Elastic
A collision is elastic if the absolute value of the velocity just before and just after the collision is the same, for every direction of the motion.
Homogeneous
A homogeneous field takes the same value at every point in space.
Fraunhofer diffraction pattern
Pattern obtained from the approximate solution of the wave equation. In this approximation there is a one-to-one correspondence between the Fourier transform of the exit plane (exit line in the present example) and the angular distribution. More details can be found in textbooks on optics.
Hamiltonian
The Hamiltonian is a notion familiar in classical mechanics, which often refers to
KINETIC ENERGY + POTENTIAL ENERGY.
Past and future
The classical equations of motion for particles that move in a conservative force field do not change when the sense of progression of time is reversed. For the spinless* particles considered in this chapter the corresponding quantum equations also possess time-reversal symmetry. After reversing the arrow of time the wave packet returns to its initial state and will further evolve according to the laws of quantum mechanics.
*The concept of spin is introduced in the chapter on the Stern-Gerlach experiment.
Time-independent Schrödinger equation
An equation of the type H F( r ) = E F( r ) is called an eigenvalue equation: A solution F( r ) is an eigenfunction of the Hamiltonian H and E is the corresponding eigenvalue. The form of the Hamiltonian H and the boundary conditions imposed on F( r ) determine the solutions of the eigenvalue equation.
