Physics
carlyo | August 1, 2013Ronald Mickens -- Research Physicist and Mathematician
Ronald Mickens is a leading authority on oscillations (repetitive, vibrating motions that occur in cycles), and in developing mathematical models for predicting the spread of disease. He has been recognized as an expert on the history of African Americans in science and mathematics.
Although he is now a respected researcher and educator, Ronald Mickens can remember as a child being constantly in trouble at home because of his curious, active mind for dangerous scientific experiments. This includes conducting experiments with caustic…
esiegel | August 1, 2013“We are not simply in the universe, we are part of it. We are born from it.” -Neil deGrasse Tyson
The story of the Universe is the story of us all; we all share the same cosmic history, coming from a hot, dense state some 13.8 billion years ago known as the Big Bang and emerging after billions of years of cosmic evolution to the Universe we know and love today.
Image credit: ESA and the Planck collaboration.
It's a beautiful story -- and one I've told before -- but it might seem, at least from our perspective, that something is missing from the astrophysicist's version of events. Yes, we…
drorzel | August 1, 2013The last post in this series on the core technologies of cold-atom physics dealt with optical molasses, where you use the scattering of light to exert forces on atoms to make them very, very cold. It turns out, they end up even colder than the simple theory would lead you to expect, which is very surprising, but also essential to the revolutionary impact of cold atom physics. If you were stuck with the Doppler cooling limit temperatures, laser cooling probably wouldn't be as big a deal as it is now.
You can do better, though, thanks to the interaction of several bits of physics that go beyond…
cwhyte | August 1, 2013By Angela Leroux-Lindsey
Hold out your hand: Look closely. If you're outside on a sunny day, you might see dust motes and pollen dance in the air, perhaps landing on your skin, and bright rays of sunlight peek between your fingers. To the naked eye, your skin provides a barrier between your body and these exterior elements. The light refracts around your palm, not through it.
But microscopically, the air is filled with particles that have the ability to traverse solid matter. Sunlight is actually composed of tiny “packets,” or quanta, of light called photons. Most structures built of wood or…
drorzel | July 31, 2013`Once upon a time there were three little sisters,' the Dormouse began in a great hurry; `and their names were Elsie, Lacie, and Tillie; and they lived at the bottom of a well--'
`What did they live on?' said Alice, who always took a great interest in questions of eating and drinking.
`They lived on treacle,' said the Dormouse, after thinking a minute or two.
`They couldn't have done that, you know,' Alice gently remarked; `they'd have been ill.'
`So they were,' said the Dormouse; `VERY ill.'
-- Lewis Carroll, Alice's Adventures in Wonderland, Chapter 7
As an undergrad, I did my senior…
drorzel | July 30, 2013This series of posts is intended to explain the tools and tricks used to create and manipulate samples of ultra-cold atoms; thus, it's appropriate to start with how we get those atoms in the first place. This will be a very quick background on the basic force used to make atoms cold, and then the technology of atom sources for a variety of experiments.
Okay, so you've got two things in the post title. Which are we going to talk about first? Well, the study of cold atoms really begins with the observation that light can be used to push atoms around. There are actually two ways to do that, but…
drorzel | July 30, 2013I have a small collection of recent research papers that I'd like to write up open in various browser tabs and suchlike, but many of these would benefit from having some relatively clear and compact explanations of the underlying techniques. And while I can either dig up some old posts, or Google somebody else's, it's been a while since I wrote some simple, straightforward explanations of physics techniques, so I thought it'd be fun to write up some new explanations for use in future posts. Thus, this introduction to a series of techniques commonly used in my corner of Atomic, Molecular, and…
drorzel | July 29, 2013Over at Galileo's Pendulum, Matthew Francis expresses an opinion that's sure to get him in trouble with the Inquisition and placed under house arrest: Carl Sagan's Cosmos isn't all that:
However, even taking into account the differences in TV between 1980 and 2013, the show is very slow-paced at times. I’m not talking about the mellow oh-so-1970s Vangelis score, or Sagan’s measured style of speech: I mean the obvious stretching of material to make hour-long episodes. I have a long attention span, so I’m not saying Cosmos should be like the frenetic Star Trek reboot; I’m just saying that a…
drorzel | July 26, 2013Some time back, I spent a bunch of time writing a VPython program that simulated the motion of a pendulum, which turned out to do some strange things. In the comments to that, there were two things worth mentioning: first and foremost, Arnoques at #5 spotted a small error in the code that fixes the odd behavior noted in that post-- when I corrected it, the stretch needed to keep the pendulum swinging smoothly without oscillating in and out along the string was exactly what you would expect (the "factor" plotted in that earlier post is infinitesimally smaller than 1.0-- I got bored trying to…
drorzel | July 25, 2013The other day, I made a suggestion to one of my research students of an experiment to try. When I checked back a day later, she told me it hadn't worked, and I immediately realized that what I had told her to do was very stupid. As penance, then, I'll explain the underlying physics, which coincidentally has a nice summer-y sort of application alluded to in the post title.
If you're the sort of person who enjoys swimming, and can either open your eyes underwater or regularly wear a mask or goggles, you've probably notice that the underside of the surface of a swimming pool or other body of…
drorzel | July 24, 2013I've spent a bunch of time recently blogging about baseball statistics, which you might be inclined to write off as some quirk of a sports-obsessed scientist. I was very amused, therefore, to see Inside Higher Ed and ZapperZ writing about a new AIP report on women in physics (PDF) that uses essentially the same sort of rudimentary statistical analysis to address an important question.
I say "amused" because of the coincidence in methods, not because of the content. And, in fact, the content is... not likely to make them friends in a certain quarter of the blogosphere. I actually flinched when…
drorzel | July 23, 2013I'm doing edits on the QED chapter of the book-in-progress today, and I'm struck again by the apparent randomness of the way credit gets attached to things. QED is a rich source of examples of this, but two in particular stand out, one experimental and the other theoretical.
On the experimental side, it's interesting to note that one of the two experimental effects that really galvanized the theoretical effort leading to QED bears the name of a particular person, while the other does not. Ask any physicist about the origin of QED, and they will almost certainly be able to cite the "Lamb shift…
drorzel | July 22, 2013I'm starting to think that maybe I need to add "Work-life Balance" to the tagline of this blog, given all the recent posting about such things (but then, one of the benefits of having done this blogging thing for eleven years is that I know this is just a phase, and I'll drift on to the next obsession soon). Anyway, the genre of work-life blogging generally just picked up a new must-read post from Radhika Nagpal at Scientific American: The-Awesomest-7-Year-Postdoc or: How I Learned to Stop Worrying and Love the Tenure-track-faculty-life:
I’ve enjoyed my seven years as junior faculty…
drorzel | July 20, 2013After Thursday's post about sports and statistics, a friend from my Williams days, Dave Ryan, raised an objection on Facebook:
There's an unstated assumption (I think) in your analysis: that there is some intrinsic and UNALTERABLE statistical probability of getting a hit inherent in every hitter. If that is the case, then yes -- a hitter whose mean is .274 that hits .330 in the first half should, reasonably, be expected to regress towards the "true" outcome of .274 in the second half; and if the hitter winds up batting .330, it's a statistical outlier. But that ONLY applies if the underlying…
drorzel | July 19, 2013The kids and conferences issue, discussed here a while ago has continued to spark discussion, with a Tenure She Wrote piece on how to increase gender diversity among conference speakers and a Physics Focus blog post on a mother who wound up taking her toddler to a meeting. There are some good points in both, though the Tenure She Wrote poster seems to be in a field whose conferences run on a different model than that used for most meetings I go to.
The Physics Focus post was particularly interesting to me, though, because I spent last weekend as the portable conference day-care while Kate…
catdynamics | July 18, 2013Simon White Director of Max Planck Institut für Astrophysik giving today's Physics Colloquium at ACP on the Planck Results
Likely to be interesting, hence the semi-liveblog.
Starts with description of the collaboration and historical perspective; Penzias and Wilson, COBE and WMAP
Cute ESA video showing Planck science
Even better ESA video explaining stuff
Very good description of baryon acoustic oscillations and polarization.
Quick glimpse of stacked and normalized Planck measurements of tangential/radial polarization of cold/hot spots at ~ 1 degree scales.
Nice animation blinking weak…
drorzel | July 18, 2013One of the chapters of the book-in-progress, as mentioned previously, takes the widespread use of statistics in sports as a starting point, noting that a lot of the techniques stat geeks use in sports are similar to those scientists use to share and evaluate data. The claim is that anyone who can have a halfway sensible argument about the relative merits of on-base-percentage and slugging percentage has the mental tools they need to understand some basic scientific data analysis.
I'm generally happy with the argument (if not the text-- it's still an early draft, and first drafts always suck…
esiegel | July 17, 2013"These neutrino observations are so exciting and significant that I think we're about to see the birth of an entirely new branch of astronomy: neutrino astronomy." -John Bahcall
You've been around here long enough to know about the Big Bang. The vast majority of galaxies are speeding away from us, but more than that, the farther away they are from us, the faster they appear to be receding.
Image credit: ESA/Hubble, NASA and H. Ebeling.
But it's more than that; when you look at a distant galaxy, because the speed of light is finite, you're actually looking at it in the distant past. Since…
pharyngula | July 17, 2013Thirty, almost forty, years ago when zebrafish were an up and coming model system and very few labs were working on them, we were used to going to conferences and reciting the zebrafish litany, a list of attributes that justified us working on such an oddball animal: we'd explain, for instance, that it was prolific, fast developing, and optically transparent, so we could see right into the nervous system in the living embryo. And you know, not once have I ever been asked the really simple and obvious question: if it's transparent, then how do see anything inside it?
I know. It takes a moment…
drorzel | July 16, 2013I forget who pointed me to the Tenure She Wrote piece on mentoring, but it's something I've been turning over for a couple of weeks now. Probably because I became aware of it right around the time my two summer students started work last week. It keeps colliding with other conversations as well, though, so I may as well get a thinking-out-loud post out of the whole thing.
I told my summer students even before they started, back when they were just writing proposals to do summer research with me, that I'm going to be very hands-off with the whole business. This is at least partly a matter of…