If you care at all about (American) football, or are trying to pretend you do, you probably saw the power go out during the Superbowl this past Sunday. Half the stadium lights, the scoreboard, and the announcers’ booth, completely out of commission. Hey, did you know there are actually people talking during the game most of the time?

Anyway, one of my friends made an offhand comment about people holding their phones up like candles, but it got me thinking, XKCD-style: what kind of light could you get on a football field from cell phones? Enough to play? Or would you have to give everyone xenon lamps? To find out, we have to delve into the, um, murky world of photometry, the science of measuring the perception of light.

Let’s start with something simple. Anyone who’s familiar with a bit of physics knows about power: the amount of energy per unit time. When you characterize a light bulb as a hundred-watt bulb, for instance, that’s a measure of the power it puts out when attached to the circuitry of a standard lamp. There’s a whole hierarchy of other measurements you can make that are all …

I goofed.

I’ve been so busy I completely forgot to write a blog post about my visit to Berkeley Lab (LBL) this week! You might have noticed if you pay very close attention to my Twitter stream, but really, who does that? So instead of an announcement of the trip, here’s a wrap-up report, from the day before I leave.

My reason for being out here in the first place is the research project I’ve been working on, with my adviser and another professor, for the last several months. Since we’re making a prediction for the LHC’s proton-ion collision run, which is going on now and ends next month, we have to rush to get some results and share them out to the physics community before the LHC experiments publish their data. So the professor I’m working with, who is spending a month at Berkeley, invited me out to work on the project and give a talk about it to the nuclear theory group at the lab. (My first invited talk, yay!) The talk itself went okay, not great, but that’s really my own fault because I had to stay awake the entire …

I’m a sucker for good (or bad) physics puns. And the latest viral physics paper (arXiv preprint) allows endless opportunities for them. It’s actually about a system with a negative temperature!

Negative temperature sounds pretty cool, but I have to admit, at first I didn’t think this was that big of a deal to anyone except condensed matter physicists. Sure, it could pave the way for some neat technological applications, but that’s far in the future. The idea of negative temperature itself is old news among physicists; in fact, this isn’t even the first time negative temperatures have been produced in a lab. But maybe you’re not a physicist. Maybe you’ve never heard about negative temperature. Well, you’re in luck, because in this post I’m going to explain what negative temperature means and why this experiment is actually such a hot topic. ⌐■_■

On Temperature

To understand negative temperature, we have to go all the way back to the basics. What is temperature, anyway? Even if you’re not entirely sure of the technical definition, you certainly know it by its feel. Temperature is what distinguishes a day you can walk …

It’s been far too long since I posted anything — almost three weeks, in fact, since the end of NaBloWriMo. So I took the time to make a solid writeup of the speculation that we may be living in a computer. Consider it my Christmas present to the blogosphere. Happy holidays everyone!

Have you ever wondered if everything you know might only exist inside some hyperintelligent alien’s computer?

It’s a fun possibility to consider, that we might be living in a computer simulation, and we might even be able to figure out how to manipulate it. It even makes for some great science fiction (as well as some terrible science fiction :-P perhaps). But in reality, figuring out whether the universe is a simulation isn’t as easy as popping a red pill and waking up in an alternate reality with one less layer of abstraction. If we are in a simulation, the way it’s going to reveal itself is in the tiny details of physical processes that take place on sub-subatomic distance scales.

There is actually a branch of physics, lattice QCD, that is entirely devoted to simulating reality. Right now it only works for very …

If you’ve been watching my blog, you’ve noticed that my posting frequency has dropped off tremendously in the past week. That’s mostly because I’ve been scrambling to finish a presentation on my research. It’s now over, so in theory I have more time to make blog posts, but still I think it’s past time to call National Blog Writing Month officially over.

Let’s look back over the past 5 weeks and see how it went. Not counting this one, I managed to get in 25 blog posts, most of which were decidedly nontrivial. For fun, I decided to estimate a word count for each of these posts — now, I can’t get an exact count easily because of the formatting, including math and especially pictures, but I can just run p.text_src.split() and it spits out some rough numbers. I want to get a sense of how this compares to the task of actually writing a 50000 word novel:

• Nov 1: “National” Blog Writing Month: Take 2, 104 words
• Nov 3: Local measurements: the Rosslyn escalator, 351 words
• Nov 4: Not really a simple regularization analogy, 391 words
• Nov 6: On the …

I discovered this little trick recently while making a presentation in Beamer. Suppose I have a drawing, done in TikZ, which I want to place such that the origin of the TikZ coordinate system is at a specific absolute position on the page — in my case, 1.5cm below the center.

\begin{tikzpicture}[remember picture,overlay]
  \tikzset{shift={(current page.center)},yshift=-1.5cm}
  % the picture
\end{tikzpicture}

TikZ defines this current page node which can be used for absolute positioning. While I can’t directly say “set the origin at (point)” (at least, not as far as I know), I can say “move the origin by (vector),” and fortunately, an anchor point or any point specification in TikZ can be used as a vector. The trick to this little code snippet is that (current page.center) gives the vector from wherever the current origin is to the center of the page. So regardless of where the picture is placed on the page, applying this shift gets you to the page center. Then you can apply any additional shift needed to get wherever you need to on the page.

This trick gets around one of the few shortcomings of Beamer …

Over the past few days, the news about the LHC possibly discovering (or even confirming, in some sources!) a new kind of matter has popped up on quite a few websites — blogs, science news sites, Twitter, Google+, Reddit, elsewhere on Reddit, you name it. Of course, I was writing about this before it was cool :-) I reported the discovery of the ridge presented by CMS at the High pT LHC Physics Workshop. Back then it wasn’t clear that anyone really knew what was going on, but of course that important fact got lost in the hype.

As I posted in a more recent update, there is a lot of speculation that this ridge might have something to do with something called the color glass condensate (CGC). This is what so many sites are calling the new state of matter that the LHC has supposedly discovered. Well, I actually know something about this! Sort of. The CGC is an incredibly complex mathematical model, but it is somewhat closely related to what I work on, so I figured I could try to explain what’s going on in some more detail.

Parton distributions

All this starts with the question: what’s …