Wikipedia:Reference desk/Archives/Science/2013 January 2

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January 2

New comet and meteor shower

C/2012 S1#Associated Meteor Shower says that the Earth will pass through the path of this new comet, and may experience a meteor shower. The comet is on a hyperbolic orbit. It seems to me that any particles that come off the comet will be on a similar orbit and would not be around to form a meteor shower. What is right? Bubba73 ^{You talkin' to me?} 02:55, 2 January 2013 (UTC)

Diagram of a comet showing the dust trail, the dust tail (or antitail) and the gas tail. NASA

Yes the dust tail will be on a similar orbit, but it is expected to be very long, and part of it will have arrived on our orbit when we come around to it.--Shantavira|^{feed me} 09:11, 2 January 2013 (UTC)

The article says "Its orbit is nearly parabolic", which presumably means that it is elliptical with an eccentricity of just below one. Bubba, why do you say it is hyperbolic?--did you read that somewhere else? "Near parabolic" appears in two different refs sourced by the article: New Scientist and Astronomy Now. Also, I don't think that the nature of the orbit (hyperbolic or elliptical near parabolic) should even affect the likelihood of a meteor shower -- the comet is from the Oort Cloud, which is way out there, so it will be a long time before the comet itself reappears even if elliptical. So as Shantavira says, any meteor shower would come from the dust tail of the current passage. Duoduoduo (talk) 13:10, 2 January 2013 (UTC)

The article gives the eccentricity as 1.0000015, which makes it hyperbolic. If particles come off the comet, wouldn't they continue on their orbit? That is, how will it make an annual shower? Bubba73 ^{You talkin' to me?} 14:55, 2 January 2013 (UTC)

Our article Comet tail has a diagram which I have copied here, showing a dust trail following the comet's orbital path, and a dust tail or antitail coming outwards away from the sun, but at a different angle to the gas tail. I'm no expert, so I stand to be corrected. Alansplodge (talk) 17:44, 2 January 2013 (UTC)

So it does. But I can't find anywhere that says the meteor shower would be annual. Where do you see that? Duoduoduo (talk) 17:44, 2 January 2013 (UTC)

Pass. Sorry, I'm already out of my depth here! Alansplodge (talk) 17:46, 2 January 2013 (UTC)

I took out the part about the possible meteor shower this morning because of wp:ball. Look back a little in the article history. It does say that the Earth will pass through the orbit annually and it did say that the first meteor shower could be in January 2014. That seemed to imply an annual meteor shower. Bubba73 ^{You talkin' to me?} 17:54, 2 January 2013 (UTC)

Unfortunately what you left in in that section was pointless without the point that you deleted. I've put it back in with a correction to conform with the source -- the source doesn't say anything about "annually". It's okay to give a statement of what astronomers predict -- many of our astronomy articles do that. Duoduoduo (talk) 18:10, 2 January 2013 (UTC)

One amateur astronomer predicted that. The Jan 2014 date will be a year after the comet passed by. I asked NASA's meteor expert on his facebook page, but I don't know if he will get back to me. Bubba73 ^{You talkin' to me?} 18:41, 2 January 2013 (UTC)

Scratch that about a year after - I forgot that it is 2013 already. Bubba73 ^{You talkin' to me?} 18:45, 2 January 2013 (UTC)

(unindenting) About the "hyperbolicity" of the orbit in question, it isn't very obvious. If I got my math right, the angle between the two asymptotes in radians is about the square root of 2(ex - 1) if the excentricity ex is close to 1. That is about .0017 radians or .01 degrees. I.e. it would not show up as hyperbolic to the naked eye even if its faintness were a non-issue.

Oops, 0.1 degrees. Stupid math fail. - ¡Ouch! (^{hurt me} / _{more pain}) 10:49, 4 January 2013 (UTC)

Bringing up the Oberth effect in reverse, i.e. inelastic collision, the solar wind could be enough to slow dust to a velocity below solar escape velocity, i.e. make its orbit elliptic without affecting the solid comet in any measurable way. Funny how that reduces to the same mass/surface ratio issue as the "animals in free-fall" topic below. - ¡Ouch! (^{hurt me} / _{more pain}) 06:47, 4 January 2013 (UTC)

One minor correction a point made above: ISON will not be a periodic comet; in fact, it is currently on an ejection orbit, which will put it out of the Solar System within a few decades. Humans won't be laying eyes on this comet between 2014 and whenever we figure out the Alcubierre drive. I did a lot of reading on this topic last week when I thought I had reason to believe that it was a reappearance of Newton's comet, which I later found out a lot of others had suspected as well. JPL numbers put that theory out of commission, though. Evanh2008 ^{(talk|contribs)} 11:55, 4 January 2013 (UTC)

Alcubierre drive is FTL, thus overkill. With a hyperbolic but near-parabolic trajectory ("orbit" has a wrong sound to it IMO - it won't "be back"), it'll slow down to 1 km/s or less eventually. v is proportional to r^-1/2 in a circular orbit and 1.414... times that on a parabolic escape course, that is v = (1650/r)^1/2 if r is in AU and v is in km/s (right? I hope my math is right this time...). One would need quite high delta v, but even a Pioneer could catch up to it, given the right planetary alignment. It's not about the speed but about finding that damn snowball in the big black void. - ¡Ouch! (^{hurt me} / _{more pain}) 18:15, 5 January 2013 (UTC)

Plants on Mars

To be clear, according to [1] no known plant can grow on Mars without artificial assistance. And yet I wonder. The atmosphere of Mars has about 600 Pa of pressure of carbon dioxide; by comparison, unless I went wrong somewhere, 0.039% of Earth's 101300 Pa is 39.5 Pa. So Mars has plenty of atmosphere for plants (provided they don't try to do respiration...). The climate of Mars includes temperatures up to as much as 81 degrees Fahrenheit. Debatably, conditions in Hellas Planitia can even allow the formation of liquid water (though we have a citation needed there) and the crater includes glaciers. And we know at least microbes can survive beneath glaciers. [2] But potentially, we might be even more ambitious: boreal trees survive freezing even in liquid nitrogen, if given a chance to prepare. [3] It is considered at least possible to develop UV-resistant plants in response to destruction of Earth's ozone layer.. [4] So ... could the NASA site be too pessimistic? Do any of the (would-be) exobiologists think that plant life, perhaps (with a little tinkering) even plants we recognize, could actually be able to grow on Mars? Wnt (talk) 03:31, 2 January 2013 (UTC)

Evidence of liquid water has been observed on Mars, but we don't really know how long it lasted. If any plants were brought to Mars and exposed to the naked atmosphere, wouldn't any water in them be prone to evaporate rather quickly? Evanh2008 ^{(talk|contribs)} 06:46, 2 January 2013 (UTC)

The Martian atmosphere has an average pressure of about 6 millibars, as I recall. By my math that would put the boiling point of water right around negative five C (I may have gotten some numbers jumbled there, though). I guess if you could find a place on Mars where there was moisture and temperatures consistently below that mark, plants should grow just fine. Evanh2008 ^{(talk|contribs)} 06:49, 2 January 2013 (UTC)

Yes, to retain water they might look more like a cactus, and perhaps use oils instead of water for their circulatory system. I certainly wouldn't say it's impossible for some form of life to exist on Mars, just that it would have to be fairly different from Earth life. However, some form of microbe living in underground damp soil seems more likely than plants, to me. StuRat (talk) 06:55, 2 January 2013 (UTC)

To clarify, I'm speaking of plants from Earth here (presumably deliberately introduced) to keep things a little less open-ended. And yes, retaining moisture seems like it would be a huge problem, though if rooted in a glacier I'd think they might have a chance of preserving water balance. But I don't actually know if any plants can endure very low pressure conditions like this; I found a cite that vegetables can survive brief vacuum. [5] Wnt (talk) 07:08, 2 January 2013 (UTC)

Boiling point can not be lower than melting point. Martian conditions are close to the triple point of water, but, taking into account the low partial pressure of water vapor in the martian atmosphere, any melted water will likely start boiling almost immediately. Ruslik_Zero 07:27, 2 January 2013 (UTC)

Lower than local melting point, no. Lower than 'sea level earth melting point, of course it can. The triple point on Mars has to be different than the triple point on earth. That's how science works. Evanh2008 ^{(talk|contribs)} 07:47, 2 January 2013 (UTC)

First, the melting point of water lowers with rising pressure. Second, the triple point is a characteristic of water only, not ambient conditions. The phase diagram of water is same everywhere in the Universe. Ruslik_Zero 08:05, 2 January 2013 (UTC)

You seem to be confusing the concept of the triple point with the temperature at which thermodynamic equilibrium between the phases occurs. On Earth the temperature needs to be about 273 K. I'm not about to compute what it is on Mars, but it has little to do with the fact that water under a six-millibar (.1771 inches Hg) atmosphere will boil at -5 C, give or take a bit. Everyone is welcome to break out a calculator and check for themselves. Evanh2008 ^{(talk|contribs)} 08:21, 2 January 2013 (UTC)

Okay, I see what you mean now; my numbers were off. In theory the boiling point is around -41 C, but you're right about the triple point. I guess there is no true boiling on Mars then? Just sublimation? Evanh2008 ^{(talk|contribs)} 08:41, 2 January 2013 (UTC)

You're forgetting plants still need oxygen as well. Yes, I know (most) plants produce an excess of oxygen, but when not actively photosynthesising (ie in the dark) they need oxygen for respiration just as much as humans do. So just having the right partial pressure of carbon dioxide isn't enough. I guess you could just keep them in constant light, but I don't know what effects that would have. Fgf10 (talk) 11:41, 2 January 2013 (UTC)

Well, I was assuming that whenever they were in the dark they'd need to be frozen/inactive anyway. In theory I suppose they could store redox potential in some other form than oxygen. Wnt (talk) 15:32, 2 January 2013 (UTC)

Hydrogen peroxide? Plasmic Physics (talk) 01:36, 4 January 2013 (UTC)

I was thinking more of some sort of melanin, if a battery-like potential could be charged from local minerals, or oxidation of hematite to goethite, etc. But if the plant can tank them effectively, I suppose peroxides would work. Wnt (talk) 03:27, 4 January 2013 (UTC)

At what distance from our sun would Sirius and the sun have the same brightness?

Pluto? The Oort Cloud? How many AUs? Thanks.Rich (talk) 04:51, 2 January 2013 (UTC)

The absolute magnitude of the Sun is 4.83, of Sirius—1.42. They will have the same brightness if the ration of distances to them from an observer is 10^{(4.83-1.42)/5}=4.81. The distance to Sirius is 2.6 pc. So this translates to the distance from the Sun of about 2.6/5.81=0.45 pc or about 90,000 AU. Ruslik_Zero 07:57, 2 January 2013 (UTC)

Which translates to beyond or near the presumed outer reaches of the outer Oort cloud (depending on how you define its extent). — Quondum 08:44, 2 January 2013 (UTC)

That calculation elided that the brightness goes down as the square of distance and the absolute brightness is got by multiplying by 0.4. Half of 0.4 is 0.2 which is 1/5. Dmcq (talk) 13:09, 2 January 2013 (UTC)

Pardon my confusion, but why did you get 4.81 and then divide 2.6 by 5.81? Why doesn't it end up 2.6/4.81, which makes 0.541 pc? Nyttend (talk) 20:52, 2 January 2013 (UTC)

You seem to be correct, there is apparenty a slip in the original calculation, making the distance more like 110,000 AU. — Quondum

The absolute magnitude of the Sun is +4.83, the absolute magnitude of Sirius is +1.42, i.e. 3.41 magnitudes lower. A source 5 magnitudes lower than another is 100 times brighter, so Sirius is 100^{(4.83-1.42)/5}=23.1206 times brighter than the Sun (at the same distance). The apparent brightness varies with distance according to the inverse-square law, so Sirius would need to be sqrt(23.1206) = 4.81 times as far away as the Sun to appear equally bright as the Sun - i.e. at 4.81AU (end of calculation). For comparison, Jupiter is 5.2AU from the Sun. --catslash (talk) 02:25, 3 January 2013 (UTC)

4.81 is ratio of distances. So, the total distance should be divided by 4.81+1=5.81. Ruslik_Zero 08:28, 3 January 2013 (UTC)

I think the OP was assuming that the Sun and Sirius are fixed - where would the observer be for them to be equally bright? Bubba73 ^{You talkin' to me?} 02:38, 3 January 2013 (UTC)

Stupid of me. Then for the two distances from the observer to be in the ratio 1:4.81, her distance from the Sun is (1/(1+4.81))2.64pc = 0.454pc = 93700AU --catslash (talk) 10:36, 3 January 2013 (UTC)

No, you had the ratio right. Bubba73 ^{You talkin' to me?} 23:30, 3 January 2013 (UTC)

Or, a more general question: given two objects of absolute magnitudes X and Y, at what distance from X are the apparent brightnesses equal? --jpgordon^{::==( o )} 07:52, 3 January 2013 (UTC)

If the distances of X from the observer is x and the distance of Y is y and the total distance is d, and the absolute magnitudes are M_x and M_y then you need to solve simultaneously

$x+y=d$

${\frac {100^{-{\frac {M_{y}}{5}}}}{y^{2}}}={\frac {100^{-{\frac {M_{x}}{5}}}}{x^{2}}}$

The latter simplifies to

${\frac {x}{y}}=10^{\frac {M_{y}-M_{x}}{5}}$

and substituting $y=d-x$ and solving for x

$x={\frac {d}{1+10^{\frac {M_{x}-M_{y}}{5}}}}$

(note that M_x and M_y are the other way around from in the preceding equation), which gives 93750AU from the Sun for the original problem. --catslash (talk) 10:36, 3 January 2013 (UTC)

The distance ratio defines an ellipsoid with one focus at the Sun and the other behind it as seen from Sirius. Most of the responses seem to concern the intersection of that ellipsoid with a sphere with Sirius at its center and Sol on its surface. —Tamfang (talk) 19:11, 30 June 2013 (UTC)

Physics and chemistry questions

I have a number of questions which are not being answered neither by my seniors nor my teachers. However, some of them are easy .It is better to ask some of them at one time instead of one by one.

1. Why do like charges repel each other and unlike charges attract each other ?
2. Why does water boil at a lower temperature at high altitudes ?
3. Why does cooking anything in water take longer time on mountain top than at sea level ?
4. When we twist our fingers, it produces sound. Why is it so ? Is there any suitable word instead of "twist" ?
5. Chemical formula of copper sulfate pentahydrate is "CuSO4·5H2O". What does ·5H2O represent ? Is it correct to say · as dot ?
   

Sorry, I have asked too much. BTW Thank you and Happy New Year. Want to be Einstein (talk) 07:31, 2 January 2013 (UTC)

1) I'm not sure that we really know why, it's just a fundamental observation that they do. It might be explained in terms of quantum mechanics, string theory, and such, but ultimately you still come to a point where we say "it's that way just because it is".

3) Since water boils at a lower temperature, that keeps the water at that lower temperature, assuming the steam is free to boil off (so not in a pressure cooker, say). It takes longer to cook things at a lower temperature, and, if the temperature is too low, it may never cook.

4) Do you mean cracking knuckles ? I believe that's caused by cavitation.

5) That means it has 5 water molecules loosely bound to the central molecule. Others can add details and how you say it. StuRat (talk) 07:47, 2 January 2013 (UTC)

Regarding item 2, Boiling point explains that the boiling point varies depending on the atmospheric pressure. The lower the pressure, the lower the boiling point. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:22, 2 January 2013 (UTC)

The "like repels like" thing with charges isn't something we have an answer for - all we know is that this is what happens. There are many situations in science where we have complete knowledge of how things behave without any understanding of why. About the best we can come up with is the Weak Anthropic Principle - which basically says that if the universe worked the other way around, then (presumably) atoms would not have formed and therefore there would be no stars, planets, people, Wikipedias and Wikipedia Science Reference Desks. Hence, only those universes where physics work the way our universe does will have people around to ask the question. It's an unsatisfying answer - but it's really all we have.

Water boils at the temperature at which the vapor pressure of steam equals or exceeds that of the air above the surface. At high altitudes, the air pressure is lower, so the vapor pressure of the steam can be lower - which happens at lower temperatures. Since cooking is mostly about getting the food up to some desired temperature, most things cook more slowly at high altitudes. Contrast this with a pressure cooker which deliberately increases the pressure inside the pot to allow the water inside to reach higher temperatures without boiling so that foods cook more quickly than they otherwise would. SteveBaker (talk) 14:38, 2 January 2013 (UTC)

I would quibble with StuRat's answer to #5, in that while water of crystallization includes water which is loosely bound (coordinated) to a central atom, this may be written (if the structure is known) in a different notation, e.g. Rhodium (III) chloride = RhCl₃(H₂O)_n. Sometimes waters not directly bound to the central atom nonetheless turn up in a structure, as with the [Cu(H₂O)₄]SO₄·H₂O mentioned in the article; but all are included when written generically in the dot notation the questioner used. There's a bit of inconsistency in the article regarding Glauber's salt - our article says only 8 of the 10 waters are directly bound, but the water of crystallization article writes it as if all 10 are. Anyway, my point is that if you look at the crystal structure the waters aren't always clearly associated with one particular molecule; it can be more like an aqueous solution that has simply become concentrated enough to take on a crystalline solidity. Wnt (talk) 15:29, 2 January 2013 (UTC)

I read this in "Microsoft Student with Encarta Premium 2007"
In one example of the electromagnetic force, two electrons repel each other because they both have negative electric charges. One electron releases a photon, and the other electron absorbs it. Even though photons have no mass, their energy gives them momentum, a property that enables them to affect other particles. The momentum of the photon pushes the two electrons apart, just as the momentum of a basketball tossed between two ice skaters will push the skaters apart.
This explains why like charges repel each other. I searched whole encyclopedia but it does not provide any information about unlike charges. Is this explanation correct ? Answer to Q.4 given by StuRat mean same as what I thought. One more thing I want to know is that Is it harmful to crack knuckles ? Want to be Einstein (talk) 16:07, 2 January 2013 (UTC)

Cracking knuckles is not harmful as far as we know yet, according to Cracking knuckles#Effects, except that "habitual knuckle-crackers were more likely to have hand swelling and lowered grip strength", which doesn't address which is cause and which is effect. From the article: "it remains unclear if knuckle cracking is in itself associated with any impaired hand function." Duoduoduo (talk) 17:52, 2 January 2013 (UTC)

With regard to the electromagnetic force question, the photon is the force carrier, a virtual particle exchanged in an exceedingly short period of time, which causes repulsion between like charges. The phenomenon is the same where attraction is concerned, in that photons are exchanged - it's just not as easy to describe intuitively as the basketball analogy does for repulsion. It is important to remember that the virtual particle model is just an interpretation of what happens, and although it gives correct results under enough conditions to be useful, it is only one possible way of looking at it, and has its limitations. 72.128.82.131 (talk) 18:27, 2 January 2013 (UTC)

The Encarta explanation is a really weak one. A logically-minded reader would have to assume that two positrons would also exchange a photon to repel each other - and then immediately ask why the photon emitted by a positron attracts rather than repelling a regular electron? A photon is a photon...there isn't a matching anti-particle - so how does the electron "know" what emitted the photon in order to know whether to be attracted or repelled. Perhaps there is some good science here - but there is no sign of it in that explanation! SteveBaker (talk) 22:02, 2 January 2013 (UTC)

Probably because the very very short explanation does not explain what a virtual photon is, or how to intuitively understand it! The electron doesn't emit a single, real photon. It emits a continuous wavelike set of virtual photons, most of which cancel out and have no effect on the universe. When encountering another charged particle, also swimming in another sea of virtual photons, some of those virtual particles cancel out, and others constructively interfere; and real momentum and energy can be exchanged, depending on how they all cancel out. Now, why a sea of imaginary semi-non-existing particles is any more satisfying than a field theory, I do not understand; but modern physicists generally agree that the model of virtual particles that cancel out is a better model. This model resolves more questions, and leaves fewer holes in the explanation, than the classical field theory we learn in first-year physics. More on this: electrostatic Coulomb force, explained as exchange of virtual particles. Rest assured, our article only barely explains this topic; physics educators generally recognize that to learn this topic, about four or six years of advanced university-level mathematics and physics are prerequisite. Nimur (talk) 22:10, 2 January 2013 (UTC)

Question 1 is fairly tautological. "Like" charges repel because we call charges that repel each other "like". If they attracted each other, we'd call them "unlike". - Nunh-huh 01:32, 3 January 2013 (UTC)

I disagree. If you group objects into two groups, based on their behavior, there are two possible attraction scenarios:

1) Everything in group A attracts everything in group B, while everything in group A repels everything else in group A and everything in group B repels everything else in group B. This is "like repels like".

2) The reverse. Everything in group A repels everything in group B, while everything in group A attracts everything else in group A and everything in group B attracts everything else in group B. This is "like attracts like".

Rearranging the groups can't change scenario 1 to scenario 2 or vice-versa.StuRat (talk) 02:51, 3 January 2013 (UTC)

Fourteen other possibilities:

• A repels all, B repels A and attracts B
• A repels all, B attracts A and repels B
• A repels all, B attracts all
• A repels A and attracts B, B repels all
• A repels A and attracts B, B repels A and attracts B
• A repels A and attracts B, B attracts A and repels B
• A repels A and attracts B, B attracts all
• A attracts A and repels B, B repels all
• A attracts A and repels B, B repels A and attracts B
• A attracts A and repels B, B attracts A and repels B
• A attracts A and repels B, B attracts all
• A attracts all, B repels all
• A attracts all, B repels A and attracts B
• A attracts all, B attracts A and repels B

But if A vs B is a continuum (e.g., quantity of charge or mass) rather than a dichotomy, I guess we're stuck with Stu's two cases. Is there an example of Stu's second case in particles? —Tamfang (talk) 19:49, 30 June 2013 (UTC)

• 1) Has been answered by several people above, but the "why" question doesn't have an answer. Some "fundemental properties" come in two opposing varieties which repel each other. That's a description of how they work, the why boils down to either the anthropic principle or "because that's the way God made it" or something. There's not a good answer for that kind of "why" question, it just is.
• 2) Has also been answered. But to say it in simplest terms: Something is a liquid or a solid because the forces holding it together exceed the forces trying to tear it apart. Thermal energy is the primary motivation for molecules to fly apart (molecules which are separated from each other is called a "gas". The process of a liquid turning into a gas at maximum effect is called "boiling"). There are several things holding molecules together in liquid form: intermolecular forces are one, but external pressure also plays a part. If you lower the external pressure on a liquid, you release some of the force holding it together, so you make it easier for thermal energy to tear the molecules from each other, and thus lower the boiling point. At high elevations, you have less air above you, so it weighs less, so it exerts less pressure.
• 3) As noted, at higher elevations, water boils at less than 100 degrees C. That means that the hottest the water can get is lower than the hottest the water can get at lower elevations. Lower maximum temperature means longer cooking times.
• 4) Joint cracking is often caused when ligaments or tendons rub against each other or against the bones they attach to. It can also be caused by the synovial bursa shifting or rearranging rapidly (the aforementioned cavitation). Some people mistakenly thinks its because the bursa are breaking or rupturing; that is incorrect: if you ruptured your bursa, you'd be in a serious amount of hurt.
• 5) This is called either Water of crystallization or water of hydration. The specific nature of the way in which the water is bound to the molecule in question is ambiguous and inconsistent between various nomenclatures; there isn't a consistent way of noting it, despite what some claim above, in the difference between •xH₂O and (H₂O)_x. It means that individual water molecules are stoichiometrically bound up in the formula unit in some way; that is water acts like an atom or ion or other moiety in the formula of the substance. The water molecule can be bonded in a coordinate bond to, say, the metal as a ligand or it can occupy a specific locale in the crystal lattice as part of the unit cell. The formula is not always clear on how the water is bound, (in either notation), but it is important because the water needs to be dealt with stoichiometrically when, say, weighing the substance out on a scale and calculating how many moles of the substance you have.

Does all that help? --Jayron32 03:15, 3 January 2013 (UTC)

---

It's a theorem of relativistic quantum field theory that like charges of even-spin forces attract and like charges of odd-spin forces repel. Gravity and the Higgs force are the only fundamental even-spin fields (spin 2 and spin 0 respectively). The other fundamental forces, including electromagnetism, are spin-1. No one knows why only those forces with those spins exist (except for gravity, which seems necessary). Still, it's interesting that there can't be a field similar to the electromagnetic field in which like charges attract. -- BenRG (talk) 05:10, 3 January 2013 (UTC)

Another fundamental factor in the universe is the speed of light. Is there an explanation for why the speed of light is what it is and not some other speed? That is, it's about 186,000 miles per second. Why is it that, rather than 150,000 or 200,000 miles per second, for example? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:18, 3 January 2013 (UTC)

It's basically a measure of how fast we think. Traditional units are chosen for human convenience. A brain is about a decimeter across and it takes about a second to "have a thought", so the time scale of thought is about 3 billion times the light travel time across the brain. (The neuronal signals travel slower than that, but the speed of light sets the standard for all other motion.) It's a random-looking number (299,792,458 m/s) because there's some arbitrariness in the selection of convenient units. -- BenRG (talk) 20:55, 3 January 2013 (UTC)

I don't follow. The speed of light is a constant (in a given medium). What is it about the nature of light that defines what its speed is? ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:44, 4 January 2013 (UTC)

Thanks to all, every question was answered more than I expected. Want to be Einstein (talk) 17:26, 3 January 2013 (UTC)

You're welcome. May we mark this Q resolved ? StuRat (talk) 18:42, 3 January 2013 (UTC)

Of course. Want to be Einstein (talk) 19:35, 3 January 2013 (UTC)

Resolved

Professional engineers

Are professional engineers used in any aspect of film production directly or indirectly? In which areas? 176.27.208.210 (talk) 11:20, 2 January 2013 (UTC)

Certifying the building drawings of the buildings (which are used in filming, as they house sets) on the studio lots. 67.163.109.173 (talk) 11:39, 2 January 2013 (UTC)

There are many different kinds of engineer, but see film crew and particularly sound engineer.--Shantavira|^{feed me} 12:10, 2 January 2013 (UTC)

Any movie with computer graphics (which these days is almost any movie!) is likely to have a bunch of professional software engineers working for them in various capacities. SteveBaker (talk) 14:16, 2 January 2013 (UTC)

We have an article, Professional engineer, which explains that in some countries like the United States, there are engineers who are licensed by the state or other government unit, and are allowed to plan projects that could impact public safety, such as electrical wiring in larger buildings, the structure of buildings, water systems, etc. This kind of licensure would not be needed for those aspects of film production that helps to make the film pleasing to the audience. Jc3s5h (talk) 14:31, 2 January 2013 (UTC)

Ah - yes. If we're talking about licensed professional engineers - then that's a different matter. I doubt that there are many jobs in the film industry that require such a license - although it might be that the strong union rules in the film industry could require a license in some cases. The use of the term "professional engineer" to denote someone in one of those niche engineering jobs that requires a state license is really annoying! I'm an engineer - and I get paid to do it - so I'm definitely a professional. So why can't I call myself a "professional engineer"? Weird! SteveBaker (talk) 14:48, 2 January 2013 (UTC)

Steve, whether you are a professional or not, and whether you are an engineer or not, you can't "directly or indirectly use or cause to be used as a professional, business, or commercial identification, title, name, representation, claim, asset, or means of advantage or benefit any of, or a variation or abbreviation of, the following terms:" (...) "professional engineer" - per Texas Occupations Code, Title 6, Chapter 1001. Similar laws apply in North Carolina, and in California, where I have also been professionally employed as an engineer, but never as a Professional Engineer. This is sort of an old-fashioned rule that was intended to prevent fraudsters from building shoddy constructions while pretending to be civil engineers; it has very limited applicability to things like electronics and software engineering. Nimur (talk) 18:38, 2 January 2013 (UTC)

Pretty sure any engineer is a "professional" - I sure hope I never meet any structure or gadget designed by a nonprofessional engineer! 72.128.82.131 (talk) 18:30, 2 January 2013 (UTC)

See Aggie Bonfire... Wnt (talk) 21:06, 2 January 2013 (UTC)

The letters I like best are MICE ;-) It stands for member of the institute of civil engineers. One can also become a chartered mathematician or information technologist in Britain. Dmcq (talk) 13:34, 3 January 2013 (UTC)

90.219.64.4 (talk) 20:48, 6 January 2013 (UTC)== Logic ==

Isnt everything logical, even creativity? I agree that being logical inhibits creativity as creativity requires thinking beyond things we already understand but the end product of creativity is logical. 176.250.156.24 (talk) 15:38, 2 January 2013 (UTC)

How does serendipity fit into your argument? — Preceding unsigned comment added by 217.158.236.14 (talk) 15:56, 2 January 2013 (UTC)

Serendipity is perfectly logical. There's always a probability that an event which is happy for some people will occur. 176.250.156.24 (talk) 18:18, 2 January 2013 (UTC)

I'm not sure you understand the definition of serendipity. It means "happy accident". Accidents aren't logical. — Preceding unsigned comment added by 217.158.236.14 (talk) 11:16, 3 January 2013 (UTC)

Why not? There's always a chance accidents will happen. 90.219.64.4 (talk) 14:59, 3 January 2013 (UTC)

You are equating logic with chance? Saying that random and logic are the same?217.158.236.14 (talk) 17:13, 3 January 2013 (UTC)

People (and many of their beliefs and actions) are not logical, as Spock liked to remind us.--Shantavira|^{feed me} 16:04, 2 January 2013 (UTC)

Thats because people aren't perfect. We act based on emotion and our beliefs are formed by past experiences, and possibly genetics. Sounds logical to me. 176.250.156.24 (talk) 18:18, 2 January 2013 (UTC)

In the real world, logic doesn't always apply, as it requires complete information to draw conclusions. We rarely have complete info when asked to decide, so must use other methods. As Kirk once convinced Spock, "there are times when the logical approach is an illogical one". StuRat (talk) 22:48, 2 January 2013 (UTC)

In your real world example, isn't that where creativity comes in? As someone said above creativity doesn't contradict logic. 90.219.64.4 (talk) 15:14, 3 January 2013 (UTC)

Logic means starting from an assumption and following it to what it implies. Some creativity involves coming up with clever assumptions. Some creativity involves finding previously unthought-of ways to go from certain assumptions to interesting conclusions. And some creativity has nothing to do with logic -- e.g. if I come up with a new painting or a new melody.

One needs to distinguish between "logical" in the sense of following the principles of logic to go from assumptions to conclusions, and the looser use of "logical" to mean "not contradicting logic". If I come up with a new melody, I'm not using the principles of logic, and I'm not contradicting them either. Duoduoduo (talk) 18:54, 2 January 2013 (UTC)

• There's no inherent conflict between emotion and logic. Without emotion, a Vulcan would never bother to get out of bed in the morning, since he simply wouldn't care. Spock obviously cares, he just doesn't like to show it. That's all a shortcoming of Gene Roddenberry's thought, and has nothing to do with logic, which is simply not acting or arguing contradictorily. μηδείς (talk) 23:03, 2 January 2013 (UTC)

Whoa there, I agree that there is no inherent conflict between emotions and logic, but I can't see the logical leap to "you need to "care" to get out of bed"... I think that's making too many assumptions, does a computer "care" to wake up when you press the on button? Vespine (talk) 00:56, 3 January 2013 (UTC)

Which makes more sense to you, to argue that Vulcans are programmed, or to argue about Vulcans? The essence of logic is non-contradiction μηδείς (talk) 03:28, 3 January 2013 (UTC)

Not sure what you mean. I just didn't buy going from "no conflict between logic and emotion" to "X" would not get out of bed without emotions. Nothing specific about vulcans. Vespine (talk) 04:40, 3 January 2013 (UTC)

I agree it's not clear he wouldn't get out of bed (if he doesn't care enough to get out of bed, maybe he also doesn't care enough to stay in bed) but I do recall lots of times when Spock would openly express things that I call emotions. He would say, for example, that he preferred some outcome; isn't that an emotion? Interesting was one of his catchwords; interest is also an emotion. --Trovatore (talk) 09:09, 3 January 2013 (UTC)

Or "fascinating", or the raising of one eyebrow. It's been a long time, but I don't think it was represented that Vulcans are emotionless, but rather that they are in control of their emotions. Spock, of course, was half-human. But Vulcans seem to have a strong sense of morality and ethics, which is hard to explain on logic alone. (And realistically, there have been countless screenwriters for Trek, which tends to muddy the continuity waters.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:15, 3 January 2013 (UTC)

I don't think vulcans are completely logical. They use it to overcome certain emotions and conflicts but they themselves aren't very logical. If anything, the Borg are more logical as they have no emotion. 90.219.64.4 (talk) 14:59, 3 January 2013 (UTC)

But can't the end result of anything be thought of as logical? As mentioned above creativity doesn't contradict logic although it does require going beyond logic. Although actions based on emotions may not seem logical in the wider context, it could be argued that the action is logical for the person feeling the emotion as its the emotion which is causing them to act in such a way. 90.219.64.4 (talk) 15:14, 3 January 2013 (UTC)

• Yes, literally, without emotion there is no motivation to move. We get out of bed in the morning because we want to assuage our hunger, or we dislike the notion of crapping ourselves, or we want to get to work on time so we can keep earning money to buy the things we want, all emotions. Even if we say we are acting on force of habit, that is simply the force of past emotions. Of course the emotions involved aren't experienced strongly the way a murderous rage is, and we hardly notice them, given we are adults with long years of practice and some levels of distance and abstraction between the action and the relevant urges. That wasn't always the case. A baby in a crib will scream to get out of it just as it will scream from hunger pains or an ear ache. Consider how you would feel if you had to go to the bathroom and found you were tied to the bed or temporarily unable to move. You may not be aware of it consciously, but in the end there is no intentional action without urges and the desire to satisfy them. Spock is a caricature of a classical stoic, not an emotionless automaton. The latter idea and the belief that logic is the opposite of emotion are mistakes based on a naive misunderstanding of human nature. μηδείς (talk) 17:34, 3 January 2013 (UTC)

"without emotion there is no motivation to move" - I don't think that's necessarily true. If you have some general, lofty goals (perhaps the idea that preservation of your species into the future is valuable) - then there can still be reason to get up in the morning, get into your big shiney starship and start kicking the butt of evil-doers. In StarTrek, we know that the Vulcans had such goals. Didn't Spock's last words include "The needs of the many outweighs the needs of the few" ? Take a few of that kind of over-arching statement and enter them into the chain of logical thinking as axioms. Wouldn't that result in much the kind of behavior one sees in the Vulcans most of the time.

Mathematically speaking, logic can't do a damned thing without a few axioms to work on. Even logical systems as basic as arithmetic and set theory require axioms. ("There exists a number who's value is zero" and "Every number has a successor" for example). So to know what a totally logical being would do upon awaking each morning depends entirely upon what axioms are inserted into that logical system.

But even in a world where those lofty goals are not present, one could logically say "It makes no logical difference whether I get up or not - so it's a free choice and therefore a random outcome is as good as any other - so I'll flip a coin - and...<flip>...it's heads, so OK, I'll get up!". But if that person takes a longer view: "It makes no difference whether my species survives into the future or not - so I'll flip a coin to decide whether that's something I should strive to achieve"...and from that point onwards, the character has all of the motivations needed to get up in the morning and do great things.

The idea that Vulcans are emotionless is kinda stupid anyway. Emotions are just biochemical signals in the brain - flows of chemicals that are placed there by sensors detecting events in the outside world - evolved over millions of years to help us pass our genetic information onto the next generation. Denying them isn't particularly logical - although recognising and controlling them where higher brain function and logic deems necessary is extremely valuable...and a close approximation of what real-world humans mostly manage to do.

SteveBaker (talk) 16:48, 5 January 2013 (UTC)

are emotions logical?

nicotine inhaler

I remember back in the 1990s I used to see commercials for a nicotine inhaler that was for quitting smoking and a alternative to patches and gum. This was available over-the-counter. This was a different thing than the E-cig. I don't believe it was electronic. Now all of a sudden it seems to have disappeared from the marketplace in the United States, what happened to it?--Jonharley667 (talk) 17:22, 2 January 2013 (UTC)

The NICORETTE® Inhalator is still available in the UK, but I haven't seen anybody using one for years. The only US product that I could find (after a very quick search) was the NICOTROL Inhaler which is "Prescription-Only". Alansplodge (talk) 17:32, 2 January 2013 (UTC)

I am certainly not a medical expert, but a nicotine inhaler sounds totally daft to me. As a general rule, a drug is more addictive if injected ior inhaled, than when eaten, because injecting or inhaling enable high concentrations to reach the brain in seconds. Contrast methodone injected versus swallowed. A nicotine inhaler would continue nictine adiction with full grip on you, whereas a patch would at least have a chance of curing physical addition as the amount of nicotine released slowly decreases over time. Of course the best way to quit is to just make up your mind and stop when you are sick. You can then assign the withdrawal symptoms to whatever made you sick (eg flu). Failing that just quit. Wickwack 120.145.8.219 (talk) 00:58, 3 January 2013 (UTC)

The point is that nicotine addiction, in itself, isn't harmful. It's the tar which is consumed along with the nicotine that causes cancer. So, if you can decouple the two, and avoid introducing any new chemicals into the lungs, people can continue to get their nicotine fix without dying from cancer or other lung diseases. I'm a bit worried about the combo of hot temperatures and plastic delivery devices, though, as that may create toxic plastic fumes. StuRat (talk) 04:26, 3 January 2013 (UTC)

Now, hold on. Nicotine#Toxicology would disagree with you on your first point. Nicotine, isn't itself carcinogenic, at least not in the way that the tar and other nasties in tobacco is, but nicotine is not itself a benign substance. Various nicotine replacement therapies (patches, gums, inhalers, etc.) are substitutes for tobacco use in the same way that Methadone is a substitute for heroin: it's less nasty than the thing it is substituting for, but it isn't candy. Nicotine is harmful enough on its own, but it is less harmful than smoking or chewing is. --Jayron32 04:31, 3 January 2013 (UTC)

Well, you can overdose on it, sure, and pregnant women should avoid it, but if you keep the dosage reasonable, it's about like caffeine, not a bad way to keep awake and focused. In an ideal world, nobody would need either, but this is the real world. StuRat (talk) 06:27, 3 January 2013 (UTC)

Nicotine#Side Effects also lists potential negative outcomes under non-overdose conditions. --Jayron32 06:40, 3 January 2013 (UTC)

Careful, Jayron. StuRat normally comes back from a rebuttal with some attempt to prove the rebuttal wrong, citing some dubious website if necessary, or trying to change the subject. If you disagree again, he'll come back again, getting a bit silly. Meanwhile, strangely, the Wiki article you cited doesn't cover nicotine's well known role in triggering TIA's, strokes, heart attacks, and other circulatory issues. It's not thought to be the prime cause but it can be strongly argued that the same applies to the role of smoking in lung cancer. Wickwack 124.178.177.194 (talk) 07:23, 3 January 2013 (UTC)

Actually, it's you who makes dubious, unsupported claims, like that Australians find 100% humidity comfortable: Wikipedia:Reference_desk/Archives/Science/2012_December_24#Suitable_conditions_for_ventilating_a_residential_property_to_reduce_humidity. StuRat (talk) 18:47, 3 January 2013 (UTC)

Unsupported claims? Pot calling kettle black there, Stu. What you haven't accepted or understood, and what makes your posts silly (like your claim in http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#Hobbitses "An elephant might die just from falling over" that you continued to argue after given videos of elephants falling over without any such problem), is that a) 100% rel humidity and very close to it occurs in various parts of the World at various times; b) humans have spread all over the World and get used to just about anything that doesn't violate natural limits; c) as pointed out by someone else, not me, in theory so long as the wet bulb temperature is below body temperture, humans can lose heat; I actually claimed that humans need a temperature low enough that the wet bulb is considerably below body temperature in order to be comfortable. Wickwack 60.230.194.70 (talk) 23:31, 3 January 2013 (UTC)

There is little doubt that nicotine has harmful effects, but my understanding, for which I offer no warranty whatsoever and claim no particular expertise, is that it's much less harmful, everything taken into account, than smoking. If I am right about that, then the focus on the e-cig as a way to quit nicotine strikes me as Puritanical (in the contemporary understanding of that word, which of course has little to do with the historical Puritans). Lots of folks who have no desire to stop using nicotine, per se, are interested in it as a less harmful, permanent, nicotine delivery vehicle, and I wish them well. -- Trovatore (talk) 08:28, 3 January 2013 (UTC)

"it's about like caffeine" Spurious speculation is a bad thing Sturat. Perhaps cite more and hypothesize less. — Preceding unsigned comment added by 217.158.236.14 (talk) 08:45, 3 January 2013 (UTC)

Whoops, wrong number of tildes. Corrected now. I'm not StuRat. --Trovatore (talk) 09:01, 3 January 2013 (UTC)

The prescription versus nonprescription issue may well be enlightening, if you have the stomach for it. Wnt (talk) 15:05, 3 January 2013 (UTC)

So.... does anybody know why the inhaler disappeared from over the counter sales in the US? --Jonharley667 (talk) 15:57, 4 January 2013 (UTC)

Did you not read what we provided? Alansplodge was the first to respond - he confimed with a link that showed that inhalers ARE available in the USA, on precription. The reason why you need a prescription is probably what I said above - such a product would be extremely addictive. And as myself and others have pointed out, medically harmfull -significantly increasing your risk of TIA's, strokes, heart attacks, and other circulatory problems severe in their impact. A dangerous drug in other words - I am surprised it is available at all. Wickwack 124.178.42.57 (talk) 10:00, 5 January 2013 (UTC)

Did you bother reading what I wrote? It used to be OTC.--Jonharley667 (talk) 00:37, 7 January 2013 (UTC)