# Quantum physics- where to start

1. Apr 18, 2013

### Hacker4life

This question has been probably posted a lot of times but I haven't found them.

Where should I start?
There are 2 things I want you to answer me:
Where to start in mathematical part of physics and what to learn and,
Where to start quantum physics after learning the mathematical part of it.

P.S I'm a very fast learner, I don't really like the current school system but I love education.
Don't think I will not understand some things, just shoot me with what you got.

Last edited: Apr 18, 2013
2. Apr 18, 2013

### Quantum_man

Mathematics wise you need to know your algebra really well, some of the rearrangement of the equations can become tricky so you need to be upto scratch. At the university level you need to know differential and integral calculus for physics. For quantum physics you need to start off with the wave-particle duality and start doing simple problems so you can see where the equations fit in and how to solve them.

Once you get into it then you need to be able to solve schrodingers equation for example to solve a particles position in a potential well etc.

Hope that helps

3. Apr 18, 2013

### Jano L.

It may depend on what is your motivation. Do you want to study it because you want to know what new it brought to solution of the problems of physics ? Because it is mathematically demanding? Because it is famous and you want to know what the fuss is about?

4. Apr 18, 2013

### Staff: Mentor

You start from wherever you are right now, of course.

Tell us where that is: how much physics and math have you already studied? Then people can intelligently suggest where you should go next (what you should study next).

5. Apr 19, 2013

### Hacker4life

Jano L:
I want to study it as a hobby, and since I know a few quantum theories and equations I find it very interesting and would like to start learning about it. I was amazed by such things: Double slit experiment, Quantum computers, Quantum teleportation and so on. I don't really understand the equations that go in it so I would like to start with the very beginning. For example: The Bell states are very confusing because I don't know what stands for what. But I could explain them.

Quantum_man:
Thanks, it did help but not enough to get started completely.

jtbell:
Lets say that I don't know physics at all, just some elementary stuff.
About my mathematics level, well I'm not sure how to tell you everything that I know. I know how to solve differential equations, I'm going to learn integrals soon, I'm not so good in functions in algebra, I can't say if I know calculus I and II because I have no idea what they are since I'm from another country where they don't mention that.
Can't you just tell me every lesson in mathematics that I need to know before I get started?
And may I say that I like your signature, I have the same opinion about them :D

6. Apr 19, 2013

### ZombieFeynman

The men who laid the groundwork of quantum theory were masters of classical physics. I think knowing classical mechanics and electrodynamics quite well can put things in context.

7. Apr 19, 2013

### Hacker4life

Don't worry about classical physics, it's just along the way. First, I actually do have a basic understanding of it, second if I come in quantum physics to something that is in classical physics I will stop and learn the lesson then continue. It's not hard to me since, as I mention earlier, I understand things fast.

8. Apr 19, 2013

### WannabeNewton

It's insane to do QM without knowing classical mechanics. It certainly "isn't" along the way. Do you know what Hamiltonian mechanics is? What poisson brackets are? How will you appreciate the development of QM without knowing classical mechanics? It's like trying to learn topology without knowing real analysis, you might be able to do it but you won't see the motivation for any of the concepts and/or definitions.

9. Apr 19, 2013

### SophusLies

I agree with WannabeNewton. Also, I want to add that classical mechanics is a beautiful subject in its own right. I remember many me and many of my physics friends thought of it as boring and "old" but little did we know that it would set the framework for QM later on. Focus on learning the basics, if you say you learn fast then what's the big deal about learning what comes before QM?

10. Apr 19, 2013

### Hacker4life

when you talk about classical mechanics, what are you actually talking about, give me some examples?

11. Apr 19, 2013

### dx

Do you recognize this, for example?

dP/dt = -∂H/∂q
dq/dt = ∂H/∂p

12. Apr 19, 2013

### micromass

Staff Emeritus
About the math prerequisites. Please study Linear Algebra before doing QM. And please study theoretical linear algebra (= proof based). It will help you so much. I highly recommend that you go through Lang's "Linear Algebra".

I realize that many people start studying QM without any knowledge of linear algebra, so it's certainly not a "hard" prerequisite. But I would recommend it nonetheless.

You should also be comfortable with, of course, Calc I-III and differential equations. Some say that knowledge of PDE's is necessary, but usually the QM book will teach you the necessary techniques.

As for physics, don't underestimate the importance of Classical Mechanics. I'm sure that QM can be studied as completely stand-alone and not dependent on CM. But this is a very bad approach.
In my point of view, QM is just the noncommutative version of CM. So if you don't know the (easier) commutative version, then you will struggle.

13. Apr 19, 2013

### WannabeNewton

Or this, $\frac{\partial L}{\partial q} - \frac{\mathrm{d} }{\mathrm{d} t}(\frac{\partial L}{\partial \dot{q}}) = 0$. I agree with Sophus, classical mechanics is extremely, extremely beautiful both in its mathematical formalisms and in the physical applications and various physical subtleties (which are the fun parts of course). I see no reason why you shouldn't study it before moving on to QM. It will only benefit you if you intend to study QM in a serious manner.

14. Apr 19, 2013

### ModusPwnd

Undergrads generally start with quantum before they do Hamiltonian mechanics or Poisson brackets. I didnt get either of those until graduate school. You certainly dont need them to do Griffiths level quantum mechanics.

15. Apr 19, 2013

### WannabeNewton

You make it seem like just because not all US universities teach Hamiltonian mechanics and proper classical mechanics at the undergraduate level, that it's a good thing. If the OP is interested in a rigorous, mathematical account of QM then an advanced study of classical mechanics cannot be ignored. If he just wants hand wavy accounts of the formalities then yes Griffiths is fine. Actually a book that is not too light on the mathematics but still has great accounts of experiments (the historical motivation in the first chapter is absolutely amazing) as well as physical insights is Zettilli's book.

16. Apr 19, 2013

### micromass

Staff Emeritus
I don't think Griffiths is a good book anyway. He will be better off studying classical mechanics including Hamiltonians, and then getting a good book on QM instead of some watered down version.

17. Apr 19, 2013

### Hacker4life

First, I have no idea what the formulas what you guys mentioned are. Second, Can you give me a good book on linear algebra? Third:I really don't know what Calc I-III is so I don't know if I know them. Can you explain it to me? It's a different education system here.

18. Apr 19, 2013

### Mmm_Pasta

First, you aren't ready to learn QM if you do not what those formulas are. You'll most likely need to start from the very basics: a book such as Fundamentals of Physics by Halliday and Resnick.

Second, Micromass suggested one to you.

Third, in the U.S., Calc I-III covers single and multivariable calculus. It's important to study calculus while you study the textbook I mentioned. However, you say your algebra is bad. You'll need to make sure this is good before you start calculus.

19. Apr 19, 2013

### ModusPwnd

I make it seem like no such thing. Here is a person who wants to learn some quantum, clearly he doesn't have the background, and you suggest classical Hamiltonian mechanics? Give me a break. Or better, give him a break. Griffiths and Zettilli may seem like trivial beginner books after having studied them, but even they are probably out of the OP's grasp.

Try to put yourself in a non-physics, non-mathematics person's shoes. Browbeating him for having the audacity to want to learn about quantum without having yet studied Hamiltonian mechanics and Poisson brackets is beyond useless, it does a disservice to our attempt at teaching mainstream, non-crackpot quantum physics to the public.

20. Apr 19, 2013

### micromass

Staff Emeritus
He recommended Hamiltonian mechanics because he actually cares about the understanding of the OP. I have no idea how a person would possibly understand things like the Schrodinger equation without knowing what a Hamiltonian is.

The inventors of QM were all extremely good in classical mechanics. They had to be to decently develop QM. I think that it would be the best if the students also know the relevant physics before moving on to QM.