Wikipedia:Reference desk/Archives/Science/2009 February 20

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February 20[edit]


On "How Things Work" on the Discovery channel, it was just stated that everything floats on molten lead except uranium. I didn't think that sounded right so I looked up a few heavy metals right quick. Plutonium, gold, and uranium all have higher densities than lead, so how could that float on it? TIA, Ζρς ι'β' ¡hábleme! 02:10, 20 February 2009 (UTC)

They all have higher densities than solid lead; molten lead will definately have a different density, solid gold may possibly float upon it. It may have also been contextual; it could be possible that everything in uranium ore except the uranium floats, so molten lead may be useful as a sepration techinique for extracting uranium from its ore. Without the exact context of the statement, it is hard to tell what they were talking about. 02:19, 20 February 2009 (UTC)
Nope - molten lead is less dense than solid lead. SteveBaker (talk) 02:25, 20 February 2009 (UTC)
I agree - it seems pretty unlikely. Molten lead is around 10g/cm3 - Gold and Uranium are both up at 19g/ doesn't make sense. Is it possible that in the context of that show - they were saying something like "Nothing in this mixture of substances we're talking about right now floats on molten lead except for the uranium that is present in that mixture." ? What was the context of this comment? SteveBaker (talk) 02:25, 20 February 2009 (UTC)
It seems they may have been talking about extracting lead from ore. I'm not sure. I didn't see it, my dad did. Ζρς ι'β' ¡hábleme! 02:50, 20 February 2009 (UTC)
Steel is 7x denser then water, but it will float in the right shape (you can make a ship out of it). (talk) 18:35, 20 February 2009 (UTC)
True, but the actual object that is floating is a combination of steel and air, the average density is less than that of water. --Tango (talk) 19:47, 20 February 2009 (UTC)

Energy transfere[edit]

Using asystem of ( man hanged to aflying object ) , at the moment the man drop him self off ,getting hanged , how many changing in energy type and way will happen , what type of energy stop the man from hitting the floor , the energy trnsfered from and to the man through the rop ... as detailed as possible ... ? —Preceding unsigned comment added by Mjaafreh2008 (talkcontribs) 02:30, 20 February 2009 (UTC)

Your question is difficult to understand as written, so it is hard to give relevant pointers. If you would like help here, you'll need to word it more clearly. --Scray (talk) 05:42, 20 February 2009 (UTC)
I agree that your question needs clarification. However, if you are discussing a man hanging from a rope on a flying object, and the energy types involved, then I believe the change in energy will be from gravitational potential to kinetic energy to heat. That said, I can't be sure unless you clarify things a bit better. —Cyclonenim (talk · contribs · email) 09:39, 20 February 2009 (UTC)

at moment 0.0 ... evry object of this system had its potentioal energy with the value x,y,...etc............................... at moment 1.0 ... the man through him self changing his altitude making the energy to change from potentioal to kinetic to heat to ... ??? I need a plan describe how this energy will transfer from form to anthor . —Preceding unsigned comment added by (talk) 18:30, 20 February 2009 (UTC)

While many energy transfers do occur, in this situation it is not straightforward or well-defined. If this is a homework question and you want an energy-transfer scenario, you might consider a simpler case, like releasing an un-tied balloon and letting it blow across a room, or something.
The person will probably behave as a pendulum, so in addition to gravitational potential, there will probably be angular momentum in the swinging body, "storing" and exchanging some linear and rotational kinetic energy and some gravitational potential energy in the swing upstrokes and downstrokes. There will probably be tension on the rope, which may have a spring-constant (albeit a stiff one); so potential energy will be stored in the fibers of the rope; there will likely be deformations (large and small) of the various materials involved, including anatomical injuries. The situation may induce the man to undergo a series of physiological responses, indirectly causing chemical (food) energy to convert to kinetic and heat energy via metabolic processes. (This list is not meant to be complete)... Nimur (talk) 23:27, 20 February 2009 (UTC)

Does electricity move with inertia?[edit]

I've always learned that when closing/opening a circuit, the current stops and goes instantly, as if there's no inertia? Is that true? (talk) 02:37, 20 February 2009 (UTC)

I don't know about "instantly", I imagine there's a speed of light delay, but that will only be a tiny fraction of a second, which can safely be ignored. Individual electrons do have a mass, and thus an inertia, but it's extremely small. StuRat (talk) 04:22, 20 February 2009 (UTC)
It is not even remotely true. If you take a course in electronics, you will likely be required to do what everyone hates: calculate the current at time t after a circuit is opened or closed. Current cannot go from, say 10amps to 0amps instantly. It will decrease from 10 to 9 to 8... to 0 over time. The time is very short - about as long as takes for a spark to jump the gap just after the circuit opens or just before the circuit closes. -- kainaw 05:05, 20 February 2009 (UTC)

So while the mass of the electron does make a (very small) contribution, the key effect is actually inductance. Moving charge induces a magnetic field, which stores energy. When you remove the external voltage source, the magnetic field begins to collapse; in collapsing, it creates a voltage in the same direction as the one that was there before. This is very much like inertia, but it isn't (or at least isn't mostly) due to the mass of the charge carriers. --Trovatore (talk) 05:34, 20 February 2009 (UTC)
That is correct. I didn't mean to imply that the continuing current was due to inertia. I was simply pointing out that the current stopping instantly was not correct. -- kainaw 05:38, 20 February 2009 (UTC)
StuRat brought up the electron mass, so I incorporated that into my response. However my response, though trying not to duplicate correct remarks made earlier, was actually to the original poster (that's why I indented only once). --Trovatore (talk) 05:44, 20 February 2009 (UTC)
When considering voltage rise/fall time at the end of two wires connected to a voltage source, resistance and distributed capacitance must be taken into consideration, as well as inductance and electron mass. (See "RC Time Constant" in Wikepedia.) Distributed capacitance, inductance, and resistance will have only a very slight affect when all the following apply:
§ The voltage is carried by two straight wires (no coiling).
§ The wires have relatively slight resistance.
§ The voltage source has relatively slight internal resistance.
The resistance of the wires and resistance of the voltage source affect the charge time of the distributed capacitance. Discharge time will be much longer than charge time because there is only leakage current (through very high resistance) to discharge the capacitance. – GlowWorm. —Preceding unsigned comment added by (talk) 08:00, 20 February 2009 (UTC)
One more word about my last post. The capacitance of two short wires is very small. The resistance of the two short wires is also very low. Similarly, the self-inductance of each wire is small. But when talking about the tiny inertia of electrons, every slight influence should be taken into acoount. – GlowWorm. —Preceding unsigned comment added by (talk) 22:15, 20 February 2009 (UTC)

A Few ?s...[edit]

I've got a ? - Why is ozone an important form of oxygen? Oh, and I have another one - How are you able to mantain the nitrogen your body needs? I believe I know the answer to the second question... but I am not sure. Help is appreciated. Thanks! ILY. -- (talk) 06:41, 20 February 2009 (UTC)

This is an encyclopedia with articles on many topics. If you type "ozone" into the search box on the left, you can find articles about it. This is not a free homework answers service, but if you tell us what you think, we can help you decide if your answer is reasonable. DMacks (talk) 06:49, 20 February 2009 (UTC)
I also suggest ozone layer and air. -- kainaw 06:50, 20 February 2009 (UTC)
Also "Nitrogen". --Milkbreath (talk) 11:21, 20 February 2009 (UTC)
For the second you might want to look up amino acids and proteins, and nucleic bases --Mark PEA (talk) 19:16, 20 February 2009 (UTC)
And the urea cycle article for the nitrogen your body doesn't need. --- Medical geneticist (talk) 19:45, 20 February 2009 (UTC)

Archimedes' Law[edit]

How would you define the specific gravity of a swimming wood cuboid with Archimedes? law? Please try to explain in easy way. —Preceding unsigned comment added by (talk) 11:41, 20 February 2009 (UTC)

Measure the side of the cube of wood. Multiply this number by itself twice. This will give you the volume of the cube. Place the cube on a scale. This will give you the weight of the cube. Weight divided by volume is density. The density of water is 1 gram per cubic centiment (or 1 gram per milliliter, equivalent measurement). Specific gravity is the density of the object divided by the density of water. So take the number you got, and divide it by 1. I don't think you'd need a calculator for that calculation... 12:24, 20 February 2009 (UTC)
While that is how to determine density with scale and ruler, it has very little to do with Archimedes' principle. The second paragraph you see after following that link should provide what you need, it is very readable. If after reading that you have a specific question, please follow up here and I'm sure we'll be able to help. --Scray (talk) 14:17, 20 February 2009 (UTC)
(after ec) To the original questioner: If you meant cube and not cuboid, Jayron's instructions should be ok for calculating the specific gravity, but they don't use Archimedes' law. From our article Buoyancy:

For a lighter-than-water object, I suppose "apparent immersed weight" would be a negative value - the force needed to keep the object from floating to the surface. You could use a spring scale that was attached both to the bottom of the container and to the wooden object, and raise the water level until the object was underwater. If you use the readout (with a negative sign) in the formula quoted, I think it should work. --NorwegianBlue talk 14:29, 20 February 2009 (UTC)
  1. The weights of displaced water and the object have to be equal. (Archimedes' principle = "Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.")
  2. Weight = density * volume.
  3. Given #1, (density of water) * (displaced volume of water) = (density of object) * (total volume of object).
  4. From this, we derive
  5. Displaced volume of water = area (length * width) * submerged height
  6. Total object volume = area (length * width) * total height
  7. Simplifying:
  8. Specific gravity = (density of object) / (density of water)
And therefore specific gravity = submerged height / total height. The area need not be a perfect square, which is why it can be a cuboid rather than a cube. arimareiji (talk) 17:34, 21 February 2009 (UTC)

Most temperate city?[edit]

Both East London, South Africa (26-10) and San Francisco, USA (23-7) have only a 16°C difference between highest month average high - lowest month average low. Anyone know example of a smaller difference [with a Mediterranean climate]? San Diego is 17°C. (This question has been asked about the USA before, I'd like to know of cities in other countries also.) -- Jeandré, 2009-02-20t14:18z, -- Jeandré, 2009-02-20t16:09z

The smallest will probably be in the tropics. The first tropical city I picked, Colombo, has a range of just 8°. Algebraist 14:41, 20 February 2009 (UTC)
Yeah, and I found tropical Medellín at 11°C (28-17)[1]. An important part is a Mediterranean (temperate) climate. By that measure East London's 26 is already a bit high. -- Jeandré, 2009-02-20t16:09z
I agree with the smallest temp change occurring in the tropics, and would add that I'd expect it to be on a small island, where the water has a moderating effect on the temp. Honolulu, for example, has a 5°C variation. A small island, closer to the equator, might have even less variation. For example, the Galapagos Islands only have a 3°C variation, although there's no big city there. StuRat (talk) 16:35, 20 February 2009 (UTC)

Dates Before Christ?[edit]

How were dates recorded before the knowledge of Christ's existence?

For example, how was the year 500BC actually chronicled at that time? —Preceding unsigned comment added by Timewatcher50 (talkcontribs) 14:30, 20 February 2009 (UTC)

A huge variety of dating systems have been used in different places and different times, before and after the birth of Jesus. There's some information at calendar, calendar era, list of calendars, and doubtless other articles. Algebraist 14:37, 20 February 2009 (UTC)
It would depend on the reigning monarch. I suspect you got more people saying, "In year 15 of King 'X's reign," for isntance; so you had to add backwards to get how many years ago something was. (Which made it confusing if there were regents, etc.)Somebody or his brother (talk) 14:39, 20 February 2009 (UTC)
If you're talking about not too long before, and in the same area of the world, I'm guessing the system associated with the dominant power was AUC, ab urbe condita, which means "from the time they put salad dressing on the city" :-) --Trovatore (talk) 19:06, 20 February 2009 (UTC)
Well, for one, the AD system was only invented in 525 CE, and that very likely is not 525 years after the birth (or conception) of Jesus. The salad dressing system was not widely used at that time, either, even in Rome. Romans counted mostly by consuls ("The year mario and kong became consuls"). Other cultures used various local system, often based on local rulers. --Stephan Schulz (talk) 22:08, 20 February 2009 (UTC)
  • Don't be confused by the CE in the answer above. It's just an over the top attempt at political correctness by not involving Christ's name in the dating process. The time frame is still the same. - Mgm|(talk) 09:57, 24 February 2009 (UTC)
...because Christ's name is in AD exactly where? --Stephan Schulz (talk) 10:12, 24 February 2009 (UTC)
anno domini = year of the lord, a strong, indirect reference to Christ --Nricardo (talk) 03:12, 25 February 2009 (UTC)
Sure...but no particular reference to his name. --Stephan Schulz (talk) 23:42, 26 February 2009 (UTC)

Why did more colds develop into pneumonia in years past?[edit]

My mom was telling me on the phone she's getting over the common cold, and said thankfully, "at least it's just a cold." That got me to thinking about the fact that, in bygone years, it seemed like more colds did develop into pneumonia. She recalled that, too, and also said it was younger people who got it from colds.

As I told her, there were two things I could think of that could be the result: 1. In the early Industrial Revolution until recently, a lot of pollutants got into the lungs that just happened to coincide with a cold to cause it; and, 2. Before central heating, a lot of homes were draftier and damper, so ther places where people could recupterate had lots of mold and such to make things worse. (I read where some castles were chillier inside than the weather outside)

But, we weren't really sure why it was. So, are one or both of my guesses right? Or, is it another reason? Or, is this just a fallacy, and about the same percent of colds as centuries before developed into pneumonia?Somebody or his brother (talk) 14:33, 20 February 2009 (UTC)

I can think of several possible reasons:
1) Improved diets mean we are less likely to have a compromised immune system which might provide an opportunity for pneumonia to develop. In particular, nutritional deficiencies are less likely. (While modern diets can lead to obesity, diabetes, high blood pressure, heart disease, etc., they do at least typically provide the necessary minimum of all nutrients.)
2) People are now more able to take off work when sick to avoid worsening the problem.
3) Less time is spent outside, exposed to the elements, now. This is due mainly to most people working indoors and to enclosed transportation, like cars.
4) People work shorter hours now, so have more time to tend to themselves and less exposure to stress factors.
5) Fewer people have compromised immune systems due to untreated diseases, now. StuRat (talk) 16:03, 20 February 2009 (UTC)
Aggressive recognition and treatment of the common cold may also contribute to the fact that pnemonia is on the decline. Although, pnemonia still impacts people with comprimised immune systems (either by an autoimmune disease or some other sort of illness), the elderly and the very young. Livewireo (talk) 20:50, 20 February 2009 (UTC)
Pneumonia is also a secondary infection, like a sinus infection, whereby the symptoms of the cold, such as mucus production, may provide a medium for the infection. When you have a cold, you make lots of mucus (snot). Mucus is an excellent medium for secondary bacterial infections. So modern medicines which decrease mucus accumulation, such as Guaifenesin, may help decrease the onset of these sorts of secondary infections. 21:07, 20 February 2009 (UTC)
"Mucus is an excellent medium for secondary bacterial infections." Really? Have a look at the second sentence of Mucus. Or, this article from Pubmed. There are many antibacterial properties of mucus - and that makes perfect sense. --Scray (talk) 00:57, 21 February 2009 (UTC)
Secondary infections set in after a virus kills the cells which protectively line the respiratory tract. When a protective lining of mucus is no longer there to constantly wash bacteria out of the respiratory tract, up to the mouth (to be spat out or swallowed into the acid bath of the stomach), it makes it much easier for the nasty little buggers to set up shop. Think of the film clips you've seen where fire hoses are used on demonstrators - only this time the "good guys" are your body's defenses, the ones wielding the fire hoses. In its normal role, mucus is good. arimareiji (talk) 17:58, 21 February 2009 (UTC)
To the original poster - look up the 1918 flu pandemic, which killed tens (possibly hundreds) of millions with a horribly-virulent form of pneumonia. Then if you really want to be disturbed, look up the WHO's reports on the emergence of H5N1, a close relative of the H1N1 strain that caused the 1918 pandemic. There's a reason they keep slaughtering millions of birds in SE Asia - it's because we've made very little progress against viruses from 1918 to 2009. Bacteria yes, viruses no. arimareiji (talk) 18:10, 21 February 2009 (UTC)
(If anything, we've become much less conscious of basic health precautions like washing your hands and covering your mouth and nose when you sneeze. Contrast this with many parts of Asia, where it's considered to be somewhere between rude and disgusting to be sick with a respiratory illness and refuse to wear a mask.) arimareiji (talk) 18:16, 21 February 2009 (UTC)

Lancet reputation[edit]

How much of an effect did the surveys of Iraq War casualties have on the reputation of the Lancet? A lot of what I read about the peer review process of the 2004 and 2006 reports makes me wonder about the objectivity of the journal. Is there much concern amongst the scientific community about the Lancet's misjudgment of publishing those papers? —Preceding unsigned comment added by ExitRight (talkcontribs) 14:37, 20 February 2009 (UTC)

As far as I can tell, the scientific community regards those studies as valid and as good as can be expected under such challenging circumstances. I'm not aware of any major problems that have been reported. As such, it had no negative influence on the Lancet's reputation, at least not among scientists. --Stephan Schulz (talk) 18:32, 20 February 2009 (UTC)
Really ? Our article seems to say there were all sorts of problems with it, and that it overestimated the numbers by around 6 times compared with every other major survey. The most obvious problem I saw was their claim that 90% of those asked were able to produce death certificates. That would mean 550,000 death certificates, when there were actually only 50,000. That's what I call "junk science". Publishing something like that certainly does diminish respect for any scientific journal. StuRat (talk) 18:41, 20 February 2009 (UTC)
You should look at the quality of the sources, and about what is claimed by the different surveys. The Lancet studies count excess dead, i.e. they include all causes, from malnutrition to cluster bombs. The IBC, for example, counts only violent civilian death reported in the English language press. A factor of 6 between violent civilian deaths reported in the English language press and all excess deaths seems entirely plausible to me. Moreover, for the first study, IBC and Lancet are entirely compatible, and for the second the factor is only about 4, not 6, if you take the 95% confidence interval into account. --Stephan Schulz (talk) 18:58, 20 February 2009 (UTC)
WHAT?? Stephan Schulz, you about blew my head off, I feel like capitalizing my entire message. Around the time when the Lancet published that bullshit, people went batshit insane, I, was obviously one of them. Junk science, politicized science, fraud science and maybe even psuedoscienceMac Davis (talk) 00:18, 21 February 2009 (UTC)
I don't give much about the opinion of people who "went batshit insane". I have found only fairly mild criticism of the study in the academic literature, and a lot of support of the core findings and the methodology. Sure, the right-wing blogosphere went berzerk. But that is entirely irrelevant to the original question. The Lancet's current impact factor is 28.600. In 2004 it was 21.713. So it seems that it's reputation, at least among academics, has not suffered. --Stephan Schulz (talk) 00:31, 21 February 2009 (UTC)
I largely agree with Stephen Schulz and would point out two things. One, the authors have been willing to discussion and engage in rational debate about resonable issues that were raised about the study, something we would expect from good scientists and this is reflected in the wikipedia article. I would suggest you read it if you haven't already since it's a decent article. Two, one of the most interesting things (to me) is the timing issue raised by numerous sources. Rather then re-invent the wheel, I'll just mention again that our article covers this well. A final comment quoting from the article which is apt in this discussion "The Chronicle of Higher Education also wrote an article discussing the differences in the survey's reception in the popular press over how it was received in the scientific community". P.S. A perhaps more relevant study on Iraq with regards to recent events is the one which raised what seems to me are valid questions on whether the surge really worked [2] [3] published in Environment and Planning and mentioned in our Iraq War troop surge of 2007. I didn't see much criticism of this perhaps because by that time everyone had forgotten about Iraq since the world economy had taken centre, heck left & right, top & bottom, stage. Nil Einne (talk) 12:45, 22 February 2009 (UTC)
The Lancet has been known to publish somewhat controversial topics, and sometimes those with poor evidence. However, it's still the World's leading medical journal and the benefits from its existence far outway some of the bad efforts they've made. That's most likely why it's reputation hasn't suffered that badly. —Cyclonenim (talk · contribs · email) 10:15, 21 February 2009 (UTC)
But Stephan, why wouldn't you think there's a wide overlap between the right-wing blogosphere and scientists/academics? ;-) arimareiji (talk) 18:20, 21 February 2009 (UTC)
Perfectly scientific hunch! --Stephan Schulz (talk) 22:23, 21 February 2009 (UTC)

limitation of human understanding[edit]

I know that human knowledge or understanding of concepts has finite limits in many respects - there are limits to how fast we can think or how many different things we can learn. What I'd like to know - is there any reason to believe that there are TYPES of things that humans simply don't have the capacity to understand? I'm not talking about things that are literally unknowable, I'm talking about things that, say, a superior alien intelligence could understand, that we humans could never hope to? If so, what types of things might fit this category? ike9898 (talk) 19:09, 20 February 2009 (UTC)

Oooh! A chance to use my favourite quote: "My own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose." J B S Haldane (otherwise known as Haldane's Law). It's a bit like Rumsfeld's "unknown unknowns" - I suspect your question is literally unanswerable. -- (talk) 20:24, 20 February 2009 (UTC)
At an individual level, there are things that I cannot understand, such as string theory, but it's not hard for me to understand that it exists and in the broadest, simplest sense, what it is about. I'm thinking of something like this, replacing the individual with the human race. ike9898 (talk) 20:30, 20 February 2009 (UTC)
We've used computers to analyse all possible chess endings with certain combinations of pieces like 2 knights vs knight and bishop, but it would be impossible for me to remember all possible positions at the sme time even though given enough time I could enumerate them. Is this, the case of limited memory, an example such as is desired? RJFJR (talk) 20:39, 20 February 2009 (UTC)
No, that's not really what I'm thinking of. A human could probably understand any individual chess ending, so this is a TYPE of thing humans can understand. I'm looking for a type of thing that we can't understand. Also, if we can build tools (computers) to help us analyze something, as far as I'm concerned, that counts as being understood by humans. ike9898 (talk) 20:47, 20 February 2009 (UTC)
For the record... unknown unknowns are common ways of thinking about military contracting—the concept existed a long time before Rummy and it's too bad it has gotten associated with him in such a silly way, because it is actually quite sensible (as was his original exposition, which was quite clear). -- (talk) 02:15, 21 February 2009 (UTC)
But there would be things to complex to understand, say with more than 8 things all happening at once. But once you factor in computers you are looking at the limits to computability. Once you have a universal computer it is basically equivalent to any other computer, and can compute the same things. Graeme Bartlett (talk) 21:32, 20 February 2009 (UTC)
I'm sure the answer is 'yes'. We had a long thread the other day about whether there are 'new' colors out there that we haven't seen yet. We know that humans see (basically) red, green and blue and mixtures of those 'primary' colors. But we can't tell the difference between 'yellow' and 'red+green'. We can't even concieve of a color that we haven't seen yet. But there are some animals out there (I believe that goldfish and freshwater shrimp are two of them) that see in as many as 12 'primary' colors. We can't understand what the world would look like to them. However, there are at least two people in the world who we know can see four 'primary' colors (they are tetrachromats). They can understand something that the rest of the world can't. That's not a limitation of the brain so much as a total failure of imagination. SteveBaker (talk) 21:43, 20 February 2009 (UTC)
On further thought - the human brain is a 'turing complete' computer. There is a theory called "The Church–Turing thesis" that says that all turing-complete computational systems are equivalent. That means that (in principle) any calculation that your brain can do could (in principle - if you had enough time and memory) be done by any computer. What I think that means is that our brains are CAPABLE of understanding anything - the fact that we can't imagine what it would be to see in four primary colors is not a failure of the computational systems in our skulls - it's a failure of imagination. The two ladies who see four primary colors have no problem 'imagining' four primaries - yet we can't even begin to do that. However, their brains are (presumably) pretty much the same as ours - and they are certainly 'equivalent' per Church-Turing. So a failure to understand may well be simply a failure to imagine. That's a very deep thought. SteveBaker (talk) 21:49, 20 February 2009 (UTC)
And another one - imagining a 4 dimensional world. We can do the math and we can predict what happens - but we really can't "understand" it. SteveBaker (talk) 21:53, 20 February 2009 (UTC)
That is interesting, but is there any reason to believe that some sort of intelligence superior to ours could understand it any better? Or is it hard for any real intelligence to understand because none will ever experience it? ike9898 (talk) 22:10, 20 February 2009 (UTC)
Isn't time the fourth dimension? That way 4 dimensional would be doable, but some of the other higher dimensions that they think up to make things fit in the upper reaches of physics I'd agree are really like a dust-mite trying to grasp cosmic background radiation. Imagining an alien who could handle that kind of thing is equally out there, though. I wonder if we'll be able to get a handle on dark matter once we have a bit more data. (talk) 22:09, 20 February 2009 (UTC)
I guess it depends on your definition of "understand". I understand n-dimensional space on an abstract level. Some people even claim to be able to visualise higher dimensional spaces (some of them are even people I would be tempted to believe - one of them told me the trick is to do it in the pitch black so there is no 3D Euclidean space to confused you). A Turing complete computer can run any program that can be run on a Turing machine, that doesn't mean if can run any program. Oh, and I'm not sure about your use of the word "primary" - I think the word is too vague to be useful without clarification, so probably best avoided entirely. --Tango (talk) 22:54, 20 February 2009 (UTC)
Forgetting for a moment that some people want to call time "the 4th dimension" (which never makes any sense to me) - let's talk about understanding 4 spatial dimensions plus one of time. I too have heard some people claim to be able to visualise 4 dimensions - but I'm not convinced. The idea of tying a knot in a 3D volume much as we can tie a knot in a 1D piece of string - really hurts my head...I really doubt anyone can truly visualise that kind of thing...and if they can, I'll just demand that they do it in 14 dimensions. There is a limit. But certainly there is no problem in doing math in more dimensions. I work in computer graphics - and I frequently have cause to do tests to see if a quadrilateral is 'planar' in 14-space. I can do the math - but I can't even begin to visualise it. As for turing machines - you REALLY need to read what Church-Turing thesis says. It's talking about computable functions...and there is zero evidence that the brain does anything more or less than that. There is little doubt that with a big enough & fast enough computer, we could accurately simulate a human brain. I used the word 'primary' to avoid getting mired up in the whole human visual system question all over again - basically we perceive color as three more or less independent variables - the 'color space' is three dimensional. Terachromats have a 4D color space - and the good old freshwater shrimp has a 12D color space. We can no more imagine those 'extra' colors than we can imagine two distinct kinds of yellow (as the tetrachromat ladies do) or 4D or 12D space. SteveBaker (talk) 02:30, 21 February 2009 (UTC)
Wandering further offtopic, thinking of (or indeed, calling) time "the 4th dimension" allows you to visualise events as existing in 4D space-time. Which is relatively useful. I can half do it, the half coming from not all of the 'visualisation' being strictly visual. And then, of course, you can abstract that mathematically for certain areas of physics. (Have you never had an astrophysics jag? I'd recommend it as good fun) (talk) 02:19, 23 February 2009 (UTC)
Are you suggesting that a human's brain is Turing-complete, while a cat's brain isn't? [citation needed]. --Sean 23:33, 20 February 2009 (UTC)
I'm certainly not claiming that. Quite the opposite. There is no way a cat could do what it does without a turing-complete brain. Hence church-turing applies. However, church-turing contains the rider that the two computational units are only equivalent providing there is sufficient time and memory to perform the same calculations. Clearly cat's brains don't have as much storage space as human brains do. SteveBaker (talk) 02:30, 21 February 2009 (UTC)
We might have hit the wall already. How would we know? In our quest to understand the universe we've gone from Newton's simple laws to E=mc2 to the gawdawful mess we have now that I don't believe even its proponents understand. What good is an answer nobody can read? We seem to have come unraveled, and the beauty of simplicity has given way to myopic intricacy. That's not to say that the answer isn't intricate, but it's always been a bad sign before. It could be that the true nature of reality is beyond our ken. --Milkbreath (talk) 22:25, 20 February 2009 (UTC)
Yes - it's kinda sad. The Victorians were so happy in their 'clockwork universe' where everything could be known and predicted with equations that had about four terms in them. Sadly, nature is as nature is - and if it really is complicated, random and chaotic - there isn't much we can do about that. SteveBaker (talk) 02:30, 21 February 2009 (UTC)

I guess I just think it's strange - For every other type of intelligent creature we know about, there are clearly things they can understand and things they literally can't (ever, no matter how hard they try or how much training they are given). A bird can understand many things, I think, but I don't a bird could ever understand The effects of Hollywood movies on the Soviet stereotype of Americans.

I usually don't think that humans are particularly "special", that our differences from animals of differences of degrees. But that would imply that we have limits on what we can understand, just like a bird does. ike9898 (talk) 22:57, 20 February 2009 (UTC)

Clarifying using another animal example - - A cat can watch people riding bicycles and be confused about what is going on; maybe he can get the gist of it, but he'll never understand why people shift gears. So I think the cat can look at something like this and be aware that he doesn't understand what is going on. I think it is possible for a brain to be aware of things it will never, ever be able to understand. ike9898 (talk) 23:05, 20 February 2009 (UTC)

How many human cyclists understand why they change gears? I think it is dangerous to generalise across an entire species. --Tango (talk) 23:12, 20 February 2009 (UTC)
I'm not talking really about any individual. It's clear that a smart human brain can comprehend gearing if it is taught well; a smart cat brain probably cannot (maybe they can, if so, replace cat with flea). ike9898 (talk) 03:21, 21 February 2009 (UTC)
Take a look at Jean Piaget's stages of development. He theorizes that children of certain ages cannot understand certain things; for example, young children cannot understand where an object goes when you put it behind your back, until they grow into the next 'stage' and gain the ability to realize that it hasn't just disappeared. Now imagine that all human beings are like children 'stuck' at a certain stage, unable to understand, for example, 5 dimensions. If an alien was the equivalent of an adult in this scenario, it would be able to understand this concept and we wouldn't. Seems very possible to me. Maybe there's a stage that, from an evolutionary perspective, we haven't reached yet. -Pete5x5 (talk) 06:57, 21 February 2009 (UTC)
Belief systems are built on fideism which insists that there are things beyond our understanding. A favourite line from a sci-fi film says "There are some things we are not meant to know." Cuddlyable3 (talk) 14:26, 21 February 2009 (UTC)
I imagine that even now a group of adolescent male lions are lounging under a tree pondering "could there exist a wildebeest so tough, even our inestimable teeth could not bite it?". Silly lions! Your teeth evolved until they were sharp enough, and there's no reason to think that they are the ultimate in teeth when that was evolutionarily unnecessary. --Sean 23:21, 21 February 2009 (UTC)

economy crises[edit]

I was listening to the news trying to understand what is happening , what is the source of this crises , what is the cause

how could it infect the whole wide world .

economy is based on trading , material vs material ... oil for cars ,,, cash is just a way to easy thing thats all

so .. as we know ... oil is still there ... factories still have the abillity to produce ... farms still producing food

so where's the problem . why evry thing is going down ,.???????? —Preceding unsigned comment added by Mjaafreh2008 (talkcontribs) 20:43, 20 February 2009 (UTC)

This podcast does a surprisingly good job of explaining the mess we are in now. 21:01, 20 February 2009 (UTC)
Our article on the Global financial crisis of 2008–2009 is also very comprehensive. What it boils down to is that the global econmoic market is not as simple as you think. We don't just trade Good A for Good B or Good C for Service Z. There are a great many of factors that impact economic systems and the failure of one or two (namely the bankruptcy of a number of huge American banks and other financial services thanks to subprime lending) send ripples through nearly every single market. Livewireo (talk) 21:06, 20 February 2009 (UTC)
Following EC: Agreed, that PBS report is good. OP your statements are only correct if you'd assume that purchase decisions are logical. They aren't. Most of the stuff we buy, we buy on a whim and based on our impression of it's worth. You don't really say this car is worth 10,000 gallons of milk. You say it's comfortable. You may say it's fuel efficient. (Compared to taking the bus, really?) But mostly you'll buy it because that's the one you want. If you think there might be a chance that you'll need those gallons or milk more urgently than a Hummer (or any other car) you'll keep driving your old clunker for another few years longer. So the Hummer factory can still produce Hummers, but no one wants them. The Mc Mansions that got built in the housing bubble are still there, but people find they'd rather not get that expensive a house (even the ones who could afford to.) They stand empty, fall into disrepair and the houses nearby all of a sudden also lose value. That is because the neighborhood has changed from "upscale" to "undesirable". So if you go to your bank for that second mortgage the (newly prudent) banker will look at the current market value of your house and tell you it's only worth half as much as it was before half the street was under foreclosure. To that you'll have to add some odd market things like insurance and pensions. They basically rely on the fact that the next generation will earn/produce/pay-in as much or more than the current employees. On top of that you get "gold rush" mentality investment cycles (stock market run, third world market exploitation, .com bubble, technology bubble, mortgage backed securities, etc.) as mentioned in the podcast and you no longer wonder why the economy fails. You rather wonder how it works as well for as long as it does between downturns. (talk) 21:41, 20 February 2009 (UTC)
Instead of thinking of everything as going down, think of it as correcting itself. Scroll to the bottom of this BBC News article and read upwards, The 12th March 2007 article about New Century Financial has a good quote:

Sub-prime lenders provide money to clients with a poor credit history, charging higher rates of interest because of the greater risks involved. New Century has been hit by a number of problems, including an increase in default rates in the sub-prime sector.

In many of the articles above that, there are some very interesting quotes. Alan Greenspan saying that the subprime crisis (not a "crisis" at the time) would not be a large problem as long as house prices continued to rise (they didn't, and this has happened). If you want to figure out how all this affects the global economy, then you must read up on things like collateralized debt obligations, mortgage-backed securities, credit default swaps, Mark-to-market - Effect on subprime crisis, securitization and: financial crisis of 2007–2010 / global financial crisis of 2008–2009 article. --Mark PEA (talk) 23:29, 20 February 2009 (UTC)
In fact, here is a very simple diagram to explain it all, in our article Subprime crisis background information: Of interest, according to this article (List of writedowns due to subprime crisis), there has been a total write down of $295 billion by banks due to decreasing value of "loans, MBS and CDOs due to the subprime mortgage crisis" --Mark PEA (talk) 00:16, 21 February 2009 (UTC)
Some people may be too young to remember Savings and loan crisis. It's not as though the current mess is something utterly new and unheard of. BTW. Lots of effects are getting swept under the subprime lending rug. Because the economy is in the pits the oil price has conveniently dropped off the radar. But some of the idustries' troubles are probably to blame on 2000s energy crisis. That was so uttlery unanticipated because these never happened and were long forgotten: 1973 oil crisis 1979 energy crisis - (talk) 01:07, 21 February 2009 (UTC)

Chemisty Question - Silicone oil[edit]

Would an organic solvent like hexane be good for cleaning silicone oil off of something? I don't know anything more about the oil (it is a standard for a viscometer). ike9898 (talk) 21:13, 20 February 2009 (UTC)

I would try something like Dimethyl sulfoxide. DMSO will take the white off of rice. Its probably one of the most universal solvents out there, and if DMSO won't dissolve it, it won't disolve. 21:22, 20 February 2009 (UTC)
Wouldn't you know what our OP is trying to clean the oil from first? If DMSO dissolves nearly everything - then whatever is covered in oil may also dissolve! SteveBaker (talk) 21:36, 20 February 2009 (UTC)
Picky picky picky. Yeah, if the silicone oil is adhered to some sort of rubber tubing or plastic, you'll end up with a sticky goopy mess if you use DMSO. If the oil is on glass or metal, you're probably OK. That's part of the problem with things like plastic and rubber; anything that would clean them would also do a pretty good job of dissolveing them... 21:41, 20 February 2009 (UTC)
Whoah, whoah, whoah…using DMSO right out of the gate is very much akin to using a tactical nuclear device to get rid of a moderately large ant hill in your lawn. Strong white vinegar (i.e., ~18% to 20% acetic acid by volume), perhaps with a small amount of detergent added, will usually do a fine job of cutting the silicone oil. Exact cleaning and after-rinse technique will depend on the substrate from which the oil is to be removed. —Scheinwerfermann T·C21:49, 20 February 2009 (UTC)

OP here. The surface to be cleaned is metal, possibly stainless steel. Although I can take the piece off to clean it and move it to a sink or fume hood, I'd rather clean it in place - rinse it with something that will thin the oil and not be super toxic (for my purposes, something like hexane is acceptable to use in this situation). ike9898 (talk) 22:02, 20 February 2009 (UTC)

Acetone and hexane would be my first tries. Methylene chloride might work similar/better/worse but is more toxic. Which of those common solvents is "best" depends on the nature of the oil..."silicone oil" comes in many flavors. Any of those three would be hella-preferable to DMSO, since they're volatile whereas with DMSO...then you've got the whole instrument covered in DMSO. DMacks (talk) 22:16, 20 February 2009 (UTC)

UPDATE: Tried acetone. Seemed to work well. ike9898 (talk) 22:46, 20 February 2009 (UTC)

This page seems to indicate that hexane, methyl ethyl ketone, acetone, and diethyl ether will all do a fine job (Table 1) — though you'll probably want to stay away from ether for safety reasons. TenOfAllTrades(talk) 23:43, 20 February 2009 (UTC)
Is the diethyl ether really more dangerous than the others you mention? Health or flammability? ike9898 (talk) 03:16, 21 February 2009 (UTC)
Both, though not to a huge degree. It used to be used for anesthesia, but it had a disturbing tendency to make unconscious people nauseous (never a good combination) and blow up the operating room. arimareiji (talk) 15:35, 21 February 2009 (UTC)

Cleaning anitfreeze ethylene glycol off concrete[edit]

While we're on cleaning things. We had an antifreeze leak in one of our cars the other day. Since it is toxic (to our cats and other critters) I didn't want to keep the puddle on the concrete. My cleaning agent of choice is usually baking soda. It soaked up the puddle and I could sweep it onto a pan an toss it in the trash. Is there something better that one would find in a household moderately well stocked with ordinary chemicals? (talk) 21:58, 20 February 2009 (UTC)

It's water soluble, so a few buckets of water or a hosepipe. As long as you use enough water, you'll dilute it to safe levels. (I doubt the total quantity was enough that you need to worry about general damage to the environment.) --Tango (talk) 22:02, 20 February 2009 (UTC)
Thanks. That would be nice, but we have water rationing. No outdoor water use, unless it's watering your veggies or your house is on fire. (I've been waiting for ages for it to be lifted so that I can power wash our entryway before re-grouting.) (talk) 22:15, 20 February 2009 (UTC)
I don't think you would have much difficulty arguing that cleaning up toxic chemicals is a good use of water. --Tango (talk) 22:48, 20 February 2009 (UTC)
Yes - I agree. Ethylene glycol is extremely nasty stuff - just one little taste of the stuff is enough to kill a young child or a dog. It's also very sweet - which attracts all sorts of animals (and when it's in a bottle - it looks exactly like gatorade - so kids think it's OK too). Diluting it is really the only safe way that I know of. I use sawdust to absorb as much as I can - then I hose down the driveway afterwards. If you have a hosepipe ban - can you use a bucket of bath water or something? Once you've got most of it soaked up, even just a single bucket of water should dilute it 100-fold - and that's probably enough. FWIW, here in Texas where it never really gets cold enough for long enough to freeze up a car - I've stopped using glycol in favor of water with 'water-wetter' and corrosion inhibitor. Pure water is more thermally conductive that water with glycol in it - so it actually cools your engine more effectively which generally gets you better gas mileage. However, you need some corrosion inhibitor - which is available at most auto parts stores as "water-wetter". Sadly, if you live in the snowy wastelands north of Dallas County - you should probably stick with regular antifreeze. SteveBaker (talk) 02:02, 21 February 2009 (UTC)
There are much less toxic antifreezes, based on propylene glycol. The principal reason ethylene glycol is toxic is that, in the body, it is first dehyodrogenated to glyoxal and then oxygenated to oxalic acid -- ironically (in the Alanis sense) this is, I believe, the pathway that the body uses to detoxify ethanol. Oxalic acid is the bad player here, largely because it forms crystals (or maybe its calcium salt does) in the kidneys, potentially destroying them.
Propylene glycol may follow the same pathway, but if it does, the end product is lactic acid or pyruvic acid, both of which are regularly dealt with by the body (they're outputs of certain metabolic pathways). --Trovatore (talk) 06:42, 21 February 2009 (UTC)
Ah, looks like I oversimplified this a bit — according to our article on ethylene glycol poisoning, the main toxicity to the kidneys is from glycolic acid, an intermediate metabolite on the way to oxalic acid. So oxalates are maybe not quite as dangerous as one might calculate from antifreeze toxicity (go ahead and have that rhubarb pie! one of my favorites). --Trovatore (talk) 09:06, 21 February 2009 (UTC)
Thanks yall. I'll try using a bucket if it should happen again. Atlanta occasionally does get quite chilly. The antifreeze is refilled in the shop and I don't think we get a lot of say as to what goes in there. (talk) 08:59, 21 February 2009 (UTC)
I'm sure they'll use propylene-glycol-based antifreeze if you ask. It's a little more expensive, but not terribly so — if someone else is changing your antifreeze then you're paying mostly for labor anyway. --Trovatore (talk) 09:06, 21 February 2009 (UTC)

←Ethylene glycol poisoning is the one I always remember due to it's somewhat fun treatment. First aid treatment consists of drinking a couple of beers. This acts as an antidotal therapy, helping to block receptors with comparatively harmless ethanol instead of ethylene glycol. —Cyclonenim (talk · contribs · email) 10:10, 21 February 2009 (UTC)

I was aware that ethanol was the antidote to methanol, I didn't know it was also the antidote to ethylene glycol, although it makes sense. Personally, I would go with something stronger than beer - a nice scotch, perhaps. --Tango (talk) 15:16, 21 February 2009 (UTC)
The principle is the same, I think — the ethanol competes for alcohol dehydrogenase, which is the enzyme that starts you down the road to the bad metabolites (glycolic acid and oxalic acid in the case of ethylene glycol; formaldehyde and formic acid in the case of methanol.
But people, seriously, if you've somehow ingested one of these things, don't screw around with a nice leisurely cocktail. Get to the hospital pronto. (Whether a shot or two of hard liquor would count as first aid, assuming someone else is driving you to the hospital, I don't know; it's an interesting question and one I'm not qualified to comment on.) --Trovatore (talk) 20:52, 21 February 2009 (UTC)
I would call an ambulance rather than get myself to the hospital. A nice gin and tonic (hold the tonic) while you wait for it to arrive might keep things from getting worse while you wait. I guess whether it's worth it depends on timing - if you're in the middle of nowhere and it's going to take a couple of hours for help to arrive, you should almost certainly down the gin. If it's a matter of a few minutes, maybe not - I believe it takes a few hours for the ADH to metabolise a significant amount (you don't have much ADH, so it can only process it so fast - that's why you are often still drunk the morning after a night out Well, I'm not, but I don't go out - I stay in and discuss the metabolic pathways of ethylene glycol with random people on the internet...). I also have absolutely no idea what the dosage would be... (my interpretation of a paper I read on the subject puts the necessary dosage at 20 times the lethal dose, so I think I got that wrong...) --Tango (talk) 23:36, 21 February 2009 (UTC)
I'll keep that in mind the next time I drink some antifreeze. ;-) More seriously, I'd be wary of feeding gin to a small child, who would be the most likely human victim of such poisoning. arimareiji (talk) 00:05, 22 February 2009 (UTC)
Indeed, that's where not knowing the right dosage becomes a real problem. With an adult I would just get them totally wasted and it would probably all work out fine. With a child, you have to get it just right, too much and they die of ethanol poisoning, too little and they die of ethylene glycol poisoning. That's why Fomepizole is the preferred treatment, unfortunately I don't keep any in my drinks cabinet... --Tango (talk) 00:32, 22 February 2009 (UTC)
@ Cyclonenim are you sure it's the alcohol in the beer that is the active ingredient here? I remember they had a couple of poisonings when some wine was mixed with ethylene glycol in Europe (quite a few years back). Ordinary beer doesn't have that much more alcohol I should think. It does contain a plethora of other things (like e.g. enzymes) that you might not find in wine. (talk) 08:19, 22 February 2009 (UTC)
A little hooch along with your antifreeze isn't going to help much (though it might delay the damage for a time). Basically you have to stay drunk (I don't know exactly how drunk, but I have the vague notion that it's pretty damn drunk) until such time as your kidneys can cleanse out the glycol. That's going to take longer than the wine is going to last you. --Trovatore (talk) 08:42, 22 February 2009 (UTC)
It's definitely the ethanol. Putting anti-freeze is wine doesn't stop it being toxic - wine is generally only 10-15% ethanol, so even a fairly small amount of anti-freeze added will result in a similar amount of ethanol to ethylene glycol. You need a lot of ethanol to keep your alcohol dehydrogenase busy until the ethylene glycol has time to leave your body. --Tango (talk) 15:26, 22 February 2009 (UTC)