Daily Archives: August 14, 2008

Spooky Speeding

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A pretty cool experiment that puts a lower bound on a speed of entanglement has been performed. The experimenters entangled photons, separated them, and then made their measurements.

Physicist Nicolas Gisin and colleagues at the University of Geneva in Switzerland split off pairs of quantum-entangled photons and sent them from the university’s campus through two fiber-optic cables to two Swiss villages located 18 kilometers apart. Thinking of the photons like traffic lights, each passed through specially designed detectors that determined what “color” they were when entering the cable and what color they appeared to be when they reached the terminus. The experiments revealed two things: First, the physical properties of the photons changed identically during their journey, just as predicted by quantum theory–when one turned “red,” so did the other. Second, there was no detectable time difference between when those changes occurred in the photons, as though an imaginary traffic controller had signaled them both.

The results show that any information connection between them would have to occur at at least 10,000 times the speed of light, which is interpreted as a pretty good indication that it’s an inherent behavior of quantum mechanics, and this “communication” isn’t actually taking place. (see also Bohm’s Bummed and the summary at Physics and Physicists)

Or not.

nature news has an article entitled Physicists spooked by faster-than-light information transfer. LiveScience’s article is Spooky Physics: Signals Seem to Travel Faster Than Light. Which is really strange, because at least in the nature summary, they discuss how it isn’t evidence of superluminal communication

A second test ensured that the scientists in the two villages weren’t missing some form of communication thanks to Earth’s motion through space. According to Einstein’s theory of relativity, observers moving at high speeds can have different ‘reference frames’, so that they can potentially get different measurements of the same event. The Geneva results could possibly be explained if the two photons were communicating through a frame of reference that wasn’t readily apparent to the scientists.”

But theoretical calculations have shown that performing tests over a full spin of the globe would test all possible reference frames. The team did just that, and they got the same result in all cases.

The bottom line, says Gisin is that “there is just no time for these two photons to communicate”.

So why use a headline that says or implies that there is FTL information transfer, when the conclusion is that there isn’t?

Do As I Say, Not As I Do

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Are we science-savvy enough to make informed decisions?

Let me guess: no. I mean, really, is this a gimme or what?

Seventy-six percent of Americans say presidential candidates should make improving science education a national priority, according to a national Harris Interactive survey of 1,304 adults in November and December. Results were released this spring.

But only 26% believe that they themselves have a good understanding of science. And 44% couldn’t identify a single scientist, living or dead, whom they’d consider a role model for the nation’s young people.

So at least some of those possessing marginal scientific literacy recognize that science education is important.

It boils down to this — if you can’t make the informed decision yourself, then you’re going to fall for whoever can lie most convincingly. And I think that accomplished liars have an advantage.

There is also a link to a quiz, which looks like the NSF Science and Engineering Indicators quiz. Unfortunately, we are told

10 or 11 right: You are a geek!

Maybe some small part of the problem is that basic science competency is being identified as geeky, though somehow I doubt that USA TODAY is the arbiter of cool amongst today’s teens.

Udate: commentary at Physics and Physicists

Deadman's Curve

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Matt discusses the disaster of grades in The Final Countdown

I just finished grading three problems worth of the final exam (the other two TAs are taking care of the rest), and I think the exam can be safely described as a debacle. It was a disaster. The scores haven’t been tallied up yet, but I think there’s a good chance the mean score will be within one standard deviation of zero. And, I dunno, about 4 or 5 standard deviations away from 100.

One mitigation technique I’ve mentioned before is to have a database of questions, so that you know the expected results, but this doesn’t necessarily work well in a university environment, and doesn’t apply here as it was already noted that the exam was made from scratch.

But there’s another option. I’ve taken and TA’d several classes where grades were neither curved, strictly speaking, nor were graded on a standard “90 and above is an A” basis. The professor who taught the class for which I TA’d pointed out that the students had a hard time adjusting to the concept that the average score was going to be about 50, since they had never encountered that system before. When it first happened to me as an undergraduate, the professor put it rather succinctly — why bother asking a lot of questions that everybody can answer? If 65 is the lowest passing score, then you’re asking a whole bunch of points worth of questions that don’t demonstrate adequate knowledge of the material. The idea was to cut out 50 points of that and add in questions that do require “passing” knowledge to answer and adjust the grading accordingly. The exams were much more complete in testing comprehension, since you could ask more questions about a particular topic. It’s not unlike the strategy taken during oral exams — asking questions until the target can’t answer them anymore. That’s when you’ve tested the depth of knowledge and comprehension.

Threading the Needle

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Another cool find by Zapperz: Threading Light Through the Opaque

Freshly fallen snow is blinding white because the jumble of flakes scatter light in all directions. Such scattering also implies that little light passes through snow, so that if you’re ever buried deep in it, you’ll find yourself in the dark. But according to theoretical physicists, it should always be possible to fiddle with light waves to make them wend their way through such a disordered material, no matter how thick. And now a duo of experimenters has demonstrated that feat.