Particle in a potential Well interacts with the wall without touching it??? The ground state Energy for a particle in an infinite potential well is given by E = h2 / 8mL2 Consider a particle with high mass, say 1 kg. Then the ground state Energy will be very very low. So the velocity of the particle is very very low. It takes thousands of years for such particle to hit the walls of a say, 1m3 box that confined it. Suppose I was able to actually setup such condition and put the particle to its lowest Energy level. Now, If I ask a Quantum Mechanical student, What is the Energy of this particle? He will calculate E = h2 / 8mL2 and tell me some value x. Now, without doing anything to the particle, I decrease the volume (hence L) of confinement by say 10%. Now, If I ask the same student about the Energy, he will use the same formula but give me another answer, say y. But y > x. Now I ask him, Why are you supposed to say that the Particles Energy has increased, For I have never touched it, even the slightly? What will he say now?????