Science
drorzel | August 21, 2013I'm writing a bit for the book-in-progress about neutrinos-- prompted by a forthcoming book by Ray Jaywardhana that I was sent for review-- and in looking for material, I ran across a great quote from Arthur Stanley Eddington, the British astronomer and science popularizer best known for his eclipse observations that confirmed the bending of light by gravity. Eddington was no fan of neutrinos, but in a set of lectures about philosophy of science, later published as a book, he wrote that he wouldn't bet against them:
My old-fashioned kind of disbelief in neutrinos is scarcely enough. Dare I…
esiegel | August 20, 2013"[S]cience is not a consumption good to be expanded in good times and restricted in bad times. The doing of science as well as the supporting of science is an expression of faith in the future. It would have been possible to have told Newton and Faraday, Maxwell and Einstein, Bohr and Heisenberg that, given the poverty and squalor around them, their research were luxuries which could not be afforded. To have done so would be to destroy the economic c progress that came out of their science and which was the main factor in relieving that poverty and squalor. We seem to be on the verge of…
drorzel | August 20, 2013A little over a year ago, I visited Mark Kasevich's labs at Stanford, and wrote up a paper proposing to use a 10-m atom interferometer to test general relativity. Now, that sounds crazy, but I saw the actual tower when I visited, so it wasn't complete nonsense. And this week, they have a new paper with experimental results, that's free to read via this Physics Focus article. Which might seem to make me blogging it redundant, but I think it's cool enough that I can't resist.
OK, dude, "Multiaxis Inertial Sensing with Long-Time Point Source Atom Interferometry" is not the sexiest title in the…
drorzel | August 20, 2013Element: Rubidium (Rb)
Atomic Number: 37
Mass: two "stable" isotopes, 85 and 87 amu (rubidium-87 is technically radioactive, but it's half-life is 48 billion years, so it might as well be stable for atomic physics purposes.
Laser cooling wavelength: 780 nm
Doppler cooling limit: 140 μK
Chemical classification: Alkali metal, column I of the periodic table. Like the majority of elements, it’s a greyish metal at room temperature. Like the other alkalis, it’s highly reactive, and bursts into flame on contact with water, even more so than sodium (in general, the alkalis get more violently reactive…
aardvarchaeology | August 19, 2013I like reading about the history of science, including my own discipline. But there is one kind of history of science that annoys me hugely, and that's the knowledge relativist kind. A knowledge relativist historian of science will chronicle a scientific debate of the past but make no comment on who – if any – of the participants turned out to be right. (If you feel the need, you're welcome to substitute “gain the eventual support of today's scientific consensus” for “be right”.)
Such history writing makes scientific debate look ridiculous and pointless. Just a lot of agitated people dreaming…
drorzel | August 19, 2013Element: Sodium (Na)
Atomic Number: 11
Mass: one stable isotope, 23 amu
Laser cooling wavelength: 589 nm
Doppler cooling limit: 240 μK
Chemical classification: Alkali metal, column I of the periodic table. Like the majority of elements, it's a greyish metal at room temperature. Like the other alkalis, it's highly reactive, and bursts into flame on contact with water. For this reason, all physicists working with sodium have True Lab Stories about accidentally blowing stuff up with it.
Other properties of interest: Scattering length of around 80 a0; Feshbach resonance at around 900 G.
History:…
drorzel | August 19, 2013At the tail end of the cold-atom toolbox series, I joked about doing a "trading card" version shortening the posts to a more web-friendly length. In idly thinking about this, though, it occurred to me that if one were going to have cold-atom trading cards, it might make more sense to have them for the atoms, rather than the techniques. And having just devoted many thousands of words to technique, I don't really feel like trying to cut those down more, but atoms...
The "featured image" up top is a slide from my laser cooling lectures for our first-year seminar class. Elements outlined in red…
drorzel | August 16, 2013This is probably the last trip into the cold atom toolbox, unless I think of something else while I'm writing it. But don't make the mistake of assuming it's an afterthought-- far from it. In some ways, today's topic is the most important, because it covers the ways that we study the atoms once we have them trapped and cooled.
What do you mean? They're atoms, not Higgs bosons of something. You just... stick in a thermometer, or weigh them, or something... OK, actually, I have no idea. They're atoms, yes, but at ultra-low temperatures and in very small numbers. You can't bring them into…
catdynamics | August 15, 2013Many physical scientists learned of the curious phenomena of the Cargo Cult from Feynman's commencement address at Caltech, as reproduced in his book, "Surely You're Joking, Mr Feynman!".
In the address, Feynman cautions us against the conceptually similar notion of Cargo Cult Science, where people go through the motions of mimicking a scientific process, while never comprehending the essential nature of science.
The Cargo Cult Scientists follow some process that bears a superficial resemblance to science without understanding the true nature of what they are doing and the results are…
drorzel | August 15, 2013Writing up the evaporative cooling post on cold atom techniques, I used the standard analogy that people in the field use for describing the process: cooling an atomic vapor to BEC is like the cooling of a cup of coffee, where the hottest component particles manage to escape the system of interest, and what's left behind is colder. The departing atoms or coffee molecules carry off more than the average energy per particle, leaving a lower average energy (and thus a lower temperature) for the remainder.
A question that sometimes comes up when I talk about this is how you can possibly use this…
drorzel | August 15, 2013In our last installment of the cold-atom toolbox series, we talked about why you need magnetic traps to get to really ultra-cold samples-- because the light scattering involved in laser cooling limits you to a temperature that's too high for making Bose-Einstein condensation (BEC). This time out, we'll talk about how you actually get to those ultra-cold temperatures.
What do you mean? I assumed it was just part of the trapping process? No, because the forces involved in magnetic trapping are like those involved in optical dipole traps. In physics jargon, they're "conservative" forces, which…
drorzel | August 14, 2013We're getting toward the end of the cold-atom technologies in my original list, but that doesn't mean we're scraping the bottom of the barrel. On the contrary, the remaining tools are among the most important for producing and studying truly ultra-cold atoms.
Wait, isn't what we've been talking about cold enough? There is, as always, more art than science in the naming of categories of things. "Cold" and "ultra-cold" get thrown around a lot in this business, and the dividing line isn't quite clear. Very roughly speaking, most people these days seem to use "cold" for the microkelving scale…
drorzel | August 13, 2013Today's dip into the cold-atom toolbox is to explain the real workhorse of cold-atom physics, the magneto-optical trap. This is the technology that really makes laser cooling useful, by letting you collect massive numbers of atoms at very low temperatures and moderate density.
Wait a minute, I thought we already had that, with optical molasses? Doesn't that make atoms really cold and stick them in space? Molasses does half the job, making the atoms really cold, but it doesn't actually confine them. The photon scattering that gives you the cooling force and Doppler cooling limit produces a "…
drorzel | August 12, 2013Via a retweeted link from Thony C. on Twitter, I ran across a blog post declaring science a "bourgeois pastime." The argument, attributed to a book by Dierdre McCloskey is that rather than being at the root of economic progress, scientific advances are a by-product of economic advances. As society got more wealthy, it was able to direct more resources to science, which made great advances possible.
And, you know, if you're looking to make a bold and contrarian argument, you can certainly do that. Unfortunately, the bit quoted from McCloskey as an illustration of the power of the argument is:…
drorzel | August 9, 2013There was some buzz Thursday about a poll showing that 40% of white people don't have any friends of a different race. Ipsos/Reuters include a spiffy "data explorer" where you can make graphs like the one above. It does not appear to provide an easy way to get at the actual wording of the question, which is kind of crucial, and thus renders most of the stories about it too vague to take all that seriously.
Of course, this is somewhat reminiscent of the gender bias story from a couple of weeks ago, where it was shown that single-gender physics departments are not a clear indication of sexism.…
catdynamics | August 8, 2013Last year EANA, the European Astrobiology Network Association put up a series of 18 introductory astrobiology video lectures constituting the AstroBiology Course Lectures:
Introduction to Astrobiology
Formation of the Solar System
Origins of Life: current theories
Comets and the origin of life
Basic prebiotic chemistry
Structures and evolution of proteins
Most simple (early) life forms
On the bias of metabolism versus genetics first
Extremophilic microorganisms
Desiccation and radiation resistance of extremophiles
Search for Life on Mars
Biosignatures of microbial life (early…
pharyngula | August 8, 2013When I heard that Steven Pinker had written a new piece decrying the accusations of scientism, I was anxious to read it. "Scientism" is a blunt instrument that gets swung in my direction often enough; I consider it entirely inappropriate in almost every case I hear it used.
Here's the thing: when I say that there is no evidence for a god, that there's no sign that there is a single specific thing this imagined being has done, I am not unfairly asking people to adopt the protocols of science — I am expecting to judge by their own standards and expectations. They are praying to Jesus in the…
drorzel | August 8, 2013This topic is an addition to the original list in the introductory post for the series, because I had thought I could deal with it in one of the other entries. Really, though, it deserves its own installment because of its important role in the history of laser cooling. Laser cooling would not be as important as it is now were it not for the fact that cooling below the "Doppler limit" in optical molasses is not only possible, but easy to arrange. That's thanks to the "Sisyphus cooling" mechanism, the explanation of which was the main reason Claude Cohen-Tannoudji got his share of the 1997…
drorzel | August 7, 2013I spent an hour or so on Skype with a former student on Tuesday, talking about how physics is done in the CMS collaboration at the Large Hadron Collider. It's always fascinating to get a look at a completely different way of doing science-- as I said when I explained my questions, the longest author list in my publication history doesn't break double digits. (I thought there was a conference proceedings with my name on it that got up to 11 authors, but the longest list ADS shows is only eight). It was a really interesting conversation, as was my other Skype interview with a CMS physicist.…
drorzel | August 6, 2013Last time in our trip through the cold-atom toolbox, we talked about light shifts, where the interaction with a laser changes the internal energy states of an atom in a way that can produce forces on those atoms. This allows the creation of "dipole traps" where cold atoms are held in the focus of a laser beam, but that's only the simplest thing you can use light shifts for. One of the essential tools of modern atomic physics is the "optical lattice," which uses patterns of light to make patterns of atoms.
OK, what do you mean "patterns of light"? Well, remember, light has both wave and…