Wikipedia:Reference desk/Archives/Science/2013 March 29

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March 29

Does Navier-Stokes work for solids?

I was looking at the article Derivation of the Navier–Stokes equations. Where in the derivation does it use the assumption that the substance is a fluid? Does Navier-Stokes work for solids?

150.203.115.98 (talk) 04:56, 29 March 2013 (UTC)

As far as I can tell it does. f = −∇·σ, where f is the body forces and σ is the stress tensor (including tension/pressure), is true for a solid in equilibrium. -- BenRG (talk) 05:27, 29 March 2013 (UTC)

Cracks could cause discontinuities in both density and velocity, making them undifferentiable.--Wikimedes (talk) 05:51, 29 March 2013 (UTC)

You show me a homogenous isotropic solid with a non-zero velocity field and no force which acts to restore particles to their equilibrium positions and I'll show you a fluid. Incidentally I think it is even only this last one, the lack of restoring force, which is sufficient to make something fluid.

Ethical obligation of professional scientists toward open accountability

I'm looking for published pieces in authoritative sources on scientific ethics concerning the reasonable amount of time that a high-profile scientist in a moderately controversial field ought to spend answering questions about their work from (1) other scientists in their field, and (2) the general public, especially when a larger than ordinary number of such questions are forthcoming. Ideally, there's a Nature or Science essay out there suggesting a specific number of hours per week for both as being reasonable, but even an editorial in a third-tier journal or monograph on the topic would really help. Sadly personal opinion on this will not help me at all. Thanks in advance. 75.166.202.252 (talk) 06:05, 29 March 2013 (UTC)

Speaking as a scientist myself, I'm pretty certain there is no rule specifying an amount of time. The basic rule is that good work should be reproducible by other scientists, and a scientist is obligated to supply any information missing from a publication that is needed in order to reproduce the findings. However long that takes is however long you are obligated to spend. Looie496 (talk) 07:30, 29 March 2013 (UTC)

The questions I'm concerned about here are asking for explanations of model assumptions and interpretation of evidence, in a less experimental science, i.e. astrophysics. 75.166.202.252 (talk) 08:18, 29 March 2013 (UTC)

Most scientists are eager to answer questions if they seem at all reasonable. If you're asking questions and not getting responses, there may be something wrong either with the questions or the way they are being asked. However, there are also people who never look at their email, or whose spam filter malfunctions, so it's hard to say anything that applies universally. Looie496 (talk) 21:54, 29 March 2013 (UTC)

I don't think there are any such authoritative pronouncements on this. I know from my scientific colleagues in universities that many of their appointments include undefined requirements of "service," which is where one might think this sort of thing might be found, but usually those are explicitly with reference to service to the department (e.g. serving on hiring committees) and not towards the general public (in fact, spending too much time doing "public" activities — even when that means testifying before Congress or serving on important panels — is sometimes seen as a negative by university departments, as absurd as that may seem). I've had one friend even complain that being President of the major professional society for his discipline (and it's not a minor discipline!) was not considered "service" by his university, which is totally nuts, but there you have it. --Mr.98 (talk) 16:52, 29 March 2013 (UTC)

one issue is that scientists are reluctant to take data they have laboriously assembled over months or years of grant-sponsored work and the rewards of which they are now reaping in terms of publications containing analysis of said data, thereby enhancing their attractiveness for future grant money and employment, until they themselves have gnawed the last publishable flesh off the bones, before they hand it over to those who, being in the same field, are competitors for the aforementioned glittering prizes, in order that said competitors might crank out their own publications. The Ant and the Grasshopper and all that. On the other hand, data and analyses derived from publicly available datasets via various transformations etc. without the same sort of investment of time and labor should be fair game. If they can't or won't cough up the methods, intermediate calculations and results, etc. of how they got from alpha to omega, time to be skeptical. [1] Gzuckier (talk) 19:34, 29 March 2013 (UTC)

Since when is astrophysics a moderately controversial field?? Dauto (talk) 16:55, 29 March 2013 (UTC)

Open Yale Courses had a course about controversies in astrophysics. Add to it the Drake equation and there is the Solar neutrino problem too. There you have your moderately controversial field. Less controversial than climatology, but more than mechanics. OsmanRF34 (talk) 00:43, 30 March 2013 (UTC)

I do research in astrophysics, and I've yet to see a single scientific paper that takes the Drake equation seriously. The solar neutrino, as the article you linked to says, was resolved in 1968 with the discovery of neutrino oscillation. --140.180.254.209 (talk) 16:14, 30 March 2013 (UTC)

I think the approach varies from university and from field to field. At the university I graduated from, teaching staff and researchers used to be most helpful in answering queries from outside about their work. I have sometimes studied a journal paper and not been able to fully understand it or thought there was some key information missing. I'm no boffin, just a practicing Engineer. I've sent emails to the authors and been amazed at the thoughtful and most useful replies I've got back. But back to my own uni: Some time ago they formed a marketing division, with a mission to commercialise and extract money from as much of their activities as possible. Since then, it's just a total waste of time to ask them anything.

It used to be that if a paper was published that drew conclusions from a great mass of numerical data, that the raw data was not published in with the paper in the journal, as it took up too much space. But if you wrote and asked, they would supply. Some journals have the data and additional information to enable replication ready for download on their website. That's great!

Trouble is, these days, in many fields, the author's conclusions were determined by computer program, or the paper is about a computer program. I am interested in 4-cycle engine combustion. There is a certain group of researchers who have claimed in a journal paper that they can accurately simulate combustion with a computer program they devised, and have drawn certain conclusions about combustion from the program results. But they will not, release the source code or even a usuable description of the algorithms. So, nobody can replicate their work; nobody can benefit from what they learnt. I think that is disgusting. Ratbone 121.215.20.145 (talk) 02:39, 30 March 2013 (UTC)

I doubt that they are publishing in high-quality journals. Looie496 (talk) 15:06, 30 March 2013 (UTC)

Actually, they have published in a well known peer reviewed proffessional journal, one I would think would, otherwise at least, be regarded as high quality. However, this is not the place to set out just who they specifically are (and they just might read Ref Desk, and work out from emails and Ref Desk posts who I am). Given that I have set out the subject, and you would assume their papers are recent, if I identify the journal, you will know who they are. Actually, if you have a similar interest in combustion, you probably should have guessed who they might be anyway, but there's no need for me to make it specific here. Ratbone 120.145.158.214 (talk) 15:28, 30 March 2013 (UTC)

Freak event

What would happen if there was a freak event where all electrical generators in the world ceased to work for an extended period of time? All generation technology is included including internal combustion engines and those torches that you shake and then they produce light. 105.227.178.237 (talk) 11:37, 29 March 2013 (UTC)

According to Revolution (TV series), the collapse of government and public order, followed by the rise of militias and warlords where for whom ability to generate electricity becomes the most powerful weapon available. - Cucumber Mike (talk) 12:11, 29 March 2013 (UTC)

I think that also happened in the Tom Cruise version of War of the Worlds. Although that wasn't exactly a freak event, it was an invasion. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:55, 29 March 2013 (UTC)

For some strange reason, in Revolution, War of the Worlds and other such shows, bicycles no longer exist and everyone has to walk or rid a horse. --Guy Macon (talk) 16:42, 29 March 2013 (UTC)

In the near future when Revoution is set, every bicycle has a generator built in for headlights, and humanity has lost the ability to make a bicycle without one. Gzuckier (talk) 20:07, 29 March 2013 (UTC)

It depends on whether you're talking about science or magic. If it's science, then anything that shuts down all electromechanical generation kills everything, among other various apocalyptic consequences. If it's magic, then it can do whatever you want it to do. The latter is obviously more interesting from a storytelling perspective, but there is no referenceable "right" answer. — Lomn 14:27, 29 March 2013 (UTC)

Note that the best real-world analogy, electromagnetic pulses, have the ability to destroy a lot of equipment, but not the ability to inhibit the function of new equipment. It's the magical "nothing new can ever work, either" part that breaks things. — Lomn 14:29, 29 March 2013 (UTC)

The problem is that you're trying to eliminate all forms of electrical generation - and that is one hell of a stretch. Waving a magnet in front of a coil of wire produces enough electricity to light a flashlight bulb. You don't need a nice man-made magnet - a simple lodestone will do...and you don't even need a manufactured "wire" - a coil of anything that conducts electricity would do...a garden hose full of seawater, for example. If that doesn't work in your hypothetical world, then very fundamental laws of physics have to be broken...and the consequences of that are very likely to be a sudden, immediate end of all things! I doubt that human brains could function in that scenario.

You can't really couch the question with enough hypotheticals and caveats to limit the damage to "What would happen to human society without electricity?" without it boiling down to being "magic"...and once you have that, all bets are off when it comes to predicting the outcome. SteveBaker (talk) 14:38, 29 March 2013 (UTC)

Well said, Steve. And so that I'm not just replying to myself in this thread, I'll stick this point here instead: the OP may also be interested in S.M. Stirling's Emberverse series, a set of novels that more or less provide the inspiration for the new Revolution show. The effect itself is "magic", to the extent that any explanation at all is attempted, but the thrust of the books is "post-apocalyptic alt-history" rather than straight-up "fantasy". — Lomn 14:43, 29 March 2013 (UTC)

There are other such books which deliberately don't use technology, but generally there are social, rather than technological or physical, reasons for doing so. For example, in the Dune franchise, there is no use of computers or any other "thinking machines"; the novel explains their non-use as a result of the Butlerian Jihad rather than any specific physical reason why they couldn't work. Similarly, by the time of the "Galactic Empire" and "Foundation" period of Isaac Asimov's extended universe, there are no working Robots, despite the fact that many earlier works in the same universe featured them. Asimov explains this as being a ban on the use of such Robots, similar to the Dune universe. So, if you want to create a future world where electricity isn't used, it may be more realistic to invoke a strong social reason (such as a religious proscription or a governmental ban or something like that) to explain why it isn't used, rather than any physical reason which, as noted, is simply ridiculous to anyone with even a basic understanding of physics. --Jayron32 16:05, 29 March 2013 (UTC)

Continuing in the theme of 'social' pressures, science fiction writers have also been known to invoke a need for concealment – either from other humans, angry aliens, or both – as a compelling reason to curtail or completely suppress the use of electricity (and the associated nearly-unavoidable leakage of electromagnetic radiation). To pick just a very few more recent works, this concept comes up in David Brin's Brightness Reef, David Weber's Safehold series, and John Scalzi's The Last Colony. TenOfAllTrades(talk) 17:33, 29 March 2013 (UTC)

well, for one thing, the ability of the earth's iron core to generate a magnetic field will cease, and we will be fried to death the next time the Sun has indigestion and burps up a stream of high energy ions. Gzuckier (talk) 20:07, 29 March 2013 (UTC)

• There are also The Waveries and Blood Music if you want good sci-fi treatments of an end to electricity. μηδείς (talk) 22:35, 30 March 2013 (UTC)