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February 22

How long does it take before a volcanic island can support trees?

I remember at some point I learned that since volcanic islands start barren, it takes a while before it develops enough top soil to support large plants like trees. Gradually, algae will build up on the rocks, then lichens and mosses, eventually building up and dying enough to lay the foundations for grasses shrubs and trees.

I've become suddenly curious about this and I was wondering if anyone had any information on how long this can take? — Preceding unsigned comment added by 184.148.114.163 (talk) 05:24, 22 February 2017 (UTC)

What type of volcanic rock is the island made from? How far is it from other land? What is the local climate? There are too many variables to give a clear answer. A tropical island may have coconut palms quite quickly - but it will take a very long time for Surtsey to turn into forest, given how few trees grow in Iceland anyway. Wymspen (talk) 08:48, 22 February 2017 (UTC)

Trees can grow without soil. A seed in a crack in a rock will germinate if it has fresh water. Here is one I photographed in Scotland.--Shantavira|^{feed me} 09:22, 22 February 2017 (UTC)

I'd expect there to be relatively few volcanic island developments in fresh water though. If they're developing as new island material, that's going to be in the sea. Andy Dingley (talk) 09:54, 22 February 2017 (UTC)

• Depends a lot on the bird population. Some plants can grow without soil, provided that there are minerals available from either seaweed (which is a very large algae from a very small attachment) or guano. If the island is near enough to other established islands that birds can occupy it, then plants can follow quite rapidly, without needing to wait for a soil layer to be generated. Andy Dingley (talk) 09:54, 22 February 2017 (UTC)

Our article on the island of Surtsey describes how plant life built up on a new volcanic island.--Phil Holmes (talk) 09:58, 22 February 2017 (UTC)

• The general process by which living things will populate a new land, or change over time, is called Ecological succession and our article on the subject will provide a good starting point for your research. Especially if you follow links to more detailed articles. --Jayron32 13:23, 22 February 2017 (UTC)

Some islands never acquire trees naturally, the Falkland Islands or the Faroe Islands for example. There needs to be a mechanism which allows seeds of the right species to gain a foothold. Birch trees will happily colonise apparently barren slate mine tips [1] but are wind blown and not carried around by birds. Alansplodge (talk) 13:47, 22 February 2017 (UTC)

Here's [2] a nice research article that has studied primary succession in NZ. They are not talking about a small volcanic island, but it's got good discussion of the processes involved and time scales. The first 10 references also comprise a nice bibliography on the subject of primary succession. SemanticMantis (talk) 15:01, 22 February 2017 (UTC)

• The biology section of our article Surtsey will be of interest. Surtsey is a volcanic island formed in the 1960s, and according to that article Salix phylicifolia was found there by 1998. DuncanHill (talk) 16:42, 22 February 2017 (UTC) Which contains the immortal words "An improperly handled human defecation..." DuncanHill (talk) 16:49, 22 February 2017 (UTC)

Bear in mind though that neighbouring Iceland has only three native "forest-forming" tree species, the downy birch, rowan which is rare and aspen found in only six locations. [3] Alansplodge (talk) 17:53, 22 February 2017 (UTC)

Other articles of relevance include Colonisation (biology) (a bit stubby, alas), and Insular biogeography. DuncanHill (talk) 16:49, 22 February 2017 (UTC)

The article was already linked to by by Phil Holmes above. Nil Einne (talk) 20:36, 22 February 2017 (UTC)

So it was! I hadn't read all the answers before I answered. DuncanHill (talk) 01:55, 23 February 2017 (UTC)

Having a caldera above sea level would tend to speed up the process, as fresh water from rain, fertilizer from birds, and sand grains eroded from the peak could collect there. On the other hand, islands in the polar regions may never grow trees (or at least not until the Earth's climate changes significantly). See tree line. StuRat (talk) 19:00, 22 February 2017 (UTC)

A point where something can be a liquid, gas and solid at the same time

I read an article here a month or two ago but can't remember where it is. The gist of the article is that at a certain temperature and at a certain pressure water (for example) can be liquid, ice and vapor all at the same time. I can't remember the term and hope I did not misread the article. I believe the term started with a "t" 198.72.29.37 (talk) 16:33, 22 February 2017 (UTC)

Try triple point. DuncanHill (talk) 16:36, 22 February 2017 (UTC)

Since the OP brought up water, a bit of trivia. The original definition of the Celsius scale set 0°C as the freezing point of water at atmospheric pressure. The modern definition of the Kelvin scale uses the triple point of water, which is almost at 0°C but at a much lower pressure. Those are not the same temperature; it only turns out that for water (and this is quite a unique case) the liquid-solid separation in the phase diagram is almost vertical, so temperature of freezing water is almost the same at the triple point pressure and at atmospheric pressure. Tigraan^{Click here to contact me} 17:08, 22 February 2017 (UTC)

Clarification: the triple point is not defined so that it becomes the new 0°C. Rather, the triple point is defined as 273.16 K, and temperature in degrees Celsius is defined as temperature in kelvins minus 273.15, which makes the triple point exactly 0.01°C. See the SI standard, section 2.1.1.5. --76.71.6.254 (talk) 18:33, 22 February 2017 (UTC)

Note that, as mentioned in the first sentence of our triple point article, that's where the 3 states coexist in "thermodynamic equilibrium". It's also possible to have all 3 states exist, but not at equilibrium, at other pressures and temps. For example, at the melting temp of ice, you will have ice and water but also some water vapor, in the form of humidity. StuRat (talk) 18:41, 22 February 2017 (UTC)

Around this time of year, in Minnesota for example, the ice on the frozen lakes starts to melt and that meltwater starts to evaporate. So a given lake is solid, liquid and gas at the same time. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:20, 23 February 2017 (UTC)

"Designer" benzodiazepine vs "legitimate" ones

Whilst speaking to a psych nurse friend of mine, she told me about dealing with overdoses of Phenazepam, a Soviet-designed benzodiazepine. The article on it led me to an area I'd never known before - List of benzodiazepine designer drugs. I'd never heard of a "designer benzo" before, and the concept intrigues me.

What do these "designer" benzos do in terms of pleasure-inducing effects, which the "legitimate" ones manufactured by big pharma do not?

As far as I'm aware, one of the highest-in-demand benzos on the street is Alprazolam, and it definitely comes from big pharma, not an illicit lab. Here in Australia, it was re-scheduled to make prescribing rules stricter for precisely this reason.

So my question is twofold:

1. Do any of these "designer benzos" work any better in terms of what a drug abuser would want, versus those variants manufactured by legitimate pharma? I understand that "legitimate" benzos are heavily regulated too, I'm just wondering why someone who wanted a "high" would want a "designer" benzo, as opposed to illicitly obtaining a "pharmaceutical" one? - Is there an "ease of manufacture" issue? Or are they actually any more "pleasure effective"? And if the latter, how so?

2. Where in the world is most of this stuff manufactured? I'd never encountered the idea of an illicit benzo drug manufacturer before. Even though Alprazolam may, gram for gram, be worth more than heroin on the street (it's more potent), the route I had known of almost always involved diversion from a "legitimate" source. Not hard at all in many countries with weak law enforcement, and quite possible even in first-world ones - rumours of "dodgy pharmacists" and "naive doctors" abound, or you just go Doctor shopping. And Darknet markets are choc-a-block with "legit-manufactured" stuff of this sort. Not illicit manufacture. So, where in the world are these labs? What keeps them financially viable, when "legitimate diversion" exists as an alternative? And how hard is it to set up a benzo manufacturing facility? (I assume it's a lot more difficult than a methamphetamine lab?).

Please note, I have ZERO intention of taking any benzo, other than one prescribed to me legitimately by a doctor, or dispensed to me by a hospital. So I can't see this as remotely "medical advice". I'm just intrigued by a new side to the "illicit" market I never knew about, and trying to understand how it operates, and what sustains it. Eliyohub (talk) 18:52, 22 February 2017 (UTC)

Benzodiazepines, desiner or not produce their effect by attaching to $GABA_{A}$ receptors in the brain. They all have different affinity, that is the ability to activate those receptors. Therapeutically speaking each of them has a potency characteristic, drugs with high potency require small milligrams or even fraction thereof to produce therapeutic effect, others have low potency and are usually prescribed with high milligrams (5-10-25). I don't think there is a principle difference between them otherwise. It is better to avoid using them because they all develop tolerance which leads to the need for a user to take higher and higher dose. Multiple problems will then develop, dependency, etc. Talk to your doctor before using any chemical but the table salt :-) --AboutFace 22 (talk) 22:02, 22 February 2017 (UTC)

I said that - any benzos I use are prescribed by a psychiatrist, and I assume he knows what he's doing. And in my experience, pharmacists tend to be savvy too. When I turned up with a prescription from a different doctor than my previous prescription, he asked me why. I explained (my main doctor was away, he knew who would be filling in for me) and invited him to notify both of them, they'd already be aware of it. But it showed that eyes are watching! Eliyohub (talk) 23:37, 22 February 2017 (UTC)

First, there's our article List of benzodiazepines, which lists them all, licit, illicit, and off in the shadows somehwere. It's worth mentioning that approval for medical use varies widely by country. Also drugs a physician can't prescribe here are probably either explicitly covered by the US Federal Controlled Substances Act (even banned if someone put them in the infamous "Schedule I"), or by one of its codicils banning "analogues" of controlled substances like benzodiazepines. For example, the "Backdoor Pharmacist" mentions three designer benzos, two of which only differ from existing, approved, US controlled substances by a functional group added on. (This is actually a common practice in Big Pharma - take a competitor's highly profitable drug, slap a methyl or hydroxyl group on its structure, and see if you have the next new leader in that market, or something too poisonous, unpleasant in its adverse effects, inert or expensive to sell).

And that's the story with almost all the designer benzodiazepines - they didn't make the cut for one reason or another, or they'd be "approved, regulated benzodiazepines", and the US Federal government explicitly bans most or all of them for being one functional group away from something they already regulate.

A short 2015 article in the journal World Psychiatry, "Designer benzodiazepines: A new challenge", Bjoern Moosmann, Leslie A King, and Volker Auwärter covers everything you were asking about in part 1 of your question. It's not a simple set of answers - the benzodiazepine family differs greatly, even among drugs which have been tested and are approved for medical use worldwide. Some have, at the prescribed dose, a calming, "anxiolytic" effect. Some, like Versed (midazolam) are strong enough they cause patients to remain calm during surgical or endoscopic procedures, and cause amnesia of events during those procedures. Each member of the benzodiazepine family has its own unique combination of effects on the taker's consciousness and mood.

Since, according to Moosmann et al, none of the "designer" benzos they mention, diclazepam, flubromazepam, pyrazolam, clonazolam, deschloroetizolam, flubromazolam, nifoxipam and meclonazepam have been approved for medical use in any country, the testing needed to show what they do to the people who take them is largely not available. Almost all of them were developed by drug companies and papers were published on them by their developers/discoverers, but it's a safe bet that a drug candidate that doesn't get as far as Phase III clinical studies just wasn't likely to be approved by the medical regulatory community for one of a number of reasons - usually toxicity, lack of a good therapeutic index (you get bad side effects at or just above the dose that does you any good), or lack of efficacy.

There's also unprofitability Let's say one of these drugs is so close to (for example) diazepam in its tox profile, therapeutic index, cost of manufacture and general effectiveness that it's a "me too" drug for a generic medication that sells for a few cents a tablet - you won't make your money back testing it in lots of patients and filing for regulatory agency approval. But we don't even know that about any "designer benzodiazepine" - just that in an industry addicted to the almighty (national currency of your choice), these chemicals were never put on the market.

So, there's a huge flashing neon sign in Gothic script over designer benzodiazepines - Noli me Tangere ("Don't fool with me"). You're dealing with potent central nervous system depressants whose only point in common is that they're either too highly toxic, too expensive to make or get approved, or too unpredictable in their effects to be used recreationally. loupgarous (talk) 22:43, 22 February 2017 (UTC)

Thanks, that helps somewhat. But even reading that article, I'm still lacking any understanding if there's any "designer benzo" which a drug abuser has shown they prefer over an "approved" equivalent? I assume human testing of this sort would be risky and ethically dubious. But has anyone surveyed the users of these drugs, and had them say they found some effect these "illegal" ones do, over what a "legal" one can? As I said, Alprazolam remains amongst the top choices in the black market, and it is most definitely "approved"! So I still await any surveys or studies on those who admit to using these drugs, and hear significant numbers of them say "this (designer benzo) does something for me which (the closest "approved" alternative) couldn't"?

The question about unprofitability would also work the other way - why would anyone pay for illicit manufactured, untested stuff, when diversion of stuff from a proper factory is so easy and widespread? How does the "illicit manufacture" market compete with the "illicit diversion from legal" market?

Also, any data on manufacturing on this stuff, and where it originates from? And how tough it is to set up a manufacturing facility? I have no idea what's involved in benzo synthesis. Eliyohub (talk) 23:31, 22 February 2017 (UTC)

Eliyohub, did you read the review of the "Backdoor Pharmacist"? The author does, actually, give some indication of three designer benzodiazepines' appeal in the illicit drug culture. That the review was largely negative doesn't mean that someone didn't like them, but that they may be a little more intelligent than to write about it to an Internet site that might capture their IP address. In that respect, I can't help you, because I don't play on the dark Net.

Nor can I say why anyone would eat stuff someone made in their bathtub after so many folks who thought they were getting fentanyl wound up dying after one last trip on 3-methylfentanyl, and a similar number of people wound up with Parkinson's disease because they thought they were getting designer Demerol and wound up with some MPTP as an added ingredient. I'll have to defer to actual illicit drug users for the answers to those questions. Good luck! loupgarous (talk) 02:32, 23 February 2017 (UTC)

The best benzodiazepine is aerobic exercise, it produces endorphins, they are close to the benzos chemically, are attached to the same receptors and have similar therapeutic effects. The exercise, although not for everyone, produces other benefits too. --AboutFace 22 (talk) 01:41, 23 February 2017 (UTC)

That's not correct. Endorphins are opiates. Opiates and benzodiazepines both reduce anxiety, but in terms of chemistry and receptor mechanisms they have virtually nothing in common. Looie496 (talk) 13:57, 23 February 2017 (UTC)

@Looie496, you are correct. Sorry for the error. --AboutFace 22 (talk) 16:11, 23 February 2017 (UTC)

Eliyohub, you may be interested (even though they deal with different designer drug families than the benzodiazepines) in the books of American designer drug chemist Sasha Shulgin, who synthesized 179 different psychedelic phenethamine compounds, documenting his psychonaut experience (both the syntheses of the drugs, and the way they made him and his friends feel) in Phenethamines I Have Known and Loved. Dr. Shulgin got away with making these designer drugs partly because he worked for the US Drug Enforcement Administration in his spare time testifying as an expert witness, and had a DEA license to make the drugs. The DEA asked him to turn his license in after they raided his home laboratory, an impressive installation with its own nuclear magnetic resonance spectrometer for analyzing his product. Dr. Shulgin's books Phenethamines I Have Known and Loved and Tryptamines I Have Known and Loved are unique in that they document extensively both the scientific side of designer drug design and synthesis and the subjective sensations these drugs created in Dr. Shulgin and other volunteer test subjects. loupgarous (talk) 21:37, 23 February 2017 (UTC)

Is there a part of North America that can grow all common and semi-common English plants without crippling them?

But with little to no human help – otherwise you could grow cactus in Antarctica. Absolutely no weather amelioration (like greenhouses, watering or frost covers). Shade/full sun and whatnot plants would only have to grow in some light regime to not disqualify a part of North America, water hungry plants like willows would only have to grow near water and lilly pad-type things would only have to grow in water. Sagittarian Milky Way (talk) 22:58, 22 February 2017 (UTC)

The Pacific Northwest of the US and into Canada has a climate similar to England, and the climate can be varied by moving closer to, or farther from, the coast and further up or down the mountains. However, they may be out-competed by native plants, lack pollinators specific to those plants, and suffer from native plant parasites. With those problems in mind, the answer is likely no. StuRat (talk) 23:05, 22 February 2017 (UTC)

There's no bees in the Pacific Northwest? Did English colonists have difficulties replicating their gardens in the PNW, Massachusetts, New York, PA, MD, or Virginia? Sagittarian Milky Way (talk) 23:28, 22 February 2017 (UTC)

No problem at all. The early English colonists only had to poke a artists paint brush in to the male sexual organs of a flower and deposit the pollen into the female sexual organs. Just like what bees do.--Aspro (talk) 00:34, 23 February 2017 (UTC)

The hardiness zone of the Boston area in the Little Ice Age must've been a problem for something. Sagittarian Milky Way (talk) 01:22, 23 February 2017 (UTC)

Oh wow. Wikipedia even has an article... as always! Hand-pollination.--Aspro (talk) 00:47, 23 February 2017 (UTC)

And then the colonists got lazy and imported the European honeybee. Sagittarian Milky Way (talk) 01:14, 23 February 2017 (UTC)

Some flowers are designed to exclude all but one specific pollinator. Here's an interesting example of this: [4]. StuRat (talk) 01:03, 23 February 2017 (UTC)

• There isn't even a part of England that can grow all common and semi-common English plants without crippling them. The vegetation of the Essex fens is very different from the vegetation of the Yorkshire moors, both of which are very different from the vegetation of the New Forest. Looie496 (talk) 13:53, 23 February 2017 (UTC)

I didn't find an answer, but this article about the difference between British and US gardening culture is quite interesting. Alansplodge (talk) 16:41, 23 February 2017 (UTC)

• See also invasive species for an understanding of why, even if you could, doesn't mean you should.--Jayron32 18:53, 24 February 2017 (UTC)

February 23

Does the brain control the heart also?

or the heart is exception and it doesn't control the heart? I'm asking it because according to what I know there are no nerves in the heart. 93.126.88.30 (talk) 00:31, 23 February 2017 (UTC)

See Heart#Nerve_supply. The heart normally beats on its own, but the rate is influenced by the brain. However, trauma to the brain alone can cause cardiac arrest, though our articles do not explain the mechanism. Someguy1221 (talk) 00:38, 23 February 2017 (UTC)

Think you'll find the most important is the Vagus nerve. Beta blockers work by damping down the brains control.--Aspro (talk) 00:41, 23 February 2017 (UTC)

Then the brain controls the heart. Isn't it? Now I'm holding a booklet of the Red Cross organization which states (translated) about the brain that it "activating and supervising on the lungs" while the brain "supervising and regulating the heart". The use different terms for the lungs and for the heart. They don't say about the heart the it's activating by the brain. I'd like to know what is the explanation for these different terms regarding to the brain and the heart. 93.126.88.30 (talk) 01:08, 23 February 2017 (UTC)

Well, it depends on what you mean by control. And brain. The normal function of the heart is primarily controlled by the Cardiac pacemaker without direct continuous input from the brain. But there can be things that happen in your brain that influence the function of your heart. --Jayron32 01:29, 23 February 2017 (UTC)

I think the reason for the difference in description is the nature of the "control". Muscle contractions that lead to breathing are caused by continuous nerve impulses from the brain. That is not the case for the heart, even if the brain can modulate its rate, and the heart cannot beat indefinitely with no input from the brain. Controlled, but not micromanaged? Semi-independent? Someguy1221 (talk) 01:31, 23 February 2017 (UTC)

I'd note that while translated, the word which seems to confuse the OP is "activating". I'd suggest removing "activating" is a fair call for the heart. The heart is supervised and regulated by the brain and does need input from the brain long term, but it isn't really activated by it. It "activates" itself by the cardiac pacemaker which is part of the heart. The lungs do need to be "activated" by the brain, if they don't receive a signal they don't work. The Pre-Bötzinger complex is part of the brainstem, not the lungs. Of course control and regulation of these organs is complicated, as with most things, we you should always be wary of reading too much into words whether English or some other language and with no disrespect to the Red Cross, I'm sure it isn't intended to be a scientific text book. Nil Einne (talk) 01:56, 23 February 2017 (UTC)

Exactly. The difference between the lungs and heart is that the heart contains its own pacemaker, and the lungs do not. No brain = no breathing, but the heart will beat autonomously... for a very brief time. - Nunh-huh 02:19, 23 February 2017 (UTC)

A very rough analogy would be the difference between driving a car and riding a bike - in the car, you control the rate the engine turns by pressing the accelerator, but don't directly affect the details of the motion (analogous to the brain's control of the heart - it can change the rate, but the heart controls the details of the movement). On a bike, your feet are turning the wheels, and there is a 1-to-1 correspondence between the movement of your foot and the movement of the bike (assuming fixed gears - this is like the brain's control of the lungs, where it will send a signal for each breath in and out). MChesterMC (talk) 10:33, 23 February 2017 (UTC)

• The heart does not require a signal from the brain to function on a basic (as opposed to regulated) level, see SA Node and Fibers of Purkinje. The lungs will entirely fail to function without a brain signal. This is called a "central apnea since the failure originates in the central nervous system. μηδείς (talk) 03:51, 23 February 2017 (UTC)

The autonomic nervous system controls heart rate.
Sleigh (talk) 19:42, 23 February 2017 (UTC)

Sudden unexpected death in epilepsy (SUDEP) is a recognized clinical event, though its causes aren't well-understood at present - but it's definitely a case where the brain controls the heart. "Cardiac arrest associated with epileptic seizures: A case report with simultaneous EEG and ECG", Fatemeh Fadaie, et al, Epilepsy & Behavior Case Reports Volume 2, 2014, Pages 145–151 reports on two patients who experienced asystole after epileptic seizures. In the 1970s, I witnessed what may have been a similar case, a young lady who presented at the hospital emergency room where I worked (as a non-medical employee) experiencing what appeared to be drug-related seizure activity which ended with cardiac failure, after which cardioversion failed and she died. loupgarous (talk) 21:58, 23 February 2017 (UTC)

Isn't the brain also involved here by sending signals such that in the absence of the signal the heart rate would rapidly increase to about 100 bpm? I remember reading somewhere that this allows for rapid stress responses. Count Iblis (talk) 22:28, 23 February 2017 (UTC)

Our article on the vagus nerve's function explains that. A properly functioning right vagus nerve does down-regulate the heart beat by controlling the sino-atrial node. The vagus nerves and spinal ganglionic nerve keep the heart rate down to normal levels in healthy people. When the vagus nerves are hyperstimulated bradyarrhythmias, pathologically slow heart beat, can result. Hyperstimulation of the left vagus nerve can cause conduction block at the sino-atrial node.

One correct answer to the OP is that in healthy people the brain does routinely help regulate heart rate through the parasympathetic nervous system - though even after a vagotomy the heart continues beating, still controlled by its internal pacemakers. The control, however, doesn't respond to external stimuli as responsively as when the vagus nerves are left intact. loupgarous (talk) 22:57, 23 February 2017 (UTC)

Ratio of circumference to diameter

Could the ratio of a circle's circumference to its diameter be possibly different in an alternate universe?

Then it wouldn't be a circle. --DHeyward (talk) 09:27, 23 February 2017 (UTC)

• (edit conflict) Everything is possible in an unspecified alternate universe, so yes.

Outside the realm of speculation, you can try reading about Non-Euclidean geometry, where such a ratio is not even constant. For instance, a circle on the Earth's surface of small dimensions compared to the Earth's curvature will have about the same properties as in planar geometry, whereas a circle on the equator has a perimeter of four times its radius (= the pole-equator distance) (assuming a spherical Earth, which is not exactly true), so that ratio is 4 rather than 2π. Tigraan^{Click here to contact me} 09:28, 23 February 2017 (UTC)

"Pi is approximately 3.1415927, given Euclidean geometry" appears to be a true statement regardless of the nature of the universe. If we lived in a universe that was obviously non-Euclidean, we would still be able to imagine a world that was not. As Tigraan mentions, certain non-Euclidean worlds give non-constant values of pi (pi here being not mathematical pi, but the circumference-to-diameter ratio of an arbitrary real circle). You could even imagine a universe in which particle movement was restricted to triangular or square grid lines on a physically realized spacetime, and wind up with pi of exactly 3 or 4, respectively. But then we could still imagine a Euclidean world, and calculate pi ~ 3.1415927. In logic this is called a logical truth, a statement that (given its underlying assumptions) appears to be true no matter what (in the words of philosophers, in every possible universe). Whether logical truths really exist, and what they mean, has been debated for millennia. Though most people just go about their day and don't worry about it. Someguy1221 (talk) 09:44, 23 February 2017 (UTC)

In Pratchett's Going Postal there´s a machine in which pi = 3. The inventor was really annoyed that pi was so "messy". As a consequence, the machine bends time and space. Gråbergs Gråa Sång (talk) 10:24, 23 February 2017 (UTC)

The USA tried that too: Indiana Pi Bill Andy Dingley (talk) 14:45, 23 February 2017 (UTC)

• It's different on this planet too.

Pi's value doesn't depend on the universe, but rather the geometry. If you have a non-Euclidean geometry, then pi doesn't have the same value one would expect for a flat plane. Nor do the angles of a triangle add up to 180º.

You can demonstrate this with a large spherical ball (easy to find), or the alternate of a hyperbolic surface (a bit harder to find physical examples of - a Pringle or a trumpet bell are sometimes used to make museum displays). With an exercise ball, some whiteboard pens and flexible tape measure and protractor you can do classroom demonstrations with measurements. As the radius is measured along the curved plane of the ball's surface it is "longer" than you might expect for a circle of such diameter, thus the value of pi is smaller than for a flat Euclidean plane. Andy Dingley (talk) 10:47, 23 February 2017 (UTC)

Minor nitpick: that supposes you define π as the ratio of circumference to diameter. Many people define it as the half-period of the cosine function, or a similar definition from calculus; you can prove that the cosine, defined as a power series, has a period without involving geometric arguments. See Pi#Definition. Tigraan^{Click here to contact me} 13:12, 23 February 2017 (UTC)

Well, that still leaves the same basic question, but worded differently "Under what mathematics systems does the half-period of the cosine function NOT equal the ratio of the diameter to the circumference of the circle?" The symbol used to represent those two concepts is identical under the mathematics we all know and love, but that's merely convention. What if they were different numbers? --Jayron32 13:15, 23 February 2017 (UTC)

The broader question is whether mathematics (so maybe try the Maths desk) works the same in an alternate universe, a question that has been asked here many times, most recently here.--Shantavira|^{feed me} 12:27, 23 February 2017 (UTC)

• The OP's question amounts to the tautology "If math were different would math be different." The simple answer is "of course it would, you've already stipulated that it was different". The more interesting questions come from asking "If math were different in this specific way how would that one change propagate through the entire system to change other things." Entire fields of mathematics are dedicated to answering that question. Besides the alternative geometries mentioned above in non-Euclidian geometry there are things like Alternative algebra or Non-associative algebra or Non-standard model of arithmetic the like in which some fundamental axiom of a mathematical system is changed, and then further implications are studied. --Jayron32 13:05, 23 February 2017 (UTC)

Newly discovered earth-size planets at nearby star 40 light years away.

This cnn.com[5] page states: "Standing on the surface of one of the planets, you would receive 200 times less light than you get from the sun, but you would still receive just as much energy to keep you warm since the star is so close." It does not make any sense to me. --AboutFace 22 (talk) 13:21, 23 February 2017 (UTC)

Compare a candle to a bonfire. To get the same heat energy from the candle as from the bonfire, you'd have to stand MUCH closer to the candle than you would the bonfire. --Jayron32 13:22, 23 February 2017 (UTC)

(EC with below) I imagine the OP's question is why you receive much less light but just as much energy (since both are referring to a planet that is very close). The CNN story doesn't explain very well, but I imagine they are talking about visible light. Since TRAPPIST-1 is an ultra-cool dwarf, the energy in what's visible light to us would be significantly reduced even on a relative basis. Of course any life evolved there would be adapted to that spectrum. Nil Einne (talk) 13:46, 23 February 2017 (UTC)

• There are multiple effects at play here, and the article seems to be mixing them up awkwardly.

Obviously, the closest from the star you are, the more energy flux (by surface area) you receive. However, that energy is transferred by radiation, and is thus distributed among the radiation spectrum according to Planck's law. This law involves temperature in two ways:

1. The hotter a body, the more radiation it emits overall (see Stefan-Boltzmann law).
2. The hotter a body, the more the bulk of the radiation is shifted to the short ("blue") wavelengths (see Wien's displacement law).

The important point is that "light" refers to the portion of energy that falls within the visible spectrum, where the Sun emits most of its radiation (which is not coincidential: life forms evolved optical sensors called "eyes" to have sensitivity in the domain where there was stuff to see).

My guess is that the star discussed in the article is cooler than the Sun, thus emitting less energy overall and having a peak emission at longer wavelengths (in the infrared domain) than the Sun. Because it is closer, it compensates for the first effect (overall energy flux), but it still emits more at non-light wavelengths. Tigraan^{Click here to contact me} 13:42, 23 February 2017 (UTC)

 

Is it possible that the article really meant that the star was 200 times less bright than the Sun? They actually wrote "200 times less light", but maybe they were just confused. You could get comparable amounts of light from a much dimmer star, if its disk is much larger in the sky.

This issue made for a difficult problem to solve at the Moon article, which claims that the Moon is second only to the Sun in terms of brightness as visible from Earth. Literally, that's false (Venus is about 10x brighter, as you can easily see when they're close to one another in the sky). But the article text goes on to explain that this is as measured by illuminance. I'm not entirely happy with the solution there but I'm not sure I have a better suggestion. --Trovatore (talk) 23:17, 23 February 2017 (UTC)

The stellar magnitude of Venus can be as much as -4.6, and that of the moon -13. The sun's is -27. A unit decrease in magnitude represents an increase in brightness of approximately 2.5. The absolute magnitude of stars is calibrated by lining them up at a distance of 32.6 light - years - for planets and asteroids the distance is a more useful one earth - orbit radius. 80.5.88.48 (talk) 08:49, 24 February 2017 (UTC)

You're missing the point. The Moon delivers more light to the Earth; there's no question about that. But Venus is brighter. Brightness is the amount of light per unit solid angle as seen by an observer, and Venus subtends a much smaller solid angle. (Relative) magnitude doesn't measure brightness, but rather illuminance.

This sounds abstract, but it really isn't. Next time Venus is close to the Moon on a clear night, just look at them. You can easily see that Venus is brighter. --Trovatore (talk) 09:03, 24 February 2017 (UTC)

sub-Q - Is CO2 a greenhouse gas?

I gotta ask... a "Venus-like atmosphere" has not been ruled out for the inner planets of the star. But if they are heated almost entirely by infrared radiation, is a Venus-like CO2-intense atmosphere a greenhouse gas for them, or does it actually make them cooler, or does it more or less cancel out? Wnt (talk) 13:46, 23 February 2017 (UTC)

Can you explain more why you think it might not be a "greenhouse gas", due to the spectrum of radiant heat? Somewhat relevant: you may enjoy this [6] critique of the word greenhouse gas, as it is a terribly misleading metaphor. An actual greenhouse acts to keep the inside warm by limiting convective transport. An actual greenhouse would keep the inside warmer than the outside, no matter what the spectrum of light. SemanticMantis (talk) 15:59, 23 February 2017 (UTC)

The thought is correct (if the star emits in the infrared, the CO2 will absorb more of the incoming radiation), but even a red dwarf has an effective surface temperature of 2300K to 3800K, while the planet would have a temperature about an order of magnitude lower. Wien's displacement law tells us that a planet at 300K will have its maximal emissions at 9.6μ, while a red dwarf at 3000K will have the maximum at 0.97μ. CO2 mainly absorbs at 2-3μ, around 4μ, and from 8-20~13-~16μ. So while the greenhouse effect would be a bit weaker than for earth, it would still contribute to warming the planet, not to cooling it. --Stephan Schulz (talk) 16:37, 23 February 2017 (UTC)

An aside on real greenhouses, and how they work. Not terribly relevant to either question above, interesting though it may be. SemanticMantis (talk) 17:08, 23 February 2017 (UTC)

My understanding is that in a physical greenhouse the windows allow the visible and ultraviolet to get inside, the latter warm the plants and the soil. The latter emit low frequency infrared light which the windows do not allow to pass, thus the energy is trapped inside. --AboutFace 22 (talk) 16:21, 23 February 2017 (UTC) That effect is tertiary at best. Actual greenhouses keep the inside warm by keeping that air in one place, while allowing light in. This is is explained more clearly by a Dr. Fraser at the link I posted above. If you could magically make the walls of a greenhouse permeable to air while keeping the exact same optical properties, it wouldn't be able to keep the inside warm in the winter. Likewise, if you contain a volume of air, butlet the IR back out, you get pretty much the same warming, as illustrated by the quote below. SemanticMantis (talk) 16:33, 23 February 2017 (UTC) (ec) One way an actual greenhouse works is that the glass is almost 100% transparent to visible light, but less so to infrared. Therefore, light enters, hits things like plants, is converted to infrared, but then reflects off the glass and stays inside. If the same is true of the greenhouse effect, then this Q would come up, if there's little visible light. StuRat (talk) 16:23, 23 February 2017 (UTC) Stu, if you'd read what you yourself just linked, you'd see that's not the relevant part at all. It's also explained in my link, and I also explained why greenhouses and the greenhouse effect are not very similar. Since you can't be bothered to read the article, Let me help you and and do some of your homework for you: “ However, R. W. Wood in 1909 constructed two greenhouses, one with glass as the transparent material, and the other with panes of rock salt, which is transparent to infrared. The two greenhouses warmed to similar temperatures, suggesting that an actual greenhouse is warmer not because of the "greenhouse effect", but by preventing convective cooling, not allowing warmed air to escape. ” Next time read and think a bit before you type up whatever you happen to recall from your distant school days. SemanticMantis (talk) 16:31, 23 February 2017 (UTC) Far am I from defending Stu (usually), but the greenhouse effect, while not the primary explanation for the warming of greenhouses, is measurable and even significant - see Greenhouse_effect#Real_greenhouses and Greenhouse#Design. Wood's experiment is interesting, but was rather crude by today's standards. --Stephan Schulz (talk) 16:42, 23 February 2017 (UTC) Sure it's measurable, but significance is... debatable at best. Do you have any sources showing it as contributing to warming in a real greenhouse in anything over small percentages? Because 8% is an interesting footnote, not the thing that we explain if we only get to explain one thing. Saying a greenhouse keeps the interior warm due to the greenhouse effect is like saying "an airplane flies by pushing air down with its wings, and that pushes the airplane up". Yeah, we have Ground_effect_(aerodynamics), but the offered explanation is still very bad and misleading, even though some aircraft can take advantage of this downward push in some circumstances. When we explain things, we should explain the bits that are important, not the bits that are not important. Anyway, I'm sorry I brought it up at all, none of this is terribly relevant to OP or Wnt's question. SemanticMantis (talk) 17:05, 23 February 2017 (UTC) SemanticMantis, I said "One way an actual greenhouse works..", not that this is the only way, or even the main way. The source I provided backs up what I said, and I said that to explain the term "greenhouse effect", since it refers to that portion of the way a greenhouse works. You owe me an apology for misrepresenting what I said. StuRat (talk) 18:16, 23 February 2017 (UTC)

• Convenience link: CO2 transmittance in the IR range. For the answer to the question, see Stephan Schulz's post, although I believe their "8-20μ" indication of an absorption window in the far infrared to be erroneous (going by the spectrum I linked, it is more like 13-17μm). And yes, in theory, the "greenhouse" effect could lead to cooling rather than heating. Tigraan^{Click here to contact me} 17:10, 23 February 2017 (UTC)

Also see anti-greenhouse effect. --Stephan Schulz (talk) 17:16, 23 February 2017 (UTC)

And you are right about the absorption - I was going by a bad web source. This is better. Note that this is maintained by the NIST, but they still claim copyright. That sounds doubly wrong to me... --Stephan Schulz (talk) 20:54, 23 February 2017 (UTC)

A very interesting and well-referenced post that was not asked for by anyone above. If you would like to read why it is unlikely that you will get to travel to one of these planets, and find it a hospitable world of easy wealth, read on.

Reality check A science fiction artist has been at work painting "What the TRAPPIST-1 planetary system may look like" of which 2-3 of the 7 planets resemble our own watery blue marble. This imaging is entirely imaginary, in the tradition of the sci-fi illustrator Chesley Bonestell 1888 - 1986. All that can be said reliably is that existence of 7 probable Exoplanets has been deduced from obscurations of a little star in Aquarius (constellation) designated TRAPPIST-1, 3 of them may be in "Goldilocks" habitable orbits, which is a factor that the speculative Drake equation uses to estimate the chances of Extraterrestrial life, but the reality is that we as yet are less able to image the TRAPPIST-1 planets properly than Sciaparelli was in 1877 to draw the Mars that he could actually see. So to you eager futurists who are already planning to terraform a TRAPPIST-1 planet, already counting the wealth in untouched natural resources to be extracted, already imagining yourselves as colonists of an extraterrestrial utopia, already imagining exquisite sunset scenes where nobody can say for sure whether there are atmospheres or that the planets are spherical, and even planning to build a Dyson sphere or two, I offer the following reality check on your dream: Suppose a long-lost relation leaves you $1 million with which you may buy the fastest car possible - it must be a model in production (but the budget allows you to tune it for higher performance). Now, disregarding little problems like refuelling, let's suppose you drive to TRAPPIST-1 at the car's full speed. Please answer here below 1) your car model, 2) your speed, and 3) your age when you finally arrive at TRAPPIST-1. Blooteuth (talk) 20:46, 23 February 2017 (UTC) EXTRATERRESTRIAL TRAVELS TO OTHER STARS ARE IMPOSSIBLE. That car of yours will take millions of years to get there. --AboutFace 22 (talk) 21:36, 23 February 2017 (UTC) Only under current technology. ←Baseball Bugs What's up, Doc? carrots→ 21:51, 23 February 2017 (UTC) There will be no technology for interstellar travels in a million years. You are up against the laws of physics in there. --AboutFace 22 (talk) 22:26, 23 February 2017 (UTC) We don't necessarily know all the laws of physics, nor all the possible ways to get from point A to point B. ←Baseball Bugs What's up, Doc? carrots→ 22:32, 23 February 2017 (UTC) I think the ref desk has work within the known parameters of physics as we understand it. It's all very well to claim we can be reborn as unicorns or we can travel at 8 million times the speed of light or Donald Trump isn't orange, but most of that is just stuff of fiction right now. Answering questions at the Ref Desk assumes that you're going to respond within the known known parameters, not the known unknown parameters. The Rambling Man (talk) 22:45, 23 February 2017 (UTC) The poster claimed interstellar travel is impossible. I don't think there is universal agreement on that. Keep in mind that in 1902 the poster might have said that about airplanes. ←Baseball Bugs What's up, Doc? carrots→ 23:14, 23 February 2017 (UTC) If you need to send a file to someone, you attach it in your email and send it electronically. You don't need to book a flight and bring a computer with you that has the file on its hard drive. Similarly, I think that advanced civilizations will have made the transition to a machine civilization who travel electronically by uploading themselves to machines at the destination via radio communications (or perhaps using lasers as they'll have a larger bandwidth ). That way you can travel at the speed of light without needing a spacecraft. This only works as long as there are suitable machines at the point of destination, so different civilizations may travel to each other, but travel to locations without technology will be more difficult. Count Iblis (talk) 22:56, 23 February 2017 (UTC) Why are you talking about art? Did someone ask about art? Why are you talking about terraforming? Pretty sure that has not been asked about here either. Can you explain to me why this post of yours, in a whole new section, is anything other than WP:SOAP? We are WP:NOTAFORUM. I don't really disagree with anything you said, but I know this is a reference desk, and not a place to post our tangential grievances with how some people may misinterpret news of scientific findings. SemanticMantis (talk) 23:08, 23 February 2017 (UTC) My launchpad and first link is this cnn report introduced by the OP. Have you noticed how much of it is artwork? Have you noticed the amount of artwork that enhances our TRAPPIST-1 article? It even has a video simulation. Those who remember the Golden Age of Science Fiction (you may not) understand the importance of conjectural art as the only way we (excepting the odd astro- or cosmonaut) will ever perceive things in space. But without a clear idea of what is fact and fiction, the artwork used in NASA's announcement can blind some to the fact that today's status of extrasolar exploration is comparable to that of the makers of Early world maps who decorated unknown lands (which in 1566 meant most of North America) with art to say "Here be dragons". NASA have good reason to popularize their work because education is the only answer to misinformed accusations of criminal, nay "lunatic" conspiracy that somehow persist among Americans who need to be persuaded by this better informed opinion: "Right now, NASA’s annual budget is half a penny on your tax dollar. For twice that—a penny on a dollar—we can transform the country from a sullen, dispirited nation, weary of economic struggle, to one where it has reclaimed its 20th century birthright to dream of tomorrow."[7]. If there are aliens with a Radio telescope on a TRAPPIST-1 planet who follow Earth affairs, they are getting news of a new US President (named Carter), the test flight of Space Shuttle Enterprise, an air collision on Tenerife and the opening of George Lucas's movie Star Wars; on audio they hear the US debut of Pavarotti and the last concerts of The Supremes and Elvis Presley; and the aliens may be delighted to receive news of the Wow! signal event, and may know who sent it. Blooteuth (talk) 02:38, 24 February 2017 (UTC) Ok. That's all fine. I would not have balked at or collapsed a brief comment clarifying that the OP's link contained a lot of speculative art. The thing is, nobody asked for an essay on the value of art in science communication, or to comment on their fantasies. Yet that's what you're doing here. If you have a problem with NASA, take it up with them, but nobody here was even talking about flying to these planets or what they look like. OP and the rest of us were talking about the actual science and physics of exoplanets. I understand your points, I am somewhat sympathetic, and you really have provided some nice references. But I think you may be missing the point, which is that this is not a place to post unsolicited essays. That's called soap-boxing, and while it's good fun in real life and in some internet fora, we have explicit rules against it here. If you and Wnt want to keep talking about it, that's fine, I'll leave you to it. SemanticMantis (talk) 22:42, 24 February 2017 (UTC) Realistically, it is at least conceivable to make a Voyager-like probe that leaves the Solar system on a slow trajectory toward these worlds. If we could make a sufficiently durable probe, it would be possible that it could be loaded with certain very long-lived microorganisms with intent of dispersing them on arrival, polluting those planets and changing them. (Caveat: I don't know about the relative velocity of that system, and if it is too much all these ideas get ever more unlikely) This might permit Earth style life to endure, for better or worse, for a thousand times longer than it would otherwise. So it is not, even with near-present technology, particularly unrealistic to think about them. Now as for looking at them - we're getting better telescopes all the time, and their atmospheres are part of the transits of the stars. It may be very difficult but it is by no means impossible to figure out what compounds are in them, their approximate temperature, maybe even look for so-called signatures of life. And then... there are the very brave or very foolhardy people who like to send radio signals at things beyond our comprehension. Wnt (talk) 11:45, 24 February 2017 (UTC) Foolhardy yes, because like Lucy we may have some 'splainin' to do. The awesome introduction to "Contact" (video) plays the babble we have already transmitted in a sphere of radius 123 Light-years (counting from Guglielmo Marconi's transmissions in 1894) that is still expanding. See History of radio. Blooteuth (talk) 15:02, 24 February 2017 (UTC)

Can a human house provide shelter for the animals, and in return, the animals provide food for humans?

Spiders and insects can somehow come into the human-constructed house. Termites can chew on the wood. Rats can enter the house through the toilet or a rat hole in the structure. Then, there are the intentional animals, like cats and dogs and chickens. Some humans live in a rural area, so chickens can enter the house and get on the furniture. While cats and dogs and chickens probably cannot survive on their own, other animals can enter and leave at will. It seems that the human house functions like a little world. If the house provides shelter for these animals and attract animals because of food, then can humans take advantage of that and use the house to lure animals in instead of going after the animals in another place? 66.213.29.17 (talk) 16:58, 23 February 2017 (UTC)

Sure. Just leave the doors and windows open, and shoot anything edible that comes in. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:06, 23 February 2017 (UTC)

What sorts of references were you looking for? I'm unclear as to what additional information you want us to provide for you. --Jayron32 17:14, 23 February 2017 (UTC)

Yes, the human house is a little world. You might be interested in reading about Commensalism. Things like house centipede and house fly house mouse and flour beetle basically only exist in human-made environments. Flour beetles are edible, but usually considered a pest. Our article on entomophagy lists some other human commensal species, and if you'd like to learn more about bug eating, see this excellent article from the FAO [8], which describes how eating bugs can increase our food security. Some people do eat mice [9]. If you try attracting mice to your house to eat, let us know how that goes! SemanticMantis (talk) 17:19, 23 February 2017 (UTC)

• A traditional Swiss chalet, and many other vernacular architectures, was a form of farmhouse where dairy animals were kept inside the same building for at least part of the year. They would also need to be fed: this was done by fattening them through the Summer on good pastures outside, then keeping them indoors over Winter on stored hay or silage. They food they provided though would mostly be in the form of cheese - this was produced from the animals during the good feeding season, then could be stored for consumption during the hard Winter. Some animals (not just under this Swiss model) would also be consumed at Christmas feasts, in the earlier part of the hard Winter, and could then be either eaten at a last feast, removed from needing to be fed through the Winter, or could be preserved as hams, sausages etc.

The problem comes down to a food supply: many farming societies have kept animals in the same house during Winter, but they've not been able to feed them there, other than from stored food. I can't think of clear examples where the animals are kept "in the house" year-round, as there's no way to produce their food in-house too. Chickens or birds in a dovecot might be "indoors" year round, but they'd need to be fed on high-value cereals too.

Could you eat termites? Only if they're eating your house too. If I eat spiders, how do I get the flies to feed my spiders? My houseflies disappear in the Winter. Andy Dingley (talk) 17:24, 23 February 2017 (UTC)

Yeah, you run into basic energetics problems with closed system that's too small. Metabolic_theory_of_ecology may be of interest to anyone pursing such plans. (My desktop salticids seem happy year-round, and never have to leave throughout the winter. They don't need to eat that often. If I were concerned, I'd just leave some old bananas around ;) SemanticMantis (talk) 17:38, 23 February 2017 (UTC)

• My grandfather used to keep livestock in the basement, which served as pets for my mother and her siblings, until holiday dinner. μηδείς (talk) 22:49, 23 February 2017 (UTC)

I wonder if a set of beehives can be built around a small house, providing free heat and well-nigh unbeatable security. ;) But no one I know of has much experience training guard bees, you'd need broad vents for the summer, and you probably have to make your whole property a flower garden. Still, there must be a place to put one in a sufficiently whimsical work of fiction... Wnt (talk) 11:58, 24 February 2017 (UTC)

• This is a quite common system, called "rented flat". Nowadays, most of the animals pay cash or even by money transfer, but paying in kind is not unknown. --Stephan Schulz (talk) 12:54, 24 February 2017 (UTC)

They do. --IEditEncyclopedia (talk) 15:27, 24 February 2017 (UTC)

Intensive farming can be of many forms. But for the OP's " It seems that the human house functions like a little world." there is a problem - these intensive farming practices require food to be brought into the "house" from outside. For dairy, this is often high value food too, grown and manufactured at some cost. Andy Dingley (talk) 16:05, 24 February 2017 (UTC)

Kinetic energy, Momentum

Is there a Conservation of kinetic energy?

For example: An object $m_{1}=2kg$ moving at a constant velocity $3{\frac {m}{s}}$ , elastically collides with a resting object $m_{2}=1kg$ .

Let us say now that $m_{1}$ is resting and $m_{2}$ is moving at a constant velocity $6{\frac {m}{s}}$ . We get

$m_{1}{\vec {v}}_{1}=m_{2}{\vec {v}}_{2}\ \Rightarrow \ 2\cdot 3=1\cdot 6$

but

${\frac {m_{1}v_{1}^{2}}{2}}={\frac {m_{2}v_{2}^{2}}{2}}\ \not \Rightarrow \ {\frac {2\cdot 3^{2}}{2}}={\frac {1\cdot 6^{2}}{2}}$

This is impossible. Where was I wrong? יהודה שמחה ולדמן (talk) 17:53, 23 February 2017 (UTC)

What is your basis for concluding that it's wrong? Akld guy (talk) 18:18, 23 February 2017 (UTC)

You assumed the final velocities are 0 and 6 m/s. As you found above, those assumptions are not consistent with an elastic collision. Dragons flight (talk) 18:26, 23 February 2017 (UTC)

Looking at elastic collision might help. Dragons flight (talk) 18:29, 23 February 2017 (UTC)

I still don't get it. יהודה שמחה ולדמן (talk) 18:42, 23 February 2017 (UTC)

• Why would you think that ${\vec {v}}_{2}>>{\vec {v}}_{1}$ ?

We don't know ${\vec {v}}_{2}$ and it's hard to predict, without understanding details of the collision, such as the elasticity of the masses. This isn't trivial in theoretical kinematics, it's near impossible for practical experiments, except by making empirical measurements. But we do know that momentum is conserved and that the KE must be reduced: it can't increase, it can't even stay constant except for a theoretical and perfectly elastic collision. So we can put an upper limit on ${\vec {v}}_{2}$

${\frac {m_{1}v_{1}^{2}}{2}}>{\frac {m_{2}v_{2}^{2}}{2}}\ \Rightarrow \ {\frac {2\cdot 3^{2}}{2}}>{\frac {1\cdot v_{2}^{2}}{2}}$

${\vec {v}}_{2}<{\sqrt {2\cdot 3^{2}}}\approx 4.24$

Andy Dingley (talk) 19:05, 23 February 2017 (UTC)

But for the conservation of momentum we get that $v_{2}=6{\frac {m}{s}}$ . So why does the kinetic energy smaller? יהודה שמחה ולדמן (talk) 19:11, 23 February 2017 (UTC)

Sorry, can't typeset that quickly!

My ${\vec {v}}_{2}$ limit above is for the case you describe where $m_{1}$ is left at rest afterwards. What this proves is that $m_{1}$ cannot be at rest afterwards, from this collision. You can't set up any physical case where all momentum is transferred and the initial mass stops dead. Andy Dingley (talk) 19:15, 23 February 2017 (UTC)

You have two boundary conditions, which you can now solve for a possible physical case: momentum is conserved (it's conserved as a principle), energy is conserved (it need not be, but that establishes a boundary) but there is no axiom that one mass ends up stationary, and we've just shown that for masses like these it's not even possible for it to do so.

To solve this, and establish both ${\vec {v}}_{1}$ and ${\vec {v}}_{2}$ after the collision, solve the simultaneous equations that you have for momentum and energy. But don't assume ${\vec {v}}_{1}=0$ Andy Dingley (talk) 19:18, 23 February 2017 (UTC)

I think Andy Dingley has covered it, but I had to write it out a different way to really see it. Maybe this will help OP as well.

One problem is that you (the OP) have overconstrained the system by specifying both an elastic collision and the final velocities. By specifying an elastic condition, you have assumed that kinetic energy is conserved. In this case, use energy equivalence (and momentum equivalence) to calculate the final velocities. If instead you specify the final velocity, use this to calculate the final kinetic energy.

A second problem is that the final velocity that you have specified results in an increase in kinetic energy of the system, which is impossible without an additional input of energy. That some final velocities for m1 are impossible is a valuable result of the thought experiment IMHO.

A third, and more minor, problem is notation. Since you have both initial and final velocities for m1 and m2, labeling velocities as simply v1 and v2 can be confusing. Using v1i, v1f, etc. might make things clearer-Wikimedes (talk) 01:54, 24 February 2017 (UTC)

In case it was unclear, $v_{2}=6{\frac {m}{s}}$ with $v_{1}=0{\frac {m}{s}}$ is one way to conserve momentum, but there are an infinite number of ways to conserve momentum. For any choice of v2, you can find a corresponding v1 that allows the total final momentum to be equal to the initial momentum. An elastic collision means finding the values for v1 and v2 that allow both momentum and kinetic energy to be conserved. Dragons flight (talk) 08:38, 24 February 2017 (UTC)

Let's pick a convenient frame of reference: the one in which the total momentum is zero. This is the centre-of-mass frame (CM-frame). As the mass ratio of $m_{1}:m_{2}$ is 2:1, the speed ratio in the CM-frame must be 1:2, so ${\vec {v}}_{1}=1m/s$ and ${\vec {v}}_{2}=-2m/s$, the CM-frame itself moving at ${\vec {v}}_{CM}=2m/s$. In case of an elastic collision, conservation of both energy and momentum dictates there are only two solutions: the initial velocities, or both velocities reversed. As the masses don't move through each other without interacting, we know that after the collision ${\vec {v}}_{1}=-1m/s$ and ${\vec {v}}_{2}=2m/s$. Converting to the original frame of reference, we see that ${\vec {v}}_{1}=1m/s$ and ${\vec {v}}_{2}=4m/s$. PiusImpavidus (talk) 10:01, 24 February 2017 (UTC)

To directly answer the boldfaced question "Is there a conservation of kinetic energy": No there isn't. Energy can be readily converted from one to another form. For example, if a ball is launched straight up, kinetic energy is created from some other form of energy in the launcher (chemical potential, mechanical potential, electromagnetic, whatever); as it slows and stops under gravity, the kinetic energy is converted to gravitational potential energy (and a little is converted to heat, through friction with the air); when it falls again, the gravitational potential energy is converted back into kinetic energy; and when it hits the ground, the remaining kinetic energy is converted into heat and sound energy. --76.71.6.254 (talk) 21:00, 24 February 2017 (UTC)

Alright, to start off with I'm not that clear on your collision calculation. An object at rest doesn't have kinetic energy in that frame... maybe one is before and one after ... I didn't follow it. Anyway, the easiest way to solve these I think is to go into a frame where the net momentum of the colliding objects is zero. So 2 kg and 1 kg collide with one another while converging at 3 m/s. The rate of convergence doesn't depend on frame unless you want to go relativistic, and right now you're not ready for warp speed. So to make the momentum equal we need 2 kg to approach the center of gravity at 1 m/s and 1 kg to approach it at 2 m/s; both have 1*2 kg m/s momentum. They bounce off each other elastically so they carry away equal energy, and their total momentum doesn't change either, so we know they move away from each other at 1 m/s and 2 m/s the same way they came in. Now if we shift the frame so that the 1 kg object started at "rest" (adding + 2 m/s to the right, assuming it was on the right), it ends up with a speed of 4 m/s, while the 2 kg object starts at 1 + 2 = 3 m/s (as you said) and ends at -1 + 2 = 1 m/s. So the kinetic energy for the two at the beginning in this frame was 0.5(2*3^2 + 1*0^2) = 9, and at the end it's 0.5(2*1^2 + 1*4^2) = 9. The kinetic energy is indeed conserved in an elastic collision when looked at in any one inertial frame of reference, assuming the objects involved aren't doing work against (or being accelerated by) any other sort of force like gravity or friction. However, viewed in another frame it will be different, just as every object at rest can be viewed in a frame where it is moving. Wnt (talk) 22:25, 24 February 2017 (UTC)

The solution with 1 m/s and 4 m/s assumes one dimension, i.e. that after the collision the objects are moving along the same line as before. This doesn't have to be the case. See Elastic collision#Two-dimensional. The speeds can become anything from 1 to 3 m/s for the large object, and 0 to 4 m/s for the small. They need 2v₁² + v₂² = 18 (m/s)² to conserve kinetic energy, and there is no solution conserving momentum if v₁ < 1 m/s or or v₂ > 4 m/s. PrimeHunter (talk) 00:34, 25 February 2017 (UTC)

Quantifying change in equilibrium compositions in gas phase reactions from halving/doubling reaction volume

Hi, I just have to double check this. If I halve the partial pressures in the Haber process gas phase equilibrium constant, do I end up square rooting the equilibrium constant? But how wouldn't this apply in say, the solution phase for acid-base equilibria? (Changing reaction volume should affect gas phase reactions but not solution phase.) Yanping Nora Soong (talk) 22:10, 23 February 2017 (UTC)

Note I am trying to quantify the change not merely note the direction. Yanping Nora Soong (talk) 22:11, 23 February 2017 (UTC)

The answer to your first question is "no"; the equilibrium constant is a constant (unless changing the volume or pressure causes a temperature change as well, or your gases are far enough from ideal that you need to take fugacity into account). The change in equilibrium concentrations or partial pressures caused by a change in initial pressures is a different matter, and I would recommend looking up "equilibrium calculations" in a freshman chemistry textbook to see how this is done. It's not hard, but it wasn't obvious to me how to do it before I saw it done.--Wikimedes (talk) 01:21, 24 February 2017 (UTC)

OK, looking at Haber process I see that the equilibrium constants K_p we give are based on partial pressure of the gases, unlike the more familiar K_c based on concentration, but they work the same way. There is a molar fraction x_A of each gas, and the partial pressure of each is that times the total pressure in the container. Then as with the concentration variant, the concentration is equal to the concentrations of all the products over all the reactants, where multiple molecules count multiple times, so it's the square of the ammonia concentration over the nitrogen multiplied by the cube of the hydrogen. The constant stays the same ... unless, as our table shows, the temperature is changed, because then the entropy term changes while the enthalpy stays the same. Wnt (talk) 22:09, 24 February 2017 (UTC)

February 24

Blood meal

The blood meal article says that the substance is useful for repelling garden pests such as rabbits. How does that work? Using Google, I found nothing more scholarly than http://creekbed.org/bandh/pest.html, which claims that rabbits smell the blood and are repelled by its scent. Nyttend (talk) 01:01, 24 February 2017 (UTC)

Right, I also find lots of ads and patents, but not much in the way of true scientific discourse. I did ultimately find this review of animal repellent studies, which includes a couple of studies that found "intermediate effectiveness" for blood meal as a deer repellent. Someguy1221 (talk) 01:16, 24 February 2017 (UTC)

One possible mechanism would be if the smell of blood indicates the possible presence of a predator nearby, and those prey animals which avoid such areas are more likely to survive and pass on those genes. StuRat (talk) 05:59, 24 February 2017 (UTC)

How to find references, for anyone who might be curious

Let me let you in on a secret. I don't have any references right now. I'm also not sure what the mechanism is. I don't know the answer, but I'm a smart person, and I have some ideas. But I'm not going to post anything. Let me do a little work, and I'll be back when I have references to share. SemanticMantis (talk) 20:35, 24 February 2017 (UTC) Ok, I'm back. I searched google scholar, starting with /"blood meal" pest deterrent/. That search wasn't all that useful, because "blood meal" is also what they call it when a mosquito or bedbug gets a meal of blood, and there is tons of research on that stuff that has nothing to do with vertebrate pest repellent. So I though maybe putting a vertebrate in would help, and also maybe "pest". Take out the quotes on blood meal since that means a thing I don't want. So I searched /blood pest deter deer/ [10], which led me to three very good references, which together will give OP access to a lot of real scientific findings about if and how this works. SemanticMantis (talk) 20:49, 24 February 2017 (UTC) And now I've skimmed the articles, pulled out some quotes, and added a few wikilinks. The post below has a few key features:1) it took me more than thirty seconds to do. In fact it probably took me at least twenty minutes, not counting this explanatory text and some other things I was up to in the intervening interval. 2) it contains relevant references both external reliable sources, and also to wikipedia. 3) It gives OP plenty of directions to go if they want to learn more 4) I offer no opinions. Now, I'm not saying that you or anyone else has to do all this. In fact, nobody has to post here at all. However, I hope that by explaining my process, people can learn how to provide helpful and well-referenced responses here, because that is what this desk is for. While posting of opinions and memories and hazy recollections and possibilities and the-way-that-one-guy-thinks-things-work are all very different, all well-referenced posts here are ultimately very similar, in that they share the four traits that I outlined above. SemanticMantis (talk) 21:13, 24 February 2017 (UTC)

Here is a freely accessible comparative study, from 2010 [11]. It says "While urine and blood-based repellents were somewhat effective in short-term pen studies, they were less effective in field studies." So maybe not the best stuff, but blood does have some beneficial effect against deer.

For mechanism, this study [12] tested "Four repellents representing different modes of action (neophobia, irritation, conditioned aversion, and flavor modification)". The experimental "data support previous studies indicating that habituation to odor limits the effectiveness of repellents that are not applied directly to food, while topically-applied irritants and animal-based products produce significant avoidance. The paper discusses mechanisms in several places, with additional references. Finally, this short work is all about the concepts of how vertebrate repellents work, and is definitely worth a read: Vertebrate repellents: mechanisms, practical applications, possibilities. [13]. SemanticMantis (talk) 21:03, 24 February 2017 (UTC)

How much vitamin b12 fortified foods must be eaten as a replacement for animal products?

Drinking fortified plant milk at every meal? How long can a human live healthfully without them? 107.77.194.188 (talk) 16:50, 24 February 2017 (UTC)

US RDA of B12 for non-lactating non-pregnant adults is 2.4 micrograms per day. The German RDA is 3 micrograms per day. You would need to look at how much B12 there is in a serving of the milk you're drinking, and calculate accordingly. Vegans suggest that 3 servings of fortified foods per day usually gets you the RDA. - Nunh-huh 17:21, 24 February 2017 (UTC)

Or, the simple solution is to just take a B12 supplement. As our article on Vitamin B12 discusses, it's impossible to give a one-size-fits-all answer to "How long can a human live healthfully without them?", because the body can store a good deal of B12, so it depends on diet, genetics, history, etc. Obviously, if you have or suspect you have a B12 deficiency, consult a medical professional; deficiency can be caused by things other than lack of B12 in the diet, in which case oral supplementation often won't do anything to treat the deficiency. --47.138.163.230 (talk) 21:35, 24 February 2017 (UTC)

• It's a matter of current research (i.e. no-one really knows) how important B12 is, and how frequently it needs to be administered. If you suffer from chronic fatigue, linked to a B12 deficiency, then you're likely to be prescribed a dietary supplement and if that doesn't have an effect, intramuscular B12 injections. Then opinions vary: there is some indication that some people (likely those suffering from the chronic fatigue) are unable to absorb B12 at the normal rate (and so the standard RDAs are too low for them) even if they're ostensibly getting an "adequate" supply. Also conventional models suggest intramuscular B12 at intervals of months, whereas those reporting the fatigue see a boost and tail off on a cycle of weeks, suggesting that more frequent doses are needed.

In general, B12 is available in a good diet in such quantities, and is only needed at such a low level, that there isn't a problem. But when there is a problem, this has been explained previously as a dietary shortage when there is now indication that it's also (and particularly so for the chronic fatigue cases) at least as much a metabolic issue of utilising what the diet does provide.

B12 is an obvious issue for vegans, and one of the very few real dietary issues for a decent Western vegan diet. Yet some doctors, particularly in the US, see this choice as tantamount to asking for poor health and will simply fail to engage with vegans, or tell them outright that a vegan diet is an inevitable cause of weakness and imminent death. The Vegan Society is a bit more balanced. https://www.vegansociety.com/resources/nutrition-and-health/vitamins-minerals-and-nutrients/vitamin-b12-your-key-facts/what-every-vegan-should-know-about-vitamin-b12 Andy Dingley (talk) 16:10, 25 February 2017 (UTC)

Why is human intention regarded as unnatural?

Natural selection is a different concept from artificial selection. Why are "natural" perceived as good, while unnatural is not good? Why are human culture and technology regarded as artificial while chimpanzee culture and technology are natural? Are the tools made by Homo erectus also artificial? Since everything made by humans stems from the human brain, and the brain is natural, shouldn't everything "artificial" or "synthetic" be natural? 107.77.192.233 (talk) 23:28, 24 February 2017 (UTC)

A is a proper subset of B.

One possible way to resolve the dilemma is if artificial selection is viewed as a proper subset of natural selection. In other words, whatever people do is both natural and artificial. As to why they are normally considered to be mutually exclusive, remember that it's only quite recently (in terms of language development) that the Theory of Evolution was proposed, and it still is far from globally accepted. StuRat (talk) 23:39, 24 February 2017 (UTC)

It took natural selection 4 billion years to make humans. It took only 0.005 billion years for humans to surpass the natural record in many things like creature power, speed, game complexity, cause the Sixth Mass Extinction, almost cause a worse one (nuclear winter), terraform much of the surface and maybe disassemble most of the observable universe with grey goo (though they could only dismantle the galaxy by 0.0001 billion years AD due to the speed of light) Sagittarian Milky Way (talk) 00:08, 25 February 2017 (UTC)

(edit conflict) Yes, technically speaking, everything humans do is part of nature, though we tend to set ourselves apart from the rest of the natural world for various reasons (nature is something to be conquered, humans are exceptional beings, etc.). There's a lot of discussion about why that is. Here's some further reading: [14], [15], [16]. See also environmental philosophy. clpo13_(talk) 00:12, 25 February 2017 (UTC)

(ec, or then again, someone here might just come through! Thanks Clpo13, looks interesting!) This seems like a very important but very difficult philosophical question. To some extent I would suspect it is cosmetic, but rooted in the tendency of life to optimize to a situation. A barren volcanic flow or a meteor impact seems less "natural" than a jungle. But to a large extent it might depend on the nature of free will itself, and its ability to create genuinely new things. It might depend more simply on the ability of cognition to recognize and favor novelty, but I'm skeptical that's the full explanation. You might have better luck (like properly referenced answers) on the Humanities desk, because this is the sort of thing Mephistopheles would say is not of his kingdom. You need something past science, I think. Wnt (talk) 00:19, 25 February 2017 (UTC)

"Natural" does not inherently equate to "good". ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:32, 25 February 2017 (UTC)

All-natural lava. Yummy! Sagittarian Milky Way (talk) 01:17, 25 February 2017 (UTC)

"Nature" in this context is a philosophical concept, it's an idea dreamed up by men. And "Nature" as used philosophically has several meanings. One of them is the inherent or defining properties of a thing. A thing (other than man) has inherent or defining properties not dependent on human action, so if one wants to know the "nature" of a thing one is necessarily studying that thing in the absence of human intervention. - Nunh-huh 01:31, 25 February 2017 (UTC)

Nature is neither good nor bad, it just is what it is. Woody Allen once described nature as "basically a gigantic restaurant." ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:05, 25 February 2017 (UTC)

This is related to the fact that people don't see themselves as biological machines subject to the laws of physics, many people are skeptical that machines could ever have human level intelligence. These feelings are not based on reality, but we do feel as if we're not part of Nature but rather are above it and are able to manipulate Nature as a sort of God. Count Iblis (talk) 03:39, 25 February 2017 (UTC)

Related to the myth that "natural" (whatever that means) is good, see naturalistic fallacy and appeal to nature. Someguy1221 (talk) 04:28, 25 February 2017 (UTC)

• If you're talking about evolution specifically, there are important differences between natural selection and artificial selection. Natural selection has no goal - mutations arise at random, and some survive for various reasons (helping a creature to survive or reproduce is the main one, but there are weird effects like sexual selection and genetic drift happening too), but there's no final destination and no deeper reason. Birds didn't evolve wings so they could fly - instead, they seem to have been creatures that lived in a forest with lots of trees to jump off, and they gradually evolved featherier arms and stronger chest muscles because creatures that had these were better at hunting and escaping predators, until one day this jumping and gliding became actual flight. Artificial selection however usually has a goal - to maximise the size of grains, maybe, or produce dogs that are loyal and intelligent. A bulldog has a squat face because this makes it easier to bite into the side of a large animal, and bulldogs were selected by breeders to have this feature. Maybe from a godlike perspective this is the same thing (bulldogs evolved squatter faces because the ones that didn't got castrated by a species of hairless ape), but when analysing evolution from a human perspective, this is an important ontological difference. Smurrayinchester 10:17, 25 February 2017 (UTC)
  • Artificial selection still operates within the "natural" genetics that the individuals already have. Compare that with genetically modified organisms, which involve really "playing God" by inserting genetic material that could never be there via cross-breeding within a species. That's an argument you'll see against GMO's vs. "conventional" breeding. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:14, 25 February 2017 (UTC)

Not really true. Artificial selection tends to be a key part of mutation breeding (including atomic gardening for example) where it's highly questionable to say you're referring to "natural" genetics the individual already have. I mean they have them sure, but only because you mutated the hell out of them to get it. Or to put it a different way, why is [17] (taken from [18]) so natural but any GMO isn't? Note that artificial selection and conventional breeding are not the same thing. Artificial selection is part of conventional breeding, but artificial selection may also be used as part of producing a GMO. Also GMO tends to cover both cisgenesis and transgenesis. Finally even with transgenetic organisms, this doesn't mean the genetic material could never be there with GMO. Depending on the complexity of the change, it may be possible to produce this somehow, perhaps by mutagenesis or looking through a wide database. It has been suggested that GM could be used as proof of concept before you spend the incredible time and resources to produce the same thing via conventional breeding somehow. Technically there would still be some small differences, particularly if you a marker is still hanging around but this isn't what you referred to. Nil Einne (talk) 16:30, 25 February 2017 (UTC)

How would you be able to get Bacillus thuringiensis genes into a maize embryo via conventional cross-breeding? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:26, 25 February 2017 (UTC)

February 25

Feynman Lectures. Lecture 49. Ch.49-4. [19]

...

There would be, if there were no spring, a certain natural frequency ω0 for this one alone. The equation of motion without a spring would be
$m\,{\tfrac {d^{2}x}{dt^{2}}}=-m\omega _{0}^{2}x.$

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

How have he derived that? If we have a coordinate system with upward Y and rightward X , then:
$m{\tfrac {d^{2}}{dt^{2}}}x=-{\tfrac {x}{L}}T$
$m{\tfrac {d^{2}}{dt^{2}}}y=-{\tfrac {y}{L}}T-mg$
$x^{2}+y^{2}=L^{2}$
$T+mg{\tfrac {y}{L}}-{\tfrac {mv^{2}}{L}}=0$
Putting the 4th eq. to 1st :

$m{\tfrac {d^{2}}{dt^{2}}}x=-{\tfrac {x}{L}}(-mg{\tfrac {y}{L}}+{\tfrac {mv^{2}}{L}})=-mx({\tfrac {-gy+v^{2}}{L^{2}}})$
But I can't see that $\omega _{0}^{2}=({\tfrac {-gy+v^{2}}{L^{2}}})$. Moreover if initial conditions are $x(0)=L,y(0)=0,v_{x}(0)=0,v_{y}(0)=0$, then $\omega _{0}=0$ and at the bottom point ($y=-L$) $\omega _{0}>0$. Username160611000000 (talk) 09:39, 25 February 2017 (UTC)

Since Feynman talks about a single equation of motion, this suggests we simplify the problem to a one dimensional one. If we work in polar co-ordinates then the distance from the pivot, r, is constant (it is always L) and we have just one equation of motion in θ, the angle of the pendulum from the vertical. This is derived in our article pendulum (mathematics). Note the approximation for small θ which makes the equation linear.:

${\frac {d^{2}\theta }{dt^{2}}}=-{\frac {g}{\ell }}\theta$

which has the same form as Feynmann's equation with

$\omega _{0}^{2}={\frac {g}{\ell }}$

This is an example of simple harmonic motion. Gandalf61 (talk) 10:24, 25 February 2017 (UTC)

Hm. Thank you. In the small angle approximation $({\tfrac {-gy+v^{2}}{L^{2}}})={\tfrac {+gL+({\tfrac {dx}{dt}})^{2}}{L^{2}}}$. And so we must put $({\tfrac {dx}{dt}})^{2}=0$. But is it correct? If x is small there is no guarantee that $({\tfrac {dx}{dt}})^{2}$ is small.Username160611000000 (talk) 11:57, 25 February 2017 (UTC)

Taste of VX

I heard a report of VX (nerve agent) being tasteless and wondered how we could know. The article itself has a [further explanation needed] tag. Could you explain? --Error (talk) 15:43, 25 February 2017 (UTC)

Since treatment is possible, it may well be possible to ask the victims if they tasted anything. A more inexplicable case is in the article on radon, where Rn is described to be tasteless; although this is stated in some actual reliable sources, it still sounds rather silly because if there was enough Rn around to taste, the alpha radiation from its decay would presumably be much more significant. Double sharp (talk) 16:01, 25 February 2017 (UTC)

Since it's tasteless, "if there was enough Rn around to taste" is an impossible condition. Henry^Flower 16:35, 25 February 2017 (UTC)

Well, being an unreactive noble gas, it is almost certainly tasteless, but what would be interesting to see how this could have been verified experimentally. Double sharp (talk) 16:41, 25 February 2017 (UTC)

There are plenty of reliable sources to confirm that it is tasteless, but nobody says how they know that, as far as I can tell. Alansplodge (talk) 18:25, 25 February 2017 (UTC)

The taste and smell of chemical weapons is a matter of some importance, as even human noses are a pretty good early warning system. Also practically every agent, even the post-war nerve agents, isn't that toxic - you can smell these things and survive, especially if you use the warning to run.

The taste/smell is known from a few sources: someone tasted it by accident and their last words were "tastes like chicken" (there are a few of these) or simply that they didn't notice any distinctive smell, the structure is close enough to less toxic analogues with recognisable smells that it can be inferred, or if the material's physical properties aren't volatile enough at ambient temperatures, it can be assumed to have little or no practical smell (it might smell of something if heated, or in concentration).

Most nerve agents simply don't smell though - their function is to be hazardous at such low concentrations that they need not be odorous. Andy Dingley (talk) 19:51, 25 February 2017 (UTC)

Having fewer early-warning signs makes it a better weapon too. See for example Phosgene#Chemical warfare. Another article I remember mentioning that a certain chemical-weapons agent that had noticeable odor was doped with another easily-smelled chemical to mask the odor, leading to the opponent recognizing the innocuous odor as the sign of a chemical weapon attack, but I can't find the article at the moment. DMacks (talk) 21:47, 25 February 2017 (UTC)

The US Army's Edgewood Arsenal has infamously done several human volunteer trials on nerve agents. There are people who claim the UK's biological/chemical defense labs at Porton Down performed similar research in human volunteers. Smell and taste are phenomena which occur at chemical concentration levels much lower than lethal cholinesterase inhibition caused by nerve agents. For VX, the LCt₅₀ for inhalation is estimated to be 30–50 mg·min/m³.

So it's plausible, at least, that a human volunteer did indeed inhale a sub-milligram dose of VX and live to tell the tale. Or at least report his impressions before dying. loupgarous (talk) 01:48, 26 February 2017 (UTC)

Porton Down did do experiments on humans, see Ronald Maddison. Widneymanor (talk) 09:02, 26 February 2017 (UTC)

That was Sarin though, not the V agents. These are too toxic (V agents maybe 10× the G agents) for such skin exposure experiments and their development also post-dates the abandonment of such testing. Although remember that they were developed as insecticides: Amiton (it's good against mites) was sold as such in the early '50s.

The point here though is that even a skin drop exposure is considerably more exposure than a potential smell. Andy Dingley (talk) 11:29, 26 February 2017 (UTC)

The newly discovered 7 earth size planets II

I am beating a dead horse. It is about this Internet cnn article: [20].I want to describe my motivation. I don't believe there is another planet in the Galaxy with intelligent life. I think the development of such life here on Earth was a result of events with extremely low probabilities, like acquiring mitochondria by unicellular organisms, so I wonder why people are so optimistic about those 7 planets. I just posted here in this desk a couple of days ago [21] Now I have a different question though. Those planets are so close to the star they must experience significant tidal forces. The magnitude of them should affect the chance for any life to develop. Could they be calculated? Thanks, - --AboutFace 22 (talk) 16:42, 25 February 2017 (UTC)

Tidal forces may be able to be calculated, but we don't understand abiogenesis nearly well enough to calculate how any particular force would affect liklihood of it occurring. Also: I wouldn't say the scientists are "optimistic", I'd say they are excited about interesting new things to look at. Popular press coverage is often breathlessly excited hype with little grounding in science or reason. Blooteuth had a lot to say about that and some good refs in the previous post, look there for more on that. SemanticMantis (talk) 17:57, 25 February 2017 (UTC)

Why the assumption of rarity? Forgetting intelligent life (since we don't have a lot of examples to look at), endosymbiosis seems to have happened at least twice in Earth biological history. --OuroborosCobra (talk) 18:12, 25 February 2017 (UTC)

Indeed. According to endosymbiont, many times.--Wikimedes (talk) 19:49, 25 February 2017 (UTC)

Multiverse theories would suggest that we live in a universe where the probability of our existence is maximized. So, if creating life in the lab is hard then that's probably only because life arising in a too easy way would have interfered with the development of more complex life that could give rise to us. Count Iblis (talk) 19:25, 25 February 2017 (UTC)

I would like to know what the magnitude of the tidal forces on those planets are. It is all speculation on my part but most of the answers so far, e.g. about the multiverses, etc. are even more speculative. So, if the tidal forces are high then first, the planets may have a lot of internal heating occur. What's the surface temperature then? Suppose one of the planets has water oceans and some land mass. If the tidal waves are high, the oceans may easily roll over the land mass every other day or so. If this is true, if the tidal forces are problematic, a certain class of earth size planets could be ruled out of consideration.

I want to give a real life example for comparison, just to appreciate the "magnitude" of very, very low probability events. It concerns Sporadic Creutzfeldt-Jakob disease. It affects prions, the structural proteins in all living forms. Imagine how many cells are in a human body, and each cell has countless number of prion molecules. They are subject to dying and regeneration, plus during the earlier development billions of them are created. This process is flawless, ALMOST. Once in a billion billion replications a quantum tunneling occurs and bingo, a misformed prion is made. It has a terrible property to convert all neighboring similar prions into this misformed state and the individual dies. Different species apparently have different probability of such an occurrence but in humans it is very low. Now listen here. At the end of WWII when missioners penetrated inner parts of New Guinea they found a tribe where almost everyone had this disease but it was not sporadic. They infected each other. It was calculated that the first case happened in 1910 and it was sporadic. Those people lived there for thousands years and never had Creutzfeldt-Jakob. Each of them had billions of prions which for generations were normal. And all of a sudden in 1910 that incredibly low probability event occurred. My point is that acquiring the mitochondria could have been even a much lower probability event the true frequency of which we don't know.

Homo sapiens developed in Africa but not in the Americas. The Americas haven't even had apes. There is one ape species in Asia but not intelligent development beyond that. This is one more strange probability that may not happen elsewhere ever again. --AboutFace 22 (talk) 21:26, 25 February 2017 (UTC)

We can speak of tidal forces in the TRAPPIST-1 system but these may be only stresses in planetary rock material; ocean tides such as we see on Earth would only be possible if liquid water (possibly on any of the 3 planets in the "Goldilocks" zone) is confirmed. We have estimates of the individual planet masses and orbits but I do not see any solution of the 8-body system that would yield an orbital almanac or Ephemerides that would be the basis for calculating tidal forces. Individual orbital periods ("years") seem short at mostly under 20 days but if the orbits are not in a simple resonance, there may be much longer time between tidal maxima than the time we have been observing the system. Note that gravitational forces are inversely proportional to the square of the distance but tidal forces are inversely proportional to the cube of the distance; the significance is that if a TRAPPIST-1 system resident were observing Earth and wondering about our tides, (s)he/it would very likely miss our tiny Moon that due to its relative closeness exerts more than double the tidal force of our Sun. Actually the near equal inclination of all 7 TRAPPIST-1 orbits is consistent with the planets being the result of the breakup by tidal forces of a previous single body, and after such short observation we don't know whether we are looking at a stable orbital system. It is not possible to make statements about chances for life to arise without invoking one's own belief system. The scientific community favours a variety of Abiogenesis mechanisms followed by a hardly-to-be-questioned evolution of the species₁ that culminates in ourselves₂. That is the background of the sourced statement here "All seven planets are likely to be tidally synchronized (one day = one year) making the development of life there "much more challenging". To the implicitly assumed Western tenet that Abiogenesis precedes Consciousness I respond with the opposing view expressed in Tibetan Buddhism that conscious existence predates the existence of bodily life. To read further: Gentle Bridges - Conversations with the Dalai Lama on the Sciences of Mind 1992, Random House / Shambhala Publications. Quote: "Buddhists cannot accept (the scientist's view) that consciousness arises from a material cause." Blooteuth (talk) 21:50, 25 February 2017 (UTC)

Note that when the Moon formed it was ten times closer to Earth and the tidal forces were as a consequence a thousand times stronger than what they are today. Count Iblis (talk) 22:53, 25 February 2017 (UTC)

Tidal forces vary with the cube of the distance ? I would have expected the square. Do you have a source for that ? StuRat (talk) 04:32, 26 February 2017 (UTC)

Yes, tidal force is approximately inversely proportional to the cube of the distance, since it depends on the difference between the gravitational force between two points. See the last equation in our tidal force article.

It should be noted that some theories of abiogenesis suggest that tides were beneficial or even essential to the development of life on earth [22]. By these theories, "water rolling over the land every other day" is a good way to get life started, since the prebiotic chemicals get concentrated in the drying tide pools. CodeTalker (talk) 05:02, 26 February 2017 (UTC)

Thanks. Does that mean (water) tides would be 1000 times higher ? StuRat (talk) 05:09, 26 February 2017 (UTC)

Yes, but the initial distance between the Earth and the Moon is believed to have been more like 60% of the current distance, not 10% a good summary of the thinking here. So more like 4.6 times higher, rather than 1000 times higher. I'm pretty sure I'd have remembered something about kilometer high tides. Someguy1221 (talk) 09:29, 26 February 2017 (UTC)

There is unlikely any tidal force at all because the planets dont rotate around their own axis but are in Synchronous rotation aka Tidal locking to the sun, like our moon orbits earth, always showing the same side to us. In such narrow orbits this tidal locking is very likely. This is also assumed for the closest known exoplanet Proxima Centauri b. --Kharon (talk) 12:20, 26 February 2017 (UTC)

Io (moon) is in a locked orbit and it experiences significant tidal heating due to the excentricity of its orbit. To quote from the discovery paper: "The TRAPPIST-1 system ...represents a unique opportunity to thoroughly characterize temperate Earth-like planets that are orbiting a much cooler and smaller star than the Sun, and, notably, to study the impact of tidal locking, tidal heating, stellar activity and an extended pre-main-sequence phase on their atmospheric properties." Scientists are optimistic that all these things (including detection of signatures of life IF there is life) can be studied in the system, but the investigations have only begun. --Wrongfilter (talk) 12:47, 26 February 2017 (UTC)

@Kharon is correct that there are no tidal forces when only 2 bodies orbit circularly around their common center of mass, and each rotates once per orbit. That is a classic soluble Two-body problem. However each body (planet or sun) of the TRAPPIST-1 system is pulled by gravity to each of the other (known) 7 bodies. Nobody promises that Celestial mechanics is easy; Celestial mechanics#Perturbation theory suggests where the work is needed on this thorny n-body problem. The article Orbital mechanics gives specific mathematical solutions. You may however enjoy the beauty of some demonstrable multi-body orbital solutions of the choreographic kind, or sketch your own, on this Java page. Blooteuth (talk) 13:38, 26 February 2017 (UTC)

Extra visual colors via eye tracking?

As I understand it, some of the VR applications? or other equipment coming out do eye tracking where they have a good idea of where the user is looking. It just occurred to me that maybe this isn't entirely for spying on people after all...

Suppose a reader frequently looks at a high resolution computer screen (or, ideally, set of binocular computer screens) that displays video content. The reader is color blind. A camera very closely tracks where he is looking, and superimposes a fine-grained pattern that goes wherever he is looking. The fineness of the grains depends on how accurately it can follow his gaze, the resolution of the system, and whether it's binocular. In half the superimposed pattern, the screen content is changed to exclude the green channel - in the other half, to exclude the red. As a result, there are small fixed regions within his vision, so long as he uses the computer, which are "red-sensitive" and others which are "green-sensitive" - perhaps with some degree of channel mixing to help them appear as one image; after all the red-green receptors themselves have overlap.

Now I've read that people can get used to looking at the world rotated 180 degrees, so I'm thinking maybe in time, supposing he has a heavy computer job for example, or the system is made a standalone prosthesis, that is all it takes to perceive different green and red color values. The person's eyes might learn to process the colors differently and he might even see them as different colors subjectively.

Some time after the experiment, I'd expect these regions to return to normal; if the experiment were repeated with a different set of random regions, I wonder if the person could relearn to see the difference between green and red in those new areas. Would green and red seem like different colors subjectively than they did the preceding time?

Of course, there's nothing in principle to keep the same experiment from being done by people who have normal 3-color vision who want to get a taste of the tetrachromat life.

Is there anything to back up any of this, and is anyone working on such lunacy? I take the X-mosaicism tetrachromats to support the idea of learning to link regions to colors can be done by simple random differentiation - is that sound, at least? Wnt (talk) 21:43, 25 February 2017 (UTC)

There's certainly work being done on representing colours via other senses: see e.g. this abstract. (Note however the mention of "low spatial resolutions"). I can't see the whole paper, but e.g. this article covers some of the same research and does say that the input can be perceived as colours (caveat again: the systems can take a long time to learn to use). Henry^Flower 22:32, 25 February 2017 (UTC)

Eye tracking describes techniques for a real-time experiment. False color images can render non-visible parts of the Visible spectrum or simulate the effect of Color blindness. Blooteuth (talk) 22:54, 25 February 2017 (UTC)

I believe that eye-tracking has been used experimentally to generate the perception of impossible colors. -- The Anome (talk) 14:15, 26 February 2017 (UTC)

February 26

Stereochemistry

This question is the result of reading Oxcarbazepine and Carbamazepine, and noticing from the infobox imagery that O... seems to be C... with an extra oxygen attached to the central ring.

How do we determine the specific structural formulas of not-so-simple molecules? I remember from high-school chemistry that the empirical formula is derived from breaking down the molecule (e.g. electrolysis of water yields twice as much hydrogen as oxygen), and I suppose that the basic chemical formula can be derived from a ratio of the empirical formula to mass (e.g. hydrogen peroxide will be twice as massive as peroxide, despite producing the same hydrogen/oxygen ratio), but neither one tells us anything about the shape. Based on the comments about Pasteur in the stereochemistry article, I'm guessing that the theoretical shape is the result of directly observed physical properties, but with molecules the size of these two anticonvulsants, I wonder how adding one oxygen would produce a molecule with distinctly different physical properties that can be determined to be independent of its chemical properties. The article refers to Stereoisomerism, so maybe my answer is there, but the article's technical enough that I don't understand it. Nyttend (talk) 12:30, 26 February 2017 (UTC)

How to hasten the separation of oil from peanut butter?

I made my own peanut butter by grinding up nuts but it's too thin. Apparently if you let it sit for a long time, the oil rises to the top and can be poured off, leaving something more viscous. How could this be easily hastened? Would vibration on top of a washing machine make it better or worse? I can't really strap it down inside the washing machine. ----Seans Potato Business 12:52, 26 February 2017 (UTC)

How far ahead can the weather be predicted with reasonable accuracy?

With the best models in use today for weather forecasting, how far ahead can the weather be predicted with reasonable accuracy? --100.34.204.4 (talk) 14:15, 26 February 2017 (UTC)