Experiment
drorzel | January 13, 2007One of my favorite experiments in physics has released a new set of results in Physical Review Letters, putting experimental limits on the size of any extra dimensions of the sort predicted by string theory:
We conducted three torsion-balance experiments to test the gravitational inverse-square law at separations between 9.53 mm and 55 µm, probing distances less than the dark-energy length scale λ~85 µm. We find with 95% confidence that the inverse-square law holds (|α|<=1) down to a length scale λ=56 µm and that an extra dimension must have a size R<=44 µm.
You'll need a…
drorzel | January 3, 2007A little bit before Christmas, I spent an afternoon swapping mirrors out of one line of the apparatus. I was losing too much of the laser light before it went into the chamber, and replacing the mirrors increased the power entering the apparatus by a factor of two or so.
Here's a picture of the two types of mirrors, side-by-side:
"Well, of course you had to replace them," you say. "The one on the left is a perfectly nice mirror, but the one on the right is utter crap. You dolt."
The thing is, the mirror on the right is the type I was putting in. The one on the left is the type that wasn't…
drorzel | December 19, 2006Via Doug Natelson, a very nice paper from the arxiv on Hanbury Brown and Twiss experiments with atoms. The Hanbury Brown and Twiss experiment (that's two guys, one with a double unhyphenated last name) is a classic experiment from the field of quantum optics, which can be interpreted as showing the bosonic nature of photons. I posted some lecture notes about it during my Quantum Optics class.
(The Hanbury Brown and Twiss experiment can also be understood classically, but that's not as much fun...)
The key idea here goes back to the symmetry business I talked about a little while back.…
drorzel | December 18, 2006Bill Hooker is a regular advocate of "open science," and is currently supporting a new subversive proposal: to make all raw data freely available on some sort of Creative Commons type license.
It sounds like a perfectly reasonable idea on the face of it, but I have to say, I'm a little dubious about it when I read things like this:
First, note that papers do not usually contain raw (useful, useable) data. They contain, say, graphs made from such data, or bitmapped images of it -- as Peter says, the paper offers hamburger when what we want is the original cow. Chris Surridge of PLoS puts it…
drorzel | December 14, 2006The physics story of the moment is probably the detection of single top quarks at Fermilab. Top quarks, like most other exotic particles, are usually produced in particle-antiparticle pairs, with some fraction of the kinetic energy of two colliding particles being converted into the mass of the quark-antiquark pair (see this old post). There's a very rare process, though, mediated by the weak nuclear force, that allows the production of a single top quark, without an anti-top (it's paired with a bottom quark and a W boson).
The D0 (or DZero) collaboration at Fermilab recently announced the…
drorzel | October 27, 2006I'm lecturing to our first-year seminar today about Bose-Einstein Condensation, using slides that haven't been updated since 2002. Given the pace of research in the field, that's a little crazy, so I spent a good while last night looking at pretty pictures on the Ketterle group web site, among others, so I can report on the latest and greatest developments, or at least that subset of the latest and greatest that I think I can boil down to one slide targeted at college frosh.
Coincidentally, the AIP news feed is also highlighting recent results from the Ketterle group, citing three new results…
drorzel | October 27, 2006Steinn reports a new metric for research productivity that some people are using: the "H-number":
The H-score, takes all your papers, ranked by citation count; then you take the largest "k" such that the kth ranked paper has at least k citations.
So, you start off with a H-score of zero.
If your 5th highest cited paper has 5 citations but your 6th highest cited paper has 4 citations then your H=5.
If your 10th highest cited paper has 11 citations, but your 11th highest cited paper has 9 citations, then your H=10.
And so on. High H is better.
Yeah, that's just what we need, another quasi-…
drorzel | October 25, 2006The recent discussion of reviews of The God Delusion has been interesting and remarkably civil, and I am grateful to the participants for both of those facts. In thinking a bit more about this, I thought of a good and relatively non-controversial analogy to explain the point I've been trying to make about the reviews (I thought of several nasty and inflammatory analogies without much effort, but I'm trying to be a Good Person...). Unfortunately it requires me to explain a bit of physics... Please, please, don't throw me into that briar patch.
Some people say that the last really significant…
drorzel | October 19, 2006I got word yesterday that the last leftover part of the work I did as a post-doc has been accepted for publication as a Rapid Communication in Physical Review A. It's not up on the web yet, but you can find an old draft on the ArXiV that will give you the basic idea.
"But wait," you say, "You haven't been a post-doc for more than five years. Why such a long delay?"
Well, for one thing, the group moved across the country in 2003 or so, which kind of puts a damper on the paper writing process. And that group isn't fast at getting papers sent out in the best of circumstances-- we managed to get…
drorzel | October 17, 2006Sean Carroll is offering more unsolicted advice (though it is in response to a comment, which makes it borderline solicited...), this time about choosing an undergraduate school. He breaks the options down into four categories, with two small errors that I'll correct in copying the list over here:
Liberal-Arts College (LAC), such as Williams or Union.
Specialized Technical School (STS), such as MIT or Caltech.
Elite Private University (EPU), such as Harvard or Stanford.
Large State School (LSS), such as UCLA or Michigan.
There. That's much better.
I should note two things up front: the…
drorzel | October 17, 2006Both the AIP and the New York Times are reporting that elements 116 and 118 have been discovered by a collaboration between Russian and American scientists working at the Joint Institute for Nuclear Research in Dubna. This is the second time it's been announced that element 118 has been seen, as a previous "discovery" turned out to be fraudulent, but everybody who comments in those articles says that they're confident this one is the real thing.
The elements in question, which nobody has attempted to attach names to yet (have they learned nothing from the Planet Wars? Name one after a tv…
drorzel | October 16, 2006The AIP Physics News service last week highlighted a new result from the Athena collaboration at CERN with the headline "First Antimatter Chemistry". That conjures images of sticking anti-carbon atoms together to make anti-buckballs, but that's not exactly what's going on...
The experiment in the case involves the interaction between anti-protons and molecular hydrogen ions. They slow and trap the anti-protons, and bring them into the same region with the H2+ molecules, and a reaction occurs that pulls the molecule apart, producing a neutral hydrogen atom and something they're calling "…
drorzel | October 11, 2006Back in late July, I got email from a writer for Physics World magazine (which is sort of the UK equivalent of Physics Today), asking my opinion on a few questions relating to particle physics funding. The basis for asking me (as opposed to, you know, a particle physicist) was presumably a post from April in which I ranted a bit about the justification of Big Science projects.
The article is now out, but not available on-line, so I haven't read it. I spent a fair amount of time typing up my response, though, so I'm going to recycle it into a blog post, because I can do that.
The original…
drorzel | October 6, 2006Third and final post in a series about "teleportation" from July 2002. This one is mostly dedicated to voicing the same complaints I have about the more recent stories that kicked this whole repost business off.
The more things change, the more I keep repeating myself.
So, having discussed how to do "quantum teleportation," how does this get us to "Beam me up, Scotty?" Well, that's the thing. It doesn't, not in any meaningful sense. What gets "teleported" is just the state of the initial quantum particle, not the particle itself. There's no reason why you couldn't do "teleportation" with…
drorzel | October 6, 2006Part two of three of an explanation of "quantum teleportation" experiments, from July of 2002. This one goes through the basics how teleportation works. I might be able to do better now, having worked through it in more detail in order to teach about it in my Quantum Optics class, but it's been a busy week, so I'll just repost the old entry for now.
So, the last whopping huge physics post here covered the idea of quantum entanglement-- how do you get from entanglement to "quantum teleportation", which is what the article that kicked the whole thing off was about?
The first step here is to…
drorzel | October 6, 2006As threatened in the previous post on new "quantum teleportation" results, here's the first of three old articles on teleportation. This one discusses EPR states and "entanglement." It's somewhat linkrotted-- in particular, the original news article is gone, but the explanation is still ok.
This dates from July of 2002, which is like 1840 in blog years.
Yet again, SciTech Daily provides me with weblog material, this time in the form of an oddball article in the Las Vegas City Life archives (how do they find this stuff? It never would've occurred to me to look there...). The article is mostly…
drorzel | October 6, 2006The latest physics news is an experimental demonstration of "teleportation" involving both light and atoms, done at the Niels Bohr Institute in Copenhagen, and reported on by the Institutes of Physics and CNN, among others, and remarked on by Dave, among others.
I wrote up some stuff about teleportation in the early days of this blog, and I'll Classic Edition those posts in a little while. "Teleportation" stories always kind of annoy me, though, because the reality isn't nearly as cool as the image that the term evokes. To some degree, it's a triumph of marketing more than a scientific…
drorzel | October 5, 2006So, there's a new issue of Physics World magazine out, with a bunch of feature stories on the Large Hadron Collider. Three of these are available free online:
Life at the high-energy frontier, a sort of overview of the accelerator and the people involved.
Expedition to inner space, a discussion of what they hope to discover at the LHC.
How the US sees the LHC, which is obvious.
I'm particularly interested in one of the articles that isn't free online, though: "Beyond the Higgs" discussing what would happen if the LHC fails to find the Higgs boson. My interest stems from the fact that the…
drorzel | September 29, 2006Physics Web has a story about new discoveries in excitonic systems with the eye-catching headline BEC's confound at higher temepratures. The main idea is that two exotic systems have been found in which quasi-particles undergo Bose-Einstein Condensation at realtively high temperatures-- 19 Kelvin for a system of "polaritons," and room temperature for a system of "magnons." If you're wondering why those sound like Star Trek particles-of-the-week rather than real particles that you might've heard of before, it's because they're quasi-particles involving several real particles coupled together…
drorzel | September 28, 2006The fourth and final post in my 2003 series attempting to explain experimental particle physics to the lay reader. This one talks about the specifics of the "pentaquark" experiment that was announced that year, and provided the inspiration for the whole thing.
It should be noted that that discovery is by no means certain, but I'm still fairly happy with the explanatory aspects of these posts. I'm certainly not bothered enough to re-write them.
So feel free to ignore pentaquark-specific comments in these reposts. If you'd like a more recent experimental hook for this, Tommaso Dorigo has you…