Wikipedia:Reference desk/Archives/Science/2009 August 15

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.

August 15

Power of gull bites - any data?

Following on from the question above - are there actually any stats available for how much pressure various gull species can bring to bear with their beaks? I just had a quick look on Google but I couldn't find anything useful. --Kurt Shaped Box (talk) 00:20, 15 August 2009 (UTC)

I feel lazy but you can use the information in this paper which is based on finches but includes various data related to gulls to extrapolate. (M. A. A. van der Meij and R. G. Bout. "Scaling of jaw muscle size and maximal bite force in finches." The Journal of Experimental Biology. 207, 2745-2753. 18 May 2004) Also this person may know the answer if you want to contact him. 152.16.15.144 (talk) 02:07, 15 August 2009 (UTC)

executive chair that has a trigger

anyone having knowledge of such a chair please contact me at [email address removed]. I am 80 years of age and probably well never be able to find this site again.

I also do not buy whatever you may be selling so please do not fill my screen with offers.

the chair is constructed entirely of bentwood and steel by a master maker. when the trigger is touched it flies into peices with enough force to knock more than one person down.

I know the history since WWII and it has never been activated in all these years. after using it since 1995 I was walkig by and strcuk it with my walker. my left shouler was bruied very badly, something hit my right arm between the shouler and elbow with enough force to damage the radial nerve so much that I may never have use of my hand.

your will be appreciated. I —Preceding unsigned comment added by 65.34.15.65 (talk) 18:06, 14 August 2009 (UTC)

I copied this from WP:VPM. --Golbez (talk) 00:39, 15 August 2009 (UTC)

I have removed your email address to prevent you getting spammed. We don't respond by email, so hopefully you will manage to find this site again. --Tango (talk) 00:45, 15 August 2009 (UTC)

Could it have been a support spring that snapped, letting some material fly? Nimur (talk) 00:58, 15 August 2009 (UTC)

One-way rocking chair. Cuddlyable3 (talk) 18:27, 16 August 2009 (UTC)

How does evolution work where sexual selection is minimal?

I’m thinking of insects like bees and ants. The queens mate with a single drone which happens to be nearby. How do possibly beneficial mutations occurring in the colony propagate when sexual selection is minimal? With mayflies, there is a virtual orgy lasting a few hours at the end of their lives. How do beneficial mutations work when indiscriminate sexual activity is the norm? Myles325a (talk) 04:39, 15 August 2009 (UTC)

Through other kinds of natural selection? --Kjoonlee 05:10, 15 August 2009 (UTC)

I think you're thinking of the sort of sexual selection where mammals choose mates that appear healthy and fertile; but simple ability to survive and breed is surely a more fundamental driver of natural selection. Also, I'm no entomologist, but are you certain that the sexual activity you mentioned is truly indiscriminate? Tempshill (talk) 06:38, 15 August 2009 (UTC)

Sexual selection was never thought of as the primary mover of evolution; it was used by Darwin and others in order to explain certain things that don't fit well with natural selection. The case of the eusocial, colony insects doesn't fit into the sexual selection model all that well, but that isn't surprising—sexual selection does not always apply, it is a sub-set of natural selection. --98.217.14.211 (talk) 15:29, 15 August 2009 (UTC)

Kinship selection is at play in populations such as bees and termites in which most workers share the same genes. Imagine Reason (talk) 20:00, 15 August 2009 (UTC)

Remember : The total number of ants in a colony is a red herring. As is the lifespan of individual worker ants. Only the life-cycle of the queen is important, evolution-wise. Consider that ant colonies have "generations" shorter than human generations, and that most ant colonies are reproduced exclusively through sexual reproduction. So really, sex in ant colonies is not "minimal". They reproduce sexually just as much as we do.

(The queen mates with a male ('for life') then she gives birth to a few daughters and a few sons. The fact that she also gives birth to about a zillion sterile workers doesn't matter.) APL (talk) 05:41, 16 August 2009 (UTC)

Nobody said sex was minimal. They said sexual selection was minimal—competition between members of the same species for the right to reproduce. --98.217.14.211 (talk) 18:00, 16 August 2009 (UTC)

Why would it be any less? A queen ant leaves her parent colony to fly around searching for a suitable mate. Male ants similarly leave their parent colonies to fly around searching for a suitable mate. Why would you assume that there's less sexual selection here than with any other insect? APL (talk) 18:37, 16 August 2009 (UTC)

Multiple universe theory proves God exists?

If multiverse theory is true, and every possible universe exists, including many with completely different laws of physics to our own, does this mean that in at least one one of these universes an omnipotent entity (God) capable of moving between universes MUST exist? Incidentally I am an atheist, but I do find the idea of a multiverse plausible. —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 09:11, 15 August 2009 (UTC)

No. --194.197.235.43 (talk) 09:27, 15 August 2009 (UTC)

No is the correct answer. The existence of other universes is metaphysical speculation. It is completely untestable and therefore of zero interest either in explaining things or proving things. On top of which despite being a mainstream Christian (by European standards) I find the idea of God being an entity moving between universes (or moving around at all for that matter) completely absurd. Before you even think about God existing though I suggest you think long and hard about whether you exist and what on earth that means. --BozMo talk 10:54, 15 August 2009 (UTC)

If it is possible to move between them then they aren't really separate universes, in my opinion. But that is semantics, the answer is "no" regardless. I don't know of any multiverse theory (there are several) where different universes have completely different laws of physics, just different fundamental constants and/or different initial conditions and/or different results of random events. --Tango (talk) 11:25, 15 August 2009 (UTC)

And even if they have completely different physical laws, omnipotent concepts of god are logically impossible - as the old "can god make a stone so heavy he cannot lift it?" question illustrates --Stephan Schulz (talk) 11:29, 15 August 2009 (UTC)

Surely it's 'a stone that cannot be lifted by an omnipotent being' that's logically impossible? In any case, such debates have little to do with either physics or the everyday practice of religion. No-one expects their god to go around lifting infinitely heavy rocks, so no-one is bothered by this purely theoretical contradiction. AlexTiefling (talk) 11:39, 15 August 2009 (UTC)

Ex falso quodlibet. Logically, if you have any contradiction in your theory, its inconsistent. But indeed, few people really think about an "omnipotent" god. Usually, they imagine only a very very potent god. Which is why I wrote about "omnipotent concepts of god" (as the original question specified an omnipotent god), not "any god". --Stephan Schulz (talk) 12:22, 15 August 2009 (UTC)

I don't understand the distinction. "God" and "omnipotent being" sound pretty synonymous to me. --Tango (talk) 11:42, 15 August 2009 (UTC)

In a polytheistic context, they're certainly not synonymous. In a monotheistic context, it's substantially irrelevant whether or not they're synonymous. Religious people don't ask if God will create an unliftable rock. They ask 'Lord, will you now restore the Kingdom of Israel?', or 'Which of your Lord's blessings would you deny?'. The idea of interpreting the idea of God in terms of a strict definition of omnipotence has absolutely no resemblance to the idea of God entertained by the typical religious person. There are many criticisms of the 'unliftable rock' problem: If God is omnipotent, why can't he create logical contradictions? If the rock is heavy enough, won't it become a planet/a star/a black hole, such that 'lifting' is a useless concept? This problem no more invalidates the idea of God than the idea of 'the set of all sets that are not members of themselves' invalidates the idea of sets. It's just a juvenile thought-experiment. AlexTiefling (talk) 12:10, 15 August 2009 (UTC)

Sorry, I meant in the context of this discussion. Stephan said "omnipotent concepts of god", so I assumed we were using "god" in a vague Abrahamic sense. There are plenty of alternative definitions of the word. --Tango (talk) 12:27, 15 August 2009 (UTC)

FWIW I think the concept of technically omnipotent is fairly modern (I would hazard 300AD without getting any books down from the top shelf). Of course there are lots of poetic statements in the psalms etc but probably not by people with any concept of what that might mean, just as pre Herodotus the concept of historical statement was dubious. I think "could win any battle" rather than "can win every battle without casualties" or as Stephan put it "very potent" is probably the Abrahamic God. But as Alex has said most people these days are not really there. The question is whether the universe can be understood with reference to a greater being in the same way that a 41 year old lump of flesh can be understood with reference to a person called Stephan. --BozMo talk 15:50, 15 August 2009 (UTC)

AFAIK, Christian and generally Abrahamic theologists have predominantly considered God to be perfect, omniscient and omnipotent in a philosophical sense. The fact that everyday practitioners can't or won't see a problem does not make it disappear. If people have more "modest" requirements and only expect God to be omnipotent in those matters that concern them personally - well, it should at least be pointed out that even this is a very ambitious claim, and that acknowledging some fundamental principles to be independent of God and pre-God moves His image in the wrong direction - towards a giant, ingenious, invisible alien floating somewhere in intergalactic space, subject to the laws of physics and to the occasional headache. --91.148.159.4 (talk) 22:18, 16 August 2009 (UTC)

AFAIK no serious Christian Theologian since Thomas Aquinas has had the view you state is "predominant". Pretty much zip. Sorry. --BozMo talk 17:38, 17 August 2009 (UTC)

Well, you see, the problem is that in this respect, Thomas Aquinas was pretty much unchallenged until secularization in the 19/20th century; and no new view on this has really become predominant and "standard" since then. Sure, in the 20th century lots of theologists have been trying to "fix" these attributes in various ways (it's their job, after all), making some modifications to them in order to save the basic idea; some, such as Charles Hartshorne, have even dared dispute some of them. But, mutatis mutandis, the divine attributes remain mainstream and are normally "rescued" in some way or other, because they are essential to the whole business: a God that has defects and limited capabilities and knowledge is simply less competitive on the market. For "omnipotence" one can check, on Google Books, "Almighty God: a study of the doctrine of divine omnipotence" by Gijsbert van den Brink. For "omniscience" - "God, foreknowledge, and freedom" by John Martin Fischer. For "perfection" - "The untamed God: a philosophical exploration of divine perfection, simplicity and immutability" by Jay Wesley Richards. For all three you can see "The Christian God" by Richard Swinburne and "Philosophical foundations for a Christian worldview" by Moreland and Craig.--91.148.159.4 (talk) 21:25, 17 August 2009 (UTC)

In addition, here are a few specific citations for the divine attributes remaining mainstream: Christian sources - "Handbook of Christian apologetics: hundreds of answers to crucial questions" by Kreeft and Tacelli, p.72; "The God who risks: a theology of providence" by Sanders, p.194 "Reason for the hope within" by Murray, p.83); neutral sources - "A companion to philosophy of religion", by Quinn and Taliaferro, p.22,56, "Philosophical Inquiry: Classic and Contemporary Readings" by Adler and Elgin, p.877. --91.148.159.4 (talk) 22:12, 17 August 2009 (UTC)

I'm a Christian, and I also think the answer to this question is a resounding 'no'. Both the existence of one or more gods, and the existence of one or more alternate universes, are metaphysical speculation. These speculations are entirely independent, and can in principle be made to say whatever an individual speculator wants. Their levels of acceptance depend on their plausibility, and the idea that the one theory is linked to the other seems quite implausible, and certainly has a very low level of acceptance. Ideas of proof and determination don't come into play at all, and I'd question if this is really a 'science' question at all. AlexTiefling (talk) 11:39, 15 August 2009 (UTC)

Modern notions of a multiverse are not metaphysical speculation; they're much more credible than the pseudoscientific claims of religion. Other universes might not be observable, but if a theory like M-theory which predicts them is confirmed to be true, that would be indirect scientific evidence for the existence of a multiverse. Granted, it wouldn't be particularly good evidence and wouldn't convince most people, but any evidence at all places the multiverse hypothesis above the level of religion. --Bowlhover (talk) 15:15, 15 August 2009 (UTC)

What multiverses does M-theory predict? If you define "universe" as a collection of causally connected events (which I would) then, by definition, you cannot make any observations of other universes, so cannot directly demonstrate their existence. --Tango (talk) 16:51, 15 August 2009 (UTC)

IMHO you are right about that Tango. As said twice it is metaphysical speculation and multiple universes is generally an "of the gaps" type argument of varying disguise used to explain extraordinary coincidences in the universe (e.g. dynamics of the big bang was just right: bigger and we would have imploded smaller we would have expanded too fast for planets). A multiverse explains by saying there are zillions of completely isolated big bangs with universes but we can only observe the one which happened to work. Polkinghorne says evidence for a God, some say evidence for mulitverse and inflation offers another theory. But its a rare example in my view of Polkinghorne's logic being flawed (because metaphysical speculation about God's extra-universal role is still metaphysical speculation, we can only look at the observable universe and infer about it). --BozMo talk 18:18, 15 August 2009 (UTC)

A zillion-big-bangs theory is not comparable to the "God of the gaps". A zillion-big-bangs theory assumes that almost the same things that we have already observed may have occurred also in instances which we haven't been able to observe, but abiding largely by the same laws of physics we know. A God theory assumes that something the like of which we have never observed has occurred, abiding by laws that we, with the state of our present knowledge, can't possibly imagine.--91.148.159.4 (talk) 22:18, 16 August 2009 (UTC)

Ignoring Omnipotence beyond logical possibility, lets just settle for Q from Star Trek then?

• I think the conclusion to come to is that the idea of multiple universes can prove or disprove nothing. The "theory" is mostly philosophical postulation and moonbeam-fondling. However, if we wanted to forget about "proving" anything and just do some philosophising, I think it's worth looking to the theology. Many predominant monothesitic religions contend that Everything (note the capital 'E') is presided over by a being somewhat beyond our space, and Judeo-Christianity follows a God that is characterised as incomprehensible and above our reality. In speaking about a deity that is, in a sense, beyond reality, it seems less than meaningful to discuss how its (or His, in the Christian case) existence relates to multiple universes. —Anonymous Dissident^Talk 16:01, 15 August 2009 (UTC)

"Only Many Worlds can explain quantum superposition effects" 81.131.16.134 (talk) 19:52, 15 August 2009 (UTC)

Wrong type of multiverse. The Many Worlds interpretation of Quantum Mechanics is about different universes for every "choice" the universe has to make, the kind of multiverse we're talking about is where each universe has different physical laws/constants (and each of those universes could split into a multiverse of the first type). It's possible the two meanings could be combined if the physical laws/constants turn out to be a result of quantum fluctuations in the early universe, I suppose, but I don't believe any such theory has become mainstream. --Tango (talk) 23:47, 15 August 2009 (UTC)

Every possible universe cannot include impossible universes where laws of physics are violated or where every mystical notion is somewhere realized. The OP as a declared atheist seems to be confident about what cannot exist, so maybe the OPs question reflects a longing to find a God. Cuddlyable3 (talk) 18:09, 16 August 2009 (UTC)

Some responses in this thread seemed somewhat abrupt (apparently the OP was judged not to treat the sensitive issue of God with due seriousness, and his thought experiment was suspected of being irreverent or even blasphemous). The last post was probably the least helpful of all (maybe writing that the OPs question reflects a longing to find a God reflects a longing to find someone longing to find a God, and my writing the above reflects my longing to find someone longing to find someone longing... never mind). Also, I think it's obvious that the idea was - if multiverse theory were to be proven, would that prove the existence of God, too? So nobody is expected to dispute multiverse theory itself here. Even under these conditions, and with a risk of repetition, I concur with everybody else that the answer is "no". If multiverse A disallows an omnipotent God and multiverse B allows an omnipotent God, this God's omnipotence would still obtain only in multiverse B, so the one thing he could never do is move to multiverse A and exercize his omnipotence there. Of course, the whole way of posing the question is a little unfair to monotheism, because it presumes that the laws of the universe predate and restrict the divine person potentially operating in it. Monotheism is, in principle, based on the opposite causation: the person comes first. I think this is naturally and intuitively appealing to us humans, taking into account how we grow up and live. In the thought experiment, the God of Multiverse B is only omnipotent because Multiverse B allows him to; since there must be a general set of rules which determine how the parameters or features of any individual Multiverse determine its God-friendliness, it's obvious that there is a more general domain within which these rules hold true, let's call it the Super-Universe, or less reverently - Universe Universe (UU), and within UU Gods are not omnipotent. At all. To obtain an omnipotent God, we need to assume instead that God comes first, s/he is the first letter of the alphabet so to speak, and all sorts of laws, concepts, attributes etc are secondary. Hard to imagine, of course, but not necessarily impossible to accept - it depends on one's motivation.--91.148.159.4 (talk) 22:18, 16 August 2009 (UTC)

Well said. But the question itself is an excellent one and can be put in another form that has nothing to do with religion or even deities. One could ask that in a multi-verse system, with an infinite number of universes, where hypothetically anything could exist, including deities or omnipotent or omniscient phenomena, surely there would be scenarios where something from one universe could encroach on another universe? To contribute to the OP's question you could posit that even if a deity/god existed in another universe, surely that would not prove its existence in ours. It's an excellent question, and someone familiar with the philosophy of multi-verses can really answer it. Rfwoolf (talk) 23:24, 16 August 2009 (UTC)

The problem is in the 'kind' of multiverse we're talking about. The one that seems like it might be true (the multiple worlds interpretation of quantum theory) is the one where the laws of physics are the same in all of them. Ergo, no magic to make gods with. Infinitely powerful beings are simply not possible in our universe. If there are other universes with OTHER laws of physics - then indeed, all bets are off. However, if a universe with the right laws of physics to allow there to be gods in it were to exist (whatever that means) - then that's certainly no guarantee that these entities can cross into our universe - because here, our laws don't permit them to exist. But if ANYTHING could "cross" from one universe to another, that would kinda blow away the idea that they are separate universes. If things could cross - you'd think we'd see evidence of peculiar laws of physics showing up all over the place in our universe - and we don't. SteveBaker (talk) 23:34, 16 August 2009 (UTC)

Infinitely anything won't fit into the universe Steve.--BozMo talk 18:23, 17 August 2009 (UTC)

If God (or gods) exists then he must be part of the omniverse (a word I just coined only to discover we have an article on it! I think the definition in there is equivalent to what I mean - it contains everything that exists in the broadest possible sense), that omniverse must have some kind of rules governing it (whether they are rules we are capable of understanding is another matter entirely) and God is subject to those rules. The idea that "God comes first" doesn't make sense - the omniverse has to exist for God to exist. Of course, the omniverse doesn't necessarily has a concept of time (it certainly doesn't have our concept of time), so the ideas of "first" and "cause and effect" doesn't necessarily apply. --Tango (talk) 00:01, 17 August 2009 (UTC)

Ever take a look at Norse mythology? Well, according to Norse legend, the High God Odin is all-powerful -- but only as long as he keeps all his covenants with all his subjects; as soon as he willfully breaks even one covenant, all his power would vanish just like that. Seems just a little like what you're talking about here, as far as your statement that "God is subject to [the rules governing the omniverse]". (Of course, in Norse mythology, Odin and all the other gods are anthropomorphic, which is a very dubious notion to say the least...) 98.234.126.251 (talk) 00:44, 17 August 2009 (UTC)

Yes, that's not a bad example, although it isn't consistent with our theories of physics that isn't really a problem - we know our theories aren't perfect because we don't have a theory of everything. There are gaps (like Quantum Gravity) that we have yet to fill. Valhalla could fit into one of those gaps. (Unlikely, but not impossible.) --Tango (talk) 13:33, 17 August 2009 (UTC)

So Tango do you think YOU fit into one of the gaps, or conscious being with free will generally do--BozMo talk 18:23, 17 August 2009 (UTC)?

As a Christian, I wouldn't say specifically that "Valhalla could fit into one of the gaps", but well, some kind of afterlife could surely be consistent with our knowledge of the universe (and I'm sure that sooner or later, afterlife will be proven to exist beyond reasonable doubt). 98.234.126.251 (talk) 23:28, 17 August 2009 (UTC)

I'm not sure the bit about Odin is true in the original mythology (I've read the Prose Edda and much of the Poetic one, though I may have forgotten something); this reminds me more of the interpretation in Wagner's Ring Cycle, and/or G.B.Shaw's interpretation of that interpretation. Anyway, certainly the restriction to not breaking covenants means that he is not really omnipotent, he is restricted by at least this law, or perhaps even by an entity that imposes the law.

Re:"Odin and all the other gods are anthropomorphic, which is a very dubious notion to say the least". The word "anthropomorphic" is POV-laden, as it literally means (1) "described as being similar to humans to some extent", but in practice is used as (2) "described as being similar to humans to an unrealistic extent", and what is an "unrealistic extent" remains to be debated. I think it's obvious that any god is anthropomorphic in sense (1) - being similar to humans to some extent - and it can be argued that any god is anthropomorphic in sense (2) as well - being similar to humans to an unrealistic extent. —Preceding unsigned comment added by 91.148.159.4 (talk) 15:32, 17 August 2009 (UTC)

By "anthropomorphic" in this context, I meant specifically "so similar to humans as to be indistinguishable from them upon casual observation". This would be true in the case of Norse gods -- or indeed most of the gods from pagan mythology of the European nations -- but in the case of Jehovah, the Judeo-Christian God, this is not necessarily true (and indeed, He is most likely NOT anthropomorphic in this sense). Same with Allah, the Islamic god, according to the Koran he is not anthropomorphic but more like some kind of cosmic force (although I really have to wonder what kind of god would choose a child molester as his prophet, but that's a whole other topic altogether). 98.234.126.251 (talk) 23:47, 17 August 2009 (UTC)

An infinitely powerful god can be anthropomorphic if he/she/it feels like it. You could imagine how that would come in handy. Odin just needed a good lawyer. I'm sure he could find a way to repeal his pact with humanity without breaking the pact in the process. SteveBaker (talk) 21:52, 17 August 2009 (UTC)

Would Loge fit the bill as a "good lawyer"? He was infamous for giving crooked advice -- which is why the other gods didn't really trust him. ;-) 98.234.126.251 (talk) 23:19, 17 August 2009 (UTC)

Tango's argument was that "God comes first" doesn't make sense, because God is inevitably pre-conditioned by the Universe in which he exists. Well, one could argue that God was the Universe in its initial state, and then he created those parts of the Universe that are not strictly speaking part of himself, but still, in view of their origin (he had created them, and being omnipotent, he had created them perfectly in accordance with his purpose), he has retained absolute control of them. In the beginning was absolute Goodness&Wisdom, then It sort of budded or secreted from itself stuff like mathematics, logic, physics etc, so as to finally produce another thing with the potential for goodness and wisdom - namely us humans. I don't think this is logically impossible.

Another possibility is that physics and logic are not even a creation of God, but have been part of God from the start. In this case, the question often asked is: can he then can violate physics and hence his own nature? The answer would be the same as to the question whether he can do something evil: "Yes, he can in the sense of being capable, but he can't in the sense of being likely to do it - because he simply doesn't want to, because he is what he is." So I still stand by the "God comes first" option as the assumption best poised to lead to the desired conclusion. Cheers! --91.148.159.4 (talk) 15:17, 17 August 2009 (UTC)

91.148, you should be a theologist. :-) 98.234.126.251 (talk) 23:31, 17 August 2009 (UTC)

All possible paths don't lead to all possible outcomes.... Elocute (talk) 21:54, 17 August 2009 (UTC)

Species of monkey

Can anyone identify what species this monkey is?  Chzz  ►  13:55, 15 August 2009 (UTC)

Rhesus macaque? --82.21.25.109 (talk) 14:53, 15 August 2009 (UTC)

Crab eating macaque according to vervet.za.org --Muhammad(talk) 17:21, 15 August 2009 (UTC)

Sounds painful. Edison (talk) 19:12, 15 August 2009 (UTC)

That must be a big crab if it can eat a whole macaque. --Jayron32 01:48, 16 August 2009 (UTC)

One of those things that you really should know about the human body...

Hi! So, I have a question that you really should have learnt the answer to in high school, but it seems to me that no one did (I've asked five people this, and gotten five different answers). As we all know, men create sperm throughout their life inside their testicles, while women only have a limited number of ova that they get at birth and are stored inside their ovaries (I'm right so far, yes?). Here's my question: on average, how many eggs does a human female have? In total? I've heard everything from a few hundred to a few hundred thousand (which was what I thought, incidentally), with most people guessing at the lower range. Neither the ovum nor the ovary article would enlighten me on the subject.

I would be most thankful if you fine fellows could make up for the collective failure of me and my friends' human biology education and provide me with an answer. Cheers! 83.250.236.75 (talk) 17:43, 15 August 2009 (UTC)

It depends, and we may be wrong. Women do not have a store mature ova, but rather progenitor cells. The number of these decreases over time, but there are apparently several million of them. See Oogenesis#Number_of_primary_oocytes. In other words, women don't "run out of eggs" in menopause. --Stephan Schulz (talk) 18:02, 15 August 2009 (UTC)

The same article sited above also states

Recently, however, two publications have challenged the ovarian biology dogma that a finite number of oocytes are
et around the time of birth.[4][5] Renewal of ovarian follicles from germline stem cells (originating from bone
marrow and peripheral blood) was reported in the postnatal mouse ovary.
Due to the revolutionary nature of these claims, further experiments are required to examine the dynamics of small
follicle formation.

So may be the premiss of the question is incorrect. Dauto (talk) 21:40, 15 August 2009 (UTC)

Human presence detection technique

Hello! I'm presently working on a personal project which would require me to detect human presence in a room of 35'x20'x12'(l x b x h),as part of my objective. I've in mind PIR sensors but i'm afraid they might not respond accurately at ambient air temperatures over 40^oCelcius. Is there any alternative way of detecting human presence in a room other than PIR? P.S. Capacitive method is not viable as room houses multiple em radiating sources. And passive millimeter-wave (MMW) sensors are seemingly over my expertise grade it would seem.

A THANK YOU before hand to whoever might help me figure this problem out. —Preceding unsigned comment added by LONGBOW001 (talk • contribs) 20:29, 15 August 2009 (UTC)

Is a computer and webcam(s) an option to try? There already exists a program called motion (also in debian repositories) that lets you define commands to run when there's motion in video camera image. --194.197.235.43 (talk) 20:54, 15 August 2009 (UTC)

To properly solve this problem, you need to define some environmental conditions. You want to detect a human, but what other things are going to be present that you need to avoid detecting? If warm objects will be present, infrared or thermal detection will have an unacceptable false-positive rate. If other animals or pets will be present, you need to identify a human distinctly from, say, a cat - or whatever else is in there. If you want to identify a specific human, you might need facial recognition software or some other biometrics. If you are willing to have the human actively participate in the identification process, such as by wearing an RFID tag, this can simplify the process. Nimur (talk) 21:42, 15 August 2009 (UTC)

Have you considered using a petoscope? 98.234.126.251 (talk) 04:54, 16 August 2009 (UTC)

Pressure-sensitive mats. Cuddlyable3 (talk) 17:51, 16 August 2009 (UTC)

Candle pendulum

What is going on in this video? --Reticuli88 (talk) 20:42, 15 August 2009 (UTC)

The side of the candle that is lower will dump the hot wax. The side that is higher will hold the hot wax. Because the lower side dumped the hot wax, it is lighter. So, it rises. Then, the lower part dumps its wax. The higher part does not. So, the lower part becomes lighter and it rises. Another way to imagine this is a see-saw with a bucket on each end. If the bucket is lower, the water will dump out. Now, continually fill the buckets with water. The lower one will dump out the water while the higher one fills up with water. The higher one will lower and dump the water. You can also toss in a bit about one end of the candle getting shorter but I seriously doubt that has much effect compared to the loss of volume by dumping out the hot wax. -- kainaw™ 21:01, 15 August 2009 (UTC)

Unless that's a really volatile candle, I suspect we're also seeing some time lapse imagery - the burn rate and oscillations look like they're sped up somewhat. Nimur (talk) 21:46, 15 August 2009 (UTC)

Not just dripping either, (Most candle wax winds up in the air.) Notice how the flame cuts into the candle more on the downward side. I assume that wax is consumed faster on that side. APL (talk) 05:32, 16 August 2009 (UTC)

The right end is lit first and starts losing weight before the left is lit, so the candle initially tilts anticlockwise. The tilt then stabilises because the left flame is angled more towards the wax body and so melts it faster. Now both ends burn in an unusual sudeways mode. Note that the flames bend towards the center. We can't see the whole airflow but hot air must rise from the flames and be replaced by cool air from beneath. Two circulating airflows close together generate more friction than a single flow, therefore the former is not stable and there is turbulent combination of the flow modes. A slight imbalance in the turbulences tilts the candle. This has a regenerative effect at the physical resonant frequency of the see-saw where the air disturbance of the candle body adds to the thermal disturbances of the flames. The oscillation of the candle builds up so it becomes obvious that the two flames are alternately contributing to the same upward convection. Factors contributing to the oscillation are the flames alternately burning into or away from the candle body, and possibly (not visible) molten wax running down the gutter at the lower end and dropping off, making that end lighter.Cuddlyable3 (talk) 17:42, 16 August 2009 (UTC)

Thank you Cuddyable3--Reticuli88 (talk) 11:59, 19 August 2009 (UTC)

Faraday Cage

I've always thought that microwaves were Faraday cages. I saw a demonstration where they put a radio inside a Faraday cage (it wasn't a very good one but somewhat effective) and naturally the radio quality turned to shit. I was wondering why when I put my phone in the microwave oven and close the microwave door (naturally not turning on the microwave) my phone still could receive calls (I called it and it rang). I thought the whole point of a Faraday cage was to shield the objects inside. Thanks 66.133.202.209 (talk) 20:53, 15 August 2009 (UTC)

The mesh on the front panel of the microwave (that let you see in) are calibrated to be just the right size to keep the microwaves inside. Signals at different wavelength can pass through it, though. (Which is why you can see through it—visible light can pass through easily). I imagine that the cell phone wavelengths are more varied than the microwaves' and can make it through. --98.217.14.211 (talk) 21:05, 15 August 2009 (UTC)

We discussed this in December 2008. My excellent response was so fantastic that nobody else even needed to follow up on it! I will copy it here for your reading pleasure: Nimur (talk) 21:49, 15 August 2009 (UTC)

The question you are asking is, roughly restated, "does the microwave have a shield?" It should be more properly restated, to be very precise, as "What is the non-linear anisotropic attenuation-vs-frequency characteristic of the microwave casing, and what frequencies of attenuation overlap those frequencies used by the cellular phone?" First of all, let's clarify a few details:

• Microwaves and cell phones commonly do operate at the same or similar frequency band (for example, 2.45 GHz). But, maybe your microwave and cell phone operate at different frequencies... it depends on whether your phone uses GSM, where you bought your microwave, etc. You can check this with the marshmallow test, or if you're smart, just read the label on the back of the microwave oven.
• Microwaves commonly include a few features, such as a wave guide or horn to guide the microwave energy in a specific direction (towards the food)
• After the microwave energy is "in the oven", it bounces around, off the walls, maybe even setting up resonant waves. So, any "shielding" should really be surrounding the entire oven, with strongest protection at the places of strongest electromagnetic fields (typically, directly opposite the "horn" where the waves come in.
• Microwave ovens probably use a "crappy" but generally single-frequency tonal magnetron to create the electromagnetic waves. So, the shielding is quite probably a "notch filter" (isolating out that single frequency and preventing it from passing).
• By the second law of thermodynamics, any (passive) shielding should be bidirectional - that is, if the energy can't get out, then energy can't get in, either.
• Shielding is also not measured as "all or nothing" - it's measured as an attenuation. That means that the shield lowers the intensity of the radiation, but does not make the signal disappear completely. Now comes the non-linear part. The case in consideration compares two very very very different orders of magnitude - nearly one kilowatt of oven radiation, blasting from eight inches away, compared to a few milliwatts transmitted by the phone and maybe nanowatts (picowatts even!) received from the tower. (Depending on "details," your phone may need bi-directional communication to initiate the reception of a call; or it may just need to receive a single incoming message from the tower). So it may not be safe to say that the shielding materials attenuate by a fixed amount over this entire range of power levels. It's possible that very-low intensity signals, like those from the phone, are not attenuated much at all; while high-power signals are brought down to safe intensities (and no further)
• Cell phones use very complicated modulation to make sure that the data can be deciphered even when the signal is very very weak. This is what advertisers often mean when they say "fewer dropped calls" (though they might also be talking about density of towers). Specifically, some of the QAM spread-spectrum coding schemes are particularly insensitive to single-frequency interferers. So if the So even if the microwave shielding is "pretty good" at notching out (stopping) that single frequency that the oven operates at, the cell phone data may be fairly undeterred.
• And the anisotropic part makes a huge difference! The cell-phone probably has a crummy antenna, which may mean it has a weird angular reception pattern. And, the microwave oven shielding is probably not uniform either (presumably concentrated on blocking regions of highest radiation while cooking!) So, if you rotate the phone, you may get dramatically different reception patterns. And this is totally assuming that there is no resonant coupling between the 2.4-GHz resonant chamber of the oven, and the 2.4-GHz dipole antenna inside the phone. Who knows what may happen to the reception pattern if that effect is non-negligible! In summary, the orientation of the phone with respect to the oven, and the orientation of the oven with respect to the nearest tower, will dramatically change the results. (see Radiation pattern for more graphical explanation).

So, it can actually be fairly complicated to say whether a given microwave will "shield" a given cell-phone from a call. Irrespective of the result of that test, it is not really a good way to determine whether the oven casing effectively blocks out the microwave energy used during cooking. Nimur (talk) 17:00, 10 December 2008 (UTC)\

Thanks for that excellent response Nimur. As for the microwave blocking the microwave energy I sure hope so because alot of times I put my head next to the microwave to watch the food that I'm heating up so if the casing doesn't I'm screwed I guess... :) 66.133.202.209 (talk) 23:41, 15 August 2009 (UTC)

Thank you Nimur for the pleasure of reading your fantastically excellent response. But the marshmallow test won't tell anything about the cell phone operating frequency. And where does your hypothesis that the oven shielding is non-linear come from, when this implies there is some material change, ionisation or arcing somewhere? By spread-spectrum modulation I think you mean CDMA not QAM. If you want the OP to investigate the effects of orienting the phone and oven, the attention should be directed to the received signal strength indicator in the phone (if it has one) rather than just whether it receives a call. The OP may be reassured that the screening is adequate by checking whether a moist rag held close to the operating oven gets warm (it shouldn't). Cuddlyable3 (talk) 16:42, 16 August 2009 (UTC)

As far as the mobile phone operating frequency, the best way to check that is to look for a label. Inside my mobile phone, underneath the battery, is a bunch of FCC information, and I can see that my phone operates at either 900MHz or 1.8 GHz. You can also check this stuff on the web, this website applies to my phone model. As far as the non-linear attenuation, my assertion is that everything, including simple stuff like dielectric "constants," are inherently nonlinear, if you analyze them over a large enough experimental range. This Google Scholar search indicates active research into such material-dependent nonlinear attenuation; it seems I may be on the right track here. Though material-changes can be responsible for nonlinear behavior, they aren't the only reason why a measured value might deviate from a simple constant. A cursory glance through some research papers suggest that atomic structures and crystal lattices in the material may play a role. Regarding the phone's signal strength meter: I don't know about your microwaves, but mine doesn't have good visibility to the interior, so I doubt that I could read the phone's signal-strength indicator; anyway, it's hard to know exactly what that readout means (there can be time-averaging; digital post-processing, etc). Nimur (talk) 17:44, 16 August 2009 (UTC)

Nimur your Nokia mobile phone is a standard model for GSM which uses TDMA and FDMA (not spread spectrum). It has a received signal strength display that is averaged over 5 to 10.5 seconds (see RXLEV[1]). The display is in logarithmic steps (decibels) exactly defined in the ETSI GSM specifications. Microwave ovens are usually internally illuminated and your phone display should be legible in some positions looking through the door grille. As the OP says, microwave ovens are constructed as a Faraday cage of steel without "exotic" materials. Alleged non-linear attenuation by this cage would imply that a significant fraction of the heating power typically 600W is absorbed by something other than the food. Asserting that everything is nonlinear doesn't quantify anything here. Cuddlyable3 (talk) 20:25, 17 August 2009 (UTC)

FDMA is a spread-spectrum technique, is it not? Nimur (talk) 17:06, 18 August 2009 (UTC)

Thanks for the excellent GSM reference on receive levels, Cuddlyable - it's very relevant to the question (though it does highlight the complexity of cellphone communications as I was discussing in December). As far as the nonlinear dielectric constant, this does not only affect attenuation, but also the reflection coefficient (so my earlier statements should not be taken to imply that the steel shielding is dissipating energy by dielectric heating alone). The ability of the shield to direct energy back into the microwave interior will depend on its material properties. A nonlinear reflection coefficient may prefer reflecting strong signals while allowing weak signals to pass. (Electromagnetic oobleck?) According to conventional straightforward treatment, the reflectivity of a material should be constant; the next level of treatment is probably some refraction, like Snell's law, and finally a version of Snell's law that accounts for frequency variability; but the most rigorous treatment will actually consider all of the above, plus incident amplitude, plus incident polarization, etc. etc. etc. In reality, the ability of a "Faraday Cage" to reflect or shield electromagnetic signals depends on all of these parameters and more. We clearly have an experimental example of this - a microwave blocks kilowatt-scale energy (as you mentioned, a damp rag is not being heated outside the oven); but this same passive shield allows microwatt-scale energy at the same frequency band to pass freely. Evidently "faraday cage" is too simplistic of an approximation for this seemingly straightforward case. Nimur (talk) 17:19, 18 August 2009 (UTC)

Musical tastes and mental health diagnosis

Can musical tastes be a factor in diagnosing a mental illness or absence thereof? NeonMerlin 23:26, 15 August 2009 (UTC)

It looks like there has at least been some research in that area, yes. E.g., see the papers "Clinical diagnosis by the IPAT music preference test"[2] and "Can music preference indicate mental health status in young people?"[3] Red Act (talk) 07:57, 16 August 2009 (UTC)

I'd imagine so in many cases of anhedonia.Mo-Al (talk) 08:03, 16 August 2009 (UTC)

You may want to check Oliver Sacks´ book "Musicophilia: Tales of Music and the Brain". --Cookatoo.ergo.ZooM (talk) 08:11, 16 August 2009 (UTC)

Feeling tired when hiking, resting, then continuing

Why do humans need to rest? What good does it do? Why cannot the body just keep on supplying the energy at a constant rate without needing rest periods? And, when you are on a long hike or march, has anyone found out the optimum length and frequency of rest periods? 78.146.247.51 (talk) 23:49, 15 August 2009 (UTC)

There are two consumers of energy -- one is the nervous system (via the action potential), and the other is the ATP-driven motor that contracts the muscle fibres. The action potential is instantaneous, releasing electrochemical gradients a bit at a time to send signals -- but if you send a lot of signals you can deplete this potential. (Sometimes you need hours to restore the gradient to full strength again, because the gradient is restored by ion pumps that pump ions one ion at a time.)You can deplete the supply of ATP within cells while blood sugar is abundant, because it takes time for the cells to absorb the sugars, metabolise it via oxygen as a terminal electron acceptor, and make ATP with it. Also, fatigue is partially a safety mechanism. The body doesn't wait till cells are completely depleted of ATP -- you'd collapse, not to mention that cells need energy to stay alive (pump in certain ions/nutrients, repair damage to DNA, membrane holes and other materials) and running out of ATP would be bad. Imagine if the body simply allowed you to walk until your heart and lungs gave out? John Riemann Soong (talk) 01:20, 16 August 2009 (UTC)

As for your last question: back during the Civil War, Stonewall Jackson had his troops march for 1 hour, then rest for 10 minutes before continuing the march for another hour, and repeating this cycle until either the troops reached the objective, or had to stop for the night. This worked really well, so I'd say that 1 hour march / 10 minutes rest would be close to optimal. FWiW 98.234.126.251 (talk) 05:06, 16 August 2009 (UTC)

A lots of exercise routines use similar cycles. 20 minutes exercise and 1 minutes rest, repeated, for example. It does seem to be effective to have short breaks every so often - the important thing seems to be resting before you reach your limit. --Tango (talk) 16:19, 16 August 2009 (UTC)

The other thing that can cause a need for rest is running out of oxygen in the relevant muscles so they have to use anaerobic respiration and get a build up of lactic acid, your muscles will then start to hurt and you eventually have to stop. That should only happen for high intensity exercise, though, I doubt hiking would cause it. It is more of a problem for 400m runners, or something. --Tango (talk) 16:19, 16 August 2009 (UTC)