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"Uncertain Principles" features the miscellaneous ramblings of a physicist at a small liberal arts college. Physics, politics, pop culture, and occasional conversations with his dog.

You've read the blog, now try the book: How to Teach Physics to Your Dog will be published December 22nd by Scribner.

Chad Orzel "Prof. Orzel gives the impression of an everyday guy who just happens to have a vast but hidden knowledge of physics." (anonymous student evaluation comment)

Emmy, the Queen of Niskayuna Emmy is a German Shepherd mix, and the Queen of Niskayuna. She likes treats, walks, chasing bunnies, and quantum physics.

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« links for 2008-07-06 | Main | Uncertain Principles, Certain Results »

Quantum Quantum Quantum

Category: Book Writing
Posted on: July 6, 2008 7:52 AM, by Chad Orzel

"2. Ever repeat a word so much it starts to lose its meaning? Writing a book is like that, only with 90,000 words."

Quantum quantum quantum, quantum quantum. Quantum.

Comments

Consider this a look of little sympathy :-)

Posted by: Michael Nielsen | July 6, 2008 8:58 AM

I felt like that at my sister's wedding last week.

"What is it that you do exactly?"

"Quantum mechanics."

"What does that mean?"

"Depends on who you ask."

Posted by: Ian Durham | July 6, 2008 10:51 AM

@Bob O'H, let's not forget the video of the presentation of that masterwork:
Chicken Chicken Chicken

Posted by: Kathryn F | July 6, 2008 11:32 AM

"Chicken chicken, chicken. Chicken chicken chicken chicken." I can't believe the guy managed to do that presentation with a straight face.

Posted by: themadlolscientist | July 6, 2008 4:23 PM

Thanks for the pdf link--I'd seen the video before, but not the written article.

I was particularly tickled by the questions in the AIR Teachers' Guide at the end:

"Is this scientist right -- and what does "right" mean, anyway?
• Can you think of even one different explanation that works as well or better?
• Did the test really, really, truly, unquestionably, completely test what the author thought he was testing?
• Is the scientist ruthlessly honest with himself about how well his idea explains everything, or could he be
suffering from wishful thinking?"

I find those questions extremely difficult to answer in this case.

Posted by: HennepinCountyLawyer | July 7, 2008 4:19 AM

What I find very odd in QM is that we can make a reliable specific superposition, like for a photon, but no one is supposed to be able to find out the details later. IOW, we can make a photon equivalent to elliptical polarization, given the wave function: A |R> + Be^(i theta) |R> and e.g. 0.6 for A and 0.8 for B. The phase then provides an angle, not just an ellipse shape, so we can be sure a filter tuned to that wave would let the photon through (as it would also have ideal 100% transmission for the equivalent classical polarized light beam.) If I am a confidante of the photon's creator, I can know just how to orient the right filter (say, combo of QWP and LPF) to get all "hits" etc. But if I don't already know, I can't find out for sure: all I can do is try a filter and orientation and I might get transmission or not. Either way, the photon is "ruined" by either being absorbed or changed into the new filter's base. (Projection postulate? I wonder why that doesn't have its own Wikipedia article.) All I really know is, that photon couldn't have been the orthogonal to the filter base if it went through. But if the trait is "real" (unlike the literal contradiction in Fourier analysis of exact momentum and exact position), why can't I find out? (I know, doing so might lead to weird effects in entangled states, like FTL communication, but suppose it didn't?)

This seems silly, like a kid saying "If you don't know, I'm not going to tell you!" In some other comments around, I explained how we might circumvent that restriction by using the accumulation of angular momentum: Keep reflecting a photon around with mirrors, sending it through the same half-wave plate over and over (re-flipped by a second HWP if needed.) The HWP reverses the rotational sense (spin) because it swaps the values of A and B (you may be surprised, but it does - known fact, and to be consistent with the affect on the classical wave.) If we did it enough, all those transits would build up detectable angular momentum in the HWP. It would be along a range, not an either/or because the result needs to be consistent with sending many many "separate" photons through (indistinguishability.) IOW, if the photon came out of a linear polarizer, the many transits wouldn't build up net spin since the average effect is no rotation. Maybe it wouldn't work, but it's worth mulling over. It seems to resemble "weak measurements" as propounded by Yakir Aharonov.

Posted by: Neil B. | July 7, 2008 7:17 PM

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