Wikipedia:Reference desk/Archives/Science/2008 April 21

= April 21 =

Age of Earth
Ok a friend of mine went to the creation museum and is telling me they presented scientific evidence that earth was only a few thousand years old. I dont buy it. But i thought i should ask, is there any cold hard scientific evidence with out religious rhetoric tied in with it that earth is only a few thousand years old?


 * No, there is not. None at all. In fact, several different sources have shown consistently that the Earth is about 4.5 billion years old. See Age of Earth for lots of information. See the external link given for more about the "evidence" Young-Earth creationists are using. &mdash; Kieff | Talk 01:26, 21 April 2008 (UTC)
 * Just to prepare you for any creationist arguments, there was a controversy of pointing to polonium halos as evidence for a young Earth (see Creation geophysics). You can also look at this article. — Æµ§œš¹  [aɪm ˈfɻɛ̃ⁿdˡi]  02:07, 21 April 2008 (UTC)


 * Also read this article. There ought to be a law against it.--Shantavira|feed me 07:59, 21 April 2008 (UTC)


 * They do have a commandment, though: "You shall not bear false witness against your neighbor". &mdash; Kieff | Talk 08:28, 21 April 2008 (UTC)


 * We have a nicely balanced article on Young Earth creationism. Problem that Young Earth creationists face is that not only do they have to find evidence that could point to a young Earth, but they also have to find an alternative explanation for all the other strands of evidence that point to a 4.5 billion year old Earth. They sometimes use the argument that God created the Earth with the appearance of being billions of years old to test the faithful, but this creates two problems. First problem is it this argument depends on God being intentionally deceitful, which is hard to explain. Second problem is that the claimed evidence for a young Earth then shows that God's forgery of an old Earth was imperfect - which is also hard to explain. Gandalf61 (talk) 09:48, 21 April 2008 (UTC)
 * A third problem is that forgery of evidence would imply that God has frat boy-philosopher tendencies and wants us to keep wondering if we're brains in vats. --69.134.124.30 (talk) 09:57, 21 April 2008 (UTC)
 * See also Donovan's Brain. Edison (talk) 18:53, 21 April 2008 (UTC)
 * If they go with the idea that the Earth was created 6,000 years ago with all that carefully-constructed ancient stuff there just to decieve us, then make the claim that the Earth was actually created 10 seconds ago. Ask them to disprove your "ten second" theory. Then suggest that Occam's razor would suggest that the simplest explanation (among all these competing "6,000 years" v. "10 seconds!" theories) is that the Earth is actually as old as it seems: 4.5 billion years. You may not convince them, but you'll have fun along the way.
 * Atlant (talk) 12:50, 21 April 2008 (UTC)


 * On this point see Omphalos (theology). --Anon, more than 10 seconds old (as far as I know), 22:03 UTC, April 21, 2008.


 * Much good fun (as it says in escaping from fundamentalism by james barr). Bear in mind though that the Bible describes Adam created as an adult man not a new-born baby and therefore "created old" isn't too much of a stretch. --BozMo talk 12:56, 21 April 2008 (UTC)


 * Not wanting to start a debate here or go OT but the God you're referring to is the same one who brutally killed 'sinners' (Noah's Ark, Sodom and Gomorrah.....), asked a father to murder his son for no good reason, used acts which would likely be considered terrorism in this day and age including biological warfare (Plagues of Egypt) etc etc; I don't think 'intentionally deceitful, which is hard to explain' is hard to explain in the eyes who believe everything in the bible should be taken literally Nil Einne (talk) 19:09, 21 April 2008 (UTC)

Alright folks let's keep this clean of ranting against Christianity shall we? ;) Regards, CycloneNimrod Talk? 19:33, 21 April 2008 (UTC)
 * Just to be clear, I wasn't ranting against Christianity, simply pointing out that if you take the bible literally, then you have far bigger issues to explain about God then him/her being 'intentionally deceitful'. Note that there are a lot of Christians who don't interpret the bible completely literally and many explanations Christians come up with for the varying complexities that arise if you intepret the bible literally which obviously don't need to be and shouldn't be discussed here. Whatever Christians want to believe, is up to them, and this obviously isn't a forum for such a discussion. Nil Einne (talk) 22:01, 21 April 2008 (UTC)

Just ignore "scientific creationism" -- it's the worst kind of oxymoron. —Steve Summit (talk) 00:31, 22 April 2008 (UTC)

There are those of certain sects that believe that the Earth must be very young in order to conform with received scripture. From that point of view they then look for evidence for it and try to find ways to discount evidence against it. It is a limited view of the scripture, and it is a view which has no scientific validity either in content or in methodology. --Captain Ref Desk (talk) 14:55, 22 April 2008 (UTC)

Energy and momentum
It is a general rule that in a collision, unless otherwise stated, momentum is conserved while energy is not. Now I can understand why energy may not be conserved (i.e. it gets transfered as heat), but why is momentum assumed to be conserved? After all, when objects collide, temperature (i.e. the motion of atoms) increase, and thus their momentum. On another point, in an ideal collision, when energy and momentum are both considered to be conserved, if an object hits another object at rest, all momentum is transfered to the second body. Now I understand the math behind it, but how can this be explained intuitively?


 * Are you talking about particles or objects? In a collision with objects, heat isn't the only way energy is lost (friction, elasticity etc). In an object, temperature is not related to the overall momentum. Momentum can only be assumed to be conserved in a closed system, because momentum in a collision is conserved (m1v1+m2v2=m1v1+m2v2). Momentum is related to velocity, thus energy.
 * In an ideal collision, no energy is lost, so it all must be conserved. Note that all momentum will only be transferred if the two objects have the same mass.

Luxosus (talk) 02:32, 21 April 2008 (UTC)


 * Momentum is conserved even if heat is produced because the thermal movement of particles is random with respect to direction (more specifically a Maxwell distribution) and thus the momenta cancel each other. If they don't cancel - well, then the object is actually moving in a certain direction which contributes to its macroscopic momentum. Icek (talk) 03:12, 21 April 2008 (UTC)


 * How is energy lost due to elasticity?


 * Internal stress due to compression\expansion. He didn't mean it in the context of elastic collisions. &mdash; Kieff | Talk 04:13, 21 April 2008 (UTC)


 * Both are conserved. However, energy has many different modes: overall linear and rotational kinetic energy, potential energy of the objects' chemical bonds (e.g. deformation), temperature, etc.  It is very difficult to predict or measure how much energy is transferred to each different mode.  Momentum, on the other hand, is awfully simple under the circumstances, scales, and velocities in which we usually pose such problems: mass is constant (and usually not exchanged significantly between the objects undergoing collision), so the only unknowns are the velocities of each of the objects involved, and there you can even analyze three directions independently.  So it is convenient to work directly with momentum, and not so convenient to work with (kinetic) energy except in a secondary fashion.  --Prestidigitator (talk) 05:04, 21 April 2008 (UTC)


 * A deeper (and therefore possibly less useful) answer to the "why" question is that conserved quantites are associated with symmetries of physical systems and laws - see Noether's theorem. Linear momentum is conserved because the laws of physics are invariant with respect to translations in space; if we move everything a metre to the left (or, equivalently, move our origin a metre to the right), we don't expect the laws of physics to change. Similarly, conservation of energy is a consequence of invariance with respect to translations in time, and conservation of angular momentum is a consequence of invariance with respect to rotations. Gandalf61 (talk) 09:21, 21 April 2008 (UTC)

Electrodynamics application
Hello,

I've found these very informative electrodynamics simulations applets : http://www.falstad.com/emwave1/ and http://www.falstad.com/emwave2/.

Does anyone know of a similar program (not necessarily an applet, maybe a downloadable application) which does essentially the same thing but in 3D ?

I would like it if it simulated Maxwell's equations totally (maybe even with magnetic charge to see what it would be like, but I suppose that would be quite unlikely).

Thanks. -- Xedi (talk) 07:40, 21 April 2008 (UTC)

Cracked Walls
What causes cement paste cracked on walls and solutions to prevent? —Preceding unsigned comment added by Tajteddy (talk • contribs) 07:51, 21 April 2008


 * Do you mean cracking of the interior plaster, or cracking of the concrete structure of the wall itself?
 * The interior plaster usually cracks due to drying in the first few months after it is applied to the wall. I don't believe much can be done about it, except to wait several months and then fill the crack with a commercially available filler.  After filling the cracks, the wall can be painted or wallpapered to cover up the repair.
 * If the concrete structure of the wall is cracked, it could be due to settlement or subsidence, and is much more serious - the wall could fall down - so contact a professional builder.
 * Astronaut (talk) 11:32, 21 April 2008 (UTC)

Try adding a synthetic resin or plastic dispersion to the mix. NB: This may not work on your particular surface and makes the plaster way more expensive! Worst case scenario you might end up with big sheets of dried plaster falling off the surface underneath. There are lots of factors contributing to cracks. A few that come to mind are: shrinkage due to (uneven) water loss in the hardening phase, water absorption and subsequent drying of the surface underneath, temperature gradients during hardening, imperfect bonding to the surface underneath etc. etc. Lisa4edit--Lisa4edit (talk) 06:41, 22 April 2008 (UTC)

eavesdropping 2G/2.5G voice calls
How can wiretapping voice calls on 2G network be done? Suppose both the users are under the same cell. In that case, what kind of electronic circuitry would be required to tune into all the carrier frequency channels, demultiplex them to the 8 channels, and record? Even after the demuxing, how can we extract the specific audio data and decode it? I am an Electronics engg. 2nd yr student. It would be quite useful for me in case you can provide me with detailed info on the circuitry,... Bobatnet (talk) 10:54, 21 April 2008 (UTC)
 * Given encryption is AFAIK used by the majority of mobile providers out there, this is probably very, very difficult and costly without the cooperation of the telephone company. Your only reasonably (but still probably rather expensive and difficult to set up) option would be to use something like an IMSI-catcher as mentioned in Telephone tapping. Note that the use of one or for that matter, any form of tapping could very well be illegal in your jurisdiction, I suggest you speak to your supervisor or some other person at university before trying anything. Nil Einne (talk) 18:56, 21 April 2008 (UTC)

Quantum devices
I know it is not possible with current technology, but would it be concieveable to use quantum entanglement to construct a nano-scale remote sensing device? Astronaut (talk) 11:38, 21 April 2008 (UTC)


 * As I understand it the answer is yes, but no useful information can be transmitted in that way. If you could read the state of an individual particle, you can then determine the state of it's entangled particle, even at a great distance.  However, changing the state of one particle does not change the state of the other, which is what would be necessary for communication.  StuRat (talk) 16:25, 21 April 2008 (UTC)

Invertase
What is invertase and why would a candy manufacturer put it in a candy? For example, it is in the ingredient list for 'Cherry Blossom'. Thanks, Wanderer57 (talk) 11:44, 21 April 2008 (UTC)


 * See invertase. --antilivedT 12:02, 21 April 2008 (UTC)

Diagrams for scientific journal articles
How are diagrams of gene promoters (particularly with many, many lines showing the positions of CpGs within a CpG island) and the contents of genetic plasmids etc constructed? Special software? Some scientists blatantly try to make do with PowerPoint but I don't think that's a very effective approach. Seans Potato Business 15:22, 21 April 2008 (UTC)
 * There's lots of specialized software for drawing biochemical structures. The biggie is probably the ChemOffice suite. DMacks (talk) 17:04, 21 April 2008 (UTC)

Rate of neutrino oscillations
At what rate, in terms of Hz, say, do neutrinos oscillate? Or am I misunderstanding the issue? The article is a bit too technical for me.--Fangz (talk) 16:56, 21 April 2008 (UTC)

This page (sorry it's not a wiki page) may clarify things a bit more http://www.ps.uci.edu/~superk/nuosc.html Hope this helps. Lisa4edit —Preceding unsigned comment added by Lisa4edit (talk • contribs) 06:11, 22 April 2008 (UTC) --Lisa4edit (talk) 06:11, 22 April 2008 (UTC) oops I forgot.

Do orbiting satellites have shadows?
topic. Bellum et Pax (talk) 17:39, 21 April 2008 (UTC)
 * Yes, just very small and likely obscured by all the other (diffuse) light present during daylight. They also move very quickly. Compare with high-flying airplanes which have shadows that are visible on the clouds below by their occupants but are likely unnoticeable by those on the ground. -- Flyguy649 talk 17:43, 21 April 2008 (UTC)
 * Um, well, sort of. The thing is, when an artificial satellite transits in front of the Sun, as seen from the Earth, it never occludes the entire disk -- it's just a little speck passing in front of it. Therefore it has no "shadow" in the sense of something with a sharp boundary. In eclipse terminology, it has a penumbra but no umbra. --Trovatore (talk) 18:40, 21 April 2008 (UTC)
 * At any point on the ground, the angular subtense (image diameter) of the sun would be larger than that of an artificial satellite. Therefore a satellite would have no Umbra or spot on the ground where there was no view of the sun; instead for an instant you might see the satellite sillhouetted against the sun. So no, there would not really be a shadow. Unless there is a really big satellite up there, say 4500 feet diameter at an altitude of 100 miles, or 2.5 miles diameter at 300 miles (please check the math). Edison (talk) 18:49, 21 April 2008 (UTC)
 * Quite right. Here's a stunning photograph of the International Space Station and the Space Shuttle transiting the sun.  Even though they are large artificial satellites, they are very small in angular size compared to the disk of the sun.  -- Coneslayer (talk) 18:54, 21 April 2008 (UTC)

Romantic implications of garlic
When two equivalent persons consume an equivalent quantity of garlic, do they both a) detect the garlic exuding from the other person or b) detect no garlic or c) other? Seans Potato Business 19:06, 21 April 2008 (UTC)
 * Well since you can usually detect garlic exuding from yourself, I would have to go with the first one Nil Einne (talk) 19:12, 21 April 2008 (UTC)


 * When both people are exhaling and have their mouths open, though, I would expect one's own smell of garlic to mask the other person's smell. Let's suppose the distance from the nose to the mouth is 10 cm, and the distance form the nose to person B's mouth is 50 cm.  Assuming smell dilutes with the square of the distance, person B's smell would be 4% one's own, which is not easily detectable.  --Bowlhover (talk) 20:17, 21 April 2008 (UTC)


 * Would you be as kind as to upload a picture of yourself on your user page? :) This mouth to nose distance of yours has me rather curious. 81.93.102.185 (talk) 20:38, 21 April 2008 (UTC)


 * Well, if I used the reasonable 5 cm, that would make Person B's relative smell even weaker. But sure, I'll give you a picture: .  --Bowlhover (talk) 03:48, 22 April 2008 (UTC)

The distance theory would work if there wasn't the fact that repeated sensory stimulus leads to heightened tolerance or more precisely diminished response. Thus difference between s.o. else's oder and one's own should be perceived more acutely. (Also see Action potential) Lisa4edit --Lisa4edit (talk) 05:36, 22 April 2008 (UTC)

Nudity addiction
I am sory if I am asking for an advice but it is urgent. I have an addiction where I like people being naked especially women and there is an free option where we can do sex on any woman or touch a single part of woman's body. the problem is as a Muslim and a Muslim cannot see a person being in a naked state because it is considered as a sin. I need your help on: how to get rid of this addiction before it is too late and when I mean that, I mean I will eventually become as a nudist. QASAP. Thank you. sorry if I used a spiritual sense in it. —Preceding unsigned comment added by 192.30.202.20 (talk) 22:26, 21 April 2008 (UTC)
 * Muslims can see nude women. How do you think they reproduce? 216.120.213.165 (talk) 22:31, 21 April 2008 (UTC)
 * I believe it's ok in marriage. -mattbuck (Talk) 23:12, 21 April 2008 (UTC)
 * I seem to recall that Saint Paul wrote in Corinthians, "It is better to marry than to burn." If you are a Muslim male, marriage might be a solution to your desire to see and touch a naked female. Edison (talk) 00:12, 22 April 2008 (UTC)
 * There are a number of belief systems (e.g. New Age philosophy) which would encourage you to embrace your addiction. You can abandon Mohammed and run to the mountain. - Kittybrewster  &#9742;  17:06, 22 April 2008 (UTC)


 * If you are legitimately concerned about addiciton and behaviors that you are having difficulty controlling/resisting, then you should speak to a doctor or mental health professional about your problem. The Reference Desk is not equipped to address physical or mental health problems. Dragons flight (talk) 01:00, 22 April 2008 (UTC)


 * I'd hardly call it an addiction, and more of a basic fact of human nature. Especially in societies where nudity is taboo, which only lends an air of mystery and "naughtiness" to it. Basically, by forcing people to cover up, we put even more emphasis on sex. Only we add to the negative pressure to avoid this natural function of our bodies, which leads to exactly the crisis you find yourself in. Humans are kinda messed up that way! -- Kesh (talk) 00:17, 23 April 2008 (UTC)

Octopi die after reproducing - why?
Our octopus article states that female octopi die soon after their eggs have hatched, explaining that endocrine secretions are the cause - but it doesn't explain *why* the octopi face such a 'genetically-programmed death' as a matter of course. What is the benefit to an octopus of reproducing on only one occasion in its lifetime? Is there even a 'benefit', as such in evolutionary terms? --Kurt Shaped Box (talk) 22:32, 21 April 2008 (UTC)


 * I don't know of an "on one occasion" benefit, but in general terms, there's no particular evolutionary harm in things that kill you exclusively after you've reproduced -- which is, of course, why old age happens at all. You could say it's only a matter of degree between an octopus mother dying 60 minutes after giving birth, and a human mother dying 60 years later. —Steve Summit (talk) 00:26, 22 April 2008 (UTC)


 * On the other hand, a human female's system does not actively 'commit suicide' directly after giving birth. I thought that it was a basic 'rule' that all living things have an instinctual desire to survive and to reproduce as often as possible - this 'chemical suicide' thing seems to run completely contrary to that in my mind. Sure, mama octopus might lay thousands of eggs in a single clutch, so there's a fairly good chance that her genes will survive - but why not live to do it all again the next year to make doubly sure (baby octopus life is fairly cheap as I understand it)? I'm struggling to understand how and why these 'suicide glands' even evolved in the first place. --Kurt Shaped Box (talk) 01:01, 22 April 2008 (UTC)


 * There are any number of possible reasons why parents might be programmed to die, such as:
 * To prevent mama from eating the babies
 * To free up resources (e.g. food) for the babies
 * To eliminate the possibility of mother/child incest
 * So the babies can eat the mother
 * Because the babies will attract fewer predators on their own
 * Because the mama no longer has viable eggs (in mammals, the progenitor cells for all viable eggs are created when the girl is still a fetus, and these cannot be replaced later on. It's possible that the mama octopus uses all her eggs in one go and similarly was never capable of making more as an adult.)
 * Because the act of producing a clutch damages the mama in a way that it cannot recover from.


 * I don't know if any of these are correct for octopi, but it is certainly possible to imagine a wide range of potentially evolutionary incentives to not having an organism continue past reproduction. Dragons flight (talk) 01:21, 22 April 2008 (UTC)

Just by the way, octopi is generally considered substandard usage. Octopus is of Greek rather than Latin origin, and the Greek plural would be octopodes (pronounced roughly ok-TOP-oh-deez). That plural is occasionally used in English, but the accepted English plural is octopuses. --Trovatore (talk) 02:28, 22 April 2008 (UTC)


 * "Octopi" has been used so much that the substandard usage has been blurred.  bibliomaniac 1 5  Do I have your trust? 02:35, 22 April 2008 (UTC)


 * Here's an article that might be relevant: Evolution of ageing. --Allen (talk) 04:08, 22 April 2008 (UTC)


 * Aww, man! Next you'll be telling me that hippopotami (another one I've always used) is 'substandard' too... :( --Kurt Shaped Box (talk) 23:59, 22 April 2008 (UTC)

There are many different reproductive strategies (many different ways to skin a cat) as mentioned in our article reproduction. Look up semelparous organisms and see our article r/K selection theory.--Eriastrum (talk) 16:00, 22 April 2008 (UTC)


 * Yes, thanks very much for all the answers, folks... :) --Kurt Shaped Box (talk) 23:59, 22 April 2008 (UTC)

I studied at several well-known college campi, and I had never heard the term "octopodes." The things one learns on Ref Desk! Actually, "The New Shorter Oxford English Dictionary" gives the plurals of "octopus" as, in order, "octopuses," "octopi," and "octopodes." "The American Heritage Dictionary of the English Language" gives the plurals, in order, as "octopuses," octopodes," and "octopi." On neither side of the pond does "octopodes" appear to be the preferred plural. Now I must go feed the mongeese. Edison (talk) 22:57, 23 April 2008 (UTC)

Speeding Up causes Decompression?
I know the air going over an aircraft's wing becomes 'Accellerated', and because of this, the same air loses pressure and the plane flies.

Is it because of the surface of the plane's wing, or is it a rule that Accellerating air Loses Pressure? P.L. —Preceding unsigned comment added by 72.39.252.217 (talk) 23:00, 21 April 2008 (UTC)


 * I believe it's because there is a fixed volume of air going over it per second, and so if it's going faster, there must be a lower pressure. But I hated fluid mechanics, hopefully someone else can answer. -mattbuck (Talk) 23:10, 21 April 2008 (UTC)


 * It's the bernoulli principle at work. But as a certain Steve who doesn't edit the RD anymore would often love to explain in obscene detail, angle of attack bears a much greater responsibility for the lift of modern planes. Someguy1221 (talk) 23:48, 21 April 2008 (UTC)