Comment by perlgeek
14 years ago
He's so totally right about the hand waving approximations used in solid state physics.
All fields of physics need to use some approximations, but those in the solid state were usually the ones with the worst reasons, just things like "it works if we do that" or even "it doesn't if we don't do this".
It went on like that in three courses (two on solid state physics, one on electronics).
Only after that did I happen to come across a decent book which explained some of the approximations in a way that didn't make me cringe, and some of the stuff started to make sense in retrospect. Others are still a mystery to me, and probably always will be.
If anyone needs a refresher in semiconductor physics, there's a good one at this Britney Spears site: http://britneyspears.ac/
edit: how the heck does a link to an excellent introduction to semiconductor physics get voted down in a thread about an article relating to semiconductor physics?
You're getting voted down because most people see the domain "britneyspears.ac" and assume you're spamming, without even visiting the link.
That site actually does have some decent articles related to semiconductor physics, the whole "Britney Spears" thing is just a gag to show how simple they've made it (though the humor is likely to be appreciated only by Physics geeks :)
This is a good joke, but too subtle for most of the people who moderate on HN.
My advice if you care about that sort of thing: link in further, e.g., http://britneyspears.ac/lasers.htm
Sweet jesus, it's true! http://britneyspears.ac/physics/vcsels/vcsels.htm
While there does appear to be some physics articles on the site, the whole thing appears to be cloaking itself in legitimacy as a scheme to get inbound links and drive up its page rank score. Their strategy is likely to get people linking for the physics so that they can sell links for heating oil prices, concert tickets, physics help, and so on. It's more about the advertising than the physics.
I'm sure there's a less spammy physics site you could have linked to?
On the contrary, the page is a piece of internet history. As you can see from the domain, it was created by an academic in an early example of titlebait.
http://replay.web.archive.org/20001002213854/http://www.brit...
Its basically a reverse rickroll. "Britney Spears" was by far the most searched-for term on the internet for a long time.
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It's often poorly explained, I completely agree, but people forget that even Planck introduced his constant just because it made the data fit. It turned out to be arguably the most fundamentally important constant (along with its reduced form) in all of physics.
Aren't all fundamental physical constants like that - they are essentially meaningless values plugged into theories to make them align with observations?
Mostly because we (humans) made up physical units (i.e. meters) while we were inventing physics. There's nothing keeping you from re-deriving physics equations without the messy constants.
http://en.wikipedia.org/wiki/Natural_units
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yeahbut, some are interrelated. Like the speed of light and the permittivity of freespace (1/c^2 * mu). If you measure that constant and solve back for c, then you better get ~3 * 10^8 m/s.
That's what they look like at present, but it's possible that future theories will allow us to calculate their values from first principles.
Do you remember the title or author of that book?
I don't necessarily know what book he's referring to, but the book that taught me solid state was Ashcroft and Mermin.
That's a book that deliberately starts out with the silliest possible model and then gradually introduces more and more sophisticated models until the book runs out of pages or your head explodes, whichever comes first. ;)
An important insight, however, is that the simple models are incredibly useful. When I was a teenager I used to fret that the teachers were showing me the simple models first because they were fools, or because they thought we were fools. But it turns out that they are doing so to call attention to certain important general features without distracting you with irrelevant detail.
My favorite class in all of science was Roald Hoffman's chemistry class, the highest numbered class in the Cornell chemistry department, a class which represented the point where chemistry and physics merge to become the same subject. And Hoffman deliberately used a relatively simple model of molecule-molecule interactions in a solid, the Hückel model:
http://en.wikipedia.org/wiki/Hückel_method
Moreover, Hoffman would communicate in pictures as much as in math.
Have you ever read Feynman's Lectures on Physics Volume 2 (Electricity and Magnetism)? One of the things I love about it is that it starts with Maxwell's equations, in their non-simplified form, then goes into the special cases of electrostatics, magnetostatics, and then uniting them into electrodynamics. Feynman goes over the special cases in a way that you never forget that they're in the end incorrect simplifications, there's even a table at the end of the statics section showing "These equations are false, these are true in general."
I don't mind simplified incorrect models so long as they're presented that way (so I don't want to read a "all that stuff we just covered? Yeah it's wrong"-ish sentence after the fact) and the full truth is eventually revealed in an understandable way. I want a full picture of something, not a partial incorrect picture of something, it scares me that some people never stop thinking of an atom as a small planetary system.
Amen to Ashcroft & Mermin. I found it much easier to use over Kittels solid state text. Or, more accurately, Shittels solid state physics
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"Electronic Transport in Mesoscopic Systems" by Supriyo Datta.
It's a very specific book, but it does explain for example why you can assume that only electrons at the Fermi energy contribute to transport phenomena (aka "current").
I guess for somebody not into mesoscopic transport, only the first three or four chapters will be of interested. But for my diploma thesis (which ended too badly to link it here) it was a real live safer.