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First of all, what are the differences between these two: Lagrangian mechanics and Hamiltonian mechanics?

And secondly, do I need to learn both in order to study quantum mechanics and quantum field theory?

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marked as duplicate by Qmechanic Sep 28 '14 at 20:59

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

This question tends to fit poorly on Phys.SE post for various reasons, e.g. it asks too many questions. I close it as a duplicate, not because it is necessarily an exact duplicate, but to point in the right direction. – Qmechanic Sep 28 '14 at 21:03

I don't think it's possible to explain the differences between the Hamiltonian and Langrangian approaches without explaining what each one is, and that would be a long answer and would in any case just reproduce the Wikipedia articles you linked to.

If you're serious about learning any form of mathematical physics I'm afraid you need to understand them both. The good news is that they're pretty straightforward. If you can muster enough brain cells to learn quantum field theory you'll have no problems learning Hamiltonian and Langrangian mechanics. Actually, when I first came across them I found them fascinating. I wish I had been taught them at school.

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Very true. He shouldn't ask which one he has to learn, but which one is considered most beautiful :D – NikolajK Apr 18 '12 at 17:57

Before you study QFT you should understand very well Classical Field Theory

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