Wikipedia:Reference desk/Archives/Science/2008 November 18

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November 18

CMBR

The article on cosmic microwave background radiation says that the radiation is isotropic except for a small blueshift because we're moving relative to the surface of last scattering. But shouldn't the side of the surface closer to the center of the universe be much warmer because there are more photons per cubic meter on the less-expanded side than on the more-expanded outer side? 71.176.180.12 (talk) 02:03, 18 November 2008 (UTC)

I think the universe is supposed to be expanding uniformly everywhere. StuRat (talk) 03:44, 18 November 2008 (UTC)

This is precisely the reason why measuring the background microwave radiation was so important. The mistake you're making is the all-too-common one of assuming that the big bang happened over 'there' and we're currently over 'here'. In fact, at the moment of the big bang, all of space was scrunched up in a teeny-tiny dot - which expanded rapidly in all directions. So there is no one particular direction you can point to and say "the big bang was over there". The big bang filled all of space at the time it happened - but space itself was very tiny. So the big bang is in every direction around us - which is why the cosmic background looks the same temperature in all directions. That discovery is the single thing that proves that the universe started with a big bang and not in some other manner. SteveBaker (talk) 04:56, 18 November 2008 (UTC)

The classic analogy to the big bang, for layman's understanding, is that of the inflating balloon. Take a balloon, and draw dots all over it. Picture yourself standing on any one dot, and blow the balloon up. All of the other dots are moving away from you. If you stand on any other dot, you observe the same thing; and yet NONE of the dots can be said to be the center of the expansion; if you run the expansion backwards beyond the empty balloon, and assume you can make the balloon infinitely small, ALL of the dots you drew are at that point; so ALL points are at the center... The universe works the same way, except in 3 dimensions instead of 2... --Jayron32.talk.contribs 18:53, 18 November 2008 (UTC)

To clarify, in that example you are a two dimensional creature living on the surface of the balloon, and can only see things along the surface. You have no ability to look inside or outside the surface. Also in that example, if you could look far enough in any direction, you would eventually see yourself. I wonder if that's true in our universe as well. StuRat (talk) 19:47, 18 November 2008 (UTC)

You're not the only one to wonder that. See Shape of the universe#Global geometry. --Tango (talk) 19:50, 18 November 2008 (UTC)

The problem is that even though the universe might have the 4-dimensional topology of a sphere or torus - it's certainly too big to be able to see all the way around it. We know that the observable part universe does not wrap back upon itself - we don't see identical copies of the same galaxies repeating off into the distance. So if it is sphere-like in topology then it's got to be too large for anyone to be able to directly observe that fact. SteveBaker (talk) 20:11, 20 November 2008 (UTC)

Or maybe we just need a larger telescope. Perhaps we can see our own galaxy now, but only as a distant, fuzzy point of light which we don't yet recognize. StuRat (talk) 02:16, 21 November 2008 (UTC)

Theremin range?

What exactly is the playing range of the theremin? I've heard it stated as just slightly higher and lower than the cello, is this true? Kenjibeast (talk) 02:23, 18 November 2008 (UTC)

The Theremin can play a range from subsonic into supersonic if it is designed to do so. In fact, even a Theremin designed for only the audio range will probably extend beyond the audio range, unknown to the designer of it, if the electrical values of the components used allow that. Basically, it's just an audio oscillator. —Preceding unsigned comment added by 98.16.67.220 (talk) 02:35, 18 November 2008 (UTC)

Alright, let's talk the Moog etherwave model in particular. That one. What's that one's range. Kenjibeast (talk) 02:40, 18 November 2008 (UTC)

That would take some complicated figuring, taking into account every component in the Theremin including its speaker. An easier way is it to have a very good microphone pick up the sound and supply it to an oscilloscope. The oscilloscope will show the basic frequency of the sounds. The microphone would have to respond to subsonic and supersonic audio, if you are interested in that and if the Theremin will go that low and that high. Or a good musician can match the lowest and highest frequencies of the Theremin on a musical instrument and name the pitch he is playing. —Preceding unsigned comment added by 98.16.67.220 (talk) 03:25, 18 November 2008 (UTC)

The Etherwave's tone is produced in a circuit configuration called a beat frequency oscillator. It consists of two high-frequency oscillators, plus a detector circuit which extracts the difference frequency, or beat frequency. One of the highfrequency oscillators (called the fixed pitch oscillator) operates at about 285 kHz, while the other high-frequency oscillator (called the variable pitch oscillator) operates over a range of about 282 - 285 kHz. The difference frequency ranges from zero to about 3 kHz, which is three and a half octaves above middle C. The pitch antenna circuit is connected to the variable pitch oscillator in such a way that increases in hand capacitance will decrease the variable pitch frequency as much as 3 kHz. This is how the pitch antenna circuit, in conjunction with the beat frequency oscillator circuit, enables the player to cover a usable pitch range of some five octaves (two octaves below to three octaves above middle C) simply by moving her right hand through a distance of two feet or so.

From here : UNDERSTANDING, CUSTOMIZING, AND HOT-RODDING YOUR ETHERWAVE ® THEREMIN. Hope this helps. APL (talk) 03:55, 18 November 2008 (UTC)

How can air barriers be permeable to vapor?

Resolved

I just read the following:

The water vapor molecule is smaller than airs other molecules - nitrogen and oxygen. Therefore, water vapor can squeeze through smaller microscopic spaces than air.

How can this be true? It certainly isn't true in a space-filling model: If H-O-H fits through an opening, so will O-O, because the former has to be at least as wide as an O atom, and the latter can't be wider than that.

It is conceivable that the picture looks different when we regard the orbital model. However, I don't think the effect is favorable for water, which has big lobes sticking out of the O on the opposite side of the two H. Moreover, it has high van der Waals forces, which should, if anything, rather contribute to the water getting stuck in narrow openings. — Sebastian 04:03, 18 November 2008 (UTC)

I'm no chemist - but hydrogen atoms are very, very tiny compared to oxygen or nitrogen. Certainly the weight of H2O is a LOT less than O2 or N2. SteveBaker (talk) 04:50, 18 November 2008 (UTC)

Water creates strong hydrogen bonds. As such, I'd expect it would be harder to squeeze through. — DanielLC 04:58, 18 November 2008 (UTC)

Yup, that's what I meant by van der Waals forces. — Sebastian 10:00, 18 November 2008 (UTC)

EC:The size of atoms isn't necessarily simply additive in molecules, as they can overlap when they share electrons or they can have empty spaces inside the molecules as in a benzene ring, buckyball, or carbon nanotube. Also, it's not as simple as the size of the molecule and the size of the holes. The molecules of the gas and container may have various attractions for each other which make passage difficult or impossible. StuRat (talk) 05:06, 18 November 2008 (UTC)

In reply to both of you: The holes could of course be hydrophobic, but that wouldn't be the same argument as the one I quoted. So, can we conclude that that argument is humbug? — Sebastian 10:00, 18 November 2008 (UTC)

On second thought, hydrophobicity should not play a role, as it is, according to our pertinent article, only a consequence of the bonds among water molecules being stronger than those with the surface - which is not the case for vapor. So, the question is: How can air barriers be permeable to vapor? — Sebastian 10:11, 18 November 2008 (UTC)

For atoms and molecules, they aren't all going to line up, they are constantly tumbling and twisting, so its not the SMALLEST dimension that matters, its the LARGEST dimension. In the case of dioxygen, the longest dimension is larger than that of water vapor. Doing a quick search, the O-H bond length in water vapor is expected to be about 95 picometers, and in dioxygen its 121 picometers. Likewise, the atomic radius of hydrogen is 25 picometers and the atomic radius of oxygen is 60 pm. I know that these are not truly additive, but doing a fermi calculation or spherical cow type aproximation should at least show that the O=O size in dioxygen (60+121+60 = 241) is much larger than the O-H size in water (25+95+60 = 180). It turns out that at these scales, molar mass is as good of a first approximation to molecular volume as any; one generally only considers that when judging the "size" of a molecule; and under that test, dioxygen (32) is much larger than water (18). --Jayron32.talk.contribs 13:09, 18 November 2008 (UTC)

Great explanation - thanks a lot! I will see if I can add that to air barrier somehow. — Sebastian 18:40, 18 November 2008 (UTC)

Advice for developing young scientists?

I am a recent graduate of microbiology at University of Texas at Austin. I want to plan a career in a relatively emerging and promising frontier of science, such as molecular genetics or cancer biology. However, the answer to these questions can be useful to any recent graduate.

What new and emerging field of science do you find have the biggest opportunity for future employment prospects i.e. what industry that is based on the science will always be in high demand? I personally had molecular genetics, cancer and developmental biology in mind.70.112.163.212 (talk) 05:15, 18 November 2008 (UTC)

Those all seem like jobs that will be in high demand, but there's another dimension you should consider. Even though such jobs may be in high demand, if they can be outsourced to someone for less pay in India, they will be, eventually (or you will need to take a drastic pay cut to compete with them). You need to find a job that can't possibly be outsourced, if you want a career for life. One that comes to mind is biowarfare, as defense related jobs can't be outsourced for security reasons. You might also be able to get some government job at the Atlanta Centers for Disease Control that would be somewhat secure. StuRat (talk) 05:35, 18 November 2008 (UTC)

What method of study besides job experience do you recommend for getting as up-to-date with that field as humanly possibly?70.112.163.212 (talk) 05:15, 18 November 2008 (UTC)

Reading trade magazines might help. If you can't find a mag specific to microbiology, you could go with some general science mags like Scientific American and Nature. Medical publications like the New England Journal of Medicine and JAMA might also be good (but beware that pharma companies routinely "plant" fake articles in those pubs to promote their products). StuRat (talk) 05:43, 18 November 2008 (UTC)

To reemphasize what StuRat said, the best way of being up-to-date in a field is to read the articles in the journals relevant to that field. This will be quite difficult to all but the most advanced undergraduates, but with time you will find yourself going through them with increasing ease. Magazines like Science and Nature are good, but they are general so a microbiology article may be beside an article on geology (there's no need worrying about things outside of your intended specialty). If you don't know the ranking of journals in your field then feel free to ask a professor or two which ones are the premier journals, they'll definitely know. There's no point paying too much attention (and spending too much time struggling through) journal articles in a journal that people do not respect. With time you'll be able to figure out which journals are rigorous and reliable, but as an undergrad you're probably going to have to rely on professors or grad-students.--droptone (talk) 19:04, 18 November 2008 (UTC)

What books do you recommend for obtaining a deep "philosophical" and practical grasping of basic tenants of science, what is its role in our modern world, what customs exist in the profession, and how researchers carry out their methodology. For instance, what percentage of experiments are novel, and what percentage are simply an extrapolation and testing of ideas that were advanced by a single or select group of researchers? What makes a good scientist a good scientist?70.112.163.212 (talk) 05:15, 18 November 2008 (UTC)

Sidestepping for a moment, you could talk to your ex-professor or one in another university and ask what the gaps for research in your area are at the moment. E.O. Wilson the ant expert invented the word "sociobiology" afaik, and said if he had his life over, he would be a microbiologist. He's a cool role model as scientists go. I would start with him and anything he's written for iinspiration. Julia Rossi (talk) 05:49, 18 November 2008 (UTC)

@StuRat: You failed to take into account the government grants that go into R&D. Whenever the govt. needs to diversify (for GDP growth etc. or like the current credit crunch) it will spend more on R&D. --Movieideas (talk) 12:33, 18 November 2008 (UTC)

I'm not sure how that counters what I said about outsourcing. Are you saying that all government grants will prohibit outsourcing ? That's clearly not the case, as many in the past have permitted this. The most ironic example is using illegal immigrants to build the wall with Mexico to prevent illegal immigration. I'd suspect that in the future, as less and less money is available for government programs and outsourcing becomes more acceptable, a larger portion of government contracts will allow outsourcing. The one exception is an actual jobs program (with the goal of giving out jobs). However, I'd expect those to provide minimal "safety net" jobs to prevent people from going onto welfare, not high-end careers. StuRat (talk) 19:38, 18 November 2008 (UTC)

Well atleast they won't be outsourcing Doctors anytime soon. So to the OP I would suggest get an MD degree. --Movieideas (talk) 00:40, 19 November 2008 (UTC)

I wouldn't be so sure about that. Test results can certainly be sent to a doc in India for him to examine and come up with a diagnosis and treatment plan. Digital photos/CAT scan images of areas of interest can be sent, too. There is even the possibility of performing surgery remotely using robotic technology. This has already been done a few times. StuRat (talk) 18:35, 19 November 2008 (UTC)

@OP: I would suggest you read this business article: Pharma struggles to adapt as patents expire http://www.reuters.com/article/Health08/idUSTRE4AF1QS20081117 --Movieideas (talk) 12:38, 18 November 2008 (UTC)

Not quite sure whether the CDC is such a great idea. Right now many researchers have abandoned ship because the work environment there has been getting steadily worse, with the tips of the icebergs scandals infrequently making it into the local paper (ajc). What does it help if your job is secure, but you'd rather do anything than go to work? This may however be about to change in the current political winds. Similarly military spending is highly dependent on political decisions. Defense contracts may not be subject to outsourcing, they can however be canceled due to budget cuts. Given that the US is currently financially over-extended I'd expect previously cushy government backed positions to be on a lot more shaky ground now. (OR example: Several communities in Germany found their economic rug pulled from underneath them when the US started closing their bases.) Droptone's assurance that reading anything outside of your immediate field would be a waste of time I can't second either. That works fine if your aim is to work at refining existing results. OP stated that he wanted to work at the frontiers of his field. Radically new ideas are usually the result of cross-pollination from other fields. I forgot whose quote it is, but some researcher said that once a sub-category in science had been given a name, all the most interesting and excitingly new science was done and what was left was filling in the gaps and fleshing out the details. On the other hand if you are looking for a secure career path the frontier is not really the place to go. For every shining star-scientist featured in magazines with their new multi million $$ IPO there are troves that slave in underfunded labs always one step away from a major breakthrough, which then comes to someone else or years after they've given up. You may be lucky and get both to do exiting new science and step onto a road to financial success, or not. Most people end up having to chose either or at some point (or more likely several times during their lives). I would not get scared out of my choice by the fact that someone else might be able to do it cheaper. No one has a crystal ball and can say what the future may hold. Today's sure thing can be tomorrow's dud. (OR: One of my relatives was convinced to choose baker as a profession because people would always need bread - shortly before factory bakeries became commonplace. Many of his peers changed fields. He specialized and made a mint with a small specialty bakery.) Given that, where would I look for advances in microbiology? The following are areas where I see a need for advances which is usually a good indicator: Bio-fuels: The EC is funding algae /sewage based projects. Maybe something similar, or novel to get from solar to gas without going via food plants and using arable land? Materials science: we are running out of resources in other things but fuel. Breeding microorganisms to reclaim waste, or build new materials with similar or better properties than what we used to have sounds interesting. Water: both turning water from various sources into drinking/potable water and removing pollutants from wastewater are fields with lots of opportunities Human-machine interfaces: Prosthetics and TBI [1] make this an area where even small advances have a a large impact. (- or you'll end up building the foundations for the next game console ;-) If you find cancer research overpopulated you might have better luck with diabetes. Human gut bacteria are not well understood from what I've read. Maybe one of those could be re-programmed to produce insulin? And totally off the wall: you could design a couple of bugs that eat/digest the explosives in the many unexploded land-mines that make farmland unusable in countless places. Also, have a peek at economics and political pages. See what companies (still) have money and what they are interested in and what projects political leaders put their weight behind. Then see if there is an angle where you could provide some advances in related sciences that they might fund. Don't worry if you don't get it right on the first try. I don't have comparative numbers, but many people go through several careers in their lives. Good luck. 76.97.245.5 (talk) 00:59, 22 November 2008 (UTC)

Resistance in space.

Does anyone know the resistance of outer space? Preferably as a function of distance from the Sun? I asked this as part of another question earlier. So far, the only answer I got was:

The resistance in space is pretty frigging huge. You need a series of actual atoms to transfer electrons along; and atoms are few and far between in space, so the resistance is likely, um, excuse the pun, "astronomically high". --Jayron32.talk.contribs 15:36, 17 November 2008 (UTC)

Let me continue from there. IIRC, space contains large numbers of ions and free electrons. This would cause the Earth's charge to slowly leak. This is quite different than how electricity normally works, so I don't know if the electrical conductance in space can be modeled the same, but I'm doing it on a planetary scale, so if there's anything slowing the charge down at all, it seems like the normal model might work. In addition, I'm dealing with a huge time-frame (5.5 billion years). Put simply, making a charge of 8e17 C once, and making it once every million years to keep it from going away, make the resulting difficulty in destroying the Earth differ by over three orders of magnitude. — DanielLC 05:26, 18 November 2008 (UTC)

Is the Earth also being constantly charged by the solar wind ? StuRat (talk) 06:42, 18 November 2008 (UTC)

Electromagnetic forces are vastly more powerful than gravity - if there was even a fraction of a volt difference in the charge on any of the planets or the sun, the solar system would be a very different place! If there is a 'charging' mechanism - then there must be a corresponding discharge mechanism...I kinda doubt that either are significant. SteveBaker (talk) 13:38, 18 November 2008 (UTC)

Steve, your intuition fails you. Yes, the electrostatic force between two protons is 10³⁶ times greater than the gravitational attraction between them, but the Earth is massive, having 10⁵¹ nucleons. So to put electrostatic forces on a similar scale to gravity you need an excess charge of say 1 electron for every 10¹⁸ nucleons, or a total of 10¹⁴ Coulombs of charge. That would give the Earth a potential of approximately 10¹⁷ V. A few volts is nothing on planetary scales. Dragons flight (talk) 17:20, 18 November 2008 (UTC)

I just noticed I didn't explain very well why I think space would conduct electricity. I mean that the ions of opposite charge would move towards the earth, and the ions of the same charge would move away, thus slightly increasing the amount of oppositely aligned ions entering the atmosphere, and decreasing the amount of similarly aligned ions. If there's nothing slowing the ions down, they'd just keep accelerating and causing the charge to go away faster and faster, but if they are slowed down, it would act the same as the atoms slowing down electrons in a conductor, just on a larger scale, making the normal models still work. — DanielLC 16:16, 18 November 2008 (UTC)

Your intuition is correct, and the solar wind is a ready-made conductor. But the problem is that neither it nor a true vacuum are ohmic conductors (only the intro of that article is relevant here); they don't have a single, well-defined "resistance" but rather a more general I-V curve. See also breakdown voltage. --Tardis (talk) 17:39, 18 November 2008 (UTC)

"Space" is a hard vacuum. A Vacuum tube usually has a hard vacuum. Both have immeasurably high resistance when there are no electrons or ions present in the space between electrodes. In some early (1930's) science fiction a plot gimmick was that the bad guy had broken the glass on the vacuum tubes, so the spaceman could not broadcast a warning message from his spaceship. The spaceman just donned his space suit and opened the hatch, making the interior of the ship a hard vacuum like outside, and the tubes worked fine. My point is that if you tested resistance of space by having metal surfaces some distance apart and applying a voltage between them while measuring the current, no current would be detected unless there were ionized gas atoms introduced between them, or unless electrons were emitted from the one with the negative charge.The Photoelectric effect describes how a metal piece will emit an electron when it absorbs electromagnetic radiation. As noted, there are some ions in space and there are some electrons, and these could carry a small current. The resistivity of space would depend on what ions and electrons were in it. Hot metal will emit electron via Thermionic emission. Edison (talk) 17:48, 18 November 2008 (UTC)

Tardis, do you know what the equation for this I-V curve is, or where I could find out? — DanielLC 06:03, 19 November 2008 (UTC)

(Sorry for the delayed response.) There isn't going to be a single curve because there isn't a single vacuum (or a single solar wind); it depends critically on the size and arrangement of your contacts, and even what material they're made of and what temperature they are. (If the current heats them, then the I-V curve changes over time and depends on the history of your voltage!) What I do konw is that for a true vacuum, there will be no current at all below the breakdown voltage (barring insignificant quantum effects like quantum tunnelling), and that above it there will be a current limited by the geometry of the system. --Tardis (talk) 22:53, 22 November 2008 (UTC)

Tankers and aircraft carriers

In this morning's reports of the hijacking of the oil tanker Sirius Star, an American Navy official is quoted as saying that the tanker, "(is) three times the size of an aircraft carrier." The Sirius Star is 330 metres long, or 1082 feet. After some googling around, I can't find any type of aircraft carrier that is shorter than about 800 feet. It isn't too easy to compare the 'weights', as there seem to be deadweight tons, shortweight tons, metric tons, and displacement. In any case, is there any measure by which this supertanker can be fairly described as 'three times the size of an aircraft carrier'? Audacious pirates anyway... —Preceding unsigned comment added by 80.101.134.43 (talk) 09:28, 18 November 2008 (UTC)

The Sirius Star has a displacement of over 300,000 tons. A Nimitz class aircraft carrier (the largest aircraft carrier ever) displaces just over 100,000 fully loaded, according to its infobox. Clarityfiend (talk) 10:07, 18 November 2008 (UTC)

See Tonnage for a bunch of ways to measure ship sizes. PrimeHunter (talk) 18:13, 18 November 2008 (UTC)

The term "size" is incredibly vague, and thus can be molded to whichever direction the writer wants. If they wanted to convince you the aircraft carrier was larger, they would likely compare the masses when unloaded and call that the "size". StuRat (talk) 19:26, 18 November 2008 (UTC)

Selective breeding pros/cons

What are the pros and cons of selective breeding? is it ethical/unethical? Discuss —Preceding unsigned comment added by Fas327 (talk • contribs) 09:57, 18 November 2008 (UTC)

That little word 'discuss' signfies...homework. As noted at the top of the page we're not here to do your homework. If you want to consider the ethics of breeding etc. perhaps search for any pro or anti organisations mentioned in your text-books with regards to it. Also read through Selective breeding and the subsequent links that page will likely contain. 194.221.133.226 (talk) 10:42, 18 November 2008 (UTC)

Not to mention the rules agreed to when posting to the ref desks: "The reference desk does not answer requests for opinions or predictions about future events. Do not start a debate; please seek an internet forum instead." -- Aeluwas (talk) 12:35, 18 November 2008 (UTC)

Rhode Island is neither a road, nor an island. Discuss. --Shaggorama (talk) 00:12, 19 November 2008 (UTC)

Brain Tumor Cells vs. Normal Brain Cells

• What is the difference between Brain Tumor Cells and Normal Brain Cells?

• The article Brain tumor states: A brain tumor is any intracranial tumor created by abnormal and uncontrolled cell division, normally either in the brain itself (neurons, glial cells (astrocytes, oligodendrocytes, ependymal cells), lymphatic tissue, blood vessels), in the cranial nerves (myelin-producing Schwann cells), in the brain envelopes (meninges), skull, pituitary and pineal gland.

• So can the body to use the tumor cells for Thinking? --Movieideas (talk) 12:24, 18 November 2008 (UTC)

No, you can not use the tumor cells for thinking, as illustrated in this fascinating article about an awake craniotomy. --Sean 13:34, 18 November 2008 (UTC)

I once read a creepy science fiction short story about a college lecturer who quoted "I think, therefore I am" and the thought took shape as a cancerous brain cell which became a tumor which grew and took over his thought processes, basically arguing with him, before he died from the effects of the rapidly growing tumor. Edison (talk) 20:27, 18 November 2008 (UTC)

Your fascinating article doesn't state why we cannot think using the tumor cells? Or what is the difference? I mean if it is uncontrolled cell division, so there would be more neurons, and then there would be neurotransmitters, to facilitate thinking? --Movieideas (talk) 00:28, 19 November 2008 (UTC)

The problem with "thinking" is that it is far more than an issue of the number of cells or the amount of neurotransmitters. What we perceive as "thinking" is the result of exceedingly complex brain architecture and neurophysiology that requires coordinated electrical and chemical signals between various parts of the brain (unfortunately, neuroanatomy and nervous system don't really do this topic justice). Even those functions of the nervous system that operate autonomously (i.e. you're not aware of them happening, like control of your breathing, heart rate and blood pressure) require an exquisite circuitry that is simply not present in a tumor mass. While the cells involved in that tumor may derive from a cell type that was once a functional neuron, or had the potential to become a functioning neuron, the uncontrolled cell division means that these cancer cells never extend functional neuronal processes that would enable cell-cell communication in any kind of coordinated fashion. In fact, a brain tumor might cause a structural or electrical distortion that impairs your function in one way or another, perhaps resulting in seizures or other neurological impairment. The simple answer to your question, as stated above, is no. Medical geneticist (talk) 15:53, 19 November 2008 (UTC)

Where does the Earth's heat go?

This has puzzled me since I was a kid. The Earth is a closed system (more or less). The Sun constantly heats the Earth. So shouldn't the Earth be constantly getting hotter and hotter? Heat is the vibration of atoms and space is a vacuum. So where does all the heat go? 67.184.14.87 (talk) 14:08, 18 November 2008 (UTC)

It emits it into space as infra-red radiation. See thermal radiation. --Tango (talk) 14:20, 18 November 2008 (UTC)

The Earth is not a closed system. If it were, it would not absorb heat from the Sun. --—— Gadget850 (Ed) ^talk - 14:31, 18 November 2008 (UTC)

By the way, Earth is also heated by radioactive decay. Omission of that factor caused a bad estimate mentioned in Age of the Earth#Early calculations: physicists, geologists and biologists. PrimeHunter (talk) 16:55, 18 November 2008 (UTC)

Most of it bounces is sent back into space as mentioned above, but some of it gets captured as chemical energy by plants. --Sean 17:07, 18 November 2008 (UTC)

There is a difference between the radiation from the sun reflecting back into space and it being absorbed and re-emitted - both happen. --Tango (talk) 17:55, 18 November 2008 (UTC)

I know, and was using "bounce" loosely. In my pedantic defense, even reflection consists of absorption and re-emission. --Sean 18:45, 18 November 2008 (UTC)

The basic error in your assumptions was that all forms of heat transfer require a medium. While this is true of convection (fluid required) and conduction (fluid or solid required), this is not true of thermal radiation, which can happen across a vacuum. Radiation is actually more effective in a vacuum, as no portion of the radiation is absorbed or reflected by the medium. StuRat (talk) 19:13, 18 November 2008 (UTC)

Yes - the confusion is that heat (the kinetic energy due to the motion of molecules) can be converted to electromagnetic radiation (like infra-red light) - which IS NOT HEAT (which is kinetic energy) but instead electromagnetic energy. The infra-red light subsequently hits some molecules and sets them off moving - thereby giving them kinetic energy (which manifests itself as heat). Hence, one way for the earth to cool off (to slow down it's molecules) is by radiating infra-red light. This is only one of three traditional ways to describe the shedding of heat (Radiation, Conduction, Convection) - the latter two don't work in a vacuum - but the first does. It's convenient to think of the heat 'flowing' from one place to another - but in the case of radiative loss/gain, it's really not. The heat is "going away" and being replaced by IR light - then (eventually) the light hits something and (typically) creates heat as a result. However, the IR light could instead hit an electron and cause an electric current to flow or cause some other kind of energy to be created. SteveBaker (talk) 19:39, 18 November 2008 (UTC)

is Jesus's 100% man/100% God dualty like quantum wave/particle dualty?

So Christians think that Jesus is completely, 100% a normal human being, he can die, everything about him is normal, he's just like you and me. At the SAME time, he's 100% God Himself. He's completely God. It's not that he's 20% Human and 80% God. He's completely a mortal human and completely immortal God. Obviously, this is ridiculously illogical and anyone who would believe that is off their rockers....I was thinking.

But wait: I remembered that reality itself has such a dualty! Light is 100% a wave, it interacts in wave patterns, by any standard you could measure it's completely a wave. But it's also a particle, it comes in photons, by any standard you could measure it completely comes in particles. So it seems you don't have to be ridiculously illogical to believe that, since our physical universe ACTUALLY has such a manifestation! But I'm not a quantum physicist so, could I ask:

Is my conclusion right? If Christians believe what I said about Jesus, is it comparable to what quantum physicists believe about light? Thank you! —Preceding unsigned comment added by 79.122.75.250 (talk) 14:28, 18 November 2008 (UTC)

You're really speaking in metaphors here all the way through so I'm not sure whether the comparison is bad or good. Light it isn't a wave or a particle—it's light, and we understand that macroscopically as being something of dual nature (we understand it in the terms in which we know how to think). You could, I suppose, make the argument that indeed, the dual humanity/Godness of Jesus is something similar, that he would be, in fact, just "Jesus", and that we abstract that in terms we understanding (either all man or all God, depending on the context). But it's not a real one-to-one scientific comparison at all, though I suppose both appeal to realms of non-standard logic, logic in spheres outside of our mere mortal comprehensions. --98.217.8.46 (talk) 14:32, 18 November 2008 (UTC)

Your first fallacy is thinking that all Christians have the same beliefs about Jesus; see Christian views of Jesus. --—— Gadget850 (Ed) ^talk - 14:40, 18 November 2008 (UTC)

Put simply, we don't say light is a wave and a particle, we say it behaves as a wave and a particle in different contexts. Whether that is similar in any way to Christian understanding of Jesus is something for another ref desk. --Tango (talk) 15:42, 18 November 2008 (UTC)

I have a magical coin in my pocket that is both perfectly round and perfectly square at the same time. The difference between the respective dual natures of light and my coin is that one of them will stand up to centuries of well-funded and intellectually rigorous scientific inquiry by the smartest people on Earth, and one of them won't. I'll let you guess which is which, and which might be more akin to Jesus's dual nature in that regard. --Sean 17:06, 18 November 2008 (UTC)

This is the science desk - not the guessing-wildly-about-the-supernatural desk. The scientific answer is that we have been given no opportunity to perform any experiments on either Jesus or God - and we actually have no evidence that either ever existed. So it's unreasonable to expect us to have an answer for you. An analogy is not a way to reason about the universe...it's a way to explain something that you already understand. SteveBaker (talk) 19:31, 18 November 2008 (UTC)

Well, that's not completely true. AFAIK, most historians believe that a Jewish religious leader named Jesus did exist 2 thousand years ago. 67.184.14.87 (talk)

Some, certainly. I don't know about most. It's far from all. We have an article, historical Jesus, but it's been a while since I've read it. --Tango (talk) 22:48, 18 November 2008 (UTC)

Then read Historicity of Jesus - which asks what actual EVIDENCE there is - as opposed to what may be inferred from the dangerous assumption that the bible is basically correct (which is what Historical Jesus discusses). The former says that aside from the (somewhat biassed) reports in the Bible - the first independent account was around 100 years after Jesus supposedly died when the whole religious thing was beginning to get off the ground. This can only be a second or third-hand account. So there really is no independent, reliable evidence. Certainly not enough to base an answer to this question on! SteveBaker (talk) 20:06, 20 November 2008 (UTC)

Anatomy

Can someone link me to some information on the evolution of the ear, or make a wikipedia page on it? Evolution of the nose wanted, too :) I'm curious... Also, any information on the evolution of blood (not individual blood types like A and B but the substance of blood) would be cool. Could someone compare and make a cross-section on the differences between different species' blood? Or at least groups of species (insects, mammals, fish etc.), please. Also, how do the immune systems of smaller organisms like insects work? Can someone further explain the system through which lymph is conveyed through the body, and also compare that to other organisms' lymph transportation? Some more questions about blood - I know that Red blood cells live about 120 days, and they go to the Liver to be "cleaned" (this is correct, right?), but how often do they go? How are they cleaned? Also, how does Hemoglobin work? I know that arteries move RBCs through peristalsis - does this mean that arteries are smooth muscle? How do veins keep that momentum of the blood up, especially far away from the heart? veins use valves, don't they? Are the valves cells of their own, or inanimate proteins or what? Oh, and evolution proponents say that one human chromosome is the fusion of 2 chimp ones or something like that. Without getting into a pro/anti-evolution debate, how could these have fused gradually/quickly?

Thanks for all your time. Answer as much as you can :) I really like learning and am curious about this stuff... —Preceding unsigned comment added by 216.102.78.170 (talk) 16:45, 18 November 2008 (UTC)

That's too many questions for a humble refdesker like me to answer, but I'll point out that arteries do not move red blood cells through peristalsis! See heart. --Sean 18:51, 18 November 2008 (UTC)

True, of course. However, the questioner is correct in asserting that the arteries have smooth muscle. Its function is vasoconstriction, which is used for the regulation of blood pressure, conservation of heat (directing blood away from the skin when it's cold) etc. --NorwegianBlue ^talk 21:17, 18 November 2008 (UTC)

Just a comment on the valve question. Those aren't valves that the body controls, they are simple valves, just a flap over an opening, such that the flap is closed when movement occurs in the opposite from normal direction, and open when flow is in the correct direction:

_____________________
           /|
 Flow  -> /   Flow
 Dir     /    Dir
 Closes /     Opens
 Valve /  <-  Valve
      /
            |        

StuRat (talk) 19:09, 18 November 2008 (UTC)

And the valves are MUCH larger than individual cells, they are macroscopic, and composed of both cells and extracellular proteins. The proteins are mostly collagen, many of the cells are fibroblasts, and the valve is covered by endothelial cells. --NorwegianBlue ^talk 20:31, 18 November 2008 (UTC)

• The lymph question is answered in the articles Lymph and Lymphatic system. Basically, what is to become lymph is part of the plasma of the blood as it leaves the heart. In the capillary network, some of the plasma leaves the blood and becomes interstitial fluid. Most of it goes back into the venous blood in the venules. The surplus enters lymphatic capillaries. Note that the lymph vessels start as "blind alleys" into which this liquid enters, before moving towards the great veins in the neck, where it enters the bloodstream. Lymph vessels have valves, and the transport of the lymph against gravity is in part caused by pressure from nearby pulsating arteries, in part by contraction of striated muscles (e.g. in your legs -- same thing as for the veins). According to our article, lymph vessels also have peristalsis. (I didn't know that, and am a bit sceptical -- could someone confirm? (User:Nunh-huh, are you reading this?))

• Well, I hadn't been, but now you've gone and invoked the name of the devil, and so I am. Small lymph vessels are thin-walled channels, typically just tubes consisting of endothelium, so they can have no peristalsis. Only the larger vessels have any muscular layer, and there is some sequential contraction in these that aid lymph flow. However, like you, I recognize that pretty much the only thing ever actually referred to as having peristalsis is the GI tract. I think the jury is out on which method of lymph propulsion is predominant: skeletal muscle compressing the lymphatics (with the one-way valves assuring that propulsion occurs in the proper direction), vs. propulsion intrinsic to the lymphatic vessel, and my money's on the importance of the former. But both have been observed, and described, and so both occur, regardless of which is more important. - Nunh-huh 03:13, 21 November 2008 (UTC)

• The liver/"blood cleaning" question: I have no idea what "cleaning" of red blood cells would mean. It is correct that the Kupffer cells of the liver may phagocytose aging red blood cells, but that is far from the most important function of the liver, and a task which is believed to be primarily performed by the spleen. See Liver. The key point in understanding its function, is realizing that it receives all the blood from the gut, with all the nutrients, and also all the nasty stuff, toxins etc. (For the exception, see Chyle - the lymph from the gut, which contains fat, and which bypasses the liver). So two of its most important tasks are buffering glucose as glycogen, to keep the blood glucose level stable between meals, and detoxifying otherwise toxic substances that are absorbed from the gut. In doing so, it also often modifies drugs that are taken orally. In addition to this, the liver has many other functions which are described in the article.
• The chimp question: see Chimpanzee genome project for a comparison of the genomes (human chromosome 2 is a fusion of two chimp chromosomes), and here for an explanation of the mechanics of how such a chromosomal rearrangement could happen. A single chromosomal rearrangement does not necessarily prevent meiosis from occurring, but heterozygotes tend to be less fertile and may have an evolutionary disadvantage. --NorwegianBlue ^talk 21:06, 18 November 2008 (UTC)

gama rays

is gama rays can break the atomic structure of water? because cosmic radiation break the water molecules in the air,bat in nuclear power station the water molecules in the steam tank dosent break down--אזרח תמים (talk) 17:41, 18 November 2008 (UTC)

Water is self-ionizing. The bonds will break (and quickly reform) if you just use harsh language towards it. -- kainaw™ 17:44, 18 November 2008 (UTC)

To clarify - water exists naturally as a mixture of H2O atoms, H+ ions and OH- ions, constantly splitting and recombining. Gamma rays may increase the rate at which that takes place, I'm not sure, but it won't make a great deal of difference (if they are splitting more often, they will recombine more often too, the proportions may shift slightly, but that's about it). --Tango (talk) 18:00, 18 November 2008 (UTC)

Plus, the number of actual gamma ray particles compared to the number of water molecules is vanishingly small. Grab a geiger counter sometime and listen to the clicks. In a normal room, they go click...pause...pause...click...pause...pause...click. Each click is a gamma ray - so just imagine how few of the 100,000,000,000,000,000,000,000 or so water molecules in that bucket over there gets hit every second! Even in the presence of low level radioactive waste, the counter doesn't go completely nuts. So the extra ionisation caused by gamma rays through the water is really pretty negligable - even when the radioactivity is off-the-chart.

Another way to think about that (although my explanation is going to be a bit superficial and will probably be poked to death by the experts here) is that each gamma ray comes about because one unstable atom of the radioactive stuff decayed to something more stable. That one gamma ray then goes on to ionize one water molecule. So in order for (say) a kilogram of water to be ionized, an equivalent number of atoms of plutonium (or whatever) would have had to decay into something less nasty. But since plutonium atoms are super-heavy compared to water molecules, it would take VASTLY more than a kilogram of plutonium decaying completely to ionize one kilogram of water. But they put a few kilos of plutonium fuel rods in thousands of gallons of water - so the fraction of the water that'll get ionised is negligable. But in any case, all of that plutonium doesn't decay immediately - that's the entire problem! It sits there S-L-O-W-L-Y decaying for thousands of years.

SteveBaker (talk) 19:26, 18 November 2008 (UTC)

When the gamma ray hits a water molecule it could cause some unusual ionization. It is more likely to run into electons in an oxygen atom, because there are more of them there, and then eject a high energy electron and make a H₂O⁺, the moving electron then goes on knocking out many more electrons, and causing more ionization. I am guessing that you may get hydrogen peroxide and hydrogen molecules formed. But as SteveBaker says above, there will actually be very few molecules involved. Graeme Bartlett (talk) 20:36, 18 November 2008 (UTC)

In a normal environment, far from unusual radioactive sources, most of the clicks you hear from a Geiger counter are caused by cosmic ray produced muons not gamma rays. Dragons flight (talk) 00:15, 19 November 2008 (UTC)

The color of Dunkleosteus

I recall reading at one point that the actual color of Dunkleosteus had been determined due to some kind of chemical analysis of the fossil (bear with me--I read this a few years ago so my memory's a bit sketchy). This was an amazing announcement, but I'm not sure if I'm willing to believe it, because this information was packaged along with the "Arsinoitherium had hollow horns" assertment, which we know now is incorrect. So I am not sure if the claim about Dunkleosteus is valid or not. I can't seem to find any verification online, but I'm not sure if this is because there really isn't any such evidence, because I somehow missed the optimal keywords that would have brought me the results I wanted, or if it's just due to the material being unavailable online or in my particular language (there are a few paleocritters I can't find anything on, but I don't doubt that they exist). So what's the deal with Dunkleosteus? Do we know what color it was, or is this just another baseless "fact" that shouldn't be taken seriously? 70.213.5.52 (talk) 19:48, 18 November 2008 (UTC)

I can think of two ways to determine the color of the skin, fur or scales of a fossil:

1) Preservation of that skin, fur or scales. It might have been damaged, though, in which case a chemical or microscopic examination might still be able to find a few traces of pigment. However, fossils over a few thousand years old aren't likely to have any of the original skin, fur or scales remaining.

2) DNA analysis. DNA in teeth and bones can last a bit longer, but usually not millions of years. However, when it does last, it could theoretically be analyzed for pigmentation genes. However, this is a very complex process, and I'm not sure if it can be done at a reasonable cost and time-frame, yet. Give us a few years, though, and we will know everything there is to know about a dino, just from it's DNA.

Since the Dunkleosteus is some 360 million years old, I'd think it unlikely that either of those methods could work. StuRat (talk) 20:52, 18 November 2008 (UTC)

Yep the DNA will not work any time in the near future, the DNA is too degraded after 360 million years. It's pretty hard getting DNA from something 1000 years old. And we don't know enough about Dunkies to interpret any sequence data we might get. Aaadddaaammm (talk) 19:17, 20 November 2008 (UTC)

hubble telescope

How far into space can the hubble telescope see? —Preceding unsigned comment added by 208.100.237.47 (talk) 20:48, 18 November 2008 (UTC)

You might need to clarify the question. The Hubble telescope, or your eyeball, can each see an infinite distance if that distance contains a pure vacuum and the object on the other side is bright enough. However, the image it sees may just be a point of light, which isn't as useful as seeing, say, the spiral arms of a galaxy like ours, or, better yet, the individual stars within the galaxy. StuRat (talk) 20:55, 18 November 2008 (UTC)

The Hubble Ultra Deep Field is an image captured by a very long exposure. It captures images said to be "13 billion years" old. The obvious answer is to say that the objects in the picture (galaxies, mostly) must be 13 billion years old. But I'm not sure that that is correct. That's a big enough distance that you might have to take the expansion of the universe into account. I'm sure if you wait a bit someone knowledgeable about astronomy will clarify.

The HUDF was taken over a couple of weeks. 'Snapshots' with the telescope will obviously be less sensitive. APL (talk) 21:31, 18 November 2008 (UTC)

The light from them was, indeed, emitted 13 billion years ago, in the usual sense. They are (now), however, more than 13 billion light years away, due to expansion. --Tango (talk) 23:15, 18 November 2008 (UTC)

To complicate the answer there's also gravitational lensing to consider.76.97.245.5 (talk) 06:24, 21 November 2008 (UTC)

It's not really a fair question to ask how "far" a telescope can see. It all depends on its limiting magnitude, and in the case of Hubble, it can see all the way to the edge of the visible universe, assuming that the objects are bright enough. For comparison, the farthest object the human unaided eye can usually see would be the Andromeda Galaxy. ~AH1^(TCU) 16:17, 22 November 2008 (UTC)

However, with the "provided the object is bright enough" qualification, the human eye could also see to the edge of the universe. (But, of course, there aren't any objects that bright in the universe.) StuRat (talk) 21:02, 24 November 2008 (UTC)

Finding the amount of moles

Suppose that I had a 60% ethanol solution (40% water). How would I go about finding the moles of ethanol boiled off if I were to boil it for a certain period of time?

Basically what I am trying to do is boil the ethanol vapors for an experiment I am doing. I need to measure the amount of moles of ethanol in the vapors. I have access to lab equipment, so do not need to be hesitant with any suggestions if they include laboratory apparatus. Thanks. This is probably really simple but for some reason I can't think of the proper method to measure.

--proficient (talk) 21:32, 18 November 2008 (UTC)

The easiest method probably involves measuring the density of the solution after a given point in time. Since the density of the solution will tell you the relative concentration of the ethanol, once you know the final and initial masses of the solution, and final and initial densities, you can determine exactly how much of the loss of mass is water vapor and how much of the loss is ethanol vapor, and just convert these masses to moles. This page: [2] contains ALL SORTS of useful calculators and tables for figuring this stuff out. --Jayron32.talk.contribs 21:57, 18 November 2008 (UTC)

Titrate it with KMnO4 before and after to find he concentration of the ethanol.124.169.74.251 (talk) 23:07, 18 November 2008 (UTC)

That'd work too... though using a hydrometer would likely save a few steps and be a bit quicker... --Jayron32.talk.contribs 00:53, 19 November 2008 (UTC)

How many human habitable planets can there be in a solar system?

I'm watching Battlestar Galactica and a thought occurred to me. In the show, their solar system has 12 planets that are inhabited by mankind. It seems to me that it would be extremely unlikely, if not impossible, for a single solar system to have 12 planets that could be inhabited by humans. In fact, I'm wondering if how possible it is to have 2 planets within a solar system's habitable zone. So, theoretically speaking, how many planets can there be within a single solar system that could be habitable by man? By 'habitable' I mean that the people could live on it naturally without the need for a space suit or 'moon base' like enclosure. 67.184.14.87 (talk) 21:39, 18 November 2008 (UTC)

It depends on the type of star, hotter stars have wider habitable zones. Greenhouse effects and similar can expand the zone as well. I can't see a problem with two or maybe three planets being in the habitable zone. If there were more, they would have to be quite close together, which would probably only be stable if they were in resonant orbits (but there's no reason why they couldn't be in resonant orbits). If you allow habitable moons (or double planets), then the number of possible habitable places increases quite significantly. I haven't seen BSG, do they do any terraforming? If so, then that could increase the number significantly (depending on the effectiveness of their technology). --Tango (talk) 22:46, 18 November 2008 (UTC)

(after edit conflict)I suppose it would depend on how closely packed together the planets' orbits are. I don't suppose that there's any reason why you couldn't have several earth-type planets orbiting within a star's habitable zone.

• How about a binary/trinary/quadruple/quintuple star system with habitable planets orbiting each star?
• Do you include terraformed planets?
• Gas giants in the HZ with several habitable earth-sized moons?
• I think it's possible for more than one planet to share the same orbit too.

--Kurt Shaped Box (talk) 22:49, 18 November 2008 (UTC)

If you were to swap Mars and Venus, the solar system could have three reasonably-habitable planets. If you start doing fancy stuff like putting Earth-like planets in each other's L4 and L5 Lagrangian points, or put Earth-like moons in orbit around a superjovian planet, the numbers can get even higher. --Carnildo (talk) 23:06, 18 November 2008 (UTC)

And to discuss the premise that prompts this, I don't think BSG (at least not the new one) claims that all 12 planets are in a single system. Now Serenity, on the other hand.... — Lomn 00:00, 19 November 2008 (UTC)

According to Twelve Colonies (yeah, Wiki has everything!): The original series had them as twelve planets in a binary star system with some orbiting one star and some the other. The new series has not stated anything on screen about their relative location, but the series creator has indicated that they are again part of a single star system (without any discussion of how they are arranged). Dragons flight (talk) 00:06, 19 November 2008 (UTC)

Serenity/Firefly has a reasonable number of planets and moons (on the high side of reasonable, maybe), it's just terraformed them all into habitable ones. --Tango (talk) 00:13, 19 November 2008 (UTC)

There's no terraforming in the new BSG, at it's least not mentioned in the show. But after they leave their solar system, they travel a substantial distance (2-3 years almost 2 years worth of episodes) before they find another habitable planet, a dreary, shabby planet. I would have preferred to stay on the ships. 67.184.14.87 (talk) 00:43, 19 November 2008 (UTC)

And the next planet they find is also dreary and shabby. Possibly for a different reason, though. (Dun dun dun...) zafiroblue05 | Talk 08:43, 19 November 2008 (UTC)

God damn you all to hell! ;) It will be interesting to see what sort of twist they put on this. 67.184.14.87 (talk) 12:55, 19 November 2008 (UTC)

How hot would Venus be if it was in Mar's orbit?

67.184.14.87 (talk) 21:39, 18 November 2008 (UTC)

Just a guess, but perhaps as hot as Mars? But maybe that's too simple an answer. —Cyclonenim (talk · contribs · email) 22:17, 18 November 2008 (UTC)

No, because Venus has a green-house effect that dramatically raises temperature. 67.184.14.87 (talk) 22:33, 18 November 2008 (UTC)

As with any of "what if" question like this, it depends on exactly what you intend to change and what you want to keep the same. If a planet of Venus' size formed in place of Mars in its orbit, then it would probably be warmer than Mars, but colder than Earth (it would still have a significant atmosphere, which would keep it warmer than Mars, but due to its distance from the Sun it wouldn't be very warm). If Venus as it is now were to move to Mars' orbit, keeping its greenhouse effect, then it would still be pretty warm, although not as hot as it is now, I'm not sure how it would compare to Earth. --Tango (talk) 22:38, 18 November 2008 (UTC)

A very crude estimate is to note that transplanting Venus into Mars' orbit doubles the distance from the sun, hence reducing the received sunlight by a factor of 4. To reduce radiant energy by 4, you have to decrease the effective temperature of thermal radiation (roughly the cloud-top temperature) by 4^1/4. If we crudely imagine that the surface temperature scales proportionally to the cloud-top temperature then it might go from the 735 K at present to around 520 K (250 C). Of course that assumes that it's atmosphere stays intact and nothing else changes. Dragons flight (talk) 23:00, 18 November 2008 (UTC)

One of the factors involved would be the "heat albedo" of Venus -- its ability to reflect incoming heat radiation from the sun. —Preceding unsigned comment added by 98.16.67.220 (talk) 22:59, 18 November 2008 (UTC)

Another issue for this imaginary waste of time is the magnetic field. If Mars was in Venus' orbit, would it get a nice gooey core and start up a magnetic field again? If so, it could rebuild an atmosphere. If Venus was in Mars' orbit, would it get a nice hard nuget center, which would inhibit the magnetic field and, as a result, leave the atmosphere unprotected as it slowly wisps away into the void of space? Without an atmosphere, there's no greenhouse effect. -- kainaw™ 02:26, 19 November 2008 (UTC)

While a magnetic field certainly helps protect the atmosphere, is it strictly required? Also, being closer to the Sun, the solar wind is stronger so it would require a greater magnetic field to protect from it. --Tango (talk) 13:48, 19 November 2008 (UTC)

But being closer to the sun ALSO increases tidal forces on the solid part, increasing temperature of the solid bits itself. A good portion of Earth's warmth, for example, is from its internal heat. --Jayron32.talk.contribs 13:58, 19 November 2008 (UTC)

Without a magnetic field, I do not see how it is possible to maintain an atmosphere for any length of time. Solar winds will keep pushing away the outer atmosphere. The planet can try to replenish it, but the planet will eventually run out of gas to fill the atmosphere and you will end up with a planet like Mars, which likely had a magnetic field when it was full of internal heat, but the magnetic field died out and now the atmosphere is thin and getting thinner. Any attempt to pump in an atmosphere will be a waste of time since solar winds will keep stripping away anything that is pumped in. It is like trying keep a balloon inflated when it has a small hole in it. You can't fill it up and quit. You have to keep adding more and more air. -- kainaw™ 14:04, 19 November 2008 (UTC)

Why would Venus have trouble maintaining its atmoshere? It has an atmosphere now. 216.239.234.196 (talk) 14:43, 19 November 2008 (UTC)

Hmmm... this was probably mentioned just a few lines above... let me see... oh yes. It helps to read first and ask second...

Quoted from above: "If Venus was in Mars' orbit, would it get a nice hard nuget center, which would inhibit the magnetic field and, as a result, leave the atmosphere unprotected as it slowly wisps away into the void of space?" -- kainaw™ 14:50, 19 November 2008 (UTC)

Your rudeness aside, thank you for your answer. 216.239.234.196 (talk) 15:24, 19 November 2008 (UTC)

No, the core dynamo is not appreciably impacted by the orbit location. Also Venus has no appreciable dynamo, so your assumptions are false. Despite lacking a magnetic dynamo Venus has the largest atmosphere of any rocky planet. The solar wind probably robbed Venus of most of it's original water, but carbon dioxide and nitrogen are too heavy to easy ablate even without a field. Dragons flight (talk) 19:44, 19 November 2008 (UTC)

I looked it up and Venus is actually hotter than Mercury even though Mercury's much closer to the Sun. 216.239.234.196 (talk) 15:04, 20 November 2008 (UTC)

Indeed, that's due to the greenhouse effect. Mercury doesn't have an atmosphere (due to a combination of it being much smaller, so having weaker gravity, and it being closer to the Sun, so the heat and solar wind erodes the atmosphere more). --Tango (talk) 23:35, 20 November 2008 (UTC)

Newton's Second Law (F=ma)

I was wondering specifically one thing about Newton's Second Law.

Giving the basic summary, Issac Newton was an English physicist among many other things. He came up with the principle of Force = mass * acceleration.

The current system used in physics, even included in Newton's equation, is in the metric system. Mass is measured in kilograms, and acceleration is also measured in meters per second squared. The metric system didn't exist in Newton's time and first used the meter in 1793. This date is way after the proposed date of death of 1727 for Issac Newton, and you should even assume he published his book before his death. My main question?

When Issac Newton first wrote his book, what did he use in place of these metric units? —Preceding unsigned comment added by 68.83.4.99 (talk) 23:39, 18 November 2008 (UTC)

If you check Newton's_Second_Law#Newton.27s_second_law:_law_of_acceleration, you will see that Newton originally wrote Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur, i.e. a textual representation of the relationship in Latin (published in 1687). Formulas like F=ma do not depend on the units used. If you use pounds for mass and furlongs per decade squared for acceleration, your force will be in very weird units, but it will still be right. --Stephan Schulz (talk) 23:46, 18 November 2008 (UTC)

(ec)Newton's statement of his second law was unit-free. From Wikisource: The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the straight line in which that force is impressed. I don't know what units he used for force or momentum when he used units at all. Algebraist 23:47, 18 November 2008 (UTC)

The metric system is just a series of standardized units. Before the metric system, people had all sorts of other units. The metric system was just an attempt to totally standardize them. There's no big mystery or innovation to it other than that. --98.217.8.46 (talk) 23:48, 18 November 2008 (UTC)

But as to what units Newton actually used when measuring something, they would have been the traditional British units. Inches and feet and yards and chains and miles for distance, seconds and minutes and hours for time, and so on. (Yes, the same seconds that are in the metric system.) --Anonymous, 23:56 UTC, November 18, 2008.

Wrong. He, probably because of his day job as Master of the Mint he could borrow some of the government's scales, liked to measure his "weights" in troy ounces--which are, of course, always units of mass, and are not and never have been units of force--rather than the avoirdupois units we now think of as normal. But for length, especially when he wanted to be precise, he was partial to using the toises and pieds and pouces of the French system. For force, he never actually expressed that in any units specific to the purpose, as far as I can tell--it would just be the mass units times the acceleration units. Gene Nygaard (talk) 20:04, 19 November 2008 (UTC)

Ah, interesting. Can you cite an example of him using French units? --Anon, 20:48 UTC, November 19, 2008.

Plan for establishing uniformity in the Coinage, Weights, and Measures of the United States, 1790, http://avalon.law.yale.edu/18th_century/jeffplan.asp footnote 2:

"Sir Isaac Newton computes the pendulum for 45 degrees to be 36 pouces 8.428 lignes. Picard made the English foot 11 pouces 2.6 lignes, and Dr. Maskelyne 11 pouces 3.11 lignes. D'Alembert states it at 11 pouces 3 lignes, which has been used in these calculations as a middle term, and gives us 36 pouces 8.428 lignes = 39.1491 inches. This length for the pendulum of 45 degrees had been adopted in this report before the Bishop of Autun's proposition was known here. He relies on Mairan's ratio for the length of the pendulum in the latitude of Paris, to wit: 504:257::72 pouces to a 4th proportional, which will be 36.71428 pouces = 39.1619 inches, the length of the pendulum for latitude 48 degrees 50'. The difference between this and the pendulum for 45 degrees is .0113 of an inch; so that the pendulum for 45 degrees would be estimated, according to Mairan, at 39.1619 - .0113 = 39.1506 inches, almost precisely the same with Newton's computation herein adopted."

Gene Nygaard (talk) 23:15, 19 November 2008 (UTC)

Thanks. --Anon, 06:33 UTC, November 20/08.