Wikipedia:Reference desk/Archives/Science/2012 May 5

= May 5 =

Dimensions of inflation
What was the diameter of the universe just before and after Inflation (cosmology)? 71.215.84.127 (talk) 01:09, 5 May 2012 (UTC)
 * See Shape of the Universe. The short answer is that we don't have a good idea about the diameter of the universe at any time.  It may not have a meaningful diameter.  -- Jayron  32  01:28, 5 May 2012 (UTC)
 * From Inflationary epoch: "This rapid expansion increased the linear dimensions of the early universe by a factor of at least 1026 (and possibly a much larger factor), and so increased its volume by a factor of at least 1078."
 * "[T]he visible universe ... radius after initial inflation was (very roughly) 10 cm...compared with 14 billion light years now." (emphasis added)
 * If those are both correct then the initial radius was about 10-17 Angstroms, right? 71.215.84.127 (talk) 05:37, 5 May 2012 (UTC)
 * Well, that depends on whether you're asking about the whole universe, or just the visible universe. Although even in the case of the visible universe, I'd be hesitant to simply apply the scale factor. Given how non-intuitive general relativity is on some issues, I'm not certain that the visible universe is still quite the same thing before and after expansion. That is to say, particles that are in your visible universe prior to inflation may be outside of your visible universe following inflation. Maybe someone better at physics can enlighten me. Someguy1221 (talk) 05:59, 5 May 2012 (UTC)
 * 1026 is a lower bound, not an estimate. It's the smallest expansion factor that's consistent with the observed flatness of the universe. It doesn't come from any theoretical model of the actual inflationary process; those tend to give much larger expansion factors. I doubt the size of the visible universe before inflation is a meaningful quantity; in any case we don't know what it is. There may not have been a beginning of inflation. -- BenRG (talk) 21:50, 5 May 2012 (UTC)
 * There was a question elsewhere about "empty space" or some such. Supposing one could somehow travel at nearly limitless speed and could somehow get to a point where all the galaxies are behind you. In front of you would be solid black, right? With no apparent end to it? ←Baseball Bugs What's up, Doc? carrots→ 03:44, 5 May 2012 (UTC)
 * That depends. Do you think that the universe is ekpyrotic? If so, then yes, unless our big bang is not unique (see cosmological principle.) Otherwise it depends on whether the topology is closed, as Jayron suggested; if so then no and if not then yes. 71.215.84.127 (talk) 05:29, 5 May 2012 (UTC)


 * Bugs, in the standard cosmological model there's no end to the galaxies. In reality there might be an end. Beyond that might be empty space (though I know no reason to believe that) or there might be something entirely different. I guess 71.* is saying that in the ekpyrotic scenario there is an end to the galaxies, but I don't know if that's true and I don't know what would be beyond it, except that I'm pretty sure it wouldn't be empty space. -- BenRG (talk) 23:04, 8 May 2012 (UTC)

Also note that the universe is about as flat as a pancake under some models (flatter, in fact). Collect (talk) 12:29, 5 May 2012 (UTC)
 * Can you link to an article about such models? I can't imagine how that could work.  Nyttend (talk) 12:44, 5 May 2012 (UTC)
 * There's some information in the article (already linked above) called Shape of the Universe. -- Jayron  32  19:34, 5 May 2012 (UTC)
 * That's flat in the sense of flat (Euclidean) three-dimensional space, not flat in the sense of having only two dimensions. -- BenRG (talk) 21:50, 5 May 2012 (UTC)
 * I think I know what Collect was talking about. The Elegant Universe mentioned a rather unusual formulation of string theory inside of a near-singularity (very very small, but not quite infinitesimal) of a universe. In this formulation, the compactness of the universe is stable and only continues to shrink, and somehow particle interactions work out in a way that would be indistinguishable to us. The theory went further to show that it works even if only some of the visible dimensions are compacted in this way (and this form of compactness is distinct from the "curled up dimensions", as they are still detectable). So, yeah, very bizarre theory. The formulators insisted that it is consistent with all confirmed predictions of GR and the standard model, but at the moment I can't find any links to it, and I don't have the book with me. Someguy1221 (talk) 21:07, 6 May 2012 (UTC)
 * I don't know what that would be. Something to do with T-duality, maybe? I don't see how that would be related to the universe being "flat as a pancake". -- BenRG (talk) 23:04, 8 May 2012 (UTC)
 * Where the internal angles of a triangle several billion light years across sum to 180° - Sky Machine   ( ++ ) 23:22, 5 May 2012 (UTC)


 * The universe is and always will be infinite by our understanding of the term. Small minds create absurdly flawed theories and models which, with no exception, rely on shit at some critical point which they often call something like a black box or unknown, it's like when you give an idiot a tangled ball of fishingline, they can't possibly untangle it, and so just try to tidy up, gathering out long 'useful' bits, and crushing the rest into as small a ball as possible. Limited universe theories always without exception offend reason at some point when you follow the long threads they do show you back further, the closer you get to the beginning the more obvious they have no idea what to make of the central mess. Anyhow, there is no idiot with a tangled ball of fishing line that won't shout he knows all about how to untangle it, just ask them, they're experts. Penyulap  ☏  11:07, 6 May 2012 (UTC)


 * this sounds just like someone shouting that he just untangled the largest ball of fishing line in the boat.68.83.98.40 (talk) 12:49, 6 May 2012 (UTC)


 * Which would make me an expert on these 'theories' as it takes one to know one, and they're full of it. So it's fine, I'm cool with the same label, however I'm not asking for absurd suspensions of all known reason and logic at any point. Penyulap  ☏  07:33, 7 May 2012 (UTC)


 * What are you complaining about, exactly? Is it something that somebody said in this thread? -- BenRG (talk) 23:04, 8 May 2012 (UTC)

Article about rain
Hi - There's been some discussion on the Talk page about "Rain" concerning my opinion that the article does not *actually* discuss why rain occurs. It gives the *appearance* of doing so, but does not, actually. This is a little surprising to me. I wonder if somebody could look into this? I think it could greatly improve the article if there were a good, easy-to-understand yet thorough, explanation of why rain occurs in the first place. (Something involving thresholds, gravity, temperatures, air pressures, "dew points," the size of the drops, the composition of clouds and why and how they "hold" the water, etc.)

Again, if you read the article carefully, you may agree that it *appears* to give an explanation of why rain forms and falls, but does not actually do so. — Preceding unsigned comment added by 68.196.248.241 (talk) 05:03, 5 May 2012 (UTC)


 * I have had a quick look at Rain. It already has Good Article status.  Most Wikipedia articles, even the best ones, can be improved by addition of a little extra information here, or an improvement in the syntax there.  Often, the first step in the improvement process is when one User clearly and precisely identifies a problem.  The second step is when another User, or even the first one, then makes suitable to edits to eliminate or mitigate the problem.  The allegation here is a most general and imprecise one - that the article appears to be scientific, but is not actually scientific.  Criticisms of this kind are unhelpful and most unlikely to bring about any improvement.  If the User at 68.196.248.241 is willing to use the Talk page to clearly and precisely identify a problem there is a possibility another User might take up the opportunity to fix the problem.  If the User at 68.196.248.241 is not willing to assist in this way then it is highly unlikely he will ever see an improvement unless he does it himself.  Dolphin  ( t ) 05:25, 5 May 2012 (UTC)


 * I'd post this on the talk page for Rain. StuRat (talk) 05:27, 5 May 2012 (UTC)

DVD player
Why can't scientists invent a DVD player where you just put the disc in and it plays - don't have to wait for all of that opening stuff and don't have to select play from the menu. Just bypass the menu - put it in and go. Also, how about one that would be as easy to fast forward and rewind as a DVR? Bubba73 You talkin' to me? 05:14, 5 May 2012 (UTC)


 * For the first part, many Disney DVDs do that. They figure they want kids to pop it in and have it play.  I've never had any trouble with FF and REW.  You hit the buttons and it starts to fast forward or rewind slowly, and push it again and again to speed up, then play to resume normal play.  What's hard about that ? StuRat (talk) 05:24, 5 May 2012 (UTC)


 * It takes a long time compared to my DVR. Also, the DVR has a button that you can press and it goes back a few seconds.  A DVR is a lot smoother operating that way than any DVD player I've had.  Bubba73 You talkin' to me? 05:32, 5 May 2012 (UTC)


 * Well, it does take some time to spin the DVD up to the proper speed, but only a second or two in my experience. Ultimately, I expect the portable video format to be something more like a flash drive, which should be quicker and more flexible. StuRat (talk) 05:37, 5 May 2012 (UTC)
 * Also, because a DVR is reading from a hard drive with high rotational speed (7200 to 10000 rpm, it can quickly jump back to any given point in its memory, where as DVDs (as with other heavier physical media) are subject to higher rotational latency, since they typically only spin between 600 and 1500 rpm. Although now that I'm looking at the figures I'm not sure it would be a noticeable difference. - Running On Brains (talk) 06:05, 5 May 2012 (UTC)


 * The licencing terms imposed by the DVD Forum do not allow consumer equipment or software to bypass opening sequences. Please report to your nearest media consumption re-education booth for suggesting that this is not entirely suitable. 71.215.84.127 (talk) 05:34, 5 May 2012 (UTC)


 * DVDs which go right to a menu don't much bother me, either, as I often want to change spoken language or subtitle settings. What I do hate is DVDs that feel the need to play a video clip after each click on the menu.  That gets annoying quickly. StuRat (talk) 05:29, 5 May 2012 (UTC)


 * The comment two above mine is the key to your first question — they can develop it and have developed it, but they're not allowed to implement it for most DVDs. Nyttend (talk) 12:46, 5 May 2012 (UTC)


 * So what happens if they do it anyway ? How about a DVD player manufacturer in a nation with no enforcement of such laws, like China ? StuRat (talk) 02:09, 6 May 2012 (UTC)


 * If they do it anyway, potentially they'd be sued for violating the terms of their licence or at least have the licence revoked (meaning they can't legally produce DVD players anymore). As for China, it's likely there's some enforcement in China, however it's possible such DVD players do exist. It doesn't help people in other countries though, unless they're going to try and important the DVD player themselves. Nil Einne (talk) 04:40, 6 May 2012 (UTC)


 * An extraneous "ant" seems to have crawled into you last sentence. :-) StuRat (talk) 06:18, 6 May 2012 (UTC)


 * To make a DVD player, you need a decryption key. To get that key, you need a license agreement with the consortium that owns the DVD format. If a potential DVD manufacturer were in a nation where the license agreement could not be enforced, they would simply never be licensed in the first place, and would never get the key. There are several such keys, intended for use in different regions of the world. DVDs made for other markets won't play on North American DVD players and vice-versa, because different decryption keys are required. --Srleffler (talk) 18:10, 7 May 2012 (UTC)


 * I can't believe that's much of a technical problem to overcome for any manufacturer (just buy a DVD player from each region and reverse engineer it to determine the key). China is massively into industrial espionage, and I'd have to think they'd have done this long ago.  StuRat (talk) 18:27, 7 May 2012 (UTC)
 * It's not. In fact, the algorithm for encoding DVDs has been determined, and can be found online. The issue is that manufacturers don't want to get sued into oblivion for using the code without licensing it. &mdash;  The Hand That Feeds You :Bite 21:54, 8 May 2012 (UTC)

Could a DVD player have a built-in hard drive? When you get the DVD, you pop it in, it copies it to the HD, and then when you are ready to watch it, it reads from the HD instead of the painfully slow DVD? Bubba73 You talkin' to me? 20:45, 7 May 2012 (UTC)


 * Technically, you could, but:


 * 1) It would take a long time to read in the entire movie. If you just got your DVD and want to watch it now, that would be annoying.


 * 2) Copyright laws are so strict, it might be considered an "illegal copy". StuRat (talk) 21:27, 7 May 2012 (UTC)


 * If you did want to watch it right away, you could watch it as a DVD player works now. Bubba73 You talkin' to me? 00:13, 8 May 2012 (UTC)


 * And, under US copyright law, you are entitled to make one backup copy, I think. As long as the copy is on your DVD/HD player, I don't see a problem (unless you didn't buy the DVD). And they could address that by making it so that it will only play back from the HD once, unless you load it again. Bubba73 You talkin' to me? 00:20, 8 May 2012 (UTC)


 * Actually, in the past year or so I believe there was a company who made one of those (DVD player with a hard drive to "rip to") but were promptly sued by major film studios. Strictly speaking, it is legal to make a backup copy for personal use. There was a lot of controvery over the Digital Milennium Copyright Act, though, as it effectively banned any devices capable of making said copies. Presumably this includes any computer with an optical drive (in other words, the one you're reading this on), but that ban has yet to be enforced on computers, as far as I know. Evanh2008 (talk) (contribs) 22:16, 8 May 2012 (UTC)


 * But with a DVR, I can record whatever comes over the cable to watch later. Bubba73 You talkin' to me? 00:04, 9 May 2012 (UTC)


 * "Can" physically, yes. "Can" legally, I'm not sure. Evanh2008 (talk) (contribs) 00:11, 9 May 2012 (UTC)


 * It is currently legal in the US. Bubba73 You talkin' to me? 03:55, 9 May 2012 (UTC)

Is Planetary Resources making a space VLBI telescope array?
This blog post suggests that Planetary Resources is working on space VLBI telescope array based on Émile Henry Labeyrie's "hypertelescope" design. Is there any corroboration for that? 71.215.84.127 (talk) 05:47, 5 May 2012 (UTC)


 * I can't find any.


 * That said, the test array in LEO is very easy to arrange though. The L2 array is fringe in a way, one gust of solar wind can blow it all away. There are craft heading for the moon that can give a lift to hitch-hikers like these, and there are pushes to send people there which are spoken of, but second priority to Mars, so it's harder to predict that it will happen, I'd give it a 10% in 20 years chance for L2 and a 80% chance for LEO in 15 years. The chances that anyone will make billions is Zero. The chances that anyone will make a similar space based array for the same purpose is 100%. Penyulap  ☏  20:33, 5 May 2012 (UTC)


 * Do you think the "interstellar missions.... allowing the capability of exploring other planetary surfaces" of http://lmr.nasa.gov will image the surfaces of extrasolar planets with lunar VLBI first? 71.215.84.127 (talk) 22:21, 5 May 2012 (UTC)
 * Well, which takes less time and energy? —Tamfang (talk) 21:41, 6 May 2012 (UTC)


 * Unfortunately no. extrasolar planets are out of the reach of mankind at the moment, the ruling mechanisms that are in place will not allow humans to leave earth and live in space independently, and extrasolar probes won't be sent so far further ahead of humanities progress, we'd need to be moving further out into space ourselves for such complex efforts to be made. Penyulap  ☏  07:41, 7 May 2012 (UTC)


 * The Labeyrie slides linked above, as excerpted by the initial blog post, say that a 100 km array could resolve details of Earth's continental features out to 10 light years. The Moon could handle a 2000 km array, and the average seismic displacement on the Moon is usually much less than 1 micron. From how far away could such a heterodyne terahertz digital VLBI imaging system resolve the 9-10 micron band for ozone, indicating the sort of life we can eat? 71.215.84.127 (talk) 22:08, 7 May 2012 (UTC)

Over-active Immune System
Is a person with an over-active immune system, i.e., multiple allergies, less likely to become sick from common illnesses such as colds and flu?

Also are they less likely to contract cancer? Thanks, Wanderer57 (talk) 17:00, 5 May 2012 (UTC)


 * I would think they might be more resistant to infectious disease, although if they have inflammation and breaks in the skin from scratching, this might make it easier for microbes to get in. As for cancer, that seems to work by fooling the immune system into thinking cancer cells are good cells, so having a stronger immune response isn't necessarily going to improve the ability to recognize cancer cells. StuRat (talk) 17:08, 5 May 2012 (UTC)


 * Yes and no. Cause and effect may not have a bearing, but the environment that causes one will cause the other. For example, multiple allergies are common in highly developed countries where people eat highly processed foods and are exposed to a wide variety of chemicals, the same places that people have the highest possible cancer rates. Avoiding the risk factors for one will avoid the risk of the other, so leading an Amish or permaculture lifestyle would decrease both, and living in the city would increase the risk of both.


 * The immune system learns from what it has seen before, the people who were old enough to survive Spanish flu never contracted swine flu, there was a simple cut-off date for elderly patients in the hospitals that doctors noticed, but as a general law of the universe, however sick you are, you can always get a little more sick, it's called Murphy's law and believe me, I know it's true, the only advantage to laying in a hospital bed is that you are slightly less likely to be hit by cars, that's pretty much it, everything else is a downside. Penyulap  ☏  21:13, 5 May 2012 (UTC)
 * There seems to be a statistical link between allergy and protection against cancer: A Danish study found a link with breast and non-melanoma skin cancer and contact allergies; people suffering from allergies had a lower risk of developing those cancers. http://healthland.time.com/2011/07/12/the-curious-link-between-allergies-and-cancer/ Ssscienccce (talk) 08:08, 6 May 2012 (UTC)
 * When it comes to the common cold, there's no advantage at all. We all get colds, but whether we notice or not depends on the reaction of our immune system. Ssscienccce (talk) 08:13, 6 May 2012 (UTC)


 * Thank you all. Intriguing.


 * I'm unclear about the last comment by Ssscienccce. Is the point that if someone gets a cold and their immune system does NOT react against it, the cold will be more severe because the immune system is not fighting it?  Or that they would not notice the cold if their immune system does NOT react, because what is noticed about a cold is specifically the symptoms caused by the immune reaction? Wanderer57 (talk) 17:06, 7 May 2012 (UTC)


 * The latter, I think, although the immune system must react to some degree, or even colds would kill you. That is, you need more white blood cells, etc., to go to the infected area.  What you don't need is all the inflammation, excess mucus production, itchiness, and coughing. (Some of those reactions are helpful to the sufferer, like coughing, but potentially spread the cold to others, while other reactions, like itchy eyes, don't help anyone.) StuRat (talk) 17:21, 9 May 2012 (UTC)

Pronunciation of vitamin?
Any ideas when and why the different pronunciations of the word vitamin emerged in American and British English? I think it would be good to explain this briefly in the article, supposing good references can be found. --John (talk) 18:58, 5 May 2012 (UTC)


 * You might have more luck pn the Lamguage Desk.--Shantavira|feed me 19:25, 5 May 2012 (UTC)
 * Thank you, I have linked to this discussion from there. --John (talk) 19:38, 5 May 2012 (UTC)

This is a bit OR, but the OED lists the "vittamin" pronunciation first. However, it then says, "orig. vitamine", with the pronunciations in the opposite order. Perhaps then the UK pron came later, as the word became more established and thus more anglicized? (On the other hand, the UK pron is what one would expect for a Latinate word; it's the US pron that's irregular.) — kwami (talk) 20:23, 5 May 2012 (UTC)
 * Why is "the UK pron . . . what one would expect for a Latinate word", Kwami? My dictionaries indicate that vitamin was formed from Latin vita and International Scientific amine, and the i in Latin vita is long; so in my understanding the traditional English pronunciation of the Latin word would be /ˈvaɪtə/—cf. vital, etc. Perhaps the pronunciation of victuals (from a related Latin word with a short i) as "vittles" had some influence. Deor (talk) 23:37, 5 May 2012 (UTC)
 * Look further at that page: "Whether a vowel letter is pronounced "long" in English (/eɪ, iː, aɪ, oʊ, juː/ ay, ee, eye, oh, you) or "short" (/æ, ɛ, ɪ, ɒ, ʌ/ a, e, i, o, u) is unrelated to the length of the original Latin or Greek vowel." and "If any other syllable [other than the penultimate] is stressed, it is closed and the vowel is short." An example is Socrates, where the first o is long in Latin and Greek but short in English. So /ˈvaɪtə/, yes, but you would expect vitamin to be /ˈvɪtəmɪn/. At various times, however, people have tried to reinstate "proper Latin vowel quantity", sometimes with success. I suspect the American pronunciation is an example of that. You may want to have a look at Fowler's entry on "false quantity". Lesgles (talk) 20:35, 7 May 2012 (UTC)
 * Interesting, so it could be hypercorrection?--John (talk) 22:33, 9 May 2012 (UTC)

Temporary change in sexual orientation
(This was inspired by a question on the humanities desk.) I believe that as of now, there's no way to permanently change a person's sexual orientation. However, suppose I'm gay and wanted to be straight. Would there be any drugs I could take to decrease my attraction to males, and increase my attraction to females? I know there are drugs that can decrease/increase libido, but how about selectively changing one's libido?

Note that this is purely out of curiosity. I'm not gay, and even if I were, I wouldn't inject random chemicals into myself. --140.180.5.49 (talk) 19:01, 5 May 2012 (UTC)
 * No. there is no such drugs. SexoPharmachology is only about ADULT Physiological arousal --- at it's Sexual context. this arousal is achieved Via Sexuali-attracting Stimuli (which could even be a "Sex-doll" if u have a Philia for it), and what is considered Sexual Stimuli is DICTATED (!), by the very stubborn NeuroPsychological mechanism of "Sexual orientation". therefor, changes, even temporal, are unlikely to occur. Blessings. Babaluba100 (talk) 19:13, 5 May 2012 (UTC)
 * See gay bomb. The reverse has been tried by the military. It didn't work, of course. - Running On Brains (talk) 19:33, 5 May 2012 (UTC)

Hormone replacement drugs used by people who have sex changes alter many aspects of their brain and thinking. The stereotypes that are factually based for men and women's cognition, such as women are better at having 5 conversations at one time, and men are better at reverse parking, actually reverse themselves as those drugs take effect. A man who is taking women's hormones actually loses his ability to reverse park and can concentrate on cooking whilst chatting on the telephone (according to studies I've seen). Sexual drive is effected by drugs and hormones, steroids, menopause and so on, so messing with hormones is going to have some effect, how pronounced will vary from patient to patient.

Permanent changes would be the result of permanent changes to the hormones in a persons body. Castrati are people who have had permanent changes to their bodies and hormone levels, with corresponding changes to libido, and injuries to critical systems like the pituitary gland will wreak havoc as well. Penyulap  ☏  21:00, 5 May 2012 (UTC)


 * Once an adult, hormones can no longer change your sexual orientation. They could only have an affect while the brain is developing.  Thus, from before birth to a bit after puberty, with earlier exposures more effective. StuRat (talk) 23:01, 5 May 2012 (UTC)


 * in addition to sturat: the in-development affect of hormones is more on gender identity, and seems to influence on Sexual orientation more INDIRECTLY, than directly..


 * The flaw in the OP's premise is the notion that it's either-or, like an on-off switch. Lots of folks are on a sliding scale, and can adopt a "straight" lifestyle if they want to. That's not a "cure", it's just a lifestyle decision. Obviously, someone at or near an extreme end of the sliding scale is not likely to be very successful at trying to be something they're basically not. ←Baseball Bugs What's up, Doc? carrots→ 00:12, 6 May 2012 (UTC)


 * Anyone can adopt a straight lifestyle, but that doesn't mean their attraction to the opposite sex suddenly goes up, or that their attraction to the same sex goes down. I'm asking about actual changes in attraction, not just forced changes in behavior.  --140.180.5.49 (talk) 00:49, 6 May 2012 (UTC)
 * Changes over time are certainly possible. Are you attracted to exactly the same type of person now as you were 10 or 20 years ago? ←Baseball Bugs What's up, Doc? carrots→ 18:23, 6 May 2012 (UTC)
 * I don't think that's a very accurate analogy. Sexual drives are deeply hard-wired and while there's certainly social pieces to all of this, it's not at all accurate to say that because people's preferences change with age their sexual orientation might too. Shadowjams (talk) 04:08, 8 May 2012 (UTC)
 * Denial is a very powerful psychological force. While the underlying orientation will not change, individuals can alter their thinking to the point where they believe they have changed orientation. Repressing these feelings can be quite detrimental to the psyche, though. &mdash;  The Hand That Feeds You :Bite 22:05, 8 May 2012 (UTC)
 * I don't see why orientation couldn't change to some degree - certainly there is enough anecdotal evidence of people switching over even in their 70s. The explanation that they were "really in denial all that time" seems very strained to me.  Likewise, I haven't seen evidence that the "gay bomb" doesn't work.  If I had to guess I would think that the relative preferences of bisexuals would be much easier to change that those who were strongly partial to one or the other; certainly they do vary to some degree. Wnt (talk) 00:10, 9 May 2012 (UTC)

Neutrons
Since neutrons can pentrate most things including quite a few feet of concrete, how is it possible to make a neutron reflector?--92.25.96.129 (talk) 21:10, 5 May 2012 (UTC)


 * Your text got a little bit garbled there, How you make it would depend upon it's purpose, if it is for a science experiment on a lab desk or as part of a building, or part of an environmental measurement device. Penyulap  ☏  21:18, 5 May 2012 (UTC)


 * (corrected initial post) I have no intention of making anything, I just wondered how neutrons can be refelected when they pass thro most things?--92.25.96.129 (talk) 21:29, 5 May 2012 (UTC)


 * Different substances have different scattering cross sections with neutrons of various energies. When that cross section is large, elastic scattering is more likely to occur. 71.215.84.127 (talk) 22:26, 5 May 2012 (UTC)

pearsons r and F TEST
When computing an F test and Person's r, if significance testing is conducted for both tests using the same set of data, why is it possible to achieve contrary results? why we are getting different results — Preceding unsigned comment added by 206.54.215.76 (talk) 23:03, 5 May 2012 (UTC)
 * The F test is sensitive to the number of degrees of freedom. Describe your data and model in more detail to get a better answer. 71.215.84.127 (talk) 23:10, 5 May 2012 (UTC)
 * Can you explain exactly what it is you are doing? Pearson's R isn't a statistical test, it's a measure of correlation... --Tango (talk) 23:21, 5 May 2012 (UTC)
 * Isn't r squared equal to variance accounted for? An F test is the ratio of  explained variance to unexplained variance, or the ratio of between-group to within-group variance, per the F test article. Edison (talk) 02:33, 6 May 2012 (UTC)