Wikipedia:Reference desk/Archives/Science/2012 July 31
Science desk | ||
---|---|---|
< July 30 | << Jun | July | Aug >> | August 1 > |
Welcome to the Wikipedia Science Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
July 31
[edit]Very specific spider question
[edit]I guess you can phrase this question in one of two ways: What is the smallest spider, in proportion to the web it weaves? OR What spider produces the largest web, in proportion to its own size? Evanh2008 (talk|contribs) 03:23, 31 July 2012 (UTC)
- Apparently, it's the Darwin's bark spider [1] [2]. 203.27.72.5 (talk) 03:29, 31 July 2012 (UTC)
- Cool! Thanks! Evanh2008 (talk|contribs) 04:03, 31 July 2012 (UTC)
Cells Experiment
[edit]Cheek Cell — Preceding unsigned comment added by 175.140.182.174 (talk) 03:39, 31 July 2012 (UTC)
- There are many such in the cheeks. Did you have a question about them? —SeekingAnswers (reply) 03:45, 31 July 2012 (UTC)
- Doctors may also be called upon to remove cells from the cheeks. (Sorry for being cheeky.) StuRat (talk) 05:07, 31 July 2012 (UTC)
- One of my fairly early biology lessons involved removing cheek cells from the inside of one's own (face!) cheeks (with a sterile spatula or suchlike, I think), and then viewing them under a microscope to confirm that one's cheeks were indeed made up of cells. I suspect this question is somehow related to such an experiment. --Demiurge1000 (talk) 08:25, 31 July 2012 (UTC)
- Ha! That's one great leap of logic there Demiurge. You got all that out of "Cell Experiment Cheek Cell"? — Preceding unsigned comment added by 101.172.42.165 (talk) 09:10, 31 July 2012 (UTC)
- Yep, but I just can't work out what the actual question is. Perhaps there isn't one. --Demiurge1000 (talk) 16:46, 1 August 2012 (UTC)
What Do Women and Gay Men Find Attractive in Men?
[edit]This is a serious question. I am a straight male but I was wondering what others who are attracted to men see in men. Most men are hairy, stinky, and overweight/obese. Also, a lot of men are very aggressive. All of these seem to be serious turn-offs, so I'm wondering if there have been any scientific studies done showing what people find sexually attractive about men? Futurist110 (talk) 06:04, 31 July 2012 (UTC)
- Muscles are attractive to many, as is height, and a deep voice. And even the attributes you list as unattractive are desired by some. StuRat (talk) 06:11, 31 July 2012 (UTC)
- I don't think that anyone finds stinkiness attractive. Futurist110 (talk) 06:17, 31 July 2012 (UTC)
- They do. There is a Greek dance where the men put handkerchiefs in their armpits to get them good and sweaty, then present them to their woman, who sniff it approvingly. It's only our culture where body odor is considered unpleasant (excluding the French, of course). :-) StuRat (talk) 06:33, 31 July 2012 (UTC)
- Yep stinkiness is attractive. LOL. Futurist110, you underestimate the range of human fetishes. Smell is actually very important in human sexuality - pheromones. See
- "Sexy" Smells Different for Gay, Straight Men, Study Says (National Geographic)
- Pheromone attracts straight women and gay men (New Scientist)
- Do Pheromones Play a Role In Our Sex Lives? (Scientific American)
- How the Nose Can Control Human Sexuality (Mental Floss Magazine)
- As for the visual and behavioral stimuli, the same things men find attractive in women: lots of different stuff. Some men like blondes, some brunettes, some like them scrawny, some like them big, some like them assertive, some like them shy, adventurous/conservative, smart/innocent, etc. I bet if I asked you what you find attractive in women your list will be very different from the next guy. Except the criteria will be different for men of course.
- If it consoles you, "gold star" (exclusively homosexual) gay men can't understand why men find women attractive as well. I can appreciate feminine beauty quite easily, but there's zero sexual attraction. Same thing with smell. Women smell pleasant enough, male sweat however is sexy. See Sexual attraction and Neuroscience and sexual orientation.-- OBSIDIAN†SOUL 06:41, 31 July 2012 (UTC)
- What school did you go to where they gave out gold stars for that ? :-) StuRat (talk) 06:44, 31 July 2012 (UTC)
- Not a school. The Gay Mafia! lulz. They send it by mail, and you get discounts at gyms and salons with it.-- OBSIDIAN†SOUL 06:54, 31 July 2012 (UTC)
- Just curious--are you into bears? Futurist110 (talk) 07:22, 31 July 2012 (UTC)
- LOL, that's a bit personal. If you're asking if body hair or size also factors into attraction. Yes. As I said, different criteria. In the same way that men have idealized archetypes of women they find attractive; so do women and gay men. i.e. the criteria is not just "must have penis". And body hair and size are some of those criteria in the same way that breasts and long legs are for straight men.
- I do notice something though. Gay men tend to be more into the idealized rugged alpha male. While women tend to be more into bishōnen-types (the success of boy bands for example) or supermodel-sh guys (what one blogger describes as the Johnny Depp factor). Not always, but often enough to be notable. Some researches link this with the economic environment and the perceived parenting skills. i.e. Women in richer countries tend to prefer the "feminized" men; while women in poorer or more dangerous places tend to be attracted to the macho men. I guess the "dangerous" part of the latter applies to gay men as well, even in rich countries. Others just link it with an innate finickiness in each gender.
- Why women now prefer Johnny Depp to Sean Connery (The Telegraph)
- Why Women Don't Want Macho Men (The Wall Street Journal)
- Gay Men Prefer Masculine-Faced Men, Study Suggests (Science Daily)
- To quote from the last article:
- "Our work showed that gay men found highly masculine male faces to be significantly more attractive than feminine male faces. Also, the types of male faces that gay men found attractive generally did not mirror the types of faces that straight women found attractive on average," says Glassenberg. "Men, gay or straight, prefer high sexual dimorphism in the faces of the sex that they are attracted to. Gay men and straight men did not agree on the types of male faces they considered attractive."
- To quote from the last article:
- Weird, huh. :P-- OBSIDIAN†SOUL 09:06, 31 July 2012 (UTC)
- Let's be very clear that the 'attractive' sort of smell is typically a fresh sweat smell, rather than a stale sweat smell. So, if you want to attract women, you do typically need to wash regularly. If you're a particularly sweaty person, or going to a particularly sweaty situation, antiperspirant will reduce the unpleasant dampness while not completely impeding fresh sweat. Spraying yourself with throat-catchingly stinky bodyspray/aftershave is a typical teenage mistake that few find actually attractive, and will mask the useful smells. Going without a shower and then spraying with boy-perfume is just unpleasant. 86.161.208.94 (talk) 14:25, 31 July 2012 (UTC)
- Word.-- OBSIDIAN†SOUL 15:18, 31 July 2012 (UTC)
- My subjective experience strongly matches the notion that response to pheromones determines sexual orientation; moreover, it is my personal belief that exposure to pheromones continues to reshape notions of sexual attractiveness throughout life (such as tolerance for gray hair or different ethnicity). I would very much like to see a study of whether exposure to concentrated pheromones can help those with sexual disorders, most notably pedophilia, to adjust and adapt their desires to more practicable goals. But I'm unaware of any such research, and don't have the appropriate position/training to conduct it. Wnt (talk) 06:14, 1 August 2012 (UTC)
- I don't think pheromones have much effect in humans. We are mostly attracted based on visual and audio stimuli. If not, we wouldn't get turned on by magazine pics, porno flicks, and phone sex, but would be attracted to ugly people with the right pheromones. StuRat (talk) 06:20, 1 August 2012 (UTC)
- My crazy notion is that the pheromone is not so much a signal to cause immediate sexual attraction as a signal that teaches sexually attractive characteristics (sort of like a positive-reinforcement electrode in a brain, which is not so much a source of direct pleasure as a means of reinforcing changes in behavior). Generally speaking, sexually attractive features tend to be average in nature; this could be seen as the aggregate outcome of someone being exposed to pheromones in the presence of many different individuals. My anecdotal observation was that exposure to the intense pheromones of a colony of breeding mice for 10-15 minutes made me start to have a quite distracting degree of sexual thought about two unquestionably unattractive women I worked with there at different times (I mean, one of them had severe acne scarring, and the other was of an ethnic group which at that time I perceived to be ugly), and while much of the effect wore off within an hour after leaving the environment, after several exposures they continued to seem moderately attractive to me even years later. Wnt (talk) 13:15, 1 August 2012 (UTC)
- And don't forget, to put it scientifically, that many are attracted to the twig and berries. StuRat (talk) 06:35, 31 July 2012 (UTC)
- Twig and berries? Futurist110 (talk) 07:49, 31 July 2012 (UTC)
- This pic should make my meaning explicit: [3]. :-) StuRat (talk) 08:25, 31 July 2012 (UTC)
- Oh yes, the package. Yeah, that's the one thing that most women find attractive in men. Futurist110 (talk) 19:13, 31 July 2012 (UTC)
- Also, consider the things men don't do, which many find unattractive in women, like menstruation/PMS/menopause/bloating/cramps and crying (well, most men don't). StuRat (talk) 06:38, 31 July 2012 (UTC)
- Women aren't too keen on most of those things either. As to the things men do that women generally don't find attractive, I don't even know where to start. ←Baseball Bugs What's up, Doc? carrots→ 12:16, 31 July 2012 (UTC)
- Sexual attraction has evolved such that in the absense of natural selection pressure leading to survival of the fittest, sexual selection will prevent degeneration. Therefore women find those features attractive that indicate fitness, men find those features attactive that indicate fertility. Count Iblis (talk) 16:20, 31 July 2012 (UTC)
- I'm going right back to the start, and calling a huge "Citation required" on "Most men are hairy, stinky, and overweight/obese". -- ♬ Jack of Oz ♬ [your turn] 07:54, 1 August 2012 (UTC)
- The OP is from the USA where;
- Thanks for that. So, if the last 2 factors, which are common to all men, are the turn-offs (? turns-off) the OP claims them to be, why would women be any less repelled by them than other men are? -- ♬ Jack of Oz ♬ [your turn] 10:49, 1 August 2012 (UTC)
- As I thought. No response. Ergo, the OP's premise is demolished. -- ♬ Jack of Oz ♬ [your turn] 11:50, 3 August 2012 (UTC)
You made the distinction between straight and gay men in your title, but not straight and gay women. It should be; "What Do Straight Women and Gay Men Find Attractive in Men?" 92.233.64.26 (talk) 10:35, 1 August 2012 (UTC)
- You also forgot bisexual women, men who have sex with men, men who rate 2 on the Kinsey scale, transgendered people and hermaphrodites. 101.172.42.143 (talk) 11:15, 1 August 2012 (UTC)
Does Occam's Razor Make the Existence of Gods Unlikely?
[edit]- Occam's Razor = The hypothesis/theory that makes the fewest assumptions is the best.
- Hypothesis 1 = Since everything is (or can/will be) explained by natural/scientific forces, God doesn't exist.
- Hypothesis 2 = There is an invisible, undetectable, walk-through, see-through, very powerful immortal being out there.
Futurist110 (talk) 07:35, 31 July 2012 (UTC)
- Well, Occam's Razor is that the simplest scientific hypothesis which explains everything should be used, and, while "God did it" is a very simple explanation for everything, it's by no means scientific. Since God isn't science, Occam's Razor doesn't apply. StuRat (talk) 08:43, 31 July 2012 (UTC)
- (EC) the application of Occam's Razor is mentioned in the article you linked and also briefly mentioned in Existence of God and also given how often it's something that's brought up in plenty of other sources e.g. [4] [5] (there must be more total discussion then the entire RD archives combined). It may be helpful if you explain what parts are still confusing you. Nil Einne (talk) 08:50, 31 July 2012 (UTC)
- Just looking at the original wording "that entities be not multiplied save of necessity" tends to suggest the answer to the question is yes. --TammyMoet (talk) 09:47, 31 July 2012 (UTC)
- Before reaching any conclusions, define "God". ←Baseball Bugs What's up, Doc? carrots→ 12:13, 31 July 2012 (UTC)
- Occam's razor is a principle for deciding between competing theories. It doesn't actually say anything about the likelihood of those theories. --Tango (talk) 12:25, 31 July 2012 (UTC)
- Actually, I was under the impression that Occam's razor does try to determine which theory is more likely based on our current knowledge and concepts. Futurist110 (talk) 00:21, 1 August 2012 (UTC)
- Read our article - there is nothing about likelihood. It's just about what theory one should chose, not which is more likely to be true. --Tango (talk) 00:35, 1 August 2012 (UTC)
- Occam's Razor itself is just one model (admittedly, a very widely adopted model, but still only one model) of how to think about things. It is not some Eternal Truth Set in Stone for All Time. You don't use it, for example, to work out which of those two cute girls you prefer. -- ♬ Jack of Oz ♬ [your turn] 02:51, 1 August 2012 (UTC)
- There's a difference between likelihood and truth. For instance, many scientists considered the existence of the Higgs boson to be very likely, but it wasn't proven as truth until this year. Likewise, it is very likely right now that Besse Cooper will reach age 116, but it is not truth until she actually does reach age 116 later this month. Occam's razor deals with likelihood, not absolute truth/fact. http://math.ucr.edu/home/baez/physics/General/occam.html And actually, I do use a variant of Occam's razor to determine which of two cute girls I prefer. If I know a lot about one cute girl but I know very little about another cute girl other than her name, I would prefer to date the first cute girl since I think that she would be a better match for me based on my current knowledge (which could obviously change in the future). Also, with the first cute girl, there would be less odds of me later finding out something very unappealing about her than with the second cute girl about whom I know much less about. Also, excluding the hair and the eyebrows, I generally tend to find girls more attractive by the frequency and amount of room on their bodies that they use a razor on. ;) Futurist110 (talk) 02:09, 2 August 2012 (UTC)
- Occam's Razor itself is just one model (admittedly, a very widely adopted model, but still only one model) of how to think about things. It is not some Eternal Truth Set in Stone for All Time. You don't use it, for example, to work out which of those two cute girls you prefer. -- ♬ Jack of Oz ♬ [your turn] 02:51, 1 August 2012 (UTC)
- Read our article - there is nothing about likelihood. It's just about what theory one should chose, not which is more likely to be true. --Tango (talk) 00:35, 1 August 2012 (UTC)
- Actually, I was under the impression that Occam's razor does try to determine which theory is more likely based on our current knowledge and concepts. Futurist110 (talk) 00:21, 1 August 2012 (UTC)
- The problem with Occam's razor is that 1. a lot of real-world things are pretty complicated, and 2. it can be quite arbitrary to decide which of two theories is the most simple. So let's say our two theories are, "there is a God" and "there is not a God." Which of those is simplest? Superficially you can count up the number of Gods in each and proclaim "not a God" the winner, but that's naive. Adding a God radically simplifies certain aspects of cosmology, biology, and morality. Getting rid of the God requires also developing elaborate and complex theories of where we came from, why the universe exists rather than doesn't, and so forth. It's not at all clear to me which is simpler — they're both pretty complex, when you start hashing out the implications. Even then, Occam's razor is, at best, a heuristic — a philosophical short-cut — and not a proof or even theory whatsoever. So I really don't see it getting one out of this sort of bind with any kind of straightforward action, if one is intellectually honest. (I say this as a subscriber to the no-omniscient-God theory, but for different reasons.) --Mr.98 (talk) 13:06, 31 July 2012 (UTC)
- Adding a god doesn't really simplify anything - the question "Where did the universe come from?" just becomes "Where did the god come from?" and you haven't actually made any progress. You've just shifted the problem back a step. --Tango (talk) 19:55, 31 July 2012 (UTC)
Very poorly worded - I would say that everyday more and more scientists are saying things like Hypothesis #2: "There is an invisible, undetectable, walk-through, see-through, very powerful immortal (being[something]) out there." Aand less and less are saying things like Hypothesis #1 because they realize that it might be immpossible for them to actually "explain everything". 165.212.189.187 (talk) 13:29, 31 July 2012 (UTC)
- Furthermore, to say everything WILL BE explained by natural/scientific forces is the same as "believing in God" i.e. it requires faith.165.212.189.187 (talk) 18:21, 31 July 2012 (UTC)
- It's not the same thing. One is faith in extrapolation of an known and measurable method, the other is a faith in the existence of a supernatural entity. Not all faith has equivalent truth status. (I can have faith that someone will probably be elected as the US President in November. It is not the same thing as me having faith that the world is going to end in 2012.) --Mr.98 (talk) 19:37, 31 July 2012 (UTC)
- define super-natural and entity. all faith is based on probability. there are risks of being wrong in each example. i have faith that one day i will throw a stack of papers in the air and they will disperse then come back together and land on the ground in the same exact ordered stack that i threw up.68.83.98.40 (talk) 06:10, 1 August 2012 (UTC)
- Exactly. Also, I think I saw or read somewhere that 93% of scientists are skeptical about the existence of gods. I'll need to find the source, though. Futurist110 (talk) 00:24, 1 August 2012 (UTC)
- That sounds a little high. Scientists are certainly less likely to be believers than the general population, but I doubt it is so overwhelming, especially in the less physical sciences (religion tends to contradict physics quite a lot, it doesn't contradict biology anywhere near as much). There is also a general trend for better educated people to be less religious, and scientists are very well educated (see Religiosity and intelligence), so pulling out an effect that is purely sure to them being scientists may actually be quite difficult. --Tango (talk) 00:35, 1 August 2012 (UTC)
- Why do you say religion contradicts physics more than it does biology? 203.27.72.5 (talk) 02:32, 1 August 2012 (UTC)
- I think the issue is that it's difficult to be scientifically curious about the very core laws of the universe, as a physicist is, while accepting on faith that the very core workings of the universe are governed by an active god who you can never hope to fully understand. There's less difficulty accepting the principles of a more specialized field like biology while maintaining that god is what's going on under the hood. While you most often hear about religious fundamentalists denying evolution, I think it's safe to say that most scientists who believe in god don't take the bible (or whatever religious text) that literally. Rckrone (talk) 04:58, 1 August 2012 (UTC)
- Well not all of physics deals with "the very core workings of the universe". There's a lot of areas like ballistics and fluid dynamics. And not all religions even have a concept of God, let alone an active one who cannot be understood (Buddhism, some forms of Hinduism, Scientology). In the USA anyway, as I understand it, the traditional battleground in the war of science vs religion was the biology classroom. You don't really hear of fundamentalist types refuting Einstein's theory of relativity, or arguing that Newton's Laws of Motion shouldn't be taught to their kids. But I don't think that it makes much sense to generalize and say that religion in and of itself conflicts more with physics than biology or vica versa. There are religions that were specifically designed not to conflict with science. 203.27.72.5 (talk) 07:30, 1 August 2012 (UTC)
- I think that's more a consequence of a lack of 20th century physics in the classroom until your second or third year of university. You can learn about the animal kingdom a lot earlier in life than you can learn about quantum mechanics. Frankly I agree with Rckrone, that biology is the easier pill to swallow; I don't see why evolution is objectionable. From a purely theological point of view, I do not understand why the supposition of an omnipotent deity precludes the possibility that said deity effected theistic evolution. Trying to invalidate religious tenets on scientific grounds is as easy as invalidating scientific principles on faith-based grounds, and the sheer absurdity of that artificial dilemma seems to be lost on most people. BigNate37(T) 07:47, 1 August 2012 (UTC)
- Well not all of physics deals with "the very core workings of the universe". There's a lot of areas like ballistics and fluid dynamics. And not all religions even have a concept of God, let alone an active one who cannot be understood (Buddhism, some forms of Hinduism, Scientology). In the USA anyway, as I understand it, the traditional battleground in the war of science vs religion was the biology classroom. You don't really hear of fundamentalist types refuting Einstein's theory of relativity, or arguing that Newton's Laws of Motion shouldn't be taught to their kids. But I don't think that it makes much sense to generalize and say that religion in and of itself conflicts more with physics than biology or vica versa. There are religions that were specifically designed not to conflict with science. 203.27.72.5 (talk) 07:30, 1 August 2012 (UTC)
- I think the issue is that it's difficult to be scientifically curious about the very core laws of the universe, as a physicist is, while accepting on faith that the very core workings of the universe are governed by an active god who you can never hope to fully understand. There's less difficulty accepting the principles of a more specialized field like biology while maintaining that god is what's going on under the hood. While you most often hear about religious fundamentalists denying evolution, I think it's safe to say that most scientists who believe in god don't take the bible (or whatever religious text) that literally. Rckrone (talk) 04:58, 1 August 2012 (UTC)
- Why do you say religion contradicts physics more than it does biology? 203.27.72.5 (talk) 02:32, 1 August 2012 (UTC)
- That sounds a little high. Scientists are certainly less likely to be believers than the general population, but I doubt it is so overwhelming, especially in the less physical sciences (religion tends to contradict physics quite a lot, it doesn't contradict biology anywhere near as much). There is also a general trend for better educated people to be less religious, and scientists are very well educated (see Religiosity and intelligence), so pulling out an effect that is purely sure to them being scientists may actually be quite difficult. --Tango (talk) 00:35, 1 August 2012 (UTC)
- It's not the same thing. One is faith in extrapolation of an known and measurable method, the other is a faith in the existence of a supernatural entity. Not all faith has equivalent truth status. (I can have faith that someone will probably be elected as the US President in November. It is not the same thing as me having faith that the world is going to end in 2012.) --Mr.98 (talk) 19:37, 31 July 2012 (UTC)
- Furthermore, to say everything WILL BE explained by natural/scientific forces is the same as "believing in God" i.e. it requires faith.165.212.189.187 (talk) 18:21, 31 July 2012 (UTC)
http://www.stephenjaygould.org/ctrl/news/file002.html - Here's the source about 93% of scientists being religious skeptics. For the record, though, even a biologist would probably have a basic grasp of physics and how it works from college. Futurist110 (talk) 07:00, 1 August 2012 (UTC)
- In the US, maybe. In the UK, you can be a professional biologist without haven't studied physics past age 16. We specialise a lot earlier in the UK. --Tango (talk) 11:39, 1 August 2012 (UTC)
- Oh, all right. Yeah here in the U.S., at least among science professors and teachers I found more skeptics than believers among those with whom I talked about religion. For the record, it's very possible to have a belief in gods that does not conflict with science (including physics), but these gods would need to be a Deistic-kind of gods in the sense of not interfering in our lives or our (pre-afterlife) affairs. Futurist110 (talk) 02:17, 2 August 2012 (UTC)
- Why??68.83.98.40 (talk) 03:04, 2 August 2012 (UTC)
- Why what? Futurist110 (talk) 03:41, 2 August 2012 (UTC)
- ...these gods would need to be a Deistic-kind of gods in the sense of not interfering in our lives or our (pre-afterlife) affairs. Oh, I guess you mean like how gravity doesnt interfere w our lives.68.83.98.40 (talk) 04:36, 2 August 2012 (UTC)
- God doesn't have to be deistic, but Deism is the easiest spiritual belief to coexist with a scientific mindset. In all seriousness, the Flying Spaghetti Monster is also perfectly consistent with science. You assume either that God does not interfere in our experiences, or that we can't tell. There is also secret option 3, which is to assume we can tell, and that everyone else is denying the obvious, even though you have no understanding of science to begin with. Someguy1221 (talk) 04:50, 2 August 2012 (UTC)
- ...these gods would need to be a Deistic-kind of gods in the sense of not interfering in our lives or our (pre-afterlife) affairs. Oh, I guess you mean like how gravity doesnt interfere w our lives.68.83.98.40 (talk) 04:36, 2 August 2012 (UTC)
- Why what? Futurist110 (talk) 03:41, 2 August 2012 (UTC)
- Why??68.83.98.40 (talk) 03:04, 2 August 2012 (UTC)
- Oh, all right. Yeah here in the U.S., at least among science professors and teachers I found more skeptics than believers among those with whom I talked about religion. For the record, it's very possible to have a belief in gods that does not conflict with science (including physics), but these gods would need to be a Deistic-kind of gods in the sense of not interfering in our lives or our (pre-afterlife) affairs. Futurist110 (talk) 02:17, 2 August 2012 (UTC)
Please continue your massive walls of opinion and debate some where more appropriate. 1.125.255.254 (talk) 09:56, 2 August 2012 (UTC) |
---|
The following discussion has been closed. Please do not modify it. |
|
- Well damn, I really like massive walls of debate in questions about the disproving of god...next time I'll just go with a "I disagree." Anyways, if anyone cares to respond in anyway, please do so on my talk page:-)Phoenixia1177 (talk) 10:14, 2 August 2012 (UTC)
- I never claimed that Occam's Razor disproves God or gods, only that it makes his/her/its/their existence unlikely. Futurist110 (talk) 22:06, 3 August 2012 (UTC)
Why would the heat shield fly forward and not go back into the parachute?
[edit]I'm talking about time 3:03 of the video in the Landing section of Curiosity rover. This big thing is hurtling toward the surface, and even if for a moment pyrotechnics on board blow it forward, I'm not seeing how that big disc, once it's free of the payload and therefore much lower mass by itself, but essentially a big frisbee, isn't getting thrown back by the wind resistance (even if Mars' atmosphere is really thin, the thing's going incredibly fast) and into that very huge parachute that is right behind it. Of all the parts of that video, that disc nicely speeding out and away in front of the craft is the strangest part to me. Can someone explain why it's acceptable to believe that that disc would behave as it does in the video from 3:03 to about 3:10 and not flit back into the parachute? 20.137.18.53 (talk) 15:37, 31 July 2012 (UTC)
- (For the benefit of others, this is the video in question: [6] AndyTheGrump (talk) 15:45, 31 July 2012 (UTC) )
- The parachute attached to the lander is causing it to decelerate. Once the heat shield detaches from the lander, it is no longer decelerating with the lander, so it falls faster. — Preceding unsigned comment added by 148.177.1.210 (talk) 15:50, 31 July 2012 (UTC)
- (ec)The huge parachute is slowing down the lander much more rapidly than the released heat shield is slowing down. Nothing is moving "back" or upwards - the downward movement of different pieces are just slowing at different rates. Roger (talk) 15:50, 31 July 2012 (UTC)
- Even if you ignore the parachute, the explosive charge that removes the shield will push in all directions, so the probe is pushed up (i.e. it's rate of descent is slowed) and the plate is pushed down (it's rate of descent is accelerated). Only if the plate was at or very close to terminal velocity before the charge detonated would it then slow down and make contact with the probe again. Also, the shield is designed to be aerodynamic, so it will have a higher terminal velocity than the probe, which is not particularly aerodynamic. Even without the parachute the probe would slow considerably once it was outside the eddy currents in the wake of the shield. 203.27.72.5 (talk) 23:25, 31 July 2012 (UTC)
- The heat shield isn't supposed to be aerodynamic - it's entire purpose is to slow the craft down with air resistance (while not allowing it to burn up). --Tango (talk) 00:39, 1 August 2012 (UTC)
- The craft still has a far lower drag coefficient with it on than with it off. It might not be designed to cut through the air like the nose of a rocket, but it is designed to be at least aerodynamic enough to maintain stability. 203.27.72.5 (talk) 02:10, 1 August 2012 (UTC)
- The heat shield isn't supposed to be aerodynamic - it's entire purpose is to slow the craft down with air resistance (while not allowing it to burn up). --Tango (talk) 00:39, 1 August 2012 (UTC)
- Even if you ignore the parachute, the explosive charge that removes the shield will push in all directions, so the probe is pushed up (i.e. it's rate of descent is slowed) and the plate is pushed down (it's rate of descent is accelerated). Only if the plate was at or very close to terminal velocity before the charge detonated would it then slow down and make contact with the probe again. Also, the shield is designed to be aerodynamic, so it will have a higher terminal velocity than the probe, which is not particularly aerodynamic. Even without the parachute the probe would slow considerably once it was outside the eddy currents in the wake of the shield. 203.27.72.5 (talk) 23:25, 31 July 2012 (UTC)
Keep in mind that at the point of separation, the two bodies have the same speed. So any deceleration (parachute) applied to the following body will necessarily separate it from the accelerated (explosively jettisoned) leading body. μηδείς (talk) 03:16, 2 August 2012 (UTC)
How much space and time is required to compute a simple weather model?
[edit]I recently ran into the problem where computing 23 recurrence plots (for a time process of about 8000 intervals) took a prohibitive amount of time and space (because I had to deal with 23 8000x8000 matrices). This made me wonder, how much time and space is required for simpler weather models? I imagine a simple resolution of 5000 intervals for experiment would require at least (5000)^4 * 32 bytes = 18 million GB of disk space. Then there are other multidimensional computational problems involving tensors, such as stress calculations.
Also, how are 9-dimensional, 11-dimensional string theory models processed for a simple particle-particle interaction ? 76.104.28.221 (talk) 15:39, 31 July 2012 (UTC)
- I don't see where your numbers come from, especially that fourth power. In a weather simulation, nodes only interact directly with their neighbors, so the memory demand is only quadratic as a function of the spatial resolution. Weather simulations are certainly demanding and are generally run on supercomputers. However the range of useful models is so broad that the term "simple weather model" does not have any concrete meaning. Looie496 (talk) 16:10, 31 July 2012 (UTC)
- Typically weather models have time steps of a few minutes or even seconds, but only produce output every 1-6 hours (depending on the application). This greatly reduces the amount of disk space needed. With parallel-processing to reduce the load on individual processors, it's quite easy to run weather models in a timely fashion. Also 8000x8000 is much larger than any domains I've seen used, what sort of dimensions/resolution are you attempting?
- As a side note, I can run moderate-resolution real-time forecasts using the Weather Research and Forecasting model and its associated data assimilation system (WRFDA) on my laptop (8GB RAM, dual-core 2.2GHz processor). You can try it if you have a Macintosh or Linux system, it's free, open-source, and public domain, and the online tutorial makes it quite easy, IMHO. -RunningOnBrains(talk) 16:25, 31 July 2012 (UTC)
- To expound further, I'll look at a typical model run: the North American Mesoscale Model (this is a regional model; most global models these days are spectral models (unlikely red link, I'll have to remedy that) which is more complicated as far as calculating space needed). The NAM is currently run at a resolution of 1337x1165x60 (sources; you need an account but it's free to sign up: [7][8]) with output every 3 hours out to 84 hours, which means our total resolution (with time included) is 1337x1165x60x28. To complicate this calculation a bit further, they use an Arakawa E grid for the diagnostic equations, so in reality the resolution is only 669x583x60x28. This means that for each output variable (assuming 32-bit floating-point numbers), you need only 2.6 GB of space; and I believe the number of vertical levels on the output is reduced, so this number is probably much lower.
- As far as computing power, the NAM is run on 30 nodes of 32 4.7GHz processors (sources; sorry, powerpoints: [9] [10]) and takes only 1669 seconds (about 28 minutes). I hope this info sheds some nice light on the issue for you! -RunningOnBrains(talk) 20:29, 31 July 2012 (UTC)
- Oh I'm running recurrence plots of an 8000-frame time series of Drosophila movement and I'm trying to pick out potential order in their seemingly random movements (velocities); a single experiment might have ~20 tracks. I ran into memory issues quite quickly. This caused me to wonder about weather models, which I imagine run in 4D space, not 2D!
- Also, does the (kind of) coarse spatial resolution cause issues, especially with convergence (or divergence) of a discrete numeric solution from a continuous/analytic solution as resolution is increased? "12 km horizontal resolution and with 1 hour temporal resolution" might be a feat of human computer science achievement, but from a differential equation POV, it does seem kinda coarse. 128.143.1.46 (talk) 22:22, 31 July 2012 (UTC)
- Could you be kind to the clueless and explain this a little more? Am I right to think that you have a two/three?-dimensional position for a labelled fly at each of 8000 time points, and you want to find resemblances between this track anywhere during the time sequence? And you've done this for 20 different flies in the same container? a) are you looking only for when the fly goes through the same exact spot in the same direction twice, or when it moves in the same direction regardless of its position, or when it's at the same spot regardless of direction? b) getting to the point, can't you 'window' this dataset somehow? I mean, this sounds more like a DNA alignment program than a weather forecaster, and that's what they do; you take some frame, maybe 100 time points, and run it against the whole dataset, and repeat with another offset from that a little bit and so forth. But I'm not a bioinformatics person. Wnt (talk) 13:28, 1 August 2012 (UTC)
- The flies are confined to a 2D arena, and I measure the magnitude of velocity and acceleration and other one-dimensional parameters, so I want to find resemblances between similar velocities at anywhere during the time sequence. I would make a recurrence plot for each fly. The time resolution between t and t+1 is at 1/15 of a second. 76.104.28.221 (talk) 21:12, 1 August 2012 (UTC)
- To answer your question about coarse spatial resolution, it is an extremely complicated issue. First off, as I mentioned, the actual timesteps of the calculation are much shorter than the output timesteps (on the order of seconds) because they must meet the CFL condition or the calculations will blow up. The actual outputs are only written to an output file every 1-6 hours because writing the output into an external file takes additional computing time, and no one really needs to see a second-by-second state of the atmosphere except for some research purposes. Second, spatial resolution is kept especially course because A) reducing the spatial resolution means decreasing the time steps as well, per the aforementioned CFL condition, which means that decreasing the grid spacing by half in 3 dimensions increases the computation time by a factor of 16, not 8, and B) in a non-hydrostatic model (i.e. one that explicitly calculates vertical pressure gradients instead of assuming vertical balance; most models these days are non-hydrostatic because it yields much better results at smaller scales) atmospheric convection becomes explicitly resolved at spatial scales approaching a few kilometers. This requires more explanation:
- In models with larger grid spacing, (say, 10+ km) convection is parametrized, i.e. treated heuristically with various calculation rules that aren't necessarily related to the physical equations in the model. As the grid spacing is reduced, convection starts to be explicitly resolved in the model; i.e. the equations of motion lead to actual localized updrafts and downdrafts which cause rain/thunderstorms. However, until the grid spacing gets down to about 0.5 km or less, this convection is not resolved in a physically realistic way, since thunderstorms are only on the order of 10-20km across. When attempting to parameterize convection while it is also being explicitly resolved (in an extremely rough and often non-physical way) it can lead to poor results at these intermediate scales (grid-spacing of 1-10km). For this reason, these smaller-scale models almost always give comparable if not poorer results than those with grid spacings around 12 km.
- As a further tidbit, there are literally dozens of processes that need to be parameterized because they will always be below the spatial scale of even the finest-resolution models. Thinks like boundary layer turbulence, surface roughness and friction, cloud processes, rain/snow/hailfall, snow cover and sea ice, soil moisture, and human processes like chemical emission and land use changes (i.e. farming areas have different albedo, soil moisture, and surface friction at different times of the year) all fit this bill.
- Sorry if this has become overly technical, I will gladly answer any questions to clear up confusion about the above summary. -RunningOnBrains(talk) 20:38, 1 August 2012 (UTC)
Should I trust these kinds of websites?
[edit]I was researching about what were the false assumptions of Bohr's model and why is it accurate despite being, well, wrong, and I reached this: http://www7b.biglobe.ne.jp/~kcy05t/index.html . Well it seems to say that Bohr's model is right, and there was a section down there "reasons why quantum mechanics is wrong" which made me even more suspicious than before. I'd like to know your opinion about this site but aside from that, considering the fact that I still don't know enough about these topics to know why quantum mechanics (or any other highly sophisticated topic) is right(?) in the first place, is it prejudice to dismiss the whole thing just because it contradicts theories that are more widely accepted in the scientific community? I mean at least in this example the website seems to have a lot of content, and at least some mathematical descriptions (not saying that these things are good criteria for good ideas!)--Irrational number (talk) 21:15, 31 July 2012 (UTC)
- It's not wrong to dismiss a theory only because it's rejected by the wider scientific community if you don't know enough about the topic (or don't have the resources) to judge it on its scientific merits. It's impossible to be an expert in all areas, and in the areas where you aren't an expert the best you can do is trust that the people who are experts have done their jobs correctly. When there's consensus among most experts, chances are much higher that they are correct compared to the dissenters. That's not to say that the consensus is never wrong, but when you have to trust in the results of others you should put your money on the best bet. Rckrone (talk) 21:38, 31 July 2012 (UTC)
- (edit conflict)Without analyzing the contents (as I am getting older and forgetting much of my quantum mechanics), anyone who claims to have proved some scientific field "wrong" is just blowing smoke. Science is not a courtroom, where a case can be dismissed on a technicality. Science is evidence for explanations and explanations for evidence, all woven into an intricate, inter-dependent non-contradictory web. If current scientific theories can't explain some isolated observation, either our assumptions about the observation was wrong (see Faster-than-light neutrino anomaly, Pioneer anomaly, or any number of sensational media stories about "new science" which are constantly proving to have mundane explanations) or our theory needs to be tweaked slightly (see Quasar#History_of_observation, Galaxy rotation curve). -RunningOnBrains(talk) 21:56, 31 July 2012 (UTC)
- One of the mose common media cliches is the "Einstein was wrong" headline. It gets dragged out every few years when some new discovery is made and completely misunderstood by the mainstream media. I groan every time I see it. Most recently for that faster then light neutrino story mentioned above. At least now you now get responses like this. Vespine (talk) 22:35, 31 July 2012 (UTC)
- We're not supposed to answer requests for opinions, but as for the other question, the reason quantum theory is considered "right" is because it makes accurate predictions. The Bohr model also made accurate predictions, (and it was the first quantized model of the atom), but modern quantum theory predicts a lot more things a lot more accurately. 203.27.72.5 (talk) 23:11, 31 July 2012 (UTC)
- One of the mose common media cliches is the "Einstein was wrong" headline. It gets dragged out every few years when some new discovery is made and completely misunderstood by the mainstream media. I groan every time I see it. Most recently for that faster then light neutrino story mentioned above. At least now you now get responses like this. Vespine (talk) 22:35, 31 July 2012 (UTC)