Monday, December 22, 2014

Schrödinger's Equation

From the post "Nothing Probabilistic, No Dice",

\(\nabla ^{ 2 }\psi +\left( \cfrac { n }{ x }  \right) ^{ 2 }\psi =0\)

we consider the fundamental frequency, \(n=1\) and \(x=a_\psi\)

\(\nabla ^{ 2 }\psi +\left( \cfrac { 1 }{ a_{ \psi  } }  \right) ^{ 2 }\psi =0\)

From the post "H Bar And No Bar",

\( \hbar =a_{ \psi  }.mv\)

\( \nabla ^{ 2 }\psi +\left( \cfrac { mv }{ \hbar  }  \right) ^{ 2 }\psi =0\)

\( \hbar ^{ 2 }\nabla ^{ 2 }\psi +\left( mv \right) ^{ 2 }\psi =0\)

But,

\( \cfrac { 1 }{ 2 } mv^{ 2 }=E -V\)

So,

\( \cfrac { \hbar ^{ 2 } }{ 2m } \nabla ^{ 2 }\psi +\left( E-V \right) \psi =0\)

\( -\cfrac { \hbar ^{ 2 } }{ 2m } \nabla ^{ 2 }\psi +V\psi =E\psi \) --- (*)

And we almost have Schrödinger's Equation.  Consider,

\( \psi=|\psi |e^{ iwt }\)

\(\dot { \psi  } =i\omega |\psi |e^{ iwt }=i\omega\psi\)

\(\hbar\dot { \psi  } =i\hbar\omega\psi=iE\psi\)

as \(E=hf=\hbar\omega\)

\(-i\hbar\dot { \psi  }=E\psi\)

Substitute the above into (*),

\( -i\hbar\dot { \psi  }= -\cfrac { \hbar ^{ 2 } }{ 2m } \nabla ^{ 2 }\psi +V\psi \)

this is the conjugated Schrödinger's Equation.

And we conjugate both sides and replace \(\psi^{*}\) with \(\psi\) (symbolically)

\( i\hbar\dot { \psi  }= -\cfrac { \hbar ^{ 2 } }{ 2m } \nabla ^{ 2 }\psi +V\psi \)

where Euler's identity \(e^{i\pi}=-1\) leads to \(e^{i\pi/2}=i\); and \(i\) rotates between orthogonal dimensions.

\(\pi/2\equiv\) orthogonal

And \(\psi\) is clearly energy density.  Thank you very much.