Physics
drorzel | February 21, 2007The AIP's Physics News Update this week highlights a paper on the laser cooling and trapping of radium by a group at Argonne National Laboratory. This is a new record for the heaviest atom ever cooled and trapped.
It's not quite as cool as the previous record, which involved the trapping of francium atoms that were produced using an accelerator-- you need to do a bit more work to get radium than just scraping off a bunch of old watch dials, but the basic apparatus is a fairly standard atomic beam system. It's still pretty cool stuff, and a good bit of work has gone into it-- before they could…
drorzel | February 20, 2007The post title is taken from the announcement for today's colloquium talk. The abstract:
Quantum gravity is the theory which is thought to underlie quantum theory and general relativity. I will introduce the subject, emphasizing recent results which suggest that spatial geometry is discrete. Such discrete geometry may have an observational signature, especially if it breaks Lorentz invariance. I will describe limits on such discrete geometry effects by astrophysical observations and will also argue that, in the not too distant future, quantum gravity may become physics and enjoy contact with…
drorzel | February 19, 2007We're back from Boskone, which included lots of fun stuff, and not enough sleep. I also cleverly forgot to bring my lecture notes home from work, which means I need to go in early to figure out what the hell I'm talking about in class today, so there's not much time for blogging at the moment.
I would be remiss in my physics-blogging duties, though, if I failed to point people to this Physics Web story about a new single-photon interference experiment (you'll need a subscription to read the Science article). A French group including Alain Aspect (who else?) has done a beautifually clean…
drorzel | February 16, 2007There's a press release on EurekAlert about new measurements limiting the change in the fine structure constant from the Time and Frequency division of NIST in Boulder:
Some astronomical and geological studies suggest there might have been very small changes in the values of fundamental constants over billions of years, although the results have been inconsistent and controversial. If fundamental constants are changing, the present-day rates of change are too small to be measured using conventional methods. However, a new comparison of NIST's cesium fountain and mercury ion clocks, scheduled…
drorzel | February 15, 2007In general, EuerkAlert has been a useful source for drawing my attention to interesting things that I might not otherwise notice. Every now and then, though, there are press releases that just make me faintly embarrassed for everyone involved.
Such as yesterday's announcement from LSU:
Subhash Kak, Delaune Distinguished Professor of Electrical and Computer Engineering at LSU, recently resolved the twin paradox, known as one of the most enduring puzzles of modern-day physics.
[...]The fact that time slows down on moving objects has been documented and verified over the years through repeated…
drorzel | February 15, 2007I'm giving an exam at 9:00 this morning-- neither snow, nor more snow, nor blowing snow, nor single-digit temperatures shall stay the progress of shaping young minds. Anyway, to keep things lively while I'm proctoring the test, here's a poll question inspired by the exam:
What's your favorite calculational shortcut?
Today's test is on basic quantum mechanics-- photoelectric effect, Compton effect, the Bohr model of hydrogen, and simple solutions of the Schrödinger equation-- and as such, features a lot of problems that are made easier by knowing some shortcut or another. Sometimes, these are…
drorzel | February 14, 2007Somebody at work had printed out a table of MCAT scores by major, compiled by the AIP. I couldn't find it on the web, but I found the original source, and made my own version of the relevant bit. This shows the average numerical scores on the three sections of the MCAT test for students majoring in biological and physical sciences (shortened to "biology" and "physics" for the table), for students who applied to med school, and students who got into med school:
The results are striking. Not only did the physics applicants do better than the biologists on the physics portion of the test, as…
drorzel | February 14, 2007Over at metadatta, Sujit is doing spectroscopy experiments with interferometers, and has posted a very nice introduction to the technique. Basically, if you have a light source emitting two different wavelengths that are very close together, you can determine the wavelength difference by shinging the light into an interferometer, and seeing how far you need to change things to make the interference patterns of the two wavelengths overlap.
That's a really sketchy description, so you should follow the link, and read Sujit's description which is, as I said, very nice. And if I find myself…
drorzel | February 13, 2007PhysicsWeb has astory about a new theory of axions that claims to resolve some discrepancies between past experiments. Two previous experiments looking for axions-- hypothetical weakly interacting particles that might be an explanation for dark matter-- have found conflicting results: the CAST experiment looking for axions produced in the Sun found nothing, while the PVLAS experiment looking for axions by studying the rotation of polarized light in a magnetic field may have seen something. (I talked a bit about the latter here.)
Of course, the new theory is not without its complications:
Now…
drorzel | February 13, 2007The New York Times reports that Purdue has officially cleared Rusi Taleyarkhan of charges of scientific wrongdoing over his claim to have produced nuclear fusion on a tabletop through the magic of sonoluminescence. You might recall that these claims were made a couple of years ago, but nobody else has been able to replicate them.
Purdue has conducted some sort of inquiry into the matter, and declared that there was nothing dishonest about the results. The inquiry was not what you'd call a model of transparancey, though:
Purdue did not reveal what allegations the committee had considered. It…
drorzel | February 10, 2007Piled Higher and Deepr nails it this week:
A Pofessor's Negation Field is the unexplained phenomenon whereby mere spatial proximity to an experimental set-up causes all working demonstrations to fail, despite the apparent laws of Physics or how many times it worked right before he/she walked in the room.
I haven't been on the faculty long enough to develop a really effective Negation Field, but my boss when I was a post-doc was the absolute king of this. I eventually stopped telling him when things were working well, because he'd invariably want to come see it, and then something would go…
drorzel | February 7, 2007So, what's the deal with last night's silly obituary? Basically, the main laser in my experiment died because I'm a jackass.
More specifically, the laser in question is a diode laser, similar to the kind found in CD and DVD players. These are broadly tunable, available in a wide range of powers and wavelengths, and relatively cheap. They're also extremely sensitive to static shock, to the point where I have to be careful to always touch something metal before working on the laser or anything close to it.
To check that we have successfully tuned the laser to the right wavelength, we need to do…
drorzel | February 6, 2007SDL 5401-G1, October 2001- February 6, 2007
SDL 5401-G1 ("Sid" to friends) died today of static shock, after five years of service in a grating-locked diode laser system. He had survived three lab floods, and more than a dozen power outages, but succombed to electric shock following a mishap with a Tesla coil.
He is survived by three siblings from the same batch, one of whom has already taken his place in the grating-locked laser mount. In lieu of flowers, the family asks that you send research grants.
Sic transit gloria laseri.
purepedantry | February 6, 2007Photons can carry enormous amount of information, but one of the problems in using them to encode information is that they are difficult to store for even short periods (they are moving at the speed of light after all!). University of Rochester scientists have taken a step in solving the practical problems of using photons to store information by creating an optical buffer for photons that slows them to more usable speeds:
Researchers at the University of Rochester have demonstrated that optical pulses in an imaging system can be buffered in a slow-light medium, while preserving the…
jstemwedel | February 3, 2007In a guest-post at Asymptotia, Sabine Hossenfelder suggests some really good reasons for scientists to communicate with non-scientists -- and not just to say, "Give us more research funding and we'll give you an even smaller iPod." She really gets to the heart of what's at stake:
I find it kind of ironic that during the last decades this ancient desire of men to just understand had to be more and more justified by the prospect of material output. Nowadays, governmental funding goes primarily into applied sciences, ideally into military applications, many of which fulfill the only purpose to…
drorzel | February 2, 2007Time spent locating the parts for the Compton Effect experiment: 15 minutes.
Time spent dragging lead bricks for radiation shielding into the lab: 10 minutes.
Time spent bulding little lead houses for the hot 137Cs source and Photo-Multiplier Tube (PMT): 15 minutes.
Time spent trying to find somebody who knew the administrator password for the computer: 20 minutes.
Time between saying "What happens if you just click 'Cancel?'" and getting the computer working: 2 seconds.
Time spent connecting the detector, amplifiers, and high-voltage power supply: 5 minutes.
Time spent swapping connections…
drorzel | February 2, 2007Late spring/ early summer is Conference Season in academic science, with lots of meetings scheduled during the academic break, so that everybody can attend without cutting into their teaching responsibilities (of course, our trimester calendar means we're still in session for most of these, but whatever...). The peak time for conferences in my subfield is late May and early June-- the main meeting I go to, the Division of Atomic, Molecular, and Optical Physics is actually later than usual this year, presumably because it's in Calgary, and they need an extra week or two to thaw out.
Of course…
drorzel | February 2, 2007I'm really bad about remembering these things-- I ought to start putting them on my calendar-- but the physics blogging carnival Philosophia Naturalis is now up, collecting many excellent posts about physics. If you've been away from the computer for the last month, or would just like a quick recap, go check it out.
drorzel | January 31, 2007Gordon Watts has deja vu:
[Leaving a colloquium], I got stopped by another member of our department, who is a good friend of particle physics, and she said basically the same thing: all particle physics talks look the same. Some of the comments: Two slides on the detector. Some pictures of quarks, and then some hard-to-understand plots. Where is the story? I only know how hard it is to do this sort of thing because I know you guys: I'd never guess how hard it is from your talks. It is the same plots over and over!
To a certain extent, he's being too hard on himself-- after a while, all sorts…
drorzel | January 27, 2007The dog is standing at the window, wagging her tail excitedly. I look outside, and the back yard is empty. "What are you looking at?" I ask.
"Bunnies made of cheese!," she says. I look again, and the yard is still empty.
"There are no bunnies out there," I say, "and there are certainly not any bunnies made of cheese. The back yard is empty."
"But particles are created out of empty space all the time, right?"
"Have you been reading my quantum physics books again?"
"It's boring here when you're not home. Anyway, answer the question."
"Well, yes, in a sense. They're called 'virtual particles,'…