Wikipedia:Reference desk/Archives/Science/2017 December 1

= 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  ; 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, 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? -
 * 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:. Gråbergs Gråa Sång (talk) 07:48, 1 December 2017 (UTC)
 * A copy of the article is at Deletionpedia:  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 What Wikipedia is not. --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)


 * 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? — Paleo  Neonate  – 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?  -- Jayron 32 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.  -- Jayron 32 13:41, 1 December 2017 (UTC)
 * 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?
 * 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"?
 * 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.
 * 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.  -- Jayron 32 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.  -- Jayron 32 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.  -- Jayron 32 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.  -- Jayron 32 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,  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 Verifiability and No original research. There is some limited allowance for using a book as a source of itself, see No original research and 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 . 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  (link to whole work ) by Jonathan Bennett (philosopher) . 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   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  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.-- Jayron 32 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.  -- Jayron 32 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  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  o riginal p oster 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)
 * It might, but Original post is a usenet standard meaning that predates twitter by a few decades. DMacks (talk) 04:51, 11 December 2017 (UTC)