Atoms and Molecules
drorzel | May 12, 2010Via Jennifer Ouellette on Twitter, I ran across a Discovery News story touting a recent arxiv preprint claiming to see variation in the fine-structure constant. It's a basically OK story, but garbles a few details, so I thought it would be worth giving it the ResearchBlogging treatment, in the now-traditional Q&A format.
What did they do? The paper looks at some spectral lines in radio emission from a moderately distant galaxy with the poetic name "PKS1413+135." These lines are produced by OH molecules in interstellar gas clouds, and the frequencies they see suggest that there may have…
drorzel | May 5, 2010Over at the Virtuosi, there's a nice discussion of the physics of letting air out of tires. Jesse opens the explanation with:
Have you ever noticed how when you let air out of a bike tire (or, I suppose, a car tire) it feels rather cold? Today we're going to explore why that is, and just how cold it is. Many people consider the air escaping from a tire as a classic example of an adiabatic process. What is an adiabatic process? It is a process that happens so quickly there is no time for heat flow to occur. For our air in the bike tire this means we're letting it out of the tire so…
drorzel | May 3, 2010Voting has closed on the Laser Smackdown poll, with 772 people recording their opinion on the most amazing of the many things that have been done with lasers in the fifty years since the invention of the first working laser (see the Laserfest web site for more on the history and applications of lasers). The candidates in the traditional suspense-building reverse order:
Lunar laser ranging 22 votes
Cat toy/ dog toy/ laser light show 41 votes
Laser guide stars/ adaptive optics 46 votes
Holography 47 votes
Laser eye surgery 53 votes
Optical storage media (CD/DVD/Blu-Ray) 60 votes
Laser…
drorzel | April 30, 2010We're just over 600 votes in the Laser Smackdown poll in honor of the 50th anniversary of the laser, as of early Friday morning. I notice that it has moved off the front page of the blog, though, so here's another signal-boosting repost, just so we have as many votes as possible, to establish maximum scientific validity when we declare the winner the Most Amazing Laser Application of All Time
Which of the following is the most amazing application of a laser?Market Research
Voting will remain open until next Sunday, May 2, just two days from now, with the ultimate winner announced on Monday…
drorzel | April 29, 2010Over in Twitter-land, S. C. Kavassalis notes a Googler who's not afraid to ask the big questions:
Weird Google search of the week: 'the "one" scientific idea that we need to believe'. Uh um, I'm sure my blog couldn't possibly answer that.
It's a good question, though, ad there are a couple of different ways to take it. You could read it as "What one scientific idea is supported by the most experimental proof?" or you could read it as "What one idea is most central to science generally?"
"The Standard Model" was quickly suggested on Twitter, which could fit either. I think it might be…
drorzel | April 26, 2010As of 1:45 Monday, 217 people have cast votes in the Laser Smackdown poll. That's not bad, but it's currently being handily beaten by the 271 people who have voted for a favorite system of units.
The nice thing about using actual poll services for this sort of thing, though, is that I can re-post the poll to boost signal a little. So, here it is again, a list of the twelve most amazing laser applications suggested by my wise and worldly readers, with links to short explanations of the pros and cons of each:
Which of the following is the most amazing application of a laser?Market Research…
drorzel | April 23, 2010In 1960, the first working laser was demonstrated, and promptly dubbed "a solution looking for a problem." In the ensuing fifty years, lasers have found lots of problems to solve, but there has been no consensus about which of the many amazing applications of lasers is the most amazing.
Now, in 2010, as we celebrate the anniversary of the laser, we finally have the technology to definitively answer the question: radio-button polls on the Internet!
Which of the following is the most amazing application of a laser?Market Research
Each of the choices above links to a post I wrote here giving…
drorzel | April 21, 2010What's the application? An optical frequency comb is a short-duration pulsed laser whose output can be viewed as a regularly spaced series of different frequencies. If the pulses are short enough, this can span the entire visible spectrum, giving a "comb" of colored lines on a traditional spectrometer. This can be used for a wide variety of applications, from precision time standards to molecular spectroscopy to astronomy.
What problem(s) is it the solution to? 1) "How do I compare this optical frequency standard to a microwave frequency standard?" 2) "How do I calibrate my spectrometer well…
drorzel | March 25, 2010I did one sketchy update from Portland last Tuesday, but never wrote up my impressions of the rest of the March Meeting-- when I got back, I was buried in grading, and then trying to put together Monday's presentation. And, for reasons that will become apparent, I was unable to write anything up before I left Portland
Anyway, for those who care, here are my impressions from the rest of the meeting:
Tuesday
In the 8am session, I went to the polymer physics prize talk by Michael Rubinstein, which was a sort of career retrospective, talking about how he wandered into the disreputable field of…
drorzel | March 15, 2010I'm terrible about taking notes on conference talks, especially when I'm jet-lagged and was sleep deprived even before I got on the plane. I do jot down the occasional paper reference, though, so here are the things I wrote down, and the talks they were associated with. This should give you some vague idea of what the meeting was like on Monday.
From Joel Moore's talk on topological insulators, one of the Hot New Topics in condensed matter, a review in Nature.
From Phillip Treutlein's talk on optomechanics, a recent preprint on coupling atoms to mechanical oscillators.
From Nathaniel Brahms'…
drorzel | February 12, 2010There have been a bunch of stories recently talking about quantum effects at room temperature-- one, about coherent transport in photosynthesis , even escaped the science blogosphere. They've mostly said similar things, but Thursday's ArxivBlog entry had a particular description of a paper about entanglement effects that is worth unpacking:
Entanglement is a strange and fragile thing. Sneeze and it vanishes. The problem is that entanglement is destroyed by any interaction with the environment and these interactions are hard to prevent. So physicists have only ever been able to study and…
drorzel | February 10, 2010What's the application? Using lasers to reduce the speed of a sample of atoms, thereby reducing their temperature to a tiny fraction of a degree above absolute zero.
What problem(s) is it the solution to? 1) "How can I make this sample of atoms move slowly enough to measure their properties very accurately?" 2) "How can I make this sample of atoms move slowly enough for their quantum wave-like character to become apparent?"
How does it work? I've written about laser cooling before, but the nickel version of the explanation is this: You can think of a beam of light as being made up of photons…
drorzel | February 2, 2010Congratulations to Alain Aspect, John Clauser, and Anton Zeilinger for winning the 2010 Wolf Prize in Phyiscs:
The 2010 Wolf Prize in Physics will be shared by Prof. John F. Clauser of the US; Prof. Alain Aspect of France's Ãcole Normale Supérieure de Cachan; and Prof. Anton Zeilinger of the University of Vienna. The jury in this field praised them "for their fundamental conceptual and experimental contributions to the foundations of quantum physics, specifically an increasingly sophisticated series of tests of Bell's inequalities, or extensions thereof, using entangled quantum states."
All…
drorzel | January 28, 2010Last week's Seven Essential Elements of Quantum Physics post sparked a fair bit of discussion, though most of it was at the expert level, well above the level of the intended audience. such is life in the physics blogosphere.
I think it's worth a little time to unpack some of the disagreement, though, as it sheds a little light on the process of writing this sort of thing for a general audience, and the eternal conflict between broad explanation and "dumbing down." And, if nothing else, it lets me put off grading the exams from last night for a little while longer.
So, what's the issue? The…
drorzel | January 25, 2010As mentioned previously, I've been reading Sean Carroll's Wheel arrow of time book, which necessarily includes a good bit of discussion of "Maxwell's Demon," a thought experiment famously proposed by James Clerk Maxwell as something that would allow you to cool a gas without obviously increasing entropy. The "demon" mans a trapdoor between a sample of gas and an initially empty space, and allows only slow-moving gas atoms to pass through. After some time, the empty volume is filled with a gas at lower temperature than the initial sample, while the gas in the original volume is hotter than…
drorzel | January 25, 2010There was a flurry of stories last week about an arxiv preprint on optical trapping of an ion. Somewhat surprisingly for an arxiv-only paper, it got a write-up in Physics World. While I generally like Physics World, I have to take issue with their description of why this is interesting:
In the past, the trapping of atomic particles has followed a basic rule: use radio-frequency (RF) electromagnetic fields for ions, and optical lasers for neutral particles, such as atoms. This is because RF fields can only exert electric forces on charges; try to use them on neutral particles and there's…
drorzel | January 25, 20102010 marks the 50th anniversary of the invention of the laser. To mark the occasion, the American Physical society has launched LaserFest, which will involve a large number of public events over the next year. The website includes a bunch of cool things explaining the physics of lasers, and a timeline of laser history with one glaring bug that you'll have to figure out for yourself. Over at Cocktail Party Physics, Jennifer Ouellette has an excellent historical survey of her own, saving me a lot of typing.
(Fun fact: Gordon Gould, who eventually won a lengthy patent fight, was a Union alumnus…
drorzel | January 19, 2010Consider the air around you, which is hopefully at something like "room temperature"-- 290-300 K (60-80 F). That temeprature is a measure of the kinetic energy of the moving atoms and molecules making up the gas. At room temperature, the atoms and molecules in the air around you are moving at something close to the speed of sound-- around 300 m/s (give or take a bit, depending on the mass).
If you're a physicist or chemist looking to study the property of these atoms and molecules, that speed is kind of a nuisance. For one thing, the atoms and molecules tend not to stick around long enough to…
drorzel | January 19, 2010Consider the air around you, which is hopefully at something like "room temperature"-- 290-300 K (60-80 F). That temeprature is a measure of the kinetic energy of the moving atoms and molecules making up the gas. At room temperature, the atoms and molecules in the air around you are moving at something close to the speed of sound-- around 300 m/s (give or take a bit, depending on the mass).
If you're a physicist or chemist looking to study the property of these atoms and molecules, that speed is kind of a nuisance. For one thing, the atoms and molecules tend not to stick around long enough to…