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December 1

multimeter died - why

hello, I've got a notebook that connects to mains via an external PSU (like all notebooks.) I wanted to test the isolating property of the PSU, so I tried to measure resistance between the notebook's chassis and the protective earth contacts in the power strip (the PSU itself has only a Euro plug with two prongs and no protective earth.) This is probably a totally wrong way to do it, but that's what I did. In any case, the multimeter (I set it to 200 Ω) died.

Thinking there must be high voltage (something must have killed the DMM) and without having another DMM, I connected a standard phase tester and also a LED with series resistor in the same manner (between chassis and PE.) Both lit up (the diode only dimly.) The PSU was emitting a hissing high-pitched sound all three times I connected anything between chassis and PE.

What happened? It is my understanding that chassis is also the (-) terminal of the PSU and there should be no conductance between either (+) or (-) terminal of the PSU and ground, but it seems there not only is conductance but non-negligible currents flowing and a potential difference, too. Why? And what's with the whistling sound? 78.53.24.242 (talk) 01:37, 1 December 2017 (UTC)

My mental image (most certainly wrong) of a PSU, even though it is a swithing type, is that, like a transformer, the "secondary" should completely float and be galvanically decoupled from everything (incl PE). 78.53.24.242 (talk) 01:56, 1 December 2017 (UTC)

Earthing systems vary in different parts of the world. For example, in the U.S. the ground connection of a building or is typically wired to join up with the neutral power wires of things in the building. Harmonic distortion could therefore create a voltage difference, I think. There was a bit of discussion about these variations in regard to a hotel in Dubai a few years ago [1] ; there had been some other fire in that part of the world caused by it, AFAIR. Wnt (talk) 10:07, 1 December 2017 (UTC)

I cannot think of any way that harmonic distortion in a mains power distribution system could occur to any significant degree, let alone to the extent that it would cause the reported problem. Care to expand on that? Akld guy (talk) 22:34, 1 December 2017 (UTC)

Per Multimeter#Safety, most multimeters include a fuse or two, so yours might be easily repaired. And if you get it working, you can us it to check for voltage. -- ToE 19:09, 1 December 2017 (UTC)

Depending on the meter ensure, the turn switch is properly locked on position. Always check wiring first. Then check for voltage, before measuring resistance. Discharge capacitors first, least on power supplies! On a damaged multimeter, check remove all probes first, the remove all plugs. Open the multimeter and check fuses. Replacement of damaged resistors may cause false measurements due not calibrated. A model DT830B can be bought for less than $5. A possible damage might be caused from probing ohms of a power grid voltage filter capacitor. Some non-certified PSUs have no bleeding resistors installed. A failed or not properly installed bleeding resistor causes the PSU keeping the voltage. Be careful on filters installed previous the main power switch. Y-caps have no bleeding. --Hans Haase (有问题吗) 15:37, 7 December 2017 (UTC)

Why was the page associated with Günter Bechly removed from Wiki? (previously "Evolution")

Why was the page associated with Günter Bechly removed from Wiki? - 75.165.137.113 (talk · contribs)

Who's Gunter Bechley? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:52, 1 December 2017 (UTC)

Günter Bechly. The discussion on proposed deletion is here. Akld guy (talk) 04:43, 1 December 2017 (UTC)

Media coverage is here: A Respected Scientist Comes Out Against Evolution – and Loses His Wikipedia Page Gråbergs Gråa Sång (talk) 07:42, 1 December 2017 (UTC)

More from a Discovery Institute blog:[2][3]. Gråbergs Gråa Sång (talk) 07:48, 1 December 2017 (UTC)

A copy of the article is at Deletionpedia: [4] Looking at it, it seems to be pretty marginal per the Wikipedia WP:GNG policy, which demands multiple sources independent of the subject. (That means "jimdo.org" references don't count) Also, the sources are supposed to be about the subject i.e. biographical, rather than just papers he wrote, for example. I didn't look at the debate, but I imagine the issue of whether coverage of him by the Discovery Institute is "independent of the subject" would have been the most interesting philosophical issue there. Note that continuing coverage of Bechly -- including coverage of the deletion of the Wikipedia entry cited above -- could end up providing the needed "notability" for Wikipedia to have an article. ("Notability" is really a measurement of whether an in-depth article can be written without borrowing the ax of one single biographer) Wikipedia is prone to both the legitimate effect that a topic in the news gets more eyes on it to check coverage matches policy and the illegitimate effect that ideological warriors turn up trying to suppress coverage of what they don't want told. But in this case I think the deletion doesn't fall outside of common practices -- provided, that is, that the deletionpedia article contains most of the content that was originally present, which is actually not something I can guarantee. The "best" ideological warriors relentlessly apply a two-track policy and try to edit out most of the good content of an article at the exact same time as they propose it for deletion so that voters looking at the current text think it is less than it is, and I can't directly check for that. Wnt (talk) 10:21, 1 December 2017 (UTC)

This guy sounds like the Erik von Daniken of paleontology. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:32, 1 December 2017 (UTC)

Well, we have an article Erik von Daniken, but that doesn't really suggest a disposition in this case. Wnt (talk) 14:22, 1 December 2017 (UTC)

Yes, the guy would have to have a few best-selling books and a lot of commentary on them. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:40, 1 December 2017 (UTC)

WP:Academic would be the relevant guideline, linked to and discussed in the deletion discussion mentioned above. Note that while I didn't read the source but the headline above suggests it's misleading. He apparently "came out" in 2015 and started working for the DI in 2016 and was even in a documentary then. The page was only deleted about 2 months ago. Reading the deletion discussion, I'm not surprised the article was deleted. Regardless of whether said subject meets WP:Academic, there was very little decent defence of the article based on it (or the GNG) instead a lot of the keeps were just basically saying keep or that the subject shouldn't be punished for supporting ID (no shit). By comparison, many of the delete arguments seemed to be based on policy. Nil Einne (talk) 15:23, 1 December 2017 (UTC)

In Intelligent design, there are several names which link to articles, so presumably they are notable by comparison to this one guy. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:34, 1 December 2017 (UTC)

As the term "intelligent design" itself, by trying to establish an intellectual Oxymoron, ironically proves as prime example, Phenomenology (philosophy) and "real" science are "worlds apart" concepts of knowledge. To cut to the case, wikipedia was, is and will be trying to stay on the "real" side or to cite our established guidlines Wikipedia:What Wikipedia is not#Wikipedia is not a publisher of original thought. --Kharon (talk) 20:46, 1 December 2017 (UTC)

O/T I read the deletion arguments and got a very strong whiff of IDONTLIKEIT, but I must admit the attempt to stack the vote probably hardened attitudes. Greglocock (talk) 20:51, 1 December 2017 (UTC)

The "best" ideological warriors relentlessly apply a two-track policy and try to edit out most of the good content of an article at the exact same time as they propose it for deletion so that voters looking at the current text think it is less than it is, and I can't directly check for that. are you sure those are not simply editors attempting to make articles comply with WP:NOTCV and remove unreliably sourced material such that what has value, if any, becomes visible? —PaleoNeonate – 07:59, 2 December 2017 (UTC)

Is spacetime a manifold?

I have heard people say that "spacetime can be modeled by a manifold" (similar language is used here for example), while others say that "spacetime is a manifold" (like the paragraph beginning "Mathematically..." in this article). Is spacetime literally an example of the mathematical structure? Or is the abstract notion of manifold simply an accurate (as far as we know) model of the physical object? Do people even think there is a distinction between these two ways of speaking?

(Let me know if this should be moved to a different section. I could see this being a better question for philosophers, or perhaps even mathematicians. Also, my background is mainly in math, so I apologize if I say incorrect things about physics.) AlfonsoAnonymous (talk) 13:04, 1 December 2017 (UTC)

There's not really a way of distinguishing between the two ways of speaking without getting deep into the philosophy of language and of serious ontological and epistimological questions regarding the nature of existence and knowledge. The answer to your question lies mostly in the scientifically unanswerable (from a Popperian falsifiability point of view) questions regarding the nature of the connection between knowledge and being; specifically how does a person (or humankind) prove that their perception of reality is reality. At one level, all models are wrong; but from an equally valid perspective all knowledge exists of nothing but models. When someone says "the universe is a..." vs. "the universe can be modeled as a..." the one is speaking as an nearly indistinguishable synonym of the other. After all, if the model is demonstratedly not consistent with observations (that is, if "can be modeled" is not measurably consistent with "is") then it's not a useful model, is it? --Jayron32 13:13, 1 December 2017 (UTC)

I actually wanted to get "deep into the philosophy of language and of serious ontological and epistimological questions regarding the nature of existence and knowledge." Before asking more questions I just want to clarify something to make sure we are on the same page. Can you elaborate on what you mean by "nearly indistinguishable synonym"? AlfonsoAnonymous (talk) 13:38, 1 December 2017 (UTC)

The point is, all knowledge is models. Your brain doesn't contain reality, it contains models of reality. When you see an object, your brain constructs a model of that object that you then perceive as the object. So the question "is there a difference between saying "Phenomenon X is" or "Phenomenon X can be modeled as" sounds different enough, but really isn't. If the model is not a sufficiently accurate representation of reality (for whatever purpose you're using the model for) then it is wrong to say it models reality. And if it does sufficiently model reality, then it is perfectly acceptable to treat it as reality. Because that's what your brain does to every experience you have anyways. --Jayron32 13:41, 1 December 2017 (UTC)

1. Why do you believe that all knowledge is models? It is at the very least a conceivable possibility that there exists an external reality independent of myself, and that I have direct access to that reality through my senses. Perhaps the world that I perceive is truly real, not a model of reality, or anything else. What are some reasons to think otherwise?
2. Let's say I agree that all knowledge is models. How do I know that two models are the same? Do physicists currently believe that the model our brain creates when we perceive reality is identical to (in the strongest possible sense) the mathematical notion of a manifold? How does one determine how good a model has to be before it can be treated as reality? How do we know that a manifold is a good enough model for spacetime that we can use the two interchangeably? What do you mean by "sufficiently"?
3. It seems like one could possibly agree with you that all knowledge is models, and that a good model of the universe is indistinguishable from the real universe, and still disagree that the model and the universe are identical. Perhaps they disagree with the identity of indiscernibles for any number of reasons. Or perhaps they argue that you are making a category error. A mathematical structure and the physical universe are completely different types of object, and so it doesn't even make sense to say that they are the same.
4. I disagree that the two are synonymous, even practically. Frequently when people say "X can be modeled as Y," they simply mean X and Y share enough properties that, for the problem at hand, we can pretend X is Y and get good enough results. You seem to be saying that anytime we use the phrase "X can be modeled as Y," we mean "X and Y cannot be distinguished using any known experiments." But that is simply not how people use the term. Even if people do use the term "models" the way I think you are, I think it is a stronger claim to believe that spacetime is a manifold than spacetime is modeled by a manifold. Perhaps I misunderstand your usage of the term. But it seems that old-school physicists were correct in saying that spacetime can be modeled by Euclidean space (since, up to that time, no evidence existed proving otherwise), but they would be incorrect in saying that spacetime is Euclidean (since we now know that this is objectively, demonstrably incorrect) AlfonsoAnonymous (talk) 14:30, 1 December 2017 (UTC)

I'll try to address these one at a time: 1) It depends on what you mean by knowledge and reality and prove. A) Can you ever establish beyond any doubt that senses accurately represent reality? We take it as axiomatic because it isn't possible to function if we didn't assume it did. But the question at hand is not whether we need to assume that our knowledge is reality, but whether we can prove our knowledge is reality. It isn't even demonstratedly true: when I say I know what an apple is, it doesn't mean I have an actual real apple in my mind. It means my mind has a sufficiently useful representation of an apple. What do we call a sufficiently useful representation? I'll give you one guess, and it starts with the letter "m". 2) We know that the model (whatever it is) is sufficient because it makes predictions which match observations to the limit of our measuring devices. That is, the model makes no predictions which are themselves not consistent with observed behavior. A great example of this process at work is the problems with Ultraviolet catastrophe. At the time, existing models of thermal radiation of light made predictions that did not match observed behavior. The model had to be discarded because it wasn't useful. The new model created (quantum mechanics) became accepted because its predictions sufficiently match observations: None of the predictions made by QM conflicts with observations in the drastic ways that the classical models did. Which is why QM is taken as a sufficient model (for the purposes we are using it) and we had to abandon the classical model. The question of whether QM is reality misses the point; it hasn't been shown to be wrong in its ability to predict observations. We can treat it like reality because it models reality in an indistinguishible way from real measurements, which means we can axiomatically treat it as reality in the same way we axiomatically treat our senses as reality. That's what sufficiency means here. If a model makes predictions which are demonstratedly wrong, it's a shitty model. 3) It isn't that the model and the universe are the same. They are not. It's that the decision whether or not they are the same isn't useful to solving the problem at hand, so it's a pointless intellectual question. That is, whether the model is reality or the model represents reality, from our point of view, is as useful to answering the scientific question as knowing the price of the tea in China. Because that's not what scientific models are doing. If we say "The universe is a manifold" or if we say "The universe can be modeled as a manifold", it isn't that those are strictly identical statements. They are not. It's that "deciding whether or not they are doesn't matter". We can say "is" here because we have no means to say that it is not. That is, the distinction between "is" and "can be modeled by" is not testable, falsifiable, etc. If the difference WERE shown to be there (that is, if I could show that, beyond a doubt, my model did not match observations, as in the ultraviolet catastrophe example above), then the model is wrong and we should not be using it. Insofar as the manifold model has not yet been shown to have any disagreements with observations then it is sufficient to say it "is". Any falsifiable premise which has not been shown to be inconsistent with reality is sufficient to say it is as close to reality as we need it to be. 4) That's what we are saying. If we had experiments that showed that modeling X as Y showed inconsistencies, it's a shitty model and we should not be using it for that purpose. --Jayron32 15:49, 1 December 2017 (UTC)

I appreciate your thought-out responses. 1. I think I am missing something. Why is it a question of proving that we experience reality as opposed to assuming that we do? What's wrong with simply taking as an axiom that my experience is not just a model, but is actually reality? And what is your point with the apple? No one is claiming that knowing what an apple is means having a physical apple in your brain. 2. So the threshold for when a model is good enough is a function of the quality of our measuring devices. But the way the universe actually exists is not (unless you have a convincing argument that the laws of physics change as our technology improves). So it is incorrect to say that "X models Y" and "X is Y" are the same, because the former's truth value is time and human dependent in a way the latter is not. And I am still not convinced that treating something like it is reality is the same thing as saying it truly is reality. 3. So here you say that the model and the universe are not the same, but elsewhere you seemed to argue that they were identical. What you are saying here makes more sense to me. I agree the question is not useful to science, but I strongly disagree that that makes it a pointless question. Do you really believe that all of philosophy is pointless? 4. I disagree with your last sentence, but I think it is somewhat of a side point. AlfonsoAnonymous (talk) 16:37, 1 December 2017 (UTC)

1) No, it's not a problem to take it as axiom that your perceptual models is realty. It's a problem to say that in case A) it's OK to take the model is reality, but in case B) to say it is not. Look at my examples. Do you say "I am thinking of a model of an apple" or do you say "I am thinking of an apple". If you can say that "I am thinking of an apple" is a valid statement, even though you don't have a real apple inside your brain, just a model of an apple in your brain, then it stands to reason that it is valid to say "The universe is a manifold" when really, all you really have is a model of the universe as a manifold. If you can trust the model of the apple your brain gives you, you should be able to trust the model of the shape of the universe science gives you. 2) The question is not "how does the universe exist". The question is "How do I have knowledge of how the universe exists". The first is literally unanswerable without axiomatically accepting that models correctly represent reality. If you do not accept that you can trust the model, then you cannot possibly say that you understand anything about the universe. Either the model is valid, and then it tells you something about the real universe, or you have established the model is wrong, at which point the nature of the universe is an open question. There's no way to know anything about the universe without a valid model. If you say there is, provide a counter example to say "Here's something we know about the universe, but we have no model of it". Please try, you won't find one. 3) What I say is that linguisticly "is" does not mean "can be modeled as". But what I also say is that philosophically, it doesn't matter because you've already established that models can be axiomatically assumed to be reality. You said it is an "axiom that my experience is not just a model, but is actually reality" even though you don't carry actual real objects in your brain, just models of objects in your brain. If we axiomatically accept that the mental models that allow us to interact with the world are trustable and equivalent to reality, then it's OK to treat the scientific models we have of reality as equivalent to reality. --Jayron32 17:54, 1 December 2017 (UTC)

Another thing to think about here is what we really mean by scientific model: a model in this context usually means a mathematical tool used to predict behavior reliably. That is, we have a series of observations of something; a collection of data points. The goal of the scientist here is to devise a mathematical function, equation, tool, etc... that when it is fed the correct inputs, reliably produces outputs that match observations. From a rigorous point of view, however, it is never possible to prove (in terms of definitive mathematically rigorous proofs) that the model chosen must be correct from the point of view of there could never be any other model which works. For any arbitrary and finite set of numbers, there always exists an infinite number of irreducable mathematical functions which would produce those numbers. Thus it is always technically possible to create an infinite number of models which sufficiently reproduce the observed data. Science has developed a workable number of conventions that allow it to be useful in the face of a lack of mathematical rigor; for example Occam's razor, which holds that in the face of multiple competing models, the one which is the simplest is the most useful. Box's famous aphorism above (all models are wrong, some models are useful) is a reminder of that: Insofar as no observation can be infinitely precise, there always exists the possibility of pernicious or as-yet-unknown factors which a model may not be built to account for. Insofar as there exists the possibility of multiple rigorous models which all reporduce the observed data, there must be a way to choose the correct model. Box's aphorism is merely another statement of Occam's razor from another perspective, we choose models based on usefulness (their ability to reproduce observed data reliably in the simplest possible way) rather than on ther "rightness" (their ability to be rigorously and uniquely proven to be correct). It's also valid here, in discussions of science and knowledge and being, to bring up again Karl Popper who reminds us rather astutely that science's job is not to prove things in the usual sense of "establish The Truth beyond any possibility of a doubt". Science's purpose is to test falsifiable propositions, and create models based on the results of those tests. --Jayron32 14:21, 1 December 2017 (UTC)

I don't mean to be rude, and I am sorry if I am missing some obvious point. This seems like general commentary on the philosophy of science, how is it relevant to what I asked? AlfonsoAnonymous (talk) 14:39, 1 December 2017 (UTC)

If anything this further emphasizes why I asked the question. Are physicists claiming that the universe is really a manifold, or merely that a manifold is one of infinitely many correct models for the universe? AlfonsoAnonymous (talk) 14:41, 1 December 2017 (UTC)

Correctness is the wrong question. Again, not to keep hammering the point home here, but Popper and falsifiability has to keep coming up. "Correctness", "rightness", "actual reality", "truth", etc. implies a sort of infinite precision and universal applicability. That is, to say something is correct implies the expectation that it could never be shown to be incorrect. Because if we entertain the possibility that it could be shown to be incorrect, then it never was correct to begin with. Valid scientific knowledge cannot be built on such a flimsy premise. Scientific knowledge is built on falsifiability and consistency. A premise is only scientific if it is falsifiable (could be shown to be wrong) and consistent (has not yet to be shown wrong). Nothing can ever be proven correct, if it could be it wouldn't be falsifiable, which by definition means it isn't testable, and non-testable ideas are just Russell's teapots, outside of the realm of scientific study. It can only be held to be not yet wrong. Any modern scientific principle you'd care to name meets those requirements. Questions of "yes, but is it REA, like REALLY REAL, like TRUE," are outside of any discussion of science. To say that space "is" a manifold is sufficient for science, because it's a falsifiable premise (there could be observations which may some day show it to be incorrect) and a consistent premise (there have not yet been any observations which have yet proven it wrong). Any other possible "models" you are coming up with simply aren't scientifically valid: to claim as valid that a model makes predictions that doesn't match observations, in the face of a model which does, is ludicrous. --Jayron32 15:49, 1 December 2017 (UTC)

Tell me if you agree with this summary. Strictly speaking, "X is Y" and "X models Y" are distinct propositions. The former can be interpreted in two ways. First, it can be read in the metaphysical sense, as an absolute statement about objective reality. Second, in a scientific context, it can be interpreted as a shorthand for something like "X and Y are the same in all ways we have so far measured, and assuming they are in fact identical does not contradict any other propositions within the leading scientific theories." This second interpretation of "X is Y" basically matches what is meant by "X models Y". Thus, in the context of science, the two are used interchangeably. AlfonsoAnonymous (talk) 16:37, 1 December 2017 (UTC)

You are correct when you said Or is the abstract notion of manifold simply an accurate (as far as we know) model of the physical object?. It is worth trying to describe a manifold is. In the lead to the article it states:

One-dimensional manifolds include lines and circles, but not figure eights (because they have crossing points that are not locally homeomorphic to Euclidean 1-space). Two-dimensional manifolds are also called surfaces. Examples include the plane, the sphere, and the torus, which can all be embedded (formed without self-intersections) in three dimensional real space, but also the Klein bottle and real projective plane, which will always self-intersect when immersed in three-dimensional real space.

In other words, it is analogous to a surface, but only a 2-manifold is strictly a surface (topology) (the kind you get in 3D space). Imagine you lived in space with 4 spatial dimensions: a "surface" in that world would be a 3-manifold. In general, a n-manifold is a "surface" in a world with n+1 spatial dimensions.

Now spacetime can be modeled as a manifold: it is a 3-manifold, as there are 4 dimensions to spacetime. But in this case there are only 3 spatial dimensions; the other dimension is time. Because of this it is technically a special case of a pseudo-Riemannian manifold, called a Lorentzian manifold: this has different properties to the "standard" 3-manifold for technical reasons.

Now the explanation for gravity is "warping" of this Lorentzian manifold. It is analogous to the warping of a piece of flat piece of paper when you crumple it. Because of this warping we feel the effects of gravity. This scientific treatment of gravity is very useful as it describes the effects of gravity in a more accurate manner; e.g. the bending of light is accurately described using this maths. The general theory of relativity, which uses the maths of a Lorentzian manifold, has been incredibly successful in accurately explaining various observed phenomena.

I hope this helps. --Jules (Mrjulesd) 14:26, 1 December 2017 (UTC)

I fail to see how the majority of your answer is relevant. I know perfectly well what a manifold is, and I am more than familiar with the basics of general relativity you describe. How does any of that information answer the question I asked? AlfonsoAnonymous (talk) 14:35, 1 December 2017 (UTC)

Well I wasn't to know that. But my basic position is that, spacetime can be modeled as a 4 dimensional Lorentzian 3-manifold, but isn't directly that mathematical concept. It's a bit like saying a hydrogen atom is spherical, but it is not the mathematical definition of a sphere; a hydrogen atom merely models a sphere in that instance. I earlier said You are correct when you said Or is the abstract notion of manifold simply an accurate (as far as we know) model of the physical object?. and that my position. --Jules (Mrjulesd) 14:46, 1 December 2017 (UTC)

I appreciate the response. I meant to ask if you were trying to make another point with the additional information, trying to provide some kind of argument for your position, or simply providing supplementary information. I see now that I cam off a bit rude in my previous comment. AlfonsoAnonymous (talk) 14:51, 1 December 2017 (UTC)

Thanks for that. I think it comes down a bit to semantics. If the definition of a manifold is "a mathematical structure" (as currently held) then a manifold merely models spacetime. But if the definition was "spacetime, and (mathematical-)structures with similar properties" then spacetime would actually be a manifold. --Jules (Mrjulesd) 16:02, 1 December 2017 (UTC)

The "spacetime is a manifold", is, as you point out, preceded by "mathematically". That is, it's isness in this context is only being referred to in the context of mathematics, which is a world of ideal abstractions. Of course it is mathematically a manifold, what you seem to be curious about is whether spacetime, in actuality, is a manifold. And one completely reasonable and defensible answer to that is "of course not". Because manifolds are mathematical abstractions, where as space is a thing. I can point to a cubic meter of space, I can put a box around it. But I cannot point to a manifold, any more than I can point at two. I can point at two apples, or the numeral "2", but twoness is just an abstract concept. At least according to some schools of thought in philosophy of mathematics. The other completely reasonable answer is "of course spacetime is a manifold", with similar rationale, just going the other way (I cannot point to spacetime, it exists only as a concept, etc).

If you want to get into the ontology and epistemology, that is admirable, but I suggest that the manifold nature of spacetime is not the right place to start. Maybe first start thinking about mathematical realism in general, or the (questionable) reality of the so-called real numbers. Even if you want to get more in to the correspondence between mathematical structures and the "real" world, something like "the path of a photon in a vacuum is a straight line" may be a simpler question to wrestle with, though it includes all the same problems as your original question.

For this kind of stuff in the philosophy of science and math, ontology, etc, I recommend not reading Wikipedia articles, and instead would point to the readings at the Stanford Encyclopedia of Philosophy. (While WP is excellent, it is not a reliable source, and my personal opinion is that we are especially bad and confusing at philosophy of science and math.)

Some relevant articles at SEP you may be interested in: Laws of nature, Physicalism, Paradox of knowability, [Identity, Logic and Ontology, The limits of Knowledge and Justification.

In closing, it's fine to ask this here, but it really is more about philosophy than science. From a strictly scientific point of view, Jayron's right, this is basically a distinction without a difference. (And while most modern scientists are implicitly Popperian, they tend to not be very professionally interested in this stuff, and leave it mostly to the philosophers) SemanticMantis (talk) 16:21, 1 December 2017 (UTC)

I appreciate the response. I know I may not sound like it, but I am actually not new to philosophy. I double majored in math and philosophy in undergrad. I was mostly wondering what the physics perspective was on the issue, since I know less about what physicists think about the world. I know that most physicists aren't terribly interested in these kinds of questions, but I thought at least a few people here might be (and it seems I was right). AlfonsoAnonymous (talk) 16:43, 1 December 2017 (UTC)

The reason I asked about this specifically, as opposed to say the trajectory of a photon, is because everything else I hear in physics is simply stated as "is." "The path of a photon in a vacuum is a straight line." I never hear can be modeled by in any other context, or at least not as frequently. So I was wondering if there was something different or special about the way physicists viewed spacetime. AlfonsoAnonymous (talk) 16:53, 1 December 2017 (UTC)

I think a lot of it is down to simplicity. If you said "the path of the photon can be modeled to the mathematical concept of a straight line" it would create a lot of complexity to a simple topic. But if you instead say "the path of the photon is a straight line" there is alot of simplicity without much in the way of loss of understanding. --Jules (Mrjulesd) 17:12, 1 December 2017 (UTC)

Sure, but then why have I heard "spacetime can be modeled by..." or "spacetime can be represented by...", and why it used multiple times here on Wikipedia? It sounds kind of ridiculous when you apply the same language to more basic physics notions. AlfonsoAnonymous (talk) 17:19, 1 December 2017 (UTC)

It's just that different editors have different ideas on how to present ideas. If you feel strongly that "spacetime can be modeled by..." etc. should be avoided perhaps you should discuss it on the relevant talk pages to get them amended. Personally I probably prefer "spacetime can be modeled by..." etc. but that probably a personal view on understandability. --Jules (Mrjulesd) 18:45, 1 December 2017 (UTC)

I think the problem is that we simply don't know what happens at the Planck scale. To take two possibilities that have been proposed, a cellular automaton is clearly not a manifold, and as to whether a quantum foam is a manifold, your guess is as good as or perhaps better than mine. So saying that spacetime "is" a manifold, at the micro level, goes beyond our knowledge. --Trovatore (talk) 19:00, 1 December 2017 (UTC)

You cab read Prolegomena_to_Any_Future_Metaphysics by Immanuel Kant where he attempted to answer precisely the question that you asked: An observer cannot know anything about objects that exist in themselves, apart from being observed. Things in themselves cannot be known a priori because this would be a mere analysis of concepts. Neither can the nature of things in themselves be known a posteriori. Experience can never give laws of nature that describe how things in themselves must necessarily exist completely apart from an observer's experience. Ruslik_Zero 20:57, 1 December 2017 (UTC)

That doesn't sound like Kant, it's far too transparent and to the point. If you are quoting him, @Ruslik0: please give the citation. If it is a summary, please identify whose commentary it is. Thanks. μηδείς (talk) 02:40, 2 December 2017 (UTC)

You should read the the article that I have linked above. Ruslik_Zero 15:55, 2 December 2017 (UTC)

That doesn't answer my question at all. It's even worse than I thought. The entire article is unreferenced, no translator is named, and no link is given to an original text. The article's an entire huge work of OR as far as one can tell. μηδείς (talk) 17:24, 2 December 2017 (UTC)

There's no requirement for a professional translation to source content on wikipedia. See Wikipedia:Verifiability#Non-English sources and Wikipedia:No original research#Translations and transcriptions. There is some limited allowance for using a book as a source of itself, see Wikipedia:No original research#Primary, secondary and tertiary sources and Wikipedia:Identifying and using primary sources. That said I agree the article has major problems and is in need of serious work probably a parring down of content and a far greater use of secondary sources be that in English or some other language.

However I don't understand your complaint about the quotation. It's clear from that article it came from the book itself, section 14. Given that, it's trivial to find the original German text using a simple Google or Bing or whatever search and then finding section 14 [5]. Or since even if you know nothing about Kant, you can find out from our article on the book it was written in the German language, you can then check out our article on the language and find out it's called Deutsch. You can then go back to the article on the book, if you look at the left bottom, you'll see a link the the Deutsch article on the book, mostly coincidentally the top link. Sure enough checking out that version, if you scroll to the bottom you see two different links to the original German text. Lots of options if you do some very basics. (Now you don't even have to do the search or whatever since I've added a link to the German text in our article, although you'll still have to find the relevant section by yourself. Incidentally, ignoring your edits and my edits, the article has been like that since June and the German one since March of last year. So I'm assuming I admit without checking templates or wikidata that you'll have seen the same thing as I saw.)

Of course, using the links already in our article, you can see an English translation en:Wikisource:Prolegomena to Any Future Metaphysics/Second Part by Paul Carus. Or [6] (link to whole work [7]) by Jonathan Bennett (philosopher) ([8]). I should note the link on our article was originally to the whole website, I've now updated it to link to Kant's works in particular but not the book itself since some people may prefer the chapter PDFs. As an added bonus, I've now replaced a dead link in the article so you can also look [9] at a modified version of the Paul Carus translation combining the efforts or James W. Ellington and James Fieser.

If you're not happy with any of these translations, I suspect a simple internet search will find more. Or you're free to ask at WP:RD/L. Well I mean someone could ask for you but the thing is, you're sort of expected to do some basic work when you ask questions at the RD be they original questions or follows up. If this doesn't suit you and you expect to be spoonfeed everything, I'm not sure the RD is the right place for you, sorry.

P.S. I'm not sure sure our article's language accurately reflects what Kant said based on the 3 English translations provided, but that's not something I'm particularly interested in. I remain uncertain why there was any need for all this fuss when some very simple effort would have found 2 of these translations, and very slightly more effort the German text. So the actual issues surrounding what our article says and what Kant said, could be discussed rather than pointless side issues. </p

Nil Einne (talk) 10:20, 3 December 2017 (UTC)

I am sorry Nil, but this "you can verify it all if you google it" justification is nonsense. The entire article is the personal essay of one user who has either plagiarized large tracts of translated material, or produced his own research. Of course properly identified primary sources can be quoted directly in small portions (not the case here) and short obvious translations--Das Boot: "The Boat"--can be given (not the case here). The whole article is unverifiable based on a lack of specific given sources, and it is not our job to provide sources for one editor's personal OR. μηδείς (talk) 21:25, 3 December 2017 (UTC)

I have no idea WTF you are talking about, I never said anything about "you can verify it all if you google it". Nor did I say the article is okay, actually the only real comments I made about the article explicitly said it was not okay. Nor did I say it is "not our job to provide sources for one editor's personal OR". Please read what I said again.

What I said is that there is no requirement for professional translations for sourcing and that non English language sources including primary sources, can be used in limited circumstances. I didn't specifically mention but note there is no requirement to provide translations to do so, although it's generally expected people will provide some translation on the talk page, and in some cases in the article, when needed or when there is dispute. Note that this means it's possible for an article to be based entirely on non English sources. And repeating myself, I also made it clear that the article has problems. Although I did emphasise the problem is not so much with regards to translation as you seem to be fixated on, since for all we know the person who wrote that doesn't even speak German and was going solely by one of the English translations. But instead the problem is that it has very little secondary sourcing, be it English or German.

And what I also said is since you apparently want to know what Kant actually said, RuslikZero was quite correct that you could trivially have found so from the linked article since despite the problems it was trivial to find.

Note that these are largely unrelated points. The problems with the article are a given, but they were insufficient to stop you finding what you wanted to know, unless you expect to be spoonfed on the RD in which case the RD is not the place for you. Note that this is not the correct place to discuss problems with article content, so my assumption is you actually wanted to know instead of simply wanting to complain about an article.

If you are only here to complain about an article, I suggest you do so in the right place, since you are after all one of the people who is always complaining about offtopic or unsuitable posts. If you do desire to learn, the information was already all there for you, whatever the problems with the article. In case there's still some confusion, let me repeat one last time, if you expect to be spoonfed answers, it's unlikely the RD is the place for you. You do have to do some basic reading, thinking and yes checking out additional linked or obvious sources if you want to learn anything on the RD.

And yes 2 of the English translations were already linked in the article, despite its problems, and the German original text was trivially findable online via various means. And besides of which, there's no requirement that sources are online be it on the RD or in articles anyway. You could also find the text in German from a decent library, whether directly or via an interlibrary loan and then get section 14 that way too. (Of course for a public domain work, you're free to ask for someone to help you find an online copy if you really can't do so yourself but there's really no reason why you couldn't. And even for a copyrighted work, it's generally acceptable to ask for a quotation, although again there's really little reason why you couldn't have done so yourself. And the thing is, and if that's really what you desired you should have clearly specified what you were after was an online copy or quotation of the original German text since you couldn't find it yourself rather than making it sound like no useful info was provided you when in actual fact all you needed to know as provided you.)

So no, there is no real reason why you couldn't have found the answer yourself from the linked article, despite the acknowledged problems. And if you really really couldn't well as I've said several times, I'm not sure if the RD is the right place fro you, but being politer in your requests will at least make it more likely people will help you.

Whatever the case, now that the original German text and 3 different translations are clearly linked despite your pointless diversions, you are free to dispute, or not, the text quoted here as taken from our flawed article. AFAICT, no one is saying you have to agree with it simply that the info was always all there for you to trivially find. Although repeating myself again, any dispute over the text here should be primarily relating to the discussion here rather than concerns over the article as those should be address elsewhere.

Nil Einne (talk) 12:42, 4 December 2017 (UTC)

Nil, I quote you verbatim: "Given that, it's trivial to find the original German text using a simple Google or Bing or whatever search and then..." That's not my job, the article is OR, and if I had the time to waste I'd RfD it until it was fixed. At this point, it seems the worst effect the article will have is to get undergrads failed for plagiarism if they use it, so caveat lector. μηδείς (talk) 22:40, 5 December 2017 (UTC)

Sure, I have read excerpts from that for class before. But I don't think Kant ever really answers my question, at least not in the parts I have read. (I know it's really short and I should just read the whole thing but I have never bothered.) And even if Kant does, that does somehow give a direct answer, that doesn't mean that his ideas are consistent with general relativity, more recent philosophical work, or the general view among physicists.AlfonsoAnonymous (talk) 10:39, 4 December 2017 (UTC)

• Gravitational waves influence the shape of spacetime. If spacetime is a manifold, rather than modelled by one, then those gravitational waves are part of that manifold, mathematically speaking, since they directly affect its shape, to some small extent. That means that colliding black holes are part of that mathematical manifold, as is their rate of mutual revolution. But even wiggling your finger is going to produce a gravitational wave, at least by a traditional relativistic model without discrete gravitons (in a QM model it would produce a wave of probability; whether that is part of the manifold, depending on whether it is observed or not by the mathematician, I leave as an exercise for the reader!) So your finger is part of the manifold. So if spacetime is a manifold, then the manifold is one that includes descriptions of the positions of every mass in it, as well of course as all the fields that contain mass-energy, if there's a difference. I guess that just means that if spacetime is a manifold then the manifold is spacetime. Hard to write down, though. Wnt (talk) 14:10, 3 December 2017 (UTC)

I don't think I follow. What do you mean by "the manifold is one that includes descriptions of the positions of every mass in it," and "if spacetime is a manifold then the manifold is spacetime." AlfonsoAnonymous (talk) 10:39, 4 December 2017 (UTC)

I should admit I've gone beyond the edge of my knowledge here, and I should bear in mind that manifolds can mean more than one thing. As I understand it a manifold is often defined in a purely topological way -- i.e. we live in a 4D space, perhaps plus some wormholes, but possibly not one tied up on itself like joining opposite faces of a dodecahedron. To argue about such a discrete classification scheme in regard to your point is like arguing whether one apple really contains the number one or whether it merely models the number one. But the other thing is that that our space is a Lorentzian manifold that apparently approximates, but is not exactly equal to, a Minkowski metric. Really, I had a dubious notion that a gravitational wave would conflict with something like the fundamental theorem of Riemannian geometry, but a quick search turns up [10][11] that seem to indicate it doesn't. So I'll punt this back into your court - is the manifold you have in mind supposed to be a precise description of the shape of spacetime, or only a classification of it? Wnt (talk) 16:03, 4 December 2017 (UTC)

pH logarithm

I cannot remember (nor find) this though I ought to be able to. pH is a logarithmic measurement, in log base 10. I'm trying to clean up the article on soil acidification, and I need to confirm that pH means that there is a 10x increase / decrease in ions per number change. This means that pH 5.0 is a 10 fold increase in cations over pH 6.0 and a 100 fold increase over pH 7.0, right? It is part of what makes buffering soil tricky.

Thanks GeeBee60 (talk) 18:21, 1 December 2017 (UTC)

Try the pH article? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:31, 1 December 2017 (UTC)

You are correct in these assumptions. Hydronium cations decrease by a tenfold going from e.g. pH 5 to 6, or 6 to 7. --Jules (Mrjulesd) 18:47, 1 December 2017 (UTC)

I should note that pH is approximately the log₁₀ of the molar concentration of the hydronium ion. Thus, pH 1 means that [H⁺] is approximately 0.1 (=10^-1), and at pH 12 it is approximately 1 x 10^-12.

That said, looking a bit further our articles kind of mush into incomprehensibility, and it's been a while since I last explored this rabbit hole. The article on pH says that it is "actually based on activity" (linking thermodynamic activity), but that article describes a dimensionless number that is not approximately equivalent to a molarity. In turn we are referred to an article on chemical potential that seems too sparing with units of measurement. In chemistry, knowing the units gives you values that you can often only assemble one way, and being confused about them means you're confused about everything, so we really need to dive in and fix this up. Wnt (talk) 21:52, 1 December 2017 (UTC)

The concept of chemical activity is a post-hoc correction to difference between calculations and actual measurement. That is, it is simply a made-up number which is impossible to actually measure that corrects for the difference between actual molar concentrations and measured values like pH. For anyone except overly pedantic physical chemists, it's a pointless discussion, and most people interested in practical chemistry can ignore such concepts. pH=-log [H⁺] is sufficient for about any application.--Jayron32 16:02, 2 December 2017 (UTC)

The thermodynamic activity article starts off with some impressive examples, and I know that there has been a lot of careful writing done in publications on the topic. There are a lot of things in science and math that are regarded as true yet one wants to dismiss them as balderdash (like 1+2+3+4...), and this actually doesn't rank very far up on that scale. Wnt (talk) 14:01, 3 December 2017 (UTC)

I never said it wasn't true. I also did not dismiss it as balderdash. I dismissed it as not helpful to answering the OP's question. --Jayron32 13:24, 4 December 2017 (UTC)

The OP wants to write a Wikipedia article. Even a basic introduction to pH in soil acidity covers this topic [12] and it comes up in a search in reference to things like the amount of fluoride or cadmium leached from soils. All I did was point out the land mine; I didn't say he had to dig it up. Wnt (talk) 15:46, 4 December 2017 (UTC)

"The OP" -- hmmmm -- is that referring to me -- the person raising the question? Might I first point out that I am not under anesthesia and I am able to participate in this conversation. While some of this discussion is way overthinking it, to Jayron32 I disagree with your acerbic comment that --Jules (Mrjulesd) and Wnt are "not helpful to answering the OP's question", (assuming that I am the OP, whatever that is). Instead, why not ASK ME if the answer is helpful or suggest how I might further clarify my inquiry. As noted I am trying to rewrite the article on Soil acidification in a way that clearly yet accurately explains what happens to soil and plants as soil becomes more acidic, and try to offer some insights why. I didn't just roll off the turnip truck, but it has been 30 years since I took my classes in soil chemistry and since then mostly I have been dealing with plants as a landscaper / gardener / etc. and not deep in soil chemistry analysis. So I'm rusty (oxidized).

Anyway, if soil pH is ten times more out of neutral at pH 5.0 than at pH 6.0, then a plant's roots needs to produce ten times more cations to successfully transfer / absorb the different alkali / base minerals that the plant requires. Yes there is more to it than that -- this is a one page article on a topic that people earn PhD's in. But the point I'd like to make (unless wrong) is that increased soil acidity makes it harder for a plant to absorb nutrients because of cation / anion exchange. I appreciate (Mrjulesd)'s acknowledgement that the pH article is (in my words) close to useless in its lack of practicality and clarity -- I did go to it before asking this question. Thank you Wnt for the reference link to Bleam's work -- I shall read it.

OK, I'll stop ranting, and if this is the wrong forum for my question, please redirect me. Thanks again, GeeBee60 (talk) 07:58, 6 December 2017 (UTC)

Thanks for providing a context! In that light, low pH can increase the solubility of certain ions by displacing them from basic sites in the soil. You just have to be careful (or at least specific) which types of nutrients you are discussing. You could discuss it as a balance, where the "proper" pH for an individual species is the one that is a sweet-spot of sufficient availability of all needed nutrients and/or reduced availability of ones that are toxic. I don't have much background in agricultural science, but even as a home gardener, I know that some plants like more acidic and some plants seem to do better at unusual pH if there are unusual soil conditions. DMacks (talk) 08:03, 7 December 2017 (UTC)

"OP" is indeed you, the original poster of the thread. DMacks (talk) 08:04, 7 December 2017 (UTC)

"Original poster" might imply that there has been some retweeting going on. "Opening poster" would be clearer. 92.27.49.50 (talk) 10:49, 7 December 2017 (UTC)

December 2

Who first analyzed the 'particle in a box' model?

This is a question about the history of quantum mechanics. Certain famous physical models are attributed to or associated with the physicists who discovered (or otherwise pioneered) them: blackbody spectrum (Planck), photoelectric effect (Einstein), hydrogen atom (Bohr).

The particle in a box model is an important model in quantum mechanics... My question is: who was the first to study the (quantum mechanical) particle in a box? Or, who was the first to promulgate/publish on/popularize it?— Preceding unsigned comment added by 72.221.67.126 (talk • contribs)

It's hard to find a definitive source, but many references I am finding in Google give a strong relationship between Paul Dirac and the problem, though it is hard to interpret if Dirac himself dealt with the problem, or if it is merely others using Dirac's mathematics in doing such problems.--Jayron32 15:54, 2 December 2017 (UTC)

This is a great question about the history of quantum mechanics - but it will be hard to find a really rigorously-defined answer unless we dive into a lot of really early 20th-century publications searching for the earliest use of the term!

I do not know who first used the name "particle in a box." But the problem itself is an excellent bridge between classical- and quantum- physics, because the fixed boundary-value wave equation had been studied for a long time before it was applied to atomic physics.

In the old days of physics education - that is, before modern quantum theory became part of the standard curriculum - physicists and physics students would spend many years studying classical mathematical methods. In specific, when studying the classical wave equation, one would practice the Dirichlet condition as a solution to a partial differential equation in one or more dimensions.

Mathematically, the Dirichlet problem is identical to the particle-in-a-box in quantum mechanics: it is a boundary-value problem with zero-values at the boundary, and can be solved by an infinite series of sinusoidal functions. With even more mathematical formalism, we can generalize the boundary condition to zero- or non-zero-, on the zeroth- or other-order derivative; and then we have the Neumann boundary condition and its standard solutions; and we have many other problem-variants, whose names are less familiar or universally-agreed-upon.

So, it is almost certain that the very first quantum mechanics theorists immediately recognized this as a useful simplified model identical to the models of classical physics, solved using standard mathematical tools. We might say that mathematicians like Dirichlet - who lived and died before most of quantum physics was empirically established - were the first to model systems in this fashion. Equally, we might blame the particle-in-a-box on any of the other great scientists who studied potential theory: Hilbert, Laplace, Cauchy and others... We can even attribute it to Fourier, whose infamous Fourier series allows us to solve the particle-in-the-box. It is his mathematical formalism that allows us to transform from a function in the domain of the continuum into a series of discrete functions over the domain of integers - in other words, Quantization - and so he solved the "particle in a box" many centuries before other scientists realized that this was an adequate model of the probability-distributions for the variation of the wave-equation that is usefully applied in atomic-scale physics.

For your reading pleasure, here is Quantization as a Eigenvalue problem, (1926, Schrödinger).

Nimur (talk) 01:53, 4 December 2017 (UTC)

December 3

Do facial toning exercises work?

Do facial toning exercises work? I don't see how face muscles could be different from other muscles and not adapt when stimulated by physical exercise, but it could all be just snake oil. Or the effect could be minimal.

The facial toning article might need some quality peer-reviewed scientific sources. Most of it are alternative medicine, Chinese medicine, providers of services and so on. --Hofhof (talk) 00:48, 3 December 2017 (UTC)

I agree the article is problematic, so I mentioned it at Wikipedia:Fringe theories/Noticeboard yesterday. It looks like someone has already significant cut down on the poorly sourced content. Nil Einne (talk) 12:02, 4 December 2017 (UTC)

Fire nozzles

How do different fire nozzles (fog nozzle, straight-tip nozzle, solid-bore nozzle, etc.) differ in terms of their internal profile? I.e. how do they create the required pattern? 2601:646:8E01:7E0B:9559:4F0F:AF97:BC2A (talk) 10:00, 3 December 2017 (UTC)

Sounds like a homework question. Have you tried googling it? Aspro (talk) 15:44, 3 December 2017 (UTC)

In principle like the exchangeable tips for Pastry bags. --Kharon (talk) 22:01, 3 December 2017 (UTC)

No, this is NOT a homework question -- unless you count a writer's book research as homework! 2601:646:8E01:7E0B:9559:4F0F:AF97:BC2A (talk) 02:57, 4 December 2017 (UTC)

A large number of U.S. patents have been issued for various fire hose nozzles: you can find images and diagrams - including cross-sections and detailed explanations - by reviewing those. The official web site of the USPTO search engine lets you search by title; you may find Google's patent-search engine interface easier to browse for images. Many of the patents are over a century old, (and probably expired); and you can probably use the imagery from any of these patent filings at no cost.

Bear in mind that not all patents-granted are for devices that actually work!

Nimur (talk) 03:14, 4 December 2017 (UTC)

Thanks, I'll try that -- in the meantime, anyone else who has this info is welcome to share! 2601:646:8E01:7E0B:9559:4F0F:AF97:BC2A (talk) 03:16, 4 December 2017 (UTC)

I suppose you could look at Spray nozzle for a start... --jpgordon^{𝄢𝄆 𝄐𝄇} 05:15, 4 December 2017 (UTC)

If the patent office examiner concludes that a device built according to the specification will not do what it claims he will not accept the application. This is only fair to others who may be working on similar lines. The patent will cite the "prior art", i.e. previous inventions which are improved upon. Of course, there's no requirement to exploit the patent once granted, but if it's not worked there's a risk of losing protection (which is only for a maximum of twenty years anyway). 92.8.221.62 (talk) 17:09, 6 December 2017 (UTC)

92.8 is substantively correct here, according to patentability, a device must be 1) eligible 2) novel (does not yet exist) 3) non-obvious and 4) useful. #4 is the relevent bit here; a device which cannot work as intended fails the usefulness criteria. That is why patent offices will generall reject any application for a perpetual motion machine, which cannot perform their intended function, and thus fail the usefulness criteria. --Jayron32 17:47, 6 December 2017 (UTC)

Construction of Britain’s railways in the 1800s

Who built Britain’s railways back in the 1800s? Did private construction companies exist back then? Who did people like Brunel work for? 90.192.100.85 (talk) 19:00, 3 December 2017 (UTC)

See History of rail transport in Great Britain - mostly small private companies applied for Acts of Parliament which allowed them to build lines between named towns. There was then a gradual process of amalgamation, leading to a small number of large companies.Wymspen (talk) 19:08, 3 December 2017 (UTC)

But did those small companies hire construction companies to build it for them? And did they hire people like Brunel? 90.192.100.85 (talk) 22:10, 3 December 2017 (UTC)

• Note that there's also a distinct split between railway companies (who are mostly speculative fund raisers during this phase), chief engineers, and then contractors. The chief engineer (Stephenson, Brunel, Locke) would be engaged by the railway company to plan the route, and to decide the important trade-offs between the quality of the finished line (its level and ease of operation) vs. the construction costs and the land purchase costs. A famous engineer might have several such projects on the go at once. They might design a major engineering work such as a bridge, or they might leave it to others. The actual building work would then be done by a contractor, such as Morton Peto, Thomas Brassey, Rowland Brotherhood or Thomas A. Walker. Andy Dingley (talk) 22:18, 3 December 2017 (UTC)

I see. So would the modern equivalents be cheif engineer = consultancy, railway company = client/infrastructure authority, contractor = construction contractor? 82.132.216.104 (talk) 17:53, 4 December 2017 (UTC)

Some very good books on Brunel are Stephen K Jones' 3 volume set Brunel in South Wales ISBN 9780752432366. Much of the general history of Brunel is coloured by Tom Rolt's old paperback biography of him, which over-emphasises Bristol and especially the suspension bridge, whilst ignoring the more voluminous work in Wales - and all Brunel's standard gauge work for the Taff Vale Railway. Andy Dingley (talk) 22:26, 3 December 2017 (UTC)

Another book worth a read is, Webster, Norman W. (1972). Britain's First Trunk Line – the Grand Junction Railway. Bath: Adams & Dart. ISBN 0-239-00105-2. {{cite book}}: Invalid |ref=harv (help) which is a history of the construction of the Grand Junction Railway, later the core of the LNWR, and the book covers the process of designing and constructing such a railway very well.Andy Dingley (talk) 12:34, 4 December 2017 (UTC)

John Brogden and Sons was a very early builder of railways in the UK, but the company failed after Brogden's death when his sons seem to have mismanaged it. The company is of interest to me because it was instrumental in building the first railway lines in New Zealand, even though it was under controversial circumstances. One of my ancestors emigrated to NZ in 1872, apparently as a Brogden employee. If anyone can shed light on employment contracts or employee lists or other circumstances, I'd be interested to hear. Akld guy (talk) 23:42, 3 December 2017 (UTC)

So most were specialist railway contractors? These days railways just seem to be built by general construction companies. 90.192.100.85 (talk) 18:03, 4 December 2017 (UTC)

Possibly because the construction of a new railway is a comparatively rare event these days and companies need to keep their expensive plant occupied. Alansplodge (talk) 15:51, 5 December 2017 (UTC)

Yes, there was railway mania at that time. A group would form a company to build a railway, issue a prospectus, and there would be heavy demand for the shares. These days not much railway building goes on, although in the past few days the government has signalled that it would like to reopen the lines which were closed in the sixties. The Channel tunnel rail link was built by a dedicated company and an alternative is joint participation - see East West Rail Link. 92.8.223.3 (talk) 18:11, 5 December 2017 (UTC)

Most of the railways (by size and length) were built after the mania period. Andy Dingley (talk) 18:18, 5 December 2017 (UTC)

America did it a bit differently. They industrialized later, the population density was lower and country was bigger and from 1850 to 1871 railroads got free land if they gave gov't freight a discount to encourage such expensive national improvements. Perhaps not coincidentally, rail exploded in the 1850s. The continent's biggest river had a rail bridge by 1856 (into Iowa) and the state's newness, farmability, treelessness, featurelessness and square land plots caused a mania of parallel railways too close to each other. To this day Iowa has too many East-West lines of unusually small major settlements. Sagittarian Milky Way (talk) 00:56, 6 December 2017 (UTC)

The men who actually built the railways (and canals, before that) were known as navvies. Carbon Caryatid (talk) 00:53, 8 December 2017 (UTC)

Difference between natural gas and coal for global warming.

People seem to say all over that the natural gas is preferable to the coal and by using the gas the global warming will be delayed or even eliminated? I don't see any difference at all with the exception that the coal gives away soot. The soot should eventually settle on the ground especially in areas with frequent rain. Both coal and natural gas contribute to $CO_{2}$ growth in the atmosphere. What is the difference? AboutFace 22 (talk) 20:43, 3 December 2017 (UTC)

In general, if you remove all subsidies, direct (tax breaks/burdens) and indiret (use of public land without remediation to the environment, scrubbing of pollutants) then whichever fuel is cheaper will generally also be cleaner, since it will involve the least cost; i.e., the least effort and waste. Coal burning, for example, also produces oxides of sulfur. There is also the relative cost of extraction and transportation.

When you have sweatheart deals, government giveaways, and artificial burdens posed by regulations meant to favor one industry over another, such market calculations become skewed, and you are dealing with hidden costs. For example, natural gas means natural gas pipelines, which means fires, construction at public cost, and use of eminent domain; while use of coal can potentially mean strip mining, coal-mine fires, and higher air pollution.

Otherwise, CO2 is CO2. See Ol Doinyo Lengai, which produces ~6,000 tons of CO2 daily. μηδείς (talk) 21:15, 3 December 2017 (UTC)

One differences among fuels is that different chemicals lead to different amounts of carbon dioxide and water vapor to supply a certain amount of energy. See Natural gas#Carbon dioxide emissions for cited info. DMacks (talk) 21:23, 3 December 2017 (UTC)

Correct. With coal C+O2=CO2+ not very much heat. With nat gas CH4+2O2=CO2+2H2O plus about twice as much heat, the extra from the oxidation of the hydrogen. So for a given whiff of harmless CO2 you get twice as much heat with gas than coal, plus of course some deadly dihydrogen oxide. Greglocock (talk) 22:15, 3 December 2017 (UTC)

Coal also contains sulphur, the burning of which can lead to acid rain, another reason why you might prefer not to use it. [13] Alansplodge (talk) 23:41, 3 December 2017 (UTC)

Flue gas desulfurization is a well-known and widely-used technology -- and if you want to go even cleaner, coal gasification allows complete removal of sulfur (at extra cost). 2601:646:8E01:7E0B:9559:4F0F:AF97:BC2A (talk) 03:02, 4 December 2017 (UTC)

Thanks for repeating this important fact, which I mentioned two days ago when I talked about scrubbing and oxides of sulfur. μηδείς (talk) 16:32, 4 December 2017 (UTC)

Thanks, the difference between coal and natural gas as an energy source is really what matters in the bottom line, I was using pure carbon equivalence as a proxy, but the same economic point holds--whatever form of energy is cheapest when all subsidies are removed and all costs factored in (including remediation, pollution, and disposal) will be the cleanest. In our case, at this point, it's nuclear. μηδείς (talk) 00:17, 4 December 2017 (UTC)

How do you propose factoring in the cost of carbon dioxide? Sagittarian Milky Way (talk) 01:53, 4 December 2017 (UTC)

Why should we? 2601:646:8E01:7E0B:9559:4F0F:AF97:BC2A (talk) 03:02, 4 December 2017 (UTC)

Well, SMW, if you are just comparing coal and natural gas, the CO2 cancels out as a factor if one assumes carbon equivalence, in which case methane at the destination (other costs ignored) is a cheaper source of heat, and the question has already been answered. If you assume CO2 is a pollutant that needs to be remediated, then the burden is on you to demonstrate this and its cost. Since I have already mentioned nuclear power, I don't see your ultimate point. μηδείς (talk) 16:32, 4 December 2017 (UTC)

I don't need to prove what all the climatology PhDs have figured out. Enough CO2 to significantly increase the greenhouse effect unless [magic] means more of it is a pollutant. Eh, here it is anyway. The drawback of nuclear power is that many people are stupid and think they cause lots of radiation in peoples' homes or they can explode with the power of Hiroshima, don't know that Chernobyl was less safe than American ones and would be against new ones being built near them even outside a seismic/tsunami zone. Even if that's a minority maybe politicians (who would have to approve permit) would rather not alienate any net voters. They also take very long to turn on after approval so the government could be different people with a different view before the plant can ever start reducing carbon and the plant gets shut down (i.e. Shoreham Nuclear Power Plant took 11 years and 6 billion dollars to build and was turned off forever during 5% power tests). So though it might be best in principle in the real world it might take a dictator. Maybe in the industrializing democracies the populace wouldn't care though, they'd rather have jobs and cheap electricity and the risk of meltdown doesn't seem as significant when many people die of things development could prevent every day (i.e. tropical diseases). Sagittarian Milky Way (talk) 19:31, 4 December 2017 (UTC)

Um, no, SMW, the burden of proof lies on the one making the claim. If you want to cite the IPCC as proof, well they are a politically appointed board who don't do any science at all (it's in the lead of their article and in their mission statement) and who by their very name start with Climate Change as their premise, not objectivity. I am making no claim as to whether man-released CO2 is a problem or not. If it is, then the cost of remediating it should be included, which I mentioned in my first post. Your insistence that I recognize your concern is moral hysteria, not reasoned discourse. μηδείς (talk) 02:29, 6 December 2017 (UTC)

Not to mention that the IPCC is organized and funded by the UN -- which means that, like the UN, they are influenced by third-world interests (so they have a vested interest in hindering industrial growth in civilized nations so that third-world nations could get ahead). 2601:646:8E01:7E0B:F9B4:9A86:7938:FC5D (talk) 05:24, 6 December 2017 (UTC)

Then couldn't I say you're making the claim "there's a realistic possibility that man-released CO2 is not a problem"? This seems like a tie then. Then I defer to the experts in the field who are both very smart and the best we've got (humans having no access to superhuman truth sources) and before even reading their papers it seems more likely that the scientists are right. And since vials of CO2 get hotter in the sun then identical vials of air, even if no research was done on climate whatsoever (hint: false) it'd be simpler and more likely (Occam's Razor) for the scientists to be right then for something to prevent that which you're sure probably exists even though you don't what. Now counterintuitive findings are not unheard of in science and to actually be science and get anywhere close to proof (you know there's no absolute proof in science) you have do the math and try to rule these out but luckily for us thousands of scientists did the math and it turns out no matter how rigorously they go (i.e. cement setting, contrail water, airplane vs. low altitude emissions and urban heat island) the salvatory homeostasic effect never happens (and I bet the very few contrarians are irrationally optimistic or bribed) Seems like you're the one with more burden of evidence. Tell me by what evidence is the greenhouse effect not working in the atmosphere the obvious way more likely. And how thousands of scientists' atmosphere calculations are wrong. Whatever evidence you have I'd love to see it. Evidence for such a popular and old-news scientific topic is so easy to find, if you're too lazy or skeptical to Google such common knowledge but still manage to have such extreme agnosticism, skepticism or whatever on the topic that's not my problem. (and I know you're not lazy or you'd be a Democrat) Since you so insist I googled "evidence for anthropogenic global warming" and the first result was https://climate.nasa.gov/evidence/ NASA] (NASA isn't bribed by a vast conspiracy right?) which has links to numerous scientific society statements (all bribed?), the doesn't do any science (strawman) IPCC, B.D. Santer et.al., “A search for human influences on the thermal structure of the atmosphere,” Nature vol 382, 4 July 1996, 39-46, Gabriele C. Hegerl, “Detecting Greenhouse-Gas-Induced Climate Change with an Optimal Fingerprint Method,” Journal of Climate, v. 9, October 1996, 2281-2306, V. Ramaswamy et.al., “Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling,” Science 311 (24 February 2006), 1138-1141, B.D. Santer et.al. and “Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes,” Science vol. 301 (25 July 2003), 479-483.

I also found this from the UK government. It says "Climate change presents a unique challenge for economics: it is the greatest example of market failure we have ever seen.". The British government can't be bribed too right? (by who? the solar companies? they're not rich). And about the UN, most of the budget is paid by rich countries: [14]. Do you have evidence the General Assembly has more influence on it than their budget sources? At any rate, gaining slightly if rich countries cut sooner (or, less insignificantly, free nuclear plants or windmills to the third world) doesn't mean their answer can't still be right. So I guess my answer then is yes you would be okay with that cost being included (consistent! great!) but you're not sure if it exists. What you agree with on sulfur is called internalizing a negative externality which is actually very similar to evil living wage and socialized medicine laws where the costs of paying employees less than needed to live is passed to the employer instead of evil Food Stamps, Medicaid, small town public transit so shitty the last bus is 5-something, taxes for the fraction of welfare office employee wages that wouldn't be needed if full-time workers didn't need welfare and other otherwise cuttable welfares. And the communist healthcare where the cost of people who take their chances without insurance but then cry to the hospital to fix their broken leg so the public pays out of mercy is then passed on to those irresponsible people (poorly implemented in America I know but the general idea's good) Consistency is good! I get that Soviet-bloc life was terrible/communism won't work/the Democratic approach on crime sucks balls but just because liberals believe something doesn't make it automatically bullshit. (the cost of switching from fossil fuels over a few decades isn't even that big. Plus the new sources will last longer than a few hundred yea Sagittarian Milky Way (talk) 07:02, 6 December 2017 (UTC)

The planet is doomed anyway and it is scary. AboutFace 22 (talk) 22:29, 3 December 2017 (UTC)

If you have three and a half minutes, here's a video on the Natural Gas Initiative from my old professor, Mark Zoback. He explains his view on why natural gas is part of the bigger picture for energy policy in the United States and the rest of the world.

Optimism is irrelevant - and for that matter, so is pessimism. Actual engineers and scientists are going to work on these problems, whether the solutions are easy or hard.

Nimur (talk) 03:23, 4 December 2017 (UTC)

The earth is not doomed, at least not anytime soon. We might be doomed, but the earth is not. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:03, 4 December 2017 (UTC)

I'm a little surprised that the above answers aren't clearer. The difference between coal and natural gas is how much CO2 is produced per unit of usable energy, a concept known as the emission intensity. A 2011 IPCC review indicated that per kilowatt-hour of electricity generated burning typical coal released 1000 grams of CO2. For comparison, you only get about 470 grams of CO2 if you burn natural gas to generate a kilowatt-hour of electricity. So, for the same amount of energy, natural gas releases only about half as much CO2. The difference arises from the fact that when you burn natural gas (e.g. CH4) you get energy by converting both the C to CO2 and the H to H2O, whereas almost all the energy in coal comes from burning carbon. See also life-cycle greenhouse-gas emissions of energy sources. Dragons flight (talk) 13:42, 4 December 2017 (UTC)

^^^ That's the correct answer, but I should add that methane released from leaky natural gas infrastructure does have a stronger short-term effect on global warming... and I would speculate we're building a lot of brand new natural gas infrastructure that eventually will be old leaky natural gas infrastructure... Wnt (talk) 15:41, 4 December 2017 (UTC)

December 4

Color and pattern convergence across unrelated species

Today I saw a Hermit Thrush and was struck by how much it looked like a Spotted Sandpiper, with its brown back and white spotted belly. The birds are not closely related and they live in different habitats, so why are their patterns so similar? I have also observed that some tropical fish have patterns similar to warblers. Why would a bird and fish have the same face pattern? Is it just a coincidence, or does the resemblance have to do with some pigmentation process shared across all vertebrates? 169.228.159.244 (talk) 05:12, 4 December 2017 (UTC)

See Convergent evolution. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:01, 4 December 2017 (UTC)

That's not really much of an answer -- one lives in coniferous forest, the other near fresh water. They both do nest on the ground, which presumably has something to do with it (they should blend in with a nest from a distance, which puts limits on the dorsal plumage). But overall, I would be lying if I tried to say if the similarity was coincidence or adaptive or if so then as an adaptation to what. Wnt (talk) 15:37, 4 December 2017 (UTC)

It's a good partial answer: mottling is good at obscuring a figure both for many types of viewers and against many backgrounds. Consider that many fish and birds both benefit from light undersides and dark top sides, and for the same reason, even though their habitats are very different.

But there's another angle too: lots of animal patterns are created by reaction diffusion systems, as described by The_Chemical_Basis_of_Morphogenesis (well ok he was guessing, but later work has confirmed this is the case in many specific examples). So there is also likely an aspect of a shared basis of pattern formation, shared even by birds and fish. Pattern_formation#Biology is sparse, but Animal_coloration#Mechanisms_of_colour_production_in_animals has plenty of good reading, links, and refs. SemanticMantis (talk) 18:21, 4 December 2017 (UTC)

And to clarify: I think the two birds in the fist example are well explained by a combination of convergent evolution, general effectiveness of mottling, and similar mechanistic basis of coat patterns. For the fish and the bird, I don't think an appeal to convergent evolution is very apt. In that case, sexual selection is likely a strong force influencing the showy pattern on the bird and fish. There may be some mechanisms of pigmentation and patterning shared between the bird and fish that makes these sorts of patterns more likely to occur, but that is just a conceptual possibility, not a claim I would make. There is a lot of research about what pigment/pattern features are common to all vertebrates, as well as the genetic basis of such. See here [15] [16] [17] for a selection of scholarly overviews. These are behind academic paywalls, I can provide copies to anyone who is interested. The first paper linked is especially relevant, using both a bird and a fish as model species in the study of pattern formation. SemanticMantis (talk) 19:12, 4 December 2017 (UTC)

This is a great answer, and I don't want to disparage it in the least. But ... I abandoned starting down a similar road in my own because I couldn't see how to get to numbers and say coincidence or not. There is no shortage of beautiful birds with spectacular plumage that can't be confused for anything else. Yet most birds look, well, kind of plain, at least for birds. If there's a mechanism that enforces plainness, then does a near match in appearance result from a random walk within a narrow set of rules that some species diverged from during evolution, or does it mean that it is a convergent set of adaptations? I'm not sure there is a difference between those two things... Wnt (talk) 23:34, 4 December 2017 (UTC)

In my circles, people get touchy about whether or not a given trait can/should be considered "adaptive", especially in the narrow sense of providing a clear fitness advantage. In that light, your two options are indeed rather different, as the one case is "this is the way it has worked, and it doesn't hinder", whereas the other is "offspring with this trait have more reproductive success than those without". My WP:OR is that truly neutral traits are vanishingly rare, much like pulling zero at random out of the (-1,1) interval has probability zero. SemanticMantis (talk) 17:13, 5 December 2017 (UTC)

Hooded Tinamou (adult)

ostrich chick

• As for birds, note that brown coloration with speckling is very widespread, and may even be a symplesiomorphy or 'common primitive trait' of the birds, especially given that it is found in many chicks (consider the speckles of ducklings, so the pattern may also be an example of neoteny. In other words, this is an old pattern still found in the young of many species, as well as even ratites like the Hooded Tinamou (right) which are more closely related to the Ostrich (speckled chick (left) than to thrushes or snipes.

agouti guinea pig

pinto horse coloration

A similar phenomenon occurs in mammals, with the brown/black -- tan/red -- white tricolor agouti pattern found in many dogs (collies, beagles, German shepherds), calico-cats, horses, and guinea pigs with a dominant color highlighted, often on the head and limbs with patches of the other colors.

All of this points to the common genetic pathways alluded to above. We should also explicitly mention counter shading, as I dont' think it's been linked to above. μηδείς (talk) 18:12, 5 December 2017 (UTC)

Another relevant article, not yet linked: Piebald (and related links in 'See also' section). 2606:A000:4C0C:E200:7851:71F8:C463:FC20 (talk) 23:54, 5 December 2017 (UTC)

Thank you all, interesting links! The camo explanation makes sense for why the thrush and sandpiper look similar. 169.228.150.149 (talk) 23:57, 5 December 2017 (UTC)

What's this arachnoid?

[18][19]

Sorry for the quality but you can still see its very thin legs. Sagittarian Milky Way (talk) 12:39, 4 December 2017 (UTC)

Hard to tell because the picture is fuzzy, but it could be a pholcus phalangioides (cellar spider), which are common worldwide and have long legs similar to your picture. --Jayron32 13:21, 4 December 2017 (UTC)

It does look like that, probably is. Almost certainly a member of the Pholcidae. SemanticMantis (talk) 18:14, 4 December 2017 (UTC)

Thanks both. I'd seen this distinctive but ugly spider body plan (are there any pretty ones?) more than once and wondered what it was. Sagittarian Milky Way (talk) 18:37, 4 December 2017 (UTC)

Beauty is in the eye of the beholder. --Jayron32 18:47, 4 December 2017 (UTC)

There are many lovely spiders. E.g. the peacock spider has many fans, even among non-spider-lovers. Spiders often pop up over at /r/awwnverts, Reddit's clearinghouse for photos of cute invertebrates. SemanticMantis (talk) 19:22, 4 December 2017 (UTC)

Spiders make me want to put shoe in hand. The peacock's.. a mixture of pretty and repulsive. Now insects I generally don't mind as long as they stay pets, not pests. Sagittarian Milky Way (talk) 19:43, 4 December 2017 (UTC)

Modifying magnetic pendulum circuit for larger pendulum swings

I want to make a pendulum swing back and forth using the power from a battery. I bought a solar-powered dancing flower thing and disassembled it to get this stuff which generates a regular magnetic pulse. The problem is that the swings are quite small. To get larger swings do I need a stronger magnetic pulse or just one with longer timing? Also, what is that coil called (so I can search AliExpress for a bigger one if needed)? Thanks.

It doesn't generate a regular pulse, it senses the pendulum approaching and then generates the pulse in response. The timing is from the mechanical behaviour of the pendulum $2\pi {\sqrt {l/g}}$. A bit more complicated for a flower linkage, and some of them do generate timed pulses.

If you increase the current through the coil, you can increase the power and the possible mass of the pendulum, or the extent of the swing. You can do this with a single transistor amplifier, but (IMHE) those flowers are so tiny and their coils wound with such thin wire that this itself is difficult.

I'd suggest starting again from scratch. It's a simple circuit, it's not hard to make. There should be circuits for it on the web. You can wind the coil yourself quite easily. Some of these sold as kits use a PCB board with a flat coil etched onto them. Those are (again IMHE) too weak, as they have too few turns. Andy Dingley (talk) 15:00, 4 December 2017 (UTC)

http://www.trainelectronics.com/Pendulum/article.htm Andy Dingley (talk) 15:03, 4 December 2017 (UTC)

Winding

Why does being winded or blunt trauma to the stomach often result in nausea straight after? I don’t mean shock which may set in later if severe enough. I mean nausea which is often immediate and goes away quickly. Is it just to do with the muscles in that area going into spasm? 82.132.216.104 (talk) 20:40, 4 December 2017 (UTC)

Our article Celiac plexus#Clinical significance gives a brief explanation. Dbfirs 21:49, 4 December 2017 (UTC)

This article from the BBC [20] gives some additional information, as does this first aid website [21]. For a more scholarly reference, see this [22] journal article that discusses what happens when people "have the wind knocked out of them" SemanticMantis (talk) 17:09, 5 December 2017 (UTC)

Wikipedia does not give medical advice. Baseball Bugs (talk • contribs) 22:22, 4 December 2017 (UTC)
The following discussion has been closed. Please do not modify it.
Wikipedia contains articles on many medical topics; however, no warranty is made that any of the articles are accurate. There is absolutely no assurance that any statement contained or cited in an article touching on medical matters is true, correct, precise, or up-to-date. The overwhelming majority of such articles are written, in part or in whole, by nonprofessionals. Even if a statement made about medicine is accurate, it may not apply to you or your symptoms. The medical information provided on Wikipedia is, at best, of a general nature and cannot substitute for the advice of a medical professional (for instance, a qualified doctor/physician, nurse, pharmacist/chemist, and so on). Wikipedia is not a doctor. None of the individual contributors, system operators, developers, sponsors of Wikipedia nor anyone else connected to Wikipedia can take any responsibility for the results or consequences of any attempt to use or adopt any of the information presented on this web site. Nothing on Wikipedia.org or included as part of any project of Wikimedia Foundation, Inc., should be construed as an attempt to offer or render a medical opinion or otherwise engage in the practice of medicine. The following is off topic, and has been swept under the hat. μηδείς (talk) 02:44, 5 December 2017 (UTC) Which is a good thing to keep in mind, in case anyone should ask for it. --Trovatore (talk) 22:56, 4 December 2017 (UTC) Don't fool around with others' edits. You can't even spell "medical". ←Baseball Bugs What's up, Doc? carrots→ 23:00, 4 December 2017 (UTC) That seems to have been Sluzzelin's typo, but I do seem to have messed up the hatting somehow. It wouldn't have been necessary if you hadn't dumped unusual HTML into the page. I'll see if I can fix the hatting. --Trovatore (talk) 23:10, 4 December 2017 (UTC) Take your complaint to whoever wrote the disclaimer originally. ←Baseball Bugs What's up, Doc? carrots→ 23:14, 4 December 2017 (UTC) Yes, Trovatore, the typo/slip was mine entirely, corrected 3 minutes later (before anyone else had posted). Whatever typos linger on, may have been originated by me, but I did not post them. ---Sluzzelin talk 23:28, 4 December 2017 (UTC) Fair enough. I made my edit based on your earlier version, I guess. I moved the comment out of the center so I could respond to it. There was an edit conflict, which I examined and resolved in favor of my text, which propagated your original version. --Trovatore (talk) 23:30, 4 December 2017 (UTC) Alright, well I corrected the propagated typo now. ---Sluzzelin talk 23:31, 4 December 2017 (UTC)

December 5

"Elastic collisions" and time travel

Can the theory of elastic collisions, extended into spacetime, still work when one of the colliding masses' velocities is timelike? IIRC, a character in HG Wells' The Time Machine raises the concern that a time traveller might be killed by arriving inside a solid object. (I'd assume that while traveling at full temporal speed, her density would be effectively reduced, and thus she'd be able to pass through solid matter without inflicting or sustaining significant damage, just as neutrinos can.) I'm wondering whether this could be avoided by colliding elastically with that other object, forcing it to time-travel out of the way in the same temporal direction. NeonMerlin 04:03, 5 December 2017 (UTC)

Whatever about about it being an elastic collision I think something like What If - Relativistic Baseball might happen. Dmcq (talk) 12:41, 5 December 2017 (UTC)

No, because one cannot move backwards in the time dimension. One of the things about Minkowski spacetime is that the time dimension only allows macroscopic objects to move in one direction according to the Arrow of time. Backwards time travel, except under highly restricted conditions (see T-symmetry) does not really happen without violating Causality. All sorts of Temporal paradoxes are introduced, both in terms of basic lay explanations (like the Grandfather paradox), and mathematically rigorous explanations (see Causal structure). Simply put, the timelike dimension does not obey the same rules as the three spacelike dimensions, and cannot be treated as such. It is true that the mathematics is arbitrary as regards to which direction time flows; but basically once you have aligned your arrow of time to designate a future and a past (time orientability), spacetime only moves in one direction if multiple observers all agree on the direction time is moving; i.e. once the universe gets going one way, it all goes that way. --Jayron32 12:55, 5 December 2017 (UTC)

In order to dispute the Arrow of time, space has to be counted as something that in some way can be dissipated. Before it might be yes as well as no. But the OP seem to be assuming some kind of Doppler effect as applied to teleportation. --Askedonty (talk) 16:47, 5 December 2017 (UTC)

Just a side note here — I am not sure that word timelike means what you think it means. A normal (bradyonic) particle's four-momentum is always timelike; the weird case would be spacelike. I can't seem to work out in my head right now just what "four-velocity" ought to be, but I think, if there is such a thing, it would normally be timelike. --Trovatore (talk) 23:32, 5 December 2017 (UTC)

Ah, four-velocity; if it'd been a snake it'd'a bit me. --Trovatore (talk) 23:45, 5 December 2017 (UTC)

Yeah, but after you de-Lorentz-transmogrify it - which you would have to do during any analysis that adds or subtracts vectors - you still get the right answer, and unsurprisingly, the constant "c" drops out exactly as you would expect. One cannot defeat conservation of momentum nor conservation of energy, which are ultimately the only laws of interest when we study collisions under relativistic conditions!

Landau & Lifschitz Mechanics Chapter IV, §16; from whence, those who care to follow, we can derive relativistically-corrected Thomson scattering, and then further, Compton scattering ...

What we have in this question is a fun use of the English language to obfuscate the actual physics - which is much simpler than our OP wants to admit. Even when we consider motion in time- and space- - irrespective of how we write out our vectors - we cannot forget to conserve energy and momentum. These simple facts are what keeps our physics, and our conclusions, grounded in reality. After all, we are all "traveling in time," and always at "velocity" "ct/ct"! We need neither fictional machinery nor new physics to describe it!

At this time, I would remind our new initiates (e.g. our OP, User:NeonMerlin) that relativistically-correct scattering theory is hard physics - it takes several years of gruelling preparation to attain anything close to a complete understanding; but after you put in all the effort and solve a few thousand sample problems, let me assure you that you will never forget your efforts!

Nimur (talk) 19:33, 7 December 2017 (UTC)

Cconceptually, I suspect there are some scenarios within an extremely large gravitational field where the same object can appear arbitrarily close yet separated by long light cones and therefore time. The Einstein Cross is in essence, the same object at different points in time affecting telescopes on earth. It's not time travel per se but an interesting phenomena. Everyones current frame is at the tip of the time arrow and and we are constantly being held by the past. --DHeyward (talk) 00:10, 6 December 2017 (UTC)

Speed of molecular machines

I've seen this video and others of molecular machines. Is the speed shown the speed at which they operate, or are they faster or slower? Bubba73 ^{You talkin' to me?} 04:47, 5 December 2017 (UTC)

The animation is pretty famous - it's an excerpt from a 2003 work called Molecular Movies by Drew Berry, whose various animations have been published, and cited, in many peer-reviewed publications including Science. The original video has detailed narration and scientific commentary.

"The dynamics and molecular shapes were based on X-ray crystallographic models and other published scientific data sets. Leading scientists, including many Nobel Laureates, critiqued the animations during their development. Particular effort was made to ensure the relative shapes, sizes and 'real-time' dynamics were as accurate as possible."

And, in this 2012 TED talk, Berry again discusses the accuracy of the animations.

Of course, the real molecules "look" nothing like this - the molecule-scale features are too small to resolve with visible light!

After all, it's just a cartoon - but it is meant to be a realistic model, and effort was put toward that end.

Nimur (talk) 05:30, 5 December 2017 (UTC)

Thanks, that is fascinating stuff. Bubba73 ^{You talkin' to me?} 18:51, 5 December 2017 (UTC)

Resolved

If you look at 1:20 into that video [23], it describes a helicase spinning at the speed of a jet engine. Now a jet engine spins at tens of thousands of RPMs [24] so at least in this case a molecular machine is depicted as moving much slower than it actually does. --Bob K31416 (talk) 19:03, 5 December 2017 (UTC)

Why do people use that "resolved" tag? Don't they know it's like waving a red flag in front of a bull would be, if bulls could see red? More about the helicase here; looks like it has useful links to further reading. The max speed is 10,000 rpm.

I should point out more generally though that molecular machines work differently than the ones we know. ATP doesn't magically jump into a binding site for a helicase to turn, for example; it will jam in this way and that, fly away, another ATP comes, that flies away, between, countless water molecules, the occasional ADP or chloride ion tries ... who knows how long until a fit is made? Which brings us to the point that these are small distances, yet according to the Boltzmann distribution the molecules are moving faster than macroscopic objects. So they are doing an unfathomable amount of stuff that isn't shown in the video between every two frames that have a result you expect. That's why the ATP requirement at all - without it, that helicase would spin 10,000 rpm backward just as often as forward. That's another thing to notice -- in the microscopic world, there's practically no momentum built up by a spinning helicase compared to, say, a jet engine. The distances are small, after all - if something is say 100 angstroms in circumference, 10,000 rpm means it moves a tenth of a millimeter every minute. By contrast, the electrons in atoms that make up that engine may be moving around their nuclei at something like 1/137 the speed of light (this should be discussed at fine structure constant). Wnt (talk) 21:51, 5 December 2017 (UTC)

How are these videos made - do they calculate what the molecules will do or are they an animation of observations? Bubba73 ^{You talkin' to me?} 03:30, 6 December 2017 (UTC)

These specific animations are “cartoons” or pictures drawn by an artist, guided by actual scientific data like x-ray crystallography (which produces graphical results that require scientific training and discipline to interpret). In specific, the digital artist uses Maya and other specialized software. Molecule movements and trajectories can be programmed, like any other computer-aided animation - in a sense, this is Digital puppetry with atom-shaped puppets. The shapes and movements are meant to illustrate molecular motion, but they are not in themselves a “simulation” in the sense of computational chemistry or molecular dynamics scientific software. The author says in his presentation that it is “expressing science through art.”

Here’s another promotional video from the Linear Coherent Light Source team: using X-ray lasers to image nucleic acid reaction kinetics. That equipment, and the data it produces, are much newer but are in the same category as the type of pictures that Drew Berry would use to inform his animations. In the SLAC video, you can see a sort of transition from raw data to “science product” and finally to cartoon-for-layperson-consumption, as the narrator explains the science.

Nimur (talk) 18:43, 6 December 2017 (UTC)

Thank you. Bubba73 ^{You talkin' to me?} 00:34, 7 December 2017 (UTC)

Just here to note that Autodesk Maya has an article, so we can learn it's "specialized" as general purpose high quality animation rather than science-specialized. DMacks (talk) 06:32, 7 December 2017 (UTC)

Anthropology and VO2 max

I am looking for information regarding how VO2 max relates to ethnicity and how it has changed since early humans (possible relating to Endurance running hypothesis). On average do certain ethnicity have better VO2 max L/min? Trick on (talk) 18:01, 5 December 2017 (UTC)

Venlafaxine

One of the reported side effects of Venlafaxine is loss of appetite. By what mechanism does Venlafaxine exert this appetite suppressing effect? — Preceding unsigned comment added by 182.253.176.176 (talk) 19:51, 5 December 2017 (UTC)

Where did you see that reported side effect? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:29, 5 December 2017 (UTC)

There's a comically long list at List of adverse effects of venlafaxine (are all these proved to a level of statistical significance?), which include weight loss, but not "loss of appetite" per se (and theoretically the two can be unlinked, as by uncoupling agents, though I doubt it here). It also gives nausea as a side effect; [25] adds constipation; so maybe that gives an explanation. But I don't know that. Since they are side effects I would be surprised to see detailed information about the mechanism but I haven't looked. Wnt (talk) 21:28, 5 December 2017 (UTC) ... Hmmm, having looked, at least the first four PubMed screens, not much obvious to me; [26] gives nausea as a side effect in meta-analysis but doesn't try (as I expected) to break down cause and effect. Found general support for antidepressants in binge eating disorder. [27] I could look harder if someone got me interested. Wnt (talk) 21:34, 5 December 2017 (UTC)

I just noticed the mixing of "adverse event" and "side effect" here to create "adverse effect." In our pharmacy school, students must know the difference between a Type A adverse event, Type B adverse event, side effect, and toxic effect. I understand that the general public doesn't need to know it, but mixing and matching words between "adverse event" and "side effect" in what claims to be an encyclopedia seems a bit clumsy to me. 209.149.113.5 (talk) 14:20, 6 December 2017 (UTC)

Since you don't have a talk page, I'll encourage here that you raise this issue at the appropriate article talk pages. I'll note that we have separate articles for adverse event and adverse effect, and at a glace they seem to be about (somewhat) distinct things. SemanticMantis (talk) 02:09, 7 December 2017 (UTC)

• At least part of the cause it that venlafaxine is a serotonin reuptake inhibitor. This means it increases serotonin levels in the brain, and one of the effects of serotonin is to reduce appetite. The well-known anti-obesity drug fen-phen relies heavily on that mechanism. Looie496 (talk) 19:36, 6 December 2017 (UTC)

Yes, venlafaxine is an "upper," that is it acts as a psychostimulant for many people, improves attention span, reduces need for sleep, may cause insomnia. It is actually a dual serotonin and norepinephrine reuptake inhibitor. - AboutFace 22 (talk) 02:18, 7 December 2017 (UTC)

Ice-free northern Greenland

The Greenland article says The extreme north of Greenland, Peary Land, is not covered by an ice sheet, because the air there is too dry to produce snow, which is essential in the production and maintenance of an ice sheet. Why doesn't the main ice sheet spread over Peary Land? Is it unable to get past the fjord south of Peary Land (i.e. the ice that would go north just goes into the ocean instead), or is there some other reason? Nyttend (talk) 23:54, 5 December 2017 (UTC)

Didn't you just quote the answer to your own question? --Jayron32 13:14, 6 December 2017 (UTC)

No. Nyttend backup (talk) 14:06, 6 December 2017 (UTC)

Question: "Why doesn't the main ice sheet spread over Peary Land?" Answer: "because the air there is too dry to produce snow, which is essential in the production and maintenance of an ice sheet". I am confused as to what you are asking if that is not the answer. If you can clarify your question in some meaningful way, then people can help you find the answer. --Jayron32 14:47, 6 December 2017 (UTC)

I believe the question meant is "Why is the air so dry there that it cannot produce snow?" I do not know the answer to that, but there are, similarly, small areas of Antarctica without snow. Our article is at Antarctic oasis and it similarly fails to account for why these areas have the low humidity that causes lack of snowfall. Matt Deres (talk) 14:21, 6 December 2017 (UTC)

The question is: "Why doesn't the ice sheet to the south of Peary Land slide North and, eventually, cover Peary Land?" For background, ice sheets move. There are ice sheets moving into Peary Land. It is easy to find many photo collections of the ice sheet edge. They don't cover Peary Land because during the summer it warms too much. The ground is permafrost, which absorbs solar light. Also, ice in dry air will melt in direct sunlight even if the air is below freezing. (Just as you can see ice melting off a roof when it is well below freezing.) So, it is a flow and ebb system. The ice sheet moves in during the winter, but melts away during the summer. Overall, Peary Land is speckled with snow in the winter, but dry and clear in the summer. You can get information on this type of system easier by looking for information on arctic deserts in Alaska and Canada. 209.149.113.5 (talk) 17:47, 6 December 2017 (UTC)

Thank you for that explanation. It didn't occur to me that summer melting would be an issue; I figured that the sheer size of the sheet was great enough that melting wouldn't be able to prevent its expansion. And on sublimation, again I'd figured that only a small percentage would be lost, so thank you for correcting me. Nyttend (talk) 00:28, 7 December 2017 (UTC)

I thought the question clearly was about the ice moving, which you have also answered. It may also be mentioned that ice in dry air and sunlight may not only melt but may also sublime, i.e. evaporate directly from the solid state. --69.159.60.147 (talk) 19:46, 6 December 2017 (UTC)

It looks like the sheet did get in to Peary Land in the past. Here [28] is a scholarly article discussing the historical and current limits of that ice sheet, here [29] is another that includes more maps. SemanticMantis (talk) 19:42, 6 December 2017 (UTC)

December 7

Effect of CO2 emissions on the metabolic energy obtained from glucose

One of the basic biology factoids is that glycolysis + Kreb's cycle + oxidative phosphorylation gets "up to" 38 ATPs out of a glucose molecule.

It occurs to me that, just as the temperature of cooling water affects the efficiency of a power plant, the concentration of CO2 should affect the efficiency of respiration. Searching I found many articles on plants, but I wanted to look at the same from an animal point of view.

Back of the envelope calculation: carbon dioxide in Earth's atmosphere has gone from 280 to 407 ppm. Gibbs free energy includes a term for RT ln (407/280) = 8.134 J/K * 300 K * 0.374, which gets me 0.93 kJ per, I think, 1 mol of CO2 that crosses a membrane between these two concentrations. Since there are 6 CO2s per glucose, that gets 6.00 kJ of energy difference between the two conditions per starting glucose! If so, well, adenosine triphosphate cites a change in free energy of 3.4 kJ/mol, so that would be 1.64 fewer ATPs per starting glucose than in pre-industrial times. (Note this goes by ln, so it takes larger and larger increases in CO2 to reduce the ATP count further; a 1000000 ppm concentration would, by this calculation, reduce it by about ... 38 ATPs).

First, did I do something stupid in the calculation? I haven't used these chemical concepts this way before.

Next, is there a way to call shenanigans on it for external reasons? For example, the CO2 concentration in the lungs will be much higher on exhalation. However, I'm thinking that this might go up somehow in proportion to the air concentration ... actually, I have no idea one way or the other.

Could a decrease in ATP production tend to turn everyone into couch potatoes, make us feel like aerobic exercise is too hard, cause overeating and so on? Just woolgathering here. Wnt (talk) 02:34, 7 December 2017 (UTC)

This appears to say the first noticeable without equipment effects don't start till 1000 ppm. Sagittarian Milky Way (talk) 03:11, 7 December 2017 (UTC)

I think that type of value is determined by acute exposure rather than lifetime exposure. Also, note that it is possible to waste significant amounts of cellular energy (e.g. uncoupling agent) with relatively little perceived effect. Something like 2,4-Dinitrophenol could be marketed as a "dieting aid" (indicating substantial loss of energy), though it causes symptoms up to and including death at sufficient levels. If the math above is correct it describes less than a 5% reduction in energy from carbohydrates (less from fats because the H2O is not affected), which is scarcely noticeable for dieting purposes. Wnt (talk) 14:06, 7 December 2017 (UTC)

It'd be interesting to do an analysis of the rate of world record breaking in as many probably steroid-free less-team/people vs people (too many variables) outdoor aerobic sports as possible. I'm not sure if you could see a signal in the noise of numerous other factors i.e. once-a-generation+ x players causing more kids to want to be pro x players, and x players with sudden big improvements on the previous best are still appearing in major sports (like a man can be many inches too tall (Usain) and still pulverize 100m records, a man can shoot well while being bumped when no one else could (LeBron) and that huge Australian high school football player could possibly not be too slow to play NFL at that size. Are the outdoor more individual aerobic sports (i.e. marathoning) also still capable of having something like that happening in the near future screwing up trying to use their world record progression to see if something more than the usual slowdown of record-breaking is happening? If your math is correct it's probably been thought of by now and you'd probably hear about it at least as much as ocean acidification or runaway clathrates warming but it'd be nice to see research on someone kept at CO2s between 280 and 1000 for a long time. I now wonder if any important sports events had enough building-related CO2 or oxygen abnormality to affect the performances lol. Or if it'd be allowed to mess with the air of sports venues to increase your team's or event's performance or even favor the home team. Do the Denver Nuggets want to try installing airlocks and O2 injection during games? Does Tokyo want more world records in their games? Make them play in 40% O2 at 60% pressure! Sagittarian Milky Way (talk) 18:40, 7 December 2017 (UTC)

You problems are: (i) you do not take into account the limited efficiency of the Kreb's cycle. 38 ATPs contain much less energy than that is released during oxidation of 1 molecule of glucose. The remaining energy turns into heat. So, when you calculate balance of Gibbs (or free) energy you need to take this into account. (ii) In addition you seems to confuse Gibbs (or free) energy and energy itself. The free energy is only useful when you want to determine the direction of a reaction: will glucose oxidase or will it form instead!? On the other hand the true energy balance does not depend much on the external CO2 concentration. So, the Kreb's cycle consists of a fixed number of steps. Each step gives the fixed number of ATPs. This will not change as the CO2 concentration increases. The changes of the Gibbs energy that you refer to are essentially changes in entropy multiplied by temperature. Ruslik_Zero 20:47, 7 December 2017 (UTC)

@Ruslik0: The Krebs cycle involves a fixed amount of reduction and phosphorylation producing 10 NADH, 2 FADH2, and 4 ATP, it is true. But oxidative phosphorylation is less certain and is said to produce "up to" 34 ATP (3 per NADH and 2 per FADH2). There are costs in moving precursors and products (e.g. NADH, ATP) to keep them on hand to make the reaction go forward. Additionally, alternate mechanisms exist that generally have a lower yield. The result is that estimates tend to say things like "30 to 38 ATP", though it looks like eukaryotes can't hit the top figure.

Whenever there is a choice of regulated mechanisms, this means that the final energy figure has a chance to talk back to the reaction. For example, if ATP is produced abundantly in the mitochondrion I think it might be valuable to let it diffuse out through a channel, though I don't know that. But if anemic amounts are produced, a proton from the gradient might be spent wringing out ATPs from a less rich storehouse inside the organelle. Similarly, one of the alternate biochemical mechanisms might serve to add some extra free energy to the reaction to keep the process going. My memory of metabolism is limited, but it is surely not a rigid reaction that can be allowed to sputter to a halt based on a small change in free energy. Note that although a typical figure lists a metabolic efficiency under 40%, it is more like 50% in cells due to free energy considerations. [30] In other words, if ATP and ADP had exactly the same amount of energy in their chemical bonds, the cell has 10 times more ATP, so any reaction ATP + X -> ADP + Y would still be pushed forward, which means that that 10% of the energy was never actually lost to begin with. Now to be sure, yes, even if it is 50% I can say a 5% difference in ATP production is a 2.5% difference in efficiency, but it seems just as relevant no matter what I compare it to. Wnt (talk) 22:36, 7 December 2017 (UTC)

Natural satellites of planets

I glanced through the Wikipedia material on the satellites (or moons) of planets. It gives very specific numbers, all of them in the order of one to a few dozens, for the known satellites of Jupiter, Saturn, Uranus and Neptune. But it also says that there's no agreed-upon threshold for size that objects have to pass so they can be considered satellites. And there doesn't seem to be any specification that a satellite mustn't be located in the planet's ring system. So why don't we say instead that these planets have billions and billions of satellites, all but a handful of which are tiny ones found in their ring systems? --Qnowledge (talk) 07:33, 7 December 2017 (UTC)

You are right to include the qualifier "natural". If you look at space debris you will see the term "satellite" is usually reserved for larger objects. 92.27.49.50 (talk) 11:06, 7 December 2017 (UTC)

Also, see Natural satellite#Definition of a moon. Dolphin (t) 12:54, 7 December 2017 (UTC)

I'm not sure, but I think some of that has to do with the Roche limit. A ring system like Saturn's contains particles that AFAIK would continue to break up under tidal forces were they not held together by chemical forces, i.e. electromagnetism rather than gravity. I think such assemblages are reasonably disqualified from being moons. (I'm not sure at the moment what distinguishes ring particles from shepherd moons, should look up later if someone doesn't explain) Wnt (talk) 14:11, 7 December 2017 (UTC) (withdrawn - see below)

Probably being big enough to be seen and have a significant shepherding effect. Ring particles in this solar system are only the size of a house or smaller. Since shepherd moons are big enough to be seen by spaceprobes the Roche limit isn't absolute and natural satellites big enough to be seen by them and thus named and numbered can have enough structural integrity to avoid being broken up by tidal forces. Sagittarian Milky Way (talk) 17:44, 7 December 2017 (UTC)

A Ring system can be regarded as one or sometimes even multiple satellite entity for originating from a satellite that broke up but also in perspective to eventually bake together a new satellite, just like all other planets and satellites evolved. Its a placeholder for a potential satellite if you like and it also has a mass and motion fitting Kepler's laws of planetary motion. Its an ongoing exploration and discussion. You can read about it in Kuiper belt and Oort cloud which can be regarded satellites of our sun or orbits with multiple satelites, maybe even planets, without one body dominating the part. In that you can also find the distinction, what is generally counted as planet, satellite, meteorite of a star- or planetary system and what is not: The origin of its matter and its orbit. --Kharon (talk) 21:30, 7 December 2017 (UTC)

It appears my confidence in the Roche limit was misplaced. According to [31], "If you broke up all the satellites within the Roche limit of Neptune, you'd get a ring system that would not look too terribly different from Saturn's." So this clearly is not a criterion to say they aren't moons. It is a good reason to watch your step on Larissa (moon)! (N.B. [32] says Larissa is inside the Roche limit while our article says it will break up someday when it passes it. Since Roche limit depends on density I'm not sure good sources don't disagree, but can someone confirm an error?) Wnt (talk) 22:00, 7 December 2017 (UTC)

Astronomy is a very bad science that is completely unable or unwilling to keep theory and facts separately. Just some weeks ago they found a super massive black hole so old that its assumed formation process can not be added up with the age of our universe according to the big bang theory. So maybe the big bang theory is bullocks but no one dares to say it out loud!! Its a very mainstream centered science like economics where you are either neoliberal or outcast (to put it slightly exaggerated). So don't expect to much! --Kharon (talk) 22:22, 7 December 2017 (UTC)

Well, if it's a choice between bad science in astronomy and bad science in our current Wikipedia draft I know which I find a priori most likely. ;) Wnt (talk) 22:37, 7 December 2017 (UTC)

The Big Bang is not bollocks, it's how'd it get from ~380,000 years after the Big Bang to galaxies that's not well understood. Sagittarian Milky Way (talk) 22:49, 7 December 2017 (UTC)

That's a new record in Dogmatism. Now even whole (known) galaxies must be wrong if they don't fit the mainstream. Btw. the mainstream core argument is not the background radiation but the Redshift. --Kharon (talk) 23:16, 7 December 2017 (UTC)

I suggest you work on your reading comprehension and check again what Sag has written. He comments on our incomplete state of knowledge, not any galaxies that "must be wrong". And while the redshift was one piece of evidence for an expanding universe, there were competing models - see Steady State theory. The CMB, on the other hand, is very well explained by the big bang theory (it's the red-shifted image of the surface of last scattering), but does not fit into e.g. Steady State. --Stephan Schulz (talk) 00:52, 8 December 2017 (UTC)

This is way off topic, but I should note [33] describes the black hole and links the original paper (I didn't check Sci-Hub though). It's 10% younger than the previous record holder. There's something there about "episodic hyper-Eddington accretion". I have no idea, but my gut feeling is it seems odd to say that a region of twisted space 800 millions times the mass of the sun forming in 800 million years would be perfectly logical, but 690 million years buggers all belief. Wnt (talk) 00:11, 8 December 2017 (UTC)

Modified Atmosphere Article -Clarification Questions & Suggestions

Hi,I am no expert in this subject, but thought I would give some feedback in the hope of making the article easier to read & understand. I was unable by clicking the Talk button to access anything other than my account page User talk:Mpe123

severity of preparation (give example to make the meaning clearer) does it mean something like processing such as washing salad or grating carrots?

A paragraph/comparison chart outlining the difference between EMAP and MAP could be helpful,to me they sounded pretty similar.(respiring product,permeability,"an equilibrium modified atmosphere will be established in the package and the shelf-life of the product will increase.")

When gas flushing & compensated vacuum are 1st mentioned (paragraph above scientific terms) it would be good to have a note mentioning that more details are given further in the article.

Isn't a potato a vegetable? I checked 2dictionary definitions & it says that they are vegetables "An example of a gas mixture used for non-vegetable packaged food (such as crisps)"

"breathable" films called EMAP are mentioned at the beginning of the article, but later(packaging films section) are referred to as "MA/MH films" are they the same?

Thanks in advance! — Preceding unsigned comment added by Mpe123 (talk • contribs) 17:58, 7 December 2017 (UTC)

Why isn't bitcoin mining causing the price of bitcoin to level off?

Bitcoin mining has now become hugely profitable at a bitcoin price of nearly $20,000. You could already make a modest profit at a bitcoin price of around $3000. So, why is the price going up and why isn't the bitcoin boom being accompanied by a boom in the sales of fast computer processors? Count Iblis (talk) 21:08, 7 December 2017 (UTC)

• Maybe it's a function of Bitcoin being a scam. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:25, 7 December 2017 (UTC)
• Bitcoin "mining" really is a misnomer. What is really going on is the creation of new blocks in the blockchain (each of which gives the successful creator a pre-defined reward). The bitcoin network automatically adjusts the difficulty of the block creation so that, on average, one new block is created every 10 minutes, independent of the total amount of compute power in the net. More miners spreads the same reward among more parties, but does not increase the supply. --Stephan Schulz (talk) 21:41, 7 December 2017 (UTC)

Your central assumption is wrong because the gratification for the mining is adaptive. There is no fixed rate like you would always get say 1 Bitcoin for solving/verifying a block. With the current high prize the gratification is most likely very very low now because there is only a limited number of blocks to be verified and many computers and computer pools try to solve one of these. Also if you add more computers and computer pools that is only more competition, more supply but not more demand, which is at the end essentially biting its own ass according to the rules of supply and demand. --Kharon (talk) 21:58, 7 December 2017 (UTC)

Are you replying to me or to the Count? The reward for mining is changing, but with a long-term predefined schedule - the reward is cut in half every 210000 "mined" blocks (which is once every couple of years). What is "adaptive" is the difficulty of creating a correct block (you need to find a nonce that will produce a hash with a given number of leading zeros, and that required number is adjusted to keep the rate of block creation roughly constant). --Stephan Schulz (talk) 22:11, 7 December 2017 (UTC)

No, i just saw an edit conflict and i did'nt want to rework it, in parts because of fearing to run into the next edit conflict and thus getting trapped into an adapting loop. --Kharon (talk) 22:31, 7 December 2017 (UTC)

• One must be aware that the mining of Bitcoin gets you two kinds of money: the "Bitcoin mining" part where you create new Bitcoins that you get to keep, and the "transaction fee" part where people pay miners to validate their transactions in priority. I think I had read somewhere that the latter is what really gets you the money these days, but the only semi-serious source I could find is [34], whose numbers do not allow to compare the recent mining/commission parts in a meaningful way. Tigraan^{Click here to contact me} 10:19, 8 December 2017 (UTC)

  While true, transaction fees don't increase the Bitcoin supply - they only move Bitcoin from one market participant to another. It may cause people to keep mining, even if the built-in rewards are no longer cost effective, but it has not direct effect on the supply/demand situation. --Stephan Schulz (talk) 11:27, 8 December 2017 (UTC)

Alternatively, many economists make the case that the price is overwhelmingly speculative, and is therefore detached from supply-and-demand economics. The actual availability of the "resource" - constrained by mathematical details, or otherwise - is no longer a contributing factor the market-price at which people are buying and selling.

Furthermore, fully 100% of the "bitcoin-to-dollar" conversion price is a snapshot of a secondary market - not "some" or "most," but fully all of that price is sustained on such a market. And it is an entirely unregulated secondary market! So this means that price arbitrage can occur with catastrophically enormous price-spreads - ratios that would be orders of magnitude larger than any other conventional marketplace.

In my opinion, I think I have composed my explanation using certain technical terms that are more ... shall we say, precise than the word "scam," but to the informed investor, these descriptions ought to carry equal weight.

For even more verbosity on the topic, here's Susan Athey, an economist specializing in internet commerce: Bitcoin Pricing, Adoption, and Usage: Theory and Evidence (2016). She's written several well-researched commentaries on bitcoin over the year. She couches her statements in even more jargon: given "the presence of frictions arising from exchange rate uncertainty," ... "the idea of bubbles seems salient for Bitcoin..."

Again, the language is florid but, in my reading, the implications are equally lurid. ...Scam.

To put it more bluntly: if you want to invest in bitcoin, just try to put a non-trivial amount of money (let's say, U.S. Dollars) into an exchange on some proverbial Monday; wait for the price to vary by some non-trivial amount; and try to get your money back out on the proverbial Friday.

See, in a regulated market, they have to give you your money. In fact, as of right now, in the United States, starting in 2017, they have to give it to you within two business days: this is called T+2 and it dramatically changed the financial marketplace this year - even though it got almost no media coverage outside of specialist investment and economics publications! But Bitcoin exchanges follow no such regulatory oversight. They can arbitrate your withdrawal, at any price, on any schedule. You won't be able to withdraw your proverbial investment return of 5%, or 50%, or 50000%, because the exchange maker sets the schedule for paying you.

The exchanges that convert bitcoin to hard-currency are ponzi schemes. What you will find is that you might be able to pull a few hundred dollars of "earnings" out of them, at a massively inflated price (so that they can sucker in the next guy with unrealistic inflated growth statistics). But macro-economics does not work via "a few hundred dollars." Even a 50x growth in an investment of a few hundred dollars still won't buy you a private jet! As soon as you attempt to invest any nontrivial amount of money, and try to reap your well-invested earnings, you will find your arbiter mysteriously goes bust in a bank run. This has already happened multiple times, but new suckers keep buying!

Nimur (talk) 22:36, 7 December 2017 (UTC)

• I believe that @David Gerard: is something of an expert on cryptocurrencies. He may be able to weigh in here. --Jayron32 01:17, 8 December 2017 (UTC)

The "boom"-part is nothing specific to bitcoin or other cryptocurrencies. There was a similar development in the Shadow banking system and we all read about how some companies that serve the tax havens lost their pants lately and what became visible. Behind all of this is a world financial system which contains more wealth than the whole world industrial economy can craft in 100 years.[35] One obvious side effect of this is a flood of "investors" desperately trying to put their wealth somewhere "save". Even a 10-year German government bond with negative interest rates was sold out in hours. There is going to be a huge financial "bloodbath" somewhere again soon and bitcoin looks like build to survive it almost as save as German government bonds. --Kharon (talk) 03:15, 8 December 2017 (UTC)

A few exchanges, including Coinbase, one of the largest, are regulated. Of course, I have no idea what kinds of standards are enforced by the regulators or how strictly they are enforced. Also, although it's true the vast majority of Bitcoin holders hold Bitcoins through a broker, Bitcoin intentionally doesn't require this. You can run Bitcoin wallet software on your computer and transact directly with others. Of course, then you are taking on the settlement risk yourself. --47.157.122.192 (talk) 03:19, 8 December 2017 (UTC)

Purely addressing the computing aspects of this: it's impossible to make a profit anymore mining Bitcoin on general-purpose CPUs, assuming those are what you mean by "fast computer processors". All "serious" Bitcoin mining today is done with custom hardware based on ASICs designed for the Bitcoin algorithm. Have you checked the price of those? --47.157.122.192 (talk) 03:19, 8 December 2017 (UTC)

A sharp rise in the price of tin has resulted in the re-opening of a mine in Cornwall. However, one mine which isn't going to be opened is this one: [36]. 82.13.208.70 (talk) 11:38, 8 December 2017 (UTC)

December 8

Please identify a weapon

What is this weapon mounted on a Ugandan Army Casspir APC? I suspect is is a type of light mortar or grenade launcher. Roger (Dodger67) (talk) 09:00, 8 December 2017 (UTC)

My best guess would be the QLZ-87 grenade launcher. Mũeller (talk) 09:20, 8 December 2017 (UTC)

Cheese Curd

From Cheese Curd:

   Most varieties, as in Ontario, Quebec, Nova Scotia, Vermont, or New York State, are naturally uncolored. The American variety is usually yellow or orange, like most American Cheddar cheese, but it does not require the artificial coloring.

So what's making American cheese curd yellow or orange, if no artificial coloring is added? Is it because of some difference between Canadian milk and American milk? Or some other factor? Mũeller (talk) 09:17, 8 December 2017 (UTC)

Annatto.--Jayron32 09:21, 8 December 2017 (UTC)