gEDA-user: smd challenge board status

[Bill Sloman]

At 05:25 1-11-2006, you wrote:
>I think I will drop into this group a brief passage fom Heisenberg's
>"Quantum Theory" translated into English in 1930.
>
>"Dirac has set up a wave equation which is valid for one electron and is
>invarient under the Lorentian transformation. It fulfills all
>requirements of the quantum theory, and is able to give a good account
>of the phenomena of the "spinning" electron, which could previously only
>be treated by, ad hoc assumptions. The essential difficulty which arises
>with all relativistic quantum theories is not eliminated however. This
>arises from the relation
>
>1/c^2 = u^2C^2  + p^2 in x + p^2 in y + p^2 in z
>
>between the energy and the momentum of a free electron. According to
>this equation there are two values of E which differ in sign associated
>with each set of P in z, P in  y and P in Z. The classical theory could
>eliminate this by arbitrarily excluding the one sign, but this is not
>possible according to the  principles og quantum theory. Here
>spontaneuos transitions may occure to the states of negative energy; as
>these have never been observed, the theory is certainly wrong. Under
>these conditions it is very remarkable that the positive energy-levels
>(at least in the case of one electron) coincide with those actually
>observed."
>
>So what was wrong? What occured that proved both theories were correct?

Dirac solved the problem by hypothesising the positron,

http://www.siam.org/siamnews/03-03/dirac.pdf

which was then sought and found by the experimental physicist Carl 
David Anderson in 1932

http://en.wikipedia.org/wiki/Carl_D._Anderson

It is one of the nicer stories from the early days of quantum physics.

Dirac's normal interaction with experimental physicists is described 
by the Dirac Effect - which, in the classic version of the story - 
had Dirac's presence in Cologne (sitting in a stationary train for a 
couple of hours) as a necessary and sufficient explanation for a 
couple of hours of temperamental behaviour by a sensitive quadrant 
electrometer.

Bill Sloman, Nijmegen