Wikipedia:Reference desk/Archives/Science/2008 February 29

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February 29

Matrix algebra

Someone discovered that matrix algebra seemed to describe accurately some fundamental law of nature. Who and what was it? —Preceding unsigned comment added by 79.76.173.143 (talk) 02:07, 29 February 2008 (UTC)

If you look at List of matrices#Matrices used in science and engineering, there are quite a few listed. Possibly what you're thinking of is the Hamiltonian matrix, which is used in quantum mechanics. Confusing Manifestation(Say hi!) 03:35, 29 February 2008 (UTC)

Or, the matrix formulation of quantum mechanics? This is a common reference name to Heisenberg's approach. Nimur (talk) 15:37, 29 February 2008 (UTC)

Water

I got flamed by some noobs on reddit for saying the earth is mostly not water. I found the surface area of the water, but not the total volume. What is it? —Preceding unsigned comment added by 138.87.180.89 (talk) 08:08, 29 February 2008 (UTC)

This page gives some estimates of the amount of water in various forms. Rough calculation: if R is the radius of the earth and h the average depth of surface water then the volume of the earth is $4\pi R^{3}/3$ and the volume of water $4\pi r^{2}h$, giving a ratio of $3h/R$. R is about 6370 km, and let's guess h = 3km, which gives 0.00141, or about 0.14%. The numbers from the USGS site give about the same answer: 0.12%. Either way, you win ;) AndrewWTaylor (talk) 08:37, 29 February 2008 (UTC)

The Earth can only be mostly water if it is flat. 206.252.74.48 (talk) 13:44, 29 February 2008 (UTC)

"The earth is mostly ___" probably is loose language to mean "most of the earth's mass is made of ___". If this more precise language is used, most of the earth's mass is iron. Alternatively, most of the earth's volume is silicon dioxide. See Earth for more details! Nimur (talk) 15:39, 29 February 2008 (UTC)

• This has been covered in QI as well. Most people know that approx. 75% of the earth is covered in water, but when you're going to look at volume and weight, only a tiny part of the earth is water because there is a lot more beneath the earth's crust. You (the questioner) were totally in what you said. - 87.211.75.45 (talk) 15:49, 1 March 2008 (UTC)

Oh NO 87.211.75.45, that answer was just too obvious. I'm afraid it's minus ten points for you! -mattbuck (Talk) 23:27, 1 March 2008 (UTC)

Concentration

Could someone please answer this question without using words like molarity and molality? If you have 50ml ethanol in cup A and 50ml ethanol + 50ml water in cup B, does A necessarily have a higher concentration of ethanol? Zain Ebrahim (talk) 13:05, 29 February 2008 (UTC)

Assuming you mean pure ethanol in each case then yes Nil Einne (talk) 13:07, 29 February 2008 (UTC)

I did and thanks! Zain Ebrahim (talk) 13:09, 29 February 2008 (UTC)

For further detail, Cup B is approximately half as concentrated. It is not exactly half as concentrated, because when mixing 50 mL of ethanol with 50 mL of water, the resulting solution has a volume less than 100 mL. (It would be about 95.6 mL, see Ethanol#Physical properties for some details). For reasons such as this, chemists use molality (e.g., amount of ethanol per mass of water), and molarity (e.g., amount of ethanol per total amount of mixture) to be very precise when discussing concentration. Hopefully if you are studying chemistry, you will become familiar with this terminology, because it exists to reduce confusion (not to increase it) - and when weird stuff happens, like "50 mL + 50 mL = 96.5 mL" you want to be sure your descriptions are as accurate as possible. Nimur (talk) 15:47, 29 February 2008 (UTC)

BTW, to preface my original response, it doesn't actually matter if the ethanol was pure provided you used the same original concentration of ethanol in both cases. If you start to talk about solutions of different original concentrations then using molarity makes it much easier to come up with an accurate answer Nil Einne (talk) 04:56, 1 March 2008 (UTC)

Light photons and other EM radiation

I heard light and other Electro magnetic radiation travels in waves. But light is composed of photons. So do these photons move in waves, rather than in straight lines? 64.236.121.129 (talk) 14:34, 29 February 2008 (UTC)

see Wave–particle duality, I think. -- Aeluwas (talk) 14:47, 29 February 2008 (UTC)

So the photons do indeed move in waves then? 64.236.121.129 (talk) 15:37, 29 February 2008 (UTC)

A common phrase is that light travels like a wave, and collides like a particle. Depending on the application, the mathematics of the situation dictate whether you can call it a wave. Nimur (talk) 15:49, 29 February 2008 (UTC)

There's no easy answer to this. Photons sometimes act like what we would call a wave, sometimes like what we would call a particle. Bohr famously called this complementarity. A photon is not a wave or a particle; it is a photon, something different, something we don't have any first-hand experience with at a macroscopic scale. We can abstract it as a wave or particle (macroscopic metaphors) depending on how we measure or observe it, but each time we are only viewing part of its true existence. Deep stuff, dude. --98.217.18.109 (talk) 15:54, 29 February 2008 (UTC)

Yea I was about to say, I still have no idea whether photons travel in a wave or not. So we don't really know is what you are saying? 64.236.121.129 (talk) 16:52, 29 February 2008 (UTC)

Well, the thing that is very much the wrong idea is the notion that photons are tiny little billiard balls, moving in a wavy line. There probably is no easy answer that says what photons are. As photon says, they have properties of waves and particles. The article Wave–particle duality linked to above may not make it clear, but that's because photons aren't like any objects we're used to. Friday (talk) 17:01, 29 February 2008 (UTC)

I wouldn't say it's so much that "we don't know" (though to be sure, there's plenty left to decipher in this area) so much as we do know that statements like "a photon is a wave" or "a photon is not a wave" are too simplistic and thus incorrect. — Lomn 17:54, 29 February 2008 (UTC)

Electromagnetic waves don't move side to side as they propagate. Pictures like this are very misleading in that respect. A "photon" is basically a certain amount of energy in the form of light. Having 3 photons is like having three liters of water—you can't point and say "here's one, there's another", you just have a total of three. In quantum theory the number of photons usually has to be an integer, so if an atom absorbs some light, it has to absorb a whole photon at once, not just a little bit. It's in that sense that photons behave like particles. Another thing to keep in mind is that even in classical electromagnetism, where there are only waves and no particles, light still moves in straight lines for many purposes. So, photons move in straight lines for many purposes; photons move in waves (they are waves); and photons don't wave side to side as they move. —Preceding unsigned comment added by BenRG (talk • contribs) 18:38, 29 February 2008 (UTC)

Question about scientific theory vs. law

Is it true that a scientific theory never becomes a scientific law? In other words, they have completely different definitions.

Let me give an example. If we were to talk about evolution being a theory. If I could live forever, and travel back in time, and I go back to the origin of life on Earth and I document, and record evolution occurring right before my eyes over the course of billions of years all the way up to today. Then today in 2008, I go up to a scientist and I show him all of my video tape displaying evolution happening right before his eyes (time lapsed), and all the other evidence I have. The he says wow this is incredible, and he adds all this evidence to the existing theory of evolution. Even with all this new evidence, the videotapes showing evolution occuring in real time, etc, the theory of evolution still remains a theory. Right? Even though I saw it with my own eyes, and videotaped it? 64.236.121.129 (talk) 15:26, 29 February 2008 (UTC)

The distinction is mainly historical. See law of gravity and theory of gravity - they're the same thing. A few major historic theories have been frequently called "laws", but there's no real difference in meaning. You can gather more and more evidence that supports a particular theory, and it's still a theory. It's just becoming better supported. See scientific theory. Friday (talk) 15:31, 29 February 2008 (UTC)

Well I'm not sure about that. I heard that Scientific Law means a description of observed phenomena, while Scientific Theory means an explaination of observed phenomena. 64.236.121.129 (talk) 15:38, 29 February 2008 (UTC)

Btw, about the gravity thing. Those two things simply redirect to the same article (it's a wiki thing, the article covers both). They aren't the same thing if I'm not mistaken. The law of gravity describes the properties of observed gravity on our planet, while the theory of gravity is Newton's attempt at explaining why gravity exists, but has since been replaced by Einstien's theory of general relativity. 64.236.121.129 (talk) 15:41, 29 February 2008 (UTC)

(ec) We do have scientific law which seems to make a bit of a distinction along those lines. In my experience, the terms are used mostly interchangably. But it may depend on what field you're working in. More to the specific point of the original question- the scientific method does not include the idea that we make an observation and then say "Look, I proved the theory! Now it's not a theory anymore!" This notion sounds like it comes from the often-exploited public misunderstanding of what a scientific theory is. In order to be a scientific theory, it must already be supported by lots of evidence. You don't prove things in science. Friday (talk) 15:46, 29 February 2008 (UTC)

There is also an article on scientific law. Also, one on evolution as theory and fact, which makes the comparison between the fact and theory of gravity and the fact and theory of evolution. Evolution, as the article discusses, is both fact and theory. It is a scientific fact (no matter how much people deny it) that species evolve over time. This is the fact of evolution. How they evolve is what is up for debate and is considered theory. -- MacAddct  1984 ^{(talk • contribs)} 15:44, 29 February 2008 (UTC)

Yes, but this can be misleading if you're not careful. In science, a theory is much bigger and more important than a "fact". A "fact" is just an observation. A theory explains it. Contrast this to common usage, where we think of a "fact" as something that's true, and a "theory" is just speculation. Science does not deal with truth. Friday (talk) 15:50, 29 February 2008 (UTC)

Yeah, I didn't mean to give off that impression. Facts are boring, theories are the interesting bit, which, despite their stigmatized name, can be backed up with an immense amount of data (a.k.a. facts). -- MacAddct  1984 ^{(talk • contribs)} 15:58, 29 February 2008 (UTC)

Well wait a minute, of course Science deals with truth. I agree you can't prove things in science, but it certainly deals with truth. 64.236.121.129 (talk) 15:53, 29 February 2008 (UTC)

Science deals with falsehood better than it does truth. It is very easy to prove something wrong. It is very hard to prove something true. Ergo Popper's famous falsifiability constraint. --98.217.18.109 (talk) 15:59, 29 February 2008 (UTC)

In my opinion, the distinction is purely philosophical. Man describes some thing he observes. He calls it a Law, which is a bold statement about Man's flawless understanding (and control) of Causality and consistency of the Universe. Alternatively, humans observe some thing and timidly postulate a theory which seems internally valid and consistent, and proposes it to the scientific community, who tirelessly debate it and use large words to make it inaccessible to the general public, antagonizing religious zealots, until everyone is so bored with it that they stop caring. It's a sort of spectrum of pomposity, ranging from:

• "So pompous as to presume that we can dictate the law of the universe" ("Law")...
• ...to "well, we've described the experiment in the simplest possible way" (good science),
• ...to "it's so complicated that only the super-intelligent elite can understand ("Theory"). In all cases, they've done the same thing, it's just how loudly they proclaim their greatness.

But, this is simply my opinion. Nimur (talk) 16:02, 29 February 2008 (UTC)

I think things in science are often often prefaced with statements like, "to the best of our current understanding". The same of can not be said of religion. -- MacAddct  1984 ^{(talk • contribs)} 16:12, 29 February 2008 (UTC)

In the world of science there is such a thing as dustbowl empiricism, in which the scientist simply collects facts. Having been an editorial consultant for a scientific journal, I claim that a paper which merely presents a set of facts or observations is less likely to get published than one which has facts/observations used to test a theoretical construct of interest. Dustbowl empiricism can go to the extent of a paper I once read called "The number of feathers in the laughing dove" which literally enumnerated facts such as "Laughing dove number one had 17,321 feathers. Laughing dove number 2 had 16,898 feathers, etc through a number of birds." (Makes one want to ask "So, bird, who's laughing now???") This can be the engineering side of scientific investigation, in which the raw data is collected by patient and careful plodders, which other insightful thinkers use to reach new heights of theory, leading to new testable predictions. Edison (talk) 16:17, 29 February 2008 (UTC)

The history of science contains many instances in which a law, based on the organisation of observations to reveal consistent patterns, is superseded by a theory, which gives a deeper causal explanation of the law. Four examples:

1. Kepler's laws of planetary motion were explained by Newton's law of universal gravitation, which was in turn explained by Einstein's theory of general relativity.
2. John Newlands' law of ocatves, Mendeleev's empirical periodic table, the law of definite proportions and the law of multiple proportions were all explained by atomic theory.
3. Mendelian inheritance was explained by the modern theory of genetics.
4. The Wallace line was explained by Darwin's theory of evolution.

Gandalf61 (talk) 19:46, 29 February 2008 (UTC)

Kanab ambersnail: two species? sub-species?

http://www.eol.org/taxa/16822383 http://www.eol.org/taxa/17245474

Is there two species with the name Kanab ambersnail? Or is this a subspecies? (Kanab was our 1.5 millionth article on en.wp.) -- Zanimum (talk) 15:48, 29 February 2008 (UTC)

Cold trap adequate to protect vacuum pump from HCl?

In my work, I have to evaporate small amounts of 6M HCl under high vacuum. I normally put a trap, which is cooled by a mixture of dry ice and alcohol, on the vacuum line to prevent the HCl vapors from reaching the pump. I've begun to wonder if this is adequate. I think the trap will equilbrate to ~ -78 C (the sublimation point of dry ice at 1 atm), and our article on HCl says it has a boiling point of -85 C. What do you think? ike9898 (talk) 16:29, 29 February 2008 (UTC)

I guess the HCL will come as an azeotrope with water.

Why not just put an acid trap eg NaOH pearls, before the pump trap.87.102.38.45 (talk) 17:33, 29 February 2008 (UTC)

I could do that but I'd still like to know if my current setup is adequate. ike9898 (talk) 18:44, 29 February 2008 (UTC)

Seeing as you have to ask you might be able to work out that the answer is no. Chances are it won't do any damage if you try anyway..

Anway given that your only using small amounts why not use an Aspirator, the hcl will be very much diluted, and 13mmHg is enough. Save you money too!87.102.38.45 (talk) 20:20, 29 February 2008 (UTC)

I don't understand the first part of your comment - why is the answer no because I had to ask? As to using an aspirator - no, a normal labortory aspirator won't generate a vacuum strong enough for my needs. This already takes hours at high vacuum. Can't someone comment on whether or not the vapors will condense in the situation I've described? ike9898 (talk) 22:15, 29 February 2008 (UTC)

Sorry, what I meant was that as you had doubts you could assume that your doubts were not founded on nothing..

A lab aspirator gives down to 13mmHg, and should easily give 20mmHg or less, a vac pump will get you down to fractions of mmHg pressure, but atmospheric pressure is 760mmHg, the extra vacuum is totally neglible. oops - the extra vacuum will just cause 'superheating' - ie bumping. You were just removing water and HCl right..

Take a look at this http://www.qvf.com/en/ProcessSystems_3/Mineral%20Acids/ConcentrationingofHydrochloricAcid.shtml it shows that the azeotrope increases in HCl concentration with decreasing pressure as you might expect. So initially your frozen hcl/water mixture will be more concentrated. But it will freeze. But this doesn't stop sublimation of this frozen mixture occuring - and your coolant is not cool enough to do it. So some hcl/water (very much enriched in hcl) will escape.. In other words - you need an acid trap for safe working.

If the time it takes to evaporate is a problem then I suggest a warm water bath combined with hand swirling, or much better a rotary evaporator - surely you can get one of these.

Good luck.87.102.79.228 (talk) 09:22, 1 March 2008 (UTC)

nitrogenous

I recenly asked a question on how to get algae to grow faster and some people said nitrogenous would help. i read the wiki> page on it but i still dont under sand completly where or what this stuff is. So i was wondering if any one knows if there are and house hold products or things like plants or bugs that might contain nitrogenous. thanks --Sivad4991 (talk) 21:11, 29 February 2008 (UTC)

How about Fertilizer?209.151.139.172 (talk) 03:42, 1 March 2008 (UTC)

you will need nitrogen containing fertilizer, which could be in the form or organics (blood and bone) or ammonia or nitrate. Other minerals are also needed by algae such as potassium, phosphate, iron, copper, magnesium, calcium. There could also be some other ultratrace elements required too like boron, molybdenum and nickel nd vanadium. Hydroponic fertilizers should do the job. Graeme Bartlett (talk) 03:34, 2 March 2008 (UTC)

Gradient rings in constant voltage particle accelerators

http://updatecenter.britannica.com/eb/image?binaryId=3367&rendTypeId=4

what are they for?

i suppose that they guide the electric field in some way, but I dont quite see how they help, surely the electric field will form a straight line from whatever the potential of the central eelctrode to the end electrode anyway, providing the field recquired.

or to create an equpotential across the area of the circle enclosed by the ring

or do they guide the charged particles through some method?

and are they connected via a series of resistors to ensure they are all an equal step down of the voltage along the length from the maximum to earth? —Preceding unsigned comment added by 172.142.196.236 (talk) 21:20, 29 February 2008 (UTC)

One possibility (guess) is that the gradient rings are charged the same as the particle- and so would keep the particle in a central line whilst moving left to ring.. that doesn#t explain the name though..87.102.38.45 (talk) 21:32, 29 February 2008 (UTC)

i dont think that would work as the area in the rings qould be an equipotential, and unable to guide the particle beam left or right. im pretty sure they are progressively stepped down voltages between the peak, central, voltage and the earth, end, voltages, but i dont see how they aid it at all, as surely the eelctric field would assume the same shape with or without the rings. —Preceding unsigned comment added by 172.142.196.236 (talk) 21:40, 29 February 2008 (UTC)

If the particle wass off centre with repsect to the rings it would experience a force pushing it back into the centre? Otherwise I agree with what you have said - ie don't see their purpose..87.102.79.228 (talk) 09:25, 1 March 2008 (UTC)

As some of the individuals above have speculated, the rings are indeed at uniformly stepped potential, from ground to peak potential at the center terminal, and back to ground again. In their absence, there would be distortions in the electric field due to the presence of other conductive, charged, and/or earthed objects inside the accelerator (the accelerator tank walls, the charging belt/chain, suspension cables, etc.). TenOfAllTrades(talk) 05:19, 1 March 2008 (UTC)

Bonus: Here are pictures and explanations from the FN tandem at the University of Notre Dame. You can see both the columns and the gradient rings. TenOfAllTrades(talk) 05:32, 1 March 2008 (UTC)

number of

I'm looking for the number of but the search box isn't helpful. —Preceding unsigned comment added by 79.122.6.248 (talk) 21:35, 29 February 2008 (UTC)

What :D\=< (talk) 21:53, 29 February 2008 (UTC)

First morning cigarette

Why is it that first cigarette in the morning always feels the best?? 77.105.46.131 (talk) 22:01, 29 February 2008 (UTC)

Because you're addicted to nicotine and overnight you're in the early stages of withdrawl.. the first cigarette restores you to the level of nicotine that your body is used to. Why do people smoke, it's filthy and disgusting.. and a waste of money. :D\=< (talk) 22:12, 29 February 2008 (UTC)

The sheets and blankets were pulled up tightly around his

head, but from somewhere half way down the length of the bed a hand slowly emerged from under the bedclothes and its fingers felt their way in little tapping movements along the floor. Working from experience, they neatly circumvented a bowl of sornething very nasty that had been sitting there since Michaelmas, and eventually happened upon a half-empty pack of untipped Gauloises and a box of matches. The fingers shook a crumpled white tube free of the pack, seized it and the box of matches, and then started to poke a way through the sheets tangled together at the top of the bed, like a magician prodding at a handkerchief from which he intends to release a flock of doves.

The cigarette was at last inserted into the hole. The cigarette was lit. For a while the bed itself appeared to be smoking the cigarette in great heaving drags. It coughed long, loud and shudderingly and then began at last to breathe in a more measured rhythm. In this way, Dirk Gently achieved

consciousness.

— Douglas Adams, The Long Dark Tea-Time of the Soul

—Preceding unsigned comment added by Keenan Pepper (talk • contribs) 23:50, 29 February 2008 (UTC)

HOW DID I NOT THINK OF THAT QUOTE O_O :D\=< (talk) 01:33, 1 March 2008 (UTC)

Anything First thing in the morning is great. You're alive again. Some Chocolate Pudding. A bite of some Strawberry Cheesecake. Maybe a fresh slice of Pizza. Some just cooked Trout from the river. Our bodies are machines. However we turn the dials, that's what makes all the difference...on differences. You individual you! Smoke em' if you got em'. --i am the kwisatz haderach (talk) 00:18, 1 March 2008 (UTC)

"Why do people smoke, it's filthy and disgusting.. and a waste of money."

"Anything First thing in the morning is great." Well,theres nothing quite like a cigarette in the morning :)...But yeah,its seems like its a withdrawl —Preceding unsigned comment added by 79.175.73.160 (talk) 00:41, 1 March 2008 (UTC)

Yeah, that's the one I *really* miss. It's the only one that gives me the 'kick' that started me smoking in the first place when I was a teenager (I have been told that it's not *just* the nicotine that causes that - rather a combination of nicotine, carbon monoxide and various toxins). Nicotine gum and this plastic cigarette that tastes a bit like smoke just don't cut it in the AM. --Kurt Shaped Box (talk) 01:12, 1 March 2008 (UTC)

I agree whole-heartly with Froth. Smoking is disgusting and a huge waste of money. I, for one, do not need some drug to be awake in the morning! *quaffs his 5th Frappuccino of the day* 206.252.74.48 (talk) 19:33, 3 March 2008 (UTC)

Hydrogen Peroxide

How dangerous is it to ingest hydrogen peroxide? Is it as dangerous as ipecac? Will it be fatal if small amounts are ingested over long periods of time? Any other information on hydrogen peroxide?

75.182.93.102 (talk) 23:40, 29 February 2008 (UTC)

According to this long abstract, it is dangerous to ingest hydrogen peroxide because it produces oxygen gas which can cause gas embolism. Concentrated solutions (much more concentrated than over-the-counter medical products) are even more dangerous because they corrode tissues. Ingesting small amounts of dilute solution over long periods of time is unlikely to be fatal because it decomposes so quickly in the body. It can't be healthy, though, because it causes oxidative stress. —Keenan Pepper 00:28, 1 March 2008 (UTC)

Is this some sort of bulimia thing? --Kurt Shaped Box (talk) 01:14, 1 March 2008 (UTC)

No there are people (read as crazy nuts) who think that it "cleanse" them somehow. Much like ozone thearapy I guess... Very sad that people can get promoting such things...But this isn't the place for rants now is it.--Shniken1 (talk) 14:08, 1 March 2008 (UTC)

Looking at the sky

Where do your eyes focus when you look up into the sky? I mean, if you traced a ray out from each eye, how far out would they intersect? Also are the lenses of each eye actually focused on this point? Is it any different when looking at the stars at night from looking at the blue sky during the day? How about clouds? :D\=< (talk) 23:45, 29 February 2008 (UTC)

1, 2, $\infty$ is how photographers often count.

When you look at a star, your eyes focus "at infinity", which means that the rays which converge at a single point on your retina were, for all practical purposes, exactly parallel before they got refracted by your corneas and lenses. The point where these rays intersect is therefore very ill-defined. It could be light-years away, or it could be only a few kilometers away, or there could even be a virtual intersection point far behind you. The amount of adjustment your eye (or any optical system) has to make is inversely proportional to the distance (see Optical power), so the farther away something is, the less important it is to know that distance accurately. Whether a star is one light-year away or a thousand makes absolutely no difference to your eye.

This is the reason why focusing rings on camera lenses have an infinity symbol which is surprisingly close to the finite numbers. —Keenan Pepper 00:08, 1 March 2008 (UTC)