Physics Is For Eternal Five-Year-Olds

Yesterday's post about differences between intro physics and chemistry sparked an interesting discussion in comments that I didn't have time to participate in. Sigh. Anyway, a question that came up in there was why we have physicists teach intro physics courses that are primarily designed to serve other departments.

It's a good question, and in my more cynical moments, I sort of suspect it's because engineering faculty are canny enough to outsource the weeding-out of the students who can't hack it in engineering. But I think there are good reasons, particularly at a liberal arts school like Union, to have intro physics taught by physicists, because there's a fundamental difference between the way physicists approach things and the way other scientists and engineers approach them. As I said not that long ago, physics is about rules, not facts. The goal of physics is to come up with the simplest possible universal rules to describe the behavior of the universe, through breaking everything down to the most basic case imaginable. Once you've got those rules, then you build back up to more complex cases.

Completely coincidentally, I had a meeting yesterday with one of my advisees, who has recently been taking a couple of chemistry courses to fulfill our graduation requirement that students take two science courses outside the physics major. I asked him how that was going, and he said he's found it intensely frustrating, because their treatment of the systems they're studying stops at a higher level of abstraction than he would like. "I keep asking 'Yes, but why does that happen?' I think I'm annoying the other students and the professors."

This neatly mirrors a story a colleague told some years back about how he wound up in physics after going to college planning to major in chemistry. He said he kept asking the same sort of questions-- "Yes, but why do p shells contain six electrons?" Eventually, he got to the class that was supposed to explain everything, which started by just writing the Schrödinger equation on the blackboard, and declaring that its solutions provided the explanation for everything. At which point he asked "Yes, but where the hell does that equation come from?" and ended up taking physics in an effort to find out. Ironically, most physics classes don't do much to explain where the Schrödinger equation comes from, either-- I remember my undergrad quantum prof spending some time making analogies to wave and diffusion equations, but nothing approaching a derivation. He found the general approach much more congenial, though, and switched career paths as a result.

I'm not relating these simply to take Rutherfordian shots at the stamp-collecting sciences, but because I think there really is a difference in the approach, and that approach can be valuable to see. Physics is more fundamentally reductionist than most other sciences, and much more likely to abstract away inconvenient details in search of universal rules. This can make physics as frustrating for students from other fields as chemistry is for some physics students-- I got a student evaluation comment a few years back complaining that we "approximated away all the interesting stuff, like friction and air resistance." Which struck me as funny, because in my world, friction and air resistance aren't interesting-- they're mathematically messy and inelegant, and obscure the universal rules that are the real point of physics. But for somebody who wants to be the right sort of engineer, those are the interesting points.

Some time ago, I read something about science communication where a researcher mentioned the "five-year-old game." The claim was that most people, even Ph.D. scientists can easily be reduced to sputtering incoherence if you ask them to explain something and then keep asking "Why?" like a five-year-old. In some sense, then, physics students like my frustrated advisee or my ex-chemist colleague are eternally five years old, always asking "Why does that happen?" to the increasing annoyance of people who are more inclined to stop with a slightly higher level of approximation in order to accomplish some particular useful task.

I think it's useful, in a cultural sense if nothing else, for students to see both sides of that process. The engineers and chemists ought to understand the physics approach of getting to the basic, universal rules that underlie everything, and the physicists ought to get a little experience working with non-ideal cases. And the ones who find even physics too messy and approximate can go on to become math majors...


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"why we have physicists teach intro physics courses that are primarily designed to serve other departments"

Chemists feel your pain. In undergrad at a small liberal arts school, the organic classes were routinely distilled down from 80+ students to between 2 and 10 chemistry majors. This isn't even counting the numbers in the first year courses (it's typical for most students drop premed after taking intro chem, not organic).

The main reason the chemistry department exists at small schools is so that the biology department doesn't have to see hopeful premeds cry. (And yes, the point of the physics department is it's a place to send students who keep asking us chemists "Why?")

The claim was that most people, even Ph.D. scientists can easily be reduced to sputtering incoherence if you ask them to explain something and then keep asking “Why?” like a five-year-old.

Strangely enough, theorists are often the ones who get the most sputtering and incoherent with "why" questions. I'm a theorist of the scaling arguments and simulations type. I know that postulates are postulates. When I pose enough "why?" questions to some of my more abstract colleagues, they eventually get down to "Well, it's a consequence of [some symmetry]." And then you ask why that is and they say something very mathematical. And then you ask why the universe follows those rules and they think you're dumb and don't get the math. And then you eventually drill into it enough and they eventually admit they don't know.

The other fun game I play with them is to take classical physics on its own terms, and try to understand the logical foundations of something without resorting to quantum (or, in some cases, relativistic) explanations. They always want to invoke that, and my reply is always that classical physics makes the predictions that it makes, and so those predictions should be understandable as consequences of some idea or assumption embedded in classical physics. This often makes them sputter...until they concede that I've found something cute.

@andre: It isn't always chemistry professors who have to weed out the pre-meds. Pre-meds are also required to take a year of physics (though not necessarily the same course that engineers have to take). When this sequence is distinct from the traditional intro physics sequence, it is even more hated and feared among physics faculty than the traditional sequence. I had the dubious pleasure of TAing such a course as a grad student, and if I ever am involved with such a course in the future, it will be too soon. One of my students in that lab called his physics lab disk (floppy, at the time) "I Hate Physics". You are never going to reach a student like that.

Part of my objection to pre-med physics is that you are expected to teach physics without recourse to calculus, and the people who end up in such a course are likely to be afraid of algebra, too. It's a lot harder to explain physics clearly without calculus. Doing so without algebra becomes Mission Impossible. I'm also of the opinion that a person who cannot handle algebra/geometry should not be considered well-educated, but that's a different rant.

By Eric Lund (not verified) on 15 Feb 2013 #permalink

I react against some of this. Perhaps it's that "Why?" is a technique first applied by 3-year-olds. "Why?" questions can be constructive, but they too often seem cheap shots. I suppose that a TV interviewer who asked nothing more than "why?" would lose our interest. Although one is always trying to step outside formulas, I currently prefer questions like "has anyone done it differently?", "does it have to be done that way?", "what would we have to change so we could do it differently?", "can the idea be presented in a different way that might be more useful?". The literature will provide answers like "this, this, and this textbook, review article, and research paper", our own research provides others.

By Peter Morgan (not verified) on 15 Feb 2013 #permalink

But having posed the question, some responses:
- Your engineering PhD is a very distinct creature than your car-engine designing engineer. I doubt that the course would lose all of its high-level-mindedness.
--And I'd be very interested to see the sort of abstraction your theoretical engineer would give. Probably a lot of "flow" of energy and momentum.
- And even if it does (somewhat), isn't Hamiltonian/Lagrangian/Griffith's E&M the perfect place to really start hammering the very abstract mindset?
- I'd also argue that a bit more of an engineering perspective would do physicists good. It would be pretty vital for anyone going into experimental work and one could really talk about successive approximations.

Though honestly, the biggest thing I think we're missing in first year physicists is some basic numerical work, and a discussion of what a computer does and does not tell us. I'm thinking along the lines of doing some really basic ODE stuff with Mathematica. Physics, engineering, whatever: you're going to have to be facile with a computer, and the sooner you start learning that the better off you'll be.


I thought, it was three. But admittedly, that may be theorists; experimentalist may need more advanced motor skills.

@Eric Lund: Oh we chemists know the physicists help with the premeds. You also help weed out the chemists who lack any math skill. We thank all of you.

Chad: I'd be interested in knowing what sort of "why?" questions your student had that weren't addressed in a chemistry course. Normally, these boil down to questions someone would know if they studied physics (that's the wall I butt up against most). I feel most courses in modern chemistry are ones that a physicist could enjoy (unless you're talking biochem or someone teaching organic like it was the 1980s, in which case, I understand the frustration).

When I get to the "but why?" game, I quickly resort to - well, that is what we have that agrees with experimental evidence. Boom. Done.

Physics isn't about the truth, physics is about models. If the model agrees with evidence then we use it.

I remember the first time this came up. A student wanted to know how to derive Coulomb's law. I ended up showing the student our experimental set up for measuring the coulomb force. It was fun.

Why questions are easy to ask but often not very fruitful. One of the most important things to learn is to ask good questions. Be that as it may, I ended up in physics in a very similar way. I recall finding physics in high school terribly frustrating because they dumped on us a big pile of loosely related equations, not all of which evidently were necessary, and it didn't make any sense to me. Frustratingly, when I asked my teachers, they would just go in circles and explain one "law" with some other "law". I ended up trying to read textbooks that were at this point pretty much incomprehensible because all the math wasn't introduced. (The situation dramatically improved with a boyfriend who was a master's student in math ;o)). You can easily see how I ended up where I am with that initial condition...

BTW, my wife says I'm an eternal five year-old, so I guess physics is the perfect career for me.

This goes back to your earlier about no one doing classical mechanics (you said Newtonian but I'm bending) any more. You have to develop action-angle variables to derive Schrodinger's equation. And you don't do that at undergraduate level. Remember what Pope Leo (forget the number) told Anselm.

By Bruce W Fowler (not verified) on 17 Feb 2013 #permalink

Reminds me of this old amazon review:…

"Anyone who's been around children (or been a child themselves) knows about the "why?" game. It starts out with something like this: "Daddy (or Mommy), why is the sky blue?" So you explain about Rayleigh scattering and the fact that molecules in the atmosphere scatter photons with an efficiency that's inversely proportional to the fourth power of the wavelength. You are hardly finished when the next question shoots across your bow: Daddy (or Mommy) why is there an atmosphere?" So you dutifully explain planetary evolution, the expulsion of vast quantities of carbon dioxide that facilitated the evolution of life forms that exploit photosynthesis, producing oxygen, etc. Then the third question comes "Daddy (or Mommy) why do planets form?" You follow this question with a short lecture on the planetary nebular hypothesis. But the questions don't stop; they just keep coming and coming and coming. There is, it seems, never an answer that cannot be followed with "why?"