Wikipedia:Reference desk/Archives/Science/2013 May 19

= May 19 =

Quantum foam, zero-point energy, the fabric of the cosmos
Various articles in Wiki point mention the paradox of a cosmological constant that should be small, but when calculated, is many orders of magnitude too large. Wiki questions: Why doesn't the zero-point energy density of the vacuum (sometimes called 'quantum foam') change with changes in the volume of the universe? And related to that, why doesn't the large constant zero-point energy density of the vacuum cause a large cosmological constant? My question is: what if the 'quantum foam' at the Planck scale doesn't change because it is the real universe (supposedly infinite and eternal), and the Big Bang was only a one-off local outburst? Could that put to rest the paradox of the large cosmological constant? A related question is: If this is a possibility, what property or condition in the 'quantum foam' could have triggered the Big Bang?Robert van der Hoff (talk) 01:49, 19 May 2013 (UTC)
 * It's hard to see the value of inventing some random bizarre idea and then asking why it isn't valid. Looie496 (talk) 02:12, 19 May 2013 (UTC)
 * How would you test this conjecture of yours? I think you're delving past science and wandering into philosophy. Praemonitus (talk) 02:17, 19 May 2013 (UTC)

Thanks for your comments, points taken, but I'm still wandering and wonderingRobert van der Hoff (talk) 10:18, 19 May 2013 (UTC)


 * By definition a cosmological constant doesn't change its energy density with the universe's scale factor, that's just one of it's characteristics. By observation, we can say that dark energy appears consistent with a cosmological constant, but we don't know for sure that it's energy density is independent of scale factor.  The observational parameter w measuring the equation of state of dark energy has a value of -0.98 +/- 0.05, where -1 means independent of scale factor and something like matter whose energy density scales in direct response to changes in the volume of the universe has a value of 0.  As you note, attempts to explain a cosmological constant based on quantum mechanical properties of the vacuum give results that are much too large.  At present, no one really knows why that is.  Dragons flight (talk) 10:21, 19 May 2013 (UTC)

Thank you. The mystery remains Robert van der Hoff (talk) 23:02, 19 May 2013 (UTC)

What time of day and date of the year would most people on earth be in darkness?
My guess would be on the Winter Solstice (Dec 21), which has the shortest day in the higher populated Northern hemisphere. I would also think it would be when the sun was over the Pacific ocean, but before dawn in Asia, so perhaps around sunset on the US west coast?

Could we also calculate (roughly) what percentage of people would be in darkness? Jaseywasey (talk) 06:50, 19 May 2013 (UTC)


 * Your logic seems to be correct. It would probably be easier to calculate the number of people with daylight in those circumstances. You would also need to define darkness more precisely. Are you ignoring twilight?--Shantavira|feed me 08:16, 19 May 2013 (UTC)


 * Could take into account this map... AnonMoos (talk) 17:14, 19 May 2013 (UTC)


 * Ha, I made a map of this once, with the winter solstice day/night curve, the "earth at night" light data, and, well, I made a guess about what time would be the "most dark". If the time isn't exactly right, it must be close. I guessed 0:30 GMT, Dec 22: http://www.flickr.com/photos/pfly/4133160304/sizes/o/ ...although I made this map with the idea of "most dark", in terms of nighttime lights being on, rather than population. Nighttime lights and population are related, but not the same. I suspect a slightly earlier time than my map shows would put more people in darkness—trading more daylight in the North America for more night in Indonesia and Japan. Pfly (talk) 08:45, 20 May 2013 (UTC)

Dark band between two lasers?
At the top right of this image, two laser beams are spreading away from the building and there is a noticeable dark band between them. Is this a form of Alexander's band? – Kerαu noςco pia ◁ gala xies 07:20, 19 May 2013 (UTC)
 * It is a retouched photo, the original is at File:The Shard, Inauguration Lightshow, 2012.jpg, there seems to be a little of the same effect but it is much less apparent. Personally I prefer the original. Dmcq (talk) 08:09, 19 May 2013 (UTC)


 * I kind of do too, it's what attracted me to it in the first place. Thanks for the mention, I've replaced the photo in the article with the original. Ok back on topic :) The dark band is still there. The image on the right is the original photo now, and it's still visible. Very curious what's causing it. – Kerαu noςco pia ◁ gala xies 09:37, 19 May 2013 (UTC)


 * I think this is an example of the optical illusion known as the contrast effect -- see http://www.michaelbach.de/ot/lum_dynsimcontrast/index.html for an especially vivid demonstration. Looie496 (talk) 14:42, 19 May 2013 (UTC)
 * It is clearly not any optical illusion as displying the picture full screen or blowing it up shows that the pixels between the two laser lines are quite a bit darker. The mostly likely explanation is that the image was "improved" by digital retouching and the person doing it messed it up.  They may have wanted to lighten the sky by chroma keying and forgot the bit isolated between the lines.  Wickwack 60.230.253.45 (talk) 15:57, 19 May 2013 (UTC)


 * Interesting. Ok thank you, I thought maybe this was a real-life occurrence. I ran the original image through "Jeffrey's Exif viewer" online and I see that Microsoft Pro Photo Tools was used, but seeing as how that's a metadata editor (maybe more, i don't know), I guess I really don't know what I'm looking at. I'd simply have to ask the original author if he did any touch-ups himself; that'd more than likely be the explanation I'm looking for. Thanks for all the replies. – Kerαu noςco pia ◁ gala xies 19:50, 19 May 2013 (UTC)


 * I disagree entirely with wickwack. I blew this up (on a 17" HD monitor) and looked at it before I read his comment, and the pixels between and outside the rays are the same color when the laser lines are obscured. μηδείς (talk) 22:02, 19 May 2013 (UTC)
 * Your eyes are mistaken, or they're just not sensitive enough, or your monitor isn't appropriately adjusted for this comparison. If you measure the sky's brightness using the tool of your choice, you can see a clear, quantifiable reduction in the area between the two beams in the upper right corner of the image.  (For a free tool, download ImageJ, select a line of pixels, and choose Analyze...Plot Profile.  The mean gray value is about 20% lower between the beams.)  Whether this is an artifact of image processing in-camera or afterwards I can't say.  TenOfAllTrades(talk) 02:38, 20 May 2013 (UTC)


 * Here is a screenshot (imgur.com) of an 11x11 pixel Photoshop analysis (on the original image as seen above) of three points, two on either side of the band. Using Lab, one can easily see that the band between the lasers is four points darker in the luminosity channel than on the sky outside of the lasers. There is also a slight shift in the a (red-green) and b (yellow-blue) color channels. It's definitely not an optical illusion. The photographer is busy and I'll have to bother him about it at a later date, but I'm not really seeing anything that might give away the fact that the image was edited outside of the lasers only. I can't read FotoForensics.com results either, if that site would even turn anything up. – Kerαu noςco pia ◁ gala xies 03:23, 20 May 2013 (UTC)


 * You don't need to go to all that trouble. You can just display the image on your monitor at full size.  Then, take a piece of cardboard (eg from a business card or a cereal box) and cut two holes in it, about 8 mm diamter and about 25 mm apart.  Then place the card against the screen and position it so that pixels from between the laser lines are viewed thru one hole, and pixels elsewhere in the sky are viewed thru the other hole.  You will clealy see that the pixels between the laser lines are darker.  The card prevents any possibilty of an optical illusion.  Medeis obviously was just being silly.  Wickwack 60.228.233.13 (talk) 04:18, 20 May 2013 (UTC)


 * Should I ask whether you are just being an idiot, wickwack? Personal comments are not necessary.  I did the same thing, blowing up the image to max on a large screen laptop, blocking out the lasers as I said above, and the sky between the beams then appeared no different from outside to me. μηδείς (talk) 08:35, 20 May 2013 (UTC)
 * So who is being an idiot then? First you posted "I dissagree entirely with Wickwack."  Now, after more than one person said you are wrong, you have again asserted what is clearly ridiculous.  You have made several silly posts recently, resulting in several people attacking you.  Are you on drugs or something?  Wickwack 60.228.233.13 (talk) 09:02, 20 May 2013 (UTC)

(unindent)
 * Please guys...this is a silly argument. Just measure it with any halfway reasonable image tool - and the debate is over.  Measuring a patch of sky from just outside of the two lasers got me an average brightness of 91/256, measuring an area between the lines got me 75/256 - so the image is DEFINITELY darker between the lasers.  It's not an optical illusion.  Furthermore, where the blue laser crosses the green ones, the blue laser is also attenuated...since the atmosphere between the two lasers would have to block that light somehow for this to be a "real" effect, we can rule out things like the two green lasers scattering light in all directions except right between them.  For the blue laser to be attenuated, the air would have to become more opaque between the two lasers...which simply isn't reasonable.  Hence this isn't any kind of peculiar real-world effect either.  Furthermore, doing a Google Images search on "Shard inauguration laser show" produced a gazillion other photos of the event - many showing two lasers right next to each other like that - none that I could see showed this darkening effect, despite many shots from many different angles showing pairs of closely-spaced lasers.
 * Odds are very good then that this is an image processing artifact. If I had to bet on a cause, I'd say that someone used a "despeckle" filter on the image in an effort to eliminate the obvious noise in the background of the sky...but it's really hard to tell for sure. SteveBaker (talk) 16:10, 20 May 2013 (UTC)

Are dogs ever allergic to wheat gluten ?
I just saw an ad for dog food without wheat gluten, and they are obviously hoping people will buy it because they think it's healthier (although I notice they never actually made this claim). So, is it really healthier or is this just a scam ?

Or perhaps they are appealing to people who remember the 2007 pet food recalls, where Chinese poisoned wheat gluten killed many pets ? StuRat (talk) 18:45, 19 May 2013 (UTC)


 * A trivial Google search show many pages devoted to discussing food allergies in dogs in general, and wheat allergies in particular. Such as .  Based on that, it seems to be a real thing.  Dragons flight (talk) 19:49, 19 May 2013 (UTC)


 * Exocrine_pancreatic_insufficiency is very common in some breeds, and can pop up in any dog. Many sources report gluten sensitivity, and recommend avoiding feeding gluten to dogs with EPI. SemanticMantis (talk) 19:53, 19 May 2013 (UTC)

Machine made of Human parts
I have a question regarding the name of a concept, and thus far have found no answers, save for some delightful articles on related subjects. Seeing as how Wikipedia knows everything, i thought this was the logical course of action.

if it is understood that a Cyborg is a hybrid between a CYBernetic being and an ORGanism, and an Android is a synthetic organism, a 'human' made of machine parts, then what would one call a 'machine' made of human parts? — Preceding unsigned comment added by 71.59.51.225 (talk) 19:02, 19 May 2013 (UTC)


 * "Frankenstein". ←Baseball Bugs What's up, Doc? carrots→ 20:03, 19 May 2013 (UTC)


 * "Frankenstein's monster", not Victor. Clarityfiend (talk) 22:59, 19 May 2013 (UTC)


 * Yes. Hence the quote marks. ←Baseball Bugs What's up, Doc? carrots→ 01:06, 20 May 2013 (UTC)


 * Interpreting 'machine' loosely, dentures were at one time sometimes made using human teeth. AndyTheGrump (talk) 20:09, 19 May 2013 (UTC)


 * Even more loosely: soy sauce, apparently.. AndrewWTaylor (talk) 11:52, 20 May 2013 (UTC)


 * The film Existenz has an interesting take on this concept. Astronaut (talk) 17:56, 20 May 2013 (UTC)


 * I don't think this concept exists outside of sci-fi. Making a machine out of human parts would have the disadvantages of both and the advantages of neither.  For example, I believe in The Matrix movie series, human "brain energy" powers the Matrix.  This is the most absurd source of energy imaginable.  It would take many times as much energy to keep the people alive as you would get from them. StuRat (talk) 06:53, 21 May 2013 (UTC)