I just started learning QM and have a question - lets say that i have the following amplitude for a particle: a*e^(-i*frequency*t) since the exponent doesn't change the probability, what is it's physical importance? from what i understood the frequency coorsponds to the energy - since energy is the tendency of the particle to stay in it's current state, a higher frequency would make the particle have more influence in the case of interference with another particle. so basically the exponent only has significance when it interacts with another particle? And one more thing, does the amplitude of the state change with time only when it's multiplied by a real exponent? Thanks.