Re: SPIN 1/2

From: Michel, de posta.unizar.es <julier_at_unizar.posta.es.cselt.it>
Date: 2000/02/28

Scusate, ma non so l'italiano abastanza bene per scriverlo, dunque
scrivero' in inglese (sono francese, ma sto en Spagnia).

> > Leggendo un libro di fisica ho letto che l'Eq.di Dirac
> > spiga matematicamente perchh l'elettrone possiede Spin 1/2.

Dirac's equation doesn't explain very much, but with very simple basis it
succeeds in discribing a particle with the classical limit. It gives a 1/2
spin (with a g factor equal to 2), and predicts negative energy states,
which can be interpreted as antiparticles if one is missing. Finally, you
get 4 states, and Dirac's equation is like a two 1/2 spins assembled in a
funny way. The more surprising is that it works, although the calculations
are usually horrible.

> L'equazione di Dirac "spiega" perche'
> l'elettrone abbia spin 1/2 in un ben preciso contesto: la meccanica
quantistica relativistica PRIMA della "seconda
> quentizzazione".

The second quantization is another business: it's a more practical way to
discribe how quantum phenomenons can create a photon, a phonon, or other
things. It is not relativistic, and you get the same results as you would
get without it, but it's easier in many cases with it.

> Esisteva
> gia' un'equazione quella di Kelin-Gordon,
> ma aveva dei problemi interpretativi (risolti con la "seconda
quantizzazione").

Klein-Gordon, which discribes particles without a spin. There too, you get
negative energy states. Indeed, why don't the particles fall to the
negative states? But it doesn't discribe the same thing as Dirac's
equation.

> Piu' avanti Pauli dimostro' un teorema generale detto "correlazione
spin-statistica"

E' dimostrato questo teorema? Me interesa se lo i, pensavo che era una
hipotesis.

Michel, Zaragoza (Spagnia)
-- 
Contesta a/Ripondre `/Answer to:   ... _at_posta.unizar.es
Received on Mon Feb 28 2000 - 00:00:00 CET

This archive was generated by hypermail 2.3.0 : Fri Nov 08 2024 - 05:10:40 CET