As a belated Christmas gift to readers of my blog (thank you!), I thought I would help answer what is probably one of the nerd sniping-est comics from XKCD. It turns out the answer is more biology than physics. The girl in the comic is right in questioning her mother’s answer; violet is a shorter wavelength than blue (if you remember your Roy G. Biv acronym ordering the colors of the rainbow, you’ve also listed the colors in order of decreasing wavelength). It actually turns out that indigo and violet light is scattered well in the sky. You just don’t see it because your eyes aren’t ideal detectors of light wavelength. The reason you can observe different colors is because you have different cone cells in your eye, and each one reacts to a different part of the visible spectrum. We only have three though, and they don’t respond to all the colors equally.
Response of cone cells to light, each curve is a different kind of cone cell
The blue curve which represents the cone that picks up short wavelengths is really sensitive to light at around 450 nm. This wavelength represents the shorter end of what we consider “blue”, which goes up to about 500 nm. The shorter wavelengths are “violet”. As you can see, the response drops off really quickly on the shorter end. This means that while there might be violet in the sky, you register the blue more in a mix of purple and blue. The Georgia Tech researchers in the MSNBC article actually say you perceive a mix of blue and violet the same as a mix of blue and white. The article the graph comes from also talks more about how the combination of different color sources affects your perception.
How we see color is actually a very complicated subject and isn’t just a straight up application of optics. Spectroscopy is a branch of physics that studies how different wavelengths of light interact with matter. Photometry and colorimetry are branches of science that study how people can actually perceive these wavelengths. This includes factors like the structural aspects of your eye (like the chemical/physical behavior of the cone cells) as well as processes that go on in your brain, as seen in the famous checker shadow illusion.
While I try to be diverse in sources, I have to link to The Atlantic again. The November/December had a great article/short fiction piece about recent advances in biotechnology. While I think it borders a bit on the paranoid at times (anyone can get genes!!11!), it also paints a pretty accurate picture of the convergence of molecular biology and computer science that is rapidly defining synthetic biology. I just think the one thing the author forgets to emphasize is that while we can combine lots of genes, we still don’t understand what many do or the reverse problem, which genes control functions we want to have in synthetic organisms. And as we learn more about epigenetics, factors that influence development beyond the genome, I wouldn’t be surprised if we learn that many things we want to splice into organisms require more complicated interactions than just inserting gene A into target B.
Our second, more whimsical bit of news for the day is also courtesy of The Atlantic. Boeing wanted to test how well its in-flight WiFi systems work. The challenge is that you also need something to account for the presence of passengers if you want to make sure the signal reaches everywhere in a crowded plane. But it’d probably be hard (and expensive) to recruit a plane’s worth of volunteers to just sit around while you check signal strength.
Not a couch potato
So what makes a suitable replacement? Potatoes. Lots and lots of potatoes, arranged in vaguely humanlike shapes. How does that work? When dealing with electromagnetism, one of the most important traits of the human body is that we’re mostly water. And water is dielectric, which basically means the electrons in water atoms align to reduce the electric field in water when it is exposed to an external field, like say the wave from a WiFi router. So if you want a quick and dirty approximation to people, you can basically model a person as an equivalent volume of water. This would be difficult to make as a physical experiment. That’s where spuds save the day. Potatoes, it turns out, are also mostly water (this is also why you avoid cutting them to make mashed potatoes – it’d be a soupy mess) . And they’re a lot easier to buy and move around than giant jugs of Aquafina.
weekmonth, a new study was published looking at ocean acidification, a (I think under-publicized) side effect of increasing CO2 concentrations. A decent summary can be found at The Atlantic (in their health section, of all places). The researchers (from a wide array of institutions in the US and Europe) focused on Arctic sea snails. While that may sound incredibly boring, there are two main reasons they’re important to study. First, their shells are calcium carbonate, which you’re probably more familiar with as limestone (or perhaps as the active ingredient in most over-the-counter heartburn medications). Calcium carbonate makes up the shells of a lot of sea creatures.
And while we mention antacids, let’s bring up their counterpart, acids. So carbon dioxide naturally dissolves in water to form a somewhat weak acid (you also see this idea come up with discussions of soda sometime – the CO2 from carbonation also dissolves in the soda and makes it acidic). Although that’s a slight simplification because it actually turns out sea water is slightly basic (think the opposite of acidic) and has a pH somewhere around 8.15 , presumably because of the several thousand minerals that are dissolved from the coasts. So if the ocean’s slightly basic, we’re fine, right? Well, the term “acidification” is still accurate because the pH is lower (i.e. more acidic) than it used to be. The process of sea creatures building up the calcium carbonate structures is sensitive to environmental conditions. The carbonate dissolves more in solution with more carbon dioxide and/or lower pH (more acidic). While that may initially sound like a good thing for any critters needing it (there’s more calcium carbonate in the water, right?), chemical equilibrium is a two way street; if it’s easier for something to dissolve, it’s harder to precipitate it back into a solid that might go into a shell. Studies have shown that coral grows slower in acidic water because of this.
So what made this study important? It looked at how acidification affects marine snails (also known more whimsically as “sea butterflies”) in the Antarctic, which are a very important part of the food chain (some marine biologists call them “potato chips of the oceans”). The snails already showed significant signs of their shells dissolving. While this isn’t a death sentence, it does make it easier for them to be eaten or catch diseases, and en masse, that could throw off population.
Of course, it’s important to note the researchers say the blame isn’t all on ocean acidification. Part of the reason the seawater was so acidic was because of upswelling, an phenomena in which deeper water is pushed up to the ocean surface. Deeper water tends to be more acidic (I can’t find why), so these upswells make the surface water abnormally acidic. But upswelling is expected to increase with climate change.
So you may recall my previous post looking at anti-science trends in the left. One of the points I made was that the anti-vaccine movement is not limited just to progressives, although I admit I’m not sure where it started. Almost as if to prove the point, the Congressman for Indiana’s 5th district, Dan Burton, recently held a House committee investigation on “autism-related issues”, which seemed to include a lot of questions about whether vaccines contribute to autism. Important for my argument, Congressman Burton and his colleague Bob Posey (of Florida) are both Republicans. And the article shows that their statements don’t just seem like basic questioning of the issue. Instead, both Congressmen seem openly hostile to the scientists they brought in to testify, and these scientists are directors of institutes in the CDC and NIH (which are pretty big deals in medical research). I can be fine with some vaccine skepticism, but you need to show you’re operating in good faith. And not recommending random medical treatments that can potentially kill people with the wrong condition.