Wikipedia:Reference desk/Archives/Science/2011 March 23

= March 23 =

Why isn't irradiation used on sushi and sashimi?
Thanks. Imagine Reason (talk) 00:54, 23 March 2011 (UTC)


 * Irradiation has to take place in a specialized irradiating facility. Sushi and sashimi is prepared using extremely fresh fish. I think it would make it rather prohibitive, unless you're imagining that every Japanese restaurant would have a gamma irradiator or a radiation source on premises. The cost would be huge. --Mr.98 (talk) 01:08, 23 March 2011 (UTC)
 * I think that food irradiation equipment is dangerous in untrained hands, they contain Cobalt-60, which is not something you'd want your waiter fiddling with. APL (talk) 01:32, 23 March 2011 (UTC)
 * Why would you want to irradiate sushi and sashimi anyway? F (talk) 01:20, 23 March 2011 (UTC)
 * Presumably to kill off the parasites that are famously a danger of improperly prepared sashimi. APL (talk) 01:32, 23 March 2011 (UTC)
 * See Anisakis, Clonorchis, Echinostoma, Diphyllobothrium latum, and others... -- Scray (talk) 01:54, 23 March 2011 (UTC)
 * Irradiation could kill the microbes in raw fish, but it wouldn't do anything to stop a variety of chemical reactions that would rapidly reduce it to slime. Any sort of raw meat is full of enzymes that will rapidly break it down if they aren't either denatured by cooking or suppressed by refrigeratiion. Looie496 (talk) 02:56, 23 March 2011 (UTC)
 * I was just expanding on the "parasites" statement. That said, while irradiation "wouldn't do anything to stop" spoilage, I also don't know that it would necessarily cause spoilage.  Couldn't one irradiate while refrigerating?  I agree with APL's comment about cost as the most obvious problem.  -- Scray (talk) 03:41, 23 March 2011 (UTC)
 * Radiation can change the taste, particularly if the food contains fat, eg fish, so it is reserved for things like herbs with strong flavour and low fat. Graeme Bartlett (talk) 09:29, 23 March 2011 (UTC)


 * The purpose of irradiation is to extend the shelf life of foodstuffs. Sashimi is not suposed to have a significant shelf life. Simply chilling the fish works well - don't fix what ain't broke. Roger (talk) 12:41, 23 March 2011 (UTC)
 * Although I would agree that one purpose (and the most prevalent current purpose) of irradiation of foodstuffs is to extend shelf life, that was not the OP's question. They asked why irradiation isn't used on sushi and sashimi.  They did not say what purpose they had in mind.  I would agree with your comment, except that chilling doesn't kill many important parasites, and User:APL previously proposed (in this thread) that it might be used to kill parasites.  I don't know whether that's been tried, but the articles I linked (and their reliable sources) do indicate that raw fish (as may be found in sushi & sashimi) are an important contributor to human parasitosis.  -- Scray (talk) 16:35, 23 March 2011 (UTC)
 * Indeed I seem to recall during one of the US spinach E. coli someone suggesting routine irradiation of spinach (and possibly other foods) would reduce those sort of outbreaks and other occasional food poisonings from such food stuffs, the primary thing stopping it was unwarranted consumer concern. (I'm not saying I agree with their view nor do I see the need to get in to discussions about whether better hygiene and farming practices may have more merit simply pointing out there are plenty of cases when irradiation is used for reasons other then improving shelf life.) Also as our article notes irradiation is used with various fruits for import into places like New Zealand, Hawaii and Australia to try and stop the introduction of pests not currently present in the local environment. Our article also notes various other examples which don't seem to be simply about improving shelf life. Nil Einne (talk) 12:03, 24 March 2011 (UTC)

Why do you believe that they are not irradiating sushi? Since a couple of weeks, indeed, they are using irradiation on sushi, sashimi and many other foodstuff. 212.169.184.141 (talk) 12:58, 23 March 2011 (UTC)
 * In case it's not perfectly clear, 212.169.184.141 is making a joke about the accident at the Fukushima power station. APL (talk) 14:01, 23 March 2011 (UTC)
 * Although it's a pretty bleak joke, and, factually, not totally correct, as far as I know. Quest09 (talk) 15:07, 23 March 2011 (UTC)

Environmental Improvement Equipment
Hello

I am writing this question in reference to President Obamas Tax Proposal on enviormental improvment projects that gives the American Peaple a Tax break when purchasing an recycling item? Please send me any in formation regaurding this issue? I am also in the means of working in a working on a enviormental project of a large scale which objectives is to confine or section off unwanted flying debris.I aim on marketing my product and can use any information that will help the future coustomer. Thank you God Bless Joseph I.Montoya Alavedga (talk) 01:00, 23 March 2011 (UTC) Jim
 * I searched, but I can find no information about such a program or a proposal to make such a program. Can you give more information about it? Where did you hear about it? When? Is it a proposal, or an actual program? Ariel. (talk) 02:06, 23 March 2011 (UTC)
 * Edit: Is it one of these? Ariel. (talk) 02:09, 23 March 2011 (UTC)

Inflation, Big Bang terminology
From what I understand it, inflationary cosmology posits a rapidly-expanding primordial false vacuum which at a certain point is punctuated by the formation and growth of low-potential true vacuum bubble universes, of which our universe is one such bubble. In this view, which genesis corresponds to what people refer to when they refer to "the big bang"-- the original initial-state of the false vacuum multiverse, or the initial formation of each bubble universe? Cevlakohn (talk) 05:40, 23 March 2011 (UTC)


 * What you're describing sounds like "old inflation", which is dead as a theory as far as I know, having been replaced by slow-roll inflation—see Inflation (cosmology) and the following section. That doesn't really affect your question, though. The answer is that the "big bang" happens at the end of inflation. Technically, though, it refers to a time just before the end of inflation, when there would have been a singularity if the post-inflationary model were correct back to the beginning of time, which it isn't since the inflationary model takes over at some point. So the "big bang" that subsequent times are measured from never actually happened. (See Age of the universe.) -- BenRG (talk) 07:56, 23 March 2011 (UTC)

Thyroxine and circadian rhythm
Is thyroxine released according to the body's circadian rhythm, or is it released continuously over the 24-hour period? I've looked at the article but it doesn't contain this information. --TammyMoet (talk) 09:52, 23 March 2011 (UTC)
 * Probably teaching you to suck eggs, but you might find further information and useful links from the Physiology section of the Thyroid article and from the Thyrotropin-releasing hormone article. At first glance it looks as if the primary known modifier is temperature, but I suppose that in turn may be affected by circadian rhythms. {The poster formerly known as 87.81.230.195} 90.201.110.155 (talk) 11:33, 23 March 2011 (UTC)


 * Just curious, why would he wan't to learn how to suck an egg? Plasmic Physics (talk) 11:41, 23 March 2011 (UTC)
 * Teaching grandmother to suck eggs 129.234.53.49 (talk) 14:09, 23 March 2011 (UTC)


 * You won't get the 'yolk' if you don't suck eggs Richard Avery (talk) 14:59, 23 March 2011 (UTC)


 * There has not been a great deal of research on this. Recent papers still cite, a study from 1977, which says that there is a rhythmicity:  "Thyroxine: Pooled data showed peak values from 8 a.m. to 12 a.m. and lowest levels from 11 p.m. to 3 a.m.". Looie496 (talk) 17:04, 23 March 2011 (UTC)
 * Thanks Looie, I hadn't found anything myself and this backs it up. Seems to be roughly circadian to me. Cheers. --TammyMoet (talk) 18:09, 23 March 2011 (UTC)

manmade earthquake
I was reading the previous posts about this and none address the possibility of setting off a bomb a a point in the fault that has been identified as having the most potential energy built up (where the most tension exists) to trigger a natural earthquake that might not have happened for another couple of years. Could this be plausible?165.212.189.187 (talk) 14:44, 23 March 2011 (UTC)


 * We've discussed this very topic before. Basically:


 * 1) The force required would exceed that of even the most powerful nuclear bombs, unless the fault was ready to go anyway, in which case it would go soon on it's own.


 * 2) The location is typically so far down that it would be difficult or impossible to dig down that far. StuRat (talk) 15:06, 23 March 2011 (UTC)


 * I don't think #1 is quite right. It's true that the comparisons are not the same (though talking about energies released is usually more misleading than clarifying), but it's not clear that large (e.g. megaton range) nuclear weapons could not induce quakes. I think a more accurate answer would say: "we don't know how to do this, we don't have great indications that it would work, but we haven't done much research on this point." Nuclear weapons have effects like small, localized earthquakes; whether one of those could, in the right set of conditions, set off a large earthquake that is "ready to pop," we don't know for sure one way or another.
 * A fairly scientifically careful discussion of this is here. --Mr.98 (talk) 15:21, 23 March 2011 (UTC)


 * The relevant article is induced seismicity. As you can see, most academic research focuses on long-term trends, mostly related to changing the structural integrity and the pore pressure in the subterranean strata because of long-term pumping/extraction of ground-water, natural gas, or petroleum.  Nimur (talk) 15:24, 23 March 2011 (UTC)

I think that any further research into controlling earthquakes should be made in the future on other planets where any adverse reactions would be of little consequence since no one is living there. ScienceApe (talk) 19:47, 23 March 2011 (UTC)


 * Sounds good to me. Using bombs to set off earthquakes is a topic that's been raised here surprisingly often - I seem to recall some that were before the recent quake in Japan - and I admit I'm mystified by the very idea. No disrespect. You get an earthquake either way, but by using a bomb to trigger it you now also have a nuclear explosion beside Los Angeles (or San Francisco or wherever) to top it off. That doesn't seem like a good trade off to me. And who is going to assume the liability for intentionally causing an earthquake? Every person who so much as chipped a nail during the intentional quake would take part in a class action suit against whoever pulled the trigger. Forget the science; operationally, this is just a terrible idea that nobody in their right mind would assume responsibility for. Matt Deres (talk) 20:47, 23 March 2011 (UTC)
 * I guess that's why the Christopher Walken character in A View to a Kill was depicted as rather looney. Deor (talk) 21:31, 23 March 2011 (UTC)

Null 4 vectors
Taking into account large scale effects (such as non-negligible evolution of the scale factor a(t)) is it right to say that the events which make up my light cone (i.e. those that I can see at a given point in spacetime) are all the points displaced by null 4-vectors (those for which the spacetime interval is zero).

Sorry, I don't know if I am being foolish, but I am having trouble taking into account the evolution of a(t) over the photons time of flight. —Preceding unsigned comment added by 92.21.86.36 (talk) 15:19, 23 March 2011 (UTC)
 * Your light-cone is formed by all the null geodesics that pass to your current world point. The tangent vectors to these geodesics are null vectors everywhere. The term "geodesic" takes into account the evolution of a(t) and also space-time curvature due to the matter distribution in the Universe (gravitational lensing). --Wrongfilter (talk) 17:16, 23 March 2011 (UTC)


 * Your confusion arises because you're viewing null four-vectors as being displacement vectors. The whole idea of a displacement vector has very little use within general relativity (none that I'm aware of), because unlike in Newtonian mechanics or special relativity, the coordinates used to label events in general relativity don't in general have any physical significance independent of the metric tensor.  For example, in general relativity you can't in general get the spatial or temporal distance between two events simply by subtracting the coordinates of the two events.  The concept of a vector that does continue to be valuable in general relativity is the tangent vector, such as is used in Wrongfilter's explanation above of a light "cone" in general relativity as consisting of a set of null geodesics.  Red Act (talk) 02:55, 24 March 2011 (UTC)

Direct cell-phone to cell-phone call
Could (with minor technical modifications) a cell-phone call another cell-phone directly? Quest09 (talk) 16:12, 23 March 2011 (UTC)


 * Only if very close to each other. Cell phones don't have the power or antennae necessary to send messages long distances. StuRat (talk) 16:17, 23 March 2011 (UTC)


 * Does very close means some hundred meters? And, is it indeed a minor technical modification, or would it be a huge source of interference among cell-phones?Quest09 (talk) 16:19, 23 March 2011 (UTC)


 * Yes, on that order (although what lies in-between has a major impact on range). They would want to use a different frequency for this to avoid interference (specifically, in the US, they would use the FRS and GMRS frequencies).  And, of course, walkie-talkies are already designed for this function, and better at it, by using more power (resulting in them going dead much sooner) and having bigger antennae.  Ironically, old cell phones were more suitable for this purpose than new ones, since they had the long antennae and big batteries required. StuRat (talk) 16:17, 23 March 2011 (UTC)


 * Smart-phones could handle this over very short distances with their Wifi or Bluetooth functionality. Probably only a software change is needed. APL (talk) 18:18, 23 March 2011 (UTC)


 * A phone is not a cell phone unless it communicates via base station(s). Cuddlyable3 (talk) 14:12, 24 March 2011 (UTC)


 * True. The OP is asking about having a cell phone (which uses base stations normally) ALSO being used to directly call other cells phones. StuRat (talk) 23:15, 24 March 2011 (UTC)

Carbon filter for iodine
Do ordinary carbon filters remove iodine? I'm thinking of the radioactive iodine found in the water in Tokyo. Ariel. (talk) 18:36, 23 March 2011 (UTC)
 * See Carbon filteringIt depends what form the iodine takes. Carbon filters are not good at removing inorganic salts, so radioactive iodine in the form of, say, sodium iodide would not be removed well.  On the other hand, most organic iodine compounds (iodomethane, for example) should be removed reasonably well.  I'm not sure what chemical form radioactive iodine fallout is likely to take, and I'm having trouble finding any references. Buddy431 (talk) 19:19, 23 March 2011 (UTC)
 * You could precipitate the iodine by adding an excess of silver nitrate. Filtering this solution and then treating with something like sodium carbonate or sodium sulfate would then precipitate the silver, excessive ingestion of which can lead to argyria.--Atemperman (talk) 20:12, 23 March 2011 (UTC)


 * Before playing around with poisonous chemicals you should consider the short half live of I-131. The simplest and safest way to deal with it is to wait until it has decayed naturally. Provided that you have access to "older" water. 95.112.197.146 (talk) 21:22, 23 March 2011 (UTC)

Amino acids and fatty acids in durian
The main site, a few minutes of Googling, and nutritiondata.com are unhelpful in providing details on the fatty-acid and amino-acid profiles of durian. Anyone have a clue? --Atemperman (talk) 20:15, 23 March 2011 (UTC)

Shape of the Universe
Hi, I'm sure my question is answered somewhere in Wikipedia, but my brain has glazed over somewhat, and I'm hoping someone can spell out the answer in simple terms. As far as I understand it, the standard model of the Universe says that at the time of the Big Bang all of space was concentrated into a tiny region, which then began to expand. I visualise this as being like surface of an expanding balloon, except in 3D space rather than 2D space (probably I got this from some science show on TV). Yet at Shape of the Universe it says "Within the Friedmann-Lemaître-Robertson-Walker (FLRW) model, the presently most popular shape of the Universe found to fit observational data according to cosmologists is the infinite flat model". Is this consistent with the earlier picture I drew? How can something closed and finite, like the 3D analogue of the surface of a sphere, ever become infinite and flat throuh expansion, without some sort of "rupture" event? If the Big Bang is accepted, then how can the Universe now be any shape other than "closed", like it was originally? 86.181.202.145 (talk) 23:20, 23 March 2011 (UTC)
 * Have you considered the possibility that it was not initially closed? Dauto (talk) 01:40, 24 March 2011 (UTC)
 * Sorry, I'm not sure if this a rhetorical way of saying that according to the usual model it wasn't initially closed, or that you don't know but want to raise it as a suggestion? 81.159.104.17 (talk) 03:49, 24 March 2011 (UTC)


 * A possible problem is that the "balloon" model is misleading. The balloon expands in 3 dimensions. All of space is represented as 2 dimensions on the surface of the balloon. Everything inside and outside the balloon is not part of space. Only the surface of the balloon is space. Then, you think that space is 3 dimensions, so it is an expanding balloon. Well, the space on the balloon is only 2 dimensions. If you want 3 dimensional space, you need a four dimensional balloon - which is very hard to imagine. So, you have to drop the idea that space is three dimensions if you want to imagine the balloon, which is a spherical model. What if, instead of a sphere, the big bang blew out a ring shape that expanded to a tube? Then, the 2D space would be on the surface of an expanding tube. What if the big bang blew a ring that wasn't hollow in the middle? It is a disk that gets wider and wider, but remains flat? Then, the 2D space would be on an every-increasing flat space. You can imagine cones, cubes, or any other kind of strange shape you like. I like the idea of two conical shapes expanding out of a singularity in opposite directions. I know the data doesn't support it, but I like imagining that shape for space. -- k a i n a w &trade; 02:23, 24 March 2011 (UTC)
 * I understand the dimensionality issues. I think the only purpose of introducing the balloon is because it's otherwise difficult for ordinary mortals to imagine any type or curved or closed space. 81.159.104.17 (talk) 03:49, 24 March 2011 (UTC)


 * Milne universe with CMBR.svg think I'll trot out this image that I made a few months ago (that I've so far used only on the reference desk). This is not an accurate depiction of our universe, but it is an accurate depiction of a FLRW universe with different values for the adjustable parameters of the FLRW model. What's nice about these particular parameter values is that the spacetime you get is the spacetime of special relativity. This diagram is plotted in special relativistic x and t coordinates, with the future at the top and the past at the bottom, and light travels along 45° diagonal lines. (To get the full four-dimensional version of the diagram, rotate it in the third dimension around a vertical axis through the center to get a cone shape, then rotate that through the fourth dimension to get a hypercone.)


 * It may look like this toy universe is finite and expanding at the speed of light, but to a cosmologist, it's infinite. Cosmological time is measured by clocks that are moving with the Hubble flow. Because of time dilation, the Hubble-flow clocks near the sides of this diagram tick slower. All clocks show the same elapsed time at the surface of last scattering (the upper boundary of the bright region marked "opaque plasma"). This surface, which is shaped like a hyperbola (or a hyperboloid when you rotate the image into four dimensions), represents the universe at a particular time (the last scattering time), and as you can probably see, it's infinite in size and contains an infinite number of galaxies (spaced more or less evenly). It's also negatively curved, even though the spacetime is flat. And it's expanding, but not at the speed of light or any other particular speed; rather, the distance between galaxies is increasing at a rate that's proportional to the distance between them.


 * So this is what it means for the universe to be "smaller in the past" and yet infinite at all times, and this is how you can get an infinite universe without any faster-than-light expansion. The details are slightly different in the real world, but the idea is the same. -- BenRG (talk) 06:56, 24 March 2011 (UTC)
 * This is very interesting and cool. But, having seen it the last time you posted it, what I'm still unable to quite figure out is, does it (or at least, can it) have infinitely many distinct baryons in a spacelike 3-d slice?  And if not, are there models that do, that are consistent with observations?  I had thought there were, but in your picture it looks like an infinite spacelike slice does not have uniform density; it falls off as you move away from the center line of the drawing, and the total number of baryon world lines could be finite (though perhaps it wouldn't have to be).  --Trovatore (talk) 19:09, 24 March 2011 (UTC)
 * Along lines of constant cosmological time, the density is uniform with respect to the spacetime interval (but not with respect to Euclidean distance on the diagram, which is why it looks like it's falling off). So, yes, there are infinitely many baryons. If you take a horizontal slice through the diagram (constant special-relativistic t coordinate), you still get a picture of the whole universe, since all of the worldlines have to cross every slice, but it's not uniformly dense; it's actually the Klein model of the hyperbolic space. -- BenRG (talk) 00:03, 25 March 2011 (UTC)
 * Here's a silly animation I just made to illustrate the uniform density (linked because inline animations are annoying). This shows the entire diagram above being successively Lorentz boosted with the bottom vertex (the "big bang") held fixed. If you look at the lines representing the Hubble flow, they don't appear to move. Actually, they are moving "one galaxy to the left" on every animation frame (as you can see by looking at the here-and-now dot). You can keep boosting like this forever in either direction, bringing new galaxies to the center, without the density ever changing. -- BenRG (talk) 03:43, 25 March 2011 (UTC)