Quantum mechanics and classical physics

[John Brindley]

“Sometimes attaining the deepest familiarity with a question is our best substitute for actually having the answer.” - Brian Greene, The Elegant Universe

In that sentence, I think that Brian Greene has summarized the attitude of many physicists, especially those whose training and experience has driven them into an over-familiarity with all the unanswered questions in quantum mechanics. The standard model proposed too many inexplicable phenomena, with which too many physicists have become too complacently over-familiar. Quantum mechanics and classical physics just cannot be reconciled, too many say. Which would be fine if quantum mechanics then went on to explain everything that classical physics could not, but it doesn't. It attains the deepest familiarity with the questions and presents that as an alternative to having any answers.

[swansont]

But on must also look at the converse of the situation. Classical physics fails to explain many phenomenon, and fails miserably. You need to have some kind of model for haw nature behaves when classical physics fails, and QM is what we have, like it or not. You are free to try and come up with something better, but it actually needs to be better and not something that is simply not as scary or intimidating.

[ajb]

Quantum mechanics and classical physics just cannot be reconciled, too many say.

Who says this and what is the context?

 

From quantum theory we have a good intuative notion of how to pass to the classical world. One can consider the limit as [math]\hbar[/math] tends to zero. Basically this allows us to relate Poisson brackets on phase spaces with commutators of operators on Hilbert spaces. The process of canonical quantisation, deformation and geometic quantisation is basically the reverse.

 

There are other ways of understanding how classical mechanics emerges from quantum mechanics. In the Feynman path integral formulation you see that the classical paths are the most dominant paths. As long as the action is much larger than Planck's constant the classical paths are just about the only paths that contribute and so we recover classical mechanics again.

Edited August 13, 2013 by ajb

[studiot]

If you find ajb's response too technical, try

 

Chad Orzel's

 

How to teach Quantum Physics to your Dog

 

This book is nearer Brian Greene's level, although Chad is actually a quantum physicist.

Edited August 13, 2013 by studiot

[roger4464]

why ? don't we have a physical model to explained the veracity of the words said._ Are we trying to hide knowledge ?

[swansont]

why ? don't we have a physical model to explained the veracity of the words said._ Are we trying to hide knowledge ?

 

The veracity of what words said?