Monthly Archives: February 2010

Einstein Passes, Again

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Most precise test yet of Einstein’s gravitational redshift

When the cesium atom matter wave enters the experiment, it encounters a carefully tuned flash of laser light. The laws of quantum mechanics step in, and each cesium atom enters two alternate realities, Müller said. In one, the laser has pushed the atom up one-tenth of a millimeter – 4/1000 of an inch – giving it a tiny boost out of Earth’s gravitational field. In the other, the atom remains unmoved inside Earth’s gravitational well, where time flies by less quickly.

While the frequency of cesium matter waves is too high to measure, Müller and his colleagues used the interference between the cesium matter waves in the alternate realities to measure the resulting difference between their oscillations, and thus the redshift.

This is the UC Berkeley press release, and if one can ignore the use of the “many worlds” reference of alternate realities, is otherwise pretty good. It also includes some laser table porn which has been filtered out of the other stories I’ve run across. I’ve only had a chance to glance at the article, but there’s a lot of interesting physics in there that is not mentioned in the press release, or in the Nature summary story that ran in addition to the article (and was somewhat disappointing in terms of how it recapped the experiment).

The basic experiment is a decade old; the original idea was to measure the local value of g, because the two paths of the atoms have an energy difference of PE = mgh, and that gives you a phase difference for the two paths. The trick here is in reinterpreting the results in terms of relativity. I’ll try and summarize the details soon.

Outsourcing

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In the era where poor scores mean punishment for the school, there appears to be a new form of cheating: the teachers or administrators changing the answers after the exam has been completed.

Georgia Schools Inquiry Finds Signs of Cheating

The erasure analysis used the same scanners that score tests to count the erasures in which answers were changed from wrong to right. “It’s not any sort of crazy technology,” Ms. Mathers said. “You just beef up the scanner so it can read varying degrees of gray scale.”

The study determined the average number of wrong-to-right erasures statewide for each grade and subject, and flagged any classroom with an unusually high number. For example, in fourth-grade math, students on average changed 1.8 answers from wrong to right, while one classroom that was flagged as suspicious had more than 6 such changes per student.

One Thing's for Certain

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I ran a cross a few infographics recently, while surfing the web because it was too snowy outside to do anything, and I was avoiding doing my own taxes, so I looked at everyone else’s.

The US federal budget, showing the inflows and outflows, broken down into several categories. One thing struck me: income tax revenue is only slightly larger than payroll tax revenue. In many political arguments about tax cuts, it’s only income tax that is mentioned, and the income tax burden is touted. But that’s missing half of the picture, because the payroll taxes are regressive; there are people who pay no income tax but pay a significant fraction of their income in payroll taxes, and are not helped by income tax cuts.

So if you analyze the tax burden incorporating the payroll taxes (as well as state and local taxes), what does the picture look like? It’s only slightly progressive — not the portrayal of woe that some would have you believe.

Tinker, Tailor …

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Tale of a Would-Be Spy, Buried Treasure, and Uncrackable Code

When officials searched the aspiring spy, they found a paper tucked under the insole of his right shoe. On it were written the addresses of several Iraqi and Chinese embassies in Europe. In a trouser pocket they discovered a spiral pad in which Regan, who had been trained in cryptanalysis by the Air Force, had written 13 seemingly unconnected words — like tricycle, rocket, and glove. Another 26 words were written on an index card. In his wallet was a paper with a string of several dozen letters and numbers beginning “5-6-N-V-O-A- I …” And in a folder Regan had been carrying, they found four pages filled with three-digit numbers, or trinomes: 952, 832, 041, and so on. The spiral pad, the index card, the wallet note, and the sheets of trinomes: The FBI suddenly had four puzzles to solve.

Stop! In the Name of Physics

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In Brookhaven Collider, Scientists Briefly Break a Law of Nature

The departure from normal physics manifested itself in the apparent ability of the briefly freed quarks to tell right from left. That breaks one of the fundamental laws of nature, known as parity, which requires that the laws of physics remain unchanged if we view nature in a mirror.

Ok, that’s interesting — that the reaction violated parity conservation, which I imagine has implications for the matter/antimatter asymmetry issue (I have long wondered if symmetry violation conditions changed with energy, and now it appears that they can and do). But if a reaction violates parity conservation, then parity conservation is not a law of nature; at best you have a “parity conservation zone.” Laws of nature describe how nature behaves. Whatever nature does, it is in accordance with these laws.

The editor who came up with the title needs to write “It is impossible to violate the laws of nature” a thousand times.

For more on the science, and confirmation that this follows, rather than breaks, the laws of physics, check out Cosmic Variance

Update: for some backstory on parity violation, check out Symmetry: It’s More Like a Guideline about the confirmation of how weak interactions don’t “keep to the code.”

Don't Sign Them, Though

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Let’s draw Feynman diagams!

So we see that the external lines correspond to incoming or outgoing particles. What about the internal lines? These represent virtual particles that are never directly observed. They are created quantum mechanically and disappear quantum mechanically, serving only the purpose of allowing a given set of interactions to occur to allow the incoming particles to turn into the outgoing particles. We’ll have a lot to say about these guys in future posts.

No, You Can't Have It

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I can recall one of the very first creationist types I met, way back when I was in the navy. He proudly proclaimed that he knew evolution was false, because a dog would never give birth to a cat. It floored me that someone with a tech background could have so completely failed in both the application of logic and in having the requisite knowledge to be preaching on the subject.

Through the years I’ve seen far too many similar argument, in which the demand for some evidence, either unreasonable at its face or required of the strawman version of the theory, is made, and the inability to provide said evidence is immediately (and erroneously) taken as the death knell of the theory in question. Basically these people are insisting on seeing a smoking gun, when the victim has been quite obviously stabbed to death.

Here’s a nice article that addresses this phenomenon:

Less Wrong: You’re Entitled to Arguments, But Not (That Particular) Proof

(ceteris paribus is a Latin phrase used in the post, and one I can’t recall having seen before. It means “all other things being equal” and has nothing to do with stories about whales)

And in a burst of evolutionary irony, the post has some useful appendices

Nits to Pick

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Blogs and news stories which list the most recent comment first. This makes no sense to me. There are comments on comments, and you need to read these chronologically to make any sense of them.

Blog archives not using previous and next (or the equivalent) in a consistent fashion. On some, previous takes you to the previously viewed page, which has a more recent timestamp, but on others it takes you to an earlier set of posts.

Sites which append their URL when you copy & paste anything. I understand the reason — to make it more likely to drive traffic back to the original site. But for a responsible blogger, who is going to link back anyway, this is just an annoyance and makes it less likely I’ll grab the story from you, if it’s something being reported elsewhere.

Great Jumping Sand Grains, Batman!

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Martian Dune Mystery Solved by Bouncing Sand Grains

The way sand grains knock each other around turns out to make all the difference, Kok says. Because Martian gravity and air density are so much lower than Earth’s, a small kick from the wind sends sand particles on Mars flying much higher, up to a meter off the ground.

“It’s like playing golf on the moon,” Kok says. Particles get caught in stronger winds as they rise, causing them to pick up speed and ultimately slam into the ground, where they kick up more particles and start the cycle over. “This splashing process is really efficient,” Kok says. “It can keep saltation, or sand blowing, going on Mars at relatively low wind speeds.” These jumping sand grains can create ripples over time even without high sustained winds, he says.

Different Kinds of Crack

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Cracking the Story of Fracture

A crack slicing through a brittle material may be a more complicated process than researchers previously thought. A team reporting in the 29 January Physical Review Letters wedged apart a piece of Plexiglas and saw three different fracture processes, depending on the speed of the moving crack. Their results help to further the basic physical understanding of material fracture and, ultimately, material failure.

Update: How could I have missed that the story was written by sciencegeekgirl?