Everybody and their siblings have been linking to this Minute Physics video, an “open letter” to President Obama complaining about the way that most high school and even intro college physics classes don’t teach anything remotely modern:
I’m not entirely sure where the date of 1865 comes from, but it’s true, the standard intro physics sequence doesn’t really touch what’s normally called “modern physics,” a term which is itself laughably out of date, as it generally refers to special relativity and quantum mechanics as it stood around 1935. We don’t teach really new stuff until about the 300 level in college courses (junior/senior year for students on the normal track), with the possible exception of hand-wavey non-majors courses.
So, why is that, anyway? Are physics teachers and professors just totally oblivious to how backwards and out-of date their curriculum is? No, of course not, especially at the college level. We’re acutely aware that what we teach is mostly old physics– it would be difficult not to notice that we’re not teaching anything remotely related to the research we do (in most cases). We’re pretty much stuck teaching the material that we do, though, because of constraints that are external to physics departments.
A factoid that I picked up at an AAPT workshop about ten years ago is that only about 3% of students taking introductory college physics ever take another physics course. Now, some of that is attributable to the fact that intro courses are often dry and boring, and we should absolutely fix that. But that tiny retention rate is in large part because the students who are taking intro physics are only taking it because it’s required for some other major. At Union, where I teach, we teach close to 140 students intro Newtonian physics every year, the vast majority of whom intend to major in engineering, with a smattering of chemists and mathematicians mixed in. While the class serves as the entry point to the physics major, in academic parlance it’s really a “service” course– something we’re doing for another department. The next biggest chunk of our enrollments, 70-ish students per year, is the Physics for Life Sciences course, which most of the pre-med students take to prepare for the Physics section of the MCAT.
The fact that these courses are service courses first and foremost constrains what we can teach. And much as we might wish it were otherwise, the engineering and chemistry departments don’t particular want us to teach the cool modern stuff. They want us to teach old physics from 1865, because that serves as the foundation for some of their courses. We have to teach classical mechanics first because that’s what the departments that provide most of our students want us to teach.
High school physics ends up covering the same basic material as intro college physics for the same reason that high school biology and chemistry resemble introductory college biology and chemistry– because that’s what high school classes do. They offer classes that cover the most basic stuff for those who will never take another science class, and provide a foundation for those who go on to take another course in college.
Why do chemistry and biology teach more modern material than physics does? Because chemistry and biology as sciences developed more recently than physics did. Lord Rutherford’s division of science into Physics and Stamp Collecting was snide, but not without some truth in 1900 or so when he said it. The existence of atoms as real physical things wasn’t definitively settled until the early 20th century, and a solid understanding of how and why atoms combine into molecules the way they do didn’t come along until quantum mechanics was worked out in the 1930’s. The theory of evolution, without which nothing in biology makes any sense, wasn’t put forth until the 1850’s, and most of the biochemistry of life wasn’t figured out until the 20th century. Chemistry and biology classes don’t spend a whole lot of time on chemistry and biology from before 1865 because most of what was known about those subjects before 1865 has been superseded or cast into a completely different light by more recent discoveries.
Physics before 1865, on the other hand, had accomplished a hell of a lot that’s still useful today. The basic laws of mechanics date from the late 1600’s, and still work brilliantly for describing the motion of macroscopic objects moving at everyday speeds. Maxwell’s equations, which might be the source of the 1865 date, provide a complete and correct description of classical electromagnetism, full stop. They’re even compatible with relativity– in fact, relativity grew out of attempts to reconcile Maxwell’s equations with the rest of physics. Classical thermodynamics, the laws of which are another possible source of the 1865 date, works extremely well for describing the flow of heat in macroscopic systems (and, in fact, thermodynamics probably accounts for most of the pre-1865 material taught in chemistry classes).
We spend a lot of time teaching students about physics from before 1865 because physics from before 1865 is pretty damn useful. It’s the same reason why the Math department spends most of their time teaching students about math that was developed before 1865 (differential and integral calculus, Euclidian geometry, trigonometry)– because “old” math is still extremely useful. Blaming math and physics for their early success is kind of ridiculous, given that the stuff works. It’s also an essential foundation for the cool modern stuff– it’s almost impossible to really understand quantum physics without first knowing a good deal about classical physics.
Yes, but what about Carl Sagan and Neil DeGrasse Tyson and Richard Feynman? Look, I love what they do, but Sagan and Tyson aren’t even in the same business as most people teaching physics. Feynman’s the only one of those three who attempts to teach people how to solve problems. As my angry quantum prof in grad school put it, though, while reading the Feynman Lectures may make you feel like you understand everything, “when you try to solve a problem, you realize that, well, that you’re not Feynman.”
Sagan and Tyson, and Feynman to a large extent, are popularizers, not educators. Their job is to get people fired up about science in a more general way, not to teach them how to do anything with their knowledge. Those are very different businesses– believe me, I know, having written two popular books about cool modern physics. And while I made every effort to ensure that How to Teach Physics to Your Dog and How to teach Relativity to Your Dog are rigorous and correct (to the point of probably limiting their sales…), I wouldn’t begin to claim that they teach people how to do physics. If you want to know that, you need to take actual physics classes at the college level, and you need to start with classical mechanics and E&M.
Finally, as much as I love modern physics, I have a problem with the suggestion that “old” physics is intrinsically boring. True, Newton’s Laws don’t fire the imagination the way Schrödinger’s Cat does, but that doesn’t mean you can’t do cool things with classical physics. If you don’t think classical physics can be cool, you’re clearly not reading enough Dot Physics. Rhett’s blog is one of the most consistently awesome things on the Internet, and he almost never talks about physics developed after 1865.
This is where there’s a glimmer of hope regarding the complaints in the video. The problem isn’t that old physics is intrinsically boring, but that the traditional way of teaching physics is kind of dull. But if you look at the stuff that Rhett, and Frank Noschese, and John Burk, and Kelly O’Shea, and the whole Global Physics Department crowd are doing, you’ll see that there’s a lot of room to teach “old” physics in new ways that make it much more interesting and appealing, while still satisfying our obligations to other programs and departments.
Of course, there’s another way to look at this, too, which is to try to do cool things with modern physics on a conceptual level even earlier– the whole Physics First approach to high school science. That’s a cool idea, and I’d be happy to see it pushed more strongly because I think it has a lot of potential. As it is, though, it runs up against a lot of entrenched interests, so I don’t give it great odds.
But anyway, if you’re wondering why it is that we teach all this old stuff in physics classes, those are my slightly rant-y thoughts about why. It’s not because we haven’t thought about it, believe me.