Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

August 29

Kepler-47

The caption on image 6 of this image gallery about Kepler-47 reads: "This screenshot from a NASA animation shows the orbital paths taken by the two known planets in the Kepler-47 system, which both orbit the same two stars." That last part seems intriguing to me. Do we know of an example where two planets in the same system orbit different stars? Dismas|^(talk) 00:26, 29 August 2012 (UTC)

My understanding was that the separate orbiting of one star in a binary system was the norm, and this "tatooine" situation was notable because it was the first confirmed where a planet orbited both binaries. μηδείς (talk) 02:59, 29 August 2012 (UTC)

The binary stars HD 20781 and HD 20782 have 2 and 1 confirmed exoplanets respectively. The binary stars HD 11964 and HD 11977 have 2 and 1 confirmed exoplanets respectively. Since these are wide-binaries, astronomers classified them as separate systems, so technically the answer to your question would be no.

In case a similar question comes up again in the reference desk, I found the answer by going to List_of_exoplanetary_host_stars, sort the table by the number of confirmed planets, and then shift-cliking every yellow row. Then I just do a ctrl-f for "binary" in each new tab.A8875 (talk) 03:54, 29 August 2012 (UTC)

Superheating and nucleation

From the superheating article: "Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites, while taking care not to disturb the liquid. ... Water is said to "boil" when bubbles of water vapor grow without bound, bursting at the surface. For a vapor bubble to expand, the temperature must be high enough that the vapor pressure exceeds the ambient pressure – the atmospheric pressure, primarily. Below that temperature, a water vapor bubble will shrink and vanish. Superheating is an exception to this simple rule: a liquid is sometimes observed not to boil even though its vapor pressure does exceed the ambient pressure. The cause is an additional force, the surface tension, which suppresses the growth of bubbles."

I have three questions: 1) what are the usual nucleation sites in a "regular" pot of water that cause it to boil at 100C? Irregularities in the surface of the pot which trap pockets of air are one. Are there any others? 2) how do these nucleation sites actually promote bubble-making. (I don't see how trapping air will make it easier to form bubbles). 3) why do these bubbles only need to overcome the ambient pressure, and not the ambient pressure + pressure due to surface tension?

Thanks. 65.92.7.148 (talk) 00:57, 29 August 2012 (UTC)

Also, in bubble chambers, why doesn't the sudden formation of bubbles cause the whole thing to boil? 65.92.7.148 (talk) 01:01, 29 August 2012 (UTC)

Metal pots likely have LOTS of good nucleation sites, metals have a crystal structure and at the microscopic level are rarely very smooth, regardless of how they feel. It is almost impossible to superheat a liquid in a metal container for this reason. Amorphous solids like glass, that lack a crystal structure, make better containers to superheat a liquid in because they are truly smooth, and so lack nucleation sites. How nucleation sites work is explained in some detail at Nucleation, but the (over)simplified version is that nucleation sites provide a place for bubbles to collect roughly the same way that surface catalysts do: they provide a mechanism which lowers the activation energy necessary to make the transition from the liquid to the gas phase. In super simple terms: they give bubbles something to cling to while they form. Once a tiny bubble forms, it creates a surface; smaller bubbles have a greater surface tension per unit volume than larger ones do (that's because surface area grows as a square function but volume as a cubic function, so as the volume goes up by a factor of 1000, the surface area only goes up by a factor of 100, and the gap between the two gets bigger as the size continues to increase). That means the greatest surface tension exists for the smallest possible bubbles, and their just isn't enough gas inside these bubbles to exert enough pressure against the surrounding liquid to overcome their own surface tension, so they collapse on themselves and never grow. Nucleation sites basically break up the surface tension of these nacent bubbles, giving them the opportunity to form a stable bubble and float to the surface. --Jayron32 03:02, 29 August 2012 (UTC)

Thanks. In bubble chambers, ions apparently act as nucleation sites. Any idea how that happens?

Also, I'm looking for a text to brush up on the physics of phase transitions. I realized I have (pretty much) no idea what's "going on" when, for example, water starts to boil. Any recommendations? 65.92.7.148 (talk) 00:17, 30 August 2012 (UTC)

See symmetry breaking. Any sort of balanced high-energy system will collapse given the slightest chance to do so. You don't need to shake a balanced pin very hard to get it to fall over. μηδείς (talk) 01:30, 30 August 2012 (UTC)

Mars Science Laboratory Flight Path

Hi, I'm looking for the Curiosity Rover's flight path, something similar to this:

I checked the Mars Science Laboratory article and some of the related articles (like the timeline), but I can't seem to find it. Basically, I want to see the placement of the Earth & Mars during the takeoff & landing, and view the orbit of the planets while also keeping track of Curiosity's position, all of this relative to the Sun.

A snapshot of the celestial bodies' positions at takeoff, and a separate snapshot of the celestial bodies' at landing, would be helpful, but what I'm looking for is either an animation, or month by month snapshots at least.

Any help is appreciated, thanks!--99.179.20.157 (talk) 03:48, 29 August 2012 (UTC)

You can quickly estimate this via any Hohmann transfer orbit image, such as the one here. Most of them (like this one) are going to show you Earth position at launch and Mars position at landing, but it's pretty easy to extrapolate the rest. A ~230 day flight means that Earth has moved approx 2/3rds around its orbit by the point of landing, and that Mars needs to be backed up approx 1/3rd around its orbit to show the correct position at launch time. The speeds of both planets and the spacecraft can be reasonably approximated as constant. — Lomn 04:26, 29 August 2012 (UTC)

One way to watch the flight is JPL's Eyes on the Solar System (Java in browser required). Enter the launch date in Date+Time and use Speed+Rate to fly forward and backward in time. Click the spacecraft's name to center on it, and use the mouse to rotate the view, and just play with the controls. You can also see a quick demo at TED.

There are other planet position simulators, search the web, e.g. [1] - won't show the spacecraft but you can move in time from launch date to landing to see how the planets moved. 88.112.47.131 (talk) 11:46, 29 August 2012 (UTC)

For a simple image, see here (scroll down to bottom): http://www.dangl.at/2011/msl/msl_e.htm --99.227.95.108 (talk) 05:22, 1 September 2012 (UTC)

professions

I've been reading these helpdesk answers for years and there are such brilliant replies. Which of the 'regulars' here actually work as scientists or as teachers/professors? I'm not looking for stats but just some short replies from the regulars. Thanks. Sandman30s (talk) 06:57, 29 August 2012 (UTC)

I used to be a freelance lecturer in colleges and universities in the UK. Now retired through ill health. --TammyMoet (talk) 08:11, 29 August 2012 (UTC)

Rocket scientist. --Stone (talk) 08:18, 29 August 2012 (UTC)

You left out an important class of knowledgeable people - Engineers. I started my career in Electronic Engineering, then when Govt policy killed off the Electronics industry in Australia, I worked in IT as a software Engineer & project manager, then became a diesel power generation Engineer. I have multiple diploma and degree level qualifications. Now semi-retired as in Australia if you are over 65 you can't be covered by accident insurance at work. I still do some consulting, and I'm also doing research. Ratbone121.215.24.39 (talk) 10:12, 29 August 2012 (UTC)

It wasn't intentional... also if you throw in engineers then there are many other classes who would regard themselves just as knowledgeable :) I was more interested in the academic/educational professions. Engineers are more than just academic... Sandman30s (talk) 11:31, 29 August 2012 (UTC)

I currently work as a scientist, and have also worked as a university lecturer. SemanticMantis (talk) 12:43, 29 August 2012 (UTC)

I'm a library technician, but I can't provide any published references to prove it. Mingmingla (talk) 20:21, 29 August 2012 (UTC)

I'm a chemistry teacher by training and exprience, but I am currently (voluntarily) not doing that. I am mostly a stay-at-home parent, and will be until my youngest child is in school. I do work some as a private tutor to keep active. --Jayron32 20:29, 29 August 2012 (UTC)

I have found that identifying yourself honestly at wikipedia (check my name at wiktionary) leads to being stalked and persecuted by rather disgusting partisan creeps, so I haven't chosen to come anywhere near my post www identity. Suffice it to say I am a credentialed professional with teaching and commercial experience and a love thereof. μηδείς (talk) 05:32, 30 August 2012 (UTC)

I own an aluminum baseball bat. --Jayron32 05:41, 30 August 2012 (UTC)

Do you discuss certain...nontraditional uses...of that on usenet? Or are you mentioning it here in terms of defense rather than previous online identities? DMacks (talk) 13:50, 30 August 2012 (UTC)

I'm a geological consultant and former university researcher (I'm more of a semi-regular here). Mikenorton (talk) 18:12, 30 August 2012 (UTC)

I've taught CAD. StuRat (talk) 03:25, 31 August 2012 (UTC)

General anaesthesia

Normally when general anaesthesia is administered to a patient, there is a lot of preparation before hand such as assessments, emptying bowels, ensurin the patient doesn't eat or drink before hand etc but how is all this done in emergency surgery in life threatening cases where patients are taken straight to surgery from emergency. Also are relaxants etc used before general anaesthesia to relax patients? Clover345 (talk) 10:56, 29 August 2012 (UTC)

Obviously they make do with what they can do. Emptying the stomach, for example, is to keep the patient from involuntarily vomiting and perhaps choking during the procedure. If you can get them to not eat anything before the procedure, it's one less thing for the anesthesiologist et al. to worry about. If you can't, it's one more thing for them to worry about. You don't let the perfect be the enemy of the good when dealing with emergencies. I've no clue about relaxants used before general anesthesia, but I have experienced cases of relaxants being used before local anesthesia, for whatever that is worth. --Mr.98 (talk) 12:36, 29 August 2012 (UTC)

It's common practice to administer a tranquilizer before general anesthesia -- see General anesthesia#Premedication. Looie496 (talk) 17:57, 29 August 2012 (UTC)

It is a question of relative risks. I have been anesthetized and sedated twice upon emergency room admission. The diagnosis was severe enough and the need to treat me so obvious that waiting for me to fast was not an option. That is for elective surgery. μηδείς (talk) 05:38, 30 August 2012 (UTC)

Come to think of it, they did pump my stomach on the second occasion they sedated me, since emergency abdominal surgery was indicated. μηδείς (talk) 16:34, 31 August 2012 (UTC)

Carl Linnaeus Belived In The Fixity Of Species By Divine Creation And Died 31 Years Before Darwin Was Born. Why Then Does The Taxonomic System That Bears His Name Support Darwin's Theory Of Common

Carl Linnaeus Belived In The Fixity Of Species By Divine Creation And Died 31 Years Before Darwin Was Born. Why Then Does The Taxonomic System That Bears His Name Support Darwin's Theory Of Common — Preceding unsigned comment added by PAOH200 (talk • contribs) 13:47, 29 August 2012 (UTC)

Linnaean taxonomy is used in broadly to describe modern taxonomy in general, but in specific many aspects were dropped. For example, we no longer use Linnaean taxonomy for minerals. The basic observation made by Linnaeus is that species show a branching pattern of relationships, which is generally true in the case of plants and animals (but not absolutely so - see horizontal gene transfer). One way to account for this is that God willed it so, and indeed, the theory of evolution does not dispute that. What evolution does do is suggest a way in which it could have happened, which has since been borne out by a great number of experiments.

To make an analogy, when you find a brick lying in your living room, you might initially hypothesize that your son carried it in while he was playing. But when you find broken glass on the floor and a hole in your window, the brick is now evidence that someone threw a brick through your window. It is one of a set of observations that can be accounted for by a specific theory. Whether your son threw it in while he was playing ... bears further investigation. Wnt (talk) 14:07, 29 August 2012 (UTC)

Linnaeus didn't make that observation; he proposed an easy-to-use system of categorizing flora, fauna, and minerals so that naturalists in disparate parts of the world could sensibly known whether they were talking about the same critters or not, independent of whatever they were called in the local dialect. There is a fundamental issue regarding Linnaean taxonomy and Darwinian evolution, namely the species problem. But the trick there is that later, post-Darwin biologists have redefined their understanding of taxonomy into something quite different from Linnaeus (e.g. cladistics). The work of taxonomy today is somewhat related to Linnaeus, but the interpretation of what the taxonomy means varies starkly from those who see it as a series of fixed species, obviously. --Mr.98 (talk) 15:14, 29 August 2012 (UTC)

Darwinism is true, and the Linnean system is coherent with the facts. It doesn't intentionally support as in "argue for" Darwinism.. rather, the truth coheres. μηδείς (talk) 01:27, 30 August 2012 (UTC)

To take a simple analogy, Mendeleev produced the first Periodic Table of the Elements significantly before the development of atomic theory in its modern form, and yet the periodicity of the elements provides a good approximate understanding of the effects of subatomic structure on the physical and chemical properties of the element. In both cases, the classification system was not developed to promote the theory; the classification and the theory both describe the same scientific domain, and so used properly, they support each other. AlexTiefling (talk) 11:57, 30 August 2012 (UTC)

Though the table of Mendeleev was supposed to reflect actual natural categories, whereas Linnaeus' original work is meant more to be functional than natural (the sexual system for categorizing plants — by number of stamen, a rather arbitrary decision — is the most blatant reflection of this.) Linnaeus himself was actually somewhat explicit about this in the short first—1735— edition, if I recall. (It's actually quite a funny little pamphlet, if you can find a good translation... if only we naturalists could figure out whether we were all talking about the same bugs, he more or less says, then we could figure out ways to get rid of all these damned bugs. How insects in particular vexed him with their many ways of annoying humankind...) --Mr.98 (talk) 01:42, 1 September 2012 (UTC)

How audible would it be to a human?

These days, Charles Bolden and Will.i.am are amusing themselves by making their voices come out of a speaker on Curiosity on Mars. But Mars' atmosphere is very thin. I haven't been able to find out what the speaker's volume settings are, but if they are about strong enough such that on Earth, the volume would be 60 dB, about as loud as conversation in restaurant, office, background music, Air conditioning unit at 100 ft (source) at 3m distance from it, how loud in dB would it be about 3m away from Curiosity on the surface of Mars to a human who miraculously could survive without a helmet on? 20.137.18.53 (talk) 14:38, 29 August 2012 (UTC)

There is no speaker on Curiosity. The song and speech were transmitted back to Earth, not played on Mars. Bazza (talk) 15:35, 29 August 2012 (UTC)

Oh, after watching a video, I see that all that really happened was an audio recording was carried in a file on Curiosity, which beamed the electronic signal back to Earth. So we've been getting visual data from Mars since the 70s, but this is the first time we get audio from the surface. My POV, but that's kind of lame, and makes this headline seem misleading to me. 20.137.18.53 (talk) 15:42, 29 August 2012 (UTC)

If you watch the August 28 news conference, you'll see that at least two reporters were confused about what exactly this stunt was supposed to demonstrate. The answer was that this is the first rover with enough communication bandwidth to do this without interfering with more important data. Not exactly a significant milestone. --99.227.95.108 (talk) 20:09, 29 August 2012 (UTC)

Who gets paid for these sorts of publicity stunts? Wnt (talk) 20:44, 29 August 2012 (UTC)

It's still a viable question, though. All of a sudden the OP doesn't care to know?165.212.189.187 (talk) 15:12, 30 August 2012 (UTC)

Does 'Curiosity' have a microphone on board? if not, then why not?

Hi,

Does the Mars Rover 'Curiosity' have a microphone on board? If not why wasn't it planned for since I vaguely remember some scientists(Perhaps Carl Sagan) hoping to put a microphone on a Mars probe to hear the sounds of the Martian winds? — Preceding unsigned comment added by Gulielmus estavius (talk • contribs) 17:05, 29 August 2012 (UTC)

No. The scientific return is not high enough to justify the extra weight. [2]--Aspro (talk) 17:22, 29 August 2012 (UTC)

Aspro's link actually doesn't say why there wasn't a microphone, just that there wasn't. Plenty of people have pushed for including a microphone on a Mars mission, most notably the Planetary Society, whose microphone actually flew on the failed Mars Polar Lander. The Phoenix lander also included a microphone, but only because its descent imager (MARDI) happened to have a microphone on its circuit board. MARDI was turned off because it had a risk of interfering with IMU measurements during landing, which could have been fatal to the spacecraft. According to an interview I heard with a Planetary Society member (Emily Lakdawalla), the Society lobbied to have their microphone included on Curiosity, but it was rejected because the rover was already complex enough (she didn't elaborate on this, and I haven't been able to find a more detailed explanation). Personally I think that's a strange reason, because a microphone is one of the smallest and simplest electronic devices possible (just look at your cellphone to see how small it could be). Having one would be great for PR, and NASA only gets funding if the public is excited and inspired by its missions. --99.227.95.108 (talk) 22:26, 29 August 2012 (UTC)

You don't just need the microphone, though. You need a microprocessor, etc., to control it. The whole thing needs to be connected to the rover's power systems, and communication systems. Everything needs to be tested to make sure it doesn't interfere with anything else. Time needs to be scheduled to transmit instructions and results. Someone needs to control it. Someone needs to analyse the data. There is a lot involved with adding one seemingly very simple extra experiment to a probe. --Tango (talk) 22:36, 29 August 2012 (UTC)

I think we know what the sound of tires grinding along bare soil sounds like. I'm not sure there's a lot of scientific data to be gathered by putting a microphone on it. It's not like there are little green men who need a karaoke machine or something. --Jayron32 22:35, 29 August 2012 (UTC)

One reason might be that sound doesn't propagate well on Mars [3]: it's apparently a very quiet place. Not that you'd really expect to hear anything but wind and machine sounds from the rover anyway, but it would be easy from the LGMs to sneak up on you if you weren't paying attention: you'd never hear them coming (and their voices would be deepened by the carbon dioxide, sort of the opposite of the effect helium has). Acroterion (talk) 14:46, 30 August 2012 (UTC)

Certainly it would be worth hearing what Mars has to say, even if it is only the sound of its wind, of blowing grains of dust, the crunching of soil beneath the tires, maybe the occasional strange drummings of settling sand dunes. Sound carries a long way and it carries a lot of information. Maybe once in the mission it would even be something spectacular, a landslide on an old weathered slope that the surveyor can then locate from orbit.

The problem of the thin atmosphere and CO2 absorbing sound, of course, is serious, and it may be very difficult to get a sufficiently sensitive microphone to Mars. But apparently the CO2 absorbs mostly high-frequency sound, over 2000 Hz [asadl.org/jasa/resource/1/jasman/v10/i2/p89_s1], and absorption is affected by impurities like water vapor [4] (though I haven't read to see how). I wouldn't dismiss the idea so quickly - seeing another planet gives us a feeling for what it is, but hearing it gives us a sense of the spirit of the place. Wnt (talk) 15:00, 30 August 2012 (UTC)

InSight will have a seismometer so we may be able to hear what Mars has to say soon, at least in the seismic domain. Sean.hoyland - talk 16:08, 30 August 2012 (UTC)

I don't disagree: there are few places that we can get to that would provide an opportunity to listen to alien winds, and it would be extremely cool. Acroterion (talk) 17:54, 30 August 2012 (UTC)

Certainly it would have been cooler to hear some Martian winds than a rather ordinary Wil.I.Am single. Gulielmus estavius (talk) 18:03, 30 August 2012 (UTC)

What is ordinary Wil? (Sorry to hear you are single.) μηδείς (talk) 23:33, 1 September 2012 (UTC)

Someone asked this question during an "Ask Me Anything" session on reddit with the Mars Rover engineers this was their response:

We took a microphone on the Phoenix Mars Lander, and we turned it on but essentially heard nothing (white noise) so it was never released. We don't really need it for any experiments.

We do have the landing signal sound as it sounded from one of the orbiters.

-Keri/@KeriOnMars

Here's a little more info on the Phoenix microphone. It was essentially a hitch-hiker. It was built into another instrument taken off the shelf for the the lander, but it was never intended for the mission. There was no science team or budget connected to it. Since it was not intended for use it was never tested before launch and never entered into the power budget for the lander. Only after Phoenix successfully completed it's mission, 5 months after landing in the polar region, was the mission somewhat willing to test it. They couldn't do it earlier because they couldn't risk the prime goals of the mission if anything went wrong. The project manager was fairly certain it wouldn't work and was against trying it because he didn't want to raise expectations. His mind changed when we got a tweet to the @MarsPhoenix account from a man who said he was blind and how much he wished he could hear Mars because he couldn't see the pictures. A couple days later, they sent the signal to Phoenix to turn it on but we got.. well.. nothing. Empty files. If we had received anything, it would have been released. The team figured the mic was frozen solid and decided to give it a second try by leaving it on longer to warm up. Unfortunately, the Phoenix mission lost its last bit of power (as expected) before it got the second instruction. -vm

-- MacAddct1984 ^{(talk • contribs)} 17:08, 2 September 2012 (UTC)

I get the advantages of sexual reproduction, but what are the advantages of having separate sexes?

I read this article which suggests lesbians could create one day create sperm from their own bone marrow cells so they would be able to have children. However, I intuit that they would only be able to produce girls. If those girls were lesbians too, I could see a self-sustaining "Amazon" type of society, without the need for men. Which makes me think, why did mammals evolve separate sexes anyway? Couldn't you have meiosis without the need for separate sexes? After all, many plants have male and female gametophytes coming from the same plant/sporophyte. It seems to me you could have twice the reproductive capacity without the need for "dedicated" males.

I understand the selfish gene argument for why the sex ratios are 1:1, but that doesn't explain how the separate sexes got created. What was the evolutionary incentive for initiating separate-sex "sporophytes"? If selfish genes could create one parasitic class which cannot directly reproduce, why didn't they end up creating many? 71.207.151.227 (talk) 17:12, 29 August 2012 (UTC)

You are asking about evolution of mating types. That article is woefully stubby, but it does mention one use, which is regulation of reproduction. Many plants go to extremes to reduce the possibility of self-pollination, because having sex with oneself takes away many of the advantages of sexual reproduction in the first place. Some fungi take multiple mating types to the extreme, and have many thousands of sexes. Other plants are happy to self, but that's a different story. In fact, many different mating systems have developed, based upon the challenges that an organism faces, which depend on its life history, habitat, etc. Many species do exist mainly as hermaphrodites, such as many slugs. Note that separate mating types don't necessarily imply polymorphism (or sexual dimorphism). That starts with anisogamy, which arose long before mammals appeared. I'm not sure, but I think all chordates animals employ anisogomy, even in the case of hermaphrodtic slugs. The other case, isogamy (but still with different mating types) is apparently restricted to algae, fungi, and a few other groups. Finally, some unusual species are confined to one sex, such as the bdelloid rotifers. But that's not really true sexual reproduction, more of some weird derived intermediate state between sexual and asexual reproduction. SemanticMantis (talk) 18:45, 29 August 2012 (UTC)

As soon as there is some sort of heritable variability in sex cells, the "male" strategy of small and motile will become hugely successful compared to medium sized and immobile, since "sperm" will be much cheaper to produce in quantity and more likely to "score" than medium sized sex cells. Once sperm become ubiquitous, the rare egg will become a much more valuable commodity, and its increased size will increase viability, while its selectiveness among sperm (sexual selection) will increase the quality of offspring produced. First the male strategy is highly successful, and then presence of males makes the female strategy itself successful, leading two two stable "solutions" to the sex problem. μηδείς (talk) 01:24, 30 August 2012 (UTC)

Sexual reproduction is actually a very difficult topic, and I don't claim to know all the relevant philosophy. But the basic point is that when you have different mating types, they tend to be nearly evenly distributed (with intriguing exceptions) because it is advantageous to join an underrepresented sex to produce more offspring. And although my intuition would suppose that penis fencing is in all regards the most advanced sexual condition, it would appear that in reality most species find that putting all the effort either into being male or being female delivers more reward than splitting it up. Wnt (talk) 06:24, 2 September 2012 (UTC)

Telomeric fusion and human evolution

It is well known that human chromosone 2 is just a fused version of primate chromosomes. But I have problems understanding how the new lineage that would eventually lead to modern humans actually propagated. If one individual had the chromosomal mutation, how could he even mate if the surrounding population had a different number of chromosomes? Or is it more likely that more than one individual had the same random chromosomal mutation? --Ghostexorcist (talk) 17:34, 29 August 2012 (UTC)

Having different chromosome numbers is not necessarily an impediment to reproducing. The various subspecies of horses have different chromosome numbers, and can still mate and produce fertile offspring. thx1138 (talk) 17:57, 29 August 2012 (UTC)

Can you give specific examples? I know mules are born sterile because they get an uneven number of chromosomes from their horse and donkey parents. A geneticist suggested several years ago that the lineages that eventually gave rise to modern humans and chimps might have continued to breed after their initial split and later split for a second and final time. Just like female mules can sometimes breed, the female hybrids could produce viable offspring. I don't think this has ever been proven, though. If the populations with different chromosomes could breed, I guess drift would play a part in making the fused chromosomes a dominant trait. --Ghostexorcist (talk) 18:15, 29 August 2012 (UTC)

Note that horse and donkey have some differences in the overall chromosome structure as well as the number - it's not as simple as the end-to-end fusion in humans.[5] Wnt (talk) 21:28, 29 August 2012 (UTC)

Stages of meiosis

It basically comes down to a question of whether meiosis can still occur, or whether it gets blocked at some stage. Looie496 (talk) 18:37, 29 August 2012 (UTC)

Note there are genes at the fusion site of substantial interest. As for the genetics of it, the 1-2 would still be homologous to 1 and 2; the only question is whether sometimes the 1-2 gets pulled between opposite poles and torn apart (embryos which would be weeded at an early stage). I haven't figured that one out, but there's at least a 50-50 chance it wouldn't happen, simply by chance. Wnt (talk) 21:16, 29 August 2012 (UTC)

These explanations are helpful, but does anyone know of a particular book or paper that describes the process in full? --Ghostexorcist (talk) 22:34, 29 August 2012 (UTC)

I don't think it is really understood. As far as I can see, the most informative paper is this one, for what it's worth. Looie496 (talk) 23:15, 29 August 2012 (UTC)

Thanks. Carl Zimmer pointed me towards this paper. I figure others interested in the subject might want to check it out. --Ghostexorcist (talk) 21:32, 31 August 2012 (UTC)

Any acquired immunity to rubella when an infant gets it pre-vaccination?

According to Rubella, the first administration of the MMR vaccine usually occurs around 12-18 months, but I wonder if a baby experiences the virus before that vaccination, does the baby's immune system get any "education" on how to combat future exposures from that? I'm not talking about CRS or an extremely young newborn, and of course this is not to say that that would preclude vaccination (that's not even my question). I was just wondering the biological question of whether or not an as-yet non-vaccinated human gets any immunological benefit after having gone through it and survived it in the specific case of Rubella. 20.137.18.53 (talk) 20:29, 29 August 2012 (UTC)

Rubella being more commonly known in the UK as "German measles" when I was growing up, the received wisdom was that you could get it more than once. I myself had it three times before I was 20. Measles, however, you only got once, and I can remember going to measles parties so that I'd get it and be immune. Vaccinations for these diseases didn't exist when I was a little girl. (This was, of course, in the dark ages BC - Before Computers.) This is, of course, completely OR and unsourced and I'd appreciate it if someone could provide some proper references. --TammyMoet (talk) 20:35, 29 August 2012 (UTC)

It is sourced, we're just not "reliable". ;) 21:59, 29 August 2012 (UTC) — Preceding unsigned comment added by Medeis (talk • contribs)

This appears to say that you only get rubella once.[6] Rmhermen (talk) 22:56, 29 August 2012 (UTC)

I always wondered what actually happened at measles parties; do you go around kissing each other? (The article doesn't say.)--Shantavira|^{feed me} 10:21, 30 August 2012 (UTC)

We basically sat and played games together as far as we could, and kissed bye-bye... --TammyMoet (talk) 14:02, 30 August 2012 (UTC)

August 30

Star positions in the past

Is there a website or a software that's capable of telling me where were certain stairs on the sky in a given year (e.g. in 1400)? 193.224.66.230 (talk) 13:11, 30 August 2012 (UTC)

This page will do it, but it's a bit tricky to navigate. Page down to the "virtual telescope" and select the "controls" link to set the date and time you wish to look at the sky for. The Earth's view of the stars has changed over time, but I think that a difference of 600 years isn't going to have changed it much; excepting the locations of the planets and comets and things like that. The star map would only look noticibly different on scales of 1000s of years or 10,000s of years. --Jayron32 13:18, 30 August 2012 (UTC)

Celestia. If you haven't used it before, and you're at all interested in space, you're missing out. I agree that 600 years isn't enough to see the stars move noticeably. To get a sense of how slowly they move, Barnard's star, the star with the highest proper motion, moves 3 degrees in 1000 years. Almost every other star moves many times slower than that. You can use Ptolemy's star charts today and they wouldn't seem wrong. --99.227.95.108 (talk) 15:40, 30 August 2012 (UTC)

As far as I can tell, Celestia doesn't model proper motion. TenOfAllTrades(talk) 21:23, 30 August 2012 (UTC)

I'd go with Stellarium as it's probably the easiest program to get the hang of. (There are download links on the article page.) But as said above, there wouldn't be a noticeable difference in the positions of stars over a 600 year period. FlowerpotmaN·(t) 19:04, 30 August 2012 (UTC)

Attractiveness

Is attractiveness subjective? From my understanding, attractiveness is based on certain dimensions an proportions of the face and body of a person. However is this subjective? And if so, are there certain faces, which people universally find attractive or unattractive? Clover345 (talk) 15:16, 30 August 2012 (UTC)

Physical attractiveness has both objective and subjective components. That is, there are some trends and nearly universal principles, but there are also many factors that are determined by individual taste, and will vary culturally or even person to person. --Jayron32 15:54, 30 August 2012 (UTC)

You may be interested in research on facial attractiveness [7]. You can also participate in real research at that site, making your preferences part of the process. Recently, many different studies have demonstrated that averaged faces are rated as more attractive than the average of many facial attractiveness ratings. This starts to get at "universally attractive" faces, but as Jayron points out, there will always be a large degree of subjectivity in attractiveness. Google /average face attractive/ for many news and pop-sci accounts. SemanticMantis (talk) 18:09, 30 August 2012 (UTC)

Physical attraction is an objective quantity.

F = G m₁ m₂ / r².

However the Greater Internet Uncertainty Principle states that you can know either m₁ or m₂ but not both. Good luck, as escape velocity is a known issue with internet dating. ;) 217.251.154.242 (talk) 07:02, 31 August 2012 (UTC)

Forget it, I will NOT add a link to "Spherical Cow Approximation."

You shouldn't ever call a girl that, you know... --Jayron32 14:15, 31 August 2012 (UTC)

A friend of mine once described fellatio from a spherical cow as like sodomizing a bowl of room temperature oatmeal. That seemed rather objective to me. μηδείς (talk) 21:59, 31 August 2012 (UTC)

Star Gazing Hobby

I want to start this hobby but with the meager savings I have. I will like to purchase a used telescope on eBay however I don't know where to begin to look or what to look for. Please give me any suggestions on how to start my hobby the right way Reticuli88 (talk) 16:25, 30 August 2012 (UTC)

One option is to see if a local astronomy club exists. Near where I live, the Morehead Planetarium and astronomy department at the University of North Carolina sponsors a monthly stargazing night at Jordan Lake, far enough away from light sources but close enough to see some cool stuff. They bring some really powerful telescopes and set them up on the beach, and it doesn't cost anything to come by and use their telescopes. This google search turns up a wealth of other similar arangements. --Jayron32 16:49, 30 August 2012 (UTC)

I strongly second Jayron's suggestion. Speaking as someone who read Astronomy at University and helped to run a local Astronomy Club myself, I'd say it would be near-impossible for someone new to the activity to choose with confidence an appropriate instrument from eBay or similar sites. You may be able to track down a local club from the back pages of Sky and Telescope or a similar magazine. Alternatively, if you can get to a specialist Astronomical Telescope vendor, they're likely to give you reliable advice because they'll be hoping to get repeat business from you when, as is likely, you trade up to better/more expensive equipment. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 17:16, 30 August 2012 (UTC)

The beauty of astronomy is that it can be done purely with the eyes alone. Learn the patterns of the constellations: learn the planets, what they look like in the skies: try and see how many of the Seven Sisters you can see with the naked eye (northern hemisphere only). If you get a cheap pair of binoculars from Ebay second hand, you can see details in some of the globular clusters. Be warned, however: you will never see the range or depth of colours you see in the professionally produced deep sky photos. I have known some enthusiastic amateurs give up when they realise that. --TammyMoet (talk) 18:38, 30 August 2012 (UTC)

Other people have written much more about this exact subject than we possibly can. See, for example, this Sky&Telescope article. --99.227.95.108 (talk) 03:48, 31 August 2012 (UTC)

I can tell you from childhood experience that a small refracting telescope will probably be worth far less than you would pay for it. You might as well get a good pair of binoculars. A friend's father had a six inch reflecting telescope. Due to its mass it was much more stable, and you could see the disks of planets which were mere dots with my "telescope". μηδείς (talk) 05:28, 31 August 2012 (UTC)

Check out Ice In Space, it's a huge website full of amateur astronomers and astro photographers. They have lots of "beginners" articles and a massive forum for support ranging from the very basics all the way to people who have had pictures published on NASA's APOD. I now own a 12" dob, but I started with a pair of 8x56 binoculars which I still use every time I go observing. That's the thing with a pair of binoculars, getting a telescope later won't make them obsolete, you'll still use them regularly to spot things or get a wider field of view, so they really are a good way to start rather then a cheap telescope which at best will become obsolete if you decide to buy a better one and at worst will be crap and will put you off entirely. Vespine (talk) 23:17, 2 September 2012 (UTC)

Raptor factoid

Concerning fish-eating raptors, such as Ospreys and Sea eagles that hunt by swooping down and grabbing fish from the water with their talons... any truth to the oft-quoted fact(oid?) that because the bird is allegedly physically unable to unclench its feet whilst they're embedded in the prey's flesh and let go, unless it returns to dry land, that if the bird happens to 'attach' itself to a fish that's too large to carry, that it will probably either drown on the surface due to becoming waterlogged - still attached to a dead fish, or be dragged under by the fish as it tries to escape - and drown that way?

I'm aware that these birds can only swim a little and do sometimes drown after miscalculating/missing their prey, getting too wet to fly and being trapped on the water's surface but that would seem to be a different scenario. --Kurt Shaped Box (talk) 20:06, 30 August 2012 (UTC)

I call shenanigans. What's so different about being on land? Does the bird have to eat the fish away from its claws before it can use them again? I think not. I think the claim is based upon a nugget of truth: the way raptor talons work. But the claim takes it to a silly extreme, and is also influenced by your observation that yes, these birds do sometimes drown.

The key principle is that raptor talons are similar to ice hooks, like this one [8], in the sense that they convert downward force (supplied by gravity and the ice/fish) into a compressive force of the hooks on the load. This means they can carry heavy things without using any more energy to grip than they would for lighter things (of course it still takes more energy to lift). This does mean that it's difficult to release under load, but it doesn't mean it's impossible. And if the fish is still in the water, it's not putting much load on the talons yet anyway. You may also be interested in this nice (freely accessible) paper "Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique" here [9]. SemanticMantis (talk) 17:24, 31 August 2012 (UTC)

Why did people in the late 1800s think an aether was necessary for the propagation of light, when Maxwell's equations show that this is unnecessary?

Maxwell described light as an electromagnetic disturbance of self-propagating E and H fields. Surely people in the late 1800s knew that magnetic and electric fields could exist in vacuum. So why did they think an aether was necessary to "carry" light waves? 71.207.151.227 (talk) 20:11, 30 August 2012 (UTC)

It is not self-evident that electric and magnetic fields can exist in a vacuum, even if you have Maxwell's equations in front of you. This requires careful, meticulous understanding of the equations, and of course the equations require a lot of experimental effort to validate. Among the relevant work that helped establish this fact: the Michelson-Morley experiment, which you've undoubtedly read about; and the experiments that established Vacuum permittivity and Vacuum permeability constants. Maxwell's original work, A Dynamical Theory of the Electromagnetic Field, which you can read online, was a study of the relationships between electric fields and magnetic fields and charges. It is not immediately obvious, just from that work, that his work implies propagation of energy in a vacuum. The science developed; the theories became more perfect, and the experiments continued to validate assertions; and eventually the majority of scientifically-minded people accepted as fact that there need not be any transmission medium to hold the fields. We can say that Faraday and Coulomb discovered these facts; but that's almost irrelevant: at what point did the consequences of these facts become well-known? There's hardly a single instant when we can say "this was the moment that people understood that electromagnetic waves propagate in vacuum." Nimur (talk) 20:34, 30 August 2012 (UTC)

The fact that waves propagate in a vacuum feels intuitively wrong when you consider what a wave is: it is a rhythmic motion that propagates through something. When light displayed wave-like properties, people began to ask "what is it propagating in". The Maxwell equations don't require a medium, but people's expectations did. --Jayron32 21:32, 30 August 2012 (UTC)

"It is not self-evident that electric and magnetic fields can exist in a vacuum.." What decade of the 19th century were the experiments done, with vacuum pumps and bell jars, to prove that magnets worked just fine in vacuum, and that electric fields in a vacuum affected charged objects? I suppose one could cavil that the bell jar vacuum is imperfect compared to the vacuum of outer space. Faraday found magnetic effects in a Torricellian vacuum (like the inside of a mercury barometer above the mercury) (p 194) in his research published as a collection in 1855, but much of the research was done and published earlier. Didn't anyone experiment in the mid or early 1800's with electrified objects in a high vacuum jar to [rove the functioning of electric fields? The writings of Brewster suggest so, though he wrote mostly about discharge and glow effects in vacua. rather than basic attraction and repulsion experiments as done in air. They knew by the 1830's that a charged object would discharge and that charge could be transferred in a Torricelian vacuum. Anyone calling himself a physicist or "natural philosopher" by 1860 would likely have been familiar with this. Edison (talk) 00:40, 31 August 2012 (UTC)

Lots of people experimented with discharges and vacuums, but it was harder than you let on to get a good vacuum in the 19th century. If your vacuum was poor, you got very messy results — the gas inside the tube would ionize, for example, insulating the discharge stream, and give you completely the opposite conclusion. The fundamental work done that established that indeed, cathode rays were affected magnetically was done only in 1896, by J.J. Thomson, and was part of the discovery of the electron. The real breakthrough experimentally was creating an unambiguously good vacuum, something that evaded even the great German experimentalists like Hertz and Lenard. All of which to say is — the point at which it became unambiguous was really quite late into the game, just a few years prior to Einstein and all that. The limitations were for the large part technical. --Mr.98 (talk) 00:56, 31 August 2012 (UTC)

I think two different meanings of vacuum are used here; "It is not self-evident that electric and magnetic fields can exist in a vacuum.." refers to an "absolute" vacuum (without aether). But in those days it was assumed that aether was still present in a vacuum, only air (gasses) was removed. As Newton wrote: "a much subtiler Medium than Air, which after the Air was drawn out remained in the Vacuum" Ssscienccce (talk) 15:12, 31 August 2012 (UTC)

Because it was known that according to Maxwell's equations, EM waves travel at a specific, finite speed c. The question immediately asks itself: relative to what? Usually, if you have a speed, you must have some definition of a stationary point with v=0. Defining stationarity at every point in space gives you a sort of aether. Of course, we know now that the speed of light is invariant and comes out the same for all observers. However, this requires us to give up any notion of absolute time, stationarity, and a lot of other notions in order to formulate special relativity. It seemed far more parsimonious to keep Newtonian physics and to suppose that light travels through an aether, than to eliminate the aether and also throw out all the known laws of mechanics. Given what was known at the time, I think this was a reasonable application of Occam's razor. --Amble (talk) 00:47, 31 August 2012 (UTC)

Just a point: the constancy of c was not in fact known until the late 19th, early 20th century. This was part of the point of Michelson-Morley. --Mr.98 (talk) 00:56, 31 August 2012 (UTC)

The constancy of c (or $1/{\sqrt {\epsilon _{0}\mu _{0}}}$ or however you want to write it) is a property of Maxwell's equations. To someone ignorant of later developments (such as Maxwell himself) the theory looked mathematically like a description of transverse sound waves in a solid, and it was natural to wonder about the properties of that solid, including its state of motion. -- BenRG (talk) 02:54, 31 August 2012 (UTC)

As I said, the invariance of c was not known until later. The fact that it's a constant comes out of the equations, and it was natural to take it as a constant velocity relative to some medium, as with other waves. Hence, the aether. --Amble (talk) 07:04, 31 August 2012 (UTC)

Sorry, what I meant was, this wasn't experimentally confirmed until much later than Maxwell. There were plenty of folks at the time who still thought this might be an open question until the measurements had come in. It was a hard thing to measure, obviously. --Mr.98 (talk) 14:46, 31 August 2012 (UTC)

That's why I said "according to Maxwell's equations." --Amble (talk) 15:26, 31 August 2012 (UTC)

Maxwell himself used the idea of the aether as a way to think through how the world worked. It was a visual metaphor to use as a means of interrogating nature. (Maxwell's own visualizations of the aether are amazing — pulleys and gears and whatnot. See figure 2 here. Very industrial age U.K.) Maxwell derived all of his original equations from these sorts of models, and had tremendous success with them. (The version of Maxwell's equations you are now familiar with are not Maxwell's own; they were re-written by Heaviside and others some time later.) When you get success out of a model, you don't turn around and throw out the major components of it immediately afterwards.

For the physicists of the day, the aether was actually considered a brilliant theoretical innovation. It was more than just the medium through which light moved — it was the interface between the world of electromagnetism and the world of matter. The theorists of the day came up with beautiful, elegant, and totally physically sensible models about how all matter arose out of whorls and knots in the aether; how this sublime otherworldly realm of pure energy lent itself towards the manifestation of all that we are and can observe. They saw it not as an appendage onto Maxwell's equations, or as an extremity on to the physical universe, but as a supremely elegant concept that also made good intuitive sense (light is a wave in something, right? Who's heard of a wave in nothing?). Beautiful physics came out of it. The problem was, well, it didn't exist, it wasn't necessary, and in fact they were going about it all the wrong way. We know that now, and it's hard to put yourself in the head of someone then, but look at the aether as the original theory of everything, the one-stop theoretical shop for All of the Rest of Physics. --Mr.98 (talk) 01:08, 31 August 2012 (UTC)

Honestly, not much has changed. The modern quantum vacuum has a lot of structure, and any particle physicist will tell you that particles are oscillations of the vacuum, not objects in the vacuum. The vacuum is similar enough to a solid that many phenomena of fundamental quantum field theory appear also in solid-state physics. The vacuum undergoes phase transitions, like the Higgs field condensation that breaks electroweak symmetry. Mechanical analogies haven't died. Quantum Field Theory in a Nutshell by Anthony Zee introduces the field as a "mattress" of weights connected by springs. It seems unlikely that the world really is a mattress simply because Lorentz invariance unifies space with time, and it would be strange if at a deep level space and time are aspects of the same thing but at an even deeper level they're not. There are hints (from gravitational holography and AdS/CFT) of a radically different underlying structure for the world. But the best modern theories of fundamental physics (general relativity and the standard model) are still mattress-based. In fact the next thing Zee does after introducing the mattress analogy is complain about the lack of anything better. -- BenRG (talk) 02:54, 31 August 2012 (UTC)

would maxwells aether be able to penetrate a black hole or its event horizon?GeeBIGS (talk) 04:04, 31 August 2012 (UTC)

Read Luminiferous aether and it should clear up any questions. The problem with the idea was that it had to be infinitely dense and infinitely malleable, which kinda doesn't work. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:27, 31 August 2012 (UTC)

Again, anyone who replies, "obviously it doesn't work" doesn't really understand it. Henri Poincaré and Hendrik Lorentz thought it worked and made sense; they were much smarter, and much deeper, than you or I. It is unilluminating to dismiss in a flip way ideas that were highly persuasive to luminaries in the not-even-that-far-back past. (Additionally, that article does not clear up the question about black holes. I have no idea how you'd make an aether world view compatible with a black hole. The former worldview was abandoned before General Relativity and my guess is that it is probably not easily compatible with it.) --Mr.98 (talk) 14:51, 31 August 2012 (UTC)

I do. The black hole is so dense that it forces the aether out of that space entirely.165.212.189.187 (talk) 15:04, 31 August 2012 (UTC)

I'm pretty ignorant about this, so take with a grain of salt, but my impression/recollection is that...

• versions of the aether that "work" with changing perspective are based on Fresnel's 1818 Aether drag hypothesis, which postulates that there is more "aether" inside glass than inside air.
• Some people, somewhere, I know not who, have tried to describe electromagnetic forces as curvature of space in some other dimension, just as gravity is described, so that objects subject to such forces actually follow straight paths (geodesics) just like objects subject to gravity.
• I would assume ...... that just as gravitational waves are transmitted as waves within the underlying spacetime (note that that is definitely a speed-of-light, inverse square transmission which by all contemporary formulations does occur in a sort of medium, i.e. spacetime!), that so electromagnetic forces are transmitted as fluctuations in this postulated electromagnetic dimension...
• And as such, the notion of the aether remains current.

Feel free to poke holes. :) Wnt (talk) 16:07, 2 September 2012 (UTC)

What are the differences between male and female human faces? In words...

This may be easy for lots of editors but not for me. Forgetting facial hair, which not all men have, how can we describe the general differences between men's and women's faces? Tom Haythornthwaite 22:41, 30 August 2012 (UTC) — Preceding unsigned comment added by Hayttom (talk • contribs)

Look at Eric Roberts and Julia Roberts and tell where you see differences - if any. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:49, 30 August 2012 (UTC)

Thank you, I think, but either you didn't understand my question or I didn't understand your answer or we have different senses of humour. It is easy to describe the general differences between male and female bodies because men are generally taller and have penises and women generally have breasts, and so on. But I cannot think of words to generally differentiate between their faces. hayttom 23:11, 30 August 2012 (UTC)

What I'm saying is that you can't, necessarily. To my mind, forgetting any facial hair, Eric and Julia look a lot alike. If you were to somehow remove all the hair anywhere on their heads and put their faces side by side, it would be hard to tell the difference. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:57, 30 August 2012 (UTC)

See this article on the role of testosterone in the development of male facial features. Alansplodge (talk) 23:34, 30 August 2012 (UTC)

My impression is that women are more likely to have the so-called "heart-shaped face", where the sides of the face slope inward as you go from the temples towards the mouth, whereas men are more likely to have straight-sided faces. Not sure I'm right; would be interested to hear about any real studies. --Trovatore (talk) 23:37, 30 August 2012 (UTC)

Leaving out individual variations, the basic difference is that female faces are more round, and male faces are more rectangular. Looie496 (talk) 00:07, 31 August 2012 (UTC)

That would be the reason rectangular, straight-side faced women, Ann Coulter for example, are sometimes referred to as "horsey" looking. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:11, 31 August 2012 (UTC)

Males tend to have more prominent brow ridges - the easiest way to tell from just a skull, as I learned in the palaeoanthropology lab at uni - though even that can be misleading sometimes. As for the heart-shaped vs straight-sided face, that is mostly due to males having more developed jaw musculature, I'd assume - and that will be rather variable. Combined, these two traits tend to make a male face look 'squarer', though I think that if you remove the cultural clues, it is often difficult to be sure just from the face. With children, it is even harder, and I suspect pre-puberty next to impossible from a casual inspection. AndyTheGrump (talk) 00:12, 31 August 2012 (UTC)

How would you characterize the brow ridge of Roy Blunt? 20.137.18.53 (talk) 13:58, 31 August 2012 (UTC)

Just to add in, those are the two things they told us in my forensic anthropology as well. The square jaw is not from musculature; it is skeletal. Women on the whole have large jaw angles than men do. Again, as you note, none of these skeletal features — even the non-facial ones, like hip bone shape — are a sure-thing, because there's a lot of variation in the species. --Mr.98 (talk) 00:47, 31 August 2012 (UTC)

How would you characterize the jaw structure of this Savannah they have on the Today show now? There's something odd-looking about her - like a squirrel with its cheeks stuffed, or something. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:30, 31 August 2012 (UTC)

The Adam's apple is one differenece. Not 100% of the time, but on the balance, men tend to have a more prominent Adam's apple than females. --Jayron32 04:11, 31 August 2012 (UTC)

Yes, always check the neck before necking. And, if going further, check for other lumps, too. :-) StuRat (talk) 09:02, 31 August 2012 (UTC)

August 31

Is there a way to help someone run faster?

Suppose a man and woman are both running away from a scary monster, and the man wants to help the woman run faster. This is a common scene in movies, and in said movies, the man usually holds the woman's arm to drag her forward. I've tried this before, thankfully without the monster, and it's an extremely uncomfortable way for both people to run. Neither person can swing their arms in synchrony with their legs, thus slowing both people down. Not only that, if the faster person pulls too hard, the slower person tends to fall forward instead of running faster. So, is there actually a way of helping someone run faster than she normally could? --99.227.95.108 (talk) 05:51, 31 August 2012 (UTC)

Being chased by a monster should do it. Emotional states and high adrenaline can cause people to outperform their own personal standards, but I don't know that there's a way, short of attaching rocket skates to her feet, for another person to aid her in running faster. --Jayron32 05:53, 31 August 2012 (UTC)

I agree that holding her arm won't work. But, if the man runs behind the woman, and with both hands on her sides, pushing her, she'll go faster. I've tried that and it works, balance is good, but there is a danger of feet contact, so the man has to run with his feet further to the sides. I should point out that my lady has longer legs than I do, so if there really was a scary monster, she most likely could outrun me. In any case, if the man is making the woman go faster by either towing or pushing, then he must be going slower than he could on his own. So, only do this if either a) you actually do love her, or b) you know for a fact that the scary monster only likes girls. I also point out that any test of strength, running speed, etc with girls is misleading. They do what they think will attract you, i.e., play the poor defenless female. Every girlfriend I've ever had has asked me to open jars etc. But they seemed to consume the contents just as much when I wasn't around. Wickwack121.221.84.138 (talk) 06:35, 31 August 2012 (UTC)

At the risk of generalizing, this reminds me of the saying/song 'the female of the species is more deadly than the male' (especially if her offspring is in danger). I think they pretend to be helpless and defenceless but when the chips are down, they are just as (if not more) capable than men to help themselves out of socially perceived 'male-only' situations. I did a test a few months back... there was a faulty handle in the bathroom and I left a screwdriver and pliers in the bathroom, telling my wife how to use it if she couldn't get out. The first time she screamed hell and highwater and I had to let her out (save her from death by extended bathroom time). The second time I was not around and she screamed/cried a bit, then actually used the tools to make her way to freedom. I wasn't popular that week but I had proved a point to myself :) Sandman30s (talk) 08:15, 31 August 2012 (UTC)

In the case of running, women really do tend to be slower. It's not just due to shorter legs. Wider hips also make running less efficient, and a higher fat-to-muscle ratio means less sprinting power (although it might help in a marathon). StuRat (talk) 08:57, 31 August 2012 (UTC)

Skinny is good when it comes to marathon running. Sprinters should be 2.5% lighter than the average person while long-distance runners should be 15% lighter according to this article. Just look at these ladies. Alansplodge (talk) 17:56, 31 August 2012 (UTC)

Certainly they can't be obese, as that would interfere with efficient running (fat thighs would have a similar effect to wide hips, resulting in more of a waddling motion, and loose, bouncing fat is bad, too). However, exactly how thin they should be would be affected by the precise conditions of the marathon. Specifically, cold weather runs (especially in strong rain and wind) without the ability to consume energy drinks along the way are conditions where having a bit more fat to burn might be helpful. StuRat (talk) 20:40, 31 August 2012 (UTC)

Everyone burns fat during a marathon, whatever the weather. Top athletes now reduce carbohydrate intake to maximise fat burn Fuel On Fat For The Long Run. But the amount of body fat needed for this is really small and I've never seen an elite marathon runner who wasn't as thin as a stick. See Wilson Kipsang, Paula Radcliffe or Deena Kastor. But we digress. Alansplodge (talk) 01:12, 1 September 2012 (UTC)

You can help someone run faster without slowing yourself down by letting them run in your slipstream. It's not a particularly large effect for humans running (it's more important for lobsters walking along the seabed, and cyclists), but every little helps. --Tango (talk) 11:37, 31 August 2012 (UTC)

As for saving your g/f from a monster, how about getting the monster to chase you, say by throwing things at it ? Also, many shoes women wear are less than useless when it comes to running, so get her to kick off her stiletto heels before running. And, as a bonus, the monster may then decide she's no longer pretty enough to chase. :-) StuRat (talk) 08:57, 31 August 2012 (UTC)

Throwing things at it assumes that the monster is too dumb to go for the easier target and then use her as a shield. Wickwack120.145.10.162 (talk) 10:42, 31 August 2012 (UTC)

In the initial sprint of a few hundred meters, pulling or pushing the slower person might not help. but urging them to kick off any inappropriate shoes and run like hell might speed things along. In movies. the woman usually falls down, to add suspense and an occasion for the film to show a view of the monster gaining on them. Similarly, in movies, the runners always stop occasionally and look back, for cinematic effect. In military and some sports training intended to build a team, the more fit runners actually do physically help the exhausted runner along once he/she is winded and unable to continue the pace. At that point, if they were ascending a grade, for instance, putting an arm around the tired runner could materially speed them along and keep them moving. So in the initial sprint its "Feets, do your stuff!" with some benefit from vocal encouragement, but when exhaustion sets in an arm around the person's back can help them move along. Edison (talk) 15:46, 31 August 2012 (UTC)

In this YouTube video, exhausted soldiers are pushed, pulled and shouted at with varying degrees of success (from 5:40). Having an impressive moustache seems to help too. Alansplodge (talk) 18:05, 31 August 2012 (UTC)

Good-looking

Duplicate Ankh.Morpork 14:19, 31 August 2012 (UTC)
The following discussion has been closed. Please do not modify it.
What makes people good-looking; is there any objective criteria such as symmetrical features which influence people's perception? Why are we predisposed towards selecting better looking people as partners? Isn't there an increased potential of infidelity? Has people's perception of 'good-looking' changed over time? Ankh.Morpork 14:11, 31 August 2012 (UTC) Didn't we just answer this question above or on another desk? See physical attractiveness and the prior discussion. --Jayron32 14:13, 31 August 2012 (UTC) Indeed. Count up 6 threads. It was asked yesterday. --Jayron32 14:14, 31 August 2012 (UTC)

Corneal vs Cataract Transplants

Hello. How are opthalmologists able to determine whether a patient has had a cornea or cataract transplanted just by looking at the eye? Thanks in advance. --Mayfare (talk) 14:13, 31 August 2012 (UTC)

As a non-expert with a dangerously small amount of knowledge I would suggest that following a cornea transplant there would be a detectable (perhaps under magnification) circular scar on the cornea. When a lens with a cataract is removed it does not require the removal of the whole cornea, just a small incision, usually near the outer edge of the iris, big enough to remove the damaged lens and (nowadays) insert a replacement. Richard Avery (talk) 21:03, 31 August 2012 (UTC)

SR & QM unification

How plausible is it that the two theories have not been unified because of some minute error way back in the 1800 -1900's that has since been so baked into the equations and laws that it is virtually undetectible now? — Preceding unsigned comment added by 165.212.189.187 (talk) 14:19, 31 August 2012 (UTC)

Special relativity and quantum mechanics have been unified for ages; there is no difficulty there. The problem is with general relativity. Looie496 (talk) 16:56, 31 August 2012 (UTC)

The article Quantum gravity describes quite well some of the issues surrounding the marriage of general relativity with quantum mechanics. As noted, special relativity has no such problems, because the sticking point is gravity, which is the domain of GR. Theory of everything and Physics beyond the Standard Model dontains some of the theories and development at the vandguard of this area. --Jayron32 17:36, 31 August 2012 (UTC)

OK General Relativity then, same question.165.212.189.187 (talk) 17:57, 31 August 2012 (UTC)

OK, same answer then. --Jayron32 17:58, 31 August 2012 (UTC)

I missed the part where you say how plausible my question is?165.212.189.187 (talk) 18:14, 31 August 2012 (UTC)

Plausibility is not something we have the ability to provide references for. You can make up your own opinions about that, for anyone here to do so would be pure speculation. I have done what the mission of this page is for, which is to provide references to information. After reading about the difficulties that exist between marrying the two theories into a single cohesive theory, you can decide for yourself how plausible that marriage is. If you have any questions about the text of those articles, something you don't understand or need explained, we would be happy to help clarify or provide more references. But questions about how "plausible" something is are not answerable in the way this forum works. It is what it is, and the two theories have not been maried as yet. The articles already cited explain why. --Jayron32 18:24, 31 August 2012 (UTC)

Relativity wrong in back in time, and QM wrong in randomly , it should have united, thanks — Preceding unsigned comment added by 81.218.91.170 (talk) 18:19, 31 August 2012 (UTC)

Special relativity is basically just Lorentz symmetry. There's no minute error you can make in defining Lorentz symmetry; if it doesn't hold, its replacement will have to be something a lot more complicated. Quantum mechanics also has a very special form and it's either right or it isn't. There's more freedom in defining a relativistic theory of gravity. General relativity is a remarkably simple theory and it's still in perfect agreement with experiment, but it has always had rivals. Still, if there were any simple alternative to GR that led naturally to quantum gravity, I'm pretty sure quantum gravity researchers would have found it by now. So I would rate this as highly implausible. -- BenRG (talk) 20:19, 31 August 2012 (UTC)

There actually isn't a real problem here, the issue is simply that the field theory you get is nonrenormalizable. Count Iblis (talk) 02:32, 1 September 2012 (UTC)

Ebola Carrier Found

I recall reading a story that bats were determined as the carrier of Ebola Virus. Apes, as well as indigenous natives apparently eat dead bats and get the virus in that manner. Why hasn't Wikipedia updated this latest scientific discovery into the Ebola web page? — Preceding unsigned comment added by 66.8.226.55 (talk) 19:33, 31 August 2012 (UTC)

I see it in Ebola#Risk factors. Well I see about eating partially-eaten fruit, rather than eating the bats themselves. It's from references going back to at least 2007. If there is newer information available, someone would have to post the actual reference/citation to support it. DMacks (talk) 19:38, 31 August 2012 (UTC)

I'm currently on holiday on an island where even the restaurants have bat on the menu. Greglocock (talk) 00:41, 1 September 2012 (UTC)

GOD, I hope for your sake your room doesn't smell of sulfur. See (or, better yet, don't see) Popo Bawa. μηδείς (talk) 01:40, 1 September 2012 (UTC)

I would ask for it to be "well done". Alansplodge (talk) 01:20, 1 September 2012 (UTC)

The explanation for why Wikipedia is not expounding on "the great new scientific finding you just read about" is always either: A) No one has volunteered to do it yet; or B) the media totally overstated the significance of a recent finding. I'm sure if you post a link to the story you read, someone here will be happy to update the article, if appropriate. Someguy1221 (talk) 01:25, 1 September 2012 (UTC)

September 1

Alkane isomers

What's the general formula for the number of isomers of the alkane with n carbons? --168.7.232.202 (talk) 01:04, 1 September 2012 (UTC)

There is no known mathematical relationship between the number of carbons in an alkane and the number of possible isomers of that alkane, but it rises as a rate that resembles an exponential function (see here for a list of alkanes 4-15,20]. The problem is further complicated by the fact that some isomers that can be represented by a line diagram are not actually stable molecules (you start running into these at C16). People have written algorithms to calculate the number of isomers, and you can find one here that can be told to remove unstable isomers. Someguy1221 (talk) 01:12, 1 September 2012 (UTC)

See our article entitled "Alkane", which has a section "Isomerism" that discusses the theoretical calculation issue. Might be a good place to add a mention that the calculated result is a theoretical maximum, whereas stable reality is more limited. DMacks (talk) 04:41, 1 September 2012 (UTC)

Delta formation

I am not able to understand how is delta formed. Why is delta formed near the mouth of the river, not in its middle course? I want to know the reason for this according to geographical as well as scientific view. Sunny Singh (DAV) (talk) 02:16, 1 September 2012 (UTC)

Who says that Deltas don't form midcourse? Have you read the article River delta? It covers inland deltas and how they form. --Jayron32 02:18, 1 September 2012 (UTC)

I know but most of the delta is formed near mouth.Sunny Singh (DAV) (talk) 03:15, 1 September 2012 (UTC)

Delta formation requires the flow speed of the river to slow enough that it can no longer keep sediments suspended. The land formation that permits such a thing to happen is simply unlikely to exist near a river. In my own original researchy hypothesis, I would assume this is because rivers tend to erode themselves a riverbed through which to travel, preventing a sufficient loss of speedy. Someguy1221 (talk) 02:40, 1 September 2012 (UTC)

I read the following statement in a Chemistry book -

"Delta is formed when river water comes in contact with sea water for a long period.
River water is mostly muddy. These mud particles are charged colloidal particles. When river comes in contact with sea, the dissolved salts present in sea water provide ions with charge opposite to the charge on mud particles. These particles get uncharged and combine with each other to form bigger particles. They settle as solid mass. Over the years, deltas appear at these places."

This is a short explanation of delta formation. I want to know more about this. Sunny Singh (DAV) (talk) 03:15, 1 September 2012 (UTC)

This is the first time I've heard that theory. The far simpler explanation above seems more likely, that river water slows when it hits the ocean, and all the sediments it carried then settle to the bottom. StuRat (talk) 03:35, 1 September 2012 (UTC)

The theory sounds silly on the surface, anyway. If the river is filled with charged colloidal particles, it must also be filled with oppositely charged particles, colloidal or otherwise. The same goes for the ocean. Either Sunny misparaphrased, or whoever came up with the theory doesn't understand even the most fundamental of chemistry or physics. Someguy1221 (talk) 03:53, 1 September 2012 (UTC)

I have written the same thing written in the book. According to you, book's statement is wrong. This means the answer you gave earlier is the real cause of delta formation. Sunny Singh (DAV) (talk) 04:16, 1 September 2012 (UTC)

For the muddy particles in suspension in river water, flocculation does occur when it encounters seawater, and is one of the reasons that mud is deposited in deltas [10]. Mikenorton (talk) 08:07, 1 September 2012 (UTC)

For coarser particles (not muds), then it is the reduction in flow velocity that causes the sediment to be deposited, as already stated. Mikenorton (talk) 09:47, 1 September 2012 (UTC)

You might be interested in this paper, "Modeling river delta formation". Also, the River delta article isn't bad. Sean.hoyland - talk 10:28, 1 September 2012 (UTC)

What Sunny Singh said is exactly right (Someguy1221 jumped the gun). The colloidal are water soluble in fresh water but become insoluble when the charges present at their surfaces is cancelled out by charges present in the salty water. Dauto (talk) 23:50, 1 September 2012 (UTC)

I still hate that explanation. It's not the presence of any oppositely charged particles that renders the suspension insoluble, but specifically ones that can stably bind to the suspended particles. Someguy1221 (talk) 00:56, 2 September 2012 (UTC)

Water - oil mixture

Why does water not get uniformly mixed with oil? One reason I read is that water is heavier than oil. Then, why does water get mixed with alcohol and doesn't make separate layer as in case of oil. Sunny Singh (DAV) (talk) 02:24, 1 September 2012 (UTC)

We have an article on this phenomenon, at Hydrophobe. You may also be interested in Chemical polarity. The general way I have seen this presented to beginning chemistry students is that polar molecules, such as water, bind extremely well to themselves and other polar molecules, very much unlike non-polar molecules such as oils. The immiscibility of water and oil is a consequence of the water molecules basically binding to themselves to the exclusion of the oil molecules. Someguy1221 (talk) 02:36, 1 September 2012 (UTC)

And no, differences in density are not the reason, in the case of water and oil, although two fluids of different densities might take a long time to mix, just because one would be at the bottom and the other on top, with a limited area of interface, which would slow the mixing. This can happen, for example, with fresh water and salt water. Even though they would mix completely if stirred up, under the proper conditions they can stay in layers for a long time, due to density differences. StuRat (talk) 03:31, 1 September 2012 (UTC)

Given that they are not miscible, they form layers even if stirred up because of different density: they "separate" rather than dissolve because of immiscibility, and the separation is top-vs-bottom because denser stuff sinks and less dense stuff floats. Two separate (sorry:) issues that have various combined effects. If you pick two immiscible materials that happen to have the similar density and mix them well, they can form an even suspension or colloid that does not visibly re-separate. Milk (especially whole homogenized milk) and Mountain Dew (thanks to [[brominated vegetable oil) are two common examples. The closer the density and/or the better you mix them, the longer time or stronger gravity it will take for them to separate. DMacks (talk) 04:51, 1 September 2012 (UTC)

Even with mixtures where the densities are somewhat different, you can create metastable suspensions that last a very long time with the help of extreme agitation or emulsifiers. But regarding the water-oil problem, let me confirm StuRat has already said: the bonding energy you would gain back by forming water-oil bonds is not enough to overcome the energy needed to seperate water molecules from each other, or to get fancy, the energy of solvation is too low between oil and water. Part of the situation with the immiscibility of water and oil is that oil is composed of essentially nonpolar molecules, and the polarized water needs to have some sort of electric charge to "hold on to". There are no localized charges in oil molecules, so water is far happier holding tightly to other molecules. --Jayron32 05:00, 1 September 2012 (UTC)

It's a shame there's no such thing as butter or mayonnaise. μηδείς (talk) 23:30, 1 September 2012 (UTC)

Exactly. Butter is a metastable mixture of fat and water, and it forms via extreme agitation. Mayonaise contains eggs, which contain lecithin, which is an emulsifier. It seems odd that you would confirm exactly the point I made about metastable mixtures of fat and water, and then take a tone as though you would be disagreeing with me. That is quite weird. --Jayron32 01:38, 2 September 2012 (UTC)

It's a shame you're not American, or you would recognize kidding sarcasm when you come acrost it. But yer not. Some sorta weird island of literal zombies called Carolina, apparently. μηδείς (talk) 01:55, 2 September 2012 (UTC)

The individual molecules in a liquid are electrically polarised - they have an unequal distrabution of electronic charge across the molecule. This means that different portions of a molecule is more negatively charged than the rest. I assume that you know that oppositely charged objects attract; molecules attract each other due to their polarity.

Water molecules are more strongly polarised than oil molecules; the attraction force between charged objects increases as the charge on the object increases. Meaning, water tends to associate more strongly with itself than with oil. Relative to water, oil doesn't associate strongly with itself at all, there is just no other alternative.

The differen density between water and oil has nothing to do with it, density just determines the order of the fractions as it sepperates due to gravity or centrifugation. Alcohol mixes with water, as even though it has a weaker polarisation, it is comparable to that of water.

Note that nothing is truely insoluble, just diminishingly soluble. Plasmic Physics (talk) 01:33, 2 September 2012 (UTC)

A lot of beginner chemistry students make the mistake of thinking that "polar" and "non-polar" are opposite terms, more accurate terms should be "weakly polar" and "strongly polar". Plasmic Physics (talk) 01:45, 2 September 2012 (UTC)

Tumor Lysis Syndrome seen in antibody dependent cell mediated cytotoxicity?

Tumor Lysis Syndrome (TLS) is of course a major adverse event in anti-cancer treatments such as Rituxan. As the monoclonal antibody kills B-cells, their contents are spilled into the bloodstream.

What I'm trying to determine is whether TLS would be a possible consequence of anti-cancer treatment that is based in antibody-dependent cell-mediated cytotoxicity, such as the kind you might find when using a therapeutic cancer vaccine.

If not, what is the difference between what activated T-cells are doing to the targeted cancer cells and their contents vs what an immunotherapeutic like Rituxan is doing?

Or God forbid am I even making sense? I'm a health/medical writer but cred-wise I'm just a lay person.

--Wolfgangus (talk) 06:25, 1 September 2012 (UTC)

Yes, TLS is listed as a possible consequence of Rituxan, see http://en.wikipedia.org/wiki/Rituxan#Adverse_events. You should also read the manufactuer's Patient Information sheets, and note the advice given. Wickwack58.164.230.22 (talk) 06:46, 1 September 2012 (UTC)

A few mechanisms of action (including ADCC) of rituximab (anti-CD20) have been proposed but it's not clear which one dominates, as described in this recent review PMID 22621628. It's not clear that the mechanism of action will be the same for different antibodies and cell types. Much may be learned from situations in which these treatments stop working, e.g. PMID 22368276 -- Scray (talk) 20:16, 1 September 2012 (UTC)

Insulation value of aluminium foil

Hi, I'm currently building an ice-box in my boat, and I intend to insulate it on all sides with 100mm of rigid urethane foam. Friends have suggested I include a layer of reflective foil around the outside of the foam. If I did, the foil would be tightly sandwiched between urethane foam on the inside, and plywood on the outside, and I can't understand how this would reduce the heat flow into the ice-box. Can someone explain this to me please?124.191.178.49 (talk) 07:02, 1 September 2012 (UTC)

I think the idea is that the aluminum foil will reflect radiated heat. If so, it should be placed on the foam, with an air gap between it and the plywood (a vacuum would be better, but I assume that's not possible here) . However, I agree that jamming it in so it fills the air gap isn't good, as that will allow the aluminum foil to conduct heat directly from the foam to the plywood. So, if there isn't room for it, leave it out (or make the plywood box a bit bigger).

Another concern is that you could get condensation on the foil, which may then soak the wood, allowing it to rot. If the air inside was completely dry and sealed from the outside, this wouldn't happen, however, an airtight seal would be difficult, so an air gap and drainage holes at the bottom are a good alternative, to allow the water to drip down and out. Put a pan under the drainage holes to collect the water. StuRat (talk) 08:48, 1 September 2012 (UTC)

Agree with Stu, foil won't do much in this situation. Careful construction of the insulation with seams minimized (and staggered if using several layers) should give best results. Ssscienccce (talk) 14:19, 1 September 2012 (UTC)

Perhaps your friends were confusing aluminum foil with mylar foil, which IS used effevtively as a thermal insulator. Though mylar is often shiny and metallic looking, it isn't interchangable with the stuff you wrap your leftovers in. Mylar may be useful for this, but I can't imagine Reynolds Wrap as being a good idea. --Jayron32 14:50, 1 September 2012 (UTC)

Aluminium foil works just as well as insulator, it reflects about 98% of radiant heat and light (source). However, aluminized Mylar is a better choice because it does not tear as easily. - Lindert (talk) 15:30, 1 September 2012 (UTC)

Yes, but foil's value as a radiative reflector is more than compensated by its value as a contact conductor of heat. That is, while it may reflect radiated heat, it is also an excellent conductor, and as such, if it is in contact with what you are trying to keep cold/warm, its reflective ability doesn't really come into play. --Jayron32 15:49, 1 September 2012 (UTC)

Yes, if it not separated by air or empty space, it is basically worthless. In this case the space should not be between the cooled object and the foil, but between the object/foil and its environment. The reverse is true if keeping something warm. The same is true if you use mylar foil though (which btw is just plastic foil with an aluminium layer). - Lindert (talk) 15:52, 1 September 2012 (UTC)

No, no, no. The aluminum foil will be useful (By reflecting radiation) even if touches the plywood layer. It would conduct heat, off course but it would still reflect radiation back to the plywood. You don't need to separate the foil from the environment with vacuum or air. You can separate with urethane foam and plywood which are good insulators. Dauto (talk) 23:40, 1 September 2012 (UTC)

Weight of atom

What will be the weight of a atom if its size expanded to a cricket ball?--Sunny Singh (DAV) (talk) 10:46, 1 September 2012 (UTC)

It would depend on the atom, since they each have different masses and sizes. The mass varies by element and isotope, and to a much lesser extent by charge. The size of an atom is a bit harder to define, as the outside edge is an electron probability envelope.

But, if we assume the atom in question is a typical atom from which a cricket ball is made, then the mass would be about the same. This is because in a solid, the atoms are packed essentially right next to each other. There is still lots of empty space, between the nucleus of each atom an the electron cloud, but that exists in both the individual atom and the collection of atoms in the cricket ball, in the same proportion. I'd say the single atom would have a slightly greater mass, since packing is never perfect with a collection of atoms. The atomic packing factor runs around 68-74% in a crystal, and might be a bit worse with an amorphous solid, let's say 50%. In that case, the single atom would have twice the mass, and so would weigh twice as much, too. StuRat (talk) 11:17, 1 September 2012 (UTC)

This is a none question because expanding atoms is not possible. It can only be answered hypothetically and depends what one assumes for the properties of the hypothetical atom. In other words the answer can be anything you like. For instance, if one postulates an atom that composed of normal protons and electrons, but has somehow contrived to place the electron shell at the diameter of a cricket ball, then the mass would be that of a single "ordinary" atom - almost nothing. On the other hand, if one postulates an atom with a nucleus the size of a cricket ball but with the same density, which is about the density of a neutron star, the weight would be something like that of the Alps. SpinningSpark 20:01, 1 September 2012 (UTC)

You seem to be assuming an atomic nucleus the size of a cricket ball--which would weigh 100,000^3 the mass of a cricket ball--but that is not what the OP said. μηδείς (talk) 20:09, 1 September 2012 (UTC)

I think we can assume that the question was asked hypothetically. 86.146.107.246 (talk) 21:03, 1 September 2012 (UTC)

An atom the size of a cricket ball (let's assume 10 cm radius for convenience, and a Helium atom, since that is the example at our atom article--the proportions of carbon twelve are the same) would have a "solid" nucleus 1/1000th of a millimeter across, containing 99.94% of the atom's mass (pretty extremely dense, huh?) and the remainder would be made of a cloud of electrons. It would in no sense resemble a cricket ball with a uniform density and a solid surface. μηδείς (talk) 20:06, 1 September 2012 (UTC)

This is an easy one, just simplify it to finding the atomic density for a given atom using its atomic mass and Van der Waal volume, and multiplying it by the standard volume of a cricket ball. Plasmic Physics (talk) 22:11, 1 September 2012 (UTC)

The Van der Waal volume being based on the size of the electron cloud, yes, that's what I said. μηδείς (talk) 23:27, 1 September 2012 (UTC)

Just a small aside, his name is Johannes Diderik van der Waals. With the 's'. Otherwise, yeah, that's how i would solve it as well. --Jayron32 00:30, 2 September 2012 (UTC)

Balanced wheel

Could I check a couple of things?

Suppose a wheel is oriented horizontally (i.e. the rim of the wheel lies in a horizontal plane), and it balances perfectly under gravity when it is resting stationary on a point (say on the tip of a spike). Does that also mean it's perfectly balanced when it rotates on that axis at any speed in any orientation?

Is it always possible to balance any wheel by adding one point mass to the rim?

86.146.107.246 (talk) 19:27, 1 September 2012 (UTC)

A wheel that was balanced on a point when horizontal will only still be balanced when tilted if it has zero width. A real wheel with thickness will have its cg shifted slightly to the side which is tilted down causing it to tilt further and then fall. The same applies to a wheel rotating slowly. If the wheel is rotating fast enough, gyroscopic action can overcome the unbalance and hold it in place. SpinningSpark 19:49, 1 September 2012 (UTC)

The guy talked about rotation along the plane of the wheel (I think) - to be precise, along the horizontal plane that is perpendicular to down - not about tilting, which wouldn't make sense. So, he says: if you can get the wheel to balance when it's still, can you rotate it 'along the horizontal plane' and it it still balanced? For me, the answer is obviously "yeah, you can still rotate it" as this is no different from "rotating the point" that it is on, since a point can rotate and it is the same. (Alternatively, you can simply walk around the wheel, rotating your view, and the effect is the same as if you had rotated the wheel along the horizontal. So, you can always rotate it and it will remain balanced.)

As to the other question I should think the answer is yes but I'm not sure. --80.99.254.208 (talk) 20:14, 1 September 2012 (UTC)

To clarify, by "when it rotates on that axis at any speed in any orientation" I am talking about putting the wheel on an axle in the same position and orientation as the spike on which it was resting. So, it's two different setups: the first resting horizontally on a spike which is where the axle will be positioned, the second with the wheel in a normal configuration on an axle, with the axle oriented in any direction. Sorry that was not very clear. 86.146.107.246 (talk) 21:01, 1 September 2012 (UTC)

can I see the observer effect in action?

Is there an experiment like the double-slit, where there is an interference pattern unobserved, but it disappears observed, and if so I would like to watch a Youtube video of someone (i.e. a piece of machinery) alternately either not observing the single photons and observing htem.

I would like to see the observer effect "in action" like toggling the interference pattern by observing or not. To be clear, I don't want to myself observe: I want to observe the *experiment (+ observer) OR (+ 0) = outcome* where the middle term is switched on and off and I can see, by the changing outcome, the observer effect. --80.99.254.208 (talk) 20:11, 1 September 2012 (UTC)

This is an interesting question. Note that if you have a photon-detecting device at one slit with, say, its readout hidden behind a door so you can't see it, opening the door is not going to make the interference pattern disappear. All that's necessary to make the interference pattern disappear is recording the passage of the photon somewhere, even if only as electrical signals in the bowels of the machine. That aside, the idea makes sense in theory, but there are practical problems:

• A milliwatt laser at a visible wavelength emits upwards of 10¹⁵ (1,000,000,000,000,000) photons per second. That's pretty dim light. To make this experiment work you need photons to pass through the slits at a rate slow enough that you can detect each one individually. So you're not actually going to be able to see the light on the screen at the far side of the slits.
• Practically speaking I don't see how you could detect a photon's passage through the slit without absorbing it, but that makes the experiment pretty boring since you're simply blocking one of the slits. The detector would need to be connected to another laser at the slit which would emit a photon whenever one was detected. Quantum mechanically it doesn't matter, but you might find the experiment less convincing this way.
• Practically speaking I think the only way to prevent measurement of the photon's passage would be to physically remove the detector (and re-emission laser) from the slit. Again, this might make the experiment less convincing, especially since single-photon detectors are not very accurate in the first place and the mere presence of one in the slit is going to make a big difference, measurement effect or no.

-- BenRG (talk) 22:33, 1 September 2012 (UTC)

Some of the difficulties pointed out by BenRG would be less problematic if you use electron instead of photons in the double slit experiment. Dauto (talk) 23:22, 1 September 2012 (UTC)

I may not know the actual way of things, but as far as I was taught in university level Special Relativity, they observer theory concerning quantum superposition of states, appears to be incomplete or faulty - everying in the universe is an observer, everything contantly communicates information through the fundamental forces. Observation should more likely to be statistically determined than definitively determined, but how? Plasmic Physics (talk) 02:12, 2 September 2012 (UTC)

September 2

Non-fatal viruses

Are there any viruses that are not potentially fatal to humans first-hand? One that I can think of is HIV (which can allow other diseases to cause death), but are there others? Thanks. 64.229.153.184 (talk) 00:17, 2 September 2012 (UTC)

There are millions of viruses which don't use humans as vectors at all, i.e. the Tobacco mosaic virus doesn't even infect animals. Bacteriophages are a class of viruses that infect bacteria. --Jayron32 00:28, 2 September 2012 (UTC)

In before this gets removed as a request for medical advice. What Jayron said, basically. I'm not even sure that a significant portion of the viruses in existence are potentially fatal to humans. That would seem to be rather oddly genus-specific, and I think most viruses tend to use a rather small number of animal vectors. As I understand it, the principle of natural selection would also make killing the majority of your hosts something of a genetic/evolutionary dead end, wouldn't it? Evanh2008 ^{(talk|contribs)} 00:34, 2 September 2012 (UTC)

It's not intended to be for medical advice, just out of curiosity. 64.229.153.184 (talk) 00:52, 2 September 2012 (UTC)

Yes, it is not evolutionarily stable for a virus to kill most of its hosts (or at least to kill them too quickly). Among viruses that infect humans (which I think is what the question is intended to focus on), I believe there are many that are rarely lethal (I do not have a handy reference, a little help here?). As for references, the OP may be interested in Virulence#Evolution, and optimal virulence. Both of these articles describe the factors that promote and inhibit lethality in pathogens. Lastly, this is a perfectly legitimate (and interesting) question. It is in no way a request for medical advice, see User:Kainaw/Kainaw's_criterion SemanticMantis (talk) 01:52, 2 September 2012 (UTC)

Are you asking for viruses that simply can't kill humans, viruses that infect humans but don't kill, or viruses that make humans more likely to die but can't kill on their own? Someguy1221 (talk) 01:46, 2 September 2012 (UTC)

Infect but don't kill, sorry for not being clearer. 64.229.153.184 (talk) 01:55, 2 September 2012 (UTC)

A couple of examples: GB virus C and Transfusion transmitted virus. -- Scray (talk) 02:08, 2 September 2012 (UTC)

We all get influenza from time to time. Only in rare cases do flue viruses kill. Various forms of the herpes virus either produces no symptoms, just a rash when the human is under stress, or just a mild rash. Wickwack124.182.34.199 (talk) 02:14, 2 September 2012 (UTC)