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July 29[edit]


The question is straightforward: should inventory control be merged with Inventory control system?Lbertolotti (talk) 01:29, 29 July 2015 (UTC)

Have you tried discussing that on those articles' talk pages? ←Baseball Bugs What's up, Doc? carrots→ 03:00, 29 July 2015 (UTC)

Yes, so far nobody said anything.Lbertolotti (talk) 03:13, 29 July 2015 (UTC)

@Lbertolotti: Although there is no real harm in raising the issue here, the Ref desks are not really the ideal means to solicit additional opinions as relates to the best policy approach to an issue on an article. I would recommend you explore Wikipedia:Proposed mergers, WP:RfC, and (for this particular case) Wikipedia talk:WikiProject Business. The first is a noticeboard to promote merger discussions, the second is a process page which will guide you in how to attract outside input to article talk page via a method known as a "request for comment", and the third is the talk page for a Wikiproject (collection of editors with a common interest) for business-related articles. One of these methods should surely attract some attention to your request for additional input. And, of course, if you feel very confident that you have reviewed the relevant policies and that a merger would be warranted in this instance, you could always WP:BEBOLD and institute the change yourself (since no one has commented despite your best efforts to raise the issue on the talk Page) and then if someone objects or reverts the change, you can invite them via their user talk page to comment on the article talk page so you can get their views and a better feeling of how to proceed. Regardless of which route you choose, I applaud your efforts to approach the change in a slow and cautious manner and to go above and beyond to seek additional input and consensus.  :) I will give my own opinion on the talk page shortly, but you should keep the above methods for outreach in mind for the future. Snow let's rap 09:51, 29 July 2015 (UTC)


I'm updating the pictures description, if there's no objection. Lbertolotti (talk) 01:34, 29 July 2015 (UTC)

The handedness of a dead body[edit]

Could a coroner tell if the person was left-handed or right-handed? Anna Frodesiak (talk) 06:13, 29 July 2015 (UTC)

It is possible if the dominant hand was used in repetitive activities, such as archery or metalworking, as the musculature will develop more and produce bone deformities. I'd say (not being a coroner but being a physical therapist) that modern life in general doesn't produce such gross deformities, the evidence would be more nuanced. --TammyMoet (talk) 08:42, 29 July 2015 (UTC)
I am not a coroner, but if I were asked I'd check the middle fingers for calluses. There is likely to be one on the dominant hand, caused by writing. DuncanHill (talk) 08:50, 29 July 2015 (UTC)
That might be harder to do these days, with people doing less writing: I can't see any obvious external differences between my middle fingers, though perhaps an export could. According to this, "[Forensic anthropologists] can tell whether the person was right or left-handed. There would be more muscle attachment on the bones on the dominant side". By the way, a coroner is a legal officer (at least in the UK), so they would not be the one doing the physical investigation. AndrewWTaylor (talk) 08:57, 29 July 2015 (UTC)
Use of a mouse on a computer affects the wrist, indicating handedness. Constantly moving a finger over a screen causes a callus, indicating handedness. That does not include muscle mass. Most people are stronger in their dominant arm. In boot camp, everyone had to work out. It was easy to identify the left handers because they had trouble lifting weights in the right hand that were easy in their left. For everyone else, lifting weights in the left hand was harder (except for the two who were body builders previous to boot camp, one put on weight control specifically to lose muscle mass). (talk) 16:11, 29 July 2015 (UTC)
Not sure this would be deterministic. My father is left handed and before wireless mice made switching easier, he simply used his right hand. I am right handed but left eye dominant so some things like shooting a rifle is left handed, while a pistol is right handed. I use the wireless mouse on the right side, but the dot mouse on the laptop I use my left index finger. Not sure why, it's just natural for me and it's not ambidextrous where I can use my right finger for the dot mouse or my left hand for the wireless mouse. Could be just training. rather than handedness. --DHeyward (talk) 21:21, 29 July 2015 (UTC)
  • Many things could interfere with such presumptions. I generally carry heavy things with whichever arm has less joint pain that day. When I'm at my computer and not typing, my right hand generally rests on the arrow keys and my left hand on the mouse, so that my mousing hand has less far to move to reach the letter keys. When I shoot a pistol one-handed, my ‘wrong’ hand is steadier. — There is a faint difference between my middle fingers, but nothing like the very obvious groove I had at age 16; I no longer grip a pen with such force! —Tamfang (talk) 06:58, 31 July 2015 (UTC)
These arguments are anecdotes vs data. Suppose I take a million computer users. I identify a spread in the wrist bones on 90% of them due to mouse use and verify that the hand use for their mouse is the hand they normally use for everything. I can then state that, after identifying a spread in the wrist bones, I am about 90% confident in identifying the handedness of the person. I work with this type of argument every day. For example, over 99% of people who have an HbA1c>6.5% are diabetic. Still, people want to talk about an anecdote about some guy they heard of who had an HbA1c of 8%, but wasn't diabetic. Therefore, they think they've invalidated the millions of other data points that support using HbA1c to identify diabetes. They are wrong, very wrong. In other words, the plural of anecdotes is not data. (talk) 16:55, 31 July 2015 (UTC)
  • With all due respect, I don't see much in the way of hard data here; it's mostly anecdotes vs conjecture. —Tamfang (talk) 06:56, 1 August 2015 (UTC)
Agree entirely.

I actually know someone who's right handed but because of RSI related problems started using the mouse left handed. I would agree however this is likely a real minority, but "likely" is very different from hard data. In particular, I'm far from convinced the percentage of people who are left handed and who uses the mouse left handed is anything close to 90%.

I found this survey which has a number of activities. [1] The activities where over 90% of left handed people do use their left hand (not sure whether they gave any clarity on what to say if you use both) are writing/drawing, brushing/combing own hair, holding a toothbrush and using a spoon by itself. Sadly using a mouse isn't anywhere on the list.

Interesting enough, using a mouse while writing is a one sample answer for the advantage of being left handed. Based on the earlier stats, we can assume this person likely means they are at least comfortable enough with using the mouse right handed that they can use it while writing.

There are plenty of other anecdotes of people using the mouse right handed despite being left handed. These aren't particularly useful in themselves, but they do give pause for thought particularly when you consider the reasons they do so and in the absence of actual data demonstrating such a high percentage of left handed people use the mouse left handed, reason to doubt it. (Obviously a real minority of computer users but it seems the first gaming mouse for left handers may have been in 2010 [2] which may be part of the reason for [3]).

It does depend on what the IP means by the statement. Since the percentage of people who are left handed is so small, it doesn't matter such much if you misidentify many left handers as being right handed in terms of overall numbers, your prediction accuracy will still be decent. In fact, if you just predict every as being right handed, you could probably achieve 90%+ accuracy. But if your purpose is to determine if someone is left handed or right handed, I'm not sure how useful a test is if you incorrectly predict a big percentage of left handers as being right handed.

OTOH you may very well prefer a test which will correctly predict 98% of right handed people and 50% of left handed people to one which will correctly predict 75% of both left handed and right handed people. But then again, your ultimate preference is probably for something better than both, so it's probably better to look for something rather then settle on one of two equally poor options.

P.S. You may assume that if someone uses both hands for the mouse, this will lead to a detectable skeletal pattern so it doesn't matter if someone uses both hands often instead of just one, you can predict this person is probably left handed. On the other hand (just noticed the possible pun), you then have to demonstrate that this skeletal pattern can be reliably detected, compared the the possibility the person just doesn't use the mouse enough to have any pattern, or whatever.

Ultimately it comes down to me and I presume Tamfang's main point. You have a hypothesis, but little actual data presented here to support it. And given the data available, the alternative hypothesis is IMO still equally valid.

Nil Einne (talk) 18:40, 1 August 2015 (UTC)

The problem with diabetic example isn't the anecdote or conjecture side, but it highlights the problem with the method he proposed. The correlation is only one way. Having the particular gene may very reliably predict that the holder of that gene is diabetic. But not having that gene doesn't correlate to not having diabetes. So if the question is "Was the person diabetic?" having the gene is a high confidence "Yes", and not having the gene isn't much better than the population percentage and the usefulness as post-mortem tool is only as great as the gene expression itself. You would have to know the predictiveness as it applies to predicting each hand. Correlations are probably not symmetric so statistical tests would have to be applied to each null hypothesis (i.e. if the right hand is larger than the left, it's 60% higher chance over than the normal population chance that the person was right handed. If the left hand is bigger than the right, there is no correlation). The asymmetric nature makes test harder (i.e. if I simply say every deceased person is right handed, I'd be right 85% of the time - the test would have to be better than that). --DHeyward (talk) 19:59, 1 August 2015 (UTC)
This book [4] has a chapter titled "Skeletal indicators of handedness". SemanticMantis (talk) 14:55, 29 July 2015 (UTC)
Sink your teeth into this! There is another way to find a deceased's handedness which I found out just 2 hours ago! I took my sister to the dentist today and had a good chat with her (the dentist). I was telling her that I had heard right-hemisphere dominant people chew on the left side of the mouth and vice versa. She told me it was true, and this affects the distribution of cavities. She then went on to tell me that right-handed people brush the teeth on the right of their mouth harder (better) than on the left (and vice versa). So, right-handed people have fewer cavities and less plaque on the teeth of the right side of their mouth! Elementary my dear Watson!DrChrissy (talk) 17:22, 29 July 2015 (UTC)
Was this what she was reporting the dentist had told her, or was it her own opinion? Is she a dentist herself? -- Jack of Oz [pleasantries] 19:30, 29 July 2015 (UTC)
Apologies for my unclear posting. This was what the dentist was saying to me. (My sister's input to the conversation was "Arrrggggh", "Ugggguuuuuhhh" and "thank God that's over".DrChrissy (talk) 20:48, 29 July 2015 (UTC)
Are you sure that you have not reversed right and left for brushing. A comment by my dentist implied that it was the other way round. Dbfirs 06:55, 30 July 2015 (UTC)
In my excitement at hearing the relationship, I might have mistaken it. However, I am right handed, and it feels like I put more pressure on the teeth on the right side of my mouth. (sample size N=1 !)DrChrissy (talk) 12:00, 30 July 2015 (UTC)
A person who writes with the left hand is more likely to use the right hand to support the right cheek, which as a result will likely tend to be more concave than the left cheek. (I searched for a reference, but found none.) This question is relevant to Wikipedia:WikiProject Medicine/Participants (including User:Doc James, User:Bluerasberry, User:Jfdwolff, User:Mattopaedia, User:Richardcavell, User:Looie496, User:Ozzie10aaaa, User:CFCF, and User:Peter.C).
Wavelength (talk) 23:35, 29 July 2015 (UTC)

Thank you all!! Very, very interesting indeed!!! Pity, though, that I can't see the book with the "Skeletal indicators of handedness" chapter. Anna Frodesiak (talk) 05:51, 30 July 2015 (UTC)

Late to the party, but FWIW, in both the novel and film In the Heat of the Night, Police Detective Vergil Tibbs determines that a suspect is left-handed (and therefore likely not the perpetrator) simply by feeling the musculature of his forearms. Unless the author John Ball thought this up off his own bat (is that a USA-known term?), it's presumably possible to do the same to a corpse. {The poster formerly known as} (talk) 13:25, 30 July 2015 (UTC)
Interesting. I will start to feel everyone's arms to see if there's a difference. Anna Frodesiak (talk) 09:17, 2 August 2015 (UTC)

Maxwell's demon and the Carnot efficiency[edit]

I'm curious whether there is a simple, straightforward way to relate the maximum efficiency of a Maxwell's demon to the maximum efficiency of a Heat engine, i.e. 1-Tc/Th. There is an impressive paper that does so [5][6] but it is somewhat difficult for the non-expert to process, and I'm not sure if the quantum mechanical features they focus on there are important for making this connection or just a distraction. Also there's a discrepancy between that paper and our entropy article on one hand and the Landauer's principle article on the other; the former use kB ln 2 for the entropy that must be produced elsewhere and/or energy cost, while the latter uses kT ln 2. I'm thinking the latter is measuring entropy in terms of joules and the former two doing something else but I'm not quite sure why. Is there a straightforward derivation by which you can start with this expression (whichever one) for the cost of erasing a bit and end up showing that the demon has the same maximum efficiency as a heat pump for reservoirs of the same temperatures? Wnt (talk) 23:46, 29 July 2015 (UTC)

Sorry, Wnt, there's no formal definition for the efficiency of a demon, so there's no meaningful way to compare it to the efficiency of a heat engine. Nimur (talk) 00:03, 30 July 2015 (UTC)
But surely it could be measured empirically? {The poster formerly known as} (talk) 13:33, 30 July 2015 (UTC)
Sure, if we can only find a cost-effective and safe way to obtain a statistically-significant number of demons! I'm still looking for a cost-effective and safe way to obtain a statistically-significant number of neutrons, which I consider to have more interesting thermodynamic properties... regrettably, the best I can find is a one-of-a-kind spallation source on the opposite side of this continent - but it's available to anyone with any experience or credential level, so long as the research proposal is meritous! Nimur (talk) 16:25, 30 July 2015 (UTC)
Not sure it's applicable but see here Bose–Einstein condensate#Superfluidity of BEC and Landau criterion. Using lasers to cool through coherence seems pretty neat. QED and QM seem fundamental. For some reason, Maxwells demon seems like the simple aerator on my pool. The hot molecules leave as evaporation, cold molecules stay and the pool is cooled. It's not a closed system though but the "demon" is a pump. At some point the demon would have too many collisions with the door (i.e. similar to space-charge region in a plasma where the atom has so much less velocity than electrons at a given temperature that a charge region forms until the collisions balance and the current is zero). I would think that barrier could be QM related distance with tunneling and other effects. Black hole formation and evaporation may also have relevance. Just a thought. --DHeyward (talk) 04:02, 30 July 2015 (UTC)
@Nimur: I'm surprised if there isn't a formula for the efficiency, but to give an example: today I had to deal with a car issue and was waiting for a long time in a room with a soda pop vending machine. (For some inexplicable reason, the supposed pleasure of having a cooled soda pop outweighs the prolonged and annoying noise of the contraption; as I don't actually refrigerate soda, it is all very mysterious to me) Anyway, the point is, I'd like to rip out the condenser and coils and replace it with a sort of refrigerator magnet lining the box that has a thin layer of water in it and many, many demons that put the hot water to one end of the layer and the cold to the other, so as to act as a heat pump and do the refrigeration. My understanding is that the power consumption of these demons is linked to the number of times that it measures the temperature (speed) of a water molecule approaching the gate, opens or shuts it, and then has to forget what it decided to do - that last part, oddly enough, is where the entropy is charged. So just like a refrigerator, there has to be a plug in the wall to keep it running; but fortunately one expects not to hear those bazillion gates clattering open and shut every second. And so the efficiency should be absolutely, directly comparable; but it can be written either as Carnot efficiency assuming that the demon can't power some kind of steam engine that powers the demon, or as the cost of erasing a whole bunch of bits of data. I think someone somewhere might have explained the relationship of those two means of calculation in terms even I can understand. Wnt (talk) 18:46, 30 July 2015 (UTC)

July 30[edit]

Why does water get loud before it boils?[edit]

I notice that when boiling water in a metal or glass kettle or metal pot, a noise slowly builds before the water actually boils. Once the water reaches a rolling boil, the noise lessens. What is causing the noise? The water? The expansion of the glass or metal kettle? --Navstar (talk) 02:05, 30 July 2015 (UTC)

It says here that the explanation is that in the hottest area of the kettle the water is boiling, but the bubbles collapse as they rise into water below the boiling point. The collapsing is what makes the noise, and it stops happening when all the water is at the boiling point. -- (talk) 03:54, 30 July 2015 (UTC)
Agreed. Note that these bubbles are too small to see, and that the large surface area to volume ratio of such microscopic bubbles allows the water vapor to instantly cool below the boiling temperature and become liquid water again, which takes up much less room, causing the bubbles to collapse. The bubbles get larger as the heating continues, and you might be able to see them collapse briefly, or at least get smaller as they rise. StuRat (talk) 14:17, 30 July 2015 (UTC)
The fancy science term for this is cavitation. Notably, it's also caused by things other than heating, like surfaces passing through a fluid at a high speed. This is an issue for things like propellers and turbines. And when cavitation bubbles form, they are indeed noisy, which is one way you can tell that it's happening to a propeller, pump, etc. -- (talk) 15:45, 30 July 2015 (UTC)

How many Earth plant species are physically possible?[edit]

If we could simulate Earth's entire history octillions of times with different random DNA mutations until we exhaust every possible species how many would there be? Is this even estimatable any time soon? Sagittarian Milky Way (talk) 02:36, 30 July 2015 (UTC)

And also randomize the shapes of the continents and their topography and when and where asteroids hit and the like cause those were random accidents. Sagittarian Milky Way (talk) 02:43, 30 July 2015 (UTC)

It's not possible to do this in a meaningful way. The largest plant genome is 150gb long. There are 4150,000,000,000 possible genomes of this size (such a big number I can't find a math program that will even display it in scientific notation). We can think about any particular variation of this genome, but without creating it, we have no way of knowing whether it would be viable in a given environment (or ever), whether it would constitute a species distinct from any other particular variation, or even whether it would classify as a plant. There's also no reason to suspect that 150gb is the upper bound for the size of a plant genome. So while we can imagine all the variations of a genome, we can't know anything useful about most of them - certainly not enough to answer your question. Someguy1221 (talk) 03:04, 30 July 2015 (UTC)
To convert a power of A into a power of B, just multiply the exponent by log A / log B (using logarithms to the same base for both numbers). log 4 / log 10 is just over 0.6, so 4150,000,000,000 is about 1090,000,000,000. -- (talk) 04:01, 30 July 2015 (UTC)
As for the continents...the number of possible outcomes depends on how different two 'shapes' have to be. If a single misplaced atom makes two topographies "different" then the answer is some kind of factorial involving the number of atoms in the earth's crust from somewhere above the height of everest to the bottom of the marianas trench. That's a truly ungodly number. I don't see much value in attempting to estimate it - the mathematical notations for such numbers start to get fairly incomprehensible.
If "different" required a difference of (say) a kilometer in the shape of a continent or the path of a river - then the number is still insanely large - but more manageable. But it's arbitrary - why one limit for "different" rather than another? That's really the problem with these "curiosity" kinds of question. Does it matter how big the number is? I can't imagine why you'd need the answer. Why bother even asking it?
It's really the same deal with the plants - there are an insane number of changes in the DNA of an Oak Tree that would still produce a viable, recognisable Oak Tree - so why count the number of possible DNA strands when it really tells you nothing about how much meaningful variation there might be.
So the best answer here is "Don't Know" - and "Don't Care" comes a close second. SteveBaker (talk) 04:19, 30 July 2015 (UTC)
I meant changes big enough to affect the evolution of species, a kilometer probably wouldn't do it. If the dinosaurs got to evolve for longer or got killed off sooner maybe plants that never existed would happen, though. I'm kind of also wondering how many Earthlike planets would have to gain DNA-based vegetation of the correct amino acid chirality to make a wheat species that could interbreed with the Earth kind. Sagittarian Milky Way (talk) 04:50, 30 July 2015 (UTC)
The problem is that the environment on Earth is 'chaotic' (in the mathematical sense of Chaos theory) - epitomised by the idea that the flapping of a butterfly wing might cause a hurricane halfway around the world a year from now. This effect (which is very real by the way) means that the most insignificant change (one atom displaced by a nanometer or so) is more than sufficient over the very long term to cause extinction or failure to evolve of an entire species. There is no lower limit beneath which you shouldn't care.
Imagine a single cosmic ray misplacing a single atom in the DNA of the sperm that was to become Richard Nixon. That resulting in it swimming 0.1% more slowly than it otherwise might - and resulting in a different sperm making it to the egg, Richard Nixon never existed but instead we got Sandra Nixon. Despite an unprecedentedly great political career, and a reputation for honesty and a high ethical standard - in 1968, America simply wasn't ready for it's first female president and Hubert Humphrey got the job instead. Being obsessed with solving the Vietnam problem, Humphrey failed in Cold War engagement with the Soviet Union. The resulting nuclear holocaust caused in the extinction of 90% of the species on earth and resulted in the eventual evolution of super-intelligent giant cockroaches who farmed genetically engineered fungi over 80% of the land area of Earth - and that caused the extinction of the wheat plant on earth. One cosmic ray - one nanometer to the left.
So, no - it's not sufficient to assume that one misplaced atom cannot make a difference!
SteveBaker (talk) 17:47, 30 July 2015 (UTC)
That is very funny. Sagittarian Milky Way (talk) 12:57, 31 July 2015 (UTC)
SteveBaker's thought experiment may be funny, but it's perfectly valid, Sagittarian Milky Way. μηδείς (talk) 00:45, 1 August 2015 (UTC)
All of them. (BTW, besides being a flip answer, there are DNA changes that aren't meaningful for species. The human genome is fairly narrow that produces lots of variability without a "species change." I'm not sure how you can specify "species change" with DNA variation. Eye color, skin color, gender, etc, etc, are all DNA differences without species implications and there are genomes that aren't so narrow and allow "inter species" creation (i.e. Ligar) as well large variation within a species such as Dogs.) --DHeyward (talk) 04:28, 30 July 2015 (UTC)
I have lots to say about this, as my research specialty is theoretical ecology of plant communities. Unfortunately I don't have much time work for free today :) The big thing everyone seems to be ignoring is that the number viable plant species depend on the community context, competition, dispersal, life history, predation, disturbance, and many other factors. The number of possible genetic combinations has nothing to do with the number of species you might expect to find in a given situation. For starters, see Chesson (2000 a,b), freely accessible here [7]. The main idea is that number of coexisting species that a system can support is limited by resident-invader differences in the covariances between environmental and competitive effects. The papers go into great detail on this if you can handle the math and follow some basic ecological terminology. If you're still interested next week, drop a line on my talk page and I'll be happy to discuss further. SemanticMantis (talk) 15:22, 30 July 2015 (UTC)
They don't seem to be asking about how many plant species can survive in one particular environment (E), but rather how many could exists (n) in every possible Earth environment (P). It's probably not as simple as n = E×P, either, as E varies widely, P is unknown, and there will be many species that could exist in multiple environments. Also note that in plants (as well as animals, etc.) with asexual reproduction, defining a species is even trickier. StuRat (talk) 15:52, 30 July 2015 (UTC)
Funny, I would have thought that every possible Earth environment would include all specific and particular Earth environments. Please don't try to teach me to suck eggs until you've gotten a relevant PhD and published at least a few peer-reviewed papers about plant ecology ;) SemanticMantis (talk) 16:49, 30 July 2015 (UTC)
Nice argument from authority fallacy. I hardly need a PhD in plant biology to be able to read a question correctly. Specifically, "randomize the shapes of the continents and their topography and when and where asteroids hits and the like" means the OP wants to know about all possible Earth environments, not merely those which currently exist. StuRat (talk) 17:25, 30 July 2015 (UTC)
If you'd taken the time to read and understand the research I linked above, you'd have seen that the framework allows for descriptions of species coexistence in environments that don't exist on Earth, as well as plants that don't exist on Earth. You seem to think I'm interpreting the question incorrectly but don't seem to be understanding what I'm saying. Whether the OP thinks my refs and responses relevant is not for you to decide. Finally, I did not appeal to my authority to support my claims, my refs do that just fine. Rather, I appealed to a well-known saying, and implied that you're trying to give your opinion to an expert in the field, who most likely knows more about this than you do. Whatever, I'm happy to discuss this with OP further as I said above, but I have no more time for you today. SemanticMantis (talk) 17:39, 30 July 2015 (UTC)
You don't seem to understand what I said. Say you determine that environment X1 can support n1 species, and environment X2 can support n2 species. You can not then conclude that the total number of species environments X1 and X2 can support is n1+n2, because you don't know how many are in common. When you have thousands or millions of possible environments, the overlapping Venn diagrams become absurdly complex. So, how do you propose to calculate the total for all possible Earth environments ? Finding the number for an individual environment is interesting, but simply doesn't lead to an answer to this Q. Then there would be the issue of determining the number of possible environments that could possibly exist on Earth. And, again, no PhD is required to read the Q, and see that it's not what you are answering. StuRat (talk) 17:58, 30 July 2015 (UTC)
I never said we'd sum the numbers of species. The relevant thing to get at overlaps in species distributions and overlapping environmental properties is Beta diversity. There's actually an entire body of research that explicitly addresses your sentences "Say" to "complex". Ok, now I'm done, have a nice day. SemanticMantis (talk) 18:27, 30 July 2015 (UTC)
Thanks for the offer. Sagittarian Milky Way (talk) 13:32, 31 July 2015 (UTC)
vital advances in plant evolution
  • How many species are physically possible is a meaningless question, since species can be genetically isolated due to differences in ploidy (chromosome number) but otherwise be indistinguishable. What really matters is the number of niches available and occupied.
Looking at the question ecologically, there are several different breakthroughs in plant evolution.
The first big question is photosynthesis in eukaryotes, assuming we are going to exclude bacteria from our definition of plants. There are plenty of different routes that evolution could have gone down to produce multicellular photosynthetic land organisms. It so happens that this has only really happened with the green plant phylum. But land plants could certainly have evolved from the red algae and green algae had the green algae not beat them to it. The former are still very important in the ocean, with kelp an example of a brown alga. There are several thousands of species of red and brown algae, and other types of algae, the classification is in flux.
The next two major advances on land were the development of vascular tissue, which allowed tall upright forms like ferns, rather than mosses, and of seeds, which allowed evolution independnt of the need of spores to swim through rain water to cause fertilization. These events caused the evolution of forests and the colonization of arid lands. Forests had evolved before amphibians and insects appeared on land, and there were seed plants by the time of the dinosaurs. During this time, however, plant diversity was much lower than it is today due to the vagaries of fertilization. Plant species tended to cover large areas of similar terrane such as todays boreal forests given distribution of pollen and seeds by the wind doesn't tend towards locally specialized species.
It was the development of the flower, and the mutual feedback between pollinators and food plants that allowed the huge boom in plant evolution that occurred with the arrival of guided fertilization. While there are only about 630 species of conifer, a very ancient group, there are some 25,000 species of orchid, a very small but highly specialized branch within the flowering plants. Many plants such as orchids have their own unique species of animal polinator. This means they can become highly specialized to microhabitats that are totally unavailable to plants like conifers. Some orchids are found only on specific mountains. Such evolution doesn't happen with more primitive plants; small ranges in them indicate either relict populations only found on certain islands or species headed toward extinction.
Even then, the total number of flowering plant species, which far outnumbers all other plants combined, is estimated to be only a few hundred thousand species.
In the end it comes down to what ecological niches are available to and accessible by plants. There are parasitic flowering plants, carnivorous flowering plants, flowering plants (e.g., bromeliads) that live in the branches of other flowering plants, flowering plants that are only fertilized by one species of flying organism, and flowering plants that are going extinct because the megafauna that ate their seeds, allowing them to germinate, have been hunted to extinction. μηδείς (talk) 00:53, 31 July 2015 (UTC)
I guess we could've had a red world then, and human connotations of red being the color of bloodshed and war might be merged with peaceful Edenity. That would be more efficient though, sunlight peaks near the color that leaves reflect. And if red algae, which I think can live near the surface, is any good at absorbing blue light then it should be able to photosynthesize deeper than any other algae and be more likely to discover the mutation first cause it can live in more of the ocean. I don't know why we didn't go that route? Sagittarian Milky Way (talk) 13:32, 31 July 2015 (UTC)
Leaves are green because they absorb red and blue light more strongly than they absorb green. See also: purple bacteria. The real point about the "possible" number of plants is that many specialized species exist only because their niches have co-evolved with other organisms. There'd be no mistletoe without birds and oak trees, no orchids without certain insect pollinators. μηδείς (talk) 16:10, 31 July 2015 (UTC)
Wouldn't red or blue leaves be better? Sunlight is strongest near green light and leaves just reflect that away. Maybe purple or even conifer-dark green leaves would overheat but why not have dark purple photosynthetic chemicals for the taiga trees? Or dark red? I guess maybe the mutations were so hard to come up with that only green algae did it. I had no idea there were so few conifer types though, it's interesting that none of the earlier kinds could have anything near the diversity the single invention of flowers can produce. Sagittarian Milky Way (talk) 17:55, 31 July 2015 (UTC)
There are red leaves on plants. Poinsettias are one of many examples. Interestingly, the leaves are green in summer and only turn red in winter, based on longer nights. This suggests that the red color helps with photosynthesis when less light is available, although I don't know if that is actually the case. (Of course, many plants also have red flowers, but that's all about attracting pollinators.) StuRat (talk) 21:13, 31 July 2015 (UTC)
The answer to your question is somewhat counterintuitive, SMW, and commonly confuses people. All other things being equal, the color of an opaque object depends on the relative amounts of which frequencies it absorbs. So leaves look green, because the light at the red and blue end of the spectrum is highly absorbed, while green is much less so. Leaves arent green in the sense of giving off (shining in) green light like a green neon sign. Instead, they are reflecting some green and absorbing the rest. Indeed, if you excite chlorophyll by shining a light through it the chlorophyll glows in a rich red color. (Blue is absorbed by auxiliary pigments in a leaf which transfer electron to chlorophyll. Because this is indirect, the chlorophyll itself only glows in red.)
One of the reasons for red in shoots and dying leaves is that again, there are auxiliary pigments in leaves beside chlorophyll. These pigments are less expensive to the plant metabolically, and hence are produced more quickly during early growth; and while a deciduous plant will actively reabsorb the components of chlorophyll in the fall, they don't waste energy pumping the other pigments out of their leaves, so these pigments get left behind causing the pretty colors of autumn.
Red leaves in Poinsettias are effective "painted" red with a pigment that reflects very strongly in the red area of the spectrum. Poinsettias are "actively" reflecting red, while green leaves are passively not absorbing as much green as they are other colors.
To forestall objections, the above is very simplified, there are lots of other side issues, but I have addressed the essence of the matter. μηδείς (talk) 00:42, 1 August 2015 (UTC)
Aren't you just saying that leaves reflect green light the best as a byproduct of absorbing everything they can? Um I've watched the Magic School Bus as a kid I know that opaque color is reflected light. I Googled chlorophyll absorption spectra and absorption in green seems to be pretty small. And reflection in green is almost twice red twice blue. If leaves fluoresce red then it can't be a big contributer to their appearance because reflectance in green isn't even twice that of red. Leaves should look banana yellow by the time those two colors equalize. But if you have to reflect some color then why not reflect a color that's not yellow or green? I'm guessing that it wouldn't help many leaves as leaves sometimes get too hot and dry out as it is, absorbing even more sunlight would cause more waste heat. There are bare forest floors (too dark), and the tree line where tree needles have trouble staying warm enough. A pigment that reflected a less major color in the sunlight spectrum would be more efficient. But if evolution didn't take alternative photosynthetic substances beyond the algae stage then it'll have to be chlorophyll. I do wonder though why no alpine or Arctic plants invented some extra non-photosyntetic pigment(s) just to become completely black (to the naked eye) for maximum warmth. Sagittarian Milky Way (talk) 02:13, 1 August 2015 (UTC)
I am not "just saying" anything, and, "um", I am not inclined to answer patronizingly worded retorts about children's shows. There does happen to be an answer why leaves absorb blue but chlorophyll fluoresces only red and why leaves don't tend to be black, but I'll leave it to others or the staff of Magic school bus to correct your misunderstanding of what has been said so far. μηδείς (talk) 02:53, 1 August 2015 (UTC)
Um, that episode where the colored light bolt is absorbed by a different color? Never mind, it was on in the 90s. Maybe you could've realized I meant the solar blackbody peak shouldn't be near the reflectance peak for max efficiency instead of thinking I thought leaves are green cause they glow or absorbed green the best. Sagittarian Milky Way (talk) 16:46, 1 August 2015 (UTC)

Galaxy merger - Andromeda and Milky Way[edit]

What will happen to the two supermassive black holes at the centers of the two galaxies when these two galaxies will merge? Will these two black holes merge to from a single black hole? --IEditEncyclopedia (talk) 05:28, 30 July 2015 (UTC)

yes Void burn (talk) 05:30, 30 July 2015 (UTC)

But supermassive black holes are much more powerful. Will not they engulf all the matter if they are disturbed? --IEditEncyclopedia (talk) 05:33, 30 July 2015 (UTC)
Why would they engulf all matter? Black holes obey the same laws of gravity as anything else. Putting two of them together will release a great deal of energy in the merger, but the gravity won't be any stronger than the sum of the two black holes. Someguy1221 (talk) 05:51, 30 July 2015 (UTC)
Why guess what could happen, when astronomers have already been studying it happen: let my type super massive black hole merger into google for you. (talk) 13:25, 30 July 2015 (UTC)
Incidentally, this week's Cosmic Video from Keck Observatory was Black Holes and the Fate of the Universe, presented by Dr. Günther Hasinger, directory of the Institute for Astronomy at University of Hawaii. This is part of the Keck Cosmic Summer School, and the videos are available at no cost. These videos are a great way to hear real scientists talking about cutting-edge research: it will help you see how they actually frame their questions.
Attention physics students: note that in his only slide with equations, the Director has conflated orbital velocity with escape velocity. Astronomers are the only scientists who can get away with such errors - a minor factor of 2x or 10x or 100x is just a "practical detail" in the field of astrophysics. Directors can get away with this type of thing, but when you calculate orbit velocity for your rocket, don't use the equation for escape velocity!.
The presentation discusses "mergers" of massive black holes, and black holes eating galaxy-sized masses, around 30 to 40 minutes into the video.
Nimur (talk) 13:38, 30 July 2015 (UTC)
Might want to be a little careful. At the event horizon, the orbital velocity is the speed of light. It's also the escape velocity as it creates Hawking radiation. Ta daaa! --DHeyward (talk) 02:51, 31 July 2015 (UTC)
Watch the video carefully. His statement, which I quote here verbatim, adding wikipedia article links is:
"When we are trying to send a rocket to the moon or even to the International Space Station, we have to give the rocket a certain speed in order for it to leave the earth... If I could throw a stone, the stone would go up and it would come down again. But if I could throw the stone with a velocity faster than the escape velocity, then it would leave the earth and go into orbit. Now, this velocity on the Earth is 11 kilometers per second."
Now do you see why I say he conflates escape- and orbit- velocity? He's talking about low earth orbit and he even specifically calls out the International Space Station, whose orbital speed is closer to 7 kilometers per second. In fact, it is possible to throw a stone with a speed slower than escape velocity, and the stone can enter a stable orbit - it may never fall back down again, provided that it is thrown in the right direction (your added velocity must impart the correct angular momentum to achieve a stable orbit)!
This is one of those cases where we need to understand conventional physics in order to describe what it is about black hole physics that makes them actually weird! The escape velocity of a black hole, measured relative to a point inside the Schwarzschild radius, is greater than the speed of light. At a different radius, the orbital speed is equal to the speed of light: this is exactly 1.5 times the Schwarzschild radius and it is called the photon sphere. Photon escape by Hawking radiation - which is a real phenomenon - defies the mathematics of conventional orbital mechanics, and is usually treated in a statistical fashion! Photons emitted by Hawking radiation are neither exceeding the escape velocity nor are they even exceeding the speed of light: they are photons, and they always travel at c - yet they are emitted! There is the novel physics of a black hole, and that is the reason that Hawking radiation is so groundbreaking. It is a different process that we cannot describe using only the equations of general relativity.
Nimur (talk) 14:42, 31 July 2015 (UTC)
The theoretical escape velocity is largely irrelevant to actual spacecraft launches because it applies to ballistic objects, not rockets. (And also because it neglects air friction.)
You can't throw an object into an orbit with a perigee higher than your hand unless there is some sort of friction or n-body dynamics. Absent that, it will follow a conic-section orbit, and a spiral (a launch from the ground converging to a closed orbit) isn't a conic section.
The idea that black holes are objects whose escape velocity is c makes little sense for a number of reasons. For starters, the calculation is Newtonian and black holes aren't. The answer is determined up to a constant factor by dimensional analysis, and I think the agreement of the constant factors is a coincidence (especially since they only agree if you use a certain definition of radius in GR). See e.g. [8]. Also, escaping from a black hole is not much like exceeding an escape velocity. Objects thrown upwards at exactly the escape velocity do escape to infinity, and self-propelled objects can leave at arbitrarily low speeds, but nothing at the event horizon can get any higher even if self-propelled or moving at c.
The slide with equations in that video shows up at 6:21. Most of what he says about it is really inaccurate. Aside from not seeming to understand escape velocity, he says that stars are "pulled inward by the gravity of the sun", which is backwards (if he means that they appear closer to the sun due to gravitational lensing, and I don't see what else he could have meant). He also seems to say starting at 13:30 that the fluctuations in the cosmic microwave background are pre-inflationary fluctuations that were magnified by inflation, which is wrong (they're from the end of inflation).
Hawking radiation can escape the black hole because it comes from outside the event horizon. Hawking radiation is still not well understood, but I think everyone agrees on that part. -- BenRG (talk) 02:08, 1 August 2015 (UTC)

To elaborate a bit, you seem to be exhibiting a common misconception about black holes: that they're all-consuming monsters that want to devour everything. Black holes are just objects that obey the same laws of physics as everything else. The only point of difference is we aren't currently quite sure what happens inside their event horizons. For that, we need a full-fledged theory of quantum gravity. But outside the event horizon, the gravitational force of a black hole works the same as that of anything else, including you. Large (meaning "having a high mass") black holes are just very very massive, so they have a correspondingly strong gravitational pull, but things on the right trajectories will still orbit a black hole just like they orbit stars and planets—indeed, we are orbiting the black hole at the center of the galaxy right now. If our Sun were replaced by a black hole of equivalent mass, the whole Solar System would continue orbiting it just the same. Of course, most life on Earth would die since it's ultimately powered by the Sun, but nothing would change Earth's orbit. -- (talk) 15:32, 30 July 2015 (UTC)

It's probably a little early to say it's quantum gravity that is missing. All physics is a mathematical representation of observation. At the end of the 19th century, theoretical physics was "being wrapped up" as Newton and Maxwell had described evreything and there were just some small details that didn't fit. Those small details turned into quantum mechanics and relativity. We were wrong at both ends of the spectrum. Black holes appear as a singularity and I suspect the mathematics needed to describe will be as revolutionary as QM and GR. Planck time and all the things that currently defy the rules (or rather the things that make our observable approximations follow our models) --DHeyward (talk) 02:51, 31 July 2015 (UTC)

What will happen will depend on how much angular momentum they have, and the relative orientation of the spin. The binary black hole that comes about will orbit faster and faster. When a merger takes place an apparent non conservation of momentum can happen with a "kick' where the result can be pushed out at 1000km/second, gravitational waves carry the complementary momentum. Maybe the black hole will be ejected from the galaxy. Perhaps 5% of the mass will be lost as gravitational waves. Material taken for a ride may be ejected at high velocity, so stars may be sprayed in all directions from the merging core. Graeme Bartlett (talk) 01:19, 31 July 2015 (UTC)

Does eating oatmeal increase or decrease the iron in the human body?[edit]

Oatmeal is rich in iron, but it seems that it hinders the absorption of iron by the body (see [9]].

Would consuming regularly some commercial product as Dr. Oetker's Oatmeal increase or decrease the iron level in the blood? Do producers enrich the product with iron to avoid a decrease of iron in the body?--Yppieyei (talk) 10:10, 30 July 2015 (UTC)

Does Dr. Oetker's actually sell plain oatmeal ? A Google search yielded products containing oatmeal, but not the oatmeal itself. Here's their oatmeal muffin mix nutrition: [10]. At only 2% RDA iron, they apparently haven't added any.
And note that when iron is added, it's just to make their numbers look better, they don't actually care if it can be absorbed or not. StuRat (talk) 14:06, 30 July 2015 (UTC)
Note that you're just being cynical and not doing any research or citing any references. Most forms of iron fortification do get absorbed by the body Human_iron_metabolism#Dietary_iron_uptake explains quite clearly that the common form of added iron is absorbed by the body at a rate of 10%-20% of intake. Animal sources of iron are absorbed at 15%-35% intake, but that is easily compensated by ingesting a bit more iron salts (Iron(II)_sulfate#Nutritional_supplement). Other forms of iron used for food fortification include Ferrous gluconate. Here's a nice report from the WHO that covers the use of food fortified with iron [11]. OP might like to take a look at that last link, it does list several foods and compounds that interfere with iron absorption. Finally, you don't even need fancy iron compounds if you get enough total iron, the Lucky Iron Fish [12] has already made huge improvements in anaemia levels, and that's just a simple lump of iron that you boil with your soup. Anemia#Oral_iron also has some good info on some of the common supplements and food additives. SemanticMantis (talk) 15:01, 30 July 2015 (UTC)
I included a reference listing the iron content of one of their products. StuRat (talk) 15:24, 30 July 2015 (UTC)
Duly noted, I should have said "any references that support your final claim" ;) SemanticMantis (talk) 15:27, 30 July 2015 (UTC)
Also, in many countries, including the U.S., the government requires that refined grains be fortified with nutrients, including iron, that are found in the bran and cereal germ, which are removed during processing. Whole grains retain these, so they aren't required to be fortified. -- (talk) 15:19, 30 July 2015 (UTC)

Train deceleration[edit]

Why do trains in Asian countries such as Japan and South Korea accelerate and decelerate so fast? — Preceding unsigned comment added by (talk) 17:41, 30 July 2015 (UTC)

Because they can? Fast acceleration gets the train up to its very high maximum velocity quicker, and fast deceleration permits it to continue at maximum speed longer before stopping. Robert McClenon (talk) 17:44, 30 July 2015 (UTC)
Hmm, let's look at some factors:
1) Reduces total trip time.
A) Uses up more energy, particularly in the rapid decel (as opposed to allowing the train to slowly decelerate due to friction). Some type of regenerative braking could reduce that.
B) In the case of traditional brakes, rapid decel causes wear on brake pads. However, in a maglev train, probably not, although heating might cause wear.
C) Can be uncomfortable for the passengers to undergo either rapid accel or decel, although depending on if the seat faces forwards or backwards, one of those should be easier on them than the other. Getting caught walking with a cup of coffee would be bad, too, so some warning would be appreciated. StuRat (talk) 18:09, 30 July 2015 (UTC)
So, they must feel the pros outweigh the cons. The main factor that might vary in Asian nations is more maglev trains, reducing concern over B. StuRat (talk) 18:09, 30 July 2015 (UTC)
It doesn't actually use more energy for the acceleration or deceleration itself. It uses more power, but uses that for a shorter time. It also uses more energy due to the higher air resistance at the higher speeds achieved earlier, of course. Regenerative braking should be fairly standard for electric trains in most advanced countries today. --Stephan Schulz (talk) 18:19, 30 July 2015 (UTC)
Of course, that's assuming that the energy-efficiency for the train's power plant is uniform at all power levels. Is this accurate for, say, the Shinkansen bullet train? Nimur (talk) 18:46, 30 July 2015 (UTC)
I believe, at least in the case of rapid braking, that it does use more energy, since more of the braking is done by the train, and less by air resistance and rolling resistance (in the case of trains with wheels). StuRat (talk) 14:15, 31 July 2015 (UTC)
In reply to StuRat's C), the comfort of passengers is determined mainly by the rate of change of acceleration (see Jerk (physics)). This can be high even on slow British trains, and is regularly felt on slow buses especially if badly driven. Dbfirs 20:08, 30 July 2015 (UTC)
To take a slightly different epistemological angle, countries like Japan and South Korea have invested heavily in high-speed rail. This means the rail infrastructure tends to be designed for higher speeds. High-speed rail also generally is designed to allow trains to accelerate and decelerate more rapidly, since the whole point is to get people to their destinations quickly. It's kind of a waste if your train has a high top speed but it takes forever to get to that speed! Designing for high top speed and rapid velocity changes generally goes hand-in-hand anyway. Tracks need to be sturdy, level, and as straight as possible, trains need to be able to withstand high stresses and have powerful engines, etc. -- (talk) 18:28, 30 July 2015 (UTC)
They can accelerate and decelerate because each axle is a traction motor (see Electrical multiple unit). By distributing the traction engine, the train isn't limited by a central traction system. Every car is driven and the distributed mass and drive improves both acceleration and deceleration. It's all electrically driven. By contrast, diesel electric trains have electric motors only on the locomotive. Synchronizing all the axles is not trivial and is why it's not done everywhere and is one of the reasons high speed trains in Europe don't accelerate or decelerate as fast (see AVE Class 102 for example of high speed train in Spain that has only 2 drive units). Most braking is done using with either regenerative brakes or more commonly, Eddy current brakes so pad wear isn't an issue. --DHeyward (talk) 21:06, 30 July 2015 (UTC)
No, this is quite wrong. Provided that there is sufficient weight on the powered axles for the necessary traction to be achieved, the maximum acceleration of a train is determined by its power-to-weight ratio. It doesn't matter if there are a large number of small motors or a small number of large ones. The two "power cars" (locomotives) of that AVE class 102 have a total of 8 motors developing 1,000 kW each, and the train weighs 322 t (metric tons), so that's a ratio of 8,000/322 = about 25 kW/t. The N700 Series Shinkansen, built about the same time, has 56 small motors developing 305 kW each, and weighs 716 t, giving almost the same ratio at 17,080/716 = 24 kW/t. The acceleration capacity of the two trains should be about the same, provided that the AVE locomotives are heavy enough for the force from the motors to be practically used. Multiple-unit trains do have two big advantages (against a downside that is mostly in cost): they're easier on the track (no heavy locomotives) and they can be made to divide into shorter trains by simply uncoupling. But they don't have an advantage in performance. Also, there is no need to "synchronize the axles". -- (talk) 04:50, 31 July 2015 (UTC)
The original question implies that trains in Asian countries DO accelerate and decelerate at a greater rate than similar trains outside Asian countries. I'm skeptical. What is the evidence before us that there IS a significant difference in rates of acceleration and deceleration? Dolphin (t) 06:44, 31 July 2015 (UTC)
Go ride them :). Japan most certainly accelerates faster. Spain acknowledges it in their design docs but it's not an issue on a long run, only when there are lots of stops. --DHeyward (talk) 07:23, 31 July 2015 (UTC)
Your caveat is why it's not equal (and also why a car with wide driving tires accelerates quicker than narrow tires for the same power to weight ratio). In practical high-speed trains power to the motor is regulated and measures slippage and creep. Power has to be reduced when wheels starts slipping too much but slippage is required for maximum acceleration. By distributing the weight and a driving motor each with it's own power control, the available torque is much higher. There's much more driving wheel surface in contact with the rail, all the weight of the train is on driving wheels (it's all the normal force of the full train weight, not just normal force of the mover weight), and each motor is driving with the optimum slippage. Top end speeds are the same but acceleration is much greater in the distributed case because the motors are running with maximum tractive force throughout the acceleration cycle. Japan has many stations and stops so they use distributed motors to maximize acceleration but it doesn't help top speed. When acceleration is a significant factor in trip time, distributed is better. For that reason, N700 Series Shinkansen accelerates to top speed much quicker than the AVE class 102 even though top speed is about the same and your power to weight is about the same. Distributed power delivery and control must be coordinated (synchronized was a bad word considering its meaning wrt motors) and it is more complicated with EMU's and is not simple and it's more expensive. --DHeyward (talk) 07:23, 31 July 2015 (UTC)
As a peripheral observation, this was also why the Southern Railway was in the forefront of electrification in the UK: it had the largest proportion of urban, suburban and rural commuter traffic (mostly to/from London) the associated high number of stations and stops, the passenger-driven motivation to minimize journey times, and the ever-present desire to minimize energy costs. Electrification enabled both better acceleration and improved efficiency (over coal/diesel). {The poster formerly known as} (talk) 13:33, 31 July 2015 (UTC)

July 31[edit]

What do the galaxies, galaxy clusters and galaxy superclusters revolve around? Do they change place?[edit]

The Moon revolves around the Earth, the Earth revolves around the Sun, the Sun revolves around the supermassive black hole at the center of the Milky Way.

Now a question will arise. What does the Milky Way revolve around? Is it that, like binary star system or triple star system, the Milky Way and other nearby galaxies revolve around themselves?

Do the galaxy groups also revolve around themselves? Do the galaxy superclusters also revolve around themselves?

But even if the galaxies, galaxy groups and galaxy superclusters revolve around themselves, this means they are fixed at a particular location in the Universe, they are not moving away from that place. The Sun is changing place within the Milky Way because it is revolving around the galactic center. But the galaxies, galaxy groups and galaxy superclusters are not revolving around something at the center of the Universe. So they are in a fixed place, right? --IEditEncyclopedia (talk) 02:30, 31 July 2015 (UTC)

The thing is, the moon doesn't technically orbit "the earth". The moon and the earth both orbit their common Barycenter. As far as galaxies go, they are definitely not "stationary", the discovery of this being one of the greatest discoveries of modern cosmology. , Vespine (talk) 04:22, 31 July 2015 (UTC)
It's all an illusion. Everything moves in a straight line. Mass and energy warp space to create the illusion. The 2D example is to travel on a great circle on the surface of the earth. You travel due east and eventually "orbit" to your origin but that doesn't change the straight line motion. The 2D plane you travel in is warped around a 3D sphere. Gravity warps 3D into at least 4D to appear to orbit. --DHeyward (talk) 04:40, 31 July 2015 (UTC)
... and there is no known unique centre of the universe: Earth is the centre, along with every other point in spacetime. See Dark flow for a possible non-rotational drift. Dbfirs 12:50, 31 July 2015 (UTC)
The Sun orbits the center of the Milky Way and there is a super-massive black hole there. But note that while the Galactic Center#Supermassive black hole weighs in at an impressive 4.31 million solar masses, it's still tiny compared to Milky Way#Size and mass with estimates around 8.5×1011 solar massess, 200000 times the black hole, and a lot of that inside the Sun's orbit. It's not the black hole that makes the Sun orbit. PrimeHunter (talk) 22:15, 31 July 2015 (UTC)
And it's nothing compared to some of the Dwarf galaxies. At some point when we realize what drove the "Big Bang" and what changes the rate of the universe expansion rate it will be as revolutionary as relativity and quantum mechanics. Personally, I'm skeptical of trying to fit cosmology to existing theories just as QM and Relativity left Newtonian mechanics and Maxwell in the dust. There's another event horizon that needs explanation. --DHeyward (talk) 04:19, 1 August 2015 (UTC)
The OP is advised to read about general relativity to understand some of the comments above. In addition, in the general n-body problem, the movement of objects is chaotic. In that sense there is not a single center of rotation because the orbits are, at a certain level, not regular enough for that concept to be defined. Note that even in an inertial reference frame the barycenter of a large number of objects will still move. The size of the universe must be finite if a "barycenter" for "everything" is to be defined. Indeed, it is nominally possible to define one for the observable universe, but it's impractically hard to compute that.--Jasper Deng (talk) 09:18, 2 August 2015 (UTC)

Sustainable harvesting of wild parrots for the pet trade[edit]

I was just reading our Common hill myna article, where it says that people sometimes encourage wild myna birds to breed near where they live and then take a sustainable number of chicks to hand-raise for the pet trade, while leaving the adults alone. Why don't people do that with parrots more often? -- (talk) 21:50, 31 July 2015 (UTC)

Telegraph Hill, San Francisco is also famous for it's feral parrots. Seems like some could be taken from there, too. StuRat (talk) 22:03, 31 July 2015 (UTC)
Because not exploiting the resource to its fullest extent means you're giving up some short-term gain. Harvesting of wild animals is a textbook example of a resource where there are significant externalities. Every person has an incentive to take as many animals as possible, even though it means in the future the animal population will go extinct, because the benefits are immediate and accrue exclusively to the people who are harvesting, while the costs are delayed and are spread among everyone who could eventually benefit from the resource. Any animals you don't harvest are available for a competitor to harvest. See also: overfishing, cap and trade, global warming. This kind of thing is a big deal in economics, with lots of attention given to designing regulatory and incentive schemes to make producers bear the costs of externalities. -- (talk) 23:01, 31 July 2015 (UTC)
See degradation of the commons. Yes, laws would need to be put in place to limit "harvesting", although if they are an invasive species, environmentalists might actually be in favor of total removal. StuRat (talk) 23:19, 31 July 2015 (UTC)

August 1[edit]

Evolution of the universe and multiverse[edit]

In string theory, there are different physical laws in different universes. I want to see how universe will evolve if there are different physical laws. I can't find any website which has a simulation where I can add different values and see the result. Some scientists are saying that there is only one way to know that we are in a multiverse, i.e, finding the gravitational waves which are formed when our universe collides with another universe. Is there any other way to know that? Supdiop (Talk🔹Contribs) 01:17, 1 August 2015 (UTC)

I doubt that any website will show how the Universe evolves with different physical laws, as it takes supercomputers many months of calculation to make these models[1]. Dja1979 (talk) 02:03, 1 August 2015 (UTC)


Pain in shrimps[edit]

There is a product that consists of sealed small aquariums which contain shrimps, algae, and bacteria among other living beings living in equilibrium in a closed eco-system. Ecosphere seems to be the most famous brand, but there are alternatives.

How can we know that whether the shrimps living in this bubble experience pain or something similar to it? If we wanted to analyze it rationally, how whould we proceed?--Scicurious (talk) 07:57, 1 August 2015 (UTC)

Pain in invertebrates is the relevant article. Tevildo (talk) 08:21, 1 August 2015 (UTC)
The shrimp have no predators inside the sphere - limited (or zero) exposure to disease - if it truly does provide for all of their needs, they never want for food. They might well be happier there...if a shrimp can be "happy".
Incidentally, these spheres are not really self-perpetuating - the shrimps rarely survive more than a couple of years, then everything goes to hell. SteveBaker (talk) 18:21, 1 August 2015 (UTC)
I have not heard of these before. Interesting concept. Presumably the only energy input is sunlight, and I find it difficult to believe they can get the balance of the biota right to prevent algal blooms while creating sufficient energy for the shrimp to survive in any long-term way. Along with Pain in invertebrates you might also look at Pain in crustaceans.DrChrissy (talk) 19:08, 1 August 2015 (UTC)
We have an article Ecosphere (aquarium). It gives a time frame of 2-3 years for the shrimp, but this is from the manufacturer. The most useful looking ref there seems to be this old one [13] from Carl Sagan (it's on the manufacturer's site but was published in a magazine), but other then being old, it doesn't seem to actually say how long it was owned. Nil Einne (talk) 21:33, 1 August 2015 (UTC)
I would think that the shrimps end their days suffocating in a marine equivalent of Xingtai like smog. Metabolism create many complex hydrocarbons. There appears not to be any activated charcoals included to help to absorb these. The (dead) coral will also increase the calcium content of the water (dissolved by the acids formed from metabolism). Planet Earth has a troposphere, stratosphere and ionosphere where these hydrocarbons get broken down again (by UV, mono-atomic oxygen etc.), into gases that are useful to biological life forms(the other spheres are nether here nor there in this). So I can’t imagine these shrimps end their days as very happy shrimps in such foul water and so probably experience great distress. --Aspro (talk) 22:39, 1 August 2015 (UTC)

Battery-powered electric toothbrush[edit]

I just bought a brand-new battery-powered electric toothbrush. I was just about to use it, but then it dawned on me. Can I use this in the shower? (In other words, brush my teeth while I am in the shower.) I read the package, and it said nothing at all about contact with water. And, of course, it is probably assumed that a toothbrush will have contact with water (whether in the bathroom sink, or shower, or wherever). But, still, it seemed like something that is maybe not a good idea? I was not sure. Any thoughts? And, if it is safe/OK to use in the shower, how can that be, seeing that it is electric and has a battery? Thanks. Sorry if the question sounds stupid. 2602:252:D13:6D70:CDE5:E7AB:66FA:70CE (talk) 19:12, 1 August 2015 (UTC)

According to Philips, yes. Other brands of electric toothbrushes are available, but I'd have thought that one you couldn't use in the shower would be at a bit of a marketing disadvantage. Tevildo (talk) 21:07, 1 August 2015 (UTC)
Mine has a battery, but no charger. It's just a stand-alone variety, not like the one in the link you provided. So, back to my second question: if indeed it is safe/OK to use in the shower (as seems to be the case), how can that be, seeing that it is electric and has a battery? 2602:252:D13:6D70:CDE5:E7AB:66FA:70CE (talk) 22:40, 1 August 2015 (UTC)
To start with, you should check the manufacturer's website (or the instructions) for confirmation that it is safe to use. As a consumer product, it's very likely to have a electrical safety certificate from the appropriate authority (such as Underwriters Laboratories). As the voltage will be low, there's no risk of electrocution - the main risk is a short-circuit causing the battery to overheat. This will have been addressed by the designer - if it uses disposable batteries, it might have a "Do not use NICAD batteries" warning, as these have a low internal resistance and are more likely to overheat than other types. As a device intended for use in wet conditions, the electrical components will be in a watertight compartment - see IP rating for the various standards applicable. Tevildo (talk) 22:59, 1 August 2015 (UTC)
Chances are it uses two or three AA cells, which if you go and chuck them into a cup of tap water do remarkably little- even if you connect them in series (well how do you think I know that?). The voltage, up to 4.5 V, is not sufficient to endanger life and limb unless you manage to surgically insert them into your body. So don't do that.;f=104;t=000779;p=1 discusses 9V batteries and tongues. On balance it seems that even 9V is extremely unlikely to hurt you, given that you hold the device in your hand and the bit in your mouth is a plastic (ie insulating) wand. Also " The lowest voltage for fatal electrocution I found in literature is 46 volts (in Patel & Lo, Stroke (1993), vol. 24 pp. 903-905), five times higher than the voltage in question. " - when discussing 9V batteries. If the device is not designed for use in damp or wet environments then it was designed by an idiot, and will probably corrode and fail. But it won't hurt you unless you drop it on your toe. Greglocock (talk) 02:22, 2 August 2015 (UTC)
I have an electric toothbrush. Its battery is rechargeable and is sealed inside the hand-piece. I agree with User:Tevildo - there is no risk of electrocution of the user if it is taken into the shower or a bath or swimming pool. The worst that could happen is rapid and premature discharge of the battery, necessitating recharging before further use; but even that is highly unlikely. Any electrical item that is likely to be used in the vicinity of moisture is either designed to be fully immersed in water; or it carries a large warning label saying "Do not use this appliance when wet or near water". Dolphin (t) 06:37, 2 August 2015 (UTC)
Why would you use a toothbrush in the shower? ←Baseball Bugs What's up, Doc? carrots→ 07:02, 2 August 2015 (UTC)
I brush my teeth while I take a shower. Don't lots of people do that? 2602:252:D13:6D70:CDE5:E7AB:66FA:70CE (talk) 07:48, 2 August 2015 (UTC)
Rinsing your mouth with warm water? ←Baseball Bugs What's up, Doc? carrots→ 11:22, 2 August 2015 (UTC)

August 2[edit]

Missing airplane MH-370[edit]

Let's just assume that the debris found near Réunion Island is, in fact, from the missing airplane MH-370. Does that conclusion in any way help searchers to actually find the plane (i.e., the rest of the plane)? If so, how so? Or does this discovery simply tell us three basic things: (1) Yes, it was MH-370; (2) Yes, it crashed; and (3) Yes, it crashed somewhere into the Indian Ocean. Other than that very basic info (those three facts that I listed), can this conclusion (that the debris is definitely MH-370) help locate the missing plane at all? Thanks. Joseph A. Spadaro (talk) 06:10, 2 August 2015 (UTC)

If examination of the recovered item proves that it came from MH-370 it won't help locate the flight data recorder or the remainder of the wreckage. However, close examination of the item may provide information as to whether the aircraft struck the ocean at very high speed, such as in a steep dive, or at the sort of speed appropriate to a controlled ditching. It may also reveal whether the item has been deeply submerged before breaking free from the wing and rising to the surface, or whether it broke free before the remainder of the wreckage sank. None of these things are likely to contribute to knowledge about where the aircraft struck the ocean but they might provide a little information that the world doesn't presently have. One thing is certain - this item will be subjected to the most intense scrutiny by a lot of people trying to find out whatever they can. Dolphin (t) 06:29, 2 August 2015 (UTC)
Can people who study waves, currents, and water paths somehow calculate a "reverse" path, to see where the debris originated? Joseph A. Spadaro (talk) 06:35, 2 August 2015 (UTC)
Yes they can back calculate likely paths, aided by a zillion little rubber ducks . More to the point any relevant wreckage at all provides confidence that they are in the right hemisphere, and not completely wasting their (my) money. Greglocock (talk) 06:40, 2 August 2015 (UTC)
Here is the Wikipedia article on that event, with the Rubber Ducky Toys: Friendly Floatees. Joseph A. Spadaro (talk) 07:39, 2 August 2015 (UTC)
Yes. But there would be many such reverse paths; and the information wouldn't show whereabouts on any of those paths the item began its languid journey towards la Reunion Is. About all such information would reveal would be a statement that the item was almost certainly released somewhere in the Indian Ocean. Even that would be useful in dispelling some of the conspiracy theories about the aeroplane being flown to a secret destination in Asia or India or China etc. Dolphin (t) 06:44, 2 August 2015 (UTC)
On the news the other day, they were saying that studying the barnacles attached to it may help determine what depth it came from, as there are apparently different types of barnacles at different depths. The report also said that the current search area appears plausible as an area of origin. Rather large, of course. As to the conspiracy theories, that garbage most likely created false hope for the relatives of the missing. ←Baseball Bugs What's up, Doc? carrots→ 07:01, 2 August 2015 (UTC)
I'm not suggesting the discoveries will silence the purveyors of conspiracy theories! I imagine they will see the item discovered on the beach as incontrovertible proof that the bad guys fabricated a piece of a B777 wing, tethered it in the sea for a year to build up a few barnacles, and then deliberately placed it on a beach on la Reunion Island to mislead the world into thinking the aircraft splashed down in the Indian Ocean, and therefore stop looking at isolated airstrips in Asia, India, China etc! Dolphin (t) 08:05, 2 August 2015 (UTC)
The finding of MH-370 wreckage in the ocean can be summarized in one quote: "They're dead, Jim." --DHeyward (talk)
I think that this discovery will lead to some very productive work in modelling the ocean currents and debris field. Already a second piece of flotsam (though I am sorely tempted to call it jetsam) has been discovered on the island ( [14] ) Previous models predicted the wreckage would turn up 4500 miles away, at Indonesia [15]. That article also says the plane didn't nose-dive, but descended gradually or ditched. I feel like there are two possibilities - one, the models are wrong, or two, the search was in the wrong place all along. It will be interesting to find out which.
I've definitely been inclined to follow the conspiracy ideas, and really, the wreckage sort of backs them up. Initially, I thought the plane might have been hijacked and hidden somewhere, but as ransom demands never turned up, that seemed less likely, and then the search proposed it was taken south somewhere it couldn't reasonably be expected to land. But if the plane turns out to have gotten most of the way to Africa instead, this could be seen as the same hijacking plan, but simply running out of fuel along the way. Wnt (talk) 11:12, 2 August 2015 (UTC)

Knee anatomy[edit]

There is a large cord I can see and feel on the lateral (outside) part of the knee and I'm curious what part of the knee it is. Here is a picture I am thinking either the LCL, the IT band, or the hamstring.--Tarhound21 (talk) 07:47, 2 August 2015 (UTC)

See Knee. That is indeed the fibular collateral ligament - the hamstring is positioned more medially (down the centre of the knee at the back, not at the side). Tevildo (talk) 08:17, 2 August 2015 (UTC)