Quantum Physics Basics: An Overview

[physicsnoob12]

What are the basic rules of quantum physics and how does it work?

 

[physicsnoob12]

Also how does it differ from quantum mechanics?

 

[lugita15]

The difference is whether Special Relativity is used. Non-relativistic quantum physics is known at quantum mechanics. To a good approximation, you can assume that there's a fixed number of discrete particles. But when relativistic effects become important, then you can't think purely in terms of particles; the notion of fields naturally arises from relativistic considerations. This is why relativistic quantum physics is known as quantum field theory.

 

[Kevin_Axion]

These are the postulates of Quantum Physics:


Postulate 1: State of a system
A system is completely specified at anyone time by a Hilbert space vector.

Postulate 2: Observables of a system
A measurable quantity corresponds to an operator with eigenvectors spanning the space.

Postulate 3: Observation of a system
Measuring a system applies the observable's operator to the system and the system collapses into the observed eigenvector.

Postulate 4: Probabilistic result of measurement
The probability of observing an eigenvector is derived from the square of its wavefunction.

Postulate 5: Time evolution of a system
The way the wavefunction evolves over time is determined by Shrodinger's equation.

 

[alxm]

The difference is whether Special Relativity is used. Non-relativistic quantum physics is known at quantum mechanics.

Whose definition is this?

And the people who work entirely with the Dirac equation (for, say, heavy-element quantum-chemical calculations), but aren't dealing with propagators
or path integrals or any real QFT formalism, are they doing 'quantum mechanics' or 'quantum physics'?

There's non-relativistic quantum field theory and relativistic quantum mechanics that doesn't involve QFT-type formalism,
the terms "quantum physics" and "quantum mechanics" are simply interchangeable.

 

[tom.stoer]

Postulate 4: Probabilistic result of measurement
The probability of observing an eigenvector is derived from the square of its wavefunction.

How does this change when non-Kopenhagen / collapse-free interpretations are being considered?

 

[yoda jedi]

These are the postulates of Quantum Physics:



Postulate 2: Observables of a system
A measurable quantity corresponds to an operator with eigenvectors spanning the space.

Rather:
Hermitian operators that act on the Hilbert space of possible states of a system.

 

[yoda jedi]

These are the postulates of Quantum Physics:



Postulate 3: Observation of a system
Measuring a system applies the observable's operator to the system and the system collapses into the observed eigenvector.

and for non collapse interpretations ?

 

[yoda jedi]

add:

when the operators corresponding to two physical quantities do not commute the two quantities cannot have simultaneous reality.

 

[nickthrop101]

a good book is " the elegant universe" is a really good beginnning for explaining, ( non-mathmatically) quantum physics and mechanics

 

[pedrapgwilym]

I downloaded a copy of Dirac's "The Principles of Quantum Mechanics" and the first chapter is (apart from some gross transcription errors) a brilliantly simple exposition of the concept of superposition. Got well into the second chapter on Dynamical Variables and Observables only to find that it is missing pp. 32 & 33. Does anyone know how I can get them?

 

[unusualname]

I downloaded a copy of Dirac's "The Principles of Quantum Mechanics" and the first chapter is (apart from some gross transcription errors) a brilliantly simple exposition of the concept of superposition. Got well into the second chapter on Dynamical Variables and Observables only to find that it is missing pp. 32 & 33. Does anyone know how I can get them?

Hmm, you can try a library or buying the book.

However, this time you have some luck since the book is browsable on amazon

You need to create an amazon account then you can use the 'Look Inside' feature to browse the book and search most pages (eg try '33' to search for page 33) (use left and right scroll arrows to move to previous/next page)

Without an account you are limited in pages you can search. You can also view parts of the book on google books, although I just checked and one of your missing pages, 33, is not in the preview.

Then use a screenshot program or similar to save the page image, or do it the old-fashioned way and copy the pages by hand, this will aid with committing the content to memory. ;)

 

[pedrapgwilym]

Many thanks to you unusualname for your advice. I shall follow it! The only problem with the purchasing of scientific books is that they are usually so b****y expensive. Cheers!

 

[pedrapgwilym]

To unusualname:
I've done just what you wrote and found both pages 32 and 33 from Amazon. Absolutely brilliant, thank you so much! I searched on 'Eigenvalues' and got page 33, then I went to the previous page by scrolling up. Job done. Diolch yn fawr iawn!