Experiment
drorzel | December 12, 2011Having covered most of what you need to know about classical physics, the traditional next step is to talk about electricity and magnetism, colloquially known as "E&M," though really, "E and B" would be more appropriate, as the fundamental quantities discussed are the electric field (symbol: E) and the magnetic field (symbol: B), whose effect is given by today's equation:
This is the "Lorentz force law," giving the force experienced by a particle with charge q moving at a velocity v through a region with both electric and magnetic fields. This is, in some sense, what defines those…
drorzel | November 22, 2011A few months back, I did a post about estimating the time required for the different routes I take to work, looking at the question of whether it's better to take a shorter route with a small number of slow traffic lights, or a longer route with a bunch of stop signs. This was primarily conceived as a way to frame a kinematics problem, but I got a bunch of comments of the form "Aren't you an experimentalist? Where's the data?"
Well, here it is:
This is a histogram plot showing the number of times my morning commute fell into a given ten-second bin over the last couple of months. The blue…
drorzel | November 18, 2011One of the more reasonable criticisms of the OPERA result showing neutrinos apparently moving faster than light was that they were claiming 20-nanosecond resolution on the timing of a neutrino pulse that was 10000 nanoseconds long. They got their timing by doing fits to the shape of the whole pulse, as described in that link, and there's always a little bit of alchemy in that sort of process, but they had big long pulses because that's what the accelerator at CERN that served as the source of the neutrino beam provided.
After the original annoucnement, they got the neutrino beam reconfigured…
drorzel | November 10, 2011I've been incredibly busy this term, but not so busy I couldn't create more work for myself. Specifically, by writing an opinion piece for Physics World about the FTL neutrino business, that just went live on their web site:
The result quickly turned into one of the most covered physics stories of the year, with numerous articles in magazines, newspapers and on television asking whether "Einstein was wrong". Just as quickly came numerous physicists denouncing the media frenzy, with Lawrence Krauss from Arizona State University and Cambridge University cosmologist Martin Rees both calling the…
drorzel | October 23, 2011It's been a while since I posted anything science-y, and I've got some time between flipping pancakes, so here's an odd thing from the last few weeks of science news. Last week, there was an article in Nature about the wonders of string theory applied to condensed matter physics. This uses the "AdS/CFT" relationship, by which theorists can take a theory describing a bunch of strongly interacting particles in three dimensions (such as the electrons inside a solid), and describe it mathematically as a theory involving a black hole in four dimensions. This might seem like a strange thing to do,…
drorzel | October 16, 2011In a lot of ways, the OPERA fast-neutrino business has been less a story about science than a story about the perils of the new media landscape. We went through another stage of this a day or two ago, with all sorts of people Twittering, resharing, and repeating in other ways a story that the whole thing has been explained as a relativistic effect due to the motion of GPS satellites. So, relativity itself has overthrown an attack on relativity. Huzzah, Einstein! Right?
Well, maybe. I'm not quite ready to call the story closed, though, for several reasons. First and foremost is the fact that…
drorzel | October 5, 2011If you want to know how stressed and busy I've been lately, you don't have to look any farther than the fact that I've totally fallen down on the shameless self-promotion front: I was on a radio show, and forgot to post about it here. I know, bad blogger, no pageviews...
Anyway, I talked about the fast neutrino experiment on the phone to Clay Naff, who runs the Science Odyssey show on KZUM in Nebraska, and he used it as part of this past weekend's show. My interview is in Part 1, and Part 2 is Alan Kostelecky, who is an actual expert on this sort of thing.
For some odd reason, it…
drorzel | September 24, 2011There have been a lot of pixels spilled over this faster-than-light neutrino business, so it might not seem like something I should take time away from pressing work to write up. It is the story of the moment, though, and too much of the commentary I've seen has been of the form "I am a {theorist, journalist} so hearing about experimental details gives me the vapors" (a snarky paraphrase, obviously). This suggests that there's still room for a canine-level write-up going into a bit more depth about what they did and where it might be wrong.
So, what did those jokers at CERN pull this time?…
drorzel | September 23, 2011The final sentence of the neutrino paper that everybody is buzzing about:
We deliberately do not attempt any theoretical or phenomenological interpretation of
the results.
From a somewhat older work in physics:
Rationem vero harum gravitatis proprietatum ex phænomenis nondum potui deducere, et hypotheses non fingo. Quicquid enim ex phænomenis non deducitur, hypothesis vocanda est; et hypotheses seu metaphysicae, seu physicae, seu qualitatum occultarum, seu mechanicae, in philosophia experimentali locum non habent. In hac philosophia Propositiones deducuntur ex phaenomenis, et redduntur…
drorzel | September 6, 2011It's been a while since I did any ResearchBlogging, first because I was trying to get some papers of my own written, and then because I was frantically preparing for my classes this term (which start Wednesday). I've piled up a number of articles worth writing up in that time, including two papers from an early-August issue of Nature, on advances in experimental quantum computation (the first is available as a free pdf because it was done at NIST, and thus is not copyrightable). These were also written up in Physics World, but they're worth digging into in more detail, in the usual Q&A…
drorzel | August 22, 2011A few people last week were linking to this press release from Fermilab, which probably says more about the state of American particle physics than anything else: it's about an experiment that they expect to be approved in 2012, to break ground in 2013, and start running in 2016. I guess with the Tevatron shutting down and nothing noteworthy from the LHC yet, this is what you have to talk about.
The experiment in question is an update of an experiment from Brookhaven in 2001, which measured the anomalous magnetic moment of the muon. The value they get differs from the best theoretical value…
drorzel | July 28, 2011Unlike the previous post, this is not a rhetorical question that I will ask and then answer. I genuinely do not know the answer. I could Google it, of course, but I'd like to see if somebody reading this is able to deduce the correct answer from the available evidence.
So, here's the deal: as an attempt to recover from a rather sedentary couple of months due to computer-based work and some plantar fascitis kind of problem in my foot that's keeping me from playing hoops as much as I'd like, I'm spending a while each day on the exercise bike we have upstairs. While I do a bunch of reading of…
drorzel | July 28, 2011A while back, I explained how polarized sunglasses work, the short version of which is that light reflected off the ground in front of you tends to be polarized, and by blocking that light, they reduce the effects of glare. This is why fishermen wear polarized sunglasses (they make it easier to see through the surface of water) and why they're good for driving (they cut down on glare off the road ahead). I almost exclusively buy polarized sunglasses, because I like this feature.
But let's say you have a pair of polarized sunglasses that broke, because they were cheap to begin with (such as…
drorzel | July 26, 2011One of the benefits of having joined AAAS in order to get a reduced registration fee at their meeting is that I now have online access to Science at home. Including the Science Express advance online papers, which I don't usually get on campus. Which means that I get the chance to talk about the few cool physics things they post when they first become available, without having to beg for a PDF on Twitter. This week's advance online publication list includes a good example of the sort of cool ultra-cold atom physics that I talked about at and after DAMOP, so let's take a look at this paper in…
drorzel | July 14, 2011I really ought to be doing other things, but this roller slide business kept nagging at me, and I eventually realized I could mock up a crude simulation of the results. This led to the production of this graph:
This looks pretty similar to the Tracker Video data from the previous post, which I'll reproduce below the fold, along with an explanation of the math that went into the model:
The two graphs are qualitatively similar, other than, you know, the godawful Excel aesthetic of the simulation results graph. One line looks relatively straight, like motion at constant speed, while the others…
drorzel | July 14, 2011On Monday, I posted a short video and asked about the underlying physics. Here's the clip again, showing SteelyKid and then me going down a slide made up of a whole bunch of rollers at a local playground:
The notable thing about this is that SteelyKid takes a much, much longer time to get down the slide than I do. This is very different than an ordinary smooth slide, where elementary physics says we should go down the slide at the same rate, and empirically I tend to be a little slower than she is.
So what's the difference?
First of all, let's be a little more quantitative about this. Here's…
drorzel | July 12, 2011Among the articles highlighted in this week's Physics is one about a new test of QED through a measurement of the g-factor of the electron in silicon ions. This comes on the heels of a measurement of proton spin flips (this includes a free PDF) a couple of weeks ago, and those, in turn, build on measurements of electrons from a few years back, which Jerry Gabrielse talked about at DAMOP. Evidently, it's magnetic moment season in the world of physics.
The media reports on the proton experiment tend to be a little garbled in a way that reveals the writers don't quite understand what's going on…
drorzel | July 12, 2011A month and a half ago, I reported on a simple experiment to measure the performance of a timer from the teaching labs. I started the timer running at a particualr time, and over the next couple of weeks checked in regularly with the Official US Time display at the NIST website, recording the delay between the timer reading and the NIST clock.
As a follow-up experiment, I did the same thing with a different timer, this one a Good Cook brand digital timer picked up for $10 in the local supermarket, and the same Fisher Scientific stopwatch/timer as the first experiment, with the Fisher…
drorzel | July 11, 2011We took SteelyKid to the playground at one of the local elementary schools on Sunday morning. this one includes an odd sort of slide, made of dozens of rollers that are 1-2 inches in diameter (they're all the same size-- the range is just because I didn't measure them carefully). They're on really good bearings, and while it's kind of noisy, it's a reasonably smooth ride.
There is, however, one slightly mysterious aspect to this slide, clearly visible in this video that Kate was good enough to shoot for me:
SteelyKid takes something like 6 seconds to go down the slide, while it only takes me…
drorzel | July 8, 2011The final content area from my DAMOP overview is Precision Measurement. This is also the smallest area, with only one invited session on the topic on Fundamental Symmetry Tests, though two of the "Hot Topics" talks (by Zheng-Tian Lu and Ed Hinds) were precision measurement talks. You might be able to make an argument that this doesn't really deserve its own category, but I was the one giving the talk, and I love this stuff (though I absolutely do not have the temperament necessary to do it), so it gets its own category.
I also think there is a fairly distinct culture to precision measurement…