Skulls in the Stars: You could learn a lot from a ducky: the van Cittert-Zernike theorem
Early this year, some colleagues of mine published a short note pointing out that one can visualize a fundamental result from optical coherence theory, the van Cittert-Zernike theorem, by watching the waves a group of ducks generate when they splash into a pond!
Amazing 3D Projections on Buildings
NuFormer is a company in the Netherlands that specializes in outdoor advertising of a very peculiar sort — done on the faces of buildings. Real buildings are mapped and modeled in 3D, and then animations are created using those models and projected back onto the building. The result is incredibly lifelike — it nearly fools the eye — and whoever designs these animations does an amazing job of taking advantage the buildings’ nooks and crannies to make things look like they’re really happening in 3D space.
If Puerto Rico were to become the 51st state—and granted, that’s at least four ifs away—federal law requires that a new star be added to the American flag. One can’t help but wonder: Where would we put it?
There’s a flag generator which allows you to vary the number of stars from 1 to 100. There is no “valid pattern” for 29, 69 or 87 stars — none of the desired symmetries are possible — and a few of the other patterns look like “why don’t you admit two states at a time” (like 79, 89 and 92)
Bad Astronomy: Resolving the iPhone resolution
In other words, at 12 inches from the eye, Jobs claims, the pixels on the new iPhone are so small that they exceed your eye’s ability to detect them. Pictures at that resolution are smooth and continuous, and not pixellated.
However, a display expert has disputed this. Raymond Soneira of DisplayMate Industries, was quoted both in that Wired article and on PC Mag (and other sites as well) saying that the claims by Jobs are something of an exaggeration: “It is reasonably close to being a perfect display, but Steve pushed it a little too far”.
This prompted the Wired article editors to give it the headline “iPhone 4’s ‘Retina’ Display Claims Are False Marketing”. As it happens, I know a thing or two about resolution as well, having spent a few years calibrating a camera on board Hubble. Having looked this over, I disagree with the Wired headline strongly, and disagree (mildly in one case and strongly in another) with Soneira. Here’s why.
Jobs’s claim is 300 dpi at 12 inches. I remember this as 600 dpi at the nearpoint of ~6 inches (15 cm), which is the same angular resolution. Closer than this and most adults can’t focus; your nearpoint is generally larger if you are older. Which is the same claim, and an explanation as to why 300-600 dpi is generally considered photo quality for images that are printed, and 1200 dpi is the highest resolution you’d ever need.
Using geotagging to determine what tourists photograph vs what the locals photograph.
Blue points on the map are pictures taken by locals (people who have taken pictures in this city dated over a range of a month or more).
Red points are pictures taken by tourists (people who seem to be a local of a different city and who took pictures in this city for less than a month).
Yellow points are pictures where it can’t be determined whether or not the photographer was a tourist (because they haven’t taken pictures anywhere for over a month). They are probably tourists but might just not post many pictures at all.
How to multiply, Roman-numeral style. A Different Kind of Multiplication
It is often said that an important advantage of the decimal notation over the Roman one is that makes multiplication of numbers much easier. Adding CLXXVII to XXIII may be relatively straightforward–but how about multiplying the two?
This is me (female subject) saying “både” (“both”). The sequence is an excerpt from a 20 second X-Ray film registred at the Danderyd Hospital in Stockholm in March 1997.
In this sequence I noticed that the lips form an interesting image as the mouth opens; I assume it’s from lipstick of uneven thickness and application, which can be seen when the mouth is fully open. I wonder what kind of heavy elements are in there that help screen higher-energy photons. The effect is absent for the male subject (and apparently “pion” in Swedish means “peony” rather than “meson made of up and down quarks.” Silly Swedes.)
You Are Not So Smart is a blog devoted to self delusion and irrational thinking.
There’s a lot of research out there suggesting you have no idea why you act or think the way you do.
It feels awful to accept such things, so you create narratives to explain your own feelings and behavior.
On the Dunning-Kruger Effect
Have you ever wondered why people with advanced degrees in climate science or biology don’t get online and debate global warming or evolution? Yet, people without a degree in psychology will write 1,200 words about a psychological bias.
The less you know about a subject, the less you believe there is to know in total. Only once you have some experience do you start to recognize the breadth and depth you have yet to plunder.
The Virtuosi: My Pepsi* Challenge
The basement of the Physics building has a Pepsi machine. Over the course of two semesters Alemi and I have deposited roughly the equivalent of the GDP of, say, Monaco to this very same Pepsi machine (see left, with most of Landau and Lifshitz to scale). It just so happens that Pepsi is now having a contest, called “Caps for Caps,” in which it is possible to win a baseball hat. There are several nice things about this contest. Firstly, I drink a lot of soda. Secondly, I like baseball hats. So far so good. Lastly (and most important for this post), is that it is fairly straightforward to calculate the statistics of winning (or at least simulate them).
On the surface this is a lesson in basic statistics and simulations. But the other lesson here is that physics graduate students have been conditioned to not value their time paricularly highly.
I’m confounded by magic.
Radioactive isotope of tin confirmed to have doubly magic nucleus
Magic proton or neutron numbers give the nucleus greater stability and stronger binding, and are therefore usually more common than nuclei with unfilled orbital shells. In doubly magic nuclei both proton and neutron shells are filled, leading to even stronger binding and stability. The outer shells of doubly magic nuclei are rigidly spherical.
OK, here’s an instance where someone is using inconsistent and/or confusing terminology. If magic numbers refer to filled shells, then Sn-132, having 50 protons and 82 neutrons, is doubly-magic by definition. The only thing you have to confirm is that it’s Sn-132. The Tin isotope whips out its ID card, and you’re done.
But no, apparently that’s not enough.
Other confirmed doubly magic nuclei include helium-4, oxygen-16, lead-208, calcium-49, and nickel-48, which are abundant and stable, and nickel-56, which was discovered in 1998 and is less stable than the others, having a half-life of just 5.9 days. Tin-132 is even more unstable with a half-life of only four seconds, which has made confirmation of its doubly magic nature difficult. It has 50 protons and 82 neutrons, and is the first confirmed doubly magic isotope that is both neutron-rich and radioactive.
The scientists investigating this seem to already know it has magic numbers of both, but that doesn’t confirm the doubly-magic nature of the isotope. They had to verify that it is spherical as well, by looking at Sn-133 and saw that it behaved as expected of having a single excess neutron (I assume in terms of a quadrupole moment). But if it hadn’t, would the nucleus still be doubly-magic? Or would it be that the model of doubly-magic nuclei was wrong? I think it’s the latter; magic numbers refer to the numbers (hence the name), and models of nuclear shape are something separate.
On a related note, I wonder if anyone is looking at Sn-100, which is also doubly-magic (using my definition). It’s listed on the table of nuclides as having a half-life of 0.94 seconds, which implies it’s been made in the lab and studied to some extent. Then again, the table of nuclides lists Sn-132 has having a half-life of 39.7 seconds, which is an order of magnitude longer than what’s given in the article. So I’m thoroughly confused. But as a Gemini, I never know what to expect.