Wikipedia:Reference desk/Archives/Science/2014 July 19

= July 19 =

May be all science always been humanitarian?
If philosophy of science knowledge always been humanitarian, may been all science always been humanitarian?--Alex Sazonov (talk) 09:16, 19 July 2014 (UTC)


 * What do you mean? ←Baseball Bugs What's up, Doc? carrots→ 11:11, 19 July 2014 (UTC)


 * It might be better to write it in your own language and use google translate to change it to English. At least I normally understand that. I think it is a pity if people don't support the Wikipedia in their own language. Dmcq (talk) 11:19, 19 July 2014 (UTC)


 * There's no way working backwards from Russian you can assume this linguistic behavior is caused by translation mistakes, μηδείς (talk) 17:49, 19 July 2014 (UTC)


 * I think I know what he means, and I have this to say: Was the Manhattan Project humanitarian? Was I. G. Farben's research into nerve gases humanitarian?  Was Alfred Nobel's invention of high explosives humanitarian?  24.5.122.13 (talk) 19:52, 19 July 2014 (UTC)


 * At least two of those (Manhattan Project, and especially much of Nobel's work) are often argued as a net humanitarian gain, either with the benefit of historical perspective and/or at their own time. Knowledge is not a moral thing; only how one uses it. DMacks (talk) 19:59, 19 July 2014 (UTC)


 * Does that make Nazi research into the atomic bomb humanitarian too? HiLo48 (talk) 23:55, 19 July 2014 (UTC)


 * If they had been destined to win WW2 in either case, then I suppose it could be argued that a quick victory, using nuclear weapons, that killed fewer people, would be better than a longer, more deadly war. Of course, if they just murdered everybody after they won anyway, then there wouldn't be any benefit. StuRat (talk) 03:20, 20 July 2014 (UTC)


 * Will, the philosophy of science knowledge in all technical is been always humanitarian too?--Alex Sazonov (talk) 08:36, 20 July 2014 (UTC)


 * Thank you, Hayne. Beisbol bean berry good to me. ←Baseball Bugs What's up, Doc? carrots→ 11:21, 20 July 2014 (UTC)


 * You do realize that the chance that he will recognize an SNL sketch from the 1970's is approximately zero ? Also, wasn't the name Jaime (pronounced Hymee), and wasn't it "berry, berry" ? StuRat (talk) 15:56, 23 July 2014 (UTC)


 * To philosophy of science is amoral, meaning neither moral (humanitarian) nor immoral (evil). That is, the goal is just to seek knowledge, and whether that knowledge is good or bad for humanity is irrelevant.  StuRat (talk) 19:36, 20 July 2014 (UTC)


 * I don't think we can really answer this question here - at best we could provide sources to discussions of the topic, but I think there may be a language barrier. As for why the question is problematic:
 * Are we talking about science as in "scientific knowledge" or as in "the practice of science" or as in "the motives that direct science"? In the first case, it would be hard to discuss a moral value, but the latter cases are a lot murkier for a ton of reasons.
 * Does "humanitarian" mean "morally good" or "for the benefit of man"? For example, animal testing to develop drugs may, or may not, be moral, but it would be hard to argue that it is not to the benefit of man.
 * Without further clarification, I don't think any real answer can be supplied.Phoenixia1177 (talk) 05:39, 21 July 2014 (UTC)


 * None of 'philosophy', 'science', 'knowledge' or 'humanitarian' have sufficiently precise definitions to answer this. Peter Grey (talk) 01:50, 23 July 2014 (UTC)


 * Thanks more for all! Did the cybernetics is been always a philosophy science, or the cybernetics is been always a method of science knowledge?--Alex Sazonov (talk) 14:32, 23 July 2014 (UTC)


 * Cybernetics is, and has always been, predominantly an applied science topic, with some attendant ethical and philosophical questions.
 * Your English is very hard to understand. People have asked you about this before. Do you understand that we have considerable difficulty understanding you? AlexTiefling (talk) 14:40, 23 July 2014 (UTC)


 * Thanks! As I been thinking, never been the national science which write up the methodology of science knowledge which been usedes by that national science.--Alex Sazonov (talk) 14:59, 23 July 2014 (UTC)


 * I been see, that methodology of science knowledge always is been a intellectually secret of mind of every person which been in a science!--Alex Sazonov (talk) 15:22, 23 July 2014 (UTC)


 * Chose agree with me that, never not been important what kind the experiment will do, but always been most important how will do this experiment!--Alex Sazonov (talk) 15:43, 23 July 2014 (UTC)


 * Did you understand what I said about your English? AlexTiefling (talk) 15:47, 23 July 2014 (UTC)


 * Thank you AlexTiefling. Yes, I been understood that is been my problem that my English is not been well for discussions.--Alex Sazonov (talk) 15:55, 23 July 2014 (UTC)
 * Be agreed that methodology always is been a key to knowledge, that’s why the science which used by the USSR and the USA is been always general, but keys of that none been general!--Alex Sazonov (talk) 16:37, 23 July 2014 (UTC)

Are you understand that a soviet science person always been not wanted to share by their methodology because this methodology always been only their intellectually privacy which the USSR is not been ensure by them.--Alex Sazonov (talk) 18:36, 23 July 2014 (UTC)
 * I been must sad that in the USSR a science person always been knew that methodology is been a mind of science person!--Alex Sazonov (talk) 19:29, 23 July 2014 (UTC)

Recommendations for textbook on galactic astrophysics ?
I have just read and enjoyed Gravity's Engines by Caleb Scharf and would like to read a more detailed book on the same subject. Can anyone recommend an undergraduate level text covering galaxy formation and evolution, active galactic nuclei, supermassive black holes, dark matter etc. ? I know this is an area of active research, so something that is up to date and includes latest observations and developments would be good. I am comfortable with undergraduate level mathematics and physics. Not looking for a popularisation - Scharf ticks that box nicely - or pretty pictures - I can get those from APOD. Thank you. Gandalf61 (talk) 09:58, 19 July 2014 (UTC)
 * I think you will find The Astrophysical Journal of interest. Abstracts of its articles are free at the website, though to read them in full you need to pay or join a subscribing library. Caleb Scharf has written widely cited articles in The Astrophysical Journal. 84.209.89.214 (talk) 13:59, 19 July 2014 (UTC)
 * The Astrophysical Journal is a research journal that publishes highly technical research papers. You'll need a degree to understand the contents of individual articles and you'll need to spend a lot of effort on synthesising the contents of many articles into something like an overview of the current status of a field of research. Not recommended for the lay person. A book that I like and that covers most of the topics mentioned by Gandalf61 at an accessible but not too simplistic level is "Extragalactic Astronomy and Cosmology: An Introduction" by Peter Schneider. There are others, of course. --Wrongfilter (talk) 17:38, 20 July 2014 (UTC)
 * Thank you. I shall take a look at Schneider. Gandalf61 (talk) 06:16, 21 July 2014 (UTC)

Improvement to Cosmological Inflationary Model?
One of the aspects of current inflation that can be recorded in our modern universe is that it is only increasing in speed with time, which as I understand was the opposite expected behaviour until not too long ago. Of what evidence or idea does the early Cosmic Inflation theory still hold validity? As I've researched, the "Metric Expansion of Space" model defines that the universe still underwent that abrupt inflation and expansion at the moment of the Big Bang, then slowed down over the next 8 billion years, then began accelerating about 5 billion years ago. This would look something like this graph for the Inflection Point article: which is more or less a graphical deviation of an otherwise straight-line, and therefore possibly a misinterpretation of data on the Scientific Community's behalf.

I still feel the existence of an "inflationary epoch" to not be a necessary or appropriate model. If inflation is only increasing with time, is there really anything stopping it from always having been that way since the moment of the birth of the universe? Is there any observable data that says the early universe couldn't have existed as is postulated, but for millions or even billions of years rather than the established fraction of a fraction of a fraction of a second? Fbushnik (talk) 19:06, 19 July 2014 (UTC)




 * Modelling of the expanding universe is initially based on the observable constant $$H_0$$ in Hubble's law . If $$H_0$$ were really constant, the age of the universe could be resolved simply by extrapolating the present rate of expansion v back in time to a Big-Bang moment 13.7 billions of years ago. Such a finite universe lifetime seems to explain both Olbers' paradox (black gaps show between the stars) and the residual background radiation. The vast timescale rules out reliable direct observation of the rate of change, if any, of $$H_0$$. Observations of Type Ia supernova now suggest an Accelerating universe (see article). Models attempting to explain accelerating expansion include some form of dark energy, dark fluid or phantom energy and lead to different estimates of the age of the universe. See the diagram at Hubble's law. 84.209.89.214 (talk) 22:26, 19 July 2014 (UTC)


 * The accelerating expansion of the universe due to dark energy is not the same as inflation. They're theoretically similar, both being apparently caused by a spin-0 field of some sort, but there's nothing to suggest that they're related beyond that. There is no evidence that the rate of the accelerating expansion is increasing with time. What is happening is that the density of ordinary matter (and dark matter) is decreasing, and a few billion years ago it fell to the point that its gravitational attraction was no longer enough to counter the gravitational repulsion of the dark energy that had, apparently, always been there. It's not certain that this is the right model, but it's the simplest model that fits all of the data so far.
 * It's not true (or not known to be true) that inflation only lasted for a fraction of a second. The observed smoothness of the universe only gives a lower bound on the duration of inflation. There's no theoretical reason to think it didn't last for much longer than that. It could have lasted for billions of years as far as anyone knows. -- BenRG (talk) 23:37, 19 July 2014 (UTC)


 * I'm not a great fan of Occam's Razor, but I have to wonder how one measured Hubble constant (with substantial disagreements in the measurements) can support the proposal of two separate mysterious universe-wide repulsive forces active at the same time. Wnt (talk) 11:50, 20 July 2014 (UTC)


 * Support for the ΛCDM model comes primarily from the cosmic microwave background, the luminosity-redshift relation of supernovas, and baryon acoustic oscillation, not from one measured Hubble constant. Ned Wright's cosmology site has some details.
 * The universe-wide repulsive force is predicted by general relativity if there is a spin-0 field with a nonzero value in the vacuum (VEV). GR is known to be very accurate, and spin-0 fields with a nonzero VEV are known to exist (the Higgs field and the QCD vacuum). A lot of the appeal of the inflationary / dark energy model is that it doesn't require new physical laws, just new fields of a familiar type. -- BenRG (talk) 16:05, 20 July 2014 (UTC)

Chemical disposal of chemical weapons
As some of you probably know, phosgene can be made harmless by reacting it with a solution of caustic:

COCl2 + 4 NaOH → 2 NaCl + Na2CO3 + 2 H2O

and cyanide gas by chemical (e.g. catalytic) oxidation:

HCN + 5/2 O2 → HNO3 + CO2

My question is, what other chemical warfare agents can be made (relatively) harmless by selective chemical reactions (other than by high-temperature incineration, which would be sort of "cheating" because it's non-selective)? 24.5.122.13 (talk) 20:15, 19 July 2014 (UTC)
 * Most mustard agents and nerve agents seem reactive towards water or aqueous-caustic. Many of their biological properties are based on a similar reaction with various N and/or O nucleophiles. DMacks (talk) 20:33, 19 July 2014 (UTC)
 * See, for example, 10.1021/jo01175a018 discussing the rates and mechanisms of hydrolysis of some nitrogen mustards. DMacks (talk) 20:48, 19 July 2014 (UTC)


 * Thanks! I was pretty sure that mustard gas would hydrolyze in alkali solution like it actually does -- wasn't sure about nerve gases, though, because I didn't remember their structure. 24.5.122.13 (talk) 22:45, 19 July 2014 (UTC)

Wave interference - What´s happen with their energy ?
My doubt is about light/wave interference and their energy. I have read all the posts about waves and I didn’t find any reference about wave energy when interference occurs.

I don´t know if it is a dumb questions but I would like to ask you a question that is bothering me and I dont know how to explain.

If two waves meet at a point and from there we have a completely destructive interference, what happen with original energy that was transported (contained) by each wave ?

In other way, Could we have light wave interference, with phase deplacement, in such way that light will disappear ? In such case what will happen with energy ?

Futurengineer (talk) 22:07, 19 July 2014 (UTC)futurengineer


 * "Destructive interference" when travelling waves interact means that the net deviation (which may be brightness, electric potential or sound, depending on the type of wave) is zero at that point. Each wave continues in its own direction and likely there will be constructive interference between the waves at a different location. But in neither case has any energy been destroyed or constructed, only the local observation is affected. For simplicity assume small sinusoidal waves in a linear medium where no intermodulation of the waves occurs. 84.209.89.214 (talk) 22:40, 19 July 2014 (UTC)


 * Agreed. To see this for yourself, fill the tub with an inch or two of water, and poke the water with fingertips at two different locations, simultaneously.  Waves will spread out from each point, and pass right through each other. StuRat (talk) 03:13, 20 July 2014 (UTC)


 * In the general case where the waves are not spatially correlated, then the energy will redistributed, but the total energy is conserved. The waves may interfere destructively in some places, in which case the energy density could be locally reduced to zero. However, the waves will interfere constructively in other places, and in those places the energy density is greater than sum of the energy densities of the two waves. This is because the energy depends on the square of the amplitude, and the square of the sum of two amplitudes is greater than the sum of the squares. For example, if the waves have equal amplitude at a point where they constructively interfere, then the amplitude at that point is twice the amplitude of that of either wave, but the energy density is locally four times the energy density of either wave. The cold and hot spots average out, so that it turns out that energy is conserved (this is half the answer). --catslash (talk) 18:34, 20 July 2014 (UTC)


 * In the special case where the interfering waves are spatially correlated (such as two plane waves of the same amplitude and same wavelength travelling in the same direction), then the source of one wave (say the second), will continually be opposed (in the case of constructive interference), or assisted (in the case of destructive interference), by the field of the first wave. This means that the second source may be working abnormally hard (radiating more energy than usual), or may actually be absorbing energy, and so energy is conserved even though the total energy in the interfering waves does differ from the sum of the energies in the separate waves (still not a complete answer). --catslash (talk) 18:56, 20 July 2014 (UTC)


 * Another point worth mentioning is that anything that obeys both the wave equation and conservation of energy consists of a pair of fields (or a field having at least two components). For example a sound wave consists of a pressure wave and a particle velocity wave, while a light wave consists of both an E-field (electric) and and H-field (magnetic). Both parts of the wave carry energy. For the sound wave, the medium holds energy both by virtue of being compressed and due to its local kinetic energy. In the case of interference between waves travelling in opposite directions (a standing wave), constructive interference of the pressure waves (or E-field waves) occurs at the same locations as destructive interference of the particle-velocity waves (or H-field waves) and vice versa, so that the total energy density is everywhere the same. --catslash (talk) 23:04, 20 July 2014 (UTC)


 * To put the above replies more simply: when waves interfere destructively, there is always somewhere else where they interfere constructively, such that the total energy in the waves is always conserved.--Srleffler (talk) 17:18, 22 July 2014 (UTC)

How thick is the skin of a balloon?
I realize that the thickness would depend on the material, and how much pressure was inside, but I'm wondering what the range is. I'm talking about an ordinary children's party balloon. I'm thinking an uninflated balloon could be several thousandths of an inch thick and it would get thinner as it was inflated. How thin could it get before it fails? One one-thousandth? A ten-thousandth? Less? — Preceding unsigned comment added by 50.43.11.252 (talk) 22:51, 19 July 2014‎


 * Party balloons...dunno. Similar looking things used for some scientific/medical purposes are described here as being "12mils" thick...about 0.3 millimeters...which is probably about what the party balloons are.


 * When you inflate them, every time you double the diameter of the balloon, the wall will have four times the surface area...so the thickness of the wall ought to be four times thinner. The thickness of the wall is inversely proportional to the square of the diameter of the balloon.  So if a 3cm diameter (uninflated) balloon might get up to 30cm diameter when fully inflated - so we would expect it to be 100 times thinner. That would be three thousandths of a millimeter...three micrometers.  That's about the same as the thickness of a human hair...which seems awfully thin to me.  I'm suspicious of the validity of this estimate...but I don't see how it could be much different than that.


 * Incidentally, I doubt the failure of the balloon directly relates to the overall wall thickness. There are bound to be weak spots in the latex that give way long before the overall thickness of the material gets too thin to hold the pressure - and we know that a microscopic flaw (like a pin-prick) rapidly propagates to a large tear. This video: https://www.youtube.com/watch?v=idfvjbScXJM shows you how they're made - basically they dunk metal molds of the uninflated balloon into a tank of liquid latex - so the thickness of the material isn't going to be all that uniform either across the whole of one balloon - or from one balloon to the next.


 * SteveBaker (talk) 03:46, 20 July 2014 (UTC)


 * Ref. Desk vs. YouTube challenge on the same question
 * What is the thickness of the rubber just before bursting? Why do the air-filled balloons break at the top while the last one with some water inside breaks at the bottom? 84.209.89.214 (talk) 11:18, 20 July 2014 (UTC)
 * Well, if the balloon was perfectly uniform, I'd say that the pressure at the bottom of the puddle of water is higher than the pressure at the top of the balloon because the weight of the water is added to the air pressure. It seems like it would be a tiny difference - but if the balloon were completely uniform, that would be the first place to go.  But there are other possibilities.  Balloons get hot as they stretch - and the water would conduct that heat away creating a thermal gradient that might affect the elasticity...there are MANY possibilities.  However, I'd guess that it was mostly coincidence.  I don't think balloons are manufactured carefully enough to ensure that they are that perfectly uniform. SteveBaker (talk) 15:19, 20 July 2014 (UTC)


 * I think the shape of the balloon is a factor in bursting. A favourite party game when I was a lad, was to blow up a balloon until it burst, and sausage balloons where always much more difficult than round ones. I think zig-zag sausage balloons might be easier to burst than straight sausage. Modelling balloons are very difficult to blow up to bursting point. I can inflate them by mouth but when I used to model at fetes I used a pump, partly in interests of hygiene but also to save my body, although it is quicker to inflate by mouth. I guess they have thicker skins than party balloons. --TrogWoolley (talk) 14:44, 20 July 2014 (UTC)


 * A link for those unfamiliar with the term: Balloon modelling. -- ToE 13:19, 21 July 2014 (UTC)