All Physics Is Not Particle Physics

A wag of my finger at the Corporate Masters, for their new article about traffic jams, with the subhead "For particle physicists who study phase transitions, a traffic jam is simply a solid made up of idling cars." In the body of the article, we find:

While the concept of critical density has been repeatedly demonstrated using computer simulations--drivers are surprisingly easy to model as a system of interacting particles--it wasn't until last year that this theory of traffic was experimentally confirmed. A team of physicists at Nagoya University wanted to see how many cars could maintain a constant speed of 19 mph around a short circular track. It turned out that the critical number was 22: Once that density was reached, tiny fluctuations started to reverberate around the track, which caused the occasional spontaneous standstill. As the scientists note, this is actually a pretty familiar scenario for particle physicists, who are used to studying phase transitions, such as the transformation of liquid water into solid ice. In this case, the critical threshold is temperature, which triggers clusters of molecules to slow down and form a crystal lattice, which then spreads to nearby molecules. A traffic jam is simply a solid made up of idling cars.

Neither of these explanations require the word "particle" in front of "physicists." While it's undoubtedly true that some particle physicists study exotic phase transitions, the vast majority of physicists working on phase transitions are not particle physicists-- they work in condensed matter physics, and statistical mechanics. Look at the author list of the Nagoya University paper-- none of the institutional affiliations are suggestive of particle physics.

There's a really deplorable trend in science journalism to discuss physics as if particle physics were the whole of physics, as if every person with a physics degree lies awake nights wondering about the Higgs Boson. In fact, particle physicists don't even constitute a plurality within physics-- condensed matter physicists outnumber them by a significant margin. Most people with physics degrees study something other than particle physics.

While it's very nice to see Seed acknowledging that there is interesting work done by physicists in other fields, turning around and calling it "particle physics" undoes whatever good was done by noting them in the first place. "Particle" is not a random intensifying adjective attached to indicate that some individual physicists are really smart. "Particle physicists" are a very specific subset of physicists, the ones whose experiments cost a billion dollars and whose theories are unmoored from petty constraints like data. Reflexively putting "particle" in front of "physicist" makes about as much sense as reflexively putting "pharmaceutical" in front of "chemist" or "disgraced" in front of "politician"-- it might cover most of the examples you run into in the news, but it's insulting to the exceptions.

(I should note that the Nagoya traffic experiment is pretty cool-- you can watch the video on YouTube, and read the New Scientist article that goes with it. It's not particle physics, though, not by any stretch.)


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Ok, I also get a little miffed when people who should know better (such as particle physicists) talk as if all physics were particle physics. But if the people from Seed come across your post, I'm afraid that they're going to feel like they did when watching arguments between the People's front of Judea and the Judean People's Front in "The Life of Brian" (also on Youtube).

Anyway, the experiment was done using "test particles" confined to travel on a large ring. That LOOKS like particle physics. And you can have charge density waves which propagate at a velocity having very little to do with the speed of the particles. It might make a joke to work into a talk about storage rings -- or about charge density waves.

By Dr. Decay (not verified) on 23 Jun 2009 #permalink

That's great that "the critical number is 22". Nevermind that they didn't say (at least not in that paragraph) how long the track was or the length of the cars . . . I guess 22 is just a magic number that wouldn't depend on any of those little things!

I agree with you, but you are not doing yourself any favors with:

""Particle physicists" are a very specific subset of physicists, the ones whose experiments cost a billion dollars and whose theories are unmoored from petty constraints like data."

It would be more accurate to say:

Non-phenomenological particle theorists, e.g. string theorists, are a very specific subset of particle physicists, the ones whose theories are unmoored from petty constraints like data. Most particle physicists, including the theorists, are busy working out what a theory that is very well-supported by data, i.e. the Standard Model, says will happen in experiments, not only at the LHC, but also in giant neutrino detectors, cosmic ray experiments, etc.

Thanks for this post, Chad. Your corporate masters (at least, the headline writers) blew this one. Dr. Decay, it's the job of people like the Seed editors to know the different branches of science and not misrepresent them, if they're going to publish a science magazine.

As a particle physicist, you had me completely agreeing with you right up to "theories are unmoored from petty constraints like data." That's a slur I take issue with - if there is a discrepancy between data and theory then the theory is probably wrong (e.g. neutrino oscillations) but one needs data first.

By Steve Boyd (not verified) on 23 Jun 2009 #permalink

I agree with you, but you are not doing yourself any favors with:

""Particle physicists" are a very specific subset of physicists, the ones whose experiments cost a billion dollars and whose theories are unmoored from petty constraints like data."

Yeah, that's probably gratuitously snarky. I liked the line, though.

...particularly if those "exceptions" aren't really exceptions at all if you look at the bigger picture!

It's unfortunate that the word "particle" does immediately imply "particle physics". The scope for confusion with quantum mechanical particles and the n-particle simulations used in other branches of physics is pretty high. It would seem to be an area that journalists should take particular care over, given that they're the medium that the general public tends to get most information from.

Incidentally, that traffic simulation is much more like astrophysics than particle physics. The motion of the cars is quite reminiscent of the motion of stars in galactic spiral arms...

Did you know that the German word for "particle " as in particle physics is also used to denote yummy Danish pastries? Gratuitous, I know. BIL is a particle physicist, so it's a popular joke chez Perceval.

Hi Chad,

just coming back from sharing a beer with Jason Slaunwhite.... Thought it was cool to let you know we have a common acquaintance. We are both at CERN, where physics is a synonym of particle physics :)


Yeah. As a grad student in neutrino physics I definitely take offense at being compared to a string theorist or a supersymmetry theorist. You should not mock SEED for grouping all physicists together and then go and group all particle physicists together :(

Chad can be excused for lumping "particle physicists" together; after all, taken together they make up a small fraction of the half of the APS that doesn't go to the national "March meeting". Big enough to be noticed, but not even a majority of that sub-group of the society.

To me, a member of a similarly sized small fraction of that other half, the centennial meeting of the APS was an eye-opener. That was the first time in ages that both halves of the society were at the same meeting.

Actually, I think I'm exaggerating when I say half. Back when it was in print form, the March meeting abstracts dwarfed the April meeting abstracts.