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August 31

Oldest functioning human body parts

I saw this article from 2008 about a 123-year-old human male cornea which is still functioning: https://www.reuters.com/article/us-norway-eye/transplanted-cornea-in-use-for-record-123-years-idUSTRE49M6BL20081023 . In turn, this got me thinking--have there been any human body parts which survived and functioned for a longer time period than this cornea?

I mean, the record for verified human longevity is 122 for women (Jeanne Calment) and 116 for men (Jiroemon Kimura), but this 123-year-old male cornea beats both of these records. Now, the question is whether there are any human body parts which have survived and functioned for a longer time period than this cornea did. Futurist110 (talk) 22:23, 31 August 2018 (UTC)

This is not what you're asking for, but you may be interested in HeLa as it is very closely related. Matt Deres (talk) 22:31, 31 August 2018 (UTC)

Yes, I know about HeLa and those cells are certainly extremely interesting given how much they've helped to advance scientific research over the years. Futurist110 (talk) 22:33, 31 August 2018 (UTC)

You don't mean "surviving", do you? You mean functioning? Otherwise, there are still parts of this "human" body that are only about 315,000 years old? Martinevans123 (talk) 22:47, 31 August 2018 (UTC)

Yes, I mean functioning. Basically, I mean body parts that are still alive/living. Futurist110 (talk) 23:10, 31 August 2018 (UTC)

Don't quote me on the exact details, but during the Second World War a lady died and some of her tissue was retained and cultured to investigate the pathology. These cells remain active today and much useful research is conducted using them, cultures having been transported to many laboratories. 195.147.104.148 (talk) 09:55, 1 September 2018 (UTC)

That's HeLa, already mentioned above. Abductive (reasoning) 12:11, 1 September 2018 (UTC)

Yep. Interestingly enough, I had to read Rebecca Skloot's book about Henrietta Lacks for one of my classes. It was certainly a very interesting read. Futurist110 (talk) 00:50, 2 September 2018 (UTC)

I just checked and this Rebecca Skloot book even has its own Wikipedia article: The Immortal Life of Henrietta Lacks. Futurist110 (talk) 00:51, 2 September 2018 (UTC)

September 1

Avective movement

I was recently reading about water movement, and came across the phrase "avective movement". I understand what advection (with a "d") is (movement of something in the water along with the bulk movement of the water itself). Is "avection" just another name for (or perhaps a misspelling of) that? Thanks. --Tryptofish (talk) 20:04, 1 September 2018 (UTC)

Its a printing error. There are only 2 words with "vection" in Fluid dynamics. Advection and convection. --Kharon (talk) 01:33, 2 September 2018 (UTC)

Thanks. I asked because I came upon it in a book, where it appears many times in various chapters, so I wasn't confident that it was just a one-time typographical error. --Tryptofish (talk) 20:50, 2 September 2018 (UTC)

What are charged polymers used for?

I'm interested in all uses. I do know the charged polymers are used as flocculants. 2600:1002:B018:80CC:DD95:93FC:45D9:2C40 (talk) 20:40, 1 September 2018 (UTC)

No clue if this is helpful, but the relevant WP article seems to be Polyelectrolyte (cf Flocculation). 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 00:49, 2 September 2018 (UTC)

Mainly used as part of Polymer capacitors which can be found in almost everything counted as electronics today. --Kharon (talk) 01:45, 2 September 2018 (UTC)

Ion exchange resins would be a large application. 202.155.85.18 (talk) 07:54, 3 September 2018 (UTC)

Doing serum electrolytes home ?

I wonder if technology exists to measure blood electrolytes in home conditions and I mean mostly sodium and potassium? Thanks, AboutFace 22 (talk) 22:38, 1 September 2018 (UTC)

There are in-home test strips for sodium only (from urine), but other electrolytes require blood sample. There was an interesting "prototype wearable microneedle device" from Sandia Labs (2014):[1]. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 01:02, 2 September 2018 (UTC)

Thank you, it is interesting. I wonder what progress has been made since 2014 when this article was published? Do you have any idea if this devices has been approved by the FDA? Or perhaps it is commercially available already? Thanks, AboutFace 22 (talk) 14:22, 2 September 2018 (UTC)

I couldn't find any subsequent references in the usual places. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 18:47, 2 September 2018 (UTC)

September 3

Fission of U-236

My inorganic chemistry textbook has a section on the origin of the elements where it goes over some nuclear physics in brief. My question relates to this excerpt. Actually I have two questions. Firstly, is the equation given for the spontaneous fission of U-236 correct? The mass doesn't seem to balance. I think the correct equation should be:

²³⁶
₉₂U
→ ¹⁴⁰
₅₄Xe
+ ⁹³
₃₈Sr
+ 3
n

Secondly, in their determination of the energy released, shouldn't we take into account the binding energy of the free neutron(s)? I'm not exactly sure how to take into account that binding energy, but I would imagine that a significant amount of energy would be needed to unbind neutrons from the nucleus. 202.155.85.18 (talk) 07:52, 3 September 2018 (UTC)

An arrow does not imply a balanced equation, only = sign does. As to the binding energy it is zero for free nucleons including neutrons, so it is correctly ignored. Ruslik_Zero 13:02, 3 September 2018 (UTC)

An arrow does not imply a balanced equation. Really? Per Nuclear reaction:

Nuclear reactions may be shown in a form similar to chemical equations, for which invariant mass must balance for each side of the equation, and in which transformations of particles must follow certain conservation laws, such as conservation of charge and baryon number (total atomic mass number).

So I think you are right that there really should have been a "3" there. But as Ruslik says, free nucleons have zero binding energy by definition of that concept, so it didn't matter here. --ToE 16:55, 3 September 2018 (UTC)

I suppose that, in fairness, an unbalanced equation is not wrong. It's just not balanced. And since we didn't need to balance it to get the correct answer, for this purpose, balancing was not required. That said, an equality sign would be wrong, because it would imply reversibility. 202.155.85.18 (talk) 01:23, 4 September 2018 (UTC)

This problem seems a bit contrived since, as far as I can tell, U-236 never undergoes spontaneous fission, but if left to its own devices, will only undergo an alpha decay (t_1⁄2=23.42x10⁶y).

According to the French Wikipedia, U-236 does undergo spontaneous fission. 202.155.85.18 (talk) 01:11, 4 September 2018 (UTC)

In The Nuclear Fission Process, data on the spontaneous fission of U-236 (among other radioactive isotopes) is given on page 37. 202.155.85.18 (talk) 01:18, 4 September 2018 (UTC)

Our isotopes of uranium gives spontaneous fission of U-236 as a known decay mode of 9.6×10⁻⁸% occurance. DMacks (talk) 02:10, 4 September 2018 (UTC)

Non-CYP2D6 pain killers

Please may you name some pain killers that hospitals routinely prescribe to patients that do not rely on the CYP2D6 pathway. For example when the patient is a poor CYP2D6 metabolizer whos body cannot convert codeine to morphine. Thanks for your time and help. — Preceding unsigned comment added by 77.101.141.178 (talk) 14:56, 3 September 2018 (UTC)

There is at least one, but (per disclaimer on top of page) ... "ask your doctor or a medical professional". 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 20:22, 3 September 2018 (UTC)

You answered your own question; morphine. Abductive (reasoning) 03:09, 4 September 2018 (UTC)

Characteristics of common wasps and bees (II)

Regarding my corresponding inquiry, I would like to once more ask for some more comments on the matter. Especially, I am still certain that common wasps and yellow jackets are indeed attracted by artificial light (e. g. cf. this information by the Oxford City Council) – very much as the table states for hornets.--Neufund (talk) 20:12, 3 September 2018 (UTC)

The article's talk page is probably the best place to discuss this; or edit the table yourself (?). Here is a source for paper wasps being attracted to light:[2]. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:10, 3 September 2018 (UTC)

I took the liberty of editing the table (inelegantly, perhaps) for paper wasps/light. 2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 21:46, 3 September 2018 (UTC)

What do these words mean in dentistry?

Any dentists around? Could someone please define the terms provisionalize (noun: provisionalization) and temporize (temporization)? I think they might be synonyms and I suppose they have something to do with temporary/short-term dental work. Equinox ◑ 21:41, 3 September 2018 (UTC)

According to a dental surgeon, which is inline with Google results, they are similar but not the same. Provisionalize has to do with an implant. The provisionalization is a quick, usually same-day, implant placed where the final implant will go. It lets you do a root canal, place a stud, and put in a provisional tooth all at once. Then, when the final tooth arrives, it is easy to remove the provisional tooth and replace it without surgery. Previously, there would be a root canal surgery, a wait, then another surgery to place the stud and implant. Apparently it is important that the provisionalization doesn't touch other teeth (or "occlude" other teeth). As for temporization, that is a temporary dental item, such as a cap or veneer. It is not temporary to be replaced with a final item. It is just temporary to eventually be discarded, possibly replaced with another temporary item. 216.59.42.36 (talk) 14:09, 4 September 2018 (UTC)

September 4

Nodes of atomic orbitals

When dealing with atomic orbitals, we say they have nodes where the wave function's value (and hence the probability density) is zero. Some nodes occur at particular angles (relative to an arbitrary origin) and are known as angular nodes, and some occur at particular radii from the nucleus and are known as radial nodes. The number of radial nodes for a given orbital is given by the relationship n-l-1 where n is the principle quantum number and l is the orbital angular momentum quantum number. Now, all orbitals have a node at the nucleus itself except for s orbitals (l=0). It stands to reason that this node must be a radial node, because it occurs at all angles, but only at the particular radius of zero. But the 3d orbital has quantum numbers n=3 and l=2, so it should have no radial nodes. I can confirm that it does have a node at the nucleus by looking at its radial wave function which shows it approaching zero at the origin as opposed to the s orbitals which do not. So I have a contradiction. Either the 3d orbital does have a radial node, or the node found at the nucleus for orbitals where l>0 is not a radial node, though I don't see how it is an angular node either...maybe it's a special type of node? 202.155.85.18 (talk) 02:51, 4 September 2018 (UTC)

Atomic orbital is our main article. Your

${\text{radial nodes}}=n-l-1$

formula is off by one for all p and d orbitals (even for 2p, n=2 and l=1 so 2-1-1=0 but your radial wave function diagram has zero amplitude at r=0) so it is definitely something special about the center vs r>0 nodes.

What is the origin of your formula? Not that I dispute it (it's easy to find in many college-level texts), but there may be an explanation in the surrounding prose. For example, [3] says: " The ‘-1’ portion accounts for the node that exists at the ends. (A half of one node exists at one end and since there are two ends, there’s a total of one node located at the ends.)" Look at the shape of the s with a maximum at r=0 vs others having a standard (amplitude=0) node at the center (as you notice, it's unusual). So the idea of a node possibly not actually existing there in the same way could mean that the –1 term is not correct in the other context (or is mis-explained in one vs the other).

The formula is from my inorganic chemistry text. They seem to be treating these "nuclear" nodes as a kind of special node, distinct from radial nodes. Fair enough. The rest is making sense to me now. I have another question though: the text also gives this relationship between the number of peaks in the radial distribution function that just seems totally wrong. A 1s orbital's RDF would have no peaks if this relationship were true, but on the very next page they give the radial distribution function of a 1s orbital with 1 peak. The relationship also fails for other orbitals' RDFs which don't display the predicted number of peaks. 202.155.85.18 (talk) 04:34, 4 September 2018 (UTC)

Other refs call the r=0 of s an "antinode", and looking at our Node (physics) article, this appears to be a good description for a "free boundary" due to the nature of the system rather than a zero amplitude. So if that counts as a node, then every calculation by the formula is off by one (1s has 1 node—the antinode) and the "–1" term is simply a bogus/fudge-factor to account for imprecise or incompletely explained other terminology. DMacks (talk) 04:26, 4 September 2018 (UTC)

My text uses the term "anti-node" to refer to anywhere there isn't a node. So in that case, the nucleus is an anti-node in the case of s orbitals, but a node in the case of all other orbitals. 202.155.85.18 (talk) 04:41, 4 September 2018 (UTC)

Gravity

Something about Einstein's theory of gravity never sounded right. Warping space time? But if time is just a series of events, and space is the absence of matter, how can it be warped by a physical object? There's nothing to warp in the first place, is there?

And if space time does exist, it would extend indefinitely into infinity, so it ain't like you have a flat surface that you can throw a ball unto. Did Einstein think the universe was 2D? Makuta Makaveli (talk) 04:57, 4 September 2018 (UTC)

Spacetime is not 2D, but to visualize the effect of a massive object on spacetime, it is convenient to consider the effect only in two dimensions. That's why you often see pictorial representations such as this one. Once you understand what is being implied in 2 dimensions, you can mentally extrapolate that to the third spacial dimension, though it's rather difficult to represent in an image. Then if you also incorporate the time dimension, it becomes even harder to represent as an image, and we use things like animated light cones to show what's going on. 202.155.85.18 (talk) 05:12, 4 September 2018 (UTC)

Is warped spavetime the only explanation for gravity? It sounds beautiful, but then again there was never any nobel prize for it, and maybe for good reason. Makuta Makaveli (talk) 05:22, 4 September 2018 (UTC)

There are no good explanations for gravity at all. We only have good descriptions of its effects. We don't know what causes it anymore than we know why two like charges repel one another. From observing the way objects behave in response to gravitational fields we can confirm that general relativity is a very good description that predicts essentially all observations to within experimental error. 202.155.85.18 (talk) 05:31, 4 September 2018 (UTC)

Special relativity has also not earned a Nobel Prize. Does it mean that it is incorrect as well? Ruslik_Zero 20:50, 4 September 2018 (UTC)

Also, I don't understand why space is often looked at as if it were a physical entity.

In the words of Douglas Grossman, "Space is volume, nothing more. It's not a physical entity. It is an idea like distance or area. When you walk through the area of a doorway, do you bump into anything? No, because area is an idea, same as space. Space is nothing, physically. It has no mass or energy, although mass and energy can be found within it. Space itself is not a physical entity and has no properties of its own other than volume. It's an abstract idea we use to understand the arrangement and movement of matter and energy in our world. Only matter and energy exist physically."

"What about the expansion of the universe? Galaxies move apart from one another in every direction, thus more volume (space) appears between them as they do so, but believing space carries the galaxies with it as it 'expands' is a misconception. Space is not expanding, galaxies are just moving apart." Makuta Makaveli (talk) 05:38, 4 September 2018 (UTC)

As far as the assertion about the motion of galaxies, that's an easily testable alternative theory: if a distant galaxy is 1 billion light years away from us and moving away from us at 0.5c, then light emitted by it now should reach us in 1 billion years. But if the space between us and the galaxy is also expanding, it will take longer. The fact that it takes longer is one way we know that relativity is correct. This is well understood aspect of the nature of the universe and is applied in astronomy as Comoving and proper distances. 202.155.85.18 (talk) 05:43, 4 September 2018 (UTC)

If space was not physical, you could not observe it, move in it, measure it (distance and time), etc. See also the information about perfect vacuums. —PaleoNeonate – 08:03, 4 September 2018 (UTC)

We're moving in space right now. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:08, 4 September 2018 (UTC)

• Maybe, just maybe, general relativity is a bit more complex that the pop-science view of "mass warps spacetime". (It is also a bit more complex than "Einstein invented it all".) The fact that it did not get a Nobel prize is, let's say, not the best test of the correctness of a scientific theory; General_relativity#Consequences_of_Einstein's_theory has a lot of experimental tests without any less worse explanation. I dunno who this Douglas Grossman fellow is, but a paragraph of pop-sci from him is hardly a refutation of experimentally-validated theories. Tigraan^{Click here to contact me} 07:26, 4 September 2018 (UTC)

FWIW, a google search on the name doesn't yield any prominent results for anyone likely to be an authority on physics. {The poster formerly known as 87.81.230.195} 90.212.15.178 (talk) 10:53, 4 September 2018 (UTC)

The above quote seems to come from a comment on Quora by someone with the name quoted above [4] Nil Einne (talk) 12:55, 4 September 2018 (UTC)

Douglas Grossman may not be an authority on physics, but I like his definition so I chose it. if a distant galaxy is 1 billion light years away from us and moving away from us at 0.5c, then light emitted by it now should reach us in 1 billion years. But if the space between us and the galaxy is also expanding, it will take longer.

General relativity can't be the only way to explain this. PaleoNeonate said, If space was not physical, you could not observe it, move in it, measure it (distance and time), etc. This can be easily refuted. When you measure space, you are measuring nothing, uninhabited and matterless void. It's the same as measuring the invisible line around the earth called the Equator, which doesn't exist. As for moving space, there is nothing to move in the first place, and nothing to observe. Instead, you'd be observing and moving matter, which may or may not be invisible. Makuta Makaveli (talk) 17:29, 4 September 2018 (UTC)

General relativity is a set of equations and assumptions that purport to model the behavior of matter on a grand scale (on ordinary scales it reduces to simple Newtonian gravitation, and on quantum scales it breaks down completely). Scientists like the theory of general relativity because it not only provides an elegant explanation for cosmological observations, it has accurately predicted many new observations since its conception. There is no alternative to general relativity that makes better predictions. You can like or dislike how spacetime is described, but the math works out regardless. Perhaps you can describe more clearly what experimental or other observational result you think contradicts general relativity, or is better explained by something else. But you shouldn't put too much stock in verbal explanations seeming wonky to you - it's just a model, after all. The important part of the theory is that it can accurately predict what you will observe when you test the effects of gravity. Someguy1221 (talk) 22:40, 4 September 2018 (UTC)

Like a lot of things in physics, you can ignore the advanced theories if you don't measure quantities very precisely. So to shift the burden to the original poster: how accurately do you measure gravity, when you measure gravity? If the answer to this question is "I don't measure gravity," then you're categorically unqualified to have an opinion on the various advanced methods that others use to predict and measure gravity. Nimur (talk) 02:06, 5 September 2018 (UTC

My main issue is with how space and time are pictured in the General Relativity. Sure, it predicts and measures just fine, but are scientists sure that space time is responsible for gravity? Makuta Makaveli (talk) 02:20, 5 September 2018 (UTC)

Scientists are sure that the equations we commonly call "general relativity" are an accurate and precise mathematical model, and this mathematical model has explanatory power when we study gravity. Equations do not cause things like gravity - rather, equations can be used to explain things like gravity.

If you don't like these explanations, or if you don't understand them, that's okay. Major league ball players don't ask you to like or understand their methodology for picking batting orders in the mid-season; economists don't ask you to like or understand their theories about quantitative easing policy or its relationship to monetary inflation; physicists don't ask you to like or understand complicated mathematical models of gravity. These pursuits, to the extent practically possible, are meritocracies that are conducted by expert professional specialists; it takes a lot of years of dedicated work to develop the fundamental skills; and until you have established credibility in these fields by following well-established career-trajectories working toward the professional level, the experts don't really care what opinions you have about their work. You are free to critique advanced physics - or to complain that you don't understand it - but it will be about as productive as if you complain about the coaching strategy for a professional sports team. Your opinion carries no weight, and your critiques don't merit attention, because you aren't playing in the same league.

One does not begin a study of physics with generalizations of gravity; one does not embark on their ball-playing career as a starting pitcher for the Yankees.

To make my point more bluntly - if you want to understand general relativity, you begin by investing five or six years studying the easier parts of mathematical physics - usually by pursuing formal undergraduate college education culminating in a degree in mathematics or physics - and then you begin to study relativistic generalizations. If you think you can skip past those first five or six years of the easy stuff, you must be a super-genius whose superior mental acuity far exceeds that of the physicists whose work you are pretending not to understand.

Nimur (talk) 02:53, 5 September 2018 (UTC)

Piscis piscātor unus sunt? I'd like to talk with you sometime, Nimur. I'm sure the conversation would be intriguing. Makuta Makaveli (talk) 06:32, 5 September 2018 (UTC)

This is quantum mechanics, not relativity, but "empty space" is anything but: see Casmir effect, quantum foam, and related articles. It sounds to me like you have aesthetic objections to how relativity is commonly visualized. That's fine, but it doesn't change anything. The math makes certain predictions, every prediction that's been tested to date is correct, so we use it. If you don't like the visualizations, don't use them. As Someguy1221 stated, it's a model. All models are wrong; some are useful.

Fun fact: modern heliocentrism took a while to get off the ground (pun intended) in part because Copernicus was wrong about planetary orbits. He insisted they must be perfect circles, not ellipses, because circles are perfect shapes, and the heavenly spheres must only contain perfect shapes (following Plato, who stated the same). Since as we now know, planetary orbits are in fact ellipses, his published system involved all kinds of epicycles to make the orbits "correct", just like the Ptolemaic system it tried to replace. Hence, it was not any more elegant, and few people thought it had much merit. It took Kepler, working from Brahe's actual observations, to deduce that orbits were ellipses. This kind of metaphysical reasoning was really the norm for most of history. The Scientific Revolution was in large part about, "Hey, let's make predictions based on observation and test our predictions, instead of deciding how things must be and then looking for evidence to confirm it." Newton was quite troubled by gravity appearing to be some invisible force that caused action at a distance, but fortunately he published his theory anyway. The universe doesn't care what some apes on a tiny dirtball think about it. I feel similarly about the debates over interpretations of quantum mechanics. If we can't test it, it's irrelevant. Shut up and calculate. --47.146.63.87 (talk) 09:30, 5 September 2018 (UTC)

GR can be derived from first principles. Count Iblis (talk) 14:17, 5 September 2018 (UTC)

No more answers are needed, Nimur has already given a satisfactory one. Thank you, you all have been exceedingly helpful for this test. Makuta Makaveli (talk) 17:41, 5 September 2018 (UTC)

The Ptolemaic theory was actually better at predicting the planetary positions than Copernicus'. The elephant in the room, however, was the lunar theory. Although it predicted the position rather well, the size of the epicycle meant that there would be a huge increase in the moon's apparent size at its closest approach. Astronomers were well aware that the apparent diameter increased only by one part in seven - they knew the theory was wrong. 86.133.58.87 (talk) 19:18, 5 September 2018 (UTC)

Spider

What spider is this one, at least at the family or genus level? Spotted in my room, 3 cm in length (with legs). Possibly orb-weaver, but not sure. Brandmeister^talk 10:54, 4 September 2018 (UTC)

Where? Looks perhaps like one of the many grass spiders; the image is perplexing, doesn't seem to follow a proper arachnid body-plan→

Arachnid anatomy:
(1) four pairs of legs
(2) prosoma (cephalothorax)
(3) opisthosoma (abdomen)

2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 17:31, 4 September 2018 (UTC) ... perhaps the abdomen is "missing"?

It's probably a male; they often have smaller, rather indistinct abdomens (lacking the egg producing organs that females need) which often don't show a clear break with the cephalothorax. The legs in the picture (the two-and-two on each side) reminds me of an orb weaver of some sort, especially the Argiope (spider) genus. --Jayron32 17:44, 4 September 2018 (UTC)

September 6

Alpha decay of Be-9?

My inorganic chemistry text book contains this practice problem. The question seems totally nonsensical to me. Firstly, Be-9 is a stable isotope. It doesn't undergo alpha decay. Secondly, even if it did undergo decay, it could not have a daughter product 3 mass units heavier than itself, plus an alpha particle and then neutrons on top of that. The text gives this answer which makes even less sense (many of the other answers to problems are obviously incorrect, so I don't put a lot of stock in what they give). The equation balances, but it involves a step where two Be-9 nuclei first fuse, which is not what I'd call simply "Be-9 undergoes alpha decay"). Any help would be appreciated. 139.194.67.236 (talk) 02:33, 6 September 2018 (UTC)

Indeed. Which kind of textbook makes basic errors like this?--Jasper Deng (talk) 02:40, 6 September 2018 (UTC)

It's Shriver & Atkins' Inorganic Chemistry, the Atkins being Peter Atkins. His physical chemistry textbooks are the go-to for many courses as they're really probably the best out there, but this inorganic text is full of errors. 139.194.67.236 (talk) 03:00, 6 September 2018 (UTC)

The problem is nonsensical, even as a hypothetical sample problem meant to demonstrate simple concepts, like conservation of mass number and atomic number in nuclear decay events. Alpha decay as a process should always produce a smaller atom, not a larger one. Strictly speaking, if Be-9 were to undergo alpha decay (not that it would, merely if we were to work out the product if it did), the product should be He-5, not C-12. Something emitting an alpha particle and gaining mass number and atomic number is nonsensical. --Jayron32 15:10, 6 September 2018 (UTC)

The fusion reaction given in the answer is allowed as a spontaneous reaction, let's see if anyone here can come up with an estimate of the reaction rate per atom in piece of Be-metal at room temperature. Count Iblis (talk) 13:54, 6 September 2018 (UTC)

That reaction is literally how the neutron was discovered. Though it is inaccurate for a textbook to refer to this as decay of ⁹Be. Someguy1221 (talk) 22:39, 6 September 2018 (UTC)

Providing the current precision limit of our measurements, what is the minimal size of the universe?

I am not referring to the observable universe, but to the entire universe.

As far I understand, current observation is that the universe is flat, and this indicate infinite universe.

However, the measurements have a precision limit, which still allow a very low curvature, beneath our measuring abilities.

Assuming the curvature is as big as possible to exist but still not to be detected, what is the size of the universe? אילן שמעוני (talk) 04:23, 6 September 2018 (UTC)

14 trillion lightyears according to this. 139.194.67.236 (talk) 11:17, 6 September 2018 (UTC)

Or it may be that the universe has a high curvature, but the part we can observe just happens to be on a flat spot. Or there may be something we don't understand yet that negates the assumption that flat=infinite. Or perhaps the Simulation hypothesis is true and the owner of the simulator doesn't bother simulating the parts that cannot be observed. --Guy Macon (talk) 16:45, 6 September 2018 (UTC)

I think we can eliminate any variation of solipsism from any scientific analysis of the universe. Once we start getting into unfalsifiable ideas, we've moved from the realm of science into something else. The axiom that reality exists and is knowable (or at least reliably modelable) by humans is necessary for any productive realm of thought to move forward; once we start dealing in fanciful and unfalsifiable possibilities, we're outside the scope of the question. --Jayron32 18:10, 6 September 2018 (UTC)

You actually think that the claim that the entire universe (not just the visible universe) has the same curvature throughout is falsifiable? How exactly would you falsify it? --Guy Macon (talk) 23:37, 6 September 2018 (UTC)

It could be in principle falsified by information from gravitational waves or neutrino radiation that predate the recombination (and thus give us a larger observable universe, maybe even all of it) or in the event of a big crunch we eventually get to observe all of the universe as it comes hurtling back to us (which ironically, is more likely to happen if we are in some sort of unrepresentative bubble that is unlike the rest of the universe with different cosomological constants and curvature and all that). Could also be primordial wormholes or other exotic phenomena that link us to regions of the "unobservable" universe. We don't have enough certainty to declare that it's definitely unfalsifiable. 202.155.85.18 (talk) 02:08, 7 September 2018 (UTC)

Every time you speak you make it clear how unworthwhile it is to listen to you. --Jayron32 11:35, 7 September 2018 (UTC)

According to The Hitchhiker's Guide to the Galaxy "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." I'm not sure we can say all that much more about the size of the entire universe at this point. Dmcq (talk) 13:02, 7 September 2018 (UTC)

September 7

Distance of electron from Hydrogen Nucleus

I have another question from my inorganic textbook. From reading the text, I more or less know what they want me to say. In its ground state, hydrogen's single electron will be in the 1s orbital. The answer to a) is that the electron's most probable location is where the radial probability density is highest (i.e. the square of the radial wave function). From this graph in the text (where the radial probability density is denoted R²), it's clear that the highest probability is at the nucleus itself. For part b) the question is asking about the radial distribution function (drawn in red in the same graph), which has a maximum at the point equal to the Bohr radius (52.9pm) on the nuclear charge (1 for hydrogen, so the answer is 52.9pm). Even though I'm pretty sure I know what they want me to say, I don't understand what it means. How can the most probable distance be 52.9pm from the nucleus when the most probable location is the nucleus itself? What does that actually mean? Is it something like "The most probable distance is 52.9pm in any direction from the nucleus, so the most probable location is the average of those points i.e. in the center"?

Also, the text gives me this relationship for determining the maximum of the radial distribution function. But it only seems to be for 1s electrons. The accompanying text notes that the number should be higher for higher n values, but there's nowhere to actually plug in n, and I need to determine the value for n=2 to solve part c) What is the most probable distance of a 2s electron from the nucleus? 202.155.85.18 (talk) 09:31, 7 September 2018 (UTC) EDIT: Actually, they also give me this graph in the text. Perhaps I'm just supposed to read off that the maximum of a 2s orbital's radial distribution function is a tiny bit over 2x the Bohr radius and leave it at that? Googling around there are some tutorials for physics students explaining how to actually determine the 2s RDF numerically and then find the maximum, but I'm fairly sure I'm not meant to be able to do that given this passage in the text. 202.155.85.18 (talk) 09:41, 7 September 2018 (UTC)

this page has a discussion of the derivations of the various radii in question. --Jayron32 11:32, 7 September 2018 (UTC)

Mistake in article

In Apollo 11, it says "Aldrin joined him about 20 minutes later". In Buzz Aldrin: "Aldrin set foot on the Moon at 03:15:16 on July 21, 1969 (UTC), 9 minutes after Armstrong first touched the surface".111.235.89.222 (talk) 11:34, 7 September 2018 (UTC)

I reviewed the details, and I'm comfortable with using the vague language, "about 20 minutes later," because the article introduction is only providing an abbreviated summary.

One of the best resources for factual details of the Apollo lunar missions is the Apollo Lunar Surface Journal. Here's the transcript for Armstrong and Aldrin during the first extravehicular activity on the moon's surface.

Ultimately, both astronauts got on the moon within "about" twenty minutes, depending on how you count - the procedures for the very first moon landing were complicated. The process of exiting the Lunar Module - just "walking out the door" - actually took several minutes. Here are Page 40 and Page 41 of the EVA checklist.

I think it's alright for our article's lead paragraph to say "twenty minutes" - readers who want more details about precisely what was going on during that time can find such details in the rest of the article and in the primary sources referenced by the article. Nimur (talk) 14:13, 7 September 2018 (UTC)

Efficient swimming: horizontal or vertical fin

Does it make any difference, even if it's a small one, whether a marine animal (imagine dolphin vs shark) has its tail fin attached horizontally or vertically? Obviously, there's an ergonomic difference. Humans will have a hard time flapping a fin horizontally. I ask discounting such issues. --Doroletho (talk) 13:50, 7 September 2018 (UTC)

Without addressing the more general scanario I would observe that, close to the surface, a horizontal fin (i.e. one moving up and down) could waste some of its energy by causing splashes where a vertical (side-to-side) fin would not. However, IANAHydrodynamicist. {The poster formerly known as 87.81.230.195} 2.122.60.253 (talk) 14:56, 7 September 2018 (UTC)