the use of hysteresis in the manner I described. As I said above, many scales wait until the reading is stable for at least 1 or 2 seconds and then feeze it. It may be that Stu's scales work this way, and are programed to detect a large change as time to unfreeze the display - I have not seen any like that. The various scales I've seen either don't freeze the display, or if they do, they stay frozen until you get off completely. It is sufficient to "cover" +,- 1 digit to solve the least significant bit ambiguity. In pactice a design engineer may choose to make it cover 2 digits in order to ensure that production variation in parts and parts aging in use is not going to be an issue, but I would not expect more than that. I've tested my scales by taking 1 reading with just a large drum of carefully measured water (20 kg), then adding 0.2 kg, and the reading went up as expected, but both readings were about 3% low. Keit120.145.181.139 (talk) 11:32, 3 August 2012 (UTC)

I've heard of fake repeatability, by storing and repeating the last weight if it's close, being a common 'feature' in cheap scales see e.g. [20] [21] [22] [23]. These primarily refer to bathroom scales but I've also heard of it occuring in some kitchen type scales. As mentioned [24] and some of the other links, most scales only seem to store the last value, so rather then doing StuRat's complicated suggestion, just start the scale then add some other weight, allow it to stablise and take it off is usually enough to avoid the (IMO) cheating circuit if you want to determine real repeatibility of the scale or just get a new result from some intentional change. Another form of (IMO) cheater circuit, particularly common in cheap kitcen scales of the brandless made in China variety yet ironically very annoying when you're actually using them for their intended purpose appears to be what you're (Keit) referring to, i.e. drift rejection; where if the weight slowly changes it assumes it's drift and does not change. So if you add stuff too slowly it can seriously reduce the accuracy from what the scale is capable of because it takes a while for the scale to accept it's being changed [25]. (P.S. Whether these are useful features to the consumer or silly cheating obviously depends on one's POV, I've made my views clear but I understand not everyone will agree.) Nil Einne (talk) 20:42, 3 August 2012 (UTC)

Thanks, Nil, I knew I wasn't imagining it. Keit, you're lucky if you've never encountered this "feature" before. My strongest objection to this practice is that you can't tell if a scale uses this method or not, until you buy it. Nothing on the label tells you, and they aren't likely to let you try out the scales first (at the stores where I shop, at any rate). You could try reading online reviews, but those unfamiliar with this deception might say the scale is extremely accurate, since they step off and back on and get the exact same weight. StuRat (talk) 23:32, 3 August 2012 (UTC)

Thanks to all for the valuable insight and input. It does, indeed, make sense now that I have read the above replies. I can now understand why the manufacturers choose the scales to display weight to 0.2 rather than 0.1 pounds. Thanks again. Much appreciated! Joseph A. Spadaro (talk) 22:57, 4 August 2012 (UTC)

Can a singularity spin?

I was watching a video by creationist Kent Hovind and he was bashing the Big Bang Theory, and one of his claims that the BBT is false is his assertion that the singularity was spinning before it "exploded" (I know it didn't explode, but rapidly expanded). He contends that due to the conservation of angular momentum, all of the galaxies must be spinning in the same direction, but he points out that some of them are spinning in opposite directions. Two questions, can a singularity spin, and if so, was the singularity that spawned the universe, spinning before it expanded during the Big Bang? 148.168.40.4 (talk) 17:55, 2 August 2012 (UTC)

The cosmos has no net angular momentum (to within experimental precision). The spins of individual galaxies come from random local perturbations in the highly uniform initial state. They point randomly in all directions.

Singularities don't really have any properties. They exist in theories and are a sign that there's something wrong with the theory (for example, the ultraviolet catastrophe is a singularity in classical physics which was solved by quantum mechanics). The big bang singularity should disappear in a better cosmological theory, perhaps based on cosmic inflation. However, a cosmos with an overall spin is possible in general relativity, so the lack of overall angular momentum does need to be explained. It is a prediction of inflationary cosmology. -- BenRG (talk) 18:35, 2 August 2012 (UTC)

I suspect that Mr. Hovind is confusing the origin of the solar system (which did start with a spinning mass of dust) and the universe. I don't think cosmologists say the early universe was spinning. thx1138 (talk) 19:11, 2 August 2012 (UTC)

It's not even clear to me what "spinning" in respect to the universe would mean. Spinning compared to what? The Universe, which emerged out of the mathematical singularity, is all that is. What would be the frame of reference to say "it was spinning"? --TheMaster17 (talk) 08:51, 3 August 2012 (UTC)

That's a difficult question. Spin is not necessarily dependant on a frame of reference. Consider two masses in deep space connected be a string. If they are spinning, the string will be pulled taut. If they aren't, it won't. Whether the string is taut or not is not a frame dependant observation. --Tango (talk) 11:38, 3 August 2012 (UTC)

Yeah, I was wondering about this frame-independence of rotation, too, after I wrote my comment. But how would this appear from inside the universe? You would need a centripetal force (for example gravity) to hold the spinning "thing" together, wouldn't you? And wouldn't that mean there had to be a "center of rotation" somewhere (and in total, a physical difference between directions: spinward, anti-spinward and perpendicular), for which we have no indication (because the observable universe is isomorphic)? But I admit I'm out of my field with this topic, my lessons regarding relativity are mere distant memories. --TheMaster17 (talk) 12:28, 3 August 2012 (UTC)

It's not really my field, either... I don't think you need a centre of rotation, but you do need an orientation. So the universe could be homogeneous but it couldn't be isotropic. As you say, that isn't consistent with our observations. --Tango (talk) 17:29, 3 August 2012 (UTC)

You can have rotating black holes, so I don't see why the initial universe couldn't also have spin. The evidence suggests it didn't, though. --Tango (talk) 11:38, 3 August 2012 (UTC)

What evidence suggests the universe is not or had not been spinning? μηδείς (talk) 06:33, 4 August 2012 (UTC)

See my short discussion with Tango above. If the universe today would be spinning, not all directions in the universe would be the same. You would expect measurable differences between spinward and anti-spinward, for example. All observations at the moment point to an isotropic universe (meaning all directions are the same). But I'm not sure how exactly spinning would manifest, and in what measurements. We need someone with more physics background to answer this in detail. --TheMaster17 (talk) 08:03, 4 August 2012 (UTC)

Unexplored Areas

Are there unexplored land areas left on earth? Reticuli88 (talk) 18:47, 2 August 2012 (UTC)

I'd imagine that the majority of Antarctica's surface area has never known a human footprint. Though humans may have looked out of the window of a plane at it. --Kurt Shaped Box (talk) 18:54, 2 August 2012 (UTC)

Of course, most of the surface is hidden under ice, and likely won't be explored until we manage to melt off the ice cap. StuRat (talk) 04:18, 3 August 2012 (UTC)

There are almost certainly caves that have never had a person in them either. New land may appear when ice melts off it, or when molten rock solidifies. There are also likely to be some small; islands that humans have never visited. A related question that was here before was: what is the last land to be discovered? Graeme Bartlett (talk) 23:43, 2 August 2012 (UTC)

Thinking back to the last time I remember a somewhat similar question to the OPs being asked here, there was talk of unclimbed mountains - e.g. Gangkhar Puensum. --Kurt Shaped Box (talk) 00:16, 3 August 2012 (UTC)

While the ocean depths are not lands per se, http://xkcd.com/1040/ is relevant here. Bear in mind as a webcomic it takes gratuities liberties with the truth; for instance, David Bowie never walked the Abyssal Plain (though I believe Freddy Mercury has). BigNate37_(T) 05:31, 3 August 2012 (UTC)

Either the author of XKCD needs to write larger or scan at higher res, because I can't read most of that. Can you ? StuRat (talk) 23:37, 3 August 2012 (UTC)

Click the image to be directed to http://xkcd.com/1040/large/, which I am able to read with relative ease. BigNate37_(T) 23:47, 3 August 2012 (UTC)

Thanks. StuRat (talk) 03:40, 4 August 2012 (UTC)

It's "liberties with the truth". Truth needs no tips. Clarityfiend (talk) 19:56, 3 August 2012 (UTC)

Just because I'm wrong doesn't mean you have to tell everyone! BigNate37_(T) 23:47, 3 August 2012 (UTC)

It depends what you mean by unexplored. There are 67 uncontacted tribes in Brazil, and even within 100 miles of Sydney, new discoveries are being made in the dense rainforest.--Shantavira|^{feed me} 07:28, 3 August 2012 (UTC)

North Sentinel Island has not had many visitors. --Daniel 23:41, 3 August 2012 (UTC)

There are vast stretches of southwest Tasmania inaccessible due to horizontal scrub. There are mountain ranges in Canada which have likely not yet been climbed. 207.224.43.139 (talk) 06:22, 4 August 2012 (UTC)

Unconscious mind

Regarding the unconscious mind:

• What evidence is there to prove that it exists?
• Does the evidence point to either nonconscious processes or actual hidden thoughts?
• Is there anyway to access the unconscious mind?

--Melab±1 ☎ 19:10, 2 August 2012 (UTC)

Unfortunately this comes down to definitions. Neither "unconscious" nor "mind" have a specific universally accepted meaning, so the answer to the first question comes down to which definition you prefer. Some people, for example, don't think that the word "mind" should be applied to anything that is not consciously experienced, so to them, "unconscious mind" is an oxymoron. The best thing would be for you to read our article on the unconscious mind and come back with any questions it leaves unanswered. Looie496 (talk) 19:27, 2 August 2012 (UTC)

(edit conflict) It depends on what you mean by these terms, which are not defined the same way by different people. If you mean "are there processes in our nervous system which we are unaware and over which we don't have any conscious control", the answer is absolutely: the Autonomic nervous system governs a range of bodily functions. If you mean the "Freudian" concept of the Unconscious mind or of subconscious, the answer is that it is a lot less likely that such models accurately represent how the mind works. Concepts like "repressed memories" and the like are very controversial and poorly accepted among actual neuroscientists. People that study the "human mind" as a "soft science" (i.e. psyschology/psychiatry etc.) are more likely to work with such models of the human mind, but those that study the actual functions of the nervous system (neurologists/neuroscientists/neurobiologists) don't find them very useful. --Jayron32 19:29, 2 August 2012 (UTC)

I don't know all about that id and ego stuff but it is quite clear to me that thinking goes on without my being aware of it. I've done things like for instance stopping the car and only figuring out why it was the right thing to do a couple of seconds afterwards. Dmcq (talk) 21:50, 2 August 2012 (UTC)

There are things like reflex, training, and instinct which affect behavior, but I'm not sure what is sturcturally different than conscious behavior. Awareness is not the same thing as consciousness. --Jayron32 03:10, 3 August 2012 (UTC)

I don't know all the definitions but I in all probability have accessed the unconscious mind. At times I have walked from my room to the dineing room without realiseing what I am doing. At other acasions I have gone into the bathroom, come out and forgotten all about it then have my parents remind me that I have been to the bathroom, then remember it, then think that it was all a dreem. The latter tipicly takes place when I am half asleep.Aliafroz1901 (talk) 11:27, 3 August 2012 (UTC)

We are rarely consciously aware of what we are going to say, until we say it. If we had to consciously deliberate every word we were going to produce before we produced it, we could only do so by thinking in words about what word we were going to use, leading to an infinite regress. Hence most of what we say spontaneously is produced by the subconscious, with us only becoming conscious of what we are saying when we vocalize it. This is why we have the phenomenon of there being something on the tip of our tongues; a thought of whose struggle to make it into consciousness we are quite aware. μηδείς (talk) 16:55, 3 August 2012 (UTC)

I mainly don't think in words so I don't have that problem :) But yes I don't normally think about the actual words I'm going to say. Dmcq (talk) 18:45, 3 August 2012 (UTC)

It's one of, probably the, main trick to writing. Don't try to edit yourself as you write. Let the words flow. Then go back and consciously edit as a separate second step. If, while doing the first "free-flow" draft, you get stuck, write FIX (or the word you know should be replaced with a better one) in capital letters and keep going. If you try to edit while you write you give your subconscious a complex, and end up with the writer's version of a stutter. This has got to be the number one problem of people whom I teach writing to. μηδείς (talk) 05:28, 4 August 2012 (UTC)

Race and obesity

Why are white and black women more likely to be obese, while obesity is much rarer among women of other races? --108.206.7.65 (talk) 20:35, 2 August 2012 (UTC)

White and black women where? Such a broad statement is unlikely to be true, so your premise is highly flawed. Certain socio-economic groups in certain countries have a gretaer propensity for obesity, so if you define which groups in which countries you seek information on, it would be very helpful. The data is very different if one is looking at Zimbabwe or the U.S. or Australia, for example. --Jayron32 20:45, 2 August 2012 (UTC)

In America. I've noticed that white and black women seem to have much higher rates of obesity than Asians, Indians, etc. --108.206.7.65 (talk) 21:27, 2 August 2012 (UTC)

Obesity is also very high e.g. among Palestinian women (31.5%, [26]), who are neither white nor black, but Arab. I would say obesity is much more correlated with culture (including subculture) and with unemployment than with race. - Lindert (talk) 21:30, 2 August 2012 (UTC)

Palestinians are white, or at least defined as white by the U.S. census bureau. In regards to the original question, I saw a lot of fat Latina women here in the U.S., and I think that nowadays there is generally greater obesity among poorer people. More black and Latino people tend to be poor nowadays, so that is probably why there is a greater % of obesity among them. A lot of white people are also poor, if you go by total numbers. As for why poor people tend to be more obese, it's because they are often unable to afford healthier food or do not have the time to cook it, and thus buy and eat much more cheap fast food than higher-income people do. Futurist110 (talk) 21:42, 2 August 2012 (UTC)

The OP might be interested in our article on Steatopygia as it seems somewhat relevant here. Dismas|^(talk) 22:13, 3 August 2012 (UTC)

A related question

Why is it that black and white women's appearances can range anywhere from very pretty to very ugly, but women from other races are almost always attractive? --108.206.7.65 (talk) 21:29, 2 August 2012 (UTC)

That is purely subjective and varies from person to person. Apperently you are of that opinion, and therefore it is only you who can answer why you feel that way. Noone can answer it for you. - Lindert (talk) 21:34, 2 August 2012 (UTC)

I agree with Lindert on this. I, for instance, have way different tastes than you do. Almost all of the women that I find sexually attractive are white and/or light-skinned. As yourself what qualities you find attractive in women and you'll probably be able to answer your own question afterwards. Futurist110 (talk) 21:39, 2 August 2012 (UTC)

The OP asked a similarly loaded question a few days ago,[27] and being from Missouri, I guess he has to be shown. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:16, 3 August 2012 (UTC)

I think that OP's opinion are right. I have seen more obesity in white people around 45 to 50 years old than caucessian and Asians. GiantBluePanda (talk) 23:51, 3 August 2012 (UTC)

Um, how does your explaination explain why you believe the OP's opinion that 'black and white women's appearances can range anywhere from very pretty to very ugly, but women from other races are almost always attractive' (which is the subtopic you're replying under) is 'right' ? Nil Einne (talk) 17:26, 4 August 2012 (UTC)

Baby bird identification

Can someone identify these birds? The caption is "min egen bild" with a marker identifying it as Swedish; the user has no other uploads, and the filename is not particularly helpful. Nyttend (talk) 22:11, 2 August 2012 (UTC)

Birds are not really my thing, but I get whip-poor-will vibes looking at them, or perhaps some other brand of nightjar. Looie496 (talk) 00:10, 3 August 2012 (UTC)

The WP:BIRDS guys might be the ones to ask about this. They have regular 'birds for identification' discussions on their talk page. I don't think that any of them regularly contribute to the refdesks, but I'm sure that they'd be able to come up with a concrete answer, or at least narrow it down to a genus, if it happens to be one where the young of many species look very similar... --Kurt Shaped Box (talk) 00:25, 3 August 2012 (UTC)

Copied over there. Thanks for the pointer. Nyttend (talk) 01:32, 3 August 2012 (UTC)

Look like baby European Robins. Definitely not nightjars of any sort (though I can see why you'd get those "vibes"), as those species don't build nests; they lay their eggs directly on the ground. MeegsC (talk) 03:21, 3 August 2012 (UTC)

what physically changes between the ages of 18 to 22 -- fourth years look older than first years, but is it senescence?

I look at the photos of my friends (now 22) when they were first years (at 18), and they look so young! I am sad that we have lost our juvenile features and we seem "less cute" than before. But puberty ends between 16-18 doesn't it? What biological processes are occurring specifically? I don't think its the same type of aging that occurs later -- for example, I think our collagen remains taut, we don't develop wrinkles (yet), but what is changing? Nothing gold can stay (talk) 23:33, 2 August 2012 (UTC)

The biggest, most noticeable, effects of puberty tend to finish by around age 18 in boys and 16 in girls, but it doesn't stop completely until quite a bit older, particularly in men. Chest hair, for instance, is often still developing by age 22. --Tango (talk) 01:34, 3 August 2012 (UTC)

It could just be normal mature aging, as noted at senescence above, but some people continue to grow and develop through puberty into their early 20s. One somewhat famous example: David Robinson (basketball) grew three inches between the ages of 18-22, while many people stop growing in height well before then; for example I reached my adult height at 13. There is a lot of variation. There are also significant effects of things like diet and exercise. I went through a lot of changes at that age, crappy college food and a lack of activity added significant weight which had a general effect on my facial features and body shape. --Jayron32 03:07, 3 August 2012 (UTC)edit: spelling error corrected --Jayron32 04:07, 3 August 2012 (UTC)

"Man people" ? :-) StuRat (talk) 04:05, 3 August 2012 (UTC)

I think it depends on sex as well. When I was studying human developmental psychology some 30 years ago, I was told that the male physique continued to develop and mature until the mid-20s, whereas the female body reached maturity some years earlier. There then followed a period of relatively little change until the mid-30s when the ageing process started to have undesirable effects. In the years since, these dates may well have changed (50 is the new 30?) but the general principle still holds good. --TammyMoet (talk) 08:05, 3 August 2012 (UTC)

My female friends definitely seem to "mature" between the age of 18 and 22. My male friends seem to age less, actually. Nothing gold can stay (talk) 15:22, 3 August 2012 (UTC)

I haven't the slightest idea of a relevant article in general, but many things cause aging during that period: taking up alcohol and cigarettes, late nights and lack of sleep, excess sun exposure, poor eating habits, stress, and even sexual activity can affect the freshness of young skin. μηδείς (talk) 16:43, 3 August 2012 (UTC)