Comment by btrettel | Hacker News Reader

Comment by btrettel | Hacker News Reader

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I've noticed before that "physics" as in what is taught for a physics degree has gaps which make little sense to me as a mechanical engineer. Continuum mechanics (including both fluid and solid mechanics) is unfortunately nearly entirely absent aside from some basic things like Hooke's law and Bernoulli's principle.

In my view, what's taught for a physics degree is more of a historical accident than a selection of the most important principles. In an extraterrestrial civilization, the boundaries between engineering, physics, and chemistry may be entirely different.

Dismissing Navier-Stokes as just a consequence of Newton's laws and thus unimportant can be extended further towards dismissing a large fraction of what's taught in physics degree programs. An undergraduate physics student may get more education on Bose-Einstein condensates (which are just a consequence of quantum mechanics :-) than they do on Navier-Stokes. The Navier-Stokes equations are a lot more important than Bose-Einstein condensates in my view.

A physics undergraduate degree is different than a lot of degrees in that it's 100% incomplete for the purpose of training towards a real profession. Nobody hires physics bachelors. It's just the four year mark of your studies to be a 8+ year trained physicist.

And for that purpose of being an intermediate degree to becoming a physics PhD, Navier-Stokes isn't relevant. You don't use it in most fields that are generating physics PhDs in the 2000s and beyond.

There's only so much time to teach somebody in four years and there are significantly more important things that are also being left out (e.g. more thorough courses on group theory).

> You don't use [Navier-Stokes] in most fields that are generating physics PhDs in the 2000s and beyond.

That's because physics degrees don't include much on fluid dynamics. If someone wants to get a PhD in fluid dynamics, they probably get a PhD in some variety of engineering. This goes back to what I said about the physics curriculum seeming weird to me, as it it's not about "physics" in itself. It's more a random selection of topics that exists for historical reasons.

> There's only so much time to teach somebody in four years and there are significantly more important things that are also being left out (e.g. more thorough courses on group theory).

In another comment, you said that you don't know what the Navier-Stokes equations are. Given that, I don't think you're in a good position to judge their value.

I have a couple of group theory books myself, and I don't agree with your assessment that group theory should get priority over fluid dynamics.

> In another comment, you said that you don't know what the Navier-Stokes equations are. Given that, I don't think you're in a good position to judge their value.

It was an exaggeration given that it never came up during my studies once. And I think that's a fantastic assessment of their value that I made it through most of a decade of studies without having to know a thing about fluid dynamics.

> I have a couple of group theory books myself, and I don't agree with your assessment that group theory should get priority over fluid dynamics.

...why? You're commenting on a physics line of education here. We don't use fluid dynamics and we extensively use group theory.

You are missing my main point. Physics education tends to exclude fluid dynamics, so of course you wouldn't hear much about it or do research in it if you only have physics degrees. If a physics degree were about physics as defined in the dictionary, fluid dynamics would be more prominent. But "physics" as studied in a "physics" department is much more narrow than the dictionary definition.

Fluid phenomena is ubiquitous. You live in a fluid. You probably drive a car through a fluid and may occasionally take a plane through a fluid at higher speed. You surely use plumbing. I don't see how you can claim that fluid dynamics is not valuable given that. It's a lot more relevant to most people than quantum mechanics.

Physics education focuses on exciting areas of research. There isn't much interesting work currently taking place in fluids. We consider it a solved problem. The fact that we drive cars through fluids is completely irrelevant.

The physics curriculum prepares people to do research on stuff that is published in "physics journals". You may not think that should be the goal but it is. Doing work on Navier-Stokes lands you in a math journal on PDEs.

On a more important note, the actual topics are completely irrelevant. What's important is learning to "think like a physicist". That's what has value even for those who don't go on to do academic research, which is most students. For any given physics topic that is relevant to real-life applications, there are engineers who actually know how to use it, something that would be ridiculous to expect from the superficial treatment a physics degree has to give any one topic.

Fluid dynamics is published in physics, engineering, and math journals, even if focused specifically on Navier-Stokes.

To do fluid dynamics research in a physics department, sometimes one has to spin it in some way that people with physics degrees care about. For example, saying that it's to understand chaos theory.

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