Wikipedia:Reference desk/Archives/Science/2010 March 25

= March 25 =

Currency manipulator

 * Question moved to the Humanities desk. Comet Tuttle (talk) 04:41, 25 March 2010 (UTC)

Questions about casting resin
Is the type of clear casting resin sold in craft stores suitable for making lenses for science experiments at home? If so, how do you make precision mold(s) that would give the lens produced the right shape? How do you give cast resin a smooth finish? What is the easiest method of replicating an object using resin casting? Thanks. —Preceding unsigned comment added by 173.49.9.9 (talk) 03:26, 25 March 2010 (UTC)


 * I don't think it's possibly to get as smooth of a surface from casting as from grinding. However, having an extremely smooth, nonstick surface on the mold would help.  You might also want to let it set while the lens is standing on it's side (I'm assuming a two-piece mold here).  That way, any bubbles will hopefully migrate to the top, which won't be a critical area of the lens. StuRat (talk) 12:58, 25 March 2010 (UTC)


 * I just did an evening class on resin casting. The stuff you are after sounds like the stuff I was interested in. Solid cast 606. clear doming epoxy. That's a product specific to the place I went but if you look at the data sheet you'll probably find something similar wherever you are. Resin copies the surface of your mould with surprising fidelity. If you have a very smooth surface on the mould the resin will also be very smooth, if you have a frosted surface the result will be frosted. If you have an existing lens you want to copy, you can get silicone casting rubber which you use to make a 2 piece mould. The easiest way to do that is using klean klay to make the 1st half of the mould, then make the other half off the 1st. If you don't have a starting lens, that will make it a lot harder I think. Let me know if you want me to clarify anything. Vespine (talk) 21:43, 25 March 2010 (UTC)


 * Thanks, Vespine, for putting everything into focus for us. I'm sure your answers will all resonate with the Original Poster. StuRat (talk) 23:23, 25 March 2010 (UTC)


 * Thanks for the answers. A few futher questions: Vespine, how do you use the 1st half of a mold to make the second half? Are you assuming some kind of symmetry here? How do you make a cast resin sculpture from scratch? Do you need to make a positive mold first using some easily sculptable material, then make a negative mold from it using silicone rubber? What kind of material would be good for making the positive mold? How do you make the final product smooth and crystal clear? Can you polish it somehow? Thanks. --173.49.9.9 (talk) 23:42, 26 March 2010 (UTC)

cosmology
Does faster than light expansion of universe during inflation violate the special relativity? Don't we need to take the movement of time backward to unify gravity physics with the non-gravity physics? —Preceding unsigned comment added by 115.186.130.253 (talk) 06:23, 25 March 2010 (UTC)


 * No, not according to cosmologists who claim to understand it. Though I haven't read it myself, this article by Davis and Lineweaver may be helpful: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf
 * --Hroðulf (or Hrothulf) (Talk) 07:35, 25 March 2010 (UTC)


 * Also, we need to establish faster than light relative to what? It is possible for two objects to move away from each other at faster than the speed of light relative to each other.  If they do so, they effectively lose contact, since they will be traveling outside of each other's light cone.  So there is nothing wrong with assuming that the "leading edge" of one side of the universe is moving away from the other "leading edge" at faster than the speed of light, relative to each other. -- Jayron  32  16:04, 25 March 2010 (UTC)


 * Jayron, your last two sentences don't make sense to me. I don't think inflation requires parts of the universe to lose contact, though it does say that there is much more to the "cosmos" that was never in touch with our universe.  If things move away from us at near light speeds, (special) relativity merely says they move away from each other at near light speed.  Am I oversimplifying inflation or Hubble expansion?  --Hroðulf (or Hrothulf) (Talk) 16:51, 25 March 2010 (UTC)


 * You may find the articles cosmic inflation and metric expansion of space interesting. As I understand it, the rapid expansion during cosmic inflation is what disconnected parts of the universe.  In other words, the universe was able to transmit information throughout itself right at the beginning of time, but cosmic inflation rapidly separated areas of it enough so the distances between points were large enough so light was (and is) not able to move between them fast enough to transmit information.  We also got our large-scale structure of the universe from the quantum fluctuations present during cosmic inflation.


 * I believe you're right about relativity saying two objects can only be moving away from each other at up to the speed of light. Implicitly, a third reference frame is used when measuring the velocities of each object, which is not allowed.  However, it is possible for two objects to be moving away from each other due to Hubble expansion.  Imagine a photon sent from Earth toward Proxima Centauri, 4.2 light-years away.  You would expect the photon to reach Proxima Centauri in 4.2 years, right?  Well, say Proxima Centauri and Earth were not gravitationally bound in the Milky Way.  Space between Earth and the star would be expanding as the photon traveled, so it would have to travel through this new space as well.  It might take 4.21 light years to get there (again, if the two objects were not gravitationally bound, as most galaxies aren't).  Now, say you send out a photon toward the most distant galaxies we see.  Eventually, more space will be created between the photon and its destination than it can travel.  Given enough distance, over one light-year of distance will be created that the photon will have to pass through, so it will never reach its destination.  This is why our observable universe is shrinking with time.  Hope this helps.  &mdash; Pie4all88  T  C 18:45, 25 March 2010 (UTC)

what, in a physical sense, is an impossibility?
I have received a definitive answer above that for anything that has ever existed, or will exist, or anything that has happened, or will happen, it is a given that the thing was/will be possible at the time that it existed/happened/will exist/will happen.

So if any thing is always possible, then what is a physical (not conceptual) impossibility?

I got some answers above, but they aren't really clear enough for me. I would like a simple answer to what, physically impossibility would be. As far as I can see, it seems to be a non property, like centrifugal force: it is not a force itself, it just seems to be. Impossibility then isn't a real aspect of the physical Universe; it just seems to be. Is this understanding correct, or is there a physical meaning of impossibility, and if so, what is it? 84.153.202.26 (talk) 10:25, 25 March 2010 (UTC)


 * Impossibilility can never be a property of any object or process which exists, because if it exists it cannot be impossible. Therefore, on initial examination I would say that your conclusion is correct. However, you are within the realms of philosophy here, and I claim no expertise in that field. You might be interested in Physics of the impossible, where Michio Kaku expounds a sort of heirarchy of impossibilities; or in "Impossibility: the limits of science and the science of limits" by the Cosmologist John D. Barrow (preview available on google books here ). Oh and here is the obligatory XKCD link for centrifugal force . Equisetum (talk) 11:02, 25 March 2010 (UTC)


 * Mathematical/logical impossibility and physical impossibility are different. Physical impossibility, like physical proof, is based on scientific theories. Such theories, while often very well supported, are strictly preliminary, and open to modification or even replacement if conflicting evidence turns up. It is physically impossible for a cannonball at rest to spontaneously and without the application of a force lift itself one meter into the air (based on both Newtonian and relativistic laws of motion). It is physically impossible for a well-mixed container of lukewarm water in a environment at normal room temperature to turn into half ice and half steam (based on classical thermodynamics). In these cases, the "impossible" phenomenon is well within the set of situations covered by the respective theories, hence we drop the quotes and call those events simply impossible without the caveats. However, both events are possible, if extremely unlikely (as in "will not happen even once in 10bignum lifetimes of the universe") under quantum theory. --Stephan Schulz (talk) 12:30, 25 March 2010 (UTC)


 * Isn't one of the fundamental truths that something can not "be" AND "not be" at the same time? Could you say that's an impossibility? Vespine (talk) 21:17, 25 March 2010 (UTC)


 * That depends on the definition of "to be" ;-). But yes, a straight contradiction describes something that is logically impossible. However, very many things that are logically possible are physically impossible. There is nothing logically wrong with ESP, or superluminal travel, or Microsoft making an OS that does not suck. --Stephan Schulz (talk) 22:23, 25 March 2010 (UTC)+
 * In case nobody has mentioned it, there's a parallel universes theory whereby there are an infinite number of universes, some of which may even have different laws of physics than our own. Therefore, all things may be possible ... somewhere. StuRat (talk) 23:03, 25 March 2010 (UTC)


 * "The difficult we can do immediately, but the impossible may take a bit longer." StuRat (talk) 23:03, 25 March 2010 (UTC)

You want an example of something that is physically impossible

122.107.207.98 (talk) 08:54, 26 March 2010 (UTC)
 * A planet made up of only electrons and held together by it's own gravitational field
 * A rocket ship capable of escaping from inside the event horizon of a black hole using only chemical propulsion
 * Pretty much anything that breaks any physical law is what we'd currently call "an impossibility" so long as it's a hypothetical event. I can say that it's impossible to build a perpetual motion machine or to travel faster than the speed of light - but if such a thing ever actually happened, it would no longer be considered to be impossible - and previous statements to the effect that this thing was impossible would have to be re-visited and corrected.  Consider a real example: when the Alchemists sought to turn lead into gold and failed, we invented chemistry and wrote laws that said that you couldn't turn lead into gold. Transmutation would have been considered possible (but incredibly difficult) in the 1600's, impossible in the 1800's after Lavoisier and Dalton claimed it was impossible - and possible again in the 1900's when Glenn Seaborg actually succeeded in doing it using Nuclear transmutation.  SteveBaker (talk) 23:39, 26 March 2010 (UTC)

this question's for you SteveBaker - is this demo rigged?
Is that demo rigged? Especially the final part, where they get sky and ground from nothing, and it looks exactly like it needs to. Is there any way to tell if they didn't REALLY start with the whole image (what seems to be the "product") and then remove parts of it, and the "tool" in the rigged demo doesn't calculate those parts at all, but puts them back from the original image?

If the demo is NOT rigged, how on EARTH can in POSSIBLY work like that?? 84.153.202.26 (talk) 10:46, 25 March 2010 (UTC)


 * Content-aware fill looks like an extension of content-aware scaling, which Photoshop CS4 featured. This is an explanatory video made by the two researchers who invented it - one of them subsequently moved to Adobe to drive the introduction of this technology into CS4. -- Finlay McWalter • Talk 10:55, 25 March 2010 (UTC)
 * For our article on the topic, see Seam carving. -- Coneslayer (talk) 11:54, 25 March 2010 (UTC)


 * I think it is genuine. It is really really clever, but not impossible. Basically, it's extrapolation. You look at what is all around the deleted area and make the interior look the same. That is, of course, easier said that done! The bit I'm really impressed by is the right-hand side of the final image. I was going to say that it looks like they've run an edge-finder on it (a tool that has existed for years, albeit with increasing quality), extrapolated the edges and then filled in the various regions. However, if you look at the foreground hill on the right, at the point where the original image ends the hill is going upwards. If it were extrapolating the edge in the obvious way you would expect it to keep going up at the same angle (which is what it does on the left-hand side, give or take), but it doesn't. It goes up for a tiny amount and then goes down. Somehow, the tool has realised that if it continued going up it would be out of proportion with the rest of the hills. They must have looked at the entire edge, done some statistics on the way it goes up and down and come up with an extrapolation that fits it. That is mindbogglingly clever! --Tango (talk) 11:47, 25 March 2010 (UTC)
 * @Tango, note that the profile of the extrapolated hill at the right is obtained by reflection about the edge of the original image and that edge (dotted line at 4:45) is not vertical. BTW it's better to view the demo here where it can be shown full-screen. Cuddlyable3 (talk) 17:43, 25 March 2010 (UTC)


 * It's clever. Will it work in all cases as well as you want? Probably not. The Magic Eraser is a similarly cool feature in CS4 that can remove spots and errors pretty instantly and works pretty well in most cases. Sometimes it goes way wrong and sometimes even when it works right, it is obvious when you zoom in that something hinky has been going on. I imagine that this will be somewhat similar... good for a quick fix at low res but probably not what you're going to want to use for something at high res. But who knows! We will wait and see. --Mr.98 (talk) 13:29, 25 March 2010 (UTC)


 * There's no reason to think it's rigged as in "the software didn't really do that", but it's extremely common in software demos to 1) do a bunch of them and present the best one, and 2) have the demo presenter walk a very specific path that is known to perform well. Finally, there's LG's refrigerator, which is programmed to detect that it's in a demo and goes into super-power-saving mode. :D  --Sean 14:44, 25 March 2010 (UTC)
 * @Sean please don't introduce issues that have nothing to do with graphics. Cuddlyable3 (talk) 17:43, 25 March 2010 (UTC)
 * I was addressing the broader practice of demonstrations not necessarily representing real-life usage. --Sean 17:59, 25 March 2010 (UTC)
 * An example of a program designed to parody programs designed to benchmark well: Lenpeg compression algorithm --Polysylabic Pseudonym (talk) 08:00, 27 March 2010 (UTC)


 * There are several tools out there that are even more impressive than that - there have been papers in SigGraph proceedings for at least 5 years describing these kinds of trick - so it's nothing new. One technique is to look at the pixels around the object you're trying to remove - then look elsewhere in the image for other places where very similar groups of pixels exist.  Then you copy the scene near to those pixels into the space occupied by the thing you're trying to remove.  You can repeat this process over and over to gradually 'erode' the object you want to get rid of.  With minor variations on this basic idea, it works amazingly well. SteveBaker (talk) 01:43, 26 March 2010 (UTC)

How might a person be exposed to (x number of) rems?
Hi guys.

I need to know just what kind of environment might expose someone to certain levels of radiation: It's been relatively easy to research higher levels of exposure, and to find out the effects of such levels. But it's just how someone might be exposed in this way which I'm finding harder to ascertain. If anyone can provide any answers, sourced preferably, it will be greatly appreciated! Thanks. 83.104.127.226 (talk) 11:09, 25 March 2010 (UTC)
 * 5-20 rem
 * 20-100 rem
 * 100-200 rem


 * See Ionizing_radiation. It is all in sieverts, but they are easily converted into rems - 1 rem=0.01 Sv, so your ranges are 0.05-0.2 Sv, 0.2-1 Sv and 1-2 Sv. (WP:WHAAOE strikes again!) --Tango (talk) 11:53, 25 March 2010 (UTC)
 * Correction - it's all in milisieverts, so your ranges are 50-200 mSv, 200-1000 mSv and 1000-2000 mSv. --Tango (talk) 11:57, 25 March 2010 (UTC)


 * Natural background radiation can produce expsoures in the range 5-20 rem per year - Ramsar in Iran has the highest level of natural background radiation in the world, and inhabitants can be exposed to up to 26 rem (260 mSv) per year. So someone living in an area with high levels of background radiation for, say, 10 years or more could have a cumulative exposure of over 100 rem. However, because the exposure is spread over time, giving the body's cells time to repair themselves, there may be no ill-effects from this exposure, whereas the same level of exposure over a time-span of minutes or hours would likely result in radiation poisoning. Gandalf61 (talk) 12:08, 25 March 2010 (UTC)

Thanks guys, this is exactly the kind of stuff I was looking for. It was interesting to read about Ramsar, and especially the seemingly counter-intuitive radioresistance of the inhabitants. Bonus points. 83.104.127.226 (talk) 12:37, 25 March 2010 (UTC)


 * By the way, I put a fact-tag and a dubious-tag on those claims. The article should cite a reliable medical study to support these very dubious claims.  Comet Tuttle (talk) 16:37, 25 March 2010 (UTC)


 * I don't think the dubious tag is warranted. The article Radiation hormesis contains some citations that could also be attached to the Ramsar article. The article states "It has also been claimed that residents have healthier and longer lives". That is not dubious at all. Claims like that have been in fact made by many studies (Just read the linked article). Whether those claims turn out to be true or not is, of course, is still controversial but the Ramsar article doesn't take sides on that controversy simply stating the true fact that claims of radiation hormesis have been made. You should remove the tag. BTW I happen to believe that there is likely some truth to those claims. Dauto (talk) 13:58, 26 March 2010 (UTC)

Political spectrum
The article says, "For almost a century, social scientists have considered the problem of how best to describe political variation; a sample of their results is given below." [edit] Early research In 1950, Leonard W. Ferguson carried out an analysis of political values using ten scales measuring attitudes toward:


 * Birth control
 * Capital punishment
 * Censorship
 * Communism
 * Evolution
 * Law
 * Patriotism
 * Theism
 * Treatment of criminals
 * War

Is there a comparison anywhere of values in terms of vehicle or highway construction, i.e. a road built according to Republican values, for instance, would have no speed limit signs and vehicles would have no speedometers? 71.100.5.192 (talk) 12:54, 25 March 2010 (UTC)


 * Confused, what do you mean? Nyttend (talk) 13:07, 25 March 2010 (UTC)
 * Do not tell anyone else this if you are a politician. 71.100.5.192 (talk) 00:00, 26 March 2010 (UTC)

I'm not aware of a comparison, but you could look at how the Autostrada and Autobahn networks were massively expanded by the Fascist governments of the 1930s, and perhaps use speed limits in the United States to compare limits in Democrat- or Republican-majority states. But I'm not sure that there's a clear correlation - the National Maximum Speed Law was brought in by Nixon. Warofdreams talk 13:36, 25 March 2010 (UTC)
 * One problem with comparing speed limits and the dominant party for different states is the population density of different states — as far as I know, speed limits are generally higher in Republican-dominated states, but a more likely explanation for that fact is that Democratic-dominated states are more densely populated. Nyttend (talk) 21:15, 25 March 2010 (UTC)


 * I'm assuming this is about US politics. I think no speed limits would be more of a Libertarian value, as Republicans are typically for strict law-and-order.  So, what differences could we expect between Democrats and Republicans ?  I would expect that Republicans would want more local funding, which would result in better roads in wealthy areas and crap roads, or none at all, in poor areas.  Democrats, on the other hand, would want national funding and be in favor of borrowing whatever money it takes to provide first class roads everywhere, no matter what the effect on the national debt. StuRat (talk) 13:53, 25 March 2010 (UTC)


 * StuRat, your bias is oozing all over the place. 169.139.217.79 (talk) 14:08, 25 March 2010 (UTC)


 * If I'm equally biased against everyone, doesn't that make me balanced (while simultaneously unbalanced)? :-) StuRat (talk) 14:15, 25 March 2010 (UTC)


 * Democrats, socialists and communists drive on the left; conservatives, aristocrats and rogues drive on the right. Cuddlyable3 (talk) 14:00, 25 March 2010 (UTC)


 * What you need to watch out for then is the centrists, because they crash into everyone. Googlemeister (talk) 14:22, 25 March 2010 (UTC)


 * It isn't so easy to lump all US Republicans and Democrats under one label. See Conservatism in the United States and Liberalism in the United States. 152.16.15.144 (talk) 17:50, 25 March 2010 (UTC)


 * I took the Liberty (*ahem*) of linking "centrist". ~ A H  1 (TCU) 00:55, 26 March 2010 (UTC)

Space colonisation
1) Would it be possible to grow crops on Mars?

2) How large an area would be needed to supply a manned base there?

3) I notice the Martian atmosphere is almost entirely CO2, which might be good for plants, and could be changed to oxygen by them as well, though I doubt an atmosphere of mostly oxygen and CO2 would be much better. Would it be possible to create a breathable atmosphere on Mars at all?

4) How long would it take for the fastest spacecraft yet built/designed to reach the moon Titan?

5) Is there anywhere I can find reasonable estimates on when different missions may be launched, those listed on here seem only to go up until around 2030?

6) Has anyone yet considered sending some sort of probe to this Gliese581?

7) Are there any other questions I've forgotten?

148.197.114.158 (talk) 13:47, 25 March 2010 (UTC)


 * I've numbered your Q's so we can reference each in our responses:


 * 1) Yes, probably using hydroponics and water from the polar caps.


 * 2) I don't understand. Do you mean how large of an area on Mars ?  This doesn't seem very important, since nobody is using any part of Mars now.


 * 3) Maybe, after thousands of years, via terraforming.


 * 5) Realize that any missions planned for over 20 years from now are little more than wild speculation, as changes in technology, economics, and politics would make them extremely unlikely to happen as planned.


 * 7) How about artificial satellites used for space colonization ? StuRat (talk) 14:00, 25 March 2010 (UTC)


 * 6) Gliese 581 is a star 20.3 light years away. Voyager 1 has taken 32 years to travel 16.8 billion km away. A light year is 10 trillion kilometers. How long do you want to wait for some sort of probe data?


 * 7) You left out little stuff like how to breathe, eat and keep warm on Mars, and who pays for all this. Cuddlyable3 (talk) 14:19, 25 March 2010 (UTC)


 * One interesting thing about the atmosphere of Mars is that if you added O2 and N2 in sufficient quantities to bring the pressure up to that which we have on Earth, the CO2 level will be about 30x higher then we have on Earth. This is right at the lower end of CO2 toxicity, so you would, in addition to needing to add O2 and an inert gas like N2, you would also need to figure out how to remove a large amount of the CO2.  Maybe not all the way down to earth levels (375ppm or so), but probably a good chunk of it, so to answer question 3, You would probably need a heck of a lot of plants to pull this off, and to keep the plants, you a heck of a lot of water.  Googlemeister (talk) 14:20, 25 March 2010 (UTC)


 * (edit conflict x2)
 * 4) New Horizons took about 2.5 years to reach Saturn's orbit from Earth, while Voyager 1 and 2 took 3 and 4 years, respectively. Presumably, the time could be cut down somewhat if you were willing to be less efficient with your fuel.


 * 6) Interstellar travel is currently non-existent (and unlikely to exist for some years), so if someone has thought of sending a probe to Gliese 581, it was either idle speculation or wishful thinking. In any case, we would surely send a probe to one of our closer neighbors first. Buddy431 (talk) 14:22, 25 March 2010 (UTC)


 * 2) Heavily dependent on how well you terraform and what techniques you use. Hydroponics are probably the most space-efficient.
 * 4) Cassini–Huygens took 7 years to reach Titan. Orbital mechanics and practical engineering dictate that that's about the best you can do with present tech.  However, throwing out those considerations, New Horizons (the fastest launch from Earth) could get there in 854 days, and Voyager I (the currently fastest man-made object) could get there in 814 days.  Again, those two numbers have no physical significance.
 * 5) 2030 is probably a good outer limit for "reasonable" estimates. I personally wouldn't consider it "reasonable" past 2020, as many factors can't be accounted for.
 * 6) Considered? Probably.  But interstellar probes aren't reasonable with present tech.  It would take Voyager nearly 400000 years to return data from a target 20 light years away.  Sure, we could improve that by orders of magnitude if we really wanted to dump the money on it, but orders of magnitude still means waiting for centuries if not millennia. &mdash; Lomn 14:22, 25 March 2010 (UTC)
 * Cassini only took so long because they used two gravitational assists from Venus and one from Earth. If you're willing to burn much more fuel, you can do it faster.  I'll grant that getting a trajectory that allows you to enter orbit may take longer than New Horizons or Voyager, but I'm sure you can do it much faster than the 7 years Cassini took (for example, it flew by Earth in 1999, for only a five year journey).  And strictly speaking, 148. didn't require the spacecraft to orbit Titan or Saturn, so I think New Horizons and Voyager qualify. Buddy431 (talk) 18:05, 25 March 2010 (UTC)
 * Good point on Cassini. On the other hand, my NH/V1 numbers assume Earth at aphelion and Saturn at perihelion plus a straight-line trajectory between them.  That's still not realistic (particularly the trajectory), as far as I know.  But bump it 30% or so and call it 3 years and that's probably a good ballpark. &mdash; Lomn 20:04, 25 March 2010 (UTC)
 * In addition to the obvious political problems of launching something that's going to take centuries or millenia to achieve results, there's also the issue of any mission potentially being overtaken by a future faster mission. IIRC, some space sim (can't remember which) had this as a minor? plot element where some colonists were sent on a sleeper ship but found when they arrived other colonists had already arrive, having left sometime after them but on faster ships (not surprisingly they weren't happy about this). For example if you can design a probe nowadays and expect results for the 10001 millenium celebration the celebration is gonna be somewhat muted if you already have results from the team who made their probe 1000 years later and got their results in time for the 8888 celebrations. (Even more muted if the results were a message from some alien civilisation warning you that if you ever attacked their system again, be prepared for war.) Of course even if your probe can travel at close to light speed and accelerate/decelerate at 3G it's still going to take you around 45+ years to achieve results (not very good at relativisitic calculations so didn't try but 25 years earth time to reach the destination may be a resonable estimation under the described conditions, plus 20 years for the signal to reach earth). And as others have state, were very, very far from being able to do something like that. Nil Einne (talk) 21:24, 25 March 2010 (UTC)
 * Glise 581 has a negative radial velocity. So in the future, it may actually be closer to Earth than it is now. ~ A H  1 (TCU) 00:53, 26 March 2010 (UTC)


 * The sad - but very, very realistic problem with projects that take thousands of years to come to completion (interstellar probes, terraforming mars, etc) is that they cost a ton of money and NO politician or industrialist will ever vote for something that doesn't offer at least some prospect of return within a human lifespan. We can't solve something as serious as global warming for chrissakes!  So if we can't do it in (let's say) 40 to 50 years - we can't do it at all.


 * The fastest interstellar-capable craft that comes within the laws of physics and the limits of technology would be Project Daedalus or the 1960's Project Orion (not to be confused with the recent proposals of the same name). They could credibly reach 10% of the speed of light and therefore make it to the nearest star in 40 to 50 years...which just about fits the maximum project span that humanity will ever attempt.  These craft would have to be gigantic - with space for thousands of people on board - because they would powered by the exploding of atom bombs...and would cost about 10% of the US GDP for a year to build.  You couldn't make a reasonable 'probe' with that technology.  However, you could set up a 'biosphere' and comfortable living space for 1000 people (sufficient for a viable colony) and shoot it to the nearest star.


 * The problem with that is that the nearest star doesn't seem to be very habitable. Gliese-876 (not as famous as -581, but closer!) is 15 lightyears away - but that's a 150 to 200 year trip - meaning that this would be a 'generational' ship.  And we're back with the funding issue.


 * The only way I can see humanity managing this is if enough rich enthusiasts could somehow fund the construction in order to live in utter luxury and safety for the rest of their lives. They might be interested in setting such a gargantuan machine in a solar orbit far from bothersome Earth.  For such a hypothetical community, they might have enough helium-3 on board to power their society and not care whether they orbit the sun or shoot off into deep space - and I suppose they might spring for the costs of the bombs to head off out of the solar system.  Then - several generations later, humans arrive at the other star.  Because (we hypothesize) they are pretty much self-sufficient, they don't really NEED a habitable world at the other end - but they're going to need to refuel their fusion reactors.


 * But that's a hell of a stretch. I think humans are going to be stuck in the solar system for a very long time.


 * SteveBaker (talk) 01:25, 26 March 2010 (UTC)

The Mars Society (founded by aerospace engineer Robert Zubrin) has sponsored and collected a wide portfolio of mission, colonization and terraforming options that answer questions 1,2,3 and 5, and probably some of the questions you forgot to ask. If I recall correctly, Zubrin's own book The Case for Mars (ISBN 9780684827575, ) summarizes a terraforming proposal that would produce a useful atmosphere and biosphere in two or three centuries, as well as describing Mars Direct.

Regarding the objection to missions that take many human lifetimes, it is worth noting that princes and popes in late medieval Europe and Asia planned many generations ahead, for example with the construction of cathedrals, universities and madrasah. I suspect that they didn't have to wait lifetimes for a payoff: the projects created employment, a sense of power and permanence, and a communal ambition. All of these could motivate modern politicians and universities to probe space, though it would be a bonus if an interstellar probe would be able to send back useful science data from the outer reaches of the solar system in a few decades, as Voyager does.

--Hroðulf (or Hrothulf) (Talk) 12:00, 26 March 2010 (UTC)
 * Most Cathedrals were not built with the intention of them taking hundreds of years, they were built with the expectation of taking 20-30 years and funding for construction or warfare stopped construction, or forced part of the building to be rebuilt. Googlemeister (talk) 13:18, 26 March 2010 (UTC)
 * That's true - but the people who paid for them believed that they'd get their reward "in heaven" - so it's not true to say that they set the work in motion with no hope of a return on their investment. I suppose if you could convince some religious nuts that god wanted them to terraform Mars or fly to the nearest star - maybe you'd get some funding. SteveBaker (talk) 23:18, 26 March 2010 (UTC)
 * Yeah, the problem is that those groups tend to wipe themselves out every time they see a decent comet, so they don't build up very much momentum. Googlemeister (talk) 14:20, 29 March 2010 (UTC)

JASSA
Hello! Can anybody get something for me out of the British Library. It is from the JASSA : Journal of applied sciences in Southern Africa.


 * A. J. Masuka: Dynamics of mushroom (Boletus edulis) production in pine plantations in Zimbabwe. In: JASSA, Journal of Applied Science in Southern Africa. 2(2). 1996. pp. 69–76

It should be available at the British Library, maybe as printed or electronic edition. Thank You very much for Your help, Doc Taxon (talk) 13:53, 25 March 2010 (UTC)


 * Here is a link for people who have access to AJOL. The article costs $18, but maybe somebody can help you. Indeterminate (talk) 14:11, 25 March 2010 (UTC)


 * British Library shelfmark is 4663.148900 (Lending Collection). Thanx again for any help ... Doc Taxon (talk) 14:28, 25 March 2010 (UTC)


 * If you belong to a British Public lending library, they should be able to get it for you via the Library interloans service. It’s worked for me. --Aspro (talk) 18:06, 25 March 2010 (UTC)


 * Sorry, but I am from Germany. Can You get this article and forward to me, please? Doc Taxon (talk) 19:18, 25 March 2010 (UTC)


 * Wouldn't it violate copyright to send someone a printout of an article the copyright holder demands ripoff high prices for? One workaround used to be to write to the principal author and say "I would greatly appreciate a copy of your article "XXXX." I collected hundreds of such reprints back in the day. Edison (talk) 19:50, 25 March 2010 (UTC)


 * If this magazine was at a German library, I can get a copy from the library too. Isn't it a copyright violation, too? If this copy is for own use only, it's okay for the library. It is a violation to publish a copyrighted article in books or internet without the confirmation of the principal author. Doc Taxon (talk) 09:01, 26 March 2010 (UTC)

Without getting into the legalities of copyright, I'd suggest asking at your local library. UK libraries can request material from the continent - admittedly the overdue fees are exorbitant and there's a week or so's wait, but I'd give this option a shot and see if German libraries can do it too rather than ask someone to break the law. Brammers (talk) 10:22, 26 March 2010 (UTC)

meat products
In some places in Eastern Europe, they make meat jelly. Though the stuff sounds quite vile, it got me to thinking, is it possible to make meat based alcoholic beverages that are not toxic? Googlemeister (talk) 14:30, 25 March 2010 (UTC)


 * I don't know about alcoholic meat, but along the lines of meat jelly, look at Spam and Yorkshire pudding. StuRat (talk) 14:38, 25 March 2010 (UTC)


 * No meat in Yorkshire pudding. Perhaps you meant black pudding. Gandalf61 (talk) 16:07, 25 March 2010 (UTC)


 * Classic Yorkshire pudding is made from fat drippings from roasting meat. StuRat (talk) 16:32, 25 March 2010 (UTC)


 * Sorry, but not so. Yorkshire pudding is made from batter. The ingredients are very similar to a plain pancake. Two hundred years ago it would have been fried in fat taken from the dripping pan, but in modern times it is baked in the oven. Gandalf61 (talk) 16:41, 25 March 2010 (UTC)


 * It looks like classic Yorkshire pudding was made from batter and fat drippings from meat, but the modern pudding skips the drippings, and gets the fat or oil from another source. StuRat (talk) 17:02, 25 March 2010 (UTC)


 * Bovril with a tot of brandy in it. As for meat jelly - not a particularly Eastern European thing. Brawn is good English food. DuncanHill (talk) 14:44, 25 March 2010 (UTC)
 * Take a look at aspic too. I don't get what Yorkshire puddings have to do with meat jelly. DuncanHill (talk) 14:50, 25 March 2010 (UTC)


 * Jell-O is meat jelly, for the record. --Sean 14:49, 25 March 2010 (UTC)
 * I do not mean adding other alcoholic beverages to meat, I mean fermenting, or distilling or whatever, the meat to make alcohol. Googlemeister (talk) 15:06, 25 March 2010 (UTC)
 * Generally, to make alcoholic beverages, you want to start with something that has a lot of sugar (like fruit juice), or starches that can be easily converted to sugar (as in potato or grain vodkas). Meat doesn't have a lot of sugar or starch.  -- Coneslayer (talk) 15:22, 25 March 2010 (UTC)


 * Not meat per se, but Alcohol can be made from milk- see Kumis from Central Asia, Blaand from Scotland, and probably others (though I don't recommend them). Staecker (talk) 16:09, 25 March 2010 (UTC)
 * Meat does ferment, but it does not produce appreciable amounts of ethanol when it does. When carbohydrates ferment, they produce two major products: usually ethanol or acetic acid, hence wine/beer and vinegar.  Meat is mostly protein, and protein contains a sizable amount of nitrogen in it.  As a result, when meat ferments it produces lots of nitrogen compounds, like ammonia and amines, some of which have lovely names like Putrescine and Cadaverine, which smell about as lovely as it sounds.  Amines are generally toxic, which is why rotten (fermented) meat is generally a bad thing to eat.  We have fermented grain and fruit products (booze), and fermented dairy products (cheese, yoghurt), but fermented meat is pretty nasty stuff.  -- Jayron  32  16:12, 25 March 2010 (UTC)
 * Our article fermentation (food) has sections Fermentation_(food) and Fermentation_(food). Neither list any alcoholic beverages. Staecker (talk) 16:15, 25 March 2010 (UTC)
 * Well I guess if Icelandic cuisine does not have a meat alcohol, it probably does not exist in a safe form regardless of palateability. Googlemeister (talk) 16:25, 25 March 2010 (UTC)
 * @Googlemeister (indenting of above threads seems screwed up so not replying there to avoid confusion):I think Sean's point is that most fruit flavoured deserts we call 'jellies' in Commonwealth countries or Jell-O in the US are made with gelatine which is derived from animal sources, usually pig or cow, occasionally seafood. From a vegetarian standpoint, all these may indeed be considered meat jellies (although most of the stuff use to make gelatine wouldn't generally be called meat). If you have an agar agar desert without any animals products then that definitely wouldn't be a meat jelly Nil Einne (talk) 19:45, 25 March 2010 (UTC)
 * Imagine being stranded in an agar agar desert. Staecker (talk) 20:03, 25 March 2010 (UTC)
 * Probably better then being stranded in a real desert. At least you shouldn't die of thirst and may be not even starvation although you will likely get malnourished eventually unless it's some super nutritionally complete agar designed as a growth media or something Nil Einne (talk) 21:35, 25 March 2010 (UTC)
 * "Meat jelly" also often refers to frozen gravy. ~ A H  1 (TCU) 00:49, 26 March 2010 (UTC)

Are ad hominen reasons sometimes reasonable?
If some scientist is well-known for faking data, could we discard his theories on the base of that? It seems like the common practice for me, but couldn't such a scientist also produce something of value? ProteanEd (talk) 17:44, 25 March 2010 (UTC)


 * Scientists would usually maintain some scepticism about results until they have been independently corroborated, regardless of whose results they are, so I guess it isn't too much of a problem anyway. Reputation is certainly important in science, though, and it can result in a "The Boy Who Cried Wolf" scenario. Ad hominen attacks are a logical fallacy, but science isn't based solely on logic. It is based on evidence. You shouldn't dispute somebody's conclusions drawn from the evidence based on who they are, but you can dispute the accuracy of the evidence presented (and if the evidence isn't credible, the conclusions drawn from it aren't either). --Tango (talk) 17:58, 25 March 2010 (UTC)


 * That's nice, in theory, but, in reality, it takes times and money to verify or disprove another person's claims. In this case, people tend not to waste time and money on the claims of obvious cranks. StuRat (talk) 18:05, 25 March 2010 (UTC)


 * I was not thinking about an "obvious crank" who may try to prove that the world will explode in 100 days. I had in mind scientists like Jan_Hendrik_Schön, who have been discovered manipulating data, but who might have done some valid honest and valuable research before that.--ProteanEd (talk) 18:20, 25 March 2010 (UTC)


 * Well, then, the same idea would apply, but to a lesser extent. That is, a scientist choosing to try to duplicate the work of another might prefer to choose one with a better track record.  But, if the "discovery" by the one with the poor track record seems feasible and important enough, maybe they would overlook his past.  StuRat (talk) 18:26, 25 March 2010 (UTC)


 * If some scientist is well-known for faking data, could we discard his theories on the base of that? Yes one could but who will be looking stupider if the scientist happens to be right? ..couldn't such a scientist also produce something of value? Yes. Jan_Hendrik_Schön...discovered manipulating data...might have done some valid honest and valuable research before that Yes, or he might in the future as he is only 40 and wiser now. Cuddlyable3 (talk) 18:59, 25 March 2010 (UTC)


 * Post EC: A situation similar to the one you describe occured in the case of Hwang Woo-Suk. He claimed to have succeeded in generating human embryonic stem cells via cloning. This result was discovered to be fabricated, but a later review of his data suggested he managed to extract generate cells from parthenogenetic human eggs which would make his group the first to do so.  Ultimately, ad hominem based dismissals of a theory still aren't "valid" because someone's choices and bad data have no bearing on the validity of their testable arguments. Scientific misconduct can set a legitimate theory back for years to decades AFTER it is exposed because scientists with legit data are afraid of being associated with it or are unfairly ignored because the dishonesty has tainted that field. This was the case when the Piltdown Man fraud effectively "supressed" real Australopithecine fossil finds. 152.16.15.144 (talk) 19:09, 25 March 2010 (UTC)


 * I think the scientific rejection of researchers who "fake" is less about them making a strictly logical argument as it is a community/social reaction to those who violate community norms. Additionally peer review is not really set up to catch willing fakers—it is meant to catch honest error. An argument could be made that expelling known fakers from the process is probably more expedient than treating all scientists like potential fakers. --Mr.98 (talk) 21:25, 25 March 2010 (UTC)

In a sense, yes. In theory, if someone makes a scientific hypothesis that seems basically reasonable, writes it up properly and gets it published in a reputable journal - and especially if they present some experimental evidence and a viable means for reproducing the experiment - or otherwise testing that claim - then in theory, other scientists will attempt to reproduce those results and either verify it or explain why it's wrong. Thus the hypothesis becomes a 'theory'.

However, in practice, scientists are limited in number and have limited time and budget - so it may be that some claims won't be tested. Now - the tricky part is the decision as to who you trust enough to make it worth-while to spend the time to check their results - and who you think so little of that you find something more useful to do with your time. In a sense, that's ad-hominem because you're using the person's prior reputation to determine whether you're even going to try to replicate his entirely new hypothesis.

Imagine in a case like Uri Geller - who claimed to be able to bend spoons with the power of his mind. The claim was tested - found to be not just bogus - but flat out fraudulant. Geller's reputation is totally in the toilet and so, if Mr Geller were now to make a much more reasonable claim...maybe to have found some clever chemistry that would make a somewhat more efficient battery for electric cars...then he'd probably be totally ignored. On the other hand, if Stephen Hawkins were to state a fairly radical hypothesis about how galaxies are formed - then even though his theory on information loss inside black holes has been effectively disproved - and even though his new galaxy-formation hypothesis seems a bit far fetched, people would certainly be prepared to spend the time needed to check out his findings. The only difference being the reputation of the person making the claim...which, is essentially what 'ad hominem' is all about.

The point though is that we don't "discard" the bad person's hypothesis - we simply fail to push it towards possibly becoming a proper theory. Scientists are unlikely to say that Uri Geller's hypothetical car battery idea is false - merely that nobody can be bothered to test it because they have better things to do. Hence the hypothesis remains unproven.

SteveBaker (talk) 00:26, 26 March 2010 (UTC)


 * Wikipedia has an article on Genetic fallacy which is the mistake of judging a claim not on its merit but instead by what one's opinion about its originator. Cuddlyable3 (talk) 12:43, 26 March 2010 (UTC)

Nicotine and the kappa-opioid receptor
Does nicotine or tobacco affect the kappa-opioid receptor in the brain in any way? If so, is it an agonist or antagonist? I understand the kappa-opioid receptor helps modulate addiction; I am more interested in if it is involved with the stimulatory affects. Several Google searches have failed me. Thanks for the help! &mdash; Pie4all88  T C 18:13, 25 March 2010 (UTC)
 * Well, a search on Google Scholar finds, if nothing else. Looie496 (talk) 18:30, 25 March 2010 (UTC)
 * This is how I see it:
 * If you look at Reward system you will see that psychotropic drugs release dopamine in a certain part of the brain. However, neither nicotine or alcohol nor probably several other drugs have a (direct) effect on the kappa Opioid receptors. To compliment the link above see also: Kappa-opioid receptor modulation of accumbal dopamine concentration during operant ethanol self-administration.But by stimulating these receptors (with a suitable agonist) it modifies (and in this case reduces) the amount of dopamine released further down the neural ‘reward system.’ There is bound to be more to this than meets the eye because,  for in the case of heroin addicts ( with the exception of those who’s addictions were iatrogenic) they all appear to be heavy smokers as well. The two addictions  go hand-in-hand. Also, another interesting point,   there is one country that escapes me for now (Burma?) that uses (very) high doses nicotine to ‘cure’ (so they say)  opiate addicts.--Aspro (talk) 19:06, 25 March 2010 (UTC)
 * As I implicitly suggested above, it is perhaps possible that nicotine may ‘indirectly’ effect these receptors (there is so much about addiction that is still unknown) by way of repeated doses of nicotine reducing  the bodies natural output  of   Endogenous_opioids. So they may end up getting less stimulation, leading to graving for more of the drug responsible. For the purposes of your question though, I would ignore this, as  I only put it in to give a broader picture. --Aspro (talk) 19:20, 25 March 2010 (UTC)
 * Excellent&mdash;thanks for everyone's help! &mdash; Pie4all88  T  C 16:52, 26 March 2010 (UTC)

Terminology for planetary orbits
I was watching a documentary about secret government atuff and the replicators sent s satellite to attack Atlantis. Down in the control room they said "It's taken up geosynchronous orbit above the city". However Atlantis is at about 45° north latitude. It would be possible to set up a geosynchronous orbit so that the satellite returned to that point once per planetary rotation but in this case the satellite stayed in the same location above the city, so it should probably have been called a geostationary orbit. My first question though is whether it would be correct to term the satellite as being "in orbit" at all? It's not revolving around a common centre of mass, so I'm thinking it would need a continuous expenditure of energy to maintain its position. Would that correctly be called "station-keeping" (but not orbital station-keeping)?

I'm not looking for comments about dramatic license in fiction or inaccuracy in SF TV shows, just about the correct way to describe an object maintaining position over a fixed point not on the equator of a planet. Bonus question would be, what direction of thrust vector would be required to maintain that position? Thanks! Franamax (talk) 19:30, 25 March 2010 (UTC)


 * Well, there is the Tundra orbit. While not fully geosynchronous, it is an approximation for areas further away from the equator where the satellite spends most of the time above the point of interest by doing lop sided figure eights.  Googlemeister (talk) 20:11, 25 March 2010 (UTC)


 * I don't think a term exists since, as you say, it isn't really an orbit and the thrust required would be impractical. We have a force towards the centre of the planet of $$\frac{GMm}{r^2}$$ and we want a force towards the centre of the circle at 45 degrees north of $$mr\omega^2$$. Those forces differ in angle by 45 degrees. Let's say we have a thrust force F at an angle $$\theta$$ to the gravitational force and we resolve forces parallel and perpendicular to the desired force. We get the following simultaneous equations:
 * $$\frac{GMm}{r^2}\cos(45^\circ)+F\cos(\theta-45^\circ)=mr\omega^2$$
 * $$\frac{GMm}{r^2}\sin(45^\circ)-F\sin(\theta-45^\circ)=0$$
 * We then need to substitute in all the values and solve. I'll come back to that in a minute! --Tango (talk) 20:22, 25 March 2010 (UTC)


 * Ok, let's solve them. The first term of each are actually equal, so we can cancel them and get that $$F(\cos(\theta-45^\circ)+\sin(\theta-45^\circ))=mr\omega^2$$. The minimum thrust will be obtained when $$\cos(\theta-45^\circ)+\sin(\theta-45^\circ)$$ is maximised, which is when $$\theta=90^\circ$$, ie. we're thrusting perpendicular to the line joining the craft and the centre of the planet. We end up with a thrust required of $$F=\frac{mr\omega^2}{\sqrt{2}}$$. I'm not going to substitute in values because I think I've made a mistake somewhere (for one thing, I've used r for two different radii, but one cancelled out so that's not a problem - the r in the final equation is the radius of the actual circle travelled, not the distance to the centre of the planet). Common sense tells me that it should be easier to do at the right altitude for a geosynchronous orbit, but my equation says it is easier the closer you are to the planet... Can anyone help me? --Tango (talk) 21:29, 25 March 2010 (UTC)
 * Geosynchronous orbit requires you to be really high above the earth - 36,000km in fact - this diagram (right) is about to scale and gives you a reasonable feel for the geometry of the situation. So even at a latitude of 45 degrees, a craft in a geostationary orbit vertically above the equator and at the same longitude as the city would be fairly high up in the sky and would still appear to be stationary from the point of view of the city.  Certainly it wouldn't be vertically overhead - but it would be well above the horizon.  So, everything depends on your strict definition of the word "above".  Certainly a satellite in that position could do surveillance and conveniently launch an attack on the city.  I'll admit that it's somewhat loose language - but I don't think it seriously impacts whatever plot point they were trying to make and it's not unreasonable that an experienced space-faring bunch of people wouldn't immediately understand what was meant by that phrase.  From the perspective of the screen-writers, saying that the satellite was "in a geosynchronous equatorial orbit at the same longitude as the city" would leave 99% of their audience having no clue as to what this meant and the other 1% having to lose track of the action while they thought through the tortured implications. SteveBaker (talk) 00:05, 26 March 2010 (UTC)
 * Does the height of the orbit make any difference to the position in the sky? I can't see why it would. --Tango (talk) 22:56, 26 March 2010 (UTC)
 * Sure it does. If the craft was infinitely far away, and positioned vertically above the equator, then it would be 45 degrees above the horizon at 45 degrees latitude.  If the craft was resting on the ground on the equator, then it would be 45 degrees below the horizon at 45 degrees latitude.  The higher the orbit it gets, the closer it gets to being 45 degrees above the horizon. SteveBaker (talk) 23:13, 26 March 2010 (UTC)

I have encountered the term "forced orbit" for an orbital path that can only be maintained by continuous thrust, but that was in science fiction; I don't know if the author invented the term. In the story it was used for an orbit with a shorter period than would otherwise be possible at that altitude, which was maintained by thrusting continuously downward; but the example in the original question seems to qualify as well.

The direction of thrust for a spacecraft maintaining a forced "geostationary" orbit above a position at altitude 45°N would have to contain a northward component and a vertical component. At low altitude the vertical component would be upward and large (basically it's just be hovering), at higher altitudes less; at some altitude similar to the one for a normal geostationary orbit the vertical thrust requirement would go away, and at a higher altitude you'd have to thrust downward (see previous paragraph). I think. --Anonymous, 00:25 UTC, latitude 43.7°N, March 26, 2010.


 * I don't see a problem and remind the OP that Stargate Atlantis is fiction and not a Documentary film. Therefore the writers at a stroke of a pen can adjust the Center of mass of the planet to latitude 45 degrees. Furthermore the word Orbit used in astronomy can be traced back to 1526 in the Ptolemaic system and therefore need not imply a Keplerean/Newtonian gravitational orbit. Cuddlyable3 (talk) 12:37, 26 March 2010 (UTC)


 * Sorry for interrupting, but I understood that a geostationary orbit has been already defined to be a type of geosynchronous orbit that is directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. So, I expect that Atlantis won't follow this definition. I think that Tango's equation can be valid, relating orbital rotation parallel to equatorial plane (i.e.: $$F_{Thrust}=mr_e\omega^2 sin(latitude)\,$$, re is the Earth's radius). This is of course provided that the equation is solved for $$r= [(\frac{GM}{\omega^2})^{2/3}-(r_e sin(latitude))^2]^{1/2}$$. However, if Tango means that orbit with radius r must also have the relation r/R=cos(latitude), where R is the distance between the two masses m, M; then the previous equation must become $$F_{Thrust}=mr\omega^2 tan(latitude)\,$$ for $$r= (\frac{GM}{\omega^2})^{1/3} cos(latitude)$$.


 * I might be misunderstanding or lack for further knowledge (My English is also weak).Email4mobile (talk) 14:23, 26 March 2010 (UTC)

What is the source of the OP's latitude for Atlantis? Plato's dialogues Timaeus and Critias say only that the island continent was located at such a latitude on the planet to allow it to have a mild Mediterranean climate for most of the year, and it produced bountiful harvests of fruits and vegetables. Wikipedia has an article about the abundent Location hypotheses of Atlantis. Cuddlyable3 (talk) 21:38, 26 March 2010 (UTC)
 * The OP is talking about the alien city in Stargate: Atlantis, not the mythological island. --Tango (talk) 22:56, 26 March 2010 (UTC)

Converting from eV to cm^-1
I have vertical excitation energy levels between the S0 and S1 states in Salicylic acid in eV and a paper that gives the energies in cm^-1 and I want to compare them. As far as I can tell the paper gives a barrier for fluorescence quenching of 1100cm^-1 which i'm guessing is the energy difference between the ground and S1 level. I know that I can convert the eV into a photon wavelength, so for a 3.9eV separation I get 317nm which sounds about right but I can't work out how to get this into cm^-1 so I can compare. —Preceding unsigned comment added by Orthas (talk • contribs) 20:24, 25 March 2010 (UTC)
 * Just convert 317 nm to 0.0000317 cm, then take the inverse (1/0.0000317 cm) to get 31545 cm-1  24.150.18.30 (talk) 01:14, 26 March 2010 (UTC)
 * Isn't that a very strange way of specifying energy? Why would they do that? Ariel. (talk) 07:45, 26 March 2010 (UTC)


 * Certain processes, like Raman spectroscopy, measure an energy difference by detecting a wavelength shift. When doing that cm-1 is a natural framework.  Dragons flight (talk) 11:25, 26 March 2010 (UTC)


 * And the inverse wavelength is sometimes called wavenumber. -- Coneslayer (talk) 11:42, 26 March 2010 (UTC)


 * From Planck's equation $$E=h\nu\,$$ we see that energy is proportional to the frequency $$\nu\,$$, and from the indentity $$\nu\lambda=c\,$$ we see that frequency is inversily proportional to the wavelength so it is actually quite natural to think of energy as the inverse wavelength of a photon. That's kind of the standard unit for people that work with spectroscopy. Dauto (talk) 13:29, 26 March 2010 (UTC)

Taxonomic promotion
How is it decided that a branch of the evolutionary tree should be "promoted" to a more fundimental branch? For example, mammals and lizards have their own orders, they aren't classified as a type of fish even though they came from fish. Birds, on the other hand, seem to be a subtype of the superclass of dinosaurs. Will birds get their own superclass in a hundred million years, or will we just keep making lower and lower categories as they evolve, so they'll have many layers of subclasses with dinosaur still at the top? On a smaller scale, panda bears have their own genus, whereas polar bears have to share a genus with grizzly bears. As grizzlies and polars evolve to be more different from each other, will one get its own genus, or will they have to diverge by going down the classification and getting their own sub-sub-sub-species? --Arctic Gnome (talk • contribs) 23:25, 25 March 2010 (UTC)


 * In the millions of years it would take for those type of changes to evolve, people may go extinct or at least develop an entirely different method of classification. StuRat (talk) 23:49, 25 March 2010 (UTC)


 * Clearly we won't see the bear example actually pan out. I was asking how the system is suppose to work.  --Arctic Gnome (talk • contribs) 00:08, 26 March 2010 (UTC)


 * I doubt if they ever considered how to address new developments in evolution, for the reasons I listed. StuRat (talk) 01:48, 26 March 2010 (UTC)


 * Okay, then I'll simply ask why are birds a subclass of their ancestors the dinosaurs but mammals get their own class and not a subclass of one of their proto-mammal ancestors like Morganucodon or Docodonta. --Arctic Gnome (talk • contribs) 02:26, 26 March 2010 (UTC)
 * Birds have distinct features that make them very different from the majority of the dinosaurs so they need their own sub-class. Mammals are relatively quite similar to the proto-mammals. SteveBaker (talk) 11:01, 26 March 2010 (UTC)


 * Cladistics and Linnaean taxonomy do not match seamlessly. Cladistics arranges the "tree of life" according to the common ancestry, but this (in cases of divergent evolution, for example) groups together fairly dissimilar critters. Taxonomy, on the other hand, works by grouping animals together by anatomical and physiological similarity, which leads to many groups being polyphyletic; this makes them incompatible with cladistic systematics (in which all groups must by monophyletic). Hope this helps. Please read the articles I linked here. Do not hesitate to ask again if something is still unclear after you've read them. --Dr Dima (talk) 08:53, 26 March 2010 (UTC)


 * Regarding birds and mammals, it is indeed a good example, although somewhat complicated. Mammals evolved from synapsid craniates. Synapsids, last time I checked, are no longer considered reptiles. Birds, on the other hand, evolved from diapsid craniates, and are therefore cladistically true reptiles. Taxonomy, however, puts birds (Aves) in a group of their own, outside Reptilia. This contradiction is of the kind I pointed out above, and is probably irreconcilable. Indeed, of the animals that evolved from the basal diapsids, only few still have two temporal fenestra in their skull; which is the defining feature of Diapsida to begin with. --Dr Dima (talk) 09:16, 26 March 2010 (UTC)
 * Re "How is it decided that a branch of the evolutionary tree should be "promoted" to a more fundimental branch?": Papers are published and reviewed and elaborated upon in other papers and eventually the paper's reclassification is either accepted (and becomes the consensus), rejected, or provisionally accepted as an alternate viewpoint subject to further proof.  For example, it is still debatable whether neanderthals and human beings are separate species; although the answer to this would not involve one or the other being "promoted" or "demoted," the same principal applies to cases (and they are numerous even within the limited arena of human evolution since Ardipithecus) in which "promotion"/"demotion" would occur.  in other words, the answer to the OP's first question is "a new academic consensus is reached after prolonged and pursuasive research and argument." 63.17.63.71 (talk) 00:10, 28 March 2010 (UTC)