What is the most direct way I can learn all about quantum physics?

November 29, 2006 6:22 AM

What is the most direct way I can learn all about quantum physics?

I've read a couple of general books like The Tao of Physics, but I'd like to have a more thorough understanding than this. I was quite handy with maths and physics in school, but it's been a while since then. I'm not in any hurry, so I'm willing to do the learning over a period of time.

posted by MetaMonkey to science & nature (34 comments total)

MIT has many open courses, including a boatload of quantum physics from undergrad to graduate level.
posted by backseatpilot at 6:39 AM on November 29, 2006

The Feyman Lectures on Physics comes to mind.
posted by kableh at 6:40 AM on November 29, 2006

"The Elegant Universe" by Brian Greene will get you as far as your maths can take you.

"A Brief History of Time" by Stephen Hawking.

"Understanding Physics" by Asimov helped me understand the experiments that led Einstein to the theory of Relativity.

"e=mc²" by David Bodanis takes a run at the famous equation.
posted by mzurer at 6:48 AM on November 29, 2006

Seconding Feynman, maybe Six Easy Pieces?
posted by ontic at 7:22 AM on November 29, 2006

The Feynman lectures are very, very good -- probably the best book-length treatment you'll find. But they're fairly advanced. You'd have to be pretty comfortable with math and underlying physics ideas to understand them. You might start there.

OCW is a good source: the intro quantum class, 8.04, is pretty good. I particularly recommend Prof. Chakrabarty, but his notes are not yet up on the OCW site. The course notes will necessarily be abbreviated, though; I'm not convinced one can really learn from them.
posted by raf at 7:23 AM on November 29, 2006

Note that none of the books recommended by mzurer are about quantum physics; they're mostly about relativity.
posted by raf at 7:24 AM on November 29, 2006

I really enjoyed Schroedinger's Kittens, which, after a thought experiment riffing off of the classic cat one, goes into a nicely detailed history of physics leading all the way up to modern day quantum physics-- a gret way to lay down some track for the more technical learning you want to do.
posted by hermitosis at 7:34 AM on November 29, 2006

I'm listening to the class Physics for Future Presidents offered by Berkeley. All of the lectures are available online via streaming video, streaming audio, or downloadable MP3 (it's even on iTunes as a podcast!). Also, the full course textbook is available online. Chapter 10 of the text is about quantum physics, and the lectures from November 7th to November 14th covered that topic.

When you say you were good at math and physics in school, you don't specify whether you're talking about high school or university classes. The course described above is an entry-level university course, with a focus on conceptual understanding rather than math and equations.
posted by gwenzel at 7:40 AM on November 29, 2006

I may be misreading the questioner's intent, but all the books I mentioned delve into various phenomena of quantum physics.
posted by mzurer at 7:49 AM on November 29, 2006

I don't want to sound like a wet blanket, but to grasp QM to any degree beyond platitudes, you're gonna have to do some serious work. You'll need to be competent in linear algebra and several variable calculus at least. Then, or concurrently, you'll have to learn about classical linear wave theory, and finally second order linear differential equations (you could add the standard methods of classical mechanics, like Lagrangian and Hamiltonian mechanics, if you were motivated). Once you've got a good grasp of these, you can work through various problems such as (in order from most to least basic, and you can google these):

• Particle in a box
• harmonic oscillator
• hydrogen atom
• 2 particles on a ring

Then, once you understand these, read about the Copenhagen Interpretation and the Measurement Problem (wherein you'll find Schrödinger's eponymous cat). If you're not exhausted by this point, continue to the Dirac equation, and possibly the Standard model.

I know this sounds daunting, but it's really the only way to get an understanding of the subject. People can write book after book with tortured metaphor after tortured metaphor, but at its base QM is fundamentally vertical and irreducibly mathematical - there really is no way of getting around it. Popular physics writing is really in the same genre as powerpoint displays - their function is fundamentally limited by their form, and they leave you with false sense of understanding.

On the positive side though, QM is, if you're motivated to work at it, maybe the most beautiful and puzzling thing you're likely to encounter in science, second perhaps only to evolution by natural selection in its elegance.
posted by claudius at 8:27 AM on November 29, 2006

These are all good answers so far, thanks all.

Just to clear up a couple of questions: I am also interested in learning about relativity (probably should have mentioned that in the question). I haven't done maths or physics at undergrad level, just high school.

I'm still a bit uncertain about getting a solid foundation - something to bridge the gap between conceptual stuff and advanced stuff. Perhaps theres some areas of math I should focus on at first?

On preview, claudius' answer is great. Thats the sort of rigorous understanding I'd like to work towards, even if it takes time. Also, the knowledge progression, starting with calculus is exactly what I'm looking for, to help me start at the start and build from there (rather than being discouraged by trying to learn beyond my means).
posted by MetaMonkey at 8:38 AM on November 29, 2006

what claudius said.

I've taught QM a few times, and I always have one or two liberal arts majors who saw 'What the *$ do we know' or read the Tao of Physics and want to learn more. A few of them even stuck it out.

BTW, best intro textbook: Quantum Chemistry by McQuarrie. For some reason the physics QM books I've seen go almost out of their way to avoid using any real world examples of anything.
posted by overhauser at 8:40 AM on November 29, 2006

As someone with a Bachelor's in physics, I can only relate an old saw that the number of people who truly understand it could comfortably fit in a bus, and I still don't have fare. It's a framework that one can operate in, but will constantly surprise you with weirdness. It often runs counter to "common sense," said common sense being the experience of humans - medium energy, low velocity, macro scale objects.

Claudius is right. If you want to get beyond hippie physics and handwaving, you must understand the math. I would recommend a little statistics, aside from what claudius already mentioned.
posted by adipocere at 8:40 AM on November 29, 2006

Seconding claudius.

I probably sound like a broken record on ask.mefi but none of the descriptive books will give you an understanding of quantum physics. They will just familiarize you with someone else's interpretation. This is true of the Greene and Hawking books for example.

The only way to learn QM is to study it and do the math. This means textbooks. You need to work throught them and play with the Shrodinger wave equation and Heisenberg bra-ket notation and Pauli spin matrices and all that good stuff.

The online courses mentioned above look pretty good. But a real understanding of QM presupposes an understanding of classical mechanics, electromagnetism and special relativity.

There's quite a few people here on mefi who have actually studied QM and its frightfully easy to tell them apart from people who have only read about QM.
posted by vacapinta at 9:01 AM on November 29, 2006

Good answer, vacapinta. The point that it is necessary to learn the foundations properly is well taken, but I'd still like to get a better idea of how to begin and what path to follow. Perhaps an undergrad physics course would be an appropriate model to follow?
posted by MetaMonkey at 9:08 AM on November 29, 2006

Jesus, I forgot to mention complex analysis. You absolutely have to be competent with complex numbers and functions of complex variables. You could in principle do all the maths I suggested above and manage to avoid them. Not so with the physics.
posted by claudius at 9:12 AM on November 29, 2006

On non-preview: yeah, I think the best path would be to find an undergrad physics syllabus and trim the fat a little. No chem unless you're really interested, and you could ignore all the solid state physics. First year statistics would probably be sufficient - you can ignore all statistics second year and above.

Or, you could do is find the entry for the final year QM course and work back from there, doing the prerequisities of prerequisites of prerequisites first, then the prerequisites of prerequisites, then...
posted by claudius at 9:18 AM on November 29, 2006

As everyone else has said, you need to work through the math to really understand quantum. I'd read a bunch of the books suggested above prior to taking quantum, and although I could talk about Schroedinger's Cat and so on, it didn't really make any sense. However, once you get a chance to really study it - math and all - it is incredibly cool [if still very unintuitive, at least for me.]

I used McQuarrie's quantum textbook and found it very clear, but you'll need a solid mathematical base to understand it. If I were you, I'd start with the math: start with single-variable calculus [review your basic knowledge about functions, trigonometry, algebra as necessary], and work your way up through multivariable calculus. You can get through McQuarrie without knowing much about differential equations or linear algebra [although knowing the basics will _certainly_ help], but you'll need multivariable calculus to make sense of even the more basic quantum stuff. Once you feel somewhat comfortable with calculus, you can start using McQuarrie [or another introductory book] to work your way through the sorts of problems that claudius mentions. [Most'll be covered in any basic text].

Note that 5.61, (the intro quantum class taught by MIT's chemistry dept and made available on OCW) uses McQuarrie; if you choose to use that as an introductory text, you'll probably find 5.61 more useful than 8.04, which uses a different pair of textbooks. My apologies for not having recommendations for math textbooks - I haven't been particularly happy with any of the ones I've used. Either way, you should pick up actual textbooks - it won't be possible to gain a real understanding of the material just from coursenotes. [Oh, just realized you said you haven't had college-level physics, either. Again, I disliked my basic physics textbooks, so I don't have good recommendations, but you should really work through basic classical mechanics and E&M before tackling quantum.]
posted by ubersturm at 9:23 AM on November 29, 2006

Just to clear up a couple of questions: I am also interested in learning about relativity (probably should have mentioned that in the question). I haven't done maths or physics at undergrad level, just high school.

Do you want to learn about special relativity or general relativity? For the former, you don't need much more than high-school algebra; a small amount of calculus is required for the more advanced stuff, but you can get a very good grasp on the subject without needing to differentiate or integrate. The best book on Special Relativity that I know of is A Traveler's Guide to Spacetime by Thomas A. Moore.

General relativity is a little trickier; there's a lot of complicated math that you need to understand what's going on with it. You would definitely need some college-level calculus (single- and multi-variable) to get a full grip on it. If you're truly interested in knowing the mathematics behind it, you might try looking up Gravity by James Hartle; it's got an interesting "physics-first" approach, in which he describes the structure of spacetimes, and how physics works in them, without (at first) telling you why they're actually valid. Only in the later chapters of the book does he "lift up the hood" and show you all the mathematical machinery required to derive these spacetimes.
posted by Johnny Assay at 10:04 AM on November 29, 2006

Albert Einstein's Theory of Relativity In Words of Four Letters or Less.
posted by weapons-grade pandemonium at 10:05 AM on November 29, 2006

I also wasn't too happy with the quantum books I used in college and so can't recommend any at this point (I am no fan of Sakurai, for example)

I can recommend an excellent book on Special Relativity: SpaceTime Physics.
posted by vacapinta at 10:58 AM on November 29, 2006

claudius: "...and you could ignore all the solid state physics...."

I agree with everything else you said, claudius, but I think it's a mistake to ignore the solid state physics if you want to actually understand why QM matters. Learning about particle in a box but never learning about a quantum well strikes me as a big mistake. I would say that understanding materials and device physics are where QM are really most directly understandable. But then, I'm clearly biased.

To further answer the questions, a textbook which I like is "Molecular Quantum Mechanics" by Atkins and Friedman. While it isn't one of the standard texts, I think it does a nice job of combining rigor with examples.
posted by JMOZ at 11:25 AM on November 29, 2006

JMOZ: heh, I just checked your profile, and I can see why you'd disagree;-). The feeling I got from the poster (and his current FPP is that he wants to understand all the brouhaha about the various interpretations. For that I'd have guessed that straight single and maybe double particle situations were what he wanted.

I see your point though - solid state examples of tunelling, square wells etc would give a sense of reality to the maths.

On the subject of (more or less) concrete examples, I think, for a student with good maths and no physics, that Quantum Computation is the distilled essence of all that's cool about QM.
posted by claudius at 11:53 AM on November 29, 2006

Having taken both 5.61 (the chemistry version) and 8.04 (the physics version), and having been a chemistry major, I would recommend 8.04 instead of 5.61. 5.61 goes too quickly into approximations and chemical models and applications. 8.04 is much more about learning the fundamental physics.

Having said that, the McQuarrie book is great.
posted by raf at 12:17 PM on November 29, 2006

[A note about my McQuarrie recommendation: it is written from a chemistry perspective. This might actually be easier for you, in some ways - it doesn't assume you've got a physics major's background, so there's a little more review in-text. Anyways, it's a straightforward and clearly-written introduction to the topic. I only took 5.61 {and not 8.04}, so I may be somewhat biased.]
posted by ubersturm at 2:18 PM on November 29, 2006

I learned quantum physics from this textbook. I'd suggest you check it out from a library before plunking down $100+. You still have to understand the math, but this is one of the most verbose texts on the subject I've seen, and it covers a lot of material.
posted by Wet Spot at 5:22 PM on November 29, 2006

I ditto the McQuarrie QM book, but it's not a starter text. You'll want at least second-year calculus to make a run at it. The second book of the Feynmann lecutres is also good, but it was written in the fifties.

The book I usually recommend when asked about this is Sudbery's "Quantum Mechanics and the Particles of Nature: An Outline for Mathematicians". It's a bit dated on the particles side now (written in the mid eighties), but the QM bits are a good now as ever. For all the title, it requires more formalism than math. Philosophy students seem to like it in particular.

My favourite texts for QM though are Messiah's "Quantum Mechanics", which, like any classic, is accessible with some effort, and Sakurai's "Modern Quantum Mechanics", which.. isn't.
posted by bonehead at 6:22 PM on November 29, 2006

(A final note: I prefer the Ira Levine's "Quantum Chemistry" to McQuarrie, particularly as a chemist, but they're both good books.)
posted by bonehead at 6:26 PM on November 29, 2006

I know this will sound strange: The Cartoon Guide to Physics, by Larry Gonick. The last section of it is about relativity and quantum mechanics, and it's really amazingly good. I learned a lot from it.
posted by Steven C. Den Beste at 7:33 PM on November 29, 2006

My great thanks to all contributors for the range of useful answers, just what I was hoping for. Now all that remains is years of studious work.
posted by MetaMonkey at 12:48 AM on November 30, 2006

Oh, I've marked as best those answers that seem to get into the practicalities of the learning process, rather than some of the helpful book/course suggestions. I was tempted to mark almost all the answers, as they're all useful (especially cumulatively), but that seemed silly. My appreciation once again to all answerers in this thread, great stuff! AskMe shines again.
posted by MetaMonkey at 1:04 AM on November 30, 2006

It but it makes things a lot easier if you're fast at algebraic manipulations, Taylor expansions and the basic rules of differentiation and integration. These things show up all the time in formulas, and if they are transparent to you, all reasoning will seem much clearer.

Since you didn't study maths in a while, let me emphasize that you learn it by exercising. You can read the book and think it makes sense, but you have to solve problems. That's how you acquire the speed and the "vision" I mentioned above, that make it possible to parse physics textbooks.

However, you don't have to be great at calculus. What you need most of all is a strong sense for what integrals and derivatives mean, one- and many-dimensional, and being comfortable with all kinds of notation. You get that from exercise, but you don't have to be able to solve every problem in the book.

Complex numbers are particular in that they are ill-suited for most practical purposes, except im QM where they are totally crucial. Make yourself fluent in those!


I second claudius on skipping most of solid state (I say this as a Phd student in experimental solid state/quantum device physics). There's a lot of nice theory there, but it's pragmatic and relies to a large extent on statistical and semiclassical reasoning, and smart assumptions about the systems it describes. Save it for later and concentrate on atoms and quantum information. The latter is something I can't recommend warmly enough - qubits are QM distilled, and don't require too difficult maths to get to the nice parts.

As a final remark, if you're into programming, it's instructive to make numerical calculations yourself and plot solutions to the Schrödinger equation. I used Matlab to apply a transfer matrix method in a course once, and it was quite magical to see a wave packet half bounce, half transmit against a potential step, in a program I made myself out of simple (stationary plane wave) solutions to the SE.

Yeah, and add a vote for the Feynman lectures.
posted by springload at 2:18 PM on November 30, 2006

If you're going to read just one book, make it "Quantum Mechanics and Experience" by Frank Z. Albert. My SO is a philosopher by training and she could follow it. It's a nice thin book and I don't think anyone explains the notion of superposition better.
posted by phliar at 6:11 PM on December 11, 2006

Roger Penrose's latest work The Road to Reality tackles physics without skipping on the mathematics.
posted by Gyan at 3:43 PM on December 28, 2006