The dynamical Casimir effect
Goal: Study the creation of real quanta from the vacuum under nonstationary boundary conditions.
Consider a one-dimensional scalar field \(\phi(t,x)\) with the boundary conditions \[\phi(t,0)=\phi(t,L(t))=0,\] where \[L(t)=L_0\bigl(1+\epsilon\sin\omega t\bigr).\]
Find the instantaneous modes of the field and their frequencies \(\omega_n(t)\).
Show that under the resonance condition \[\omega \approx 2\omega_n\] the number of quanta grows exponentially.
Compute numerically the radiated energy as a function of time.
Discuss the physics: where the energy of the created quanta comes from (the work of the external force that moves the boundary) and why energy is conserved.