You make me suddenly, intensely curious to find out what a Reynolds number is and why it can make streamlining increase drag. I am also abruptly realising that I know less than I thought about STEM fields, given I just kind of assumed that astrophysicists were the official People Who Know About Space and therefore rocketry must be part of their domain. I don’t know whether I want to ask if you can recommend any good fluid dynamics introductions, or whether I don’t want to add to the several feet high pile of books next to my bed...
Okay—so why do you think quantum mechanics became more “cool” than fluid dynamics? Was there a time when fluid dynamics held the equivalent prestige and mystery that quantum mechanics has today? It clearly seems to be more useful, and something that you could easily become curious about just from everyday events like carrying a cup of tea upstairs and pondering how near-impossible it is not to spill a few drops if you’ve overfilled it.
The best non-mathematical introduction I have seen is Shape and Flow: The Fluid Dynamics of Drag. This book is fairly short; it has 186 pages, but each page is small and there are many pictures. It explains some basic concepts of fluid dynamics like the Reynolds number, what controls drag at low and high Reynolds numbers, why golf balls (or roughened spheres in general) have less drag than smooth spheres at high Reynolds number (this does not imply that roughening always reduces drag; it does not on streamlined bodies as is explained in the book), how drag can decrease as you increase speed in certain cases, how wind tunnels and other similar scale modeling works, etc.
Beyond that, the most popular undergraduate textbook by Munson is quite good. I’d suggest buying an old edition if you want to learn more; the newer editions do not add anything of value to an autodidact. I linked to the fifth edition, which is what I own.
I’ll offer a few possibilities about why fluids is generally seen as less attractive than QM, but I want to be clear that I think these ideas are all very tentative.
This study suggests that in an artificial music market, the popularity charts are only weakly influenced by the quality of the music. (Note that I haven’t read this beyond the abstract.) Social influence had a much stronger effect. One possible application of this idea to different fields is that QM became more attractive for social reasons, e.g., the Matthew effect is likely one reason.
The vast majority of the field of fluid mechanics is based on classical mechanics, i.e., F = m a is one of the fundamental equations used to derive the Navier-Stokes equations. Maybe because the field is largely based on classical effects, it’s seen as less interesting. This could be particularly compelling for physicists, as novelty is often valued over everything else.
I’ve also previously mentioned that fluid dynamics is more useful than quantum mechanics, so people who believe useless things are better might find QM more interesting.
There also is the related issue that a wide variety of physical science is lumped into the category “physics” at the high school level, so someone with a particular interest might get the mistaken impression that physics covers everything. I majored in mechanical engineering in college, and basically did it because my father did. My interest even when I was a teenager was fluids, but I hadn’t realized that physicists don’t study the subject in any depth. I was lucky to have picked the right major. I suppose this is a social effect of the type mentioned above.
(Also, to be clear, I don’t want to give the impression that more people do QM than fluids. I actually think the opposite is more likely to be true. I’m saying that QM is “cooler” than fluids.)
Fluid mechanics used to be “cooler” back in the late 1800s. Physicists like Rayleigh and Kelvin both made seminal contributions to the subject, but neither received their Nobel for fluids research. I recall reading that two very famous fluid dynamicists in the early 20th century, Prandtl and Taylor, were recommended for the prize in physics, but neither received it. These two made foundational contributions to physics in the broadest sense of the word. Taylor speculated the lack of Nobels for fluid mechanics was due to how the Nobel prize is rewarded. I also recall reading that there was indications that the committee found the mathematical approximations used to be distasteful even when they were very accurate. Unfortunately those approximations were necessary at the time, and even today we still use approximations, though they are different. Maybe the lack of Nobels contributes to fluids not being as “cool” today.
Ooh, yay, free knowledge and links! Thankyou, you’re awesome!
The linked study was a fun read. I was originally a bit skeptical—it feels like songs are sufficiently subjective that you’ll just like what your friends like or is ‘cool’, but what subjects you choose to study ought to be the topic of a little more research and numbers—but after further reflection the dynamics are probably the same, since often the reason you listen to a song at all is because your friend recommended it, and the reason you research a potential career in something is because your careers guidance counselor or your form tutor or someone told you to. And among people who’ve not encountered 80k hours or EA, career choice is often seen as a subjective thing. It’d be like with Asch’s conformity experiments where participants aren’t even aware that they’re conforming because it’s subconscious, except even worse because it’s subconscious and seen as subjective...
That seems like a very plausible explanation. There could easily be a kind of self-reinforcing loop, as well, like, “I didn’t learn fluid dynamics in school and there aren’t any fluid dynamics Nobel prize winners, therefore fluid dynamics isn’t very cool, therefore let’s not award it any prizes or put it into the curriculum...”
At its heart, this is starting to seem like a sanity-waterline problem like almost everything else. Decrease the amount that people irrationally go for novelty and specific prizes and “application is for peasants” type stuff, and increase the amount they go for saner things like the actual interest level and usefulness of the field, and prestige will start being allocated to fields in a more sensible way. Fluid dynamics sounds really really interesting, by the way.
Also perhaps worth noting that the effect within the LW subculture in particular may have to do with lots of LW users knowing a lot about ideas or disciplines where there are a lot of popular but wrong positions so they know how not to go astray. Throughout the Sequences, before you figure out how to do it right, you hear about how a bunch of other people have done it wrong: MWI, p-zombies, value theory, evolutionary biology, intellectual subcultures, etc. I don’t know that there are any sexy controversies in fluid mechanics.
Interesting points. There are controversies in fluid mechanics, and they are discussed at great length in the field, but I don’t know of any popular treatments of them.
In particular, there a large number of debates centering around turbulence modeling which actually are extremely relevant to modeling in general. The LES vs. RANS debate is interesting, and while in some sense LES has “won”, this does not mean that LES is entirely satisfactory. A lot of turbulence theory is also quite controversial. I recall reading a fair bit about isotropic turbulence decay in 2012 and I was surprised by the wide variety of results different theoretical and experimental approaches give. Isotropic turbulence decay, by the way, is the among easiest turbulence problems you could devise.
The debate in turbulence about the log law vs. power law is a waste of time, and should be recognized as such. Both basically give you the same result, so which you use is inconsequential. There are some differences in interpretation that I don’t think are important or even remember to be honest.
Thinking about it, things like QM are a fair bit easier to explain than turbulence. To actually explain these things in detail beyond what I’ve mentioned would take a considerable amount of time.
“I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.” (Horace Lamb)
You make me suddenly, intensely curious to find out what a Reynolds number is and why it can make streamlining increase drag. I am also abruptly realising that I know less than I thought about STEM fields, given I just kind of assumed that astrophysicists were the official People Who Know About Space and therefore rocketry must be part of their domain. I don’t know whether I want to ask if you can recommend any good fluid dynamics introductions, or whether I don’t want to add to the several feet high pile of books next to my bed...
Okay—so why do you think quantum mechanics became more “cool” than fluid dynamics? Was there a time when fluid dynamics held the equivalent prestige and mystery that quantum mechanics has today? It clearly seems to be more useful, and something that you could easily become curious about just from everyday events like carrying a cup of tea upstairs and pondering how near-impossible it is not to spill a few drops if you’ve overfilled it.
The best non-mathematical introduction I have seen is Shape and Flow: The Fluid Dynamics of Drag. This book is fairly short; it has 186 pages, but each page is small and there are many pictures. It explains some basic concepts of fluid dynamics like the Reynolds number, what controls drag at low and high Reynolds numbers, why golf balls (or roughened spheres in general) have less drag than smooth spheres at high Reynolds number (this does not imply that roughening always reduces drag; it does not on streamlined bodies as is explained in the book), how drag can decrease as you increase speed in certain cases, how wind tunnels and other similar scale modeling works, etc.
You could also watch this series of videos on drag. They were made by the same person who wrote Shape and Drag. There is also a related collection of videos on other topics in fluid dynamics.
Beyond that, the most popular undergraduate textbook by Munson is quite good. I’d suggest buying an old edition if you want to learn more; the newer editions do not add anything of value to an autodidact. I linked to the fifth edition, which is what I own.
I’ll offer a few possibilities about why fluids is generally seen as less attractive than QM, but I want to be clear that I think these ideas are all very tentative.
This study suggests that in an artificial music market, the popularity charts are only weakly influenced by the quality of the music. (Note that I haven’t read this beyond the abstract.) Social influence had a much stronger effect. One possible application of this idea to different fields is that QM became more attractive for social reasons, e.g., the Matthew effect is likely one reason.
The vast majority of the field of fluid mechanics is based on classical mechanics, i.e., F = m a is one of the fundamental equations used to derive the Navier-Stokes equations. Maybe because the field is largely based on classical effects, it’s seen as less interesting. This could be particularly compelling for physicists, as novelty is often valued over everything else.
I’ve also previously mentioned that fluid dynamics is more useful than quantum mechanics, so people who believe useless things are better might find QM more interesting.
There also is the related issue that a wide variety of physical science is lumped into the category “physics” at the high school level, so someone with a particular interest might get the mistaken impression that physics covers everything. I majored in mechanical engineering in college, and basically did it because my father did. My interest even when I was a teenager was fluids, but I hadn’t realized that physicists don’t study the subject in any depth. I was lucky to have picked the right major. I suppose this is a social effect of the type mentioned above.
(Also, to be clear, I don’t want to give the impression that more people do QM than fluids. I actually think the opposite is more likely to be true. I’m saying that QM is “cooler” than fluids.)
Fluid mechanics used to be “cooler” back in the late 1800s. Physicists like Rayleigh and Kelvin both made seminal contributions to the subject, but neither received their Nobel for fluids research. I recall reading that two very famous fluid dynamicists in the early 20th century, Prandtl and Taylor, were recommended for the prize in physics, but neither received it. These two made foundational contributions to physics in the broadest sense of the word. Taylor speculated the lack of Nobels for fluid mechanics was due to how the Nobel prize is rewarded. I also recall reading that there was indications that the committee found the mathematical approximations used to be distasteful even when they were very accurate. Unfortunately those approximations were necessary at the time, and even today we still use approximations, though they are different. Maybe the lack of Nobels contributes to fluids not being as “cool” today.
Ooh, yay, free knowledge and links! Thankyou, you’re awesome!
The linked study was a fun read. I was originally a bit skeptical—it feels like songs are sufficiently subjective that you’ll just like what your friends like or is ‘cool’, but what subjects you choose to study ought to be the topic of a little more research and numbers—but after further reflection the dynamics are probably the same, since often the reason you listen to a song at all is because your friend recommended it, and the reason you research a potential career in something is because your careers guidance counselor or your form tutor or someone told you to. And among people who’ve not encountered 80k hours or EA, career choice is often seen as a subjective thing. It’d be like with Asch’s conformity experiments where participants aren’t even aware that they’re conforming because it’s subconscious, except even worse because it’s subconscious and seen as subjective...
That seems like a very plausible explanation. There could easily be a kind of self-reinforcing loop, as well, like, “I didn’t learn fluid dynamics in school and there aren’t any fluid dynamics Nobel prize winners, therefore fluid dynamics isn’t very cool, therefore let’s not award it any prizes or put it into the curriculum...”
At its heart, this is starting to seem like a sanity-waterline problem like almost everything else. Decrease the amount that people irrationally go for novelty and specific prizes and “application is for peasants” type stuff, and increase the amount they go for saner things like the actual interest level and usefulness of the field, and prestige will start being allocated to fields in a more sensible way. Fluid dynamics sounds really really interesting, by the way.
Also perhaps worth noting that the effect within the LW subculture in particular may have to do with lots of LW users knowing a lot about ideas or disciplines where there are a lot of popular but wrong positions so they know how not to go astray. Throughout the Sequences, before you figure out how to do it right, you hear about how a bunch of other people have done it wrong: MWI, p-zombies, value theory, evolutionary biology, intellectual subcultures, etc. I don’t know that there are any sexy controversies in fluid mechanics.
Interesting points. There are controversies in fluid mechanics, and they are discussed at great length in the field, but I don’t know of any popular treatments of them.
In particular, there a large number of debates centering around turbulence modeling which actually are extremely relevant to modeling in general. The LES vs. RANS debate is interesting, and while in some sense LES has “won”, this does not mean that LES is entirely satisfactory. A lot of turbulence theory is also quite controversial. I recall reading a fair bit about isotropic turbulence decay in 2012 and I was surprised by the wide variety of results different theoretical and experimental approaches give. Isotropic turbulence decay, by the way, is the among easiest turbulence problems you could devise.
The debate in turbulence about the log law vs. power law is a waste of time, and should be recognized as such. Both basically give you the same result, so which you use is inconsequential. There are some differences in interpretation that I don’t think are important or even remember to be honest.
Thinking about it, things like QM are a fair bit easier to explain than turbulence. To actually explain these things in detail beyond what I’ve mentioned would take a considerable amount of time.
“I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.” (Horace Lamb)
(Indeed, today quantum electrodynamics makes correct predictions within one part per billion and fluid dynamics has an open million-dollar question.)