Author Archives: David Guarrera


Coffee is very important for grad students.

Circuits by Analogy

Some not so useful useful but cool sounding and true analogies I have used during my office hours while teaching undergrads about circuits:

Charging a capacitor is like falling out of an airplane.

“Charging” an inductor is like a bunch of uranium decaying.

A circuit with an inductor and a capacitor is like a pendulum.

A circuit with an inductor, capacitor, and resistor is like a pendulum in oil.

A circuit with an inductor, capacitor, resistor and AC power source is like pushing a kid on a swing.


Instant Anger Relief

No physics today, just the incredibly adorable and surprisingly watchable puppycam

Instant stress/anger relief.

Compactification in String Theory Part I: Motivation

A new attempt to reinvigorate the blog!

Yes, I am aware that I already have two physics related threads that have started and ended at “Part I” (false vacua and string theory). However, I’m really motivated by the introductory explanations. I promise to come back and finish the other ones real soon. But for a while, I’d like to talk about compactification.

A word about the word…I’ve had at least two scientist friends laugh when I’ve said “compactification”. Also, the text editor I’m typing this in thinks its a misspelling. Apparently in all other science fields, the correct word for taking big things and making them small is “compaction”. 

Well, we string theorists are just a little bit cooler then you “real scientists.”  We’re not taking some obsidian and making it smaller (like my roommate, the geologist, and one of the laughers), we’re making goddamned extra dimensions smaller. You read right, the extra dimensions.

For casual, non-specialist readers (if there are any left) the first few posts will be an introduction–an attempt to explain WHY we need to “make the dimensions smaller,” what that means, and why its so hard. I hope to follow up much later with more technical issues and a few comments of my own very small research in this subject. At the very least, you will be able to read pretentious, unfunny Woody Allen short stories and chuckle with smugness.

Ok, so let’s get on with it.

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What is String Theory Good For (Part I)?

This is, I guess, my foray into the bloggy string wars (or the stringy blog wars?). But not really. I just want to give you some of my brief perspectives on why string theory is kind of a big deal. This will possibly precipitate screaming and gnashing of teeth in the comments section, but whatever. It is not my intention to get into some sort of flamewar (or whatever the kids are calling it nowadays) so I probably won’t respond to any comments.

A short list of what you might think string theory is good for.

1. Nothing–unlike a lot of my colleagues, I think this is a perfectly reasonable perspective. In fact, if you had this perspective about all of particle physics, I think it also would be perfectly reasonable. In short, what we do benefits absolutely nobody. We should all probably be using our brains to search for a cancer cure.

However, I find to stomach arguments that other completely useless things–like calculating the QCD beta function to n loops, or calculating the homotopy groups of spheres is somehow more worthy. Usefulness is not why most people engage in many areas of math and physics. 

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I was told on friday that Sidney Coleman’s famous Quantum Field Theory course was actually videotaped in the 70’s and now exists online, and it’s true ! It’s kind of awesome, but also a little bit depressing, like when someone gives you the most recent season of the Wire on DVD–you know you have to now devote a huge amount of time to it (75 hours of QFT!). I just watched the first lecture, and the man is compelling, even when talking about sign conventions! The video doesn’t pick up the board real well (I remember a while back, there were some written circulating notes from this course, does anybody know where I can get them?). I haven’t felt so learned in black in white since that one summer when I stumbled upon the oddly magnetic Bishop Fulton J. Sheen on public television (for the good bishop on the subject of temptation, see here . I love his blackboard work!). A few comments about the Coleman videos:

1. Man, the 70’s looked like they sucked. Glad I didn’t live through them.

2. Sidney Coleman is a nerd’s nerd right from his Wallace Shawn voice to Urkel-esque laugh.

3. He’s also kind of a badass. Throughout this first class, I think he must smoke about twenty cigarettes. He also gets obvious glee from twisting his moustache at several points. And there’s nothing not awesome about that.


LHC Fever! (And more bad science journalism)

The LHC has turned on! W00t! Last night a few of us had an LHC “party” where we stayed up until 3 am to watch the webcast of the machine turning on. Of course, the webcast didn’t work, and we all just went home and today I’ve been exhausted and gotten no work done. 

I’ve been impressed by the media coverage of the LHC; with a few exceptions. Once again James Owen Weatherall has graced the pages of Slate with his dubious writings on particle physics. His articles continue to baffle me. In his  most recent one,  the main points seem to be:

1. The discovery of the Higgs is bad for particle physics because then the standard model would be complete, and there would be nothing else.

This was the subject of his first article which came out last year here, and which I tried to refute  here. Let’s reiterate: no. Everyone (at least, everyone who knows what they’re talking about) expects some new TeV physics besides the Higgs. There are all sorts of indications that this should be the case, from cosmological constraints on dark matter, to suggestions from the hierarchy problem.

2. Even so, there’s no reason to expect us to find the Higgs. Glashow, Weinberg and Salam included it as the simplest way to induce electroweak symmetry breaking (ok, he doesn’t quite put it this way), but there are many other possibilities. 

Well, sort of. There are many other ways of inducing electroweak symmetry breaking (a higgs sector, little higgs, technicolor, etc), but my understanding is that precision electroweak constraints can rule out a lot of these models (for example, I think technicolor is mostly considered ruled out), and that plain old vanilla Higgs still looks like the best bet. Anyway, it doesn’t matter, it’s not really the point. When physicist say the “Higgs” what they really mean is “the Higgs, or something very much like it” (a higgs sector, little higgs, technicolor, etc, i.e. a particle or particles responsible for electroweak symmetry breaking). 

Again, Mr. Weatherall might have cleared up his numerous misunderstandings had he talked to any actual physicists (Glashow, Weinberg, Salam, Higgs seem like good possibilities, since he’s talking about them all over the article). In what sense is this man qualified to write articles about particle physics?!

I leave you with an  article  about what some actual physicists think the LHC will find.

Mazel Tov!

Let’s not let this blog die, posters!

It’s my pleasure to congratulate co-blogger, Dr. Bonna Newman, who successfully defended last week. Congrats Bonna! 

I think one of the Homer’s is up next.

Podcast Self Promotion!

Sorry for the long time since last post. Today I have a shortish lunch talk to all types of physics graduate students. The talk was titled “Physics at Strong Coupling: Why String Theory and Supersymmetry are Ridiculously Cool, Part I,” with future parts to follow in the coming years. The talk went ok, I hope I convinced some graduate students that string theorists are not completely crazy.

But maybe now I can convince you! A friend helped me make the talk a podcast, with audio track and all. You can subscribe to it (and future, podcasts, I guess) here. Hitting “subscribe” on that page imports it into your i-tunes. Let me know if you enjoyed it! I guess, also let me know if you did not enjoy it…

Quantum Mechanics in Your Face

If, today, you feel as if you should be doing work, but don’t really want to do any, may I suggest a video of a Sidney Coleman Lecture: Quantum Mechanics in Your Face? You’ll learn and be entertained.

The lecture is fantastic and consists of the late, great Coleman discussing a version of Bell’s theorem (which is much easier to understand than the standard treatment), and then going on to discuss the “mysterious” “collapse of the wavefunction”. It’s great stuff. All that’s required for enjoyment is a basic undergrad QM course…