Monthly Archives: December 2011

Comprende?

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What is it like to have an understanding of very advanced mathematics?

You can answer many seemingly difficult questions quickly. But you are not very impressed by what can look like magic, because you know the trick. The trick is that your brain can quickly decide if question is answerable by one of a small number of powerful general purpose “machines” (e.g. continuity arguments, combinatorial arguments, correspondence between geometric and algebraic objects, linear algebra, compactness arguments that reduce the infinite to the finite, dynamical systems, etc.).

One of a long list.

It’s hard to convince those that don’t “speak” math how necessary it is, rather than being forced to explain things in a much less precise language (be it English or something else) that the audience understands.

via @seanmcarroll

The Nose Knows Physics

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@neiltyson tweeted

According to the song, Rudolph’s nose is shiny, which means it reflects rather than emits light. Useless for navigating fog.

To which I responded

Nose also glows & bright. Since it’s red we could determine temperature if a thermal source & estimate Rudolph’s calorie needs

If Rudolph’s nose is a thermal source it will follow the Stefan-Boltzmann power law, which tells us the radiated power depends on the fourth power of temperature. Something red-hot will have a temperature of about 1000 K. Now this is an estimate and since it’s raised to the fourth power, will give us a large error bar on our answer. But let’s go with that because I don’t have a calculator handy. For the emitted power we multiply by the area, a few square centimeters (converted to square meters) and Stefan’s constant. Assuming I did the math correctly, we get about 10 Watts. The temperature should not be as large as 2000 K, which would give us and answer 16 times as large. (I am ignoring the “power absorbed” term in the equation, because at these temperatures it’s going to be small — 300K or less)

There’s also the emissivity. The nose is shiny, meaning the emissivity is not close to 1. So perhaps we double our guesstimate. Tens of Watts, maybe as large as 100 Watts as a probable value.

A thermal source has a maximum luminous efficacy of 95 lumens/Watt, at a temperature of around 6600 K but actual bulb filaments that give us white(ish) light are a lot closer to 10 lumens/Watt. So the nose probably emits around 1000 lumens at best — this is not even as bright as a traditional 100W light bulb, but is around what low-beam halogen headlights emit. However, those have reflectors on them to direct most of the light into a beam. Rudolph’s nose emits into a much larger area.

So perhaps the nose is not a thermal source (unless it’s much larger than I estimated) — the radiation is not because it is hot. We could check this if we knew the spectrum of the light being emitted. Perhaps it is some other type — does Rudolph have an LED nose?

Baby, it's Cold Inside

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How cold is cold enough? Eliminating entropy picokelvins from absolute zero

The team demonstrated their technique with two experiments, using a gas of rubidium-87 atoms in a square optical lattice. In the first, they started with a known number of atoms at each site (between one and four) all at the ground energy level. Then, by modulating the frequency, they gradually removed all the extra atoms, finishing with only one in each lattice site—a minimal entropy configuration.

In the second experiment, instead of starting with a known number of atoms all at the ground level, they loaded the lattice with a random number per site, with some excited and some at the ground level. As before, by sweeping the frequency, they removed all the extra atoms.

Pop Quiz, Hotshot

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Are you scientifically literate? Take our quiz

Took this the other day but am only now getting around to posting (holiday distraction). And with the taking of any scientific literacy quiz, there is the obligatory comment on what scientific literacy is or is not.

It’s not a bad quiz, other than the slide-show implementation of it and reloading the page to grade each question, but it’s not great, either, and it suffers from the problem that any multiple-choice quiz is going to have: it becomes a test of facts rather than concepts, and science literacy is more than memorization of facts.

I won’t hazard a guess where the literacy cutoff is, because some of the questions lean toward trivia and from my view, knowing trivia is not really synonymous with literacy. Knowing why Pluto was demoted from planet status shows more literacy than knowing the name of the orbiting body whose discovery led to that act, for example. Knowing what Mendel discovered is more important than remembering what plant he used to discover it, unless you can take it up a notch and know why he was lucky to have studied that plant for study (it had a simple structure which facilitated the discovery — one gene per feature). Knowing what two planets don’t have moons is not as important as being able to use some physics to reason why this might be, and a test like this doesn’t distinguish between the two approaches.

But you do have to have some facts at your disposal. Knowing the major constituent of air is important, too, as is knowing your way around the periodic table, and other things that show up on the quiz. Scientifically literate people will do well, overall, because they will probably know the trivia, having picked it up in the process of learning the concepts.

Casual Physics Friday

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hyper-efficient solar cells that aren’t actually efficient! or, giving good science a bad title

It’s ironic (or perhaps siliconic since this is about solar cells) to find a takedown article (which is otherwise OK) that says things like “relaxed momentum conservation” and explain it like this:

These strange little beasties are tiny bits of semiconductor material — tiny enough that lots of strict physical laws (like conservation of momentum) get to relax in some ways, making all sorts of fantastic things possible.

The phrase show up in a few places on the net, but the context there is not that the law is relaxed, but that the conditions are. Silicon is an indirect-bandgap material, meaning that the bands on either side of the bandgap do not line up if you lot energy vs. momentum, as you can see here. This requires a “phonon assist” for an excitation — you need the right vibration, with the right momentum at the time the photon arrives in order to promote the election. In other words, it’s harder to meet the conditions of momentum conservation.

But that’s in a crystal. So what I suspect is that in a quantum dot, the conditions are easier to meet, because it looks more like a direct bandgap material. Not that the law itself is more relaxed.

Relax, It's not a Puppy Pulley

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Dog Cam

[A] team of U.S., Dutch, and Belgian researchers have developed an eye tracking device called a “DogCam” to see what a dog actually looks at when it studies the subtle cues of its owner and its surroundings.

The scientists will also be able to see other dogs take the subject’s lunch money for looking like this.

2nd Objoke: the editor on the video should be Seymour Butz

The View from Nowhere

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The View from Nowhere: Questions and Answers

In pro journalism, American style, the View from Nowhere is a bid for trust that advertises the viewlessness of the news producer. Frequently it places the journalist between polarized extremes, and calls that neither-nor position “impartial.” Second, it’s a means of defense against a style of criticism that is fully anticipated: charges of bias originating in partisan politics and the two-party system. Third: it’s an attempt to secure a kind of universal legitimacy that is implicitly denied to those who stake out positions or betray a point of view. American journalists have almost a lust for the View from Nowhere because they think it has more authority than any other possible stance.
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[I]t has unearned authority in the American press. If in doing the serious work of journalism–digging, reporting, verification, mastering a beat–you develop a view, expressing that view does not diminish your authority. It may even add to it. The View from Nowhere doesn’t know from this.

That’s in the context of politics, where you have two (or possibly more) opinions or ideologies. It’s worse in science, where the rush to be in between (i.e. nowhere) means you move away from where the evidence is, and can give undeserved weight to groundless rants.

Now You're Cooking With Gas

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You need to a flashplayer enabled browser to view this YouTube video

“Pyro board” is unfortunately as detailed as it gets; it appears to be a 2-D version of a Rubens tube. The sound waves give you high- and low-pressure regions, which show up as little/no flame or big flame (lower pressure = more flow, from Bernoulli’s principle).

The video of a one-dimensional system I linked to a while ago has some explanation to go along with it.

Is it Still Right Twice a Day?

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Astrophile: Stopped clocks deepen pulsar enigmas

Some pulsars go dark, though, and Camilo’s was not the first. In the 1970s, some regular pulsars were spotted switching off for a few seconds to a few minutes, a phenomenon known as “nulling”. And in the past decade, a new class of pulsars has been found , in which the silences can range from minutes to a few hours. They were dubbed rotating radio transients, or RRATs. Around the same time, a pulsar was found that pulsed for about a week and then switched off for about a month before repeating the cycle.

There are papers discussing the possibility that precession could cause this, i.e. the pulsar is still “on” but not pointing at us during the nulling interval, but I didn’t see that brought up in the article.